Does Insulin Resistance Contribute to Neuroinflammation, Cognitive Decline and Brain Senescence in Obesity?

Abstract

The burgeoning prevalence of obesity and overweight conditions from the age of adolescence and throughout the lifespan has reached epidemic proportions in industrialized nations throughout the globe. The development of insulin resistance is one of the most common observations in obesity and is associated with a systemic hypoxia in adipose tissue and a chronic inflammatory state. The insulin resistance affects multiple elements of substrate oxidation and oxidative free radical generation in both somatic and neural tissues and with cytokine-linked chronic inflammation likely originating in adipose tissue depots. In studies with aging congenic lean and obese rats chronic hyperinsulinemia and brain shrinkage has now been reported, albeit it in the absence of Type 2 diabetes (NIDDM), hypertension (HTN) or other comorbidities, thereby suggesting that aspects of disordered substrate metabolism including insulin resistance as commonly observed in obesity may be a key contributory factor in the development of a neuroinflammatory linked brain shrinkage with accompanying decreases in brain mass, protein and DNA content, and which were further compromised when fed an isocaloric high vs. a low glycemic insulinogenic diet containing sucrose vs. cornstarch respectively. These results suggest that chronic insulin resistance of obesity secondary at least in part to dietary factors represents a likely independent risk factor in the progression of neuroinflammation, DNA damage, brain shrinkage and neural senescence in this strain of obese rats.