Secretion of glucagon-like peptide-1 in patients with type 2 diabetes mellitus: systematic review and meta-analyses of clinical studies

Zein nanoparticles extend lifespan in C. elegans and SAMP8 mice

Empty zein nanoparticles (NP) have been shown to lower glycemia in rats by stimulating the secretion of endogenous GLP-1. This study evaluated the effect of these nanoparticles on the lifespan of two animal models: C. elegans fed with a glucose-rich diet and the senescence accelerated mouse-prone 8 (SAMP8 mice). In C. elegans, NP increased the mean lifespan of worms by 7 days (from 17.1 for control to 24.5 days). This observation was in line with the observed significant reductions of glucose and fat contents, lipofuscin accumulation, and ROS expression. Furthermore, NP supplementation led to an upregulation of the expression of daf-16 and skn-1 genes. DAF-16 (orthologue of the FOXO family) and SKN-1 (orthologue of mammalian Nrf/CNC proteins) are implicated in activating detoxification mechanisms against oxidative damage. In SAMP8, oral administration of NP also extended the mean lifespan of mice (by 28 % compared to controls), corroborating the protective effect of these nanoparticles.

The Association of Cardiometabolic, Diet and Lifestyle Parameters With Plasma Glucagon-like Peptide-1: An IMI DIRECT Study

CONTEXT

The role of glucagon-like peptide-1 (GLP-1) in type 2 diabetes (T2D) and obesity is not fully understood.

OBJECTIVE

We investigate the association of cardiometabolic, diet, and lifestyle parameters on fasting and postprandial GLP-1 in people at risk of, or living with, T2D.

METHODS

We analyzed cross-sectional data from the two Innovative Medicines Initiative (IMI) Diabetes Research on Patient Stratification (DIRECT) cohorts, cohort 1 (n = 2127) individuals at risk of diabetes; cohort 2 (n = 789) individuals with new-onset T2D.

RESULTS

Our multiple regression analysis reveals that fasting total GLP-1 is associated with an insulin-resistant phenotype and observe a strong independent relationship with male sex, increased adiposity, and liver fat, particularly in the prediabetes population. In contrast, we showed that incremental GLP-1 decreases with worsening glycemia, higher adiposity, liver fat, male sex, and reduced insulin sensitivity in the prediabetes cohort. Higher fasting total GLP-1 was associated with a low intake of wholegrain, fruit, and vegetables in people with prediabetes, and with a high intake of red meat and alcohol in people with diabetes.

CONCLUSION

These studies provide novel insights into the association between fasting and incremental GLP-1, metabolic traits of diabetes and obesity, and dietary intake, and raise intriguing questions regarding the relevance of fasting GLP-1 in the pathophysiology T2D.

The impact of GLP-1 signalling on the energy metabolism of pancreatic islet β-cells and extrapancreatic tissues

Glucagon-like peptide-1 signalling impacts glucose homeostasis and appetite thereby indirectly affecting substrate availability at the whole-body level. The incretin canonically produces an insulinotropic effect, thereby lowering blood glucose levels by promoting the uptake and inhibiting the production of the sugar by peripheral tissues. Likewise, GLP-1 signalling within the central nervous system reduces the appetite and food intake, whereas its gastric effect delays the absorption of nutrients, thus improving glycaemic control and reducing the risk of postprandial hyperglycaemia. We review the molecular aspects of the GLP-1 signalling, focusing on its impact on intracellular energy metabolism. Whilst the incretin exerts its effects predominantly via a Gs receptor, which decodes the incretin signal into the elevation of intracellular cAMP levels, the downstream signalling cascades within the cell, acting on fast and slow timescales, resulting in an enhancement or an attenuation of glucose catabolism, respectively.

Mechanisms of action and therapeutic applications of GLP-1 and dual GIP/GLP-1 receptor agonists

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are two incretins that bind to their respective receptors and activate the downstream signaling in various tissues and organs. Both GIP and GLP-1 play roles in regulating food intake by stimulating neurons in the brain's satiety center. They also stimulate insulin secretion in pancreatic β-cells, but their effects on glucagon production in pancreatic α-cells differ, with GIP having a glucagonotropic effect during hypoglycemia and GLP-1 exhibiting glucagonostatic effect during hyperglycemia. Additionally, GIP directly stimulates lipogenesis, while GLP-1 indirectly promotes lipolysis, collectively maintaining healthy adipocytes, reducing ectopic fat distribution, and increasing the production and secretion of adiponectin from adipocytes. Together, these two incretins contribute to metabolic homeostasis, preventing both hyperglycemia and hypoglycemia, mitigating dyslipidemia, and reducing the risk of cardiovascular diseases in individuals with type 2 diabetes and obesity. Several GLP-1 and dual GIP/GLP-1 receptor agonists have been developed to harness these pharmacological effects in the treatment of type 2 diabetes, with some demonstrating robust effectiveness in weight management and prevention of cardiovascular diseases. Elucidating the underlying cellular and molecular mechanisms could potentially usher in the development of new generations of incretin mimetics with enhanced efficacy and fewer adverse effects. The treatment guidelines are evolving based on clinical trial outcomes, shaping the management of metabolic and cardiovascular diseases.

The Potential Mechanism of Remission in Type 2 Diabetes Mellitus After Vertical Sleeve Gastrectomy

In recent years, there has been a gradual increase in the prevalence of obesity and type 2 diabetes mellitus (T2DM), with bariatric surgery remaining the most effective treatment strategy for these conditions. Vertical sleeve gastrectomy (VSG) has emerged as the most popular surgical procedure for bariatric/metabolic surgeries, effectively promoting weight loss and improving or curing T2DM. The alterations in the gastrointestinal tract following VSG may improve insulin secretion and resistance by increasing incretin secretion (especially GLP-1), modifying the gut microbiota composition, and through mechanisms dependent on weight loss. This review focuses on the potential mechanisms through which the enhanced action of incretin and metabolic changes in the digestive system after VSG may contribute to the remission of T2DM.

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.

Tirzepatide: A novel cardiovascular protective agent in type 2 diabetes mellitus and obesity

Cardiovascular disease (CVD) remains a major global health concern, and obesity and diabetes mellitus have been found to be important risk factors. Tirzepatide a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP1) receptor agonist has been shown to have cardioprotective effects. Noteworthy benefits of Tirzepatide include decreased cardiovascular risk factors in people with Type 2 diabetes mellitus (T2DM). In the SURPASS-4 trial, tirzepatide significant decreased blood pressure, body weight, and HbA1c. Furthermore, the SURMOUNT-1 trial demonstrated the effectiveness of tirzepatide in reducing cardiometabolic risk factors in people with obesity without T2DM. Together, the dual receptor agonism improves lipid profiles, increases insulin secretion, reduces inflammation, and promotes endothelial integrity. Tirzepatide shows promise as a comprehensive therapeutic option for managing cardiovascular risk factors in patients with T2DM and obesity. While further studies are needed to assess the long-term cardiovascular benefits, current evidence supports tirzepatide's potential impact on cardiovascular health beyond its antidiabetic properties.

Timosaponin A3 Induces Anti-Obesity and Anti-Diabetic Effects In Vitro and In Vivo

Obesity is a serious global health challenge, closely associated with numerous chronic conditions including type 2 diabetes. Anemarrhena asphodeloides Bunge (AA) known as Jimo has been used to address conditions associated with pathogenic heat such as wasting-thirst in Korean Medicine. Timosaponin A3 (TA3), a natural compound extracted from AA, has demonstrated potential therapeutic effects in various disease models. However, its effects on diabetes and obesity remain largely unexplored. We investigated the anti-obesity and anti-diabetic properties of TA3 using in vitro and in vivo models. TA3 treatment in NCI-H716 cells stimulated the secretion of glucagon-like peptide 1 (GLP-1) through the activation of phosphorylation of protein kinase A catalytic subunit (PKAc) and 5'-AMP-activated protein kinase (AMPK). In 3T3-L1 adipocytes, TA3 effectively inhibited lipid accumulation by regulating adipogenesis and lipogenesis. In a high-fat diet (HFD)-induced mice model, TA3 administration significantly reduced body weight gain and food intake. Furthermore, TA3 improved glucose tolerance, lipid profiles, and mitigated hepatic steatosis in HFD-fed mice. Histological analysis revealed that TA3 reduced the size of white adipocytes and inhibited adipose tissue generation. Notably, TA3 downregulated the expression of lipogenic factor, including fatty-acid synthase (FAS) and sterol regulatory element-binding protein 1c (SREBP1c), emphasizing its potential as an anti-obesity agent. These findings revealed that TA3 may be efficiently used as a natural compound for tackling obesity, diabetes, and associated metabolic disorders, providing a novel approach for therapeutic intervention.

Isomaltulose Enhances GLP-1 and PYY Secretion to a Mixed Meal in People With or Without Type 2 Diabetes as Compared to Saccharose

SCOPE

Secretion of the gut hormones glucagon-like peptide (GLP-1) and peptide YY (PYY) are induced by nutrients reaching the lower small intestine which regulate insulin and glucagon release, inhibit appetite, and may improve β-cell regeneration. The aim is to test the effect of a slowly digested isomaltulose (ISO) compared to the rapidly digested saccharose (SAC) as a snack given 1 h before a standardized mixed meal test (MMT) on GLP-1, PYY, glucose-dependent insulinotropic peptide (GIP), and metabolic responses in participants with or without type 2 diabetes (T2DM).

METHODS AND RESULTS

Fifteen healthy volunteers and 15 patients with T2DM consumed either 50 g ISO or SAC 1 h preload of MMT on nonconsecutive days. Clinical parameters and incretin hormones are measured throughout the whole course of MMT. Administration of 50 g ISO as compared to SAC induced a significant increase in GLP-1, GIP, and PYY responses over 2 h after intake of a typical lunch in healthy controls. Patients with T2DM showed reduced overall responses of GLP-1 and delayed insulin release compared to controls while ISO significantly enhanced the GIP and almost tripled the PYY response compared to SAC.

CONCLUSION

A snack containing ISO markedly enhances the release of the metabolically advantageous gut hormones PYY and GLP-1 and enhances GIP release in response to a subsequent complex meal.

The Road towards Triple Agonists: Glucagon-Like Peptide 1, Glucose-Dependent Insulinotropic Polypeptide and Glucagon Receptor - An Update

Obesity is the fifth leading risk factor for global deaths with numbers continuing to increase worldwide. In the last 20 years, the emergence of pharmacological treatments for obesity based on gastrointestinal hormones has transformed the therapeutic landscape. The successful development of glucagon-like peptide-1 (GLP-1) receptor agonists, followed by the synergistic combined effect of glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonists achieved remarkable weight loss and glycemic control in those with the diseases of obesity and type 2 diabetes. The multiple cardiometabolic benefits include improving glycemic control, lipid profiles, blood pressure, inflammation, and hepatic steatosis. The 2023 phase 2 double-blind, randomized controlled trial evaluating a GLP-1/GIP/glucagon receptor triagonist (retatrutide) in patients with the disease of obesity reported 24.2% weight loss at 48 weeks with 12 mg retatrutide. This review evaluates the current available evidence for GLP-1 receptor agonists, dual GLP-1/GIP receptor co-agonists with a focus on GLP-1/GIP/glucagon receptor triagonists and discusses the potential future benefits and research directions.

Nutrient Combinations Sensed by L-Cell Receptors Potentiate GLP-1 Secretion

Obesity is a risk factor for cardiometabolic diseases. Nutrients stimulate GLP-1 release; however, GLP-1 has a short half-life (<2 min), and only <10-15% reaches the systemic circulation. Human L-cells are localized in the distal ileum and colon, while most nutrients are absorbed in the proximal intestine. We hypothesized that combinations of amino acids and fatty acids potentiate GLP-1 release via different L-cell receptors. GLP-1 secretion was studied in the mouse enteroendocrine STC-1 cells. Cells were pre-incubated with buffer for 1 h and treated with nutrients: alpha-linolenic acid (αLA), phenylalanine (Phe), tryptophan (Trp), and their combinations αLA+Phe and αLA+Trp with dipeptidyl peptidase-4 (DPP4) inhibitor. After 1 h GLP-1 in supernatants was measured and cell lysates taken for qPCR. αLA (12.5 µM) significantly stimulated GLP-1 secretion compared with the control. Phe (6.25-25 mM) and Trp (2.5-10 mM) showed a clear dose response for GLP-1 secretion. The combination of αLA (6.25 µM) and either Phe (12.5 mM) or Trp (5 mM) significantly increased GLP-1 secretion compared with αLA, Phe, or Trp individually. The combination of αLA and Trp upregulated GPR120 expression and potentiated GLP-1 secretion. These nutrient combinations could be used in sustained-delivery formulations to the colon to prolong GLP-1 release for diminishing appetite and preventing obesity.

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.

Mendelian randomization analyses suggest a causal role for circulating GIP and IL-1RA levels in homeostatic model assessment-derived measures of β-cell function and insulin sensitivity in Africans without type 2 diabetes

BACKGROUND

In vitro and in vivo studies have shown that certain cytokines and hormones may play a role in the development and progression of type 2 diabetes (T2D). However, studies on their role in T2D in humans are scarce. We evaluated associations between 11 circulating cytokines and hormones with T2D among a population of sub-Saharan Africans and tested for causal relationships using Mendelian randomization (MR) analyses.

METHODS

We used logistic regression analysis adjusted for age, sex, body mass index, and recruitment country to regress levels of 11 cytokines and hormones (adipsin, leptin, visfatin, PAI-1, GIP, GLP-1, ghrelin, resistin, IL-6, IL-10, IL-1RA) on T2D among Ghanaians, Nigerians, and Kenyans from the Africa America Diabetes Mellitus study including 2276 individuals with T2D and 2790 non-T2D individuals. Similar linear regression models were fitted with homeostatic modelling assessments of insulin sensitivity (HOMA-S) and β-cell function (HOMA-B) as dependent variables among non-T2D individuals (n = 2790). We used 35 genetic variants previously associated with at least one of these 11 cytokines and hormones among non-T2D individuals as instrumental variables in univariable and multivariable MR analyses. Statistical significance was set at 0.0045 (0.05/11 cytokines and hormones).

RESULTS

Circulating GIP and IL-1RA levels were associated with T2D. Nine of the 11 cytokines and hormones (exceptions GLP-1 and IL-6) were associated with HOMA-S, HOMA-B, or both among non-T2D individuals. Two-stage least squares MR analysis provided evidence for a causal effect of GIP and IL-RA on HOMA-S and HOMA-B in multivariable analyses (GIP ~ HOMA-S β =  - 0.67, P-value = 1.88 × 10-6 and HOMA-B β = 0.59, P-value = 1.88 × 10-5; IL-1RA ~ HOMA-S β =  - 0.51, P-value = 8.49 × 10-5 and HOMA-B β = 0.48, P-value = 5.71 × 10-4). IL-RA was partly mediated via BMI (30-34%), but GIP was not. Inverse variance weighted MR analysis provided evidence for a causal effect of adipsin on T2D (multivariable OR = 1.83, P-value = 9.79 × 10-6), though these associations were not consistent in all sensitivity analyses.

CONCLUSIONS

The findings of this comprehensive MR analysis indicate that circulating GIP and IL-1RA levels are causal for reduced insulin sensitivity and increased β-cell function. GIP's effect being independent of BMI suggests that circulating levels of GIP could be a promising early biomarker for T2D risk. Our MR analyses do not provide conclusive evidence for a causal role of other circulating cytokines in T2D among sub-Saharan Africans.

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.

Glucagon-Like Peptide-1 Receptor Agonists for Chronic Weight Management

Rates of obesity have risen over the past few decades. Subsequently, the popularity of the pharmaceutical weight-loss drug market has grown over the past few years to meet growing demand. Among the most commonly prescribed drugs for weight management, many are glucagon-like peptide-1 receptor agonists (GLP-1 agonists) which are also utilized for the management of type 2 diabetes. There is a substantial and growing body of research comparing the efficacy of different clinical trials and examining long-term safety. This literature review examines the rise of off-label prescribing practices in the management of weight, with a focus on GLP-1 agonists. Physicians and patients should be aware of the unique aspects of existing treatment options, the impacts of off-label prescribing, and the effects of these medications. This review emphasizes the importance of informed decision-making, as well as the need for further research to guide future clinical practice.

Diabetes and fatty liver: Involvement of incretin and its benefit for fatty liver management

Fatty liver disease is defined as liver condition characterized by hepatic steatosis, closely related to pathological conditions in type 2 diabetes and obesity. The high prevalence of fatty liver disease in obese patients with type 2 diabetes reached 70%, reflecting the importance of these conditions with fatty liver. Although the exact pathological mechanism of fatty liver disease, specifically non-alcoholic fatty liver disease (NAFLD) remains not completely revealed, insulin resistance is suggested as the major mechanism that bridged the development of NAFLD. Indeed, loss of the incretin effect leads to insulin resistance. Since incretin is closely related to insulin resistance and the resistance of insulin associated with the development of fatty liver disease, this pathway suggested a potential me-chanism that explains the association between type 2 diabetes and NAFLD. Furthermore, recent studies indicated that NAFLD is associated with impaired glucagon-like peptide-1, resulting in decreased incretin effect. Nevertheless, improving the incretin effect becomes a reasonable approach to manage fatty liver disease. This review elucidates the involvement of incretin in fatty liver disease and recent studies of incretin as the management for fatty liver disease.

Tirzepatide: A Promising Drug for Type 2 Diabetes and Beyond

Tirzepatide is a promising drug with dual-acting glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) receptor activation that has revolutionized the treatment of type 2 diabetes mellitus (T2DM) as an adjunct to diet and exercise. In phase 3 clinical trials (SURPASS 1-5), the dose-dependent efficacy and safety of tirzepatide were assessed by once-weekly subcutaneous injection (5 mg, 10 mg, and 15 mg), as monotherapy or combination therapy, in individuals with T2DM. Tirzepatide has been shown to achieve better glycemic control in terms of glycosylated hemoglobin reduction and improved fasting and postprandial glucose levels as compared to other diabetic medications. Moreover, the studies demonstrate a reduction in body weight (-6.2 to -12.9 kg), and other cardiovascular benefits by altering the lipid profile, reducing blood pressure, and visceral adiposity. Tirzepatide has acceptable side effects and is well tolerated, with a low risk of hypoglycemia. The SURPASS 4 clinical trial has shown positive cardiovascular outcomes in people with T2DM and elevated cardiovascular risk. Additionally, encouraging results from SURMOUNT trials and ongoing SURPASS-CVOT studies will shed more light on cardiovascular safety in the future. In this review, we have summarized the clinical trials and their respective outcomes and highlighted the potential future indications for tirzepatide in the management of obesity, heart failure, and nonalcoholic steatohepatitis.

Circulating glucagon-like peptide-1 level in patients with liver cirrhosis

BACKGROUND

Glucagon-like peptide-1 (GLP-1), a gut-derived incretin hormone, plays a pivotal role in glucose-induced insulin secretion. Currently, the role of incretin hormones in the pathogenesis of cirrhosis is not clearly defined. This study aimed to investigate circulating levels of GLP-1 in liver cirrhosis and its association with the severity of liver disease.

METHODS

A total of 80 participants including 39 patients with a definite diagnosis of liver cirrhosis and 41 healthy controls recruited in this cross-sectional study. Circulating levels of GLP-1 were determined using the ELISA method. The severity of liver cirrhosis was assessed according to the Child-Pugh, MELD (i), MELD-Na, MELD New, and UK end-stage liver disease score (UKELD) criteria.

RESULTS

The mean age of patients and healthy subjects was 42.51 ± 12.80 and 42.07 ± 10.92 years, respectively (p value = .869). The mean MELD (i), MELD-Na, MELD New, UKELD, and Child-Pugh scores were 14.36 ± 4.26, 15.26 ± 4.81, 14.74 ± 4.66, 52.33 ± 3.82, and 7.28 ± 1.50, respectively. In this study, circulating levels of GLP-1 were statistically lower in cirrhotic patients compared with healthy controls (95.26 ± 17.15 vs 111.84 ± 38.14 pg/mL; p value = .017).

CONCLUSION

Larger prospective studies are needed to explore the incretin effect in cirrhosis patients compared with healthy individuals.

Circulating levels of gastrointestinal hormones in prediabetes reversing to normoglycemia or progressing to diabetes in a year-A cross-sectional and prospective analysis

AIMS

We aimed to compare the concentrations of GLP-1, glucagon and GIP (established regulators of glucose homeostasis) and glicentin (emerging new metabolic marker)during an OGTT in patients with normal glucose tolerance (NGT), prediabetes and diabetes at onset, and one-year before, when all had prediabetes.

METHODS

GLP-1, glucagon, GIP and glicentin concentrations were measured and compared with markers of body composition, insulin sensitivity and β-cell function at a 5-timepoint OGTT in 125 subjects (30 diabetes, 65 prediabetes, 30 NGT) and in 106 of them one-year before, when all had prediabetes.

RESULTS

At baseline, when all subjects were in prediabetic state, hormonal levels did not differ between groups. One year later, patients progressing to diabetes had lower postprandial increases of glicentin and GLP-1, lower postprandial decrease of glucagon, and higher levels of fasting GIP compared to patients regressing to NGT. Changes in glicentin and GLP-1 AUC within this year correlated negatively with changes in Glucose AUC of OGTT and with changes in markers of beta cell function.

CONCLUSION

Incretins, glucagon and glicentin profiles in prediabetic state cannot predict future glycemic traits, but prediabetes progressing to diabetes is accompanied by deterioration of postprandial increases of GLP-1 and glicentin.

Glucagon-like peptide-1 secretion in people with versus without type 2 diabetes: a systematic review and meta-analysis of cross-sectional studies

AIMS/HYPOTHESIS

The aim of this systematic review was to synthesise the study findings on whether GLP-1 secretion in response to a meal tolerance test is affected by the presence of type 2 diabetes (T2D). The influence of putative moderators such as age, sex, meal type, meal form, and assay type were also explored.

METHODS

A literature search identified 32 relevant studies. The sample mean and SD for fasting GLP-1TOTAL and GLP-1TOTAL iAUC were extracted and used to calculate between-group standardised mean differences (SMD), which were meta-analysed using a random-effects model to derive pooled estimates of Hedges' g and 95 % prediction intervals (PI).

RESULTS

Pooled across 18 studies, the overall SMD in GLP-1TOTAL iAUC between individuals with T2D (n = 270, 1047 ± 930 pmol·L-1·min) and individuals without T2D (n = 402, 1204 ± 937 pmol·L-1·min) was very small, not statistically significant and heterogenous across studies (g = -0.15, p = 0.43, PI: -1.53, 1.23). Subgroup analyses demonstrated an effect of assay type whereby Hedges' g for GLP-1 iAUC was greater in individuals with, versus those without T2D when using ELISA or Mesoscale (g = 0.67 [moderate], p = 0.009), but not when using RIA (g = -0.30 [small], p = 0.10). Pooled across 30 studies, the SMD in fasting GLP-1TOTAL between individuals with T2D (n = 580, 16.2 ± 6.9 pmol·L-1) versus individuals without T2D (n = 1363, 12.4 ± 5.7 pmol·L-1) was small and heterogenous between studies (g = 0.24, p = 0.21, PI: -1.55, 2.02).

CONCLUSIONS

Differences in fasting GLP-1TOTAL and GLP-1TOTAL iAUC between individuals with, versus those without T2D were generally small and inconsistent between studies. Factors influencing study heterogeneity such as small sample sizes and poor matching of groups may help to explain the wide prediction intervals observed. Considerations to improve comparisons of GLP-1 secretion in T2D and potential mediating factors more important than T2D diagnosis per se are outlined.

PROSPERO ID

CRD42020195612.

The Effect of Non-Nutritive Sweetened Beverages on Postprandial Glycemic and Endocrine Responses: A Systematic Review and Network Meta-Analysis

Background: There has been an emerging concern that non-nutritive sweeteners (NNS) can increase the risk of cardiometabolic disease. Much of the attention has focused on acute metabolic and endocrine responses to NNS. To examine whether these mechanisms are operational under real-world scenarios, we conducted a systematic review and network meta-analysis of acute trials comparing the effects of non-nutritive sweetened beverages (NNS beverages) with water and sugar-sweetened beverages (SSBs) in humans. Methods: MEDLINE, EMBASE, and The Cochrane Library were searched through to January 15, 2022. We included acute, single-exposure, randomized, and non-randomized, clinical trials in humans, regardless of health status. Three patterns of intake were examined: (1) uncoupling interventions, where NNS beverages were consumed alone without added energy or nutrients; (2) coupling interventions, where NNS beverages were consumed together with added energy and nutrients as carbohydrates; and (3) delayed coupling interventions, where NNS beverages were consumed as a preload prior to added energy and nutrients as carbohydrates. The primary outcome was a 2 h incremental area under the curve (iAUC) for blood glucose concentration. Secondary outcomes included 2 h iAUC for insulin, glucagon-like peptide 1 (GLP-1), gastric inhibitory polypeptide (GIP), peptide YY (PYY), ghrelin, leptin, and glucagon concentrations. Network meta-analysis and confidence in the network meta-analysis (CINeMA) were conducted in R-studio and CINeMA, respectively. Results: Thirty-six trials involving 472 predominantly healthy participants were included. Trials examined a variety of single NNS (acesulfame potassium, aspartame, cyclamate, saccharin, stevia, and sucralose) and NNS blends (acesulfame potassium + aspartame, acesulfame potassium + sucralose, acesulfame potassium + aspartame + cyclamate, and acesulfame potassium + aspartame + sucralose), along with matched water/unsweetened controls and SSBs sweetened with various caloric sugars (glucose, sucrose, and fructose). In uncoupling interventions, NNS beverages (single or blends) had no effect on postprandial glucose, insulin, GLP-1, GIP, PYY, ghrelin, and glucagon responses similar to water controls (generally, low to moderate confidence), whereas SSBs sweetened with caloric sugars (glucose and sucrose) increased postprandial glucose, insulin, GLP-1, and GIP responses with no differences in postprandial ghrelin and glucagon responses (generally, low to moderate confidence). In coupling and delayed coupling interventions, NNS beverages had no postprandial glucose and endocrine effects similar to controls (generally, low to moderate confidence). Conclusions: The available evidence suggests that NNS beverages sweetened with single or blends of NNS have no acute metabolic and endocrine effects, similar to water. These findings provide support for NNS beverages as an alternative replacement strategy for SSBs in the acute postprandial setting.

Incretin and Pancreatic β-Cell Function in Patients with Type 2 Diabetes

To maintain normal glucose homeostasis after a meal, it is essential to secrete an adequate amount of insulin from pancreatic β-cells. However, if pancreatic β-cells solely depended on the blood glucose level for insulin secretion, a surge in blood glucose levels would be inevitable after the ingestion of a large amount of carbohydrates. To avoid a deluge of glucose in the bloodstream after a large carbohydrate- rich meal, enteroendocrine cells detect the amount of nutrient absorption from the gut lumen and secrete incretin hormones at scale. Since insulin secretion in response to incretin hormones occurs only in a hyperglycemic milieu, pancreatic β-cells can secrete a "Goldilocks" amount of insulin (i.e., not too much and not too little) to keep the blood glucose level in the normal range. In this regard, pancreatic β-cell sensitivity to glucose and incretin hormones is crucial for maintaining normal glucose homeostasis. In this Namgok lecture 2022, we review the effects of current anti-diabetic medications on pancreatic β-cell sensitivity to glucose and incretin hormones.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 secretion in humans: Characteristics and regulation

AIMS/INTRODUCTION

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are important incretin hormones. They are released from the gut after meal ingestion and potentiate glucose-stimulated insulin secretion. Their release after meal ingestion and oral glucose are well established and have been characterized previously. During recent years, knowledge of other regulatory aspects that potentially may affect GIP and GLP-1 secretion after meal ingestion have also begun to emerge. Here, the results of human studies on these novel aspects of meal- and nutrient-stimulated incretin hormone secretion are reviewed.

MATERIALS AND METHODS

The human literature was revisited by identifying articles in PubMed using key words GIP, GLP-1, secretion, meal, and nutrients.

RESULTS

The results show that all macronutrients individually stimulate GIP and GLP-1 secretion. However, there was no synergistic action when given in combination. A pre-load 30 min before a meal augments the GIP and GLP-1 response. GIP and GLP-1 secretion have a diurnal variation with a higher response to an identical meal in the morning than in the afternoon. There is no difference in GIP and GLP-1 secretion whether a meal is ingested slowly or rapidly. GIP and GLP-1 secretion after dinner are the same whether or not breakfast and lunch have been ingested. The temperature of the food may be of importance for the incretin hormone response.

CONCLUSIONS

These novel findings have increased our knowledge on the regulation of the complexity of the incretin system and are also important knowledge when designing future studies.

Pharmacotherapy of type 2 diabetes: An update and future directions

Type 2 diabetes (T2D) is a widely prevalent disease with substantial economic and social impact for which multiple conventional and novel pharmacotherapies are currently available; however, the landscape of T2D treatment is constantly changing as new therapies emerge and the understanding of currently available agents deepens. This review aims to provide an updated summary of the pharmacotherapeutic approach to T2D. Each class of agents is presented by mechanism of action, details of administration, side effect profile, cost, and use in certain populations including heart failure, non-alcoholic fatty liver disease, obesity, chronic kidney disease, and older individuals. We also review targets of novel therapeutic T2D agent development. Finally, we outline an up-to-date treatment approach that starts with identification of an individualized goal for glycemic control then selection, initiation, and further intensification of a personalized therapeutic plan for T2D.

Endogenous GLP-1 levels play an important role in determining the efficacy of DPP-IV Inhibitors in both prediabetes and type 2 diabetes

Background

In contrast to Western population, glucagon-like peptide-1 (GLP-1) levels are preserved in some East Asian population with type 2 diabetes (T2D), explaining why dipeptidyl peptidase-IV (DPP-IV) inhibitors are more effective in East Asians. We assessed whether differences in endogenous GLP-1 levels resulted in different treatment responses to DPP-IV inhibitors in prediabetes and T2D.

Methods

A prospective 12-week study using linagliptin 5mg once daily in 50 subjects (28 prediabetes and 22 T2D) who were stratified into high versus low fasting GLP-1 groups. A 75-g oral glucose tolerance test (OGTT) was performed at week 0 and 12. Primary outcomes were changes in HbA1c, fasting and post-OGTT glucose after 12 weeks. Secondary outcomes included changes in insulin resistance and beta cell function indices.

Results

There was a greater HbA1c reduction in subjects with high GLP-1 compared to low GLP-1 levels in both the prediabetes and T2D populations [least-squares mean (LS-mean) change of -0.33% vs. -0.11% and -1.48% vs. -0.90% respectively)]. Linagliptin significantly reduced glucose excursion by 18% in high GLP-1 compared with 8% in low GLP-1 prediabetes groups. The reduction in glucose excursion was greater in high GLP-1 compared to low GLP-1 T2D by 30% and 21% respectively. There were significant LS-mean between-group differences in fasting glucose (-0.95 mmol/L), 2-hour glucose post-OGTT (-2.4 mmol/L) in the high GLP-1 T2D group. Improvement in insulin resistance indices were seen in the high GLP-1 T2D group while high GLP-1 prediabetes group demonstrated improvement in beta cell function indices. No incidence of hypoglycemia was reported.

Conclusions

Linagliptin resulted in a greater HbA1c reduction in the high GLP-1 prediabetes and T2D compared to low GLP-1 groups. Endogenous GLP-1 level play an important role in determining the efficacy of DPP-IV inhibitors irrespective of the abnormal glucose tolerance states.

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.

Glucagon and other proglucagon-derived peptides in the pathogenesis of obesity

Because of differential processing of the hormone precursor, proglucagon, numerous peptide products are released from the pancreatic alpha cells and the intestinal L-cells in which the (pro)glucagon gene is expressed. Of particular interest in relation to obesity are glucagon from the pancreas and oxyntomodulin and GLP-1 from the gut, all of which inhibit food intake, but the other products are also briefly discussed, because knowledge about these is required for selection and evaluation of the methods for measurement of the hormones. The distal intestinal L-cells also secrete the appetite-inhibiting hormone PYY. Characteristics of the secretion of the pancreatic and intestinal products are described, and causes of the hypersecretion of glucagon in obesity and type 2 diabetes are discussed. In contrast, the secretion of the products of the L-cells is generally impaired in obesity, raising questions about their role in the development of obesity. It is concluded that the impairment probably is secondary to obesity, but the lower plasma levels may contribute to the development.

Glucagon-like Peptide-1 Secretion Is Inhibited by Lysophosphatidic Acid

Glucagon-like peptide-1 (GLP-1) potentiates glucose-stimulated insulin secretion (GSIS). While dozens of compounds stimulate GLP-1 secretion, few inhibit. Reduced GLP-1 secretion and impaired GSIS occur in chronic inflammation. Lysophosphatidic acids (LPAs) are bioactive phospholipids elevated in inflammation. The aim of this study was to test whether LPA inhibits GLP-1 secretion in vitro and in vivo. GLUTag L-cells were treated with various LPA species, with or without LPA receptor (LPAR) antagonists, and media GLP-1 levels, cellular cyclic AMP and calcium ion concentrations, and DPP4 activity levels were analyzed. Mice were injected with LPA, with or without LPAR antagonists, and serum GLP-1 and DPP4 activity were measured. GLUTag GLP-1 secretion was decreased ~70–90% by various LPAs. GLUTag expression of Lpar1, 2, and 3 was orders of magnitude higher than Lpar4, 5, and 6, implicating the former group in this effect. In agreement, inhibition of GLP-1 secretion was reversed by the LPAR1/3 antagonist Ki16425, the LPAR1 antagonists AM095 and AM966, or the LPAR2 antagonist LPA2-antagonist 1. We hypothesized involvement of Gαi-mediated LPAR activity, and found that intracellular cyclic AMP and calcium ion concentrations were decreased by LPA, but restored by Ki16425. Mouse LPA injection caused an ~50% fall in circulating GLP-1, although only LPAR1 or LPAR1/3 antagonists, but not LPAR2 antagonism, prevented this. GLUTag L-cell and mouse serum DPP4 activity was unchanged by LPA or LPAR antagonists. LPA therefore impairs GLP-1 secretion in vitro and in vivo through Gαi-coupled LPAR1/3 signaling, providing a new mechanism linking inflammation with impaired GSIS.

Circulating GLP-1 Levels in Patients with Pheochromocytoma/Paraganglioma

The sympathoadrenal system has been shown to stimulate the secretory activity of enteroendocrine cells, although the response is transient. Our aim was to investigate the effects of long-term catecholamine excess on circulating glucagon-likepeptide-1 (GLP-1) levels in patients with pheochromocytoma/paraganglioma (PPGL). Thirty patients diagnosed with PPGL were analyzed. A significant negative association was observed between fasting plasma GLP-1 levels and elevated plasma-free metanephrine (r = -0.407, p = 0.026). After adjustment for age, sex, body mass index (BMI), serum creatinine, and the presence of hyperglycemia, the negative association between plasma GLP-1 and metanephrine persisted by multiple linear regression analysis (β = -0.493, p = 0.013). Positive correlations between fasting glucose and plasma metanephrine (r = 0.380, p = 0.038) and normetanephrine levels (r = 0.450, p = 0.013) were also found. Mean fasting levels of total GLP-1 increased significantly from 25.81 to 39.01 pmol/L (p = 0.017) after PPGL resection. In conclusion, long-term overproduction of catecholamines appears to induce suppression of GLP-1 production compared to an acute response to a stress stimulus. Further studies are required to elucidate the mechanism of GLP-1 secretion with chronic exposure to catecholamine.

A perspective on the benefits of consumption of parboiled rice over brown rice for glycaemic control

PURPOSE

Rice is a staple food for over 3.5 billion people worldwide. The nutritional content of rice varies with different post-harvest processing techniques. Major varieties include brown rice (BR), white rice (WR) and parboiled rice (PBR). While consumption of BR is advocated due to its higher nutritional content compared to other varieties, some studies have indicated lower post-prandial blood glucose (PPBG) levels when PBR is consumed. This apparent benefit of PBR consumption is not well publicised and no commentaries on underlying mechanisms are available in literature.

METHODS

In this review, we looked into differential nutrient content of PBR, as compared to BR and WR, and tried to understand how their consumption could be associated with glycaemic control. Various roles played by these nutrients in mechanisms of insulin secretion, insulin resistance, nutrient absorption and T2DM-associated inflammation were reviewed from literature-based evidence.

RESULTS

We report differential nutritional factors in PBR, with respect to BR (and WR), such as higher calcium and selenium content, lower phytic acids, and enriched vitamin B6 which might aid PBR's ability to provide better glycaemic control than BR.

CONCLUSION

Our interpretation of reviewed literature leads us to suggest the possible benefits of PBR consumption in glycaemic control and its inclusion as the preferred rice variant in diets of T2DM patients and at-risk individuals.

Incretin Hormones: Pathophysiological Risk Factors and Potential Targets for Type 2 Diabetes

Type 2 diabetes (T2D) is a multifaceted metabolic disorder associated with distinctive pathophysiological disturbances. One of the pathophysiological risk factors observed in T2D is dysregulation of the incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Both hormones stimulate insulin secretion by acting postprandially on pancreatic β-cell receptors. Oral glucose administration stimulates increased insulin secretion in comparison with isoglycemic intravenous glucose administration, a phenomenon known as the incretin effect. While the evidence for incretin defects in individuals with T2D is growing, the etiology behind this attenuated incretin effect in T2D is not clearly understood. Given their central role in T2D pathophysiology, incretins are promising targets for T2D therapeutics. The present review synthesizes the recent attempts to explain the biological importance of incretin hormones and explore potential pharmacological approaches that target the incretins.

The evolving story of incretins (GIP and GLP-1) in metabolic and cardiovascular disease: A pathophysiological update

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) have their main physiological role in augmenting insulin secretion after their nutrient-induced secretion from the gut. A functioning entero-insular (gut-endocrine pancreas) axis is essential for the maintenance of a normal glucose tolerance. This is exemplified by the incretin effect (greater insulin secretory response to oral as compared to "isoglycaemic" intravenous glucose administration due to the secretion and action of incretin hormones). GIP and GLP-1 have additive effects on insulin secretion. Local production of GIP and/or GLP-1 in islet α-cells (instead of enteroendocrine K and L cells) has been observed, and its significance is still unclear. GLP-1 suppresses, and GIP increases glucagon secretion, both in a glucose-dependent manner. GIP plays a greater physiological role as an incretin. In type 2-diabetic patients, the incretin effect is reduced despite more or less normal secretion of GIP and GLP-1. While insulinotropic effects of GLP-1 are only slightly impaired in type 2 diabetes, GIP has lost much of its acute insulinotropic activity in type 2 diabetes, for largely unknown reasons. Besides their role in glucose homoeostasis, the incretin hormones GIP and GLP-1 have additional biological functions: GLP-1 at pharmacological concentrations reduces appetite, food intake, and-in the long run-body weight, and a similar role is evolving for GIP, at least in animal studies. Human studies, however, do not confirm these findings. GIP, but not GLP-1 increases triglyceride storage in white adipose tissue not only through stimulating insulin secretion, but also by interacting with regional blood vessels and GIP receptors. GIP, and to a lesser degree GLP-1, play a role in bone remodelling. GLP-1, but not GIP slows gastric emptying, which reduces post-meal glycaemic increments. For both GIP and GLP-1, beneficial effects on cardiovascular complications and neurodegenerative central nervous system (CNS) disorders have been observed, pointing to therapeutic potential over and above improving diabetes complications. The recent finding that GIP/GLP-1 receptor co-agonists like tirzepatide have superior efficacy compared to selective GLP-1 receptor agonists with respect to glycaemic control as well as body weight has renewed interest in GIP, which previously was thought to be without any therapeutic potential. One focus of this research is into the long-term interaction of GIP and GLP-1 receptor signalling. A GLP-1 receptor antagonist (exendin [9-39]) and, more recently, a GIP receptor agonist (GIP [3-30] NH₂ ) and, hopefully, longer-acting GIP receptor agonists for human use will be helpful tools to shed light on the open questions. A detailed knowledge of incretin physiology and pathophysiology will be a prerequisite for designing more effective incretin-based diabetes drugs.

The incessant increase curve during oral glucose tolerance tests in Chinese adults with type 2 diabetes and its association with gut hormone levels

Glucose curve shapes during oral glucose tolerance tests (OGTTs) are mainly classified as incessant increase, monophasic and biphasic. Youth with an incessant increase curve have worse β-cell function. The aim of this paper was to investigate the incessant increase curve in Chinese adults with type 2 diabetes (T2DM), and its association with β-cell function and gut hormone levels. Eighty-nine Chinese patients (59 males and 30 females) were included in this study with a mean age of 50.56 ± 16.00 years. They were all recently diagnosed with T2DM and underwent 180-min OGTTs. Data on demographics, β-cell function, and insulin sensitivity were also collected. Gut hormones, including glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and ghrelin, were also detected during the OGTT. A total of 39.3 % of subjects had an incessant increase in the glucose response curve, while 59.6 % had a monophasic curve. Because only one curve was classified as biphasic, patients with a biphasic curve were omitted from further research. Lower plasma C-peptide, HOMA2-β, area under the curve (AUC) of C-peptide, and ratio of AUC of insulin to AUC of glucose were found in patients with incessant increase curves compared to those with monophasic curves (P < 0.05). Higher glycated hemoglobin (HbA_1c) was found in subjects with an incessant increase curve (P < 0.05). Importantly, fasting plasma ghrelin was lower and incremental ghrelin at 120 min was higher in the incessant increase group (P < 0.05), irrespective of age, sex, body mass index (BMI), fasting glucose, and fasting insulin. Time to peak is also a parameter of the OGTT curve shape. In the late-peak group, GLP-1 at 120 min and the AUC of GLP-1 were elevated compared with those in the early-peak group (P < 0.05). In Chinese adults with T2DM, the incessant increase in OGTT shape indicated impaired insulin secretion. Lower fasting ghrelin and absence of ghrelin drops after glucose load may be associated with the incessant increase OGTT shape. In addition, compensatory elevated GLP-1 dose not prevent peak delay in the OGTT curve. Gut hormones may have an effect on OGTT shapes in T2DM adults.

Reduction in GLP-1 secretory capacity may be a novel independent risk factor of coronary artery stenosis

Multiple factors regulate glucagon-like peptide-1 (GLP-1) secretion, but a group of apparently healthy subjects showed blunted responses of GLP-1 secretion in our previous study. In this study, we examined whether the reduction in GLP-1 secretory capacity is associated with increased extent of coronary artery stenosis in non-diabetic patients. Non-diabetic patients who were admitted for coronary angiography without a history of coronary interventions were enrolled. Coronary artery stenosis was quantified by Gensini score (GS), and GS ≥ 10 was used as an outcome variable based on its predictive value for cardiovascular events. The patients (mean age, 66.5 ± 8.8 years; 71% males, n = 173) underwent oral 75 g-glucose tolerant tests for determination of glucose, insulin and active GLP-1 levels. The area under the curve of plasma active GLP-1 (AUC-GLP-1) was determined as an index of GLP-1 secretory capacity. AUC-GLP-1 was not correlated with fasting glucose, AUC-glucose, serum lipids or indices of insulin sensitivity. In multivariate logistic regression analysis for GS ≥ 10, AUC-GLP-1 < median, age and hypertension were selected as explanatory variables, though fasting GLP-1 level was not selected. The findings suggest that reduction in GLP-1 secretory capacity is a novel independent risk factor of coronary stenosis.

Breast Cancer, Diabetes Mellitus and Glucagon-Like Peptide-1 Receptor Toward Exploring Their Possible Associations

PURPOSE

Diabetes Mellitus (DM) has been one of the well known risk factors of breast cancer (BC) development and also associated with adverse clinical outcomes of BC patients. Glucagon-like peptide-1 (GLP-1) receptor agonists have been used as antidiabetic therapeutic agents and recent epidemiological studies have reported their use to be correlated with increased BC risks. However, biological or pathological details have remained unknown. Therefore, in this study, we examined the status of GLP-1 receptor (GLP-1R) in BC with and without DM and correlated the findings with the clinicopathological factors of the patients to explore the possible involvement of GLP-1 in BC pathology.

METHODS

We immunolocalized GLP-1R in cancer and adjacent non-pathological breast tissues in BC patients with DM (125 cases) and without DM (58 cases). We then compared the status of GLP-1R with that of fibroblast growth factor 7 (FGF7) and fibroblast growth factor receptor 2 (FGFR2), Ki-67 labeling index (Ki-67 LI) and disease free survival (DFS) of the patients and also between cancerous and non-pathological breast tissues.

RESULTS

GLP-1R immunoreactivity was significantly higher (p = 0.044) in the patients with DM than without in carcinoma tissues. However, this was detected only in invasive carcinoma (p < 0.01) and not in non-invasive carcinoma nor non-pathological mammary glands. FGF7 was significantly correlated with the status of GLP-1R in BC (p = 0.045). In addition, in ER positive BC cases, those with GLP-1R positive status tended to have higher Ki-67 LI of more than 14% (p = 0.070).

CONCLUSION

These findings all demonstrated the possible association between GLP-1R status and biological features of BC, especially of invasive BC in DM patients.

Improvement of Glucose Tolerance by Food Factors Having Glucagon-Like Peptide-1 Releasing Activity

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone released from enteroendocrine L cells in response to meal ingestion. GLP-1 receptor agonists and GLP-1 enhancers have been clinically employed to treat diabetes owing to their glucose-dependent insulin-releasing activity. The release of GLP-1 is primarily stimulated by macronutrients such as glucose and fatty acids, which are nutritionally indispensable; however, excessive intake of sugar and fat is responsible for the development of obesity and diabetes. Therefore, GLP-1 releasing food factors, such as dietary peptides and non-nutrients, are deemed desirable for improving glucose tolerance. Human and animal studies have revealed that dietary proteins/peptides have a potent effect on stimulating GLP-1 secretion. Studies in enteroendocrine cell models have shown that dietary peptides, amino acids, and phytochemicals, such as quercetin, can directly stimulate GLP-1 secretion. In our animal experiments, these food factors improved glucose metabolism and increased GLP-1 secretion. Furthermore, some dietary peptides not only stimulated GLP-1 secretion but also reduced plasma peptidase activity, which is responsible for GLP-1 inactivation. Herein, we review the relationship between GLP-1 and food factors, especially dietary peptides and flavonoids. Accordingly, utilization of food factors with GLP-1-releasing/enhancing activity is a promising strategy for preventing and treating obesity and diabetes.

Chronic peptide-based GIP receptor inhibition exhibits modest glucose metabolic changes in mice when administered either alone or combined with GLP-1 agonism

Combinatorial gut hormone therapy is one of the more promising strategies for identifying improved treatments for metabolic disease. Many approaches combine the established benefits of glucagon-like peptide-1 (GLP-1) agonism with one or more additional molecules with the aim of improving metabolic outcomes. Recent attention has been drawn to the glucose-dependent insulinotropic polypeptide (GIP) system due to compelling pre-clinical evidence describing the metabolic benefits of antagonising the GIP receptor (GIPR). We rationalised that benefit might be accrued from combining GIPR antagonism with GLP-1 agonism. Two GIPR peptide antagonists, GIPA-1 (mouse GIP(3–30)NH2) and GIPA-2 (NαAc-K10[γEγE-C16]-Arg18-hGIP(5–42)), were pharmacologically characterised and both exhibited potent antagonist properties. Acute in vivo administration of GIPA-1 during an oral glucose tolerance test (OGTT) had negligible effects on glucose tolerance and insulin in lean mice. In contrast, GIPA-2 impaired glucose tolerance and attenuated circulating insulin levels. A mouse model of diet-induced obesity (DIO) was used to investigate the potential metabolic benefits of chronic dosing of each antagonist, alone or in combination with liraglutide. Chronic administration studies showed expected effects of liraglutide, lowering food intake, body weight, fasting blood glucose and plasma insulin concentrations while improving glucose sensitivity, whereas delivery of either GIPR antagonist alone had negligible effects on these parameters. Interestingly, chronic dual therapy augmented insulin sensitizing effects and lowered plasma triglycerides and free-fatty acids, with more notable effects observed with GIPA-1 compared to GIPA-2. Thus, the co-administration of both a GIPR antagonist with a GLP1 agonist uncovers interesting beneficial effects on measures of insulin sensitivity, circulating lipids and certain adipose stores that seem influenced by the degree or nature of GIP receptor antagonism.

Neuroendocrine Peptides of the Gut and Their Role in the Regulation of Food Intake

The regulation of food intake encompasses complex interplays between the gut and the brain. Among them, the gastrointestinal tract releases different peptides that communicate the metabolic state to specific nuclei in the hindbrain and the hypothalamus. The present overview gives emphasis on seven peptides that are produced by and secreted from specialized enteroendocrine cells along the gastrointestinal tract in relation with the nutritional status. These established modulators of feeding are ghrelin and nesfatin-1 secreted from gastric X/A-like cells, cholecystokinin (CCK) secreted from duodenal I-cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY) secreted from intestinal L-cells and uroguanylin (UGN) released from enterochromaffin (EC) cells. © 2021 American Physiological Society. Compr Physiol 11:1679-1730, 2021.

Irisin and Incretin Hormones: Similarities, Differences, and Implications in Type 2 Diabetes and Obesity

Incretins are gut hormones that potentiate glucose-stimulated insulin secretion (GSIS) after meals. Glucagon-like peptide-1 (GLP-1) is the most investigated incretin hormone, synthesized mainly by L cells in the lower gut tract. GLP-1 promotes β-cell function and survival and exerts beneficial effects in different organs and tissues. Irisin, a myokine released in response to a high-fat diet and exercise, enhances GSIS. Similar to GLP-1, irisin augments insulin biosynthesis and promotes accrual of β-cell functional mass. In addition, irisin and GLP-1 share comparable pleiotropic effects and activate similar intracellular pathways. The insulinotropic and extra-pancreatic effects of GLP-1 are reduced in type 2 diabetes (T2D) patients but preserved at pharmacological doses. GLP-1 receptor agonists (GLP-1RAs) are therefore among the most widely used antidiabetes drugs, also considered for their cardiovascular benefits and ability to promote weight loss. Irisin levels are lower in T2D patients, and in diabetic and/or obese animal models irisin administration improves glycemic control and promotes weight loss. Interestingly, recent evidence suggests that both GLP-1 and irisin are also synthesized within the pancreatic islets, in α- and β-cells, respectively. This review aims to describe the similarities between GLP-1 and irisin and to propose a new potential axis-involving the gut, muscle, and endocrine pancreas that controls energy homeostasis.

Glucolipotoxicity and GLP-1 secretion

INTRODUCTION

The concept of glucolipotoxicity refers to the combined, deleterious effects of elevated glucose and/or fatty acid levels.

RESEARCH DESIGN AND METHODS

To investigate the effects of chronic glucolipotoxicity on glucagon-like peptide-1-(7-36) amide (GLP-1) secretion, we generated glucolipotoxic conditions in human NCI-H716 enteroendocrine cells using either 5 or 25 mM glucose with or without 500 µM palmitate for 72 hours. For in vivo study, we have established a chronic nutrient infusion model in the rat. Serial blood samples were collected for 2 hours after the consumption of a mixed meal to evaluate insulin sensitivity and β-cell function.

RESULTS

Chronic glucolipotoxic conditions decreased GLP-1 secretion and the expressions of pCREB, pGSK3β, β-catenin, and TCF7L2 in NCI-H716 cells. Glucolipotoxicity conditions reduced glucose transporter expression, glucose uptake, and nicotinamide-adenine dinucleotide phosphate (NADPH) levels in L-cells, and increased triglyceride accumulation. In contrast, PPARα and ATP levels were reduced, which correlated well with decreased levels of SUR1 and Kir6.2, cAMP contents and expressions of pCAMK2, EPAC and PKA. We also observed an increase in reactive oxygen species production, UCP2 expression and Complex I activity. Simultaneous treatment with insulin restored the GLP-1 secretion. Glucolipotoxic conditions decreased insulin secretion in a time-dependent manner in INS-1 cells, which was recovered with exendin-4 cotreatment. Glucose and SMOFlipid infusion for 6 hours decreased GLP-1 secretion and proglucagon mRNA levels as well as impaired the glucose tolerance, insulin and C-peptide secretion in rats.

CONCLUSION

These results provide evidence for the first time that glucolipotoxicity could affect GLP-1 secretion through changes in glucose and lipid metabolism, gene expressions, and proglucagon biosynthesis and suggest the interrelationship between glucolipotoxicities of L-cells and β-cells which develops earlier than that of L-cells.

The Emerging Role of Polyphenols in the Management of Type 2 Diabetes

Type 2 diabetes (T2D) is a fast-increasing health problem globally, and it results from insulin resistance and pancreatic β-cell dysfunction. The gastrointestinal (GI) tract is recognized as one of the major regulatory organs of glucose homeostasis that involves multiple gut hormones and microbiota. Notably, the incretin hormone glucagon-like peptide-1 (GLP-1) secreted from enteroendocrine L-cells plays a pivotal role in maintaining glucose homeostasis via eliciting pleiotropic effects, which are largely mediated via its receptor. Thus, targeting the GLP-1 signaling system is a highly attractive therapeutic strategy to treatment T2D. Polyphenols, the secondary metabolites from plants, have drawn considerable attention because of their numerous health benefits, including potential anti-diabetic effects. Although the major targets and locations for the polyphenolic compounds to exert the anti-diabetic action are still unclear, the first organ that is exposed to these compounds is the GI tract in which polyphenols could modulate enzymes and hormones. Indeed, emerging evidence has shown that polyphenols can stimulate GLP-1 secretion, indicating that these natural compounds might exert metabolic action at least partially mediated by GLP-1. This review provides an overview of nutritional regulation of GLP-1 secretion and summarizes recent studies on the roles of polyphenols in GLP-1 secretion and degradation as it relates to metabolic homeostasis. In addition, the effects of polyphenols on microbiota and microbial metabolites that could indirectly modulate GLP-1 secretion are also discussed.

Incretin Hormones in Obesity and Related Cardiometabolic Disorders: The Clinical Perspective

The prevalence of obesity continues to grow rapidly worldwide, posing many public health challenges of the 21st century. Obese subjects are at major risk for serious diet-related noncommunicable diseases, including type 2 diabetes mellitus, cardiovascular disease, and non-alcoholic fatty liver disease. Understanding the mechanisms underlying obesity pathogenesis is needed for the development of effective treatment strategies. Dysregulation of incretin secretion and actions has been observed in obesity and related metabolic disorders; therefore, incretin-based therapies have been developed to provide new therapeutic options. Incretin mimetics present glucose-lowering properties, together with a reduction of appetite and food intake, resulting in weight loss. In this review, we describe the physiology of two known incretins—glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and their role in obesity and related cardiometabolic disorders. We also focus on the available and incoming incretin-based medications that can be used in the treatment of the above-mentioned conditions.

A randomized controlled trial protocol of the cardiovascular safety and efficacy of liraglutide in the treatment of type 2 diabetes

BACKGROUND

Recently, many clinical experiments have evaluated the influences of liraglutide in the treatment of type 2 diabetes. However, the outcomes of these studies are inconsistent, and the number of high-quality prospective trials that conducted to assess the cardiovascular safety is limited. Hence, for this research, it was implemented for the assessment of the cardiovascular effectiveness and safety of liraglutide in type 2 diabetes patients.

METHODS

This research was a 26-week active controlled and randomized trial. Our research protocol follows the guidelines of Good Clinical Practice issued via the Helsinki Declaration and International Conference on Coordination. All the patients will receive the written informed consent in order to involve in our clinical experiment. The participants with type 2 diabetes aged from 18 years to 80 years, patients with 45.0 kg/m2 body-mass index or less, and with glycosylated hemoglobin of 7.5 to 10.0 percent, and received metformin (daily 1500 mg or more) for 3 months or longer were eligible. All the patients were randomized to 1 of 2 interventions (in the ratio of 1:1): liraglutide placebo once daily (blinded) and liraglutide once daily (blinded), respectively, both combined with the glimepiride and metformin (open-labeled). For the efficacy variable, the major endpoint was the baseline glycated hemoglobin change after treating for 26 weeks. The secondary end points involved: the percentage of participants who achieved the goals of postprandial blood glucose, fasting blood glucose, and glycosylated hemoglobin; the changes of mean postprandial blood glucose, fasting blood glucose, and the body weight, pancreatic B-cell function index, and changes in blood pressure and insulin resistance assessed by homeostasis model.

CONCLUSIONS

For this research, the limitations involve the short trial period and the limitation of glimepiride in some countries, thus excluding the maximum doses of glimepiride.

TRIAL REGISTRATION

This study protocol was registered in Research Registry (researchregistry6306).

From Entero-Endocrine Cell Biology to Surgical Interventional Therapies for Type 2 Diabetes

The physiological roles of the enteroendocrine system in relation to energy and glucose homeostasis regulation have been extensively studied in the past few decades. Considerable advances were made that enabled to disclose the potential use of gastro-intestinal (GI) hormones to target obesity and type 2 diabetes (T2D). The recognition of the clinical relevance of these discoveries has led the pharmaceutical industry to design several hormone analogues to either to mitigate physiological defects or target pharmacologically T2D.Amongst several advances, a major breakthrough in the field was the unexpected observation that enteroendocrine system modulation to T2D target could be achieved by surgically induced anatomical rearrangement of the GI tract. These findings resulted from the widespread use of bariatric surgery procedures for obesity treatment, which despite initially devised to induce weight loss by limiting the systemic availably of nutrients, are now well recognized to influence GI hormone dynamics in a manner that is highly dependent on the type of anatomical rearrangement produced.This chapter will focus on enteroendocrine system related mechanisms leading to improved glycemic control in T2D after bariatric surgery interventions.

The Role of Tirzepatide, Dual GIP and GLP-1 Receptor Agonist, in the Management of Type 2 Diabetes: The SURPASS Clinical Trials

Glucagon-like peptide 1 (GLP-1) based therapy is an established treatment option for the management of type 2 diabetes mellitus (T2DM) and is recommended early in the treatment algorithm owing to glycaemic efficacy, weight reduction and favourable cardiovascular outcomes. Glucose-dependent insulinotropic polypeptide (GIP), on the other hand, was thought to have no potential as a glucose-lowering therapy because of observations showing no insulinotropic effect from supraphysiological infusion in people with T2DM. However, emerging evidence has illustrated that co-infusion of GLP-1 and GIP has a synergetic effect, resulting in significantly increased insulin response and glucagonostatic response, compared with separate administration of each hormone. These observations have led to the development of a dual GIP/GLP-1 receptor agonist, known as a 'twincretin'. Tirzepatide is a novel dual GIP/GLP-1 receptor agonist formulated as a synthetic peptide containing 39 amino acids, based on the native GIP sequence. Pre-clinical trials and phase 1 and 2 clinical trials indicate that tirzepatide has potent glucose lowering and weight loss with adverse effects comparable to those of established GLP-1 receptor agonists. The long-term efficacy, safety and cardiovascular outcomes of tirzepatide will be investigated in the SURPASS phase 3 clinical trial programme. In this paper, we will review the pre-clinical and phase 1 and 2 trials for tirzepatide in the management of T2DM and give an overview of the SURPASS clinical trials.

Chronic Effects of a High Sucrose Diet on Murine Gastrointestinal Nutrient Sensor Gene and Protein Expression Levels and Lipid Metabolism

The gastrointestinal tract (GIT) plays a key role in regulating nutrient metabolism and appetite responses. This study aimed to identify changes in the GIT that are important in the development of diet related obesity and diabetes. GIT samples were obtained from C57BL/6J male mice chronically fed a control diet or a high sucrose diet (HSD) and analysed for changes in gene, protein and metabolite levels. In HSD mice, GIT expression levels of fat oxidation genes were reduced, and increased de novo lipogenesis was evident in ileum. Gene expression levels of the putative sugar sensor, slc5a4a and slc5a4b, and fat sensor, cd36, were downregulated in the small intestines of HSD mice. In HSD mice, there was also evidence of bacterial overgrowth and a lipopolysaccharide activated inflammatory pathway involving inducible nitric oxide synthase (iNOS). In Caco-2 cells, sucrose significantly increased the expression levels of the nos2, iNOS and nitric oxide (NO) gas levels. In conclusion, sucrose fed induced obesity/diabetes is associated with changes in GI macronutrient sensing, appetite regulation and nutrient metabolism and intestinal microflora. These may be important drivers, and thus therapeutic targets, of diet-related metabolic disease.

Role of GLP-1 Receptor Agonists in Pediatric Obesity: Benefits, Risks, and Approaches to Patient Selection

PURPOSE OF REVIEW

Effective treatments for pediatric obesity are limited. Glucagon-like peptide-1 receptor (GLP-1R) agonists have emerged as therapeutic agents for obesity in adults and have shown benefits outside of weight loss. Here we explore the evidence for GLP-1R agonist use in pediatric obesity.

RECENT FINDINGS

Emerging evidence suggests that GLP-1R agonists have a role in pediatric obesity treatment. A recently published, randomized, placebo-controlled trial found a greater reduction in BMI z-score (- 0.22 SDs) in adolescents receiving liraglutide compared with placebo. As in adults, gastrointestinal adverse effects were commonly seen. GLP-1R agonists appear to perform favorably compared with other approved pharmacological agents for pediatric obesity. However, heterogeneity in weight loss response, cost, side effects, and need for injections may limit their use in many pediatric patients. Rather than broadly applying this therapy if it is approved, we suggest careful patient selection and monitoring by clinicians pending further studies.

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.