Role of caspases and NF-kappa B signaling in hydrogen peroxide- and superoxide-induced hepatocyte apoptosis

Reactive oxygen intermediates (ROI) have been implicated as mediators of he patocyte death resulting from a variety of forms of liver injury. To deline ate the mechanisms that underlie ROI-induced apoptosis, the roles of caspas e activation and nuclear factor-kappa B (NF-kappa B) signaling were determi ned in the rat hepatocyte cell line RALA255-10G after treatment with H2O2 o r the superoxide generator menadione. By 8 h, H2O2 and menadione caused 26% and 33% cell death, respectively. Death from both ROI occurred by apoptosi s as indicated by morphology under fluorescence microscopy, the induction o f caspase activation and DNA fragmentation, and the cleavage of poly(ADP-ri bose) polymerase. Despite the presence of caspase activation in both forms of apoptosis, caspase inhibition blocked H2O2- but not menadione-induced ap optosis. In contrast, inhibition of NF-kappa B activation decreased cell de ath from both ROI. Different ROI, therefore, induce distinct apoptotic path ways in RALA hepatocytes that are both caspase dependent and independent. I n contrast to the known protective effect of NF-kappa B activation in tumor necrosis factor-alpha-induced hepatocyte apoptosis, NF-kappa B promotes he patocellular death from ROI in these cells.