Induction of apoptosis by [6]-gingerol associated with the modulation of p53 and involvement of mitochondrial signaling pathway in B[a]P-induced mouse skin tumorigenesis

Abstract

Purpose: To unravel the molecular mechanisms underlying the chemopreventive potential of [6]-gingerol, a pungent ingredient of ginger rhizome (Zingiber officinale Roscoe, Zingiberaceae), against benzo[a]pyrene (B[a]P)-induced mouse skin tumorigenesis. Methods: Topical treatment of [6]-gingerol (2.5 μM/animal) was given to the animals 30 min prior and post to B[a]P (5 μg/animal) for 32 weeks. At the end of the study period, the skin tumors/tissues were dissected out and examined histopathologically. Flow cytometry was employed for cell cycle analysis. Further immunohistochemical localization of p53 and regulation of related apoptogenic proteins were determined by Western blotting. Results: Chemopreventive properties of [6]-gingerol were reflected by delay in onset of tumorigenesis, reduced cumulative number of tumors, and reduction in tumor volume. Cell cycle analysis revealed that the appearance of sub-G1 peak was significantly elevated in [6]-gingerol treated animals with post treatment showing higher efficacy in preventing tumorigenesis induced by B[a]P. Moreover, elevated apoptotic propensity was observed in tumor tissues than the corresponding non-tumor tissues. Western blot analysis also showed the same pattern of chemoprevention with [6]-gingerol treatment increasing the B[a]P suppressed p53 levels, also evident by immunohistochemistry, and Bax while decreasing the expression of Bcl-2 and Survivin. Further, [6]-gingerol treatment resulted in release of Cytochrome c, Caspases activation, increase in apoptotic protease-activating factor-1 (Apaf-1) as mechanism of apoptosis induction. Conclusions: On the basis of the results we conclude that [6]-gingerol possesses apoptotic potential in mouse skin tumors as mechanism of chemoprevention hence deserves further investigation. © 2009 Springer-Verlag.