The role of NADPH oxidase 1-derived reactive oxygen species in paraquat-mediated dopaminergic cell death.

Oxidative stress is the common downstream effect of a variety of environmental neurotoxins that are strongly implicated in the pathogenesis of Parkinson's disease. We demonstrate here that the activation of NADPH oxidase 1 (Nox1), a specialized superoxide-generating enzyme complex, plays a key role in the oxidative stress and subsequent dopaminergic cell death elicited by paraquat. Paraquat increased the expression of Nox1 in a concentration-dependent manner in rat dopaminergic N27 cells. Rac1, a key component necessary for Nox1-mediated superoxide generation, also was activated by paraquat. Paraquat-induced reactive oxygen species generation and dopaminergic cell death were significantly reduced after pretreatment with apocynin, a putative NADPH oxidase inhibitor, and Nox1 knockdown with siRNA. Male C57BL/6 mice received intraperitoneal (IP) injections of paraquat (10 mg/kg) once every 3 days and showed increased Nox1 levels in the substantia nigra as well as a 35% reduction in tyrosine hydroxylase-positive dopaminergic neurons 5 days after the last injection. Preadministration of apocynin (200 mg/kg, IP) led to a significant decrease in dopaminergic neuronal loss. Our results suggest that Nox1-generated superoxide is implicated in the oxidative stress elicited by paraquat in DA cells, and it can serve as a novel target for pharmacologic intervention.