AIMS:To determine whether gastric emptying of an oral glucose load is related to the glucagon-like peptide-1 (GLP-1) response to intestinal glucose exposure in healthy individuals. MATERIALS AND METHODS:42 healthy participants (20F/22 M, age: 35.1 ± 2.1 years; BMI 24.5 ± 0.6 kg/m2) were evaluated on 2 days. On Day 1, participants ingested a 75 g glucose drink containing 150 mg 13C-acetate, with the gastric half-emptying time (T50) (breath test) and blood glucose concentrations determined over 180 min. On Day 2, participants received an intraduodenal glucose infusion at 4kcal/min for 30 min. Plasma insulin, C-peptide and total GLP-1 concentrations were measured at frequent intervals. RESULTS:There was a direct relationship between the T50 of oral glucose and the incremental area under the curve (iAUC) for GLP-1 (t = 0-120 min) in response to intraduodenal glucose (r = 0.33, P = 0.03). When participants were stratified into tertiles according to T50, GLP-1 iAUC0-120min in response to intraduodenal glucose infusion was greater in participants with slower vs. faster gastric emptying (P = 0.02). CONCLUSIONS:In healthy individuals, gastric emptying of a glucose drink is related to the magnitude of the GLP-1 response to intestinal glucose exposure. This finding supports the concept of intestinal 'sensitivity' to nutrients as a determinant of gastric emptying.

Secreted by enteroendocrine L-cells along the intestinal epithelium, glucagon-like peptide-1 (GLP-1) is a key regulator of glucose and energy homeostasis in health, obesity and type 2 diabetes. Understanding the stimuli and mechanisms governing GLP-1 secretion is fundamental to the development of novel therapies for metabolic disorders. Mechanistic studies have, hitherto, relied largely on well-based static incubation of immortalised cell lines or primary intestinal tissues, approaches that have limited physiological relevance and lack the capacity to monitor dynamic hormone release under biomimetic conditions. This study aimed to develop a microfluidic 'gut-on-a-chip' (GOC) platform to enable assessment of dynamic GLP-1 secretion from primary mouse intestinal tissue in a biomimetic environment. We initially characterised regional GLP-1 secretion capacity along the mouse small intestine to inform device design. A polymethyl methacrylate microchip was then micromachined to accommodate a segment of intestinal tissue and support parallel luminal and serosal perfusion via peristaltic microfluidic pumps. In proof-of-concept experiments, physiological GLP-1 secretagogues (taurocholic acid and glucose) were subsequently delivered to the luminal or serosal surface of duodenal and colonic tissue under continuous or intermittent perfusion. The GOC platform demonstrated superiority over static incubation for studying GLP-1 secretion in primary intestinal tissue, capturing dynamic serosal concentration changes over 2 h while better preserving tissue viability and morphology. This novel system provides a powerful tool to elucidate the mechanisms underlying gut hormone release and to screen candidate GLP-1 secretagogues for potential therapeutic development.

Introduction and Objective: Portal glucose sensing is key to glucose homeostasis, conveying metabolic information to the brain via vagal afferent pathways. In type 2 diabetes, this signaling is impaired due to reduced GLP-1R expression in portal afferent nerves. We evaluated whether restoration of portal GLP-1R expression by local low dose dihydrotestosterone (DHT) alters brain processing. Methods: In twelve minipigs, diabetes was induced using an obesogenic diet combined with a small dose of streptozotocin (80 mg/kg, IV). Animals were randomized to receive a peri-portal implant delivering dihydrotestosterone (DHT; 100 µg/day; n=6) to restore GLP-1R expression and vagal afferent signaling, or a sham implant (n=6). Five months later, peripheral GLP-1R expression was quantified by abdominal PET imaging using 68Ga-NODAGA-Exendin-4 and brain metabolic activity was assessed by 18F-FDG PET imaging. Brain images were normalized to a probabilistic pig brain atlas and analyzed using region-wise statistical parametric mapping (SPM 12). Network-level connectivity analyses were also performed (NetPET). Results: DHT-treated animals demonstrated a marked increase in portal GLP-1R expression compared with sham controls (Vt 3.12 ± 0.049 vs 0.16 ± 0.007 mL/cm3 for DHT vs sham, P < 0.001). The engagement of central autonomic and limbic networks was strongly and positively correlated with increased GLP-1R expression (r²=0.88 and 0.87, P = 0.0002 and 0.0002 respectively), independent of treatment assignment. Conversely, higher GLP-1R expression was associated with reduced activation of the anterior prefrontal cortex (r2=0.78, P =0.021). Conclusion: Restoration of impaired portal GLP-1R-dependent glucose sensing selectively enhances autonomic and limbic network engagement while reducing recruitment of anterior prefrontal executive regions, indicative of central reprogramming capabilities linked to portal glucose sensing. Disclosure C. Malbert: Research Support; Current; Paltech. M.R. Allouche: Stock/Shareholder; Current; Paltech. M. Horowitz: None. K.L. Jones: None.

Aims Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are key regulators of glucose homeostasis in health and type 2 diabetes (T2D). Whether their secretion is influenced by antecedent glycaemic control in T2D remains unclear. This study compared GLP-1 and GIP responses to intraduodenal glucose infusion between individuals with well- and poorly-controlled T2D. Methods 24 diet-controlled participants with T2D (n = 12 with HbA1c < 7.0% and n = 12 with HbA1c > 8.5%) received an intraduodenal infusion of 30 g glucose with 3 g 3-O-methylglucose (3-OMG; a marker of intestinal glucose absorption) over 30 min. Blood glucose was maintained comparably (6.4 ± 0.4 vs. 6.1 ± 0.3 mmol/L) by intravenous insulin. Plasma GIP, GLP-1 and C-peptide and serum 3-OMG were measured at frequent intervals. Results Basal hormone concentrations were comparable between groups. In response to intraduodenal glucose infusion, the GIP response was greater in the poorly-controlled group (P = 0.02 for time*group interaction), with a trend for higher iAUC0-60min compared with well-controlled group (1329.9 ± 163.7 vs. 1009.5 ± 108.3 pmol/L*min, P = 0.12 unadjusted; P = 0.09 adjusted for age, sex and BMI). GLP-1 responses were lower in the poorly-controlled group (P = 0.007 for time*group interaction), with lower iAUC0-60min (453.3 ± 110.6 vs. 1037.5 ± 177.1 pmol/L*min, P = 0.01), but this difference became non-significant after adjustment for age, sex and BMI. C-peptide and 3-OMG responses were comparable. Conclusions Poor glycaemic control in T2D is associated with a greater GIP, and lower GLP-1, response to small intestinal glucose, independent of intestinal glucose absorption. However, differences in GLP-1 may be influenced by age, sex and BMI, so should be interpreted cautiously and validated in larger cohorts.

The interaction of dietary nutrients with chemoreceptors in the gastrointestinal tract after a meal stimulates the secretion of gut hormones, which trigger the key processes of digestion and absorption, and also regulate energy intake and postprandial glycemia. One of these receptors, first recognized for its capacity to gauge extracellular calcium (Ca2+), is the calcium-sensing receptor (CaSR). Subsequent to its cloning, the CaSR was found to sense not only Ca2+, but also L-amino acids (AAs) and, based on solved protein structures, distinct binding sites have been reported for Ca2+ ions and the aromatic AA, L-tryptophan (L-Trp). In the stomach and small intestine, the CaSR is expressed in enteroendocrine cells, and a substantial body of preclinical work has demonstrated that it mediates gut hormone secretion in response to L-Trp and another aromatic AA, L-phenylalanine (L-Phe), and that extracellular Ca2+ promotes these effects. In humans, intraluminal administration of L-Trp or L-Phe increases plasma levels of gut hormones, associated with reductions in both energy intake and the plasma glucose response to a subsequent meal. In addition, co-administration of Ca2+ enhances the effect of L-Trp to increase plasma levels of gut hormones (including cholecystokinin, glucagon-like peptide-1 and peptide YY) and reduce energy intake. These observations have implications for the development of novel nutrient-based management strategies for obesity and type 2 diabetes. This review considers preclinical and clinical evidence that CaSR activators, including extracellular Ca2+ as well as the aromatic AAs, L-Trp and L-Phe, stimulate gut hormones and lower both energy intake and postprandial glycemia.

Introduction and Objective: The hepatoportal glucose sensor, which converts portal glucose flux into metabolic signals that regulate systemic glucose homeostasis, is impaired in type 2 diabetes and not targeted by current glucose-lowering therapies. We have shown that portal sensing is restored by local administration of low-dose dihydrotestosterone (DHT) and have now evaluated the chronic impact of low-dose DHT on insulin sensitivity and clearance, and β-cell responsiveness in a large-animal model of diabetes Methods: In twelve minipigs, diabetes was induced using an obesogenic diet combined with streptozotocin (80 mg/kg IV). Six animals received an implant which delivered DHT (100 μg/day) close to the defective portal sensor, as identified by GLP-1 receptor PET imaging (DHT group), while six other animals received a sham implant (Sham group). Five months after implantation, all animals underwent a frequent sampling, oral glucose tolerance test (1.5 g glucose/kg body weight). Plasma glucose, insulin, and C-peptide concentrations were measured to evaluate whole-body insulin sensitivity, β-cell responsivity, disposition indices (DI), and hepatic insulin extraction using minimal models. Results: In the DHT group there was a marked improvement in insulin sensitivity (15.8 ± 2.90 DHT vs 9.2 ± 1.01 Sham dL/kg/min per µU/mL*1E-3, P<0.01), with three-fold and six-fold increases in dynamic and static β-cell responsivity, respectively, leading to a ten-fold increase in total DI (0.807 ± 0.0028 DHT vs 0.036 ± 0.0035 Sham dL/kg/min 2 per pmol/L, P<0.01), compared to the Sham group. Hepatic insulin extraction also increased in the DHT group, indicative of enhanced first-pass hepatic insulin uptake. Conclusion: In a porcine model of diabetes, restoration of portal glucose sensing using DHT improves insulin sensitivity, insulin clearance and β-cell function, markedly indicative of the importance of impaired portal glucose sensing as a therapeutic target. Disclosure C. Malbert: Research Support; Current; Paltech. M.R. Allouche: Stock/Shareholder; Current; Paltech. M. Horowitz: None. K.L. Jones: None.

Gastric emptying, which exhibits a substantial interindividual, but much lesser intraindividual, variation in health and is frequently disordered (particularly delayed) in diabetes, is now appreciated to be a major determinant of postprandial glycemia. The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are secreted in the proximal and distal small intestine, respectively, in response to nutrients. GLP-1, together with peptide tyrosine-tyrosine (PYY), stimulates potent negative feedback on gastric emptying. Modulation of gastric emptying, through dietary, pharmacologic, and surgical therapies, has been utilized in current clinical practice for the treatment of hyperglycemia, particularly relating to type 2 diabetes. We review the complex, interdependent relationships between gastric emptying, small intestinal transit, glucose absorption, neurohormonal regulatory responses, and postprandial glycemia. We discuss how this has informed fundamental advances in the understanding and rational management of obesity, stress hyperglycemia, type 1 and 2 diabetes, and gestational diabetes, and we provide recommendations for research priorities that have the potential to impact practice. We also discuss the frequent complication of abnormally delayed gastric emptying (gastroparesis) in both type 1 and type 2 diabetes, the implications for management of diabetes, and the impact of treatment on gastric emptying. With the increasing recognition of the importance of gastric emptying in the management of conditions associated with disordered glucose metabolism, and the advent and increasing use of GLP-1 receptor agonists, an improved definition of the interactions between gastrointestinal motility (gastric emptying and small intestinal transit) and enteropancreatic hormonal responses is essential.

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are widely used for the treatment of type 2 diabetes and/or obesity. The physiological actions of endogenous GLP-1, and synthetic GLP-1RAs include inhibition of gastric emptying. This has peri-procedural implications due to the potential increased risk of retained gastric contents which may result in pulmonary aspiration. There is a need for local evidence-based guidelines to best manage patients on GLP-1RAs and dual GLP-1 and glucose-dependent insulinotropic polypeptide receptor co-agonists (GLP-1/GIPRAs) presenting for surgical and medical procedures requiring sedation or anaesthesia. A panel of experts was formed to consider the peri-procedural implications of GLP-1RA and GLP-1/GIPRA use and establish best practice recommendations based on the current evidence.We recommend that all patients should be asked about glucagon-like peptide-1 receptor agonist (GLP-1RA) and dual GLP-1 and glucose-dependent insulinotropic polypeptide receptor co-agonist (GLP-1/GIPRA) use prior to anaesthesia or sedation for surgical and endoscopic procedures and be informed of the benefits and risks. We also recommend that GLP-1RAs and GLP-1/GIPRAs be continued in the peri-procedural period. Preprocedural diet modification with a 24-h clear fluid diet, followed by standard 6-h fasting, should be recommended for all patients receiving GLP-1RAs or GLP-1/GIPRAs. In patients who have not completed or are unable to have a 24-h liquid diet, risk stratification using gastric ultrasound or minimally sedated gastroscopy to assess gastric contents is recommended, as is the use of intravenous erythromycin. We cannot currently recommend using the absence of gastrointestinal symptoms for risk stratification, nor can we recommend an adequate cessation period for GLP-1RAs and GLP-1/GIPRAs to ensure gastric emptying has returned to baseline levels. This clinical guideline, developed by multiple professional bodies, outlines current best practice recommendations for patients taking GLP-1RAs and combined GLP-1/GIPRAs who require general anaesthesia, sedation and/or endoscopic procedures. The guide provides a structure for Australian and New Zealand primary health practitioners, gastroenterologists, surgeons, endocrinologists, anaesthetists and perioperative physicians to support clinical decisions in these patients.

Fibrocalculous pancreatic diabetes mellitus (FCPD) is characterised by pancreatic calcification, intraductal calculi and severe insulin deficiency, yet abnormalities in glucagon regulation and incretin hormone responses remain incompletely understood. We evaluated the glucagon, incretins and oxyntomodulin secretory responses to oral and intravenous glucose administration in participants with FCPD. Participants with FCPD (cases; n = 9; mean age 34 ± 7.2 years) and healthy individuals (controls; n = 6; mean age 29.8 ± 7.7 years) underwent an extended oral glucose tolerance test (OGTT) and isoglycaemic intravenous glucose infusion (IIGI). Serial measurements of plasma glucose, insulin, C-peptide, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), oxyntomodulin (OXM), and pancreatic polypeptide (PP) were done. Serial hormone responses were analysed using linear mixed-effects models, with area-under-the-curve analyses using trapezoidal rule, performed as secondary summaries. On primary mixed-model analysis, the participants with FCPD exhibited significantly higher fasting and post-OGTT glucagon concentrations with glucagon exposure being greater following OGTT than IIGI in the group with FCPD, whereas no route-dependent difference was observed in control participants. GLP-1 and OXM responses were similarly increased in participants with FCPD, particularly following, oral glucose tolerance test, while GIP responses were attenuated. In contrast, C-peptide and pancreatic polypeptide responses were profoundly suppressed during both OGTT and IIGI in FCPD, consistent with severe pancreatic endocrine failure. Despite matched glycaemic exposure, the incretin effect and gastrointestinal glucose disposal were reduced in the FCPD group. These findings demonstrate persistent hyperglucagonemia accompanied by a distinctive pattern of incretin secretion in FCPD, characterised by exaggerated L-cell-derived hormone secretion with attenuated K-cell (GIP) response and impaired pancreatic peptide responses, highlighting altered entero-pancreatic hormonal regulation in this condition.

Background Insulin-like peptide 5 (INSL5) is an enteroendocrine hormone expressed in distal colonic ‘L cells’. Bile acid receptor agonists are known to stimulate INSL5 secretion in primary cell culture, and administration of an INSL5 analogue in animals promotes colonic motility. Objective This study used a new immunoassay to measure INSL5 in human blood samples, enabling assessment of whether rectal bile acids stimulate INSL5 release in humans and whether INSL5 levels are altered in patients with chronic diarrhoea. Design Serum/plasma samples from previously performed studies were used, including healthy volunteers (n=7) who received a rectal enema of taurocholic acid (TCA); fasting and post prandial samples from healthy volunteers (n=10); patients with bile acid diarrhoea (BAD) (n=19) or irritable bowel syndrome with diarrhoea (IBS-D) (n=8); and patients with IBS-D (n=64) treated with ondansetron or placebo. Results Rectal TCA but not a control enema promptly elevated plasma INSL5, with the increase in INSL5 correlating negatively with time to, and positively with desire to, defecate post enema. Healthy volunteers had low INSL5 levels (<100 pg/mL), with no change following a mixed meal. Patients with BAD had elevated INSL5 levels, with average stool consistency being positively correlated with serum INSL5 (p<0.001). In people with IBS-D, INSL5 was elevated (>100 pg/mL) in 42%, and this subgroup showed greater improvements in stool consistency with ondansetron therapy (p<0.05). Conclusion The study highlights that rectal bile acids stimulate INSL5 secretion in humans, and that INSL5 levels are associated with a colonic pro-motility response and pathophysiology of chronic diarrhoea.

Foods and beverages sweetened with non-nutritive sweeteners (NNSs) are increasingly common in modern diets and widely promoted as healthy alternatives to their sugar-sweetened counterparts, with attendant benefits for individuals with preclinical or clinical metabolic disease. Despite this position, the evidence base supporting the purported health benefits of NNSs is limited and equivocal, particularly in individuals with type 2 diabetes. This review discusses the metabolic effects of NNSs from the standpoint of epidemiological studies and focuses on evidence from the hitherto limited number of prospective clinical trials, as well as potential modes of interaction. Non-nutritive sweeteners are capable of binding to sweet taste receptors (STRs, a heterodimer of T1R2-T1R3) in a wide variety of tissues, including the tongue, pancreas, and small intestine. In cellular, tissue and preclinical models, the binding of NNSs to intestinal STRs triggers the release of the incretin hormones glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which, in turn, evoke pancreatic insulin release. Sweet taste receptor activation also triggers release of the intestinotrophic peptide, glucagon-like peptide 2 (GLP-2), which augments the expression and function of the primary apical glucose transporter in the intestine, sodium-glucose co-transporter-1 (SGLT-1). In addition, the NNSs saccharin and sucralose disrupt the composition of the gut microbiome in both pre-clinical and clinical settings in health, and do so in a manner that is individualized and causally related to glucose intolerance. Correspondingly, NNSs have the potential to impact metabolic outcomes directly via host-mediated pathways, as well as secondary to changes in the hosted microbiota. To date, most clinical trials have focused on the acute or subacute effects of NNSs on gut hormone release, glycemic control, and weight management. There is now broad recognition that longer-term, prospective randomized clinical trials are required to add mechanistic insight into how NNSs impact glycemic control in health and in type 2 diabetes.

AIMS:Glucose-dependent insulinotropic polypeptide (GIP) may exert both insulinotropic and glucagonotropic effects. While its insulinotropic action is reportedly attenuated or abolished with worsening of glycaemic control in type 2 diabetes (T2D), the relationship between GIP and glucagon secretion across different levels of glycaemic control remains unclear. This study evaluated the relationship between postprandial GIP and glucagon responses to a mixed meal in T2D and to intraduodenal fat and glucose infusion in healthy and/or T2D individuals. MATERIALS AND METHODS:Data were analysed from three clinical studies: mixed-meal testing in T2D (n = 79), intraduodenal fat infusion (2 kcal/min over 120 min) in T2D (n = 15) and intraduodenal glucose infusion (2 kcal/min over 60 min) in health and T2D (n = 10 each). Relationships between postprandial GIP and glucagon or insulin following the mixed meal were also determined after stratification by HbA1c (< 6.5%, 6.5%-7.0%, > 7.0%). RESULTS:Following mixed-meal ingestion, early postprandial (0-30 min) glucagon secretion correlated positively with GIP, with the strength of this association increasing with higher HbA1c levels. In contrast, the insulinogenic index correlated with GIP only in subgroups with HbA1c < 6.5% and between 6.5%-7.0%. During intraduodenal fat infusion, glucagon and GIP responses correlated strongly in T2D. Following intraduodenal glucose infusion, early glucagon and GIP increments (0-15 min) were closely related in T2D, but not in healthy individuals. CONCLUSIONS:These observations indicate a glycaemia-dependent shift in endogenous GIP action in T2D, characterised by attenuation of insulinotropic effects and relative amplification of glucagonotropic effects with deteriorating glycaemic control. TRIAL REGISTRATION:ACTRN12614001131640, ACTRN12614001117606 and ACTRN12615001240538.

Understanding the relative contributions of basal and postprandial hyperglycaemia (BH and PPH) to hyperglycaemia is pivotal to optimising the therapeutic strategies for type 2 diabetes (T2D). We used continuous glucose monitoring (CGM) to quantify longitudinal changes in the relative contributions of BH and PPH to overall hyperglycaemia in 22 treatment-naïve Han Chinese adults with T2D before and after 3 months of intensive glucose-lowering therapy. At baseline (HbA1c 10.0 ± 0.3%), BH predominated, contributing ~73-77% of overall hyperglycaemia. Following treatment (HbA1c 7.1 ± 0.2%), the contribution of BH decreased markedly (~35-38%), while PPH became the dominant contributor of hyperglycaemia (~62-66%). The improvement in glycaemic control was also accompanied by enhanced insulin secretion and sensitivity, without changes in gastric emptying. These findings provide longitudinal, CGM-based evidence of a dynamic shift in glycaemic determinants with therapy. Therapeutic strategies should be adapted accordingly, with initial focus on BH followed by increasing emphasis on PPH as glycaemic control improves.

Glucagon-like peptide-1 (GLP-1) receptor agonists improve dyslipidemia and reduce cardiovascular risk in type 2 diabetes (T2D), but the role of endogenous GLP-1 in lipid metabolism remains unclear. We evaluated the effect of dipeptidyl peptidase 4 (DPP-4) inhibition on the plasma triglycerides (TGs) response to intraduodenal lipid and a mixed meal, and the impact of GLP-1 receptor blockade with exendin(9-39) in T2D. Fifteen participants with T2D, managed by diet and/or metformin were studied on three occasions in a double-blind, randomized, crossover design. Vildagliptin (50 mg) or placebo was administered orally (t=-60min), followed by intravenous (i.v.) exendin(9-39) from t=-60-150min on one of the two vildagliptin days or 0.9% saline on two other days. A lipid emulsion was infused intraduodenally (2 kcal/min, t=0-120min), followed by a mixed meal (t=120-150min). Plasma TG levels, quantified by liquid chromatography-tandem mass spectrometry, increased after lipid and meal, with most individual TGs corresponding to those in the lipid emulsion. Vildagliptin reduced TG(54:4) and TG(54:5) concentrations (each P<0.01), without affecting total TGs. Blocking endogenous GLP-1 during vildagliptin treatment increased plasma total TGs (P<0.001), associated with ten individual TG species elevated significantly (P<0.05 each). These outcomes suggest that endogenous GLP-1 contributes to the physiological modulation of postprandial TG appearance in T2D.

GLP-1 receptor agonist (GLP-1RA) medications have transformed the treatment of type 2 diabetes (T2D) and obesity, with robust evidence for cardiovascular and renal benefits. Nevertheless, GLP-1RA therapy is associated with a pattern of adverse events affecting their safety and tolerability. Here, we delineate mechanisms potentially leading to adverse responses to GLP-1RAs, describe the impact of side effects on treatment persistence, discuss potential mitigation strategies, and identify areas requiring further studies. Concerns that GLP-1RAs raise the risk for acute pancreatitis and pancreatic cancer have been dispelled by long-term clinical trials. However, GLP-1RAs may confer an increased risk for thyroid cancer. Sight-threatening eye complications resulting from rapid reductions in glycemia may be avoided by retinal screening and ophthalmologic treatment before GLP-1RA initiation. The slowing of gastric emptying with GLP-1RA treatment increases the propensity for retained gastric contents, which could increase the risk of aspiration during upper gastrointestinal endoscopy or general anesthesia. These risks may, however, be elevated in individuals with long-standing T2D even in the absence of GLP-1RA treatment. Improved pharmacovigilance and a more standardized, quantitative assessment of adverse events in clinical trials, particularly in the assessment of gastrointestinal symptoms, would facilitate definition of the benefit-risk relationship for individual medications and indications.