Oxidative stress and Parkinson's disease: conflict of oxidant-antioxidant systems.

Parkinson's disease (PD) is defined as a chronic neurodegenerative disorder which is diagnosed mostly by its clinical manifestations. Reactive oxygen species (ROS) are considered as key modulators in the development of PD. Despite the intensive investigations, antioxidant-dependent molecular mechanisms of initiation and development of PD are controversial. Free radicals cause serious damage and death of dopamine producing cells when antioxidant capacity of the cells is reduced against oxidative stress (OxS). Many intracellular reactions create ROS, including activation of NADPH oxidase (NOX), mitochondrial dysfunction, and hydrogen peroxide (H₂O₂) decomposition. On the contrary, natural antioxidants, vitamins, proteins, and antioxidant signaling pathways are major factors to neutralize ROS and its destructive effects. The functional role of nuclear factor E2-related factor 2, Heme oxygenase-1, and selenium against ROS-dependent initiation and progression of PD is elucidated. In this review, we collected multiple factors that play the main role in the initiation, development, and pathogenesis of PD and we discussed their function in the PD.