Hydroxyl radicals and nitric oxide in neurotoxicity and neuroprotection.

In the light of both neurodestructive and neuroprotective properties of nitric oxide, we have analysed the influence of hydroxyl radicals in these actions of nitric oxide. Requirement of superoxide anions to generate the neurotoxic peroxynitrite and the fact that it decomposes to form the more cytotoxic hydroxyl radicals at physiological pH, indicate the active involvement of the latter molecule in the neurotoxic action. Recent evidences also indicates that nitric oxide can act as an antioxidant in vitro and in vivo. Hence, it is suggested that it is time for a critical in vivo analysis of this molecule during a number of neurotoxic events to conclusively establish its role in neuroprotection and/or neurotoxicity.