Preeclampsia : an accelerator–brake defect disorder

Life's perfect partnership starts with the placenta. If we get this right, we have the best chance of healthy life. In preeclampsia, we have a failing placenta. Preeclampsia kills one pregnant woman every minute and the life expectancy of those who survive is greatly reduced. Preeclampsia is treated roughly the same way it was when Thomas Edison was making the first silent movie. Globally, millions of women risk death to give birth each year and almost 300,000 lose their lives in this process. Over half a million babies around the world die each year as a consequence of preeclampsia. Despite decades of research, we lack pharmacological agents to treat it. Maternal endothelial dysfunction is a central phenomenon responsible for the clinical signs of preeclampsia. In the late nineties, we discovered that vascular endothelial growth factor (VEGF) stimulated nitric oxide release. This led us to suggest that preeclampsia arises due to the loss of VEGF activity, possibly due to a rise in soluble Flt-1 (sFlt-1), the natural antagonist of VEGF. Researchers have shown that high sFlt-1 elicits preeclampsia-like signs in pregnant rats and sFlt-1 increases before the clinical signs of preeclampsia in pregnant women. We demonstrated that removing or reducing this culprit protein from preeclamptic placenta restored the angiogenic balance. Heme oxygenase-1 (HO-1 or Hmox1) that generates carbon monoxide (CO), biliverdin (rapidly converted to bilirubin) and iron is cytoprotective. We showed that the Hmox1/CO pathway prevents human placental injury caused by pro-inflammatory cytokines and suppresses sFlt-1 and soluble endoglin release, factors responsible for preeclampsia phenotypes. The other key enzyme we identified is the hydrogen sulfide generating cystathionine-gamma-lyase (CSE or Cth). These are the only two enzyme systems shown to suppress sFlt-1 and to act as protective pathways against preeclampsia phenotypes in animal models. We also showed that when hydrogen sulfide restores placental vasculature, it also improves lagging fetal growth. These molecules act as the inhibitor systems in pregnancy and when they fail, this triggers preeclampsia. Discovering that statins induce these enzymes led us to an RCT to develop a low-cost therapy (StAmP Trial) to prevent or treat preeclampsia. If you think of pregnancy as a car then preeclampsia is an accelerator–brake defect disorder. Inflammation, oxidative stress and an imbalance in the angiogenic milieu fuel the ‘accelerator’. It is the failure in the braking systems (the endogenous protective pathway) that results in the ‘accelerator’ going out of control until the system crashes, manifesting itself as preeclampsia.

Hydrogen sulphide rescues preeclampsia-like phenotype aggravated by high sFlt-1 in Placenta Growth Factor (PlGF) deficiency

INTRODUCTION: Low circulating levels of placenta growth factor (PlGF) is strongly associated with the onset of preeclampsia, a maternal hypertensive disorder characterized by high blood pressure and proteinuria after 20 weeks of gestation. Although, PlGF-deficient mice are born healthy and fertile at a Mendelian ratio, the physiological importance of PlGF in the pathogenesis of preeclampsia is unclear. We hypothesised that decreased levels of PlGF in pregnancy exacerbates the fetal growth restriction associated with preeclampsia in the presence of high sFlt-1. METHODS: Pregnant PlGF-/- mice were injected with adenovirus encoding sFlt-1 (Ad-sFlt-1) at high (i) 1.5x109 pfu/ml and low (ii) 0.5x109 pfu/ml doses. Mean arterial blood pressure (MBP), biochemical and histological assessments of maternal kidney, placenta and embryos were performed. RESULTS: Ad-sFlt-1 significantly increased MBP and induced severe glomerular endotheliosis in PlGF-/- mice at E10.5 gestation compared to wild-type animals. High sFlt-1 also significantly elevated albumincreatinine ratio and increased levels of urinary kidney injury molecule-1, a marker for proximal tubule injury.At a high dose of sFlt-1, there was complete fetal resorption in the pregnant PlGF-/- mice, and even the lower dose of sFlt-1 induced severe fetal resorption and abnormal placental vascularization. Hydrogen sulphide-releasing agent, GYY4137, significantly reduced resorption, hypertension and proteinuria in Ad-sFlt-1 treated pregnant PlGF-/- mice. To determine if placental PlGF is critical for preventing fetal growth restriction associated with preeclampsia, we generated haploinsufficient PlGF+/- placentas and embryos were generated in wild-time dams and exposed to high sFlt-1 environment. This resulted in reduced fetal resorption, gestational hypertension and proteinuria when compared to pregnant PlGF-/- mice. CONCLUSIONS: Placental PlGF is a critical protective factor against the damaging effects of high sFlt-1 in preeclampsia and the hydrogen sulphide pathway may rescue preeclampsia phenotypes.

Glutaredoxin-1 Is up-regulated in preeclampsia and increases soluble Flt-1 expression

INTRODUCTION: Preeclampsia is a vascular disorder in pregnancyand is biochemical characterization by high soluble Flt-1 and lowplacenta growth factor as well as an imbalance in redox homeostasis.During conditions of high oxidative stress, cysteine residues on keyproteins are reversibly altered by S-glutathionylation, modifying theirfunction. Glutaredoxin-1 (Glrx) enzymatically catalyzes the removal of S-glutathione adducts, conferring reversible signaling dynamics toproteins with redox-sensitive cysteines. The role of Glrx in preeclampsiais unknown.METHODS: Immunohistochemistry and Western blot analysis for Glrx orglutathione were conducted on human placenta samples collected pre-termfrom early onset preeclamptic patients (n=10) or non-preeclamptic induceddeliveries (n=9). Human endothelial cells were infected with adenovirusencoding Glrx or LacZ prior to the cells being exposed to hypoxia (0.1%O2, 24h) to measure changes in soluble Flt-1 (sFlt-1). Quantitative PCRand ELISA were used to measure sFlt-1 at mRNA and protein level.RESULTS: Immunohistochemical staining for GSH revealed lowerS-glutathionylation adducts in preeclampsia placenta in comparison tocontrols. Glrx expression, which catalyses de-glutathionylation wasenhanced in early onset preeclampsia compared to pre-term controlsamples. In contrast, no change was observed in preeclamptic and IUGRplacentas at full term. In endothelial cells overexpressing Glrx, sFlt-1expression was dramatically enhanced at mRNA (3-fold P<0.05) andprotein level (5 fold P>0.01, n=4) after hypoxia andoverexpressing Glrxin mice enhanced levels of circulating sFlt-1 during in vivo ischemia.CONCLUSIONS: Enhanced Glrx expression in preeclamptic placentain line with an apparent decrease in S-glutathionylation may leavekey proteins susceptible to irreversible oxidation in conditions of highoxidative stress.