A second look into the oxidant mechanisms in Alzheimer's disease

Oxidative damage is a major feature of Alzheimer's disease pathophysiology. Instead of succumbing to these oxidative abnormalities, neurons upregulate antioxidant defenses, which suggest a novel balance in oxidant homeostasis in Alzheimer's disease. Evidence indicates that in the initial phase of Alzheimer's disease development, amyloid-beta deposition and hyperphosphorylated tau are consequences of oxidative stress and function as a primary line of antioxidant defense. However, during the progression of the disease, the antioxidant activity of both agents evolves into pro-oxidant, representing a typical gain-of-function transformation. This transformation is due to an increase in reactive species and a decrease in clearance mechanisms. However, the notion that amyloid-beta and hyperphosphorylated tau function as protective components in the early stages of Alzheimer's disease brings into serious question the rationale of current therapeutic strategies aimed to remove both amyloid-beta and hyperphosphorylated tau.