**3.3 Free radical cause lipid peroxidation**

The brain oxidative damage contributes to AD pathogenesis by the Aβ accumulation and amyloid plaque formation in the Alzheimer's disease of Tg2576 mice [58]. The imbalance of functioning endogenous antioxidant system leads to accumulation of free radicals, which not only induces the process of lipid peroxidation but also plays a central role in neurodegeneration [59]. Lipids are critical for plasticity and function of neuronal development. The abnormalities in lipid metabolism contribute to the pathogenesis of several neurodegenerative disorders like Alzheimer's disease and Parkinson's disease [60]. The relationship between lipid alterations in energy metabolism and mitochondrial dysfunction in neurodegenerative disorders [61]. Deposition of abnormal aggregated proteins and disruption of metal ion homeostasis are highly associated with oxidative stress [62]. The antioxdant and free radicals of lipid peroxidation and cognition, and cognitive response to an exercise intervention program, in adults with coronary artery disease at risk of dementia [63]. The brain is more susceptible to lipid peroxidation due to its high oxygen consumption, high level of redox metal ions, reduced antioxidant defense mechanism, and high level of polyunsaturated fatty acids [64].
