Real-time detection of hepatic gluconeogenic and glycogenolytic states using hyperpolarized [2-13c]dihydroxyacetone

Glycogenolysis and gluconeogenesis are sensitive to nutritional state, and the net direction of flux is controlled by multiple enzymatic steps. This delicate balance in the liver is disrupted by a variety of pathological states including cancer and diabetes mellitus. Hyperpolarized carbon-13 magnetic resonance is a new metabolic imaging technique that can probe intermediary metabolism nondestructively. There are currently no methods to rapidly distinguish livers in a gluconeogenic from glycogenolytic state. Here we use the gluconeogenic precursor dihydroxyacetone (DHA) to deliver hyperpolarized carbon-13 to the perfused mouse liver. DHA enters gluconeogenesis at the level of the trioses. Perfusion conditions were designed to establish either a gluconeogenic or a glycogenolytic state. Unexpectedly, we found that [2-¹³C]DHA was metabolized within a few seconds to the common intermediates and end products of both glycolysis and gluconeogenesis under both conditions, including [2,5-¹³C]glucose, [2-¹³C]glycerol 3-phosphate, [2-¹³C]phosphoenolpyruvate (PEP), [2-¹³C]pyruvate, [2-¹³C]alanine, and [2-¹³C]lactate. [2-¹³C]Phosphoenolpyruvate, a key branch point in gluconeogenesis and glycolysis, was monitored in functioning tissue for the first time. Observation of [2-¹³C]PEP was not anticipated as the free energy difference between PEP and pyruvate is large. Pyruvate kinase is the only regulatory step of the common glycolytic-gluconeogenic pathway that appears to exert significant control over the kinetics of any metabolites of DHA. A ratio of glycolytic to gluconeogenic products distinguished the gluconeogenic from glycogenolytic state in these functioning livers. This work was supported, in whole or in part, by National Institutes of Health Grants P41 EB015908 (to K. X. M., C. R. M., and M. E. M.), R01 DK058398 (to S. S. and S. C. B.), R01 CA157996 (to R. J. D.), and R21 EB016197 and R37 HL34557 (to M. E. M.). This work was also supported by Robert A. Welch Foundation Grants I-1733 (to R. J. D.) and I-1804-01 (to S. C. B.) and the Damon Runyon Cancer Research Foundation (to R. J. D.), and Cancer Prevention Research Institute of Texas (CPRIT) Grant RP-101243 (to M. E. M.).