Endogenous Glucose Production Rate Research Articles

Post Prandial Glucose Turnover Differs Between Adolescents & Adults with Type 1 Diabetes: Triple Tracer Mixed Meal Study.

Insulin sensitivity (SI) varies with age in Type 1 diabetes (T1D). To compare postprandial glucose turnover and insulin sensitivity between adolescents and adults with T1D. Cross-sectional comparison. Clinical Research Unit. 21 early adolescents with T1D (T1D-adol) [12F; age: 11.5 ± 0.5yrs.; BMI: 19 ± 2 kg/m2], 13 adults with T1D (T1D-adult) [5F; 37.8 ± 9.1yrs.; BMI: 27 ± 2 kg/m2] and 14 anthropometrically matched adults without diabetes (ND) [7F; 26.9 ± 7.0yrs.; BMI: 25 ± 2.5 kg/m2]. Triple-tracer mixed meal study and oral glucose models. SI between T1D-adol and T1D-adult. Post-prandial glucose excursions were not different in T1D-adol vs T1D-adult (p = 0.111) but higher than in ND (p < 0.01). Insulin excursions were also similar in T1D-adol vs. T1D-adult (p = 0.600) and they were both lower (p < 0.05) compared to ND, while glucagon excursions were lower (p < 0.01) in T1D-adol than in T1D-adult and ND. Integrated rates of endogenous glucose production and glucose disappearance were lower in T1D-adol than in T1D-adult and in ND vs. T1D-adult but did not differ between T1D-adol and ND. Meal glucose appearance did not differ between groups. Insulin sensitivity (SI) in T1D-adol vs ND was similar (p = 0.299). However, SI was higher in T1D-adol and ND vs. T1D-adult (p < 0.01). We report differences in parameters of postprandial glucose turnover and insulin sensitivity between adults and early adolescents with T1D that could, at least in part, be due to the shorter duration of diabetes among T1D-adol. These data support the concept that over time with T1D endogenous glucose production increases and SI deteriorates.

An E115A Missense Variant in CERS2 Is Associated With Increased Sleeping Energy Expenditure and Hepatic Insulin Resistance in American Indians.

Genetic determinants of inter-individual differences in energy expenditure (EE) are largely unknown. Sphingolipids, such as ceramides, have been implicated in the regulation of human EE via mitochondrial uncoupling. In this study, we investigated whether genetic variants within enzymes involved in sphingolipid synthesis and degradation affect EE and insulin-related traits in a cohort of American Indians informative for 24-hour EE and glucose disposal rates during a hyperinsulinemic-euglycemic clamp. Association analysis of 10,084 genetic variants within 28 genes involved in sphingolipid pathways identified a missense variant (rs267738, A>C, E115A) in exon 4 of CERS2 that was associated with higher sleeping EE (+116 kcal/day) and increased rates of endogenous glucose production during basal (+5%) and insulin-stimulated (+43%) conditions, both indicators of hepatic insulin resistance. The rs267738 variant did not affect ceramide synthesis in HepG2 cells but resulted in a 30% decrease in basal mitochondrial respiration. In conclusion, we provide evidence that the CERS2 rs267738 missense variant may influence hepatic glucose production and post-absorptive sleeping metabolic rate.

Quantifying insulin-mediated and noninsulin-mediated changes in glucose dynamics during resistance exercise in type 1 diabetes.

Exercise can cause dangerous fluctuations in blood glucose in people living with type 1 diabetes (T1D). Aerobic exercise, for example, can cause acute hypoglycemia secondary to increased insulin-mediated and noninsulin-mediated glucose utilization. Less is known about how resistance exercise (RE) impacts glucose dynamics. Twenty-five people with T1D underwent three sessions of either moderate or high-intensity RE at three insulin infusion rates during a glucose tracer clamp. We calculated time-varying rates of endogenous glucose production (EGP) and glucose disposal (Rd) across all sessions and used linear regression and extrapolation to estimate insulin- and noninsulin-mediated components of glucose utilization. Blood glucose did not change on average during exercise. The area under the curve (AUC) for EGP increased by 1.04 mM during RE (95% CI: 0.65-1.43, P < 0.001) and decreased proportionally to insulin infusion rate (0.003 mM per percent above basal rate, 95% CI: 0.001-0.006, P = 0.003). The AUC for Rd rose by 1.26 mM during RE (95% CI: 0.41-2.10, P = 0.004) and increased proportionally with insulin infusion rate (0.04 mM per percent above basal rate, CI: 0.03-0.04, P < 0.001). No differences were observed between the moderate and high resistance groups. Noninsulin-mediated glucose utilization rose significantly during exercise before returning to baseline roughly 30-min postexercise. Insulin-mediated glucose utilization remained unchanged during exercise sessions. Circulating catecholamines and lactate rose during exercise despite relatively small changes observed in Rd. Results provide an explanation of why RE may pose a lower overall risk for hypoglycemia.NEW & NOTEWORTHY Aerobic exercise is known to cause decreases in blood glucose secondary to increased glucose utilization in people living with type 1 diabetes (T1D). However, less is known about how resistance-type exercise impacts glucose dynamics. Twenty-five participants with T1D performed in-clinic weight-bearing exercises under a glucose clamp. Mathematical modeling of infused glucose tracer allowed for quantification of the rate of hepatic glucose production as well as rates of insulin-mediated and noninsulin-mediated glucose uptake experienced during resistance exercise.

222-OR: Metformin Reduces Fasting Glycemia in Well-Controlled Type 2 Diabetes by Promoting Aerobic Glycolysis Independent of Decreasing Endogenous Glucose Production

It is well established that metformin improves glycemic control in individuals with poorly-controlled type 2 diabetes (T2D) by reducing rates of endogenous glucose production (EGP) mediated by inhibition of hepatic gluconeogenesis. However, the mechanism by which metformin reduces blood glucose levels in well-controlled individuals with T2D is still unknown. To address this question, we examined rates of EGP, lactate turnover and hepatic triglyceride (TAG), ATP and glycogen content in near-normoglycemic individuals with T2D (n=10, HbA1c 7±1%) with (M+; 1000 mg bid x 2 wks) and without (M-; 2 wks) metformin treatment using the PINTA method with [2H7]glucose and [3-13C]lactate tracer infusions in combination with 1H- /31P- /13C- magnetic resonance spectroscopy. Metformin treatment did not affect rates of EGP, but reduced fasting plasma glucose concentrations by 30% (p&amp;lt;0.01 vs. M-), which could be attributed to increased rates of glucose clearance (+18%, p&amp;lt;0.005 vs. M-) resulting in increased lactate production (+14%, p&amp;lt;0.01 vs. M-). These changes were associated with decreased hepatic ATP content (-20%, p&amp;lt;0.05 vs. M-), increased hepatic glycogen content (+40%, p&amp;lt;0.05 vs. M-) and no changes in hepatic TAG content. Conclusion: In contrast to the glucose-lowering effect of metformin in poorly-controlled T2D, which is due to reductions in gluconeogenesis, this study demonstrates that in well-controlled T2D metformin reduces fasting glycemia - independent of reductions in EGP - primarily by increasing rates of aerobic glycolysis as reflected by increased peripheral glucose clearance and lactate production as well as reduced hepatic ATP content, which is consistent with metformin-induced inhibition of mitochondrial electron transport chain activity. Disclosure T.Sarabhai: None. T.E.Lamoia: None. S.Friesl: None. M.Jonuscheit: None. K.Petersen: Advisory Panel; Novo Nordisk, Research Support; Merck Sharp &amp; Dohme Corp., Gilead Sciences, Inc. G.I.Shulman: Consultant; Novo Nordisk, DiCerna Pharmaceuticals, Inc., Bayer Consumer Care AG, Kriya Therapeutics, Arrowhead Pharmaceuticals, Inc., ESPERION Therapeutics, Inc., Other Relationship; AstraZeneca, Merck &amp; Co., Inc., Janssen Research &amp; Development, LLC, iMetabolic Biopharma Corporation, Maze Therapeutics, 89bio, Inc., Equator Therapeutics, Inc., Generian Pharmaceuticals, Fortress Biotech, Inc., OrsoBio, Aro Biotherapeutics Company, Stock/Shareholder; Levels Health, Inc. M.Roden: Advisory Panel; Eli Lilly and Company, Consultant; TARGET PharmaSolutions, Inc., Research Support; Boehringer-Ingelheim, Novo Nordisk, Novartis, Sanofi.

Acute sub-diaphragmatic anterior vagus nerve stimulation increases peripheral glucose uptake in anaesthetized rats

The sub-diaphragmatic vagus innervates various organs involved in the control of glucose homeostasis including the liver, pancreas and the intestines. In the current study, we investigated the effect of acute electrical stimulation of the anterior trunk of the sub-diaphragmatic vagus on glucose fluxes in anaesthetized adult male rats.After overnight fast, rats underwent either vagus nerve stimulation (VNS+, n = 11; rectangular pulses at 5 Hz, 1.5 mA, 1 msec pulse width) or sham stimulation (VNS-; n = 11) for 120 min under isoflurane anesthesia. Before stimulation, the rats received an i.v. bolus of 1 mL/kg of a sterilized aqueous solution containing 125 mg/mL of D-[6,6-2H2] glucose. Endogenous glucose production (EGP) and glucose clearance rate (GCR) were calculated by kinetic analysis from the wash-out of injected D-[6,6–2H2]glucose from the circulation.VNS+ resulted in lower glucose levels compared to the VNS- group (p < 0.05), with similar insulin levels. EGP was similar in both groups, but the GCR was higher in the VNS+ group compared to the VNS- group (p < 0.001). Circulating levels of the sympathetic transmitter norepinephrine were reduced by VNS+ relative to VNS- treatment (p < 0.01).It is concluded that acute anterior sub-diaphragmatic VNS causes stimulation of peripheral glucose uptake, while plasma insulin levels remained similar, and this is associated with lower activity of the sympathetic nervous system.

240-OR: Quantifying Glucose Utilization and Endogenous Glucose Production during Resistance Exercise in People with Type 1 Diabetes (T1D)

Glucose dynamics during and after resistance exercise in people with T1D is not well understood. We recruited 25 people with T1D to perform 3 separate sessions of in-clinic resistance exercise under low (basal) , medium (1.5x basal) , or high (3.0x basal) insulin infusion levels. Blood glucose was clamped by intravenous dextrose infusion 3 hours prior to, and 4 hours after a 45-minute session of strength training. Glucose tracer was infused to match the rate of endogenous glucose production (EGP) . Glucose and tracer data were used to fit a two-compartment model and quantify the rate of glucose disposal (Rd) and EGP. For 58 sessions across 25 participants, blood glucose levels remained constant during and after resistance exercise. The mean change in area under the curve (AUC) for Rd was not higher during resistance exercise compared to baseline (+1.2 mM, p=0.69) , but increased during previously published aerobic exercise (+12.5 mM, p&amp;lt;0.01) . Mean AUC for EGP rose during resistance exercise (+6.5 mM, p&amp;lt;0.01) primarily due to non-insulin mediated factors and the increase was higher than during aerobic exercise (+2.mM, p&amp;lt;0.01) . Resistance exercise is characterized by a strong rise in EGP that is predominantly driven by non-insulin mediated effects. This may mitigate drops in blood glucose caused by increased glucose utilization in peripheral tissues during anaerobic activity. Disclosure G.Young: None. M.Riddell: Advisory Panel; Zealand Pharma A/S, Zucara Therapeutics, Consultant; Eli Lilly and Company, Jaeb Center for Health Research, Speaker's Bureau; Dexcom, Inc., Eli Lilly and Company, Novo Nordisk. J.El youssef: None. P.G.Jacobs: Other Relationship; Pacific Diabetes Technologies, Research Support; Dexcom, Inc. N.S.Tyler: None. T.P.Nguyen: None. J.R.Castle: Advisory Panel; Insulet Corporation, Novo Nordisk, Zealand Pharma A/S, Stock/Shareholder; Pacific Diabetes Technologies. L.M.Wilson: n/a. D.Branigan: None. V.Gabo: None. F.H.Guillot: Stock/Shareholder; Pacific Diabetes Technologies. Funding National Institutes of Health (5R01DK110175, 1F30DK128914)

151-LB: Postprandial Glucose Metabolism Differs between Early Adolescents and Adults with Type 1 Diabetes

Postprandial glucose turnover in adolescents with type 1 diabetes (T1D) has not been investigated. To do so, we studied adolescents (n=15, age 11.5±0.5 yrs, BMI 19±2.3 kg/m2, HbA1c 7.5±1%, diabetes duration 4.6±3 yrs) and adults (n=15, age 36.3±9.4 yrs, BMI 27.1±2.1 kg/m2, HbA1c 6.9±1.1%, diabetes duration 18.1±9.6 yrs) with T1D after a mixed meal. Healthy adults (n=14, age 26.9 ± 7 yrs, BMI 24.9±2.5 kg/m2, HbA1c 5.0±0.3%) served as controls. T1D subjects administered their customary insulin bolus dose at meal onset. Rates of endogenous glucose production (EGP) , meal glucose appearance (MRa) and glucose disappearance (Rd) were calculated by the triple tracer method with stable isotopes ([1-13C] glucose, [2-13C] glucose and [6, 6-2H2] glucose) . Integrated glucose excursions did not differ between adolescents and adults with T1D during early (0-120 min) and total (0-300 min) postprandial periods. While basal EGP at start of the meal was higher (p&amp;lt;0.01) , integrated rates of EGP, MRa, Rd and glucose clearance were all lower (p&amp;lt;0.03) in adolescents than in adults with T1D during the early postprandial period and were numerically lower (p=0.08) during the total postprandial period (Figure1) . Taken together, the data demonstrates significant differences in postprandial glucose metabolism between adolescents and adults with T1D. Additional studies are ongoing to determine the causes of these differences. Disclosure F. Ruchi: None. D. Romeres: None. S. Gururaj: None. M. D. Deboer: Research Support; Dexcom, Inc., Tandem Diabetes Care, Inc. R. Basu: Consultant; Sparrow Pharmaceuticals Inc, Research Support; Abbott Diabetes, AstraZeneca. A. Basu: Speaker's Bureau; Zealand Pharma A/S. Funding DK 124886, DK 085516, DK 029953

195-OR: A Novel 13C5 Glutamine Tracer Method (Q Flux) Reveals a Key Role of Succinyl CoA Anaplerosis in Promoting Increased Rates of Hepatic Gluconeogenesis during Hyperglucagonemia

Hyperglucagonemia is a hallmark of type 2 diabetes mellitus (T2DM) and contributes to increased rates of endogenous glucose production (EGP) , mostly through increased rates of hepatic gluconeogenesis (GNG) , but the anaplerotic pathways and respective substrates that support this process are unclear. To address this question, we developed a novel and extensively validated 13C5 glutamine-based in vivo metabolic flux analysis method (Q Flux) , which allows for quantitation of both the relative and absolute rates of hepatic gluconeogenesis from pyruvate (via pyruvate carboxylase [PC]) , succinyl CoA (via methylmalonyl CoA mutase [MUT]) , glutamine (via glutaminase [GLS2]) , and glycerol. Male Sprague-Dawley rats (∼300 g) were infused for 90 minutes with either low-dose (LD) glucagon (1.25 ng/[kg-min]) or high-dose (HD) glucagon (ng/[kg-min]) , plus insulin (0.5 mU/[kg-min]) , somatostatin (4 μg/[kg-min]) , and 13C5 glutamine (3 μmol/[kg-min]) after a 16-hour fast to deplete hepatic glycogen. HD animals displayed significantly increased plasma glucose concentrations and EGP relative to LD controls. Analyses of liver tissues collected at sacrifice revealed that in LD animals, 70% of mitochondrial GNG was from pyruvate, 15% from succinyl CoA, and 15% from glutamine. In HD animals, 59% of mitochondrial GNG was derived from pyruvate (p=0.vs. LD) , 26% from succinyl CoA (p=0.0vs. LD) , and 15% from glutamine (p=0.99 vs. LD) . Conclusion: We find an unexpected role for succinyl CoA anaplerosis and methylmalonyl CoA mutase flux in supporting increased rates of mitochondrial GNG during hyperglucagonemia. Furthermore, relative contributions of glutamine to hepatic gluconeogenesis were unchanged, contrary to previous reports. Taken together, these results identify novel targets to reduce hyperglucagonemia-induced increases in rates of gluconeogenesis and hyperglycemia in T2DM. Disclosure B.T.Hubbard: None. G.I.Shulman: Advisory Panel; 89bio, Inc., AstraZeneca, Equator Therapeutics, Inc., Janssen Research &amp; Development, LLC, Merck &amp; Co., Inc., Consultant; DiCerna Pharmaceuticals, Inc. , Novo Nordisk, Other Relationship; Generian Pharmaceuticals, iMetabolic Biopharma Corporation, Maze Therapeutics, The Liver Company, Stock/Shareholder; Levels Health, Inc. .

The SGLT2 Inhibitor Dapagliflozin Increases the Oxidation of Ingested Fatty Acids to Ketones in Type 2 Diabetes.

To investigate the mechanism for increased ketogenesis following treatment with the SGLT2 inhibitor dapagliflozin in people with type 2 diabetes. The design was a double-blind, placebo-controlled, crossover study with a 4-week washout period. Participants received dapagliflozin or placebo in random order for 4 weeks. After each treatment, they ingested 30 mL of olive oil containing [U-13C]palmitate to measure ketogenesis, with blood sampling for 480 min. Stable isotopes of glucose and glycerol were infused to measure glucose flux and lipolysis, respectively, at 450-480 min. Glucose excretion rate was higher and peripheral glucose uptake lower with dapagliflozin than placebo. Plasma β-hydroxybutyrate (BOHB) concentrations and [13C2]BOHB concentrations were higher and glucose concentrations lower with dapagliflozin than placebo. Nonesterified fatty acids (NEFAs) were higher with dapagliflozin at 300 and 420 min, but lipolysis at 450-480 min was not different. Triacylglycerol at all time points and endogenous glucose production rate at 450-480 min were not different between treatments. The increase in ketone enrichment from the ingested palmitic acid tracer suggests that meal-derived fatty acids contribute to the increase in ketones during treatment with dapagliflozin. The increase in BOHB concentration with dapagliflozin occurred with only minimal changes in plasma NEFA concentration and no change in lipolysis. This finding suggests a metabolic switch to increase ketogenesis within the liver.

1172-P: Estimation of Glucose Turnover Using Naturally Enriched Complex Carbohydrate Meal in Type 2 Diabetes: Comparison with Triple-Tracer Meal

We have recently established a method utilizing the natural abundance of [13C] polysaccharide enabling measurement of enrichment of [13C] glucose in healthy humans. We now compare complex carb (CC) meal with a single tracer infusion of [6,6-2H2] glucose at -120 min to the established simple carb (SC) triple tracer protocol with infusion of [6,6-2H2] glucose at -120 min and [2-13C] glucose at 0 min with meal ingested at time 0. Six type 2 diabetes subjects (4M, age 65±6 y; BMI 33±4 kg/m2; HbA1c 50±10 mM/mol) were studied in random order with SC labeled with [1-13C] glucose and CC meal with sorghum grain. All meals had ~75 g carbohydrates with matched macronutrient content. Steele’s non-steady state equations were used to calculate glucose fluxes: rates of meal glucose appearance (Rameal), glucose disappearance (Rd) and endogenous glucose production (EGP) (Results in Fig1). Glucose, insulin and C-peptide concentrations achieved as well as iAUC of Rameal and Rd were significantly lower with CC than SC meal (p<0.05). However, EGP was similar between groups, (p=0.07). The results provide new insights into post prandial glucose physiology with CC meals that are healthier option for patients with diabetes. We can now conduct successful single stable tracer infusion based measurement of postprandial fluxes with real-world CC containing mixed meals in people with type 2 diabetes.View largeDownload slideView largeDownload slide DisclosureY. R. Yadav: None. A. Asfa: None. F. Ruchi: None. A. Weaver: None. C. M. Amarasekarage: None. C. Lane: None. A. Basu: None. R. Basu: None.FundingNational Institutes of Health (R01DK029953 to R.B.), (R01DK085516 to A.B.), (DK059637, DK020593)

Lactation Versus Formula Feeding: Insulin, Glucose, and Fatty Acid Metabolism During the Postpartum Period.

Milk production may involve a transient development of insulin resistance in nonmammary tissues to support redistribution of maternal macronutrients to match the requirements of the lactating mammary gland. In the current study, adipose and liver metabolic responses were measured in the fasting state and during a two-step (10 and 20 mU/m2/min) hyperinsulinemic-euglycemic clamp with stable isotopes, in 6-week postpartum women who were lactating (n = 12) or formula-feeding (n = 6) their infants and who were closely matched for baseline characteristics (e.g., parity, body composition, and intrahepatic lipid). When controlling for the low insulin concentrations of both groups, the lactating women exhibited a fasting rate of endogenous glucose production (EGP) that was 2.6-fold greater and a lipolysis rate that was 2.3-fold greater than the formula-feeding group. During the clamp, the groups exhibited similar suppression rates of EGP and lipolysis. In the lactating women only, higher prolactin concentrations were associated with greater suppression rates of lipolysis and lower intrahepatic lipid and plasma triacylglycerol concentrations. These data suggest that whole-body alterations in glucose transport may be organ specific and facilitate nutrient partitioning during lactation. Recapitulating a shift toward noninsulin-mediated glucose uptake could be an early postpartum strategy to enhance lactation success in women at risk for delayed onset of milk production.

Combination Therapy With Canagliflozin Plus Liraglutide Exerts Additive Effect on Weight Loss, but Not on HbA1c, in Patients With Type 2 Diabetes.

OBJECTIVETo examine the effect of combination therapy with canagliflozin plus liraglutide on HbA1c, endogenous glucose production (EGP), and body weight versus each therapy alone.RESEARCH DESIGN AND METHODSForty-five patients with poorly controlled (HbA1c 7–11%) type 2 diabetes mellitus (T2DM) on metformin with or without sulfonylurea received a 9-h measurement of EGP with [3-3H]glucose infusion, after which they were randomized to receive 1) liraglutide 1.2 mg/day (LIRA), 2) canagliflozin 100 mg/day (CANA), or 3) liraglutide 1.2 mg plus canagliflozin 100 mg (CANA/LIRA) for 16 weeks. At 16 weeks, the EGP measurement was repeated.RESULTSThe mean decrease from baseline to 16 weeks in HbA1c was −1.67 ± 0.29% (P = 0.0001), −0.89 ± 0.24% (P = 0.002), and −1.44 ± 0.39% (P = 0.004) in patients receiving CANA/LIRA, CANA, and LIRA, respectively. The decrease in body weight was −6.0 ± 0.8 kg (P < 0.0001), −3.5 ± 0.5 kg (P < 0.0001), and −1.9 ± 0.8 kg (P = 0.03), respectively. CANA monotherapy caused a 9% increase in basal rate of EGP (P < 0.05), which was accompanied by a 50% increase (P < 0.05) in plasma glucagon-to-insulin ratio. LIRA monotherapy reduced plasma glucagon concentration and inhibited EGP. In CANA/LIRA-treated patients, EGP increased by 15% (P < 0.05), even though the plasma insulin response was maintained at baseline and the CANA-induced rise in plasma glucagon concentration was blocked.CONCLUSIONSThese results demonstrate that liraglutide failed to block the increase in EGP caused by canagliflozin despite blocking the rise in plasma glucagon and preventing the decrease in plasma insulin concentration caused by canagliflozin. The failure of liraglutide to prevent the increase in EGP caused by canagliflozin explains the lack of additive effect of these two agents on HbA1c.

Regulation of hepatic mitochondrial oxidation by glucose-alanine cycling during starvation in humans.

In order to determine whether the glucose-alanine cycle regulates rates of hepatic mitochondrial oxidation in humans, we applied positional isotopomer NMR tracer analysis (PINTA) to assess rates of hepatic mitochondrial oxidation and pyruvate carboxylase flux in healthy volunteers following both an overnight (12 hours) and a 60-hour fast. Following the 60-hour fast, rates of endogenous glucose production and mitochondrial oxidation decreased, whereas rates of hepatic pyruvate carboxylase flux remained unchanged. These reductions were associated with reduced rates of alanine turnover, assessed by [3-13C]alanine, in a subgroup of participants under similar fasting conditions. In order to determine whether this reduction in alanine turnover was responsible for the reduced rates of hepatic mitochondrial oxidation, we infused unlabeled alanine into another subgroup of 60-hour fasted subjects to increase rates of alanine turnover, similar to what was measured after a 12-hour fast, and found that this perturbation increased rates of hepatic mitochondrial oxidation. Taken together, these studies demonstrate that 60 hours of starvation induce marked reductions in rates of hepatic mitochondrial oxidation, which in turn can be attributed to reduced rates of glucose-alanine cycling, and reveal a heretofore undescribed role for glucose-alanine in the regulation of hepatic mitochondrial oxidation in humans.

225-OR: Key Role for Glucose-Alanine Cycling in the Regulation of Hepatic Mitochondrial Oxidation during Starvation in Humans

We examined whether starvation alters rates of hepatic mitochondrial oxidation in humans by applying a novel 13C Positional Isotopomer NMR Tracer Analysis (PINTA) method to assess rates of hepatic mitochondrial oxidation in healthy volunteers (n=15) following an overnight (12h) and a 60h fast. A 3h intravenous infusion of [3-13C] lactate (4.3 μmol/Kg-min), [1,2,3,4,5,6,6-2H7] glucose (0.22 μmol/Kg-min), and [13C4]-β-hydroxybutyrate (BOHB) (0.01 mg/Kg-min) was administered and blood was collected for GC-MS, LC-MS/MS and 13C MRS PINTA analyses. Following the 60h fast rates of endogenous glucose production decreased by 27% (p=0.0002) and rates of hepatic mitochondrial oxidation decreased by 52% (p=0.0014) whereas rates of hepatic pyruvate carboxylase flux remained unchanged. To ascertain whether decreased rates of alanine turnover during starvation play a role in promoting decreased rates of hepatic mitochondrial oxidation we infused [3-13C] alanine in a subgroup (n=5) of subjects and found that 60h of fasting promoted a 28% reduction in alanine turnover (p=0.044 vs. 12h fast). In order to determine whether this reduction in alanine turnover was responsible for the reduced rates of hepatic mitochondrial oxidation we infused unlabeled alanine to a subgroup (n=9) of the 15 subjects in a repeat 60h fasting study to increase rates of alanine turnover to rates measured after 12h of fasting and found that this perturbation increased rates of hepatic mitochondrial oxidation by 63% (p=0.009 vs. 60h fast) to rates similar to the 12h fasting state (60h+ala: 232±21 vs. 12h: 295±44 μmol/min, p=0.303). Conclusion: These studies demonstrate that 60h of starvation in humans induces marked reductions in rates of hepatic mitochondrial oxidation, which in turn can be attributed to reduced rates of glucose-alanine cycling. Disclosure K. Petersen: Advisory Panel; Spouse/Partner; Aegerion Pharmaceuticals, AstraZeneca, AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc., Novo Nordisk A/S. Consultant; Spouse/Partner; Gilead Sciences, Inc. Consultant; Self; Merck &amp; Co., Inc. Consultant; Spouse/Partner; Nimbus Discoverey. Consultant; Self; Novo Nordisk A/S. S. Dufour: None. G. Cline: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc. Advisory Panel; Spouse/Partner; Merck &amp; Co., Inc. Board Member; Self; Novo Nordisk A/S. Consultant; Self; Aegerion Pharmaceuticals, IMetabolic BioPharma Corporation, Longitude Capital, Nimbus Discovery, Inc., Staten Biotechnology B.V. Funding National Institutes of Health

Metformin increases endogenous glucose production in non-diabetic individuals and individuals with recent-onset type 2 diabetes.

Metformin is the endorsed first-line glucose-lowering drug for treating patients with type 2 diabetes but despite more than 50years of use, no consensus has been reached on its mechanisms of action. In this study, we investigated the glucose-lowering effects of metformin in individuals with type 2 diabetes and non-diabetic individuals. We performed a randomised, placebo-controlled trial in 24 individuals with recent-onset type 2 diabetes (diabetes duration 50 [48] months) who had good glycaemic control (HbA1c 48mmol/mmol [6.5%]). The studies were conducted at Aarhus University Hospital between 2013 and 2016. Participants were randomised to receive either metformin (2000mg/day, n = 12, MET group) or placebo (n = 12, PLA group) for 90days, using block randomisation set up by an unblinded pharmacist. Two participants withdrew from the study prior to completion and were replaced with two new participants receiving the same treatment. In addition, we recruited a group of non-diabetic individuals with similar age and BMI (n = 12, CONT group), who were all treated with 2000mg metformin daily. Before and after treatment all individuals underwent studies of whole-body glucose metabolism by non-steady-state [3-3H]glucose kinetics, hyperinsulinaemic-euglycaemic clamping, indirect calorimetry, metabolomics, dual x-ray absorptiometry and muscle biopsies. The primary study endpoint was the effect of metformin treatment on lipid kinetics as well as glucose rate of disappearance (Rd) and endogenous glucose production (EGP). One participant from the CONT group withdrew due to intolerable gastrointestinal side-effects and was excluded from analysis. As expected, metformin treatment lowered fasting plasma glucose (FPG) in the MET group (~1.5mmol/l, p < 0.01), whereas no effect was observed in the PLA and CONT groups. Body weight and composition did not change in any of the groups. In both of the metformin-treated groups (MET and CONT), basal glucose Rd, EGP and glucagon levels increased by ~30% (p < 0.05) whereas this was not the case in the PLA group. Ninety days of metformin treatment resulted in similar increases in EGP and glucose Rd in individuals with recent-onset type 2 diabetes and in non-diabetic control individuals. These results challenge the existing paradigm that metformin primarily acts in the liver by inhibiting EGP, at least in individuals with type 2 diabetes of short duration and who have discretely affected glycaemic status. Whether metformin increases basal glucose Rd by facilitating glucose uptake in other tissues such as the intestines remains to be further clarified. ClinicalTrials.gov NCT01729156 FUNDING: This study was supported by grants from The Danish Council for Independent Research | Medical Sciences, Aase Danielsen Fund, the Novo Nordisk Foundation, the Danish Diabetes Association and the Danish Diabetes Academy supported by the Novo Nordisk Foundation.

Modest changes to glycemic regulation are sufficient to maintain glucose fluxes in healthy young men following overfeeding with a habitual macronutrient composition

Currently, it is unclear whether short-term overfeeding in healthy people significantly affects postprandial glucose regulation, as most human overfeeding studies have utilized induced experimental conditions such as the euglycemic-hyperinsulinemic clamp technique to assess glucoregulation. The aim of this study was to quantify glucose fluxes [rates of meal glucose appearance (Ra), disposal (Rd), and endogenous glucose production (EGP)] in response to 5 and 28 days of overfeeding (+45% energy) while maintaining habitual macronutrient composition (31.0 ± 1.9% fat, 48.6 ± 2.2% carbohydrate, 16.7 ± 1.4% protein) in healthy, lean young men. Meal tolerance testing was combined with the triple-stable isotope glucose tracer approach. Visceral adipose volume increased by ~15% with 5 days of overfeeding, while there was no further change at 28 days. In contrast, body mass (+1.6 kg) and fat mass (+1.3 kg) were significantly increased only after 28 days of overfeeding. Fasting EGP, Rd, and insulin were increased at 5 but unchanged after 28 days. Postprandial glucose and insulin responses were unaltered by 5 days of overfeeding but were modestly increased after 28 days (P < 0.05). However, meal Ra and glucose Rd were significantly increased after both 5 and 28 days of overfeeding (P < 0.05). Despite this, overfeeding did not lead to alterations to postprandial EGP suppression. Thus, in contrast to findings from euglycemic-hyperinsulinemic clamp studies, chronic overfeeding did not affect the ability to suppress EGP or stimulate Rd under postprandial conditions. Rather, glucose flux was appropriately maintained following 28 days of overfeeding through modest increases in postprandial glycemia and insulinemia.

Hepatitis C virus infection is associated with hepatic and adipose tissue insulin resistance that improves after viral cure.

SummaryBackgroundChronic hepatitis C (CHC) is associated with systemic insulin resistance, yet there are limited data on the tissue‐specific contribution in vivo to this adverse metabolic phenotype, and the effect of HCV cure.MethodsWe examined tissue‐specific insulin sensitivity in a cohort study involving 13 patients with CHC compared to 12 BMI‐matched healthy control subjects. All subjects underwent a two‐step clamp incorporating the use of stable isotopes to measure carbohydrate and lipid flux (hepatic and global insulin sensitivity) with concomitant subcutaneous adipose tissue microdialysis and biopsy (subcutaneous adipose tissue insulin sensitivity). Investigations were repeated in seven patients with CHC following antiviral therapy with a documented sustained virological response.ResultsAdipose tissue was more insulin resistant in patients with CHC compared to healthy controls, as evidence by elevated glycerol production rate and impaired insulin‐mediated suppression of both circulating nonesterified fatty acids (NEFA) and adipose interstitial fluid glycerol release during the hyperinsulinaemic euglycaemic clamp. Hepatic and muscle insulin sensitivity were similar between patients with CHC and controls. Following viral eradication, hepatic insulin sensitivity improved as demonstrated by a reduction in endogenous glucose production rate. In addition, circulating NEFA decreased with sustained virological response (SVR) and insulin was more effective at suppressing adipose tissue interstitial glycerol release with a parallel increase in the expression of insulin signalling cascade genes in adipose tissue consistent with enhanced adipose tissue insulin sensitivity.ConclusionChronic hepatitis C patients have profound subcutaneous adipose tissue insulin resistance in comparison with BMI‐matched controls. For the first time, we have demonstrated that viral eradication improves global, hepatic and adipose tissue insulin sensitivity.

Type 2 Diabetes: An Updated Overview.

The prevalence of type 2 diabetes (T2D) is increasing worldwide. This study provides essential information about the classification, diagnosis, pathogenesis, treatment, and complications of T2D. Glucose homeostasis is controlled by the rates of endogenous glucose production (EGP) and glucose utilization. EGP is ~2 mg/kg/min in humans and is equal to the rate of basal glucose utilization. During fasting, ~75-85% of EGP occurs in the liver and the remainder in the kidney. Hepatic glucose production is the main determinant of fasting blood glucose concentration. In the fed state, when insulin secretion is stimulated and glucagon secretion is inhibited, EGP decreases and glucose uptake in splanchnic (liver and gut) and peripheral (primarily muscle) tissues increases. β-cell dysfunction and insulin resistance represent core pathophysiological defects in T2D. Although the pathogenesis of T2D was previously focused on dysfunctions of "ominous triumvirate" (liver, skeletal muscle, and β-cell), it has been extended to "ominous octet," which includes defects in adipocytes (increased lipolysis), gastrointestinal tract (incretin deficiency/resistance), pancreatic α-cells (hyperglucagonemia), kidneys (increased glucose reabsorption), and brain (insulin resistance); endothelial dysfunction, inflammation, increased oxidative stress, and hypoxia are also involved in the pathogenesis of T2D. In conclusion, diabetes is one of the leading causes of morbidity and mortality worldwide. More insights into the pathophysiology of T2D necessitate revising the treatment approaches from only glycemic control to a pathophysiological-based view. In addition, new emerging complications of T2D such as cancer warrant further attention.

Glucose lowering and vascular protective effects of cycloset added to GLP-1 receptor agonists in patients with type 2 diabetes.

SummaryObjectiveTo determine the glucose‐lowering mechanism of action and the effects of a quick‐release bromocriptine‐QR, a D2‐dopamine agonist (Cycloset) on vascular function in patients with type 2 diabetes (T2D).Study design and methodsFifteen poorly controlled T2D treated with metformin plus glucagon‐like peptide‐1 receptor agonists (GLP‐1RA) were studied after 4 months of Cycloset, 3.2 mg/d. Subjects received a 5‐hour double‐tracer (iv 3‐3H‐glucose and oral 14C‐glucose) mixed meal test (MMT) to quantitate rates of endogenous glucose production (EGP), oral glucose appearance (RaO) and disappearance (Rd) pre‐ and post‐Cycloset. Vascular assessments included 2‐day continuous BP monitoring, reactive hyperaemia index (RHI) and arterial stiffness (AS).ResultsHbA1c decreased from 8.3 ± 0.3% to 7.7 ± 0.2% (P < 0.05), fasting plasma glucose did not change (143 ± 4 vs 147 ± 5) and mean plasma glucose during MTT decreased from 223 ± 3 to 210 ± 4 mg/dL (P < 0.05) after Cycloset. Basal EGP (2.2 ± 0.2 vs 2.1 ± 0.2 mg/kg min) was unchanged, but there was greater MMT suppression (1.1 ± 0.1 vs 0.7 ± 0.1, P < 0.05). After Cycloset, RaO declined from 2.0 ± 0.1 to 1.7 ± 0.2 mg/kg min and peripheral oral glucose appearance from 53.1 ± 3.2 to 44.4 ± 3.1 g (P < 0.01). There were no changes in plasma insulin or glucagon concentration. Systolic (134 ± 4 vs 126 ± 6), diastolic (78 ± 3 vs 73 ± 4), mean BP (97 ± 5 vs 90 ± 4) and pulse pressure (54 ± 2 vs 51 ± 2 mm Hg) were reduced; RHI increased from 1.4 ± 0.1 to 1.9 ± 0.3 au and AS decreased modestly (19.8 ± 4.1 to 16.2 ± 3.7 au, P = NS).ConclusionsAddition of Cycloset to GLP‐1 RA improved vascular indices and postprandial hyperglycaemia in T2DM primarily by lowering oral glucose appearance, suggesting that hepatic glucose uptake was enhanced. Improved vascular indices may explain the reduction in cardiovascular events observed with Cycloset therapy in patients with T2DM.

Youth With Type 1 Diabetes Have Adipose, Hepatic, and Peripheral Insulin Resistance.

Adolescents with type 1 diabetes (T1D) have difficulty obtaining optimal glucose control, which may relate to insulin resistance (IR), especially during puberty. Moreover, IR increases the risk for cardiovascular disease, the leading cause of death in T1D. However, the tissue specificity of IR in adolescents with T1D has not been fully phenotyped. To assess adipose, hepatic, and peripheral insulin sensitivity in adolescents with and without T1D. Thirty-five youth with T1D [median age, 16 (first and third quartiles, 14, 17) years; 53% female; median body mass index (BMI) percentile, 82nd (55th, 96th); late puberty; median hemoglobin A1c, 8.3% (7.3%, 9.4%)] and 22 nondiabetic youth of similar age, BMI, pubertal stage, and level of habitual physical activity were enrolled. Insulin action was measured with a four-phase hyperinsulinemic euglycemic clamp (basal and 10, 16, and 80 mU/m2/min) with glucose and glycerol isotope tracers. Adolescents with T1D had a significantly higher rate of lipolysis (P < 0.0001) and endogenous glucose production (P < 0.001) and lower peripheral glucose uptake (glucose rate of disappearance, 6.9 ± 2.9 mg/kg/min for patients with T1D vs 11.3 ± 3.3 for controls; P < 0.0001) during hyperinsulinemia compared with controls. In youth with T1D, glucose rate of disappearance correlated with free fatty acid at the 80-mU/m2/min phase (P = 0.005), markers of inflammation (IL-6; P = 0.012), high-sensitivity C-reactive protein (P = 0.001), and leptin (P = 0.008)], but not hemoglobin A1c. Adolescents with T1D have adipose, hepatic and peripheral IR. This IR occurs regardless of obesity and metabolic syndrome features. Youth with T1D may benefit from interventions directed at improving IR in these tissues, and this area requires further research.