Insulin to treat Alzheimer's disease: just follow your nose?

Alzheimer's disease (AD) is linked to CNS insulin resistance, decreased expression of insulin and insulin receptor genes, and lower cerebrospinal insulin levels. Against this background, impaired brain insulin signaling may account for some of the cognitive deficits associated with this disease. Using the intranasal method, which effectively bypasses the blood-brain barrier to deliver and target insulin directly from the nose to the brain, a series of acute clinical trials involving healthy humans and AD patients have shown that increased CNS insulin action enhances learning and memory processes. This article summarizes and evaluates data from a recently published clinical trial, in which 4 months of intranasal insulin administration (20 IU insulin/day) preserved not only general cognition but also reduced the loss of metabolic integrity of the brain in adults with mild-to-moderate AD.