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

Pancreatic GLP-1r binding potential is reduced in insulin-resistant pigs

INTRODUCTION

The insulinotropic capacity of exogenous glucagon like peptide-1 (GLP-1) is reduced in type 2 diabetes and the insulin-resistant obese. We have tested the hypothesis that this response is the consequence of a reduced pancreatic GLP-1 receptor (GLP-1r) density in insulin-resistant obese animals.

RESEARCH DESIGN AND METHODS

GLP-1r density was measured in lean and insulin-resistant adult miniature pigs after the administration of a ⁶⁸Ga-labeled GLP-1r agonist. The effect of hyperinsulinemia on GLP-1r was assessed using sequential positron emission tomography (PET), both in the fasted state and during a clamp. The impact of tissue perfusion, which could account for changes in GLP-1r agonist uptake, was also investigated using ⁶⁸Ga-DOTA imaging.

RESULTS

GLP-1r binding potential in the obese pancreas was reduced by 75% compared with lean animals. Similar reductions were evident for fat tissue, but not for the duodenum. In the lean group, induced hyperinsulinemia reduced pancreatic GLP-1r density to a level comparable with that of the obese group. The reduction in blood to tissue transfer of the GLP-1r ligand paralleled that of tissue perfusion estimated using ⁶⁸Ga-DOTA.

CONCLUSIONS

These observations establish that a reduction in abdominal tissue perfusion and a lower GLP-1r density account for the diminished insulinotropic effect of GLP-1 agonists in type 2 diabetes.

The Impact of Amino Acids on Postprandial Glucose and Insulin Kinetics in Humans: A Quantitative Overview

Different amino acids (AAs) may exert distinct effects on postprandial glucose and insulin concentrations. A quantitative comparison of the effects of AAs on glucose and insulin kinetics in humans is currently lacking. PubMed was queried to identify intervention studies reporting glucose and insulin concentrations after acute ingestion and/or intravenous infusion of AAs in healthy adults and those living with obesity and/or type 2 diabetes (T2DM). The systematic literature search identified 55 studies that examined the effects of l-leucine, l-isoleucine, l-alanine, l-glutamine, l-arginine, l-lysine, glycine, l-proline, l-phenylalanine, l-glutamate, branched-chain AAs (i.e., l-leucine, l-isoleucine, and l-valine), and multiple individual l-AAs on glucose and insulin concentrations. Oral ingestion of most individual AAs induced an insulin response, but did not alter glucose concentrations in healthy participants. Specific AAs (i.e., leucine and isoleucine) co-ingested with glucose exerted a synergistic effect on the postprandial insulin response and attenuated the glucose response compared to glucose intake alone in healthy participants. Oral AA ingestion as well as intravenous AA infusion was able to stimulate an insulin response and decrease glucose concentrations in T2DM and obese individuals. The extracted information is publicly available and can serve multiple purposes such as computational modeling.

GIP(3-30)NH2 - a tool for the study of GIP physiology

Glucose-dependent insulinotropic polypeptide (GIP) is a gut hormone impacting glucose, lipid and bone metabolism through the GIP receptor (GIPR). The GIP system has key species differences complicating the translation of findings from rodent to human physiology. Furthermore, the effects of endogenous GIP in humans have been difficult to tease out due to the lack of a suitable GIPR antagonist. The naturally occurring GIP(3-30)NH₂ has turned out to constitute a safe and efficacious GIPR antagonist for rodent and human use. To study GIP physiology, it is recommended to use the species-specific GIP(3-30)NH₂ peptide sequence, and for human intravenous infusions, an antagonist:agonist ratio of a minimum of 600 with a 20min infusion time before the intervention of interest is recommended. Several studies using GIP(3-30)NH₂ are coming, hopefully providing new insights into the physiology of GIP, the pathophysiologic involvement of GIP in several diseases and the therapeutic potential of the GIPR.

A Reduced Incretin Effect Mediated by the rs7903146 Variant in the TCF7L2 Gene Is an Early Marker of β-Cell Dysfunction in Obese Youth

OBJECTIVE

The risk genotype for the common variant rs7903146 of the transcription factor 7-like-2 (TCF7L2) gene has been found to affect the incretin response in healthy and obese adults; however, whether a similar functional defect is also present in obese adolescents remains unexplored. Herein, we examined the functional effect of the rs7903146 variant in the TCF7L2 gene on the incretin effect and determined its translational metabolic manifestation by performing deep phenotyping of the incretin system, β-cell function relative to insulin sensitivity, the gastrointestinal-induced glucose disposal (GIGD) in obese youth with normal and impaired glucose tolerance.

RESEARCH DESIGN AND METHODS

Thirty-nine obese adolescents without diabetes (median age 15 [25th, 75th percentile 14, 18] years; BMI 37 [33, 43] kg/m²) were genotyped for the rs7903146 variant of TCF7L2 and underwent a 3-h oral glucose tolerance test (OGTT) followed by an isoglycemic intravenous glucose infusion (iso-intravenous glucose tolerance test [IVGTT]) to match the plasma glucose concentrations during the OGTT and a hyperglycemic clamp with arginine stimulation. The incretin effect was measured as 100 * (AUC-SR_OGTT - AUC-SR_iso-IVGTT) / AUC-SR_OGTT, where AUC-SR = area under the curve of C-peptide secretion rate. Participants were grouped into tertiles according to the percentage incretin effect (high, moderate, and low) to describe their metabolic phenotype.

RESULTS

The presence of T risk allele for TCF7L2 was associated with a markedly reduced incretin effect compared with the wild-type genotype (0.3% [-7.2, 14] vs. 37.8% [12.5, 52.4], P < 0.002). When the cohort was stratified by incretin effect, the high, moderate, and low incretin effect groups did not differ with respect to anthropometric features, while the low incretin effect group exhibited higher 1-h glucose (P = 0.015) and a reduced disposition index, insulin sensitivity, and insulin clearance compared with the high incretin effect group. GIGD was reduced in the low incretin effect group (P = 0.001). The three groups did not differ with respect to intravenous glucose-induced insulin secretion and arginine response during the hyperglycemic clamp.

CONCLUSIONS

A reduced incretin effect and its association with the TCF7L2 variant rs7903146 identify an early metabolic phenotype in obese youth without diabetes, featuring a higher plasma glucose peak at 1 h; lower insulin secretion, sensitivity, and clearance; and GIGD.

A Narrative Review of the Anti-Hyperglycemic and Satiating Effects of Fish Protein Hydrolysates and Their Bioactive Peptides

Prevalence of type 2 diabetes and overweight/obesity are increasing globally. Food supplementation as a preventative option has become an attractive option in comparison to increased pharmacotherapy dependency. Hydrolysates of fish processing waste and by-products have become particularly interesting in a climate of increased food wastage awareness and are rapidly gaining traction in food research. This review summarizes the available research so far on the potential effect of these hydrolysates on diabetes and appetite suppression. Scopus and Web of Science are searched using eight keywords (fish, hydrolysate, peptides, satiating, insulinotropic, incretin, anti-obesity, DPP-4 [dipeptidylpeptidase-4/IV]) returning a total of 2549 results. Following exclusion criteria (repeated appearances, non-fish marine sources [e.g., macroalgae], and irrelevant bioactivities [e.g., immunomodulatory, anti-thrombotic]), 44 relevant publications are included in this review. Stimulation of hormone secretion, regulation of glucose uptake, anorexigenic potential, identified mechanisms of action, and research conducted on the most potent bioactive peptides identified within these hydrolysates are all specifically addressed. Results of this review conclude that despite wide methodological variation between studies, there is significant potential for the application of fish protein hydrolysates in the management of bodyweight and hyperglycemia.

Intermittent versus continuous enteral nutrition attenuates increases in insulin and leptin during short-term bed rest

PURPOSE

To compare endocrine responses to intermittent vs continuous enteral nutrition provision during short-term bed rest.

METHODS

Twenty healthy men underwent 7 days of bed rest, during which they were randomized to receive enteral nutrition (47%E as carbohydrate, 34%E as fat, 16%E as protein and 3%E as fibre) in a continuous (CONTINUOUS; n = 10; 24 h day-1 at a constant rate) or intermittent (INTERMITTENT; n = 10; as 4 meals per day separated by 5 h) pattern. Daily plasma samples were taken every morning to assess metabolite/hormone concentrations.

RESULTS

During bed rest, plasma leptin concentrations were elevated to a lesser extent with INTERMITTENT vs CONTINUOUS (iAUC: 0.42 ± 0.38 vs 0.95 ± 0.48 nmol L-1, respectively; P = 0.014) as were insulin concentrations (interaction effect, P < 0.001) which reached a peak of 369 ± 225 pmol L-1 in CONTINUOUS, compared to 94 ± 38 pmol L-1 in INTERMITTENT (P = 0.001). Changes in glucose infusion rate were positively correlated with changes in fasting plasma GLP-1 concentrations (r = 0.44, P = 0.049).

CONCLUSION

Intermittent enteral nutrition attenuates the progressive rise in plasma leptin and insulinemia seen with continuous feeding during bed rest, suggesting that continuous feeding increases insulin requirements to maintain euglycemia. This raises the possibility that hepatic insulin sensitivity is impaired to a greater extent with continuous versus intermittent feeding during bed rest. To attenuate endocrine and metabolic changes with enteral feeding, an intermittent feeding strategy may, therefore, be preferable to continuous provision of nutrition. This trial was registered on clinicaltrials.gov as NCT02521025.

Gut-Pancreas-Liver Axis as a Target for Treatment of NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD) represents the most common form of chronic liver disease worldwide. Due to its association with obesity and diabetes and the fall in hepatitis C virus morbidity, cirrhosis in NAFLD is becoming the most frequent indication to liver transplantation, but the pathogenetic mechanisms are still not completely understood. The so-called gut-liver axis has gained enormous interest when data showed that its alteration can lead to NAFLD development and might favor the occurrence of non-alcoholic steatohepatitis (NASH). Moreover, several therapeutic approaches targeting the gut-pancreas-liver axis, e.g., incretins, showed promising results in NASH treatment. In this review, we describe the role of incretin hormones in NAFLD/NASH pathogenesis and treatment and how metagenomic/metabolomic alterations in the gut microbiota can lead to NASH in the presence of gut barrier modifications favoring the passage of bacteria or bacterial products in the portal circulation, i.e., bacterial translocation.

COVID-19: is there a link between the course of infection and pharmacological agents in diabetes?

BACKGROUND

The Coronavirus disease 2019 (COVID-19) and type 2 diabetes (T2D) are two pandemics that share the dramatic impact on global mortality and economic resources. COVID-19 largely exhibits mild to moderate clinical manifestations. However, severe pneumonia with high fatality rate may occur, especially in the elderly and in patients with underlying conditions, such as diabetes and cardiovascular disease. SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) binds to the angiotensin-converting enzyme 2 (ACE2), a ubiquitous trans-membrane carboxypeptidase, to enter the cells.

AIMS

This short review discusses some open questions about the link between COVID-19 and diabetes, principally focusing on the possible effects of commonly used drugs in patients with diabetes.

RESULTS

Preclinical studies have reported that angiotensin receptor blockers (ARBs) and ACE inhibitors might increase ACE2 expression in several cell types. Hence, it has been speculated that the treatment with these agents might influence the course of the infection, and both harmful and beneficial effects have been supposed. Other pharmacological agents are thought to increase ACE2 expression, including statins and proliferator-activated receptor gamma (PPAR-γ) agonists. All these drug classes are broadly adopted in T2D. Besides ACE2, other unknown co-factors might be involved in cell infection. It has been recently observed that dipeptidyl peptidase-4 (DPP4), the receptor for MERS-CoV (Middle East respiratory syndrome-related coronavirus) and ACE2 have similar expression profiles in the lung. DPP4 has important metabolic and immune functions and is a target for commonly used therapies in T2D.

CONCLUSIONS

Although clinical data supporting an influence of all these drugs on the course of the disease are limited, this is an interesting background for further research that might help unravel the complex mechanisms underlying the link between COVID-19 and diabetes.

Lixisenatide for Type 2 Diabetes Mellitus Patients Inadequately Controlled on Oral Antidiabetic Drugs: A Mixed-Treatment Comparison Meta-analysis and Cost-Utility Analysis

INTRODUCTION

The aim of this study was to compare the efficacy, safety and cost-utility (from the Chinese health insurance perspective) of lixisenatide and insulin regimens in patients with type 2 diabetes mellitus (T2DM) inadequately controlled on oral antidiabetic drugs (OADs).

METHODS

A comprehensive literature search of English (PubMed and Cochrane Library) and Chinese (CNKI and WanFang) language databases was performed, and head-to-head relevant randomized controlled trials (RCTs) were retrieved and analyzed by performing a mixed-treatment comparison (MTC) meta-analysis for efficacy and safety endpoints. A cost-utility analysis was then conducted using the IQVIA CORE Diabetes Model to compare the lifetime pharmacoeconomic profiles among the treatment groups.

RESULTS

Eleven RCTs were included in this MTC meta-analysis. Regarding glycated hemoglobin targets, lixisenatide was similar to both basal insulin (mean difference [MD] 0.27%; 95% credible interval [CrI] 0.02%, 0.57%) and premixed insulin (MD 0.32%; 95% CrI - 0.01%, 0.66%), respectively. Statistically significant differences were found for changes in body weight in favor of lixisenatide compared with basal insulin (MD - 3.22 kg; 95% CrI - 5.51 kg, - 0.94 kg) and premixed insulin (MD - 2.68 kg; 95% CrI - 5.16 kg, - 0.20 kg). The relative risk (RR) of symptomatic hypoglycemia associated with lixisenatide was also significantly lower than that associated with basal insulin (RR 0.22; 95% CrI 0.09, 0.52) and premixed insulin (RR 0.17; 95% CrI 0.07, 0.41). The cost-utility analysis yielded results of ¥61,072 ($8565, vs. basal insulin) and ¥127,169 ($17,836, vs. premixed insulin) per quality-adjusted life year gained, with both values falling within the willingness-to-pay threshold in China.

CONCLUSIONS

For T2DM patients inadequately controlled on OADs, lixisenatide was shown to be comparable to basal insulin and premixed insulin in terms of HbA1c and better than both of the latter in terms of both body weight loss and hypoglycemia. Lixisenatide was also a cost-effective treatment option from the perspective of Chinese health insurance.

Assessing insulin sensitivity and resistance in syndromes of severe short stature

Individuals affected with two genetic syndromes identified in Ecuador have severe short stature and diminished insulin secretion, along with essentially different GH counterregulatory effects on insulin action, which leads to the appearance of opposing metabolic phenotypes. In the case of Laron syndrome, subjects have enhanced insulin sensitivity and diminished incidence of type 2 diabetes mellitus. In the other clinical entity, individuals have innate insulin resistance, a varying degree of carbohydrate metabolism disturbances, glucose intolerance, and eventually insulin-resistant diabetes mellitus. Since both groups have diminished insulin secretion, the standard homeostatic minimal models for assessment of insulin sensitivity and resistance were used to see if they could properly identify the metabolic status, especially considering that these methodologies are simple and non-invasive procedures.

METHODS

Fasting insulin concentrations, fasting glucose/fasting insulin ratio and various minimal models were determined in individuals from the two syndromic cohorts, as well as in a control group made of first-degree normal relatives of the insulin-resistant phenotype subjects.

RESULTS

The metabolic characteristics of enhanced insulin sensitivity in one of the syndromes and innate insulin resistance in the other could not be properly ascertained by the selected methodology. Furthermore, results were confusing and even discrepant with the clinical findings.

CONCLUSIONS

The standard homeostatic minimal models could not properly identify or discriminate insulin sensitivity and resistance in subjects with inherently diminished secretion. It is thereby suggested that these models should be used with caution in clinical situations where reduced secretion of the metabolic peptide is found or suspected.

Metabolic and cardiovascular outcomes of bariatric surgery

PURPOSE OF REVIEW

Bariatric surgery is an effective therapy for morbid obesity that also improves weight-related metabolic parameters and reduces morbidity and mortality. The purpose of this review is to consolidate our current understanding of metabolic, macrovascular and microvascular benefits of bariatric surgery and to provide an update.

RECENT FINDINGS

Early resolution of insulin resistance and type 2 diabetes mellitus (T2DM) varies by type of bariatric surgery and appears to be mediated by changes in secretion of gut hormones, metabolism of bile acids, expression of glucose transporters and the gut microbiome. Dyslipidaemia, atherosclerosis, microvascular complications of obesity and diabetes, systemic and tissue-level inflammation show evidence of regression and hypertension improves significantly after bariatric surgery.

SUMMARY

Bariatric surgery leads to improvements in obesity-related metabolic comorbidities such as dyslipidaemia, HDL functionality, hypertension, T2DM, insulin resistance and inflammation. It slows the atherosclerotic process and reduces cardiovascular and all-cause mortality. Recent data have demonstrated regression of the microvascular complications of obesity and diabetes including the regeneration of small nerve fibres. The magnitude of change in short-term metabolic effects depends on the surgical procedure whilst longer term effects are related to the amount of sustained excess weight loss.

Review article: the impact of liver-directed therapies on the atherogenic risk profile in non-alcoholic steatohepatitis

BACKGROUND

Patients with non-alcoholic fatty liver disease (NAFLD), the most common cause of chronic liver disease, are at higher risk of cardiovascular disease (CVD) and associated mortality. Therefore, it is important to understand how new therapies for non-alcoholic steatohepatitis (NASH) may impact CVD risk factors in these patients.

AIMS

To summarise the effects of drug therapies on lipid and lipoprotein levels in patients with NASH and provide insight into the potential mechanisms for the observed changes.

METHODS

PubMed searches of the literature were performed and results were compiled.

RESULTS

Recent clinical trials have highlighted the safety and efficacy of drug candidates for the treatment of NASH. Several agents have shown improvements in the histological features of NASH and liver function. Pioglitazone, a drug that is currently available for type 2 diabetes and may be useful for NASH, exhibits beneficial effects on lipids. However, agents such as farnesoid X receptor agonists, which are in development for NASH, may adversely affect circulating lipids and lipoproteins.

CONCLUSIONS

NASH is a multi-system disease with a disproportionate CVD burden. Current and future drugs for NASH have had variable impact on the atherogenic risk profile. Potential co-administration of a statin may help mitigate the negative impact of some of these therapies on lipid and lipoprotein levels.

Islet cell dysfunction in patients with chronic pancreatitis

Chronic pancreatitis (CP) is characterized by progressive inflammation and fibrosis of the pancreas that eventually leads to pancreatic exocrine and endocrine insufficiency. Diabetes in the background of CP is very difficult to manage due to high glycemic variability and concomitant malabsorption. Progressive beta cell loss leading to insulin deficiency is the cardinal mechanism underlying diabetes development in CP. Alpha cell dysfunction leading to deranged glucagon secretion has been described in different studies using a variety of stimuli in CP. However, the emerging evidence is varied probably because of dependence on the study procedure, the study population as well as on the stage of the disease. The mechanism behind islet cell dysfunction in CP is multifactorial. The intra-islet alpha and beta cell regulation of each other is often lost. Moreover, secretion of the incretin hormones such as glucagon like peptide-1 and glucose-dependent insulinotropic polypeptide is dysregulated. This significantly contributes to islet cell disturbances. Persistent and progressive inflammation with changes in the function of other cells such as islet delta cells and pancreatic polypeptide cells are also implicated in CP. In addition, the different surgical procedures performed in patients with CP and antihyperglycemic drugs used to treat diabetes associated with CP also affect islet cell function. Hence, different factors such as chronic inflammation, dysregulated incretin axis, surgical interventions and anti-diabetic drugs all affect islet cell function in patients with CP. Newer therapies targeting alpha cell function and beta cell regeneration would be useful in the management of pancreatic diabetes in the near future.

Efficacy and tolerability of tirzepatide, a dual glucose-dependent insulinotropic peptide and glucagon-like peptide-1 receptor agonist in patients with type 2 diabetes: A 12-week, randomized, double-blind, placebo-controlled study to evaluate different dose-escalation regimens

AIM

To assess the efficacy and tolerability of tirzepatide treatment using three different dose-escalation regimens in patients with type 2 diabetes.

MATERIALS AND METHODS

In this double-blind, placebo-controlled study, patients were randomized (1:1:1:1) to receive either once-weekly subcutaneous tirzepatide or placebo. The tirzepatide dose groups and dose-escalation regimens were: 12 mg (4 mg weeks 0-3; 8 mg weeks 4-7; 12 mg weeks 8-11), 15 mg-1 (2.5 mg weeks 0-1; 5 mg weeks 2-3; 10 mg weeks 4-7; 15 mg weeks 8-11) and 15 mg-2 (2.5 mg weeks 0-3; 7.5 mg weeks 4-7; 15 mg weeks 8-11). The primary objective was to compare tirzepatide with placebo in HbA1c change from baseline at 12 weeks.

RESULTS

Overall, 111 patients were randomized: placebo, 26; tirzepatide 12 mg, 29; tirzepatide 15 mg-1, 28; tirzepatide 15 mg-2, 28. The mean age was 57.4 years, HbA1c 8.4% and body mass index 31.9 kg/m² . At week 12, absolute HbA1c change from baseline (SE) was greater in the tirzepatide treatment groups compared with placebo (placebo, +0.2% [0.21]; 12 mg, -1.7% [0.19]; 15 mg-1, -2.0% [0.20]; 15 mg-2, -1.8% [0.19]). The incidence of nausea was: placebo, 7.7%; 12 mg group, 24.1%; 15 mg-1 group, 39.3%; 15 mg-2 group, 35.7%. Three patients discontinued the treatment because of adverse events, one from each of the placebo, 12 mg and 15 mg-1 groups.

CONCLUSIONS

Tirzepatide treatment for 12 weeks resulted in clinically significant reductions in HbA1c. This suggests that lower starting doses and smaller dose increments are associated with a more favourable side effect profile.

Insights into incretin-based therapies for treatment of diabetic dyslipidemia

Derangements in triglyceride and cholesterol metabolism (dyslipidemia) are major risk factors for the development of cardiovascular diseases in obese and type-2 diabetic (T2D) patients. An emerging class of glucagon-like peptide-1 (GLP-1) analogues and next generation peptide dual-agonists such as GLP-1/glucagon or GLP-1/GIP could provide effective therapeutic options for T2D patients. In addition to their role in glucose and energy homeostasis, GLP-1, GIP and glucagon serve as regulators of lipid metabolism. This review summarizes the current knowledge in GLP-1, glucagon and GIP effects on lipid and lipoprotein metabolism and frames the emerging therapeutic benefits of GLP-1 analogs and GLP-1-based multiagonists as add-on treatment options for diabetes associated dyslipidemia.

Leveraging the Gut to Treat Metabolic Disease

25 years ago, the future of treating obesity and diabetes focused on end organs known to be involved in energy balance and glucose regulation, including the brain, muscle, adipose tissue, and pancreas. Today, the most effective therapies are focused around the gut. This includes surgical options, such as vertical sleeve gastrectomy and Roux-en-Y gastric bypass, that can produce sustained weight loss and diabetes remission but also extends to pharmacological treatments that simulate or amplify various signals that come from the gut. The purpose of this Review is to discuss the wealth of approaches currently under development that seek to further leverage the gut as a source of novel therapeutic opportunities with the hope that we can achieve the effects of surgical interventions with less invasive and more scalable solutions.

No evidence of tachyphylaxis for insulinotropic actions of glucose-dependent insulinotropic polypeptide (GIP) in subjects with type 2 diabetes, their first-degree relatives, or in healthy subjects

BACKGROUND, AIMS

In patients with type 2 diabetes, the lost insulinotropic effect of the incretin hormone glucose-dependent insulinotropic polypeptide (GIP) is more apparent after continuous versus bolus administration. To test whether the difference might be explained by rapid tachyphylaxis in response to elevated concentrations of GIP, and whether patients with type 2 diabetes and their relatives are more susceptible to tachyphylaxis than healthy subjects.

PATIENTS AND METHODS

In a two-way crossover design, insulinotropic responses to repeated bolus injection (50 pmol/kg body weight at 30 and 120 min) and continuous infusion of GIP (2 pmol.kg-1.min-1 from 30 to 180 min) under hyperglycaemic clamp conditions (8.5 mmol/l) was compared in age- gender- and weight-matched patients with type 2 diabetes, first degree relatives of such patients, and healthy subjects.

RESULTS

Insulin secretory responses to the first and second GIP bolus were not significantly different in any of the subject groups. Subjects with type 2 diabetes had a significant relative impairment versus healthy subjects with continuous (C-peptide, -13.2 %, p < 0.05), but not with repeated bolus administration of GIP (+11.1 %, n.s.). First-degree relatives tended to hyper-secrete insulin with bolus or continuous administrations of GIP.

CONCLUSIONS

Rapid tachyphylaxis in response to continuous exposure to slightly supraphysiological concentrations of GIP does not explain the reduced insulinotropic response to GIP infusions in patients with type 2 diabetes or their first-degree relatives.

Predictive effect of GIPR SNP rs10423928 on glucose metabolism liver fat and adiposity in prediabetic and diabetic subjects

The gastric inhibitory polypeptide receptor (GIPR) regulates postprandial metabolism. In this context GIPR SNP rs10423928 seems toplay an important role in modulating glucose metabolism and insulinsensitivity. However, evidence regarding thisparticular SNP is still vague. In this study, we collected baseline data from four different dietaryintervention studies. We genotyped 424 subjects with prediabetes and 73with diabetes for GIPR SNP rs10423928 and examined its impact on glucosemetabolism, insulin sensitivity and body fat accumulation. We extended previous data by showing that carriers of the A allele withprediabetes displayed increased fasting glucose (p = 0.015). Unexpectedly,A allele carriers showed lower glucose levels 2 h (p = 0.021) after anoral glucose challenge compared to T/T homozygous individuals. A allelecarriers also showed significantly higher insulin sensitivity (p < 0.001)(assessed by Cederholm Index), indicating an enhanced ß-cell response. This study points to a potential protective role for rs10423928 inglucose metabolism and insulin sensitivity in subjects with prediabetes.Further studies are necessary to confirm these results.

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

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

Inadequate β-cell mass is essential for the pathogenesis of type 2 diabetes

For patients with type 1 diabetes, it is accepted among the scientific community that there is a marked reduction in β-cell mass; however, with type 2 diabetes, there is disagreement as to whether this reduction in mass occurs in every case. Some have argued that β-cell mass in some patients with type 2 diabetes is normal and that the cause of the hyperglycaemia in these patients is a functional abnormality of insulin secretion. In this Personal View, we argue that a deficient β-cell mass is essential for the development of type 2 diabetes. The main point is that there are enormous (≥10 fold) variations in insulin sensitivity and insulin secretion in the general population, with a very close correlation between these two factors for any individual. Although β-cell mass cannot be accurately measured in living patients, it is highly likely that it too is highly correlated with insulin sensitivity and secretion. Thus, our argument is that a person with type 2 diabetes can have a β-cell mass that is the same as a person without type 2 diabetes, but because they are insulin resistant, the mass is inadequate and responsible for their diabetes. Because the abnormal insulin secretion of diabetes is caused by dysglycaemia and can be largely reversed with glycaemic control, it is a less serious problem than the reduction in β-cell mass, which is far more difficult to restore.

Single-Anastomosis Duodenal Jejunal Bypass Improve Glucose Metabolism by Regulating Gut Microbiota and Short-Chain Fatty Acids in Goto-Kakisaki Rats

In recent years, bariatric surgery has emerged as a promising treatment for type 2 diabetes. Bariatric surgery is known to cause alterations in the relative abundance and composition of gut microbiota, which may lead to alterations in the levels of Short-Chain Fatty Acids (SCFAs) that are produced during fermentation by gut microbes. However, little is known about the mechanism of improved glucose metabolism mediated by gut microbiota following bariatric surgery. The aim of our study was to explore whether changes in gut microbiota and in fecal SCFA could be detected following single-anastomosis duodenal jejunal bypass (DJB-sa) surgery, a type of bariatric surgery, and whether these alterations might be related to the improvement of glucose metabolism. To this end, we performed DJB-sa or SHAM surgery on Goto-Kakisaki (GK) rats. We then compared the glucose metabolism as well as changes in gut microbiota and SCFAs levels between both groups. Our results showed that DJB-sa surgery was associated with a significant decrease in fasting blood glucose (FBG), intraperitoneal glucose tolerance test (IPGTT), and fasting serum insulin (FSI). And, DJB-sa led to a change in the composition of gut microbiota including an increase in the relative abundance of SCFA-producing bacteria (Bifidobacterium and Subdoligranulum). Moreover, the levels of six SCFAs in feces, as well as the intestinal expression of SCFA receptors including G-protein-coupled receptor 41 (GPR41), G-protein-coupled receptor 43 (GPR43), and G-protein-coupled receptor 109A (GPR109A), and the expression of Glucagon-like peptide-1 (GLP-1) displayed a significant increase following DJB-sa compared with the Sham group. Thus, the gut microbiota may contribute to the improvement of glucose metabolism in type 2 diabetes following DJB-sa. In conclusion, our study shows that DJB-sa improves glucose metabolism by modulating gut microbiota and by increasing short-chain fatty acid production.

What Is GLP-1 Really Doing in Obesity?

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone released in response to meal ingestion and enhances insulin secretion from pancreatic β cells. In several human studies, GLP-1 secretory responses to oral glucose load or a meal were decreased in subjects with obesity, glucose intolerance, or diabetes compared with those in healthy subjects. However, the results of meta-analysis and cohort studies do not necessarily support this concept. Results from animal studies are also inconsistent; in multiple studies, GLP-1 secretory responses to a meal were repeatedly higher in diet-induced obese rats than in control rats. Thus, the postprandial GLP-1 response is not necessarily decreased but rather enhanced during obesity development, which is likely to play a protective role against glucose intolerance.

Porcine models for studying complications and organ crosstalk in diabetes mellitus

The worldwide prevalence of diabetes mellitus and obesity is rapidly increasing not only in adults but also in children and adolescents. Diabetes is associated with macrovascular complications increasing the risk for cardiovascular disease and stroke, as well as microvascular complications leading to diabetic nephropathy, retinopathy and neuropathy. Animal models are essential for studying disease mechanisms and for developing and testing diagnostic procedures and therapeutic strategies. Rodent models are most widely used but have limitations in translational research. Porcine models have the potential to bridge the gap between basic studies and clinical trials in human patients. This article provides an overview of concepts for the development of porcine models for diabetes and obesity research, with a focus on genetically engineered models. Diabetes-associated ocular, cardiovascular and renal alterations observed in diabetic pig models are summarized and their similarities with complications in diabetic patients are discussed. Systematic multi-organ biobanking of porcine models of diabetes and obesity and molecular profiling of representative tissue samples on different levels, e.g., on the transcriptome, proteome, or metabolome level, is proposed as a strategy for discovering tissue-specific pathomechanisms and their molecular key drivers using systems biology tools. This is exemplified by a recent study providing multi-omics insights into functional changes of the liver in a transgenic pig model for insulin-deficient diabetes mellitus. Collectively, these approaches will provide a better understanding of organ crosstalk in diabetes mellitus and eventually reveal new molecular targets for the prevention, early diagnosis and treatment of diabetes mellitus and its associated complications.

Effect of Dietary Macronutrients on Postprandial Glucagon and Insulin Release in Obese and Normal-Weight Women

The aim of the study was to assess the effect of dietary macronutrients on circulating glucagon and insulin levels in obese and normal-weight women. Potentially, the impaired release of glucagon may proceed abnormal glucose metabolism in obese patients ahead of overt diabetes. In 20 insulin-sensitive women (11 obese and 9 normal-weight), plasma concentrations of insulin and glucagon levels were assessed before and after 3 different macronutrient test meals. AUC_total insulin in the obese group was increased after protein and carbohydrates compared to fatty test meal consumption (3981 ± 2171 and 4869 ± 2784 vs. 2349 ± 1004 μIU∗h/m, p < 0.05, respectively), but without a difference between protein and carbohydrates ingestion. However, in the normal-weight group, AUC_total insulin was increased after carbohydrates compared to fatty test meal ingestion (3929 ± 1719 vs. 2231 ± 509 μIU∗h/ml, p < 0.05) and similar after carbohydrate and protein as well as after fatty and protein test meals (3929 ± 1719 vs. 2231 ± 509 vs. 3046 ± 1406 μIU∗h/ml, respectively). However, AUC_total insulin was significantly increased in obese compared to normal-weight women only after carbohydrate test meal ingestion (4869 ± 2784 vs. 3929 ± 1719 μIU∗h/ml, p < 0.05). AUC_total glucagon was similar after carbohydrate, protein, and fatty test meals ingestion in obese and normal-weight women (921 ± 356 vs. 957 ± 368 vs. 926 ± 262 ng∗h/ml and 1196 ± 14 vs. 1360 ± 662 vs. 1792 ± 1176 ng∗h/ml, respectively). AUC_total glucagon was significantly lower in obese than normal-weight women after a fatty meal (926 ± 262 vs. 1792 ± 1176 ng∗h/ml, p < 0.01). Postprandial glucagon secretion is not related to the macronutrient composition of the meal in normal-weight women since postprandial glucagon concentrations were stable and did not change after carbohydrate, protein, and fatty test meals. Lower glucagon secretion was observed in obese subjects after fatty meal consumption when compared to normal-weight subjects. Postprandial insulin profile was significantly higher after carbohydrate than fatty test meal intake in the obese group and did not differ between obese and normal-weight groups after carbohydrate, protein, and fatty test meals consumption. Impaired glucagon secretion after fatty meat suggests early pancreatic alpha-cell dysfunction, after a carbohydrate meal is a compensatory mechanism.

Intestinal Fructose and Glucose Metabolism in Health and Disease

The worldwide epidemics of obesity and diabetes have been linked to increased sugar consumption in humans. Here, we review fructose and glucose metabolism, as well as potential molecular mechanisms by which excessive sugar consumption is associated to metabolic diseases and insulin resistance in humans. To this end, we focus on understanding molecular and cellular mechanisms of fructose and glucose transport and sensing in the intestine, the intracellular signaling effects of dietary sugar metabolism, and its impact on glucose homeostasis in health and disease. Finally, the peripheral and central effects of dietary sugars on the gut-brain axis will be reviewed.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent β-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases.

MAJOR CONCLUSIONS

Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Subjects with high fasting insulin also have higher postprandial GLP-1 and glucagon levels than controls with lower insulin

Little is known about postprandial release of serum ghrelin, glucagon, and glucagon-like peptide-1 (GLP-1) in relation with differing fasting insulin levels. We hypothesized that these hormones are affected by insulin resistance, and hence, we compared different postprandial responses of GLP-1, glucagon, and ghrelin in subjects with relatively high (RHI) or relatively low (RLI) fasting insulin levels. The trial was a randomized crossover study with 4 different meal conditions. Fourteen nonobese or obese, healthy, men and 14 women were randomly assigned to the order of supervised intake of a 750 kcal drink with the same protein contents but with 20 energy-percent (E%) or 55 E% from carbohydrates, and the remaining energy from fat. Participants were also randomized to consume the drinks as 1 large beverage or as five 150-kcal portions every 30 minutes. The 28 subjects were divided into 2 equally sized groups based on fasting insulin levels. Statistics were done with general linear mixed model. Fasting insulin levels were 3-fold higher in the group with RHI compared with the RLI group (RHI: 1004 ± 510 pg/mL, RLI: 324 ± 123 pg/mL, P < .0005). Serum GLP-1 was highest in the RHI group after both single meals and after 5 drinks and following high- and low-carbohydrate meals (both P ≤ .002), and this was the case also for glucagon levels (both P ≤ .018), whereas ghrelin levels did not differ between groups. Thus, subjects with RHI displayed both higher postprandial serum GLP-1 and glucagon than the participants with RLI, suggesting that glucagon could play a role in the advent of dysglycemia by insulin resistance.

Loss of incretin effect contributes to postprandial hyperglycaemia in cystic fibrosis-related diabetes

AIM

To investigate the incretin axis in people with cystic fibrosis.

METHODS

Adults with cystic fibrosis-related diabetes, cystic fibrosis without diabetes, and controls (adults without cystic fibrosis and without diabetes) underwent an oral glucose tolerance test and then a closely matched isoglycaemic i.v. glucose infusion. On each occasion, glucose, insulin, C-peptide, total and active glucagon-like peptide-1 and gastric inhibitory polypeptide responses were recorded and incremental areas under curves were calculated for 60 and 240 min.

RESULTS

Five adults with cystic fibrosis-related diabetes, six with cystic fibrosis without diabetes and six controls, matched for age and BMI, completed the study. Glucose during oral glucose tolerance test closely matched those during isoglycaemic i.v. glucose infusion. The calculated incretin effect was similar in the control group and the cystic fibrosis without diabetes group (28% and 29%, respectively), but was lost in the cystic fibrosis-related diabetes group (cystic fibrosis-related diabetes vs control group: -6% vs 28%; p=0.03). No hyposecretion of glucagon-like peptide-1 or gastric inhibitory polypeptide was observed; conversely, 60-min incremental area under the curve for total glucagon-like peptide-1 was significantly higher in the cystic fibrosis-related diabetes group than in the control group [1070.4 (254.7) vs 694.97 (308.1); p=0.03] CONCLUSIONS: The incretin effect was lost in cystic fibrosis-related diabetes despite adequate secretion of the incretin hormones. These data support the concept that reduced incretin hormone insulinotropic activity contributes significantly to postprandial hyperglycaemia in cystic fibrosis-related diabetes.

Milk in the prevention and management of type 2 diabetes: The potential role of milk proteins

Globally, diabetes mellitus is not only considered a leading cause of mortality and morbidities but has also created a substantial economic burden. There is growing evidence that foods and their components can be implemented in the prevention and management of type 2 diabetes mellitus (T2DM). Increased dairy consumption has been linked to a lower risk of T2DM. The protective role of dairy foods in the development of T2DM is thought to be largely attributable to dairy nutrients, one of them being dairy protein. There is considerable evidence that milk proteins increase the postprandial insulin response and lower the postprandial blood glucose response in both healthy subjects and patients with T2DM. The exact mechanisms by which milk proteins lower postprandial glucose levels are yet to established; however, the amino acids and bioactive peptides derived from milk proteins are thought to modify a physiological milieu, which includes delayed gastric emptying and the enhancement of incretin and insulin responses, consequently leading to lower postprandial glucose levels. The present review will focus on providing a clear presentation of the potential implementation of milk proteins as a dietary supplement in the prevention and management of T2DM by summarizing the relevant supporting evidence for this particular topic.

The Liver-α-Cell Axis and Type 2 Diabetes

Both type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD) strongly associate with increasing body mass index, and together these metabolic diseases affect millions of individuals. In patients with T2D, increased secretion of glucagon (hyperglucagonemia) contributes to diabetic hyperglycemia as proven by the significant lowering of fasting plasma glucose levels following glucagon receptor antagonist administration. Emerging data now indicate that the elevated plasma concentrations of glucagon may also be associated with hepatic steatosis and not necessarily with the presence or absence of T2D. Thus, fatty liver disease, most often secondary to overeating, may result in impaired amino acid turnover, leading to increased plasma concentrations of certain glucagonotropic amino acids (e.g., alanine). This, in turn, causes increased glucagon secretion that may help to restore amino acid turnover and ureagenesis, but it may eventually also lead to increased hepatic glucose production, a hallmark of T2D. Early experimental findings support the hypothesis that hepatic steatosis impairs glucagon's actions on amino acid turnover and ureagenesis. Hepatic steatosis also impairs hepatic insulin sensitivity and clearance that, together with hyperglycemia and hyperaminoacidemia, lead to peripheral hyperinsulinemia; systemic hyperinsulinemia may itself contribute to worsen peripheral insulin resistance. Additionally, obesity is accompanied by an impaired incretin effect, causing meal-related glucose intolerance. Lipid-induced impairment of hepatic sensitivity, not only to insulin but potentially also to glucagon, resulting in both hyperinsulinemia and hyperglucagonemia, may therefore contribute to the development of T2D at least in a subset of individuals with NAFLD.

The effect of oral essential amino acids on incretin hormone production in youth and ageing

BACKGROUND

The effect of substantive doses of essential amino acids (EAA) on incretin and insulin production, and the impact of age upon this effect, is ill-defined.

METHODS

A 15-g oral EAA drink was administered to young (N = 8; 26 ± 4.4 years) and older (N = 8; 69 ± 3.8 years) healthy volunteers. Another group of younger volunteers (N = 9; 21 ± 1.9 years) was given IV infusions to achieve equivalent plasma amino acids (AA) profiles. Plasma AA, insulin, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) were quantified over 2 hours.

RESULTS

In younger recruits, EAA-induced rapid insulinaemia and aminoacidaemia with total amino acids(AA), EAA and branched chain amino acids (BCAA) matched between oral and IV groups. Insulin peaked at 39 ± 29 pmol L-1 at 30 minutes following oral feeding compared to 22 ± 9 pmol L-1 at 60 minutes following IV feeding (P: NS). EAA peaked at 3395 μmol L-1 at 45 minutes during IV infusion compared to 2892 μmol L-1 following oral intake (Feeding effect: P < 0.0001. Oral vs IV feeding: P: NS). There was an 11% greater increase in insulin levels in the 120 minutes duration of the study in response to oral EAA as opposed to IV EAA. GIP increased following oral EAA (452 pmol L-1 vs 232 pmol L-1, P < 0.05). Age did not impact insulin or incretins production.

CONCLUSION

Postprandial rises in EAA levels lead to rapid insulinaemia which is higher with oral compared with IV EAA, that is attributed more to GIP and unaffected by age. This finding supports EAA, on their own or as part of high-protein meal, as nutritive therapeutics in impaired glycaemia and ageing.

Glucagon-like peptide 1 and Glucagon-like peptide 2 in relation to osteoporosis in non-diabetic postmenopausal women

Osteoporosis results from an imbalance in bone remodeling, which is known to follow a circadian rhythm determined by a functional relationship between intestine and bone tissue. Specific intestinal peptides have been identified as mediators. Glucagon-like peptide 1 and glucagon-like peptide 2, have been associated with bone health. Our main objective was to determine whether postprandial plasma levels of glucagon-like peptide 1, glucagon-like peptide 2 and dipeptidyl-peptidase 4 activity, are associated with osteoporosis in non-diabetic postmenopausal women. We studied non-diabetic postmenopausal women with osteoporosis diagnosed by dual-energy X-ray absorptiometry (cases, n = 43) and age-matched (±1 yr) controls without osteoporosis or a history of osteoporotic fracture (n = 43). We measured postprandial plasma levels of glucagon-like peptide 1, glucagon-like peptide 2, and dipeptidyl-peptidase 4 activity, bone mineral density, and baseline levels of bone remodeling markers and analyzed the food intake using a food-frequency questionnaire. Postprandial glucagon-like peptide 1 values were lower (p < 0.001) in cases, μ (SEM) = 116.25 (2.68), than in controls, μ (SEM) = 126.79 (2.68). Glucagon-like peptide 1 was associated with reduced osteoporosis risk in the crude logistic regression analysis [OR (95% CI) = 0.724 (0.53-0.97), p = 0.031] and adjusted analysis [OR = 0.603 (0.38-0.94), p = 0.027]. We found no association of glucagon-like peptide 2, or dipeptidyl-peptidase 4 activity with osteoporosis. Postprandial glucagon-like peptide 1 levels are related to osteoporosis and osteoporosis risk in non-diabetic postmenopausal women. Further studies are required to verify these findings.

New Insights into Beta-Cell GLP-1 Receptor and cAMP Signaling

Harnessing the translational potential of the GLP-1/GLP-1R system in pancreatic beta cells has led to the development of established GLP-1R-based therapies for the long-term preservation of beta cell function. In this review, we discuss recent advances in the current research on the GLP-1/GLP-1R system in beta cells, including the regulation of signaling by endocytic trafficking as well as the application of concepts such as signal bias, allosteric modulation, dual agonism, polymorphic receptor variants, spatial compartmentalization of cAMP signaling and new downstream signaling targets involved in the control of beta cell function.

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

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

Incretin Hormones: The Link between Glycemic Index and Cardiometabolic Diseases

This review aimed to describe the potential mechanisms by which incretin hormones could mediate the relationship between glycemic index and cardiometabolic diseases. A body of evidence from many studies suggests that low glycemic index (GI) diets reduces the risk for type 2 diabetes and coronary heart disease. In fact, despite the extensive literature on this topic, the mechanisms underlying unfavorable effects of high GI foods on health remain not well defined. The postprandial and hormonal milieu could play a key role in the relationship between GI and cardiovascular risk. Incretin hormones, glucagon-like peptide1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are important regulators of postprandial homeostasis by amplifying insulin secretory responses. Response of GIP and GLP-1 to GI have been studied more in depth, also by several studies on isomaltulose, which have been taken as an ideal model to investigate the kinetics of incretin secretion in response to foods’ GI. In addition, extrapancreatic effects of these incretin hormones were also recently observed. Emerging from this have been exciting effects on several targets, such as body weight regulation, lipid metabolism, white adipose tissue, cardiovascular system, kidney, and liver, which may importantly affect the health status.

Factors Related to Blood Intact Incretin Levels in Patients with Type 2 Diabetes Mellitus

BACKGROUND

We performed this study to identify factors related to intact incretin levels in patients with type 2 diabetes mellitus (T2DM).

METHODS

We cross-sectionally analyzed 336 patients with T2DM. Intact glucagon-like peptide 1 (iGLP-1) and intact glucose-dependent insulinotropic polypeptide (iGIP) levels were measured in a fasted state and 30 minutes after ingestion of a standard mixed meal. The differences between 30 and 0 minute iGLP-1 and iGIP levels were indicated as ΔiGLP-1 and ΔiGIP.

RESULTS

In simple correlation analyses, fasting iGLP-1 was positively correlated with glucose, C-peptide, creatinine, and triglyceride levels, and negatively correlated with estimated glomerular filtration rate. ΔiGLP-1 was positively correlated only with ΔC-peptide levels. Fasting iGIP showed positive correlations with glycosylated hemoglobin (HbA1c) and fasting glucose levels, and negative correlations with ΔC-peptide levels. ΔiGIP was negatively correlated with diabetes duration and HbA1c levels, and positively correlated with Δglucose and ΔC-peptide levels. In multivariate analyses adjusting for age, sex, and covariates, fasting iGLP-1 levels were significantly related to fasting glucose levels, ΔiGLP-1 levels were positively related to ΔC-peptide levels, fasting iGIP levels were related to fasting C-peptide levels, and ΔiGIP levels were positively related to ΔC-peptide and Δglucose levels.

CONCLUSION

Taken together, intact incretin levels are primarily related to C-peptide and glucose levels. This result suggests that glycemia and insulin secretion are the main factors associated with intact incretin levels in T2DM patients.

Effect of Oral Nutritional Supplements with Sucromalt and Isomaltulose versus Standard Formula on Glycaemic Index, Entero-Insular Axis Peptides and Subjective Appetite in Patients with Type 2 Diabetes: A Randomised Cross-Over Study

Oral diabetes-specific nutritional supplements (ONS-D) induce favourable postprandial responses in subjects with type 2 diabetes (DM2), but they have not been correlated yet with incretin release and subjective appetite (SA). This randomised, double-blind, cross-over study compared postprandial effects of ONS-D with isomaltulose and sucromalt versus standard formula (ET) on glycaemic index (GI), insulin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1) and SA in 16 individuals with DM2. After overnight fasting, subjects consumed a portion of supplements containing 25 g of carbohydrates or reference food. Blood samples were collected at baseline and at 30, 60, 90, 120, 150 and 180 min; and SA sensations were assessed by a visual analogue scale on separate days. Glycaemic index values were low for ONS-D and intermediate for ET (p < 0.001). The insulin area under the curve (AUC0-180 min) (p < 0.02) and GIP AUC (p < 0.02) were lower after ONS-D and higher GLP-1 AUC when compared with ET (p < 0.05). Subjective appetite AUC was greater after ET than ONS-D (p < 0.05). Interactions between hormones, hunger, fullness and GI were found, but not within the ratings of SA; isomaltulose and sucromalt may have influenced these factors.

Sacubitril/valsartan augments postprandial plasma concentrations of active GLP-1 when combined with sitagliptin in men

CONTEXT

Combined inhibition of neprilysin and dipeptidyl peptidase 4 (DPP-4) has been shown to augment plasma concentrations of glucagon-like peptide-1(GLP-1) in animal models, but whether this occurs in humans is unknown.

OBJECTIVE

To investigate the effects of inhibition of neprilysin by sacubitril/valsartan alone or in combination with a DPP-4 inhibitor (sitagliptin) on plasma concentrations of GLP-1 in healthy men.

DESIGN

Two open-labeled crossover studies were performed in human subjects.

SETTING

General community.

PARTICIPANTS

Nine and 10 healthy young males were included in study 1 and study 2, respectively.

INTERVENTION

Study participants received a standardized meal (34% carbohydrates, 45% fat, 21% protein, total caloric content of 2106kJ) combined with a prior dose of either sacubitril/valsartan (194/206mg) or control in study 1, and in study 2, with a prior dose of sitagliptin (2x100mg, given ∼10 hours apart) either alone or with sacubitril/valsartan (194/206mg).

MAIN OUTCOME MEASURES

Plasma concentrations of total and intact GLP-1.

RESULTS

Sacubitril/valsartan increased postprandial plasma concentrations of total GLP-1 by 67% (tAUC0-240min: 3929±344 vs. 2348±181 min × pmol/L P=0.0023), and increased concentrations of intact GLP-1 plasma concentrations more than sitagliptin alone (tAUC0-240min: 1021±114 vs. 660±80 min × pmol/L, P=0.01). Plasma concentrations of glucose, insulin, and GIP were not significantly (P>0.10) changed upon sacubitril/valsartan treatment.

CONCLUSIONS

Sacubitril/valsartan combined with a DPP-4 inhibitor lead to markedly higher concentrations of intact GLP-1 than DPP-4 inhibition alone, supporting a role for both neprilysin and DPP-4 in the metabolism of GLP-1 in humans, a finding which may have therapeutic implications.

Separate and Combined Glucometabolic Effects of Endogenous Glucose-Dependent Insulinotropic Polypeptide and Glucagon-like Peptide 1 in Healthy Individuals

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are secreted postprandially and contribute importantly to postprandial glucose tolerance. In this study, we assessed the individual and combined contributions of endogenous GIP and GLP-1 to the postprandial changes in glucose and glucoregulatory hormones using the novel GIP receptor antagonist GIP(3-30)NH₂ and the well-established GLP-1 receptor antagonist exendin(9-39)NH₂ During 4-h oral glucose tolerance tests (75 g) combined with an ad libitum meal test, 18 healthy men received on four separate days in randomized, double-blinded order intravenous infusions of A) GIP(3-30)NH₂ (800 pmol/kg/min) plus exendin(9-39)NH₂ (0-20 min: 1,000 pmol/kg/min; 20-240 min: 450 pmol/kg/min), B) GIP(3-30)NH₂, C) exendin(9-39)NH₂, and D) saline, respectively. Glucose excursions were significantly higher during A than during B, C, and D, while glucose excursions during B were higher than during C and D. Insulin secretion (assessed by C-peptide/glucose ratio) was reduced by 37 ± 16% (A), 30 ± 17% (B), and 8.6 ± 16% (C) compared with D (mean ± SD). A and C resulted in higher glucagon levels and faster gastric emptying. In conclusion, endogenous GIP affects postprandial plasma glucose excursions and insulin secretion more than endogenous GLP-1, but the hormones contribute additively to postprandial glucose regulation in healthy individuals.

New pharmacological strategies for protecting kidney function in type 2 diabetes

Type 2 diabetes is the leading cause of impaired kidney function, albuminuria, and renal replacement therapy globally, thus placing a large burden on health-care systems. Current treatment strategies rely on intensive glucose lowering as well as strict blood pressure control through blockade of the renin-angiotensin-aldosterone system. Such approaches might slow decline in kidney function, but many patients progress to end-stage kidney failure despite optimal therapy. In recent clinical trials, new-generation glucose-lowering drug classes, the sodium-glucose co-transporter-2 inhibitors and agents that target the incretin pathway, have been shown to improve kidney outcomes in patients with type 2 diabetes. Other new approaches, which have been developed on the basis of an improved understanding of the mechanisms that contribute to kidney damage in the context of diabetes, include use of drugs that block endothelin receptors (eg, atrasentan) and non-steroidal mineralocorticoid receptors (eg, finerenone). In this Review, we provide an overview of recent clinical data relevant to these new therapeutic approaches for management of kidney disease in the context of type 2 diabetes.

Glucose-dependent Insulinotropic Polypeptide (GIP) Resistance and β-cell Dysfunction Contribute to Hyperglycaemia in Acromegaly

Impaired insulin sensitivity (IS) and β-cell dysfunction result in hyperglycaemia in patients of acromegaly. However, alterations in incretins and their impact on glucose-insulin homeostasis in these patients still remain elusive. Twenty patients of active acromegaly (10 each, with and without diabetes) underwent hyperinsulinemic euglycaemic clamp and mixed meal test, before and after surgery, to measure indices of IS, β-cell function, GIP, GLP-1 and glucagon response. Immunohistochemistry (IHC) for GIP and GLP-1 was also done on intestinal biopsies of all acromegalics and healthy controls. Patients of acromegaly, irrespective of presence or absence of hyperglycaemia, had similar degree of insulin resistance, however patients with diabetes exhibited hyperglucagonemia, and compromised β-cell function despite significantly higher GIP levels. After surgery, indices of IS improved, GIP and glucagon levels decreased significantly in both the groups, while there was no significant change in indices of β-cell function in those with hyperglycaemia. IHC positivity for GIP, but not GLP-1, staining cells in duodenum and colon was significantly lower in acromegalics with diabetes as compared to healthy controls possibly because of high K-cell turnover. Chronic GH excess induces an equipoise insulin resistance in patients of acromegaly irrespective of their glycaemic status. Dysglycaemia in these patients is an outcome of β-cell dysfunction consequent to GIP resistance and hyperglucagonemia.

The effect of sodium-glucose cotransporter 2 inhibitors and glucagon-like peptide 1 agonists on cardiovascular disease in patients with type 2 diabetes

Patients with type 2 diabetes have a significantly increased risk of cardiovascular disease (CVD) compared to the general population-with CVD accounting for two out of every three deaths in patients with diabetes. In 2008, the FDA suggested that CVD risk should be evaluated for any new antidiabetic therapy, leading to a multitude of large CVD outcome trials to assess CVD risk from these medications. Interestingly, several of these outcome trials with new novel antidiabetic therapies have demonstrated a clear and definite CVD advantage at mid-term follow up in high-risk patients with T2DM. In this review, we discuss two relatively new classes of diabetic drugs, sodium-glucose cotransporter 2 inhibitors and glucagon-like peptide 1 agonists, and their efficacy in improving cardiovascular outcomes.

Early glycemic control and incretin improvement after gastric bypass: the role of oral and gastrostomy route

BACKGROUND

Patients with obesity have a suppressed incretin effect and a consequent imbalance of glycemic homeostasis. Several studies have shown improved type 2 diabetes after Roux-en-Y gastric bypass (RYGB). The mechanisms of early action are linked to caloric restriction, improvement of insulin resistance, pancreatic beta cell function, and the incretin effect of glycogen-like protein 1 and gastric inhibitory polypeptide, but reported data are conflicting.

OBJECTIVE

The objective of this study was to evaluate glycemic metabolism, including the oral glucose tolerance test and enterohormonal profile in the early postoperative period in severely obese patients who underwent RYGB with gastrostomy, comparing the preoperative supply of a standard bolus of nutrient against the postoperative administration through an oral and a gastrostomy route.

SETTING

Clinics Hospital of University of São Paulo, Brazil.

METHODS

Eleven patients with obesity and diabetes underwent RYGB with a gastrostomy performed in the excluded gastric remnant. Patients were given preoperative assessments of glycemic and enterohormone profiles and an oral glucose tolerance test; these were compared with early postoperative assessments after oral and gastrostomy route administrations.

RESULTS

The mean preoperative body mass index of the group was 44.1 ± 6.6 kg/m², mean fasting blood glucose of 194.5 ± 62.4 mg/dL, and glycated hemoglobin 8.7 ± 1.6%. In 77.7% of the patients, there was normalization of the glycemic curve in the early postoperative period as evaluated by the oral glucose tolerance test. Significant decreases in glycemia, insulinemia, and homeostatic model assessment-insulin resistance were also observed, regardless of the route of administration. There was significant increase in glycogen-like protein 1 by the postoperative oral route and reduction of gastric inhibitory polypeptide in both routes. Ghrelin did not change.

CONCLUSION

Glycemia and peripheral insulin resistance reductions were observed in early-postoperative RYGB, independent of the oral or gastrostomy route. Incretin improvement, mediated by glycogen-like protein 1 increased was observed only in the postoperative oral route, while GIP reduced for both routes.