Pifithrin-alpha has a p53-independent cytoprotective effect on docosahexaenoic acid-induced cytotoxicity in human hepatocellular carcinoma HepG2 cells

Pifithrin-alpha (PFT) is an inhibitor of p53 and is known to protect against a variety of p53-mediated genotoxic agents. In this report, we examined the inhibitory effects of PFT against docosahexaenoic acid (DHA)-induced cytotoxicity in the human hepatocellular carcinoma (HCC) cell line HepG2. PFT significantly abrogated DHA-induced cytotoxicity in wild-type HepG2 cells (normal expression of p53) and after p53-knockdown by siRNA, as well as in Hep3B (p53 null) and Huh7 (p53 mutant) cells. DHA-induced cytotoxicity is mediated by induction of oxidative stress, and PFT inhibited this event, but it does not exert antioxidant effects. PFT significantly suppressed the release of cytochrome c from mitochondria to cytosol, as well as changes in the mitochondrial membrane potential (ΔΨM) by DHA. Therefore, protection of mitochondria by PFT is crucial for its inhibition of DHA-induced cytotoxicity. Although it has been reported that PFT is able to block p53 function, our data suggest that PFT also has a p53-independent inhibition mechanism. This work provided insights into the mechanisms of PFT action on DHA-induced cytotoxicity in HCC.