Central KATP Channels Modulate Glucose Effectiveness in Humans and Rodents.

Hyperglycemia is a potent regulator of endogenous glucose production (EGP). Loss of this "glucose effectiveness" is a major contributor to elevated plasma glucose concentrations in type 2 diabetes (T2D). KATP channels in the central nervous system have been shown to regulate EGP in humans and rodents. We examined the contribution of central KATP channels to glucose effectiveness. Under fixed hormonal conditions (studies using a pancreatic clamp), hyperglycemia suppressed EGP by ∼50% in both humans without diabetes and normal Sprague-Dawley rats. By contrast, antagonism of KATP channels with glyburide significantly reduced the EGP-lowering effect of hyperglycemia in both humans and rats. Furthermore, the effects of glyburide on EGP and gluconeogenic enzymes were abolished in rats by intracerebroventricular administration of the KATP channel agonist diazoxide. These findings indicate that about half of the suppression of EGP by hyperglycemia is mediated by central KATP channels. These central mechanisms may offer a novel therapeutic target for improving glycemic control in subjects with T2D.

Insulin sensitizing and anti-inflammatory effects of thiazolidinediones are heightened in obese patients.

OBJECTIVE: The American Diabetes Association has called for further research on how patients' demographics should determine drug choices for individuals with type 2 diabetes mellitus (T2DM). Here, using in-depth physiology studies, we investigate whether obese patients with T2DM are likely to benefit from thiazolidinediones, medications with a known adverse effect of weight gain. MATERIALS AND METHODS: Eleven obese and 7 nonobese individuals with T2DM participated in this randomized, placebo-controlled, double-blind, crossover study. Each subject underwent a pair of "stepped" pancreatic clamp studies with subcutaneous adipose tissue biopsies after 21 days of pioglitazone (45 mg) or placebo. RESULTS: Obese subjects demonstrated significant decreases in insulin resistance and many adipose inflammatory parameters with pioglitazone relative to placebo. Specifically, significant improvements in glucose infusion rates, suppression of hepatic glucose production, and whole fat expression of certain inflammatory markers (IL-6, IL-1B, and inducible nitric oxide synthase) were observed in the obese subjects but not in the nonobese subjects. Additionally, adipose tissue from the obese subjects demonstrated reduced infiltration of macrophages, dendritic cells, and neutrophils as well as increased expression of factors associated with fat "browning" (peroxisome proliferator-activated receptor gamma coactivator-1α and uncoupling protein-1). CONCLUSIONS: These findings support the efficacy of pioglitazone to improve insulin resistance and reduce adipose tissue inflammation in obese patients with T2DM.