Mitochondrial involvement in regulation of apoptosis via redox state of external cytochrome c

Abstract

There is accumulating evidence that mitochondrial pathway of apoptosis can be regulated at post-cytochrome c level by the mechanism involving reduction of cytosolic cytochrome c. We and others have shown that oxidized cytochrome c is more potent in caspase activation than reduced form and that chemicals and enzymes that reduce cytochrome c may prevent caspase activation in several models of mitochondria-mediated cell death. In this study, we present our findings demonstrating that polyphenolic redox active plant compounds anthocyanins may prevent ischaemia-induced caspase activation in perfused rat heart and that this capacity of anthocyanins correlates with their cytochrome c reducing activity. We also demonstrate that the redox state of cytosolic cytochrome c may be regulated by mitochondria. In apoptotic cells with leaky outer membrane, cytosolic cytochrome c may be oxidized by cytochrome oxidase. Besides cytochrome c-oxidizing activity, mitochondria have NADH-dependent external cytochrome c-reducing activity. We found that mitochondria from different tissues have variable NADH-dependent external cytochrome c-reducing activity: the highest activity was found in liver mitochondria, the lowest — in brain mitochondria. External NADH-cytochrome c reductase activity was found to be insensitive to nitric oxide, but was inhibitable by S-nitrosothiols indicating involvement of -SH groups in activity of the enzyme. This NADH-dependent cytochrome c reducing activity is also suppressed in some pathological states such as during heart ischaemia. The activity is partially inhibited by DIDS, a selective inhibitor of anion channels. In liver mitochondria, cytochrome b5 reductase is the main enzyme responsible for NADH-dependent reduction of external cytochrome c. In contrast, heart mitochondria have relatively low content of this enzyme, and when VDAC (porin) was purified from heart mitochondria it was found to possess [...].