Involvement of hydroperoxide in mitochondria in the induction of apoptosis by the eicosapentaenoic acid.

Eicosapentaenoic acid (EPA) induced apoptosis of rat basophilic leukemia cells (RBL2H3 cells), whereas 100 microM linoleic acid (LA) had no significant effect. Cytochrome c was released at 4 h. Apoptosis was detected at 6 h after exposure to EPA and docosahexaenoic acid (DHA), and preceded the activation of caspase-3. Liberation of apoptosis-inducing factor (AIF) from mitochondria and its translocation into the nucleus were observed at 4 h. A broad-specificity caspase inhibitor, z-VAD-fmk, failed to suppress the apoptosis, suggesting that EPA induced caspase-independent apoptosis. On other hand, a poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor that blocks AIF translocation to the nucleus suppressed EPA-induced apoptosis. The level of hydroperoxide in the cells and mitochondria increased at the early phase of apoptosis within 2 h. On the contrary, elevation of hydroperoxide in mitochondria was not observed after treatment with LA. The EPA-induced apoptosis was abolished by prevention of the hydroperoxide elevation in mitochondria via overexpression of mitochondrial phospholipid hydroperoxide glutathione peroxidase (PHGPx). Neither cytochrome c nor AIF were released from mitochondria in the mitochondrial PHGPx-overexpressing cells. EPA also induced apoptosis in HeLa cells, but not in L929 or RAW264.7 cells. Enhancement of the hydroperoxide level in mitochondria was found in the EPA-sensitive HeLa cells after treatment with EPA, whereas no such enhancement was observed in the apoptosis-resistant L929 and RAW264.7 cells. These results suggest that the generation of hydroperoxide in mitochondria induced by EPA is associated with AIF release from mitochondria and the induction of apoptosis.