Hydrogen peroxide alters signal transduction in human endothelial cells

Lytic H2O2-induced injury to human umbilical vein endothelial cells provides a model for endothelial cell damage in diverse states including acute respiratory distress and septic shock. Endothelial cell lysis is an extreme result of inflammatory cell activation. Functional alterations such as responsiveness to endothelial cell agonists and eicosanoid production might be impaired by exposure to inflammatory cell products including H2O2. Soluble mediators such as thrombin or histamine cause endothelial cell activation via a signal transduction mechanism that hydrolyzes phosphatidylinositol 4,5-bisphosphate (IP), liberating inositol trisphosphate (IP3). Accordingly, pretreatment of endothelial cells with H2O2 blocked the subsequent production of IP3 in response to thrombin and histamine. H2O2 inhibition of IP3 was time- and concentration-dependent. The endothelial cells were viable by trypan blue dye exclusion and chromium release. H2O2 inhibition of signaling was completely prevented by catalase. Iron-dependent oxidant radical formation appears critical because deferoxamine (10(-4) mol/L) pretreatment of endothelial cells prevented H2O2 inhibition of IP hydrolysis. Prostacyclin and platelet activating factor production in response to thrombin have been linked to IP hydrolysis. Pretreatment of endothelial cells with H2O2 reduced prostacyclin and platelet-activating factor production by thrombin by at least 50%. It appears H2O2 can induce defects in signaling pathways with sequelae (decreased prostacyclin and platelet-activating factor) short of endothelial cell death. The possible consequences of H2O2 interaction with endothelial cells is reviewed with the aim of presenting a hypothesis to integrate these various observations.