Comparative analysis of in vitro neurotoxicity of methylmercury, mercury, cadmium, and hydrogen peroxide on SH-SY5Y cells

Mercury (Hg) and cadmium (Cd) are the major toxic heavy metals and are known to induce neurotoxicity. Although many studies have shown that several heavy metals have neurotoxic effects, the cellular and molecular mechanisms thereof are still not clear. Oxidative stress is reported to be a common and important mechanism in cytotoxicity induced by heavy metals. However, the assays for identifying toxic mechanisms were not performed under the same experimental conditions, making it difficult to compare toxic properties of the heavy metals. In this study, we investigated the mechanisms underlying neurotoxicity induced by heavy metals and H₂O₂, focusing on cell death, cell proliferation, and oxidative stress under the same experimental condition. Our results showed that MeHg caused lactate dehydrogenase (LDH) release, caspase activation and cell-cycle alteration, and ROS generation in accordance with decreased cell viability. HgCl₂ caused LDH release and cell-cycle alteration, but not caspase activation. CdCl₂ had a remarkable effect on the cell cycle profiles without induction of LDH release, caspase activation, or ROS generation. Pretreatment with N-acetyl-l-cysteine (NAC) prevented the decrease in cell viability induced by MeHg and HgCl₂, but not CdCl₂. Our results demonstrate a clear difference in neurotoxic mechanisms induced by MeHg, HgCl₂, CdCl₂ or H₂O₂ in SH-SY5Y cells. Elucidating the characteristics and mechanisms of each heavy metal under the same experimental conditions will be helpful to understand the effect of heavy metals on health and to develop a more effective therapy for heavy metal poisoning.