Endogenous Glucose Output Research Articles

Origins and History of the Minimal Model of Glucose Regulation.

It has long been hoped that our understanding of the pathogenesis of diabetes would be helped by the use of mathematical modeling. In 1979 Richard Bergman and Claudio Cobelli worked together to find a “minimal model” based upon experimental data from Bergman’s laboratory. Model was chosen as the simplest representation based upon physiology known at the time. The model itself is two quasi-linear differential equations; one representing insulin kinetics in plasma, and a second representing the effects of insulin and glucose itself on restoration of the glucose after perturbation by intravenous injection. Model would only be sufficient if it included a delay in insulin action; that is, insulin had to enter a remote compartment, which was interstitial fluid (ISF). Insulin suppressed endogenous glucose output (by liver) slowly. Delay proved to be due to initial suppression of lipolysis; resultant lowering of free fatty acids reduced liver glucose output. Modeling also demanded that normalization of glucose after injection included an effect of glucose itself on glucose disposal and endogenous glucose production – these effects were termed “glucose effectiveness.” Insulin sensitivity was calculated from fitting the model to intravenous glucose tolerance test data; the resulting insulin sensitivity index, SI, was validated with the glucose clamp method in human subjects. Model allowed us to examine the relationship between insulin sensitivity and insulin secretion. Relationship was described by a rectangular hyperbola, such that Insulin Secretion x Insulin Sensitivity = Disposition Index (DI). Latter term represents ability of the pancreatic beta-cells to compensate for insulin resistance due to factors such as obesity, pregnancy, or puberty. DI has a genetic basis, and predicts the onset of Type 2 diabetes. An additional factor was clearance of insulin by the liver. Clearance varies significantly among animal or human populations; using the model, clearance was shown to be lower in African Americans than Whites (adults and children), and may be a factor accounting for greater diabetes prevalence in African Americans. The research outlined in the manuscript emphasizes the powerful approach by which hypothesis testing, experimental studies, and mathematical modeling can work together to explain the pathogenesis of metabolic disease.

Plasma cathepsin D activity is negatively associated with hepatic insulin sensitivity in overweight and obese humans

Aims/hypothesisInsulin resistance in skeletal muscle and liver plays a major role in the pathophysiology of type 2 diabetes. The hyperinsulinaemic–euglycaemic clamp is considered the gold standard for assessing peripheral and hepatic insulin sensitivity, yet it is a costly and labour-intensive procedure. Therefore, easy-to-measure, cost-effective approaches to determine insulin sensitivity are needed to enable organ-specific interventions. Recently, evidence emerged that plasma cathepsin D (CTSD) is associated with insulin sensitivity and hepatic inflammation. Here, we aimed to investigate whether plasma CTSD is associated with hepatic and/or peripheral insulin sensitivity in humans.MethodsAs part of two large clinical trials (one designed to investigate the effects of antibiotics, and the other to investigate polyphenol supplementation, on insulin sensitivity), 94 overweight and obese adults (BMI 25–35 kg/m2) previously underwent a two-step hyperinsulinaemic–euglycaemic clamp (using [6,6-2H2]glucose) to assess hepatic and peripheral insulin sensitivity (per cent suppression of endogenous glucose output during the low-insulin-infusion step, and the rate of glucose disappearance during high-insulin infusion [40 mU/(m2 × min)], respectively). In this secondary analysis, plasma CTSD levels, CTSD activity and plasma inflammatory cytokines were measured.ResultsPlasma CTSD levels were positively associated with the proinflammatory cytokines IL-8 and TNF-α (IL-8: standardised β = 0.495, p < 0.001; TNF-α: standardised β = 0.264, p = 0.012). Plasma CTSD activity was negatively associated with hepatic insulin sensitivity (standardised β = −0.206, p = 0.043), independent of age, sex, BMI and waist circumference, but it was not associated with peripheral insulin sensitivity. However, plasma IL-8 and TNF-α were not significantly correlated with hepatic insulin sensitivity.Conclusions/interpretationWe demonstrate that plasma CTSD activity, but not systemic inflammation, is inversely related to hepatic insulin sensitivity, suggesting that plasma CTSD activity may be used as a non-invasive marker for hepatic insulin sensitivity in humans.

Predicting Glucose Effectiveness in Chinese Participants Using Routine Measurements.

Glucose effectiveness (GE) is the capacity of glucose to increase its own uptake and to maintain endogenous hepatic glucose output under basal insulin levels. In addition to decreased insulin sensitivity (IS) and impaired insulin secretion, GE plays a critical role in glucose balance in patients with type 2 diabetes (T2DM). In the study, we developed an equation for predicting GE. We enrolled 227 participants with glucose tolerances ranging from normal glucose tolerance to diabetes. Of the participants, 75% (171) participants were randomly assigned to the study group, whose data were used to construct the equation for estimating GE. The remaining 56 participants comprised the validation group. All participants underwent a frequently sampled intravenous glucose tolerance test; IS, GE, and the acute insulin response after the glucose load were determined. Age, triglyceride (TG), and fasting plasma glucose (FPG) were independently correlated with GE and selected for inclusion in multiple linear regression analysis. We constructed the following equation: GE = (29.196 - 0.103 × age - 2.722 × TG - 0.592 × FPG) × 10-3. Using this same equation, we also calculated the GE of the validation group. The calculated GE was significantly correlated with the measured GE (r = 0.430, P = 0.001). Using the equation based on routine measurements enabled the GE to be predicted with acceptable accuracy (r = 0.430). This method of predicting GE may aid clinicians in further understanding the underlying pathological mechanisms of T2DM.

Comparative Aspects of Human, Canine, and Feline Obesity and Factors Predicting Progression to Diabetes

Obesity and diabetes mellitus are common diseases in humans, dogs and cats and their prevalence is increasing. Obesity has been clearly identified as a risk factor for type 2 diabetes in humans and cats but recent data are missing in dogs, although there is evidence that the unprecedented rise in canine obesity in the last decade has led to a rise in canine diabetes of similar magnitude. The insulin resistance of obesity has often been portrayed as major culprit in the loss of glucose control; however, insulin resistance alone is not a good indicator of progression to diabetes in people or pets. A loss of beta cell function is necessary to provide the link to impaired fasting and post-prandial plasma glucose. Increased endogenous glucose output by the liver is also a prerequisite for the increase in fasting blood glucose when non-diabetic obese humans and pets develop diabetes. This may be due to decreased hepatic insulin sensitivity, decreased insulin concentrations, or a combination of both. While inflammation is a major link between obesity and diabetes in humans, there is little evidence that a similar phenomenon exists in cats. In dogs, more studies are needed to examine this important issue.

Long-Term Effects of Bariatric Surgery on Meal Disposal and β-Cell Function in Diabetic and Nondiabetic Patients

Gastric bypass surgery leads to marked improvements in glucose tolerance and insulin sensitivity in obese type 2 diabetes (T2D); the impact on glucose fluxes in response to a physiological stimulus, such as a mixed meal test (MTT), has not been determined. We administered an MTT to 12 obese T2D patients and 15 obese nondiabetic (ND) subjects before and 1 year after surgery (10 T2D and 11 ND) using the double-tracer technique and modeling of β-cell function. In both groups postsurgery, tracer-derived appearance of oral glucose was biphasic, a rapid increase followed by a sharp drop, a pattern that was mirrored by postprandial glucose levels and insulin secretion. In diabetic patients, surgery lowered fasting and postprandial glucose levels, peripheral insulin sensitivity increased in proportion to weight loss (∼30%), and β-cell glucose sensitivity doubled but did not normalize (compared with 21 nonsurgical obese and lean controls). Endogenous glucose production, however, was less suppressed during the MMT as the combined result of a relative hyperglucagonemia and the rapid fall in plasma glucose and insulin levels. We conclude that in T2D, bypass surgery changes the postprandial response to a dumping-like pattern and improves glucose tolerance, β-cell function, and peripheral insulin sensitivity but worsens endogenous glucose output in response to a physiological stimulus.

Abstract 140: LRP6 Influences Body Fat and Glucose Homeostasis in Mouse by Activating mTOR Pathway and Inhibiting Mitochondrial Energy Expenditure

Background: Body fat, insulin resistance and type2 diabetes are often linked together. Wnt signaling regulates adipogenesis and its altered activity has been implicated in the pathogenesis of type 2 diabetes and metabolic syndrome. Mutations in Wnt coreceptor LRP6 have been associated with diabetes, coronary heart disease and metabolic syndrome in humans, but the molecular mechanisms are largely unknown. Methods: We study the role of LRP6 in regulation of glucose and energy metabolism in heterozygote LRP6 knockout mice on high fat diet by using glucose tolerance test, hyperinsulinemic-euglycemic clamp studies and dissection of insulin signaling pathway. Results: LRP6+/- mice on high fat diet were protected against diet -induced obesity and hepatic and adipose tissue insulin resistance compared to wildtype littermates. Brown adipose tissue insulin sensitivity and lean body of LRP +/- mice were caused by diminished Wnt -dependent mTORC1/S6K activity and enhanced expression of brown adipose tissue PGC1-α and UCP1. LRP6 +/- mice also exhibited reduced endogenous hepatic glucose output which was due to diminished FoxO1-dependent activity of G6Pase. In addition, in vivo and in vitro studies showed that loss of LRP6 allele is associated with tissue specific increase of leptin receptor expression, which is a likely cause of hepatic insulin sensitivity in LRP6 +/- mice. Conclusion: Our study identifies LRP6 as a nutrient-sensitive regulator of the body weight and glucose metabolism and as a potential target for pharmacological interventions in obesity and diabetes.

Low Density Lipoprotein (LDL) Receptor-related Protein 6 (LRP6) Regulates Body Fat and Glucose Homeostasis by Modulating Nutrient Sensing Pathways and Mitochondrial Energy Expenditure

Body fat, insulin resistance, and type 2 diabetes are often linked together, but the molecular mechanisms that unify their association are poorly understood. Wnt signaling regulates adipogenesis, and its altered activity has been implicated in the pathogenesis of type 2 diabetes and metabolic syndrome. LRP6(+/-) mice on a high fat diet were protected against diet-induced obesity and hepatic and adipose tissue insulin resistance compared with their wild-type (WT) littermates. Brown adipose tissue insulin sensitivity and reduced adiposity of LRP6(+/-) mice were accounted for by diminished Wnt-dependent mTORC1 activity and enhanced expression of brown adipose tissue PGC1-α and UCP1. LRP6(+/-) mice also exhibited reduced endogenous hepatic glucose output, which was due to diminished FoxO1-dependent expression of the key gluconeogenic enzyme glucose-6-phosphatase (G6pase). In addition, in vivo and in vitro studies showed that loss of LRP6 allele is associated with increased leptin receptor expression, which is a likely cause of hepatic insulin sensitivity in LRP6(+/-) mice. Our study identifies LRP6 as a nutrient-sensitive regulator of body weight and glucose metabolism and as a potential target for pharmacological interventions in obesity and diabetes.

Effects of colesevelam on glucose absorption and hepatic/peripheral insulin sensitivity in patients with type 2 diabetes mellitus

Colesevelam lowers glucose and low-density lipoprotein cholesterol levels in patients with type 2 diabetes mellitus. This study examined the mechanisms by which colesevelam might affect glucose control. In this 12-week, randomized, double-blind, placebo-controlled study, subjects with type 2 diabetes and haemoglobin A(1c) (HbA(1c)) ≥7.5% on either stable diet and exercise or sulphonylurea therapy were randomized to colesevelam 3.75 g/day (n = 16) or placebo (n = 14). Hepatic/peripheral insulin sensitivity was evaluated at baseline and at week 12 by infusion of (3) H-labelled glucose followed by a 2-step hyperinsulinemic-euglycemic clamp. Two 75-g oral glucose tolerance tests (OGTTs) were conducted at baseline, one with and one without co-administration of colesevelam. A final OGTT was conducted at week 12. HbA(1c) and fasting plasma glucose (FPG) levels were evaluated pre- and post-treatment. Treatment with colesevelam, compared to placebo, had no significant effects on basal endogenous glucose output, response to insulin or on maximal steady-state glucose disposal rate. At baseline, co-administration of colesevelam with oral glucose reduced total area under the glucose curve (AUC(g)) but not incremental AUC(g). At week 12, neither total AUC(g) nor incremental AUC(g) were changed from pre-treatment values in either group. Post-load insulin levels increased with colesevelam at 30 and 120 min, but these changes in total area under the insulin curve (AUC(i)) and incremental AUC(i) did not differ between groups. Both HbA(1c) and FPG improved with colesevelam, but treatment differences were not significant. Colesevelam does not affect hepatic or peripheral insulin sensitivity and does not directly affect glucose absorption.

Deficiency in Interferon-γ Results in Reduced Body Weight and Better Glucose Tolerance in Mice

Obesity is a chronic low-grade inflammatory disease caused by increased energy intake and reduced energy expenditure. Studies using animal models with deletion of inflammatory cytokines have produced conflicting results with some showing increased weight gain and others showing no effect or even reduced body weights. Clearly, more work is necessary to understand the role of cytokines on body weight control. The aim of this study was to determine the effect of interferon-γ deletion (IFNγ(-/-)) on body weight regulation and glucose metabolism. Male IFNγ(-/-) and wild-type C57BL/6 mice were fed a low-fat chow diet, and body weight, food intake, and energy expenditure were monitored over 20 wk. At the end of the study, ip glucose tolerance test, insulin tolerance test, basal glucose turnover, and hyperinsulinemic/euglycemic clamps were performed. Expression levels of arcuate nucleus neuropeptide Y, Agouti-related peptide, and proopiomelanocortin mRNA as well as circulating leptin levels were also determined. IFNγ(-/-) mice had improved glucose tolerance with reduced rate of glucose appearance and increased insulin sensitivity due to greater suppression of endogenous glucose output, which was associated with decreased hepatic glucose-6-phosphatase activity. In addition, we also observed reduced body weight associated with decreased food intake and increased physical activity. Neuropeptide Y and Agouti-related peptide mRNA expression was reduced, whereas proopiomelanocortin mRNA expression was increased, as were plasma leptin levels. Global deletion of IFNγ in mice resulted in reduced body weight associated with negative energy balance, improved glucose tolerance, and hepatic insulin sensitivity. Our findings demonstrate that IFNγ plays a critical role in the regulation of body weight and glucose metabolism.

Piragliatin (RO4389620), a Novel Glucokinase Activator, Lowers Plasma Glucose Both in the Postabsorptive State and after a Glucose Challenge in Patients with Type 2 Diabetes Mellitus: A Mechanistic Study

Glucokinase plays a key role in glucose homeostasis. Glucokinase activators can lower glucose levels in both animal and human type 2 diabetes, but their mechanism of action has never been explored in humans. The objective of the study was to investigate the effects of the glucokinase activator piragliatin (RO4389620) on β-cell function and glucose fluxes in both fasting and fed (oral glucose tolerance test) states in patients with type 2 diabetes. This was a phase Ib randomized, double-blind, placebo-controlled crossover trial of two (25 and 100 mg) doses of piragliatin. This study was conducted at a clinical research center. Patients included 15 volunteer ambulatory patients with mild type 2 diabetes. Interventions included three 10-h (-300' to +300') studies, with an interval of at least 14 d. Administration of a single dose of placebo or piragliatin 25 mg or piragliatin 100 mg at -120'. Oral glucose tolerance test (at 0') with dual (iv and oral routes) tracer dilution technique was conducted. The primary measure was plasma glucose concentration. The secondary measure was model assessed β-cell function and tracer-determined glucose fluxes. Piragliatin caused a dose-dependent reduction of glucose levels in both fasting and fed states (P < 0.01). In the fasting state, piragliatin caused a dose-dependent increase in β-cell function, a fall in endogenous glucose output, and a rise in glucose use (all P < 0.01). In the fed state, the primary effects of piragliatin were on β-cell function (P < 0.01). The glucokinase activator piragliatin has an acute glucose-lowering action in patients with mild type 2 diabetes, mainly mediated through a generalized enhancement of β-cell function and through fasting restricted changes in glucose turnover.

High-fat diets rich in medium- versus long-chain fatty acids induce distinct patterns of tissue specific insulin resistance

Excess dietary long-chain fatty acid (LCFA) intake results in ectopic lipid accumulation and insulin resistance. Since medium-chain fatty acids (MCFA) are preferentially oxidized over LCFA, we hypothesized that diets rich in MCFA result in a lower ectopic lipid accumulation and insulin resistance compared to diets rich in LCFA. Feeding mice high-fat (HF) (45% kcal fat) diets for 8 weeks rich in triacylglycerols composed of MCFA (HFMCT) or LCFA (HFLCT) revealed a lower body weight gain in the HFMCT-fed mice. Indirect calorimetry revealed higher fat oxidation on HFMCT compared to HFLCT (0.011.0±0.0007 vs. 0.0096±0.0015 kcal/g body weight per hour, P<.05). In line with this, neutral lipid immunohistochemistry revealed significantly lower lipid storage in skeletal muscle (0.05±0.08 vs. 0.30±0.23 area%, P <.05) and in liver (0.9±0.4 vs. 6.4±0.8 area%, P<.05) after HFMCT vs. HFLCT, while ectopic fat storage in low fat (LF) was very low. Hyperinsulinemic euglycemic clamps revealed that the HFMCT and HFLCT resulted in severe whole body insulin resistance (glucose infusion rate: 53.1±6.8, 50.8±15.3 vs. 124.6±25.4 μmol min −1 kg −1, P<.001 in HFMCT, HFLCT and LF-fed mice, respectively). However, under hyperinsulinemic conditions, HFMCT revealed a lower endogenous glucose output (22.6±8.0 vs. 34.7±8.5 μmol min −1 kg −1, P<.05) and a lower peripheral glucose disappearance (75.7±7.8 vs. 93.4±12.4 μmol min −1 kg −1, P<.03) compared to HFLCT-fed mice. In conclusion, both HF diets induced whole body insulin resistance compared to LF. However, the HFMCT gained less weight, had less ectopic lipid accumulation, while peripheral insulin resistance was more pronounced compared to HFLCT. This suggests that HF-diets rich in medium- versus long-chain triacylglycerols induce insulin resistance via distinct mechanisms.

Sex differences in the control of glucose homeostasis

A markedly higher prevalence of impaired glucose tolerance has been reported in women than in men, whereas the opposite was seen for impaired fasting glucose. The present review focuses on the underlying mechanisms. An increased meal glucose appearance and disturbances in postprandial glucose disposal may contribute to higher glucose concentrations in women. An increased, similar or reduced insulin sensitivity has been reported in women than in men, which makes it unclear to what extent a disturbed insulin-mediated glucose disposal may contribute to increased postprandial glucose concentrations in women. This discrepancy may be explained by differences in the phase of menstrual cycle during the study, the use of oral contraceptives and different degrees of physical fitness. Nevertheless, there are consistent data indicating that women are protected against fatty acid-induced insulin resistance. Furthermore, both disturbances in endogenous glucose output and metabolic clearance of glucose may contribute to the reduced fasting glucose concentrations in women. There is an urgent need for studies that test whether sex-related disturbances in glucose metabolism may be involved in the pathogenesis of type 2 diabetes and the metabolic syndrome, taking age, menstrual cycle, the use of oral contraceptives and physical activity into account.

Differential effects of fatness, fitness and physical activity energy expenditure on whole-body, liver and fat insulin sensitivity

The relative contributions of fitness (maximal oxygen uptake), physical activity energy expenditure (PAEE) and fatness to whole-body, liver and fat insulin sensitivity is uncertain. The aim of this study was to determine whether fitness and PAEE are associated with whole-body, liver and fat insulin sensitivity independently of body fat. We recruited 25 men (mean [SD] age 53 [6] years). Whole-body (M value) and liver (percentage suppression of endogenous glucose output) insulin sensitivity were estimated using a hyperinsulinaemic-euglycaemic clamp. Insulin sensitivity in fat (insulin sensitivity index for NEFA) was estimated during an OGTT. Total and truncal fat were measured by dual-energy X-ray absorptiometry, fitness by treadmill, and PAEE (n = 21) by 3 day heart rate monitoring and Baecke questionnaire. In univariate analyses, fatness was strongly associated with insulin sensitivity (whole-body, liver and fat). Fitness was associated with whole-body (r = 0.53, p < 0.007) and liver (0.42, p = 0.04) insulin sensitivity, while PAEE was associated with liver insulin sensitivity (r = 0.55, p = 0.01). Regression models were established to describe associations between fatness, fitness and physical activity and measures of insulin sensitivity (whole-body, fat and liver) as outcomes. Only fatness was independently associated with whole-body insulin sensitivity (B coefficient -0.01, p = 0.001). Fitness was not associated with any outcome. Only PAEE was independently associated with liver insulin sensitivity (B coefficient 13.5, p = 0.02). Fatness explains most of the variance in whole-body insulin sensitivity. In contrast, PAEE explains most of the variance in liver insulin sensitivity.

Effects of Recombinant Human IGF-I/IGF-Binding Protein-3 Complex on Glucose and Glycerol Metabolism in Type 1 Diabetes

Recombinant human IGF-I (rhIGF-I) complexed with its natural binding protein IGF-binding protein (IGFBP)-3 (rhIGF-I/IGFBP-3) is a novel formulation that has been shown to improve insulin sensitivity in type 1 diabetes, yet the mechanisms are not clear. We used stable isotopes to investigate the effects of rhIGF-I/IGFBP-3 on glucose and glycerol metabolism in type 1 diabetes. Fifteen subjects (age 13-24 years; 10 males) were studied on three occasions in random order. Each study period lasted for two days, and an injection of either placebo or rhIGF-I/IGFBP-3 (0.1-0.8 mg x kg(-1) x day (-1)) was given subcutaneously at 6:00 p.m. on days 1 and 2. Following the second injection, the subjects were kept euglycemic overnight by a variable rate insulin infusion, followed by a 4-h, two-step (insulin 0.6 and 1.5 mU x kg(-1) x min (-1)) hyperinsulinemic-euglycemic clamp. During the overnight basal steady state, rhIGF-I/IGFBP-3 dose-dependently reduced endogenous glucose production rate (R(a)) (P = 0.004), while peripheral glucose uptake (R(d)) was not different from placebo. The increase in glucose R(d) during hyperinsulinemic clamp was greater following rhIGF-I/IGFBP-3 than placebo, both during the first (P = 0.008) and second step (P = 0.008) of the clamp. No significant differences were found in glycerol R(a), a measure of lipolysis, between rhIGF-I/IGFBP-3 and placebo. In conclusion, rhIGF-I/IGFBP-3 enhances glucose metabolism by controlling both endogenous glucose output and peripheral glucose uptake.

Association of a F479L variant in the cytosolic phospholipase A2 gene ( PLA2G4A) with decreased glucose turnover and oxidation rates in Pima Indians

Phospholipase A2, Group IVA (PLA2G4A) belongs to the class of cytosolic calcium-dependent phospholipases (cPLA2s) that preferentially cleave arachidonic acid (AA) from membrane glycerophospholipids. AA and AA metabolites play key roles in glucose disposal and insulin secretion. PLA2G4A is located on Chromosome 1q, where a number of groups have reported linkage to type 2 diabetes mellitus. We have screened the PLA2G4A gene and identified a C→G variant, which predicts a phenylalanine to leucine substitution. In logistic regression analyses adjusted for age, sex, ethnicity, and birth year, we found a trend toward association between this SNP and diabetes [OR=1.53 (0.97–2.40); p=0.06]. Individuals with the variant genotype had lower mean basal endogenous glucose output (1.8±0.03 vs. 1.9±0.01 mg/ kg EMBS/ min ; p=0.04) and lower mean basal glucose oxidation (1.2±0.11 vs. 1.4±0.03 mg/ kg EMBS/ min ; p=0.005) compared to individuals with the wild-type genotype. During a low dose insulin infusion, non-diabetic individuals with the variant genotype had a lower mean glucose oxidation (1.9±0.11 vs. 2.0±0.03 mg/ kg EMBS/ min ; p=0.04) and total glucose turnover rate (2.5±0.22 vs. 2.6±0.06 mg/ kg EMBS/ min ; p=0.01) compared to subjects with the wild-type genotype. In addition, under basal conditions, individuals with the variant genotype had a higher mean lipid oxidation rate compared to individuals with the wild-type genotype (0.77±0.25 vs. 0.67±0.23 mg/ kg EMBS/ min ; p=0.02). These results provide evidence supporting a role for the eicosanoid biosynthesis pathway in type 2 diabetes mellitus pathophysiology.

Metabolic effects of visceral fat accumulation in type 2 diabetes.

Visceral fat (VF) excess has been associated with decreased peripheral insulin sensitivity and has been suggested to contribute to hepatic insulin resistance. However, the mechanisms by which VF impacts on hepatic glucose metabolism and the quantitative role of VF in glycemic control have not been investigated. In the present study 63 type 2 diabetic subjects (age, 55 +/- 1 yr; fasting plasma glucose, 5.5-14.4 mmol/liter; hemoglobin A(1c), 6.1-11.7%) underwent measurement of 1) fat-free mass ((3)H(2)O technique), 2) sc and visceral abdominal fat area (magnetic resonance imaging), 3) insulin sensitivity (euglycemic insulin clamp), 4) endogenous glucose output ([(3)H]glucose infusion technique), and 5) gluconeogenesis ((2)H(2)O method). After adjustment for sex, age, body mass index, diabetes duration, ethnicity, and sc fat area, VF area was positively related to fasting hyperglycemia (partial r = 0.46; P = 0.001) as well as to hemoglobin A(1c) (partial r = 0.50; P = 0.0003). Insulin sensitivity was reciprocally related to VF independently of body mass index (partial r = 0.33; P = 0.01). In contrast, the relation of basal endogenous glucose output to VF was not statistically significant. This lack of association was explained by the fact that VF was positively associated with gluconeogenesis flux (confounder-adjusted, partial r = 0.45; P = 0.003), but was reciprocally associated with glycogenolysis (partial r = 0.31; P < 0.05). We conclude that in patients with established type 2 diabetes, VF accumulation has a significant negative impact on glycemic control through a decrease in peripheral insulin sensitivity and an enhancement of gluconeogenesis.

Determinants of postabsorptive endogenous glucose output in non-diabetic subjects. European Group for the Study of Insulin Resistance (EGIR).

To gain insight into the physiologic determinants of postabsorptive endogenous glucose output (EGO) in humans. We analysed the data of 344 non-diabetic subjects (212 men and 132 women) with a wide range of age (18-85 years) and body mass index (15-55 kg/m2) who participated in the European Group for the Study of Insulin Resistance (EGIR) project. Whole-body endogenous glucose output was measured by tracer ([3H]glucose) dilution at steady-state, peripheral insulin sensitivity (alpha glucose clearance/alpha insulin) was measured by the euglycaemic insulin (7 pmol x min(-1) x kg(-1)) clamp technique. Whole-body endogenous glucose output showed a large variability (mean = 768 +/- 202 micromol x min(-1), range 209-1512) and was strongly related to lean body mass (r = 0.63,p < 0.0001). This association entirely explained the endogenous glucose output being higher in men than in women (827 +/- 189 vs 674 x 187 micromol x min(-1), p < 0.0001), its relation to body mass (+ 10 +/- 2 per unit of body mass index, p < 0.0001) and its trend to decline with age (-1.1 +/- 0.7 micromol x min(-1) per year, p = 0.10). Although inversely related to one another (r = -0.41, p < 0.0001), peripheral insulin sensitivity and fasting plasma insulin were both independently associated with endogenous glucose output in an inverse fashion (with partial r's of 0.19 and 0.21, respectively, after adjusting for lean body mass and centre, p < 0.0001 for both). Among non-diabetic subjects in the postabsorptive condition, total body endogenous glucose output variability is wide and is largely explained by the amount of lean mass; this, in turn, explains differences in total endogenous glucose output due to sex, obesity and age. Independently of the amount of lean mass, peripheral insulin resistance is associated with a higher endogenous glucose output independently of fasting plasma insulin concentration, suggesting coupled regulation of insulin action in peripheral tissues and the liver.

Influence of obesity and type 2 diabetes on gluconeogenesis and glucose output in humans: a quantitative study.

The contribution of gluconeogenesis (GNG) to endogenous glucose output (EGO) in type 2 diabetes is controversial. Little information is available on the separate influence of obesity on GNG. We measured percent GNG (by the 2H2O technique) and EGO (by 6,6-[2H]glucose) in 37 type 2 diabetic subjects (9 lean and 28 obese, mean fasting plasma glucose [FPG] 8.3 +/- 0.3 mmol/l) and 18 control subjects (6 lean and 12 obese) after a 15-h fast. Percent GNG averaged 47 +/- 5% in lean control subjects and was significantly increased in association with both obesity (P < 0.01) and diabetes (P = 0.004). By multivariate analysis, percent GNG was independently associated with BMI (partial r = 0.27, P < 0.05, with a predicted increase of 0.9% per BMI unit) and FPG (partial r = 0.44, P = 0.0009, with a predicted increase of 2.7% per mmol/l of FPG). In contrast, EGO was increased in both lean and obese diabetic subjects (15.6 +/- 0.5 micromol x min(-1) x kg(-1) of fat-free mass, n = 37, P = 0.002) but not in obese nondiabetic control subjects (13.1 0.7, NS) as compared with lean control subjects (12.4 +/- 1.4). Consequently, gluconeogenic flux (percent GNG x EGO) was increased in obesity (P = 0.01) and markedly elevated in diabetic subjects (P = 0.0004), whereas glycogenolytic flux was reduced only in association with obesity (P = 0.05). Fasting plasma glucagon levels were significantly increased in diabetic subjects (P < 0.05) and positively related to EGO, whereas plasma insulin was higher in obese control subjects than lean control subjects (P = 0.05) and unrelated to measured glucose fluxes. We conclude that the percent contribution of GNG to glucose release after a 15-h fast is independently and quantitatively related to the degree of overweight and the severity of fasting hyperglycemia. In obese individuals, reduced glycogenolysis ensures a normal rate of glucose output. In diabetic individuals, hyperglucagonemia contributes to inappropriately elevated rates of glucose output from both GNG and glycogenolysis.

Mice with gene disruption of both endothelial and neuronal nitric oxide synthase exhibit insulin resistance.

Studies from our laboratory using acute pharmacologic blockade of nitric oxide synthase (NOS) activity have suggested that nitric oxide (NO) has an important role in regulating carbohydrate metabolism. We now report on insulin sensitivity in mice with targeted disruptions in endothelial NOS (eNOS) and neuronal NOS (nNOS) genes compared with their wild-type (WT) counterparts. Mice underwent hyperinsulinemic-euglycemic clamp studies after a 24-h fast, during an insulin infusion of 20 mU x kg(-1) x min(-1). Glucose levels were measured at baseline and every 10 min during the clamp. Insulin levels were measured at baseline and at the end of the clamp study. Glucose infusion rates (GIRs) during the last 30 min of the clamp study were in a steady state. Tritiated glucose infusion was used to measure rates of endogenous glucose output (EGO) both at baseline and during steady-state euglycemia. Glucose disposal rates (GDRs) were computed from the GIR and EGO. Fasting and steady-state glucose and insulin levels were comparable in the 3 groups of mice. No differences in fasting EGO were noted between the groups. GIR was significantly reduced (37%, P = 0.001) in the eNOS knockout (KO) mice compared with the WT mice, with values for the nNOS mice being intermediate. EGO was completely suppressed in the nNOS and WT mice during insulin infusion, but not in the eNOS mice. Even so, the eNOS mice displayed significantly reduced whole-body GDRs compared with those of the WT mice (82.67+/-10.77 vs. 103.67+/-3.47 mg x kg(-1) x min(-1), P = 0.03). eNOS KO mice are insulin resistant at the level of the liver and peripheral tissues, whereas the nNOS KO mice are insulin resistant only in the latter. These data indicate that NO plays a role in modulating insulin sensitivity and carbohydrate metabolism and that the eNOS isoform may play a dominant role relative to nNOS.

Metabolic characteristics of individuals with impaired fasting glucose and/or impaired glucose tolerance.

With the release of the new 1997 American Diabetes Association diagnostic criteria, a new category was introduced, termed "impaired fasting glucose" (IFG). The metabolic abnormalities of individuals with IFG, compared with those with impaired glucose tolerance (IGT) (World Health Organization criteria), remain to be elucidated. We assessed insulin action (hyperinsulinemic clamp), insulin secretion (25-g intravenous glucose tolerance test), and endogenous glucose output (EGO) (3-(3)H-glucose) in 434 nondiabetic Pima Indians with either normal (NFG; <6.1 mmol/l) or impaired (IFG; 6.1-7.0 mmol/l) fasting glucose and with either normal (NGT; 2-h glucose <7.8 mmol/l) or impaired (IGT; 2-h glucose 7.8-11.1 mmol/l) glucose tolerance: NFG/NGT (n = 307), IFG/NGT (n = 11), NFG/IGT (n = 98), and IFG/IGT (n = 18). Compared with the NFG/NGT group, individuals with IFG/NGT had lower maximal insulin-stimulated glucose disposal (M; -20%, P < 0.01), a lower acute insulin response (AIR) to intravenous glucose (-33%, P < 0.05), and higher EGO (8%, P = 0.055). Individuals with NFG/IGT also had lower M (-21%, P < 0.001) and lower AIR (-8%, P < 0.05), but normal EGO (-1%, NS). Individuals with IFG/IGT showed the most severe abnormalities in M (-27%), AIR (-51%), and EGO (+13%) (all P < 0.001 compared with NFG/NGT). These group differences could be explained by the observation that AIR and EGO, but not M, were more strongly related to the fasting than to the 2-h glucose concentration. Thus, Pima Indians with isolated IFG and isolated IGT show similar impairments in insulin action, but those with isolated IFG have a more pronounced defect in early insulin secretion and, in addition, increased EGO. More severe metabolic abnormalities are present in Pima Indians with combined IFG and IGT.