Resveratrol induces apoptosis involving mitochondrial pathways in mouse skin tumorigenesis

Resveratrol, a plant constituent enriched in the skin of grapes, is one of the most promising agents for chemoprevention. In the present study, resveratrol-induced apoptosis in 7, 12-dimethylbenz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA) promoted, mouse skin tumors. The chemopreventive effects of resveratrol in terms of delayed onset of tumorigenesis, cumulative number of tumors and average number of tumors/mouse were recorded. Resveratrol treatment resulted in regression of tumors (28%) after withdrawal of the TPA treatment. Induction of apoptosis by resveratrol in DMBA-TPA induced skin tumors was recorded by the appearance of a sub-G1 fraction (30%) using flow cytometry and an increase in the number of apoptotic cells by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay. Western blot analysis combined with multivariable flow cytometry, showed that resveratrol application induces the expression of the p53 and pro-apoptotic Bax, with concomitant decrease in anti-apoptotic protein Bcl-2. Alteration in Bax/Bcl2 ratio by resveratrol treatment resulted in apoptosis, which was associated with the release of cytochrome c and induction of apoptotic protease-activating factor-1(APAF-1). Further, this effect was found to result in cleaved fragments of caspase-9,-3, and poly (ADP-ribose) polymerase (PARP). These findings demonstrate for the first time that resveratrol induces apoptosis through activation of p53 activity in mouse skin tumors, thereupon suggesting its chemopreventive activity, through the modulation of proteins involved in mitochondrial pathway of apoptosis.