Protective effects of cadmium chloride against UVB injury in mouse skin and in cultured human cells: a possible role of cadmium-induced metallothionein.

Metallothionein (MT) is a cysteine-rich protein with antioxidant and metal-chelating activities that is readily inducible by exposure to a variety of stimuli including heavy metals such as cadmium (Cd2+). We have investigated the protective effects of Cd2+ treatment on sunburn cell (SBC) induction in mouse skin in vivo and human cell survival in vitro after UVB exposure. The number of SBC in mouse ear skin was significantly reduced in Cd(2+)-treated mice (10 mumol CdCl2/kg) with each UVB dose (25, 50 and 100 mJ/cm2) compared with controls. Delay of UVB exposure after Cd2+ administration (24 h) and higher doses of CdCl2 (10-30 mumol/kg) were more efficient in reducing SBC formation. Human bladder cancer cells (MGH-U1) made tolerant to Cd2+ by repeated low dose exposure, or cells acutely exposed to high Cd2+ concentration showed increased tolerance (cell survival) to UVB injury. Electrophoretic-autoradiographic analysis of [35S]-cysteine-labeled protein synthesized by cultured cells after Cd2+ treatment revealed increased MT-like protein content. These results suggest that MT is inducible by exposure to Cd2+ in our system and may be a photoprotective agent against UVB-induced oxidative damage in mammalian skin.