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

Reactive oxygen intermediates (ROI) have been implicated as mediators of hepatocyte death resulting from a variety of forms of liver injury. To delineate the mechanisms that underlie ROI-induced apoptosis, the roles of caspase activation and nuclear factor-κB (NF-κB) signaling were determined in the rat hepatocyte cell line RALA255-10G after treatment with H₂O₂ or the superoxide generator menadione. By 8 h, H₂O₂ and menadione caused 26% and 33% cell death, respectively. Death from both ROI occurred by apoptosis as indicated by morphology under fluorescence microscopy, the induction of caspase activation and DNA fragmentation, and the cleavage of poly(ADP- ribose) polymerase. Despite the presence of caspase activation in both forms of apoptosis, caspase inhibition blocked H₂O₂- but not menadione-induced apoptosis. In contrast, inhibition of NF-κB activation decreased cell death from both ROI. Different ROI, therefore, induce distinct apoptotic pathways in RALA hepatocytes that are both caspase dependent and independent. In contrast to the known protective effect of NF-κB activation in tumor necrosis factor-α-induced hepatocyte apoptosis, NF-κB promotes hepatocellular death from ROI in these cells.