The T allele of rs7903146 TCF7L2 is associated with impaired insulinotropic action of incretin hormones, reduced 24?h profiles of plasma insulin and glucagon, and increased hepatic glucose production in young healthy men

Aims/hypothesis  We studied the physiological, metabolic and hormonal mechanisms underlying the elevated risk of type 2 diabetes in carriers of TCF7L2 gene. Methods  We undertook genotyping of 81 healthy young Danish men for rs7903146 of TCF7L2 and carried out various beta cell tests including: 24 h glucose, insulin and glucagon profiles; OGTT; mixed meal test; IVGTT; hyperglycaemic clamp with co-infusion of glucagon-like peptide (GLP)-1 or glucose-dependent insulinotropic polypeptide (GIP); and a euglycaemic–hyperinsulinaemic clamp combined with glucose tracer infusion to study hepatic and peripheral insulin action. Results  Carriers of the T allele were characterised by reduced 24 h insulin concentrations (p < 0.05) and reduced insulin secretion relative to glucose during a mixed meal test (beta index: p < 0.003), but not during an IVGTT. This was further supported by reduced late-phase insulinotropic action of GLP-1 (p = 0.03) and GIP (p = 0.07) during a 7 mmol/l hyperglycaemic clamp. Secretion of GLP-1 and GIP during the mixed meal test was normal. Despite elevated hepatic glucose production, carriers of the T allele had significantly reduced 24 h glucagon concentrations (p < 0.02) suggesting altered alpha cell function. Conclusions/interpretation  Elevated hepatic glucose production and reduced insulinotropic effect of incretin hormones contribute to an increased risk of type 2 diabetes in carriers of the rs7903146 risk T allele of TCF7L2. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Insulin sensitivity, insulin release and glucagon-like peptide-1 levels in persons with impaired fasting glucose and/or impaired glucose tolerance in the EUGENE2 study

Aims/hypothesis We examined the phenotype of individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) with regard to insulin release and insulin resistance. Methods Non-diabetic offspring (n = 874; mean age 40 ± 10.4 years; BMI 26.6 ± 4.9 kg/m²) of type 2 diabetic patients from five different European Centres (Denmark, Finland, Germany, Italy and Sweden) were examined with regard to insulin sensitivity (euglycaemic clamps), insulin release (IVGTT) and glucose tolerance (OGTT). The levels of glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) were measured during the OGTT in 278 individuals. Results Normal glucose tolerance was found in 634 participants, while 110 had isolated IFG, 86 had isolated IGT and 44 had both IFG and IGT, i.e. about 28% had a form of reduced glucose tolerance. Participants with isolated IFG had lower glucose-corrected first-phase (0–10 min) and higher second-phase insulin release (10–60 min) during the IVGTT, while insulin sensitivity was reduced in all groups with abnormal glucose tolerance. Similarly, GLP-1 but not GIP levels were reduced in individuals with abnormal glucose tolerance. Conclusions/interpretation The primary mechanism leading to hyperglycaemia in participants with isolated IFG is likely to be impaired basal and first-phase insulin secretion, whereas in isolated IGT the primary mechanism leading to postglucose load hyperglycaemia is insulin resistance. Reduced GLP-1 levels were seen in all groups with abnormal glucose tolerance and were unrelated to the insulin release pattern during an IVGTT.     

Metabolic inflexibility is a common feature of impaired fasting glycaemia and impaired glucose tolerance

Metabolic flexibility reflects the ability to switch from lipid to carbohydrate oxidation during insulin stimulation. Impaired metabolic flexibility is related to insulin resistance and type 2 diabetes, but whether metabolic flexibility is impaired in individuals with the pre-diabetic states isolated impaired fasting glycaemia (i-IFG) and isolated impaired glucose tolerance (i-IGT) is unknown. Using the gold standard euglycaemic hyperinsulinaemic clamp technique combined with indirect calorimetry, we measured peripheral insulin sensitivity, lipid and glucose oxidation, and thus metabolic flexibility in 66 individuals with normal glucose tolerance (NGT, n = 20), i-IFG (n = 18) and i-IGT (n = 28). During insulin stimulation, individuals with i-IGT displayed reduced insulin sensitivity including reduced glucose oxidation. Interestingly, those with i-IFG exhibited reduced glucose oxidation and a slightly elevated lipid oxidation rate during insulin infusion despite having normal total peripheral glucose disposal. Thus, metabolic flexibility was significantly reduced in individuals with both i-IFG and i-IGT even after adjustment for BMI and insulin sensitivity. The data indicate that metabolic inflexibility may precede the development of overt peripheral insulin resistance in pre-diabetic individuals. However, prospective studies are needed to confirm this notion.     

Influence of gestational diabetes on the long-term control of glucose tolerance

Aims/hypothesis Gestational diabetes (GDM) carries a high risk of subsequent diabetes. We asked what impact prior GDM has on beta cell function and insulin action in women who maintain normal glucose tolerance (NGT) for a long time. Methods Ninety-one women with NGT (aged 41 ± 8 years, mean±SD) were studied (by mathematical modelling of the C-peptide response to an OGTT) 7 [6] years (median [interquartile range]) after the index pregnancy, during which 52 had GDM (pGDM) and 39 had NGT (pNGT). In all women an OGTT had also been performed at 29 ± 3 weeks of the index pregnancy. Results Women with pGDM were matched with women with pNGT for age, familial diabetes, time and weight gain since index pregnancy, parity, BMI (25.4 ± 3.9 vs 26.8 ± 6.4 kg/m²), and fasting (4.64 ± 0.56 vs 4.97 ± 0.46 mmol/l) and 2 h plasma glucose levels (5.91 ± 1.14 vs 5.91 ± 1.21 mmol/l). Nonetheless, fasting (49 [29] vs 70 [45] pmol min⁻¹ m⁻², p < 0.001) and total insulin secretion (32 [17] vs 48 [21] nmol m⁻², p < 0.0001) and beta cell glucose sensitivity (slope of the insulin secretion/plasma glucose concentration–response function) (95 [71] vs 115 [79] pmol min⁻¹ m⁻² (mmol/l)⁻¹, p = 0.025) were reduced in the pGDM group compared with the pNGT group, while insulin sensitivity was preserved (424 [98] vs 398 [77] ml min⁻¹ m⁻²). At index pregnancy, women with pGDM and those with pNGT had similar age and BMI. However, both insulin sensitivity (359 [93] vs 417 [92] ml min⁻¹ m⁻², p = 0.0012) and the insulin/glucose incremental area ratio (an empirical index of beta cell function; 98 [74] vs 138 [122] pmol/mmol, p = 0.028) were reduced in women with pGDM. Conclusions Even in women who maintain normal insulin sensitivity, impaired beta cell function is carried over into the NGT status several years after a GDM pregnancy.     

Polymorphisms in the gene encoding the voltage-dependent Ca<Superscript>2+</Superscript> channel Ca<Subscript>V</Subscript>2.3 (<Emphasis Type="Italic">CACNA1E</Emphasis>) are associated with type 2 diabetes and impaired insulin secretion

Aims/hypothesis Glucose-stimulated insulin secretion is dependent on the electrical activity of beta cells; hence, genes encoding beta cell ion channels are potential candidate genes for type 2 diabetes. The gene encoding the voltage-dependent Ca²⁺ channel Ca_V2.3 (CACNA1E), telomeric to a region that has shown suggestive linkage to type 2 diabetes (1q21-q25), has been ascribed a role for second-phase insulin secretion. Methods Based upon the genotyping of 52 haplotype tagging single nucleotide polymorphisms (SNPs) in a type 2 diabetes case–control sample (n = 1,467), we selected five SNPs that were nominally associated with type 2 diabetes and genotyped them in the following groups (1) a new case–control sample of 6,570 individuals from Sweden; (2) 2,293 individuals from the Botnia prospective cohort; and (3) 935 individuals with insulin secretion data from an IVGTT. Results The rs679931 TT genotype was associated with (1) an increased risk of type 2 diabetes in the Botnia case–control sample [odds ratio (OR) 1.4, 95% CI 1.0–2.0, p = 0.06] and in the replication sample (OR 1.2, 95% CI 1.0–1.5, p = 0.01 one-tailed), with a combined OR of 1.3 (95% CI 1.1–1.5, p = 0.004 two-tailed); (2) reduced insulin secretion [insulinogenic index at 30 min p = 0.02, disposition index (D _I) p = 0.03] in control participants during an OGTT; (3) reduced second-phase insulin secretion at 30 min (p = 0.04) and 60 min (p = 0.02) during an IVGTT; and (4) reduced D _I over time in the Botnia prospective cohort (p = 0.05). Conclusions/interpretation We conclude that genetic variation in the CACNA1E gene contributes to an increased risk of the development of type 2 diabetes by reducing insulin secretion. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Glucokinase, the pancreatic glucose sensor, is not the gut glucose sensor

Aims/hypothesis  The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotrophic peptide (GIP) are released from intestinal endocrine cells in response to luminal glucose. Glucokinase is present in these cells and has been proposed as a glucose sensor. The physiological role of glucokinase can be tested using individuals with heterozygous glucokinase gene (GCK) mutations. If glucokinase is the gut glucose sensor, GLP-1 and GIP secretion during a 75 g OGTT would be lower in GCK mutation carriers compared with controls. Methods  We compared GLP-1 and GIP concentrations measured at five time-points during a 75 g OGTT in 49 participants having GCK mutations with those of 28 familial controls. Mathematical modelling of glucose, insulin and C-peptide was used to estimate basal insulin secretion rate (BSR), total insulin secretion (TIS), beta cell glucose sensitivity, potentiation factor and insulin secretion rate (ISR). Results  GIP and GLP-1 profiles during the OGTT were similar in GCK mutation carriers and controls (p = 0.52 and p = 0.44, respectively). Modelled variables of beta cell function showed a reduction in beta cell glucose sensitivity (87 pmol min⁻¹ m⁻² [mmol/l]⁻¹ [95% CI 66–108] vs 183 pmol min⁻¹ m⁻² [mmol/l]⁻¹ [95% CI 155–211], p < 0.001) and potentiation factor (1.5 min [95% CI 1.2–1.8] vs 2.2 min [95% CI 1.8–2.7], p = 0.007) but no change in BSR or TIS. The glucose/ISR curve was right-shifted in GCK mutation carriers. Conclusions/interpretation  Glucokinase, the major pancreatic glucose sensor, is not the main gut glucose sensor. By modelling OGTT data in GCK mutation carriers we were able to distinguish a specific beta cell glucose-sensing defect. Our data suggest a reduction in potentiation of insulin secretion by glucose that is independent of differences in incretin hormone release.     

Glucagon-like peptide-1, but not glucose-dependent insulinotropic peptide,inhibits glucagon secretion via somatostatin (receptor subtype 2) in the perfused rat pancreas

Aims/hypothesis  The glucose-lowering effect of glucagon-like peptide-1 (GLP-1) is based not only upon its potent insulinotropic actions but also on its ability to restrain glucagon secretion. Surprisingly, the closely related glucose-dependent insulinotropic peptide (GIP) stimulates glucagon release. We examined whether the islet hormone somatostatin, which strongly inhibits glucagon secretion, is involved in this divergent behaviour. Methods  At 1.5 mmol/l glucose and therefore minimal insulin secretion, the glucagon, insulin and somatostatin responses to 20 mmol/l glucose, GLP-1, GIP and somatostatin were studied in the presence of a high-affinity monoclonal somatostatin antibody and of a highly specific somatostatin receptor subtype 2 (SSTR2) antagonist (PRL-2903) in the isolated perfused rat pancreas. Results  In control experiments, GLP-1 at 1 and 10 nmol/l reduced glucagon secretion significantly to 59.0 ± 6.3% (p < 0.004; n = 5; SSTR2 series; each vs pre-infusion level) and to 48.0 ± 2.6% (p < 0.001; n = 6; somatostatin antibody series) respectively. During somatostatin antibody administration, GLP-1 still inhibited glucagon secretion significantly, but the effect was less pronounced than in control experiments (p < 0.018). Co-infusion of the SSTR2 antagonist completely abolished the GLP-1-induced suppression of glucagon secretion. In contrast, neither the GIP-induced stimulation of glucagon release nor its inhibition by 20 mmol/l glucose was altered by somatostatin antibody or SSTR2 antagonist administration. Conclusions/interpretation  We conclude that GLP-1 is capable of inhibiting glucagon secretion even in the absence of secretory products from the beta cell. It is highly likely that this is mediated via somatostatin interacting with SSTR2 on rat alpha cells. In contrast, GIP and glucose seem to influence the alpha cell independently of somatostatin secretion.     

Elevated serum levels of visfatin in gestational diabetes: a comparative study across various degrees of glucose tolerance

Aims/hypothesis Concentrations of visfatin are increased in insulin-resistant conditions, but the relationship between visfatin and insulin and/or insulin resistance indices in pregnancy remains unclear. Insulin resistance in pregnancy is further accentuated in women with gestational diabetes mellitus (GDM). Thus we assessed serum levels of visfatin in pregnant women with varying degrees of glucose tolerance. Materials and methods Fasting visfatin levels were measured at 28 weeks of gestation in 51 women divided according to their response to a 50-g glucose challenge test (GCT) and a 75-g OGTT: control subjects (n = 20) had normal responses to both a GCT and an OGTT; the intermediate group (IG; n = 15) had a false-positive GCT, but a normal OGTT; the GDM group (n = 16) had abnormal GCTs and OGTTs. Results There were no age or BMI differences between analysed groups. Across the subgroups there was a progressive increase in glucose and insulin at 120 min of the OGTT (p < 0.01). This was accompanied by an increase in visfatin, from 76.8 ± 14.1 ng/ml in the control subjects, to 84.0 ± 14.7 ng/ml in the IG group and 93.1 ± 12.3 ng/ml in the GDM group (p < 0.01 for GDM vs control subjects). There was a positive correlation between visfatin and fasting insulin (r = 0.38, p = 0.007) and insulin at 120 min of the OGTT (r = 0.39, p = 0.006). Conclusions/interpretation An increase in fasting visfatin, the levels of which correlate with both fasting and post-glucose-load insulin concentrations, accompanies worsening glucose tolerance in the third trimester of pregnancy. However, the significance of these findings, and in particular the role of visfatin in the regulation of insulin sensitivity during pregnancy, remains to be elucidated. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. G. M. Prelevic and H. S. Randeva are both senior authors.     

Brothers of women with polycystic ovary syndrome are characterised by impaired glucose tolerance,reduced insulin sensitivity and related metabolic defects

Aims/hypothesis Since it has been shown that polycystic ovary syndrome (PCOS) is highly inherited and characterised by insulin resistance, we hypothesised that male siblings of PCOS women would also be insulin resistant. Thus, our aim was to assess insulin sensitivity and metabolic parameters in brothers of women with PCOS and male control individuals. Methods Seventeen brothers of PCOS women and 28 male control volunteers were assessed with 75 g OGTTs and euglycaemic–hyperinsulinaemic clamps. PCOS index women were identified using criteria developed at the 1990 National Institutes of Health conference. Results Brothers and control individuals were similar in terms of BMI, waist circumference, percentage body fat and BP. However, brothers had increased triacylglycerol (p = 0.02), plasminogen activator inhibitor-1 (PAI-1; p = 0.02), factor VIII (p = 0.02), 2 h glucose (p < 0.001), AUC_glucose (p < 0.001) and AUC_insulin (p < 0.001). Insulin sensitivity was reduced by 38% in brothers (p < 0.001), and this was primarily due to a 65% decrease in insulin-stimulated non-oxidative carbohydrate metabolism (p < 0.001). These differences remained significant after adjustment for age and BMI, except for triacylglycerol, PAI-1 and fasting glucose. The main findings also persisted after excluding individuals with impaired glucose tolerance or diabetic siblings. Significant interactions with BMI status were found for sex hormone-binding globulin, androstenedione, PAI-1 and AUC_insulin, which were significantly altered only in obese brothers (vs control individuals). Conclusions/interpretation Brothers of PCOS women are characterised by decreased insulin sensitivity and glucose tolerance, as well as hypercoagulability, independently of obesity. Therefore, brothers of PCOS women may have inherited the insulin resistance and metabolic syndrome typical of PCOS.     

Association of fasting glucagon and proinsulin concentrations with insulin resistance

Aims/hypothesis Hyperproinsulinaemia and relative hyperglucagonaemia are features of type 2 diabetes. We hypothesised that raised fasting glucagon and proinsulin concentrations may be associated with insulin resistance (IR) in non-diabetic individuals. Methods We measured IR [by a euglycaemic–hyperinsulinaemic (240 pmol min⁻¹ m⁻²) clamp technique] in 1,296 non-diabetic (on a 75 g OGTT) individuals [716 women and 579 men, mean age 44 years, BMI 26 kg/m² (range 18–44 kg/m²)] recruited at 19 centres in 14 European countries. IR was related to fasting proinsulin or pancreatic glucagon concentrations in univariate and multivariate analyses. Given its known relationship to IR, serum adiponectin was used as a positive control. Results In either sex, both glucagon and proinsulin were directly related to IR, while adiponectin was negatively associated with it (all p < 0.0001). In multivariate models, controlling for known determinants of insulin sensitivity (i.e. sex, age, BMI and glucose tolerance) as well as factors potentially affecting glucagon and proinsulin (i.e. fasting plasma glucose and C-peptide concentrations), glucagon and proinsulin were still positively associated, and adiponectin was negatively associated, with IR. Finally, when these associations were tested as the probability that individuals in the top IR quartile would have hormone levels in the top quartile of their distribution independently of covariates, the odds ratio was ∼2 for both glucagon (p = 0.05) and proinsulin (p = 0.02) and 0.36 for adiponectin (p < 0.0001). Conclusions/interpretation Whole-body IR is independently associated with raised fasting plasma glucagon and proinsulin concentrations, possibly as a result of IR at the level of alpha cells and beta cells in pancreatic islets. Electronic supplementary material The online version of this article (doi:) contains a list of the European Group for the Study of Insulin Resistance RISC investigators, which is available to authorised users.     

Circadian rhythms of GIP and GLP1 in glucose-tolerant and in type 2 diabetic patients after biliopancreatic diversion

Aims/hypothesis  We tested the hypothesis that the reversibility of insulin resistance and diabetes observed after biliopancreatic diversion (BPD) is related to changes in circadian rhythms of gastrointestinal hormones. Methods  Ten morbidly obese participants, five with normal glucose tolerance (NGT) and five with type 2 diabetes, were studied before and within 2 weeks after BPD. Within-day variations in glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP1) levels were assessed using a single cosinor model. Insulin sensitivity was assessed by euglycaemic–hyperinsulinaemic clamp. Results  Basal GLP1 relative amplitude (amplitude/mesor × 100) was 25.82–4.06% in NGT; it increased to 41.38–4.32% after BPD but was unchanged in diabetic patients. GLP1 and GIP mesor were shifted in time after surgery in diabetic patients but not in NGT participants. After BPD, the GLP1 AUC significantly increased from 775 ± 94 to 846 ± 161 pmol l⁻¹ min in NGT, whereas GIP AUC decreased significantly from 1,373 ± 565 to 513 ± 186 pmol l⁻¹ min in diabetic patients. Two-way ANOVA showed a strong influence of BPD on both GIP (p = 0.010) and GLP1 AUCs (p = 0.033), which was potentiated by the presence of diabetes, particularly for GIP (BPD × diabetes, p = 0.003). Insulin sensitivity was markedly improved (p < 0.01) in NGT (from 9.14 ± 3.63 to 36.04 ± 8.55 μmol [kg fat-free mass]⁻¹ min⁻¹) and diabetic patients (from 9.49 ± 3.56 to 38.57 ± 4.62 μmol [kg fat-free mass]⁻¹ min⁻¹). Conclusions/interpretation  An incretin circadian rhythm was shown for the first time in morbid obesity. The effect of BPD on the 24 h pattern of incretin differed between NGT and diabetic patients. GLP1 secretion impairment was reversed in NGT and could not be overcome by surgery in diabetes. On the other hand, GIP secretion was blunted after the operation only in diabetic patients, suggesting a role in insulin resistance and diabetes.     

Glucagon receptor antagonism improves islet function in mice with insulin resistance induced by a high-fat diet

Aims/hypothesis Increased glucagon secretion predicts deterioration of glucose tolerance, and high glucagon levels contribute to hyperglycaemia in type 2 diabetes. Inhibition of glucagon action may therefore be a potential novel target to reduce hyperglycaemia. Here, we investigated whether chronic treatment with a glucagon receptor antagonist (GRA) improves islet dysfunction in female mice on a high-fat diet (HFD). Materials and methods After 8 weeks of HFD, mice were treated with a small molecule GRA (300 mg/kg, gavage once daily) for up to 30 days. Insulin secretion was studied after oral and intravenous administration of glucose and glucagon secretion after intravenous arginine. Islet morphology was examined and insulin secretion and glucose oxidation were measured in isolated islets. Results Fasting plasma glucose levels were reduced by GRA (6.0 ± 0.2 vs 7.4 ± 0.5 mmol/l; p = 0.017). The acute insulin response to intravenous glucose was augmented (1,300 ± 110 vs 790 ± 64 pmol/l; p < 0.001). The early insulin response to oral glucose was reduced in mice on HFD + GRA (1,890 ± 160 vs 3,040 ± 420 pmol/l; p = 0.012), but glucose excursions were improved. Intravenous arginine significantly increased the acute glucagon response (129 ± 12 vs 36 ± 6 ng/l in controls; p < 0.01), notably without affecting plasma glucose. GRA caused a modest increase in alpha cell mass, while beta cell mass was similar to that in mice on HFD + vehicle. Isolated islets displayed improved glucose-stimulated insulin secretion after GRA treatment (0.061 ± 0.007 vs 0.030 ± 0.004 pmol islet⁻¹ h⁻¹ at 16.7 mmol/l glucose; p < 0.001), without affecting islet glucose oxidation. Conclusions/interpretation Chronic glucagon receptor antagonism in HFD-fed mice improves islet sensitivity to glucose and increases insulin secretion, suggesting improvement of key defects underlying impaired glucose tolerance and type 2 diabetes.     

Pathophysiology and aetiology of impaired fasting glycaemia and impaired glucose tolerance: does it matter for prevention and treatment of type 2 diabetes?

Prior to the development of type 2 diabetes, glucose levels increase into the prediabetic states of isolated impaired fasting glycaemia (i-IFG), isolated impaired glucose tolerance (i-IGT), or combined IFG/IGT. A better understanding of the aetiology and pathophysiology of the prediabetic states might give a basis for the development of individualised prevention and treatment strategies for type 2 diabetes. Several studies have examined mechanisms and potential aetiological factors leading to the development of the different prediabetic states. The pathophysiology of i-IFG seems to include the following key defects: reduced hepatic insulin sensitivity, stationary beta cell dysfunction and/or chronic low beta cell mass, altered glucagon-like peptide-1 secretion and inappropriately elevated glucagon secretion. Conversely, the prediabetic state i-IGT is characterised by reduced peripheral insulin sensitivity, near-normal hepatic insulin sensitivity, progressive loss of beta cell function, reduced secretion of glucose-dependent insulinotropic polypeptide and inappropriately elevated glucagon secretion. Individuals developing combined IFG/IGT exhibit severe defects in both peripheral and hepatic insulin sensitivity as well as a progressive loss of beta cell function. The aetiologies of i-IFG and i-IGT also seem to differ, with i-IFG being predominantly related to genetic factors, smoking and male sex, while i-IGT is predominantly related to physical inactivity, unhealthy diet and short stature. Since the transition from the prediabetic states to overt type 2 diabetes is characterised by a non-reversible vicious cycle that includes severe deleterious effects on glucose metabolism, there are good reasons to use the well-established aetiological and pathophysiological differences in i-IFG, i-IGT and IFG/IGT to design individualised preventive strategies.     

Chemical gastric inhibitory polypeptide receptor antagonism protects against obesity,insulin resistance,glucose intolerance and associated disturbances in mice fed high-fat and cafeteria diets

Aims/hypothesis Gastric inhibitory polypeptide (GIP) receptor antagonism with (Pro³)GIP improves glucose tolerance and ameliorates insulin resistance and abnormalities of islet structure/function in ob/ob mice. This study examined the ability of (Pro³)GIP to counter the development of obesity, insulin resistance and diabetes in mice fed high-fat and cafeteria diets. Materials and methods Young Swiss TO mice on standard chow or high-fat, cafeteria or high-carbohydrate diets received daily injections of either saline or (Pro³)GIP (25 nmol kg^-1day^-1) over 16 weeks. Food intake, body weight, and circulating glucose and insulin were measured frequently. At 16 weeks, glucose tolerance, insulin sensitivity, HbA_1c, circulating hormones and plasma lipids were assessed. Adipose tissue, liver and muscle were excised and weighed, and their histology and triacylglycerol content were further examined. Results (Pro³)GIP significantly reduced body weight, enhanced locomotor activity, and improved HbA_1c, glucose tolerance, beta cell responsiveness and insulin sensitivity in mice fed high-fat and cafeteria diets (p < 0.05 to p < 0.01). Similarly, (Pro³)GIP significantly reduced plasma corticosterone and triacylglycerols (p < 0.05 to p < 0.001), while glucagon, resistin and adiponectin were unchanged. (Pro³)GIP decreased adipose tissue mass (p < 0.01) and the triacylglycerol content of liver, muscle and adipose tissue (p < 0.01 to p < 0.001). Adipocyte size and liver morphology were partially normalised. (Pro³)GIP did not significantly affect any of these parameters in mice fed a high-carbohydrate diet. Conclusions/interpretation (Pro³)GIP protects against obesity, insulin resistance, glucose intolerance and associated disturbances in mice fed high-fat and cafeteria diets. This highlights chemical GIP receptor antagonism as a new possibility for the treatment of obesity and associated metabolic disturbances.     

The effect of salsalate on insulin action and glucose tolerance in obese non-diabetic patients: results of a randomised double-blind placebo-controlled study

Aim/hypothesis  Low-grade inflammation may contribute to obesity-related insulin resistance and has been associated with increased risk of type 2 diabetes mellitus. The present study evaluated whether treatment with salsalate, a traditional anti-inflammatory medication, would improve insulin action in obese non-diabetic individuals. Methods  The study was a randomised, double-blind, placebo-controlled, parallel trial conducted at the inpatient clinical research unit of the NIDKK (Phoenix, AZ, USA). Participants were 54 adults (18 to 45 years of age) with BMI ≥ 30 kg/m². The intervention was salsalate (3 g/day, n = 28) or identical placebo (n = 26) for 7 days. The allocation was kept concealed by giving the investigator only a number corresponding to a vial of placebo or salsalate sequentially randomised in blocks by sex. Main outcomes were changes in insulin action assessed as rate of glucose disposal (R _d) by euglycaemic–hyperinsulinaemic clamp (insulin infusion rate 40 mU m⁻² min⁻¹) and glucose tolerance by 75 g OGTT. Results  The study was completed by 47 participants, of which 40 were analysed (salsalate n = 22, placebo n = 18). Salsalate treatment resulted in decreased fasting plasma glucose concentration (mean [SD]; 4.83 [0.28] vs 5.11 [0.33] mmol/l, p = 0.001) and glucose AUC during the OGTT (p = 0.01), and in increased R _d (20 [8] vs 18 [6] μmol [kg estimated metabolic body size]⁻¹ min⁻¹, p = 0.002), while there was no significant change in these variables with placebo (p > 0.3 for all). The effect of salsalate on R _d disappeared (p = 0.9) after normalising to increased insulin concentrations (701 [285] vs 535 [201] pmol/l, p < 0.0001) measured during the clamp. No side effects of salsalate were observed during the study. Conclusions/interpretation  The glucose-lowering potential of salicylates appears to be due to effects on insulin concentration rather than improved insulin action. Salicylate-based compounds may be useful for the treatment and prevention of type 2 diabetes. Trial registration: ClinicalTrials.gov NCT 00339833. Funding: Intramural research programme of the NIDDK/NIH/DHHS. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users. J. Koska and E. Ortega contributed equally to this work.     

Early administration of the glucose-dependent insulinotropic polypeptide receptor antagonist (Pro3)GIP prevents the development of diabetes and related metabolic abnormalities associated with genetically inherited obesity in ob/ob mice

Aims/hypothesis Ablation of gastric inhibitory polypeptide (GIP) receptor action is reported to protect against obesity and associated metabolic abnormalities. The aim of this study was to use prediabetic ob/ob mice to examine whether 60 days of chemical GIP receptor ablation with (Pro³)GIP is able to counter the development of genetic obesity-related diabetes. Materials and methods Young (5–7 weeks) ob/ob mice received once daily i.p. injections of either saline vehicle or (Pro³)GIP (25 nmol kg⁻¹ day⁻¹) over a 60 day period. Food intake, body weight and circulating glucose and insulin were measured at frequent intervals. At 60 days, glucose tolerance, response to native GIP, postprandial responses, insulin sensitivity, HbA_1c, circulating hormones and plasma lipids were assessed. Results Body weight and food intake in (Pro³)GIP-treated mice did not differ from ob/ob controls. GIP receptor blockade significantly improved non-fasting glucose (p < 0.001), HbA_1c (p < 0.05), glucose tolerance (p < 0.001), meal tolerance (p < 0.001) and insulin sensitivity (p < 0.05). Remarkably, (Pro³)GIP treatment prevented the age-related development of diabetes, as none of these parameters differed significantly between treated ob/ob mice and normal age-matched lean controls. Circulating levels of glucagon, corticosterone, adiponectin and total cholesterol were unchanged by (Pro³)GIP, while levels of triacylglycerol, LDL-cholesterol and resistin were decreased (p < 0.05) compared with those in control ob/ob mice. Plasma and pancreatic insulin concentrations were generally lower after (Pro³)GIP treatment than in control ob/ob mice (p < 0.01), but plasma insulin levels remained substantially raised (p < 0.001) compared with those observed in lean controls. Conclusions/interpretation These data indicate that sustained GIP receptor antagonism provides an effective means of preventing the development of many of the metabolic abnormalities of obesity-driven diabetes.     

Impaired glucose tolerance (IGT) is associated with reduced insulin-induced suppression of glucagon concentrations

Aims/hypothesis: We aimed to examine whether impaired glucose tolerance is associated with reduced suppression of glucagon concentrations. Methods: Eighty-four non-diabetic women of Caucasian origin and 61 years of age, of whom 48 had normal glucose tolerance (NGT) and 36 had IGT, underwent a 75 g OGTT and a hyperinsulinaemic, euglycaemic clamp with measurement of glucagon, insulin and glucose concentrations. Results: At 2 h after 75 g oral glucose, glucagon concentrations were reduced by 7.1 ± 1.1 ng/l in NGT vs 8.0 ± 1.4 ng/l in IGT, (NS). However, the 2 h reductions in glucagon per mmol/l increase in 2 h glucose or per pmol/l increase in 2 h insulin were both impaired in IGT (p = 0.002 and p = 0.043, respectively) because the 2 h increases in glucose and insulin were higher in IGT than in NGT. Furthermore, suppression of glucagon concentrations during a euglycaemic clamp at hyperinsulinaemic concentrations (NGT: 607 ± 19 pmol/l, IGT: 561 ± 21 pmol/l) was lower in IGT (13.6 ± 1.6 ng/l) than in NGT (23.1 ± 1.2 ng/l; p < 0.001). The suppression of glucagon concentrations during the hyperinsulinaemic, euglycaemic clamp correlated with insulin sensitivity (r = 0.24, p = 0.027) and with the 2 h glucose value during the OGTT (r = –0.52, p < 0.001). Conclusion/interpretation: Impaired glucose tolerance is associated with reduced insulin-induced suppression of glucagon secretion, which could be caused by A-cell insulin resistance. Inappropriately high glucagon secretion could therefore contribute to the metabolic perturbations in IGT. [Diabetologia (2001) 44: 1998–2003] Received: 15 May 2001 and in revised form: 13 July 2001     

Plasma gastric inhibitory polypeptide and glucagon‐like peptide‐1 levels after glucose loading are associated with different factors in Japanese subjects

Aims/Introduction: Gastric inhibitory polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are major incretins that potentiate insulin secretion from pancreatic β‐cells. The factors responsible for incretin secretion have been reported in Caucasian subjects, but have not been thoroughly evaluated in Japanese subjects. We evaluated the factors associated with incretin secretion during oral glucose tolerance test (OGTT) in Japanese subjects with normal glucose tolerance (NGT). Materials and Methods: We measured plasma GIP and GLP‐1 levels during OGTT in 17 Japanese NGT subjects and evaluated the factors associated with GIP and GLP‐1 secretion using simple and multiple regression analyses. Results: GIP secretion (AUC‐GIP) was positively associated with body mass index (P < 0.05), and area under the curve (AUC) of C‐peptide (P < 0.05) and glucagon (P < 0.01), whereas GLP‐1 secretion (AUC‐GLP‐1) was negatively associated with AUC of plasma glucose (P < 0.05). The insulinogenic index was most strongly associated with GIP secretion (P < 0.05); homeostasis model assessment β‐cell was the most the strongly associated factor in GLP‐1 secretion (P < 0.05) among the four indices of insulin secretion and insulin sensitivity. Conclusions: Several distinct factors might be associated with GIP and GLP‐1 secretion during OGTT in Japanese subjects. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00078.x, 2011)     

Associations between depressive symptoms and insulin resistance: The Hoorn Study

Aims/hypothesis The association between depression and insulin resistance has been investigated in only a few studies, with contradictory results reported. The aim of this study was to determine whether the association between symptoms of depression and insulin resistance varies across glucose tolerance status and between men and women.Subjects and methods Cross-sectional data from a population-based cohort study in Hoorn, a medium-sized town in the Netherlands, were analysed. The study sample consisted of 541 men and women aged 55–75 years, of whom 260 had NGT, 164 had IGT and 117 had established type 2 diabetes mellitus. Main outcome measures were insulin resistance defined by the homeostasis model assessment for insulin resistance (HOMA-IR) and symptoms of depression using the Centre for Epidemiologic Studies Depression Scale (CES-D).Results In the total sample, we found a weak positive correlation between the depressive symptoms CED-D scores and HOMA-IR scores (r _s = 0.156, p < 0.001). Even weaker associations were found in subjects with NGT (r _s = 0.041, p=0.509), in subjects with IGT (r _s = 0.112, p = 0.160) and in subjects with type 2 diabetes (r _s = 0.007, p = 0.942). The association between depressive symptoms and insulin resistance was similar for men and women.Conclusions/interpretation We found only weak associations between depressive symptoms and insulin resistance, which did not differ among different glucose metabolism subgroups or between men and women.     

Low hepatic stearoyl-CoA desaturase 1 activity is associated with fatty liver and insulin resistance in obese humans

Aims/hypothesis Stearoyl-CoA desaturase 1 (SCD1) is the rate-limiting enzyme in monounsaturated fatty acid synthesis. It is imperative for the assembly of VLDL particles, which transport triacylglycerol (TG) from liver to adipose tissue and other sites. We aimed to determine the role of hepatic SCD1 activity in human glucose and lipid metabolism. Methods We studied 54 people participating in a lifestyle intervention programme with diet modification and increased physical activity. Insulin sensitivity was determined during a euglycaemic–hyperinsulinaemic clamp and estimated from an OGTT. Liver fat was quantified by ¹H-magnetic resonance spectroscopy at baseline and after 9 months of intervention. The pattern of fatty acids in serum VLDL-TGs was determined by ultracentrifugation followed by thin layer and gas chromatography, with the 18:1 n-9: 18:0 ratio providing an index of hepatic SCD1 activity. Results The hepatic SCD1 activity index correlated negatively with liver fat (r = −0.29, p = 0.04) and positively with insulin sensitivity, both OGTT-derived (r = 0.42, p = 0.003) and clamp-derived (r = 0.27, p = 0.07). These correlations depended on overall adiposity. They were absent in leaner participants (n = 27, liver fat: p = 0.34, insulin sensitivity [OGTT]: p = 0.75, insulin sensitivity [clamp]: p = 0.24), but were strong in obese individuals (n = 27, p = 0.004, p = 0.0002 and p = 0.006, respectively). Furthermore, during intervention a high SCD1 activity index at baseline predicted a decrease in liver fat only in obese participants (r = −0.46, p = 0.02). Conclusions/interpretation Our data suggest that high hepatic SCD1 activity may regulate fat accumulation in the liver and possibly protects from insulin resistance in obesity. N. Stefan and A. Peter contributed equally to this work.