Xanthine oxidase interaction with vascular endothelial growth factor in human endothelial cell angiogenesis

Objectives: Reduced capillary density occurs early in cardiovascular diseases. Oxidant stress, is implicated in endothelial apoptosis. We investigated the effects of xanthine oxidase (XO) on endothelial survival signaling: protein kinase B/Akt, its cross-talk with p38 MAPK and apoptosis pathways, and its effect on vascular tube formation in vascular endothelial growth factor (VEGF)-simulated human umbilical vein cells. Methods: We studied primary cultured human endothelial cells from the umbilical cord. Reactive oxygen species (ROS) production was detected by dibydroethidium staining, cell-signaling pathways by western blots, cell survival by western blots, and nuclear chromatin and angiogenesis response by MTT proliferation assay and three-dimensional Matrigel cultures. Results: Exogenous XO increased cellular ROS production and caused superoxide-dependent inhibition of Akt phosphorylation and enhancement of p38 MAPK phosphorylation in a time- and dose-dependent mariner. In contrast, application of the XO inhibitor oxypurinol or allopurinol inhibited VEGF-stimulated Akt phosphorylation, indicating that endogenous XO promotes VEGF-induced endothelial cell (EC) survival signaling. Exogenous XO induced activation of caspase-3 and reduced expression of the anti-apoptosis protein Bcl-2. Exogenous XO also reduced EC viability, proliferation, and vascular tube formation by p38 MAPK-dependent, phospboinositide 3-kinase (P13-K) reversible mechanisms; whereas VEGF promoted EC survival by PT3-K-dependent, p38 MAPK-independent effects. Conclusions: Exogenous XO activity is an important contributor to endothelial mechanisms for microvascular rarefaction., by modulation of cell survival signaling pathways; however, endogenons XO is necessary for maintaining EC survival