Inorganic mercury pre-exposures protect against methyl mercury toxicity in NSC-34 (neuron x spinal cord hybrid) cells.

A neuron spinal chord x hybrid (NSC-34) cell culture derived from neonatal mouse was characterized for studies on mercury toxicity. Exposure of NSC-34 cells to methyl mercury chloride (MeHgCl) (0-16 microM) resulted in significant dose-dependent cell damage and death (P < 0.05). MeHgCl was more toxic than inorganic mercury (Hg2+) for both the NSC-34 cells and its parent neuroblastoma cell line N18TG-2 (P < 0.05). Hg2+, but not ZnCl2 or MeHg exposure induced metallothionein (MT) (P < 0.05). To mimic the increase in Hg2+ in the mammalian brain with long term MeHg exposure, the cells were treated with 1 microM mercuric chloride (HgCl2) for five passages before exposure to MeHgCl (1-16 microM) for 48 h. MeHgCl toxicity was measured by trypan blue exclusion, reduction of resazurin dye and acid phosphatase activity. Pre-exposure to HgCl2 lessened the toxicity as shown by trypan blue exclusion (P = 0.0559) and reduction of resazurin (P = 0.0001). Pre-exposure to HgCl2 also resulted in induction of MT (P = 0.0066) and lessened the decrease of reduced glutathione (GSH) (P = 0.0013). These results suggest that MT and GSH may play a protective role in methyl mercury induced neurotoxicity of neuron spinal chord cells. The NSC-34 hybrid cell line can be a useful model for the study of MeHg neurotoxicity.