INS and Alzheimer disease: What is particularly alarming is that peripheral insulin resistance, as occurs in Type 2 diabetes mellitus (T2DM), contributes to AD and cognitive impairment by reducing brain insulin uptake and increasing brain levels of Aβ, tau-phosphorylation, oxidative stress, pro-inflammatory cytokines, advanced glycation end products, dyslipidemia, and apoptosis [12,13,37–41].