Cyclosporin A targets involved in protection against glutamate excitotoxicity

The toxicity of glutamate in neuronal cultures has been attributed in part to a mitochondrial dysfunction involving the permeability transition pore. The participation of the permeability transition pore in this process has b een pharmacologically demonstrated by the use of cyclosporin A, which inhib its pore opening by interaction with mitochondrial cyclophilin and, thus, p revents cell death and upstream events. Since cyclosporin A also acts on ca lcineurin, we have investigated which of the targets of cyclosporin A was r esponsible for the inhibition of glutamate-excitotoxicity in cerebrocortica l primary neuronal cultures. Reactive oxygen species production and early ( 30 min to 2 h) drop in ATP levels are initial events in glutamate excitotox icity taking place before neuronal death. Cyclosporin A did not inhibit rea ctive oxygen species production, but reduced the drop in ATP levels and sub sequent neuronal death. However, cyclosporin derivatives that do not bind t o calcineurin had smaller effect on survival than cyclosporin A. (regardles s of whether they were able to bind cyclophilin), indicating that cyclospor in A protects against glutamte toxicity also through calcineurin-related me chanisms. Consistent with this view, ATP loss appears to result from nitric oxide synthase (NOS) activation (including ealcineurin-dependent dephospho rylation) and nitric oxide (NO)/peroxinitrite-dependent increase in poly (A DP-ribose) polymerase activity, since it was reduced by inhibitors of these activities. Collectively, these results suggest that cyclosporin A exerts its: protective effects through calcineurin-dependent and independent mecha nisms. (C) 2000 Elsevier Science B.V. All rights reserved.