BACKGROUND. Dietary intake of saturated fat is a likely contributor to nonalcoholic fatty liver disease (NAFLD) and insulin resistance, but the mechanisms that initiate these abnormalities in humans remain unclear. We examined the effects of a single oral saturated fat load on insulin sensitivity, hepatic glucose metabolism, and lipid metabolism in humans. Similarly, initiating mechanisms were examined after an equivalent challenge in mice. METHODS. Fourteen lean, healthy individuals randomly received either palm oil (PO) or vehicle (VCL). Hepatic metabolism was analyzed using in vivo ¹³C/³¹P/¹H and ex vivo ²H magnetic resonance spectroscopy before and during hyperinsulinemic-euglycemic clamps with isotope dilution. Mice underwent identical clamp procedures and hepatic transcriptome analyses. RESULTS. PO administration decreased whole-body, hepatic, and adipose tissue insulin sensitivity by 25%, 15%, and 34%, respectively. Hepatic triglyceride and ATP content rose by 35% and 16%, respectively. Hepatic gluconeogenesis increased by 70%, and net glycogenolysis declined by 20%. Mouse transcriptomics revealed that PO differentially regulates predicted upstream regulators and pathways, including LPS, members of the TLR and PPAR families, NF-κB, and TNF-related weak inducer of apoptosis (TWEAK). CONCLUSION. Saturated fat ingestion rapidly increases hepatic lipid storage, energy metabolism, and insulin resistance. This is accompanied by regulation of hepatic gene expression and signaling that may contribute to development of NAFLD. REGISTRATION. ClinicalTrials.gov NCT01736202. FUNDING. Germany: Ministry of Innovation, Science, and Research North Rhine–Westfalia, German Federal Ministry of Health, Federal Ministry of Education and Research, German Center for Diabetes Research, German Research Foundation, and German Diabetes Association. Portugal: Portuguese Foundation for Science and Technology, FEDER – European Regional Development Fund, Portuguese Foundation for Science and Technology, and Rede Nacional de Ressonância Magnética Nuclear.

Intracellular lipids and their synthesis contribute to the mechanisms and complications of obesity associated diseases. We describe an NMR approach that provides an abbreviated lipidomic analysis and concurrent lipid biosynthetic fluxes. Following deuterated water administration, positional isotopomer analysis by deuterium NMR of specific lipid species was used to examine flux through de novo lipogenesis (DNL), fatty acid (FA) elongation, desaturation and triglyceride-glycerol synthesis. The NMR method obviated certain assumptions regarding sites of enrichment and exchangeable hydrogens required by mass isotope methods. The approach was responsive to genetic and pharmacologic gain or loss of function of DNL, elongation, desaturation and glyceride synthesis. BDF1 mice consuming a high fat or matched low fat diet for 35 weeks were examined across feeding periods to determine how flux through these pathways contribute to diet induced fatty liver and obesity. HFD mice had increased rates of fatty acid elongation and glyceride synthesis. However DNL was markedly suppressed despite insulin resistance and obesity. We conclude that most hepatic triglycerides in the liver of HFD mice were formed from the re-esterification of existing or ingested lipids, not DNL.

Context: People with prediabetes are at high risk of developing diabetes. Objective: The objective of this study was to determine the pathogenesis of fasting and postprandial hyperglycemia in prediabetes. Design: Glucose production, gluconeogenesis, glycogenolysis, and glucose disappearance were measured before and during a hyperinsulinemic clamp using [6,6-²H₂]glucose and the deuterated water method corrected for transaldolase exchange. Setting: The study was conducted at the Mayo Clinic Clinical Research Unit. Participants: Subjects with impaired fasting glucose (IFG)/normal glucose tolerance (NGT) (n = 14), IFG/impaired glucose tolerance (IGT) (n = 18), and normal fasting glucose (NFG)/NGT (n = 16) were studied. Intervention: A hyperinsulinemic clamp was used. Outcome Measures: Glucose production, glucose disappearance, gluconeogenesis, and glycogenolysis were measured. Results: Fasting glucose production was higher (P < .0001) in subjects with IFG/NGT than in those with NFG/NGT because of increased rates of gluconeogenesis (P = .003). On the other hand, insulin-induced suppression of glucose production, gluconeogenesis, glycogenolysis, and stimulation of glucose disappearance all were normal. Although fasting glucose production also was increased (P = .0002) in subjects with IFG/IGT, insulin-induced suppression of glucose production, gluconeogenesis, and glycogenolysis and stimulation of glucose disappearance were impaired (P = .005). Conclusions: Fasting hyperglycemia is due to excessive glucose production in people with either IFG/NGT or IFG/IGT. Both insulin action and postprandial glucose concentrations are normal in IFG/NGT but abnormal in IFG/IGT. This finding suggests that hepatic and extrahepatic insulin resistance causes or exacerbates postprandial glucose intolerance in IFG/IGT. Elevated gluconeogenesis in the fasting state in IFG/NGT and impaired insulin-induced suppression of both gluconeogenesis and glycogenolysis in IFG/IGT suggest that alteration in the regulation of these pathways occurs early in the evolution of type 2 diabetes.

Hepatic glucose synthesis from glycogen, glycerol, and the tricarboxylic acid (TCA) cycle was measured in five overnight-fasted subjects by¹H,²H, and¹³C NMR analysis of blood glucose, urinary acetaminophen glucuronide, and urinary phenylacetylglutamine after administration of [1,6-¹³C₂]glucose,²H₂O, and [U-¹³C₃]propionate. This combination of tracers allows three separate elements of hepatic glucose production (GP) to be probed simultaneously in a single study: 1) endogenous GP, 2) the contribution of glycogen, phospho enolpyruvate (PEP), and glycerol to GP, and 3) flux through PEP carboxykinase, pyruvate recycling, and the TCA cycle. Isotope-dilution measurements of [1,6-¹³C₂] glucose by¹H and¹³C NMR indicated that GP in 16-h-fasted humans was 10.7 ± 0.9 μmol · kg⁻¹· min⁻¹.²H NMR spectra of monoacetone glucose (derived from plasma glucose) provided the relative²H enrichment at glucose H-2, H-5, and H-6 S, which, in turn, reflects the contribution of glycogen, PEP, and glycerol to total GP (5.5 ± 0.7, 4.8 ± 1.0, and 0.4 ± 0.3 μmol · kg⁻¹· min⁻¹, respectively). Interestingly,¹³C NMR isotopomer analysis of phenylacetylglutamine and acetaminophen glucuronide reported different values for PEP carboxykinase flux (68.8 ± 9.8 vs. 37.5 ± 7.9 μmol · kg⁻¹· min⁻¹), PEP recycling flux (59.1 ± 9.8 vs. 27.8 ± 6.8 μmol · kg⁻¹· min⁻¹), and TCA cycle flux (10.9 ± 1.4 vs. 5.4 ± 1.4 μmol · kg⁻¹· min⁻¹). These differences may reflect zonation of propionate metabolism in the liver.