Importance of early phase insulin secretion to intravenous glucose tolerance in subjects with type 2 diabetes mellitus

Rationale, Design and Participants Baseline Characteristics of a Crossover Randomized Controlled Trial of the Effect of Replacing SSBs with NSBs versus Water on Glucose Tolerance, Gut Microbiome and Cardiometabolic Risk in Overweight or Obese Adult SSB Consumer: Strategies to Oppose SUGARS with Non-Nutritive Sweeteners or Water (STOP Sugars NOW) Trial and Ectopic Fat Sub-Study

BACKGROUND

Health authorities are near universal in their recommendation to replace sugar-sweetened beverages (SSBs) with water. Non-nutritive sweetened beverages (NSBs) are not as widely recommended as a replacement strategy due to a lack of established benefits and concerns they may induce glucose intolerance through changes in the gut microbiome. The STOP Sugars NOW trial aims to assess the effect of the substitution of NSBs (the "intended substitution") versus water (the "standard of care substitution") for SSBs on glucose tolerance and microbiota diversity.

DESIGN AND METHODS

The STOP Sugars NOW trial (NCT03543644) is a pragmatic, "head-to-head", open-label, crossover, randomized controlled trial conducted in an outpatient setting. Participants were overweight or obese adults with a high waist circumference who regularly consumed ≥1 SSBs daily. Each participant completed three 4-week treatment phases (usual SSBs, matched NSBs, or water) in random order, which were separated by ≥4-week washout. Blocked randomization was performed centrally by computer with allocation concealment. Outcome assessment was blinded; however, blinding of participants and trial personnel was not possible. The two primary outcomes are oral glucose tolerance (incremental area under the curve) and gut microbiota beta-diversity (weighted UniFrac distance). Secondary outcomes include related markers of adiposity and glucose and insulin regulation. Adherence was assessed by objective biomarkers of added sugars and non-nutritive sweeteners and self-report intake. A subset of participants was included in an Ectopic Fat sub-study in which the primary outcome is intrahepatocellular lipid (IHCL) by 1H-MRS. Analyses will be according to the intention to treat principle.

BASELINE RESULTS

Recruitment began on 1 June 2018, and the last participant completed the trial on 15 October 2020. We screened 1086 participants, of whom 80 were enrolled and randomized in the main trial and 32 of these were enrolled and randomized in the Ectopic Fat sub-study. The participants were predominantly middle-aged (mean age 41.8 ± SD 13.0 y) and had obesity (BMI of 33.7 ± 6.8 kg/m2) with a near equal ratio of female: male (51%:49%). The average baseline SSB intake was 1.9 servings/day. SSBs were replaced with matched NSB brands, sweetened with either a blend of aspartame and acesulfame-potassium (95%) or sucralose (5%).

CONCLUSIONS

Baseline characteristics for both the main and Ectopic Fat sub-study meet our inclusion criteria and represent a group with overweight or obesity, with characteristics putting them at risk for type 2 diabetes. Findings will be published in peer-reviewed open-access medical journals and provide high-level evidence to inform clinical practice guidelines and public health policy for the use NSBs in sugars reduction strategies.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT03543644.

Post-Load Insulin Secretion Patterns are Associated with Glycemic Status and Diabetic Complications in Patients with Type 2 Diabetes Mellitus

BACKGROUND

To examine whether the different patterns of post-load insulin secretion can identify the heterogeneity of type 2 diabetes mellitus (T2DM).

METHODS

Six hundred twenty-five inpatients with T2DM at Jining No. 1 People's Hospital were recruited from January 2019 to October 2021. The 140 g steamed bread meal test (SBMT) was conducted on patients with T2DM, and glucose, insulin, and C-peptide levels were recorded at 0, 60, 120, and 180 min. To avoid the effect of exogenous insulin, patients were categorized into three different classes by latent class trajectory analysis based on the post-load secretion patterns of C-peptide. The difference in short- and long-term glycemic status and prevalence of complications distributed among the three classes were compared by multiple linear regression and multiple logistic regression, respectively.

RESULTS

There were significant differences in long-term glycemic status (e. g., HbA1c) and short-term glycemic status (e. g., mean blood glucose, time in range) among the three classes. The difference in short-term glycemic status was similar in terms of the whole day, daytime, and nighttime. The prevalence of severe diabetic retinopathy and atherosclerosis showed a decreasing trend among the three classes.

CONCLUSIONS

The post-load insulin secretion patterns could well identify the heterogeneity of patients with T2DM in short- and long-term glycemic status and prevalence of complications, providing recommendations for the timely adjustment in treatment regimes of patients with T2DM and promotion of personalized treatment.

Dorzagliatin in drug-naïve patients with type 2 diabetes: a randomized, double-blind, placebo-controlled phase 3 trial

Improving glucose sensitivity remains an unmet medical need in treating type 2 diabetes (T2D). Dorzagliatin is a dual-acting, orally bioavailable glucokinase activator that enhances glucokinase activity in a glucose-dependent manner, improves glucose-stimulated insulin secretion and demonstrates effects on glycemic control in patients with T2D. We report the findings of a randomized, double-blind, placebo-controlled phase 3 clinical trial to evaluate the efficacy and safety of dorzagliatin in patients with T2D. Eligible drug-naïve patients with T2D (n = 463) were randomly assigned to the dorzagliatin or placebo group at a ratio of 2:1 for 24 weeks of double-blind treatment, followed by 28 weeks of open-label treatment with dorzagliatin for all patients. The primary efficacy endpoint was the change in glycated hemoglobin from baseline to week 24. Safety was assessed throughout the trial. At week 24, the least-squares mean change in glycated hemoglobin from baseline (95% confidence interval) was -1.07% (-1.19%, -0.95%) in the dorzagliatin group and -0.50% (-0.68%, -0.32%) in the placebo group (estimated treatment difference, -0.57%; 95% confidence interval: -0.79%, -0.36%; P < 0.001). The incidence of adverse events was similar between the two groups. There were no severe hypoglycemia events or drug-related serious adverse events in the dorzagliatin group. In summary, dorzagliatin improved glycemic control in drug-naïve patients with T2D and showed a good tolerability and safety profile.

Physiologic Insulin Resensitization as a Treatment Modality for Insulin Resistance Pathophysiology

Prevalence of type 2 diabetes increased from 2.5% of the US population in 1990 to 10.5% in 2018. This creates a major public health problem, due to increases in long-term complications of diabetes, including neuropathy, retinopathy, nephropathy, skin ulcers, amputations, and atherosclerotic cardiovascular disease. In this review, we evaluated the scientific basis that supports the use of physiologic insulin resensitization. Insulin resistance is the primary cause of type 2 diabetes. Insulin resistance leads to increasing insulin secretion, leading to beta-cell exhaustion or burnout. This triggers a cascade leading to islet cell destruction and the long-term complications of type 2 diabetes. Concurrent with insulin resistance, the regular bursts of insulin from the pancreas become irregular. This has been treated by the precise administration of insulin more physiologically. There is consistent evidence that this treatment modality can reverse the diabetes-associated complications of neuropathy, diabetic ulcers, nephropathy, and retinopathy, and that it lowers HbA1c. In conclusion, physiologic insulin resensitization has a persuasive scientific basis, significant treatment potential, and likely cost benefits.

Goji Berry (Lycium barbarum) Supplementation during Pregnancy Influences Insulin Sensitivity in Rabbit Does but Not in Their Offspring

This study investigated the effects of Goji berry (Lycium barbarum) dietary supplementation during pregnancy on insulin sensitivity of rabbit does and their offspring. Starting from two months before the artificial insemination, 75 New Zealand White does were fed only commercial standard diet (C) or supplemented with 1% (G1) and 3% (G3) of Goji berries. Their offspring received a standard diet but kept the nomenclature of the mother’s group. Fasting and intravenous glucose tolerance test-derived indices were estimated at 21 days of pregnancy on rabbit does and at 90 days of age on the offspring. No difference was found in the fasting indices, while the diet modulated the response to glucose load of rabbit does. In particular, G3 group had the lowest glucose concentrations 5 min after the bolus administration (p < 0.05) and, as a result, differed in the parameters calculated during the elimination phase such as the elimination rate constant (Kel), the half-life of the exogenous glucose load (t1/2), and apparent volume of distribution (Vd; for all, p < 0.05). The high dose of Goji supplementation could thus enhance the first-phase glucose-induced insulin secretion. Findings on the offspring were inconsistent and therefore a long-term effect of Goji supplementation during pregnancy could not be demonstrated. Further study on the effect of Goji on the secretory pathway of insulin could clarify its hypoglycaemic action, while different protocols are needed to investigate its potential effects on foetal programming.

Saliva 1,5-anhydroglucitol is associated with early-phase insulin secretion in Chinese patients with type 2 diabetes

INTRODUCTION

Saliva collection is a non-invasive test and is convenient. 1,5-anhydroglucitol (1,5-AG) is a new indicator reflecting short-term blood glucose levels. This study aimed to explore the relationship between saliva 1,5-AG and insulin secretion function and insulin sensitivity.

RESEARCH DESIGN AND METHODS

Adult patients with type 2 diabetes who were hospitalized were enrolled. Based on blood glucose and C-peptide, homeostasis model assessment 2 for β cell secretion function, C-peptidogenic index (CGI), △2-hour C-peptide (2hCP)/△2-hour postprandial glucose (2hPG), ratio of 0-30 min area under the curve for C-peptide and area under the curve for glucose (AUC_CP30/AUC_PG30), and AUC_2hCP/AUC_2hPG were calculated to evaluate insulin secretion function, while indicators such as homeostasis model assessment 2 for insulin resistance were used to assess insulin sensitivity.

RESULTS

We included 284 subjects (178 men and 106 women) with type 2 diabetes aged 20-70 years. The saliva 1,5-AG level was 0.133 (0.089-0.204) µg/mL. Spearman's correlation analysis revealed a significantly negative correlation between saliva 1,5-AG and 0, 30, and 120 min blood glucose, glycated hemoglobin A_1c, and glycated albumin (all p<0.05), and a significantly positive association between saliva 1,5-AG and CGI (r=0.171, p=0.004) and AUC _CP30 /AUC _PG30 (r=0.174, p=0.003). The above correlations still existed after adjusting for age, sex, body mass index, and diabetes duration. In multiple linear regression, saliva 1,5-AG was an independent factor of CGI (standardized β=0.135, p=0.015) and AUC _CP30 /AUC _PG30 (standardized β=0.110, p=0.020).

CONCLUSIONS

Saliva 1,5-AG was related to CGI and AUC_CP30/AUC_PG30 in patients with type 2 diabetes.

TRIAL REGISTRATION NUMBER

ChiCTR-SOC-17011356.

Electrogenetic cellular insulin release for real-time glycemic control in type 1 diabetic mice

Sophisticated devices for remote-controlled medical interventions require an electrogenetic interface that uses digital electronic input to directly program cellular behavior. We present a cofactor-free bioelectronic interface that directly links wireless-powered electrical stimulation of human cells to either synthetic promoter–driven transgene expression or rapid secretion of constitutively expressed protein therapeutics from vesicular stores. Electrogenetic control was achieved by coupling ectopic expression of the L-type voltage-gated channel CaV1.2 and the inwardly rectifying potassium channel Kir2.1 to the desired output through endogenous calcium signaling. Focusing on type 1 diabetes, we engineered electrosensitive human β cells (Electroβ cells). Wireless electrical stimulation of Electroβ cells inside a custom-built bioelectronic device provided real-time control of vesicular insulin release; insulin levels peaked within 10 minutes. When subcutaneously implanted, this electrotriggered vesicular release system restored normoglycemia in type 1 diabetic mice.

AAV8-mediated gene transfer of microRNA-132 improves beta cell function in mice fed a high-fat diet

MicroRNAs have emerged as essential regulators of beta cell function and beta cell proliferation. One of these microRNAs, miR-132, is highly induced in several obesity models and increased expression of miR-132 in vitro modulates glucose-stimulated insulin secretion. The aim of this study was to investigate the therapeutic benefits of miR-132 overexpression on beta cell function in vivo. To overexpress miR-132 specifically in beta cells, we employed adeno-associated virus (AAV8)-mediated gene transfer using the rat insulin promoter in a double-stranded, self-complementary AAV vector to overexpress miR-132. Treatment of mice with dsAAV8-RIP-mir132 increased miR-132 expression in beta cells without impacting expression of miR-212 or miR-375. Surprisingly, overexpression of miR-132 did not impact glucose homeostasis in chow-fed animals. Overexpression of miR-132 did improve insulin secretion and hence glucose homeostasis in high-fat diet-fed mice. Furthermore, miR-132 overexpression increased beta cell proliferation in mice fed a high-fat diet. In conclusion, our data show that AAV8-mediated gene transfer of miR-132 to beta cells improves beta cell function in mice in response to a high-fat diet. This suggests that increased miR-132 expression is beneficial for beta cell function during hyperglycemia and obesity.

Biogenesis of the Insulin Secretory Granule in Health and Disease

The secretory granules of pancreatic beta cells are specialized organelles responsible for the packaging, storage and secretion of the vital hormone insulin. The insulin secretory granules also contain more than 100 other proteins including the proteases involved in proinsulin-to insulin conversion, other precursor proteins, minor co-secreted peptides, membrane proteins involved in cell trafficking and ion translocation proteins essential for regulation of the intragranular environment. The synthesis, transport and packaging of these proteins into nascent granules must be carried out in a co-ordinated manner to ensure correct functioning of the granule. The process is regulated by many circulating nutrients such as glucose and can change under different physiological states. This chapter discusses the various processes involved in insulin granule biogenesis with a focus on the granule composition in health and disease.

24-h severe energy restriction impairs postprandial glycaemic control in young, lean males

Intermittent energy restriction (IER) involves short periods of severe energy restriction interspersed with periods of adequate energy intake, and can induce weight loss. Insulin sensitivity is impaired by short-term, complete energy restriction, but the effects of IER are not well known. In randomised order, fourteen lean men (age: 25 (sd 4) years; BMI: 24 (sd 2) kg/m2; body fat: 17 (4) %) consumed 24-h diets providing 100 % (10 441 (sd 812) kJ; energy balance (EB)) or 25 % (2622 (sd 204) kJ; energy restriction (ER)) of estimated energy requirements, followed by an oral glucose tolerance test (OGTT; 75 g of glucose drink) after fasting overnight. Plasma/serum glucose, insulin, NEFA, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) and fibroblast growth factor 21 (FGF21) were assessed before and after (0 h) each 24-h dietary intervention, and throughout the 2-h OGTT. Homoeostatic model assessment of insulin resistance (HOMA2-IR) assessed the fasted response and incremental AUC (iAUC) or total AUC (tAUC) were calculated during the OGTT. At 0 h, HOMA2-IR was 23 % lower after ER compared with EB (P<0·05). During the OGTT, serum glucose iAUC (P<0·001), serum insulin iAUC (P<0·05) and plasma NEFA tAUC (P<0·01) were greater during ER, but GLP-1 (P=0·161), GIP (P=0·473) and FGF21 (P=0·497) tAUC were similar between trials. These results demonstrate that severe energy restriction acutely impairs postprandial glycaemic control in lean men, despite reducing HOMA2-IR. Chronic intervention studies are required to elucidate the long-term effects of IER on indices of insulin sensitivity, particularly in the absence of weight loss.

Delay in glucose peak time during the oral glucose tolerance test as an indicator of insulin resistance and insulin secretion in type 2 diabetes patients

Aims/Introduction

Previous studies have shown that glucose peak time during the oral glucose tolerance test varies in type 2 diabetes patients; however, characteristics of this heterogeneity remain unclear. This research aimed to investigate the characteristics of delayed glucose peak time in type 2 diabetes.

Materials and Methods

A total of 178 participants who underwent the oral glucose tolerance test were divided into five groups according to glucose peak time.

Results

A total of 25 participants with normal glucose tolerance had a glucose peak at 30 min. Among participants with type 2 diabetes, 28 had a glucose peak at 60 min, 48 at 90 min, 45 at 120 min and 32 at 150 min. With the glucose peak time delayed, glycated hemoglobin, area under the glucose curve and homeostatic model assessment of insulin resistance increased gradually (P = 0.038, P < 0.0001, P < 0.0001, respectively), and oral glucose insulin sensitivity, homeostatic model assessment of β‐cell function, insulinogenic index, modified β‐cell function index and disposition indices decreased (P < 0.0001 for all). On multinominal logistic regression, insulinogenic index (odds ratio 0.73, 95% confidence interval 0.57–0.93, P = 0.01), modified β‐cell function index (odds ratio 0.67, 95% confidence interval 0.47–0.94, P = 0.023) and oral glucose insulin sensitivity (odds ratio 0.91, 95% confidence interval 0.87–0.96, P < 0.0001) were independently correlated with delayed glucose peak time.

Conclusions

Delay in glucose peak time indicated an increase in blood glucose and a decrease in insulin sensitivity and secretion. Furthermore, insulinogenic index, modified β‐cell function index and oral glucose insulin sensitivity contributed to delayed glucose peak time.

The association between elevated serum uric acid levels and islet β-cell function indexes in newly diagnosed type 2 diabetes mellitus: a cross-sectional study

Background

Serum uric acid (UA) has been reported as a risk factor for type 2 diabetes mellitus (T2DM). However, whether serum UA is associated with insulin resistance and insulin secretion, and the effect of gender on it in the case of the existed association, both remain undefined.

Methods

A cross-sectional study was designed and performed, which enrolled a total of 403 newly diagnosed T2DM patients (mean age, 50.21 ± 13.34 years (62.5% males)). Clinical characteristics and islet function indexes of all participants were analyzed based on gender-specific tertiles of serum UA levels. In addition, multiple linear regression analysis was conducted to investigate covariates associated with islet function indexes.

Results

The mean levels of serum UA were 331.05 μmol/L (interquartile range (IQR): 60.6, 400.9 μmol/L) and 267.9 μmol/L (IQR: 204.7, 331.9 μmol/L) in men and women, respectively. The values of insulin secretion indexes involving AUCins30/glu30, AUCins120/glu120 and total insulin disposition index (DI120) in females were significantly higher than those in males. Apart from the homeostasis model assessment insulin resistance of men, serum UA was positively associated with insulin secretion and insulin resistance indexes both in men and women. Multivariable linear regression analysis showed serum UA exerted an independent impact on insulin secretion in females, but not on insulin resistance. In males, islet function was simultaneously affected by serum UA age, body mass index (BMI), and serum lipids.

Conclusion

Serum UA harbored a positive correlation with insulin secretion and insulin resistance indexes in newly diagnosed T2DM patients, which was influenced by gender, BMI, serum lipids. Hence, serum UA may be considered as a predictor for islet function in clinical practice.

Clinical Pharmacokinetics and Pharmacodynamics of Antihyperglycemic Medications in Children and Adolescents with Type 2 Diabetes Mellitus

The incidence of type 2 diabetes mellitus (T2DM) among children and adolescents has been rising. This condition is associated with obesity, and it's prevalence is higher among minority or female youth. Lifestyle modification including diet and exercise is only successful in a small proportion of patients; therefore, pharmacotherapy approaches are needed to treat T2DM among youth. Currently, in the USA, only metformin and insulin are approved for the treatment of T2DM in children. However, several antihyperglycemic agents including exenatide, glimepiride, glyburide, liraglutide, pioglitazone, and rosiglitazone are also used off-label in this population. Moreover, a number of clinical trials are ongoing that are aimed at addressing the safety and efficacy of newer antihyperglycemic agents in this population. Little is known about the safety, efficacy, or pharmacokinetics of antihyperglycemic agents in children or adolescents. Our ability to predict the pharmacokinetics of these agents in youth is hampered first by the lack of information about the expression and activity of drug-metabolizing enzymes and transporters in this population and second by the presence of comorbid conditions such as obesity and fatty liver disease. This article reviews the prevalence of obesity and T2DM in children and adolescents (youth). We then summarize published studies on safety and effectiveness of antihyperglycemic medications in youth. Drug disposition may be affected by age or puberty and thus the expression and activity of different pathways for drug metabolism and xenobiotic transporters are compared between youth and adults followed by a summary of pharmacokinetics studies of antihyperglycemic agents currently used in this population.

The Assessment of the Serum C-Peptide and Plasma Glucose Levels by Orally Administered Whey Proteins in Type 2 Diabetes Mellitus

A personalized antidiabetic therapy is not yet part of the official guidelines of professional societies for clinical practice. The aim of this study was to evaluate the serum C-peptide and plasma glucose levels in patients with type 2 diabetes mellitus (T2DM) after oral administration of whey proteins. Sixteen overweight T2DM Caucasians with good glycemic control and with preserved fasting serum C-peptide levels (>200 nmol/l) were enrolled in this study. Two oral stimulation tests – one with 75 g of glucose (OGTT) and the other with 75 g of whey proteins (OWIST) – were administered for assessing serum C-peptide and plasma glucose levels in each participant. Both oral tests induced similar pattern of C-peptide secretion, with a peak at 90 min. The serum C-peptide peak concentration was 2.91±0.27 nmol/l in OWIST, which was 22 % lower than in OGTT. Similarly, the C-peptide iAUC0-180 were 32 % lower in the OWIST than in the OGTT (p<0.01). Contrary to OGTT the OWIST did not cause a significant increase of glycemia (p<0.01). Our study showed that the OWIST represents a useful tool in estimation of stimulated serum C-peptide levels in patients with T2DM.

A 4D view on insulin secretory granule turnover in the β-cell

Insulin secretory granule (SG) turnover consists of several highly regulated processes allowing for proper β-cell function and insulin secretion. Besides the spatial distribution of insulin SGs, their age has great impact on the likelihood of their secretion and their behaviour within the β-cell. While quantitative measurements performed decades ago demonstrated the preferential secretion of young insulin, new experimental approaches aim to investigate insulin ageing at the granular level. Live-cell imaging, automated image analysis and correlative light and electron microscopy have fostered knowledge of age-defined insulin SG dynamics, their interaction with the cytoskeleton and ultrastructural features. Here, we review our recent work in regards to the connection between insulin SG age, SG dynamics, intracellular location and interaction with other proteins.

Metabolism disrupting chemicals and metabolic disorders

The recent epidemics of metabolic diseases, obesity, type 2 diabetes(T2D), liver lipid disorders and metabolic syndrome have largely been attributed to genetic background and changes in diet, exercise and aging. However, there is now considerable evidence that other environmental factors may contribute to the rapid increase in the incidence of these metabolic diseases. This review will examine changes to the incidence of obesity, T2D and non-alcoholic fatty liver disease (NAFLD), the contribution of genetics to these disorders and describe the role of the endocrine system in these metabolic disorders. It will then specifically focus on the role of endocrine disrupting chemicals (EDCs) in the etiology of obesity, T2D and NAFLD while finally integrating the information on EDCs on multiple metabolic disorders that could lead to metabolic syndrome. We will specifically examine evidence linking EDC exposures during critical periods of development with metabolic diseases that manifest later in life and across generations.

Serum Uric Acid and Impaired Glucose Tolerance: The Cardiometabolic Risk in Chinese (CRC) Study

Serum uric acid (SUA) elevation has been previously related to impaired fasting glucose and type 2 diabetes. The present study was comprehensive to examine the associations between SUA and impaired glucose tolerance (IGT) in Chinese adults. For this purpose, data were collected from a community-based health examination survey conducted in Central China; 2-h glucose (OGTT) and SUA were measured in 1956 men and women. In multivariate models, SUA levels were significantly associated with an increasing trend of 2-h glucose (OGTT) (P for trend < 0.0001). The odds ratios (OR; 95 % CI) of IGT across increasing quartiles of SUA were 1.0, 1.354 (0.948-2.087), 1.337 (0.959-2.251), and 2.192 (1.407-3.416), after adjusting for age, sex, body mass index, waist circumference, fasting insulin, blood pressure, serum lipids, serum creatinine, and estimated glomerular filtration rate. (P for trend = 0.001). In addition, we found an additive pattern between SUA and triglyceride (TG; P = 0.038) or between SUA and low-density lipoprotein cholesterol (LDL-C; P = 0.041) in relation to IGT. SUA was related to IGT in the Chinese adults, independent of other conventional metabolic risk factors. TG and LDL-C might modify the associations.

Effect of nateglinide and glimepiride in reducing postprandial hyperglycaemia in patients with type 2 diabetes mellitus

Aim — The purpose of this study was to compare the effect of nateglinide on two-hour post-meal glucose levels with that of glimepiride in patients with type 2 diabetes mellitus. Methods — Glucose and insulin levels were measured during 14-hour profiles (comprising three meal challenges) and intravenous glucose tolerance tests performed before and after five-weeks of treatment with nateglinide (120 mg, a.c.) or glimepiride (1 mg, o.d.) in a randomised, two-centre, double-blind, crossover study in 26 patients with type 2 diabetes and fasting initial glucose levels < 13.9 mmol/L. Results — Mean two-hour postprandial glucose levels were significantly lower during nateglinide treatment than during glimepiride treatment (9.46 vs. 10.00 mmol/L, respectively; p<0.05). The 14-hour incremental glucose area under the curve was -2.2 mmol•h/L during nateglinide treatment and +6.2 mmol•h/L during glimepiride treatment (p<0.01). Nateglinide improved both the early insulin response during meals and the acute insulin response during intravenous glucose tolerance tests, restoring the biphasic insulin secretion pattern. Both insulin secretagogues improved intravenous glucose tolerance relative to the pre-treatment period, but only nateglinide restored a biphasic insulin profile. Conclusions — By restoring a more physiological post-load insulin response, nateglinide is more effective than glimepiride in controlling postprandial glucose excursions.

Synaptotagmin-7 phosphorylation mediates GLP-1-dependent potentiation of insulin secretion from β-cells

Glucose stimulates insulin secretion from β-cells by increasing intracellular Ca(2+). Ca(2+) then binds to synaptotagmin-7 as a major Ca(2+) sensor for exocytosis, triggering secretory granule fusion and insulin secretion. In type-2 diabetes, insulin secretion is impaired; this impairment is ameliorated by glucagon-like peptide-1 (GLP-1) or by GLP-1 receptor agonists, which improve glucose homeostasis. However, the mechanism by which GLP-1 receptor agonists boost insulin secretion remains unclear. Here, we report that GLP-1 stimulates protein kinase A (PKA)-dependent phosphorylation of synaptotagmin-7 at serine-103, which enhances glucose- and Ca(2+)-stimulated insulin secretion and accounts for the improvement of glucose homeostasis by GLP-1. A phospho-mimetic synaptotagmin-7 mutant enhances Ca(2+)-triggered exocytosis, whereas a phospho-inactive synaptotagmin-7 mutant disrupts GLP-1 potentiation of insulin secretion. Our findings thus suggest that synaptotagmin-7 is directly activated by GLP-1 signaling and may serve as a drug target for boosting insulin secretion. Moreover, our data reveal, to our knowledge, the first physiological modulation of Ca(2+)-triggered exocytosis by direct phosphorylation of a synaptotagmin.

PKA Enhances the Acute Insulin Response Leading to the Restoration of Glucose Control

Diabetes arises from insufficient insulin secretion and failure of the β-cell mass to persist and expand. These deficits can be treated with ligands to Gs-coupled G-protein-coupled receptors that raise β-cell cAMP. Here we studied the therapeutic potential of β-cell cAMP-dependent protein kinase (PKA) activity in restoring glucose control using β-caPKA mice. PKA activity enhanced the acute insulin response (AIR) to glucose, which is a primary determinant of the efficacy of glucose clearance. Enhanced AIR improved peripheral insulin action, leading to more rapid muscle glucose uptake. In the setting of pre-established glucose intolerance caused by diet-induced insulin resistance or streptozotocin-mediated β-cell mass depletion, PKA activation enhanced β-cell secretory function to restore glucose control, primarily through augmentation of the AIR. Enhanced AIR and improved glucose control were maintained through 16 weeks of a high-fat diet and aging to 1 year. Importantly, improved glucose tolerance did not increase the risk for hypoglycemia, nor did it rely upon hyperinsulinemia or β-cell hyperplasia, although PKA activity was protective for β-cell mass. These data highlight that improving β-cell function through the activation of PKA has a large and underappreciated capacity to restore glucose control with minimal risk for adverse side effects.

Aged insulin granules display reduced microtubule-dependent mobility and are disposed within actin-positive multigranular bodies

Insulin secretion is key for glucose homeostasis. Insulin secretory granules (SGs) exist in different functional pools, with young SGs being more mobile and preferentially secreted. However, the principles governing the mobility of age-distinct SGs remain undefined. Using the time-reporter insulin-SNAP to track age-distinct SGs we now show that their dynamics can be classified into three components: highly dynamic, restricted, and nearly immobile. Young SGs display all three components, whereas old SGs are either restricted or nearly immobile. Both glucose stimulation and F-actin depolymerization recruit a fraction of nearly immobile young, but not old, SGs for highly dynamic, microtubule-dependent transport. Moreover, F-actin marks multigranular bodies/lysosomes containing aged SGs. These data demonstrate that SGs lose their responsiveness to glucose stimulation and competence for microtubule-mediated transport over time while changing their relationship with F-actin.

Higher Risk of Hypoglycemia with Glimepiride Versus Vildagliptin in Patients with Type 2 Diabetes is not Driven by High Doses of Glimepiride: Divergent Patient Susceptibilities?

INTRODUCTION

In a previously published study, vildagliptin showed a reduced risk of hypoglycemia versus glimepiride as add-on therapy to metformin at similar efficacy. Glimepiride was titrated from a starting dose of 2 mg/day to a maximum dose of 6 mg/day. It is usually assumed that the increased hypoglycemia with glimepiride was driven by the 6 mg/day dose; it was therefore of interest to assess whether the risk of hypoglycemia is also different between vildagliptin and a low (2 mg/day) dose of glimepiride.

METHODS

Data (n = 3,059) were from the aforementioned randomized, double-blind study. Comparisons between vildagliptin (50 mg twice daily) and glimepiride (subgroups of patients on 2 mg/day, 6 mg/day, and 'other', and overall glimepiride group) were done by modeling hypoglycemia risk as a function of time and last-measured glycated hemoglobin (HbA1c) using discrete event time modeling, with treatment, age, gender as additional covariates.

RESULTS

The hypoglycemia risk was significantly lower in patients receiving vildagliptin versus patients remaining on glimepiride 2 mg/day throughout the study, with similar results unadjusted or adjusted for last HbA1c [adjusted hazard ratio (HR) = 0.06 (95% CI 0.03, 0.11)]. The risk of hypoglycemia was very low with vildagliptin over the full HbA1c range, while the risk with glimepiride 2 mg/day increased with lower HbA1c. The increase for lower levels of HbA1c was more pronounced in the glimepiride 2 mg/day than 6 mg/day subgroup, with the 6 mg/day subgroup showing the lowest hypoglycemia risk among the glimepiride groups [adjusted HR vildagliptin vs. 6 mg/day glimepiride = 0.21 (95% CI 0.11, 0.40)].

CONCLUSION

The data show a substantially lower risk of confirmed hypoglycemia with vildagliptin compared to low-dose (2 mg/day) glimepiride. The analysis indicates that the previously reported results are not driven by high doses of glimepiride and points to interesting differences among patients regarding the susceptibility to hypoglycemia with sulfonylureas.

Profound defects in β-cell function in screen-detected type 2 diabetes are not improved with glucose-lowering treatment in the Early Diabetes Intervention Program (EDIP)

BACKGROUND

Few studies have measured the ability of interventions to affect declining β-cell function in screen-detected type 2 diabetes. The Early Diabetes Intervention Programme (ClinicalTrials.gov NCT01470937) was a randomized study based on the hypothesis that improving postprandial glucose excursions with acarbose would slow the progression of fasting hyperglycaemia in screen-detected type 2 diabetes. In the Early Diabetes Intervention Programme, the effect of acarbose plus lifestyle advice on progression of fasting hyperglycaemia over a 5-year period was not greater than that of placebo. However, there was an early glucose-lowering effect of the trial. The objective of the current secondary analysis was to describe β-cell function changes in response to glucose lowering.

METHODS

Participants were overweight adult subjects with screen-detected type 2 diabetes. β-cell function was measured using hyperglycaemic clamps and oral glucose tolerance testing. The primary outcome was the change in β-cell function from baseline to year 1, the time point where the maximal glucose-lowering effect was seen.

RESULTS

At baseline, participants exhibited markedly impaired first-phase insulin response. Despite significant reductions in weight, fasting plasma glucose (PG) and 2-h PG, there was no clinically significant improvement in the first-phase insulin response. Late-phase insulin responses declined despite beneficial glycaemic effects of interventions.

CONCLUSIONS

Insulin secretion is already severely impaired in early, screen-detected type 2 diabetes. Effective glucose-lowering intervention with acarbose was not sufficient to improve insulin secretion or halt the decline of β-cell function.

Acute administration of unacylated ghrelin has no effect on Basal or stimulated insulin secretion in healthy humans

Unacylated ghrelin (UAG) is the predominant ghrelin isoform in the circulation. Despite its inability to activate the classical ghrelin receptor, preclinical studies suggest that UAG may promote β-cell function. We hypothesized that UAG would oppose the effects of acylated ghrelin (AG) on insulin secretion and glucose tolerance. AG (1 µg/kg/h), UAG (4 µg/kg/h), combined AG+UAG, or saline were infused to 17 healthy subjects (9 men and 8 women) on four occasions in randomized order. Ghrelin was infused for 30 min to achieve steady-state levels and continued through a 3-h intravenous glucose tolerance test. The acute insulin response to glucose (AIRg), insulin sensitivity index (SI), disposition index (DI), and intravenous glucose tolerance (kg) were compared for each subject during the four infusions. AG infusion raised fasting glucose levels but had no effect on fasting plasma insulin. Compared with the saline control, AG and AG+UAG both decreased AIRg, but UAG alone had no effect. SI did not differ among the treatments. AG, but not UAG, reduced DI and kg and increased plasma growth hormone. UAG did not alter growth hormone, cortisol, glucagon, or free fatty acid levels. UAG selectively decreased glucose and fructose consumption compared with the other treatments. In contrast to previous reports, acute administration of UAG does not have independent effects on glucose tolerance or β-cell function and neither augments nor antagonizes the effects of AG.

Youth-onset type 2 diabetes mellitus: lessons learned from the TODAY study

Type 2 diabetes mellitus is increasingly diagnosed in obese children and adolescents. Evidence suggests that this disease commonly progresses more rapidly in youth compared with adults and is associated with high rates of early microalbuminuria, hypertension, and dyslipidemia. The Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study was the first multiethnic, multicenter randomized trial in the United States to compare 3 treatment approaches in obese youth with new-onset type 2 diabetes (n=699; ages 10-17 years): monotherapy with metformin, metformin with rosiglitazone, and metformin with an intensive lifestyle intervention. The primary outcome was glycemic control. Diabetes-related complications and cardiovascular risk factors were also examined. Approximately half of the participants could not maintain glycemic control by using metformin alone. Combination therapy with metformin and rosiglitazone resulted in better durability of glycemic control, and metformin plus intensive lifestyle intervention was intermediate but not superior to metformin alone. Deterioration in glycemic control was associated with rapid loss of beta cell function, not worsened insulin sensitivity, and could not be explained by differences in adherence or body mass index. After 3.9 years, 236 (33.8%) of participants had hypertension and 116 participants (16.6%) had microalbuminuria. Only 55.9% of participants had a low-density lipoprotein cholesterol level less than 100 mg/dL (to convert to mmol/L, multiply by 0.0259) after 3 years, and 71 of 517 participants (13.7%) had retinopathy. The significance of the findings from this important trial for the management of youth and young adults with youth-onset type 2 diabetes and its complications is discussed. An aggressive multifaceted approach is needed to prevent or forestall premature microvascular and macrovascular complications in youth-onset type 2 diabetes.

Assessment of pancreatic β-cell function: review of methods and clinical applications

Type 2 diabetes mellitus (T2DM) is characterized by a progressive failure of pancreatic β-cell function (BCF) with insulin resistance. Once insulin over-secretion can no longer compensate for the degree of insulin resistance, hyperglycemia becomes clinically significant and deterioration of residual β-cell reserve accelerates. This pathophysiology has important therapeutic implications. Ideally, therapy should address the underlying pathology and should be started early along the spectrum of decreasing glucose tolerance in order to prevent or slow β-cell failure and reverse insulin resistance. The development of an optimal treatment strategy for each patient requires accurate diagnostic tools for evaluating the underlying state of glucose tolerance. This review focuses on the most widely used methods for measuring BCF within the context of insulin resistance and includes examples of their use in prediabetes and T2DM, with an emphasis on the most recent therapeutic options (dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 receptor agonists). Methods of BCF measurement include the homeostasis model assessment (HOMA); oral glucose tolerance tests, intravenous glucose tolerance tests (IVGTT), and meal tolerance tests; and the hyperglycemic clamp procedure. To provide a meaningful evaluation of BCF, it is necessary to interpret all observations within the context of insulin resistance. Therefore, this review also discusses methods utilized to quantitate insulin-dependent glucose metabolism, such as the IVGTT and the euglycemic-hyperinsulinemic clamp procedures. In addition, an example is presented of a mathematical modeling approach that can use data from BCF measurements to develop a better understanding of BCF behavior and the overall status of glucose tolerance.

Actin dynamics regulated by the balance of neuronal Wiskott-Aldrich syndrome protein (N-WASP) and cofilin activities determines the biphasic response of glucose-induced insulin secretion

Actin dynamics in pancreatic β-cells is involved in insulin secretion. However, the molecular mechanisms of the regulation of actin dynamics by intracellular signals in pancreatic β-cells and its role in phasic insulin secretion are largely unknown. In this study, we elucidate the regulation of actin dynamics by neuronal Wiskott-Aldrich syndrome protein (N-WASP) and cofilin in pancreatic β-cells and demonstrate its role in glucose-induced insulin secretion (GIIS). N-WASP, which promotes actin polymerization through activation of the actin nucleation factor Arp2/3 complex, was found to be activated by glucose stimulation in insulin-secreting clonal pancreatic β-cells (MIN6-K8 β-cells). Introduction of a dominant-negative mutant of N-WASP, which lacks G-actin and Arp2/3 complex-binding region VCA, into MIN6-K8 β-cells or knockdown of N-WASP suppressed GIIS, especially the second phase. We also found that cofilin, which severs F-actin in its dephosphorylated (active) form, is converted to the phosphorylated (inactive) form by glucose stimulation in MIN6-K8 β-cells, thereby promoting F-actin remodeling. In addition, the dominant-negative mutant of cofilin, which inhibits activation of endogenous cofilin, or knockdown of cofilin reduced the second phase of GIIS. However, the first phase of GIIS occurs in the G-actin predominant state, in which cofilin activity predominates over N-WASP activity. Thus, actin dynamics regulated by the balance of N-WASP and cofilin activities determines the biphasic response of GIIS.

Antidiabetic actions of an estrogen receptor β selective agonist

The estrogen receptor β (ERβ) is emerging as an important player in the physiology of the endocrine pancreas. We evaluated the role and antidiabetic actions of the ERβ selective agonist WAY200070 as an insulinotropic molecule. We demonstrate that WAY200070 enhances glucose-stimulated insulin secretion both in mouse and human islets. In vivo experiments showed that a single administration of WAY200070 leads to an increase in plasma insulin levels with a concomitant improved response to a glucose load. Two-week treatment administration increased glucose-induced insulin release and pancreatic β-cell mass and improved glucose and insulin sensitivity. In addition, streptozotocin-nicotinamide-induced diabetic mice treated with WAY200070 exhibited a significant improvement in plasma insulin levels and glucose tolerance as well as a regeneration of pancreatic β-cell mass. Studies performed in db/db mice demonstrated that this compound restored first-phase insulin secretion and enhanced pancreatic β-cell mass. We conclude that ERβ agonists should be considered as new targets for the treatment of diabetes.

Physiologic concentrations of exogenously infused ghrelin reduces insulin secretion without affecting insulin sensitivity in healthy humans

BACKGROUND

Infusion of ghrelin to supraphysiologic levels inhibits glucose-stimulated insulin secretion, reduces insulin sensitivity, and worsens glucose tolerance in humans.

OBJECTIVE

The purpose of this study was to determine the effects of lower doses of ghrelin on insulin secretion and insulin sensitivity in healthy men and women.

METHODS

Acyl ghrelin (0.2 and 0.6 nmol kg(-1) h(-1)) or saline was infused for 225 minutes in 16 healthy subjects on 3 separate occasions in randomized order. An i.v. glucose tolerance test was performed, and the insulin sensitivity index (SI) was derived from the minimal model. Insulin secretion was measured as the acute insulin response to glucose (AIRg) and the disposition index was computed as AIRg × SI.

RESULTS

Ghrelin infusions at 0.2 and 0.6 nmol kg(-1) h(-1) raised steady-state plasma total ghrelin levels 2.2- and 6.1-fold above fasting concentrations. Neither dose of ghrelin altered fasting plasma insulin, glucose, or SI, but both doses reduced insulin secretion compared with the saline control, computed either as AIRg (384 ± 75 and 354 ± 65 vs 520 ± 110 pM · min [mean ± SEM], respectively; P < .01 for both low- and high-dose vs saline) or disposition index (2238 ± 421 and 2067 ± 396 vs 3339 ± 705, respectively; P < .02 for both comparisons). The high-dose ghrelin infusion also decreased glucose tolerance.

CONCLUSIONS

Ghrelin infused to levels occurring in physiologic states such as starvation decreases insulin secretion without affecting insulin sensitivity. These findings are consistent with a role for endogenous ghrelin in the regulation of insulin secretion and suggest that ghrelin antagonism could improve β-cell function.

Clinical evolution of beta cell function in youth with diabetes: the SEARCH for Diabetes in Youth study

AIMS/HYPOTHESIS

Few studies have explored the epidemiology of beta cell loss in youth with diabetes. This report describes the evolution and major determinants of beta cell function, assessed by fasting C-peptide (FCP), in the SEARCH for Diabetes in Youth study.

METHODS

Participants were 1,277 youth with diabetes (948 positive for diabetes autoantibodies [DAs] and 329 negative for DAs), diagnosed when aged <20 years, who were followed from a median of 8 months post diagnosis, for approximately 30 months. We modelled the relationship between rate of change in log FCP and determinants of interest using repeated measures general linear models.

RESULTS

Among DA-positive youth, there was a progressive decline in beta cell function of 4% per month, independent of demographics (age, sex, race/ethnicity), genetic susceptibility to autoimmunity (HLA risk), HbA(1c) and BMI z score, or presence of insulin resistance. Among DA-negative youth, there was marked heterogeneity in beta cell loss, reflecting an aetiologically mixed group. This group likely includes youths with undetected autoimmunity (whose decline is similar to that of DA-positive youth) and youth with non-autoimmune, insulin-resistant diabetes, with limited decline (~0.7% per month).

CONCLUSIONS/INTERPRETATION

SEARCH provides unique estimates of beta cell function decline in a large sample of youth with diabetes, indicating that autoimmunity is the major contributor. These data contribute to a better understanding of clinical evolution of beta cell function in youth with diabetes, provide strong support for the aetiological classification of diabetes type and may inform tertiary prevention efforts targeted at high-risk groups.

High physiological omega-3 Fatty Acid supplementation affects muscle Fatty Acid composition and glucose and insulin homeostasis in obese adolescents

Obese adolescents have high concentrations of saturated fatty acids and low omega-3 long-chain polyunsaturated fatty acids (LCUFAs) in plasma phospholipids. We aimed to investigate effects of omega-3 LCPUFA supplementation to obese adolescents on skeletal muscle lipids and glucose and insulin homeostasis. Twenty-five obese adolescents (14–17 years old, 14 females) completed a randomized double-blind crossover study supplying capsules containing either 1.2 g omega-3 LCPUFAs or placebo, for 3 months each with a six-week washout period. Fasting blood glucose, insulin, leptin, adiponectin, and lipids were measured. Intravenous glucose tolerance test (IVGTT) and euglycemic-hyperinsulinemic clamp were performed, and skeletal muscle biopsies were obtained at the end of each period. The concentrations of EPA, DHA, and total omega-3 PUFA in muscle phospholipids increased in both sexes. In the females, omega-3 LCPUFA supplementation improved glucose tolerance by 39% (P = 0.04) and restored insulin concentration by 34% (P = 0.02) during IVGTT. Insulin sensitivity improved 17% (P = 0.07). In males, none of these parameters was influenced by omega-3 supplementation. Thus, three months of supplementation of omega-3 LCPUFA improved glucose and insulin homeostasis in obese girls without influencing body weight.

Pharmacokinetics and pharmacodynamics of insulin analogs in special populations with type 2 diabetes mellitus

INTRODUCTION

The goal of insulin therapy in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM) is to match as closely as possible normal physiologic insulin secretion to control fasting and postprandial plasma glucose. Modifications of the insulin molecule have resulted in two long-acting insulin analogs (glargine and detemir) and three rapid-acting insulins (aspart, lispro, and glulisine) with improved pharmacokinetic/pharmacodynamic (PK/PD) profiles. These agents can be used together in basal-bolus therapy to more closely mimic physiologic insulin secretion patterns.

METHODS

This study reviews effects of the multiple demographic and clinical parameters in the insulin analogs glargine, detemir, lispro, aspart, and glulisine in patients with T2DM. A search was conducted on PubMed for each major topic considered (effects of injection site, age, race/ethnicity, obesity, renal or hepatic dysfunction, pregnancy, exercise, drug interactions) using the topic words and name of each type of insulin analog. Information was also obtained from the prescribing information for each insulin analog.

RESULTS

The PK/PD profiles for insulin analogs may be influenced by many variables including age, weight, and hepatic and renal function. However, these variables do not have equivalent effects on all long-acting or rapid-acting insulin analogs.

CONCLUSION

Rapid-acting and long-acting insulin analogs represent major advances in treatment for patients with T2DM who require insulin therapy. However, there are potentially important PK and PD differences between the two long-acting agents and among the three rapid-acting insulin analogs, which should be considered when designing treatment regimens for special patient groups.

Comparison of glucostatic parameters after hypocaloric diet or bariatric surgery and equivalent weight loss

Weight-loss independent mechanisms may play an important role in the improvement of glucose homeostasis after Roux-en-Y gastric bypass (RYGB). The objective of this analysis was to determine whether RYGB causes greater improvement in glucostatic parameters as compared with laparoscopic adjustable gastric banding (LAGB) or low calorie diet (LCD) after equivalent weight loss and independent of enteral nutrient passage. Study 1 recruited participants without type 2 diabetes mellitus (T2DM) who underwent LAGB (n = 8) or RYGB (n = 9). Study 2 recruited subjects with T2DM who underwent LCD (n = 7) or RYGB (n = 7). Insulin-supplemented frequently-sampled intravenous glucose tolerance test (fsIVGTT) was performed before and after equivalent weight reduction. MINMOD analysis of insulin sensitivity (Si), acute insulin response to glucose (AIRg) and C-peptide (ACPRg) response to glucose, and insulin secretion normalized to the degree of insulin resistance (disposition index (DI)) were analyzed. Weight loss was comparable in all groups (7.8 ± 0.4%). In Study 1, significant improvement of Si, ACPRg, and DI were observed only after LAGB. In Study 2, Si, ACPRg, and plasma adiponectin increased significantly in the RYGB-DM group but not in LCD. DI improved in both T2DM groups, but the absolute increase was greater after RYGB (258.2 ± 86.6 vs. 55.9 ± 19.9; P < 0.05). Antidiabetic medications were discontinued after RYGB contrasting with 55% reduction in the number of medications after LCD. No intervention affected fasting glucagon-like peptide (GLP)-1, peptide YY (PYY) or ghrelin levels. In conclusion, RYGB produced greater improvement in Si and DI compared with diet at equivalent weight loss in T2DM subjects. Such a beneficial effect was not observed in nondiabetic subjects at this early time-point.

PWD/PhJ and WSB/EiJ mice are resistant to diet-induced obesity but have abnormal insulin secretion

Recently, novel inbred mouse strains that are genetically distinct from the commonly used models have been developed from wild-caught mice. These wild-derived inbred strains have been included in many of the large-scale genomic projects, but their potential as models of altered obesity and diabetes susceptibility has not been assessed. We examined obesity and diabetes-related traits in response to high-fat feeding in two of these strains, PWD/PhJ (PWD) and WSB/EiJ (WSB), in comparison with C57BL/6J (B6). Young PWD mice displayed high fasting insulin levels, although they had normal insulin sensitivity. PWD mice subsequently developed a much milder and delayed-onset obesity compared with B6 mice but became as insulin resistant. PWD mice had a robust first-phase and increased second-phase glucose-stimulated insulin secretion in vivo, rendering them more glucose tolerant. WSB mice were remarkably resistant to diet-induced obesity and maintained very low fasting insulin throughout the study. WSB mice exhibited more rapid glucose clearance in response to an insulin challenge compared with B6 mice, consistent with their low percent body fat. Interestingly, in the absence of a measurable in vivo insulin secretion, glucose tolerance of WSB mice was better than B6 mice, likely due to their enhanced insulin sensitivity. Thus PWD and WSB are two obesity-resistant strains with unique insulin secretion phenotypes. PWD mice are an interesting model that dissociates hyperinsulinemia from obesity and insulin resistance, whereas WSB mice are a model of extraordinary resistance to a high-fat diet.

How neural mediation of anticipatory and compensatory insulin release helps us tolerate food

Learned anticipatory and compensatory responses allow the animal and human to maintain metabolic homeostasis during periods of nutritional challenges, either acutely within each meal or chronically during periods of overnutrition. This paper discusses the role of neurally-mediated anticipatory responses in humans and their role in glucoregulation, focusing on cephalic phase insulin and pancreatic polypeptide release as well as compensatory insulin release during the etiology of insulin resistance. The necessary stimuli required to elicit CPIR and vagal activation are discussed and the role of CPIR and vagal efferent activation in intra-meal metabolic homeostasis and during chronic nutritional challenges are reviewed.

Mitochondrial dynamics in diabetes

Mitochondria are at the center of cellular energy metabolism and regulate cell life and death. The cell biological aspect of mitochondria, especially mitochondrial dynamics, has drawn much attention through implications in human pathology, including neurological disorders and metabolic diseases. Mitochondrial fission and fusion are the main processes governing the morphological plasticity and are controlled by multiple factors, including mechanochemical enzymes and accessory proteins. Emerging evidence suggests that mitochondrial dynamics plays an important role in metabolism-secretion coupling in pancreatic β-cells as well as complications of diabetes. This review describes an overview of mechanistic and functional aspects of mitochondrial fission and fusion, and comments on the recent advances connecting mitochondrial dynamics with diabetes and diabetic complications.

Inflammation of the hypothalamus leads to defective pancreatic islet function

Type 2 diabetes mellitus results from the complex association of insulin resistance and pancreatic β-cell failure. Obesity is the main risk factor for type 2 diabetes mellitus, and recent studies have shown that, in diet-induced obesity, the hypothalamus becomes inflamed and dysfunctional, resulting in the loss of the perfect coupling between caloric intake and energy expenditure. Because pancreatic β-cell function is, in part, under the control of the autonomic nervous system, we evaluated the role of hypothalamic inflammation in pancreatic islet function. In diet-induced obesity, the earliest markers of hypothalamic inflammation are present at 8 weeks after the beginning of the high fat diet; similarly, the loss of the first phase of insulin secretion is detected at the same time point and is restored following sympathectomy. Intracerebroventricular injection of a low dose of tumor necrosis factor α leads to a dysfunctional increase in insulin secretion and activates the expression of a number of markers of apoptosis in pancreatic islets. In addition, the injection of stearic acid intracerebroventricularly, which leads to hypothalamic inflammation through the activation of tau-like receptor-4 and endoplasmic reticulum stress, produces an impairment of insulin secretion, accompanied by increased expression of markers of apoptosis. The defective insulin secretion, in this case, is partially dependent on sympathetic signal-induced peroxisome proliferator receptor-γ coactivator Δα and uncoupling protein-2 expression and is restored after sympathectomy or following PGC1α expression inhibition by an antisense oligonucleotide. Thus, the autonomic signals generated in concert with hypothalamic inflammation can impair pancreatic islet function, a phenomenon that may explain the early link between obesity and defective insulin secretion.

Ghrelin suppresses glucose-stimulated insulin secretion and deteriorates glucose tolerance in healthy humans

OBJECTIVE

The orexigenic gut hormone ghrelin and its receptor are present in pancreatic islets. Although ghrelin reduces insulin secretion in rodents, its effect on insulin secretion in humans has not been established. The goal of this study was to test the hypothesis that circulating ghrelin suppresses glucose-stimulated insulin secretion in healthy subjects.

RESEARCH DESIGN AND METHODS

Ghrelin (0.3, 0.9 and 1.5 nmol/kg/h) or saline was infused for more than 65 min in 12 healthy patients (8 male/4 female) on 4 separate occasions in a counterbalanced fashion. An intravenous glucose tolerance test was performed during steady state plasma ghrelin levels. The acute insulin response to intravenous glucose (AIRg) was calculated from plasma insulin concentrations between 2 and 10 min after the glucose bolus. Intravenous glucose tolerance was measured as the glucose disappearance constant (Kg) from 10 to 30 min.

RESULTS

The three ghrelin infusions raised plasma total ghrelin concentrations to 4-, 15-, and 23-fold above the fasting level, respectively. Ghrelin infusion did not alter fasting plasma insulin or glucose, but compared with saline, the 0.3, 0.9, and 1.5 nmol/kg/h doses decreased AIRg (2,152 +/- 448 vs. 1,478 +/- 2,889, 1,419 +/- 275, and 1,120 +/- 174 pmol/l) and Kg (0.3 and 1.5 nmol/kg/h doses only) significantly (P < 0.05 for all). Ghrelin infusion raised plasma growth hormone and serum cortisol concentrations significantly (P < 0.001 for both), but had no effect on glucagon, epinephrine, or norepinephrine levels (P = 0.44, 0.74, and 0.48, respectively).

CONCLUSIONS

This is a robust proof-of-concept study showing that exogenous ghrelin reduces glucose-stimulated insulin secretion and glucose disappearance in healthy humans. Our findings raise the possibility that endogenous ghrelin has a role in physiologic insulin secretion, and that ghrelin antagonists could improve beta-cell function.

Consequences of a compromised intrauterine environment on islet function

Low birth weight is an important risk factor for impaired glucose tolerance and diabetes later in life. One hypothesis is that fetal beta-cells inherit a persistent defect as a developmental response to fetal malnutrition, a primary cause of intrauterine growth restriction (IUGR). Our understanding of fetal programing events in the human endocrine pancreas is limited, but several animal models of IUGR extend our knowledge of developmental programing in beta-cells. Pathological outcomes such as beta-cell dysfunction, impaired glucose tolerance, and diabetes are often observed in adult offspring from these animal models, similar to the associations of low birth weight and metabolic diseases in humans. However, the identified mechanisms underlying beta-cell dysfunction across models and species are varied, likely resulting from the different methodologies used to induce experimental IUGR, as well as from intraspecies differences in pancreas development. In this review, we first present the evidence for human beta-cell dysfunction being associated with low birth weight or IUGR. We then evaluate relevant animal models of IUGR, focusing on the strengths of each, in order to define critical periods and types of nutrient deficiencies that can lead to impaired beta-cell function. These findings frame our current knowledge of beta-cell developmental programing and highlight future research directions to clarify the mechanisms of beta-cell dysfunction for human IUGR.

Visceral nerves: vagal and sympathetic innervation

The autonomic nervous system is the primary neural mediator of physiological responses to internal and external stimuli. It is composed of 2 branches: the sympathetic nervous system, which mediates catabolic responses, and the parasympathetic nervous system, composed of the vagus nerve, which regulates anabolic responses. As the vagus nerve innervates most tissues involved in nutrient metabolism, including the stomach, pancreas, and liver, activation of vagal efferent activity has the potential to influence how nutrients are absorbed and metabolized. Vagal efferent activity is initially activated at the onset of food intake by receptors in the oropharyngeal cavity and then during food intake postprandially. Vagal efferent innervation of the pancreas contributes to early-phase insulin release as well as to optimizing postprandial insulin release. In the absence of vagal activation, which occurs when glucose is administered intragastrically, postprandial glucose levels are higher and insulin levels blunted compared with when there is activation of oropharyngeal receptors by food. An induction of vagal efferent activity also occurs during chronic pancreatic B-cell challenge with 48-hour glucose infusions. Under these conditions, the compensatory increase in insulin secretion is partially mediated by an increase in vagal efferent activity. In conclusion, the vagus nerve, part of the parasympathetic nervous system, plays a critical role in the regulation of blood glucose levels and is an often overlooked factor contributing to glucose homeostasis.

Plasma proteome changes in subjects with Type 2 diabetes mellitus with a low or high early insulin response

Circulating proteins contribute to the pathogenesis of T2DM (Type 2 diabetes mellitus) in various ways. The aim of the present study was to investigate variations in plasma protein levels in subjects with T2DM and differences in β-cell function, characterized by the EIR (early insulin response), and to compare these protein levels with those observed in individuals with NGT (normal glucose tolerance). Ten subjects with NGT+high EIR, ten with T2DM+high EIR, and ten with T2DM+low EIR were selected from the community-based ULSAM (Uppsala Longitudinal Study of Adult Men) cohort. Plasma protein profiling was performed using SELDI-TOF (surface-enhanced laser-desorption ionization–time-of-flight) MS. In total, nine plasma proteins differed between the three study groups (P<0.05, as determined by ANOVA). The levels of two forms of transthyretin, haemoglobin α-chain and haemoglobin β-chain were decreased in plasma from subjects with T2DM compared with subjects with NGT, irrespective of the EIR of the subjects. Apolipoprotein H was decreased in plasma from individuals with T2DM+high EIR compared with subjects with NGT. Four additional unidentified plasma proteins also varied in different ways between the experimental groups. In conclusion, the proteins detected in the present study may be related to the development of β-cell dysfunction.

Impaired insulin secretion and glucose intolerance in synaptotagmin-7 null mutant mice

Vertebrates express at least 15 different synaptotagmins with the same domain structure but diverse localizations and tissue distributions. Synaptotagmin-1,-2, and -9 act as calcium sensors for the fast phrase of neurotransmitter release, and synaptotagmin-12 acts as a calcium-independent modulator of release. The exact functions of the remaining 11 synaptotagmins, however, have not been established. By analogy to the role of synaptotagmin-1, -2, and -9 in neurotransmission, these other synaptotagmins may serve as Ca(2+) transducers regulating other Ca(2+)-dependent membrane processes, such as insulin secretion in pancreatic beta-cells. Of these other synaptotagmins, synaptotagmin-7 is one of the most abundant and is present in pancreatic beta-cells. To determine whether synaptotagmin-7 regulates Ca(2+)-dependent insulin secretion, we analyzed synaptotagmin-7 null mutant mice for glucose tolerance and insulin release. Here, we show that synaptotagmin-7 is required for the maintenance of systemic glucose tolerance and glucose-stimulated insulin secretion. Mutant mice have normal insulin sensitivity, insulin production, islet architecture and ultrastructural organization, and metabolic and calcium responses but exhibit impaired glucose-induced insulin secretion, indicating a calcium-sensing defect during insulin-containing secretory granule exocytosis. Taken together, our findings show that synaptotagmin-7 functions as a positive regulator of insulin secretion and may serve as a calcium sensor controlling insulin secretion in pancreatic beta cells.

Type 2 diabetes: Gaining insight into the disease process using proteomics

The incidence of diabetes mellitus is growing rapidly, with an increasing disease related morbidity and mortality. This is caused by macro- and microvascular complications, as a consequence of the often late diagnosis of type 2 diabetes (T2D), but especially by the difficulties to control glucose homeostasis due to the progressive nature of the disease. T2D is moreover a dual disease, with components of beta-cell failure and components of insulin resistance in peripheral organs, such as liver, fat, and muscle. Understanding the pathogenesis of the disease by gaining insight into the molecular pathways involved in both phenomena is one of the major assets of proteomic approaches. Moreover, proteomics and peptidomics may provide us with robust biomarkers for beta-cell failure, insulin resistance in pheripheral organs, but also for the development of diabetic complications. This review focuses on the knowledge gained by use of proteomic and peptidomic techniques in the study of the pathophysiology of T2D and in the attempts to discover new therapeutic targets.

48-h glucose infusion in humans: effect on hormonal responses, hunger and food intake

Experimentally-induced hyperglycemia by prolonged glucose infusion allows investigation of the effects of sustained stimulation of the pancreatic beta-cell on insulin secretion and sensitivity. Hormonal responses to a meal following prolonged glucose infusions have not been investigated. To determine if a 48-h glucose infusion alters hormonal responses to a test meal as well as food intake and hunger in normal weight individuals, 16 subjects (8 men, 8 women, age 18-30 years, mean BMI=21.7+/-1.6 kg/m2) were infused for 48 h with either saline (50 ml/h) or 15% glucose (200 mg/m2/min). Subjects ingested a 600 kcal mixed nutrient meal 3 h after infusion termination. Blood samples were taken during the 48 h and for 4 h following food ingestion. The 48-h glucose infusion elicited a metabolic profile of a glucose intolerant obese subjects, with increased plasma glucose, insulin and leptin (all P<0.01) and increased HOMA-IR (P<0.001). During meal ingestion, early insulin secretion was increased (P<0.05) but post-prandial glucose (P<0.01) and insulin (P<0.01) excursions were lower following the glucose infusion. Post-prandial plasma triglyceride concentrations were increased after glucose compared with saline. Food intake and hunger ratings were not different between the two conditions. Plasma leptin levels were inversely correlated with hunger (P<0.03) in both conditions and with food intake (P<0.003) during the glucose condition only. Thus, a 48-h glucose infusion does not impair post-prandial hormonal responses, alter food intake or hunger in normal weight subjects. The glucose-induced increases in plasma leptin result in a stronger inverse relationship between plasma leptin and hunger as well as food intake. These data are the first to demonstrate a relationship between leptin and hunger in normal weight, non-calorically restricted human subjects.

Meglitinide analogues for type 2 diabetes mellitus

BACKGROUND

In type 2 diabetes mellitus, impairment of insulin secretion is an important component of the disease. Meglitinide analogues are a class of oral hypoglycaemic agents that increase insulin secretion, in particular, during the early phase of insulin release.

OBJECTIVES

The aim of this review was to assess the effects of meglitinide analogues in patients with type 2 diabetes mellitus.

SEARCH STRATEGY

We searched several databases including The Cochrane Library, MEDLINE and EMBASE. We also contacted manufacturers and searched ongoing trials databases, and the American Diabetes Association (ADA) and European Association for the Study of Diabetes (EASD) websites.

SELECTION CRITERIA

We included randomised controlled, parallel or cross-over trials comparing at least 10 weeks of treatment with meglitinide analogues to placebo, head-to-head, metformin or in combination with insulin.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed trial quality.

MAIN RESULTS

Fifteen trials involving 3781 participants were included. No studies reported the effect of meglitinides on mortality or morbidity. In the eleven studies comparing meglitinides to placebo, both repaglinide and nateglinide resulted in a reductions in glycosylated haemoglobin (0.1% to 2.1% reduction in HbA1c for repaglinide; 0.2% to 0.6% for nateglinide). Only two trials compared repaglinide to nateglinide (342 participants), with greater reduction in glycosylated haemoglobin in those receiving repaglinide. Repaglinide (248 participants in three trials) had a similar degree of effect in reducing glycosylated haemoglobin as metformin. Nateglinide had a similar or slightly less marked effect on glycosylated haemoglobin than metformin (one study, 355 participants). Weight gain was generally greater in those treated with meglitinides compared with metformin (up to three kg in three months). Diarrhoea occurred less frequently and hypoglycaemia occurred more frequently but rarely severely enough as to require assistance.

AUTHORS' CONCLUSIONS

Meglitinides may offer an alternative oral hypoglycaemic agent of similar potency to metformin, and may be indicated where side effects of metformin are intolerable or where metformin is contraindicated. However, there is no evidence available to indicate what effect meglitinides will have on important long-term outcomes, particularly mortality.

Beta-cell response to metformin-glibenclamide combination tablets (Glucovance) in patients with type 2 diabetes

This exploratory double-blind, randomised, 20-week study evaluated the mechanism of action of metformin-glibenclamide combination tablets (Glucovance) vs. metformin and glibenclamide in 50 type 2 diabetes patients inadequately controlled by diet and exercise. A glycaemic target of HbA1C 7.0% was used. Final HbA(1C), fasting glucose and post-oral glucose tolerance test (OGTT) glucose were similar between groups, although average doses of metformin and glibenclamide from combination tablets (708 and 3.5 mg) were lower than monotherapy doses (1500 and 6.6 mg). Second-phase insulin during a hyperglycaemic clamp increased by 93% with combination tablets, 36% with metformin and 46% with glibenclamide. The insulin response post-OGTT was more rapid with the combination tablets vs. glibenclamide. First-phase insulin responses improved modestly in all groups, possibly due to reduced glucotoxicity. Changes in insulin sensitivity were minor. Larger beta-cell responses between combination tablets and glibenclamide may reflect more rapid glibenclamide absorption.