
<ArticleTitle>Differential protection with inhibitors of <prot>caspase-8</prot> and <prot>caspase-3</prot> in murine models of tumor necrosis factor and <prot>Fas receptor</prot>-mediated hepatocellular apoptosis.</ArticleTitle>
<AbstractText>Excessive apoptosis has been implicated in a number of acute and chronic human diseases. The activation of caspases has been shown to be critical for the apoptotic process. The objective of this investigation was to evaluate the beneficial effects and mechanism of action of the <prot>caspase-8</prot> inhibitor IETD-CHO and the <prot>caspase-3</prot> inhibitor DEVD-CHO against tumor necrosis factor (TNF)-induced hepatocellular apoptosis in vivo and compare these results to effects of the same inhibitors against Fas-induced apoptosis. Treatment of C3Heb/FeJ mice with 700 mg/kg galactosamine/100 microg/kg endotoxin induced parenchymal apoptosis (indicated by <prot>caspase-3</prot> activation and morphology) and severe liver injury (indicated by the increase in plasma alanine aminotransferase activities and histology) at 7 h. Treatment with IETD-CHO or DEVD-CHO (10 mg/kg at 3, 4.5, and 5.5 h) significantly attenuated <prot>caspase-3</prot> activation and liver injury. Western analysis showed that DEVD-CHO had no effect while IETD-CHO substantially reduced <prot>procaspase-3</prot> and <prot>procaspase-9</prot> processing. On the other hand, <prot>caspase-3</prot> activation and liver injury by the anti-Fas antibody Jo-2 was completely prevented by a single dose of DEVD-CHO and, as previously shown, by IETD-CHO at 90 min. Both inhibitors prevented <prot>procaspase-3</prot> and <prot>procaspase-9</prot> processing. Thus, there are fundamental differences in the efficacy of caspase inhibitors in these two models. We conclude that Fas may rely exclusively on <prot>caspase-8</prot> activation and mitochondria to activate <prot>caspase-3</prot>, which can process more <prot>procaspase-8</prot> and thus propagate the amplification of the apoptotic signal. TNF can activate a similar signaling pathway. However, alternative signaling mechanisms seem to exist, which can compensate if the main pathway is blocked.</AbstractText>
