The World Health Organization estimates that 422 million adults or 8.5% of the world?s adult population has diabetes. Despite the development of promising new treatments for the prevention and treatment of diabetes, the expense and inconvenience of newer therapies, coupled with new side effect profiles, mandate that we continue to develop novel strategies to direct therapies to those at greatest risk of developing type 2 diabetes mellitus (T2DM) and to identify potential new drug targets. This proposal addresses the contribution of the epoxyeicosatrienoic acids (EETs)/ soluble epoxide hydrolase (sEH) pathway to insulin sensitivity/resistance in humans. The EETs, P450 metabolites of arachidonic acid, are well-established naturally occurring vasodilators and anti-inflammatory lipids. Hydrolysis by sEH limits the activity of EETs, and reducing the hydrolysis of EETs by sEH prevents vascular, cardiovascular, and renal injury in rodent models. Expression and activity of sEH are increased in rodent models of obesity and diabetes. Studies in rodent models further suggest that decreasing the activity of sEH improves insulin sensitivity either by increasing signaling in insulin-sensitive tissues or by enhancing capillary recruitment. Our group has found that humans who carry a loss-of-function variant of the gene encoding for sEH (EPHX2, rs751141 or Arg287Gln) have decreased vascular resistance and increased insulin sensitivity, but we do not yet know the mechanism for increased insulin sensitivity and have not assessed insulin sensitivity using the most rigorous methods. In addition, we do not know the effect of human obesity on sEH activity. The purpose of the present proposal is to test the overarching hypothesis that genetic or pharmacological factors that decrease sEH activity improve insulin sensitivity, increase insulin-stimulated vasodilation, and increase tissue insulin signaling in obese individuals.
In Aim 1, we will test the hypothesis that the loss-of-function EPHX2 variant is associated with increased insulin sensitivity measured using hyperinsulinemic-euglycemic clamp, enhanced insulin-stimulated vasodilation, and increased insulin-signaling in muscle and adipose tissue in obesity. We will assess the effect of genotype on tissue sEH activity and EET concentrations.
In Aim 2, we will test the hypothesis that a novel orally bioavailable specific small molecule inhibitor of sEH will improve insulin sensitivity in obese individuals with prediabetes. This small molecule inhibitor of sEH, GSK2256294, has already been tested safely in over one hundred people and we hold an IND for its use. These studies promise to elucidate the physiological role of the EETs/sEH pathway in glucose homeostasis and insulin sensitivity in humans. Moreover, these studies could lead to strategies to identify those at highest risk of developing T2DM, as well as to the development of new pharmacological targets for the prevention and treatment of T2DM.
As the worldwide epidemic of obesity and diabetes grows, we must develop new strategies to identify those at highest risk for diabetes so we can target prevention, as well as discover new drug targets for treatment. Studies in animals, and now in people, suggest that genetic factors that decrease the activity of a naturally occurring enzyme called soluble epoxide hydrolase improve the sensitivity of the body to insulin. The purpose of this study is to understand how the activity of soluble epoxide hydrolase affects risk of diabetes and to develop pharmacological approaches to decrease the activity of this enzyme that could lead to new treatments for diabetes.