Hepatic and Cardiovascular Consequences of Familial Hypobetalipoproteinemia
http://www.100md.com
动脉硬化血栓血管生物学 2005年第9期
From the Departments of Vascular Medicine (R.R.S., S.W.F., S.H., E.G., J.J.P.K., E.S.G.S.) and Clinical Epidemiology and Biostatistics (B.H.), Academic Medical Center, Amsterdam, the Netherlands.
Correspondence to Raaj R. Sankatsing, MD, Department of Vascular Medicine, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands. E-mail r.r.sankatsing@amc.uva.nl
Abstract
Objective— Individuals with familial hypobetalipoproteinemia (FHBL) have been reported to be prone to fatty liver disease (FLD). Conversely, the profound reduction of low-density lipoprotein (LDL) cholesterol in this disorder might decrease cardiovascular risk. In the present study, we assessed hepatic steatosis as well as noninvasive surrogate markers for cardiovascular disease (CVD) in subjects with FHBL and in matched controls.
Methods and Results— Hepatic steatosis was assessed by abdominal ultrasonography. Carotid intima-media thickness (IMT) and distal common carotid arterial wall stiffness as surrogate markers for CVD risk were measured using high-resolution B-mode ultrasonography. Whereas transaminase levels were only modestly elevated, both prevalence (54% versus 29%; P=0.01) and severity of steatosis were significantly higher in FHBL individuals compared with controls. Despite similar IMT measurements, arterial stiffness was significantly lower in FHBL (P=0.04) compared with controls. Additionally, the increase in arterial stiffness as seen in the presence of traditional risk factors was attenuated, suggesting that very low levels of apoB-containing lipoproteins can negate the adverse effects of other risk factors on the vasculature.
Conclusions— FHBL is characterized by an increased prevalence and severity of fatty liver disease. The observed decreased level of arterial wall stiffness, most pronounced in the presence of nonlipid risk factors, is indicative of cardiovascular protection in these subjects.
We investigated the risk for fatty liver disease (FLD) and cardiovascular disease (CVD) in familial hypobetalipoproteinemia (FHBL) subjects and in healthy controls. Whereas the prevalence of FLD was increased in FHBL, carotid arterial wall stiffness, a surrogate marker for CVD, was decreased suggesting that these subjects are relatively protected against developing CVD.
Key Words: apolipoprotein B ? arterial stiffness ? cardiovascular risk ? familial hypobetalipoproteinemia ? fatty liver disease
Introduction
Familial hypobetalipoproteinemia (FHBL) is a hereditary disorder of lipoprotein metabolism characterized by very low levels of apolipoprotein (apo) B-100. Plasma levels below the fifth percentile are distinctive for this condition that inherits as an autosomal dominant trait. The prevalence in the general population is estimated to vary from 0.1% to 1.9%.1,2 Genetic causes of hypobetalipoproteinemia include FHBL, abetalipoproteinemia, and chylomicron remnant disease (OMIM numbers 601519, 246700, and 200100, respectively). A small percentage of FHBL can be explained by mutations in the gene-encoding apolipoprotein B-100 (APOB). These include nonsense, frame-shift, and splicing mutations. Recently, it was reported that a missense mutation in the APOB gene can also lead to FHBL.3 APOB gene mutations lead to truncated forms of apolipoprotein B (apoB) and are characterized by slower hepatic secretion, as well as more rapid plasma clearance compared with wild-type apoB-100 particles.4,5 Because apoB is the main constituent of such lipoproteins, including very low-density lipoprotein (VLDL), intermediate-density lipoprotein, and low-density lipoprotein (LDL), FHBL subjects are characterized by exceptionally low levels of these proatherogenic particles from birth onwards. Whereas subjects with heterozygous FHBL are generally asymptomatic, 2 potential implications have been attributed to this particular condition. First, the impairment of hepatic VLDL-triglycerides (TG) secretion in FHBL may contribute to fat accumulation in the liver. Potential consequences of fat accumulation are highlighted by the occurrence of hepatic steatosis in subjects with nonalcoholic steatohepatitis in whom progression toward cirrhosis has been observed.6–8 Case reports and smaller studies have reported a relationship between fatty liver disease (FLD) and FHBL.9–12 This is best illustrated by 2 recent studies by Schonfeld et al who showed that hepatic fat percentage, as assessed by magnetic resonance spectroscopy, was significantly increased in subjects with FHBL as compared with healthy controls.13,14 Nevertheless, the natural course of this potential fat accumulation in FHBL is as yet unknown. Second, FHBL offers a unique opportunity to evaluate the impact of life-long exposure to unusually low levels of apoB-containing atherogenic lipoproteins. In this respect, FHBL subjects might be regarded as a natural model for "intensive lipid-lowering therapy." In fact, the potential success of intensive lipid-lowering therapy has recently been reinforced by data from the REVERSAL15 and PROVE-IT studies,16 showing a more pronounced reduction of cardiovascular disease risk on intensive lowering of LDL cholesterol levels.
In the present study, we evaluated the impact of FHBL on hepatic steatosis as well as on surrogate markers for cardiovascular disease. Here we present the results of these investigations.
Methods
Subjects and Protocols
For a detailed description of methods please http://atvb.ahajournals.org.
Eighty-two subjects were enrolled in study, 41 with FHBL and 41 healthy controls, matched for sex and body mass index (Table 1). Autosomal codominant inheritance was a necessary characteristic for the clinical diagnosis of FHBL. FHBL subjects were identified from a group of individuals who were referred to our lipid clinic because of extreme low LDL levels. These subjects were characterized by direct sequencing of the entire apoB gene, as published previously.17 Secondary causes for low LDL cholesterol levels, ie, (strict) vegetarian diet or generalized diseases such as cancer, were excluded. The controls consisted of unaffected family members as well as unrelated volunteers. In the FHBL group, 4 subjects had diabetes mellitus (DM) compared with none in the control group. Because DM is strongly associated with both liver steatosis18–21 and carotid IMT/arterial stiffness,22–25 we repeated the analyses after excluding the 4 diabetic subjects in the FHBL group (FHBL minus DM) to assess whether possible differences between groups were obscured by the presence of DM.
TABLE 1. Clinical Characteristics for FHBL Subjects and Controls
Liver Ultrasound
In all subjects ultrasound examination of the liver was performed by a single radiologist blinded to the disease state of the subjects. The extent of hepatic fatty infiltration was classified according to previously published criteria.26
Carotid Ultrasound
B-mode ultrasound intima-media thickness (IMT) measurements were performed in the far walls of the carotid arteries and M-mode arterial stiffness was measured bilaterally in the common carotid arteries.
Statistical Analysis
Statistical analyses were performed using linear or logistic regression analyses with generalized estimating equations in the SAS procedure GENMOD to account for correlations within families. Analyses were performed using SAS software (release 8.02; SAS Institute Inc). P<0.05 was considered significant.
Results
Clinical characteristics of FHBL subjects and controls are presented in Table 1. Forty-one subjects who met the clinical criteria of FHBL (apoB and LDL cholesterol less than fifth percentile adjusted by age, gender, and race) participated in the study. Thirty-three of these subjects had mutations in the apoB gene, characteristic of FHBL. These genetically affected subjects were recruited from 8 families with different apoB mutations. The following apoB mutations were identified in the FHBL group: 2534delA apoB-18, Q1309X apoB-29, R2507X apoB-55, and 11712delC apo-B8617 (Table 2). Subjects did not use lipid-lowering drugs. There was no significant difference in blood pressure, smoking, body mass index, or alcohol consumption between FHBL subjects and controls. In line with their diagnosis, apoB, LDL cholesterol, and total cholesterol levels were significantly lower in the FHBL group. The type of apoB truncation, but not plasma LDL cholesterol or apoB levels, was modestly correlated with the degree of liver steatosis using Spearman rho method (r=0.336, P=0.002). Mean levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and -glutamyltransferase levels were significantly higher in the FHBL group as compared with the controls (Table 3).
TABLE 2. Apolipoprotein B Mutations
TABLE 3. Laboratory Characteristics for FHBL Subjects and Controls
However, this was mainly caused by the 7 subjects with severe steatosis who had the highest levels of transaminases. Three of these 7 subjects had ALT levels more than twice the upper limit of normal (ULN) but still <3x ULN. The highest value of ALT, observed in a diabetic patient, was 102. None of these 7 subjects had AST values >2x ULN. AST and ALT were both significantly associated with hepatic steatosis (P=0.04 and P=0.0002, respectively). Levels of high-sensitivity C-reactive protein (hs-CRP) and glucose were comparable between the 2 groups. HDL cholesterol levels were significantly higher in the FHBL minus DM group compared with the controls (1.76±0.59 mmol/L versus 1.55±0.33 mmol/L, P=0.01).
Liver Ultrasound
We observed a significantly higher prevalence of liver steatosis in the FHBL group compared with the control group (54% versus 29%; P=0.01). In addition, FHBL subjects were also characterized by a more severe degree of hepatic steatosis. Seven (17%) of the subjects in the FHBL group were classified as severe steatosis compared with none in the control group (Figure 1). The distribution of steatosis severity was significantly different between groups (P=0.004). This was even more apparent when comparing the controls with the subgroup of FHBL with mutations (P=0.001). The 4 diabetic subjects were equally distributed over the 4 steatosis categories. Separate analyses with exclusion of these 4 subjects lead to an equal statistical difference for steatosis severity between groups.
Figure 1. Grade of liver steatosis.
Hepatic steatosis was not more severe in those subjects carrying truncated apoB not secreted into the plasma (apoB-18 and ApoB-29) compared with the carriers of longer truncations (P=0.68). Plasma LDL cholesterol and apoB levels were also not different between these subgroups (P=0.77 and P=0.81, respectively). Nine of the 14 carriers of Apo-86 had liver steatosis compared with 3 of the 8 FHBL subjects without mutations. FHBL was positively associated with liver steatosis on univariate analysis (P=0.02). When adjusted for gender and smoking on multivariate analysis, FHBL, age, and body mass index were independent predictors for the development of liver steatosis (P=0.001, P<0.0001, and P=0.0014, respectively). Similar significant results were found when running the analyses with the subgroup of FHBL subjects with mutations (n=33) compared with the healthy controls. Results were not significant when this was done for the subgroup of FHBL without mutations (n=8). However, the latter is likely to be caused by a lack of power attributable to the limited number of subjects in this group.
Vascular Measurements
Mean carotid IMT (±SD) was 0.63±0.14 mm in the FHBL group compared with 0.65±0.15 mm in the control group. The latter difference on univariate analysis (P=0.049) lost significance when adjusting for age, gender, smoking, and body mass index on multivariate analysis. Arterial stiffness was significantly lower in the FHBL minus DM group compared with the controls on univariate analysis (P=0.04), whereas a similar trend was seen for the whole FHBL group (P=0.06). When comparing the 2 subgroups of FHBL, (with and without mutations), FHBL was still significantly associated with arterial stiffness in the first group (P=0.04), but this was not significant for the subgroup without mutations. Again, this could reflect a lack of power, because the subgroup without mutations contained only 8 subjects. To evaluate a potential interaction between risk factors and apoB-containing lipoproteins, we attributed a cumulative risk score to each subject. The cumulative risk score comprised age, systolic blood pressure, and smoking. These variables were chosen because their individual relationship with cardiovascular risk has been proven beyond any doubt as attested to by their incorporation in both the PROCAM27 and Framingham Risk Score,28 the 2 most widely used risk calculators for predicting cardiovascular disease. Moreover, these risk factors have an independent strong association with arterial stiffness.29–35 In our study these parameters were also strongly correlated with arterial stiffness with the exception of smoking (r=0.732, P<0.001, r=0.550, P<0.001, and r=0.267, P=0.018, respectively). Both FHBL and control subjects showed a gradual increase in arterial stiffness with increasing cumulative risk scores. However, using linear regression analysis, the slope for the FHBL group was markedly decreased compared with the controls, indicating decreased stiffening in the presence of nonlipid risk factors in the FHBL group (P=0.03) (Figure 2). This difference remained significant (P=0.04) when comparing the FHBL minus DM group with the control subjects.
Figure 2. Arterial stiffness versus cumulative risk score in FHBL. The cumulative risk score is based on 3 variables: age, smoking, and systolic blood pressure (SBP). Results of each variable, except for smoking, were divided into tertiles. For age and SBP, patients received scores of 1, 2, or 3 with each increasing tertile. Smoking was scored as either 0 for nonsmoking or 3 for smoking. Minimal and maximal attainable scores were 2 and 9, respectively. The probability value indicates the difference in slope between the 2 regression lines.
Discussion
Subjects with FHBL are characterized by an increased prevalence of fat accumulation in the liver as well as by a more severe degree of such hepatic steatosis. Whereas these findings are not novel, we show that FHBL subjects exhibit decreased arterial stiffness. Notably, the increase in arterial stiffness under the influence of "traditional" nonlipid risk factors was markedly attenuated in FHBL subjects.
Biochemical Analyses
Subjects with FHBL are characterized by significantly decreased levels of apoB-containing lipoproteins, including low LDL cholesterol as well as low triglyceride-rich particles. Also, slightly higher levels of HDL cholesterol were found in these FHBL subjects. Presumably, the latter is the consequence of low levels of triglycerides, thus minimizing exchange of cholesterol esters from HDL cholesterol to apoB-containing particles through the action of cholesterol ester transfer protein. Another explanation could be that the truncated apoB are only present in the density range of HDL. However, we excluded the latter option by performing agarose gel electrophoresis on HDL fractions, from patients with apoB-55 and apoB-86, which were isolated after ultracentrifugation. No LDL bands were present in the HDL density range. Additionally, apoB could also not be detected in the HDL fraction using immunonephelometry (data not shown).
Hepatosteatosis
The prevalence of fatty liver disease in healthy controls (29%) is in the same order of magnitude as reported by others.19,36 The increased prevalence of hepatosteatosis in subjects with FHBL is in agreement with previous results from Schonfeld and Tanoli who showed that these subjects had 3-fold increase in mean liver fat content, as assessed by magnetic resonance spectroscopy.13,14 The most likely cause for this increase in hepatic steatosis is the impaired secretion of VLDL-TG from the liver, leading to accumulation of VLDL-TG in the liver. There is a large body of evidence suggesting that accumulation of liver triglycerides may give rise to increased oxidative stress in the hepatocytes.37–39 However, distinct proof, in the human setting, that this process invariably translates into progression of liver steatosis to nonalcoholic steatohepatitis is lacking.40 Recent work by Youssef et al revealed that up to 25% of patients with FLD may progresses to nonalcoholic steatohepatitis,21 of whom 20% may eventually even progress into cirrhosis.19,20 Notably, in our FHBL group, transaminase levels were only modestly elevated with none of the subjects exceeding a 3-fold increase in upper limit of normal. Most studies reporting long-term outcome of fatty liver disease, use the AST/ALT ratio as a marker for the risk of disease progression. A ratio of <1 indicates a "low risk" for steatosis41,42 and in our FHBL subjects, AST/ALT ratios were all <1. It should be kept in mind, however, that the absence of liver enzyme elevations8,43 does not completely preclude advanced fibrosis or cirrhosis in these subjects.43 To date, long-term follow-up data with regard to liver outcome in FHBL are lacking. Nevertheless, risk factors for FLD such as hypertriglyceridemia, obesity, alcohol, diabetes mellitus, and certain drugs are likely to aggravate hepatic steatosis in FHBL. Hence, it is prudent to avoid these risk factors and recommend a diet with low to moderate amounts of fat and energy, limited use of alcohol, as well as avoiding obesity in these individuals.
Cardiovascular Risk
Numerous studies have established a strong correlation between levels of LDL cholesterol and progression of IMT.44 In the present study, however, we could not show an independent statistical difference in terms of carotid IMT values between FHBL subjects and controls. Nevertheless, data have accumulated recently that show the predictive value of the assessment of vascular function, such as arterial stiffness, for future cardiovascular events.23,45–48 Arterial stiffness is closely correlated with increasing age, smoking, and hypertension.31,32,49–51 The impact of these risk factors is augmented in the presence of hypercholesterolemia and can be reverted by statin therapy.52,53 In our FHBL group, we observed a significant decrease in arterial stiffness. Of note, this difference was observed despite the fact that traditional risk factors such as smoking and diabetes occurred more frequently in the FHBL group compared with controls. In earlier studies, apoB-containing lipoproteins have been put forward as a pivotal "permissive" factor for the development of atherogenic changes of the vessel wall. To evaluate a potential interaction between apoB-containing lipoproteins and other traditional risk factors, we constructed a cumulative risk index including age, smoking, and systolic blood pressure in FHBL subjects as well as controls. In both groups, there was a linear relationship between increased risk score and arterial stiffness. Interestingly, the increase in arterial stiffness, also in presence of these risk factors was decreased significantly in the FHBL group compared with controls. These data suggest that apoB-containing lipoproteins indeed have the ability to potentiate the impact of traditional risk factors on vascular function. Tentatively, these observations might suggest that lowering of apoB-containing lipoproteins should have a beneficial impact also in subjects with "noncholesterol" risk factors. Recent studies have validated the beneficial effects of statin therapy in normocholesterolemic subjects with nonlipid risk factors, such as hypertension.54
This study has some limitations. We used the less sensitive ultrasonography method to evaluate fatty liver disease rather than magnetic resonance spectroscopy. However, in view of the carefully standardized methodology and the fact that both patients and controls were evaluated using the same methodology, it is unlikely that the latter has affected our outcomes. With regard to the IMT measurement, we could not find a clear relationship between LDL cholesterol levels and carotid IMT. Several reasons may have attributed to the absence of a relation. First, we studied a relatively young cohort with an inherently low risk for cardiovascular disease and hence low IMT values. Second, we studied IMT in a case control design to show thinner IMTs compared with healthy controls. A priori, it is very difficult to demonstrate decreased IMT thickness in "low-risk" groups compared with healthy controls. We have estimated that inclusion of more than 1000 subjects per group would have been necessary to be able to detect significantly thinner IMTs compared with healthy controls with a "normal" risk factor distribution, as seen in western populations.
In summary, our study shows that subjects with FHBL are at increased risk of developing FLD. Whereas long-term sequelae of FLD in FHBL subjects remain to be established, it is prudent to give lifestyle advice in affected individuals. As is illustrated by decreased vascular wall stiffness, our findings suggest that the vessel wall in FHBL subjects is relatively protected by the (life-long) reduced levels of exposure to apoB-containing lipoproteins. The attenuated gradual increase in vascular stiffness in the presence of classical, nonlipid cardiovascular risk factors in FHBL subjects is of interest and suggests that apoB-containing particles constitute a central factor in atherogenesis, amplifying any risk mediated by nonlipid risk factors. Further confirmation of this finding is needed in larger cohorts to ascertain its impact on cardiovascular risk.
Acknowledgments
S.W.F. is supported by the Netherlands Heart Foundation (grant 2000B138). J.J. P.K. is an established investigator of the Netherlands Heart Foundation (2000D039). The cooperation of all study subjects is greatly appreciated. We are grateful to Patrick Rol and Johan Gort for assistance with carotid ultrasound examinations and to Dr Nico Smits for assistance with liver data analysis.
References
Welty FK, Lahoz C, Tucker KL, Ordovas JM, Wilson PWF, Schaefer EJ. Frequency of ApoB and ApoE gene mutations as causes of hypobetalipoproteinemia in the Framingham offspring population. Arterioscler Thromb Vasc Biol. 1998; 18: 1745–1751.
Linton MF, Farese RV Jr, Young SG. Familial hypobetalipoproteinemia. J Lipid Res. 1993; 34: 521–541.
Burnett JR, Shan J, Miskie BA, Whitfield AJ, Yuan J, Tran K, McKnight CJ, Hegele RA, Yao Z. A novel nontruncating APOB gene mutation, R463W, causes familial hypobetalipoproteinemia. J Biol Chem. 2003; 278: 13442–13452.
Chen Z, Fitzgerald RL, Li G, Davidson NO, Schonfeld G. Hepatic secretion of apoB-100 is impaired in hypobetalipoproteinemic mice with an apoB-38.9-specifying allele. J Lipid Res. 2004; 45: 155–163.
Zhu XF, Noto D, Seip R, Shaish A, Schonfeld G. Organ loci of catabolism of short truncations of apoB. Arterioscler Thromb Vasc Biol. 1997; 17: 1032–1038.
Lee RG. Nonalcoholic steatohepatitis: a study of 49 patients. Hum Pathol. 1989; 20: 594–598.
Powell EE, Cooksley WG, Hanson R, Searle J, Halliday JW, Powell LW. The natural history of nonalcoholic steatohepatitis: a follow-up study of forty-two patients for up to 21 years. Hepatology. 1990; 11: 74–80.
Bacon BR, Farahvash MJ, Janney CG, Neuschwander-Tetri BA. Nonalcoholic steatohepatitis: an expanded clinical entity. Gastroenterology. 1994; 107: 1103–1109.
Tarugi P, Lonardo A, Ballarini G, Erspamer L, Tondelli E, Bertolini S, Calandra S. A study of fatty liver disease and plasma lipoproteins in a kindred with familial hypobetalipoproteinemia due to a novel truncated form of apolipoprotein B (APO B-54.5). J Hepatol. 2000; 33: 361–370.
Tarugi P, Lonardo A, Ballarini G, Grisendi A, Pulvirenti M, Bagni A, Calandra S. Fatty liver in heterozygous hypobetalipoproteinemia caused by a novel truncated form of apolipoprotein B. Gastroenterology. 1996; 111: 1125–1133.
Whitfield AJ, Barrett PH, van Bockxmeer FM, Burnett JR. Lipid disorders and mutations in the APOB gene. Clin Chem. 2004; 50: 1725–1732.
Whitfield AJ, Barrett PH, Robertson K, Havlat MF, van Bockxmeer FM, Burnett JR. Liver dysfunction and steatosis in familial hypobetalipoproteinemia. Clin Chem. 2005; 51: 266–269.
Schonfeld G, Patterson BW, Yablonskiy DA, Tanoli TS, Averna M, Elias N, Yue P, Ackerman J. Fatty liver in familial hypobetalipoproteinemia: triglyceride assembly into VLDL particles is affected by the extent of hepatic steatosis. J Lipid Res. 2003; 44: 470–478.
Tanoli T, Yue P, Yablonskiy D, Schonfeld G. Fatty liver in familial hypobetalipoproteinemia: roles of the APOB defects, intra-abdominal adipose tissue, and insulin sensitivity. J Lipid Res. 2004; 45: 941–947.
Nissen SE, Tuzcu EM, Schoenhagen P, Brown BG, Ganz P, Vogel RA, Crowe T, Howard G, Cooper CJ, Brodie B, Grines CL, DeMaria AN. Effect of intensive compared with moderate lipid-lowering therapy on progression of coronary atherosclerosis: a randomized controlled trial. J Am Med Assoc. 2004; 291: 1071–1080.
Cannon CP, Braunwald E, McCabe CH, Rader DJ, Rouleau JL, Belder R, Joyal SV, Hill KA, Pfeffer MA, Skene AM. The Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis in Myocardial Infarction. Intensive versus moderate lipid lowering with statins after acute coronary syndromes. N Engl J Med. 2004; 350: 1495–1504.
Fouchier SW, Sankatsing RR, Peter J, Castillo S, Pocovi M, Alonso R, Kastelein JJP, Defesche JC. High frequency of APOB gene mutations causing familial hypobetalipoproteinaemia in patients of Dutch and Spanish descent. J Med Genet. 2005; 42: e23.
Angulo P. Treatment of nonalcoholic fatty liver disease. Ann Hepatol. 2002; 1: 12–19.
Yu AS, Keeffe EB. Nonalcoholic fatty liver disease. Rev Gastroenterol Disord. 2002; 2: 11–19.
Harrison SA, Di Bisceglie AM. Advances in the understanding and treatment of nonalcoholic fatty liver disease. Drugs. 2003; 63: 2379–2394.
Youssef W, McCullough AJ. Diabetes mellitus, obesity, and hepatic steatosis. Semin Gastrointest Dis. 2002; 13: 17–30.
Salomaa V, Riley W, Kark JD, Nardo C, Folsom AR. Non-insulin-dependent diabetes mellitus and fasting glucose and insulin concentrations are associated with arterial stiffness indexes: the ARIC Study. Circulation. 1995; 91: 1432–1443.
Boutouyrie P, Tropeano AI, Asmar R, Gautier I, Benetos A, Lacolley P, Laurent S. Aortic stiffness is an independent predictor of primary coronary events in hypertensive patients: a longitudinal study. Hypertension. 2002; 39: 10–15.
Schiffrin EL. Vascular stiffening and arterial compliance: implications for systolic blood pressure. Am J Hypertens. 2004; 17: S39–S48.
Schram MT, Henry RMA, van Dijk RAJM, Kostense PJ, Dekker JM, Nijpels G, Heine RJ, Bouter LM, Westerhof N, Stehouwer CDA. Increased central artery stiffness in impaired glucose metabolism and Type 2 diabetes: The Hoorn Study. Hypertension. 2004; 43: 176–181.
Scatarige JC, Scott WW, Donovan PJ, Siegelman SS, Sanders RC. Fatty infiltration of the liver: ultrasonographic and computed tomographic correlation. J Ultrasound Med. 1984; 3: 9–14.
Assmann G, Cullen P, Schulte H. Simple scoring scheme for calculating the risk of acute coronary events based on the 10-year follow-up of the Prospective Cardiovascular Munster (PROCAM) Study. Circulation. 2002; 105: 310–315.
Wilson PW, Castelli WP, Kannel WB. Coronary risk prediction in adults (the Framingham Heart Study). Am J Cardiol. 1987; 59: 91G–94G.
Tomiyama H, Yamashina A, Arai T, Hirose K, Koji Y, Chikamori T, Hori S, Yamamoto Y, Doba N, Hinohara S. Influences of age and gender on results of noninvasive brachial-ankle pulse wave velocity measurement–a survey of 12517 subjects. Atherosclerosis. 2003; 166: 303–309.
Mitchell GF, Parise H, Benjamin EJ, Larson MG, Keyes MJ, Vita JA, Vasan RS, Levy D. Changes in arterial stiffness and wave reflection with advancing age in healthy men and women: the Framingham Heart Study. Hypertension. 2004; 43: 1239–1245.
Stefanadis C, Tsiamis E, Vlachopoulos C, Stratos C, Toutouzas K, Pitsavos C, Marakas S, Boudoulas H, Toutouzas P. Unfavorable effect of smoking on the elastic properties of the human aorta. Circulation. 1997; 95: 31–38.
Stefanadis C, Vlachopoulos C, Tsiamis E, Diamantopoulos L, Toutouzas K, Giatrakos N, Vaina S, Tsekoura D, Toutouzas P. Unfavorable effects of passive smoking on aortic function in men. Ann Intern Med. 1998; 128: 426–434.
Vlachopoulos C, Kosmopoulou F, Panagiotakos D, Ioakeimidis N, Alexopoulos N, Pitsavos C, Stefanadis C. Smoking and caffeine have a synergistic detrimental effect on aortic stiffness and wave reflections. J Am Coll Cardiol. 2004; 44: 1911–1917.
Smulyan MD, Safar MD. Systolic blood pressure revisited. J Am Coll Cardiol. 1997; 29: 1407–1413.
Li S, Chen W, Srinivasan SR, Berenson GS. 847–5 Systolic blood pressure measured serially from childhood to adulthood predicts arterial stiffness in young adults: the Bogalusa heart study. J Am Coll Cardiol. 2004; 43: A515.
Angulo P. Nonalcoholic fatty liver disease. N Engl J Med. 2002; 346: 1221–1231.
Seki S, Kitada T, Yamada T, Sakaguchi H, Nakatani K, Wakasa K. In situ detection of lipid peroxidation and oxidative DNA damage in non-alcoholic fatty liver diseases. J Hepatol. 2002; 37: 56–62.
Lieber CS. CYP2E1: from ASH to NASH. Hepatol Res. 2004; 28: 1–11.
Araya J, Rodrigo R, Videla LA, Thielemann L, Orellana M, Pettinelli P, Poniachik J. Increase in long-chain polyunsaturated fatty acid n - 6/n - 3 ratio in relation to hepatic steatosis in patients with non-alcoholic fatty liver disease. Clin Sci (Lond). 2004; 106: 635–643.
Browning JD, Horton JD. Molecular mediators of hepatic steatosis and liver injury. J Clin Invest. 2004; 114: 147–152.
Williams AL, Hoofnagle JH. Ratio of serum aspartate to alanine aminotransferase in chronic hepatitis. Relationship to cirrhosis. Gastroenterology. 1988; 95: 734–739.
Angulo P, Keach JC, Batts KP, Lindor KD. Independent predictors of liver fibrosis in patients with nonalcoholic steatohepatitis. Hepatology. 1999; 30: 1356–1362.
Matteoni CA, Younossi ZM, Gramlich T, Boparai N, Liu YC, McCullough AJ. Nonalcoholic fatty liver disease: a spectrum of clinical and pathological severity. Gastroenterology. 1999; 116: 1413–1419.
Kastelein JJP, de Groot E, Sankatsing R. Atherosclerosis measured by B-Mode ultrasonography: effect of statin therapy on disease progression. Am J Med. 2004; 116: 31–36.
Laurent S, Katsahian S, Fassot C, Tropeano AI, Gautier I, Laloux B, Boutouyrie P. Aortic stiffness is an independent predictor of fatal stroke in essential hypertension. Stroke. 2003; 34: 1203–1206.
Laurent S, Boutouyrie P, Asmar R, Gautier I, Laloux B, Guize L, Ducimetiere P, Benetos A. Aortic stiffness is an independent predictor of all-cause and cardiovascular mortality in hypertensive patients. Hypertension. 2001; 37: 1236–1241.
Blacher J, Guerin AP, Pannier B, Marchais SJ, Safar ME, London GM. Impact of aortic stiffness on survival in end-stage renal disease. Circulation. 1999; 99: 2434–2439.
Meaume S, Benetos A, Henry OF, Rudnichi A, Safar ME. Aortic pulse wave velocity predicts cardiovascular mortality in subjects >70 years of age. Arterioscler Thromb Vasc Biol. 2001; 21: 2046–2050.
Avolio AP, Chen SG, Wang RP, Zhang CL, Li MF, O’Rourke MF. Effects of aging on changing arterial compliance and left ventricular load in a northern Chinese urban community. Circulation. 1983; 68: 50–58.
Vlachopoulos C, Alexopoulos N, Panagiotakos D, O’Rourke MF, Stefanadis C. Cigar smoking has an acute detrimental effect on arterial stiffness. Am J Hypertens. 2004; 17: 299–303.
Laurent S, Caviezel B, Beck L, Girerd X, Billaud E, Boutouyrie P, Hoeks A, Safar M. Carotid artery distensibility and distending pressure in hypertensive humans. Hypertension. 1994; 23: 878–883.
Smilde TJ, van den Berkmortel FW, Wollersheim H, van Langen H, Kastelein JJ, Stalenhoef AF. The effect of cholesterol lowering on carotid and femoral artery wall stiffness and thickness in patients with familial hypercholesterolaemia. Eur J Clin Invest. 2000; 30: 473–480.
Ferrier KE, Muhlmann MH, Baguet JP, Cameron JD, Jennings GL, Dart AM, Kingwell BA. Intensive cholesterol reduction lowers blood pressure and large artery stiffness in isolated systolic hypertension. J Am Coll Cardiol. 2002; 39: 1020–1025.
Sever PS, Dahlof B, Poulter NR, Wedel H, Beevers G, Caulfield M, Collins R, Kjeldsen SE, Kristinsson A, McInnes GT. Prevention of coronary and stroke events with atorvastatin in hypertensive patients who have average or lower-than-average cholesterol concentrations, in the Anglo-Scandinavian Cardiac Outcomes Trial–Lipid Lowering Arm (ASCOT-LLA): a multicentre randomised controlled trial. Lancet. 2003; 361: 1149–1158.(Raaj R. Sankatsing; Sigri)
Correspondence to Raaj R. Sankatsing, MD, Department of Vascular Medicine, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands. E-mail r.r.sankatsing@amc.uva.nl
Abstract
Objective— Individuals with familial hypobetalipoproteinemia (FHBL) have been reported to be prone to fatty liver disease (FLD). Conversely, the profound reduction of low-density lipoprotein (LDL) cholesterol in this disorder might decrease cardiovascular risk. In the present study, we assessed hepatic steatosis as well as noninvasive surrogate markers for cardiovascular disease (CVD) in subjects with FHBL and in matched controls.
Methods and Results— Hepatic steatosis was assessed by abdominal ultrasonography. Carotid intima-media thickness (IMT) and distal common carotid arterial wall stiffness as surrogate markers for CVD risk were measured using high-resolution B-mode ultrasonography. Whereas transaminase levels were only modestly elevated, both prevalence (54% versus 29%; P=0.01) and severity of steatosis were significantly higher in FHBL individuals compared with controls. Despite similar IMT measurements, arterial stiffness was significantly lower in FHBL (P=0.04) compared with controls. Additionally, the increase in arterial stiffness as seen in the presence of traditional risk factors was attenuated, suggesting that very low levels of apoB-containing lipoproteins can negate the adverse effects of other risk factors on the vasculature.
Conclusions— FHBL is characterized by an increased prevalence and severity of fatty liver disease. The observed decreased level of arterial wall stiffness, most pronounced in the presence of nonlipid risk factors, is indicative of cardiovascular protection in these subjects.
We investigated the risk for fatty liver disease (FLD) and cardiovascular disease (CVD) in familial hypobetalipoproteinemia (FHBL) subjects and in healthy controls. Whereas the prevalence of FLD was increased in FHBL, carotid arterial wall stiffness, a surrogate marker for CVD, was decreased suggesting that these subjects are relatively protected against developing CVD.
Key Words: apolipoprotein B ? arterial stiffness ? cardiovascular risk ? familial hypobetalipoproteinemia ? fatty liver disease
Introduction
Familial hypobetalipoproteinemia (FHBL) is a hereditary disorder of lipoprotein metabolism characterized by very low levels of apolipoprotein (apo) B-100. Plasma levels below the fifth percentile are distinctive for this condition that inherits as an autosomal dominant trait. The prevalence in the general population is estimated to vary from 0.1% to 1.9%.1,2 Genetic causes of hypobetalipoproteinemia include FHBL, abetalipoproteinemia, and chylomicron remnant disease (OMIM numbers 601519, 246700, and 200100, respectively). A small percentage of FHBL can be explained by mutations in the gene-encoding apolipoprotein B-100 (APOB). These include nonsense, frame-shift, and splicing mutations. Recently, it was reported that a missense mutation in the APOB gene can also lead to FHBL.3 APOB gene mutations lead to truncated forms of apolipoprotein B (apoB) and are characterized by slower hepatic secretion, as well as more rapid plasma clearance compared with wild-type apoB-100 particles.4,5 Because apoB is the main constituent of such lipoproteins, including very low-density lipoprotein (VLDL), intermediate-density lipoprotein, and low-density lipoprotein (LDL), FHBL subjects are characterized by exceptionally low levels of these proatherogenic particles from birth onwards. Whereas subjects with heterozygous FHBL are generally asymptomatic, 2 potential implications have been attributed to this particular condition. First, the impairment of hepatic VLDL-triglycerides (TG) secretion in FHBL may contribute to fat accumulation in the liver. Potential consequences of fat accumulation are highlighted by the occurrence of hepatic steatosis in subjects with nonalcoholic steatohepatitis in whom progression toward cirrhosis has been observed.6–8 Case reports and smaller studies have reported a relationship between fatty liver disease (FLD) and FHBL.9–12 This is best illustrated by 2 recent studies by Schonfeld et al who showed that hepatic fat percentage, as assessed by magnetic resonance spectroscopy, was significantly increased in subjects with FHBL as compared with healthy controls.13,14 Nevertheless, the natural course of this potential fat accumulation in FHBL is as yet unknown. Second, FHBL offers a unique opportunity to evaluate the impact of life-long exposure to unusually low levels of apoB-containing atherogenic lipoproteins. In this respect, FHBL subjects might be regarded as a natural model for "intensive lipid-lowering therapy." In fact, the potential success of intensive lipid-lowering therapy has recently been reinforced by data from the REVERSAL15 and PROVE-IT studies,16 showing a more pronounced reduction of cardiovascular disease risk on intensive lowering of LDL cholesterol levels.
In the present study, we evaluated the impact of FHBL on hepatic steatosis as well as on surrogate markers for cardiovascular disease. Here we present the results of these investigations.
Methods
Subjects and Protocols
For a detailed description of methods please http://atvb.ahajournals.org.
Eighty-two subjects were enrolled in study, 41 with FHBL and 41 healthy controls, matched for sex and body mass index (Table 1). Autosomal codominant inheritance was a necessary characteristic for the clinical diagnosis of FHBL. FHBL subjects were identified from a group of individuals who were referred to our lipid clinic because of extreme low LDL levels. These subjects were characterized by direct sequencing of the entire apoB gene, as published previously.17 Secondary causes for low LDL cholesterol levels, ie, (strict) vegetarian diet or generalized diseases such as cancer, were excluded. The controls consisted of unaffected family members as well as unrelated volunteers. In the FHBL group, 4 subjects had diabetes mellitus (DM) compared with none in the control group. Because DM is strongly associated with both liver steatosis18–21 and carotid IMT/arterial stiffness,22–25 we repeated the analyses after excluding the 4 diabetic subjects in the FHBL group (FHBL minus DM) to assess whether possible differences between groups were obscured by the presence of DM.
TABLE 1. Clinical Characteristics for FHBL Subjects and Controls
Liver Ultrasound
In all subjects ultrasound examination of the liver was performed by a single radiologist blinded to the disease state of the subjects. The extent of hepatic fatty infiltration was classified according to previously published criteria.26
Carotid Ultrasound
B-mode ultrasound intima-media thickness (IMT) measurements were performed in the far walls of the carotid arteries and M-mode arterial stiffness was measured bilaterally in the common carotid arteries.
Statistical Analysis
Statistical analyses were performed using linear or logistic regression analyses with generalized estimating equations in the SAS procedure GENMOD to account for correlations within families. Analyses were performed using SAS software (release 8.02; SAS Institute Inc). P<0.05 was considered significant.
Results
Clinical characteristics of FHBL subjects and controls are presented in Table 1. Forty-one subjects who met the clinical criteria of FHBL (apoB and LDL cholesterol less than fifth percentile adjusted by age, gender, and race) participated in the study. Thirty-three of these subjects had mutations in the apoB gene, characteristic of FHBL. These genetically affected subjects were recruited from 8 families with different apoB mutations. The following apoB mutations were identified in the FHBL group: 2534delA apoB-18, Q1309X apoB-29, R2507X apoB-55, and 11712delC apo-B8617 (Table 2). Subjects did not use lipid-lowering drugs. There was no significant difference in blood pressure, smoking, body mass index, or alcohol consumption between FHBL subjects and controls. In line with their diagnosis, apoB, LDL cholesterol, and total cholesterol levels were significantly lower in the FHBL group. The type of apoB truncation, but not plasma LDL cholesterol or apoB levels, was modestly correlated with the degree of liver steatosis using Spearman rho method (r=0.336, P=0.002). Mean levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and -glutamyltransferase levels were significantly higher in the FHBL group as compared with the controls (Table 3).
TABLE 2. Apolipoprotein B Mutations
TABLE 3. Laboratory Characteristics for FHBL Subjects and Controls
However, this was mainly caused by the 7 subjects with severe steatosis who had the highest levels of transaminases. Three of these 7 subjects had ALT levels more than twice the upper limit of normal (ULN) but still <3x ULN. The highest value of ALT, observed in a diabetic patient, was 102. None of these 7 subjects had AST values >2x ULN. AST and ALT were both significantly associated with hepatic steatosis (P=0.04 and P=0.0002, respectively). Levels of high-sensitivity C-reactive protein (hs-CRP) and glucose were comparable between the 2 groups. HDL cholesterol levels were significantly higher in the FHBL minus DM group compared with the controls (1.76±0.59 mmol/L versus 1.55±0.33 mmol/L, P=0.01).
Liver Ultrasound
We observed a significantly higher prevalence of liver steatosis in the FHBL group compared with the control group (54% versus 29%; P=0.01). In addition, FHBL subjects were also characterized by a more severe degree of hepatic steatosis. Seven (17%) of the subjects in the FHBL group were classified as severe steatosis compared with none in the control group (Figure 1). The distribution of steatosis severity was significantly different between groups (P=0.004). This was even more apparent when comparing the controls with the subgroup of FHBL with mutations (P=0.001). The 4 diabetic subjects were equally distributed over the 4 steatosis categories. Separate analyses with exclusion of these 4 subjects lead to an equal statistical difference for steatosis severity between groups.
Figure 1. Grade of liver steatosis.
Hepatic steatosis was not more severe in those subjects carrying truncated apoB not secreted into the plasma (apoB-18 and ApoB-29) compared with the carriers of longer truncations (P=0.68). Plasma LDL cholesterol and apoB levels were also not different between these subgroups (P=0.77 and P=0.81, respectively). Nine of the 14 carriers of Apo-86 had liver steatosis compared with 3 of the 8 FHBL subjects without mutations. FHBL was positively associated with liver steatosis on univariate analysis (P=0.02). When adjusted for gender and smoking on multivariate analysis, FHBL, age, and body mass index were independent predictors for the development of liver steatosis (P=0.001, P<0.0001, and P=0.0014, respectively). Similar significant results were found when running the analyses with the subgroup of FHBL subjects with mutations (n=33) compared with the healthy controls. Results were not significant when this was done for the subgroup of FHBL without mutations (n=8). However, the latter is likely to be caused by a lack of power attributable to the limited number of subjects in this group.
Vascular Measurements
Mean carotid IMT (±SD) was 0.63±0.14 mm in the FHBL group compared with 0.65±0.15 mm in the control group. The latter difference on univariate analysis (P=0.049) lost significance when adjusting for age, gender, smoking, and body mass index on multivariate analysis. Arterial stiffness was significantly lower in the FHBL minus DM group compared with the controls on univariate analysis (P=0.04), whereas a similar trend was seen for the whole FHBL group (P=0.06). When comparing the 2 subgroups of FHBL, (with and without mutations), FHBL was still significantly associated with arterial stiffness in the first group (P=0.04), but this was not significant for the subgroup without mutations. Again, this could reflect a lack of power, because the subgroup without mutations contained only 8 subjects. To evaluate a potential interaction between risk factors and apoB-containing lipoproteins, we attributed a cumulative risk score to each subject. The cumulative risk score comprised age, systolic blood pressure, and smoking. These variables were chosen because their individual relationship with cardiovascular risk has been proven beyond any doubt as attested to by their incorporation in both the PROCAM27 and Framingham Risk Score,28 the 2 most widely used risk calculators for predicting cardiovascular disease. Moreover, these risk factors have an independent strong association with arterial stiffness.29–35 In our study these parameters were also strongly correlated with arterial stiffness with the exception of smoking (r=0.732, P<0.001, r=0.550, P<0.001, and r=0.267, P=0.018, respectively). Both FHBL and control subjects showed a gradual increase in arterial stiffness with increasing cumulative risk scores. However, using linear regression analysis, the slope for the FHBL group was markedly decreased compared with the controls, indicating decreased stiffening in the presence of nonlipid risk factors in the FHBL group (P=0.03) (Figure 2). This difference remained significant (P=0.04) when comparing the FHBL minus DM group with the control subjects.
Figure 2. Arterial stiffness versus cumulative risk score in FHBL. The cumulative risk score is based on 3 variables: age, smoking, and systolic blood pressure (SBP). Results of each variable, except for smoking, were divided into tertiles. For age and SBP, patients received scores of 1, 2, or 3 with each increasing tertile. Smoking was scored as either 0 for nonsmoking or 3 for smoking. Minimal and maximal attainable scores were 2 and 9, respectively. The probability value indicates the difference in slope between the 2 regression lines.
Discussion
Subjects with FHBL are characterized by an increased prevalence of fat accumulation in the liver as well as by a more severe degree of such hepatic steatosis. Whereas these findings are not novel, we show that FHBL subjects exhibit decreased arterial stiffness. Notably, the increase in arterial stiffness under the influence of "traditional" nonlipid risk factors was markedly attenuated in FHBL subjects.
Biochemical Analyses
Subjects with FHBL are characterized by significantly decreased levels of apoB-containing lipoproteins, including low LDL cholesterol as well as low triglyceride-rich particles. Also, slightly higher levels of HDL cholesterol were found in these FHBL subjects. Presumably, the latter is the consequence of low levels of triglycerides, thus minimizing exchange of cholesterol esters from HDL cholesterol to apoB-containing particles through the action of cholesterol ester transfer protein. Another explanation could be that the truncated apoB are only present in the density range of HDL. However, we excluded the latter option by performing agarose gel electrophoresis on HDL fractions, from patients with apoB-55 and apoB-86, which were isolated after ultracentrifugation. No LDL bands were present in the HDL density range. Additionally, apoB could also not be detected in the HDL fraction using immunonephelometry (data not shown).
Hepatosteatosis
The prevalence of fatty liver disease in healthy controls (29%) is in the same order of magnitude as reported by others.19,36 The increased prevalence of hepatosteatosis in subjects with FHBL is in agreement with previous results from Schonfeld and Tanoli who showed that these subjects had 3-fold increase in mean liver fat content, as assessed by magnetic resonance spectroscopy.13,14 The most likely cause for this increase in hepatic steatosis is the impaired secretion of VLDL-TG from the liver, leading to accumulation of VLDL-TG in the liver. There is a large body of evidence suggesting that accumulation of liver triglycerides may give rise to increased oxidative stress in the hepatocytes.37–39 However, distinct proof, in the human setting, that this process invariably translates into progression of liver steatosis to nonalcoholic steatohepatitis is lacking.40 Recent work by Youssef et al revealed that up to 25% of patients with FLD may progresses to nonalcoholic steatohepatitis,21 of whom 20% may eventually even progress into cirrhosis.19,20 Notably, in our FHBL group, transaminase levels were only modestly elevated with none of the subjects exceeding a 3-fold increase in upper limit of normal. Most studies reporting long-term outcome of fatty liver disease, use the AST/ALT ratio as a marker for the risk of disease progression. A ratio of <1 indicates a "low risk" for steatosis41,42 and in our FHBL subjects, AST/ALT ratios were all <1. It should be kept in mind, however, that the absence of liver enzyme elevations8,43 does not completely preclude advanced fibrosis or cirrhosis in these subjects.43 To date, long-term follow-up data with regard to liver outcome in FHBL are lacking. Nevertheless, risk factors for FLD such as hypertriglyceridemia, obesity, alcohol, diabetes mellitus, and certain drugs are likely to aggravate hepatic steatosis in FHBL. Hence, it is prudent to avoid these risk factors and recommend a diet with low to moderate amounts of fat and energy, limited use of alcohol, as well as avoiding obesity in these individuals.
Cardiovascular Risk
Numerous studies have established a strong correlation between levels of LDL cholesterol and progression of IMT.44 In the present study, however, we could not show an independent statistical difference in terms of carotid IMT values between FHBL subjects and controls. Nevertheless, data have accumulated recently that show the predictive value of the assessment of vascular function, such as arterial stiffness, for future cardiovascular events.23,45–48 Arterial stiffness is closely correlated with increasing age, smoking, and hypertension.31,32,49–51 The impact of these risk factors is augmented in the presence of hypercholesterolemia and can be reverted by statin therapy.52,53 In our FHBL group, we observed a significant decrease in arterial stiffness. Of note, this difference was observed despite the fact that traditional risk factors such as smoking and diabetes occurred more frequently in the FHBL group compared with controls. In earlier studies, apoB-containing lipoproteins have been put forward as a pivotal "permissive" factor for the development of atherogenic changes of the vessel wall. To evaluate a potential interaction between apoB-containing lipoproteins and other traditional risk factors, we constructed a cumulative risk index including age, smoking, and systolic blood pressure in FHBL subjects as well as controls. In both groups, there was a linear relationship between increased risk score and arterial stiffness. Interestingly, the increase in arterial stiffness, also in presence of these risk factors was decreased significantly in the FHBL group compared with controls. These data suggest that apoB-containing lipoproteins indeed have the ability to potentiate the impact of traditional risk factors on vascular function. Tentatively, these observations might suggest that lowering of apoB-containing lipoproteins should have a beneficial impact also in subjects with "noncholesterol" risk factors. Recent studies have validated the beneficial effects of statin therapy in normocholesterolemic subjects with nonlipid risk factors, such as hypertension.54
This study has some limitations. We used the less sensitive ultrasonography method to evaluate fatty liver disease rather than magnetic resonance spectroscopy. However, in view of the carefully standardized methodology and the fact that both patients and controls were evaluated using the same methodology, it is unlikely that the latter has affected our outcomes. With regard to the IMT measurement, we could not find a clear relationship between LDL cholesterol levels and carotid IMT. Several reasons may have attributed to the absence of a relation. First, we studied a relatively young cohort with an inherently low risk for cardiovascular disease and hence low IMT values. Second, we studied IMT in a case control design to show thinner IMTs compared with healthy controls. A priori, it is very difficult to demonstrate decreased IMT thickness in "low-risk" groups compared with healthy controls. We have estimated that inclusion of more than 1000 subjects per group would have been necessary to be able to detect significantly thinner IMTs compared with healthy controls with a "normal" risk factor distribution, as seen in western populations.
In summary, our study shows that subjects with FHBL are at increased risk of developing FLD. Whereas long-term sequelae of FLD in FHBL subjects remain to be established, it is prudent to give lifestyle advice in affected individuals. As is illustrated by decreased vascular wall stiffness, our findings suggest that the vessel wall in FHBL subjects is relatively protected by the (life-long) reduced levels of exposure to apoB-containing lipoproteins. The attenuated gradual increase in vascular stiffness in the presence of classical, nonlipid cardiovascular risk factors in FHBL subjects is of interest and suggests that apoB-containing particles constitute a central factor in atherogenesis, amplifying any risk mediated by nonlipid risk factors. Further confirmation of this finding is needed in larger cohorts to ascertain its impact on cardiovascular risk.
Acknowledgments
S.W.F. is supported by the Netherlands Heart Foundation (grant 2000B138). J.J. P.K. is an established investigator of the Netherlands Heart Foundation (2000D039). The cooperation of all study subjects is greatly appreciated. We are grateful to Patrick Rol and Johan Gort for assistance with carotid ultrasound examinations and to Dr Nico Smits for assistance with liver data analysis.
References
Welty FK, Lahoz C, Tucker KL, Ordovas JM, Wilson PWF, Schaefer EJ. Frequency of ApoB and ApoE gene mutations as causes of hypobetalipoproteinemia in the Framingham offspring population. Arterioscler Thromb Vasc Biol. 1998; 18: 1745–1751.
Linton MF, Farese RV Jr, Young SG. Familial hypobetalipoproteinemia. J Lipid Res. 1993; 34: 521–541.
Burnett JR, Shan J, Miskie BA, Whitfield AJ, Yuan J, Tran K, McKnight CJ, Hegele RA, Yao Z. A novel nontruncating APOB gene mutation, R463W, causes familial hypobetalipoproteinemia. J Biol Chem. 2003; 278: 13442–13452.
Chen Z, Fitzgerald RL, Li G, Davidson NO, Schonfeld G. Hepatic secretion of apoB-100 is impaired in hypobetalipoproteinemic mice with an apoB-38.9-specifying allele. J Lipid Res. 2004; 45: 155–163.
Zhu XF, Noto D, Seip R, Shaish A, Schonfeld G. Organ loci of catabolism of short truncations of apoB. Arterioscler Thromb Vasc Biol. 1997; 17: 1032–1038.
Lee RG. Nonalcoholic steatohepatitis: a study of 49 patients. Hum Pathol. 1989; 20: 594–598.
Powell EE, Cooksley WG, Hanson R, Searle J, Halliday JW, Powell LW. The natural history of nonalcoholic steatohepatitis: a follow-up study of forty-two patients for up to 21 years. Hepatology. 1990; 11: 74–80.
Bacon BR, Farahvash MJ, Janney CG, Neuschwander-Tetri BA. Nonalcoholic steatohepatitis: an expanded clinical entity. Gastroenterology. 1994; 107: 1103–1109.
Tarugi P, Lonardo A, Ballarini G, Erspamer L, Tondelli E, Bertolini S, Calandra S. A study of fatty liver disease and plasma lipoproteins in a kindred with familial hypobetalipoproteinemia due to a novel truncated form of apolipoprotein B (APO B-54.5). J Hepatol. 2000; 33: 361–370.
Tarugi P, Lonardo A, Ballarini G, Grisendi A, Pulvirenti M, Bagni A, Calandra S. Fatty liver in heterozygous hypobetalipoproteinemia caused by a novel truncated form of apolipoprotein B. Gastroenterology. 1996; 111: 1125–1133.
Whitfield AJ, Barrett PH, van Bockxmeer FM, Burnett JR. Lipid disorders and mutations in the APOB gene. Clin Chem. 2004; 50: 1725–1732.
Whitfield AJ, Barrett PH, Robertson K, Havlat MF, van Bockxmeer FM, Burnett JR. Liver dysfunction and steatosis in familial hypobetalipoproteinemia. Clin Chem. 2005; 51: 266–269.
Schonfeld G, Patterson BW, Yablonskiy DA, Tanoli TS, Averna M, Elias N, Yue P, Ackerman J. Fatty liver in familial hypobetalipoproteinemia: triglyceride assembly into VLDL particles is affected by the extent of hepatic steatosis. J Lipid Res. 2003; 44: 470–478.
Tanoli T, Yue P, Yablonskiy D, Schonfeld G. Fatty liver in familial hypobetalipoproteinemia: roles of the APOB defects, intra-abdominal adipose tissue, and insulin sensitivity. J Lipid Res. 2004; 45: 941–947.
Nissen SE, Tuzcu EM, Schoenhagen P, Brown BG, Ganz P, Vogel RA, Crowe T, Howard G, Cooper CJ, Brodie B, Grines CL, DeMaria AN. Effect of intensive compared with moderate lipid-lowering therapy on progression of coronary atherosclerosis: a randomized controlled trial. J Am Med Assoc. 2004; 291: 1071–1080.
Cannon CP, Braunwald E, McCabe CH, Rader DJ, Rouleau JL, Belder R, Joyal SV, Hill KA, Pfeffer MA, Skene AM. The Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis in Myocardial Infarction. Intensive versus moderate lipid lowering with statins after acute coronary syndromes. N Engl J Med. 2004; 350: 1495–1504.
Fouchier SW, Sankatsing RR, Peter J, Castillo S, Pocovi M, Alonso R, Kastelein JJP, Defesche JC. High frequency of APOB gene mutations causing familial hypobetalipoproteinaemia in patients of Dutch and Spanish descent. J Med Genet. 2005; 42: e23.
Angulo P. Treatment of nonalcoholic fatty liver disease. Ann Hepatol. 2002; 1: 12–19.
Yu AS, Keeffe EB. Nonalcoholic fatty liver disease. Rev Gastroenterol Disord. 2002; 2: 11–19.
Harrison SA, Di Bisceglie AM. Advances in the understanding and treatment of nonalcoholic fatty liver disease. Drugs. 2003; 63: 2379–2394.
Youssef W, McCullough AJ. Diabetes mellitus, obesity, and hepatic steatosis. Semin Gastrointest Dis. 2002; 13: 17–30.
Salomaa V, Riley W, Kark JD, Nardo C, Folsom AR. Non-insulin-dependent diabetes mellitus and fasting glucose and insulin concentrations are associated with arterial stiffness indexes: the ARIC Study. Circulation. 1995; 91: 1432–1443.
Boutouyrie P, Tropeano AI, Asmar R, Gautier I, Benetos A, Lacolley P, Laurent S. Aortic stiffness is an independent predictor of primary coronary events in hypertensive patients: a longitudinal study. Hypertension. 2002; 39: 10–15.
Schiffrin EL. Vascular stiffening and arterial compliance: implications for systolic blood pressure. Am J Hypertens. 2004; 17: S39–S48.
Schram MT, Henry RMA, van Dijk RAJM, Kostense PJ, Dekker JM, Nijpels G, Heine RJ, Bouter LM, Westerhof N, Stehouwer CDA. Increased central artery stiffness in impaired glucose metabolism and Type 2 diabetes: The Hoorn Study. Hypertension. 2004; 43: 176–181.
Scatarige JC, Scott WW, Donovan PJ, Siegelman SS, Sanders RC. Fatty infiltration of the liver: ultrasonographic and computed tomographic correlation. J Ultrasound Med. 1984; 3: 9–14.
Assmann G, Cullen P, Schulte H. Simple scoring scheme for calculating the risk of acute coronary events based on the 10-year follow-up of the Prospective Cardiovascular Munster (PROCAM) Study. Circulation. 2002; 105: 310–315.
Wilson PW, Castelli WP, Kannel WB. Coronary risk prediction in adults (the Framingham Heart Study). Am J Cardiol. 1987; 59: 91G–94G.
Tomiyama H, Yamashina A, Arai T, Hirose K, Koji Y, Chikamori T, Hori S, Yamamoto Y, Doba N, Hinohara S. Influences of age and gender on results of noninvasive brachial-ankle pulse wave velocity measurement–a survey of 12517 subjects. Atherosclerosis. 2003; 166: 303–309.
Mitchell GF, Parise H, Benjamin EJ, Larson MG, Keyes MJ, Vita JA, Vasan RS, Levy D. Changes in arterial stiffness and wave reflection with advancing age in healthy men and women: the Framingham Heart Study. Hypertension. 2004; 43: 1239–1245.
Stefanadis C, Tsiamis E, Vlachopoulos C, Stratos C, Toutouzas K, Pitsavos C, Marakas S, Boudoulas H, Toutouzas P. Unfavorable effect of smoking on the elastic properties of the human aorta. Circulation. 1997; 95: 31–38.
Stefanadis C, Vlachopoulos C, Tsiamis E, Diamantopoulos L, Toutouzas K, Giatrakos N, Vaina S, Tsekoura D, Toutouzas P. Unfavorable effects of passive smoking on aortic function in men. Ann Intern Med. 1998; 128: 426–434.
Vlachopoulos C, Kosmopoulou F, Panagiotakos D, Ioakeimidis N, Alexopoulos N, Pitsavos C, Stefanadis C. Smoking and caffeine have a synergistic detrimental effect on aortic stiffness and wave reflections. J Am Coll Cardiol. 2004; 44: 1911–1917.
Smulyan MD, Safar MD. Systolic blood pressure revisited. J Am Coll Cardiol. 1997; 29: 1407–1413.
Li S, Chen W, Srinivasan SR, Berenson GS. 847–5 Systolic blood pressure measured serially from childhood to adulthood predicts arterial stiffness in young adults: the Bogalusa heart study. J Am Coll Cardiol. 2004; 43: A515.
Angulo P. Nonalcoholic fatty liver disease. N Engl J Med. 2002; 346: 1221–1231.
Seki S, Kitada T, Yamada T, Sakaguchi H, Nakatani K, Wakasa K. In situ detection of lipid peroxidation and oxidative DNA damage in non-alcoholic fatty liver diseases. J Hepatol. 2002; 37: 56–62.
Lieber CS. CYP2E1: from ASH to NASH. Hepatol Res. 2004; 28: 1–11.
Araya J, Rodrigo R, Videla LA, Thielemann L, Orellana M, Pettinelli P, Poniachik J. Increase in long-chain polyunsaturated fatty acid n - 6/n - 3 ratio in relation to hepatic steatosis in patients with non-alcoholic fatty liver disease. Clin Sci (Lond). 2004; 106: 635–643.
Browning JD, Horton JD. Molecular mediators of hepatic steatosis and liver injury. J Clin Invest. 2004; 114: 147–152.
Williams AL, Hoofnagle JH. Ratio of serum aspartate to alanine aminotransferase in chronic hepatitis. Relationship to cirrhosis. Gastroenterology. 1988; 95: 734–739.
Angulo P, Keach JC, Batts KP, Lindor KD. Independent predictors of liver fibrosis in patients with nonalcoholic steatohepatitis. Hepatology. 1999; 30: 1356–1362.
Matteoni CA, Younossi ZM, Gramlich T, Boparai N, Liu YC, McCullough AJ. Nonalcoholic fatty liver disease: a spectrum of clinical and pathological severity. Gastroenterology. 1999; 116: 1413–1419.
Kastelein JJP, de Groot E, Sankatsing R. Atherosclerosis measured by B-Mode ultrasonography: effect of statin therapy on disease progression. Am J Med. 2004; 116: 31–36.
Laurent S, Katsahian S, Fassot C, Tropeano AI, Gautier I, Laloux B, Boutouyrie P. Aortic stiffness is an independent predictor of fatal stroke in essential hypertension. Stroke. 2003; 34: 1203–1206.
Laurent S, Boutouyrie P, Asmar R, Gautier I, Laloux B, Guize L, Ducimetiere P, Benetos A. Aortic stiffness is an independent predictor of all-cause and cardiovascular mortality in hypertensive patients. Hypertension. 2001; 37: 1236–1241.
Blacher J, Guerin AP, Pannier B, Marchais SJ, Safar ME, London GM. Impact of aortic stiffness on survival in end-stage renal disease. Circulation. 1999; 99: 2434–2439.
Meaume S, Benetos A, Henry OF, Rudnichi A, Safar ME. Aortic pulse wave velocity predicts cardiovascular mortality in subjects >70 years of age. Arterioscler Thromb Vasc Biol. 2001; 21: 2046–2050.
Avolio AP, Chen SG, Wang RP, Zhang CL, Li MF, O’Rourke MF. Effects of aging on changing arterial compliance and left ventricular load in a northern Chinese urban community. Circulation. 1983; 68: 50–58.
Vlachopoulos C, Alexopoulos N, Panagiotakos D, O’Rourke MF, Stefanadis C. Cigar smoking has an acute detrimental effect on arterial stiffness. Am J Hypertens. 2004; 17: 299–303.
Laurent S, Caviezel B, Beck L, Girerd X, Billaud E, Boutouyrie P, Hoeks A, Safar M. Carotid artery distensibility and distending pressure in hypertensive humans. Hypertension. 1994; 23: 878–883.
Smilde TJ, van den Berkmortel FW, Wollersheim H, van Langen H, Kastelein JJ, Stalenhoef AF. The effect of cholesterol lowering on carotid and femoral artery wall stiffness and thickness in patients with familial hypercholesterolaemia. Eur J Clin Invest. 2000; 30: 473–480.
Ferrier KE, Muhlmann MH, Baguet JP, Cameron JD, Jennings GL, Dart AM, Kingwell BA. Intensive cholesterol reduction lowers blood pressure and large artery stiffness in isolated systolic hypertension. J Am Coll Cardiol. 2002; 39: 1020–1025.
Sever PS, Dahlof B, Poulter NR, Wedel H, Beevers G, Caulfield M, Collins R, Kjeldsen SE, Kristinsson A, McInnes GT. Prevention of coronary and stroke events with atorvastatin in hypertensive patients who have average or lower-than-average cholesterol concentrations, in the Anglo-Scandinavian Cardiac Outcomes Trial–Lipid Lowering Arm (ASCOT-LLA): a multicentre randomised controlled trial. Lancet. 2003; 361: 1149–1158.(Raaj R. Sankatsing; Sigri)