A novel neuroprotective mechanism of riluzole: Direct inhibition of protein kinase C

In addition to its antiexcitotoxic action, the anti-amyotrophic lateral scl erosis (ALS) neuroprotectant riluzole protects against nonexcitotoxic oxida tive neuronal injury. In light of evidence that protein kinase C (PKC) medi ates oxidative stress in cortical culture, we examined the possibility that riluzole's antioxidative neuroprotection involves PKC inhibition. Riluzole (30 mu M) blocked phorbol 12-myristate 13-acetate (PMA)-induced increases in membrane PKC activity in cultured cortical cells. Suggesting a direct ac tion, riluzole also inhibited the activity of purified PKC. Consistently, b oth PKC depletion and oxidative neuronal death induced by PMA were markedly attenuated by riluzole. The site of action of riluzole on PKC was not like ly the diacylglycerol binding site but the catalytic domain, since riluzole did not alter radiolabeled phorbol-12,13-dibutyrate binding, but inhibited PKM, the catalytic domain of PKC. However, increasing ATP concentrations d id not alter the inhibition of PKC by riluzole, making it unlikely that ril uzole is a competitive inhibitor of ATP binding at PKM. Present results hav e demonstrated that riluzole directly inhibits PKC, which action may contri bute to its antioxidative neuroprotective effects. In addition, it appears possible that PKC inhibition may be able to explain some of its well-known channel inhibitory and neuroprotective effects. Combined with findings that PKC activity is increased in ALS, the present results suggest that PKC may be a potential therapeutic target in ALS. (C) 2000 Academic Press.