Insulin resistance (IR) in type 2 diabetes mellitus, as well as in obesity, is expressed in a tissue specific manner. To gain new insight into the pathogenesis of IR and for assessing therapy, it would be very useful to have tissue specific methods of assessment that can be used in human investigations. The goal of this proposal is to develop and validate a novel triple-tracer positron emission tomography (PET) imaging method to examine in vivo insulin-stimulated blood flow, glucose transport and glucose phosphorylation in skeletal muscle in healthy and insulin resistant individuals. We will use this method to test the hypothesis that control over insulin stimulated glucose metabolism in skeletal muscle in distributed across flow, transport and phosphorylation. We also posit that insulin resistance derives from an impairment of this system of distributed control rather than from a single dominating constriction. We have identified five specific aims.
The first aim that of developing the triple tracer PET method, will be to use 15O-H2O to measure blood flow and tissue perfusion, 11C-3-O-methyl glucose as a selective tracer for glucose transport and 18F-2-deoxy-2-fluoro-glucose as a selective tracer for glucose transport and phosphorylation. Because of the differences in half-life of the three positrons (15O, 11C and 18F), these analogs will be used in series during one metabolic study in the same individual. We will use dynamic PET imaging to monitor the time course of tissue metabolism and our second aim is to develop and test mathematical models to extract quantitative physiological information. We will use compartmental and non-compartmental models, and parametric mapping, and test the appropriateness of each approach by statistical principles. The biochemical specificity of the 3 tracers will provide rigorous criteria for testing and optimizing these modeling methods.
The third aim will be to use the triple tracer PET method and modeling to study insulin resistance in type 2 diabetes mellitus and obesity.
The fourth aim will be to examine the effects of elevated FFA (achieved by lipid infusion) upon insulin-stimulated tissue perfusion, glucose transport and phosphorylation, and the fifth aim will be to examine enhancement of insulin sensitivity by exercise.
