H2O2 acts on cellular membranes to generate ceramide signaling and initiate apoptosis in tracheobronchial epithelial cells

Hydrogen peroxide (H2O2) is an inflammatory oxidant which contributes to th e pathogenesis of chronic diseases such as lung injury of the respiratory t ract, atherosclerosis and cancer, The mechanisms and target sites of this r eactive oxidant are mainly unknown. So far there are opposing reports as to whether reactive oxidants inhibit or promote apoptosis, We activated the d eath pathway in primary tracheobronchial epithelial (TBE) cells with H2O2 ( 20-200 mu M) and observed the morphological changes, DNA laddering patterns , and DNA fragmentation associated with apoptosis, Elevation of ceramide wi th exogenous ceramide analogs was sufficient for apoptosis induction with t he same characteristics and in the same time frame. H2O2 induced rapid sphi ugomyelin hydrolysis to ceramide, the elevation of which paralleled the ind uction of apoptosis, Furthermore, H2O2 acted directly on TEE cells membrane preparations devoid of nuclei, stimulating sphingomyelin hydrolysis throug h a neutral Mg2+ dependent sphingomyelinase (SMase), These data suggest tha t the formation of ceramide from sphingomyelin in the plasma membrane is a key event in H2O2-induced apoptosis in tracheobronchial epithelial cells.