Quantitative neurotoxic effects of heavy metals and glutamate in mouse hippocampal neuronal cells

Exposure to toxic heavy metals, such as lead, mercury, arsenic, and cadmium (Pb²⁺, Hg²⁺, As⁵⁺, As³⁺, and Cd²⁺), is a known contributor to neurological dysfunction. Although the individual neurotoxicity of these metals has been well established, their synergistic effects with endogenous neurotoxins such as glutamate remain insufficiently explored. In this study, we investigated neurotoxic effects of the combination of glutamate and heavy metals using the HT-22 hippocampal neuronal cell line. The cells were exposed to each heavy metal alone or in combination with glutamate at low [LCR; glutamate: heavy metal = 1:0.0025] and high [HCR; glutamate: heavy metal = 1:0.025] concentration ratios. Cell viability was measured by the MTT assay, and synergistic effects were quantitatively assessed by the Chou-Talalay method using CompuSyn software. The results showed that Pb²⁺ exhibited consistent synergistic effects with glutamate at both concentration ratios. In addition, Hg²⁺ and As⁵⁺ demonstrated synergistic effects with glutamate under high concentration conditions. These findings highlight that certain heavy metals can potentiate glutamate-induced neurotoxicity through synergistic mechanisms. This study provides quantitative evidence for the enhanced neurotoxic potential of environmental heavy metals when combined with endogenous excitotoxins such as glutamate.