Protective effects of [alpha]-Lipoic acid and its Polyrotaxanes complexes against cisplatin induced DNA damage and its Apoptotic mechanism inducing in human lung epitherial cancer cells

Abstract

[alpha]-Lipoic acid(LA) is a naturally-occurring antioxidant found in mitochondria of plant and human being. Thai spinach (Spinacea oleracea) was selected to extract natural LA. It formed complex with polyrotaxanes (PRx) to deliver and enhance the permeation through the skin to prevent DNA damage. Double strand DNA (dsDNA), human lung cancer H-460 cells and skin fibroblast cells were used in this study. The result showed that LA could protect the DNA damage and prevent the formation of DNA-platinum adducts those inducing cytotoxicity. Moreover, it had high efficacy to recover the DNA damage when compared with other antioxidants. For enhancing the topical absorption of LA, PRx and cholesterol modified PRx complexes were developed. The ex-vivo permeation study was investigated using the stratum corneum (SC) as a model membrance in Franze diffusion cell. LA-PRx complex enhance the permeation of LA through the SC when compared with LA solution. The cholesterol modified Prx gave the better permeation of free LA than LA-PRx complex. Both delivery systems were not toxic to fibroblast cells and they could stimulate the cell growth. Together, cholesterol modified PRx and even PRx might be a good approach for creating new biodegradable systems for topical application in term of enhancing the penetration through the skin. Studying the effect of LA in cancer cell, LA was found to be prooxidant by an induction of mitochondrial reactive oxygen species (ROS) generation and a concomitant increase in apoptosis in human lung epithelial cancer H-460 cells. The mechanism to induce the apoptosis of LA was found to be mediated through the mitochondrial death pathway which requires caspase-9 activation. Inhibition of caspase activity by pan-caspase inhibitor (z-VAD-fmk) or caspasd-9-specific inhibitor (z-LEHD-fmk) completely inhibited the apoptotic effect of LA. ROS inducing from LA activated the caspase-9 cascade and caused the downregulation of mitochondrial Bcl-2 protein through peroxide-dependent proteasomal degradation. Furthermore a novel prooxidant role of LA in apoptosis induction may be exploited for the treatment of cancer and related apoptosis disorders.