The effect of curcumin on the cadmium-induced mitochondrial apoptosis pathway by metallothionein 2A regulation

Cadmium (Cd) is one of the most toxic heavy metals used in various industries, including metal plating, batteries and plastics and environmental pollutant. Cd in the environment is a detrimental factor that cannot be biodegraded and accumulates in human organs. The skin is the first target organ after Cd topical exposure. Curcumin is a natural dietary polyphenolic compound with many beneficial effects, including antioxidant, anti-inflammatory and anticancer activities. However, the effect of curcumin against Cd-induced toxicity in human keratinocytes has not been reported. In this study, we investigated the effects of curcumin against Cd-induced apoptosis in keratinocytes and the underlying molecular mechanisms. Cd resulted in apoptosis as shown by Annexin V/7-AAD double staining. Cd promoted the cleavage of poly (ADP ribose) polymerase-1 (PARP-1) and caspase 3 and suppressed Bcl-2. In addition, Cd induced the release of cytochrome c and Smac from the mitochondria into the cytosol, which is an intrinsic apoptosis-specific process. Curcumin inhibited the early and late apoptosis caused by Cd. The changes in apoptotic markers induced by Cd were significantly reversed by curcumin. Next, we evaluated the effect of curcumin on metallothionein (MT), a cysteine-rich protein that plays a key role in metal detoxification. Curcumin increased the level of MT2A mRNA and the expression of MT2. Interestingly, the antiapoptotic effects of curcumin were reversed under the knockdown of MT2A, suggesting that MT2A is a critical target of curcumin. These findings indicate the potential of curcumin as a novel compound for protection against Cd-mediated skin damage by MT2A modulation.