Oxidation reactions in Parkinson's disease. Free radicals generated from oxidation reactions may contribute to the pathogenesis of Parkinson's disease (PD). Free radicals are capable of reacting almost instantaneously with membrane lipids and causing lipid peroxidation, membrane injury, and cell death. Dopamine is metabolized by oxidation reactions capable of generating free radicals. Recent evidence indicates that the substantia nigra of patients with PD contains increased iron, which enhances oxidation, and decreased glutathione, which protects against the formation of free radicals. Further, the end products of lipid peroxidation are increased in the substantia nigra of patients with PD, supporting the notions that free radicals are being generated and may contribute to dopamine neuronal death. This hypothesis suggests that antioxidant therapies may slow the rate of progression of PD and raises concern that metabolites of levodopa therapy may accelerate the rate of neuronal degeneration. 