Activation of neutral sphingomyelinase participates in ethanol-induced apoptosis in hep G2 cells

The mechanism underlying ethanol-induced apoptosis in liver cells is not cl ear. Sphingomyelin (SM) metabolism is a novel signal transduction pathway t hat has an impact on apoptosis in many cell types. We investigated whether the SM pathway is involved in ethanol-induced apoptosis in the liver. Hep G 2 cells were treated with ethanol followed by assaying apoptosis, sphingomy elinase (SMase) activity, caspase-3 activity, and the changes of SM content in the cells. We found that ethanol dose-dependently increased apoptosis a nd the effect was accompanied by increases of caspase-3 activity and neutra l SMase activity. At concentrations of 80 and 160 mM, ethanol significantly increased caspase-3 activity by 120% and neutral SMase activity by 24%. Th e activity of acid SMase was only slightly increased without statistical si gnificance. C-2-ceramide, the exogenous SM metabolite, mimicked the effects of ethanol on apoptosis and caspase-3 activation. When the SM content was determined 24h after treatment with ethanol, its level was 15% lower than t hat of controls. The results indicate that metabolism of SM triggered by ne utral SMase participates in ethanol-induced apoptosis in Hep G2 cells and a ctivation of caspase-3 is involved in the apoptotic pathway.