Cytotoxic effects of cadmium and zinc co-exposure in PC12 cells and the underlying mechanism

Abstract Cadmium (Cd 2+ ) is a well studied inducer of cellular necrosis and apoptosis. Zinc (Zn 2+ ) is known to inhibit apoptosis induced by toxicants including Cd 2+ both in vitro and in vivo . The mechanism of Zn 2+ -mediated protection from Cd 2+ -induced cytotoxicity is not established. In this study, we aimed to understand the effects of Zn 2+ on Cd 2+ -induced cytotoxicity and apoptosis using PC12 cells. Cell viability and DNA fragmentation assays in PC12 cells exposed to Cd 2+ and/or Zn 2+ revealed that Cd 2+ (5 and 10 μmol/L) alone induced significant cell death, and co-exposure to Zn 2+ (5, 10, and 100 μmol/L) for 48 h had a protective effect. Assessment of intracellular free sulfhydryl levels and lactate dehydrogenase activity suggested that Cd 2+ (10 μmol/L) induced oxidative stress and disrupted cell membrane integrity. Addition of Zn 2+ (10 and 100 μmol/L) reduced Cd 2+ -mediated cytotoxicity. Changes in expression of the apoptotic factors Bax, Bcl-2, Bcl-x, and cytochrome c were measured via western blot and expression of caspase 9 was detected via reverse transcriptase polymerase chain reaction. Western blots showed that Zn 2+ (10 and 100 μmol/L) suppressed Cd 2+ -induced apoptosis (10 μmol/L) by reducing cytochrome c release into the cytosol, and downregulating the proapoptotic protein, Bax. In addition, expression of caspase 9 was lower in Cd 2+ (5 μmol/L)-treated PC12 cells when co-treated with Zn 2+ (2 and 5 μmol/L). These findings suggest that the effective inhibition of Cd 2+ -induced apoptosis in PC12 cells by Zn 2+ might be due to suppression of mitochondrial apoptosis pathway and inhibition of Cd 2+ -induced production of reactive oxygen species.