Impaired beta cell sensitivity to incretins in type 2 diabetes is insufficiently compensated by higher incretin response.

BACKGROUND AND AIMS: The incretin effect is impaired in type 2 diabetes (T2D), but the underlying mechanisms are only partially understood. We investigated the relationships between the time course of the incretin effect and that of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) during oral glucose tolerance tests (OGTTs), thereby estimating incretin sensitivity of the beta cell, and its associated factors. METHODS AND RESULTS: Eight patients with T2D and eight matched subjects with normal glucose tolerance (NGT) received 25, 75, and 125 g OGTTs and corresponding isoglycemic glucose infusions (IIGI). The time course of the incretin effect, representing potentiation of insulin secretion by incretins (PINCR), was determined by mathematical modelling as the time-dependent fold increase in insulin secretion during OGTT compared to IIGI. The time course of PINCR was correlated with that of both GIP and GLP-1 in each subject (median r = 0.67 in NGT and 0.45 in T2D). We calculated an individual beta cell sensitivity to incretins (SINCR) using a weighted average of GIP and GLP-1 (pooled incretin concentration, PIC), as the slope of the relationship between PINCR and PIC. SINCR was reduced in T2D (p < 0.01). In the whole group, mean PIC, GIP and GLP-1 concentrations during the OGTT were inversely correlated with SINCR, but T2D had lower PIC, GIP and GLP-1 levels at the same SINCR (p < 0.05). CONCLUSION: Relative incretin insensitivity is partly compensated for by higher incretin secretory responses. However, T2D shows both impairment in incretin sensitivity and abnormal compensation by incretin secretion.

The amino acid response to a mixed meal in patients with type 2 diabetes: effect of sitagliptin treatment.

AIMS: Amino acid (AA) metabolism is altered in type 2 diabetes (T2D), and fasting levels of α-hydroxybutyrate (α-HB), a biomarker for insulin resistance, have been suggested to track AA metabolism. We investigated the changes in AA and α-HB induced by a mixed-meal tolerance test (MTT) and the effects of sitagliptin treatment. METHODS: Forty-seven T2D patients [56 ± 7 years, body mass index (BMI) 29.9 ± 4.2 kg/m(2) ] were randomized to sitagliptin (100 mg/day, 6 weeks) or placebo. Seven age- and BMI-matched non-diabetic subjects served as control (CT). RESULTS: During a 5-h MTT, branched-chain AA (BCAA) peaked earlier in T2D than CT [75(25) vs. 62(3) mmol/l · h over 2 h, median(interquartile range), p = 0.05], and rose higher [5-h increment: 31(23) vs. 19(24) mmol/l · h, p = 0.05]. Fasting α-HB was higher [7.5(2.7) vs. 5.9(1.3) µg/ml, p = 0.04 T2D vs. CT], and its meal-induced increments were larger [24(99) vs. -41(86) µg/ml · h, p = 0.006]. Plasma non-esterified fatty acids (NEFA) declined during MTT, but their increments were greater in patients (53 ± 16 vs. 35 ± 10 mEq/l · h, p = 0.005). Compared to placebo, both BCAA [-6.4(21.1) vs. 0.0(48.0) mmol/l · h, p = 0.01] and α-HB increments [-114(250) vs. 114(428) µg/ml · h, p = 0.002] decreased with sitagliptin, and meal-induced NEFA suppression was improved. Changes in BCAA and α-HB were reciprocally related to changes in insulin sensitivity (ρ = -0.37 and -0.43, p ≤ 0.01). CONCLUSIONS: T2D is associated with a hyperaminoacidaemic response to MTT, which circulating α-HB levels track. Sitagliptin-induced glycaemic improvement was associated with reductions in BCAA and α-HB excursions and better NEFA suppression, in parallel with improved insulin sensitivity, confirming that α-HB is a readout of metabolic overload.

Impact of mild to moderate reductions of glomerular filtration rate on coronary artery disease severity.

BACKGROUND & AIMS: The bases of the link between reduced glomerular filtration rate (GFR) and coronary artery disease (CAD) are complex and to some extent still unclear. We performed this observational, single referral center, cohort study to evaluate whether mild to moderate GFR reduction is associated with more severe CAD and/or with a worse cardiac prognosis independently of proteinuria, diabetes and traditional risk factors. METHODS AND RESULTS: In 1752 consecutive non-diabetic patients without proteinuria or moderate/severe kidney disease undergoing a clinically driven coronary angiography, coronary arteries lesions, myocardial function and hypertrophy and 10-yrs incidence of cardiac events and death were evaluated in relation to classes of estimated GFR defined according the lowest eGFR value (105+, 90+, 75+, 60+, 45+). A reduced eGFR was independently associated with hypertension, myocardial hypertrophy and stress induced ischemia, while the excess coronary lesions and the worse myocardial systolic function were both largely explained by age and cardiovascular risk factors. When compared to subjects 75+, both the risk of cardiac death (1.67[1.10-2.57] and 3.06[1.85-5.10]) and non-fatal myocardial infarction (2.58[1.12-6.49] and 2.73[1.31-6.41]) adjusted for age and comorbidities were higher in eGFR 60+ and 45+ patients. CONCLUSIONS: A mild-moderate reduction of eGFR is closely associated to higher rates of stress-induced ischemia, myocardial hypertrophy and higher risk of fatal and non-fatal cardiac events. The associations of reduced eGFR with coronary atherosclerosis and myocardial systolic dysfunction are both largely explained by age and traditional risk factors.

HDL lipid composition is profoundly altered in patients with type 2 diabetes and atherosclerotic vascular disease.

BACKGROUND AND AIMS: We have previously shown that the anti-inflammatory and anti-oxidant functions of HDL are impaired in T2D patients. In this study, we examined whether HDL from T2D patients contains elevated levels of oxidized fatty acids and whether those levels correlate with cardiovascular disease (CVD). METHODS AND RESULTS: HETEs and HODEs on HDL were determined by LC-MS/MS in 40 non-diabetic controls (ND), 40 T2D without CVD (D⁺CVD⁻) and 38 T2D with known history of CVD (D⁺CVD⁺). HDL oxidant index was evaluated by a cell-free assay using dichlorofluorescein. Twenty-six randomly selected subjects from the three groups underwent coronary calcium score evaluation (CAC). Major cardiovascular risk factors were similar among the groups. HETEs and HODEs content were significantly increased in HDL from D⁺CVD⁺ when compared to D⁺CVD⁻ and ND patients. HDL oxidant index was not different among the three groups; however, it was significantly higher in patients with CAC score >100 when compared to patients with CAC score <100. CONCLUSION: Patients with D⁺CVD⁻ and D⁺CVD⁺ are characterized by a severe, graded enrichment of oxidized fatty acids on HDL. In the present study, a loss of HDL function (as estimated by the HDL oxidant index) is observed only in patients with more advanced atherosclerosis.

Direct effect of GLP-1 infusion on endogenous glucose production in humans.

AIMS/HYPOTHESIS: Glucagon-like peptide-1 (GLP-1) lowers glucose levels by potentiating glucose-induced insulin secretion and inhibiting glucagon release. The question of whether GLP-1 exerts direct effects on the liver, independently of the hormonal changes, is controversial. We tested whether an exogenous GLP-1 infusion, designed to achieve physiological postprandial levels, directly affects endogenous glucose production (EGP) under conditions mimicking the fasting state in diabetes. METHODS: In 14 healthy volunteers, we applied the pancreatic clamp technique, whereby plasma insulin and glucagon levels are clamped using somatostatin and hormone replacement. The clamp was applied in paired, 4 h experiments, during which saline (control) or GLP-1(7-37)amide (0.4 pmol min⁻¹ kg⁻¹) was infused. RESULTS: During the control study, plasma insulin and glucagon were maintained at basal levels and plasma C-peptide was suppressed, such that plasma glucose rose to a plateau of ~10.5 mmol/l and tracer-determined EGP increased by ~60%. During GLP-1 infusion at matched plasma glucose levels, the rise of EGP from baseline was fully prevented. Lipolysis (as indexed by NEFA concentrations and tracer-determined glycerol rate of appearance) and substrate utilisation (by indirect calorimetry) were similar between control and GLP-1 infusion. CONCLUSIONS/INTERPRETATION: GLP-1 inhibits EGP under conditions where plasma insulin and glucagon are not allowed to change and glucose concentrations are matched, indicating either a direct effect on hepatocytes or neurally mediated inhibition.

Systemic inhibition of nitric oxide synthesis in non-diabetic individuals produces a significant deterioration in glucose tolerance by increasing insulin clearance and inhibiting insulin secretion.

AIMS/HYPOTHESIS: Endogenous NO inhibits insulin release in isolated beta cells and insulin-degrading enzyme activity in hepatocytes, while NO release from endothelial cells has been suggested to enhance insulin action. We assessed the overall effect of systemic inhibition of endogenous NO synthesis on glucose homeostasis in humans. METHODS: Twenty-four non-diabetic volunteers underwent two hyperglycaemic (+7 mmol/l) clamps with either saline or L-NG-nitroarginine methyl ester (L-NAME, at rates of 2.5, 5, 10 and 20 µg min⁻¹ kg⁻¹) infusion. Another five volunteers underwent an OGTT with either saline or L-NAME (20 µg min⁻¹ kg⁻¹) infusion. Blood pressure and heart rate were measured to monitor NO blockade; during the OGTT, endothelial function was assessed by peripheral arterial tonometry and insulin secretion by C-peptide deconvolution and insulin secretion modelling. RESULTS: Compared with saline, L-NAME at the highest dose raised mean blood pressure (+20 ± 2 mmHg), depressed heart rate (-12 ± 2 bpm) and increased insulin clearance (+50%). First-phase insulin secretion was impaired, but insulin sensitivity (M/I index) was unchanged. During the OGTT, L-NAME raised 2 h plasma glucose by 1.8 mmol/l (p < 0.01), doubled insulin clearance and impaired beta cell glucose sensitivity while depressing endothelial function. CONCLUSIONS/INTERPRETATION: In humans, systemic NO blockade titrated to increase blood pressure and induce endothelial dysfunction does not affect insulin action but significantly impairs glucose tolerance by increasing plasma insulin clearance and depressing insulin secretion, namely first-phase and beta cell glucose sensitivity.

Efficacy and safety of ipragliflozin in patients with type 2 diabetes inadequately controlled on metformin: a dose-finding study.

AIMS: Ipragliflozin is a novel, selective inhibitor of sodium glucose co-transporter 2 (SGLT2 inhibitor) in clinical development for type 2 diabetes mellitus (T2DM) treatment. This study assessed the efficacy and safety of different doses of ipragliflozin. METHODS: In a 12-week, multicentre, double-blind, randomized, placebo-controlled, dose-finding study patients with inadequate glycaemic control on metformin monotherapy (≥1500 mg/day) were randomized to one of four ipragliflozin treatment groups (12.5, 50, 150 or 300 mg once daily) or placebo. Primary efficacy outcome was mean change from baseline in haemoglobin A1c (HbA1c) compared to placebo at week 12. Adverse events (AEs), vital signs and laboratory safety measurements were assessed. RESULTS: Ipragliflozin dose dependently decreased HbA1c from baseline to week 12 compared to placebo (-0.22, -0.34, -0.40 and -0.48% for ipragliflozin 12.5, 50, 150 and 300 mg, respectively). Decreases in body weight and blood pressure were observed for all ipragliflozin groups. AEs occurred in 39.7-51.4% of the ipragliflozin groups and 39.4% of placebo patients. Urinary tract infections (1.4-6.9 vs. 6.1%), genital infections (0-4.3 vs. 1.5%) and hypoglycaemia (0-5.9 vs. 3.0%) were similar in the ipragliflozin and placebo groups, respectively, without dose dependency. There were no clinically relevant effects on other safety measurements. CONCLUSIONS: Ipragliflozin treatment improved glycaemic control when added to metformin therapy and may be associated with weight loss and reductions in blood pressure compared to placebo. No safety or tolerability concerns were identified at any of the tested doses supporting the further development of ipragliflozin at ≥50 mg doses in T2DM patients.

A Phase IIb, randomized, placebo-controlled study of the SGLT2 inhibitor empagliflozin in patients with type 2 diabetes.

AIM: This Phase IIb, randomized, double-blind, placebo-controlled trial evaluated the efficacy, safety, tolerability and pharmacokinetics of empagliflozin in patients with type 2 diabetes. METHODS: Four hundred and eight patients (treatment-naïve or after a 4-week wash-out period) were randomized to receive empagliflozin 5, 10 or 25 mg once daily, placebo or open-label metformin for 12 weeks. The primary endpoint was change in haemoglobin A1c (HbA1c) after 12 weeks. RESULTS: After 12 weeks' treatment, empagliflozin showed dose-dependent reductions in HbA1c from baseline [5 mg: -0.4%, 10 mg: -0.5%, 25 mg: -0.6%; all doses p < 0.0001 vs. placebo (+0.09%)]. Fasting plasma glucose (FPG) decreased with empagliflozin [5 mg: -1.29 mmol/l, 10 mg: -1.61 mmol/l, 25 mg: -1.72 mmol/l; all doses p < 0.0001 vs. placebo (+0.04 mmol/l)]. Body weight decreased in all empagliflozin groups (all doses p < 0.001 vs. placebo). The incidence of adverse events (AEs) was similar in the placebo (32.9%) and empagliflozin (29.1%) groups. The most frequently reported AEs on empagliflozin were pollakiuria (3.3% vs. 0% for placebo), thirst (3.3% vs. 0% for placebo) and nasopharyngitis (2.0% vs. 1.2% for placebo). AEs consistent with urinary tract infections (UTIs) were reported in four (1.6%) patients on empagliflozin vs. one (1.2%) on placebo. Genital infections were reported in five (2%) patients on empagliflozin vs. 0% on placebo. No UTIs or genital infections led to premature discontinuation. CONCLUSIONS: In patients with type 2 diabetes, empagliflozin resulted in dose-dependent, clinically meaningful reductions in HbA1c and FPG, and reductions in body weight compared with placebo. Empagliflozin was well-tolerated with a favourable safety profile.

Endothelial dysfunction in type 2 diabetes.

The mechanisms responsible for the accelerated atherosclerosis observed in type 2 diabetes are not fully understood. One of the earliest events in the development of atherosclerosis is endothelial dysfunction, namely, a reduction in nitric oxide (NO) synthesis or its bioavailability within the peri-endothelial environment, where it is responsible for maintenance of vascular tissue integrity. The clinical evaluation of this pathway is hampered by the fact that in vivo NO cannot be directly measured; however, exploiting a novel, complex and elegant experimental setup, McVeigh and co-workers (Diabetologia 1992;35:771-776) were the first to document that NO bioavailability in type 2 diabetic patients is indeed reduced. In this edition of 'Then and now' that paper is reappraised not only for its originality, but also for the broad and extensive evaluation of the vascular functions explored, the complete clinical characterisation of patients enrolled and for the fact that all the major findings were subsequently replicated.

Similar patterns of myocardial metabolism and perfusion in patients with type 2 diabetes and heart disease of ischaemic and non-ischaemic origin.

AIMS/HYPOTHESIS: Type 2 diabetes and insulin resistance are often associated with the co-occurrence of coronary atherosclerosis and cardiac dysfunction. The aim of this study was to define the independent relationships between left ventricular dysfunction or ischaemia and patterns of myocardial perfusion and metabolism in type 2 diabetes. METHODS: Twenty-four type 2 diabetic patients--12 with coronary artery disease (CAD) and preserved left ventricular function and 12 with non-ischaemic heart failure (HF)--were enrolled in a cross-sectional study. Positron emission tomography (PET) was used to assess myocardial blood flow (MBF) at rest, after pharmacological stress and under euglycaemic hyperinsulinaemia. Insulin-mediated myocardial glucose disposal was determined with 2-deoxy-2-[(18)F]fluoroglucose PET. RESULTS: There was no difference in myocardial glucose uptake (MGU) between the healthy myocardium of CAD patients and the dysfunctional myocardium of HF patients. MGU was strongly influenced by levels of systemic insulin resistance in both groups (CAD, r = 0.85, p = 0.005; HF, r = 0.77, p = 0.01). In HF patients, there was an inverse association between MGU and the coronary flow reserve (r = -0.434, p = 0.0115). A similar relationship was observed in non-ischaemic segments of CAD patients. Hyperinsulinaemia increased MBF to a similar extent in the non-ischaemic myocardial of CAD and HF patients. CONCLUSIONS/INTERPRETATION: In type 2 diabetes, similar metabolic and perfusion patterns can be detected in the non-ischaemic regions of CAD patients with normal cardiac function and in the dysfunctional non-ischaemic myocardium of HF patients. This suggests that insulin resistance, rather than diagnosis of ischaemia or left ventricular dysfunction, affects the metabolism and perfusion features of patients with type 2 diabetes.

Impact of increased visceral and cardiac fat on cardiometabolic risk and disease.

OBJECTIVE: Previous studies have highlighted the associations between abdominal, cardiac or total fat accumulation and cardiovascular disease. The aim of this study was to investigate the impact of different ectopic fat depots on measurements of metabolic dysfunction and cardiovascular disease risk. METHODS: Using magnetic resonance imaging in 113 subjects, we measured abdominal (visceral and subcutaneous) and cardiac (epicardial and extra-pericardial) fat depots and examined their association with overall (BMI) and abdominal obesity (waist circumference), dyslipidaemia (triglycerides, total and HDL cholesterol), glucose tolerance (by an oral glucose tolerance test) and insulin sensitivity, blood pressure and 10-year coronary heart disease risk by Framingham score. RESULTS: Fat accumulation was proportional to the degree of obesity, with body fat ranging from 14 to 33 kg, visceral fat from 0.8 to 1.8 kg and cardiac fat from 134 to 236 g. Most cardiac fat (70% on average) was extra-pericardial, with a wide variability for both cardiac depots (epicardial: 172-2008 mm(2); extra-pericardial: 100-5056 mm(2)). Only visceral and extra-pericardial fat, but not epicardial or subcutaneous fat, could discriminate between subjects with three or more factors of the metabolic syndrome or medium-to-high coronary heart disease risk score. Controlling for gender and BMI by multivariable analysis, the best marker of reduced insulin sensitivity was visceral fat (partial r = -0.35); extra-pericardial fat was the closest associate of increased blood pressure (partial r = 0.26) and both extra-pericardial and visceral fat clustered with hypertriglyceridaemia (partial r = 0.29 and 0.24; both P < 0.02). CONCLUSION: Increased epicardial fat per se does not necessarily translate into presence or prediction of disease. In contrast, increased deposition of visceral abdominal and extra-pericardial mediastinal fat are both associated with an enhanced cardiovascular disease risk profile.

High serum levels of CXC (CXCL10) and CC (CCL2) chemokines in untreated essential hypertension.

Hypertension has been suggested to exert pro-inflammatory actions through increased expression of several mediators, including chemokines. Chemokines are involved in inflammatory and autoimmune disorders, and in the formation of atherosclerotic lesions through promotion of inflammatory cell migration. The aim of this study is to evaluate the influence of high blood pressure on circulating levels of the prototype chemokines C-X-C motif ligand (CXCL)10 and C-C motif ligand (CCL)2 in 140 patients with essential hypertension not affected by thyroid disorders or overt autoimmune or inflammatory diseases, and 140 gender- and age-matched healthy controls. Mean CXCL10 and CCL2 levels were significantly higher in hypertensive patients than in controls. Among hypertensive patients, chemokines levels were higher in those with systo-diastolic hypertension compared to those with isolated systolic hypertension. In a multiple linear regression model using CXCL10 or CCL2 as dependent variables and age, body mass index, glycemia, serum creatinine, high-density-lipoprotein (HDL) and low-density-lipoprotein (LDL) cholesterol, triglycerides, and systolic or diastolic blood pressure values as covariates, only systolic or diastolic blood pressure values were significantly related to CXCL10 or CCL2 levels. In conclusion, this study demonstrates increased circulating levels of the prototype chemokines CXCL10 and CCL2 in patients with hypertension.

Predictors of type 2 diabetes relapse after Roux-en-Y Gastric Bypass: A ten-year follow-up study.

AIMS: To assess the impact of bariatric surgery on remission and relapse of type 2 diabetes mellitus (T2DM) at 10 years of follow-up and analyze predictive factors. MATERIALS AND METHODS: Eighty-eight obese subjects undergoing Roux-en-Y gastric bypass (RYGB) and 25 subjects assigned to medical therapy (MT) were evaluated every year for 10 years. T2DM remission was defined by the American Diabetes Association criteria. RESULTS: Body mass index (BMI), fasting glucose, and haemoglobin A1c (HbA1c) improved more markedly in RYGB than MT patients throughout the 10-year period. Post-surgery remission rates were 74% and 53% at 1 and 10 years, respectively, while remission did not occur in MT patients. One-year post-surgery, BMI decreased more in subjects with remission than in those without, but no further decrease was observed thereafter. By partial-least-squares analysis, T2DM duration, baseline HbA1c, and ensuing insulin therapy were the strongest predictors of remission. Remission was achieved at one year in 91% of patients with T2DM duration < 4 years, and 79% of them remained in remission at 10 years. On the contrary only 42% of patients with T2DM duration ≥ 4 years achieved remission, which was maintained only in 6% at the end of 10 years. By survival analysis, patients with T2DM duration < 4 years had higher remission rates than those with duration ≥ 4 years (hazards ratio (HR) 3.1 [95%CI 1.8-5.7]). Relapse did not occur before two years post-surgery and was much less frequent in patients with < 4- vs ≥ 4-year duration (HR 11.8 [4.9-29.4]). CONCLUSIONS: Short T2DM duration and good glycemic control before RYGB surgery were the best requisites for a long-lasting T2DM remission, whereas weight loss had no impact on the long-term relapse of T2DM.

A novel surrogate index for hepatic insulin resistance.

AIMS/HYPOTHESIS: In epidemiological and genetic studies surrogate indices are needed to investigate insulin resistance in different insulin-sensitive tissues. Our objective was to develop a surrogate index for hepatic insulin resistance. METHODS: A sample of 368 non-diabetic participants (age 43.0 ± 8.2 years, BMI 26.0 ± 4.0 kg/m(2); mean ± SD) whose endogenous glucose production (EGP) was measured with [6-6(2)H(2)]glucose in the fasting state and during the euglycaemic-hyperinsulinaemic clamp were included in the study. EGP multiplied by fasting plasma insulin (FPI) concentration was the reference measurement for liver insulin resistance (liver IR). Liver IR index was calculated with linear regression analysis including age, obesity indices, lipids, lipoproteins and several variables regulating glucose metabolism. RESULTS: The following variables were significantly associated with liver IR in multiple forward stepwise regression analysis: insulin AUC in an OGTT, fat mass, HDL-cholesterol and BMI. Liver IR index correlated significantly with EGP×FPI (r = 0.65, p < 0.001). In participants with abnormal glucose tolerance, the correlation of liver IR with EGP×FPI was slightly stronger (r = 0.69, p < 0.001) than in those with normal glucose tolerance (r = 0.62, p < 0.001). CONCLUSIONS/INTERPRETATION: We generated a novel surrogate index for liver insulin resistance correlating strongly with EGP × FPI.

Natural history and physiological determinants of changes in glucose tolerance in a non-diabetic population: the RISC Study.

AIMS/HYPOTHESIS: The natural history and physiological determinants of glucose intolerance in subjects living in Europe have not been investigated. The aim of this study was to increase our understanding of this area. METHODS: We analysed the data from a population-based cohort of 1,048 non-diabetic, normotensive men and women (aged 30-60 years) in whom insulin sensitivity was measured by the glucose clamp technique (M/I index; average glucose infusion rate/steady-state insulin concentration) and beta cell function was estimated by mathematical modelling of the oral glucose tolerance test at baseline and 3 years later. RESULTS: Seventy-seven per cent of the participants had normal glucose tolerance (NGT) and 5% were glucose intolerant both at baseline and follow up; glucose tolerance worsened in 13% (progressors) and improved in 6% (regressors). The metabolic phenotype of the latter three groups was similar (higher prevalence of familial diabetes, older age, higher waist-to-hip ratio, higher fasting and 2 h plasma glucose, higher fasting and 2 h plasma insulin, lower insulin sensitivity and reduced beta cell glucose sensitivity with increased absolute insulin secretion). Adjusting for these factors in a logistic model, progression was predicted by insulin resistance (bottom M/I quartile, OR 2.52 [95% CI 1.51-4.21]) and beta cell glucose insensitivity (bottom quartile, OR 2.39 [95% CI 1.6-3.93]) independently of waist-to-hip ratio (OR 1.44 [95% CI 1.13-1.84] for one SD). At follow up, insulin sensitivity and beta cell glucose sensitivity were unchanged in the stable NGT and stable non-NGT groups, worsened in progressors and improved in regressors. CONCLUSIONS/INTERPRETATION: Glucose tolerance deteriorates over time in young, healthy Europids. Progressors, regressors and glucose-intolerant participants share a common baseline phenotype. Insulin sensitivity and beta cell glucose sensitivity predict and track changes in glucose tolerance independently of sex, age and obesity.

Association of indices of liver and adipocyte insulin resistance with 19 confirmed susceptibility loci for type 2 diabetes in 6,733 non-diabetic Finnish men.

AIMS/HYPOTHESIS: Of the confirmed type 2 diabetes susceptibility loci only a few are known to affect insulin sensitivity. We examined the association of indices of hepatic and adipocyte insulin resistance (IR) with 19 confirmed type 2 diabetes risk loci in a large population-based study. METHODS: Non-diabetic participants (n = 8,460, age 57.3 ± 7.0 years, BMI 26.8 ± 3.8 kg/m(2); mean ± SD) from a population-based cohort underwent an OGTT. Of them, 6,733 non-diabetic men were genotyped for single nucleotide polymorphisms (SNPs) in or near PPARG2 (also known as PPARG), KCNJ11, TCF7L2, SLC30A8, HHEX, CDKN2B, IGF2BP2, CDKAL1, HNF1B, WFS1, JAZF1, CDC123, TSPAN8, THADA, ADAMTS9, NOTCH2, KCNQ1, MTNR1B and SNP rs7480010. We investigated hepatic IR with a new index of liver IR. The adipocyte IR index was defined as a product of fasting NEFA and plasma insulin levels. RESULTS: Type 2 diabetes risk SNPs in or near KCNJ11 and HHEX were significantly (p < 0.0013), and those in or near CDKN2B, NOTCH2 and MTNR1B were nominally (p < 0.05), associated with decreased liver IR index. The Pro12 allele of PPARG2 was significantly associated with a high adipocyte IR index and nominally associated with high liver IR. CONCLUSIONS/INTERPRETATION: The Pro12 allele of PPARG2 seems to impair insulin's antilipolytic effect, leading to high NEFA release in the fasting state and IR. In addition, the type 2 diabetes risk alleles of KCNJ11 and HHEX, which are known to impair insulin secretion, were associated with increased hepatic insulin sensitivity.

Early and longer term effects of gastric bypass surgery on tissue-specific insulin sensitivity and beta cell function in morbidly obese patients with and without type 2 diabetes.

AIMS/HYPOTHESIS: Bariatric surgery consistently induces remission of type 2 diabetes. We tested whether there are diabetes-specific mechanisms in addition to weight loss. METHODS: We studied 25 morbidly obese patients (BMI 51.7 ± 1.5 kg/m(2) [mean ± SEM]), 13 with non-insulin-treated type 2 diabetes (HbA(1c) 7.1 ± 0.5% [54 ± 5 mmol/mol]), before and at 2 weeks and 1 year after Roux-en-Y gastric bypass (RYGB). Lean (n = 8, BMI 23.0 ± 0.5 kg/m(2)) and obese (n = 14) volunteers who were BMI-matched (36.0 ± 1.2) to RYGB patients at 1 year after surgery served as controls. We measured insulin-stimulated glucose disposal (M) and substrate utilisation (euglycaemic clamp/indirect calorimetry), endogenous glucose production (EGP) by 6,6-[(2)H(2)]glucose, lipolysis (rate of appearance of [(2)H(5)]glycerol) and beta cell function (acute insulin response to i.v. glucose [AIR] as determined by C-peptide deconvolution). RESULTS: At baseline, all obese groups showed typical metabolic abnormalities, with M, glucose oxidation and non-oxidative disposal impaired, and EGP, lipolysis, lipid oxidation and energy expenditure increased. Early after RYGB plasma glucose and insulin levels, and energy expenditure had decreased, while lipid oxidation increased, with M, EGP and AIR unchanged. At 1 year post-RYGB (BMI 34.4 ± 1.1 kg/m(2)), all diabetic patients were off glucose-lowering treatment and mean HbA(1c) was 5.4 ± 0.14% (36 ± 2 mmol/mol) (p = 0.03 vs baseline); AIR also improved significantly. In all RYGB patients, M, substrate oxidation, EGP, energy expenditure and lipolysis improved in proportion to weight loss, and were therefore similar to values in obese controls, but still different from those in lean controls. CONCLUSIONS/INTERPRETATION: In morbidly obese patients, RYGB has metabolic effects on liver, adipose tissue, muscle insulin sensitivity and pattern of substrate utilisation; these effects can be explained by energy intake restriction and weight loss, the former prevailing early after surgery, the latter being dominant in the longer term.

High-density lipoprotein-cholesterol and not HbA1c was directly related to cardiovascular outcome in PROactive.

AIM: In PROactive, pioglitazone reduced the incidence of death, myocardial infarction and stroke, and significantly improved HbA1c, systolic blood pressure (SBP), triglycerides and high-density lipoprotein (HDL)-cholesterol relative to placebo. As these glycaemic and lipid parameters are major cardiovascular (CV) risk factors, we assessed their separate contribution to the reduced incidence of CV outcomes. METHODS: Patients (n = 5238) with type 2 diabetes and macrovascular disease were randomized to 45 mg pioglitazone or placebo. Relationships among treatment, outcome (time to first event of all-cause mortality, myocardial infarction and stroke) and 10 laboratory measurements and vital signs were investigated using log-linear models. Continuous variable measurements (percent changes from baseline to average of all postbaseline values prior to censoring) were made discrete by categorizing into tertiles. Log-linear models were fitted to multiway tables of discrete data and analysis of deviance used to summarize sources of variation in the data. RESULTS: Although pioglitazone treatment was associated with a decrease in HbA1c and an increase in HDL-cholesterol (HDL-C), only the change from baseline HDL-C predicted the outcome (χ(2) = 28.89, p < 0.0001). No other variables, including HbA1c, triglycerides and systolic blood pressure, showed significant direct associations with outcome. When the analysis was extended to include baseline statin use, this was associated with an improved outcome independently of HDL-C changes. CONCLUSIONS: This post hoc analysis suggests that HDL-C, but probably not HbA1c, is a driver of pioglitazone's favourable influence on CV outcome.

Metabolic effects of muraglitazar in type 2 diabetic subjects.

AIM: To assess the effect of muraglitazar, a dual peroxisome proliferator-activated receptor (PPAR)γ-α agonist, versus placebo on metabolic parameters and body composition in subjects with type 2 diabetes mellitus (T2DM). METHODS: Twenty-seven T2DM subjects received oral glucose tolerance test (OGTT), euglycaemic insulin clamp with deuterated glucose, measurement of total body fat (DEXA), quantitation of muscle/liver (MRS) and abdominal subcutaneous and visceral (MRI) fat, and then were randomized to receive, in addition to diet, muraglitazar (MURA), 5 mg/day, or placebo (PLAC) for 4 months. RESULTS: HbA1c(c) decreased similarly (2.1%) during both MURA and PLAC treatments despite significant weight gain with MURA (+2.5 kg) and weight loss with PLAC (-0.7 kg). Plasma triglyceride, LDL cholesterol, free fatty acid (FFA), hsCRP levels all decreased with MURA while plasma adiponectin and HDL cholesterol increased (p < 0.05-0.001). Total body (muscle), hepatic and adipose tissue sensitivity to insulin and ß cell function all improved with MURA (p < 0.05-0.01). Intramyocellular, hepatic and abdominal visceral fat content decreased, while total body and subcutaneous abdominal fat increased with MURA (p < 0.05-0.01). CONCLUSIONS: Muraglitazar (i) improves glycaemic control by enhancing insulin sensitivity and ß cell function in T2DM subjects, (ii) improves multiple cardiovascular risk factors, (iii) reduces muscle, visceral and hepatic fat content in T2DM subjects. Despite similar reduction in A1c with PLAC/diet, insulin sensitivity and ß cell function did not improve significantly.

Impaired beta cell glucose sensitivity rather than inadequate compensation for insulin resistance is the dominant defect in glucose intolerance.

AIMS/HYPOTHESIS: It is commonly thought that hyperglycaemia results from insufficient compensation of insulin secretion for insulin resistance. To verify this hypothesis, we assessed beta cell function and insulin sensitivity (IS) in a large cohort of volunteers with normal glucose tolerance (NGT) or impaired glucose regulation (IGR), i.e. impaired glucose tolerance or impaired fasting glucose. METHODS: In men and women with NGT (n=1,123) or IGR(n=156) (age 44 +/- 8 years, BMI 25+/-4 kg/m2, mean +/- SD)we measured: (1) IS by clamp; (2) insulin secretion rates(ISR) and beta cell glucose sensitivity (=slope of the insulin secretion/plasma glucose dose-response) by C-peptide deconvolution and OGTT modelling; and (3) acute insulin response to intravenous glucose. RESULTS: After controlling for centre, sex, age and BMI, fasting and total ISR were inversely related to IS in both groups,whereas beta cell glucose sensitivity was not. Acute insulin response was reciprocally related to IS in both groups, but the relationships were incompatible with inadequate compensation and significance was lost after controlling for fasting ISR. InIGR vs NGT, IS was impaired (92 [75] vs 133 [86] micromol min(-1)[kg fat-free mass](-1) [nmol/l](-1), median [interquartile range],p<0.0001) as was beta cell glucose sensitivity (69 [46] vs 119[83] pmol min(-1) m(-2) [nmol/l](-1), p<0.0001), whereas fasting and total ISR were increased (35% and 25%, respectively, p<0.0001). In fully adjusted models, beta cell glucose sensitivity was the strongest determinant of OGTT glucose levels. CONCLUSIONS/INTERPRETATION: Insulin resistance normally upregulates the secretory tone, with no evidence of defective compensation in IGR. In contrast, beta cell glucose sensitivity is independent of insulin resistance, but a key determinant of glucose tolerance. This suggests that hyperglycaemia results from an intrinsic beta cell defect rather than from inadequate compensation for insulin resistance.