Comparative neurotoxic effects and mechanism of cadmium chloride and cadmium sulfate in neuronal cells

Cadmium (Cd), a known food pollutant, has been demonstrated in numerous studies to induce neurological damage. The pathogenic mechanisms of cadmium chloride (CdCl₂) and cadmium sulfate (CdSO₄) are generally attributed to the induction of oxidative stress and apoptosis. Nevertheless, the extent to which these two cadmium compounds exhibit differential concentration-dependent neurotoxic effects, as well as the specific underlying mechanisms involved, remain to be elucidated. In this study, the differential neurotoxic effects and underlying mechanisms were explored in PC12 cells which were treated with 0, 0.5, 1 and 2 μmol/L of CdCl₂ and CdSO₄ for 24 h, and C57BL/6J mice which were exposed to 0, 50, 100, and 200 mg/L CdSO₄ in drinking water for 18 weeks. Our present data indicate that both CdCl₂ and CdSO₄ elicit oxidative damage, genetic material damage, and apoptosis in PC12 cells, in which CdCl₂ exhibits higher toxicity than CdSO₄ at lower concentrations but lower toxicity at higher concentrations. Further mechanism analysis was conducted with the help of Non-labelled quantitative proteomics techniques and bioinformatics. The results indicated that the events related to oxidative stress as well as DNA damage and repair, such as Base excision repair, DNA replication, nucleotide excision repair, and chemical carcinogenesis-reactive oxygen species, are involved in the cadmium-induced neurotoxicity. Validation results basing on PC12 cells and mouse model indicated that the expressions of oxidative stress-related proteins Nrf2, Hmox1, Gsta3, and the DNA repair protein Nqo1 are upregulated, while the expressions of Pole, which involved in regulation DNA replication and repair, are downregulated. These results together revealed that oxidative damage occurs in PC12 cells under cadmium treatment, leading to genetic material damage and a decrease in DNA repair protein expression, which fails to repair damage promptly and induces cell death. Consequently, this study represents the first comprehensive comparison of the differential neurotoxic effects of CdCl₂ and CdSO₄ in neuronal cells across a range of concentrations. Furthermore, our findings also first reveal that cadmium may mediate its neurotoxic effects through the Nrf2/Hmox1/Gsta3/Nqo1/Pole signaling pathway. These results provide novel insights into the molecular underpinnings of cadmium-induced neurotoxicity.