Isosinensetin Stimulates Glucagon-like Peptide-1 Secretion via Activation of hTAS2R50 and the Gßγ-Mediated Signaling Pathway.

Bitter taste receptors (TAS2Rs) are G protein-coupled receptors localized in the taste buds of the tongue. They may also be present in non-lingual organs, including the brain, lung, kidney, and gastrointestinal (GI) tract. Recent studies on bitter taste receptor functions have suggested TAS2Rs as potential therapeutic targets. The human bitter taste receptor subtype hTAS2R50 responds to its agonist isosinensetin (ISS). Here, we demonstrated that, unlike other TAS2R agonists, isosinensetin activated hTAS2R50 as well as increased Glucagon-like peptide 1 (GLP-1) secretion through the Gßγ-mediated pathway in NCI-H716 cells. To confirm this mechanism, we showed that ISS increased intracellular Ca2+ and was suppressed by the IP3R inhibitor 2-APB as well as the PLC inhibitor U73122, suggesting that TAS2Rs alters the physiological state of enteroendocrine L cells in a PLC-dependent manner. Furthermore, we demonstrated that ISS upregulated proglucagon mRNA and stimulated GLP-1 secretion. ISS-mediated GLP-1 secretion was suppressed in response to small interfering RNA-mediated silencing of Gα-gust and hTAS2R50 as well as 2-APB and U73122. Our findings improved the understanding of how ISS modulates GLP-1 secretion and indicates the possibility of using ISS as a therapeutic agent in the treatment of diabetes mellitus.

Blue Whiting (Micromesistius poutassou) Protein Hydrolysates Increase GLP-1 Secretion and Proglucagon Production in STC-1 Cells Whilst Maintaining Caco-2/HT29-MTX Co-Culture Integrity.

Inducing the feeling of fullness via the regulation of satiety hormones presents an effective method for reducing excess energy intake and, in turn, preventing the development of obesity. In this study, the ability of blue whiting soluble protein hydrolysates (BWSPHs) and simulated gastrointestinal digested (SGID) BWSPHs, to modulate the secretion and/or production of satiety hormones, such as glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK) and peptide YY (PYY), was assessed in murine enteroendocrine STC-1 cells. All BWSPHs (BW-SPH-A to BW-SPH-F) (1.0% w/v dw) increased active GLP-1 secretion and proglucagon production in STC-1 cells compared to the basal control (Krebs-Ringer buffer) (p < 0.05). The signaling pathway activated for GLP-1 secretion was also assessed. A significant increase in intracellular calcium levels was observed after incubation with all BWSPHs (p < 0.05) compared with the control, although none of the BWSPHs altered intracellular cyclic adenosine monophosphate (cAMP) concentrations. The secretagogue effect of the leading hydrolysate was diminished after SGID. Neither pre- nor post-SGID hydrolysates affected epithelial barrier integrity or stimulated interleukin (IL)-6 secretion in differentiated Caco-2/HT-29MTX co-cultured cells. These results suggest a role for BWSPH-derived peptides in satiety activity; however, these peptides may need to be protected by some means to avoid loss of activity during gastrointestinal transit.

GLP-1R activation ameliorated novel-object recognition memory dysfunction via regulating hippocampal AMPK/NF-κB pathway in neuropathic pain mice.

Growing evidences indicate that neuropathic pain is frequently accompanied with cognitive impairments, which aggravate the decrease in the quality of life of chronic pain patients. Furthermore, it has been shown that the activation of Glucagon-like-peptide-1receptor (GLP-1R) improved memory deficit in multiple diseases, including Alzheimer's disease (AD), stroke. However, whether GLP-1R activation could improve memory impairment induced by neuropathic pain and the mechanisms underlying the effect of the activation of GLP-1R on memory protection have not yet been established. The spared nerve injury (SNI) model was established as a kind of neuropathic pain. And novel-object recognition memory (hippocampus-dependent memory) was tested by the novel object recognition test (NORT). The expression levels of GLP-1, GLP-1R, adenosine monophosphate-activated protein kinase (AMPK), p-AMPKThr172, nuclear factor κ B p65 (NF-κB p65), interleukin-1beta (IL-1ß), IL-1ß p17 (mature IL-1ß), tumor necrosis factor-alpha (TNF-α) and the synaptic proteins were tested in the murine hippocampus with memory deficits caused by neuropathic pain. Then, exenatide acetate (Ex-4, a GLP-1R agonist), exendin (9-39) (Ex(9-39), a GLP-1R antagonist) and Compound C dihydrochloride (CC, an AMPK inhibitor) were used to test the effects of the activation of GLP-1R in the mice with neuropathic pain. First, we uncovered that neuropathic pain could inhibit GLP-1/GLP-R axis, disturb inflammatory signaling pathway, increase the expression of IL-1ß, IL-1ß p17 and TNF-α, downregulate the synaptic proteins (postsynaptic density protein 95 (PSD95) and Arc). Subsequently, we reported that Ex-4 treatment could improve recognition memory impairment, increase the ratio of p-AMPKThr172/AMPK, inhibit the phosphorylation NF-κB p65 and decrease the expression of IL-1ß, IL-1ß p17 and TNF-α, upregulate the levels of PSD95 and Arc. Moreover, we found that Ex(9-39) and CC treatment could abrogate the memory protection of activation of GLP-1R in mice with neuropathic pain. The results indicated that the activation of GLP-1R could improve recognition memory impairment via regulating AMPK/NF-κB pathway, improving neuroinflammation, reversing the decreased level of synaptic proteins in neuropathic pain mice.

Dipeptidyl Peptidase-4 Inhibitor Decreases Allograft Vasculopathy Via Regulating the Functions of Endothelial Progenitor Cells in Normoglycemic Rats.

PURPOSE: Chronic rejection induces the occurrence of orthotopic allograft transplantation (OAT) vasculopathy, which results in failure of the donor organ. Numerous studies have demonstrated that in addition to regulating blood sugar homeostasis, dipeptidyl peptidase-4 (DPP-4) inhibitors can also provide efficacious therapeutic and protective effects against cardiovascular diseases. However, their effects on OAT-induced vasculopathy remain unknown. Thus, the aim of this study was to investigate the direct effects of sitagliptin on OAT vasculopathy in vivo and in vitro. METHODS: The PVG/Seac rat thoracic aorta graft to ACI/NKyo rat abdominal aorta model was used to explore the effects of sitagliptin on vasculopathy. Human endothelial progenitor cells (EPCs) were used to investigate the possible underlying mechanisms. RESULTS: We demonstrated that sitagliptin decreases vasculopathy in OAT ACI/NKyo rats. Treatment with sitagliptin decreased BNP and HMGB1 levels, increased GLP-1 activity and stromal cell-derived factor 1α (SDF-1α) expression, elevated the number of circulating EPCs, and improved the differentiation possibility of mononuclear cells to EPCs ex vivo. However, in vitro studies showed that recombinant B-type natriuretic peptide (BNP) and high mobility group box 1 (HMGB1) impaired EPC function, whereas these phenomena were reversed by glucagon-like peptide 1 (GLP-1) receptor agonist treatment. CONCLUSIONS: We suggest that the mechanisms underlying sitagliptin-mediated inhibition of OAT vasculopathy probably occur through a direct increase in GLP-1 activity. In addition to the GLP-1-dependent pathway, sitagliptin may regulate SDF-1α levels and EPC function to reduce OAT-induced vascular injury. This study may provide new prevention and treatment strategies for DPP-4 inhibitors in chronic rejection-induced vasculopathy.

Study on the Mechanism of the Blood-Glucose-Lowering Effect of Collagen Peptides from Sturgeon By-Products.

In a previous study, we found that the collagen peptides prepared from the by-products of Bester sturgeon had an inhibitory effect on elevated blood glucose levels in a glucose tolerance test with ICR mice. In the present study, we examine the mechanism of the effect of sturgeon collagen peptides (SCPs) in detail. When glucose was orally administered to mice along with the SCPs, it was found that the glucose remained in the stomach for a longer time. In the above tests, the amount of glucose excreted in the feces of mice also increased. On the contrary, it was revealed that the SCPs have a dipeptidyl-peptidase-IV (DPP-IV) inhibitory ability in an in vitro test. In subsequent oral and intravenous glucose administration tests, glucagon-like peptide-1 (GLP-1) and insulin levels in the blood of mice were maintained at high levels. These results suggested the following three mechanisms: SCPs slow the rate of transportation of glucose from the stomach into the small intestine, resulting in delayed glucose absorption; SCPs suppress the absorption of glucose in the small intestine and excrete it from the body; SCPs inhibit DPP-IV in the blood and maintain a high GLP-1 level in blood, which in turn stimulates insulin secretion.

Novel strategy for oral peptide delivery in incretin-based diabetes treatment.

OBJECTIVE: To fulfil an unmet therapeutic need for treating type 2 diabetes by developing an innovative oral drug delivery nanosystem increasing the production of glucagon-like peptide-1 (GLP-1) and the absorption of peptides into the circulation. DESIGN: We developed a nanocarrier for the oral delivery of peptides using lipid-based nanocapsules. We encapsulated the GLP-1 analogue exenatide within nanocapsules and investigated in vitro in human L-cells (NCl-H716) and murine L-cells (GLUTag cells) the ability of the nanosystem to trigger GLP-1 secretion. The therapeutic relevance of the nanosystem in vivo was tested in high-fat diet (HFD)-induced diabetic mice following acute (one administration) or chronic treatment (5 weeks) in obese and diabetic mice. RESULTS: We demonstrated that this innovative nanosystem triggers GLP-1 secretion in both human and murine cells as well as in vivo in mice. This strategy increases the endogenous secretion of GLP-1 and the oral bioavailability of the GLP-1 analogue exenatide (4% bioavailability with our nanosystem).The nanosystem synergizes its own biological effect with the encapsulated GLP-1 analogue leading to a marked improvement of glucose tolerance and insulin resistance (acute and chronic). The chronic treatment decreased diet-induced obesity, fat mass, hepatic steatosis, together with lower infiltration and recruitment of immune cell populations and inflammation. CONCLUSION: We developed a novel nanosystem compatible with human use that synergizes its own biological effect with the effects of increasing the bioavailability of a GLP-1 analogue. The effects of the formulation were comparable to the results observed for the marketed subcutaneous formulation. This nanocarrier-based strategy represents a novel promising approach for oral peptide delivery in incretin-based diabetes treatment.

The effect of acute dual SGLT1/SGLT2 inhibition on incretin release and glucose metabolism after gastric bypass surgery.

Enhanced meal-related enteroendocrine secretion, particularly of glucagon-like peptide-1 (GLP-1), contributes to weight-loss and improved glycemia after Roux-en-Y gastric bypass (RYGB). Dietary glucose drives GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) secretion postoperatively. Understanding how glucose triggers incretin secretion following RYGB could lead to new treatments of diabetes and obesity. In vitro, incretin release depends on glucose absorption via sodium-glucose cotransporter 1 (SGLT1). We investigated the importance of SGLT1/SGLT2 for enteropancreatic hormone concentrations and glucose metabolism after RYGB in a randomized, controlled, crossover study. Ten RYGB-operated patients ingested 50 g of oral glucose with and without acute pretreatment with 600 mg of the SGLT1/SGLT2-inhibitor canagliflozin. Paracetamol and 3-O-methyl-d-glucopyranose (3-OMG) were added to the glucose drink to evaluate rates of intestinal entry and absorption of glucose, respectively. Blood samples were collected for 4 h. The primary outcome was 4-h plasma GLP-1 (incremental area-under the curve, iAUC). Secondary outcomes included glucose, GIP, insulin, and glucagon. Canagliflozin delayed glucose absorption (time-to-peak 3-OMG: 50 vs. 132 min, P < 0.01) but did not reduce iAUC GLP-1 (6,067 vs. 7,273·min·pmol-1·L-1, P = 0.23), although peak GLP-1 concentrations were lowered (-28%, P = 0.03). Canagliflozin reduced GIP (iAUC -28%, P = 0.01; peak concentrations -57%, P < 0.01), insulin, and glucose excursions, whereas plasma glucagon (AUC 3,216 vs. 4,160 min·pmol·L-1, P = 0.02) and amino acids were increased. In conclusion, acute SGLT1/SGLT2-inhibition during glucose ingestion did not reduce 4-h plasma GLP-1 responses in RYGB-patients but attenuated the early rise in GLP-1, GIP, and insulin, whereas late glucagon concentrations were increased. The results suggest that SGLT1-mediated glucose absorption contributes to incretin hormone secretion after RYGB.

Paracrine crosstalk between intestinal L- and D-cells controls secretion of glucagon-like peptide-1 in mice.

DPP-4 inhibitors, used for treatment of type 2 diabetes, act by increasing the concentrations of intact glucagon-like peptide-1 (GLP-1), but at the same time, they inhibit secretion of GLP-1, perhaps by a negative feedback mechanism. We hypothesized that GLP-1 secretion is feedback regulated by somatostatin (SS) from neighboring D-cells, and blocking this feedback circuit results in increased GLP-1 secretion. We used a wide range of experimental techniques, including gene expression analysis, immunohistochemical approaches, and the perfused mouse intestine to characterize the paracrine circuit controlling GLP-1 and SS. We show that 1) antagonizing the SS receptor (SSTr) 2 and SSTr5 led to increased GLP-1 and SS secretion in the mouse, 2) SS exhibits strong tonic inhibition of GLP-1 secretion preferentially through SSTr5, and 3) the secretion of S was GLP-1 receptor dependent. We conclude that SS is a tonic inhibitor of GLP-1 secretion, and interventions in the somatostain-GLP-1 paracrine loop lead to increased GLP-1 secretion.

Could hop-derived bitter compounds improve glucose homeostasis by stimulating the secretion of GLP-1?

Hops (Humulus lupulus L.) is by far the greatest contributors to the bitter property of beer. Over the past years, a large body of evidence demonstrated the presence of taste receptors in different locations of the oral cavity. In addition to the taste buds of the tongue, cells expressing these receptors have been identified in olfactory bulbs, respiratory and gastrointestinal tract. In the gut, the attention was mainly directed to sweet Taste Receptor (T1R) and bitter Taste Receptor (T2R) receptors. In particular, T2R has shown to modulate secretion of different gut hormones, mainly Glucagon-like Peptide 1 (GLP-1), which are involved in the regulation of glucose homeostasis and the control of gut motility, thereby increasing the sense of satiety. Scientific interest in the activity of bitter taste receptors emerges because of their wide distribution in the human species and the large range of natural substances that interact with them. Beer, whose alcohol content is lower than in other common alcoholic beverages, contains a considerable amount of bitter compounds and current scientific evidence shows a direct effect of beer compounds on glucose homeostasis. The purpose of this paper is to review the available literature data in order to substantiate the novel hypothesis of a possible direct effect of hop-derived bitter compounds on secretion of GLP-1, through the activation of T2R, with consequent improvement of glucose homeostasis.

Postprandial hypoglycaemia after Roux-en-Y gastric bypass and the effects of acarbose, sitagliptin, verapamil, liraglutide and pasireotide.

AIM: To investigate the effects of acarbose, sitagliptin, verapamil, liraglutide and pasireotide on post-bariatric hypoglycaemia (PBH) after Roux-en-Y gastric bypass. MATERIALS AND METHODS: In a randomized crossover study, 11 women who had undergone Roux-en-Y gastric bypass and had documented hypoglycaemia were each evaluated during a baseline period without treatment and during five treatment periods with the following interventions: acarbose 50 mg for 1 week, sitagliptin 100 mg for 1 week, verapamil 120 mg for 1 week, liraglutide 1.2 mg for 3 weeks and pasireotide 300 µg as a single dose. Treatment effects were evaluated by a mixed-meal tolerance test (MMTT) and, for all treatment periods except pasireotide, by 6 days of continuous glucose monitoring (CGM). RESULTS: Treatment with acarbose and treatment with pasireotide both significantly lifted nadir glucose levels (mean ± SEM 3.9 ± 0.2 and 7.9 ± 0.4 vs 3.4 ± 0.2; P < .03) and reduced time in hypoglycaemia during the MMTTs. Acarbose reduced peak glucose levels and time in hyperglycaemia, whereas pasireotide greatly increased both variables. Acarbose and pasireotide reduced insulin and C-peptide levels, and pasireotide also diminished glucagon-like peptide-1 levels. Sitagliptin lowered nadir glucose values, while verapamil and liraglutide had no effect on hypoglycaemia. During the CGM periods, the treatments had no impact on hypoglycaemia, whereas acarbose and liraglutide reduced hyperglycaemia and glycaemic variability. CONCLUSIONS: In an experimental setting, treatment with acarbose and pasireotide reduced PBH. Acarbose appears to have an overall glucose-stabilizing effect, whereas pasireotide leads to increased and sustained hyperglycaemia.

Growth hormone therapy in children with idiopathic short stature - the effect on appetite and appetite-regulating hormones: a pilot study.

AIM: To investigate the effect of growth hormone (GH) therapy on appetite-regulating hormones and to examine the association between these hormones and the response to GH, body composition, and resting energy expenditure (REE). METHODS: Nine pre-pubertal children with idiopathic short stature underwent a standard meal test before and 4 months following initiation of GH treatment. Ghrelin, GLP-1, leptin, and insulin levels were measured; area under the curve (AUC) was calculated. Height, weight, body composition, REE, and insulin-like growth factor levels were recorded at baseline and after 4 and 12 months. RESULTS: Following 4 months of GH therapy, food intake increased, with increased height-standard deviation score (SDS), weight-SDS, and REE (p < .05). Significant changes in appetite-regulating hormones included a decrease in postprandial AUC ghrelin levels (p = .045) and fasting GLP-1 (p = .038), and an increase in fasting insulin (p = .043). Ghrelin levels before GH treatment were positively correlated with the changes in weight-SDS (fasting: r = .667, p = .05; AUC: r = .788, p = .012) and REE (fasting: r = .866, p = .005; AUC: r = .847, p = .008) following 4 months of GH therapy. Ghrelin AUC at 4 months was positively correlated with the changes in height-SDS (r = .741, p = .022) and fat-free-mass (r = .890, p = .001) at 12 months of GH treatment. CONCLUSIONS: The reduction in ghrelin and GLP-1 following GH treatment suggests a role for GH in appetite regulation. Fasting and meal-AUC ghrelin levels may serve as biomarkers for predicting short-term (4 months) changes in weight and longer term (12 months) changes in height following GH treatment. The mechanisms linking GH with changes in appetite-regulating hormones remain to be elucidated. ABBREVIATIONS: SDS: standard deviation score; REE: resting energy expenditure; SMT: standard meal test; AUC: area under the curve; ISS: idiopathic short stature; SGA: small for gestational age; FFM: fat-free-mass; FM: fat mass; EER: estimated energy requirements; DRI: dietary reference intakes; IQR: inter-quartile range.

Colesevelam attenuates cholestatic liver and bile duct injury in Mdr2-/- mice by modulating composition, signalling and excretion of faecal bile acids.

BACKGROUND AND AIMS: Interruption of the enterohepatic circulation of bile acids (BAs) may protect against BA-mediated cholestatic liver and bile duct injury. BA sequestrants are established to treat cholestatic pruritus, but their impact on the underlying cholestasis is still unclear. We aimed to explore the therapeutic effects and mechanisms of the BA sequestrant colesevelam in a mouse model of sclerosing cholangitis. METHODS: Mdr2-/- mice received colesevelam for 8 weeks. Gene expression profiles of BA homeostasis, inflammation and fibrosis were explored in liver, intestine and colon. Hepatic and faecal BA profiles and gut microbiome were analysed. Glucagon-like peptide 1 (GLP-1) levels in portal blood were measured by ELISA. Furthermore, Mdr2-/- mice as well as wild-type 3,5-diethoxy-carbonyl-1,4-dihydrocollidine-fed mice were treated with GLP-1-receptor agonist exendin-4 for 2 weeks prior to analysis. RESULTS: Colesevelam reduced serum liver enzymes, BAs and expression of proinflammatory and profibrogenic markers. Faecal BA profiling revealed increased levels of secondary BAs after resin treatment, while hepatic and biliary BA composition showed a shift towards more hydrophilic BAs. Colonic GLP-1 secretion, portal venous GLP-1 levels and intestinal messenger RNA expression of gut hormone Proglucagon were increased, while ileal Fgf15 expression was abolished by colesevelam. Exendin-4 treatment increased bile duct mass without promoting a reactive cholangiocyte phenotype in mouse models of sclerosing cholangitis. Microbiota analysis showed an increase of the phylum δ-Proteobacteria after colesevelam treatment and a shift within the phyla Firmicutes from Clostridiales to Lactobacillus. CONCLUSION: Colesevelam increases faecal BA excretion and enhances BA conversion towards secondary BAs, thereby stimulating secretion of GLP-1 from enteroendocrine L-cells and attenuates liver and bile duct injury in Mdr2-/- mice.

A sandwich ELISA for measurement of the primary glucagon-like peptide-1 metabolite.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted from the gastrointestinal tract. It is best known for its glucose-dependent insulinotropic effects. GLP-1 is secreted in its intact (active) form (7-36NH2) but is rapidly degraded by the dipeptidyl peptidase 4 (DPP-4) enzyme, converting >90% to the primary metabolite (9-36NH2) before reaching the targets via the circulation. Although originally thought to be inactive or antagonistic, GLP-1 9-36NH2 may have independent actions, and it is therefore relevant to be able to measure it. Because reliable assays were not available, we developed a sandwich ELISA recognizing both GLP-1 9-36NH2 and nonamidated GLP-1 9-37. The ELISA was validated using analytical assay validation guidelines and by comparing it to a subtraction-based method, hitherto employed for estimation of GLP-1 9-36NH2 Its accuracy was evaluated from measurements of plasma obtained during intravenous infusions (1.5 pmol × kg-1 × min-1) of GLP-1 7-36NH2 in healthy subjects and patients with type 2 diabetes. Plasma levels of the endogenous GLP-1 metabolite increased during a meal challenge in patients with type 2 diabetes, and treatment with a DPP-4 inhibitor fully blocked its formation. Accurate measurements of the GLP-1 metabolite may contribute to understanding its physiology and role of GLP-1 in diabetes.

Incretin secretion in humans is under the influence of cannabinoid receptors.

The mechanisms regulating incretin secretion are not fully known. Human obesity is associated with altered incretin secretion and elevated endocannabinoid levels. Since cannabinoid receptors (CBRs) are expressed on incretin-secreting cells in rodents, we hypothesized that endocannabinoids are involved in the regulation of incretin secretion. We compared plasma glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) responses during oral glucose tolerance test (OGTT) in 20 lean and 20 obese participants from the Baltimore Longitudinal Study of Aging (BLSA). Next, we recruited 20 healthy men to evaluate GIP and GLP-1 responses during OGTT after administering placebo or nabilone (CBR agonist) in a randomized, double-blind, crossover fashion. Compared with the BLSA lean group, the BLSA obese group had significantly higher fasting and post-OGTT GIP levels, but similar fasting GLP-1 and significantly lower post-OGTT GLP-1 levels. In the nabilone vs. placebo study, when compared with placebo, nabilone resulted in significantly elevated post-dose fasting GIP levels and post-OGTT GIP levels, but no change in post-dose fasting GLP-1 levels together with significantly lower post-OGTT GLP-1 levels. Glucose levels were not different with both interventions. We conclude that elevated GIP levels in obesity are likely a consequence of increased endocannabinoid levels. CBRs exert tonic control over GIP secretion, which may have a homeostatic effect in suppressing GLP-1 secretion. This raises the possibility that gut hormones are influenced by endocannabinoids.

Metformin reduces the rate of small intestinal glucose absorption in type 2 diabetes.

In rodents, metformin slows intestinal glucose absorption, potentially increasing exposure of the distal gut to glucose to enhance postprandial glucagon-like peptide-1 (GLP-1) secretion. We evaluated the effects of metformin on serum 3-O-methylglucose (3-OMG; a marker of glucose absorption) and plasma total GLP-1 concentrations during a standardized intraduodenal infusion of glucose and 3-OMG in patients with type 2 diabetes. A total of 12 patients, treated with metformin 850 mg twice daily or placebo for 7 days each in a double-blind, randomized, crossover design (14 days' washout between treatments), were evaluated on days 5 or 8 of each treatment (6 subjects each). On each study day, 30 minutes after ingesting 850 mg metformin or placebo, patients received an infusion of glucose (60 g + 5 g 3-OMG, dissolved in water to 240 mL) via an intraduodenal catheter over the course of 120 minutes. Compared with placebo, metformin was associated with lower serum 3-OMG ( P < .001) and higher plasma total GLP-1 ( P = .003) concentrations. The increment in plasma GLP-1 after metformin vs placebo was related to the reduction in serum 3-OMG concentrations ( P = .019). Accordingly, metformin inhibits small intestinal glucose absorption, which may contribute to augmented GLP-1 secretion in type 2 diabetes.

Sustained influence of metformin therapy on circulating glucagon-like peptide-1 levels in individuals with and without type 2 diabetes.

AIMS: To investigate, in the Carotid Atherosclerosis: Metformin for Insulin Resistance (CAMERA) trial (NCT00723307), whether the influence of metformin on the glucagon-like peptide (GLP)-1 axis in individuals with and without type 2 diabetes (T2DM) is sustained and related to changes in glycaemia or weight, and to investigate basal and post-meal GLP-1 levels in patients with T2DM in the cross-sectional Diabetes Research on Patient Stratification (DIRECT) study. MATERIALS AND METHODS: CAMERA was a double-blind randomized placebo-controlled trial of metformin in 173 participants without diabetes. Using 6-monthly fasted total GLP-1 levels over 18 months, we evaluated metformin's effect on total GLP-1 with repeated-measures analysis and analysis of covariance. In the DIRECT study, we examined active and total fasting and 60-minute post-meal GLP-1 levels in 775 people recently diagnosed with T2DM treated with metformin or diet, using Student's t-tests and linear regression. RESULTS: In CAMERA, metformin increased total GLP-1 at 6 (+20.7%, 95% confidence interval [CI] 4.7-39.0), 12 (+26.7%, 95% CI 10.3-45.6) and 18 months (+18.7%, 95% CI 3.8-35.7), an overall increase of 23.4% (95% CI 11.2-36.9; P < .0001) vs placebo. Adjustment for changes in glycaemia and adiposity, individually or combined, did not attenuate this effect. In the DIRECT study, metformin was associated with higher fasting active (39.1%, 95% CI 21.3-56.4) and total GLP-1 (14.1%, 95% CI 1.2-25.9) but not post-meal incremental GLP-1. These changes were independent of potential confounders including age, sex, adiposity and glycated haemoglobin. CONCLUSIONS: In people without diabetes, metformin increases total GLP-1 in a sustained manner and independently of changes in weight or glycaemia. Metformin-treated patients with T2DM also have higher fasted GLP-1 levels, independently of weight and glycaemia.

Effect of exenatide on postprandial glucose fluxes, lipolysis, and ß-cell function in non-diabetic, morbidly obese patients.

AIMS: To investigate the effect of exenatide on glucose disposal, insulin secretion, ß-cell function, lipolysis and hormone concentrations in non-diabetic, morbidly obese subjects under physiological conditions. MATERIALS AND METHODS: Patients were assigned to exenatide 10 µg twice daily (EXE, n = 15) or control (CT, n = 15) for 3 months. Patients received a meal test/tracer study (MTT) to measure endogenous glucose production (EGP), rate of oral glucose appearance (RaO), insulin secretion rate (ISR), ß-cell function, hepatic insulin resistance (HIR) and adipose tissue insulin resistance (AT-IR) and insulin sensitivity (IS). RESULTS: Post treatment, the EXE group showed a significant reduction in body weight ( P < .001). The postmeal time-course of glucose, insulin and ISR showed a lower peak between 60 and 180 minutes in phase with a reduction in RaO ( P < .01). After an initial similar suppression, EGP resumed at higher rates between 60 and 180 minutes ( P = .02) in EXE vs CT, while total RaO and EGP were similar throughout the MTT. In EXE, the postmeal glucagon, GLP1 and GIP responses were reduced ( P < .05). Fasting and postprandial lipolysis and ß-cell function were unaltered by active treatment. HIR, AT-IR and IS were all improved after exenatide treatment ( P < .05). CONCLUSIONS: In morbidly obese non-diabetic subjects, exenatide causes weight loss, decreased postprandial glycaemia and glucagon response without changes in ß-cell function. These effects are consequent upon delayed oral glucose appearance in the circulation. Exenatide treatment is also associated with an improvement in hepatic, adipose tissue and whole-body IS with no influence on postprandial lipolysis.

The diet-derived short chain fatty acid propionate improves beta-cell function in humans and stimulates insulin secretion from human islets in vitro.

AIMS: Diet-derived short chain fatty acids (SCFAs) improve glucose homeostasis in vivo, but the role of individual SCFAs and their mechanisms of action have not been defined. This study evaluated the effects of increasing colonic delivery of the SCFA propionate on ß-cell function in humans and the direct effects of propionate on isolated human islets in vitro. MATERIALS AND METHODS: For 24 weeks human subjects ingested an inulin-propionate ester that delivers propionate to the colon. Acute insulin, GLP-1 and non-esterified fatty acid (NEFA) levels were quantified pre- and post-supplementation in response to a mixed meal test. Expression of the SCFA receptor FFAR2 in human islets was determined by western blotting and immunohistochemistry. Dynamic insulin secretion from perifused human islets was quantified by radioimmunoassay and islet apoptosis was determined by quantification of caspase 3/7 activities. RESULTS: Colonic propionate delivery in vivo was associated with improved ß-cell function with increased insulin secretion that was independent of changes in GLP-1 levels. Human islet ß-cells expressed FFAR2 and propionate potentiated dynamic glucose-stimulated insulin secretion in vitro, an effect that was dependent on signalling via protein kinase C. Propionate also protected human islets from apoptosis induced by the NEFA sodium palmitate and inflammatory cytokines. CONCLUSIONS: Our results indicate that propionate has beneficial effects on ß-cell function in vivo, and in vitro analyses demonstrated that it has direct effects to potentiate glucose-stimulated insulin release and maintain ß-cell mass through inhibition of apoptosis. These observations support ingestion of propiogenic dietary fibres to maintain healthy glucose homeostasis.

Effect of Salt Intake on Serum Glucagon-Like Peptide-1 Levels in Normotensive Salt-Sensitive Subjects.

BACKGROUND/AIMS: Excess dietary salt is a critical risk factor of salt-sensitive hypertension. Glucagon-like peptide-1 (GLP-1) , a gut incretin hormone, conferring benefits for blood pressure by natriuresis and diuresis. We implemented a randomized trial to verify the effect of altered salt intake on serum GLP-1 level in human beings. METHODS: The 38 subjects were recruited from a rural community of Northern China. All subjects were sequentially maintained a baseline diet period for 3 days, a low-salt diet period for 7 days (3.0g/day of NaCl) , and a high-salt diet period for additional 7 days (18.0g/day of NaCl). RESULTS: Serum GLP-1 level increased significantly with the change from the baseline period to the low-salt diet period and decreased with the change from the low-salt to high-salt diet in normotensive salt-sensitive (SS) but not salt-resistant (SR) individuals. There was a significant inverse correlation between the serum GLP-1 level and the MAP in SS subjects. Inverse correlation between the serum GLP-1 level and 24-h urinary sodium excretion was also found among different dietary interventions in SS subjects. CONCLUSIONS: Our study indicates that variations in dietary salt intake affect the serum GLP-1 level in normotensive salt-sensitive Chinese adults.

Jejunal administration of glucose enhances acyl ghrelin suppression in obese humans.

Ghrelin is a gastric hormone that stimulates hunger and worsens glucose metabolism. Circulating ghrelin is decreased after Roux-en-Y gastric bypass (RYGB) surgery; however, the mechanism(s) underlying this change is unknown. We tested the hypothesis that jejunal nutrient exposure plays a significant role in ghrelin suppression after RYGB. Feeding tubes were placed in the stomach or jejunum in 13 obese subjects to simulate pre-RYGB or post-RYGB glucose exposure to the gastrointestinal (GI) tract, respectively, without the confounding effects of caloric restriction, weight loss, and surgical stress. On separate study days, the plasma glucose curves obtained with either gastric or jejunal administration of glucose were replicated with intravenous (iv) infusions of glucose. These "isoglycemic clamps" enabled us to determine the contribution of the GI tract and postabsorptive plasma glucose to acyl ghrelin suppression. Plasma acyl ghrelin levels were suppressed to a greater degree with jejunal glucose administration compared with gastric glucose administration (P < 0.05). Jejunal administration of glucose also resulted in a greater suppression of acyl ghrelin than the corresponding isoglycemic glucose infusion (P ≤ 0.01). However, gastric and isoglycemic iv glucose infusions resulted in similar degrees of acyl ghrelin suppression (P > 0.05). Direct exposure of the proximal jejunum to glucose increases acyl ghrelin suppression independent of circulating glucose levels. The enhanced suppression of acyl ghrelin after RYGB may be due to a nutrient-initiated signal in the jejunum that regulates ghrelin secretion.