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Background and aims Growth differentiation factor 15 (GDF15) is a strong predictor of cardiovascular morbidity and mortality found to be both marker and target of impaired glucose metabolism. GDF15 increases following glucose administration and is up-regulated in obesity and diabetes. We investigate here the relationship between GDF15 and beta cell function. Methods and results In this cross-sectional study we evaluated GDF15 concentrations in 160 obese subjects (BMI 35–63 kg/m2, age 39.4 ± 18.6 years, m/f 38/122) who underwent a 75 g oral glucose tolerance test (OGTT). Based on the OGTT results, the cohort was divided into two groups: 1) normal fasting glucose and normal glucose tolerance (n = 80), 2) impaired fasting glucose, impaired glucose tolerance or type 2 diabetes (n = 80). The relationship of GDF15 to fasting and OGTT-based dynamic insulin sensitivity and insulin secretion parameters was evaluated. GDF15 was higher in the prediabetes and diabetes groups and correlated with HbA1c, glucose, insulin as well as baseline and dynamic indices of insulin sensitivity and estimated beta cell function. Multiple regression analysis revealed that age, waist-to-height ratio, glomerular filtration rate and prehepatic beta cell function, but not the grade of impairment of glucose metabolism, were independent predictors of GDF15. Subgroup analysis showed that of all parameters of glucose metabolism only C-peptide, fasting prehepatic beta cell function and insulinogenic index remained significantly related to GDF15 in both groups. Conclusion We conclude that in patients with severe obesity, GDF15 strongly relates to beta cell function and should be further investigated as a potential therapeutic target and biomarker guiding treatment options.

The aim of the study was to investigate, whether type 2 diabetes independently influences adipokines and inflammatory markers in patients with metabolic syndrome.36 patients with metabolic syndrome without type 2 diabetes and 39 patients with metabolic syndrome with type 2 diabetes, carefully matched for age, sex, and BMI, were investigated. Primary outcome measures were circulating adipokines and inflammatory markers (adiponectin, leptin, visfatin, vaspin, resistin, TNF-α, IL-6, monocyte chemoattractant protein-1 (MCP-1), retinol binding protein 4 (RBP-4), growth differentiation factor-15 (GDF-15)). In addition, we determined parameters of glucose and lipid metabolism.Patients with metabolic syndrome and type 2 diabetes had significantly lower levels of plasma total cholesterol, low-density lipoprotein cholesterol and triglycerides (p0.05). They displayed higher GDF-15 concentrations (1,113 ± 135 vs. 656 ± 63 pg/ml, p = 0.005) and lower visfatin concentrations (3.7 ± 0.3 vs. 4.8 ± 0.2 ng/ml, p = 0.009). There were no differences in other adipokines and inflammatory markers between both groups.In patients with metabolic syndrome, type 2 diabetes leads to decreased visfatin and increased GDF-15 serum levels when compared to carefully matched non-diabetic subjects. Whether the increase in GDF-15 is an indicator or a causal factor for the increased cardiovascular risk in diabetic subjects remains to be investigated in further studies.

BACKGROUNDGrowth differentiation factor-15 (GDF-15) is a stress-responsive cytokine linked to obesity comorbidities such as cardiovascular disease, inflammation, and cancer. GDF-15 also has adipokine properties and recently emerged as a prognostic biomarker for cardiovascular events.METHODSWe evaluated the relationship of plasma GDF-15 concentrations with parameters of obesity, inflammation, and glucose and lipid metabolism in a cohort of 118 morbidly obese patients [mean (SD) age 37.2 (12) years, 89 females, 29 males] and 30 age- and sex-matched healthy lean individuals. All study participants underwent a 75-g oral glucose tolerance test; 28 patients were studied before and 1 year after Roux-en-Y gastric bypass surgery.RESULTSObese individuals displayed increased plasma GDF-15 concentrations (P < 0.001), with highest concentrations observed in patients with type 2 diabetes. GDF-15 was positively correlated with age, waist-to-height ratio, mean arterial blood pressure, triglycerides, creatinine, glucose, insulin, C-peptide, hemoglobin A1c, and homeostatic model assessment insulin resistance index and negatively correlated with oral glucose insulin sensitivity. Age, homeostatic model assessment index, oral glucose insulin sensitivity, and creatinine were independent predictors of GDF-15 concentrations. Roux-en-Y gastric bypass led to a significant reduction in weight, leptin, insulin, and insulin resistance, but further increased GDF-15 concentrations (P < 0.001).CONCLUSIONSThe associations between circulating GDF-15 concentrations and age, insulin resistance, and creatinine might account for the additional cardiovascular predictive information of GDF-15 compared to traditional risk factors. Nevertheless, GDF-15 changes following bariatric surgery suggest an indirect relationship between GDF-15 and insulin resistance. The clinical utility of GDF-15 as a biomarker might be limited until the pathways directly controlling GDF-15 concentrations are better understood.

Background: Because women have been excluded from many study populations in investigations of diabetes care, there is insufficient information on sex-specific differences in glycemic control. Objective: The aim of the present study was to assess whether treatment goals for glycemic and cardiovascular risk factor control are achieved equally in older, Central European, female and male patients with type 2 diabetes mellitus (T2DM). Methods: In a retrospective cross-sectional study, data were analyzed from consecutive older (aged ≥60 years) female and male patients with insulin-treated T2DM who attended a diabetes outpatient clinic between January 2007 and April 2008 at the Medical University of Vienna, Austria. Sex-specific differences in glycosylated hemoglobin (HbA1c) levels were assessed as the primary outcome. LDL-C and HDL-C, as well as systolic and diastolic blood pressure (SBP and DBP, respectively), were assessed as secondary outcomes and were adjusted for age, duration of diabetes, duration of insulin treatment, body mass index, insulin units per kilogram per day, and secondary causes of diabetes. P values were adjusted using the Bonferroni correction. Results: Data were analyzed from 183 female and 209 male patients with insulin-treated T2DM. In multivariate linear regression models, women had significantly higher levels of LDL-C (P = 0.008), HDL-C (P < 0.001), SBP (P < 0.001), and DBP (P = 0.034), but not HbA1c (P = NS). Multivariate logistic regression models revealed that women were significantly less likely to meet treatment goals for blood pressure (SBP, P = 0.044; DBP, P = 0.024), but not for cholesterol or HbA1c levels (P = NS for LDL-C, HDL-C, and HbA1c). Conclusion: In this study of older patients with insulin-treated T2DM, whereas glycemic control was comparable between women and men, a more adverse cardiovascular risk factor profile was observed in female patients.

The first-degree offspring of patients with type 2 diabetes are prone to develop type 2 diabetes, and have both insulin resistance and beta cell impairment. However, it is still unclear whether both pathophysiological features are inseparably combined and which is the outstanding determinant in the offspring.Glucose metabolism, insulin sensitivity (calculated as M value divided by insulin [M/I]) and beta cell function were studied in the offspring of individuals with type 2 diabetes (n = 187; 57% females; age 43.8 +/- 8.1 years; BMI 26.8 +/- 4.5 kg/m(2)) and in individuals without a family history of type 2 diabetes (controls, n = 519, 55% females; age 43.4 +/- 8.2 years; BMI 26.4 +/- 3.7 kg/m(2), no significant differences between the groups for any characteristic) by performance of 75 g OGTT and 2 h hyperinsulinaemic (40 mU min(-1) m(-2))-isoglycaemic clamp tests. Beta cell function was evaluated by calculating insulinogenic index (IGI) from C-peptide AUC:glucose AUC ratios from the first hour of OGTT (IGI[60 min]) and from the total OGTT (IGI[120 min]).During the OGTT, the offspring of individuals with type 2 diabetes showed 4-14% higher plasma glucose from 30 to 120 min (p0.05) and 20-29% higher serum insulin from 90 to 120 min, but decreased IGI(60 min) and IGI(120 min) (p0.05). M/I was 11% lower in the offspring of affected individuals than in controls (p0.01). To study the offspring of patients with type 2 diabetes with insulin sensitivity similar to that of the control group, the offspring of affected patients were divided into M/I quartiles. Those in the third M/I quartile showed M/I values and major anthropometric characteristics similar to those of the controls, but insulin AUC and C-peptide AUC values were lower in the first hour and the total OGTT (p0.05). The third M/I quartile had lower IGI values at 60 min and 120 min: 11% and 14% lower, respectively (p0.02).The first-degree offspring of type 2 diabetic patients show insulin resistance and beta cell dysfunction in response to oral glucose challenge. Beta cell impairment exists in insulin-sensitive offspring of patients with type 2 diabetes, suggesting beta cell dysfunction to be a major defect determining diabetes development in diabetic offspring.

Context: Recent data suggest that circulating retinol-binding protein (RBP) might be involved in the pathogenesis of insulin resistance. Moreover, protein C inhibitor (PCI), which specifically binds retinoic acid, was found to be increased in myocardial infarction survivors who are also insulin resistant.Objective: The objective of this study was to investigate the association of insulin resistance with RBP factors and PCI active antigen.Design and Setting: This was a clinical study.Patients: Nondiabetic humans with high (IS; n = 20, 14 females, six males, aged 47.2 ± 1.9 yr, body mass index 26 ± 1 kg/m2) and low (IR; n = 20, 14 females, six males, aged 45.5 ± 1.7 yr, body mass index 28 ± 1 kg/m2) insulin-stimulated glucose-disposal (M) participated in this study.Main Outcome Measures: M was measured by 2-h hyperinsulinemic (40 mU·min−1·m−2)-isoglycemic clamp tests. Measurements of RBP were performed using a nephelometric method and validated using quantitative Western blotting.Results: M (80–120 min) was higher in IS (10.9 ± 0.6 mg·min−1·kg−1) than IR (4.0 ± 0.2; P < 10−12). Fasting plasma RBP concentrations were comparable between IS and IR measured by both nephelometry (IS: 4.4 ± 0.3; IR: 4.6 ± 0.3 mg/dl, P = 0.6) and quantitative Western blot (IS 7.9 ± 0.5, IR 8.3 ± 0.6 mg/dl; P = 0.6). Fasting plasma PCI active antigen was similar in both groups. Plasma RBP and PCI were not significantly related to M. RBP was positively correlated with uric acid (r = 0.488, P = 0.003), triglycerides (r = 0.592, P < 0.001), prealbumin (r = 0.63, P < 0.0001), and vitamin A (r = 0.75, P < 10−6).Conclusions: Our data demonstrate that healthy, insulin-resistant humans do not show altered plasma retinol binding factors, such as RBP and PCI. Both do not significantly correlate with insulin sensitivity. Thus, our findings do not support the hypothesis of insulin sensitivity modulation by proteins involved in retinol transport.

Obestatin, a recently discovered 23-amino acid peptide, is involved in the regulation of appetite and body weight in antagonistic fashion to ghrelin, both deriving from a common precursor peptide. Ghrelin was shown to be associated with insulin resistance, which may also affect obestatin. We investigated the association between insulin resistance and plasma concentrations of obestatin and ghrelin in nondiabetic individuals with high (IS; n = 18, 13 females and 5 males, age 47 ± 2 yr, BMI = 25.5 ± 0.9 kg/m2) and low (IR; n = 18, 12 females and 6 males, age 45 ± 2 yr, P = 0.49, BMI = 27.5 ± 1.1 kg/m2, P = 0.17) insulin-stimulated glucose disposal (M), measured by 2-h hyperinsulinemic (40 mU·min−1·m−2) isoglycemic clamp tests. M100–120 min was higher in IS (10.7 ± 0.7) than in IR (4.4 ± 0.2 mg·min−1·kg−1, P < 10−9), whereas insulin-dependent suppression of free fatty acids (FFA) in plasma was reduced in IR (71 ± 6% vs. IS: 82 ± 5%, P < 0.02). In both groups, plasma ghrelin concentrations were comparable at fasting and similarly reduced by 24–28% during insulin infusion. IR had lower fasting plasma obestatin levels (383 ± 26 pg/ml vs. IS: 469 ± 23 pg/ml, P < 0.02). Clamp insulin infusion reduced plasma obestatin to ∼81% of basal values in IS ( P < 0.00002), but not in IR. Fasting plasma obestatin was correlated positively with M ( r = 0.34, P = 0.04), HDL cholesterol ( r = 0.45, P = 0.01), and plasma ghrelin concentrations ( r = 0.80, P < 0.000001) and negatively with measures of adiposity, plasma FFA during clamp ( r = −0.42, P < 0.01), and systolic blood pressure ( r = −0.33, P < 0.05). In conclusion, fasting plasma concentrations of obestatin, but not of ghrelin, are reduced in insulin resistance and are positively associated with whole body insulin sensitivity in nondiabetic humans. Furthermore, plasma obestatin is reduced by insulin in insulin-sensitive but not in insulin-resistant persons.

Background Elevated circulating free fatty acids (FFAs) induce insulin resistance and play a crucial role in the development of type 2 diabetes, in which fasting hepatic glucose production (HGP) is increased. However, direct effects of FFAs on fasting HGP are still unclear because indirect endocrine and metabolic effects contribute to FFA action. Thus, we aimed to investigate acute direct effects of specific FFAs on fasting HGP, lactate uptake, and insulin signalling. Materials and methods Isolated livers obtained from 20 h fasted rats were perfused with albumin-bound palmitate or oleate (200 µ mol L ‐1 each) or vehicle (control) for 180 min ( n = 5‐7/group). Results Compared to control, hepatic lactate uptake was increased by palmitate and oleate (~+40%; P < 0·05), while HGP from lactate (~3 mmol L ‐1 ) and liver glycogen content were similar. Tyrosine phosphorylation (pY) of insulin-receptor-substrate-(IRS)-2 and p70S6kinase phosphorylation were not affected by FFAs. Palmitate decreased insulin-receptor- β pY, IRS-1 pY and phosphoinositol-3-kinase expression by 46 ± 16%, 46 ± 11% and 20 ± 9%, respectively ( P < 0·03), while oleate reduced Akt phosphorylation by 85 ± 7% ( P < 0·006). Conclusions Isolated liver perfusion with saturated or unsaturated FFAs reduced insulin signalling protein phosphorylation at different sites and increased lactate uptake without affecting HGP or glycogen content. These results suggest that at fasting, both saturated and unsaturated FFAs increase hepatic glucose precursor uptake and may, independently of insulin’s presence, accelerate protein dephosphorylation of the insulin signalling cascade at different sites.

Critical illness is characterized by a hypermetabolic state associated with increased mortality, which is partly ascribed to the occurrence of hyperglycemia caused by enhanced endogenous glucose production and insulin resistance (IR). Insulin resistance is well described in patients after surgery and trauma. However, it is less clearly quantified in critically ill medical patients. In this clinical cohort study, IR (M value) was quantified in 40 critically ill medical patients and 25 matched, healthy controls by isoglycemic hyperinsulinemic clamps after an overnight fast on the day after admission to a medical intensive care unit. Energy and substrate metabolism were measured by using indirect calorimetry in the patients before and during the clamp. The severity of illness was assessed by the acute physiology and chronic health evaluation (APACHE) III score. M values of critically ill medical patients were significantly lower compared with healthy controls (2.29 +/- 1.0 and 7.6 +/- 2.9 mg/kg per minute, respectively; P < .001) and were closely related to APACHE III scores (r = -0.43, P < .01), body mass index (r = -0.41, P < .01), and resting energy expenditure (r = 0.40, P < .05). The M value was not associated with age, basal glucose concentrations, and respiratory quotient, and it did not differ among patients with various admission diagnoses. In conclusion, insulin sensitivity was found to be reduced by 70% in critically ill medical patients. The severity of IR was associated with the severity of illness, body mass index, and resting energy expenditure, but not with substrate oxidation rates. In addition, the severity of IR did not vary among patients with different admission diagnoses.

Aims: We investigated long-term mortality and requirement of renal replacement therapy (RRT) in type 1 diabetes mellitus (T1DM) to study risk factors and late complication incidence of T1DM in a prospective cohort study at Lainz Hospital, Vienna, Austria. Methods: In 1983–1984, T1DM patients [n = 648; 47% females, 53% males; age, 30 ± 11 yr; T1DM duration, 15 ± 9 yr; body mass index, 24 ± 4 kg/m2; glycated hemoglobin (HbA1c), 7.6 ± 1.6%] were stratified into HbA1c quartiles [1st, 5.9 ± 0.5% (range, 4.2–6.5%); 2nd, 6.9 ± 0.3% (6.6–7.4%); 3rd, 7.9 ± 0.3% (7.5–8.4%); and 4th, 9.6 ± 1.3% (8.5–14.8%)]. Twenty years later, both endpoints (death and RRT) were investigated by record linkage with national registries. Results: At baseline, creatinine clearance, blood pressure, and body mass index were comparable among the HbA1c quartiles, whereas albuminuria was more frequent in the 4th quartile (+15%; P < 0.03). After the 20-yr follow-up, 13.0% of the patients had died [rate, 708 per 100,000 person-years (95% confidence interval, 557–859)], and 5.6% had received RRT [311 per 100,000 person-years (95% confidence interval, 210–412)]. Patients with the highest HbA1c values (4th quartile) had a higher mortality rate and a greater incidence of RRT (P < 0.04). In the Cox proportional hazards analysis, age, male gender, increased HbA1c, albuminuria, and reduced creatinine clearance were predictors of mortality (P < 0.05). Predictors of RRT were albuminuria (P < 0.001), reduced creatinine clearance (P < 0.001), and belonging to the 4th HbA1c quartile (P = 0.06). In Kaplan-Meier analysis, mortality was linearly associated with poor glycemia, whereas RRT incidence appeared to rise at a HbA1c threshold of approximately 8.5%. Conclusion/Interpretation: In the Lainz T1DM cohort, 13.0% mortality and 5.6% RRT were directly associated with and more frequently found in poor glycemia, showing that good glycemic control is essential for the longevity and quality of life in T1DM.

Endocrine defensive mechanisms provide for energy supply during hypoglycemia. Intramyocellular lipids (IMCL) were recently shown to contribute to energy supply during exercise.The objective of this study was to assess the contribution of IMCL compared with lipolysis and endogenous glucose production (EGP) to insulin-mediated hypoglycemia counterregulation in patients with type 1 diabetes mellitus (T1DM).This was a prospective explorative study performed in a university research facility.Six well-controlled T1DM (age, 29 +/- 4 yr; body mass index, 23.4 +/- 1.0 kg/m2; hemoglobin A1c, 6.3 +/- 0.1%) and six nondiabetic humans (controls; age, 28 +/- 2 yr; body mass index, 23.4 +/- 1.0 kg/m2; hemoglobin A1c, 5.1 +/- 0.1%) were studied.We performed 240-min hypoglycemic (approximately 3 mM)-hyperinsulinemic (0.8 mU/kg x min) clamps on separate days to measure: 1) systemic lipolysis ([2H5]glycerol turnover), EGP ([6,6-(2)H2]glucose), and local lipolysis in abdominal s.c. adipose tissue and gastrocnemius muscle (microdialysis); and 2) IMCL (by 1H nuclear magnetic resonance spectroscopy) in soleus and tibialis anterior muscle.The main outcome measures were changes in IMCL during prolonged hypoglycemia.At baseline, EGP, glycerol turnover, and IMCL were not different between the groups. During hypoglycemia, hormonal counterregulation was blunted in T1DM (peak: glucagon, 68 +/- 4 vs. 170 +/- 37 pg/ml; cortisol, 16 +/- 2 vs. 24 +/- 2 microg/dl; epinephrine, 274 +/- 84 vs. 597 +/- 212 pg/ml; all P0.05 vs. control). T1DM had approximately 50% lower EGP (4.6 +/- 0.6 vs. 10.9 +/- 0.5 micromol/kg x min; P0.005), but approximately 40% higher glycerol turnover (374 +/- 21 vs. 272 +/- 19 micromol/kg x min; P0.01). Glycerol concentrations in muscle (T1DM, 302 +/- 22 control, 346 +/- 17 micromol/liter) and adipose tissue (264 +/- 25 vs. 318 +/- 25 micromol/liter) did not differ between groups. IMCL in soleus and tibialis anterior muscle did not change from baseline during hypoglycemia.In well-controlled T1DM, impaired hypoglycemia counterregulation is associated with decreased glucose production and augmented whole body lipolysis, which cannot be explained by either hydrolysis of muscle triglycerides or increased abdominal s.c. adipose tissue lipolysis.

Background Leptin is primarily secreted by the adipose tissue. It binds not only to hypothalamic structures involved in energy regulation but also to many peripheral tissues including the liver. Leptin circulates in free and receptor-bound forms. Both components are differentially regulated under various pathophysiological conditions and serve different physiological functions. They are released from adipose tissue but previous data suggest an additional formation outside the fat compartment. Here we tested the contribution of the liver in binding and modulating leptin in the circulation. Materials and methods In vivo experiments were performed with radioactive labelled leptin with and without pretreatment with unlabelled leptin in freely moving, chronic intravenously cannulated male rats. Livers were investigated by immunohistochemistry and in situ hybridization and immunoblotting was performed, followed by ex vivo liver perfusion studies with human recombinant leptin. Results In in vivo experiments radioactively labelled leptin (at low concentrations) is avidly bound to rat liver (greater than 80% of basal serum values 90 min following i.v. infusion). Pre-treatment with excess of unlabelled leptin in vivo revealed a rapid hepatic down-regulation of leptin receptor isoforms when tested by in situ hybridization, immunoblotting or immunohistochemistry. Ex vivo perfusion of rat liver with human recombinant leptin induced a dose- and time-dependent formation of receptor-bound leptin in the perfusate. Conclusions The present data support an active role of the liver in the modulation of the leptin signal through different regulation of the soluble leptin receptor, the bound and free forms of the hormone, which may have important implications for leptin's central efficacy and the development of ‘leptin resistance’.

The efficacy of DMARD therapy in rheumatoid arthritis (RA) can be judged by radiological analysis. This study aimed to determine the time-dependent progression of joint damage, acute-phase response, and rates of radiologic progression in early DMARD-treated RA patients over 10 years.We evaluated outpatient records, and radiographs of hands and feet of 54 early RA patients on DMARDs for 10 years. Radiographs were quantified by the Larsen method using recently developed quantification software.Radiological damage attenuated, with disease progression from baseline to Year 10 [correlation coefficient (r)=0.95, probability (p)0.001]. Radiographic scores progressed more rapidly during the first 5 years than thereafter. Cumulative erythrocyte sedimentation rate (ESR) was strongly correlated with radiological progression (p0.001, r=0.88).Our findings reveal a higher amount of radiographic RA progression during the first years of DMARD treatment. Thus, our data provide strong evidence for the importance of both early DMARD therapy and continuous radiographic assessments in RA.

The study was designed to examine the contribution of direct (substrate-mediated) and indirect (hormone-mediated) effects of amino acids on hepatic glucose metabolism in healthy men.The protocols were: (i) CON+S (n=7): control conditions with somatostatin to inhibit endogenous hormone release resulting in fasting plasma concentrations of amino acids, insulin (approximately 28 pmol/l) and glucagon (approximately 65 ng/l), (ii) AA+S ( n=7): amino acid infusion-fasting insulinaemia-fasting glucagonaemia, (iii) GLUC+S ( n=6): fasting amino acids-fasting insulinaemia-hyperglucagonaemia (approximately 99 ng/l) and (iv) AA-S (n=5): amino acid infusion without somatostatin resulting in amino acid-induced hyperinsulinaemia (approximately 61 pmol/l)-hyperglucagonaemia (approximately 147 ng/l). Net glycogenolysis was calculated from liver glycogen concentrations using (13)C nuclear magnetic resonance spectroscopy. Total gluconeogenesis (GNG) was calculated by subtracting net glycogenolysis from endogenous glucose production (EGP) which was measured with [6,6-(2)H(2)]glucose. Net GNG was assessed with the (2)H(2)O method.During AA+S and GLUC+S, plasma glucose increased by about 50% (p0.01) due to a comparable rise in EGP. This was associated with a 53-% (p0.05) and a 65% increase (p0.01) of total and net GNG during AA+S, whereas net glycogenolysis rose by 70% (p0.001) during GLUC+S. During AA-S, plasma glucose remained unchanged despite nearly-doubled (p0.01) total GNG.Conditions of postprandial amino acid elevation stimulate secretion of insulin and glucagon without affecting glycaemia despite markedly increased gluconeogenesis. Impaired insulin secretion unmasks the direct gluconeogenic effect of amino acids and increases plasma glucose.

Leptin has recently been suggested to play a role in the pathogenesis of hepatic steatosis. Consequently, this study was designed to examine the direct effects of portal leptin on the intrahepatic lipid contents in the postabsorptive state. Rat livers (n = 6 per group) were perfused in a recirculating system and portally infused with leptin (0.5 nmol/L, 5 nmol/L, and 25 nmol/L), insulin (10 nmol/L), leptin (5 nmol/L) plus insulin (10 nmol/L), glucagon (1 nmol/L), or vehicle (control). Intrahepatic contents of triglycerides, free cholesterol, cholesteryl esters, and free fatty acids were determined from the lipid extract of frozen livers by capillary gas chromatography. Short-term leptin infusion increased total triglycerides in a concentration-dependent (0.5 nmol/L: 2.8 ± 0.4 mg/g, 5 nmol/L: 7.0 ± 0.5 mg/g, 25 nmol/L: 8.3 ± 1.0 mg/g) and time-dependent manner. Total triglycerides also rose during exposure to insulin plus leptin (7.2 ± 0.6 mg/g) but fell during glucagon infusion (2.6 ± 0.2 mg/g; control: 4.3 ± 0.3 mg/g;P < .05). Leptin, insulin, and glucagon increased intrahepatic free cholesterol (P < .05). Free fatty acids were also higher during leptin exposure (0.5 nmol/L: 1.28 ± 0.08 mg/g, 5 nmol/L: 0.47 ± 0.01 mg/g, 25 nmol/L: 0.48 ± 0.04 mg/g, control: 0.38 ± 0.03 mg/g; P < .05). In conclusion, hyperleptinemia increases hepatic triglyceride content and may therefore contribute to hepatic steatosis in hyperleptinemic obese patients. (Hepatology 2000;32:1045-1049.)

Obesity, a state of apparent "leptin resistance" is well known to be associated with insulin resistance. In diet-induced obesity (DIO), hepatic insulin signaling is impaired but the link between leptin and insulin signaling pathways is only incompletely defined. The aim of the present study was to evaluate the effects of DIO on leptin and insulin cross-signaling in the liver. Leptin receptor expression was measured by in situ hybridization with pan-leptin receptor probes and by immunoblotting. Furthermore, intracellular signaling was investigated in vivo under basal conditions and at 45 and 360 min after stimulation with a bolus of human recombinant leptin (hrec-leptin; 1 mg/kg body wt) or saline. At baseline, all forms of the leptin receptor were markedly to completely down-regulated in DIO rats. Hrec-leptin bolus injection stimulated leptin-dependent signaling with a fivefold increase in JAK-2pY in lean but not in DIO rats. Basal IRpY, IRS-1pY, IRS-1p85, IRS-2pY, IRSp85, and PKBpT308 levels were reduced (P0.01) in DIO rats as compared with lean controls. Basal GSK-3beta serine phosphorylation (S9) was higher (P0.01) in lean animals along with lower basal PEPCK activity compared with DIO rats consistent with the insulin and leptin resistance of the latter. Only in lean animals phosphorylation of PKB (T308) and GSK-3beta (S9) was acutely stimulated by leptin at 45 min followed by inhibition at 6 h after application. AMPKalpha protein levels as well as basal and leptin-stimulated total and alpha-specific AMPK activity were comparable in both groups. These data show that in a model of dietary-induced obesity 1) leptin receptors and subsequent signaling events are down-regulated, 2) basal insulin signaling is impaired, and 3) the cross-talk between leptin and insulin signaling is differentially regulated by the nutritional status, which is sensed by AMPK in rat liver. Thus, the liver seems to play a major role in the modulation of the leptin signal and insulin resistance in obesity.

Aims Thiazoledinediones decrease blood glucose by their insulin-sensitizing properties. Here, we examined whether pioglitazone plus nateglinide (PIO) interferes with hepatocellular lipid (HCL) content and/or improves insulin sensitivity in well-controlled non-obese patients with type 2 diabetes mellitus (T2DM). Methods Sixteen patients [body mass index (BMI): 28 ± 1 kg/m2; HbA1c: 7.1 ± 0.6%] were studied in a randomized, double-blind, 12-week parallel group trial, whereas matched healthy humans [non-diabetic control subjects (CON), BMI: 26 ± 1 kg/m2] were studied once. Treatment with pioglitazone (30 mg/day) plus nateglinide (PIO arm) to control for glimepiride-induced insulin secretion was compared to treatment with glimepiride (2 mg/day) plus placebo (GLI arm). Multinuclei magnetic resonance spectroscopy (MRS) was combined with pancreatic normoglycaemic-two-step-insulin clamps and stable isotopes to assess glucose turnover, glucose transport/phosphorylation, HCL and intramyocellular lipid (IMCL) contents, non-esterified fatty acids (NEFA) and adipokines. Results At baseline, HCL was approximately 5.6-fold higher in T2DM (p

The aim of the study was to evaluate the 3 years incidence of cardiometabolic risk factors, such as impaired fasting glucose, reduced high-density lipoprotein (HDL)-cholesterol, increased plasma triglycerides or blood pressure as well as impaired glucose tolerance in overweight or obese (ow/ob) and normal body weight (nbw) subjects metabolically normal at baseline. Subjects from the Relationship between Insulin Sensitivity and Cardiovascular Disease (RISC) study were analyzed. We analyzed 284 nbw and 152 ow/ob subjects who, at baseline, did not show any of the above-mentioned cardiometabolic risk factors. At 3 years, these parameters were re-evaluated. Intima-media thickness (IMT) of the common carotid artery (CCA) was echographically measured. At follow-up, the incidence of one or more cardiometabolic risk factors was 57.2% in ow/ob vs. 31.7% in nbw (P < 0.0001). After adjustment for age, sex, menopause status, lifestyle parameters, insulin sensitivity, and fasting insulinemia, BMI remained significantly linked to the development of one or more cardiometabolic risk factors (P = 0.02). An increased BMI at follow-up was significantly associated with the development of cardiometabolic alterations, in both nbw and ow/ob groups (P = 0.04). Ow/ob subjects who, at 3 years follow-up, remained metabolically normal, showed a less favourable cardiometabolic profile, when compared to nbw counterparts. In ow/ob metabolically normal males and females, intima-media of the common carotid at follow-up was thicker than in nbw (P = 0.03 for males, P = 0.04 for females). In conclusion, metabolically normal obese subjects show a higher incidence of cardiometabolic risk factors, in a short follow-up period. Weight gain is significantly associated with the development of these factors, in both nbw and ow/ob subjects.

OBJECTIVE Recent work has shown that insulin stimulates its own secretion in insulin-sensitive humans, suggesting that insulin resistance in the β-cell could cause β-cell dysfunction. We have tested whether insulin exposure and insulin sensitivity modulate β-cell function in subjects with normal glucose tolerance (NGT) and whether they contribute to dysglycemia in impaired glucose regulation (IGR). RESEARCH DESIGN AND METHODS Insulin sensitivity (by euglycemic clamp), insulin-induced secretory response at isoglycemia (IISR) (as C-peptide percent change from basal during the clamp), glucose-induced secretory response (GISR) to an intravenous glucose bolus, and β-cell glucose sensitivity (β-GS) (by oral glucose tolerance test [OGTT] modeling) were measured in 1,151 NGT and 163 IGR subjects from the RISC (Relationship between Insulin Sensitivity and Cardiovascular Disease) study. RESULTS In NGT, IISR was related to both insulin sensitivity and antecedent insulin exposure; GISR was related to insulin exposure. IISR was positively, if weakly, related to β-GS (r= 0.16, P < 0.0001). Both IISR (−23 [39] vs. −9 [2]%, median [interquartile range], P < 0.03) and β-GS (69 [47] vs. 118 [83] pmol ⋅ min–1 ⋅ m–2 ⋅ mmol–1 ⋅ L, P < 0.0001) were decreased in IGR compared with NGT. Insulin sensitivity and β-GS were the major determinants of mean OGTT glucose in both NGT and IGR, with a minor role for IISR. In a multivariate logistic model, IGR was predicted by β-GS (odds ratio 4.84 [95% CI 2.89–8.09]) and insulin sensitivity (3.06 [2.19–4.27]) but not by IISR (1.11 [0.77–1.61]). CONCLUSIONS Pre-exposure to physiological hyperinsulinemia stimulates insulin secretion to a degree that depends on insulin sensitivity. However, this phenomenon has limited impact on β-cell dysfunction and dysglycemia.

OBJECTIVE Glucose is the major stimulus for insulin release. Time course and amount of insulin secreted after glycemic stimulus are different between type 2 diabetes mellitus (T2DM) patients and healthy subjects. In rodents, it was demonstrated that insulin can modulate its own release. Previous studies in humans yielded contrasting results: Insulin was shown to have an enhancing effect, no effect, or a suppressive effect on its own secretion. Thus, we aimed to evaluate short-term effects of human insulin infusion on insulin secretion during normoglycemia in healthy humans and T2DM subjects of both sex. RESEARCH DESIGN AND METHODS Hyperinsulinemic-isoglycemic clamps with whole-body insulin-sensitivity (M) and C-peptide measurements for insulin secretion modeling were performed in 65 insulin-sensitive (IS) subjects (45 ± 1 year, BMI: 24.8 ± 0.5 kg/m2), 17 insulin-resistant (IR) subjects (46 ± 2 years, 28.1 ± 1.3 kg/m2), and 20 T2DM patients (56 ± 2 years, 28.0 ± 0.8 kg/m2; HbA1c = 6.7 ± 0.1%). RESULTS IS subjects (M = 8.8 ± 0.3 mg · min−1 · kg−1) had higher (P < 0.00001) whole-body insulin sensitivity than IR subjects (M = 4.0 ± 0.2) and T2DM patients (M = 4.3 ± 0.5). Insulin secretion profiles during clamp were different (P < 0.00001) among the groups, increasing in IS subjects (slope: 0.56 ± 0.11 pmol/min2) but declining in IR (−0.41 ± 0.14) and T2DM (−0.87 ± 0.12, P < 0.00002 IR and T2DM vs. IS) subjects. Insulin secretion changes during clamp directly correlated with M (r = 0.6, P < 0.00001). CONCLUSIONS Insulin release during normoglycemia can be modulated by exogenous insulin infusion and directly depends on whole-body insulin sensitivity. Thus, in highly sensitive subjects, insulin increases its own secretion. On the other hand, a suppressive effect of insulin on its own secretion occurs in IR and T2DM subjects.

Roux-en-Y-Gastric-Bypass (RYGB) reduces overall and diabetes-specific mortality by 40% and over 90%. This study aims to gain insight into the underlying mechanisms of this effect. We evaluated time-courses of glucose, insulin, C-peptide, and the incretin glucagon like peptide-1 (GLP-1) following an oral glucose load. Insulin-sensitivity was measured by a hyperinsulinemic-isoglycemic-clamp-test; glucose-turnover was determined using D-[6,6-(2)H(2)] glucose. Examinations were performed in six nondiabetic patients with excess weight before (PRE: BMI: 49.3 +/- 3.2 kg/m(2)) and 7 months after RYGB (POST: BMI: 36.7 +/- 2.9 kg/m(2)), in a lean (CON: BMI: 22.6 +/- 0.6 kg/m(2)) and an obese control group (CONob) without history of gastrointestinal surgery (BMI: 34.7 +/- 1.2 kg/m(2)). RYGB reduced fasting plasma concentrations of insulin and C-peptide (P < 0.01, respectively) whereas fasting glucose concentrations remained unchanged. After RYGB increase of C-peptide concentration following glucose ingestion was significantly higher compared to all other groups (dynamic-area under the curve (Dyn-AUC): 0-90 min: POST: 984 +/- 115 ng.min/ml, PRE: 590 +/- 67 ng.min/ml, CONob: 440 +/- 44 ng.min/ml, CON: 279 +/- 22 ng.min/ml, P < 0.01 respectively). Early postprandial increase of glucose concentration was however not affected. GLP-1 concentrations following glucose ingestion were sixfold higher after RYBG than before (P = 0.01). Insulin-stimulated glucose uptake tended to increase postoperatively (M-value: PRE: 1.8 +/- 0.5, POST: 3.0 +/- 0.3, not significant (n.s.)). Endogenous glucose production (EGP) was unaffected by RYGB. Hepatic insulin resistance index improved after RYGB and was then comparable to both control groups (PRE: 29.2 +/- 4.3, POST: 12.6 +/- 1.1, P < 0.01). RYGB results in hyper-secretion of insulin and C-peptide, whereas improvements of insulin resistance are minor and seem to occur rather in the liver and the adipose tissue than in the skeletal muscle.

Background:Several epidemiological studies revealed sex-specific differences during oral glucose tolerance tests (OGTTs), such as higher prevalence of glucose intolerance (i.e. increased glucose at the end of the OGTT) in females, which was not yet explained. Thus, we aimed to analyze sex-related distinctions on OGTT glucose metabolism, including gut absorption, in healthy humans.Methods:Females (n = 48) and males (n = 26) with comparable age (females, 45 ± 1 yr; males, 44 ± 2 yr) and body mass index (both, 25 ± 1 kg/m2) but different height (females, 166 ± 1 cm; males, 180 ± 2 cm; P < 0.000001), all normally glucose tolerant, as tested by frequently sampled, 3-h (75-g) OGTTs, underwent hyperinsulinemic [40 mU/(min · m2)] isoglycemic clamp tests with simultaneous measurement of endogenous glucose (d-[6,6-2H2]glucose) production (EGP). EGP and glucose disappearance during OGTT were calculated from logarithmic relationships with clamp test insulin concentrations. After reliable model validation by double-tracer technique (r = 0.732; P < 0.007), we calculated and modeled gut glucose absorption (ABS).Results:Females showed lower (P < 0.05) fasting EGP [1.4 ± 0.1 mg/(kg · min)] than males [1.7 ± 0.1 mg/(kg · min)] but comparable whole-body insulin sensitivity in clamp tests [females, 8.1 ± 0.4 mg/(kg · min); males, 8.3 ± 0.6 mg/(kg · min)]. Plasma glucose OGTT concentrations were higher (P < 0.04) from 30–40 min in males but from 120–180 min in females. Glucose absorption rates were 21–46% increased in the initial 40 min in males but in females by 27–40% in the third hour (P < 0.05). Gut glucose half-life was markedly higher in females (79 ± 2 min) than in males (65 ± 3 min, P < 0.0001) and negatively related to body height (r = −0.481; P < 0.0001).Conclusions:This study in healthy, glucose-tolerant humans shows for the first time different ABS rates during OGTT in women and men and a negative relationship between body height and gut glucose half-life. Prolonged ABS in females might therefore contribute to higher plasma glucose concentrations at the end of OGTT.

Hyperlipidemia and obesity are associated with metabolic syndrome and increased risk in developing diabetes and cardiovascular disease. Nutritional supplements, e.g. L-carnitine and polyunsaturated fatty acids (PUFAs), exert lipid-lowering effects. Hence, the hypothesis that dietetic intervention reduces plasma lipid levels and metabolic enzymes in overweight hyperlipidemic subjects was tested.In a prospective placebo-controlled double-blind study in 22 moderately hyperlipidemic obese humans consuming low-fat yoghurt enriched with a combination of low-dose PUFAs, polyphenols and L-carnitine (PPC) twice a day for 12 weeks were compared to 20 matching participants ingesting low-fat yoghurt. The effects on plasma lipids and expression of enzymes involved in regulation of fatty acid oxidation in peripheral blood mononuclear cells (PBMCs) and HepG2 cells were evaluated.PPC consumption led to significantly reduced plasma free fatty acid (-29%) and triglyceride (-24%) concentrations (each p0.05). PPC application increased significantly peroxisome proliferator-activated receptor α (PPARα) mRNA abundances and those of PPARα target genes (carnitine palmitoyltransferases-1, CPT1A and CPT1B, carnitine acetyltransferase and organic cation transporter 2; each p0.05) in PBMCs. In controls, plasma lipid levels and PBMC gene expression did not change. These findings were substantiated by the results of cell culture experiments in HepG2 cells.Supplementation of PPC had marked lipid-lowering effects and PBMC gene expression profiles seemed to reflect nutrition-related metabolic changes.

OBJECTIVE So far it is unclear whether chronic peripheral hyperinsulinemia per se might contribute to ectopic lipid accumulation and consequently insulin resistance. We investigated the effects of systemic instead of portal insulin release in type 1 diabetic patients after successful pancreas-kidney transplantation (PKT) with systemic venous drainage on the intracellular lipid content in liver and soleus muscle, endogenous glucose production (EGP), and insulin sensitivity. RESEARCH DESIGN AND METHODS In nine PKT patients and nine matching nondiabetic control subjects, intrahepatocellular lipids (IHCLs) and intramyocellular lipids (IMCLs) were measured using 1H nuclear magnetic resonance spectroscopy. Fasting EGP was measured using d-[6,6-2H2]glucose tracer dilution. A 3-h 75-g oral glucose tolerance test (OGTT) allowed us to assess kinetics of glucose, free fatty acids, insulin, and C-peptide concentrations in plasma and to calculate the clamp-like index (CLIX) for insulin sensitivity and the hepatic insulin resistance (HIR) index. RESULTS The PKT patients displayed approximately twofold increased fasting insulin (20 ± 6 vs. 9 ± 3 μU/ml; P < 0.0002) compared with that in nondiabetic control subjects and ∼10% increased fasting glucose (P < 0.02) concentrations, but during the OGTT areas under the concentration curves of C-peptide and insulin were similar. IHCL (PKT, 2.9 ± 2.5%; nondiabetic control subjects, 4.4 ± 6.6%), IMCL (PKT, 1.0 ± 0.4%; nondiabetic control subjects, 1.0 ± 0.5%), CLIX (PKT, 8 ± 2; nondiabetic control subjects, 7 ± 3), HIR (PKT, 25.6 ± 13.2; nondiabetic control subjects, 35.6 ± 20 [mg · min−1 · kg−1] × [μU/ml]), and EGP (PKT, 1.6 ± 0.2; nondiabetic control subjects, 1.7 ± 0.2 mg · min−1 · kg−1) were comparable between PKT patients and nondiabetic control subjects. IHCL was negatively correlated with CLIX in all participants (r = −0.55; P < 0.04). CONCLUSIONS Despite fasting peripheral hyperinsulinemia because of systemic venous drainage, type 1 diabetic patients after PKT show similar IHCL, IMCL, insulin sensitivity, and fasting EGP in comparison with nondiabetic control subjects. These results suggest that systemic hyperinsulinemia per se does not cause ectopic lipid accumulation in liver and skeletal muscle.

Successful simultaneous pancreas-kidney transplantation (SPK) in Type 1 diabetic (T1DM) patients results in improved cardiovascular outcome and survival. However, it is doubtful whether the impairment of cardiovascular and endothelial function in T1DM can be completely reversed.Pulse-wave velocity, stroke volume, heart rate, serological markers of endothelial dysfunction (soluble intercellular, vascular cell-adhesion molecules, E-selectin, and plasminogen-activator-inhibitor-1) were measured in 10 T1DM patients after SPK with non-diabetic glucose levels, 10 T1DM patients with poor [T1DM8; glycated haemoglobin (HbA1c)8%], and 10 with good glucose control (T1DM7, HbA1c7%), in 6 non-diabetic patients after kidney transplantation (KT) and 9 non-diabetic control subjects (CON), matching for major anthropometric characteristics.Pulse-wave velocity was increased in SPK (P0.02 vs. CON, KT, T1DM7) and in T1DM8 (P0.02 vs. T1DM7). Systolic blood pressure was increased in SPK (P0.05 vs. CON). Stroke volume was reduced in SPK, T1DM8 and T1DM7 and KT (P0.01 vs. CON). Heart rate was elevated in SPK and in T1DM8 (P0.0003 vs. CON and T1DM7). In SPK, soluble intercellular and vascular cell-adhesion molecules were 100% and 44% higher (P0.03 vs. CON), respectively, while plasminogen-activator-inhibitor-1 was decreased in SPK (P0.02 vs. CON).T1DM patients after SPK experience arterial stiffness, a higher heart-rate and blood pressure, reduced stroke volume and serological signs of endothelial dysfunction. Thus, functional and structural cardiovascular alterations as a result of glucotoxicity, uraemia and hypertension in T1DM might not be completely resolved by SPK.

In type 1 diabetes mellitus (T1DM), the release of many hormones, not only from beta-cells, but also from adipocytes (adipokines) may be altered. After successful pancreas-kidney-transplantation (PKTx), T1DM patients can revert to a nondiabetic metabolism, but it is unclear whether alterations of adipokines are still present after PKTx.Concentrations of adipokines [visfatin, retinol-binding protein-4 (RBP-4), adiponectin, high molecular weight (HMW) adiponectin] were measured at fasting in 10 PKTx and in 19 T1DM. Nondiabetic healthy controls (CON, n = 9) and six nondiabetic patients after kidney transplantation (KTx) were examined as control groups. In PKTx, KTx and CON, indices of insulin sensitivity (OGIS) and beta cell function (adaptation index, AI) were calculated from 75 g oral glucose tolerance test (OGTT) data.Fasting serum visfatin (T1DM: 56 +/- 4 microg/l, PKTx: 42 +/- 6 microg/l, KTx: 39 +/- 3 microg/l, CON: 40 +/- 3 microg/l) and RBP-4 (T1DM: 490 +/- 26 microg/l, PKTx: 346 +/- 39 microg/l, KTx: 401 +/- 13 microg/l, CON: 359 +/- 36 microg/l) was increased by 40% and 36%, respectively (each P0.03) in T1DM only. Levels were positively correlated with HbA1c in all subjects (visfatin: r = 0.43, P0.004; RBP-4: r = 0.46, P0.03). Fasting plasma adiponectin was 80% higher in T1DM and in PKTx (T1DM: 18 +/- 2 mg/l, PKTx: 18 +/- 3 mg/l, KTx: 12 +/- 3 mg/l, CON: 10 +/- 1 mg/l; P0.04) and was positively correlated with diabetes duration (r = 0.37, P0.02). HMW/total adiponectin ratio was increased in T1DM (P0.02). PKTx displayed a normoglycaemic metabolism as insulin sensitive as CON, but AI was lower than in CON and KT (P0.01).T1DM after successful PKTx show normal fasting visfatin and RBP-4 levels and HMW-adiponectin/adiponectin-ratio, which are elevated in T1DM, whereas total adiponectin levels are similarly increased in T1DM and PKTx patients.

Background First-degree offspring (OFF) of type 2 diabetic (T2DM) patients bear a ~40% lifetime risk of developing T2DM. They are insulin resistant and carry a risk of premature atherosclerosis, the extent of which can be estimated by intima media thickness (IMT) of the carotid artery (CA). Thus, this study examines parameters of glucose and lipid metabolism, insulin sensitivity, beta cell function (BCF) and IMT with their interrelationships in middle-aged OFF. Materials and methods T2DM-OFF (n = 18, 14f/4m, 45·6 ± 2·1 years, BMI: 26 ± 1 kg m –2 ) were compared with 18 matching humans without a family history of diabetes (CON; 14f/4m, 44·5 ± 2·1 years, BMI: 24 ± 1 kg m –2 ; each P > 0·30), all with normal glucose tolerance as tested by three-hour (75 g) oral glucose tolerance tests (OGTT). Two-hour hyperinsulinaemic (40 mU min –1 ·m –2 )isoglycaemic clamp tests were performed with simultaneous measurement of endogenous glucose (D-[6,6- 2 H2]glucose) production (EGP). IMT [internal (ICA), common CA, and bulb] were measured sonographically. BCF was assessed by Adaptation Index (AI). Results Before and during OGTT, both groups were similar in plasma glucose, insulin, C-peptide and free fatty acids (FFA), whereas OFF showed ~30% lower (P < 0·03) fasting plasma triglycerides before OGTT. During hyperinsulinaemic clamps, insulin sensitivity was ~38% lower (P < 0·03) in OFF who showed higher plasma FFA (44 ± 9 μmol L –1 ) than CON (26 ± 3 μmol L –1 , P < 0·05) after 90 min. EGP was similar in both groups. OFF had 38% (P < 0·007) reduced AI. ICA-IMT was ~18% higher in OFF (P < 0·002), but did not correlate with insulin sensitivity. Conclusion The data obtained show middle-aged T2DM-OFF with normal glucose tolerance displaying reduced total insulin sensitivity and impaired beta cell function, which relates to impaired insulin-dependent suppression of plasma FFA and increased ICA-IMT.

Insulin resistance, the underlying pathophysiological mechanism of the metabolic syndrome, can not only predict type 2 diabetes development but also cardiovascular disease. Thus, precise insulin resistance measurement in individuals at risk for metabolic diseases would support clinical risk stratification. However, the gold standard for measuring insulin resistance, the hyperinsulinemic clamp test, is too labor intensive to be performed in large clinical studies/settings.Using plasma glucose and C-peptide concentrations from oral glucose tolerance tests (OGTTs), we developed the novel "clamp-like index" (CLIX) for insulin sensitivity calculation and compared CLIX to clamp glucose infusion rates (GIR) (100-120 min). We evaluated CLIX in 89 nondiabetic subjects (58 female and 31 male, aged 45 +/- 1 years, BMI 27.5 +/- 0.8 kg/m(2)) who underwent frequently sampled 3-h 75-g OGTTs and 2-h hyperinsulinemic-isoglycemic clamp (40 mU/min per m(2)) tests.CLIX, calculated as serum creatinine (x0.85 if male)/(mean AUC(glucose) x mean AUC(C-peptide)) x 6,600, was highly correlated (r = 0.670, P10(-12)) with and comparable to clamp GIRs(100-120 min). In subgroup analyses, GIRs(100-120 min) were lower (P0.005) in type 2 diabetic offspring (6.2 +/- 0.7 mg x min(-1) x kg(-1)) than in sex-, age-, and BMI-matched subjects without a family history of type 2 diabetes (8.6 +/- 0.5 mg x min(-1) x kg(-1)), which was also reflected by CLIX (insulin-resistant offspring 6.4 +/- 0.6 vs. those without a family history of type 2 diabetes 9.0 +/- 0.5; P0.002). When compared with normal-weight subjects (GIR 8.8 +/- 0.4 mg x min(-1) x kg(-1); CLIX 9.0 +/- 0.5), both GIRs(100-120 min) and CLIX of obese (5.2 +/- 0.9 mg x min (-1) x kg(-1); 5.7 +/- 0.9) and morbidly obese (2.4 +/- 0.4 mg x min (-1) x kg(-1); 3.3 +/- 0.5) humans were lower (each P0.02).CLIX, a novel index obtained from plasma OGTT glucose and C-peptide levels and serum creatinine, without inclusion of anthropometrical measures to calculate insulin sensitivity in nondiabetic humans, highly correlates with clamp GIRs and reveals even slight insulin sensitivity alterations over a broad BMI range and is as sensitive as the hyperinsulinemic clamp test.

The nutrient-sensitive kinase mammalian target of rapamycin (mTOR) and its downstream target S6 kinase (S6K) are involved in amino acid-induced insulin resistance. Whether the mTOR/S6K pathway directly modulates glucose metabolism in humans is unknown. We studied 11 healthy men (29 years old, BMI 23 kg/m(2)) twice in random order after oral administration of 6 mg rapamycin, a specific mTOR inhibitor, or placebo. An amino acid mixture was infused to activate mTOR, and somatostatin-insulin-glucose clamps created conditions of low peripheral hyperinsulinemia (approximately 100 pmol/l, 0-180 min) and prandial-like peripheral hyperinsulinemia (approximately 450 pmol/l, 180-360 min). Glucose turnover was assessed using d-[6,6-(2)H(2)]glucose infusion (n = 8). Skeletal muscle biopsies were performed at baseline and during prandial-like peripheral hyperinsulinemia (n = 3). At low peripheral hyperinsulinemia, whole-body glucose uptake was not affected by rapamycin. During prandial-like peripheral hyperinsulinemia, rapamycin increased glucose uptake compared with placebo by 17% (R(d 300-360 min), 75 +/- 5 vs. 64 +/- 5 micromol x kg(-1) x min(-1), P = 0.0008). Rapamycin affected endogenous glucose production neither at baseline nor during low or prandial-like peripheral hyperinsulinemia. Combined hyperaminoacidemia and prandial-like hyperinsulinemia increased S6K phosphorylation and inhibitory insulin receptor substrate-1 (IRS-1) phosphorylation at Ser312 and Ser636 in the placebo group. Rapamycin partially inhibited this increase in mTOR-mediated S6K phosphorylation and IRS-1 Ser312 and Ser636 phosphorylation. In conclusion, rapamycin stimulates insulin-mediated glucose uptake in man under conditions known to activate the mTOR/S6K pathway.

GW501516, an agonist of peroxisome proliferator-activated receptor-delta (PPAR-delta), increases lipid combustion and exerts antidiabetic action in animals, effects which are attributed mainly to direct effects on skeletal muscle. We explored such actions further in isolated rat skeletal muscle.Specimens of rat skeletal muscle were pretreated with GW501516 (0.01-30 mumol/l) for 0.5, 4 or 24 h and rates of fuel metabolism were then measured. In addition, effects on mitochondrial function were determined in isolated rat liver mitochondria.At concentrations between 0.01 and 1 mumol/l, GW501516 dose-dependently increased fatty acid oxidation but reduced glucose utilisation in isolated muscle. Thus after 24 h of preincubation with 1 mumol/l GW501516, palmitate oxidation increased by +46+/-10%, and the following decreased as specified: glucose oxidation -46+/-8%, glycogen synthesis -42+/-6%, lactate release -20+/-2%, glucose transport -15+/-6% (all p0.05). Reduction of glucose utilisation persisted independently of insulin stimulation or muscle fibre type, but depended on fatty acid availability (the effect on glucose transport in the absence of fatty acids was an increase of 30+/-9%, p0.01), suggesting a role for the glucose-fatty acid cycle. At higher concentrations, GW501516 uncoupled oxidative phosphorylation by direct action on isolated mitochondria.GW501516-induced activation of PPAR-delta reduces glucose utilisation by skeletal muscle through a switch in mitochondrial substrate preference from carbohydrate to lipid. High concentrations of GW501516 induce mitochondrial uncoupling independently of PPAR-delta.

Decreased skeletal muscle glucose disposal and increased endogenous glucose production (EGP) contribute to postprandial hyperglycemia in type 2 diabetes, but the contribution of hepatic glycogen metabolism remains uncertain. Hepatic glycogen metabolism and EGP were monitored in type 2 diabetic patients and nondiabetic volunteer control subjects (CON) after mixed meal ingestion and during hyperglycemic-hyperinsulinemic-somatostatin clamps applying 13C nuclear magnetic resonance spectroscopy (NMRS) and variable infusion dual-tracer technique. Hepatocellular lipid (HCL) content was quantified by 1H NMRS. Before dinner, hepatic glycogen was lower in type 2 diabetic patients (227 +/- 6 vs. CON: 275 +/- 10 mmol/l liver, P < 0.001). After meal ingestion, net synthetic rates were 0.76 +/- 0.16 (type 2 diabetic patients) and 1.36 +/- 0.15 mg x kg(-1) x min(-1) (CON, P < 0.02), resulting in peak concentrations of 283 +/- 15 and 360 +/- 11 mmol/l liver. Postprandial rates of EGP were approximately 0.3 mg x kg(-1) x min(-1) (30-170 min; P < 0.05 vs. CON) higher in type 2 diabetic patients. Under clamp conditions, type 2 diabetic patients featured approximately 54% lower (P < 0.03) net hepatic glycogen synthesis and approximately 0.5 mg x kg(-1) x min(-1) higher (P < 0.02) EGP. Hepatic glucose storage negatively correlated with HCL content (R = -0.602, P < 0.05). Type 2 diabetic patients exhibit 1) reduction of postprandial hepatic glycogen synthesis, 2) temporarily impaired suppression of EGP, and 3) no normalization of these defects by controlled hyperglycemic hyperinsulinemia. Thus, impaired insulin sensitivity and/or chronic glucolipotoxicity in addition to the effects of an altered insulin-to-glucagon ratio or increased free fatty acids accounts for defective hepatic glycogen metabolism in type 2 diabetic patients.

The gastric peptide ghrelin augments and the adipocyte-derived hormone leptin reduces appetite and food intake. In the central nervous system, insulin directly decreases hunger sensation but could also act indirectly by modulating ghrelin and leptin secretion. This study examines dose-dependent effects of insulin on plasma ghrelin and leptin concentrations during hyperinsulinemic (1, 2, and 4 mU · kg−1 · min−1)-euglycemic clamp tests in six nondiabetic (control subjects) and six type 2 diabetic patients. Type 2 diabetic patients were studied before and after prolonged (12-h and 67-h) variable intravenous insulin treatment aiming at near-normoglycemia (115 ± 4 mg/dl). Nondiabetic subjects were also studied during saline infusion, which did not affect ghrelin but decreased leptin by 19 ± 6% (P < 0.03). In control subjects, plasma ghrelin decreased at all clamp steps (−17 ± 1, −27 ± 6, and −33 ± 4%, respectively; P < 0.006 vs. baseline), whereas leptin increased by 35 ± 11% (P < 0.05). In type 2 diabetic patients without insulin treatment, ghrelin decreased by 18 ± 7% (P < 0.05) only after 4 mU · kg−1 · min−1 insulin infusion and leptin increased by 19 ± 6% (P < 0.05). After prolonged insulin treatment and near-normoglycemia, ghrelin and leptin remained unchanged in type 2 diabetic patients during the clamps. In conclusion, insulin reduces plasma ghrelin in nondiabetic patients and, to a lesser extent, in type 2 diabetic patients before insulin therapy. These findings indicate an indirect effect of insulin via ghrelin on the suppression of hunger sensation and appetite.

Insulin resistance is frequently associated with increased lipid content in muscle and liver. Insulin excess stimulates tissue lipid accumulation. To examine the effects of insulin and improved glycemia on insulin sensitivity and intracellular lipids, we performed stepped (1, 2, and 4 mU · min−1 · kg−1) hyperinsulinemic-euglycemic clamps in eight type 2 diabetic and six nondiabetic control subjects at baseline and after 12 and 67 h of insulin-mediated near-normoglycemia (118 ± 7 mg/dl). Intrahepatocellular lipids (IHCLs) and intramyocellular lipids (IMCLs) of soleus (IMCL-S) and tibialis anterior muscle (IMCL-TA) were measured with 1H nuclear magnetic resonance spectroscopy. At baseline, nondiabetic subjects had an approximate twofold higher insulin sensitivity (P < 0.02) and lower IHCLs than diabetic patients (5.8 ± 1.2 vs. 18.3 ± 4.2%, P < 0.03), in whom IMCL-TA negatively correlated with insulin sensitivity (r = −0.969, P < 0.001). After a 67-h insulin infusion in diabetic patients, IMCL-S and IHCLs were increased (P < 0.05) by ∼36 and ∼18%, respectively, and correlated positively with insulin sensitivity (IMCL-S: r = 0.982, P < 0.0005; IHCL: r = 0.865, P < 0.03), whereas fasting glucose production, measured with d-[6,6-2H2]glucose, decreased by ∼10% (P < 0.04). In conclusion, these results indicate that IMCLs relate to insulin resistance in type 2 diabetic patients at baseline and that insulin-mediated near-normoglycemia for ∼3 days reduces fasting glucose production but stimulates lipid accumulation in liver and muscle without affecting insulin sensitivity.

R (+)-alpha-lipoic acid (RLA) has been suggested for the treatment of liver diseases, but has also been shown to improve glucose utilization in diabetic patients. Because detailed information of RLA action on carbohydrate metabolism in intact liver is lacking, we examined concentration-dependent effects of RLA on hepatic glucose production.RLA (10(-6-)10(-3) mol L(-1)) or buffer (control) was infused in isolated livers of fasted rats during recirculating perfusion for 90 min (n = 4-6/group). Hepatic glucose and lactate fluxes and bile secretion were continuously monitored.RLA reduced lactate (10 mmol L(-1))-dependent glucose production in concentration-dependent fashion (R = - 0.780, P0.001) by up to 67% compared with control (0.36 +/- 0.02 micromol min(-1) g(-1)). In parallel, RLA dose dependently decreased lactate uptake (R = - 0.592, P0.001) also by up to 67% (control: 0.58 +/- 0.08 micromol min(-1) g(-1)). RLA (10(-4) mol L(-1) and 10(-3) mol L(-1)) stimulated bile flow by approximately 20 and approximately 50%, respectively (P0.02 vs. control). After 10(-3) mol L(-1) RLA infusion, liver glycogen was approximately 3 fold higher (5.2 +/- 1.1 vs. control: 1.8 +/- 0.2 micromol g(-1), P0.002). Also at low lactate concentrations (1 mmol L(-1)), 10(-3) mol L(-1) RLA reduced glucose production by approximately 53% and lactate uptake by approximately 60%, but stimulated bile secretion by approximately 50% (P0.05).RLA reduces hepatic glucose release by inhibiting lactate-dependent glucose production in a concentration-dependent fashion.

Leptin has both insulin-like and insulin-antagonistic effects on glucose metabolism. To test whether leptin interferes directly with insulin signaling, we perfused isolated rat livers with leptin (0.1, 0.5, 5, and 25 nmol/liter), leptin + insulin (5 nmol/liter + 10 nmol/liter), insulin (10 nmol/liter), or vehicle (control). Leptin reduced L-lactate-(10 mmol/liter)-stimulated glucose production by 39-66% (P0.006 vs. control) and phosphoenolpyruvate carboxykinase (PEPCK) activity by 22-52% (P0.001). Physiological leptin concentrations (0.1-5 nmol/liter) stimulated the tyrosine phosphorylation (pY) of insulin receptor substrate-2 (IRS-2) (280-954%; P0.05) and its associated phosphatidylinositol-3 kinase activity (122-621%; P0.003). Leptin (0.5-25 nmol/liter) inhibited IRS-1 pY and its associated phosphatidylinositol-3 kinase activity (20-89%; P0.03) but stimulated janus kinase-2 pY (272-342%; P0.001). Leptin also down-regulated its short receptor isoform in a time- and concentration-dependent manner (28-54%; P0.05). Exposure to leptin + insulin additively reduced glucose production and PEPCK activity (approximately 50%; P0.001 vs. control) and doubled IRS-2 pY (P0.01 vs. insulin). However, leptin + insulin decreased IRS-1 pY by 57% (P0.01 vs. insulin). Insulin alone (P0.01), but not leptin, increased autophosphorylation of nonreceptor tyrosine kinases (pp59(Lyn) + pp125(Fak)). In conclusion, leptin both alone and in combination with insulin reduces hepatic glucose production by decreasing the synthesis of the key enzyme of gluconeogenesis, PEPCK, which results mainly from the stimulation of the IRS-2 pathway.

Plasma concentrations of amino acids are frequently elevated in insulin-resistant states, and a protein-enriched diet can impair glucose metabolism. This study examined effects of short-term plasma amino acid (AA) elevation on whole-body glucose disposal and cellular insulin action in skeletal muscle. Seven healthy men were studied for 5.5 h during euglycemic (5.5 mmol/l), hyperinsulinemic (430 pmol/l), fasting glucagon (65 ng/l), and growth hormone (0.4 microg/l) somatostatin clamp tests in the presence of low (approximately 1.6 mmol/l) and increased (approximately 4.6 mmol/l) plasma AA concentrations. Glucose turnover was measured with D-[6,6-(2)H(2)]glucose. Intramuscular concentrations of glycogen and glucose-6-phosphate (G6P) were monitored using (13)C and (31)P nuclear magnetic resonance spectroscopy, respectively. A approximately 2.1-fold elevation of plasma AAs reduced whole-body glucose disposal by 25% (P < 0.01). Rates of muscle glycogen synthesis decreased by 64% (180--315 min, 24 plus minus 3; control, 67 plus minus 10 micromol center dot l(-1) center dot min(-1); P < 0.01), which was accompanied by a reduction in G6P starting at 130 min (DeltaG6P(260--300 min), 18 plus minus 19; control, 103 plus minus 33 micromol/l; P < 0.05). In conclusion, plasma amino acid elevation induces skeletal muscle insulin resistance in humans by inhibition of glucose transport/phosphorylation, resulting in marked reduction of glycogen synthesis.

AIMS/HYPOTHESIS: Recent evidence suggests a link between myocardial steatosis and diabetic cardiomyopathy. Insulin, as a lipogenic and growth-promoting hormone, might stimulate intramyocardial lipid (MYCL) deposition and hypertrophy. Therefore, the aim of the present study was to investigate the short-term effects of insulin therapy (IT) on myocardial lipid content and morphology in patients with T2DM. METHODS: Eighteen patients with T2DM were recruited (age 56 ± 2 years; HbA1c: 10.5 ± 0.4%). In 10 patients with insufficient glucose control under oral medication IT was initiated due to secondary failure of oral glucose lowering therapy (IT-group), while 8 individuals did not require additional insulin substitution (OT-group). In order to assess MYCL and intrahepatic lipid (IHLC) content as well as cardiac geometry and function magnetic resonance spectroscopy (MRS) and imaging (MRI) examinations were performed at baseline (IT and OT) and 10 days after initiation of IT. Follow up measurements took place 181 ± 49 days after IT. RESULTS: Interestingly, basal MYCLs were 50% lower in IT- compared to OT-group (0.41 ± 0.12 vs. 0.80 ± 0.11% of water signal; p = 0.034). After 10 days of IT, an acute 80%-rise in MYCL (p = 0.008) was observed, while IHLC did not change. Likewise, myocardial mass (+13%; p = 0.004), wall thickness in end-diastole (+13%; p = 0.030) and concentricity, an index of cardiac remodeling, increased (+28%; p = 0.026). In the long-term MYCL returned to baseline, while IHCL significantly decreased (-31%; p = 0.000). No acute changes in systolic left ventricular function were observed. CONCLUSIONS/INTERPRETATION: The initiation of IT in patients with T2DM was followed by an acute rise in MYCL concentration and myocardial mass.