Endogenous Glucose Production Rate Research Articles

Effect of Glucagon on Nocturnal Rates of Endogenous Glucose Production in Type 2 Diabetes

The role of nocturnal glucagon on regulation of overnight endogenous glucose production (EGP) in T2D is unknown. We studied 13 T2D and 13 age, BMI matched nondiabetic subjects (ND) on two occasions at the Clinical Research Unit at Mayo Clinic. Deuterated water was provided to measure gluconeogenesis (GNG) and glycogenolysis (GGL) using the HMT (hexamethylenetetramine) method. A somatostatin pancreatic clamp was initiated at 10 PM with 0.25 mU/kg/min insulin infusion until 7 AM along with [3-3H] glucose to measure turnover in the presence of glucagon infusions at 0.65 ng/kg/min (basal) or 1.5 ng/kg/min (high) in random order. Blood was sampled periodically for the measurements of plasma glucose, [3-3H] glucose, hormones; EGP rates were measured at 7AM. Results are presented in the Table. Fasting glucose, insulin and c-peptide concentrations were not different in either group during either visit. Glucose infusion rates (GIR) required to maintain euglycemia were lower during high glucagon in both groups and lower in T2D vs. ND regardless of visit indicating insulin resistance. Rates of EGP at 7AM were higher in both groups with the high vs. basal glucagon (matched data shown for calculation). Partial GNG data that are available indicate increased rates of GGL at 7 AM in the presence of high glucagon. In T2D higher glucagon overnight could contribute to higher rates of GGL and EGP. Therapies to reduce GGL may help lower overnight EGP.{F280D615-E887-4E30-8C76-ED88282D5E23}All data are Mean +/- SD. Statistical analyses was not performed on EGP and HMT data as it is preliminary.Diabetes StatusBasal Glucagon 7 AMHigh Glucagon 7 AM7 AM p-value Basal vs HighGlucose (mmol/L)ND T2D5.4 ± 0.6 8.2 ± 4.0 (p < 0.001)5.2 ± 0.6 8.2 ± 4.0 (p < 0.001)0.4 0.9Glucagon (pg/ml)ND T2D82.0 ± 14.0 90.5 ± 12.5 (p = 0.56)138.3 ± 15.4 151.5 µ 17.2 (p = 0.20)p < 0.01 p < 0.01GIR (µmol/kgFFM/min)ND T2D23.0 ± 12.8 6.7 ± 8.4 (p <0.001)21.0 ± 11.4 4.0 ± 6.8 (p <0.001)p < 0.01 p < 0.01EGP (µmol/kgFFM/min)ND n=13 T2D n=138.0 ± 4.2 13.3 ± 4.710.3 ± 6.6 15.8 ± 4.3HMT data (EGP) (µmol/kgFFM/min)ND n=4 T2D n=710.3 ± 4.8 15.2 ± 5.615.1 ± 8.7 22.0 ± 5.0GluconeogenesisND n=4 T2D n=73.8 ± 1.3 5.6 ± 2.24.7 ± 3.4 9.4 ± 1.6GlycogenolysisND n=4 T2D n=76.5 ± 3.4 9.6 ± 3.310.4 ± 1.2 12.6 ± 3.5 Disclosure A. Basu: Research Support; Spouse/Partner; AstraZeneca. Research Support; Self; Novo Nordisk A/S. Advisory Panel; Self; Voluntis France. H. Zhai: None. R. Carter: None. R. Basu: Research Support; Self; AstraZeneca.

Comprehensive assessment of insulin resistance in non-obese Asian Indian and Chinese men.

Aims/IntroductionIndian individuals are more insulin resistant (IR) than Chinese individuals, even among those with a non‐obese body mass index (BMI). However, BMI often underestimates body fat in Indian individuals, and it remains unclear whether Indians would remain more IR than Chinese individuals when both BMI and body fat are equally matched.Materials and MethodsUsing the hyperinsulinemic‐euglycemic clamp with stable‐isotope infusion, we comprehensively assessed IR between 13 non‐obese Indian men with 13 Chinese men matched for age, BMI and body fat. We further compared the differences in insulin metabolic clearance rate (MCR) between the two groups and its relationship with various metabolic parameters. The response of lipid and amino acid metabolism to insulin stimulation was also evaluated using metabolomic profiling.ResultsThe rates of endogenous glucose production during fasting were similar, and endogenous glucose production was completely suppressed during insulin clamp for both ethnic groups. Glucose disappearance during insulin clamp was also similar between the two groups, even after accounting for differences in insulin concentration. Metabolomic profiles of amino acids and various acylcarnitines were similar during both fasting and insulin clamp. However, plasma insulin during clamp was significantly higher in Indian men, indicating that insulin MCR was lower. Insulin MCR correlated significantly with total adiposity and skeletal muscle insulin sensitivity.ConclusionWhen equally matched for body fat, non‐obese Indian men had similar skeletal muscle insulin sensitivity and endogenous glucose production to Chinese men. The effects of insulin on lipid and amino acid metabolism were also similar. Low insulin MCR is associated with greater adiposity and lower skeletal muscle insulin sensitivity.

Effect of Progressive Weight Loss on Lactate Metabolism: A Randomized Controlled Trial.

ObjectiveLactate is an intermediate of glucose metabolism that has been implicated in the pathogenesis of insulin resistance. This study evaluated the relationship between glucose kinetics and plasma lactate concentration ([LAC]) before and after manipulating insulin sensitivity by progressive weight loss.MethodsForty people with obesity (BMI=37.9±4.3 kg/m2) were randomized to weight maintenance (n=14) or weight loss (n=19). Subjects were studied before and after 6 months of weight maintenance and before and after 5%, 11% and 16% weight loss. A hyperinsulinemic-euglycemic clamp procedure in conjunction with [6,6-2H2]glucose tracer infusion was used to assess glucose kinetics.ResultsAt baseline, fasting [LAC] correlated positively with endogenous glucose production rate (r=0.532, p=0.001) and negatively with insulin sensitivity, assessed as the insulin-stimulated glucose disposal (r=−0.361, p=0.04). Progressive (5% through 16%) weight loss caused a progressive decrease in fasting [LAC], and the decrease in fasting [LAC] after 5% weight loss was correlated with the decrease in endogenous glucose production (r=0.654, p=0.002) and the increase in insulin sensitivity (r=−0.595, p=0.007).ConclusionThis study demonstrates the inter-relationships among weight loss, hepatic and muscle glucose kinetics, insulin sensitivity, and [LAC], and suggests that [LAC] can serve as an additional biomarker of glucose-related insulin resistance.

Impact of C-Peptide Status on the Response of Glucagon and Endogenous Glucose Production to Induced Hypoglycemia in T1DM.

Complete loss of β-cell function in patients with type 1 diabetes mellitus (T1DM) may lead to an increased risk of severe hypoglycemia. We aimed to determine the impact of C-peptide status on glucagon response and endogenous glucose production (EGP) during hypoglycemia in patients with T1DM. We conducted an open, comparative trial. Ten C-peptide positive (C-pos) and 11 matched C-peptide negative (C-neg) patients with T1DM were enrolled. Plasma glucose was normalized over the night fast, and after a steady-state (baseline) plateau all patients underwent a hyperinsulinemic, stepwise hypoglycemic clamp with glucose plateaus of 5.5, 3.5, and 2.5 mmol/L and a recovery phase of 4.0 mmol/L. Blood glucagon was measured with a specific and highly sensitive glucagon assay. EGP was determined with a stable isotope tracer technique. Impact of C-peptide status on glucagon response and EGP during hypoglycemia. Glucagon concentrations were significantly lower in C-pos and C-neg patients than previously reported. At baseline, C-pos patients had higher glucagon concentrations than C-neg patients (8.39 ± 4.6 vs 4.19 ± 2.4 pmol/L, P = 0.016, mean ± standard deviation) but comparable EGP rates (2.13 ± 0.2 vs 2.04 ± 0.3 mg/kg/min, P < 0.391). In both groups, insulin suppressed glucagon levels, but hypoglycemia revealed significantly higher glucagon concentrations in C-pos than in C-neg patients. EGP was significantly higher in C-pos patients at hypoglycemia (2.5 mmol/L) compared with C-neg patients. Glucagon concentrations and EGP during hypoglycemia were more pronounced in C-pos than in C-neg patients, which indicates that preserved β-cell function may contribute to counterregulation during hypoglycemia in patients with T1DM.

A Partial Loss-of-Function Variant in AKT2 Is Associated With Reduced Insulin-Mediated Glucose Uptake in Multiple Insulin-Sensitive Tissues: A Genotype-Based Callback Positron Emission Tomography Study.

Rare fully penetrant mutations in AKT2 are an established cause of monogenic disorders of glucose metabolism. Recently, a novel partial loss-of-function AKT2 coding variant (p.Pro50Thr) was identified that is nearly specific to Finns (frequency 1.1%), with the low-frequency allele associated with an increase in fasting plasma insulin level and risk of type 2 diabetes. The effects of the p.Pro50Thr AKT2 variant (p.P50T/AKT2) on insulin-stimulated glucose uptake (GU) in the whole body and in different tissues have not previously been investigated. We identified carriers (N = 20) and matched noncarriers (N = 25) for this allele in the population-based Metabolic Syndrome in Men (METSIM)study and invited these individuals back for positron emission tomography study with [18F]-fluorodeoxyglucose during euglycemic hyperinsulinemia. When we compared p.P50T/AKT2 carriers to noncarriers, we found a 39.4% reduction in whole-body GU (P = 0.006) and a 55.6% increase in the rate of endogenous glucose production (P = 0.038). We found significant reductions in GU in multiple tissues—skeletal muscle (36.4%), liver (16.1%), brown adipose (29.7%), and bone marrow (32.9%)—and increases of 16.8–19.1% in seven tested brain regions. These data demonstrate that the p.P50T substitution of AKT2 influences insulin-mediated GU in multiple insulin-sensitive tissues and may explain, at least in part, the increased risk of type 2 diabetes in p.P50T/AKT2 carriers.

Constant hepatic ATP concentrations during prolonged fasting and absence of effects of Cerbomed Nemos® on parasympathetic tone and hepatic energy metabolism

ObjectiveBrain insulin-induced improvement in glucose homeostasis has been proposed to be mediated by the parasympathetic nervous system. Non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) activating afferent branches of the vagus nerve may prevent hyperglycemia in diabetes models. We examined the effects of 14-min taVNS vs sham stimulation by Cerbomed Nemos® on glucose metabolism, lipids, and hepatic energy homeostasis in fasted healthy humans (n = 10, age 51 ± 6 yrs, BMI 25.5 ± 2.7 kg/m2). MethodsHeart rate variability (HRV), reflecting sympathetic and parasympathetic nerve activity, was measured before, during and after taVNS or sham stimulation. Endogenous glucose production was determined using [6,6-2H2]glucose, and hepatic concentrations of triglycerides (HCL), adenosine triphosphate (ATP), and inorganic phosphate (Pi) were quantified from 1H/31P magnetic resonance spectroscopy at baseline and for 180 min following stimulation. ResultstaVNS did not affect circulating glucose, free fatty acids, insulin, glucagon, or pancreatic polypeptide. Rates of endogenous glucose production (P = 0.79), hepatic HCL, ATP, and Pi were also not different (P = 0.91, P = 0.48 and P = 0.24) between taVNS or sham stimulation. Hepatic HCL, ATP, and Pi remained constant during prolonged fasting for 3 h. No changes in heart rate or shift in cardiac autonomic function from HRV towards sympathetic or parasympathetic predominance were detected. ConclusionNon-invasive vagus stimulation by Cerbomed Nemos® does not acutely modulate the autonomic tone to the visceral organs and thereby does not affect hepatic glucose and energy metabolism. This technique is therefore unable to mimic brain insulin-mediated effects on peripheral homeostasis in humans.

Adult male northernelephant seals maintain high rates of glucose production during extended breeding fasts.

Many species undergo natural fasts as part of their life histories. Extended fasting is associated with increased β-oxidation of fatty acids and reduced oxidation of glucose to minimize commitment of body protein to gluconeogenesis. However, the metabolic strategies used to sustain extended fasts simultaneous with high rates of energy expenditure are not well understood. Studies in fasting adult female and weanling northern elephant seals (NES) have revealed high rates of endogenous glucose production (EGP) under constraints of high nutrient demand for lactation or development but relatively low rates of metabolism. These studies revealed low rates of glucose oxidation and high rates of glucose recycling through the Cori cycle. We measured rates of glucose flux in fasting adult male NES to assess how significantly longer fasting durations, higher metabolic rates, and greater rates of muscular activity affect glucose kinetics. We measured glucose turnover in 18 adult males using the clearance of [6-H3] glucose during breeding and molting. Adult male NES maintain high rates of EGP across extended fasts. EGP greatly exceeded estimated needs for glucose-dependent tissues, varied directly with plasma insulin and lactate concentrations, and was inversely related to plasma ketoacid concentrations. Together, these findings suggest that high rates of glucose production and recycling during breeding maintain high blood glucose levels to support glucose-dependent tissues while minimizing production of ketoacids and commitment of protein stores to glucose production.

Metabolic effects of insulin in a human model of ketoacidosis combining exposure to lipopolysaccharide and insulin deficiency: a randomised, controlled, crossover study in individuals with type 1 diabetes.

Diabetic ketoacidosis (DKA) is often caused by concomitant systemic inflammation and lack of insulin. Here we used an experimental human model to test whether and how metabolic responses to insulin are impaired in the early phases of DKA with a specific focus on skeletal muscle metabolism. Nine individuals with type 1 diabetes from a previously published cohort were investigated twice at Aarhus University Hospital using a 120min infusion of insulin (3.0/1.5mUkg-1min-1) after an overnight fast under: (1) euglycaemic conditions (CTR) or (2) hyperglycaemic ketotic conditions (KET) induced by an i.v. bolus of lipopolysaccharide and 85% reduction in insulin dosage. The primary outcome was insulin resistance in skeletal muscle. Participants were randomly assigned to one of the two arms at the time of screening using www.randomizer.org . The study was not blinded. All nine volunteers completed the 2days and are included in the analysis. Circulating concentrations of glucose and 3-hydroxybutyrate increased during KET (mean±SEM 17.7±0.6mmol/l and 1.6±0.2mmol/l, respectively), then decreased after insulin treatment (6.6±0.7mmol/l and 0.1±0.07mmol/l, respectively). Prior to insulin infusion (KET vs CTR) isotopically determined endogenous glucose production rates were 17±1.7μmolkg-1min-1 vs 8±1.3μmolkg-1min-1 (p=0.003), whole body phenylalanine fluxes were 2.9±0.5μmolkg-1min-1 vs 3.1±0.4μmolkg-1min-1 (p=0.77) and urea excretion rates were 16.9±2.4g/day vs 7.3±1.7g/day (p=0.01). Insulin failed to stimulate forearm glucose uptake and glucose oxidation in KET compared with CTR (p<0.05). Glycogen synthase phosphorylation was impaired in skeletal muscle. In KET, hyperglycaemia is primarily driven by increased endogenous glucose production. Insulin stimulation during early phases of DKA is associated with reduced glucose disposal in skeletal muscle, impaired glycogen synthase function and lower glucose oxidation. This underscores the presence of muscle insulin resistance in the pathogenesis of DKA. Trial registration www.clinicaltrials.gov (ID number: NCT02157155). Funding This work was funded by the Danish Council for Strategic Research (grant no. 0603-00479B).

The impact of kidney transplantation on insulin sensitivity.

To investigate the impact of kidney transplantation (KTx) on insulin sensitivity affecting glucose metabolism. 9 nondiabetic patients awaiting living donor KTx were examined prior to transplantation with an oral glucose tolerance test and a 3-h hyperinsulinaemic-euglycaemic clamp. The clamp was repeated 6 months after KTx. Nine age-, gender- and body mass index (BMI)-matched individuals with normal kidney function served as controls. Endogenous glucose production and glucose disappearance rate (N = 6) were measured in a subgroup of patients with corresponding controls. Results presented as mean [range]. Two patients had pretransplant prediabetes, whereas all others had normal glucose tolerance. After KTx, average glucose infusion rate to maintain euglycaemia during clamp declined significantly from 15.1 [9.1-23.7] to 9.8 [2.8-14.6] μmol/kg/min (P < 0.01) with 20.2 [9.9-33.7] μmol/kg/min in controls. Endogenous glucose production increased from 7.0 [4.8-8.5] to 9.4 [7.4-11.8] μmol/kg/min (P < 0.05) with 7.0 [-3.8 to 10.1] μmol/kg/min in controls. Glucose disappearance rate was unchanged (18.1 [12.9-24.5] vs. 17.1 [12.2-22.7] μmol/kg/min, NS) with 22.3 [14.6-34.3] in controls. In conclusion, insulin sensitivity is reduced 6 months after KTx and characterized mainly by impaired suppression of the endogenous glucose production.

Effect of testosterone on insulin sensitivity, oxidative metabolism and body composition in aging men with type 2 diabetes on metformin monotherapy.

To evaluate the effect of testosterone replacement therapy (TRT) on body composition, insulin sensitivity, oxidative metabolism and glycaemic control in aging men with lowered bioavailable testosterone (BioT) levels and type 2 diabetes mellitus (T2D) controlled on metformin monotherapy. We conducted a randomized, double-blind, placebo-controlled study in 39 men aged 50-70 years with BioT levels <7.3 nmol/L and T2D treated with metformin monotherapy. Patients were randomized to testosterone gel (TRT, n = 20) or placebo (n = 19) for 24 weeks. Lean body mass (LBM), total and regional fat mass were measured using whole-body dual-energy X-ray absorptiometry scans. Whole-body peripheral insulin sensitivity, endogenous glucose production (EGP) and substrate oxidation were assessed by euglycaemic-hyperinsulinaemic clamp with glucose tracer and combined with indirect calorimetry. Coefficients (β) represent the placebo-controlled mean effect of intervention. LBM (β = 1.9 kg, p = 0.001) increased after TRT, while total fat mass (β = -1.3 kg, p = 0.009), fat mass trunk (β = -0.7 kg, p = 0.043), fat mass legs (β = -0.7 kg, p = 0.025), fat mass arms (β = -0.3 kg, p = 0.001), and HDL cholesterol (β = -0.11 mmol/L, p = 0.009) decreased after TRT compared with placebo. Insulin-stimulated glucose disposal rates did not change in response to TRT compared with placebo (p = 0.18). Moreover, glycated haemoglobin, and basal and insulin-stimulated rates of EGP, lipid- and glucose-oxidation were unaltered after TRT. TRT in aging men with lowered BioT levels and T2D controlled on metformin monotherapy improved body composition; however, glycaemic control, peripheral insulin sensitivity, EGP and substrate metabolism were unchanged.

Gluconeogenesis during endurance exercise in cyclists habituated to a long-term low carbohydrate high-fat diet.

Blood glucose is an important fuel for endurance exercise. It can be derived from ingested carbohydrate, stored liver glycogen and newly synthesized glucose (gluconeogenesis). We hypothesized that athletes habitually following a low carbohydrate high fat (LCHF) diet would have higher rates of gluconeogenesis during exercise compared to those who follow a mixed macronutrient diet. We used stable isotope tracers to study glucose production kinetics during a 2h ride in cyclists habituated to either a LCHF or mixed macronutrient diet. The LCHF cyclists had lower rates of total glucose production and hepatic glycogenolysis but similar rates of gluconeogenesis compared to those on the mixed diet. The LCHF cyclists did not compensate for reduced dietary carbohydrate availability by increasing glucose synthesis during exercise but rather adapted by altering whole body substrate utilization. Endogenous glucose production (EGP) occurs via hepatic glycogenolysis (GLY) and gluconeogenesis (GNG) and plays an important role in maintaining euglycaemia. Rates of GLY and GNG increase during exercise in athletes following a mixed macronutrient diet; however, these processes have not been investigated in athletes following a low carbohydrate high fat (LCHF) diet. Therefore, we studied seven well-trained male cyclists that were habituated to either a LCHF (7% carbohydrate, 72% fat, 21% protein) or a mixed diet (51% carbohydrate, 33% fat, 16% protein) for longer than 8months. After an overnight fast, participants performed a 2h laboratory ride at 72% of maximal oxygen consumption. Glucose kinetics were measured at rest and during the final 30min of exercise by infusion of [6,6-(2) H2 ]-glucose and the ingestion of (2) H2 O tracers. Rates of EGP and GLY both at rest and during exercise were significantly lower in the LCHF group than the mixed diet group (Exercise EGP: LCHF, 6.0±0.9mgkg(-1) min(-1) , Mixed, 7.8±1.1mgkg(-1) min(-1) , P<0.01; Exercise GLY: LCHF, 3.2±0.7mgkg(-1) min(-1) , Mixed, 5.3±0.9mgkg(-1) min(-1) , P<0.01). Conversely, no difference was detected in rates of GNG between groups at rest or during exercise (Exercise: LCHF, 2.8±0.4mgkg(-1) min(-1) , Mixed, 2.5±0.3mgkg(-1) min(-1) , P=0.15). We conclude that athletes on a LCHF diet do not compensate for reduced glucose availability via higher rates of glucose synthesis compared to athletes on a mixed diet. Instead, GNG remains relatively stable, whereas glucose oxidation and GLY are influenced by dietary factors.

Propionate Increases Hepatic Pyruvate Cycling and Anaplerosis and Alters Mitochondrial Metabolism

In mammals, pyruvate kinase (PK) plays a key role in regulating the balance between glycolysis and gluconeogenesis; however, in vivo regulation of PK flux by gluconeogenic hormones and substrates is poorly understood. To this end, we developed a novel NMR-liquid chromatography/tandem-mass spectrometry (LC-MS/MS) method to directly assess pyruvate cycling relative to mitochondrial pyruvate metabolism (VPyr-Cyc/VMito) in vivo using [3-13C]lactate as a tracer. Using this approach, VPyr-Cyc/VMito was only 6% in overnight fasted rats. In contrast, when propionate was infused simultaneously at doses previously used as a tracer, it increased VPyr-Cyc/VMito by 20–30-fold, increased hepatic TCA metabolite concentrations 2–3-fold, and increased endogenous glucose production rates by 20–100%. The physiologic stimuli, glucagon and epinephrine, both increased hepatic glucose production, but only glucagon suppressed VPyr-Cyc/VMito. These data show that under fasting conditions, when hepatic gluconeogenesis is stimulated, pyruvate recycling is relatively low in liver compared with VMito flux and that liver metabolism, in particular pyruvate cycling, is sensitive to propionate making it an unsuitable tracer to assess hepatic glycolytic, gluconeogenic, and mitochondrial metabolism in vivo.

Interleukin-6 is a negative regulator of hepatic glucose production in the isolated rat liver

The mechanism underlying the increased rate of endogenous glucose production from the liver during exercise remains unknown. The cytokine interleukin-6 (IL-6) is known to be released during exercise and is thought that either IL-6 directly or via a “contraction factor” stimulates the release of stored glucose from the liver. Here we show that IL-6 does not directly increase hepatic glucose output (HGO). Moreover, IL-6 infused at the same time as glucagon caused a significant reduction in HGO. IL-6 infused with epinephrine caused no synergenic increase in HGO. To test if an unknown “contraction factor” was needed along with IL-6 to increase HGO, we used human fasted and exercised plasma perfused with or without IL-6 in our isolated liver system. We found that exercised plasma increased HGO, as expected, but when infused with IL-6, reductions in HGO were found. Our results provide evidence that IL-6 works as a negative regulator of HGO.

Maternal Glucose and Fatty Acid Kinetics and Infant Birth Weight in Obese Women With Type 2 Diabetes.

The objectives of this study were 1) to describe maternal glucose and lipid kinetics and 2) to examine the relationships with infant birth weight in obese women with pregestational type 2 diabetes during late pregnancy. Using stable isotope tracer methodology and mass spectrometry, maternal glucose and lipid kinetic rates during the basal condition were compared in three groups: lean women without diabetes (Lean, n = 25), obese women without diabetes (OB, n = 26), and obese women with pregestational type 2 diabetes (OB+DM, n = 28; total n = 79). Glucose and lipid kinetics during hyperinsulinemia were also measured in a subset of participants (n = 56). Relationships between maternal glucose and lipid kinetics during both conditions and infant birth weight were examined. Maternal endogenous glucose production (EGP) rate was higher in OB+DM than OB and Lean during hyperinsulinemia. Maternal insulin value at 50% palmitate Ra suppression (IC50) for palmitate suppression with insulinemia was higher in OB+DM than OB and Lean. Maternal EGP per unit insulin and plasma free fatty acid concentration during hyperinsulinemia most strongly predicted infant birth weight. Our findings suggest maternal fatty acid and glucose kinetics are altered during late pregnancy and might suggest a mechanism for higher birth weight in obese women with pregestational diabetes.

Prevention of diet-induced hepatic steatosis and hepatic insulin resistance by second generation antisense oligonucleotides targeted to the longevity gene mIndy (Slc13a5).

Reducing the expression of the Indy (I'm Not Dead Yet) gene in lower organisms extends life span by mechanisms resembling caloric restriction. Similarly, deletion of the mammalian homolog, mIndy (Slc13a5), encoding for a plasma membrane tricarboxylate transporter, protects from aging- and diet-induced adiposity and insulin resistance in mice. The organ specific contribution to this phenotype is unknown. We examined the impact of selective inducible hepatic knockdown of mIndy on whole body lipid and glucose metabolism using 2'-O-methoxyethyl chimeric anti-sense oligonucleotides (ASOs) in high-fat fed rats. 4-week treatment with 2'-O-methoxyethyl chimeric ASO reduced mIndy mRNA expression by 91% (P=0.001) compared to control ASO. Besides similar body weights between both groups, mIndy-ASO treatment lead to a 74% reduction in fasting plasma insulin concentrations as well as a 35% reduction in plasma triglycerides. Moreover, hepatic triglyceride content was significantly reduced by the knockdown of mIndy, likely mediating a trend to decreased basal rates of endogenous glucose production as well as an increased suppression of hepatic glucose production by 25% during a hyperinsulinemic-euglycemic clamp. Together, these data suggest that inducible liver-selective reduction of mIndy in rats is able to ameliorate hepatic steatosis and insulin resistance, conditions occurring with high calorie diets and during aging.

Effects of glucagon-like peptide-1 on glucagon secretion in patients with non-alcoholic fatty liver disease

We evaluated the glucagon-suppressive effect of glucagon-like peptide-1 (GLP-1) and its potential effects on endogenous glucose production and whole body lipolysis in non-diabetic patients with non-alcoholic fatty liver disease (NAFLD). On two separate days, 10 non-diabetic patients with liver biopsy-verified NAFLD (NAFLD activity score 2.5±1.0) and 10 matched controls underwent 2h intravenous infusions of GLP-1 (0.8 pmol×kg(-1)×min(-1)) and placebo. Since GLP-1-mediated glucagon suppression has been shown to be glucose-dependent, plasma glucose was clamped at fasting level during the first hour, and then raised and clamped at 'postprandial level' (fasting plasma glucose level plus 3 mmol/L) for the remaining hour. We evaluated relative plasma levels of glucagon, endogenous glucose production and whole body lipolysis rates with stable isotopes and respiratory quotient using indirect calorimetry. Compared to controls, patients with NAFLD were insulin resistant (homeostasis model assessment (HOMA(IR)): 3.8±2.2 vs. 1.6±1.5, p=0.003) and had fasting hyperglucagonaemia (7.5±5.3 vs. 5.8±1.5 mmol/L, p=0.045). Similar relative glucagon suppression was seen in both groups during GLP-1 infusion at fasting (-97±75 vs. -93±41 pmol/L×min(-1)p=0.566) and 'postprandial' plasma glucose levels (-108±101 vs. -97±53 pmol/L×min(-1), p=0.196). Increased insulinotropic effect of GLP-1 was observed in NAFLD patients. No effect of GLP-1 on endogenous glucose production was observed in any of the groups. Patients with NAFLD exhibited fasting hyperglucagonaemia, but intact GLP-1-mediated glucagon suppression independently of plasma glucose concentrations. Preserved glucagonostatic effect and increased insulinotropic effects of GLP-1 in NAFLD may be important to maintain normo-glycaemia in these patients.

3,5 Diiodo-L-Thyronine (T2) Does Not Prevent Hepatic Steatosis or Insulin Resistance in Fat-Fed Sprague Dawley Rats.

Thyroid hormone mimetics are alluring potential therapies for diseases like dyslipidemia, nonalcoholic fatty liver disease (NAFLD), and insulin resistance. Though diiodothyronines are thought inactive, pharmacologic treatment with 3,5- Diiodo-L-Thyronine (T2) reportedly reduces hepatic lipid content and improves glucose tolerance in fat-fed male rats. To test this, male Sprague Dawley rats fed a safflower-oil based high-fat diet were treated with T2 (0.25 mg/kg-d) or vehicle. Neither 10 nor 30 days of T2 treatment had an effect on weight, adiposity, plasma fatty acids, or hepatic steatosis. Insulin action was quantified in vivo by a hyperinsulinemic-euglycemic clamp. T2 did not alter fasting plasma glucose or insulin concentration. Basal endogenous glucose production (EGP) rate was unchanged. During the clamp, there was no difference in insulin stimulated whole body glucose disposal. Insulin suppressed EGP by 60% ± 10 in T2-treated rats as compared with 47% ± 4 suppression in the vehicle group (p = 0.32). This was associated with an improvement in hepatic insulin signaling; insulin stimulated Akt phosphorylation was ~2.5 fold greater in the T2-treated group as compared with the vehicle-treated group (p = 0.003). There was no change in expression of genes thought to mediate the effect of T2 on hepatic metabolism, including genes that regulate hepatic lipid oxidation (ppara, carnitine palmitoyltransferase 1a), genes that regulate hepatic fatty acid synthesis (srebp1c, acetyl coa carboxylase, fatty acid synthase), and genes involved in glycolysis and gluconeogenesis (L-pyruvate kinase, glucose 6 phosphatase). Therefore, in contrast with previous reports, in Sprague Dawley rats fed an unsaturated fat diet, T2 administration failed to improve NAFLD or whole body insulin sensitivity. Though there was a modest improvement in hepatic insulin signaling, this was not associated with significant differences in hepatic insulin action. Further study will be necessary before diiodothyronines can be considered an effective treatment for NAFLD and dyslipidemia.

SGLT-2 inhibition and glucagon: Cause for alarm?

Recent studies raised the alarm that the inhibition of sodium-coupled glucose transporter type-2 in humans increases endogenous glucose production rates by an unclear mechanism. Surprisingly, a potential explanation may be linked directly to the alpha-cell. Is this a mechanistic spoiler or an added benefit?

Effect of Global ATGL Knockout on Murine Fasting Glucose Kinetics.

Mice deficient in adipose triglyceride lipase (ATGL−/−) present elevated ectopic lipid levels but are paradoxically glucose-tolerant. Measurement of endogenous glucose production (EGP) and Cori cycle activity provide insights into the maintenance of glycemic control in these animals. These parameters were determined in 7 wild-type (ATGL+/−) and 6 ATGL−/− mice by a primed-infusion of [U-13C6]glucose followed by LC-MS/MS targeted mass-isotopomer analysis of blood glucose. EGP was quantified by isotope dilution of [U-13C6]glucose while Cori cycling was estimated by analysis of glucose triose 13C-isotopomers. Fasting plasma free fatty-acids were significantly lower in ATGL−/− versus control mice (0.43 ± 0.05 mM versus 0.73 ± 0.11 mM, P < 0.05). Six-hour fasting EGP rates were identical for both ATGL−/− and control mice (79 ± 11 versus 71 ± 7 μmol/kg/min, resp.). Peripheral glucose metabolism was dominated by Cori cycling (80 ± 2% and 82 ± 7% of glucose disposal for ATGL−/− and control mice, resp.) indicating that peripheral glucose oxidation was not significantly upregulated in ATGL−/− mice under these conditions. The glucose 13C-isotopomer distributions in both ATGL−/− and control mice were consistent with extensive hepatic pyruvate recycling. This suggests that gluconeogenic outflow from the Krebs cycle was also well compensated in ATGL−/− mice.

Pharmacokinetics and pharmacodynamics of insulin glargine given in the evening as compared with in the morning in type 2 diabetes.

To compare pharmacokinetics (PK) and pharmacodynamics (PD) of insulin glargine in type 2 diabetes mellitus (T2DM) after evening versus morning administration. Ten T2DM insulin-treated persons were studied during 24-h euglycemic glucose clamp, after glargine injection (0.4 units/kg s.c.), either in the evening (2200 h) or the morning (1000 h). The 24-h glucose infusion rate area under the curve (AUC0-24h) was similar in the evening and morning studies (1,058 ± 571 and 995 ± 691 mg/kg × 24 h, P = 0.503), but the first 12 h (AUC0-12h) was lower with evening versus morning glargine (357 ± 244 vs. 593 ± 374 mg/kg × 12 h, P = 0.004), whereas the opposite occurred for the second 12 h (AUC12-24h 700 ± 396 vs. 403 ± 343 mg/kg × 24 h, P = 0.002). The glucose infusion rate differences were totally accounted for by different rates of endogenous glucose production, not utilization. Plasma insulin and C-peptide levels did not differ in evening versus morning studies. Plasma glucagon levels (AUC0-24h 1,533 ± 656 vs. 1,120 ± 344 ng/L/h, P = 0.027) and lipolysis (free fatty acid AUC0-24h 7.5 ± 1.6 vs. 8.9 ± 1.9 mmol/L/h, P = 0.005; β-OH-butyrate AUC0-24h 6.8 ± 4.7 vs. 17.0 ± 11.9 mmol/L/h, P = 0.005; glycerol, P < 0.020) were overall more suppressed after evening versus morning glargine administration. The PD of insulin glargine differs depending on time of administration. With morning administration insulin activity is greater in the first 0-12 h, while with evening administration the activity is greater in the 12-24 h period following dosing. However, glargine PK and plasma C-peptide levels were similar, as well as glargine PD when analyzed by 24-h clock time independent of the time of administration. Thus, the results reflect the impact of circadian changes in insulin sensitivity in T2DM (lower in the night-early morning vs. afternoon hours) rather than glargine per se.