Neurodegenrative Diseases The central nervous system (CNS) is particularly susceptible to the oxidants due to the presence of high lipid content, high consumption of oxygen, and low levels of antioxidant enzymes, for example, SOD is localized primarily in neurons, and GSH and GPx are localized in astrocytes [109]. The lipid peroxidation by ROS leads to progressive loss of membrane fluidity, decreases mem- brane potential, and increases permeability to ions such as Ca2?. The regions of the brain such as hippocampus, substantia nigra, and the striatum are particularly susceptible to attack by free radicals [110, 111]. The oxidative- stress state has been also implicated in several neurode- generative diseases such as Alzheimer's [112], Parkinson's [113], Huntington's, lateral amyotrophic sclerosis [114], and multiple Sclerosis [115]. Parkinson's Disease (PD) Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons (involve in learning, memory and motor control), especially in the midbrain area called the substantia nigra, accompanied by deposition of inclusion bodies (Lewy bodies) of a-synuclein. The redox imbalance causes oxidative damage to these neurons and begins to alter the synthesis and metabolic pathway of dopamine leads to a further increase in oxidative stress because of quinine formation [111]. The characteristic clinical symptoms of PD include, jerky movements, trembling of the hands and lips, and tremors [116]. Dopamine, a neuro-transmitter, can also act as a metal chelator, has the ability to generate H2O2 via Fenton reaction. Ceruloplasmin (an extracellular ferroxidase required for regulating cellular iron load and transport) oxidation results in the decreased ferroxidase activity followed by the accumulation of intracellular iron in neurons in PD. The increased levels of Fe?3 mediate the production of hydroxyl radicals, results in the damage of dopaminergic neurons in PD [117].
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