Evidence supporting a role for blockade of the vascular endothelial growth factor system in the pathophysiology of preeclampsia. Young Investigator Award

Soluble endoglin contributes to the pathogenesis of preeclampsia

Preeclampsia is a pregnancy-specific hypertensive syndrome that causes substantial maternal and fetal morbidity and mortality. Maternal endothelial dysfunction mediated by excess placenta-derived soluble VEGF receptor 1 (sVEGFR1 or sFlt1) is emerging as a prominent component in disease pathogenesis. We report a novel placenta-derived soluble TGF-beta coreceptor, endoglin (sEng), which is elevated in the sera of preeclamptic individuals, correlates with disease severity and falls after delivery. sEng inhibits formation of capillary tubes in vitro and induces vascular permeability and hypertension in vivo. Its effects in pregnant rats are amplified by coadministration of sFlt1, leading to severe preeclampsia including the HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome and restriction of fetal growth. sEng impairs binding of TGF-beta1 to its receptors and downstream signaling including effects on activation of eNOS and vasodilation, suggesting that sEng leads to dysregulated TGF-beta signaling in the vasculature. Our results suggest that sEng may act in concert with sFlt1 to induce severe preeclampsia.

New Insights into the Biology of Preeclampsia

Despite recent research progress, the biology of preeclampsia is still poorly understood and neither effective prediction nor causal therapy have yet emerged. Nevertheless, recent studies have documented new and exciting pathophysiological mechanisms for the origin and development of preeclampsia. These studies provide a more differentiated view on alterations of particular peptide systems with strong impact on angiogenesis and cardiovascular regulation in this pregnancy disorder. With the identification of the antiangiogenic factor soluble fms-like tyrosine kinase 1 and the agonistic autoantibody to the angiotensin II type 1 receptor, two factors have been described with a clear linkage to the development of the disease. This review focuses on the most recent and relevant insights into the biology of preeclampsia and develops hypotheses regarding possible links between the reported aspects of preeclampsia.

Serum sFlt1 concentration during preeclampsia and mid trimester blood pressure in healthy nulliparous women

OBJECTIVE

The purpose of this study was to determine whether serum fms-like tyrosine kinase 1 (sFlt1) concentration during preeclampsia were associated with mid trimester blood pressure, other maternal characteristics, or pregnancy outcomes.

STUDY DESIGN

We performed a nested case-control study within the Calcium for Preeclampsia Prevention study cohort. Each woman with preeclampsia (case) was matched to 1 normotensive control. A total of 120 pairs of women was chosen randomly. Serum concentrations of sFlt1 and placental growth factor were measured throughout pregnancy, but before labor and delivery. We focused on data from 40 women with blood specimens that were obtained after the onset of preeclampsia. After logarithmic transformation, we determined mean serum sFlt1 concentrations of all control specimens within gestational age windows during which case specimens had been obtained after the onset of preeclampsia. Within each of these gestational age windows, we computed an upper bound for the control specimens equal to 2 standard deviations above the mean. After the onset of preeclampsia, 16 women with log-transformed serum sFlt1 values greater than the upper bound of the control specimens were considered to have high preeclampsia serum sFlt1 levels. The 24 other women were considered to have low preeclampsia serum sFlt1 levels.

RESULTS

Women with high or low concentrations of serum sFlt1 during preeclampsia (arithmetic means, 5746 and 3007 pg/mL, respectively) had similar pregnancy outcomes and similar maternal characteristics, except for blood pressure at Calcium for Preeclampsia Prevention study enrollment. Systolic and diastolic blood pressure at enrollment at 13 to 21 weeks of gestation were significantly higher in the 24 women with low serum sFlt1 concentrations during preeclampsia (systolic blood pressure, 114 mm Hg; diastolic blood pressure, 65 mm Hg) than in the 16 women who had preeclampsia at high serum sFlt1 concentrations (systolic blood pressure, 106 mm Hg; diastolic blood pressure, 59 mm Hg). Blood pressure at 13 to 21 weeks among the women with high preeclampsia serum sFlt1 concentrations was identical to the blood pressure among normotensive control subjects. In linear regression analyses of data from all 40 women, both systolic (P < .0001) and diastolic (P = .014) blood pressures at enrollment were correlated negatively with natural logarithm serum sFlt1 concentration after onset of preeclampsia.

CONCLUSION

Women with higher mid trimester blood pressure had preeclampsia at lower serum sFlt1 concentrations. Because higher blood pressure may reflect occult endothelial damage, these observations may explain increased susceptibility to preeclampsia among women with pre-existing vascular disease.

Circulating angiogenic proteins in trisomy 13

OBJECTIVE

Women who are carrying a trisomy 13 fetus are more prone to develop preeclampsia. Excess circulating soluble fms-like tyrosine kinase-1 has been implicated recently in the pathogenesis of preeclampsia. Since the fms-like tyrosine kinase-1/soluble fms-like tyrosine kinase-1 gene is located on chromosome 13q12, we hypothesized that the extra copy of this gene in trisomy 13 may lead to excess circulating soluble fms-like tyrosine kinase-1, reduced free placental growth factor level, and increased soluble fms-like tyrosine kinase-1/placental growth factor ratio. This may then contribute to the increased risk of preeclampsia that has been observed in these patients. Our objective was to characterize the maternal circulating angiogenic proteins in trisomy 13 pregnancies.

STUDY DESIGN

Maternal serum samples of trisomy 13, 18, 21 and normal karyotype pregnancies were obtained from first and second trimester screening programs. We chose 17 cases of trisomy 13 that were matched for maternal age, freezer storage time, and parity with 85 normal karyotype control samples. Additionally, 20 cases of trisomy 18 and 17 cases of trisomy 21 were included. Cases and control samples were assayed for levels of soluble fms-like tyrosine kinase-1 and placental growth factor by enzyme-linked immunosorbent assay in a blinded fashion. Because of the skewed distributions of soluble fms-like tyrosine kinase-1 and placental growth factor, nonparametric analytic techniques were used, and the results are reported as median and ranges.

RESULTS

In early pregnancy trisomy 13 cases and control samples, the median circulating soluble fms-like tyrosine kinase-1/placental growth factor ratios were 17.0 (range, 1.2-61.3) and 6.7 (range, 0.8-62.9), respectively (P = .003). The median soluble fms-like tyrosine kinase-1/placental growth factor ratios in trisomy 18 and 21 were 4.8 (range, 0.9-53.9) and 5.1 (range, 1.0-18.1), which were not significantly different than the control samples. Furthermore, the differences between trisomy 13 and control samples were more pronounced in the second trimester specimens than in the specimens from the first trimester.

CONCLUSION

These data suggest that alterations in circulating angiogenic factors may be involved intimately in the pathogenesis of preeclampsia in trisomy 13. A larger clinical study that measures these factors longitudinally and correlates them with pregnancy outcomes is needed to further establish the link between trisomy 13, altered angiogenic factors, and preeclampsia.

Differential expression of vascular endothelial growth factor, placenta growth factor and their receptors in placentae from pregnancies complicated by placenta accreta

Placenta accreta is a pregnancy complication characterized by the presence of life-threatening uteroplacental neovascularization. The factors involving its development are unknown. Vascular endothelial growth factor (VEGF), placenta growth factor (PlGF) and their receptors (VEGFR) have important roles in vascular remodeling. We have investigated the differential expression of these proteins in placentae from placenta accreta (cases) and normal placentation (controls). Immunohistochemically, the expression of VEGFR-2 in the syncytiotrophoblast was significantly lower in cases than in controls during both the second and third trimesters (P = 0.005 and 0.002, respectively). However, VEGFR-2 expression in the cytotrophoblastic and extravillous trophoblastic cells and VEGFR-1, -3 and Ki-67 in the trophoblast populations were not significantly different between controls and cases (P > 0.05). Ki-67 immunostaining also showed that endothelial cells of the larger vessels were stained weaker in normal placenta than in placenta accreta. The majority of VEGFR-2 expression, as demonstrated by Western blot or reverse transcription polymerase chain reaction, was consistent with the immunohistochemical findings in the syncytiotrophoblast. Furthermore, enzyme-linked immunosorbent assay in the placental lysates showed that the women with placenta accreta demonstrated significantly higher VEGF (P = 0.001) and lower soluble VEGFR-2 (P = 0.015) concentrations than did women with normal pregnancy. PlGF and soluble VEGFR-1 levels did not show any significance in study groups (P > 0.05). These observations suggest that the participation of up-regulated VEGF and down-regulated VEGFR-2 (both membrane-bound and soluble forms) may be associated with the development of placenta accreta.

Significance of vascular endothelial growth factor expression in renal tissue of patients with preeclamptic nephropathy

OBJECTIVE

It was the aim of this study to evaluate the distribution and expression of vascular endothelial growth factor (VEGF) in kidneys of patients with preeclamptic nephropathy and their relationship with clinical and pathological manifestations.

METHODS

From May 1993 to August 2004, 19 patients with a mean age of 28.1 +/- 4.53 years (range 23-40), diagnosed with preeclamptic nephropathy by renal biopsy, were enrolled in this study. Fifteen were nulliparous and 4 multipara. Their renal tissues were subjected to immunohistochemical staining by a four-layer peroxidase-antiperoxidase method using monoclonal anti-VEGF. Residual normal renal tissue obtained at nephrectomy served as control. The relationship between the expression pattern of VEGF and clinicopathological features was also investigated.

RESULTS

The expression of VEGF markedly increased in renal tissues of patients with preeclamptic nephropathy at the early stage of gestation termination in comparison with normal controls. However, over time, it gradually decreased and reached the level of normal controls (100 vs. 71.43 vs. 20%, p < 0.05). The degree of endothelial proliferation in the glomeruli was closely related to the expression of VEGF, which was stronger in patients with diffuse endothelial proliferation than in those with segment proliferation (p < 0.05). In addition, there was a proportional relationship between the expression of VEGF and the level of urinary protein excretion (p < 0.05).

CONCLUSION

The patients with preeclamptic nephropathy showed strong expressions of VEGF in glomeruli, which were closely associated with glomerular endothelial lesions and proteinuria, and over time, gradually weakened to normal level after gestation termination.

Circulating Angiogenic Factors in the Pathogenesis and Prediction of Preeclampsia

Preeclampsia is a major cause of maternal, fetal, and neonatal mortality worldwide. Although the etiology of preeclampsia is still unclear, recent studies suggest that its major phenotypes, high blood pressure and proteinuria, are due in part to excess circulating soluble fms-like tyrosine kinase-1 concentrations. Soluble fms-like tyrosine kinase-1 is an endogenous antiangiogenic protein that is made by the placenta and acts by neutralizing the proangiogenic proteins vascular endothelial growth factor and placental growth factor. High serum soluble fms-like tyrosine kinase-1 and low serum free placental growth factor and free vascular endothelial growth factor have been observed in preeclampsia. Abnormalities in these circulating angiogenic proteins are not only present during clinical preeclampsia but also antedate clinical symptoms by several weeks. Therefore, this raises the possibility of measuring circulating angiogenic proteins in the blood and the urine as a diagnostic and screening tool for preeclampsia. The availability of a test to predict preeclampsia would be a powerful tool in preventing preeclampsia-induced mortality, especially in developing nations, where high-risk specialists are limited. This review will summarize our current understanding of the role of circulating angiogenic proteins in the pathogenesis and clinical diagnosis/prediction of preeclampsia.

An elevated maternal plasma, but not amniotic fluid, soluble fms-like tyrosine kinase-1 (sFlt-1) at the time of mid-trimester genetic amniocentesis is a risk factor for preeclampsia

OBJECTIVE

The purpose of this study was to determine if an elevated concentration of soluble fms-like tyrosine kinase-1(sFlt-1) in maternal plasma and amniotic fluid is a risk factor for the subsequent development of preeclampsia.

STUDY DESIGN

A case-control study was conducted to compare mid-trimester concentrations of maternal plasma and amniotic fluid sFlt-1 in patients who developed preeclampsia with those who did not. The study included 32 cases with preeclampsia (18 cases: severe preeclampsia) and 128 matched controls with normal outcomes. Patients with an abnormal fetal karyotype or major anomaly, multiple pregnancies, chronic hypertension, diabetes, and renal disease were excluded. Soluble Flt-1 concentration was measured by specific immunoassay. Nonparametric techniques were used for statistical analysis.

RESULTS

1) The median maternal plasma, but not amniotic fluid, sFlt-1 concentration in patients who developed preeclampsia was significantly higher than in the control cases (maternal plasma: median 730 pg/mL, range 60-3375 pg/mL vs median 441 pg/mL, range 58-1959 pg/mL, P < .05; amniotic fluid: median 10,504 pg/mL, range 5253-38,023 pg/mL vs median 10,236 pg/mL, range 4326-87,684 pg/mL, P = .65). 2) The median plasma concentration of sFlt-1 was higher in cases of severe preeclampsia than in those with mild preeclampsia without reaching statistical significance (median 762 pg/mL, range 261-3309 pg/mL vs median 334 pg/mL, range 60-3375 pg/mL; P = .07). However, there was no significant difference in the median amniotic fluid sFlt-1 concentrations between patients with severe preeclampsia and those with mild preeclampsia (P = .45). 3) An elevated maternal plasma sFlt-1 concentration (higher than 700 pg/mL) is a risk factor for the development of preeclampsia (OR 3.9, 95% CI 1.7-8.6) and severe preeclampsia (OR 7.4, 95% CI 2.5-22.1) after genetic amniocentesis. 4) The median interval from amniocentesis to the diagnosis of preeclampsia in patients with maternal plasma sFlt-1 concentrations higher than 700 pg/mL was 117 days (range 19-154 days).

CONCLUSION

An elevated concentration of sFlt-1 in maternal plasma at the time of mid-trimester amniocentesis is a risk factor for the subsequent development of preeclampsia.

Preeclampsia: a renal perspective

Preeclampsia is a syndrome that affects 5% of all pregnancies, producing substantial maternal and perinatal morbidity and mortality. The aim of this review is to summarize our current understanding of the pathogenesis of preeclampsia with special emphasis on the recent discovery that circulating anti-angiogenic proteins of placental origin may play an important role in the pathogenesis of proteinuria and hypertension of preeclampsia.

Soluble Fms-like tyrosine kinase 1 and endothelial dysfunction in the pathogenesis of preeclampsia

Preeclampsia, a pregnancy-specific syndrome of hypertension and proteinuria, is characterized by defective placental vasculogenesis and widespread maternal endothelial dysfunction. Although the manifestations of preeclampsia are primarily maternal, the burden of morbidity and mortality is often on the neonate, since the only effective treatment-delivery of the fetus and placenta-often results in iatrogenic prematurity. In this review, we summarize recent advances in our understanding of the pathophysiology of preeclampsia, including normal and aberrant placental vascular development and evidence for endothelial dysfunction. We describe recent evidence that supports a novel mechanism in which a maladaptive shift in placental production of angiogenic factors such as soluble fms-like tyrosine kinase 1 (a circulating antiangiogenic protein) may play an important role in the pathogenesis of preeclampsia.

Pre-eclampsia

Pre-eclampsia is a major cause of maternal mortality (15-20% in developed countries) and morbidities (acute and long-term), perinatal deaths, preterm birth, and intrauterine growth restriction. Key findings support a causal or pathogenetic model of superficial placentation driven by immune maladaptation, with subsequently reduced concentrations of angiogenic growth factors and increased placental debris in the maternal circulation resulting in a (mainly hypertensive) maternal inflammatory response. The final phenotype, maternal pre-eclamptic syndrome, is further modulated by pre-existing maternal cardiovascular or metabolic fitness. Currently, women at risk are identified on the basis of epidemiological and clinical risk factors, but the diagnostic criteria of pre-eclampsia remain unclear, with no known biomarkers. Treatment is still prenatal care, timely diagnosis, proper management, and timely delivery. Many interventions to lengthen pregnancy (eg, treatment for mild hypertension, plasma-volume expansion, and corticosteroid use) have a poor evidence base. We review findings on the diagnosis, risk factors, and pathogenesis of pre-eclampsia and the present status of its prediction, prevention, and management.

Angiogenic Factors in the Pathogenesis of Preeclampsia

Preeclampsia affects 5-10% of pregnancies and is responsible for substantial maternal and neonatal morbidity and mortality. It is believed to be a two-stage disease with an initial placental trigger with no maternal symptoms followed by a maternal syndrome characterized by hypertension, proteinuria, and endothelial dysfunction. The first stage is thought to be due to shallow cytotrophoblast invasion of maternal spiral arterioles leading to placental insufficiency. The diseased placenta in turn releases soluble angiogenic factors that induce systemic endothelial dysfunction and clinical preeclampsia during the second stage. This review will discuss the role of circulating angiogenic factors of placental origin as potential mediators of the systemic endothelial dysfunction and the clinical syndrome of preeclampsia and provide an evolutionary explanation for this phenomenon.