Protective effects of Alpha-lipoic acid on MeHg-induced oxidative damage and intracellular Ca2+ dyshomeostasis in primary cultured neurons

Methylmercury (MeHg) is one of the ubiquitous environmental toxicant that leads to long-lasting neurological deficits in animals and humans. However, the mechanisms of MeHg-induced neuronal cell death are incompletely understood. Treatment of neuronal cells with MeHg (0-2M) for 0.5-12h, or pretreated with LA (12.5-100M) for 0.5-6h resulted in toxic effects of primary cultured neurons concentration- and time-dependently. For further experiments, 12.5, 25, and 50M of LA pretreatment for 3h followed by 1M MeHg for 6h were performed for the examination of the responses of neurons. Exposure of MeHg resulted in damages of neurons, which were shown by a loss of cell viability, and supported by high levels of lactate dehydrogenase (LDH) release, apoptosis, and morphological changes. In addition, neurons were sensitive to MeHg-mediated oxidative stress, a finding that is consistent with ROS over-production, leading to decrease Ca2+-ATPase activity and increase intracellular free calcium. Moreover, expressions of NMDA receptor subunits in neurons were down-regulated after MeHg exposure, and expression of NR2A mRNA and protein were much more sensitive to MeHg than those of NR1 and NR2B. On the contrary, pretreatment with LA presented a concentration-dependent prevention against MeHg-mediated cytotoxic effects of neurons. In conclusion, present results showed that oxidative stress and intracellular Ca(2+)dyshomeostasis resulting from MeHg exposure contributed to neuronal injury. LA could attenuate MeHg-induced neuronal toxicity via its antioxidant properties in primary cultured neurons.