Abstract 18237: Inhibition of Adenylyl Cyclase Type 5 Protects Against Obesity and Diabetes

Abstract

Adenylyl cyclase type 5 (AC5) is one of 9 major isoforms of AC. Mice with AC5 gene disruption (knockout, KO) live one third longer than wild type (WT) littermates. Like caloric restriction, the most commonly studied model of longevity, the AC5KO mice weigh 12% less than WT (p<0.05) and have less body fat, i.e., adiposity index, calculated by dividing the sum weights of the three major fat pads (inguinal, retroperitoneal, gonadal) by the body weight, was 50% lower than WT (p<0.05). The first goal of this study was to determine if AC5KO mice are protected, not only against obesity, but also diabetes. Insulin sensitivity, assessed by blood glucose measurement following insulin injection, was improved by 24% compared to WT. Glucose tolerance was also improved, p<0.05. A major limitation of studies in genetically altered mouse models, is that it is difficult to translate these results to the bedside, since it is not possible to knock out a gene in patients. Accordingly, we identified a pharmacological inhibitor of AC5, vidaribine, and examined the extent to which it ameliorated obesity and diabetes. First we demonstrated its selectivity for AC5; the inhibitor reduced inotropic responses to isoproterenol more than WT only in AC5 cardiac transgenic mice, but not in AC6 cardiac transgenic mice. To induce obesity, WT mice were fed a high fat diet feeding for 2 months, increasing body weight by 51% over mice fed a standard diet. WT mice with high fat diet and AC5 inhibitor on board for an additional 3 months, compared with WT mice on vehicle and high fat diet, increased body weight and adiposity index less, p<0.05, by 20% and 28%, respectively, while insulin resistance was reduced by 76% and glucose tolerance was improved by 66% (p<0.05). In AC5KO mice on the high fat diet insulin resistance was also reduced and glucose tolerance was also improved compared to WT on the high fat diet, similar to that observed with the AC5 inhibitor on the high fat diet. Thus, inhibition of AC5 provides a novel target for obesity and diabetes; the effective pharmacological inhibitor of AC5 enhances its clinical relevance.