Carbon-13 based dynamic nuclear polarization (DNP) experiments have shown tremendous potential for measuring glycolytic flux and pyruvate oxidation in living tissues and in vivo. However, the current stable of imaging agents cannot measure hepatic gluconeogenesis (GNG). We propose to develop [2- 13C]dihydroxyacetone (DHA) as an agent for measuring both GNG and hepatic glycolysis simultaneously. A ratio of three-carbon to hexose metabolites derived from DHA will provide a metric of net hepatic GNG. HP experiments will be compared to gold standard [U-13C]propionate/D2O based estimates of GNG and to targeted metabolomic profiles of glycolytic intermediates. We will measure GNG and glycolysis in three different rodent models.
Aims 1 and 2 will target metabolism in the perfused liver of the C57BLKS/J mouse (control) and the well-accepted db/db model of diabetes and hepatic glucose overproduction. We will also assess the sensitivity of the method to treatment using a protocol based on metformin administration.
Aim 3 of the grant transitions to in vivo experiments at 7 T that will be developed at the MD Anderson Center in collaboration with Dr. James Bankson. Dr. Bankson proposes to develop new constrained reconstruction algorithms that will enhance the localization of the 13C images, an extremely challenging issue for all hyperpolarized carbon-13 based imaging methods. We will use the Zucker (fa/fa) rat as a model of Type II diabetes. Subsequent experiments will be transferred back to UF for completion using the 11 T imaging system available through the National High Magnetic Field Lab at the McKnight Brain Institute. Relevance Diabetes is a worldwide epidemic that is projected to affect 300 million people worldwide by the year 2025. Methods for studying hepatic GNG are all based on tracer methodologies that require admittance to a general research center and administration of large amounts of isotopically labeled substrates. The method proposed here could be developed into a single exam that is integrated with standard magnetic resonance imaging protocols. We anticipate that the method proposed could be used to guide treatment plans for diabetes and determine the effectiveness of pharmacological interventions. Also, as a research target, the new method allows simultaneous measures of glycolysis and GNG. This observation is a fundamentally new insight into hepatic metabolism, and draws into light the nature of net hepatic GNG; it is the sum of the glycolytic and gluconeogenic activities within the tissue.
In this R01 we hypothesize that hepatic gluconeogenesis and glycolysis can be measured using hyperpolarized [2-13C]dihydroxyacetone. This hypothesis will be tested in the perfused mouse liver using protocols based upon feeding, fasting, the db/db mouse model of increased hepatic glucose output, and with treatment of elevated GNG by metformin. Separately, the same method will also be used to evaluate gluconeogenesis in vivo in a rat model of diabetes. This method should be diagnostic of changes associated with the onset of insulin resistance as well as the development of frank diabetes. Not only should the method be of use for research but could also potentially be developed for monitoring the response to treatment of a variety of hepatic pathologies that perturb metabolism.
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