Chronic cadmium exposure induces Parkinson-like syndrome by eliciting sphingolipid disturbance and neuroinflammation in the midbrain of C57BL/6J mice

Cadmium (Cd) is known as a widespread environmental neurotoxic pollutant. Cd exposure is recently recognized as an etiological factor of Parkinson's disease (PD) in humans. However, the mechanism underlying Cd neurotoxicity in relation to Parkinsonism pathogenesis is unclear. In our present study, C57BL/6 J mice were exposed to 100 mg/L CdCl2 in drinking water for 8 weeks. It was found Cd exposure caused motor deficits, decreased DA neurons and induced neuropathological changes in the midbrain. Non-targeted lipidomic analysis uncovered that Cd exposure altered lipid profile, increased the content of proinflammatory sphingolipid ceramides (Cer), sphingomyelin (SM) and ganglioside (GM3) in the midbrain. In consistency with increased proinflammatory lipids, the mRNA levels of genes encoding sphingolipids biosynthesis in the midbrain were dysregulated by Cd exposure. Neuroinflammation in the midbrain was evinced by the up-regulation of proinflammatory cytokines at mRNA and protein levels. Blood Cd contents and lipid metabolites in Parkinsonism patients by ICP-MS and LC-MS/MS analyses demonstrated that elevated blood Cd concentration and proinflammatory lipid metabolites were positively associated with the score of Unified Parkinson's Disease Rating Scale (UPDRS). 3 ceramide metabolites in the blood showed good specificity as the candidate biomarkers to predict and monitor Parkinsonism and Cd neurotoxicity (AUC>0.7, p < 0.01). In summary, our present study uncovered that perturbed sphingomyelin lipid metabolism is related to the Parkinsonism pathogenesis and Cd neurotoxicity, partially compensated for the deficiency in particular metabolic biomarkers for Parkinsonism in relation to Cd exposure, and emphasized the necessity of reducing Cd exposure at population level.