Mechanisms of the apoptotic and necrotic actions of trimethyltin in cerebellar granule cells

In evaluating mechanisms of trimethyltin (TMT)-initiated neuronal damage, t he present study focused on involvement of reactive oxygen species, protein kinase C (PKC), and glutamate receptors. Exposure of cerebellar granule ce lls to TMT (0.01-0.1 muM) produced primarily apoptosis, but higher concentr ations were associated with cellular lactate dehydrogenase efflux and necro sis. TMT increased generation of cellular reactive oxygen species, which wa s inhibited by either L-NAME (inhibitor of nitric oxide synthase, NOS) or c atalase, indicating that both NO and H2O2, are formed on TMT exposure. Sinc e chelerythrine (selective PKC inhibitor) also inhibited oxidative species generation, PKC appears to play a significant role in TMT-induced oxidative stress. The metabotropic glutamate receptor antagonist, MCPG, (but not MK- 801) prevented oxidative species generation, indicating significant involve ment of metabotropic receptors (but not NMDA receptors) in TMT-induced oxid ative stress. NOS involvement in the action of TMT was confirmed through me asurement of nitrite, which increased concentration dependently. Nitrite ac cumulation was blocked by L-NAME, chelerythrine, or MCPG, showing that NO i s generated by TMT and that associated changes in NOS are regulated by a PK C-mediated mechanism. Oxidative damage by TMT was demonstrated by detection of elevated malondialdehyde levels. It was concluded that low concentratio ns of TMT (0.01-0.1 muM) cause apoptotic cell death in which oxidative sign aling is an important event. Higher concentrations of TMT initiate necrotic death, which involves both an oxidative and a non-oxidative component. TMT -induced necrosis but not apoptosis in granule cells is mediated by glutama te receptors.