Excess Soluble fms-Like Tyrosine Kinase 1 and Low Platelet Counts in Premature Neonates of Preeclamptic Mothers
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《小儿科》
Pediatrics Department of Medical Genetics
Department of Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan
ABSTRACT
Objective. To investigate the relationship of neonatal platelet count and preeclampsia to levels of soluble fms-like tyrosine kinase 1 (sFlt-1), placental growth factor (PlGF), and vascular endothelial growth factor (VEGF) in the cord blood of preterm infants.
Methods. Sixty-nine preterm infants with a gestational age between 26 and 37 weeks at birth were enrolled. sFlt-1, PlGF, and VEGF levels in the cord blood of preterm neonates, with or without maternal preeclampsia, were measured using a standardized sandwich enzyme-linked immunosorbent assay method.
Results. Infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF levels. There was a significantly positive relationship between neonatal platelet count and birth weight and a significantly negative relationship between neonatal platelet count and cord blood sFlt-1 levels. Multiple regression analysis revealed that only birth weight and cord blood sFlt-1 levels were independently related to neonatal platelet count, whereas maternal preeclampsia, gestational age (GA), and small for GA (SGA) were not related. Neonates with thrombocytopenia had higher cord blood sFlt-1 levels but lower birth weight. A significant correlation was also found between birth weight and cord blood sFlt-1 levels. Multiple regression with birth weight as the dependent variable found that only GA and cord blood sFlt-1 levels were independently related. Furthermore, infants with high cord blood sFlt-1 were more likely to have lower platelet count and maternal preeclampsia, be SGA, and have a trend toward lower birth weight.
Conclusion. Excess sFlt-1 may play an important role in the development of maternal preeclampsia- induced neonatal thrombocytopenia, and SGA.
Key Words: sFlt-1 vascular endothelial growth factor placenta growth factor preeclampsia platelets
Abbreviations: SGA, small for gestational age VEGF, vascular endothelial growth factor PlGF, placenta growth factor sFlt-1, soluble fms-like tyrosine kinase 1 GA, gestational age VLBW, very low birth weight Tpo, thrombopoietin Mk, megakaryocytic
Infants who are born to preeclamptic mothers have been shown to have higher risk for being small for gestational age (SGA) and having neonatal thrombocytopenia or neutropenia.1–6 Neonatal thrombocytopenia is observed in 26% to 47% of infants who are delivered to mothers with preeclampsia complicated with hemolysis, elevated liver enzymes, and low platelets syndrome.7–11 This abnormality affects the long-term outcome when extreme prematurity or intrapartum asphyxia is coexistent.12
Several studies have demonstrated decreased circulating vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF) levels during preeclampsia, even before onset.13–17 However, the cause of preeclampsia remains unclear. Recently, some reports demonstrated that excess circulating soluble fms-like tyrosine kinase 1 (sFlt-1), a natural antagonist for Flt-1 that captures only PlGF and VEGF, may have a pathologic role in preeclampsia.18–21 In addition, Casella et al22 demonstrated that VEGF and PlGF contributed to optimal megakaryocyte maturation through Flt-1. This indicates that Flt-1 signaling regulates megakaryocytic development and may contribute to the pathogenesis of maternal preeclampsia-induced neonatal thrombocytopenia. However, the relationship between Flt-1 signaling and maternal preeclampsia-induced thrombocytopenia in preterm infants has not been evaluated. This study analyzed the relationship of neonatal platelet counts and maternal preeclampsia to cord blood levels of sFlt-1, PlGF, and VEGF in preterm infants.
METHODS
Study Group
This study was performed at National Taiwan University Hospital after approval was obtained from the institutional review board. All infants who were born from 26 to 37 weeks' gestation at National Taiwan University Hospital from July 1, 1998, to June 31, 2000, were enrolled in this study. Infants were excluded when there was evidence of prenatal maternal infection or any infection within the first 3 days of life. Cord blood was collected in heparinized syringes on delivery and centrifuged within 15 minutes of collection. Gestational age (GA) was estimated by last menstrual date or prenatal ultrasound. SGA status was determined according to the published intrauterine growth curve specific for Taiwan.23 The diagnosis of preeclampsia was made according to the criteria of Davey et al.24 Hypertension was defined as either 1 measurement of diastolic blood pressure of 110 mm Hg or above or 2 consecutive measurements of diastolic blood pressure of 90 mm Hg or above. Proteinuria was defined as a total proteinuria excretion of 300 mg or more in 24 hours. Neonatal thrombocytopenia was defined arbitrarily as a platelet count of <150000 mm3. Very low birth weight (VLBW) was defined as birth weight <1500 g.
Collection of Cord Blood and Measurement of sFlt-1, VEGF, and PlGF
Venous cord blood was collected in heparinized syringes on delivery and centrifuged within 15 minutes of collection. The plasma was kept at –70°C until analysis by a technician who was blinded to the patients' condition. The levels of sFlt-1, VEGF, and PlGF in the cord blood were assayed by a standardized sandwich enzyme-linked immunosorbent assay method (Quantikine ELISA; R&D Systems, Minneapolis, MN) in duplicate according to the manufacturer's protocol.
Data Analysis
Comparisons between unpaired groups were performed by Mann-Whitney rank sum test and 2 test. The relationships between angiogenic factors and GA, birth weight, and platelet count were analyzed by Spearman correlation coefficients. Multivariate analyses were conducted using logistic and linear regression. P .05 was considered statistically significant.
RESULTS
Patient Characteristics
Seventy-four neonates were collected during this period. Four infants with maternal fever and 1 with elevated C-reactive protein were excluded. The 69 premature neonates who were enrolled in this study had a mean gestational age of 31.4 ± 3.0 weeks and a mean birth weight of 1.45 ± 0.52 kg. Of these premature neonates, 33 were associated with maternal preeclampsia, 35 had a GA of <32 weeks, 32 were SGA, and 38 had VLBW. The female/male ratio was 40/29. The preeclampsia group had a higher GA and a greater incidence of SGA but had lower birth weight and platelet counts. The sFlt-1 and VEGF levels in cord blood all were above the sensitivity (5 pg/ml) of our assay. However, PlGF levels were below the sensitivity (7.0 pg/ml) of the assay in 14 (42%) infants with maternal preeclampsia and 6 (17%) infants without maternal preeclampsia. In addition, infants with maternal preeclampsia had higher cord blood sFlt-1 (P = .003; Fig 1) but lower PlGF (P = .011) and VEGF (P = .046) levels (Table 1).
Neonatal Platelet Count and Cord Blood sFlt-1 Levels
The neonatal platelet count was significantly lower in infants with VLBW (P = .005), with SGA (P = .002), and with maternal preeclampsia (P = .045). There was a significantly positive relationship between the neonatal platelet count and birth weight (r = 0.349; P = .003) and maternal platelet count (r = 0.351; P = .009) and a negative relationship between the neonatal platelet count and cord blood sFlt-1 levels (r = –0.438; P < .001). Multiple regression with neonatal platelet count as the dependent variable found that only birth weight (P = .015) and cord blood sFlt-1 levels (P = .036) were significantly independently related, whereas maternal preeclampsia (P = .189), GA (P = .276), and SGA (P = .921) were not.
In addition, when we performed correlation coefficients separately among the infants with maternal preeclampsia and among the infants without maternal preeclampsia, the negative relationship between neonatal count and cord blood sFlt-1 levels was present only in infants with maternal preeclampsia (r = –0.534; P = .001; Fig 2). There was no effect of sFlt1 in the infants whose mothers did not develop preeclampsia (P = .138).
Seven infants had thrombocytopenia (6 in the preeclampsia group and 1 in the nonpreeclampsia group; P = .049). The median platelet count during the first day of life was 126 x 103/μL (range: 7–144 x 103/μL) and at the nadir was 90 x 103/μL (range: 7–141 x 103/μL). The platelet nadir occurred at a median of 6 days of age (range: 1–13 days). Thrombocytopenia persisted for at least 7 days. Neonatal thrombocytopenia was correlated with maternal preeclampsia (P = .034) and VLBW (P = .012). In addition, neonates with thrombocytopenia had higher cord blood sFlt-1 levels (P = .008) but lower birth weight (P = .009) when compared with infants without preeclampsia.
Birth Weight and Cord Blood sFlt-1 Levels
Birth weight was significantly correlated with GA (r = 0.599; P < .001), cord blood sFlt-1 levels (r = –0.328; P = .006), and PlGF levels (r = –0.315; P = .016). Multiple regression analysis with birth weight as the dependent variable found that only GA (P < .001) and cord blood sFlt-1 levels (P = .015) were significantly independently related, whereas PlGF levels (P = .309) and VEGF levels (P = .450) were not.
It is interesting that the same result for the relationship between birth weight and cord blood sFlt-1 levels was found when we performed correlation coefficients separately among the infants with maternal preeclampsia and among the infants without maternal preeclampsia. The negative relationship between birth weight and cord blood sFlt-1 levels was present only in infants with maternal preeclampsia (r = -0.598; P < .001; Fig 3) but not in the infants whose mothers did not develop preeclampsia (P = .850).
Twenty-nine infants were SGA. The SGA group had a higher GA (P = .023) and a greater incidence of maternal preeclampsia (P = .013) but had lower platelet counts (P = .002). Furthermore, cord blood sFlt-1 levels (P = .002) but not VEGF (P = .433) or PlGF (P = .261) levels were significantly higher in the SGA group than in the non-SGA group. Multiple regression analysis revealed that only cord blood sFlt-1 levels were significantly independently related to SGA.
Excess Circulating sFlt-1 Correlated With Neonatal Low Platelet Count and SGA
Infants were classified into low and high cord blood sFlt-1 groups on the basis of levels above or below the median value (127.3 pg/ml). High cord blood sFlt-1 in infants was correlated with lower platelet count (P < .001), maternal preeclampsia (P = .003), and SGA (P = .01) and showed a trend toward correlation with lower birth weight (P = .058).
Furthermore, we performed the statistical analysis separately among the infants whose mothers had preeclampsia and among the infants whose mothers did not have preeclampsia. It is interesting that there was no difference in infants without maternal preeclampsia whether their cord blood sFlt-1 levels were above or below the median value (98.8 pg/ml). However, in infants with maternal preeclampsia, high cord blood sFlt-1 in infants was correlated with lower platelet count (P = .006) and lower birth weight (P = .004) and showed a trend toward correlation with SGA (P = .058; Table 2).
DISCUSSION
Infants with maternal preeclampsia frequently demonstrate neonatal thrombocytopenia and SGA.1–7 This study confirmed previous findings of a greater incidence of SGA but lower platelet counts in preterm infants with maternal preeclampsia. To the best of our knowledge, this is the first study to demonstrate that infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF levels. In addition, sFlt-1 levels in cord blood were significantly correlated with neonatal platelet count and birth weight.
Thrombopoietin (Tpo) is the major regulator of circulating platelet count.25 However, in our previous study, we found no difference between the cord blood level of Tpo in infants who were born to mothers with or without preeclampsia.6 In addition, we found no correlation between the Tpo level and the neonatal platelet count. This indicates that Tpo may not be the only regulator of thrombocyte production in preterm infants. It is interesting that in our study, we also found that neonatal thrombocytopenia was correlated with maternal thrombocytopenia. Burrows et al26,27 had similar findings and suggested that maternal thrombocytopenia is a benign marker of fetal thrombocytopenia. This finding suggests the hypothesis that some maternal factors not only induce maternal thrombocytopenia but also result in neonatal thrombocytopenia.
It has been proposed that placental angiogenesis is defective in preeclampsia, as evidenced by failure of the cytotrophoblasts to convert from an epithelial to an endothelial phenotype and invade maternal spiral arteries.28 Several studies have demonstrated that preeclampsia is characterized by low VEGF and PlGF levels.13,14,17 Flt-1, binding VEGF and PlGF, exists in 2 forms: a membrane-bound receptor tyrosine kinase, which transmits angiogenic signals (Flt1), and a soluble secreted ectodomain, lacking the transmembrane and cytoplasmic domains, which captures only VEGF and PlGF (sFlt1).29,30 As sFlt-1 lacks a cytosolic domain, its function is restricted to reducing the levels of free VEGF and PlGF available to signal via intact Flt-1. Recently, some reports demonstrated that excess circulating sFlt-1 may have a pathologic role in preeclampsia.18–21
Although Tpo is the major regulator of megakaryocytic (Mk) development, it fails to induce a level of Mk polyploidization in vitro comparable to that observed in vivo.31–33 Casella et al22 demonstrated that VEGF and PlGF contribute to optimal Mk maturation through Flt-1. In addition, molecules that prevent the VEGF-Flt1 interaction on the precursor membrane (eg, soluble Flt1 receptors) significantly inhibit Mk polyploidization. This indicates that Flt-1 signaling regulates Mk development and may contribute to the pathogenesis of maternal preeclampsia-induced neonatal thrombocytopenia.
In this study, we demonstrated that infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF levels. These levels are also characteristic of preeclamptic mothers.13–17,19–21 These data mean that the amount of VEGF and PlGF available to signal via intact Flt1 is decreased. In addition, sFlt-1 levels in cord blood were significantly correlated with neonatal platelet count in this study, and the neonatal thrombocytopenia group also had higher cord blood sFlt-1 levels. Furthermore, infants in the high cord blood sFlt-1 group had a higher incidence of lower platelet count and maternal preeclampsia. These data suggest that excess sFlt-1 may play an important role in maternal preeclampsia-induced neonatal thrombocytopenia.
In this study, we found that cord blood sFlt-1 levels were independently negatively correlated to birth weight and independently correlated with SGA. In addition, infants with high cord blood sFlt-1 had a higher incidence of SGA, another important complication of maternal preeclampsia. Levine et al19 reported similar findings that women with preeclampsia and SGA infants had higher maternal circulating sFlt-1 levels than women who had preeclampsia and did not have SGA infants. This suggests that excess sFlt-1, an antiangiogenic factor, also may play an important role in maternal preeclampsia-induced SGA.
Finally, the negative relationship between cord blood sFlt-1 and neonatal platelet count, SGA, or birth weight was found only in infants with maternal preeclampsia but not in infants whose mothers did not have preeclampsia. A possible explanation is that the lack of effect of sFlt1 in the infants whose mothers did not develop preeclampsia may be because the levels of sFlt1 were not high enough to have a noticeable effect.
CONCLUSIONS
Infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF. The neonatal platelet count was significantly negatively correlated with cord blood sFlt-1 levels. In addition, neonates with thrombocytopenia had higher cord blood sFlt-1 levels. Cord blood sFlt-1 levels also were independently related to birth weight. Infants with high cord blood sFlt-1 were more likely to have lower platelet count and maternal preeclampsia and be SGA and showed a trend toward lower birth weight. In conclusion, our findings indicate that excess sFlt-1 was associated with maternal preeclampsia-induced neonatal thrombocytopenia and SGA.
ACKNOWLEDGMENTS
We would like to thank the second Core Lab of the Department of Medical Research of National Taiwan University Hospital for technical assistance. This study was supported by National Taiwan University Hospital grant 93M0011.
FOOTNOTES
Accepted Dec 2, 2004.
No conflict of interest declared.
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Department of Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan
ABSTRACT
Objective. To investigate the relationship of neonatal platelet count and preeclampsia to levels of soluble fms-like tyrosine kinase 1 (sFlt-1), placental growth factor (PlGF), and vascular endothelial growth factor (VEGF) in the cord blood of preterm infants.
Methods. Sixty-nine preterm infants with a gestational age between 26 and 37 weeks at birth were enrolled. sFlt-1, PlGF, and VEGF levels in the cord blood of preterm neonates, with or without maternal preeclampsia, were measured using a standardized sandwich enzyme-linked immunosorbent assay method.
Results. Infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF levels. There was a significantly positive relationship between neonatal platelet count and birth weight and a significantly negative relationship between neonatal platelet count and cord blood sFlt-1 levels. Multiple regression analysis revealed that only birth weight and cord blood sFlt-1 levels were independently related to neonatal platelet count, whereas maternal preeclampsia, gestational age (GA), and small for GA (SGA) were not related. Neonates with thrombocytopenia had higher cord blood sFlt-1 levels but lower birth weight. A significant correlation was also found between birth weight and cord blood sFlt-1 levels. Multiple regression with birth weight as the dependent variable found that only GA and cord blood sFlt-1 levels were independently related. Furthermore, infants with high cord blood sFlt-1 were more likely to have lower platelet count and maternal preeclampsia, be SGA, and have a trend toward lower birth weight.
Conclusion. Excess sFlt-1 may play an important role in the development of maternal preeclampsia- induced neonatal thrombocytopenia, and SGA.
Key Words: sFlt-1 vascular endothelial growth factor placenta growth factor preeclampsia platelets
Abbreviations: SGA, small for gestational age VEGF, vascular endothelial growth factor PlGF, placenta growth factor sFlt-1, soluble fms-like tyrosine kinase 1 GA, gestational age VLBW, very low birth weight Tpo, thrombopoietin Mk, megakaryocytic
Infants who are born to preeclamptic mothers have been shown to have higher risk for being small for gestational age (SGA) and having neonatal thrombocytopenia or neutropenia.1–6 Neonatal thrombocytopenia is observed in 26% to 47% of infants who are delivered to mothers with preeclampsia complicated with hemolysis, elevated liver enzymes, and low platelets syndrome.7–11 This abnormality affects the long-term outcome when extreme prematurity or intrapartum asphyxia is coexistent.12
Several studies have demonstrated decreased circulating vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF) levels during preeclampsia, even before onset.13–17 However, the cause of preeclampsia remains unclear. Recently, some reports demonstrated that excess circulating soluble fms-like tyrosine kinase 1 (sFlt-1), a natural antagonist for Flt-1 that captures only PlGF and VEGF, may have a pathologic role in preeclampsia.18–21 In addition, Casella et al22 demonstrated that VEGF and PlGF contributed to optimal megakaryocyte maturation through Flt-1. This indicates that Flt-1 signaling regulates megakaryocytic development and may contribute to the pathogenesis of maternal preeclampsia-induced neonatal thrombocytopenia. However, the relationship between Flt-1 signaling and maternal preeclampsia-induced thrombocytopenia in preterm infants has not been evaluated. This study analyzed the relationship of neonatal platelet counts and maternal preeclampsia to cord blood levels of sFlt-1, PlGF, and VEGF in preterm infants.
METHODS
Study Group
This study was performed at National Taiwan University Hospital after approval was obtained from the institutional review board. All infants who were born from 26 to 37 weeks' gestation at National Taiwan University Hospital from July 1, 1998, to June 31, 2000, were enrolled in this study. Infants were excluded when there was evidence of prenatal maternal infection or any infection within the first 3 days of life. Cord blood was collected in heparinized syringes on delivery and centrifuged within 15 minutes of collection. Gestational age (GA) was estimated by last menstrual date or prenatal ultrasound. SGA status was determined according to the published intrauterine growth curve specific for Taiwan.23 The diagnosis of preeclampsia was made according to the criteria of Davey et al.24 Hypertension was defined as either 1 measurement of diastolic blood pressure of 110 mm Hg or above or 2 consecutive measurements of diastolic blood pressure of 90 mm Hg or above. Proteinuria was defined as a total proteinuria excretion of 300 mg or more in 24 hours. Neonatal thrombocytopenia was defined arbitrarily as a platelet count of <150000 mm3. Very low birth weight (VLBW) was defined as birth weight <1500 g.
Collection of Cord Blood and Measurement of sFlt-1, VEGF, and PlGF
Venous cord blood was collected in heparinized syringes on delivery and centrifuged within 15 minutes of collection. The plasma was kept at –70°C until analysis by a technician who was blinded to the patients' condition. The levels of sFlt-1, VEGF, and PlGF in the cord blood were assayed by a standardized sandwich enzyme-linked immunosorbent assay method (Quantikine ELISA; R&D Systems, Minneapolis, MN) in duplicate according to the manufacturer's protocol.
Data Analysis
Comparisons between unpaired groups were performed by Mann-Whitney rank sum test and 2 test. The relationships between angiogenic factors and GA, birth weight, and platelet count were analyzed by Spearman correlation coefficients. Multivariate analyses were conducted using logistic and linear regression. P .05 was considered statistically significant.
RESULTS
Patient Characteristics
Seventy-four neonates were collected during this period. Four infants with maternal fever and 1 with elevated C-reactive protein were excluded. The 69 premature neonates who were enrolled in this study had a mean gestational age of 31.4 ± 3.0 weeks and a mean birth weight of 1.45 ± 0.52 kg. Of these premature neonates, 33 were associated with maternal preeclampsia, 35 had a GA of <32 weeks, 32 were SGA, and 38 had VLBW. The female/male ratio was 40/29. The preeclampsia group had a higher GA and a greater incidence of SGA but had lower birth weight and platelet counts. The sFlt-1 and VEGF levels in cord blood all were above the sensitivity (5 pg/ml) of our assay. However, PlGF levels were below the sensitivity (7.0 pg/ml) of the assay in 14 (42%) infants with maternal preeclampsia and 6 (17%) infants without maternal preeclampsia. In addition, infants with maternal preeclampsia had higher cord blood sFlt-1 (P = .003; Fig 1) but lower PlGF (P = .011) and VEGF (P = .046) levels (Table 1).
Neonatal Platelet Count and Cord Blood sFlt-1 Levels
The neonatal platelet count was significantly lower in infants with VLBW (P = .005), with SGA (P = .002), and with maternal preeclampsia (P = .045). There was a significantly positive relationship between the neonatal platelet count and birth weight (r = 0.349; P = .003) and maternal platelet count (r = 0.351; P = .009) and a negative relationship between the neonatal platelet count and cord blood sFlt-1 levels (r = –0.438; P < .001). Multiple regression with neonatal platelet count as the dependent variable found that only birth weight (P = .015) and cord blood sFlt-1 levels (P = .036) were significantly independently related, whereas maternal preeclampsia (P = .189), GA (P = .276), and SGA (P = .921) were not.
In addition, when we performed correlation coefficients separately among the infants with maternal preeclampsia and among the infants without maternal preeclampsia, the negative relationship between neonatal count and cord blood sFlt-1 levels was present only in infants with maternal preeclampsia (r = –0.534; P = .001; Fig 2). There was no effect of sFlt1 in the infants whose mothers did not develop preeclampsia (P = .138).
Seven infants had thrombocytopenia (6 in the preeclampsia group and 1 in the nonpreeclampsia group; P = .049). The median platelet count during the first day of life was 126 x 103/μL (range: 7–144 x 103/μL) and at the nadir was 90 x 103/μL (range: 7–141 x 103/μL). The platelet nadir occurred at a median of 6 days of age (range: 1–13 days). Thrombocytopenia persisted for at least 7 days. Neonatal thrombocytopenia was correlated with maternal preeclampsia (P = .034) and VLBW (P = .012). In addition, neonates with thrombocytopenia had higher cord blood sFlt-1 levels (P = .008) but lower birth weight (P = .009) when compared with infants without preeclampsia.
Birth Weight and Cord Blood sFlt-1 Levels
Birth weight was significantly correlated with GA (r = 0.599; P < .001), cord blood sFlt-1 levels (r = –0.328; P = .006), and PlGF levels (r = –0.315; P = .016). Multiple regression analysis with birth weight as the dependent variable found that only GA (P < .001) and cord blood sFlt-1 levels (P = .015) were significantly independently related, whereas PlGF levels (P = .309) and VEGF levels (P = .450) were not.
It is interesting that the same result for the relationship between birth weight and cord blood sFlt-1 levels was found when we performed correlation coefficients separately among the infants with maternal preeclampsia and among the infants without maternal preeclampsia. The negative relationship between birth weight and cord blood sFlt-1 levels was present only in infants with maternal preeclampsia (r = -0.598; P < .001; Fig 3) but not in the infants whose mothers did not develop preeclampsia (P = .850).
Twenty-nine infants were SGA. The SGA group had a higher GA (P = .023) and a greater incidence of maternal preeclampsia (P = .013) but had lower platelet counts (P = .002). Furthermore, cord blood sFlt-1 levels (P = .002) but not VEGF (P = .433) or PlGF (P = .261) levels were significantly higher in the SGA group than in the non-SGA group. Multiple regression analysis revealed that only cord blood sFlt-1 levels were significantly independently related to SGA.
Excess Circulating sFlt-1 Correlated With Neonatal Low Platelet Count and SGA
Infants were classified into low and high cord blood sFlt-1 groups on the basis of levels above or below the median value (127.3 pg/ml). High cord blood sFlt-1 in infants was correlated with lower platelet count (P < .001), maternal preeclampsia (P = .003), and SGA (P = .01) and showed a trend toward correlation with lower birth weight (P = .058).
Furthermore, we performed the statistical analysis separately among the infants whose mothers had preeclampsia and among the infants whose mothers did not have preeclampsia. It is interesting that there was no difference in infants without maternal preeclampsia whether their cord blood sFlt-1 levels were above or below the median value (98.8 pg/ml). However, in infants with maternal preeclampsia, high cord blood sFlt-1 in infants was correlated with lower platelet count (P = .006) and lower birth weight (P = .004) and showed a trend toward correlation with SGA (P = .058; Table 2).
DISCUSSION
Infants with maternal preeclampsia frequently demonstrate neonatal thrombocytopenia and SGA.1–7 This study confirmed previous findings of a greater incidence of SGA but lower platelet counts in preterm infants with maternal preeclampsia. To the best of our knowledge, this is the first study to demonstrate that infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF levels. In addition, sFlt-1 levels in cord blood were significantly correlated with neonatal platelet count and birth weight.
Thrombopoietin (Tpo) is the major regulator of circulating platelet count.25 However, in our previous study, we found no difference between the cord blood level of Tpo in infants who were born to mothers with or without preeclampsia.6 In addition, we found no correlation between the Tpo level and the neonatal platelet count. This indicates that Tpo may not be the only regulator of thrombocyte production in preterm infants. It is interesting that in our study, we also found that neonatal thrombocytopenia was correlated with maternal thrombocytopenia. Burrows et al26,27 had similar findings and suggested that maternal thrombocytopenia is a benign marker of fetal thrombocytopenia. This finding suggests the hypothesis that some maternal factors not only induce maternal thrombocytopenia but also result in neonatal thrombocytopenia.
It has been proposed that placental angiogenesis is defective in preeclampsia, as evidenced by failure of the cytotrophoblasts to convert from an epithelial to an endothelial phenotype and invade maternal spiral arteries.28 Several studies have demonstrated that preeclampsia is characterized by low VEGF and PlGF levels.13,14,17 Flt-1, binding VEGF and PlGF, exists in 2 forms: a membrane-bound receptor tyrosine kinase, which transmits angiogenic signals (Flt1), and a soluble secreted ectodomain, lacking the transmembrane and cytoplasmic domains, which captures only VEGF and PlGF (sFlt1).29,30 As sFlt-1 lacks a cytosolic domain, its function is restricted to reducing the levels of free VEGF and PlGF available to signal via intact Flt-1. Recently, some reports demonstrated that excess circulating sFlt-1 may have a pathologic role in preeclampsia.18–21
Although Tpo is the major regulator of megakaryocytic (Mk) development, it fails to induce a level of Mk polyploidization in vitro comparable to that observed in vivo.31–33 Casella et al22 demonstrated that VEGF and PlGF contribute to optimal Mk maturation through Flt-1. In addition, molecules that prevent the VEGF-Flt1 interaction on the precursor membrane (eg, soluble Flt1 receptors) significantly inhibit Mk polyploidization. This indicates that Flt-1 signaling regulates Mk development and may contribute to the pathogenesis of maternal preeclampsia-induced neonatal thrombocytopenia.
In this study, we demonstrated that infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF levels. These levels are also characteristic of preeclamptic mothers.13–17,19–21 These data mean that the amount of VEGF and PlGF available to signal via intact Flt1 is decreased. In addition, sFlt-1 levels in cord blood were significantly correlated with neonatal platelet count in this study, and the neonatal thrombocytopenia group also had higher cord blood sFlt-1 levels. Furthermore, infants in the high cord blood sFlt-1 group had a higher incidence of lower platelet count and maternal preeclampsia. These data suggest that excess sFlt-1 may play an important role in maternal preeclampsia-induced neonatal thrombocytopenia.
In this study, we found that cord blood sFlt-1 levels were independently negatively correlated to birth weight and independently correlated with SGA. In addition, infants with high cord blood sFlt-1 had a higher incidence of SGA, another important complication of maternal preeclampsia. Levine et al19 reported similar findings that women with preeclampsia and SGA infants had higher maternal circulating sFlt-1 levels than women who had preeclampsia and did not have SGA infants. This suggests that excess sFlt-1, an antiangiogenic factor, also may play an important role in maternal preeclampsia-induced SGA.
Finally, the negative relationship between cord blood sFlt-1 and neonatal platelet count, SGA, or birth weight was found only in infants with maternal preeclampsia but not in infants whose mothers did not have preeclampsia. A possible explanation is that the lack of effect of sFlt1 in the infants whose mothers did not develop preeclampsia may be because the levels of sFlt1 were not high enough to have a noticeable effect.
CONCLUSIONS
Infants with maternal preeclampsia had higher cord blood sFlt-1 but lower PlGF and VEGF. The neonatal platelet count was significantly negatively correlated with cord blood sFlt-1 levels. In addition, neonates with thrombocytopenia had higher cord blood sFlt-1 levels. Cord blood sFlt-1 levels also were independently related to birth weight. Infants with high cord blood sFlt-1 were more likely to have lower platelet count and maternal preeclampsia and be SGA and showed a trend toward lower birth weight. In conclusion, our findings indicate that excess sFlt-1 was associated with maternal preeclampsia-induced neonatal thrombocytopenia and SGA.
ACKNOWLEDGMENTS
We would like to thank the second Core Lab of the Department of Medical Research of National Taiwan University Hospital for technical assistance. This study was supported by National Taiwan University Hospital grant 93M0011.
FOOTNOTES
Accepted Dec 2, 2004.
No conflict of interest declared.
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