Glucagon-like peptide 1 and dysglycemia: Conflict in incretin science

Diet-induced obesity enhances postprandial glucagon-like peptide-1 secretion in Wistar rats, but not in diabetic Goto-Kakizaki rats

Glucagon-like peptide-1 (GLP-1) is postprandially secreted from enteroendocrine L-cells and enhances insulin secretion. Currently, it is still controversial whether postprandial GLP-1 responses are altered in obesity and diabetes. To address the issue and to find out possible factors related, we compared postprandial GLP-1 responses in normal rats and in diabetic rats chronically fed an obesogenic diet. Male Wistar rats and diabetic Goto-Kakizaki (GK) rats were fed either a control diet or a high-fat/high-sucrose (HFS, 30 % fat and 40 % sucrose) diet for 26 weeks. Meal tolerance tests were performed for monitoring postprandial responses after a liquid diet administration (62·76 kJ/kg body weight) every 4 or 8 weeks. Postprandial glucose, GLP-1 and insulin responses in Wistar rats fed the HFS diet (WH) were higher than Wistar rats fed the control diet (WC). Although GK rats fed the HFS diet (GH) had higher glycaemic responses than GK rats fed the control diet (GC), these groups had similar postprandial GLP-1 and insulin responses throughout the study. Jejunal and ileal GLP-1 contents were increased by the HFS diet only in Wistar rats. Furthermore, mRNA expression levels of fatty acid receptors (Ffar1) in the jejunum were mildly (P = 0·053) increased by the HFS diet in Wistar rats, but not in GK rats. These results demonstrate that postprandial GLP-1 responses are enhanced under an obesogenic status in normal rats, but not in diabetic rats. Failure of adaptive enhancement of GLP-1 response in GK rats could be partly responsible for the development of glucose intolerance.

Efficacy and Safety of Semaglutide for Type 2 Diabetes by Race and Ethnicity: A Post Hoc Analysis of the SUSTAIN Trials

CONTEXT

Variations in the prevalence and etiology of type 2 diabetes (T2D) across race and ethnicity may affect treatment responses. Semaglutide is a glucagon-like peptide-1 analog approved for once-weekly, subcutaneous treatment of T2D.

OBJECTIVE

To compare semaglutide efficacy and safety in race and ethnicity subgroups across the SUSTAIN trials.

DESIGN

Post hoc analysis of data from phase 3 randomized SUSTAIN 1-5 and 7 (pooled), and SUSTAIN 6 trials.

PARTICIPANTS

3074 subjects (SUSTAIN 1-5 and 7) and 1648 subjects (SUSTAIN 6).

INTERVENTIONS

Semaglutide 0.5 or 1.0 mg, placebo, or active comparator (sitagliptin 100 mg, exenatide extended release 2.0 mg, insulin glargine 100IU/ml and dulaglutide 0.75 or 1.5 mg).

MAIN OUTCOME MEASURES

Change in hemoglobin A1C (HbA1c) and body weight from baseline to weeks 30, 40 and 104, and other efficacy and safety endpoints.

RESULTS

HbA1c was reduced from baseline by 1.0 to 1.5 percentage points and 1.3 to 2.0 percentage points, and body weight was reduced by 2.3 to 4.7 kg and 3.6 to 6.1 kg with semaglutide 0.5 and 1.0 mg, respectively, across race and ethnicity subgroups. Minor changes in blood pressure and lipid profiles were observed. Adverse events (AEs) were reported in similar proportions of subjects across trials. More Asian versus other race subgroups discontinued treatment prematurely due to AEs. The most commonly reported AEs were gastrointestinal disorders.

CONCLUSIONS

In this SUSTAIN trials post hoc analysis, semaglutide was associated with consistent and clinically relevant reductions in HbA1c and body weight in subjects with T2D, with minor variations in efficacy and safety outcomes associated with race or ethnicity.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.

Enhanced postprandial glucagon-like peptide-1 secretion during obesity development has a protective role against glucose intolerance induction in rats

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that regulates postprandial glycaemic response by enhancing insulin secretion. We previously demonstrated that the postprandial GLP-1 response was enhanced during the development of diet-induced obesity in rats. However, the physiological relevance of the enhanced GLP-1 response remained unclear. We aimed to determine the role of endogenous GLP-1 during obesity development. Male Sprague-Dawley rats were given either a control diet or a high-fat/high-sucrose (HFS, 30 % fat and 40 % sucrose, weight basis) diet with or without continuous administration of the GLP-1 receptor antagonist, exendin (9-39) (Ex9, 100 µg/d), for 5 weeks. Meal tolerance tests (MTT) were performed to assess postprandial glucose, insulin and GLP-1 responses to a liquid diet administration (15 kcal (63 kJ)/10 ml per kg body weight) every 2 weeks. The AUC of postprandial glucose in the HFS group was similar to the control group in both MTT (P = 0·9665 and P = 0·3475, respectively), whereas AUC of postprandial GLP-1 (after 4 weeks,P = 0·0457) and of insulin (after 2 and 4 weeks, P = 0·0486 and P = 0·0110) was higher in the HFS group compared with the control group. In the Ex9 group, AUC of postprandial glucose (P = 0·0297 and P = 0·0486) was higher along with a lower insulin response compared with the HFS group (P = 0·0564 and P = 0·0281). These results suggest that enhancement of the postprandial GLP-1 response during obesity development has a role in maintaining a normal postprandial glycaemic response. Hence, enhancing endogenous GLP-1 secretion by certain materials could be a potential target for prevention of glucose intolerance.

The effect of a low-carbohydrate high-fat diet and ethnicity on daily glucose profile in type 2 diabetes determined by continuous glucose monitoring

BACKGROUND AND AIMS

Nutrition is an integral part of type 2 diabetes (T2DM) treatment, but the optimal macronutrient composition is still debated and previous studies have not addressed the role of ethnicity in dietary response. The current study aims were to compare the effect of short-term glycemic response to low-carbohydrate high-fat (LC-HF) diet vs. high-carbohydrate low-fat (HC-LF) diet using continuous glucose monitoring (CGM) and to evaluate the response of individuals with T2DM of Yemenite (Y-DM) and non-Yemenite origin (NY-DM).

METHODS

Twenty T2DM males, ten Y-DM and ten NY-DM underwent meal tolerance test and indexes of insulin resistance and secretion were calculated. Subsequently, patients were connected to CGM to assess daily glycemic control and glucose variability in response to isocaloric HC-LF or LC-HF diet, receiving each diet for 2 days by providing prepared meals. Daily glucose levels, area under the glucose curve (G-AUC) and parameters of glucose variability [standard deviation (SD), mean amplitude of glycemic excursions (MAGE) and mean absolute glucose (MAG)] were evaluated.

RESULTS

The LC-HF resulted in a significantly lower G-AUC (p < 0.001) and in lower variability parameters (p < 0.001) vs. the HC-LF diet. However, Y-DM showed less reduction in glucose variability indices upon diet-switching vs. NY-DM; MAGE decreased, respectively, by 69% vs. 89%, p = 0.043 and MAG by 34% vs. 45%, p = 0.007 in Y-DM compared to NY-DM.

CONCLUSIONS

These results suggest that LC-HF diet is effective in reducing glycemic fluctuation in T2DM and that ethnicity may have a role in the response to dietary regime.

Continuous feeding of a combined high-fat and high-sucrose diet, rather than an individual high-fat or high-sucrose diet, rapidly enhances the glucagon-like peptide-1 secretory response to meal ingestion in diet-induced obese rats

OBJECTIVES

Glucagon-like peptide-1 (GLP-1) is secreted by enteroendocrine L-cells in response to nutrient ingestion. To date, GLP-1 secretion in diet-induced obesity is not well characterized. We aimed to examine GLP-1 secretion in response to meal ingestion during the progression of diet-induced obesity and determinewhether a combined high-fat and high-sucrose (HFS) diet, an individual high-fat (HiFat), or a high-sucrose (HiSuc) diet affect adaptive changes in the postprandial GLP-1 response.

METHODS

Rats were fed a control, HiFat diet (30% weight), HiSuc diet (40% weight), or HFS (30% fat and 40% sucrose) diet for 5 wk. Meal tolerance tests were conducted to determine postprandial glucose, insulin, and GLP-1 responses to standard (control) diet ingestion every 2 wk.

RESULTS

After 5 wk, body weight gain of the HiFat (232.3 ± 7.8 g; P = 0.021) and HFS groups (228.0 ± 7.8; P = 0.039), but not the HiSuc group (220.3 ± 7.9; P = 0.244), were significantly higher than that of the control group (200.7 ± 5.4 g). In meal tolerance tests after 2 wk, GLP-1 concentration was significantly elevated in the HFS group only (17.2 ± 2.6 pM; P < 0.001) in response to meal ingestions, but the HiFat group (16.6 ± 3.7 pM; P = 0.156) had a similar response as the HFS group. After 4 wk, GLP-1 concentrations were similarly elevated at 15min in the HFS (14.1 ± 4.4; P = 0.010), HiFat (13.2 ± 2.0; P < 0.001), and HiSuc (13.0 ± 3.3; P = 0.016) groups, but the HFS (9.8 ± 1.0; P = 0.019) and HiFat (8.3 ± 1.5; P = 0.010) groups also had significant elevation at 30min.

CONCLUSIONS

These results demonstrate that the continuous ingestion of excessive fat and sucrose rapidly enhances the GLP-1 secretory response to luminal nutrients, and the HiFat diet may have a potent effect compared with the HiSuc diet on GLP-1 secretory responses. The increment of postprandial GLP-1 and insulinsecretion may have a role in normalizing postprandial glycaemia and slowing the establishment of glucose intolerance.

Purification of family B G protein-coupled receptors using nanodiscs: Application to human glucagon-like peptide-1 receptor

Family B G protein-coupled receptors (GPCRs) play vital roles in hormone-regulated homeostasis. They are drug targets for metabolic diseases, including type 2 diabetes and osteoporosis. Despite their importance, the signaling mechanisms for family B GPCRs at the molecular level remain largely unexplored due to the challenges in purification of functional receptors in sufficient amount for biophysical characterization. Here, we purified the family B GPCR human glucagon-like peptide-1 (GLP-1) receptor (GLP1R), whose agonists, e.g. exendin-4, are used for the treatment of type 2 diabetes mellitus. The receptor was expressed in HEK293S GnTl- cells using our recently developed protocol. The protocol incorporates the receptor into the native-like lipid environment of reconstituted high density lipoprotein (rHDL) particles, also known as nanodiscs, immediately after the membrane solubilization step followed by chromatographic purification, minimizing detergent contact with the target receptor to reduce denaturation and prolonging stabilization of receptor in lipid bilayers without extra steps of reconstitution. This method yielded purified GLP1R in nanodiscs that could bind to GLP-1 and exendin-4 and activate Gs protein. This nanodisc purification method can potentially be a general strategy to routinely obtain purified family B GPCRs in the 10s of microgram amounts useful for spectroscopic analysis of receptor functions and activation mechanisms.

Glucagon-Like Peptide 1: A Predictor of Type 2 Diabetes?

BACKGROUND

The incretin effect is impaired in patients with type 2 diabetes.

AIM

To assess the relation between the incretin hormone GLP-1 and the prediabetic subtypes: impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and the combined IFG/IGT to investigate whether a low GLP-1 response may be a predictor of prediabetes in adults.

METHOD

298 articles were found using a broad search phrase on the PubMed database and after the assessment of titles and abstracts 19 articles were included.

RESULTS AND DISCUSSION

Studies assessing i-IFG/IFG and i-IGT/IGT found both increased, unaltered, and reduced GLP-1 levels. Studies assessing IFG/IGT found unaltered or reduced GLP-1 levels. When assessing the five studies with the largest sample size, it clearly suggests a decreased GLP-1 response in IFG/IGT subjects. Several other factors (BMI, glucagon, age, and nonesterified fatty acids (NEFA)), including medications (metformin), may also influence the secretion of GLP-1.

CONCLUSION

This review suggests that the GLP-1 response is a variable in prediabetes possibly due to a varying GLP-1-secreting profile during the development and progression of type 2 diabetes or difference in the measurement technique. Longitudinal prospective studies are needed to assess whether a reduced GLP-1 response is a predictor of diabetes.

Bariatric surgery and diabetes remission: Who would have thought it?

Type 2 diabetes mellitus (T2DM) and obesity are increasingly common and major global health problems. The Edmonton obesity staging system clearly pointed towards increased mortality proportionate to the severity of obesity. Obesity itself triggers insulin resistance and thereby poses the risk of T2DM. Both obesity and T2DM have been associated with higher morbidity and mortality and this calls for institution of effective therapies to deal with the rising trend of complications arising out of this dual menace. Although lifestyle changes form the cornerstone of therapy for both the ailments, sustained results from this modalities is far from satisfactory. While Look AHEAD (action for HEAalth in diabetes) study showed significant weight loss, reduction in glycated hemoglobin and higher remission rate of T2DM at 1(st) year following intensive lifestyle measures; recurrence and relapse rate bounced back in half of subjects at 4 years, thereby indicating that weight loss and glycemic control is difficult to maintain in the long term with lifestyle interventions. Same recurrence phenomenon was also observed with pharmacotherapy with rimonabant, sibutramine and orlistat. Bariatric surgery has been seen to associate with substantial and sustained weight loss in morbidly obese patients. Interestingly, bariatric surgeries also induce higher rates of short and long-term diabetes remission. Although the exact mechanism behinds this diabetes remission are not well understood; improved insulin action, beta-cell function and complex interplay of hormones in the entero-insular axis appears to play a major role. This article reviews the effectiveness of bariatric procedures on remission or improvement in diabetes and put a perspective on its implicated mechanisms.

Bariatric surgery and diabetes remission: how far have we progressed?

Obesity and type 2 diabetes mellitus have been associated with higher morbidity and mortality. Bariatric surgery results in substantial and sustained weight loss in morbidly obese patients and improves obstructive sleep apnea. Furthermore, bariatric surgery improves diabetes control, hypertension, quality of life, stroke, myocardial infarction and reduces mortality. Interestingly, bariatric surgery induces high rates of short and long-term diabetes remission. While the exact mechanisms behind this are not completely understood, improved insulin action, β-cell function and a complex interplay of hormones in the entero-insular axis appear to play major roles. Insulin action improves proportionally to weight loss and it gets completely normalized especially after bilio-pancreatic diversion. β-Cell function also seems to improve after a variety of bariatric surgeries. Seemingly, baseline β-cell function is able to predict future diabetes remission. This article will review the effectiveness of bariatric procedures on the remission and improvement of diabetes and its implicated mechanisms.

Multiple Factors Related to the Secretion of Glucagon-Like Peptide-1

The glucagon-like peptide-1 is secreted by intestinal L cells in response to nutrient ingestion. It regulates the secretion and sensitivity of insulin while suppressing glucagon secretion and decreasing postprandial glucose levels. It also improves beta-cell proliferation and prevents beta-cell apoptosis induced by cytotoxic agents. Additionally, glucagon-like peptide-1 delays gastric emptying and suppresses appetite. The impaired secretion of glucagon-like peptide-1 has negative influence on diabetes, hyperlipidemia, and insulin resistance related diseases. Thus, glucagon-like peptide-1-based therapies (glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors) are now well accepted in the management of type 2 diabetes. The levels of glucagon-like peptide-1 are influenced by multiple factors including a variety of nutrients. The component of a meal acts as potent stimulants of glucagon-like peptide-1 secretion. The levels of its secretion change with the intake of different nutrients. Some drugs also have influence on GLP-1 secretion. Bariatric surgery may improve metabolism through the action on GLP-1 levels. In recent years, there has been a great interest in developing effective methods to regulate glucagon-like peptide-1 secretion. This review summarizes the literature on glucagon-like peptide-1 and related factors affecting its levels.