Introduction In fetal growth restriction (FGR), early placentation defects result in placental insufficiency and vasoconstriction, which cumulate in organ failure at the severe end of the spectrum. In other placental pathologies, including preeclampsia, extracellular free fetal haemoglobin (fHbF) is overproduced, where it inactivates the vasodilator nitric oxide (NO). We have previously shown that excess fetoplacental fHbF also occurs in FGR pregnancy, sequestering NO and evoking vasoconstriction. Here, we explore the further effects of fHbF on fetoplacental endothelium, considering altered angiogenesis, altered vasculoprotection, and an immunological response.

Methods We assessed the fHbF evoked synthesis of the pro-angiogenic and pro-inflammatory cell stress mediators DKK-4, NFkB and FABP-1, produced by human chorionic plate arterial endothelial cells (HPAECs) under conditions of unidirectional laminar flow. Secondly, we studied fHbF-evoked NFÃ&noentity;°B nuclear translocation using fluorescent microscopy; and the downstream NFkB-actuated cytokine profile (IF1α, TNFα) measured in cell medium and lysate by ELISA. Observations were expanded to assessment of fHbF effects on branching and non-branching angiogenesis of HPAECs grown on Matrigel, and expressed as an average of tubule length multiplied by tubule number as a net measure of angiogenesis. As a correlate, endothelial morphology of fHbF and non-exposed static chorionic artery sections was qualitatively analysed by scanning electron microscopy.

Results A cell stress proteome assay demonstrated that fHbF increased synthesis of DKK-4 (>50% increase from control), NFκB (>50% increase) and FABP1 (>100% increase). A pro-angiogenic effect was further corroborated by assessment of villous angiogenesis on Matrigel, where 0.3 mg/ml fHbF was found to promote branching angiogenesis in HPAECs (n=5; p<0.01). In a separate study of NFκB-mediated endothelial inflammation, 0.3 mg/ml fHbF-evoked NFkB signal transduction demonstrable by nuclear translocation within 2.5 hours, whilst in controls no evidence of NFkB activation was observed (n=4 paired lines). In the fHbF group this was paralleled by increased release of NFκB-actuated cytokines into flow-conditioned medium, IFN1± (n=7; control vs. fHbF-exposed at 0.2 mg/ml fHbF median fold change 1.42 (range 1.09–2.2) vs. 1 (0); Wilcoxon p<0.05), and for TNFα ?(control vs. fHbF-exposed at 0.2 mg/ml fHbF median fold-change 1.54 (range 1.09–2.22) vs. 1 (0); Wilcoxon p<0.05). Morphologically, fHbF evoked widespread blebbing of the luminal endothelium.

Conclusion fHbF causes aberrant pro-angiogenesis, promotes acute inflammation and loss of structural organisation in fetoplacental endothelium. Our findings are relevant to widening understanding the pathophysiology of FGR and exploring the link between FGR and stillbirth, where overproduction of extracellular fetal haemoglobin could represent a novel therapeutic target.