Decreased brain antioxidant systems, such as SOD, GPx, and catalase → failure in counterbalancing the increase in ROS production.SOD levels can be induced or reduced by OS, with various studies showing differing results.Similar to SOD, GPx levels may vary under OS conditions.Studies also indicate a significant decrease in catalase activity in specific brain regions of patients with AD, such as the parietotemporal cortex, basal ganglia, and amygdala, which aligns with the observed decline in antioxidant defenses in AD [61,62,63]. This evidence concerns the gene CAT and Alzheimer disease.