Protective effects of 1α,25-(OH)₂D₃ against the neurotoxicity of glutamate and reactive oxygen species in mesencephalic culture

This study was undertaken to determine whether 1α,25-dihydroxyvitamin D3 [1α,25-(OH)₂D₃], an active metabolite of vitamin D, protects dopaminergic neurons against the neurotoxic effects of glutamate and dopaminergic toxins using rat mesecephalic culture. Brief glutamate exposure elicited cytotoxicity in both dopaminergic and non-dopaminergic neurons. Pretreatment, but not co-administration, of 1α,25-(OH)₂D₃ protected both types of neurons against the cytotoxicity of glutamate in a concentration- and time-dependent manner. The neuroprotective effect of 1α,25-(OH)₂D₃ was inhibited by the protein synthesis inhibitor, cycloheximide. To investigate the mechanisms of these neuroprotective effects, we examined the effects of 1α,25-(OH)₂D₃ on neurotoxicity induced by calcium ionophore and reactive oxygen species (ROS). Pretreatment with 1α,25-(OH)₂D₃ protected both types of neurons against the cytotoxicity induced by A23187 in a concentration-dependent manner. Furthermore, 24-h pretreatment with 1α,25-(OH)₂D₃ concentration-dependently protected both types of neurons from ROS-induced cytotoxicity. A 24-h incubation with 1α,25-(OH)₂D₃ inhibited the increase in intracellular ROS level following H₂O₂ exposure. A 24-h exposure to 1-methyl-4-phenylpyridium ion (MPP⁺) or 6-hydroxydopamine (6-OHDA) exerted selective neurotoxicity on dopaminergic neurons, and these neurotoxic effects were ameliorated by 1α,25-(OH)₂D₃. These results suggest that 1α,25-(OH)₂D₃ provides protection of dopaminergic neurons against cytotoxicity induced by glutamate and dopaminergic toxins by facilitating cellular functions that reduce oxidative stress.