The impact of type 2 diabetes and glycaemic control on mortality and clinical outcomes in hospitalized patients with COVID-19 in the capital region of Denmark.

AIM: To explore the impact of type 2 diabetes (T2D), glycaemic control and use of glucose-lowering medication on clinical outcomes in hospitalized patients with COVID-19. MATERIALS AND METHODS: For all patients admitted to a hospital in the Capital Region of Denmark (1 March 2020 to 1 December 2021) with confirmed COVID-19, we extracted data on mortality, admission to intensive care unit (ICU), demographics, comorbidities, medication use and laboratory tests from the electronic health record system. We compared patients with T2D to patients without diabetes using Cox proportional hazards models adjusted for available confounding variables. Outcomes were 30-day mortality and admission to an ICU. For patients with T2D, we also analysed the association of baseline haemoglobin A1c (HbA1c) levels and use of specific glucose-lowering medications with the outcomes. RESULTS: In total, 4430 patients were analysed, 1236 with T2D and 2194 without diabetes. The overall 30-day mortality was 19% (n = 850) and 10% (n = 421) were admitted to an ICU. Crude analyses showed that patients with T2D both had increased mortality [hazard ratio (HR) 1.37; 95% CI 1.19-1.58] and increased risk of ICU admission (HR 1.28; 95% CI 1.04-1.57). When adjusted for available confounders, this discrepancy was attenuated for both mortality (adjusted HR 1.13; 95% CI 0.95-1.33) and risk of ICU admission (adjusted HR 1.01; 95% CI 0.79-1.29). Neither baseline haemoglobin A1c nor specific glucose-lowering medication use were significantly associated with the outcomes. CONCLUSION: Among those hospitalized for COVID-19, patients with T2D did not have a higher risk of death and ICU admission, when adjusting for confounders.

The importance of glucose-dependent insulinotropic polypeptide receptor activation for the effects of tirzepatide.

Tirzepatide is a unimolecular co-agonist of the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors recently approved for the treatment of type 2 diabetes by the US Food and Drug Administration and the European Medicine Agency. Tirzepatide treatment results in an unprecedented improvement of glycaemic control and lowering of body weight, but the contribution of the GIP receptor-activating component of tirzepatide to these effects is uncertain. In this review, we present the current knowledge about the physiological roles of the incretin hormones GLP-1 and GIP, their receptors, and previous results of co-targeting the two incretin hormone receptors in humans. We also analyse the molecular pharmacological, preclinical and clinical effects of tirzepatide to discuss the role of GIP receptor activation for the clinical effects of tirzepatide. Based on the available literature on the combination of GLP-1 and GIP receptor activation, tirzepatide does not seem to have a classical co-activating mode of action in humans. Rather, in vitro studies of the human GLP-1 and GIP receptors reveal a biased GLP-1 receptor activation profile and GIP receptor downregulation. Therefore, we propose three hypotheses for the mode of action of tirzepatide, which can be addressed in future, elaborate clinical trials.

The Gut-Bone Axis in Diabetes.

PURPOSE OF REVIEW: To describe recent advances in the understanding of how gut-derived hormones regulate bone homeostasis in humans with emphasis on pathophysiological and therapeutic perspectives in diabetes. RECENT FINDINGS: The gut-derived incretin hormone glucose-dependent insulinotropic polypeptide (GIP) is important for postprandial suppression of bone resorption. The other incretin hormone, glucagon-like peptide 1 (GLP-1), as well as the intestinotrophic glucagon-like peptide 2 (GLP-2) has been shown to suppress bone resorption in pharmacological concentrations, but the role of the endogenous hormones in bone homeostasis is uncertain. For ambiguous reasons, both patients with type 1 and type 2 diabetes have increased fracture risk. In diabetes, the suppressive effect of endogenous GIP on bone resorption seems preserved, while the effect of GLP-2 remains unexplored both pharmacologically and physiologically. GLP-1 receptor agonists, used for the treatment of type 2 diabetes and obesity, may reduce bone loss, but results are inconsistent. GIP is an important physiological suppressor of postprandial bone resorption, while GLP-1 and GLP-2 may also exert bone-preserving effects when used pharmacologically. A better understanding of the actions of these gut hormones on bone homeostasis in patients with diabetes may lead to new strategies for the prevention and treatment of skeletal frailty related to diabetes.

Effects of combined GIP and GLP-1 infusion on energy intake, appetite and energy expenditure in overweight/obese individuals: a randomised, crossover study.

AIMS/HYPOTHESIS: Glucagon-like peptide 1 (GLP-1) reduces appetite and energy intake in humans, whereas the other incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), seems to have no effect on eating behaviour. Interestingly, studies in rodents have shown that concomitant activation of GIP and GLP-1 receptors may potentiate the satiety-promoting effect of GLP-1, and a novel dual GLP-1/GIP receptor agonist was recently shown to trigger greater weight losses compared with a GLP-1 receptor agonist in individuals with type 2 diabetes. The aim of this study was to delineate the effects of combined GIP and GLP-1 receptor activation on energy intake, appetite and resting energy expenditure in humans. METHODS: We examined 17 overweight/obese men in a crossover design with 5 study days. On day 1, a 50 g OGTT was performed; on the following 4 study days, the men received an isoglycaemic i.v. glucose infusion (IIGI) plus saline (154 mmol/l NaCl; placebo), GIP (4 pmol kg-1 min-1), GLP-1 (1 pmol kg-1 min-1) or GIP+GLP-1 (4 and 1 pmol kg-1 min-1, respectively). All IIGIs were performed in a randomised order blinded for the participant and the investigators. The primary endpoint was energy intake as measured by an ad libitum meal after 240 min. Secondary endpoints included appetite ratings and resting energy expenditure, as well as insulin, C-peptide and glucagon responses. RESULTS: Energy intake was significantly reduced during IIGI+GLP-1 compared with IIGI+saline infusion (2715 ± 409 vs 4483 ± 568 kJ [mean ± SEM, n = 17], p = 0.014), whereas there were no significant differences in energy intake during IIGI+GIP (4062 ± 520 kJ) or IIGI+GIP+GLP-1 (3875 ± 451 kJ) infusion compared with IIGI+saline (p = 0.590 and p = 0.364, respectively). Energy intake was higher during IIGI+GIP+GLP-1 compared with IIGI+GLP-1 infusion (p = 0.039). CONCLUSIONS/INTERPRETATION: While GLP-1 infusion lowered energy intake in overweight/obese men, simultaneous GIP infusion did not potentiate this GLP-1-mediated effect. TRIAL REGISTRATION: ClinicalTrials.gov NCT02598791 FUNDING: This study was supported by grants from the Innovation Fund Denmark and the Vissing Foundation.

GIP(3-30)NH2 is an efficacious GIP receptor antagonist in humans: a randomised, double-blinded, placebo-controlled, crossover study.

AIMS/HYPOTHESIS: Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted postprandially from enteroendocrine K cells, but despite therapeutically interesting effects, GIP physiology in humans remains incompletely understood. Progress in this field could be facilitated by a suitable GIP receptor antagonist. For the first time in humans, we investigated the antagonistic properties of the naturally occurring GIP(3-30)NH2 in in vivo and in in vitro receptor studies. METHODS: In transiently transfected COS-7 cells, GIP(3-30)NH2 was evaluated with homologous receptor binding and receptor activation (cAMP accumulation) studies at the glucagon-like peptide 1 (GLP-1), glucagon-like peptide-2 (GLP-2), glucagon, secretin and growth hormone-releasing hormone (GHRH) receptors. Ten healthy men (eligibility criteria: age 20-30 years, HbA1c less than 6.5% [48 mmol/mol] and fasting plasma glucose [FPG] less than 7 mmol/l) were included in the clinical study. Data were collected as plasma and serum samples from a cubital vein cannula. As primary outcome, insulin secretion and glucose requirements were evaluated together with in a randomised, four-period, crossover design by infusing GIP(3-30)NH2 (800 pmol kg-1 min-1), GIP (1.5 pmol kg-1 min-1), a combination of these or placebo during hyperglycaemic clamp experiments. The content of the infusions were blinded to the study participants and experimental personnel. No study participants dropped out. RESULTS: GIP(3-30)NH2 neither bound, stimulated nor antagonised a series of related receptors in vitro. The elimination plasma half-life of GIP(3-30)NH2 in humans was 7.6 ± 1.4 min. Markedly larger amounts of glucose were required to maintain the clamp during GIP infusion compared with the other days. GIP-induced insulin secretion was reduced by 82% (p < 0.0001) during co-infusion with GIP(3-30)NH2, and the need for glucose was reduced to placebo levels. There were no effects of GIP(3-30)NH2 alone or of GIP with or without GIP(3-30)NH2 on plasma glucagon, GLP-1, somatostatin, triacylglycerols, cholesterol, glycerol or NEFA. GIP(3-30)NH2 administration was well tolerated and without side effects. CONCLUSIONS/INTERPRETATION: We conclude that GIP(3-30)NH2 is an efficacious and specific GIP receptor antagonist in humans suitable for studies of GIP physiology and pathophysiology. TRIAL REGISTRATION: ClinicalTrials.gov registration no. NCT02747472. FUNDING: The study was funded by Gangstedfonden, the European Foundation for the Study of Diabetes, and Aase og Ejnar Danielsens fond.

The bile acid-sequestering resin sevelamer eliminates the acute GLP-1 stimulatory effect of endogenously released bile acids in patients with type 2 diabetes.

AIMS: Discovery of the specific bile acid receptors farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5) in enteroendocrine L cells has prompted research focusing on the impact of bile acids on glucagon-like peptide-1 (GLP-1) secretion and glucose metabolism. The aim of the present study was to assess the GLP-1 secretory and gluco-metabolic effects of endogenously released bile, with and without concomitant administration of the bile acid-sequestering resin, sevelamer, in patients with type 2 diabetes. MATERIALS AND METHODS: We performed a randomized, placebo-controlled, double-blinded cross-over study including 15 metformin-treated patients with type 2 diabetes. During 4 experimental study days, either sevelamer 3200 mg or placebo in combination with intravenous infusion of cholecystokinin (CCK) (0.4 pmol sulfated CCK-8/kg/min) or saline was administered in randomized order. The primary endpoint was plasma GLP-1 excursions as measured by incremental area under the curve. Secondary endpoints included plasma responses of glucose, triglycerides, insulin, CCK, fibroblast growth factor-19 and 7α-hydroxy-4-cholesten-3-one (C4). In addition, gallbladder dynamics, gastric emptying, resting energy expenditure, appetite and ad libitum food intake were assessed. RESULTS: CCK-mediated gallbladder emptying was demonstrated to elicit a significant induction of GLP-1 secretion compared to saline, whereas concomitant single-dose administration of the bile acid sequestrant sevelamer was shown to eliminate the acute bile acid-induced increase in plasma GLP-1 excursions. CONCLUSIONS: Single-dose administration of sevelamer eliminated bile acid-mediated GLP-1 secretion in patients with type 2 diabetes, which could be explained by reduced bile acid stimulation of the basolaterally localized TGR5 on enteroendocrine L cells.

Safety of native glucose-dependent insulinotropic polypeptide in humans.

In this systematic review, we assessed the safety and possible safety events of native glucose-dependent insulinotropic polypeptide (GIP)(1-42) in human studies with administration of synthetic human GIP. We searched the PubMed database for all trials investigating synthetic human GIP(1-42) administration. A total of 67 studies were included. Study duration ranged from 30 min to 6 days. In addition to healthy individuals, the studies included individuals with impaired glucose tolerance, type 2 diabetes, type 1 diabetes, chronic pancreatitis and secondary diabetes, latent autoimmune diabetes in adults, diabetes caused by a mutation in the hepatocyte nuclear factor 1-alpha gene, end-stage renal disease, chronic renal insufficiency, critical illness, hypoparathyroidism, or cystic fibrosis-related diabetes. Of the included studies, 78% did not mention safety events, 10% of the studies reported that no safety events were observed in relation to GIP administration, and 15% of the studies reported safety events in relation to GIP administration with most frequently reported event being a moderate and transient increased heart rate. Gastrointestinal safety events, and changes in blood pressure were also reported. Plasma concentration of active GIP(1-42) increased linearly with dose independent of participant phenotype. There was no significant correlation between achieved maximal concentration of GIP(1-42) and reported safety events. Clearance rates of GIP(1-42) were similar between participant groups. In conclusion, the available data indicate that GIP(1-42) in short-term (up to 6 days) infusion studies is generally well-tolerated. The long-term safety of continuous GIP(1-42) administration is unknown.

Intestinal expression profiles and hepatic expression of LEAP2, ghrelin and their common receptor, GHSR, in humans.

Liver-expressed antimicrobial peptide 2 (LEAP2) and ghrelin have reciprocal effects on their common receptor, the growth hormone secretagogue receptor (GHSR). Ghrelin is considered a gastric hormone and LEAP2 a liver-derived hormone and both have been proposed to be involved in the pathophysiology of obesity and type 2 diabetes (T2D). We investigated the mRNA expression of LEAP2, ghrelin and GHSR along the intestinal tract of individuals with and without TD2, and in the liver of men with and without obesity. Mucosal biopsies retrieved with 30-cm intervals throughout the small intestine and from 7 well-defined locations along the large intestine from 12 individuals with T2D and 12 healthy controls together with liver biopsies from 15 men with obesity and 15 lean men were subjected to bulk transcriptomics analysis. Both in individuals with and without T2D, mRNA expression of LEAP2 increased through the small intestine until dropping at the ileocecal valve, with little LEAP2 mRNA expression in the large intestine. Pronounced LEAP2 expression was observed in the liver of men with and without obesity. Robust ghrelin mRNA expression was observed in the duodenum of individuals with and without T2D, gradually decreasing along the small intestine with little expression in the large intestine. Ghrelin mRNA expression was not detected in the liver biopsies, and GHSR mRNA expression was not. In conclusion, we provide unique mRNA expression profiles of LEAP2, ghrelin and GHSR along the human intestinal tract showing no T2D-associated changes, and in the liver showing no differences between men with and without obesity.

Two weeks of acarbose treatment shows no effect on gut microbiome composition in patients with type 2 diabetes: a randomised, placebo-controlled, double-blind, crossover study.

Aim: The alpha-glucosidase inhibitor acarbose is approved for the treatment of type 2 diabetes (T2D). It acts in the lumen of the gut by reducing intestinal hydrolysis and absorption of ingested carbohydrates. This reduces postprandial blood glucose concentration and increases the content of carbohydrates in the distal parts of the intestine potentially influencing gut microbiome (GM) composition and possibly impacting the gut microbiome (GM) dysbiosis associated with T2D. Here, we investigated the effect of acarbose on GM composition in patients with T2D. Methods: Faecal samples were collected in a previously conducted randomised, placebo-controlled, double-blind, crossover study in which 15 individuals with metformin-treated T2D (age 57-85 years, HbA1c 40-74 mmol/mol, BMI 23.6-34.6 kg/m2) were subjected to two 14-day treatment periods with acarbose and placebo, respectively, separated by a 6-week wash-out period. Faecal samples were collected before and by the end of each treatment period. The GM profiles were evaluated by 16S rRNA gene amplicon sequencing. Results: The GM profiles after the treatment periods with acarbose or placebo remained unaffected (P > 0.7) when compared with the GM profiles before treatment. This applied to the analysis of within-sample diversity (α-diversity) and between-sample bacterial composition diversity (ß-diversity). Additionally, no dominant bacterial species differentiated the treatment groups, and only minor increases in the relative abundances of Klebsiella spp. and Escherichia coli (P < 0.05) were observed after acarbose treatment. Conclusion: In patients with metformin-treated T2D, 14 days of treatment with acarbose showed only minor effects on GM as seen in increased relative abundances of Klebsiella spp. and Escherichia coli.

Gluco-metabolic response to exogenous oxytocin in totally pancreatectomized patients and healthy individuals.

Oxytocin has been proposed to possess glucose-stabilizing effects through the release of insulin and glucagon from the pancreas. Also, exogenous oxytocin has been shown to stimulate extrapancreatic glucagon secretion in depancreatized dogs. Here, we investigated the effect of exogenous oxytocin on circulating levels of pancreatic and gut-derived glucose-stabilizing hormones (insulin [measured as C-peptide], glucagon, glucagon-like peptide 1 [GLP-1], and glucose-dependent insulinotropic polypeptide). We studied nine pancreatectomized (PX) patients and nine healthy controls (CTRLs) (matched on age and body mass index) before, during, and after an intravenous infusion of 10 IU of oxytocin administered over 12 min. Oxytocin did not increase plasma glucagon levels, nor induce any changes in plasma glucose, C-peptide, or GIP in any of the groups. Oxytocin decreased plasma glucagon levels by 19 ± 10 % in CTRLs (from 2.0 ± 0.5 [mean ± SEM] to 1.3 ± 0.2 pmol/l, P = 0.0025) and increased GLP-1 by 42 ± 22 % in PX patients (from 9.0 ± 1.0-12.7 ± 1.0 pmol/l, P = 0.0003). Fasting plasma glucose levels were higher in PX patients compared with CTRLs (13.1 ± 1.1 vs. 5.1 ± 0.1 mmol/l, P < 0.0001). In conclusion, the present findings do not support pancreas-mediated glucose-stabilizing effects of acute oxytocin administration in humans and warrant further investigation of oxytocin's gluco-metabolic effects.

Effects of Exogenous GIP and GLP-2 on Bone Turnover in Individuals With Type 2 Diabetes.

CONTEXT: Individuals with type 2 diabetes (T2D) have an increased risk of bone fractures despite normal or increased bone mineral density. The underlying causes are not well understood but may include disturbances in the gut-bone axis, in which both glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2) are regulators of bone turnover. Thus, in healthy fasting participants, both exogenous GIP and GLP-2 acutely reduce bone resorption. OBJECTIVE: The objective of this study was to investigate the acute effects of subcutaneously administered GIP and GLP-2 on bone turnover in individuals with T2D. METHODS: We included 10 men with T2D. Participants met fasting in the morning on 3 separate test days and were injected subcutaneously with GIP, GLP-2, or placebo in a randomized crossover design. Blood samples were drawn at baseline and regularly after injections. Bone turnover was estimated by circulating levels of collagen type 1 C-terminal telopeptide (CTX), procollagen type 1 N-terminal propeptide (P1NP), sclerostin, and PTH. RESULTS: GIP and GLP-2 significantly reduced CTX to (mean ± SEM) 66 ± 7.8% and 74 ± 5.9% of baseline, respectively, compared with after placebo (P = .001). In addition, P1NP and sclerostin increased acutely after GIP whereas a decrease in P1NP was seen after GLP-2. PTH levels decreased to 67 ± 2.5% of baseline after GLP-2 and to only 86 ± 3.4% after GIP. CONCLUSION: Subcutaneous GIP and GLP-2 affect CTX and P1NP in individuals with T2D to the same extent as previously demonstrated in healthy individuals.

Characterization of genetic variants of GIPR reveals a contribution of ß-arrestin to metabolic phenotypes.

Incretin-based therapies are highly successful in combatting obesity and type 2 diabetes1. Yet both activation and inhibition of the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) in combination with glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) activation have resulted in similar clinical outcomes, as demonstrated by the GIPR-GLP-1R co-agonist tirzepatide2 and AMG-133 (ref. 3) combining GIPR antagonism with GLP-1R agonism. This underlines the importance of a better understanding of the GIP system. Here we show the necessity of ß-arrestin recruitment for GIPR function, by combining in vitro pharmacological characterization of 47 GIPR variants with burden testing of clinical phenotypes and in vivo studies. Burden testing of variants with distinct ligand-binding capacity, Gs activation (cyclic adenosine monophosphate production) and ß-arrestin 2 recruitment and internalization shows that unlike variants solely impaired in Gs signalling, variants impaired in both Gs and ß-arrestin 2 recruitment contribute to lower adiposity-related traits. Endosomal Gs-mediated signalling of the variants shows a ß-arrestin dependency and genetic ablation of ß-arrestin 2 impairs cyclic adenosine monophosphate production and decreases GIP efficacy on glucose control in male mice. This study highlights a crucial impact of ß-arrestins in regulating GIPR signalling and overall preservation of biological activity that may facilitate new developments in therapeutic targeting of the GIPR system.

Protocol for assessing the effects of exogenous hormone administration on human postprandial glucose metabolism, appetite sensations, and food intake.

Here, we present a protocol for a randomized, double-blind, placebo-controlled, crossover trial to evaluate the effects of a continuous intravenous infusion of a native liver-derived hormone, liver-expressed antimicrobial peptide 2 (LEAP2), on postprandial glucose metabolism, appetite and satiety sensations, and ad libitum food intake in humans. We describe the preparation of the exogenous hormone administration and participants. We then detail the liquid mixed meal, ad libitum meal test, and blood sampling procedures for assessing postprandial glucose metabolism and food intake. For complete details on the use and execution of this protocol, please refer to Hagemann et al. (2022).1.

Separate and combined effects of long-term GIP and GLP-1 receptor activation in patients with type 2 diabetes: a structured summary of a study protocol for a double-blind, randomised, placebo-controlled clinical trial.

INTRODUCTION: Due to reports of severely reduced insulinotropic effect of the incretin hormone glucose-dependent insulinotropic polypeptide (GIP) in type 2 diabetes (T2D), GIP has not been considered therapeutically viable. Recently, however, tirzepatide, a novel dual incretin receptor agonist (activating the GIP receptor and the glucagon-like peptide 1 (GLP-1) receptor) has demonstrated greater glucose and body weight-lowering properties as compared to GLP-1 receptor agonist therapy. The contribution of GIP receptor activation to effects of tirzepatide remains unknown. We will evaluate the glucose-lowering effect of exogenous GIP in the context of pharmacological GLP-1 receptor activation in patients with T2D. METHODS AND ANALYSIS: In this randomised, double-blind, four-arm parallel, placebo-controlled trial, 60 patients with T2D will be included (18-74 of age; on diet and exercise and/or metformin therapy only; glycated haemoglobin 6.5-10.5% (48-91 mmol/mol)). Participants will be randomised to an 8-week run-in period with subcutaneous (s.c.) placebo or semaglutide injections once-weekly (0.5 mg). Participants will then be randomised to 6 weeks' add-on treatment with continuous s.c. placebo or GIP infusion (16 pmol/kg/min). The primary endpoint is change in mean glucose levels (assessed by 14-day continuous glucose monitoring) from the end of the run-in period to end of trial. ETHICS AND DISSEMINATION: The present study was approved by the Regional Committee on Health Research Ethics in the Capitol Region of Denmark (identification no. H-20070184) and by the Danish Medicines Agency (EudraCT no. 2020-004774-22). All results, positive, negative and inconclusive, will be disseminated at national and/or international scientific meetings and in peer-reviewed scientific journals. TRIAL REGISTRATION NUMBERS: NCT05078255 and U1111-1259-1491.

Acarbose diminishes postprandial suppression of bone resorption in patients with type 2 diabetes.

AIMS: The alpha-glucosidase inhibitor acarbose is an antidiabetic drug delaying assimilation of carbohydrates and, thus, increasing the amount of carbohydrates in the distal parts of the intestines, which in turn increases circulating levels of the gut-derived incretin hormone glucagon-like peptide 1 (GLP-1). As GLP-1 may suppress bone resorption, acarbose has been proposed to potentiate meal-induced suppression of bone resorption. We investigated the effect of acarbose treatment on postprandial bone resorption in patients with type 2 diabetes and used the GLP-1 receptor antagonist exendin(9-39)NH2 to disclose contributory effect of acarbose-induced GLP-1 secretion. METHODS: In a randomised, placebo-controlled, double-blind, crossover study, 15 participants with metformin-treated type 2 diabetes (2 women/13 men, age 71 (57-85 years), BMI 29.7 (23.6-34.6 kg/m2), HbA1c 48 (40-74 mmol/mol)/6.5 (5.8-11.6 %) (median and range)) were subjected to two 14-day treatment periods with acarbose and placebo, respectively, separated by a six-week wash-out period. At the end of each period, circulating bone formation and resorption markers were assessed during two randomised 4-h liquid mixed meal tests (MMT) with infusions of exendin(9-39)NH2 and saline, respectively. Glucagon-like peptide 2 (GLP-2) was also assessed. RESULTS: Compared to placebo, acarbose impaired the MMT-induced suppression of CTX as assessed by baseline-subtracted area under curve (P = 0.0037) and nadir of CTX (P = 0.0128). During acarbose treatment, exendin(9-39)NH2 infusion lowered nadir of CTX compared to saline (P = 0.0344). Neither parathyroid hormone or the bone formation marker procollagen 1 intact N-terminal propeptide were affected by acarbose or GLP-1 receptor antagonism. Acarbose treatment induced a greater postprandial GLP-2 response than placebo treatment (P = 0.0479) and exendin(9-39)NH2 infusion exacerbated this (P = 0.0002). CONCLUSIONS: In patients with type 2 diabetes, treatment with acarbose reduced postprandial suppression of bone resorption. Acarbose-induced GLP-1 secretion may contribute to this phenomenon as the impairment was partially reversed by GLP-1 receptor antagonism. Also, acarbose-induced reductions in other factors reducing bone resorption, e.g. glucose-dependent insulinotropic polypeptide, may contribute.

The Importance of Endogenously Secreted GLP-1 and GIP for Postprandial Glucose Tolerance and ß-Cell Function After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy Surgery.

Enhanced secretion of glucagon-like peptide 1 (GLP-1) seems to be essential for improved postprandial ß-cell function after Roux-en-Y gastric bypass (RYGB) but is less studied after sleeve gastrectomy (SG). Moreover, the role of the other major incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), is relatively unexplored after bariatric surgery. We studied the effects of separate and combined GLP-1 receptor (GLP-1R) and GIP receptor (GIPR) blockade during mixed-meal tests in unoperated (CON), SG-operated, and RYGB-operated people with no history of diabetes. Postprandial GLP-1 concentrations were highest after RYGB but also higher after SG compared with CON. In contrast, postprandial GIP concentrations were lowest after RYGB. The effect of GLP-1R versus GIPR blockade differed between groups. GLP-1R blockade reduced ß-cell glucose sensitivity and increased or tended to increase postprandial glucose responses in the surgical groups but had no effect in CON. GIPR blockade reduced ß-cell glucose sensitivity and increased or tended to increase postprandial glucose responses in the CON and SG groups but had no effect in the RYGB group. Our results support that GIP is the most important incretin hormone in unoperated people, whereas GLP-1 and GIP are equally important after SG, and GLP-1 is the most important incretin hormone after RYGB.

The naturally occurring GIP(1-30)NH2 is a GIP receptor agonist in humans.

OBJECTIVE: The gut hormone glucose-dependent insulinotropic polypeptide (GIP) is an important regulator of glucose and bone metabolism. In rodents, the naturally occurring GIP variant, GIP(1-30)NH2, has shown similar effects as full-length GIP (GIP(1-42)), but its effects in humans are unsettled. Here, we investigated the actions of GIP(1-30)NH2 compared to GIP(1-42) on glucose and bone metabolism in healthy men and in isolated human pancreatic islets. METHODS: Nine healthy men completed three separate three-step glucose clamps (0-60 minutes at fasting plasma glucose (FPG) level, 60-120 minutes at 1.5× FPG, and 120-180 minutes at 2× FPG) with infusion of GIP(1-42) (4 pmol/kg/min), GIP(1-30)NH2 (4 pmol/kg/min), and saline (9 mg/mL) in randomised order. Blood was sampled for measurement of relevant hormones and bone turnover markers. Human islets were incubated with low (2 mmol/L) or high (20 mmol/L) d-glucose with or without GIP(1-42) or GIP(1-30)NH2 in three different concentrations for 30 minutes, and secreted insulin and glucagon were measured. RESULTS: Plasma glucose (PG) levels at FPG, 1.5× FPG, and 2× FPG were obtained by infusion of 1.45 g/kg, 0.97 g/kg, and 0.6 g/kg of glucose during GIP(1-42), GIP(1-30)NH2, and saline, respectively (P = .18), and were similar on the three experimental days. Compared to placebo, GIP(1-30)NH2 resulted in similar glucagonotropic, insulinotropic, and carboxy-terminal type 1 collagen crosslinks-suppressing effects as GIP(1-42). In vitro experiments on human islets showed similar insulinotropic and glucagonotropic effects of the two GIP variants. CONCLUSIONS: GIP(1-30)NH2 has similar effects on glucose and bone metabolism in healthy individuals and in human islets in vitro as GIP(1-42).

Rare Heterozygous Loss-of-Function Variants in the Human GLP-1 Receptor Are Not Associated With Cardiometabolic Phenotypes.

CONTEXT: Lost glucagon-like peptide 1 receptor (GLP-1R) function affects human physiology. OBJECTIVE: This work aimed to identify coding nonsynonymous GLP1R variants in Danish individuals to link their in vitro phenotypes and clinical phenotypic associations. METHODS: We sequenced GLP1R in 8642 Danish individuals with type 2 diabetes or normal glucose tolerance and examined the ability of nonsynonymous variants to bind GLP-1 and to signal in transfected cells via cyclic adenosine monophosphate (cAMP) formation and ß-arrestin recruitment. We performed a cross-sectional study between the burden of loss-of-signaling (LoS) variants and cardiometabolic phenotypes in 2930 patients with type 2 diabetes and 5712 participants in a population-based cohort. Furthermore, we studied the association between cardiometabolic phenotypes and the burden of the LoS variants and 60 partly overlapping predicted loss-of-function (pLoF) GLP1R variants found in 330 566 unrelated White exome-sequenced participants in the UK Biobank cohort. RESULTS: We identified 36 nonsynonymous variants in GLP1R, of which 10 had a statistically significant loss in GLP-1-induced cAMP signaling compared to wild-type. However, no association was observed between the LoS variants and type 2 diabetes, although LoS variant carriers had a minor increased fasting plasma glucose level. Moreover, pLoF variants from the UK Biobank also did not reveal substantial cardiometabolic associations, despite a small effect on glycated hemoglobin A1c. CONCLUSION: Since no homozygous LoS nor pLoF variants were identified and heterozygous carriers had similar cardiometabolic phenotype as noncarriers, we conclude that GLP-1R may be of particular importance in human physiology, due to a potential evolutionary intolerance of harmful homozygous GLP1R variants.

GLP-1 and GIP receptor signaling in beta cells - A review of receptor interactions and co-stimulation.

Glucagon-like peptide 1 receptor (GLP-1R) and glucose-dependent insulinotropic polypeptide receptor (GIPR) are two class B1 G protein-coupled receptors, which are stimulated by the gastrointestinal hormones GLP-1 and GIP, respectively. In the pancreatic beta cells, activation of both receptors lead to increased cyclic adenosine monophosphate (cAMP) and glucose-dependent insulin secretion. Marketed GLP-1R agonists such as dulaglutide, liraglutide, exenatide and semaglutide constitute an expanding drug class with beneficial effects for persons suffering from type 2 diabetes and/or obesity. In recent years another drug class, the GLP-1R-GIPR co-agonists, has emerged. Especially the peptide-based, co-agonist tirzepatide is a promising candidate for a better treatment of type 2 diabetes by improving glycemic control and weight reduction. The mechanism of action for tirzepatide include biased signaling of the GLP-1R as well as potent GIPR signaling. Since the implications of co-targeting these closely related receptors concomitantly are challenging to study in vivo, the pharmacodynamic mechanisms and downstream signaling pathways of the GLP-1R-GIPR co-agonists in general, are not fully elucidated. In this review, we present the individual signaling pathways for GLP-1R and GIPR in the pancreatic beta cell with a focus on the shared signaling pathways of the two receptors and interpret the implications of GLP-1R-GIPR co-activation in the light of recent co-activating therapeutic compounds.