High Levels of Urinary Vascular Endothelial Growth Factor in Women with Severe Preeclampsia

Potential urinary biomarkers in preeclampsia: a narrative review

INTRODUCTION

Preeclampsia (PE) is a highly relevant pregnancy-related disorder. An early and accurate diagnosis is crucial to prevent major maternal and neonatal complications and mortality. Due to the association of kidney dysfunction with the pathophysiology of the disease, urine samples have the potential to provide biomarkers for PE prediction, being minimally invasive and easy to perform. Therefore, searching for novel biomarkers may improve outcomes. This narrative review aimed to summarize the scientific literature about the traditional and potential urinary biomarkers in PE and to investigate their applicability to screen and diagnose the disorder.

METHODS

A non-systematic search was performed in PubMed/MEDLINE, Scopus, and SciELO databases.

RESULTS

There is significant divergence in the literature regarding traditionally used serum markers creatinine, cystatin C, and albuminuria, accuracy in PE prediction. As for the potential renal biomarkers investigated, including vascular epithelial growth factor (VEGF), placental growth factor (PlGF), and soluble fms-like tyrosine kinase (sFlt-1), urinary levels of PlGF and sFtl-1/PlGF ratio in urine seem to be the most promising as screening tests. The assessment of the global load of misfolded proteins through urinary congophilia, podocyturia, and nephrinuria has also shown potential for screening and diagnosis. Studies regarding the use of proteomics and metabolomics have shown good accuracy, sensitivity, and specificity for predicting the development and severity of PE.

CONCLUSION

However, there are still many divergences in the literature, which requires future and more conclusive research to confirm the predictive role of urinary biomarkers in pregnant women with PE.

An unexpected tail of VEGF and PlGF in pre-eclampsia

PET (pre-eclamptic toxaemia), characterized by pregnancy-related hypertension and proteinuria, due to widespread endothelial dysfunction, is a primary cause of maternal morbidity. Altered circulating factors, particularly the VEGF (vascular endothelial growth factor) family of proteins and their receptors, are thought to be key contributors to this disease. Plasma from patients with PET induces numerous cellular and physiological changes in endothelial cells, indicating the presence of a circulating imbalance of the normal plasma constituents. These have been narrowed down to macromolecules of the VEGF family of proteins and receptors. It has been shown that responses of endothelial cells in intact vessels to plasma from patients with pre-eclampsia is VEGF-dependent. It has recently been shown that this may be specific to the VEGF₁₆₅b isoform, and blocked by addition of recombinant human PlGF (placental growth factor). Taken together with results that show that sVEGFR1 (soluble VEGF receptor 1) levels are insufficient to bind VEGF-A in human plasma from patients with pre-eclampsia, and that other circulating macromolecules bind, but do not inactivate, VEGF-A, this suggests that novel hypotheses involving altered bioavailability of VEGF isoforms resulting from reduced or bound PlGF, or increased sVEGFR1 increasing biological activity of circulating plasma, could be tested. This suggests that knowing how to alter the balance of VEGF family members could prevent endothelial activation, and potentially some symptoms, of pre-eclampsia.

Characterization of discriminatory urinary proteomic biomarkers for severe preeclampsia using SELDI-TOF mass spectrometry

OBJECTIVE

To analyze the proteomic pattern in urine for distinguishing severe preeclampsia from mild preeclampsia and normotensive controls using surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS).

STUDY DESIGN

Urine samples were collected from women with severe preeclampsia (n=11 [sPE]), mild preeclampsia (n=7 [mPE]), and normotensive controls (n=8) and analyzed by SELDI-TOF-MS to identify discriminatory protein peaks in the sPE cohort. A scoring system was constructed--designated as Preeclampsia Proteomic Score of Urine (PPSU)--to differentiate sPE from mPE and normotensive controls.

RESULTS

Four discriminatory protein peaks were identified (m/z ratio: 4155, 6044, 6663, and 7971), all of which were down-regulated in women with sPE. PPSU scores in women with sPE were significantly lower than that in both mPE and controls (sPE 0 [0-4] vs. mPE 3 [0-4] vs. controls 4 [2-4]; median [range]; P<0.05). PPSU<2 had a sensitivity of 90.9% and specificity of 93.3% in discriminating patients with sPE from mPE and controls.

CONCLUSION

Proteomic analysis of urine can accurately distinguish sPE from mPE and normotensive controls.

Lethality in an anti-angiogenic tumor gene therapy model upon constitutive but not inducible expression of the soluble vascular endothelial growth factor receptor 1

BACKGROUND

Neoangiogenesis is essential for tumor growth. The present study aimed to test the hypothesis that vector-mediated expression of sflt1 at high levels would result in the blockade of vascular endothelial growth factor (VEGF) function and therefore the inhibition of tumor growth.

METHODS

To sequester VEGF, we tested, in a subcutaneous LLC tumor model, 'gutless' high-capacity adenovirus vectors expressing the soluble VEGF receptor 1 (sflt1) in a liver-specific manner, either in a constitutive or in a RU486 induced manner.

RESULTS

High serum levels of sflt1 were observed upon in vivo injection of both vectors. Despite the differences in expression kinetics, both modes of sflt1 expression resulted in significant though transient suppression of tumor growth. Unexpectedly, constitutive but not intermittent sflt1 expression resulted in ascites and death of all animals. Morphological analyses by light and electron microscopy indicated that the animals had died from a nephropathy, which apparently was due to the blockade of VEGF function.

CONCLUSIONS

Although confirming earlier results of toxic effects of prolonged VEGF sequestration, the present study suggests that therapeutic anti-tumor effects can be achieved without side-effects with intermittent VEGF blockade or the use of drugs with short half-lives, as shown by the use of an inducible gene expression system.

The endogenous anti-angiogenic family of splice variants of VEGF, VEGFxxxb, are down-regulated in pre-eclamptic placentae at term

PET (pre-eclamptic toxaemia) has recently been linked with alterations in production of a VEGFR1 [VEGF (vascular endothelial growth factor) receptor 1] splice variant that acts as a circulating inhibitor. We have recently described a family of naturally occurring splice variants of VEGF, termed VEGFxxxb, that also appear to act as inhibitors of conventional VEGFxxx-mediated angiogenesis. To determine whether alteration in splicing of VEGF-VEGFR family members extended beyond VEGFR1, we investigated the effect of pre-eclampsia on placental VEGFxxxb mRNA and protein expression. VEGFxxx and VEGFxxxb mRNA and protein were both found in normal human term placentae. VEGFxxx protein formed the majority of the total VEGF protein (980+/-195 pg/mg), whereas VEGFxxxb (11.5 pg/mg) was found to form a small part of the total VEGF protein expression (1.5+/-0.24%). Evidence for VEGF165b, VEGF121b and VEGF145b expression was found. In pre-eclamptic placentae, there was a significant down-regulation of VEGFxxxb isoforms, but a small up-regulation of VEGFxxx isoforms. In normal placenta VEGFxxxb and VEGFxxx concentrations were positively correlated (r=0.69, P<0.02), whereas in pre-eclamptic placentae, there was a significant negative correlation between VEGFxxxb and VEGFxxx protein expression (r=-0.8, P<0.02), indicating that there was a significant uncoupling of the splicing regulation of the VEGF isoforms. Combined with previous studies showing increased soluble VEGFR1 isoforms in human pre-eclampsia, these data suggest that there may be a common mechanism in pre-eclampsia that involves dysregulation of mRNA splicing of members of the VEGF-VEGFR axis.

Fractional Excretion of Angiogenic Factors in Women With Severe Preeclampsia

OBJECTIVE

We estimated the fractional excretions of soluble fms-like tyrosine kinase 1 (sFlt-1), vascular endothelial growth factor, and placental growth factor of severely preeclamptic women at the time of disease clinical manifestation.

METHODS

Levels of free sFlt-1, vascular endothelial growth factor, and placental growth factor were measured by immunoassay from time-matched serum-urine samples from 64 women in the following groups: nonpregnant reproductive aged (n = 9), healthy pregnant controls (n = 13), mildly preeclamptic women (n = 15), and women with severe preeclampsia (n = 27). Urinary concentrations of angiogenic factors were normalized to creatinine and fractional excretions calculated. Correlations were estimated between fractional excretions of angiogenic factors, albuminuria, nonspecific proteinuria and urine protein-to-creatinine ratio.

RESULTS

Severely preeclamptic women had more than double urinary vascular endothelial growth factor (P = .01) and fractional excretion of vascular endothelial growth factor compared with mildly preeclamptic women (P = .007) or pregnant controls (P < .001). Serum, urine and fractional excretion levels of sFlt-1 were much higher among severely preeclamptic women compared with all the other pregnant groups (P < .001). Conversely, severely preeclamptic women had lower serum placental growth factor levels compared with healthy pregnant women (P < .05) and mildly preeclamptic groups (P < .05). Severely preeclamptic women had increased fractional excretions of placental growth factor, albumin, proteinuria, and random urine total protein/creatinine ratio. Among severely preeclamptic women there was no correlation between proteinuria and fractional excretion of vascular endothelial growth factor (r = 0.30, P = .127) or sFlt-1 (r = 0.35, P = .07). There was a significant correlation between fractional excretion for placental growth factor, random urine total protein/creatinine ratio (r = 0.60, P = .002), and nonspecific proteinuria (r = 0.50, P = .01).

CONCLUSION

Severe preeclampsia is characterized by increased fractional excretion of angiogenic factors and especially of vascular endothelial growth factor, likely reflecting 2 separate phenomena that may have additive effects: "endogenous" renal production and glomerular "leakage."

Urinary angiogenic factors cluster hypertensive disorders and identify women with severe preeclampsia

OBJECTIVE

Serum levels of soluble fms-like tyrosine kinase 1 (sFlt-1), vascular endothelial growth factor (VEGF), and placental growth factor (PlGF) are altered in women with clinical preeclampsia. We sought to identify whether similar alterations in urinary levels of these proteins cluster hypertensive disorders in pregnancy, and identify women with severe preeclampsia (sPE).

STUDY DESIGN

Free urinary levels of sFlt-1, VEGF, and PlGF were measured by immunoassay in 68 women enrolled prospectively in the following groups: nonpregnant reproductive age (NP-CTR n = 14), healthy pregnant control (P-CTR n = 16), pregnant hypertensive and proteinuric women who did not meet criteria for severe preeclampsia (pHTN n = 21), and women with sPE (n = 17).

RESULTS

There was no difference in gestational age at the time of enrollment among groups (median [range]: sPE: 31 [24-40], pHTN: 34 [16-40], P-CTR: 28 [7-39] wks). Urinary excretion of VEGF was significantly increased in sPE women compared with NP-CTR (P = .023), but did not differ among pregnant groups. Urinary PlGF levels were significantly increased in pregnant compared with nonpregnant women, but were decreased in all hypertensive women compared with healthy P-CTR (P < .001). Urinary sFlt-1 concentrations were significantly increased in women with sPE relative to all other groups (P < .001). pHTN women had higher sFlt-1 urinary output compared with P-CTR group (P = .001). A cutoff >2.1 in the ratio log [sFlt-1/PlGF] had 88.2% sensitivity and 100% specificity in differentiating women with sPE from normotensive controls. We also described that the log[sFlt-1/PlGF] ratio identified women with sPE better than proteinuria alone (P = .03). Our regression model revealed that uric acid correlated best with log[sFlt-1/PlGF] ratio (r = 0.628; P = .005).

CONCLUSION

sPE is associated with increased urinary output of the antiangiogenic factor sFlt-1 and a decreased output of PlGF at the time of clinical manifestation, providing a rapid noninvasive screening of hypertensive women based on a sFlt/PlGF ratio. This ratio may be used as representation for severity of the disease, and appears to be superior to random urinary protein measurements.