Zinc homeostasis may reverse the synergistic neurotoxicity of heavy metal mixtures in Caenorhabditis elegans

Heavy metal mixtures can cause nerve damage. However, the combined effects of metal mixtures are extremely complex and rarely studied. Zinc (Zn) homeostasis plays an integral role in neural function, but the role of Zn homeostasis in the toxicity of metal mixtures is not well understood. Here, we investigated the combined effects of manganese (Mn), lead (Pb) and arsenic (As) on nerves and the effect of Zn homeostasis on metal toxicity. Caenorhabditis elegans (Maupas, 1900) were exposed to single and multiple metals for 8 days, their movement, behavior, neurons and metal concentration were detected to evaluate the combined effect of metal mixtures. After nematodes were co-treated with metal mixtures and Zn, the nerve function, Zn concentration and redox balance were detected to evaluate the effect of Zn homeostasis on metal toxicity. The results showed that Mn + Pb and Pb + As mixtures induced synergistic toxicity for nematode nerves, which damaged movement, behavior and neurons, and decreased Zn concentration. While Zn supplementation recovered Zn homeostasis and promoted redox balance on nematodes, and then improved the nerve function. Our study demonstrated the combined effects of metal mixtures and the neuroprotective effect of Zn homeostasis. Therefore, assessment of metal mixtures toxicity should consider their interaction and the impacts of essential metals homeostasis.