Search

The incretin effect on insulin secretion was investigated in 8 subjects with type 2 diabetes (T2D) and 8 with normal glucose tolerance (NGT), using 25, 75, and 125 g oral glucose tolerance tests (OGTT) and isoglycemic intravenous glucose infusions (IIGI). The ß-cell response was evaluated using a model embedding a dose-response (slope = glucose sensitivity), an early response (rate sensitivity), and potentiation (time-related secretion increase). The incretin effect, as OGTT/IIGI ratio, was calculated for each parameter. In NGT, the incretin effect on total secretion increased with dose (1.3±0.1, 1.7±0.2, 2.2±0.2 fold of IIGI, P<0.0001), mediated by a dose-dependent increase of the incretin effect on glucose sensitivity (1.9±0.4, 2.4±0.4, 3.1±0.4, P = 0.005), and a dose-independent enhancement of the incretin effect on rate sensitivity (894 [1145], 454 [516], 783 [1259] pmol m−2 L mmol−1 above IIGI; median [interquartile range], P<0.0001). The incretin effect on potentiation also increased (0.97±0.06, 1.45±0.20, 1.24±0.16, P<0.0001). In T2D, the incretin effect on total secretion (1.0±0.1, 1.1±0.1, 1.3±0.1, P = 0.004) and glucose sensitivity (1.2±0.2, 1.3±0.2, 2.0±0.2, P = 0.005) were impaired vs NGT; however, the incretin effect on rate sensitivity increased already at 25 g (269 [169], 284 [301], 193 [465] pmol m−2 L mmol−1 above IIGI; negligible IIGI rate sensitivity in T2D prevented the calculation of the fold increment). OGTT did not stimulate potentiation above IIGI (0.94±0.04, 0.89±0.06, 1.06±0.09; P<0.01 vs NGT). In the whole group, the incretin effect was inversely associated with total secretion during IIGI, although systematically lower in T2D. In conclusion, 1) In NGT, glucose sensitivity and potentiation mediate the dose-dependent incretin effect increase; 2) In T2D, the incretin effect is blunted vs NGT, but rate sensitivity is enhanced at all loads; 3) Relatively lower incretin effect in NGT is associated with higher secretion during IIGI, suggesting that the reduced incretin effect does not result from ß-cell dysfunction. [ABSTRACT FROM AUTHOR]

To characterize the defects in β-cell function in subjects with impaired fasting glucose (IFG) and compare the results to impaired glucose tolerance (IGT) and normal glucose tolerance (NGT) subjects, β-cell glucose sensitivity and rate sensitivity during the oral glucose tolerance test were measured with the model by Mari in 172 Mexican Americans. A subgroup (n = 70) received a 2-h hyperglycemic clamp (+125 mg/dL), and first- and second-phase insulin secretion were quantitated. Compared with NGT, subjects with IFG and IGT manifested a decrease in b-cell glucose sensitivity; IFG subjects, but not IGT subjects, had decreased β-cell rate sensitivity. In IFG subjects, the defect in β-cell glucose sensitivity was time dependent, began to improve after 60 min, and was comparable to NGT after 90 min. The incremental area under the plasma C-peptide concentration curve during the first 12 min of the hyperglycemic clamp (ΔC-pep [AUC]0-12) was inversely related with the increase in FPG concentration (r = 236, r = 0.001), whereas ΔC-pep[AUC]15-120 positively correlated with FPG concentration (r = 0.29, r , 0.05). When adjusted for the prevailing level of insulin resistance, first-phase insulin secretion was markedly decreased in both IFG and IGT, whereas second-phase insulin secretion was decreased only in IGT. These results demonstrate distinct defects in β-cell function in IFG and IGT. [ABSTRACT FROM AUTHOR]

OBJECTIVE--To quantitate the separate impact of obesity and hyperlycemia on the incretin effect (i.e., the gain in β-cell function after oral glucose versus intravenous glucose). RESEARCH DESIGN AND METHODS--Isoglycemic oral (75 g) and intravenous glucose administration was performed in 51 subjects (24 with normal glucose tolerance [NGT], 17 with impaired glucose tolerance [IGT], and 10 with type 2 diabetes) with a wide range of BMI (20-61 kg/m[sup 2]). C-peptide deconvolution was used to reconstruct insulin secretion rates, and β-cell glucose sensitivity (slope of the insulin secretion/glucose concentration doseresponse curve) was determined by mathematical modeling. The incretin effect was defined as the oral-to-intravenous ratio of responses. In 8 subjects with NGT and 10 with diabetes, oral glucose appearance was measured by the double-tracer technique. RESULTS--The incretin effect on total insulin secretion and β-cell glucose sensitivity and the GLP-1 response to oral glucose were significantly reduced in diabetes compared with NGT or IGT (P ≤ 0.05). The results were similar when subjects were stratified by BMI tertile (P ≤ 0.05). In the whole dataset, each manifestation of the incretin effect was inversely related to both glucose tolerance (2-h plasma glucose levels) and BMI (partial r = 0.27-0.59, P ≤ 0.05) in an independent, additive manner. Oral glucose appearance did not differ between diabetes and NGT and was positively related to the GLP-1 response (r = 0.53, P < 0.01). Glucagon suppression during the oral glucose tolerance test was blunted in diabetic patients. CONCLUSIONS--Potentiation of insulin secretion, glucose sensing, glucagon-like peptide-1 release, and glucagon suppression are physiological manifestations of the incretin effect. Glucose tolerance and obesity impair the incretin effect independently of one another. Diabetes 57:1340-1348, 2008 [ABSTRACT FROM AUTHOR]

OBJECTIVE -- We studied the effects of the oral insulin secretagogue nateglinide on insulin secretion using a modeling approach to obtain β-cell function parameters from a meal test and examined the impact of the β-cell improvement on glucose tolerance. RESEARCH DESIGN AND METHODS -- Mild type 2 diabetic men and women (n = 108; fasting glucose 7.0-8.3 mmol/l) on diet treatment alone randomly received 30, 60, or 120 mg nateglinide or placebo for 24 weeks. β-Cell function parameters were derived by modeling (based on C-peptide deconvolution) from a standardized meal test at baseline and after 24 weeks of treatment. RESULTS -- The baseline demographic and metabolic characteristics of the four groups were similar. Nateglinide treatment resulted in dose-dependent reductions in the mean postprandial glucose response and at the 120-mg dose in fasting glucose. Fasting or total insulin secretion during the meal were not different. In contrast, we found differences in the model parameters. Rate sensitivity (expressing early insulin secretion when glucose is rising) was significantly enhanced at 24 weeks with the lowest nateglinide dose, with no further stimulation at higher doses. Early potentiation (expressing an initial insulin secretion enhancement), glucose sensitivity (the slope of the glucose-insulin secretion relationship), and insulin secretion at a fixed-reference 7-mmol/l glucose concentration all showed a trend toward increasing, with increasing nateglinide dose, and were significantly greater than placebo at the 120-mg dose. In multiple regression analyses, changes in rate sensitivity, glucose sensitivity, and potentiation all contributed to the observed glucose changes. CONCLUSIONS -- The model-derived parameters are sensitive measures of β-cell function, showing improvements after nateglinide treatment and predicting changes in glucose tolerance. [ABSTRACT FROM AUTHOR]

Pancreatic β cell dysfunction is a key feature of type 2 diabetes, and novel regulators of insulin secretion are desirable. Here, we report that succinate receptor 1 (SUCNR1) is expressed in β cells and is upregulated in hyperglycemic states in mice and humans. We found that succinate acted as a hormone-like metabolite and stimulated insulin secretion via a SUCNR1-GqPKC–dependent mechanism in human β cells. Mice with β cell–specific Sucnr1 deficiency exhibited impaired glucose tolerance and insulin secretion on a high-fat diet, indicating that SUCNR1 is essential for preserving insulin secretion in diet-induced insulin resistance. Patients with impaired glucose tolerance showed an enhanced nutrition-related succinate response, which correlates with the potentiation of insulin secretion during intravenous glucose administration. These data demonstrate that the succinate/SUCNR1 axis is activated by high glucose and identify a GPCR-mediated amplifying pathway for insulin secretion relevant to the hyperinsulinemia of prediabetic states. [ABSTRACT FROM AUTHOR]

Type 2 diabetes (T2D) risk is lower in females than males. It has been reported that females have greater pancreatic 훽‐cell function than males, which may at least in part contribute to the T2D risk in females. 훽‐cell function is influenced by exercise training; however, previous trials comparing 훽‐cell function between the sexes have not included participants matched for training status. Furthermore, the acute effects of different modes of exercise on 훽‐cell function, and whether sex inherently influences these effects, are largely unexamined. Males and females (12/sex) completed a 120‐min oral glucose tolerance test (OGTT) at rest (CON) and following acute bouts of high‐intensity interval exercise (HIIE), moderate intensity continuous (MIC) exercise, and low‐load high‐repetition (LLHR) resistance exercise to assess whether sex inherently influences baseline and/or post‐exercise pancreatic function in the absence of pathology. We found no sex differences in basal pancreatic 훽‐cell function. Females had greater basal insulin clearance following MIC exercise compared to males (p = 0.01) and males tended to have a higher potentiation ratio following HIIE (p = 0.07). Females also had lower glucose sensitivity following MIC exercise compared to HIIE (p = 0.007) and LLHR (p = 0.003). Insulin clearance during the OGTT was greater following HIIE as compared with CON and MIC exercise (p = 0.02). 2‐H oral glucose insulin sensitivity was greater following LLHR compared to CON (p = 0.01). Acute bouts of different modes of exercise do not differentially influence 훽‐cell function but do influence insulin clearance and insulin sensitivity. Therefore, sex and exercise mode interact to differentially influence insulin clearance and glucose sensitivity. [ABSTRACT FROM AUTHOR]

The article focuses on the study that aims to assess the effects of liraglutide on β-cell function in normal living. The study examined thirteen type 2 diabetic patients. The β-cell function of the patients was assessed using a model that describes the relationship between insulin secretion (ISR) and glucose concentration. It concludes that liraglutide treatment significantly enhances β-cell function evaluated under conditions of normal living.

Relatives of type 1 diabetic patients are at enhanced risk of developing diabetes (DM). We investigated the mechanisms by which risk progresses to disease. In 144 islet-cell autoantibody-positive, non-diabetic relatives from the close observation (control) group of the DPT-1 Parenteral Insulin Trial (73 female, age=12 [10] years (median [interquartile range]), BMI=18.3 [6.1] kg⋅m[sup -2], 42 IGT and 102 NGT). A frequently-sampled OGTT was performed at baseline and again 2.5 [2.8] years later, when 61 subjects (33 female/28 male, 28 from IGT, 33 from NGT) had developed DM. β-cell glucose sensitivity (β-GS, slope of the insulin-secretion/plasma glucose dose-response function) and insulin sensitivity (IS) were obtained by mathematical modelling of glucose/C-peptide responses to OGTT. Relatives progressing to DM had worse β-GS at follow up (18 [21] vs 62 [50] pmol⋅min[sub -1]⋅m[sub -2], p<0.0001 [Mann Whitney]) as well as at baseline (41 [30] vs 75 [68] pmol⋅min[sup -1]⋅m[sup -2]⋅mM[sup -1], p<0.0001). In contrast, IS was only marginally lower in progressors than non-progressors both at baseline (418 [79] vs 427 [61 ] ml⋅min[sup -1]⋅m[sup -2], p=0.77) and follow up (386 [66] vs 405 [64] ml⋅min[sup -1]⋅m[sup -2], p=0.12). By Kaplan-Meier modelling, DM-free survival was significantly (log-rank p<0.0001) worse in the bottom β-GS tertile (30 [21] pmol⋅min[sup -1]⋅m[sup -2]⋅mM[sup -1]) as compared to the middle (56 [13]) or top tertile (117 [53]). By proportional hazards analysis, incident DM was predicted (as relative risk, RR and [95% confidence interval] per 1 SD of the predictor) by baseline β-GS (RR=0.42 [0.32-0.56]), age (RR=0.27 [0.14-0.52]), female gender (RR=3.08 [1.73-5.45]), baseline IS (RR=0.66 [0.49-0.90]) and baseline BMI (RR=1.64 [0.98-2.73]), in that order of strength (χ²=36.9, 15.3, 14.8, 6.8 and 3.6, respectively). In this multivariate model, baseline glucose tolerance, fasting and 2-hour plasma glucose levels were not significant predictors. We conclude that, in high-risk relatives of type 1 patients progression to DM is mainly predicted by impaired β-cell glucose sensitivity, with younger age, female sex, reduced insulin sensitivity and higher BMI making additional contributions to DM risk. ADA-Funded Research [ABSTRACT FROM AUTHOR]

We studied whether parameters of beta cell function were similar during an oral glucose tolerance test (OGTT) and a -physiologically more relevant-mixed meal tolerance test (MTT) in different glucose tolerance groups. Individuals with normal glucose tolerance (NGT, n=150), intermediate hyperglycaemia (IH, n=19) and diabetes (DM, n=19) underwent an OGTT and an MTT, both containing 75g carbohydrates. The meal also contained 50g fat and 24g proteins. Plasma glucose, insulin and C-peptide were sampled before and 15, 30, 60, 90 and 120 minutes after OGTT and MTT. Insulin secretion rate (ISR) and beta cell function parameters were calculated from C-peptide using a mathematical model. These parameters included beta cell glucose sansitivity, i.e., the slope of the glucose concentration - ISR relationship and potentiation, which expresses a relative increase of ISR from the beginning to the end of the test. ANOVA and dependent t-tests with Bonferroni corrections were used to test for differences. Beta cell glucose sensitivity was higher during MTT than during OGTT in all groups (Table 1). Diabetic subjects had significantly lower beta cell glucose sensitivity than IH- and NGT-subjects. Potentiation was similar (NGT-or DM-subjects) or slightly higher (IH-subjects) during MTT. Beta cells were more sensitive to glucose (i.e. insulin secretion per glucose unit was higher) during a mixed meal load than during a glucose load while the ability to modulate this relationship (potentiation) was similar or slightly higher. Individuals with IH, unlike diabetic subjects, did not have lower beta cell sensitivity than NGT-individuals. We conclude that beta cell response is stronger after a mixed meal than after an OGTT with equal-carbohydrate quantity. [ABSTRACT FROM AUTHOR]

Introduction: It is uncertain whether lixisenatide has postprandial insulinotropic effects when its effect on slowing gastric emptying is considered, in healthy subjects and type 2 diabetes mellitus (T2DM). We evaluated the effects of single administration of 10 μg sc lixisenatide on glycaemia, insulin secretion and gastric emptying (GE), measured using the 'gold standard' technique of scintigraphy following an oral glucose load (75 g glucose). Methods: Fifteen healthy subjects (nine men, six women; age 67.2 ± 2.3 years) and 15 patients with T2DM (nine men, six women; age 61.9 ± 2.3 years) had measurements of GE, plasma glucose, insulin and C-peptide for 180 min after a radiolabeled 75 g glucose drink on two separate days. All subjects received lixisenatide (10 μg sc) or placebo in a randomised, double-blind, crossover fashion 30 min before the drink. Insulin secretory response (ISR) was determined using the C-peptide deconvolution method. Results: GE was markedly slowed by lixisenatide compared with placebo in both healthy subjects (1.45 ± 0.10 kcal/min for placebo vs. 0.60 ± 0.14 kcal/min for lixisenatide) and diabetes (1.57 ± 0.06 kcal/min for placebo vs. 0.75 ± 0.13 kcal/min for lixisenatide) (both P < 0.001) with no difference between the two groups (P = 0.42). There was a moderate to strong inverse correlation between the early insulin secretory response calculated at 60 min and gastric retention at 60 min with lixisenatide treatment in healthy subjects (r = − 0.8, P = 0.0003) and a trend in type 2 diabetes (r = − 0.4, P = NS), compared with no relationships in the placebo arms (r = − 0.02, P = NS, healthy subjects) and (r = − 0.16, P = NS, type 2 diabetes). Conclusion: The marked slowing of GE of glucose induced by lixisenatide is associated with attenuation in the rise of postprandial glucose in both healthy subjects and diabetes and early insulin secretory response in healthy subjects. Clinical Trials Registration Number: NCT02308254. [ABSTRACT FROM AUTHOR]

Objective: Endogenous insulin clearance (EIC) is physiologically reduced at increasing insulin secretion rate (ISR). Computing EIC at the prevailing ISR does not distinguish the effects of hypersecretion from those of other mechanisms of glucose homeostasis. We aimed to measure EIC in standardized ISR conditions (i.e., at fixed ISR levels) and to analyze its associations with relevant physiologic factors.Research Design and Methods: We estimated standardized EIC (EICISR) by mathematical modeling in nine different studies with insulin and glucose infusions (N = 2,067). EICISR association with various traits was analyzed by stepwise multivariable regression in studies with both euglycemic clamp and oral glucose tolerance test (OGTT) (N = 1,410). We also tested whether oral glucose ingestion, as opposed to intravenous infusion, has an independent effect on EIC (N = 1,555).Results: Insulin sensitivity (as M/I from the euglycemic clamp) is the strongest determinant of EICISR, approximately four times more influential than insulin resistance-related hypersecretion. EICISR independently associates positively with M/I, fasting and mean OGTT glucose or type 2 diabetes, and β-cell glucose sensitivity and negatively with African American or Hispanic race, female sex, and female age. With oral glucose ingestion, an ISR-independent ∼10% EIC reduction is necessary to explain the observed insulin concentration profiles.Conclusions: Based on EICISR, we posit the existence of two adaptive processes involving insulin clearance: the first reduces EICISR with insulin resistance (not with higher BMI per se) and is more relevant than the concomitant hypersecretion; the second reduces EICISR with β-cell dysfunction. These processes are dysregulated in type 2 diabetes. Finally, oral glucose ingestion per se reduces insulin clearance. [ABSTRACT FROM AUTHOR]

Objective: Tachyphylaxis for slowing of gastric emptying is seen with continuous exposure to glucagon-like peptide 1 (GLP-1). We therefore aimed to establish whether prolonged use of a "short-acting" GLP-1 receptor agonist, lixisenatide, achieves sustained slowing of gastric emptying and reduction in postprandial glycemia.Research Design and Methods: A total of 30 patients with metformin-treated type 2 diabetes underwent assessment of gastric emptying (scintigraphy) and glucose metabolism (dual tracer technique) after a 75-g glucose drink, before and after 8 weeks' treatment with lixisenatide (20 μg subcutaneously daily) or placebo, in a double-blind randomized parallel design.Results: Gastric retention of the glucose drink was markedly increased after lixisenatide versus placebo (ratio of adjusted geometric means for area under the curve [AUC] over 240 min of 2.19 [95% CI 1.82, 2.64], P < 0.001), associated with substantial reductions in the rate of systemic appearance of oral glucose (P < 0.001) and incremental AUC for blood glucose (P < 0.001). Lixisenatide suppressed both glucagon (P = 0.003) and insulin (P = 0.032), but not endogenous glucose production, over 120 min after oral glucose intake. Postprandial glucose lowering over 240 min was strongly related to the magnitude of slowing of gastric emptying by lixisenatide (r = -0.74, P = 0.002) and to the baseline rate of emptying (r = 0.52, P = 0.048) but unrelated to β-cell function (assessed by β-cell glucose sensitivity).Conclusions: Eight weeks' treatment with lixisenatide is associated with sustained slowing of gastric emptying and marked reductions in postprandial glycemia and appearance of ingested glucose. Short-acting GLP-1 receptor agonists therefore potentially represent an effective long-term therapy for specifically targeting postprandial glucose excursions. [ABSTRACT FROM AUTHOR]

The article offers information on the results of a study on β-cell function among severely obese patients with type 2 diabetes. It says that the intravenous glucose tolerance test was utilized to determine the impact of bariatric surgery on β-cell function in diabetic subjects. It mentions that the bariatric surgery can improve insulin sensitivity.

Increased proinsulin secretion, which characterizes type 2 diabetes and insulin resistance, may be due to an intrinsic, primitive defect in proinsulin processing or be secondary to increased demand on β-cells (hyperinsulinemia secondary to insulin resistance). An alternative way to investigate the relation between relative hyperproinsulinemia and increased secretory demand is to study the dynamic changes in the proinsulin-to-insulin ratio after partial pancreatectomy, a model of acute increased β-cell workload on the remaining pancreas. To pursue this aim, patients without diabetes, scheduled for partial pancreatectomy, underwent 4-h mixed-meal tests and hyperinsulinemic-euglycemic clamps before and after surgery. After acute β-cell mass reduction, no changes were observed in the fasting proinsulin-to-insulin ratio, whereas the fold change in the proinsulin-to-insulin ratio significantly increased over time after the meal. Further, our data demonstrate that whole-body insulin resistance is associated with underlying defects in proinsulin secretion, which become detectable only in the presence of increased insulin secretion demand. [ABSTRACT FROM AUTHOR]

In vivo studies have investigated the role of β-cell dysfunction in type 2 diabetes (T2D), whereas in vitro research on islets has elucidated key mechanisms that control the insulin secretion rate. However, the relevance of the cellular mechanisms identified in vitro (i.e., the triggering and amplifying pathways) has not been established in vivo. Furthermore, the mechanisms underpinning β-cell dysfunction in T2D remain undetermined. We propose a unifying explanation of several characteristic features of insulin secretion both in vitro and in vivo by using a mathematical model. The model describes the triggering and amplifying pathways and reproduces a variety of in vitro and in vivo tests in subjects with and without T2D, identifies the mechanisms modulating first-phase insulin secretion rate in response to basal hyperglycemia or insulin resistance, and shows that β-cell dysfunction in T2D can be explained by an impaired amplifying pathway with no need to postulate defects in intracellular calcium handling. [ABSTRACT FROM AUTHOR]

Bariatric surgery results in notable weight loss and alleviates hyperglycemia in patients with type 2 diabetes (T2D). We aimed to characterize the vascular effects of a mixed meal and infusion of exogenous glucose-dependent insulinotropic polypeptide (GIP) in the splanchnic region in 10 obese patients with T2D before and after bariatric surgery and in 10 lean control subjects. The experiments were carried out on two separate days. Pancreatic and intestinal blood flow (BF) were measured at baseline, 20 min, and 50 min with 15O-water by using positron emission tomography and MRI. Before surgery, pancreatic and intestinal BF responses to a mixed meal did not differ between obese and lean control subjects. Compared with presurgery, the mixed meal induced a greater increase in plasma glucose, insulin, and GIP concentrations after surgery, which was accompanied by a marked augmentation of pancreatic and intestinal BF responses. GIP infusion decreased pancreatic but increased small intestinal BF similarly in all groups both before and after surgery. Taken together, these results demonstrate that bariatric surgery leads to enhanced splanchnic vascular responses as a likely consequence of rapid glucose appearance and GIP hypersecretion. [ABSTRACT FROM AUTHOR]

Background: Insulin secretion correlates inversely with insulin sensitivity, which may suggest the existence of a crosstalk between peripheral organs and pancreas. Such interaction might be mediated through glucose oxidation that may drive the release of circulating factors with action on insulin secretion. Aim: To evaluate the association between whole-body carbohydrate oxidation and circulating factors with insulin secretion to consecutive oral glucose loading in non-diabetic individuals. Methods: Carbohydrate oxidation was measured after an overnight fast and for 6 hours after two 3-h apart 75-g oral glucose tolerance tests (OGTT) in 53 participants (24/29 males/females; 34±9 y; 27±4 kg/m2). Insulin secretion was estimated by deconvolution of serum C-peptide concentration, β cell function by mathematical modelling and insulin sensitivity from an OGTT. Circulating lactate, free-fatty acids (FFA) and candidate chemokines were assessed before and after OGTT. The effect of recombinant RANTES (regulated on activation, normal T cell expressed and secreted) and IL8 (interleukin 8) on insulin secretion from isolated mice islets was also measured. Results: Carbohydrate oxidation assessed over the 6-h period did not relate with insulin secretion (r = -0.11; p = 0.45) or β cell function indexes. Circulating lactate and FFA showed no association with 6-h insulin secretion. Circulating chemokines concentration increased upon oral glucose stimulation. Insulin secretion associated with plasma IL6 (r = 0.35; p<0.05), RANTES (r = 0.30; p<0.05) and IL8 (r = 0.41; p<0.05) determined at 60 min OGTT. IL8 was independently associated with in vivo insulin secretion; however, it did not affect in vitro insulin secretion. Conclusion: Whole-body carbohydrate oxidation appears to have no influence on insulin secretion or putative circulating mediators. IL8 may be a potential factor influencing insulin secretion. [ABSTRACT FROM AUTHOR]

Demonstrates an approach for estimating insulin secretion based on the measurement of plasma C-peptide. Equality of systematic appearance of c-peptide and pancreatic release of insulin; Evaluation of 24 hour profiles of insulin secretion.

OBJECTIVE -- Previons studies have found that high insulin sensitivity predicts weight gain; this association has not been confirmed. Our aim was to systematically analyze metabolic predictors of spontaneous weight changes. RESEARCH DESIGN AND METHODS -- In 561 women an 467 men from the Relationship Between Insulin Sensitivity and Cardiovascular Disease (RISC) cohort (mean age 44 years, BMI range 19-44 kg/m² 9% impaired glucose tolerance) followed up for 3 years, we measured insulin sensitivity (by a euglycemic clamp) and β-cell function (by modeling of the C-peptide response to oral glucose and by acute insulin response to intravenous glucose). RESULTS -- Insulin sensitivity was similar in weight gainers (top 20% of the distribution of BMI changes), weight losers (bottom 20%), and weight stable subjects across quartiles of baseline BMI. By multiple logistic or linear regression analyses controlling for center, age, sex, and baseline BMI, neither insulin sensitivity nor any β-cell function parameter showed an independent association with weight gain; this was true in normal glucose tolerance, impaired glucose tolerance, and whether subjects progressed to dysglycemia or not. Baseline BMI was significantly higher in gainers (26.1 ± 4.1 kg/m² and losers (26.6 ± 3.7 kg/m²) than in weight stable subjects (24.8 ± 3.8 kg/m² P < 0.0001 for both gainers and losers). Baseline waist circumference (or equivalently, BMI or weight) was a positive, independent predictor of both weight gain and weight loss (odds ratio 1.48 [95% CI 1.12-1.97]) in men and (1.67 [1.28-2.12]) in women. In men only, better insulin sensitivity was an additional independent predictor of weight loss. CONCLUSIONS -- Neither insulin sensitivity nor insulin secretion predicts spontaneous weight gain. Individuals who have attained a higher weight are prone to either gaining or losing weight regardless of their glucose tolerance. [ABSTRACT FROM AUTHOR]

OBJECTIVE--The pathophysiological mechanisms to explain the association between risk of type 2 diabetes and elevated concentrations of γ/-glutamyltransferase (GGT) and alanineaminotransferase (ALT) remain poorly characterized. We explored the association of liver enzymes with peripheral and hepatic insulin resistance, insulin secretion, insulin clearance, and glucagon concentration. RESEARCH DESIGN AND METHODS--We studied 1,309 nondiabetic individuals from the Relationship between Insulin Sensitivity and Cardiovascular disease (RISC) study; all had a euglycemic-hyperinsulinemic clamp and an oral glucose tolerance test (OGTT) with assessment of insulin secretion and hepatic insulin extraction. The hepatic insulin resistance index was calculated in 393 individuals. RESULTS--In both men and women, plasma concentrations of GGT and ALT were inversely related with insulin sensitivity (M/I) (all P < 0.01). Likewise, the hepatic insulin resistance index was positively correlated with both GGT (r = 0.37, P < 0.0001, men; r = 0.36, P < 0.0001, women) and ALT (r = 0.25, P = 0.0005, men; r = 0.18, P = 0.01, women). These associations persisted in multivariable models. Increased GGT and ALT were significantly associated with higher insulin secretion rates and with both reduced endogenous clearance of insulin and hepatic insulin extraction during the OGTT (P = 0.0005 in men; P = 0.003 in women). Plasma fasting glucagon levels increased over ALT quartiles (men, quartile 4 vs. quartile 1 11.2 ± 5.1 vs. 9.3 ± 3.8 pmol/L, respectively, P = 0.0002; women, 9.0 ± 4.3 vs. 7.6 ± 3.1, P = 0.001). CONCLUSIONS--In healthy individuals, increased GGT and ALT were biomarkers of both systemic and hepatic insulin resistance with concomitant increased insulin secretion and decreased hepatic insulin clearance. The novel finding of a positive correlation between ALT and fasting glucagon level concentrations warrants confirmation in type 2 diabetes. [ABSTRACT FROM AUTHOR]

OBJECTIVE--To study insulin sensitivity and perfusion in skeletal muscle together with the β-cell function in subjects with the m.3243A>G mutation in mitochondrial DNA, the most common cause of mitochondrial diabetes. RESEARCH DESIGN AND METHODS--We measured skeletal muscle glucose uptake and perfusion using positron emission tomography and 2-[[sup 18]F]fluoro-2-deoxyglucose and [[sup 15]O]H[sub 2]O during euglycemic hyperinsulinemia in 15 patients with m.3243A>G. These patients included five subjects with no diabetes as defined by the oral glucose tolerance test (OGTT) (group 1), three with GHb <6.1% and newly found diabetes by OGTT (group 2), and seven with a previously diagnosed diabetes (group 3). Control subjects consisted of 13 healthy individuals who were similar to the carriers of, m.3243A>G with respect to age and physical activity. β-Cell function was assessed using the OGTT and subsequent mathematical modeling. RESULTS--Skeletal muscle glucose uptake was significantly lower in groups 1, 2, and 3 than in the control subjects. The glucose sensitivity of β-cells in group 1 patients was similar to that of the control subjects, whereas in group 2 and 3 patients, the glucose sensitivity was significantly lower. The insulin secretion parameters correlated strongly with the proportion of m.3243A>G mutation in muscle. CONCLUSIONS---Our findings show that subjects with m.3243A >G are insulin resistant in skeletal muscle even when β-cell function is not markedly impaired or glucose control compromised. We suggest that both the skeletal muscle insulin sensitivity and the β-cell function are affected before the onset of the mitochondrial diabetes caused by the m.3243A>G mutation. Diabetes 58:543-549, 2009 [ABSTRACT FROM AUTHOR]

Thiazolidinediones (TZDs) improve glycemic control and insulin sensitivity in patients with type 2 diabetes mellitus (T2DM). There is growing evidence from in vivo and in vitro studies that TZDs improve pancreatic β-cell function. The aim of this study was to determine whether TZD-induced improvement in glycemic control is associated with improved β-cell function. We studied 11 normal glucose-tolerant and 53 T2DM subjects [age 53 ± 2 yr; BMI 29.4 ± 0.8 kg/m² fasting plasma glucose (FPG) 10.3 ± 0.4 mM; Hb A1c 8.2 ± 0.3%]. Diabetic patients were randomized to receive placebo or TZD for 4 mo. Subjects received 1) 2-h OGTT with determination of plasma glucose, insulin, and C-peptide concentrations and 2) two-step euglycemic insulin (40 and 160 mU·m-2min-1) clamp with [3-³H]glucose. T2DM patients were then randomized to receive 4 mo of treatment with pioglitazone (45 mg/day), rosiglitazone (8 mg/day), or placebo. Pioglitazone and rosiglitazone similarly improved FPG, mean plasma glucose during OGTT, Hb A1c, and insulin-mediated total body glucose disposal (Rd) and decreased mean plasma FFA during OGTT (all P < 0.01, ANOVA). The insulin secretion/insulin resistance (disposition) index [ΔSR(AUC)/Δglucose(AUC) ÷ IR] was significantly improved in all TZD-treated groups: + 1.8 ± 0.7 (PlO + drug-naive diabetics), +0.7 ± 0.3 (PlO + sulfonylurea-treated diabetics), and 0.7 ± 0.2 (ROSI + sulfonylurea-withdrawn diabetics) vs. -0.2 ± 0.3 in the two placebo groups (P < 0.01, all TZDs vs. placebo, ANOVA). Improved insulin secretion correlated positively with increased body weight, fat mass, and Rd and inversely with decreased plasma glucose and FFA during the OGTT In T2DM patients, TZD treatment leads to improved β-cell function, which correlates strongly with improved glycemic control. [ABSTRACT FROM AUTHOR]

We determined the effect of 48-h elevation of plasma free fatty acids (FFA) on insulin secretion during hyperglycemic clamps in control female Wistar rats (group a) and in the following female rat models of progressive β-cell dysfunction: lean Zucker diabetic fatty (ZDF) rats, both wild-type (group b) and heterozygous for the fa mutation in the leptin receptor gene (group c); obese (fa/fa) Zucker rats (nonprediabetic; group d); obese prediabetic (fa/fa) ZDF rats (group e); and obese (fa/fa) diabetic ZDF rats (group f). FFA induced insulin resistance in all groups but increased C-peptide levels (index of absolute insulin secretion) only in obese prediabetic ZDF rats. Insulin secretion corrected for insulin sensitivity using a hyperbolic or power relationship (disposition index or compensation index, respectively, both indexes of β-cell function) was decreased by FFA. The decrease was greater in normoglycemic heterozygous lean ZDF rats than in Wistar controls. In obese "prediabetic" ZDF rats with mild hyperglycemia, the FFA-induced decrease in 3-cell function was no greater than that in obese Zucker rats. However, in overtly diabetic obese ZDF rats, FFA further impaired β-cell function. In conclusion, 1) the FFA-induced impairment in β-cell function is accentuated in the presence of a single copy of a mutated leptin receptor gene, independent of hyperglycemia. 2) In prediabetic ZDF rats with mild hyperglycemia, lipotoxicity is not accentuated, as the β-cell mounts a partial compensatory response for FFA-induced insulin resistance. 3) This compensation is lost in diabetic rats with more marked hyperglycemia and loss of glucose sensing. [ABSTRACT FROM AUTHOR]

Currently, there are no data in the literature regarding the pathophysiological mechanisms involved in the rapid resolution of type 2 diabetes after bariatric surgery, which was reported as an additional benefit of the surgical treatment for morbid obesity. With this question in mind, insulin sensitivity, using euglycemic-hyperinsulinemic clamp, and insulin secretion, by the C-peptide deconvolution method after an oral glucose load, together with the circulating levels of intestinal incretins and adipocytokines, have been studied in 10 diabetic morbidly obese subjects before and shortly after biliopancreatic diversion (BPD) to avoid the weight loss interference. Diabetes disappeared 1 week after BPD, while insulin sensitivity (32.96 ± 4.3 to 65.73 ± 3.22 µmol ⋅ kg fat-free mass-1 ⋅ min-1 at 1 week and to 64.73 ± 3.42 µmol ⋅ kg fat-free mass-1 ⋅ min-1 at 4 weeks; P < 0.0001) was fully normalized. Fasting insulin secretion rate (148.16 ± 20.07 to 70.0.2 ± 8.14 and 83.24 ± 8.28 pmol/min per m²; P < 0.01) and total insulin output (43.76 ± 4.07 to 25.48 ± 1.69 and 30.50 ± 4.71 nmol/m²; P < 0.05) dramatically decreased, while a significant improvement in β-cell glucose sensitivity was observed. Both fasting and glucose-stimulated gastrointestinal polypeptide (13.40 ± 1.99 to 6.58 ± 1.72 pmol/l at 1 week and 5.83 ± 0.80 pmol/l at 4 weeks) significantly (P < 0.001) decreased, while glucagon-like peptide 1 significantly increased (1.75 ± 0.16 to 3.42 ± 0.41 pmol/l at 1 week and 3.62 ± 0.21 pmol/l at 4 weeks; P < 0.001). BPD determines a prompt reversibility of type 2 diabetes by normalizing peripheral insulin sensitivity and enhancing β-cell sensitivity to glucose, these changes occurring very early after the operation. This operation may affect the enteroinsular axis function by diverting nutrients away from the proximal gastrointestinal tract and by delivering incompletely digested nutrients to the ileum. Diabetes 55:2025-2031, 2006 [ABSTRACT FROM AUTHOR]

In nondiabetic subjects, obesity is associated with a modest expansion of β-cell mass, possibly amounting--according to the best available estimates--to 10-30% for each 10 kg of weight excess. Whether age of onset and duration of obesity, recent changes in body weight, and body fat distribution have any effect on β-cell mass in humans is unknown. Both fasting insulin secretion and the total insulin response to oral glucose have the following characteristics: 1) they increase with BMI in an approximately linear fashion, 2) both fat-free and fat mass are significant positive correlates, and 3) BMI exerts a positive effect separate from that of insulin resistance (i.e., obesity may be a state of primary insulin hypersecretion). The mechanisms are currently unknown, though chronic small increments in plasma glucose may play a role. In contrast, dynamic properties of β-cell function, such as glucose sensitivity (i.e., dose-response function), rate sensitivity, and potentiation, do not appear to be substantially altered by the presence of obesity, body fat distribution, or insulin resistance as long as glucose tolerance is maintained. Weight loss, by diet or restrictive bariatric surgery, is associated with consensual decrements in insulin resistance and insulin hypersecretion. The latter, however, seems to be more persistent, suggesting that the postobese state may reproduce the primary insulin hypersecretion of the obese state. Malabsorptive bariatric surgery, in contrast, normalizes insulin sensitivity and abolishes insulin hypersecretion even before achievement of ideal body weight. Lipid-triggered messages from the gastrointestinal tract to the insulin target tissues and endocrine pancreas are the subject of intense investigation. Diabetes 53 (Suppl. 3):S26-S33, 2004 [ABSTRACT FROM AUTHOR]

Gestational diabetes (GDM) carries a high risk of incident diabetes. We asked the question, whether prior GDM has any impact on B-cell function and insulin action in women who have normal glucose tolerance (NGT). Ninety-one NGT women (age 41±8 years, mean±SD) were studied (by mathematical modelling of a frequently-sampled OGTT) 7 [6] years (median [interquartile range]) after the index pregnancy, during which 52 of them were GDM. Fasting (4.64±0.56 vs 4.97±0.46 mM) and 2-h plasma glucose (5.91±1.14 vs 5.914-1.21 mM) were similar in prior-GDM (age 41 ± 5 y, BMI 25.4±3.9 kg/m²) and non-prior-GDM women (age 41 ± 5 y, BMI 26.8±6.4 kg/m²). However, β-cell glucose sensitivity (slope of the insulin-secretion/plasma glucose dose-response function) (95 [71] vs 115 [79] pmol⋅min[sup -1] ⋅m[sup -2]⋅mM[sup -1], p=0.025 [Mann Whitney]) and insulin sensitivity (398 [77] vs 424 [98] ml⋅min[sup -1]⋅m[sup -2], p=0.025) were both reduced in prior-GDM women. At the time of the index pregnancy, GDM and non-GDM had similar age and BMI; however, insulin sensitivity was significantly lower (359 [93] vs 417 [92] ml⋅min[sup -1]⋅ m[sup -2], p=0.001) and the ratio of incremental insulin area/incremental glucose area (as an empirical index of β-cell function) was reduced (18 [13] vs 27 [26] µU/mmol, p=0.02) in GDM vs non-GDM women. Both at the index pregnancy and follow up, β-cell function and insulin sensitivity were idependent determinants of mean OGTT glucose levels (r²'s of 0.40 and 0.22, p<0.0001 for both) independently of age and BMI. We conclude that the impairment in B-cell function and insulin sensitivity that characterise GDM are carried over into the NGT status even years after a GDM pregnancy. [ABSTRACT FROM AUTHOR]