Influence of Liver Triglycerides on Suppression of Glucose Production by Insulin in Men

Context: The ability of insulin to suppress hepatic glucose production is impaired among subjects with increased intrahepatic triglycerides (IHTG). However, little is known about the roles of insulin on the supporting fluxes of glucose production among patients with fatty liver. Objective: To evaluate the effects of insulin on fluxes through the three potential sources of plasma glucose (glycerol, the citric acid cycle, and glycogen) among patients with fatty liver. Design, Settings, Participants, and Intervention: Nineteen men with a range of IHTG (similar to 0.5% to 23%) were studied after an overnight fast and during hyperinsulinemia using magnetic resonance spectroscopy and stable isotope tracers. Main Outcome Measures: IHTG, gluconeogenesis from glycerol, gluconeogenesis from the citric acid cycle, glycogenolysis, and C-13-labeled glucose produced from the citric acid cycle during hyperinsulinemia were measured. Results: Men with high IHTG had higher fluxes through all pathways contributing to glucose production during hyperinsulinemia, compared to men with low IHTG, but they had similar fluxes after the fast. Consequently, men with fatty liver had impaired insulin efficiency in suppressing total glucose production as well as fluxes through all three biochemical pathways contributing to glucose. The detection of glucose isotopomers with C-13 arising from [U-C-13(3)] propionate ingested during hyperinsulinemia demonstrated continuous gluconeogenesis from the citric acid cycle in all subjects. Conclusions: These findings challenge the concept that individual glucose production pathways are selectively dysregulated during hepatic insulin resistance. Overproduction of glucose during hyperinsulinemia in men with fatty liver results from inadequate suppression of all the supporting fluxes of glucose production in response to insulin.