Role of Aldose Reductase and Oxidative Damage in Diabetes and the Consequent Potential for Therapeutic Options
http://www.100md.com
内分泌进展 2005年第3期
Department of Human Biological Chemistry and Genetics (S.K.S., K.V.R.), University of Texas Medical Branch, Galveston, Texas 77555
Division of Cardiology (A.B.), Department of Medicine, University of Louisville, Louisville, Kentucky 40202
Abstract
Aldose reductase (AR) is widely expressed aldehyde-metabolizing enzyme. The reduction of glucose by the AR-catalyzed polyol pathway has been linked to the development of secondary diabetic complications. Although treatment with AR inhibitors has been shown to prevent tissue injury in animal models of diabetes, the clinical efficacy of these drugs remains to be established. Recent studies suggest that glucose may be an incidental substrate of AR, which appears to be more adept in catalyzing the reduction of a wide range of aldehydes generated from lipid peroxidation. Moreover, inhibition of the enzyme has been shown to increase inflammation-induced vascular oxidative stress and prevent myocardial protection associated with the late phase of ischemic preconditioning. On the basis of these studies, several investigators have ascribed an important antioxidant role to the enzyme. Additionally, ongoing work indicates that AR is a critical component of intracellular signaling, and inhibition of the enzyme prevents high glucose-, cytokine-, or growth factor-induced activation of protein kinase C and nuclear factor--binding protein. Thus, treatment with AR inhibitors prevents vascular smooth muscle cell growth and endothelial cell apoptosis in culture and inflammation and restenosis in vivo. Additional studies indicate that the antioxidant and signaling roles of AR are interlinked and that AR regulates protein kinase C and nuclear factor-B via redox-sensitive mechanisms. These data underscore the need for reevaluating anti-AR interventions for the treatment of diabetic complications. Potentially, the development of newer drugs that selectively inhibit ARmediated glucose metabolism and signaling, without affecting aldehyde detoxification, may be useful in preventing inflammation associated with the development of diabetic complications, particularly micro- and macrovascular diseases.
I. Introduction: Aldose Reductase and Diabetic Complications
II. AR and Antioxidant Protection
III. Redox Regulation of AR Activity
IV. Regulation of Intracellular Signaling by AR
V. AR Inhibitors and the Treatment of Secondary Diabetic Complications
VI. Conclusion
I. Introduction: Aldose Reductase and Diabetic Complications
ALDOSE REDUCTASE (AR) is a monomeric reduced nicotinamide adenine dinucleotide (NAD) phosphate (NADPH)-dependent enzyme and a member of aldo-keto reductase superfamily. The enzyme was described in 1956 by Hers (1) as a glucose-reducing activity. It was subsequently reported by van Heyningen (2) that high levels of AR activity are present in the rat lens and that during diabetic and galactosemic cataractogenesis, AR-derived polyols—sorbitol and galactitol—accumulate in the ocular lens. Building on this observation, Kinoshita et al. (3) and Varma and Kinoshita (4) demonstrated that treatment with pharmacological inhibitors of AR ameliorated cataractogenesis in diabetic rats and galactose-exposed rabbits. Based on these observations it was proposed that accumulation of sorbitol in the lens, due to AR-catalyzed reduction of glucose, causes osmotic swelling resulting in ionic imbalance and protein insolubilization leading to cataractogenesis (5, 6, 7). A similar sequence of events could also account for hyperglycemic injury associated with diabetic retinopathy, nephropathy, and neuropathy (Fig. 1).
The osmotic hypothesis that diabetic complications are due to sorbitol accumulation in tissues has engendered extensive investigations over the last three decades. Several drugs with varying AR-inhibiting efficacy (e.g., sorbinil, statil, tolrestat, and zopolrestat) have been synthesized and tested (8, 9, 10, 11). Initial trials in animal models showed significant protection against diabetic complications (12, 13, 14). AR inhibitors, in addition to preventing diabetic and galactosemic cataracts (3, 4), ameliorated some of the features of diabetic nephropathy (15, 16) and neuropathy (17, 18, 19). However, clinical trials with AR inhibitors have yielded uncertain results, in part due to the high nonspecific toxicity of this class of drugs.
In the mid-1980s we demonstrated that most of the inhibitors synthesized by pharmaceutical companies were not selective for AR but also inhibited other members of the aldo-keto reductase superfamily such as aldehyde reductase (20). In addition, we also demonstrated that increased osmotic pressure due to accumulation of polyols in galactosemic and diabetic cataractogenesis could not be the main cause of cataractogenesis (21, 22, 23). Antioxidants such as butylated hydroxytoluene and 6-hydroxy-2,5,7,8-tetramethenyl-chroman-2-carboxylic acid (Trolox) prevented diabetic cataractogenesis in rats and significantly attenuated lens opacity in galactose-fed rats even though the polyol levels in the lens were extremely high (80–90 mM), indicating that polyol accumulation per se is not sufficient for cataractogenesis and that other metabolic changes accompanying AR activation may be critical and important modulators of the cataractous effects of hyperglycemia and diabetes (Fig. 2).
Because AR utilizes NADPH to catalyze glucose reduction, we, as well as other investigators, suggested that tissue injury associated with high glucose may be due, in part, to increased NADPH utilization by the reduction of glucose by AR (24, 25). In the presence of normal glucose (5.5 mM), AR-catalyzed reduction represents less than 3% of total glucose utilization, whereas in the presence of high glucose (20 mM), more than 30% of the glucose is used by AR (26), suggesting that the profound increase in the AR-catalyzed reductive pathway may impose a significant strain on NADPH supply. Because NADPH is used for several critical reductive metabolic steps, such as the detoxification of reactive oxygen species and hydroperoxides (e.g., by the glutathione reductase/glutathione peroxidase system), a large drain on the NADPH pool could compromise the ability of the cell to protect itself from oxidative stress.
Another reason for the inconsistent effects of AR inhibitors may relate to posttranslation modification of the enzyme. As documented extensively in our previous publications (26, 27, 28), the oxidation state of a single cysteine residue located at the active site of the enzyme regulates both substrate and inhibitor binding and thus, given the extensive oxidative changes in diabetes, it is likely that in diabetic tissues AR is insensitive to inhibitors due to oxidative modification. In support of this view, we have demonstrated that AR in human erythrocytes exists in two forms, activated and unactivated, and in hyperglycemia total activity of AR increases (29). Multiple forms of AR have also been reported by other investigators (30, 31), and our in vitro data suggest that oxidants can induce a variety of changes in the catalytic activity of the enzyme, although which of these forms occur in vivo and how they are interconverted remains unclear. Nevertheless, the view that the hyperglycemia changes the sensitivity of AR to inhibition is further supported by the observation that prolonged culture of endothelial cells in high glucose progressively decreases the efficacy of sorbinil in preventing sorbitol accumulation (32).
In contrast to inhibitor data, newer molecular approaches have provided more unambiguous evidence for the involvement of AR in diabetic complications. In these studies transgenic overexpression of AR gene selectively in the lens was found to accelerate diabetic and galactosemic cataract formation in mice (33). Additionally, ubiquitous overexpression of the AR gene increased the rate of neuropathic changes in diabetic animals (34, 35, 36). Collectively, these data argue strongly that AR is an important component of high glucose-induced metabolic changes that underlie the development of secondary diabetic complications. Nevertheless, despite this evidence, the exact mechanism by which AR contributes to the development of diabetic complications remains unclear. Persistent increase in extracellular glucose levels induces pleiotrophic changes in metabolism that elicit polygenic responses (Fig. 3). Extensive changes in the activation of protein kinases and the accumulation of advanced glycation end products have been reported (37, 38, 39), although their relationships with modulatory influences on AR remain unclear. In principle, AR could contribute to both protein kinase activation and advanced glycation end product accumulation. In addition, AR could catalyze the formation of potent protein glycating agents and induce oxidative stress.
Reduction of glucose by AR leads to the formation of sorbitol, which, in some tissues, is further oxidized to fructose upon sorbitol dehydrogenase-catalyzed oxidation. The conversion of glucose to fructose (the "polyol pathway") results not only in the utilization of NADPH, but also NAD+. As a result, increased activity of the polyol pathway during hyperglycemia could lead to a depletion of NADPH and accumulation of reduced NAD. This shift in the redox state of pyridine coenzymes recapitulates the metabolic phenotype of hypoxia and has been proposed to induce a state of pseudohypoxia resulting in hypoxia-like responses (40, 41, 42). Polyol pathway-mediated alterations in pyridine nucleotides have been linked to diverse metabolic changes such as the synthesis of nitric oxide (NO) and activation of protein kinases (39). Specifically, it has been proposed that the increase in NADH due to elevated polyol pathway activity could increase the synthesis of diacylglycerol (DAG) from dihydroxyacetone phosphate (43). DAG levels could also increase by stress that activates phospholipase C (PLC in Fig. 4). DAG is an essential activator of the classical and novel members of the protein kinase C family, and DAG-dependent activation of these kinases is thought to play a key role in mesangial expansion and smooth muscle cells proliferation induced by high glucose (44, 45, 46). Inhibitors of specific protein kinase C (PKC) isoforms are currently under clinical trial for the treatment of diabetic complications (47, 48).
II. AR and Antioxidant Protection
Due to its ability to reduce glucose, AR is involved in several tissue-specific metabolic pathways. For instance, in the kidney, AR participates in osmoregulation (49, 50) and, in seminal vesicles, in the generation of fructose (1). The observation that AR and related proteins are up-regulated by fibroblast growth factor (FGF) and other mitogens suggests that AR may be involved in cell growth or growth factor-induced changes in cellular metabolism (51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61). Our studies show that in vitro homogenous AR catalyzes the reduction of a large series of saturated and unsaturated aldehydes with 103- to 104-fold higher efficiency than glucose (62). The enzyme is particularly efficient in reducing medium- to long-chain (C-6 to C-18) aldehydes such as those generated in high abundance during lipid peroxidation (63, 64). The enzyme also catalyzes the reduction of the glutathione conjugates of unsaturated aldehydes, in many cases with efficiency higher than that of the parent free aldehyde (65, 66, 67). The reduction of glutathione conjugates by AR may be a protective mechanism that may be useful in minimizing the reactivity of the aldehyde function unquenched by glutathiolation. In addition, our recent studies show that AR is also an efficient catalyst for the reduction of core aldehydes—or aldehydes generated in oxidized phospholipids (Refs. 65, 66, 67, 68, 69, 70 and Fig. 5).
The role of AR in detoxification is supported by structural studies showing that the active site of AR lacks ionic residue characteristic of carbohydrate-binding proteins (71, 72, 73, 74, 75, 76). Instead, x-ray analyses of AR crystals reveal a highly plastic and hydrophobic active site (73, 74). This site could potentially accommodate a wide range of structures if the aldehyde function were to orient itself appropriately between the two ionic active site residues, His-110 and Tyr-48, which participate in acid-base catalysis. The structure of the binary complex of the enzyme with NADP+ also indicates a profound conformational change upon NADPH binding (72). It has been suggested that the energy released as a result of this interaction is used for stabilization of the transition state with little demand from energy stabilization due to substrate binding (77). Hence, as a result of high-affinity interaction with NADPH, AR functions as an unusually promiscuous aldehyde removase, features that seem to be critically required of a detoxification enzyme involved in the removal of a wide range of aldehydes and glutathione aldehyde adducts generated during lipid peroxidation.
Based on our substrate specificity studies showing high-affinity reduction of glutathione conjugates by AR (66, 67), we reasoned that the active site of the enzyme must conform to a specific glutathione-binding domain. Consistent with the presence of specific interactions between the amino acid residues of glutathione and the AR active site, we found that alterations in the structure of glutathione diminished the catalytic efficiency for the reduction of glutathione-aldehyde conjugates and that nonaldehydic conjugates of glutathione or glutathione analogs displayed active site inhibition (67). Molecular dynamics calculations suggest that the conjugates adopt a specific low-energy configuration at the active site (Fig. 6). Mutations of the active site residues identified by these calculations selectively decreased catalysis of the glutathione-aldehyde conjugates, without affecting reduction of the free aldehyde. The high specificity and selectivity with which the enzyme catalyzes the reduction of glutathione conjugates suggest that such conjugates may be in vivo substrates of the enzyme. Indeed, our metabolic studies with 4-hydroxynonenal (HNE) show AR-dependent reduction of its glutathione adduct in heart, smooth muscle, and erythrocytes (78, 79, 80, 81).
Reduction of aldehyde-glutathione conjugates by AR may be of physiological significance, particularly under conditions of oxidative stress when other antioxidant mechanisms are overwhelmed. Under these conditions, AR, by reducing both free aldehydes and their glutathione conjugates, could promote efficient removal and detoxification of unsaturated aldehydes, which are the major electrophilic end products of lipid peroxidation. Thus, investigations into the structure and kinetics of AR point toward a general detoxification role of the enzyme, indicating that lipid aldehydes and their glutathione conjugates are physiological substrates of the enzyme and that glucose is perhaps an incidental substrate, which is used only when it is high in concentration or occasionally for tissue-specific metabolism.
Consistent with its role as a detoxification enzyme, AR has been found to be regulated by aldehydes generated from lipid peroxidation (64, 70, 82), thiol-reducing agents (83, 84, 85, 86, 87, 88), metal ions (89, 90, 91), and NO (92, 93, 94, 95, 96, 97). Tissue levels of AR are also increased under conditions of high oxidative stress such as iron overload (98), alcoholic liver disease (99), heart failure (100), and vascular inflammation (53, 101). Moreover, AR is also specifically up-regulated during vasculitis, specifically in the areas of high HNE formation, and inhibition of AR increases the concentration of free HNE and protein-HNE adducts, accompanied by a 3-fold increase in the number of apoptotic cells (102). Our studies show that AR is also up-regulated in the heart by brief episodes of ischemia (103). This increase in AR was prevented by inhibitors of PKC and NO synthase, indicating that the up-regulation of AR is regulated by cardioprotective signaling associated with the late phase of ischemic preconditioning. Furthermore, a posttranslational activation of AR during myocardial ischemia has been reported (104). The functional significance of the increase in AR in the ischemic heart is underscored by the observation that inhibition of AR abolishes the cardioprotective effects of late preconditioning (105, 106, 107). Collectively, these data provide support to the view that AR is a component of an antioxidant defense mechanism, which protects tissues from the harmful effect of lipid peroxidation products such as HNE that accumulate during conditions of oxidative stress such as ischemia and inflammation.
Although HNE and related aldehydes are metabolized by several different pathways, metabolism via AR could represent a true detoxification mechanism. In most cells, HNE and related aldehydes readily form glutathione conjugates; however, the formation of glutathione-HNE itself may not be sufficient for detoxification. The glutathione-aldehyde conjugates are toxic. They induce DNA damage and stimulate radical formation (108, 109, 110). Therefore, reduction of the glutathione-aldehyde conjugates by AR may be necessary to substantially annul the reactivity of the conjugate and to decrease free radical generation. Nonetheless, the mechanisms by which AR-dependent aldehyde metabolism regulates the development of diabetic complications remain unclear, and the contribution of AR to cell growth and antioxidant defense requires further elucidation. In particular, it remains to be clarified how AR expression and activity are regulated and which components of intracellular signaling are regulated by AR.
III. Redox Regulation of AR Activity
As discussed above, a component of the hyperglycemic injury is due to an increased flux of glucose through the polyol pathway because the inhibition of AR prevents some of the diabetic complications. Although inefficacy of AR inhibitors could be due to their nonspecificity and hypersensitivity of selected individuals, the limited long-term efficacy of the AR inhibitors could be attributed to the posttranslational modification in AR that alters ligand binding and catalysis. In our earlier studies we found that AR isolated from individuals with different levels of hyperglycemia displayed altered kinetic properties and was less sensitive to hydantoin inhibitors such as sorbinil compared with the enzyme isolated from the tissues of normoglycemic subjects (29). Similar changes were observed at various stages of purification of AR in the absence of a reducing reagent such as dithiothreitol or ?-mercaptoethanol from the tissues of normal subjects or from recombinant bacteria overexpressing AR (30, 31). Both the Michaelis-Menten constant (Km) and inhibition constant (Ki) values of the enzyme significantly increased upon its in vitro thiol modification by HNE (64, 82), nitrosoglutathione (GSNO) (92), and oxidized glutathione (GSSG) (83).
The high sensitivity of AR to oxidants such as H2O2 and NO was attributed to a highly reactive cysteine (Cys-298) residue present at the active site of the enzyme (88). Oxidants such as H2O2 cause enzyme inactivation. Also glutathiolation of the Cys-298 results in a significant inactivation of the enzyme (83, 88, 92). However, depending on the conditions of the reaction and the nature of the NO donor used, AR is either S-thiolated (inactivated enzyme) or S-nitrosated (activated enzyme). On the basis of these observations, we hypothesized that NO regulates the intracellular activity of AR and consequently the flux of glucose via the polyol pathway (92, 93, 94, 95, 96, 97, 98). Because, in hyperglycemia, NO synthesis is significantly less compared with normoglycemic subjects, it has been reasoned that the AR activity may be up-regulated in diabetic tissues (111, 112).
Cardiovascular complications are one of the major causes of mortality in patients with prolonged diabetes (113). The role of AR in cardiovascular complications, especially in atherosclerosis (100), restenosis subsequent to balloon injury (53, 57), and cardiac preconditioning (103, 104, 105, 106), has been extensively investigated. Vascular endothelial cells are the main source of NO for vascular smooth muscle cells because in the vasculature, NO synthase is present mainly in the endothelium (114). The NO secreted by endothelial cells could readily form GSNO with glutathione that is abundant in vascular smooth muscle cells (VSMC). The GSNO formed could, in turn, readily S-glutathiolate AR at Cys-298 (92). Although GSSG (50–100 μM) also S-glutathiolates AR, it is unlikely that the physiological source of S-glutathiolation of AR (or other proteins) could be GSSG because the concentration of GSSG in cells rarely exceeds 20–25 μM. Because S-glutathiolation inactivates AR, under normoglycemic conditions, it appears likely that a significant fraction of AR in vascular tissues is present in an inactive form, whereas in hyperglycemia a decrease in NADPH/NADP+ ratio and other factors would decrease NO and the AR would be in the active form. Indeed, we have demonstrated that, in diabetic rat aorta, both AR activity and sorbitol levels are more than 20-fold higher than nondiabetic aorta (95). Daily ip injections of NO synthase inhibitor, NG-nitro-L-argininemethyl ester or application of nitroglycerin patch significantly increased the activity of aorta AR as well as sorbitol formation in both nondiabetic and streptozotocin-diabetic rats. On the other hand, daily injections of NO synthase substrate, L-arginine, significantly decreased AR activity and sorbitol content in aortas of both diabetic and nondiabetic rats. Similar results were obtained when aortic rings from normal and diabetic mice were incubated with L-arginine and NG-nitro-L-argininemethyl ester, whereas, both NO synthase substrate and inhibitor had no effect on AR activity or sorbitol content of aorta from endothelial NO synthase-null mice (97). Interestingly, it was observed that S-glutathiolation of AR in VSMC by NO donors such as GSNO, which inactivates the enzyme, is reversible. Thus, the changes in glucose levels that alter the levels of NO would change the AR activity, sorbitol levels, and related effects in diabetic subjects. Hence, in addition to glycemic control, NO donors or drugs that increase NO levels could represent one treatment modality for the prevention or treatment of diabetic complications. Because hyperglycemia causes increased generation of reactive oxygen species by autooxidation of glucose and other metabolic pathways, antioxidants would also have beneficial effects. Diabetic complications such as cataractogenesis, retinopathy, and cardiovascular effects have been shown to be ameliorated by antioxidants such as butylated hydroxytoluene, butylated hydroxyanisole, Trolox, ascorbate, vitamin E, N-acetyl cysteine, pyruvate, etc. (115, 116, 117, 118, 119, 120).
IV. Regulation of Intracellular Signaling by AR
Diabetes is a major risk factor for the development of cardiovascular disease. It is associated with a 2- to 4-fold higher risk of cardiovascular disease, and it accelerates the progression and increases the severity of atherosclerotic lesion formation in peripheral, coronary, and cerebral arteries (121, 122, 123, 124, 125). Moreover, diabetics have a higher propensity for restenosis after percutaneous transluminal coronary angioplasty (126). Even though coronary stenting significantly reduces restenosis, diabetes remains a powerful predictor of in-stent restenosis (127). Processes that lead to an increase in smooth muscle cell growth in diabetic as well as nondiabetic restenotic vessels have not been identified but, given the observation that high levels of protein-HNE adducts are associated with proliferative vascular lesion, it appears that products of lipid peroxidation, such as HNE, play a significant role in modulating the growth of vascular lesion. This is supported by our observation that treatment with low concentrations (<2 μM) of HNE increases VSMC growth in culture, although at higher concentrations HNE induced apoptotic cell death (53). To test the role of HNE in vascular proliferation, we determined how changes in its metabolism via AR would affect its mitogenic activity. Surprisingly, we found that inhibition of AR prevented VSMC growth in culture (53). Serum-starved VSMC cultured in 1 μM HNE showed increased proliferation compared with cells cultured without HNE, as determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay and cell count, whereas under similar conditions, HNE caused apoptosis in vascular endothelial cells and lens epithelial cells (Fig. 7). Both proliferation and apoptosis were attenuated by inhibiting AR using two structurally different AR inhibitors, sorbinil and tolrestat, and also by using antisense AR or small interfering RNA. In addition to HNE-stimulated growth, smooth muscle cells growing in response to serum FGF, TNF, or high glucose were also sensitive to AR inhibitors (128). Moreover, inhibition of AR also prevented smooth muscle cell growth in vivo: we balloon-injured normal and diabetic rat carotid artery and followed restenosis by quantifying the neointima formation (101). In both normal and diabetic rats, AR inhibitor significantly (45%) prevented neointimal hyperplasia (Fig 8). Interestingly, the neointimal hyperplasia was associated with increased nuclear factor--binding protein (NF-B) activation (128). This was significantly prevented by sorbinil, suggesting that AR is required for signaling pathways responsible for NF-B activation and for the proliferation of smooth muscle cells in vascular lesions. Together, these observations suggest that AR is essential for smooth muscle cell growth induced by several mitogenic pathways and that inhibition of AR interrupts their growth in culture and in vivo (53, 57, 128).
Although the mechanism by which AR regulates growth remains unclear, several of the key signaling pathways related to cell growth are sensitive to AR inhibition. Significantly, our studies reveal that inhibition of AR prevents activation of the transcription factor NF-B stimulated with either TNF (Fig. 9), FGF, angiotensin II, or high glucose (101, 128). Inhibition of AR, however, does not seem to directly interfere with the DNA binding of NF-B, but prevents NF-B activation by extinguishing signaling events upstream to dissociation of NF-B from IB and the nuclear translocation of NF-B. This appears to be due to the inhibition of phosphorylation and degradation of IB in cells treated with AR inhibitors. Significantly, inhibition of AR does not prevent NF-B when the cells are stimulated by phorbol esters, indicating that inhibition of AR does not interfere with the IB-NF-B signaling pathway but prevents signaling events upstream to PKC (128).
Similar to the effects observed with TNF, inhibition or ablation of AR also interrupts the activation of the PKC-NF-B by high glucose (101). The sensitivity of both high glucose- and TNF-mediated cell growth to AR inhibitors suggests that both stimuli might activate overlapping pathways. Indeed, previous studies have shown that treatment with anti-TNF antibodies prevents accelerated restenosis in diabetic vessels (129), and in our laboratory treatment with anti-TNF antibodies was effective in preventing high glucose-induced smooth muscle cell growth in culture (K. V. Ramana, R. Tammali, A. Bhatnagar, and S. K. Srivastava, unpublished observations). Hence, it appears that the mitogenic effects of high glucose may be mediated, in part, by stimulation of cytokine release and autocrine activation of the cell growth pathways. How glucose could induce the release of cytokines is unclear. However, the recent observation that the release of TNF is regulated by PKC (130, 131, 132) suggests that activation of PKC by high glucose could trigger TNF release and stimulate growth. Because inhibition/ablation of AR prevents both PKC activation (Fig. 10) and TNF signaling, it could interrupt the initial trigger events as well as subsequent autocrine stimulation of mitogenic signaling in cells exposed to high glucose (101, 133).
Studies delineating the role of AR in intracellular signaling suggest an alternative paradigm for understanding the contribution of this enzyme to the development of diabetic complications and the efficacy of AR inhibitors against secondary diabetic complications, despite the detoxification role of the enzyme. Hence, inhibition of inflammation could represent one mechanism by which beneficial effects could be derived from inhibiting AR. Our studies show that key steps in the inflammatory process, such as NF-B activation and the increase in the expression of adhesion molecules ICAM-1 and VCAM-1 and monocyte adhesion, could be prevented by inhibiting AR (Fig. 11) (134). Moreover, inhibition of AR also prevents the cytotoxic effects of TNF on endothelial cells.
Our studies have also shown that inhibition of AR by sorbinil or tolrestat prevents TNF-induced increase in Bax and Bad and the down-regulation of Bcl-2 (135, 136). Inhibition of AR also abrogates activator protein 1 DNA binding activity and prevents the activation of caspase-3, c-Jun N-terminal kinase, and p38 MAPK in cells stimulated by TNF, suggesting that AR could be a critical regulator of TNF-induced apoptotic signaling in endothelial cells (136). Given the key role of the endothelium in regulating atherogenesis and restenosis, the salutary effects of AR inhibitors on these cells could further contribute to the ability of these drugs to limit inflammation and vascular adhesion. Although the overall effects of inhibiting AR during atherosclerotic lesion formation remain to be studied, they are likely to be complex. Given that inhibition of AR could prevent inflammatory changes as well as increase the accumulation of lipid peroxidation products, inhibition of AR could yield highly context-dependent results, and the benefits of inhibiting AR may be specific to the extent of lesion progression and hyperglycemia and/or may require concurrent administration of antioxidants. Such duality and complexity of effects is, however, expected. AR regulates oxidative and inflammatory responses, both of which could be beneficial or harmful depending upon the context and the extent to which they are stimulated and the rate at which they are resolved. Regardless, much work remains to be done to further our understanding of the enigmatic role of AR and its contribution of antioxidant defenses as well as the development of secondary diabetic complications.
V. AR Inhibitors and the Treatment of Secondary Diabetic Complications
Despite the initial promise, outcomes of clinical trials with AR inhibitors have been disappointing. Most studies reveal only modest improvement with multiple side effects. However, despite such negative data, it would be unfortunate if anti-AR therapy were to be relegated to a historical footnote. Clinical trials with AR inhibitors were designed and conducted with only limited information about the enzyme and with little or no understanding of its physiological role in processes other than the reduction of glucose. Moreover, most clinical trials were designed to examine only a limited set of physiological and pathological end points and were mostly focused on diabetic neuropathy. However, subsequent to initial clinical trials, much has been learned about the enzyme and its role in glucose metabolism, detoxification, inflammation, and growth that will be critical in redesigning clinical trials with a larger number of pathological indices and end points.
Given the extensive data showing that by catalyzing the reduction of lipid-derived aldehydes and their glutathione conjugates (62, 66, 67), AR protects against oxidative stress (101, 128), it may be beneficial to try a combination therapy with AR inhibitor and antioxidants. Because long-term diabetes is associated with increased oxidative stress, the beneficial effects of AR inhibitors may be diminished by a concurrent accumulation of lipid peroxidation products. Therefore, to prevent this, it may be necessary to concurrently administer antioxidants that prevent lipid peroxidation or enhance the expression of antioxidant enzymes that can compensate for the lack of AR. Treatment with antioxidants may also keep the enzyme in the reduced form and thus prevent drug resistance that develops due to AR modification under conditions of chronic hyperglycemia. Additionally, treatment with AR inhibitors could be restricted to a specific stage of disease development. Thus, for instance, inhibition of AR may be more beneficial during early stages of diabetes, when oxidative stress is low, than during later stages of the disease when, due to increased oxidative stress and oxidative modification of the enzyme, it may be difficult to inhibit AR or to accrue significant benefits from anti-AR interventions without further increasing oxidative stress.
Although changes in cellular metabolism and tissue injury have been monitored in both animal studies and clinical trials, changes in inflammation and inflammatory markers have not been carefully examined. In view of recent studies showing that inhibition of AR prevents multiple inflammatory pathways (Refs. 101 , 128 , and 134 ; Fig. 12), it may be necessary to examine how AR inhibitors affect systemic and local inflammation during diabetes. This appears to be particularly critical because chronic inflammation has emerged to be one of the critical features of diabetic complications, particularly cardiovascular disease. Moreover, based on data showing that inhibition of AR prevents restenosis, vascular smooth muscle growth, and endothelial cell apoptosis (101, 134, 135, 136), it may be possible to design animal and clinical studies to test the efficacy of anti-AR therapy against micro- and macrovascular complications of diabetes, which appear to be the most serious and prevalent outcomes of prolonged diabetes. Because protection against vascular changes was accompanied by an inhibition of cell signaling involved in inflammation, it appears likely that AR inhibitors may be effective against diseases other than diabetes, particularly those that are associated with high levels of cytokine generation and inflammation such as rheumatoid arthritis and sepsis. Acute intervention with AR inhibitors during sepsis appears to be particularly attractive because short-term treatment will promote recovery by inhibiting both cytokine signaling and production, without the risk of long-term treatment with AR inhibitors that may chronically increase oxidative stress.
Finally, to derive maximal benefits from AR inhibition, it is imperative to have specific and selective inhibitors. Although the currently available AR inhibitors bind to the enzyme with high affinity, they also display high levels of nonspecific toxicity. Moreover, in the absence of detailed pharmacokinetic studies, it is unclear whether the dose of AR inhibitors used for clinical studies was effective in inhibiting AR. Hence, further studies are warranted to carefully determine the extent of enzyme inhibition in human tissues for a given dose of AR inhibitor and whether their efficacy persists in diabetic tissues. More importantly, however, it appears that it may be necessary to design more specific inhibitors of AR that could selectively inhibit the ability of the enzyme to catalyze the reduction of glutathione conjugates and glucose, without inhibiting aldehyde detoxification. Our structure-activity studies (66, 67) with free and glutathione-conjugated aldehydes suggest that there are distinct glutathione- and aldehyde-binding domains on the enzyme, and selective modification of the enzyme active site could prevent recognition and reduction of glutathione conjugates without affecting aldehyde reduction. These results suggest the interesting possibility that the signaling and detoxification roles of AR could be regulated independently of each other and that more selective inhibitors could be designed to selectively prevent cell injury without compromising antioxidant defense.
VI. Conclusion
Due to its ability to reduce a wide variety of aldehydes, ranging from membrane phospholipids to glucose, AR plays a complex role in cellular metabolism and signaling. Although identified initially as a glucose-reducing enzyme, the enzyme is now believed to be an important component of antioxidant defense involved in the removal and detoxification of reactive aldehydes generated by lipid peroxidation. Inhibition of AR has been shown to prevent the development of diabetic complications in animal models; however, a critical evaluation of the clinical efficacy of AR inhibitors awaits a clearer understanding of the role of AR in regulating inflammation and cell growth. More selective and effective inhibitors are needed to specifically inhibit the cytotoxic role of AR in cell signaling without affecting its detoxification role. Such inhibitors are likely to be more effective in treating secondary diabetic complications by preventing inflammation due to chronic hyperglycemia.
Footnotes
This work was supported, in part, by NIH Grants DK36118, EY01677, HL55477, and HL59378.
First Published Online April 6, 2005
Abbreviations: AR, Aldose reductase; DAG, diaceylglycerol; DHN, 1,4-dihydroxy-2-nonene; FGF, fibroblast growth factor; GSNO, nitrosoglutathione; GSSG, oxidized glutathione; HNE, 4-hydroxynonenal; NAD, nicotinamide adenine dinucleotide; NADPH, reduced NAD phosphate; NF-B, nuclear factor--binding protein; NO, nitric oxide; PKC, protein kinase C; PLC, phospholiase C; VSMC, vascular smooth muscle cells.
References
Hers HG 1956 The mechanism of the transformation of glucose in fructose in the seminal vesicles. Biochim Biophys Acta 22:202–203
van Heyningen R 1959 Formation of polyols by the lens of the rat with ‘sugar’ cataract. Nature 468:194–195
Kinoshita JH, Dvornik D, Kraml M, Gabbay KH 1968 The effect of an aldose reductase inhibitor on the galactose-exposed rabbit lens. Biochim Biophys Acta 158:472–475
Varma SD, Kinoshita JH 1976 Inhibition of lens aldose reductase by flavonoids–their possible role in the prevention of diabetic cataracts. Biochem Pharmacol 25:2505–2513
Varma SD, Mizuno A, Kinoshita JH 1977 Diabetic cataracts and flavonoids. Science 195:205–206
Kinoshita JH, Fukushi S, Kador P, Merola LO 1979 Aldose reductase in diabetic complications of the eye. Metabolism 28:462–469
Kinoshita JH, Kador P, Catiles M 1981 Aldose reductase in diabetic cataracts. JAMA 246:257–261
Kador PF, Robison Jr WG, Kinoshita JH 1985 The pharmacology of aldose reductase inhibitors. Annu Rev Pharmacol Toxicol 25:691–714
Dvornik D 1992 Aldose reductase inhibitors as pathobiochemical probes. J Diabetes Complications 6:25–34
Tsai SC, Burnakis TG 1993 Aldose reductase inhibitors: an update. Ann Pharmacother 27:751–754
Pfeifer MA, Schumer MP, Gelber DA 1997 Aldose reductase inhibitors: the end of an era or the need for different trial designs? Diabetes 46:S82–S89
Pitts NE, Gundersen K, Mehta DJ, Vreeland F, Shaw GL, Peterson MJ, Collier J 1986 Aldose reductase inhibitors in clinical practice. Preliminary studies on diabetic neuropathy and retinopathy. Drugs 32:30–35
Stribling D 1990 Clinical trials with aldose reductase inhibitors. Exp Eye Res 50:621–624
Hotta N, Kakuta H, Ando F, Sakamoto N 1990 Current progress in clinical trials of aldose reductase inhibitors in Japan. Exp Eye Res 50:625–628
Ranganathan S, Krempf M, Feraille E, Charbonnel B 1993 Short term effect of an aldose reductase inhibitor on urinary albumin excretion rate (UAER) and glomerular filtration rate (GFR) in type 1 diabetic patients with incipient nephropathy. Diabetes Metab 19:257–261
Passariello N, Sepe J, Marrazzo G, De Cicco A, Peluso A, Pisano MC, Sgambato S, Tesauro P, D’Onofrio F 1993 Effect of aldose reductase inhibitor (tolrestat) on urinary albumin excretion rate and glomerular filtration rate in IDDM subjects with nephropathy. Diabetes Care 16:789–795
Handelsman DJ, Turtle JR 1981 Clinical trial of an aldose reductase inhibitor in diabetic neuropathy. Diabetes 30:459–464
Jaspan J, Maselli R, Herold K, Bartkus C 1983 Treatment of severely painful diabetic neuropathy with an aldose reductase inhibitor: relief of pain and improved somatic and autonomic nerve function. Lancet 2:758–762
Jaspan JB, Towle VL, Maselli R, Herold K 1986 Clinical studies with an aldose reductase inhibitor in the autonomic and somatic neuropathies of diabetes. Metabolism 35:83–92
Srivastava SK, Petrash JM, Sadana IJ, Ansari NH, Partridge CA 1982 Susceptibility of aldehyde and aldose reductases of human tissues to aldose reductase inhibitors. Curr Eye Res 2:407–410
Srivastava SK, Ansari NH 1988 Prevention of sugar-induced cataractogenesis in rats by butylated hydroxytoluene. Diabetes 37:1505–1508
Ansari NH, Srivastava SK 1990 Allopurinol promotes and butylated hydroxy toluene prevents sugar-induced cataractogenesis. Biochem Biophys Res Commun 168:939–943
Ansari NH, Bhatnagar A, Fulep E, Khanna P, Srivastava SK 1994 Trolox protects hyperglycemia-induced cataractogenesis in cultured rat lens. Res Commun Chem Pathol Pharmacol 84:93–104
Bhatnagar A, Srivastava SK 1992 Aldose reductase: congenial and injurious profiles of an enigmatic enzyme. Biochem Med Metab Biol 48:91–121
Sheetz MJ, King GL 2002 Molecular understanding of hyperglycemia’s adverse effects for diabetic complications. JAMA 288:2579–2588
Gonzalez RG, Barnett P, Aguayo J, Cheng HM, Chalack LT 1984 Direct measurement of polyol pathway activity in the ocular lens. Diabetes 33:196–199
Liu SQ, Bhatnagar A, Ansari NH, Srivastava SK Identification of the reactive cysteine residue in human placenta aldose reductase. Biochim Biophys Acta 1993 1164:268–272
Bhatnagar A, Liu SQ, Ueno N, Chakrabarti B, Srivastava SK 1994 Human placental aldose reductase: role of Cys-298 in substrate and inhibitor binding. Biochim Biophys Acta 1205:207–214
Srivastava SK, Hair GA, Das B 1985 Activated and unactivated forms of human erythrocyte aldose reductase. Proc Natl Acad Sci USA 82:7222–7226
Del Corso A, Barsacchi D, Camici M, Garland D, Mura U 1989 Bovine lens aldose reductase: identification of two enzyme forms. Arch Biochem Biophys 270:604–610
Grimshaw CE 1990 Chromatographic separation of activated and unactivated forms of aldose reductase. Arch Biochem Biophys 278:273–276
Lorenzi M, Toledo S, Boss GR, Lane MJ, Montisano DF 1987 The polyol pathway and glucose 6-phosphate in human endothelial cells cultured in high glucose concentrations. Diabetologia 30:222–227
Lee AY, Chung SK, Chung SS 1995 Demonstration that polyol accumulation is responsible for diabetic cataract by the use of transgenic mice expressing the aldose reductase gene in the lens. Proc Natl Acad Sci USA 92:2780–2784
Yagihashi S, Yamagishi S, Wada R, Sugimoto K, Baba M, Wong HG, Fujimoto J, Nishimura C, Kokai Y 1996 Galactosemic neuropathy in transgenic mice for human aldose reductase. Diabetes 45:56–59
Yagihashi S, Yamagishi SI, Wada Ri R, Baba M, Hohman TC, Yabe-Nishimura C, Kokai Y 2001 Neuropathy in diabetic mice overexpressing human aldose reductase and effects of aldose reductase inhibitor. Brain 124:2448–2458
Song Z, Fu DT, Chan YS, Leung S, Chung SS, Chung SK 2003 Transgenic mice overexpressing aldose reductase in Schwann cells show more severe nerve conduction velocity deficit and oxidative stress under hyperglycemic stress. Mol Cell Neurosci 23:638–647
Leto G, Pricci F, Amadio L, Iacobini C, Cordone S, Diaz-Horta O, Romeo G, Barsotti P, Rotella CM, di Mario U, Pugliese G 2001 Increased retinal endothelial cell monolayer permeability induced by the diabetic milieu: role of advanced non-enzymatic glycation and polyol pathway activation. Diabetes Metab Res Rev 17:448–458
Yan SF, Ramasamy R, Naka Y, Schmidt AM 2003 Glycation, inflammation, and RAGE: a scaffold for the macrovascular complications of diabetes and beyond. Circ Res 93:1159–1169
Nishikawa T, Edelstein D, Du XL, Yamagishi S, Matsumura T, Kaneda Y, Yorek MA, Beebe D, Oates PJ, Hammes HP, Giardino I, Brownlee M 2000 Normalizing mitochondrial superoxide production blocks three pathways of hyperglycaemic damage. Nature 404:787–790
Williamson JR, Chang K, Frangos M, Hasan KS, Ido Y, Kawamura T, Nyengaard JR, van den Enden M, Kilo C, Tilton RG 1993 Hyperglycemic pseudohypoxia and diabetic complications. Diabetes 42:801–813
Ido Y, Williamson JR 1997 Hyperglycemic cytosolic reductive stress ‘pseudohypoxia’: implications for diabetic retinopathy. Invest Ophthalmol Vis Sci 38:1467–1470
Obrosova IG, Stevens MJ, Lang HJ 2001 Diabetes-induced changes in retinal NAD-redox status: pharmacological modulation and implications for pathogenesis of diabetic retinopathy. Pharmacology 62:172–180
Thomas TP, Porcellati F, Kato K, Stevens MJ, Sherman WR, Greene DA 1994 Effects of glucose on sorbitol pathway activation, cellular redox, and metabolism of myo-inositol, phosphoinositide, and diacylglycerol in cultured human retinal pigment epithelial cells. J Clin Invest 93:2718–2724
Derubertis FR, Craven PA 1994 Activation of protein kinase C in glomerular cells in diabetes. Mechanisms and potential links to the pathogenesis of diabetic glomerulopathy. Diabetes 43:1–8
Koya D, King GL Protein kinase C activation and the development of diabetic complications. Diabetes 47:859–866
Graier WF, Grubenthal I, Dittrich P, Wascher TC, Kostner GM 1995 Intracellular mechanism of high D-glucose-induced modulation of vascular cell proliferation. Eur J Pharmacol 294:221–229
Frank RN 2002 Potential new medical therapies for diabetic retinopathy: protein kinase C inhibitors. Am J Ophthalmol 133:693–698
Tuttle KR, Anderson PW 2003 A novel potential therapy for diabetic nephropathy and vascular complications: protein kinase C ? inhibition. Am J Kidney Dis 42:456–465
Burg MB 1988 Role of aldose reductase and sorbitol in maintaining the medullary intracellular milieu. Kidney Int 33:635–641
Burg MB 1995 Molecular basis of osmotic regulation. Am J Physiol 268:F983–F996
Donohue PJ, Alberts GF, Hampton BS, Winkles JA 1994 A delayed-early gene activated by fibroblast growth factor-1 encodes a protein related to aldose reductase. J Biol Chem 269:8604–8609
Iwata T, Sato S, Jimenez J, McGowan M, Moroni M, Dey A, Ibaraki N, Reddy VN, Carper D 1999 Osmotic response element is required for the induction of aldose reductase by tumor necrosis factor-. J Biol Chem 274:7993–8001
Ruef J, Liu SQ, Bode C, Tocchi M, Srivastava S, Runge MS, Bhatnagar A 2000 Involvement of aldose reductase in vascular smooth muscle cell growth and lesion formation after arterial injury. Arterioscler Thromb Vasc Biol 20:1745–1752
Spycher SE, Tabataba-Vakili S, O’Donnell VB, Palomba L, Azzi A 1997 Aldose reductase induction: a novel response to oxidative stress of smooth muscle cells. FASEB J 11:181–188
Tawata M, Ohtaka M, Hosaka Y, Onaya T 1992 Aldose reductase mRNA expression and its activity are induced by glucose in fetal rat aortic smooth muscle (A10) cells. Life Sci 51:719–726
Ramana KV, Chandra D, Srivastava S, Bhatnagar A, Srivastava SK 2003 Aldose reductase mediates the mitogenic signals of cytokines. Chem Biol Interact 143–144:587–596
Bhatnagar A, Ruef J, Liu S, Srivastava S, Srivastava SK 2001 Regulation of vascular smooth muscle cell growth by aldose reductase. Chem Biol Interact 130–132:627–636
Sibbitt Jr WL, Mills RG, Bigler CF, Eaton RP, Griffey RH, Vander Jagt DL 1989 Glucose inhibition of human fibroblast proliferation and response to growth factors is prevented by inhibitors of aldose reductase. Mech Ageing Dev 47:265–279
Derylo B, Babazono T, Glogowski E, Kapor-Drezgic J, Hohman T, Whiteside C 1998 High glucose-induced mesangial cell altered contractility: role of the polyol pathway. Diabetologia 41:507–515
Asnaghi V, Gerhardinger C, Hoehn T, Adeboje A, Lorenzi M 2003 A role for the polyol pathway in the early neuroretinal apoptosis and glial changes induced by diabetes in the rat. Diabetes 52:506–511
Price SA, Agthong S, Middlemas AB, Tomlinson DR 2004 Mitogen-activated protein kinase p38 mediates reduced nerve conduction velocity in experimental diabetic neuropathy: interactions with aldose reductase. Diabetes 53:1851–1856
Srivastava S, Watowich SJ, Petrash JM, Srivastava SK, Bhatnagar A 1999 Structural and kinetic determinants of aldehyde reduction by aldose reductase. Biochemistry 38:42–54
Srivastava S, Liu SQ, Conklin DJ, Zacarias A, Srivastava SK, Bhatnagar A 2001 Involvement of aldose reductase in the metabolism of atherogenic aldehydes. Chem Biol Interact 130–132:563–571
Srivastava S, Chandrasekar B, Bhatnagar A, Prabhu SD2002 Lipid peroxidation-derived aldehydes and oxidative stress in the failing heart: role of aldose reductase. Am J Physiol Heart Circ Physiol 283:H2612–H2619
Ramana KV, Dixit BL, Srivastava S, Bhatnagar A, Balendiran GK, Watowich SJ, Petrash JM, Srivastava SK 2001 Characterization of the glutathione binding site of aldose reductase. Chem Biol Interact 130–132:537–548
Ramana KV, Dixit BL, Srivastava S, Balendiran GK, Srivastava SK, Bhatnagar A 2000 Selective recognition of glutathiolated aldehydes by aldose reductase. Biochemistry 39:12172–12180
Dixit BL, Balendiran GK, Watowich SJ, Srivastava S, Ramana KV, Petrash JM, Bhatnagar A, Srivastava SK 2000 Kinetic and structural characterization of the glutathione-binding site of aldose reductase. J Biol Chem 275:21587–21595
Srivastava S, Spite M, Trent JO, West MB, Ahmed Y, Bhatnagar A 2004 Aldose reductase-catalyzed reduction of aldehyde phospholipids. J Biol Chem 279:53395–53406
Bhatnagar A, Srivastava S, Wang LF, Chandra A, Ansari NH, Srivastava SK 1999 Cardiac metabolism of enals. Adv Exp Med Biol 463:223–229
Srivastava SK, Chandra A, Srivastava S, Petrash JM, Bhatnagar A 1999 Regulation of aldose reductase by aldehydes and nitric oxide. Adv Exp Med Biol 463:501–507
Nakano T, Petrash JM 1996 Kinetic and spectroscopic evidence for active site inhibition of human aldose reductase. Biochemistry 35:11196–11202
Schade SZ, Early SL, Williams TR, Kezdy FJ, Heinrikson RL, Grimshaw CE, Doughty CC 1990 Sequence analysis of bovine lens aldose reductase. J Biol Chem 265:3628–3635
Wilson DK, Bohren KM, Gabbay KH, Quiocho FA 1992 An unlikely sugar substrate site in the 1.65 A structure of the human aldose reductase holoenzyme implicated in diabetic complications. Science 257:81–84
Wilson DK, Tarle I, Petrash JM, Quiocho FA 1993 Refined 1.8 A structure of human aldose reductase complexed with the potent inhibitor zopolrestat. Proc Natl Acad Sci USA 90:9847–9851
Tarle I, Borhani DW, Wilson DK, Quiocho FA, Petrash JM 1993 Probing the active site of human aldose reductase. Site-directed mutagenesis of Asp-43, Tyr-48, Lys-77, and His-110. J Biol Chem 268:25687–25693
Petrash JM, Tarle I, Wilson DK, Quiocho FA 1994 Aldose reductase catalysis and crystallography. Insights from recent advances in enzyme structure and function. Diabetes 43:955–959
Borhani DW, Harter TM, Petrash JM 1992 The crystal structure of the aldose reductase. NADPH binary complex. J Biol Chem 267:24841–24847
Srivastava S, Chandra A, Ansari NH, Srivastava SK, Bhatnagar A 1998 Identification of cardiac oxidoreductase(s) involved in the metabolism of the lipid peroxidation-derived aldehyde-4-hydroxynonenal. Biochem J 329:469–475
Srivastava S, Chandra A, Wang LF, Seifert Jr WE, DaGue BB, Ansari NH, Srivastava SK, Bhatnagar A 1998 Metabolism of the lipid peroxidation product, 4-hydroxy-trans-2-nonenal, in isolated perfused rat heart. J Biol Chem 273:10893–10900
Srivastava S, Dixit BL, Cai J, Sharma S, Hurst HE, Bhatnagar A, Srivastava SK 2000 Metabolism of lipid peroxidation product, 4-hydroxynonenal (HNE) in rat erythrocytes: role of aldose reductase. Free Radic Biol Med 29:642–651
Srivastava S, Conklin DJ, Liu SQ, Prakash N, Boor PJ, Srivastava SK, Bhatnagar A 2001 Identification of biochemical pathways for the metabolism of oxidized low-density lipoprotein derived aldehyde-4-hydroxy trans-2-nonenal in vascular smooth muscle cells. Atherosclerosis 158:339–350
Del Corso A, Dal Monte M, Vilardo PG, Cecconi I, Moschini R, Banditelli S, Cappiello M, Tsai L, Mura U 1998 Site-specific inactivation of aldose reductase by 4-hydroxynonenal. Arch Biochem Biophys 350:245–248
Cappiello M, Voltarelli M, Giannessi M, Cecconi I, Camici G, Manao G, Del Corso A, Mura U 1994 Glutathione dependent modification of bovine lens aldose reductase. Exp Eye Res 58:491–501
Cappiello M, Amodeo P, Mendez BL, Scaloni A, Vilardo PG, Cecconi I, Dal Monte M, Banditelli S, Talamo F, Micheli V, Giblin FJ, Corso AD, Mura U 2001 Modulation of aldose reductase activity through S-thiolation by physiological thiols. Chem Biol Interact 130–132:597–608
Cappiello M, Vilardo PG, Cecconi I, Leverenz V, Giblin FJ, Del Corso A, Mura U 1995 Occurrence of glutathione-modified aldose reductase in oxidatively stressed bovine lens. Biochem Biophys Res Commun 207:775–782
Cappiello M, Voltarelli M, Cecconi I, Vilardo PG, Dal Monte M, Marini I, Del Corso A, Wilson DK, Quiocho FA, Petrash JM, Mura U 1996 Specifically targeted modification of human aldose reductase by physiological disulfides. J Biol Chem 271:33539–33544
Del Corso A, Camici M, Mura U 1987 In vitro modification of bovine lens aldose reductase activity. Biochem Biophys Res Commun 148:369–375
Petrash JM, Harter TM, Devine CS, Olins PO, Bhatnagar A, Liu S, Srivastava SK 1992 Involvement of cysteine residues in catalysis and inhibition of human aldose reductase. Site-directed mutagenesis of Cys-80, -298, and -303. J Biol Chem 267:24833–24840
Cecconi I, Scaloni A, Rastelli G, Moroni M, Vilardo PG, Costantino L, Cappiello M, Garland D, Carper D, Petrash JM, Del Corso A, Mura U 2002 Oxidative modification of aldose reductase induced by copper ion. Definition of the metal-protein interaction mechanism. J Biol Chem 277:42017–42027
Halder AB, James M, Crabbe C 1985 Chemical modification studies on purified bovine lens aldose reductase. Ophthalmic Res 17:185–188
Cecconi I, Moroni M, Vilardo PG, Dal Monte M, Borella P, Rastelli G, Costantino L, Garland D, Carper D, Petrash JM, Del Corso A, Mura U 1998 Oxidative modification of aldose reductase induced by copper ion. Factors and conditions affecting the process. Biochemistry 37:14167–14174
Chandra A, Srivastava S, Petrash JM, Bhatnagar A, Srivastava SK 1997 Active site modification of aldose reductase by nitric oxide donors. Biochim Biophys Acta 1341:217–222
Dixit BL, Ramana KV, Chandra D, Jackson EB, Srivastava S, Bhatnagar A, Srivastava SK 2001 Metabolic regulation of aldose reductase activity by nitric oxide donors. Chem Biol Interact 130–132:573–581
Srivastava S, Dixit BL, Ramana KV, Chandra A, Chandra D, Zacarias A, Petrash JM, Bhatnagar A, Srivastava SK 2001 Structural and kinetic modifications of aldose reductase by S-nitrosothiols. Biochem J 358:111–118
Chandra D, Jackson EB, Ramana KV, Kelley R, Srivastava SK, Bhatnagar A 2002 Nitric oxide prevents aldose reductase activation and sorbitol accumulation during diabetes. Diabetes 51:3095–3101
Srivastava SK, Ramana KV, Chandra D, Srivastava S, Bhatnagar A 2003 Regulation of aldose reductase and the polyol pathway activity by nitric oxide. Chem Biol Interact 143–144:333–340
Ramana KV, Chandra D, Srivastava S, Bhatnagar A, Srivastava SK 2003 Nitric oxide regulates the polyol pathway of glucose metabolism in vascular smooth muscle cells. FASEB J 17:417–425
Barisani D, Meneveri R, Ginelli E, Cassani C, Conte D 2000 Iron overload and gene expression in HepG2 cells: analysis by differential display. FEBS Lett 469:208–212
O’connor T, Ireland LS, Harrison DJ, Hayes JD 1999 Major differences exist in the function and tissue-specific expression of human aflatoxin B1 aldehyde reductase and the principal human aldo-keto reductase AKR1 family members. Biochem J 343:487–504
Srivastava S, Chandrasekar B, Bhatnagar A, Prabhu SD 2002 Lipid peroxidation-derived aldehydes and oxidative stress in the failing heart: role of aldose reductase. Am J Physiol 283:H2612–H2619
Ramana KV, Friedrich B, Srivastava S, Bhatnagar A, Srivastava SK 2004 Activation of nuclear factor-B by hyperglycemia in vascular smooth muscle cells is regulated by aldose reductase. Diabetes 53:2910–2920
Rittner HL, Hafner V, Klimiuk PA, Szweda LI, Goronzy JJ, Weyand CM 1999 Aldose reductase functions as a detoxification system for lipid peroxidation products in vasculitis. J Clin Invest 103:1007–1013
Shinmura K, Bolli R, Liu SQ, Tang XL, Kodani E, Xuan YT, Srivastava S, Bhatnagar A 2002 Aldose reductase is an obligatory mediator of the late phase of ischemic preconditioning. Circ Res 91:240–246
Hwang YC, Sato S, Tsai JY, Yan S, Bakr S, Zhang H, Oates PJ, Ramasamy R 2002 Aldose reductase activation is a key component of myocardial response to ischemia. FASEB J 16:243–245
Ramasamy R, Oates PJ, Schaefer S 1997 Aldose reductase inhibition protects diabetic and nondiabetic rat hearts from ischemic injury. Diabetes 46:292–300
Kaneko M, Ramasamy R 2004 Aldose reductase: a key player in myocardial ischemic injury. Exerc Sport Sci Rev 32:19–23
Hwang YC, Kaneko M, Bakr S, Liao H, Lu Y, Lewis ER, Yan S, Ii S, Itakura M, Rui L, Skopicki H, Homma S, Schmidt AM, Oates PJ, Szabolcs M, Ramasamy R 2004 Central role for aldose reductase pathway in myocardial ischemic injury. FASEB J 18:1192–1199
Horvath JJ, Witmer CM, Witz G 1992 Nephrotoxicity of the 1:1 acrolein-glutathione adduct in the rat. Toxicol Appl Pharmacol 117:200–207
Chakrabarti S, Malick MA 1991 In vivo nephrotoxic action of an isomeric mixture of S-(1-phenyl-2-hydroxyethyl)glutathione and S-(2-phenyl-2-hydroxyethyl)glutathione in Fischer-344 rats. Toxicology 67:15–27
Boon PJ, Marinho HS, Oosting R, Mulder GJ 1999 Glutathione conjugation of 4-hydroxy-trans-2,3-nonenal in the rat in vivo, the isolated perfused liver and erythrocytes. Toxicol Appl Pharmacol 159:214–223
Kicic E, Palmer TN 1996 Increased white cell aldose reductase mRNA levels in diabetic patients. Diabetes Res Clin Pract 33:31–36
Shimizu H, Ohtani KI, Tsuchiya T, Sato N, Tanaka Y, Takahashi H, Uehara Y, Inukai T, Mori M 2000 Aldose reductase mRNA expression is associated with rapid development of diabetic microangiopathy in Japanese type 2 diabetic (T2DM) patients. Diabetes Nutr Metab 13:75–79
Spallarossa P, Barsotti A, Cordera R, Ghigliotti G, Maggi D, Brunelli C 2004 Reduction of cardiovascular morbidity and mortality in type 2 diabetes. A rational approach to hypoglycemic therapy. J Endocrinol Invest 27:485–495
Moncada S, Palmer RM, Higgs EA 1991 Nitric oxide: physiology, pathophysiology, and pharmacology. Pharmacol Rev 43:109–142
Wu SY, Leske MC 2000 Antioxidants and cataract formation: a summary review. Int Ophthalmol Clin 40:71–81
Richer S 2000 Antioxidants and the eye. Int Ophthalmol Clin 40:1–16
Kowluru RA, Kennedy A 2001 Therapeutic potential of anti-oxidants and diabetic retinopathy. Expert Opin Investig Drugs 10:1665–1676
Dickinson PJ, Carrington AL, Frost GS, Boulton AJ 2002 Neurovascular disease, antioxidants and glycation in diabetes. Diabetes Metab Res Rev 18:260–272
Vaziri ND 2004 Roles of oxidative stress and antioxidant therapy in chronic kidney disease and hypertension. Curr Opin Nephrol Hypertens 13:93–99
Ruhe RC, McDonald RB 2001 Use of antioxidant nutrients in the prevention and treatment of type 2 diabetes. J Am Coll Nutr 20:363S–369S
Basta G, Schmidt AM, De Caterina R 2004 Advanced glycation end products and vascular inflammation: implications for accelerated atherosclerosis in diabetes. Cardiovasc Res 63:582–592
Dandona P, Chaudhuri A, Aljada A 2004 Endothelial dysfunction and hypertension in diabetes mellitus. Med Clin North Am 88:911–931
Wilson Tang WH, Maroo A, Young JB 2004 Ischemic heart disease and congestive heart failure in diabetic patients. Med Clin North Am 88:1037–1061
Lim HS, Lip 2003 GY Diabetes, the renin-angiotensin system and heart disease. Curr Vasc Pharmacol 1:225–238
Lim HS, MacFadyen RJ, Lip GY 2004 Diabetes mellitus, the renin-angiotensin-aldosterone system, and the heart. Arch Intern Med 164:1737–1748
Morgan KP, Kapur A, Beatt KJ 2004 Anatomy of coronary disease in diabetic patients: an explanation for poorer outcomes after percutaneous coronary intervention and potential target for intervention. Heart 90:732–738
Indolfi C, Mongiardo A, Curcio A, Torella D 2003 Molecular mechanisms of in-stent restenosis and approach to therapy with eluting stents. Trends Cardiovasc Med 3:142–148
Ramana KV, Chandra D, Srivastava S, Bhatnagar A, Aggarwal BB, Srivastava SK 2002 Aldose reductase mediates mitogenic signaling in vascular smooth muscle cells. J Biol Chem 277:32063–32070
Zhou Z, Lauer MA, Wang K, Forudi F, Zhou X, Song X, Solowski N, Kapadia SR, Nakada MT, Topol EJ, Lincoff AM 2002 Effect of anti-tumor necrosis factor- polyclonal antibody on restenosis after balloon angioplasty in a rabbit atherosclerotic model. Atherosclerosis 161:153–159
Catley MC, Cambridge LM, Nasuhara Y, Ito K, Chivers JE, Beaton A, Holden NS, Bergmann MW, Barnes PJ, Newton R 2004 Inhibitors of protein kinase C (PKC) prevent activated transcription: role of events downstream of NF-B DNA binding. J Biol Chem 279:18457–18466
Foey AD, Brennan FM 2004 Conventional protein kinase C and atypical protein kinase C differentially regulate macrophage production of tumor necrosis factor- and interleukin-10. Immunology 112:44–53
Satoh A, Gukovskaya AS, Nieto JM, Cheng JH, Gukovsky I, Reeve Jr JR, Shimosegawa T, Pandol SJ 2004 PKC- and - regulate NF-B activation induced by cholecystokinin and TNF- in pancreatic acinar cells. Am J Physiol Gastrointest Liver Physiol 287:G582–G591
Ramana KV, Friedrich B, Bhatnagar A, Srivastava SK 2003 Aldose reductase mediates cytotoxic signals of hyperglycemia and TNF- in human lens epithelial cells. FASEB J 17:315–317
Ramana KV, Bhatnagar A, Srivastava SK 2004 Inhibition of aldose reductase attenuates TNF--induced expression of adhesion molecules in endothelial cells. FASEB J 18:1209–1218
Chandra D, Ramana KV, Friedrich B, Srivastava S, Bhatnagar A, Srivastava SK 2003 Role of aldose reductase in TNF--induced apoptosis of vascular endothelial cells. Chem Biol Interact 143–144:605–612
Ramana KV, Bhatnagar A, Srivastava SK 2004 Aldose reductase regulates TNF--induced cell signaling and apoptosis in vascular endothelial cells. FEBS Lett 570:189–194
Srivastava S, Ramana KV, Srivastana SK, D’Souza SE, Bhatnagar A2004 Role of aldose reductase in the detoxification of oxidized phospholipids. ACS Symposium Series 865:49–64
Vander Jagt DL, Hassebrook RK, Hunsaker LA, Brown WM, Royer RE 2001 Metabolism of the 2-oxoaldehyde methylglyoxal by aldose reductase and by glyoxalase-I: roles for glutathione in both enzymes and implications for diabetic complications. Chem Biol Interact 130–132:549–562
Wermuth B, Monder C 1983 Aldose and aldehyde reductase exhibit isocorticosteroid reductase activity. Eur J Biochem 131:423–426
Matsuura K, Deyashiki Y, Bunai Y, Ohya I, Hara A 1996 Aldose reductase is a major reductase for isocaproaldehyde, a product of side-chain cleavage of cholesterol, in human and animal adrenal glands. Arch Biochem Biophys 328:265–271
Petrash JM, Harter TM, Murdock GL 1996 A potential role for aldose reductase in steroid metabolism. In: Weiner H, Lindahl R, Crabb DW, Flynn TG, eds. Enzymology and molecular biology of carbonyl metabolism. Vol 6. New York: Plenum Press; 465–473
Srivastava S, Liu SQ, Bhatnagar A 2003 Cellular metabolism of base propanols. FASEB J 17:A175–A176(Satish K. Srivastava, Kot)
Division of Cardiology (A.B.), Department of Medicine, University of Louisville, Louisville, Kentucky 40202
Abstract
Aldose reductase (AR) is widely expressed aldehyde-metabolizing enzyme. The reduction of glucose by the AR-catalyzed polyol pathway has been linked to the development of secondary diabetic complications. Although treatment with AR inhibitors has been shown to prevent tissue injury in animal models of diabetes, the clinical efficacy of these drugs remains to be established. Recent studies suggest that glucose may be an incidental substrate of AR, which appears to be more adept in catalyzing the reduction of a wide range of aldehydes generated from lipid peroxidation. Moreover, inhibition of the enzyme has been shown to increase inflammation-induced vascular oxidative stress and prevent myocardial protection associated with the late phase of ischemic preconditioning. On the basis of these studies, several investigators have ascribed an important antioxidant role to the enzyme. Additionally, ongoing work indicates that AR is a critical component of intracellular signaling, and inhibition of the enzyme prevents high glucose-, cytokine-, or growth factor-induced activation of protein kinase C and nuclear factor--binding protein. Thus, treatment with AR inhibitors prevents vascular smooth muscle cell growth and endothelial cell apoptosis in culture and inflammation and restenosis in vivo. Additional studies indicate that the antioxidant and signaling roles of AR are interlinked and that AR regulates protein kinase C and nuclear factor-B via redox-sensitive mechanisms. These data underscore the need for reevaluating anti-AR interventions for the treatment of diabetic complications. Potentially, the development of newer drugs that selectively inhibit ARmediated glucose metabolism and signaling, without affecting aldehyde detoxification, may be useful in preventing inflammation associated with the development of diabetic complications, particularly micro- and macrovascular diseases.
I. Introduction: Aldose Reductase and Diabetic Complications
II. AR and Antioxidant Protection
III. Redox Regulation of AR Activity
IV. Regulation of Intracellular Signaling by AR
V. AR Inhibitors and the Treatment of Secondary Diabetic Complications
VI. Conclusion
I. Introduction: Aldose Reductase and Diabetic Complications
ALDOSE REDUCTASE (AR) is a monomeric reduced nicotinamide adenine dinucleotide (NAD) phosphate (NADPH)-dependent enzyme and a member of aldo-keto reductase superfamily. The enzyme was described in 1956 by Hers (1) as a glucose-reducing activity. It was subsequently reported by van Heyningen (2) that high levels of AR activity are present in the rat lens and that during diabetic and galactosemic cataractogenesis, AR-derived polyols—sorbitol and galactitol—accumulate in the ocular lens. Building on this observation, Kinoshita et al. (3) and Varma and Kinoshita (4) demonstrated that treatment with pharmacological inhibitors of AR ameliorated cataractogenesis in diabetic rats and galactose-exposed rabbits. Based on these observations it was proposed that accumulation of sorbitol in the lens, due to AR-catalyzed reduction of glucose, causes osmotic swelling resulting in ionic imbalance and protein insolubilization leading to cataractogenesis (5, 6, 7). A similar sequence of events could also account for hyperglycemic injury associated with diabetic retinopathy, nephropathy, and neuropathy (Fig. 1).
The osmotic hypothesis that diabetic complications are due to sorbitol accumulation in tissues has engendered extensive investigations over the last three decades. Several drugs with varying AR-inhibiting efficacy (e.g., sorbinil, statil, tolrestat, and zopolrestat) have been synthesized and tested (8, 9, 10, 11). Initial trials in animal models showed significant protection against diabetic complications (12, 13, 14). AR inhibitors, in addition to preventing diabetic and galactosemic cataracts (3, 4), ameliorated some of the features of diabetic nephropathy (15, 16) and neuropathy (17, 18, 19). However, clinical trials with AR inhibitors have yielded uncertain results, in part due to the high nonspecific toxicity of this class of drugs.
In the mid-1980s we demonstrated that most of the inhibitors synthesized by pharmaceutical companies were not selective for AR but also inhibited other members of the aldo-keto reductase superfamily such as aldehyde reductase (20). In addition, we also demonstrated that increased osmotic pressure due to accumulation of polyols in galactosemic and diabetic cataractogenesis could not be the main cause of cataractogenesis (21, 22, 23). Antioxidants such as butylated hydroxytoluene and 6-hydroxy-2,5,7,8-tetramethenyl-chroman-2-carboxylic acid (Trolox) prevented diabetic cataractogenesis in rats and significantly attenuated lens opacity in galactose-fed rats even though the polyol levels in the lens were extremely high (80–90 mM), indicating that polyol accumulation per se is not sufficient for cataractogenesis and that other metabolic changes accompanying AR activation may be critical and important modulators of the cataractous effects of hyperglycemia and diabetes (Fig. 2).
Because AR utilizes NADPH to catalyze glucose reduction, we, as well as other investigators, suggested that tissue injury associated with high glucose may be due, in part, to increased NADPH utilization by the reduction of glucose by AR (24, 25). In the presence of normal glucose (5.5 mM), AR-catalyzed reduction represents less than 3% of total glucose utilization, whereas in the presence of high glucose (20 mM), more than 30% of the glucose is used by AR (26), suggesting that the profound increase in the AR-catalyzed reductive pathway may impose a significant strain on NADPH supply. Because NADPH is used for several critical reductive metabolic steps, such as the detoxification of reactive oxygen species and hydroperoxides (e.g., by the glutathione reductase/glutathione peroxidase system), a large drain on the NADPH pool could compromise the ability of the cell to protect itself from oxidative stress.
Another reason for the inconsistent effects of AR inhibitors may relate to posttranslation modification of the enzyme. As documented extensively in our previous publications (26, 27, 28), the oxidation state of a single cysteine residue located at the active site of the enzyme regulates both substrate and inhibitor binding and thus, given the extensive oxidative changes in diabetes, it is likely that in diabetic tissues AR is insensitive to inhibitors due to oxidative modification. In support of this view, we have demonstrated that AR in human erythrocytes exists in two forms, activated and unactivated, and in hyperglycemia total activity of AR increases (29). Multiple forms of AR have also been reported by other investigators (30, 31), and our in vitro data suggest that oxidants can induce a variety of changes in the catalytic activity of the enzyme, although which of these forms occur in vivo and how they are interconverted remains unclear. Nevertheless, the view that the hyperglycemia changes the sensitivity of AR to inhibition is further supported by the observation that prolonged culture of endothelial cells in high glucose progressively decreases the efficacy of sorbinil in preventing sorbitol accumulation (32).
In contrast to inhibitor data, newer molecular approaches have provided more unambiguous evidence for the involvement of AR in diabetic complications. In these studies transgenic overexpression of AR gene selectively in the lens was found to accelerate diabetic and galactosemic cataract formation in mice (33). Additionally, ubiquitous overexpression of the AR gene increased the rate of neuropathic changes in diabetic animals (34, 35, 36). Collectively, these data argue strongly that AR is an important component of high glucose-induced metabolic changes that underlie the development of secondary diabetic complications. Nevertheless, despite this evidence, the exact mechanism by which AR contributes to the development of diabetic complications remains unclear. Persistent increase in extracellular glucose levels induces pleiotrophic changes in metabolism that elicit polygenic responses (Fig. 3). Extensive changes in the activation of protein kinases and the accumulation of advanced glycation end products have been reported (37, 38, 39), although their relationships with modulatory influences on AR remain unclear. In principle, AR could contribute to both protein kinase activation and advanced glycation end product accumulation. In addition, AR could catalyze the formation of potent protein glycating agents and induce oxidative stress.
Reduction of glucose by AR leads to the formation of sorbitol, which, in some tissues, is further oxidized to fructose upon sorbitol dehydrogenase-catalyzed oxidation. The conversion of glucose to fructose (the "polyol pathway") results not only in the utilization of NADPH, but also NAD+. As a result, increased activity of the polyol pathway during hyperglycemia could lead to a depletion of NADPH and accumulation of reduced NAD. This shift in the redox state of pyridine coenzymes recapitulates the metabolic phenotype of hypoxia and has been proposed to induce a state of pseudohypoxia resulting in hypoxia-like responses (40, 41, 42). Polyol pathway-mediated alterations in pyridine nucleotides have been linked to diverse metabolic changes such as the synthesis of nitric oxide (NO) and activation of protein kinases (39). Specifically, it has been proposed that the increase in NADH due to elevated polyol pathway activity could increase the synthesis of diacylglycerol (DAG) from dihydroxyacetone phosphate (43). DAG levels could also increase by stress that activates phospholipase C (PLC in Fig. 4). DAG is an essential activator of the classical and novel members of the protein kinase C family, and DAG-dependent activation of these kinases is thought to play a key role in mesangial expansion and smooth muscle cells proliferation induced by high glucose (44, 45, 46). Inhibitors of specific protein kinase C (PKC) isoforms are currently under clinical trial for the treatment of diabetic complications (47, 48).
II. AR and Antioxidant Protection
Due to its ability to reduce glucose, AR is involved in several tissue-specific metabolic pathways. For instance, in the kidney, AR participates in osmoregulation (49, 50) and, in seminal vesicles, in the generation of fructose (1). The observation that AR and related proteins are up-regulated by fibroblast growth factor (FGF) and other mitogens suggests that AR may be involved in cell growth or growth factor-induced changes in cellular metabolism (51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61). Our studies show that in vitro homogenous AR catalyzes the reduction of a large series of saturated and unsaturated aldehydes with 103- to 104-fold higher efficiency than glucose (62). The enzyme is particularly efficient in reducing medium- to long-chain (C-6 to C-18) aldehydes such as those generated in high abundance during lipid peroxidation (63, 64). The enzyme also catalyzes the reduction of the glutathione conjugates of unsaturated aldehydes, in many cases with efficiency higher than that of the parent free aldehyde (65, 66, 67). The reduction of glutathione conjugates by AR may be a protective mechanism that may be useful in minimizing the reactivity of the aldehyde function unquenched by glutathiolation. In addition, our recent studies show that AR is also an efficient catalyst for the reduction of core aldehydes—or aldehydes generated in oxidized phospholipids (Refs. 65, 66, 67, 68, 69, 70 and Fig. 5).
The role of AR in detoxification is supported by structural studies showing that the active site of AR lacks ionic residue characteristic of carbohydrate-binding proteins (71, 72, 73, 74, 75, 76). Instead, x-ray analyses of AR crystals reveal a highly plastic and hydrophobic active site (73, 74). This site could potentially accommodate a wide range of structures if the aldehyde function were to orient itself appropriately between the two ionic active site residues, His-110 and Tyr-48, which participate in acid-base catalysis. The structure of the binary complex of the enzyme with NADP+ also indicates a profound conformational change upon NADPH binding (72). It has been suggested that the energy released as a result of this interaction is used for stabilization of the transition state with little demand from energy stabilization due to substrate binding (77). Hence, as a result of high-affinity interaction with NADPH, AR functions as an unusually promiscuous aldehyde removase, features that seem to be critically required of a detoxification enzyme involved in the removal of a wide range of aldehydes and glutathione aldehyde adducts generated during lipid peroxidation.
Based on our substrate specificity studies showing high-affinity reduction of glutathione conjugates by AR (66, 67), we reasoned that the active site of the enzyme must conform to a specific glutathione-binding domain. Consistent with the presence of specific interactions between the amino acid residues of glutathione and the AR active site, we found that alterations in the structure of glutathione diminished the catalytic efficiency for the reduction of glutathione-aldehyde conjugates and that nonaldehydic conjugates of glutathione or glutathione analogs displayed active site inhibition (67). Molecular dynamics calculations suggest that the conjugates adopt a specific low-energy configuration at the active site (Fig. 6). Mutations of the active site residues identified by these calculations selectively decreased catalysis of the glutathione-aldehyde conjugates, without affecting reduction of the free aldehyde. The high specificity and selectivity with which the enzyme catalyzes the reduction of glutathione conjugates suggest that such conjugates may be in vivo substrates of the enzyme. Indeed, our metabolic studies with 4-hydroxynonenal (HNE) show AR-dependent reduction of its glutathione adduct in heart, smooth muscle, and erythrocytes (78, 79, 80, 81).
Reduction of aldehyde-glutathione conjugates by AR may be of physiological significance, particularly under conditions of oxidative stress when other antioxidant mechanisms are overwhelmed. Under these conditions, AR, by reducing both free aldehydes and their glutathione conjugates, could promote efficient removal and detoxification of unsaturated aldehydes, which are the major electrophilic end products of lipid peroxidation. Thus, investigations into the structure and kinetics of AR point toward a general detoxification role of the enzyme, indicating that lipid aldehydes and their glutathione conjugates are physiological substrates of the enzyme and that glucose is perhaps an incidental substrate, which is used only when it is high in concentration or occasionally for tissue-specific metabolism.
Consistent with its role as a detoxification enzyme, AR has been found to be regulated by aldehydes generated from lipid peroxidation (64, 70, 82), thiol-reducing agents (83, 84, 85, 86, 87, 88), metal ions (89, 90, 91), and NO (92, 93, 94, 95, 96, 97). Tissue levels of AR are also increased under conditions of high oxidative stress such as iron overload (98), alcoholic liver disease (99), heart failure (100), and vascular inflammation (53, 101). Moreover, AR is also specifically up-regulated during vasculitis, specifically in the areas of high HNE formation, and inhibition of AR increases the concentration of free HNE and protein-HNE adducts, accompanied by a 3-fold increase in the number of apoptotic cells (102). Our studies show that AR is also up-regulated in the heart by brief episodes of ischemia (103). This increase in AR was prevented by inhibitors of PKC and NO synthase, indicating that the up-regulation of AR is regulated by cardioprotective signaling associated with the late phase of ischemic preconditioning. Furthermore, a posttranslational activation of AR during myocardial ischemia has been reported (104). The functional significance of the increase in AR in the ischemic heart is underscored by the observation that inhibition of AR abolishes the cardioprotective effects of late preconditioning (105, 106, 107). Collectively, these data provide support to the view that AR is a component of an antioxidant defense mechanism, which protects tissues from the harmful effect of lipid peroxidation products such as HNE that accumulate during conditions of oxidative stress such as ischemia and inflammation.
Although HNE and related aldehydes are metabolized by several different pathways, metabolism via AR could represent a true detoxification mechanism. In most cells, HNE and related aldehydes readily form glutathione conjugates; however, the formation of glutathione-HNE itself may not be sufficient for detoxification. The glutathione-aldehyde conjugates are toxic. They induce DNA damage and stimulate radical formation (108, 109, 110). Therefore, reduction of the glutathione-aldehyde conjugates by AR may be necessary to substantially annul the reactivity of the conjugate and to decrease free radical generation. Nonetheless, the mechanisms by which AR-dependent aldehyde metabolism regulates the development of diabetic complications remain unclear, and the contribution of AR to cell growth and antioxidant defense requires further elucidation. In particular, it remains to be clarified how AR expression and activity are regulated and which components of intracellular signaling are regulated by AR.
III. Redox Regulation of AR Activity
As discussed above, a component of the hyperglycemic injury is due to an increased flux of glucose through the polyol pathway because the inhibition of AR prevents some of the diabetic complications. Although inefficacy of AR inhibitors could be due to their nonspecificity and hypersensitivity of selected individuals, the limited long-term efficacy of the AR inhibitors could be attributed to the posttranslational modification in AR that alters ligand binding and catalysis. In our earlier studies we found that AR isolated from individuals with different levels of hyperglycemia displayed altered kinetic properties and was less sensitive to hydantoin inhibitors such as sorbinil compared with the enzyme isolated from the tissues of normoglycemic subjects (29). Similar changes were observed at various stages of purification of AR in the absence of a reducing reagent such as dithiothreitol or ?-mercaptoethanol from the tissues of normal subjects or from recombinant bacteria overexpressing AR (30, 31). Both the Michaelis-Menten constant (Km) and inhibition constant (Ki) values of the enzyme significantly increased upon its in vitro thiol modification by HNE (64, 82), nitrosoglutathione (GSNO) (92), and oxidized glutathione (GSSG) (83).
The high sensitivity of AR to oxidants such as H2O2 and NO was attributed to a highly reactive cysteine (Cys-298) residue present at the active site of the enzyme (88). Oxidants such as H2O2 cause enzyme inactivation. Also glutathiolation of the Cys-298 results in a significant inactivation of the enzyme (83, 88, 92). However, depending on the conditions of the reaction and the nature of the NO donor used, AR is either S-thiolated (inactivated enzyme) or S-nitrosated (activated enzyme). On the basis of these observations, we hypothesized that NO regulates the intracellular activity of AR and consequently the flux of glucose via the polyol pathway (92, 93, 94, 95, 96, 97, 98). Because, in hyperglycemia, NO synthesis is significantly less compared with normoglycemic subjects, it has been reasoned that the AR activity may be up-regulated in diabetic tissues (111, 112).
Cardiovascular complications are one of the major causes of mortality in patients with prolonged diabetes (113). The role of AR in cardiovascular complications, especially in atherosclerosis (100), restenosis subsequent to balloon injury (53, 57), and cardiac preconditioning (103, 104, 105, 106), has been extensively investigated. Vascular endothelial cells are the main source of NO for vascular smooth muscle cells because in the vasculature, NO synthase is present mainly in the endothelium (114). The NO secreted by endothelial cells could readily form GSNO with glutathione that is abundant in vascular smooth muscle cells (VSMC). The GSNO formed could, in turn, readily S-glutathiolate AR at Cys-298 (92). Although GSSG (50–100 μM) also S-glutathiolates AR, it is unlikely that the physiological source of S-glutathiolation of AR (or other proteins) could be GSSG because the concentration of GSSG in cells rarely exceeds 20–25 μM. Because S-glutathiolation inactivates AR, under normoglycemic conditions, it appears likely that a significant fraction of AR in vascular tissues is present in an inactive form, whereas in hyperglycemia a decrease in NADPH/NADP+ ratio and other factors would decrease NO and the AR would be in the active form. Indeed, we have demonstrated that, in diabetic rat aorta, both AR activity and sorbitol levels are more than 20-fold higher than nondiabetic aorta (95). Daily ip injections of NO synthase inhibitor, NG-nitro-L-argininemethyl ester or application of nitroglycerin patch significantly increased the activity of aorta AR as well as sorbitol formation in both nondiabetic and streptozotocin-diabetic rats. On the other hand, daily injections of NO synthase substrate, L-arginine, significantly decreased AR activity and sorbitol content in aortas of both diabetic and nondiabetic rats. Similar results were obtained when aortic rings from normal and diabetic mice were incubated with L-arginine and NG-nitro-L-argininemethyl ester, whereas, both NO synthase substrate and inhibitor had no effect on AR activity or sorbitol content of aorta from endothelial NO synthase-null mice (97). Interestingly, it was observed that S-glutathiolation of AR in VSMC by NO donors such as GSNO, which inactivates the enzyme, is reversible. Thus, the changes in glucose levels that alter the levels of NO would change the AR activity, sorbitol levels, and related effects in diabetic subjects. Hence, in addition to glycemic control, NO donors or drugs that increase NO levels could represent one treatment modality for the prevention or treatment of diabetic complications. Because hyperglycemia causes increased generation of reactive oxygen species by autooxidation of glucose and other metabolic pathways, antioxidants would also have beneficial effects. Diabetic complications such as cataractogenesis, retinopathy, and cardiovascular effects have been shown to be ameliorated by antioxidants such as butylated hydroxytoluene, butylated hydroxyanisole, Trolox, ascorbate, vitamin E, N-acetyl cysteine, pyruvate, etc. (115, 116, 117, 118, 119, 120).
IV. Regulation of Intracellular Signaling by AR
Diabetes is a major risk factor for the development of cardiovascular disease. It is associated with a 2- to 4-fold higher risk of cardiovascular disease, and it accelerates the progression and increases the severity of atherosclerotic lesion formation in peripheral, coronary, and cerebral arteries (121, 122, 123, 124, 125). Moreover, diabetics have a higher propensity for restenosis after percutaneous transluminal coronary angioplasty (126). Even though coronary stenting significantly reduces restenosis, diabetes remains a powerful predictor of in-stent restenosis (127). Processes that lead to an increase in smooth muscle cell growth in diabetic as well as nondiabetic restenotic vessels have not been identified but, given the observation that high levels of protein-HNE adducts are associated with proliferative vascular lesion, it appears that products of lipid peroxidation, such as HNE, play a significant role in modulating the growth of vascular lesion. This is supported by our observation that treatment with low concentrations (<2 μM) of HNE increases VSMC growth in culture, although at higher concentrations HNE induced apoptotic cell death (53). To test the role of HNE in vascular proliferation, we determined how changes in its metabolism via AR would affect its mitogenic activity. Surprisingly, we found that inhibition of AR prevented VSMC growth in culture (53). Serum-starved VSMC cultured in 1 μM HNE showed increased proliferation compared with cells cultured without HNE, as determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay and cell count, whereas under similar conditions, HNE caused apoptosis in vascular endothelial cells and lens epithelial cells (Fig. 7). Both proliferation and apoptosis were attenuated by inhibiting AR using two structurally different AR inhibitors, sorbinil and tolrestat, and also by using antisense AR or small interfering RNA. In addition to HNE-stimulated growth, smooth muscle cells growing in response to serum FGF, TNF, or high glucose were also sensitive to AR inhibitors (128). Moreover, inhibition of AR also prevented smooth muscle cell growth in vivo: we balloon-injured normal and diabetic rat carotid artery and followed restenosis by quantifying the neointima formation (101). In both normal and diabetic rats, AR inhibitor significantly (45%) prevented neointimal hyperplasia (Fig 8). Interestingly, the neointimal hyperplasia was associated with increased nuclear factor--binding protein (NF-B) activation (128). This was significantly prevented by sorbinil, suggesting that AR is required for signaling pathways responsible for NF-B activation and for the proliferation of smooth muscle cells in vascular lesions. Together, these observations suggest that AR is essential for smooth muscle cell growth induced by several mitogenic pathways and that inhibition of AR interrupts their growth in culture and in vivo (53, 57, 128).
Although the mechanism by which AR regulates growth remains unclear, several of the key signaling pathways related to cell growth are sensitive to AR inhibition. Significantly, our studies reveal that inhibition of AR prevents activation of the transcription factor NF-B stimulated with either TNF (Fig. 9), FGF, angiotensin II, or high glucose (101, 128). Inhibition of AR, however, does not seem to directly interfere with the DNA binding of NF-B, but prevents NF-B activation by extinguishing signaling events upstream to dissociation of NF-B from IB and the nuclear translocation of NF-B. This appears to be due to the inhibition of phosphorylation and degradation of IB in cells treated with AR inhibitors. Significantly, inhibition of AR does not prevent NF-B when the cells are stimulated by phorbol esters, indicating that inhibition of AR does not interfere with the IB-NF-B signaling pathway but prevents signaling events upstream to PKC (128).
Similar to the effects observed with TNF, inhibition or ablation of AR also interrupts the activation of the PKC-NF-B by high glucose (101). The sensitivity of both high glucose- and TNF-mediated cell growth to AR inhibitors suggests that both stimuli might activate overlapping pathways. Indeed, previous studies have shown that treatment with anti-TNF antibodies prevents accelerated restenosis in diabetic vessels (129), and in our laboratory treatment with anti-TNF antibodies was effective in preventing high glucose-induced smooth muscle cell growth in culture (K. V. Ramana, R. Tammali, A. Bhatnagar, and S. K. Srivastava, unpublished observations). Hence, it appears that the mitogenic effects of high glucose may be mediated, in part, by stimulation of cytokine release and autocrine activation of the cell growth pathways. How glucose could induce the release of cytokines is unclear. However, the recent observation that the release of TNF is regulated by PKC (130, 131, 132) suggests that activation of PKC by high glucose could trigger TNF release and stimulate growth. Because inhibition/ablation of AR prevents both PKC activation (Fig. 10) and TNF signaling, it could interrupt the initial trigger events as well as subsequent autocrine stimulation of mitogenic signaling in cells exposed to high glucose (101, 133).
Studies delineating the role of AR in intracellular signaling suggest an alternative paradigm for understanding the contribution of this enzyme to the development of diabetic complications and the efficacy of AR inhibitors against secondary diabetic complications, despite the detoxification role of the enzyme. Hence, inhibition of inflammation could represent one mechanism by which beneficial effects could be derived from inhibiting AR. Our studies show that key steps in the inflammatory process, such as NF-B activation and the increase in the expression of adhesion molecules ICAM-1 and VCAM-1 and monocyte adhesion, could be prevented by inhibiting AR (Fig. 11) (134). Moreover, inhibition of AR also prevents the cytotoxic effects of TNF on endothelial cells.
Our studies have also shown that inhibition of AR by sorbinil or tolrestat prevents TNF-induced increase in Bax and Bad and the down-regulation of Bcl-2 (135, 136). Inhibition of AR also abrogates activator protein 1 DNA binding activity and prevents the activation of caspase-3, c-Jun N-terminal kinase, and p38 MAPK in cells stimulated by TNF, suggesting that AR could be a critical regulator of TNF-induced apoptotic signaling in endothelial cells (136). Given the key role of the endothelium in regulating atherogenesis and restenosis, the salutary effects of AR inhibitors on these cells could further contribute to the ability of these drugs to limit inflammation and vascular adhesion. Although the overall effects of inhibiting AR during atherosclerotic lesion formation remain to be studied, they are likely to be complex. Given that inhibition of AR could prevent inflammatory changes as well as increase the accumulation of lipid peroxidation products, inhibition of AR could yield highly context-dependent results, and the benefits of inhibiting AR may be specific to the extent of lesion progression and hyperglycemia and/or may require concurrent administration of antioxidants. Such duality and complexity of effects is, however, expected. AR regulates oxidative and inflammatory responses, both of which could be beneficial or harmful depending upon the context and the extent to which they are stimulated and the rate at which they are resolved. Regardless, much work remains to be done to further our understanding of the enigmatic role of AR and its contribution of antioxidant defenses as well as the development of secondary diabetic complications.
V. AR Inhibitors and the Treatment of Secondary Diabetic Complications
Despite the initial promise, outcomes of clinical trials with AR inhibitors have been disappointing. Most studies reveal only modest improvement with multiple side effects. However, despite such negative data, it would be unfortunate if anti-AR therapy were to be relegated to a historical footnote. Clinical trials with AR inhibitors were designed and conducted with only limited information about the enzyme and with little or no understanding of its physiological role in processes other than the reduction of glucose. Moreover, most clinical trials were designed to examine only a limited set of physiological and pathological end points and were mostly focused on diabetic neuropathy. However, subsequent to initial clinical trials, much has been learned about the enzyme and its role in glucose metabolism, detoxification, inflammation, and growth that will be critical in redesigning clinical trials with a larger number of pathological indices and end points.
Given the extensive data showing that by catalyzing the reduction of lipid-derived aldehydes and their glutathione conjugates (62, 66, 67), AR protects against oxidative stress (101, 128), it may be beneficial to try a combination therapy with AR inhibitor and antioxidants. Because long-term diabetes is associated with increased oxidative stress, the beneficial effects of AR inhibitors may be diminished by a concurrent accumulation of lipid peroxidation products. Therefore, to prevent this, it may be necessary to concurrently administer antioxidants that prevent lipid peroxidation or enhance the expression of antioxidant enzymes that can compensate for the lack of AR. Treatment with antioxidants may also keep the enzyme in the reduced form and thus prevent drug resistance that develops due to AR modification under conditions of chronic hyperglycemia. Additionally, treatment with AR inhibitors could be restricted to a specific stage of disease development. Thus, for instance, inhibition of AR may be more beneficial during early stages of diabetes, when oxidative stress is low, than during later stages of the disease when, due to increased oxidative stress and oxidative modification of the enzyme, it may be difficult to inhibit AR or to accrue significant benefits from anti-AR interventions without further increasing oxidative stress.
Although changes in cellular metabolism and tissue injury have been monitored in both animal studies and clinical trials, changes in inflammation and inflammatory markers have not been carefully examined. In view of recent studies showing that inhibition of AR prevents multiple inflammatory pathways (Refs. 101 , 128 , and 134 ; Fig. 12), it may be necessary to examine how AR inhibitors affect systemic and local inflammation during diabetes. This appears to be particularly critical because chronic inflammation has emerged to be one of the critical features of diabetic complications, particularly cardiovascular disease. Moreover, based on data showing that inhibition of AR prevents restenosis, vascular smooth muscle growth, and endothelial cell apoptosis (101, 134, 135, 136), it may be possible to design animal and clinical studies to test the efficacy of anti-AR therapy against micro- and macrovascular complications of diabetes, which appear to be the most serious and prevalent outcomes of prolonged diabetes. Because protection against vascular changes was accompanied by an inhibition of cell signaling involved in inflammation, it appears likely that AR inhibitors may be effective against diseases other than diabetes, particularly those that are associated with high levels of cytokine generation and inflammation such as rheumatoid arthritis and sepsis. Acute intervention with AR inhibitors during sepsis appears to be particularly attractive because short-term treatment will promote recovery by inhibiting both cytokine signaling and production, without the risk of long-term treatment with AR inhibitors that may chronically increase oxidative stress.
Finally, to derive maximal benefits from AR inhibition, it is imperative to have specific and selective inhibitors. Although the currently available AR inhibitors bind to the enzyme with high affinity, they also display high levels of nonspecific toxicity. Moreover, in the absence of detailed pharmacokinetic studies, it is unclear whether the dose of AR inhibitors used for clinical studies was effective in inhibiting AR. Hence, further studies are warranted to carefully determine the extent of enzyme inhibition in human tissues for a given dose of AR inhibitor and whether their efficacy persists in diabetic tissues. More importantly, however, it appears that it may be necessary to design more specific inhibitors of AR that could selectively inhibit the ability of the enzyme to catalyze the reduction of glutathione conjugates and glucose, without inhibiting aldehyde detoxification. Our structure-activity studies (66, 67) with free and glutathione-conjugated aldehydes suggest that there are distinct glutathione- and aldehyde-binding domains on the enzyme, and selective modification of the enzyme active site could prevent recognition and reduction of glutathione conjugates without affecting aldehyde reduction. These results suggest the interesting possibility that the signaling and detoxification roles of AR could be regulated independently of each other and that more selective inhibitors could be designed to selectively prevent cell injury without compromising antioxidant defense.
VI. Conclusion
Due to its ability to reduce a wide variety of aldehydes, ranging from membrane phospholipids to glucose, AR plays a complex role in cellular metabolism and signaling. Although identified initially as a glucose-reducing enzyme, the enzyme is now believed to be an important component of antioxidant defense involved in the removal and detoxification of reactive aldehydes generated by lipid peroxidation. Inhibition of AR has been shown to prevent the development of diabetic complications in animal models; however, a critical evaluation of the clinical efficacy of AR inhibitors awaits a clearer understanding of the role of AR in regulating inflammation and cell growth. More selective and effective inhibitors are needed to specifically inhibit the cytotoxic role of AR in cell signaling without affecting its detoxification role. Such inhibitors are likely to be more effective in treating secondary diabetic complications by preventing inflammation due to chronic hyperglycemia.
Footnotes
This work was supported, in part, by NIH Grants DK36118, EY01677, HL55477, and HL59378.
First Published Online April 6, 2005
Abbreviations: AR, Aldose reductase; DAG, diaceylglycerol; DHN, 1,4-dihydroxy-2-nonene; FGF, fibroblast growth factor; GSNO, nitrosoglutathione; GSSG, oxidized glutathione; HNE, 4-hydroxynonenal; NAD, nicotinamide adenine dinucleotide; NADPH, reduced NAD phosphate; NF-B, nuclear factor--binding protein; NO, nitric oxide; PKC, protein kinase C; PLC, phospholiase C; VSMC, vascular smooth muscle cells.
References
Hers HG 1956 The mechanism of the transformation of glucose in fructose in the seminal vesicles. Biochim Biophys Acta 22:202–203
van Heyningen R 1959 Formation of polyols by the lens of the rat with ‘sugar’ cataract. Nature 468:194–195
Kinoshita JH, Dvornik D, Kraml M, Gabbay KH 1968 The effect of an aldose reductase inhibitor on the galactose-exposed rabbit lens. Biochim Biophys Acta 158:472–475
Varma SD, Kinoshita JH 1976 Inhibition of lens aldose reductase by flavonoids–their possible role in the prevention of diabetic cataracts. Biochem Pharmacol 25:2505–2513
Varma SD, Mizuno A, Kinoshita JH 1977 Diabetic cataracts and flavonoids. Science 195:205–206
Kinoshita JH, Fukushi S, Kador P, Merola LO 1979 Aldose reductase in diabetic complications of the eye. Metabolism 28:462–469
Kinoshita JH, Kador P, Catiles M 1981 Aldose reductase in diabetic cataracts. JAMA 246:257–261
Kador PF, Robison Jr WG, Kinoshita JH 1985 The pharmacology of aldose reductase inhibitors. Annu Rev Pharmacol Toxicol 25:691–714
Dvornik D 1992 Aldose reductase inhibitors as pathobiochemical probes. J Diabetes Complications 6:25–34
Tsai SC, Burnakis TG 1993 Aldose reductase inhibitors: an update. Ann Pharmacother 27:751–754
Pfeifer MA, Schumer MP, Gelber DA 1997 Aldose reductase inhibitors: the end of an era or the need for different trial designs? Diabetes 46:S82–S89
Pitts NE, Gundersen K, Mehta DJ, Vreeland F, Shaw GL, Peterson MJ, Collier J 1986 Aldose reductase inhibitors in clinical practice. Preliminary studies on diabetic neuropathy and retinopathy. Drugs 32:30–35
Stribling D 1990 Clinical trials with aldose reductase inhibitors. Exp Eye Res 50:621–624
Hotta N, Kakuta H, Ando F, Sakamoto N 1990 Current progress in clinical trials of aldose reductase inhibitors in Japan. Exp Eye Res 50:625–628
Ranganathan S, Krempf M, Feraille E, Charbonnel B 1993 Short term effect of an aldose reductase inhibitor on urinary albumin excretion rate (UAER) and glomerular filtration rate (GFR) in type 1 diabetic patients with incipient nephropathy. Diabetes Metab 19:257–261
Passariello N, Sepe J, Marrazzo G, De Cicco A, Peluso A, Pisano MC, Sgambato S, Tesauro P, D’Onofrio F 1993 Effect of aldose reductase inhibitor (tolrestat) on urinary albumin excretion rate and glomerular filtration rate in IDDM subjects with nephropathy. Diabetes Care 16:789–795
Handelsman DJ, Turtle JR 1981 Clinical trial of an aldose reductase inhibitor in diabetic neuropathy. Diabetes 30:459–464
Jaspan J, Maselli R, Herold K, Bartkus C 1983 Treatment of severely painful diabetic neuropathy with an aldose reductase inhibitor: relief of pain and improved somatic and autonomic nerve function. Lancet 2:758–762
Jaspan JB, Towle VL, Maselli R, Herold K 1986 Clinical studies with an aldose reductase inhibitor in the autonomic and somatic neuropathies of diabetes. Metabolism 35:83–92
Srivastava SK, Petrash JM, Sadana IJ, Ansari NH, Partridge CA 1982 Susceptibility of aldehyde and aldose reductases of human tissues to aldose reductase inhibitors. Curr Eye Res 2:407–410
Srivastava SK, Ansari NH 1988 Prevention of sugar-induced cataractogenesis in rats by butylated hydroxytoluene. Diabetes 37:1505–1508
Ansari NH, Srivastava SK 1990 Allopurinol promotes and butylated hydroxy toluene prevents sugar-induced cataractogenesis. Biochem Biophys Res Commun 168:939–943
Ansari NH, Bhatnagar A, Fulep E, Khanna P, Srivastava SK 1994 Trolox protects hyperglycemia-induced cataractogenesis in cultured rat lens. Res Commun Chem Pathol Pharmacol 84:93–104
Bhatnagar A, Srivastava SK 1992 Aldose reductase: congenial and injurious profiles of an enigmatic enzyme. Biochem Med Metab Biol 48:91–121
Sheetz MJ, King GL 2002 Molecular understanding of hyperglycemia’s adverse effects for diabetic complications. JAMA 288:2579–2588
Gonzalez RG, Barnett P, Aguayo J, Cheng HM, Chalack LT 1984 Direct measurement of polyol pathway activity in the ocular lens. Diabetes 33:196–199
Liu SQ, Bhatnagar A, Ansari NH, Srivastava SK Identification of the reactive cysteine residue in human placenta aldose reductase. Biochim Biophys Acta 1993 1164:268–272
Bhatnagar A, Liu SQ, Ueno N, Chakrabarti B, Srivastava SK 1994 Human placental aldose reductase: role of Cys-298 in substrate and inhibitor binding. Biochim Biophys Acta 1205:207–214
Srivastava SK, Hair GA, Das B 1985 Activated and unactivated forms of human erythrocyte aldose reductase. Proc Natl Acad Sci USA 82:7222–7226
Del Corso A, Barsacchi D, Camici M, Garland D, Mura U 1989 Bovine lens aldose reductase: identification of two enzyme forms. Arch Biochem Biophys 270:604–610
Grimshaw CE 1990 Chromatographic separation of activated and unactivated forms of aldose reductase. Arch Biochem Biophys 278:273–276
Lorenzi M, Toledo S, Boss GR, Lane MJ, Montisano DF 1987 The polyol pathway and glucose 6-phosphate in human endothelial cells cultured in high glucose concentrations. Diabetologia 30:222–227
Lee AY, Chung SK, Chung SS 1995 Demonstration that polyol accumulation is responsible for diabetic cataract by the use of transgenic mice expressing the aldose reductase gene in the lens. Proc Natl Acad Sci USA 92:2780–2784
Yagihashi S, Yamagishi S, Wada R, Sugimoto K, Baba M, Wong HG, Fujimoto J, Nishimura C, Kokai Y 1996 Galactosemic neuropathy in transgenic mice for human aldose reductase. Diabetes 45:56–59
Yagihashi S, Yamagishi SI, Wada Ri R, Baba M, Hohman TC, Yabe-Nishimura C, Kokai Y 2001 Neuropathy in diabetic mice overexpressing human aldose reductase and effects of aldose reductase inhibitor. Brain 124:2448–2458
Song Z, Fu DT, Chan YS, Leung S, Chung SS, Chung SK 2003 Transgenic mice overexpressing aldose reductase in Schwann cells show more severe nerve conduction velocity deficit and oxidative stress under hyperglycemic stress. Mol Cell Neurosci 23:638–647
Leto G, Pricci F, Amadio L, Iacobini C, Cordone S, Diaz-Horta O, Romeo G, Barsotti P, Rotella CM, di Mario U, Pugliese G 2001 Increased retinal endothelial cell monolayer permeability induced by the diabetic milieu: role of advanced non-enzymatic glycation and polyol pathway activation. Diabetes Metab Res Rev 17:448–458
Yan SF, Ramasamy R, Naka Y, Schmidt AM 2003 Glycation, inflammation, and RAGE: a scaffold for the macrovascular complications of diabetes and beyond. Circ Res 93:1159–1169
Nishikawa T, Edelstein D, Du XL, Yamagishi S, Matsumura T, Kaneda Y, Yorek MA, Beebe D, Oates PJ, Hammes HP, Giardino I, Brownlee M 2000 Normalizing mitochondrial superoxide production blocks three pathways of hyperglycaemic damage. Nature 404:787–790
Williamson JR, Chang K, Frangos M, Hasan KS, Ido Y, Kawamura T, Nyengaard JR, van den Enden M, Kilo C, Tilton RG 1993 Hyperglycemic pseudohypoxia and diabetic complications. Diabetes 42:801–813
Ido Y, Williamson JR 1997 Hyperglycemic cytosolic reductive stress ‘pseudohypoxia’: implications for diabetic retinopathy. Invest Ophthalmol Vis Sci 38:1467–1470
Obrosova IG, Stevens MJ, Lang HJ 2001 Diabetes-induced changes in retinal NAD-redox status: pharmacological modulation and implications for pathogenesis of diabetic retinopathy. Pharmacology 62:172–180
Thomas TP, Porcellati F, Kato K, Stevens MJ, Sherman WR, Greene DA 1994 Effects of glucose on sorbitol pathway activation, cellular redox, and metabolism of myo-inositol, phosphoinositide, and diacylglycerol in cultured human retinal pigment epithelial cells. J Clin Invest 93:2718–2724
Derubertis FR, Craven PA 1994 Activation of protein kinase C in glomerular cells in diabetes. Mechanisms and potential links to the pathogenesis of diabetic glomerulopathy. Diabetes 43:1–8
Koya D, King GL Protein kinase C activation and the development of diabetic complications. Diabetes 47:859–866
Graier WF, Grubenthal I, Dittrich P, Wascher TC, Kostner GM 1995 Intracellular mechanism of high D-glucose-induced modulation of vascular cell proliferation. Eur J Pharmacol 294:221–229
Frank RN 2002 Potential new medical therapies for diabetic retinopathy: protein kinase C inhibitors. Am J Ophthalmol 133:693–698
Tuttle KR, Anderson PW 2003 A novel potential therapy for diabetic nephropathy and vascular complications: protein kinase C ? inhibition. Am J Kidney Dis 42:456–465
Burg MB 1988 Role of aldose reductase and sorbitol in maintaining the medullary intracellular milieu. Kidney Int 33:635–641
Burg MB 1995 Molecular basis of osmotic regulation. Am J Physiol 268:F983–F996
Donohue PJ, Alberts GF, Hampton BS, Winkles JA 1994 A delayed-early gene activated by fibroblast growth factor-1 encodes a protein related to aldose reductase. J Biol Chem 269:8604–8609
Iwata T, Sato S, Jimenez J, McGowan M, Moroni M, Dey A, Ibaraki N, Reddy VN, Carper D 1999 Osmotic response element is required for the induction of aldose reductase by tumor necrosis factor-. J Biol Chem 274:7993–8001
Ruef J, Liu SQ, Bode C, Tocchi M, Srivastava S, Runge MS, Bhatnagar A 2000 Involvement of aldose reductase in vascular smooth muscle cell growth and lesion formation after arterial injury. Arterioscler Thromb Vasc Biol 20:1745–1752
Spycher SE, Tabataba-Vakili S, O’Donnell VB, Palomba L, Azzi A 1997 Aldose reductase induction: a novel response to oxidative stress of smooth muscle cells. FASEB J 11:181–188
Tawata M, Ohtaka M, Hosaka Y, Onaya T 1992 Aldose reductase mRNA expression and its activity are induced by glucose in fetal rat aortic smooth muscle (A10) cells. Life Sci 51:719–726
Ramana KV, Chandra D, Srivastava S, Bhatnagar A, Srivastava SK 2003 Aldose reductase mediates the mitogenic signals of cytokines. Chem Biol Interact 143–144:587–596
Bhatnagar A, Ruef J, Liu S, Srivastava S, Srivastava SK 2001 Regulation of vascular smooth muscle cell growth by aldose reductase. Chem Biol Interact 130–132:627–636
Sibbitt Jr WL, Mills RG, Bigler CF, Eaton RP, Griffey RH, Vander Jagt DL 1989 Glucose inhibition of human fibroblast proliferation and response to growth factors is prevented by inhibitors of aldose reductase. Mech Ageing Dev 47:265–279
Derylo B, Babazono T, Glogowski E, Kapor-Drezgic J, Hohman T, Whiteside C 1998 High glucose-induced mesangial cell altered contractility: role of the polyol pathway. Diabetologia 41:507–515
Asnaghi V, Gerhardinger C, Hoehn T, Adeboje A, Lorenzi M 2003 A role for the polyol pathway in the early neuroretinal apoptosis and glial changes induced by diabetes in the rat. Diabetes 52:506–511
Price SA, Agthong S, Middlemas AB, Tomlinson DR 2004 Mitogen-activated protein kinase p38 mediates reduced nerve conduction velocity in experimental diabetic neuropathy: interactions with aldose reductase. Diabetes 53:1851–1856
Srivastava S, Watowich SJ, Petrash JM, Srivastava SK, Bhatnagar A 1999 Structural and kinetic determinants of aldehyde reduction by aldose reductase. Biochemistry 38:42–54
Srivastava S, Liu SQ, Conklin DJ, Zacarias A, Srivastava SK, Bhatnagar A 2001 Involvement of aldose reductase in the metabolism of atherogenic aldehydes. Chem Biol Interact 130–132:563–571
Srivastava S, Chandrasekar B, Bhatnagar A, Prabhu SD2002 Lipid peroxidation-derived aldehydes and oxidative stress in the failing heart: role of aldose reductase. Am J Physiol Heart Circ Physiol 283:H2612–H2619
Ramana KV, Dixit BL, Srivastava S, Bhatnagar A, Balendiran GK, Watowich SJ, Petrash JM, Srivastava SK 2001 Characterization of the glutathione binding site of aldose reductase. Chem Biol Interact 130–132:537–548
Ramana KV, Dixit BL, Srivastava S, Balendiran GK, Srivastava SK, Bhatnagar A 2000 Selective recognition of glutathiolated aldehydes by aldose reductase. Biochemistry 39:12172–12180
Dixit BL, Balendiran GK, Watowich SJ, Srivastava S, Ramana KV, Petrash JM, Bhatnagar A, Srivastava SK 2000 Kinetic and structural characterization of the glutathione-binding site of aldose reductase. J Biol Chem 275:21587–21595
Srivastava S, Spite M, Trent JO, West MB, Ahmed Y, Bhatnagar A 2004 Aldose reductase-catalyzed reduction of aldehyde phospholipids. J Biol Chem 279:53395–53406
Bhatnagar A, Srivastava S, Wang LF, Chandra A, Ansari NH, Srivastava SK 1999 Cardiac metabolism of enals. Adv Exp Med Biol 463:223–229
Srivastava SK, Chandra A, Srivastava S, Petrash JM, Bhatnagar A 1999 Regulation of aldose reductase by aldehydes and nitric oxide. Adv Exp Med Biol 463:501–507
Nakano T, Petrash JM 1996 Kinetic and spectroscopic evidence for active site inhibition of human aldose reductase. Biochemistry 35:11196–11202
Schade SZ, Early SL, Williams TR, Kezdy FJ, Heinrikson RL, Grimshaw CE, Doughty CC 1990 Sequence analysis of bovine lens aldose reductase. J Biol Chem 265:3628–3635
Wilson DK, Bohren KM, Gabbay KH, Quiocho FA 1992 An unlikely sugar substrate site in the 1.65 A structure of the human aldose reductase holoenzyme implicated in diabetic complications. Science 257:81–84
Wilson DK, Tarle I, Petrash JM, Quiocho FA 1993 Refined 1.8 A structure of human aldose reductase complexed with the potent inhibitor zopolrestat. Proc Natl Acad Sci USA 90:9847–9851
Tarle I, Borhani DW, Wilson DK, Quiocho FA, Petrash JM 1993 Probing the active site of human aldose reductase. Site-directed mutagenesis of Asp-43, Tyr-48, Lys-77, and His-110. J Biol Chem 268:25687–25693
Petrash JM, Tarle I, Wilson DK, Quiocho FA 1994 Aldose reductase catalysis and crystallography. Insights from recent advances in enzyme structure and function. Diabetes 43:955–959
Borhani DW, Harter TM, Petrash JM 1992 The crystal structure of the aldose reductase. NADPH binary complex. J Biol Chem 267:24841–24847
Srivastava S, Chandra A, Ansari NH, Srivastava SK, Bhatnagar A 1998 Identification of cardiac oxidoreductase(s) involved in the metabolism of the lipid peroxidation-derived aldehyde-4-hydroxynonenal. Biochem J 329:469–475
Srivastava S, Chandra A, Wang LF, Seifert Jr WE, DaGue BB, Ansari NH, Srivastava SK, Bhatnagar A 1998 Metabolism of the lipid peroxidation product, 4-hydroxy-trans-2-nonenal, in isolated perfused rat heart. J Biol Chem 273:10893–10900
Srivastava S, Dixit BL, Cai J, Sharma S, Hurst HE, Bhatnagar A, Srivastava SK 2000 Metabolism of lipid peroxidation product, 4-hydroxynonenal (HNE) in rat erythrocytes: role of aldose reductase. Free Radic Biol Med 29:642–651
Srivastava S, Conklin DJ, Liu SQ, Prakash N, Boor PJ, Srivastava SK, Bhatnagar A 2001 Identification of biochemical pathways for the metabolism of oxidized low-density lipoprotein derived aldehyde-4-hydroxy trans-2-nonenal in vascular smooth muscle cells. Atherosclerosis 158:339–350
Del Corso A, Dal Monte M, Vilardo PG, Cecconi I, Moschini R, Banditelli S, Cappiello M, Tsai L, Mura U 1998 Site-specific inactivation of aldose reductase by 4-hydroxynonenal. Arch Biochem Biophys 350:245–248
Cappiello M, Voltarelli M, Giannessi M, Cecconi I, Camici G, Manao G, Del Corso A, Mura U 1994 Glutathione dependent modification of bovine lens aldose reductase. Exp Eye Res 58:491–501
Cappiello M, Amodeo P, Mendez BL, Scaloni A, Vilardo PG, Cecconi I, Dal Monte M, Banditelli S, Talamo F, Micheli V, Giblin FJ, Corso AD, Mura U 2001 Modulation of aldose reductase activity through S-thiolation by physiological thiols. Chem Biol Interact 130–132:597–608
Cappiello M, Vilardo PG, Cecconi I, Leverenz V, Giblin FJ, Del Corso A, Mura U 1995 Occurrence of glutathione-modified aldose reductase in oxidatively stressed bovine lens. Biochem Biophys Res Commun 207:775–782
Cappiello M, Voltarelli M, Cecconi I, Vilardo PG, Dal Monte M, Marini I, Del Corso A, Wilson DK, Quiocho FA, Petrash JM, Mura U 1996 Specifically targeted modification of human aldose reductase by physiological disulfides. J Biol Chem 271:33539–33544
Del Corso A, Camici M, Mura U 1987 In vitro modification of bovine lens aldose reductase activity. Biochem Biophys Res Commun 148:369–375
Petrash JM, Harter TM, Devine CS, Olins PO, Bhatnagar A, Liu S, Srivastava SK 1992 Involvement of cysteine residues in catalysis and inhibition of human aldose reductase. Site-directed mutagenesis of Cys-80, -298, and -303. J Biol Chem 267:24833–24840
Cecconi I, Scaloni A, Rastelli G, Moroni M, Vilardo PG, Costantino L, Cappiello M, Garland D, Carper D, Petrash JM, Del Corso A, Mura U 2002 Oxidative modification of aldose reductase induced by copper ion. Definition of the metal-protein interaction mechanism. J Biol Chem 277:42017–42027
Halder AB, James M, Crabbe C 1985 Chemical modification studies on purified bovine lens aldose reductase. Ophthalmic Res 17:185–188
Cecconi I, Moroni M, Vilardo PG, Dal Monte M, Borella P, Rastelli G, Costantino L, Garland D, Carper D, Petrash JM, Del Corso A, Mura U 1998 Oxidative modification of aldose reductase induced by copper ion. Factors and conditions affecting the process. Biochemistry 37:14167–14174
Chandra A, Srivastava S, Petrash JM, Bhatnagar A, Srivastava SK 1997 Active site modification of aldose reductase by nitric oxide donors. Biochim Biophys Acta 1341:217–222
Dixit BL, Ramana KV, Chandra D, Jackson EB, Srivastava S, Bhatnagar A, Srivastava SK 2001 Metabolic regulation of aldose reductase activity by nitric oxide donors. Chem Biol Interact 130–132:573–581
Srivastava S, Dixit BL, Ramana KV, Chandra A, Chandra D, Zacarias A, Petrash JM, Bhatnagar A, Srivastava SK 2001 Structural and kinetic modifications of aldose reductase by S-nitrosothiols. Biochem J 358:111–118
Chandra D, Jackson EB, Ramana KV, Kelley R, Srivastava SK, Bhatnagar A 2002 Nitric oxide prevents aldose reductase activation and sorbitol accumulation during diabetes. Diabetes 51:3095–3101
Srivastava SK, Ramana KV, Chandra D, Srivastava S, Bhatnagar A 2003 Regulation of aldose reductase and the polyol pathway activity by nitric oxide. Chem Biol Interact 143–144:333–340
Ramana KV, Chandra D, Srivastava S, Bhatnagar A, Srivastava SK 2003 Nitric oxide regulates the polyol pathway of glucose metabolism in vascular smooth muscle cells. FASEB J 17:417–425
Barisani D, Meneveri R, Ginelli E, Cassani C, Conte D 2000 Iron overload and gene expression in HepG2 cells: analysis by differential display. FEBS Lett 469:208–212
O’connor T, Ireland LS, Harrison DJ, Hayes JD 1999 Major differences exist in the function and tissue-specific expression of human aflatoxin B1 aldehyde reductase and the principal human aldo-keto reductase AKR1 family members. Biochem J 343:487–504
Srivastava S, Chandrasekar B, Bhatnagar A, Prabhu SD 2002 Lipid peroxidation-derived aldehydes and oxidative stress in the failing heart: role of aldose reductase. Am J Physiol 283:H2612–H2619
Ramana KV, Friedrich B, Srivastava S, Bhatnagar A, Srivastava SK 2004 Activation of nuclear factor-B by hyperglycemia in vascular smooth muscle cells is regulated by aldose reductase. Diabetes 53:2910–2920
Rittner HL, Hafner V, Klimiuk PA, Szweda LI, Goronzy JJ, Weyand CM 1999 Aldose reductase functions as a detoxification system for lipid peroxidation products in vasculitis. J Clin Invest 103:1007–1013
Shinmura K, Bolli R, Liu SQ, Tang XL, Kodani E, Xuan YT, Srivastava S, Bhatnagar A 2002 Aldose reductase is an obligatory mediator of the late phase of ischemic preconditioning. Circ Res 91:240–246
Hwang YC, Sato S, Tsai JY, Yan S, Bakr S, Zhang H, Oates PJ, Ramasamy R 2002 Aldose reductase activation is a key component of myocardial response to ischemia. FASEB J 16:243–245
Ramasamy R, Oates PJ, Schaefer S 1997 Aldose reductase inhibition protects diabetic and nondiabetic rat hearts from ischemic injury. Diabetes 46:292–300
Kaneko M, Ramasamy R 2004 Aldose reductase: a key player in myocardial ischemic injury. Exerc Sport Sci Rev 32:19–23
Hwang YC, Kaneko M, Bakr S, Liao H, Lu Y, Lewis ER, Yan S, Ii S, Itakura M, Rui L, Skopicki H, Homma S, Schmidt AM, Oates PJ, Szabolcs M, Ramasamy R 2004 Central role for aldose reductase pathway in myocardial ischemic injury. FASEB J 18:1192–1199
Horvath JJ, Witmer CM, Witz G 1992 Nephrotoxicity of the 1:1 acrolein-glutathione adduct in the rat. Toxicol Appl Pharmacol 117:200–207
Chakrabarti S, Malick MA 1991 In vivo nephrotoxic action of an isomeric mixture of S-(1-phenyl-2-hydroxyethyl)glutathione and S-(2-phenyl-2-hydroxyethyl)glutathione in Fischer-344 rats. Toxicology 67:15–27
Boon PJ, Marinho HS, Oosting R, Mulder GJ 1999 Glutathione conjugation of 4-hydroxy-trans-2,3-nonenal in the rat in vivo, the isolated perfused liver and erythrocytes. Toxicol Appl Pharmacol 159:214–223
Kicic E, Palmer TN 1996 Increased white cell aldose reductase mRNA levels in diabetic patients. Diabetes Res Clin Pract 33:31–36
Shimizu H, Ohtani KI, Tsuchiya T, Sato N, Tanaka Y, Takahashi H, Uehara Y, Inukai T, Mori M 2000 Aldose reductase mRNA expression is associated with rapid development of diabetic microangiopathy in Japanese type 2 diabetic (T2DM) patients. Diabetes Nutr Metab 13:75–79
Spallarossa P, Barsotti A, Cordera R, Ghigliotti G, Maggi D, Brunelli C 2004 Reduction of cardiovascular morbidity and mortality in type 2 diabetes. A rational approach to hypoglycemic therapy. J Endocrinol Invest 27:485–495
Moncada S, Palmer RM, Higgs EA 1991 Nitric oxide: physiology, pathophysiology, and pharmacology. Pharmacol Rev 43:109–142
Wu SY, Leske MC 2000 Antioxidants and cataract formation: a summary review. Int Ophthalmol Clin 40:71–81
Richer S 2000 Antioxidants and the eye. Int Ophthalmol Clin 40:1–16
Kowluru RA, Kennedy A 2001 Therapeutic potential of anti-oxidants and diabetic retinopathy. Expert Opin Investig Drugs 10:1665–1676
Dickinson PJ, Carrington AL, Frost GS, Boulton AJ 2002 Neurovascular disease, antioxidants and glycation in diabetes. Diabetes Metab Res Rev 18:260–272
Vaziri ND 2004 Roles of oxidative stress and antioxidant therapy in chronic kidney disease and hypertension. Curr Opin Nephrol Hypertens 13:93–99
Ruhe RC, McDonald RB 2001 Use of antioxidant nutrients in the prevention and treatment of type 2 diabetes. J Am Coll Nutr 20:363S–369S
Basta G, Schmidt AM, De Caterina R 2004 Advanced glycation end products and vascular inflammation: implications for accelerated atherosclerosis in diabetes. Cardiovasc Res 63:582–592
Dandona P, Chaudhuri A, Aljada A 2004 Endothelial dysfunction and hypertension in diabetes mellitus. Med Clin North Am 88:911–931
Wilson Tang WH, Maroo A, Young JB 2004 Ischemic heart disease and congestive heart failure in diabetic patients. Med Clin North Am 88:1037–1061
Lim HS, Lip 2003 GY Diabetes, the renin-angiotensin system and heart disease. Curr Vasc Pharmacol 1:225–238
Lim HS, MacFadyen RJ, Lip GY 2004 Diabetes mellitus, the renin-angiotensin-aldosterone system, and the heart. Arch Intern Med 164:1737–1748
Morgan KP, Kapur A, Beatt KJ 2004 Anatomy of coronary disease in diabetic patients: an explanation for poorer outcomes after percutaneous coronary intervention and potential target for intervention. Heart 90:732–738
Indolfi C, Mongiardo A, Curcio A, Torella D 2003 Molecular mechanisms of in-stent restenosis and approach to therapy with eluting stents. Trends Cardiovasc Med 3:142–148
Ramana KV, Chandra D, Srivastava S, Bhatnagar A, Aggarwal BB, Srivastava SK 2002 Aldose reductase mediates mitogenic signaling in vascular smooth muscle cells. J Biol Chem 277:32063–32070
Zhou Z, Lauer MA, Wang K, Forudi F, Zhou X, Song X, Solowski N, Kapadia SR, Nakada MT, Topol EJ, Lincoff AM 2002 Effect of anti-tumor necrosis factor- polyclonal antibody on restenosis after balloon angioplasty in a rabbit atherosclerotic model. Atherosclerosis 161:153–159
Catley MC, Cambridge LM, Nasuhara Y, Ito K, Chivers JE, Beaton A, Holden NS, Bergmann MW, Barnes PJ, Newton R 2004 Inhibitors of protein kinase C (PKC) prevent activated transcription: role of events downstream of NF-B DNA binding. J Biol Chem 279:18457–18466
Foey AD, Brennan FM 2004 Conventional protein kinase C and atypical protein kinase C differentially regulate macrophage production of tumor necrosis factor- and interleukin-10. Immunology 112:44–53
Satoh A, Gukovskaya AS, Nieto JM, Cheng JH, Gukovsky I, Reeve Jr JR, Shimosegawa T, Pandol SJ 2004 PKC- and - regulate NF-B activation induced by cholecystokinin and TNF- in pancreatic acinar cells. Am J Physiol Gastrointest Liver Physiol 287:G582–G591
Ramana KV, Friedrich B, Bhatnagar A, Srivastava SK 2003 Aldose reductase mediates cytotoxic signals of hyperglycemia and TNF- in human lens epithelial cells. FASEB J 17:315–317
Ramana KV, Bhatnagar A, Srivastava SK 2004 Inhibition of aldose reductase attenuates TNF--induced expression of adhesion molecules in endothelial cells. FASEB J 18:1209–1218
Chandra D, Ramana KV, Friedrich B, Srivastava S, Bhatnagar A, Srivastava SK 2003 Role of aldose reductase in TNF--induced apoptosis of vascular endothelial cells. Chem Biol Interact 143–144:605–612
Ramana KV, Bhatnagar A, Srivastava SK 2004 Aldose reductase regulates TNF--induced cell signaling and apoptosis in vascular endothelial cells. FEBS Lett 570:189–194
Srivastava S, Ramana KV, Srivastana SK, D’Souza SE, Bhatnagar A2004 Role of aldose reductase in the detoxification of oxidized phospholipids. ACS Symposium Series 865:49–64
Vander Jagt DL, Hassebrook RK, Hunsaker LA, Brown WM, Royer RE 2001 Metabolism of the 2-oxoaldehyde methylglyoxal by aldose reductase and by glyoxalase-I: roles for glutathione in both enzymes and implications for diabetic complications. Chem Biol Interact 130–132:549–562
Wermuth B, Monder C 1983 Aldose and aldehyde reductase exhibit isocorticosteroid reductase activity. Eur J Biochem 131:423–426
Matsuura K, Deyashiki Y, Bunai Y, Ohya I, Hara A 1996 Aldose reductase is a major reductase for isocaproaldehyde, a product of side-chain cleavage of cholesterol, in human and animal adrenal glands. Arch Biochem Biophys 328:265–271
Petrash JM, Harter TM, Murdock GL 1996 A potential role for aldose reductase in steroid metabolism. In: Weiner H, Lindahl R, Crabb DW, Flynn TG, eds. Enzymology and molecular biology of carbonyl metabolism. Vol 6. New York: Plenum Press; 465–473
Srivastava S, Liu SQ, Bhatnagar A 2003 Cellular metabolism of base propanols. FASEB J 17:A175–A176(Satish K. Srivastava, Kot)