The incretin effect in Korean subjects with normal glucose tolerance or type 2 diabetes

The integrated incretin effect is reduced by both glucose intolerance and obesity in Japanese subjects

Introduction

Incretin-based drugs are extensively utilized in the treatment of type 2 diabetes (T2D), with remarkable clinical efficacy. These drugs were developed based on findings that the incretin effect is reduced in T2D. The incretin effect in East Asians, whose pancreatic β-cell function is more vulnerable than that in Caucasians, however, has not been fully examined. In this study, we investigated the effects of incretin in Japanese subjects.

Methods

A total of 28 Japanese subjects (14 with normal glucose tolerance [NGT], 6 with impaired glucose tolerance, and 8 with T2D) were enrolled. Isoglycemic oral (75 g glucose tolerance test) and intravenous glucose were administered. The numerical incretin effect and gastrointestinally-mediated glucose disposal (GIGD) were calculated by measuring the plasma glucose and entero-pancreatic hormone concentrations.

Results and discussion

The difference in the numerical incretin effect among the groups was relatively small. The numerical incretin effect significantly negatively correlated with the body mass index (BMI). GIGD was significantly lower in participants with T2D than in those with NGT, and significantly negatively correlated with the area under the curve (AUC)-glucose, BMI, and AUC-glucagon. Incretin concentrations did not differ significantly among the groups. We demonstrate that in Japanese subjects, obesity has a greater effect than glucose tolerance on the numerical incretin effect, whereas GIGD is diminished in individuals with both glucose intolerance and obesity. These findings indicate variances as well as commonalities between East Asians and Caucasians in the manifestation of incretin effects on pancreatic β-cell function and the integrated capacity to handle glucose.

Rectal sensitivity correlated with gastrointestinal-mediated glucose disposal, but not the incretin effect

OBJECTIVE

The mechanisms behind the diminished incretin effect in type 2 diabetes are uncertain, but impaired vagal transmission has been suggested. We aimed to investigate the association between the incretin effect and autonomic neuropathy, and the degree of dysglycaemia and duration of diabetes.

DESIGN AND METHODS

For a cross-sectional study, we included participants with either longstanding type 2 diabetes, recent onset, untreated diabetes and controls without diabetes matched for age, sex and body mass index. Autonomic nerve function was assessed with cardiovascular reflex tests, heart rate variability and sudomotor function. Visceral afferent nerves in the gut were tested performing rapid rectal balloon distention. An oral glucose tolerance test and an intravenous isoglycaemic glucose infusion were performed to calculate the incretin effect and gastrointestinal-mediated glucose disposal (GIGD).

RESULTS

Sixty-five participants were recruited. Participants with diabetes had rectal hyposensitivity for earliest sensation (3.7 ± 1.1 kPa in longstanding, 4.0 ± 1.3 in early), compared to controls (3.0 ± 0.9 kPa), p = .005. Rectal hyposensitivity for earliest sensation was not associated with the incretin effect (rho = -0.204, p = .106), but an association was found with GIGD (rho -0.341, p = .005). Incretin effect and GIGD were correlated with all glucose values, HbA1c and duration of diabetes.

CONCLUSIONS

Rectal hyposensitivity was uncovered in both longstanding and early type 2 diabetes, and was not associated with the incretin effect, but with GIGD, implying a potential link between visceral neuropathy and gastrointestinal handling of glucose. Both the incretin effect and GIGD were associated with the degree of dysglycaemia and the duration of diabetes.

PREVIOUSLY PUBLISHED

Some of the data have previously been published and presented as a poster on the American Diabetes Association 83rd Scientific Sessions: Meling et al; 1658-P: Rectal Hyposensitivity, a Potential Marker of Enteric Autonomic Nerve Dysfunction, Is Significantly Associated with Gastrointestinally Mediated Glucose Disposal in Persons with Type 2 Diabetes. Diabetes 20 June 2023; 72 (Supplement_1): 1658-P. https://doi.org/10.2337/db23-1658-P.

Incretin hormones and type 2 diabetes

Incretin hormones (glucose-dependent insulinotropic polypeptide [GIP] and glucagon-like peptide-1 [GLP-1]) play a role in the pathophysiology of type 2 diabetes. Along with their derivatives they have shown therapeutic success in type 2 diabetes, with the potential for further improvements in glycaemic, cardiorenal and body weight-related outcomes. In type 2 diabetes, the incretin effect (greater insulin secretory response after oral glucose than with 'isoglycaemic' i.v. glucose, i.e. with an identical glycaemic stimulus) is markedly reduced or absent. This appears to be because of a reduced ability of GIP to stimulate insulin secretion, related either to an overall impairment of beta cell function or to specific defects in the GIP signalling pathway. It is likely that a reduced incretin effect impacts on postprandial glycaemic excursions and, thus, may play a role in the deterioration of glycaemic control. In contrast, the insulinotropic potency of GLP-1 appears to be much less impaired, such that exogenous GLP-1 can stimulate insulin secretion, suppress glucagon secretion and reduce plasma glucose concentrations in the fasting and postprandial states. This has led to the development of incretin-based glucose-lowering medications (selective GLP-1 receptor agonists or, more recently, co-agonists, e.g. that stimulate GIP and GLP-1 receptors). Tirzepatide (a GIP/GLP-1 receptor co-agonist), for example, reduces HbA1c and body weight in individuals with type 2 diabetes more effectively than selective GLP-1 receptor agonists (e.g. semaglutide). The mechanisms by which GIP receptor agonism may contribute to better glycaemic control and weight loss after long-term exposure to tirzepatide are a matter of active research and may change the pessimistic view that developed after the disappointing lack of insulinotropic activity in people with type 2 diabetes when exposed to GIP in short-term experiments. Future medications that stimulate incretin hormone and other receptors simultaneously may have the potential to further increase the ability to control plasma glucose concentrations and induce weight loss.

The relationship between glucose and the liver-alpha cell axis - A systematic review

Until recently, glucagon was considered a mere antagonist to insulin, protecting the body from hypoglycemia. This notion changed with the discovery of the liver-alpha cell axis (LACA) as a feedback loop. The LACA describes how glucagon secretion and pancreatic alpha cell proliferation are stimulated by circulating amino acids. Glucagon in turn leads to an upregulation of amino acid metabolism and ureagenesis in the liver. Several increasingly common diseases (e.g., non-alcoholic fatty liver disease, type 2 diabetes, obesity) disrupt this feedback loop. It is important for clinicians and researchers alike to understand the liver-alpha cell axis and the metabolic sequelae of these diseases. While most of previous studies have focused on fasting concentrations of glucagon and amino acids, there is limited knowledge of their dynamics after glucose administration. The authors of this systematic review applied PRISMA guidelines and conducted PubMed searches to provide results of 8078 articles (screened and if relevant, studied in full). This systematic review aims to provide better insight into the LACA and its mediators (amino acids and glucagon), focusing on the relationship between glucose and the LACA in adult and pediatric subjects.

Circulatory Adipokines and Incretins in Adolescent Idiopathic Scoliosis: A Pilot Study

Adolescent idiopathic scoliosis (AIS) is a three-dimensional malformation of the spine of unknown cause that develops between 10 and 18 years old and affects 2-3% of adolescents, mostly girls. It has been reported that girls with AIS have a taller stature, lower body mass index (BMI), and bone mineral density (BMD) than their peers, but the causes remain unexplained. Energy metabolism discrepancies, including alterations in adipokine and incretin circulatory levels, could influence these parameters and contribute to disease pathophysiology. This pilot study aims to compare the anthropometry, BMD, and metabolic profile of 19 AIS girls to 19 age-matched healthy controls. Collected data include participants' fasting metabolic profile, anthropometry (measurements and DXA scan), nutritional intake, and physical activity level. AIS girls (14.8 ± 1.7 years, Cobb angle 27 ± 10°), compared to controls (14.8 ± 2.1 years), were leaner (BMI-for-age z-score ± SD: -0.59 ± 0.81 vs. 0.09 ± 1.11, p = 0.016; fat percentage: 24.4 ± 5.9 vs. 29.2 ± 7.2%, p = 0.036), had lower BMD (total body without head z-score ± SD: -0.6 ± 0.83 vs. 0.23 ± 0.98, p = 0.038; femoral neck z-score: -0.54 ± 1.20 vs. 0.59 ± 1.59, p = 0.043), but their height was similar. AIS girls had higher adiponectin levels [56 (9-287) vs. 32 (7-74) μg/mL, p = 0.005] and lower leptin/adiponectin ratio [0.042 (0.005-0.320) vs. 0.258 (0.024-1.053), p = 0.005]. AIS participants with a Cobb angle superior to 25° had higher resistin levels compared to controls [98.2 (12.8-287.2) vs. 32.1 (6.6-73.8), p = 0.0013]. This pilot study suggests that adipokines are implicated in AIS development and/or progression, but more work is needed to confirm their role in the disease.

Effect of metformin monotherapy and dual or triple concomitant therapy with metformin on glycemic control and lipid profile management of patients with type 2 diabetes mellitus

Background

In this study, we aimed to compare the effects of metformin-based dual therapy versus triple therapy on glycemic control and lipid profile changes in Taiwanese patients with type 2 diabetes mellitus (T2DM).

Methods

In total, 60 patients were eligible for participation in this study. Patients received at least 24 months of metformin monotherapy, dual therapy, or triple therapy with metformin plus linagliptin (a dipeptidyl peptidase 4 (DPP-4) inhibitor) or dapagliflozin (a sodium-glucose cotransporter-2 (SGLT2) inhibitor). Blood samples were collected from each patient, followed by evaluation of changes in their blood glucose control and lipid profile-related markers.

Results

A combination of metformin and DPP4 and SGLT2 inhibitor therapy more effectively reduced low-density lipoprotein cholesterol (LDL-C) (p = 0.016) than metformin monotherapy. A combination of metformin and DPP4 and SGLT2 inhibitor therapy more effectively improved total cholesterol (Chol, p = 0.049) and high-density lipoprotein cholesterol (HDL-C) than metformin monotherapy (p = 0.037). Metformin plus linagliptin dual therapy was more effective than metformin monotherapy in reducing glycosylated hemoglobin (HbA1C, p = 0.011). Patients who received a combination of linagliptin and empagliflozin showed a significant reduction in their fasting blood glucose (p = 0.019), HbA1c (p = 0.036), and Chol (p = 0.010) compared with those who received linagliptin dual therapy. Furthermore, patients who received metformin plus dapagliflozin and saxagliptin showed significantly reduced Chol (p = 0.011) and LDL-C (p = 0.035) levels compared with those who received metformin plus dapagliflozin.

Conclusion

In conclusion, dual therapy with metformin and linagliptin yields similar glycemic control ability to triple therapy. Among metformin combination triple therapy, triple therapy of empagliflozin and linagliptin might have a better glycemic control ability than dual therapy of linagliptin. Moreover, Triple therapy of dapagliflozin and saxagliptin might have a better lipid control ability than dual therapy of dapagliflozin.

The glucagon receptor antagonist LY2409021 does not affect gastrointestinal-mediated glucose disposal or the incretin effect in individuals with and without type 2 diabetes

OBJECTIVE

Gastrointestinal-mediated glucose disposal (GIGD) during oral glucose tolerance test (OGTT) reflects the percentage of glucose disposal caused by mechanisms elicited by the oral route of glucose administration. GIGD is reduced in patients with type 2 diabetes (T2D) due to a reduced incretin effect and possibly also due to inappropriate suppression of glucagon after oral glucose. We investigated the effect of glucagon receptor antagonism on GIGD, the incretin effect and glucose excursions in patients with T2D and controls without diabetes.

DESIGN

A double-blind, randomised, placebo-controlled crossover study was conducted.

METHODS

Ten patients with T2D and 10 gender-, age- and BMI-matched controls underwent two 50 g OGTTs and 2 isoglycaemic i.v. glucose infusions, succeeding (~10 h) single-dose administration of 100 mg of the glucagon receptor antagonist LY2409021 or placebo, respectively.

RESULTS

Compared to placebo, LY2409021 reduced fasting plasma glucose in patients with T2D and controls. Plasma glucose excursions after oral glucose assessed by baseline-subtracted area under the curve were increased by LY2409021 compared to placebo in both groups, but no effect of LY2409021 on GIGD or the incretin effect was observed. LY2409021 increased fasting glucagon concentrations three-fold compared to placebo concentrations.

CONCLUSIONS

Glucagon receptor antagonism with LY2409021 had no effect on the impaired GIGD or the impaired incretin effect in patients with T2D and did also not affect these parameters in the controls. Surprisingly, we observed reduced oral glucose tolerance with LY2409021 which may be specific for this glucagon receptor antagonist.

Fasting and stimulated glucagon-like peptide-1 exhibit a compensatory adaptive response in diabetes and pre-diabetes states: A multi-ethnic comparative study

Background

Impaired secretion of glucagon-like peptide-1 (GLP-1) among Caucasians contributes to reduced incretin effect in type 2 diabetes mellitus (T2DM) patients. However, studies emanating from East Asia suggested preserved GLP-1 levels in pre-diabetes (pre-DM) and T2DM. We aimed to resolve these conflicting findings by investigating GLP-1 levels during oral glucose tolerance test (OGTT) among Malay, Chinese, and Indian ethnicities with normal glucose tolerance (NGT), pre-DM, and T2DM. The association between total GLP-1 levels, insulin resistance, and insulin sensitivity, and GLP-1 predictors were also analyzed.

Methods

A total of 174 subjects were divided into NGT (n=58), pre-DM (n=54), and T2DM (n=62). Plasma total GLP-1 concentrations were measured at 0, 30, and 120 min during a 75-g OGTT. Homeostasis model assessment of insulin resistance (HOMA-IR), HOMA of insulin sensitivity (HOMA-IS), and triglyceride-glucose index (TyG) were calculated.

Results

Total GLP-1 levels at fasting and 30 min were significantly higher in T2DM compared with pre-DM and NGT (27.18 ± 11.56 pmol/L vs. 21.99 ± 10.16 pmol/L vs. 16.24 ± 7.79 pmol/L, p=0.001; and 50.22 ± 18.03 pmol/L vs. 41.05 ± 17.68 pmol/L vs. 31.44 ± 22.59 pmol/L, p<0.001; respectively). Ethnicity was a significant determinant of AUCGLP-1, with the Indians exhibiting higher GLP-1 responses than Chinese and Malays. Indians were the most insulin resistant, whereas Chinese were the most insulin sensitive. The GLP-1 levels were positively correlated with HOMA-IR and TyG but negatively correlated with HOMA-IS. This relationship was evident among Indians who exhibited augmented GLP-1 responses proportionately to their high insulin-resistant states.

Conclusion

This is the first study that showed GLP-1 responses are augmented as IR states increase. Fasting and post-OGTT GLP-1 levels are raised in T2DM and pre-DM compared to that in NGT. This raises a possibility of an adaptive compensatory response that has not been reported before. Among the three ethnic groups, the Indians has the highest IR and GLP-1 levels supporting the notion of an adaptive compensatory secretion of GLP-1.

Loss of the Incretin Effect in Type 2 Diabetes: A Systematic Review and Meta-analysis

CONTEXT

Loss of the incretin effect (IE) in type 2 diabetes (T2D) contributes to hyperglycemia and the mechanisms underlying this impairment are unclear.

OBJECTIVE

To quantify the IE impairment in T2D and to investigate the factors associated with it using a meta-analytic approach.

METHODS

PubMed, Scopus, and Web-of-Science were searched. Studies measuring IE by the gold-standard protocol employing an oral glucose tolerance test (OGTT) and an intravenous glucose infusion at matched glucose levels were selected. We extracted IE, sex, age, body mass index (BMI), and hemoglobin A1c, fasting values, and area under curve (AUC) of glucose, insulin, C-peptide, glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1). In subjects with T2D, we also recorded T2D duration, age at diagnosis, and the percentage of subjects taking antidiabetic medications.

RESULTS

The IE weighted mean difference between subjects with T2D and those with normal glucose tolerance (NGT) was -27.3% (CI -36.5% to -18.1%; P < .001; I2 = 86.6%) and was affected by age (P < .005). By meta-regression of combined NGT and T2D data, IE was inversely associated with glucose tolerance (lower IE in T2D), BMI, and fasting GIP (P < .05). By meta-regression of T2D studies only, IE was associated with the OGTT glucose dose (P < .0001). IE from insulin was larger than IE from C-peptide (weighted mean difference 11.2%, CI 9.2-13.2%; P < .0001; I2 = 28.1%); the IE difference was inversely associated with glucose tolerance and fasting glucose.

CONCLUSION

The IE impairment in T2D vs NGT is consistent though considerably variable, age being a possible factor affecting the IE difference. Glucose tolerance, BMI, and fasting GIP are independently associated with IE; in subjects with T2D only, the OGTT dose is a significant covariate.

Beta cell function, incretin hormones, and incretin effect in obese children and adolescents with prediabetes

BACKGROUND

Defects of incretin hormones and incretin effect may be underlying mechanisms of abnormal glucose metabolism in youth.

OBJECTIVE

To assess incretin hormone dynamics during an oral glucose tolerance test (OGTT) and incretin effect in obese children with prediabetes in comparison with those with normal glucose tolerance (NGT).

METHODS

Overweight and obese children were enrolled and classified according to OGTT results as NGT and prediabetes. Insulin sensitivity, insulin secretion, incretin hormone concentrations during OGTT; and incretin effect derived from OGTT and intravenous glucose tolerance test were determined and compared between NGT and prediabetes groups.

RESULTS

Sixty-three patients (43 NGT and 20 prediabetes) were enrolled. Their median (interquartile range) age was 12.5 (11.1, 13.8) years. Peak glucagon-like peptide-1 (GLP-1) was demonstrated at 30 min during OGTT and was higher in the prediabetes group (49.2 [35.6, 63.6] versus 36.5 [27.6, 44.2] pmol/L, p = 0.009). However, incremental areas under the curves (iAUCs) of GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) were not different between the two groups. There was no difference in incretin effect between NGT and prediabetes (NGT: 66.5% [60.2%, 77.5%] vs. prediabetes: 70.0% [61.5%, 75.0%], p = 0.645). Incretin effect had positive correlations with iAUCs of both GLP-1 and GIP (GLP-1: r = 0.40, p = 0.004 and GIP: r = 0.37, p = 0.009).

CONCLUSIONS

Comparing between obese children with prediabetes and NGT, there were no differences in overall incretin hormone changes during OGTT and incretin effect. Incretin effect was positively correlated with iAUCs of GLP-1 and GIP.

The Change in Glucagon Following Meal Ingestion Is Associated with Glycemic Control, but Not with Incretin, in People with Diabetes

BACKGROUND

We aimed to investigate the changes in glucagon levels in people with diabetes after the ingestion of a mixed meal and the correlations of variation in glucagon levels with incretin and clinico-biochemical characteristics.

METHODS

Glucose, C-peptide, glucagon, intact glucagon-like peptide 1 (iGLP-1), and intact glucose-dependent insulinotropic polypeptide (iGIP) were measured in blood samples collected from 317 people with diabetes before and 30 min after the ingestion of a standard mixed meal. The delta (Δ) is the 30-min value minus the basal value.

RESULTS

At 30 min after meal ingestion, the glucagon level showed no difference relative to the basal value, whereas glucose, C-peptide, iGLP-1, and iGIP levels showed a significant increase. In univariate analysis, Δglucagon showed not only a strong correlation with HbA1c but also a significant correlation with fasting glucose, Δglucose, and estimated glomerular filtration rate. However, Δglucagon showed no significant correlations with ΔiGLP-1 and ΔiGIP. In the hierarchical multiple regression analysis, HbA1c was the only variable that continued to show the most significant correlation with Δglucagon.

CONCLUSIONS

People with diabetes showed no suppression of glucagon secretion after meal ingestion. Patients with poorer glycemic control may show greater increase in postprandial glucagon level, and this does not appear to be mediated by incretin.

Evaluation of the incretin effect in humans using GIP and GLP-1 receptor antagonists

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) potentiate glucose-induced insulin secretion and are therefore thought to be responsible for the incretin effect. The magnitude of the incretin effect, defined as the fraction of postprandial insulin secretion stimulated by intestinal factors, has been reported to be up to ∼60% in healthy individuals. In several pathological conditions but especially in patients with type 2 diabetes, the incretin effect is severely reduced or even absent. In line with this, the insulinotropic effects of GIP and GLP-1 are impaired in patients with type 2 diabetes, even when administered in supraphysiological doses. In healthy individuals, GIP has been proposed to be the most important incretin hormone of the two, but the individual contribution of the two is difficult to determine. However, using incretin hormone receptor antagonists: the novel GIP receptor antagonist GIP(3-30)NH₂ and the widely used GLP-1 receptor antagonist exendin(9-39)NH₂, we can now distinguish between the effects of the two hormones. In this review, we present and discuss studies in which the individual contribution of GIP and GLP-1 to the incretin effect in healthy individuals have been estimated and discuss the limitations of using incretin hormone receptor antagonists.

Development of therapeutic options on type 2 diabetes in years: Glucagon-like peptide-1 receptor agonist’s role intreatment; from the past to future

Diabetes mellitus (DM) is a chronic metabolic disease characterized by hypergly-cemia. Type 2 diabetes (T2DM) accounting for 90% of cases globally. The worldwide prevalence of DM is rising dramatically over the last decades, from 30 million cases in 1985 to 382 million cases in 2013. It’s estimated that 451 million people had diabetes in 2017. As the pathophysiology was understood over the years, treatment options for diabetes increased. Incretin-based therapy is one of them. Glucagon-like peptide-1 receptor agonist (GLP-1 RA) not only significantly lower glucose level with minimal risk of hypoglycemia but also, they have an important advantage in themanagement of cardiovascular risk and obesity. Thus, we will review here GLP-1 RAsrole in the treatment of diabetes.

EJE PRIZE 2018: A gut feeling about glucagon

Hyperglucagonaemia (in the fasting as well as in the postprandial state) is considered a core pathophysiological component of diabetes and is found to contribute substantially to the hyperglycaemic state of diabetes. Hyperglucagonaemia is usually viewed upon as a consequence of pancreatic alpha cell insensitivity to the glucagon-suppressive effects of glucose and insulin. Since we observed that the well-known hyperglucagonaemic response to oral glucose in patients with type 2 diabetes is exchanged by normal suppression of plasma glucagon levels following isoglycaemic intravenous glucose administration in these patients, we have been focusing on the gut and gut-derived factors as potential mediators of diabetic hyperglucagonaemia. In a series of clinical experiments, we have elucidated the role of gut-derived factors in diabetic hyperglucagonaemia and shown that glucose-dependent insulinotropic polypeptide promotes hyperglucagonaemia and that glucagon, hitherto considered a pancreas-specific hormone, may also be secreted from extrapancreatic tissues - most likely from proglucagon-producing enteroendocrine cells. Furthermore, our observation that fasting hyperglucagonaemia is unrelated to the diabetic state, but strongly correlates with obesity, liver fat content and circulating amino acids, has made us question the common 'pancreacentric' and 'glucocentric' understanding of hyperglucagonaemia and led to the hypothesis that steatosis-induced hepatic glucagon resistance (and reduced amino acid turnover) and compensatory glucagon secretion mediated by increased circulating amino acids constitute a complete endocrine feedback system: the liver-alpha cell axis. This article summarises the physiological regulation of glucagon secretion in humans and considers new findings suggesting that the liver and the gut play key roles in determining fasting and postabsorptive circulating glucagon levels.

Sodium-glucose cotransporter-2 inhibition improves incretin sensitivity of pancreatic β-cells in people with type 2 diabetes

AIM

To test the hypothesis that dapagliflozin, a sodium-glucose cotransporter-2 inhibitor, improves β-cell responses to incretin hormones (or β-cell incretin sensitivity) by alleviating glucose toxicity in people with type 2 diabetes mellitus (T2DM).

METHODS

A total of 19 people with T2DM underwent a 3-hour hyperglycaemic clamp study with incretin infusion before and after 8-week treatment with dapagliflozin added to the background treatment. In addition, 10 people with normal glucose tolerance (NGT) underwent a single hyperglycaemic clamp study. The hyperglycaemic clamp was targeted at 15.5 mmol/L for 3 hours, with synthetic glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) infusion over a 60- to 180-minute and a 120- to 180-minute period, respectively.

RESULTS

Compared with baseline, the C-peptide response to GLP-1 (incremental area under the curve [iAUC] of C-peptide_{60-120 minutes} ) significantly increased (83.6 ± 42.1 to 106.6 ± 45.7 nmol/L × min; P = .011), and the C-peptide response to GIP/GLP-1 (iAUC of C-peptide_{120-180 minutes} ) tended to increase after dapagliflozin treatment (82.5 ± 58.4 to 101.9 ± 50.3 nmol/L × min; P = .087), whereas both the insulin responses to GLP-1 and GIP/GLP-1 increased significantly. First-phase C-peptide response, which reflects β-cell function, significantly increased after dapagliflozin treatment; however, all these improved values in the participants with T2DM were far lower than those in the participants with NGT. In addition, the improvement in insulin responses to hyperglycaemia was correlated with the improvement in insulin responses to incretin infusion.

CONCLUSIONS

Dapagliflozin improved β-cell responses to incretin hormones as well as glucose during the hyperglycaemic clamp in patients with inadequately controlled T2DM.

Albiglutide for the management of type 2 diabetes

Albiglutide is a long acting GLP-1 receptor agonist (GLP-1 RA) administered by weekly injection and approved for use in type 2 diabetes. It has less gastrointestinal side effects than other GLP-1 RAs in current use but does not improve HbA1c or promote weight loss to the same extent as some competitor agents. Area covered: The current use of albiglutide is discussed. The review encompassed a search of PubMed and a thorough analysis of the European Union and US Food and Drug Administration approval documents. Expert opinion: Unlike competitor agents, the gastrointestinal side effects of albiglutide are not much greater than placebo. It has been studied and appears safe at all stages of renal failure. There exists concern about an imbalance of pancreatitis cases in the approval program as well as injection site reactions which led to discontinuance of therapy in up to 2% of participants. A large long-term study is now underway to determine if albiglutide, with its relatively favorable GI tolerance, has a place in the treatment of patients with increased risk of cardiovascular events. At present, albiglutide is a safe agent to introduce GLP-1 RA treatment into the regimen for type 2 diabetes patients and may be the GLP-1 agent of choice in patients with renal insufficiency.

The safety of albiglutide for the treatment of type 2 diabetes

INTRODUCTION

Albiglutide is a marketed long acting GLP-1 receptor agonist (GLP-1 RA) administered by weekly injection. It has significantly less gastrointestinal side effects than other GLP-1 RAs in current use but does not improve HbA1c or promote weight loss to the same extent as competitor agents such as liraglutide. Area Covered: The safety of albiglutide is discussed. The review encompassed a search of PubMed and a thorough analysis of the European Union and US Food and Drug Administration approval documents. Expert Opinion: Unlike competitor agents, the gastrointestinal side effects of albiglutide are not much greater than placebo. It has been studied and appears safe at all stages of renal failure. There exists concern about an imbalance of pancreatitis cases in the approval program as well as injection site reactions which led to discontinuance of therapy in up to 2% of participants. A large long term study now underway will determine if albiglutide, with its relatively favorable GI tolerance, has a place in the treatment of patients with increased risk of cardiovascular events.

One-hour postload plasma glucose concentration in people with normal glucose homeostasis predicts future diabetes mellitus: a 12-year community-based cohort study

OBJECTIVE

In Caucasians, plasma glucose concentration at 1 h during an oral glucose tolerance test (OGTT) may be a better predictor of future diabetes mellitus than the fasting or 2-h postload glucose concentration. We investigated whether the 1-h glucose concentration could be used to predict future diabetes mellitus in Asian ethnicity.

MEASUREMENTS

A total of 5703 Koreans with normal glucose tolerance were enrolled from the Korean Genome and Epidemiology Study. Indices of insulin sensitivity and β-cell function estimated from standard 75-g OGTTs performed every 2 years for 12 years were used to identify whether the 1-h glucose concentration could predict future diabetes mellitus.

RESULTS

The mean age and body mass index at baseline were 51·3 ± 8·7 years and 24·2 ± 3·0 kg/m² , respectively. During the 12-year follow-up, 593 subjects (10·3%) developed diabetes mellitus. The area under the receiver-operating characteristic curve for incident diabetes mellitus was higher for the 1-h postload glucose concentration than for the fasting or postload 2-h glucose concentration (0·74 vs 0·61 or 0·63). The cut-off value of ≥8·0 mmol/l identified incident diabetes mellitus with 70% sensitivity and 68% specificity. After adjusting for typical risk factors, subjects with a 1-h postload glucose concentration ≥8·0 mmol/l had lower β-cell function and a 2·84-fold increased risk of incident diabetes mellitus compared with their counterparts.

CONCLUSIONS

In this community-based 12-year prospective cohort study, 1-h postload plasma glucose concentration was an independent predictor of future diabetes mellitus and 8·0 mmol/l was suggested as a cut-off value.

Comparison of Exenatide and Metformin Monotherapy in Overweight/Obese Patients with Newly Diagnosed Type 2 Diabetes

AIMS

The present study assessed the therapeutic effect of exenatide and metformin as the initial therapy on overweight/obese patients with newly diagnosed type 2 diabetes (T2D).

METHODS

The prospective, nonrandomized, interventional study enrolled a total of 230 overweight or obese patients with newly diagnosed T2D who were administrated exenatide or metformin hydrochloride for 12 weeks.

RESULTS

224/230 patients, including 106 in the exenatide group and 118 in the metformin group, completed the 12-week treatment. Both exenatide and metformin significantly decreased the HbA1c levels in overweight/obese patients with newly diagnosed T2D (all P < 0.05). The reduction in HbA1c and the proportion of patients with HbA1c < 7.0% (53 mmol/mol) were higher in the exenatide group than in the metformin group (all P < 0.05). The exenatide treatment caused a greater decline in the body weight and BMI as compared to the metformin treatment (all P < 0.01). The exenatide treatment (β = 0.41, P < 0.01) and baseline HbA1c level (β = -0.84, P < 0.01) were independent influencing factors for the decrease in HbA1c level.

CONCLUSIONS

For an initial therapy in overweight/obese patients with newly diagnosed T2D, exenatide causes a better glycemic control than metformin. This trial is registered with NCT03297879.

The incretin effect in healthy individuals and those with type 2 diabetes: physiology, pathophysiology, and response to therapeutic interventions

The incretin effect describes the phenomenon whereby oral glucose elicits higher insulin secretory responses than does intravenous glucose, despite inducing similar levels of glycaemia, in healthy individuals. This effect, which is uniformly defective in patients with type 2 diabetes, is mediated by the gut-derived incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The importance of the incretin effect for the maintenance of glucose homoeostasis is clearly established, and incretin-based therapies are among the most promising new therapies for type 2 diabetes. However, despite the effectiveness of these therapies in many patients, the idea that they restore the incretin effect is a common misconception. In type 2 diabetes, the endocrine pancreas remains responsive to GLP-1 but is no longer responsive to GIP, which is the most likely reason for a reduced or absent incretin effect. Incretin-based drugs, including GLP-1 receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors, stimulate GLP-1 receptors and thus augment insulin secretion in response to both oral and intravenous glucose stimulation, thereby abolishing any potential difference in the responses to these stimuli. These drugs therefore do not restore the defective incretin effect in patients. By contrast, some bariatric surgical procedures enhance GLP-1 responses and also restore the incretin effect in obese individuals with type 2 diabetes. Thus, not all biological actions elicited by the stimulation of GLP-1 receptors lead to quantitative changes to the incretin effect.

Mechanisms for the cardiovascular effects of glucagon-like peptide-1

Over the past three decades, at least 10 hormones secreted by the enteroendocrine cells have been discovered, which directly affect the cardiovascular system through their innate receptors expressed in the heart and blood vessels or through a neural mechanism. Glucagon-like peptide-1 (GLP-1), an important incretin, is perhaps best studied of these gut-derived hormones with important cardiovascular effects. In this review, I have discussed the mechanism of GLP-1 release from the enteroendocrine L-cells and its physiological effects on the cardiovascular system. Current evidence suggests that GLP-1 has positive inotropic and chronotropic effects on the heart and may be important in preserving left ventricular structure and function by direct and indirect mechanisms. The direct effects of GLP-1 in the heart may be mediated through GLP-1R expressed in atria as well as arteries and arterioles in the left ventricle and mainly involve in the activation of multiple pro-survival kinases and enhanced energy utilization. There is also good evidence to support the involvement of a second, yet to be identified, GLP-1 receptor. Further, GLP-1(9-36)amide, which was previously thought to be the inactive metabolite of the active GLP-1(7-36)amide, may also have direct cardioprotective effects. GLP-1's action on GLP-1R expressed in the central nervous system, kidney, vasculature and the pancreas may indirectly contribute to its cardioprotective effects.

Glucose-Dependent Insulinotropic Peptide Level Is Associated with the Development of Type 2 Diabetes Mellitus

BACKGROUND

Incretin hormone levels as a predictor of type 2 diabetes mellitus have not been fully investigated. Therefore, we measured incretin hormone levels to examine the relationship between circulating incretin hormones, diabetes, and future diabetes development in this study.

METHODS

A nested case-control study was conducted in a Korean cohort. The study included the following two groups: the control group (n=149), the incident diabetes group (n=65). Fasting total glucagon-like peptide-1 (GLP-1) and total glucose-dependent insulinotropic peptide (GIP) levels were measured and compared between these groups.

RESULTS

Fasting total GIP levels were higher in the incident diabetes group than in the control group (32.64±22.68 pmol/L vs. 25.54±18.37 pmol/L, P=0.034). There was no statistically significant difference in fasting total GLP-1 levels between groups (1.14±1.43 pmol/L vs. 1.39±2.13 pmol/L, P=0.199). In multivariate analysis, fasting total GIP levels were associated with an increased risk of diabetes (odds ratio, 1.005; P=0.012) independent of other risk factors.

CONCLUSION

Fasting total GIP levels may be a risk factor for the development of type 2 diabetes mellitus. This association persisted even after adjusting for other metabolic parameters such as elevated fasting glucose, hemoglobin A1c, and obesity in the pre-diabetic period.

In Vivo Models for Incretin Research: From the Intestine to the Whole Body

Incretin hormones are produced by enteroendocrine cells (EECs) in the intestine in response to ingested nutrient stimuli. The incretin effect is defined as the difference in the insulin secretory response between the oral glucose tolerance test and an isoglycemic intravenous glucose infusion study. The pathophysiology of the decreased incretin effect has been studied as decreased incretin sensitivity and/or β-cell dysfunction per se. Interestingly, robust increases in endogenous incretin secretion have been observed in many types of metabolic/bariatric surgery. Therefore, metabolic/bariatric surgery has been extensively studied for incretin physiology, not only the hormones themselves but also alterations in EECs distribution and genetic expression levels of gut hormones. These efforts have given us an enormous understanding of incretin biology from synthesis to in vivo behavior. Further innovative studies are needed to determine the mechanisms and targets of incretin hormones.

In-Silico Trials for Glucose Control in Hospitalized Patients with Type 2 Diabetes

Although various basal-bolus insulin therapy (BBIT) protocols have been used in the clinical environment, safer and more effective BBIT protocols are required for glucose control in hospitalized patients with type 2 diabetes (T2D). Modeling approaches could provide an evaluation environment for developing the optimal BBIT protocol prior to clinical trials at low cost and without risk of danger. In this study, an in-silico model was proposed to evaluate subcutaneous BBIT protocols in hospitalized patients with T2D. The proposed model was validated by comparing the BBIT protocol and sliding-scale insulin therapy (SSIT) protocol. The model was utilized for in-silico trials to compare the protocols of adjusting basal-insulin dose (BBIT1) versus adjusting total-daily-insulin dose (BBIT2). The model was also used to evaluate two different initial total-daily-insulin doses for various levels of renal function. The BBIT outcomes were superior to those of SSIT, which is consistent with earlier studies. BBIT2 also outperformed BBIT1, producing a decreased daily mean glucose level and longer time-in-target-range. Moreover, with a standard dose, the overall daily mean glucose levels reached the target range faster than with a reduced-dose for all degrees of renal function. The in-silico studies demonstrated several significant findings, including that the adjustment of total-daily-insulin dose is more effective than changes to basal-insulin dose alone. This research represents a first step toward the eventual development of an advanced model for evaluating various BBIT protocols.

Incretin secretion in obese Korean children and adolescents with newly diagnosed type 2 diabetes

OBJECTIVE

The role of incretins in type 2 diabetes is controversial. This study investigated the association between incretin levels in obese Korean children and adolescents newly diagnosed with type 2 diabetes.

DESIGN

We performed a 2-hr oral glucose tolerance test (OGTT) in obese children and adolescents with type 2 diabetes and with normal glucose tolerance.

PATIENTS

Twelve obese children and adolescents with newly diagnosed type 2 diabetes (DM group) and 12 obese age-matched subjects without type 2 diabetes (NDM group) were included.

MEASUREMENTS

An OGTT was conducted and insulin, C-peptide, glucagon, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were measured during the OGTT.

RESULTS

The mean age of the patients was 13·8 ± 2·0 years, and the mean body mass index (BMI) Z-score was 2·1 ± 0·5. The groups were comparable in age, sex, BMI Z-score and waist:hip ratio. The DM group had significantly lower homeostasis model assessment of β and insulinogenic index values (P < 0·001). The homeostasis model assessment of insulin resistance index was not different between the two groups. Insulin and C-peptide secretions were significantly lower in the DM group than in the NDM group (P < 0·001). Total GLP-1 secretion was significantly higher in the DM group while intact GLP-1 and GIP secretion values were not significantly different between the two groups.

CONCLUSION

Impaired insulin secretion might be important in the pathogenesis of type 2 diabetes in obese Korean children and adolescents, however, which may not be attributed to incretin secretion.

A Computational Method to Determine Glucose Infusion Rates for Isoglycemic Intravenous Glucose Infusion Study

The results of the isoglycemic intravenous glucose infusion (IIGI) study need to mimic the dynamic glucose profiles during the oral glucose tolerance test (OGTT) to accurately calculate the incretin effect. The glucose infusion rates during IIGI studies have historically been determined by experienced research personnel using the manual ad-hoc method. In this study, a computational method was developed to automatically determine the infusion rates for IIGI study based on a glucose-dynamics model. To evaluate the computational method, 18 subjects with normal glucose tolerance underwent a 75 g OGTT. One-week later, Group 1 (n = 9) and Group 2 (n = 9) underwent IIGI studies using the ad-hoc method and the computational method, respectively. Both methods were evaluated using correlation coefficient, mean absolute relative difference (MARD), and root mean square error (RMSE) between the glucose profiles from the OGTT and the IIGI study. The computational method exhibited significantly higher correlation (0.95 ± 0.03 versus 0.86 ± 0.10, P = 0.019), lower MARD (8.72 ± 1.83% versus 13.11 ± 3.66%, P = 0.002), and lower RMSE (10.33 ± 1.99 mg/dL versus 16.84 ± 4.43 mg/dL, P = 0.002) than the ad-hoc method. The computational method can facilitate IIGI study, and enhance its accuracy and stability. Using this computational method, a high-quality IIGI study can be accomplished without the need for experienced personnel.

Correlation of the incretin effect with first- and second-phase insulin secretions in Koreans with various glucose tolerance statuses

OBJECTIVE

To examine the relationship between beta-cell function and the incretin effect.

DESIGN

We performed a 180-min hyperglycaemic clamp study with oral glucose administration at 60 min in Korean subjects with normal glucose tolerance (NGT, n = 9), impaired fasting glucose (IFG, n = 6) and type 2 diabetes mellitus (T2DM, n = 6).

MEASUREMENTS

First- and second-phase insulin secretions were measured during the first 60 min. The insulin response to intravenous glucose during the 60- to 120-min interval (Insiv) was calculated using a prediction method. The insulin response to oral glucose (Ins(oral)) was calculated by subtracting the Insiv from the overall insulin response during the 60- to 120-min interval (Ins(overall)). The incretin effect under the hyperglycaemic clamp condition (IE(clamp)) was calculated by the equation: 100 × [(Ins(overall) - Insiv)/Ins(overall)].

RESULTS

The IE(clamp) was comparable among the three groups (46.3 ± 6.4%, 35.7 ± 8.8% and 51.4 ± 7.4% for the NGT, IFG and T2DM group, respectively, P = 0.327) and was not correlated with the first- and second-phase insulin secretions. However, the Ins(oral) (mU/l 60 min) was significantly different between the NGT, IFG and T2DM groups (5199 ± 1185, 2164 ± 956 and 1034 ± 355, respectively; P = 0.010) and was well correlated with the first- and second-phase insulin secretions.

CONCLUSIONS

The incretin effect measured by the hyperglycaemic clamp with oral glucose loading was neither correlated with beta-cell function nor different between NGT, IFG and T2DM groups in Koreans.

β cell dysfunction versus insulin resistance in the pathogenesis of type 2 diabetes in East Asians

Type 2 diabetes (T2DM) is one of the most serious global health problems and is mainly a result of the drastic increase in East Asia, which includes over a fourth of the global diabetes population. Lifestyle factors and ethnicity are two determinants in the etiology of T2DM, and lifestyle changes such as higher fat intake and less physical activity link readily to T2DM in East Asians. It is widely recognized that T2DM in East Asians is characterized primarily by β cell dysfunction, which is evident immediately after ingestion of glucose or meal, and less adiposity compared to the disease in Caucasians. These pathophysiological differences have an important impact on therapeutic approaches. Here, we revisit the pathogenesis of T2DM in light of β cell dysfunction versus insulin resistance in East Asians and discuss ethnic differences in the contributions of insulin secretion and insulin resistance, together with incretin secretin and action, to glucose intolerance.

Early phase glucagon and insulin secretory abnormalities, but not incretin secretion, are similarly responsible for hyperglycemia after ingestion of nutrients

AIMS

Hypersecretion of glucagon and reduced insulin secretion both contribute to hyperglycemia in type 2 diabetes (T2DM). However, the relative contributions of impaired glucagon and insulin secretions in glucose excursions at the various stages of T2DM development remain to be determined.

METHODS

The responses of glucagon and insulin as well as those of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) were examined before and after ingestion of glucose or mixed meal in Japanese subjects with normal or impaired glucose tolerance (NGT and IGT) and in non-obese, untreated T2DM of short duration.

RESULTS

In OGTT, T2DM showed a rise in glucagon at 0-30 min, unlike NGT and IGT, along with reduced insulin. In MTT, all three groups showed a rise in glucagon at 0-30 min, with that in T2DM being highest, while T2DM showed a significant reduction in insulin. Linear regression analyses revealed that glucose area under the curve (AUC)0-120 min was associated with glucagon-AUC0-30 min and insulin-AUC0-30 min in both OGTT and MTT. Total and biologically intact GIP and GLP-1 levels were similar among the three groups.

CONCLUSIONS

Disordered early phase insulin and glucagon secretions but not incretin secretion are involved in hyperglycemia after ingestion of nutrients in T2DM of even a short duration.

Incretin physiology and pathophysiology from an Asian perspective

Incretin hormones, such as glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1, are secreted on oral nutrient ingestion and regulate postprandial glucose homeostasis by conveying the signal of intestinal glucose flux. In East Asians, the secretion of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 is not reduced in type 2 diabetes relative to normal glucose tolerance. Although the incretin effect is blunted in European patients with type 2 diabetes, a few East Asian studies showed no difference in the incretin effect between type 2 diabetes and normal glucose tolerance. Interestingly, the glucose-lowering efficacy of dipeptidyl peptidase-4 inhibitors or glucagon-like peptide-1 receptor agonists was reported to be greater in Asians than in non-Asians. The difference in the treatment responses could be ascribed to a different pathophysiology of type 2 diabetes (lower insulin secretory function and less insulin resistance), lower body mass index, different genetic makeups, preserved incretin effect and different food compositions in East Asians compared with other ethnic groups. Based on the currently available data, incretin-based therapies appear to be safe and well tolerated in East Asians. Nevertheless, continuous pharmacovigilance is required. The characteristics of incretin biology and treatment responses to incretin-based therapies should be considered in developing ethnicity-specific treatment guidelines and making patient-centered decisions for patients with type 2 diabetes.

Effect of the combination of metformin and fenofibrate on glucose homeostasis in diabetic Goto-Kakizaki rats

Metformin has been reported to increase the expression of the glucagon-like peptide-1 (GLP-1) receptor in pancreatic beta cells in a peroxisome proliferator-activated receptor (PPAR)-α-dependent manner. We investigated whether a PPARα agonist, fenofibrate, exhibits an additive or synergistic effect on glucose metabolism, independent of its lipid-lowering effect, when added to metformin. Non-obese diabetic Goto-Kakizaki (GK) rats were divided into four groups and treated for 28 days with metformin, fenofibrate, metformin plus fenofibrate or vehicle. The random blood glucose levels, body weights, food intake and serum lipid profiles were not significantly different among the groups. After 4 weeks, metformin, but not fenofibrate, markedly reduced the blood glucose levels during oral glucose tolerance tests, and this effect was attenuated by adding fenofibrate. Metformin increased the expression of the GLP-1 receptor in pancreatic islets, whereas fenofibrate did not. During the intraperitoneal glucose tolerance tests with the injection of a GLP-1 analog, metformin and/or fenofibrate did not alter the insulin secretory responses. In conclusion, fenofibrate did not confer any beneficial effect on glucose homeostasis but reduced metformin's glucose-lowering activity in GK rats, thus discouraging the addition of fenofibrate to metformin to improve glycemic control.