Peptide B7–33, a Single‐Chain Derivative of the Relaxin Hormone Protects Cytotrophoblasts from Marinobufagenin‐Induced Preeclampsia Phenotype

Abstract

BackgroundPreeclampsia (PreE) is a hypertensive pregnancy disorder, which occurs in approximately 10% of all gestations. Recently, a digitalis‐like factor, marinobufagenin (MBG) has been implicated as a causative factor in preE. We demonstrated that MBG inhibits the proliferation, migration, and invasion of cytotrophoblast (CTB) cells. Relaxin is a peptide hormone that allows vasodilation and plays an important role in the process of parturition. The literature suggests potential therapeutic role of H2 relaxin in PreE, however, there is a controversy on hypotensive action of the peptide. Due to the complex insulin‐like structure of relaxin (A‐ and B‐ chains, 53 amino acids, 3 disulfide bonds), a novel H2 relaxin B‐chain‐only peptide variant B7–33 (27 amino acids without any disulfide bonds) has recently been developed. This single‐chain peptide displayed equivalent efficacy to the natural H2 relaxin in several functional assays both in vitro and in vivo. Importantly, B7–33 was shown to have H2 relaxin‐like RXFP1 specific effects, particularly in endogenously expressing RXFP1 cells, thus we hypothesized that B7–33 could be an alternative and cost‐effective treatment option for PreE compared with H2 relaxin.MethodsHuman CTBs were treated with DMSO (vehicle) or 0.1, 1, 10 or 100 nM of MBG for 48 h and were co‐treated with B7–33 (25 nM) with MBG exposure, while some cells were treated with 5, 10, 25 and 50 nM B7–33 alone. Levels of vascular endothelial growth factor (VEGF), placental growth factor (PlGF), soluble fms‐like tyrosine kinase‐1 (sFlt‐1), and soluble endoglin (sEng) were measured in culture media using ELISA kits. Cell lysates were utilized to evaluate the expression of mTOR, pAKT and MMP‐9 by western blotting. Statistical comparisons were performed using analysis of variance with Duncan's post hoc test.ResultsSecretion of sFlt‐1 and sEng were increased while VEGF and PIGF were decreased in CTBs treated with ≥1.0 nM MBG (*p < 0.05 for each). B7–33 co‐treatment significantly rescued CTBs from MBG‐induced anti‐angiogenic profile (p < 0.05 for each). There is no effect of B7–33 on sFLT‐1, sEng and PlGF; however, it increases the expression of VEGF, while CTBs were treated only with B7–33. B7–33 also causes increased expression of mTOR, pAKT and MMP‐9 in CTBs.ConclusionsB7–33 mitigates the MBG‐induced dysfunction of CTBs by attenuating anti‐angiogenic phenotype similar to that seen in PreE. This study supports the importance of continuing research of B7–33 in preE prevention.