Synergistic action of anti-angiogenic factors and pro-inflammatory cytokines cause severe endothelial dysfunction

M. Kabasakal^1,2, S. A. Broadway-Stringer¹, K. Wang¹, I. Alp Yildirim², A. Ahmed¹. ¹Aston Medical Research Institute, Birmingham, United Kingdom, ²Istanbul University, Faculty of Pharmacy, Istanbul, Turkey.

Introduction: Angiogenic imbalance in the form of high soluble Flt-1 (sFlt-1) and soluble endoglin (sEng) paired with low levels of protective factors is associated with preeclampsia, a life threatening hypertensive pregnancy disorder (1,2). Also associated with this disorder is the sustained activation of the endothelium leading to vascular dysfunction in maternal vessels that would otherwise adapt to support increased blood flow in healthy pregnancy (1). We hypothesised that the anti-angiogenic factors pre-dispose the vascular endothelium to damage by pro-inflammatory cytokines.

Methods: Using flow cytometric analysis, endothelial activation markers; ICAM-1 and VCAM-1 were measured in HUVECs, overexpressing sFlt-1 and sEng, incubated with different concentrations of TNF-α for 6 hours. To determine the effects of sFlt-1 and TNF-α on endothelium function, vessel reactivities were measured by wire myography using mesenteric resistance arteries isolated at E17.5 gestation time from 12-16 week old wild-type pregnant mice treated with Adenovirus encoding sFlt-1 or Empty vector

Results: Flow cytometric analysis revealed overexpression of sFlt-1 and sEng in endothelial cells significantly enhanced TNF-α induced VCAM-1(p<0.001; n=3) and ICAM-1(p<0.05; n=3) expression in a dose dependent manner. Acetylcholine-induced endothelial dependent vessel dilation was reduced in TNF-α treated vessels. Soluble Flt-1 overexpression exacerbated the TNF-α induced impairment of endothelial dependent relaxation.

Conclusion: This study suggests sFlt-1 and sEng synergistically sensitise the endothelium to activation in vitro and overexpression of sFlt-1, paired with pro-inflammatory TNF-α, exacerbates the already dysfunctional endothelial dependent relaxation. Although inflammation per se is not the primary cause of preeclampsia, vascular inflammation is likely to contribute to the severity of the disorder.

References:

1) S.E. Maynard, J.Y. Min, J. Merchan, S. Mondal, T.A. Libermann, J.P. Morgan, F.H. Epstein, V.P. Sukhatme, S.A. Karumanchi, K.H. Lim, J. Li, F.W. Sellke, I.E. Stillman, (2003) Excess placental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endothelial dysfunction hypertension, and proteinuria in preeclampsia, Journal of Clinical Investigation 111(5) 649-658.

2) S. Ahmad and A. Ahmed, (2004) Elevated placental soluble vascular endothelial growth factor receptor-1 inhibits angiogenesis in preeclampsia, CIRCULATION RESEARCH 95(9) 884-891.