Metabolism and toxicity of methyl iodide in primary dissociated neural cell cultures

The metabolism and the toxicity of methyl iodide (Mel) has been studied in primary dissociated neuronal and glial murine cell cultures to further characterize the mechanisms of monohalomethane neurotoxicity. Measurement of intracellular glutathione (GSH) concentrations in cerebellar and cerebral cultures revealed GSH levels (21.6 +/- 1.9 and 29.1 +/- 1.9 nmol/mg protein, respectively) close to brain GSH levels measured in vivo. A GSH-depleting effect of Mel was demonstrated, with an ED50 for a 5 min exposure of 0.2 and 0.5 mM for glial and mixed (neurons + glia) cultures, respectively. Mel-induced GSH depletion was correlated with its neurotoxicity as the two powerful protective agents of monohalomethane toxicity, 3-amino-1-[m-(trifluoromethyl) phenyl]-2-pyrazoline (BW 755C, 1 mM) and nordihydroguaiaretic acid (NDGA, 10 microM) provided a 20-fold protection against depletion of GSH levels following Mel exposure. When glia and neurons from cerebral cultures were exposed in suspension to increasing concentrations of Mel for 30 min at 37 degrees C, a concentration-dependent increase in the production of formaldehyde resulted. Formaldehyde appeared to be an indicator of Mel metabolism as its production was decreased by sulfasalazine, a compound which was shown to be an inhibitor of the glutathione-S-transferases in this culture system. Since BW 755C and NDGA had no effect on formaldehyde production, while sulfasalazine as well as semicarbazide, a protective agent against formaldehyde-producing toxicants, failed to protect the cells against Mel toxicity, mechanism(s) of Mel neurotoxicity appeared independent of the GSH-mediated metabolism of this compound. It is concluded that GSH-mediated metabolic biotransformation is not necessary for the neurotoxicity of the monohalomethanes, that GSH depletion may act as a starting point in the chain of events leading to neural cell death, and that glia may be more sensitive than neurons to this primary effect. Moreover, these results demonstrate the value of primary dissociated neuronal cell cultures for studies of biochemical mechanisms of neurotoxicity.