1861-P: Pioglitazone Modulates Hepatic Pyruvate Dehydrogenase and TCA Cycle Flux

Abstract

Background: The insulin sensitizing actions of the antidiabetic drug Pioglitazone (PIO) have classically been ascribed to the reversal of ectopic lipid accumulation. We recently demonstrated acute, direct metabolic effects of PIO in hepatocytes, linking the suppression of hepatic glucose production to an inhibition of mitochondrial pyruvate metabolism. As the relevance of this mechanism in vivo is unclear, we studied the effects of PIO on hepatic pyruvate metabolism in a mouse model of insulin resistance. Methods: Eight-week-old male ob/ob mice were placed on a regular diet (10% kcal fat) with (n=10) or without (n=10) 300 mg/kg PIO for four weeks before study during euglycemic-hyperinsulinemic clamp (5 mU/kg min). Endogenous glucose production (EGP), hepatic glycogen synthesis and anabolic/oxidative pyruvate flux ratio (PC/PDH) were determined from [3-3H] glucose infusion and 13C NMR isotopomer analysis using [2,3-13C] pyruvate. Livers were freeze-clamped in situ for pyruvate dehydrogenase (PDH), metabolite and protein analysis. Results: PIO treatment lowered EGP by 62% (4.6 ± 1.0 vs. 12.1 ± 1.7 mg/kg min; P<0.01) and increased glycogen synthesis 10-fold (19.7 ± 4.8 vs. 1.9 ± 0.8 μ mol/kg liver min; P<0.005), whereas PC/PDH remained unchanged. PIO also suppressed liver PDH activation (14.6 ± 3.4 vs. 29.6 ± 4.3 µmol/kg liver min; P<0.05), as well as acetylcarnitine (140 ± 18 vs. 297 ± 40) and acetyl-CoA (17.7 ± 2.4 vs. 47.8 ± 8.8 µmol/kg liver) concentrations (P<0.01), whilst liver PDK4 protein expression was increased 46% compared to controls (P<0.05). Conclusions: Inhibition of PDH activation by Pioglitazone curtails mitochondrial acetyl-CoA delivery, relieving allosteric stimulation of pyruvate carboxylase and gluconeogenesis. Parallel reductions in PDH flux and EGP reconcile an unchanged PC/PDH ratio, suggesting an overall slowing of TCA cycle flux with PIO. These novel data highlight the therapeutic relevance of hepatic mitochondrial metabolism in the treatment of type 2 diabetes and liver disease. Disclosure C. Shannon: None. M. Ragavan: None. R.A. DeFronzo: Advisory Panel; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Elcelyx Therapeutics, Inc., Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Novo Nordisk Inc. Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Merck & Co., Inc. Speaker's Bureau; Self; AstraZeneca, Novo Nordisk Inc. M. Merritt: None. L. Norton: None. Funding University of Florida’s Southeast Center for Integrated Metabolomics (U24DK097209); National Institutes of Health