Heme Oxygenase-1 Attenuates Hypoxia-Induced sFlt-1 and Oxidative Stress in Placental Villi through Its Metabolic Products CO and Bilirubin

One of the most prevalent complications of pregnancy is preeclampsia, a hypertensive disorder which is a leading cause of maternal and perinatal morbidity and premature birth with no effective pharmacological intervention. While the underlying cause is unclear, it is believed that placental ischemia/hypoxia induces the release of factors into the maternal vasculature and lead to widespread maternal endothelial dysfunction. Recently, HO-1 has been shown to downregulate two of these factors, reactive oxygen species and sFlt-1, and we have reported that HO-1 induction attenuates many of the pathological factors of placental ischemia experimentally. Here, we have examined the direct effect of HO-1 and its bioactive metabolites on hypoxia-induced changes in superoxide and sFlt-1 in placental vascular explants and showed that HO-1 and its metabolites attenuate the production of both factors in this system. These findings suggest that the HO-1 pathway may be a promising therapeutic approach for the treatment of preeclampsia

Bioflavonoid luteolin prevents sFlt-1 release via HIF-1α inhibition in cultured human placenta

Preeclampsia (PE) is a serious hypertensive complication of pregnancy and is a leading cause of maternal death and major contributor to maternal and perinatal morbidity, including establishment of long-term complications. The continued prevalence of PE stresses the need for identification of novel treatments which can target prohypertensive factors implicated in the disease pathophysiology, such as soluble fms-like tyrosine kinase 1 (sFlt-1). We set out to identify novel compounds to reduce placental sFlt-1 and determine whether this occurs via hypoxia-inducible factor (HIF)-1α inhibition. We utilized a commercially available library of natural compounds to assess their ability to reduce sFlt-1 release from primary human placental cytotrophoblast cells (CTBs). Human placental explants from normotensive (NT) and preeclamptic (PE) pregnancies were treated with varying concentrations of luteolin. Protein and mRNA expression of sFlt-1 and upstream mediators were evaluated using ELISA, western blot, and real-time PCR. Of the natural compounds examined, luteolin showed the most potent inhibition of sFlt-1 release, with >95% reduction compared to vehicle-treated. Luteolin significantly inhibited sFlt-1 in cultured placental explants compared to vehicle-treated in a dose- and time-dependent manner. Additionally, significant decreases in HIF-1α expression were observed in luteolin-treated explants, suggesting a mechanism for sFlt-1 downregulation. The ability of luteolin to inhibit HIF-1α may be mediated through the Akt pathway, as inhibitors to Akt and its upstream regulator phosphatidylinositol-3 kinase (PI3K) resulted in significant HIF-1α reduction. Luteolin reduces anti-angiogenic sFlt-1 through inhibition of HIF-1α, making it a novel candidate for the treatment of PE

Postpartum increases in cerebral edema and inflammation in response to placental ischemia during pregnancy

Reduced placental blood flow results in placental ischemia, an initiating event in the pathophysiology of preeclampsia, a hypertensive pregnancy disorder. While studies show increased mortality risk from Alzheimer's disease, stroke, and cerebrovascular complications in women with a history of preeclampsia, the underlying mechanisms are unknown. During pregnancy, placental ischemia, induced by reducing uterine perfusion pressure (RUPP), leads to cerebral edema and increased blood-brain barrier (BBB) permeability; however whether these complications persist after delivery is not known. Therefore, we tested the hypothesis that placental ischemia contributes to postpartum cerebral edema and neuroinflammation. On gestational day 14, time-pregnant Sprague Dawley rats underwent Sham (n = 10) or RUPP (n = 9) surgery and brain tissue collected 2 months post-delivery. Water content increased in posterior cortex but not hippocampus, striatum, or anterior cerebrum following RUPP. Using a rat cytokine multi-plex kit, posterior cortical IL-17, IL-1α IL-1β Leptin, and MIP2 increased while hippocampal IL-4, IL-12(p70) and RANTES increased and IL-18 decreased following RUPP. Western blot analysis showed no changes in astrocyte marker, Glial Fibrillary Acidic Protein (GFAP); however, the microglia marker, ionized calcium binding adaptor molecule (Iba1) tended to increase in hippocampus of RUPP-exposed rats. Immunofluorescence staining revealed reduced number of posterior cortical microglia but increased activated (Type 4) microglia in RUPP. Astrocyte number increased in both regions but area covered by astrocytes increased only in posterior cortex following RUPP. BBB-associated proteins, Claudin-1, Aquaporin-4, and zonular occludens-1 expression were unaltered; however, posterior cortical occludin decreased. These results suggest that 2 months postpartum, neuroinflammation, along with decreased occludin expression, may partly explain posterior cortical edema in rats with history of placental ischemia

Reduced uterine perfusion pressure as a model for preeclampsia and fetal growth restriction in murine: a systematic review and meta-analysis

The reduced uterine perfusion pressure (RUPP) model is frequently used to study preeclampsia and fetal growth restriction. An improved understanding of influential factors might improve reproducibility and reduce animal use considering the variability in RUPP phenotype. We performed a systematic review and meta-analysis by searching Medline and Embase (until 28 March, 2023) for RUPP studies in murine. Primary outcomes included maternal blood pressure (BP) or proteinuria, fetal weight or crown-rump length, fetal reabsorptions, or antiangiogenic factors. We aimed to identify influential factors by meta-regression analysis. We included 155 studies. Our meta-analysis showed that the RUPP procedure results in significantly higher BP (MD = 24.1 mmHg; [22.6; 25.7]; n = 148), proteinuria (SMD = 2.3; [0.9; 3.8]; n = 28), fetal reabsorptions (MD = 50.4%; [45.5; 55.2]; n = 42), circulating soluble FMS-like tyrosine kinase-1 (sFlt-1) (SMD = 2.6; [1.7; 3.4]; n = 34), and lower fetal weight (MD = -0.4 g; [-0.47; -0.34]; n = 113. The heterogeneity (variability between studies) in primary outcomes appeared ≥90%. Our meta-regression identified influential factors in the method and time point of BP measurement, randomization in fetal weight, and type of control group in sFlt-1. The RUPP is a robust model considering the evident differences in maternal and fetal outcomes. The high heterogeneity reflects the observed variability in phenotype. Because of underreporting, we observed reporting bias and a high risk of bias. We recommend standardizing study design by optimal time point and method chosen for readout measures to limit the variability. This contributes to improved reproducibility and thereby eventually improves the translational value of the RUPP model

Role of 20-Hydroxyeicosatetraenoic Acid in Mediating Hypertension in Response to Chronic Renal Medullary Endothelin Type B Receptor Blockade

BACKGROUND: The renal medullary endothelin (ET-1) system plays an important role in the control of sodium excretion and arterial pressure (AP) through the activation of renal medullary ET-B receptors. We have previously shown that blockade of endothelin type B receptors (ET-B) leads to salt-sensitive hypertension through mechanisms that are not fully understood. One possible mechanism is through a reduction in renal medullary production of 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE, a metabolite of arachidonic acid, has natriuretic properties similar to ET-B activation. While these findings suggest a possible interaction between ET-B receptor activation and 20-HETE production, it is unknown whether blockade of medullary ET-B receptors in rats maintained on a high sodium intake leads to reductions in 20-HETE production. METHODOLOGY/PRINCIPAL FINDINGS: The effect of increasing sodium intake from low (NS = .8%) to high (HS = 8%) on renal medullary production of 20-HETE in the presence and absence of renal medullary ET-B receptor antagonism was examined. Renal medullary blockade of ET-B receptors resulted in salt sensitive hypertension. In control rats, blood pressure rose from 112.8±2.4 mmHg (NS) to 120.7±9.3 mmHg (HS). In contrast, when treated with an ET-B receptor blocker, blood pressure was significantly elevated from 123.7±3.2 (NS) to 164.2±7.1 (HS). Furthermore, increasing sodium intake was associated with elevated medullary 20-HETE (5.6±.8 in NS vs. 14.3±3.7 pg/mg in HS), an effect that was completely abolished by renal medullary ET-B receptor blockade (4.9±.8 for NS and 4.5±.6 pg/mg for HS). Finally, the hypertensive response to intramedullary ET-B receptor blockade was blunted in rats pretreated with a specific 20-HETE synthesis inhibitor. CONCLUSION: These data suggest that increases in renal medullary production of 20-HETE associated with elevating salt intake may be, in part, due to ET-B receptor activation within the renal medulla