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.

Atlantic City memories.

Fifty years ago, the Atlantic City meetings, held the first week in May of every year, were attended by all the elite of American academic medicine and all who wanted to join that group. Part of the magic of those meetings was that professors and neophytes took each other seriously and talked to each other.

Soluble endoglin and other circulating antiangiogenic factors in preeclampsia.

BACKGROUND: Alterations in circulating soluble fms-like tyrosine kinase 1 (sFlt1), an antiangiogenic protein, and placental growth factor (PlGF), a proangiogenic protein, appear to be involved in the pathogenesis of preeclampsia. Since soluble endoglin, another antiangiogenic protein, acts together with sFlt1 to induce a severe preeclampsia-like syndrome in pregnant rats, we examined whether it is associated with preeclampsia in women. METHODS: We performed a nested case-control study of healthy nulliparous women within the Calcium for Preeclampsia Prevention trial. The study included all 72 women who had preterm preeclampsia (<37 weeks), as well as 480 randomly selected women--120 women with preeclampsia at term (at > or =37 weeks), 120 women with gestational hypertension, 120 normotensive women who delivered infants who were small for gestational age, and 120 normotensive controls who delivered infants who were not small for gestational age. RESULTS: Circulating soluble endoglin levels increased markedly beginning 2 to 3 months before the onset of preeclampsia. After the onset of clinical disease, the mean serum level in women with preterm preeclampsia was 46.4 ng per milliliter, as compared with 9.8 ng per milliliter in controls (P<0.001). The mean serum level in women with preeclampsia at term was 31.0 ng per milliliter, as compared with 13.3 ng per milliliter in controls (P<0.001). Beginning at 17 weeks through 20 weeks of gestation, soluble endoglin levels were significantly higher in women in whom preterm preeclampsia later developed than in controls (10.2 ng per milliliter vs. 5.8 ng per milliliter, P<0.001), and at 25 through 28 weeks of gestation, the levels were significantly higher in women in whom term preeclampsia developed than in controls (8.5 ng per milliliter vs. 5.9 ng per milliliter, P<0.001). An increased level of soluble endoglin was usually accompanied by an increased ratio of sFlt1:PlGF. The risk of preeclampsia was greatest among women in the highest quartile of the control distributions for both biomarkers but not for either biomarker alone. CONCLUSIONS: Rising circulating levels of soluble endoglin and ratios of sFlt1:PlGF herald the onset of preeclampsia.

Circulating angiogenic factors in gestational proteinuria without hypertension.

OBJECTIVE: Our goal was to determine whether obstetric outcomes and serum angiogenic factors are altered in women with gestational proteinuria without hypertension. STUDY DESIGN: We performed a nested case-control study of 108 women with gestational proteinuria and compared them with 1564 randomly selected women with normotension without proteinuria during pregnancy (control subjects) and with 319 women who experienced preeclampsia. RESULTS: Women with gestational proteinuria had greater body-mass index and higher blood pressure at study enrollment. Adverse obstetric outcomes were infrequent. Levels of free placental growth factor were lower than control levels beginning early in gestation. Compared with gestational-age matched control subjects, free placental growth factor was reduced beginning 6-8 weeks before proteinuria. Although soluble fms-like tyrosine kinase 1 and soluble endoglin concentrations were elevated 1-2 weeks before proteinuria, these elevations were modest and transient. After the onset of proteinuria, angiogenic factor levels generally did not differ significantly from control levels. CONCLUSION: Gestational proteinuria in healthy nulliparous women appears to be a mild variant of preeclampsia.

Use of circulating antiangiogenic factors to differentiate other hypertensive disorders from preeclampsia in a pregnant woman on dialysis.

Preeclampsia is a serious complication during pregnancy that includes potentially life-threatening risks to the mother and fetus. It may be challenging to distinguish this from other causes of rapidly escalating hypertension, especially in women with end-stage renal disease, because current diagnostic criteria for preeclampsia cannot be easily applied. We report a woman undergoing hemodialysis who was considered to be preeclamptic when her blood pressure suddenly increased during her 29th week of gestation. At that time, she underwent emergent cesarean section. The presence of a normal-sized placenta with no histological evidence of preeclampsia and retrospective analyses of maternal antiangiogenic biomarkers (soluble fms-like tyrosine kinase-1 and soluble endoglin) that were within normal levels for pregnancy suggest an alternative diagnosis. There is growing evidence that circulating levels of these proteins cause the preeclamptic phenotypes and also are sensitive and specific predictors and markers of this disease, suggesting that measurements of soluble fms-like tyrosine kinase-1 and soluble endoglin be considered in such difficult diagnostic dilemmas as the cause of hypertension in pregnant dialysis patients. Additional studies in this particular group of patients are required.

Twin pregnancy and the risk of preeclampsia: bigger placenta or relative ischemia?

OBJECTIVE: Twin pregnancies are a risk factor for preeclampsia with a reported incidence of 2-3 times higher than singleton pregnancies. Soluble fms-like tyrosine kinase 1 (sFlt1), which is a circulating antiangiogenic molecule of placental origin, plays a central role in preeclampsia by antagonizing placental growth factor (PlGF) and vascular endothelial growth factor signaling in the maternal vasculature. Increased sFlt1 and the ratio sFlt1/free PlGF have been shown to antedate clinical signs in preeclampsia. Although the cause of the upregulated sFlt1 in preeclampsia still is not understood clearly, placental ischemia with accompanying hypoxia is thought to play an important role. We therefore hypothesized that the higher risk of preeclampsia in twin pregnancies results from high sFlt1 (or sFlt1/PlGF) and that the sFlt1 upregulation was due to either relative placental hypoxia and/or increased placental mass. STUDY DESIGN: Maternal serum samples and placentas from third-trimester twin and singleton pregnancies without preeclampsia were used. Serum samples were analyzed for levels of sFlt1 and free PlGF by enzyme-linked immunosorbent assay and reported as means (in nanograms per milliliter and picograms per milliliter, respectively). Placentas were weighed and examined for content of sFlt1 and PlGF messenger RNA (mRNA) by quantitative polymerase chain reaction and hypoxia inducible factor-1alpha (HIF-1alpha) protein by Western blot. RESULTS: Soluble Flt1 concentrations in twin pregnancy maternal serum were 2.2 times higher than those that were measured in singleton pregnancy maternal serum samples (30.98 +/- 9.78 ng/mL vs 14.14 +/- 9.35 ng/mL, respectively; P = .001). Free PlGF concentrations were not significantly different between twin and singleton maternal serum samples, but the mean sFlt1/PlGF ratio of twin pregnancy maternal serum samples was 2.2 times higher than the equivalent ratio in singleton pregnancy samples (197.58 +/- 126.86 ng/mL vs 89.91 +/- 70.63 ng/mL, respectively; P = .029). Quantitative polymerase chain reaction for sFlt1 and PlGF mRNA revealed no significant differences between the 2 study groups. Western blot analysis of placental samples for HIF-1alpha revealed a mean ratio HIF-1alpha/actin of 0.53 vs 0.87, for the twins vs singletons placental samples respectively (twins showed lower HIF-1alpha, not higher). The mean weights of twin and singleton placentas were 1246 vs 716 g, respectively (P < .001). Importantly, the placental weights correlated very well with the circulating sFlt1 levels (R(2) = .75). CONCLUSION: In twin pregnancies, circulating sFlt1 levels and sFlt1/PlGF ratios were twice as high as those in singleton pregnancies. The increased serum sFlt1 levels in twin pregnancies were not accompanied by any changes in the levels of sFlt1 mRNA and HIF-1alpha protein in the twin placentas but were correlated with increased placental weight. These findings suggest that the increased risk of preeclampsia in twin pregnancies may be due to increased placental mass that leads to increased circulating levels of sFlt1.

Excess placental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.

Preeclampsia, a syndrome affecting 5% of pregnancies, causes substantial maternal and fetal morbidity and mortality. The pathophysiology of preeclampsia remains largely unknown. It has been hypothesized that placental ischemia is an early event, leading to placental production of a soluble factor or factors that cause maternal endothelial dysfunction, resulting in the clinical findings of hypertension, proteinuria, and edema. Here, we confirm that placental soluble fms-like tyrosine kinase 1 (sFlt1), an antagonist of VEGF and placental growth factor (PlGF), is upregulated in preeclampsia, leading to increased systemic levels of sFlt1 that fall after delivery. We demonstrate that increased circulating sFlt1 in patients with preeclampsia is associated with decreased circulating levels of free VEGF and PlGF, resulting in endothelial dysfunction in vitro that can be rescued by exogenous VEGF and PlGF. Additionally, VEGF and PlGF cause microvascular relaxation of rat renal arterioles in vitro that is blocked by sFlt1. Finally, administration of sFlt1 to pregnant rats induces hypertension, proteinuria, and glomerular endotheliosis, the classic lesion of preeclampsia. These observations suggest that excess circulating sFlt1 contributes to the pathogenesis of preeclampsia.

Circulating angiogenic factors and the risk of preeclampsia.

BACKGROUND: The cause of preeclampsia remains unclear. Limited data suggest that excess circulating soluble fms-like tyrosine kinase 1 (sFlt-1), which binds placental growth factor (PlGF) and vascular endothelial growth factor (VEGF), may have a pathogenic role. METHODS: We performed a nested case-control study within the Calcium for Preeclampsia Prevention trial, which involved healthy nulliparous women. Each woman with preeclampsia was matched to one normotensive control. A total of 120 pairs of women were randomly chosen. Serum concentrations of angiogenic factors (total sFlt-1, free PlGF, and free VEGF) were measured throughout pregnancy; there were a total of 655 serum specimens. The data were analyzed cross-sectionally within intervals of gestational age and according to the time before the onset of preeclampsia. RESULTS: During the last two months of pregnancy in the normotensive controls, the level of sFlt-1 increased and the level of PlGF decreased. These changes occurred earlier and were more pronounced in the women in whom preeclampsia later developed. The sFlt-1 level increased beginning approximately five weeks before the onset of preeclampsia. At the onset of clinical disease, the mean serum level in the women with preeclampsia was 4382 pg per milliliter, as compared with 1643 pg per milliliter in controls with fetuses of similar gestational age (P<0.001). The PlGF levels were significantly lower in the women who later had preeclampsia than in the controls beginning at 13 to 16 weeks of gestation (mean, 90 pg per milliliter vs. 142 pg per milliliter, P=0.01), with the greatest difference occurring during the weeks before the onset of preeclampsia, coincident with the increase in the sFlt-1 level. Alterations in the levels of sFlt-1 and free PlGF were greater in women with an earlier onset of preeclampsia and in women in whom preeclampsia was associated with a small-for-gestational-age infant. CONCLUSIONS: Increased levels of sFlt-1 and reduced levels of PlGF predict the subsequent development of preeclampsia.

Circulating angiogenic factors and placental abruption.

OBJECTIVE: Abnormalities in circulating angiogenic factors have been reported in diseases of abnormal placentation, such as preeclampsia and intrauterine growth restriction. Our objective was to determine whether circulating angiogenic factors are altered in another placental vascular disease, abruptio placentae. METHODS: In a nested case-control study of nulliparous pregnancies, we examined levels of placental growth factor (PlGF) and soluble fms-like tyrosine kinase 1 (sFlt-1) in serum collected prospectively from 31 women who later developed placental abruption and from 31 normal control subjects. All serum specimens were collected before the onset of hypertension or abruption and before labor or delivery. Serum angiogenic factors were compared within 3 gestational age windows: early (20 weeks or less), middle (21-32 weeks), and late (33 weeks or more) pregnancy. RESULTS: During early pregnancy women who developed placental abruption had lower PlGF and higher sFlt-1 concentrations and higher sFlt-1/PlGF ratios than women with normal pregnancies. In mid-pregnancy these differences became greater, reaching statistical significance for PlGF concentration (431 versus 654 pg/mL, P<.01) and the sFlt-1/PlGF ratio (25.3 versus 2.5, P<.01). When the women with placental abruption were subdivided into those who did (n=10) and those who did not (n=21) develop preeclampsia or gestational hypertension, significant alterations in angiogenic factors were noted only in women who later developed hypertension in pregnancy. Among these women, PlGF concentrations were decreased in mid-pregnancy (160 versus 723 pg/mL, P<.001), and the mid-pregnancy sFlt-1/PlGF ratio was increased (70.1 versus 2.3, P=.001). CONCLUSION: Serum levels of the proangiogenic factor PlGF were decreased, and those of the antiangiogenic ratio sFlt-1/PlGF were increased in nulliparous women who subsequently developed hypertension and placental abruption.

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.

A perspective on the value of aquatic models in biomedical research.

For at least 150 years, biological scientists have congregated at marine laboratories, located at the edge of the sea, to explore aquatic life. The purpose of this minireview is to offer a brief perspective on the relevance of this activity to our knowledge of human physiology and disease, drawing heavily on the experience of the authors and without attempting to offer a comprehensive history of the many contributions of marine models to biomedical research.

Effect of specific and non-specific inhibition of COX-2 on renal oxygenation before and after water diuresis.

BACKGROUND/AIMS: Water diuresis usually increases medullary oxygenation as a result of increased medullary synthesis of prostaglandins, but it is not clear whether this involves activation of cyclooxygenase-1 (COX-1) or cyclooxygenase-2 (COX-2). METHODS: The effects of celecoxib, a selective inhibitor of COX-2, and of ibuprofen, a non-specific inhibitor of COX-1 and COX-2, upon renal oxygenation during water diuresis were studied in a double-blind, prospective manner in 13 young women (age 24-34 years) using blood-oxygen level dependent magnetic resonance imaging. Celecoxib 200 mg b.i.d. for 4 days was compared with ibuprofen 80 mg b.i.d. for 4 days and with a placebo. RESULTS: There was no effect of either drug on urinary volume, urinary osmolal concentration, or creatinine clearance. Water diuresis alone elicited a significant increase in oxygenation in borderline areas between cortex and medulla, which was eliminated by celecoxib or ibuprofen. CONCLUSION: Renal medullary oxygenation is improved by water diuresis in normal young women in a way that is blocked by a selective inhibitor of COX-2 as well as non-selective cyclooxygenase inhibitors. Selective COX-2 may be expected to have significant effects on renal functions.

Urinary placental growth factor and risk of preeclampsia.

CONTEXT: Preeclampsia may be caused by an imbalance of angiogenic factors. We previously demonstrated that high serum levels of soluble fms-like tyrosine kinase 1 (sFlt1), an antiangiogenic protein, and low levels of placental growth factor (PlGF), a proangiogenic protein, predict subsequent development of preeclampsia. In the absence of glomerular disease leading to proteinuria, sFlt1 is too large a molecule to be filtered into the urine, while PlGF is readily filtered. OBJECTIVE: To test the hypothesis that urinary PlGF is reduced prior to onset of hypertension and proteinuria and that this reduction predicts preeclampsia. DESIGN, SETTING, AND PATIENTS: Nested case-control study within the Calcium for Preeclampsia Prevention trial of healthy nulliparous women enrolled at 5 US university medical centers during 1992-1995. Each woman with preeclampsia was matched to 1 normotensive control by enrollment site, gestational age at collection of the first serum specimen, and sample storage time at -70 degrees C. One hundred twenty pairs of women were randomly chosen for analysis of serum and urine specimens obtained before labor. MAIN OUTCOME MEASURE: Cross-sectional urinary PlGF concentrations, before and after normalization for urinary creatinine. RESULTS: Among normotensive controls, urinary PlGF increased during the first 2 trimesters, peaked at 29 to 32 weeks, and decreased thereafter. Among cases, before onset of preeclampsia the pattern of urinary PlGF was similar, but levels were significantly reduced beginning at 25 to 28 weeks. There were particularly large differences between controls and cases of preeclampsia with subsequent early onset of the disease or small-for-gestational-age infants. After onset of clinical disease, mean urinary PlGF in women with preeclampsia was 32 pg/mL, compared with 234 pg/mL in controls with fetuses of similar gestational age (P<.001). The adjusted odds ratio for the risk of preeclampsia to begin before 37 weeks of gestation for specimens obtained at 21 to 32 weeks, which were in the lowest quartile of control PlGF concentrations (<118 pg/mL), compared with all other quartiles, was 22.5 (95% confidence interval, 7.4-67.8). CONCLUSION: Decreased urinary PlGF at mid gestation is strongly associated with subsequent early development of preeclampsia.

Effect of diabetes on renal medullary oxygenation during water diuresis.

OBJECTIVES: To study the effect of water diuresis on renal medullary and cortical oxygenation in patients with diabetes using blood oxygenation level--dependent magnetic resonance imaging (BOLD MRI). RESEARCH DESIGN AND METHODS: Nine mild diabetic subjects (48 +/- 2.7 years of age, six women) and nine nondiabetic subjects of similar age and sex, all without known vascular or renal disease, were studied noninvasively by MRI before and during water diuresis. RESULTS: Water diuresis induced an increase in medullary oxygenation in control subjects, producing a decrease in R2* (apparent spin-spin relaxation time) of 1.89 +/- 0.27 (P < 0.01), but no significant change in the group of diabetic subjects. CONCLUSIONS: These findings in middle-aged diabetic subjects, which resembled those previously described in elderly subjects >65 years of age, suggest early impairment of adaptive vasodilatation within the renal medulla in diabetes.