Hepatic glucose synthesis from glycogen, glycerol, and the tricarboxylic acid (TCA) cycle was measured in five overnight-fasted subjects by 1H,2H, and 13C 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 by 1H and 13C 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 relative 2H 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.

A triple-tracer method was developed to provide absolute fluxes contributing to endogenous glucose production and hepatic tricarboxylic acid (TCA) cycle fluxes in 24-h-fasted rats by (2)H and (13)C nuclear magnetic resonance (NMR) analysis of a single glucose derivative. A primed, intravenous [3,4-(13)C(2)]glucose infusion was used to measure endogenous glucose production; intraperitoneal (2)H(2)O (to enrich total body water) was used to quantify sources of glucose (TCA cycle, glycerol, and glycogen), and intraperitoneal [U-(13)C(3)] propionate was used to quantify hepatic anaplerosis, pyruvate cycling, and TCA cycle flux. Plasma glucose was converted to monoacetone glucose (MAG), and a single (2)H and (13)C NMR spectrum of MAG provided the following metabolic data (all in units of micromol/kg/min; n = 6): endogenous glucose production (40.4+/-2.9), gluconeogenesis from glycerol (11.5+/-3.5), gluconeogenesis from the TCA cycle (67.3+/-5.6), glycogenolysis (1.0+/-0.8), pyruvate cycling (154.4+/-43.4), PEPCK flux (221.7+/-47.6), and TCA cycle flux (49.1+/-16.8). In a separate group of rats, glucose production was not different in the absence of (2)H(2)O and [U-(13)C]propionate, demonstrating that these tracers do not alter the measurement of glucose turnover.

Simple equations that relate glucose and glutamate 13 C-NMR multiplet areas to gluconeogenesis and pyruvate recycling during metabolism of |l,2,3-13 C3lpropionate are presented. In isolated rat livers, gluconeogenic flux was 1.2 times TCA cycle flux and about 40% of the oxaloacetate pool underwent recycling to pyruvate prior to formation of glucose. The 13 C spectra of glucose collected from rats after gastric versus intravenous administration of [l,2,3-13 C 3 ]propionate indicated that pyruvate recycling was slightly higher in vivo (49%) while glucose production was unchanged. This indicates that a direct measure of gluconeogenesis and pyruvate recycling may be obtained from a single 13 C-NMR spectrum of blood collected after oral administration of enriched propionate.

H and ex vivo2 H magnetic resonance spectroscopy before and during hyperinsulinemiceuglycemic 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. PO results in increased circulating TG, glucagon, and incretins. After PO administration, TG in plasma rose by 59% (area under the time curve [AUC], P < 0.001) and by 156% in chylomicrons (AUC, P = 0.009) (Figure 2A). The AUC for plasma free fatty acids (FFA) ( Figure 2B) and insulin concentrations ( Figure 2C) was unchanged, while the AUC for plasma C-peptide was 28% higher after PO ingestion versus VCL (P < 0.005, Figure 2D). Of note, FFA were increased at 300, 420, and 480 minutes. Blood glucose levels were not different between PO-and VCL-treated groups ( Figure 2E). Plasma glucagon rose by 41% (AUC, P < 0.0001) only after PO ingestion ( Figure 2F). Also, glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP) levels were markedly increased and remained elevated after PO ingestion (both P < 0.005) (Supplemental Figure 2; supplemental material available online with this article; https://doi.org/10.1172/ JCI89444DS1). Circulating levels of TNF-α, IL-6, fetuin-A, chemerin, omentin, and cortisol were not different between PO and VCL groups (P > 0.5 for all) (Supplemental Table 1). REGISTRATION. The Journal of Clinical Investigation C L I N I C A L M E D I C I N EPO induces insulin resistance at whole-body, liver, and adipose tissue levels. Insulin sensitivity was measured using hyperinsulinemic-euglycemic clamp tests in healthy humans. Steady state was reached (Supplemental Figure 1), and pertinent parameters were analyzed during this time. PO ingestion reduced WBIS by 25% compared with VCL treatment (P = 0.0005, Figure 3A). Furthermore, after PO, volunteers also showed a decrease of 22% (P = 0.002) in the rate of glucose disappearance (Rd), mostly due to a 33% (P = 0.01) reduction in glucose oxidation (GOX), while the rate of nonoxidative glucose disposal remained unchanged

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The liver has a central role in the regulation of systemic glucose and lipid fluxes during feeding and fasting and also relies on these substrates for its own energy needs. These parallel requirements are met by coordinated control of carbohydrate and lipid fluxes into and out of the Krebs cycle, which is highly tuned to nutrient availability and heavily regulated by insulin and glucagon. During progression of type 2 diabetes, hepatic carbohydrate and lipid biosynthesis fluxes become elevated, thus contributing to hyperglycaemia and hypertriacylglycerolaemia. Over this interval there are also significant fluctuations in hepatic energy state. To date, it is not known to what extent abnormal glucose and lipid fluxes are causally linked to altered energy states. Recent evidence that the glucose-lowering effects of metformin appear to be mediated by attenuation of hepatic energy generation places an additional spotlight on the interdependence of hepatic biosynthetic and oxidative fluxes. The transition from fasting to feeding results in a significant re-direction of hepatic glucose and lipid fluxes and may also incur a temporary hepatic energy deficit. At present, it is not known to what extent these variables are additionally modified by type 2 diabetes and/or non-alcoholic fatty liver disease. Thus, there is a compelling need to measure fluxes through oxidative, gluconeogenic and lipogenic pathways and determine their relationship with hepatic energy state in both fasting and fed conditions. New magnetic resonance-based technologies allow these variables to be non-invasively studied in animal models and humans.

Berberine (BBR) has recently been shown to improve insulin sensitivity in rodent models of insulin resistance. Although this effect was explained partly through an observed activation of AMP-activated protein kinase (AMPK), the upstream and downstream mediators of this phenotype were not explored. Here, we show that BBR supplementation reverts mitochondrial dysfunction induced by High Fat Diet (HFD) and hyperglycemia in skeletal muscle, in part due to an increase in mitochondrial biogenesis. Furthermore, we observe that the prevention of mitochondrial dysfunction by BBR, the increase in mitochondrial biogenesis, as well as BBR-induced AMPK activation, are blocked in cells in which SIRT1 has been knocked-down. Taken together, these data reveal an important role for SIRT1 and mitochondrial biogenesis in the preventive effects of BBR on diet-induced insulin resistance.

Mammalian liver disposes of acetaminophen and other ingested xenobiotics by forming soluble glucuronides that are subsequently removed via renal filtration. When given in combination with the stable isotopes 2H and 13C, the glucuronide of acetaminophen isolated from urine provides a convenient "chemical biopsy" for evaluating intermediary metabolism in the liver. Here, we describe isolation and purification of urinary acetaminophen glucuronide and its conversion to monoacetone glucose (MAG). Subsequent 2H and 13C NMR analysis of MAG from normal volunteers after ingestion of 2H2O and [U-13C3]propionate allowed a noninvasive profiling of hepatic gluconeogenic pathways. The method should find use in metabolic studies of infants and other populations where blood sampling is either limited or problematic.