Glucagon-like Peptide-1 In Regulation Research Articles

Low-intensity pulsed ultrasound ameliorates insulin resistance in type 2 diabetes mice via promoting glucagon-like peptide-1 release

Abstract Glucagon-like peptide-1 (GLP-1) is a hormone secreted by intestinal L-cells. It regulates glucose levels by boosting insulin secretion, inhibiting glucagon release, and preventing β-cell death. GLP-1 is increasingly used in managing type 2 diabetes mellitus (T2DM). This study assessed the effectiveness of low-intensity pulsed ultrasound (LIPUS), a non-pharmacological intervention, in enhancing insulin resistance in diabetic mice by stimulating GLP-1 release. T2DM was induced in C57BL/6J mice through a high-fat diet and streptozotocin injection. Mice were divided into Control, T2D-sham and T2D-LIPUS groups. The T2D-LIPUS group received LIPUS treatment with a frequency of 1MHz, intensity of 120mW/cm2, and duty cycle of 20%for 20 minutes/day, 5 days/week for 4 weeks. Glucose tolerance and insulin resistance were measured through tests. Pancreatic histology and GLP-1 expression in serum were evaluated. Results showed that T2DM increased insulin resistance, but LIPUS treatment alleviated it. GLP-1 levels significantly increased in the T2D-LIPUS group compared to the T2D-sham group, approaching the control group’s level. LIPUS also reduced apoptosis of islet β cells. These findings suggest that LIPUS stimulation of the intestine can enhance islet β-cell activity through GLP-1 regulation of the gut-pancreas axis, mitigating insulin resistance in T2DM.

Metabolic Changes Following Smoking Cessation in Patients with Type 2 Diabetes Mellitus.

Smoking cessation is crucial for reducing complications of type 2 diabetes mellitus (T2DM), but associated weight gain can worsen glycemic control, discouraging quitting attempts. Varenicline, a partial agonist of α4β2 nicotinic receptors, aids smoking cessation. This study examines the effects of varenicline on body weight and metabolic parameters in patients with T2DM and prediabetes. Fifty-three patients were enrolled, of which 32 successfully quit smoking after a three-month course of varenicline and were examined after an additional month with no medication. Measurements taken at baseline, 2.5 months, and 4 months included body weight, blood pressure, resting metabolic rate (RMR), glycated hemoglobin (HbA1c), fasting glucose, blood lipids, C-reactive protein (CRP), appetite-related hormones, and physical activity. Post-treatment, there were no significant changes in body weight, blood pressure, RMR, or glycemic control. Total (CHOL) and low-density lipoprotein (LDL-C) cholesterol decreased significantly at 4 months of the study (from 168 to 156 mg/dL, p = 0.013, and from 96 to 83 mg/dL, p = 0.013, respectively). Leptin levels increased (from 11 to 13.8 ng/dL, p = 0.004), as did glucagon-like peptide-1 (GLP-1) levels (from 39.6 to 45.8 pM, p = 0.016) at 4 months of follow-up. The percentage of participants who reported moderate-intensity activity increased from 28% to 56%, while those reporting high-intensity activity increased from 19% to 22%, respectively (p = 0.039). Our study showed that smoking cessation with varenicline in smokers with T2DM and prediabetes led to significant improvements in lipid profile, significant increase in plasma leptin and GLP-1 levels, and increased physical activity, without significant weight gain. Thus, smoking cessation without weight gain or deteriorated glycemic control is feasible for these smokers, with added benefits to lipid profiles, GLP-1 regulation, and physical activity.

Effect of Milk Protein-Polyphenol Conjugate on the Regulation of GLP-1 Hormone.

Modern functional foods are designed to provide health benefits beyond basic nutrition. They are enriched with bioactive ingredients like probiotics, vitamins, minerals, and antioxidants. These foods support overall health, enhance immune function, and help prevent chronic diseases. Milk proteins and tea are known to influence satiety and regulate body weight. Studies have shown that green tea polyphenols, namely, (-)-epigallocatechin gallate (EGCG), and whey proteins, predominantly lactoferrin (LF) from milk, play a role in regulating satiety. This study aims to investigate the effect of conjugating EGCG with apo-lactoferrin (Apo-LF) and assessing these effects on satiety through monitoring glucagon-like peptide-1 (GLP-1) regulation in a human colon (NCI-H716) cell line. Apo-LF-EGCG conjugates were synthesized and characterized in terms of structural and functional properties. The effect on GLP-1 regulation was assessed by real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) to monitor gene and protein expressions, respectively. The results revealed that the protein-polyphenol interaction occurs through the complex formation of hydrogen bonds at the O-H and carbonyl groups of EGCG. The conjugates also showed a significant up-regulation of gene and protein expression levels of GLP-1 while also preventing EGCG from degradation, thereby preserving its antioxidant properties. The Apo-LF-EGCG conjugates increase satiety via increasing GLP-1 secretion in human colon cells while simultaneously retaining the antioxidant properties of EGCG. Therefore, these conjugates show potential for use as dietary supplements to enhance satiety.

Dipeptidyl peptidase-4 disturbs adipocyte differentiation via the negative regulation of the glucagon-like peptide-1/adiponectin-cathepsin K axis in mice under chronic stress conditions.

Exposure to chronic psychosocial stress is a risk factor for metabolic disorders. Because dipeptidyl peptidase-4 (DPP4) and cysteinyl cathepsin K (CTSK) play important roles in human pathobiology, we investigated the role(s) of DPP4 in stress-related adipocyte differentiation, with a focus on the glucagon-like peptide-1 (GLP-1)/adiponectin-CTSK axis invivo and invitro. Plasma and inguinal adipose tissue from non-stress wild-type (DPP4+/+), DPP4-knockout (DPP4-/-) and CTSK-knockout (CTSK-/-) mice, and stressed DPP4+/+, DPP4-/-, CTSK-/-, and DPP4+/+ mice underwent stress exposure plus GLP-1 receptor agonist exenatide loading for 2 weeks and then were analyzed for stress-related biological and/or morphological alterations. On day 14 under chronic stress, stress decreased the weights of adipose tissue and resulted in harmful changes in the plasma levels of DPP4, GLP-1, CTSK, adiponectin, and tumor necrosis factor-α proteins and the adipose tissue levels of CTSK, preadipocyte factor-1, fatty acid binding protein-4, CCAAT/enhancer binding protein-α, GLP-1 receptor, peroxisome proliferator-activated receptor-γ, perilipin2, secreted frizzled-related protein-4, Wnt5α, Wnt11 and β-catenin proteins and/or mRNAs as well as macrophage infiltration in adipose tissue; these changes were rectified by DPP4 deletion. GLP-1 receptor activation and CTSK deletion mimic the adipose benefits of DPP4 deficiency. Invitro, CTSK silencing and overexpression respectively prevented and facilitated stress serum and oxidative stress-induced adipocyte differentiation accompanied with changes in the levels of pref-1, C/EBP-α, and PPAR-γ in 3T3-L1 cells. Thus, these findings indicated that increased DPP4 plays an essential role in stress-related adipocyte differentiation, possibly through a negative regulation of GLP-1/adiponectin-CTSK axis activation in mice under chronic stress conditions.

RNA sequencing unravels novel L cell constituents and mechanisms of GLP-1 secretion in human gastric bypass-operated intestine

Aims/hypothesisRoux-en-Y gastric bypass surgery (RYGB) frequently results in remission of type 2 diabetes as well as exaggerated secretion of glucagon-like peptide-1 (GLP-1). Here, we assessed RYGB-induced transcriptomic alterations in the small intestine and investigated how they were related to the regulation of GLP-1 production and secretion in vitro and in vivo.MethodsHuman jejunal samples taken perisurgically and 1 year post RYGB (n=13) were analysed by RNA-seq. Guided by bioinformatics analysis we targeted four genes involved in cholesterol biosynthesis, which we confirmed to be expressed in human L cells, for potential involvement in GLP-1 regulation using siRNAs in GLUTag and STC-1 cells. Gene expression analyses, GLP-1 secretion measurements, intracellular calcium imaging and RNA-seq were performed in vitro. OGTTs were performed in C57BL/6j and iScd1−/− mice and immunohistochemistry and gene expression analyses were performed ex vivo.ResultsGene Ontology (GO) analysis identified cholesterol biosynthesis as being most affected by RYGB. Silencing or chemical inhibition of stearoyl-CoA desaturase 1 (SCD1), a key enzyme in the synthesis of monounsaturated fatty acids, was found to reduce Gcg expression and secretion of GLP-1 by GLUTag and STC-1 cells. Scd1 knockdown also reduced intracellular Ca2+ signalling and membrane depolarisation. Furthermore, Scd1 mRNA expression was found to be regulated by NEFAs but not glucose. RNA-seq of SCD1 inhibitor-treated GLUTag cells identified altered expression of genes implicated in ATP generation and glycolysis. Finally, gene expression and immunohistochemical analysis of the jejunum of the intestine-specific Scd1 knockout mouse model, iScd1−/−, revealed a twofold higher L cell density and a twofold increase in Gcg mRNA expression.Conclusions/interpretationRYGB caused robust alterations in the jejunal transcriptome, with genes involved in cholesterol biosynthesis being most affected. Our data highlight SCD as an RYGB-regulated L cell constituent that regulates the production and secretion of GLP-1.Graphical

Glucagon-like peptide-1 and glucagon-like peptide-2 regulation during human liver regeneration

Accumulating evidence suggests that metabolic demands of the regenerating liver are met via lipid metabolism and critical regulators of this process. As such, glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) critically affect hepatic regeneration in rodent models. The present study aimed to evaluate potential alterations and dynamics of circulating GLP-1 and GLP-2 in patients undergoing liver resections, focusing on post-hepatectomy liver failure (PHLF). GLP-1, GLP-2, Interleukin-6 (IL-6) and parameters of lipid metabolism were determined perioperatively in fasting plasma of 46 patients, who underwent liver resection. GLP-1 and GLP-2 demonstrated a rapid and consistently inverse time course during hepatic regeneration with a significant decrease of GLP-1 and increase of GLP-2 on POD1. Importantly, these postoperative dynamics were significantly more pronounced when PHLF occurred. Of note, the extent of resection or development of complications were not associated with these alterations. IL-6 mirrored the time course of GLP-2. Assessing the main degradation protein dipeptidyl peptidase 4 (DPP4) no significant association with either GLP-1 or -2 could be found. Additionally, in PHLF distinct postoperative declines in plasma lipid parameters were present and correlated with GLP-2 dynamics. Our data suggest dynamic inverse regulation of GLP-1 and GLP-2 during liver regeneration, rather caused by an increase in expression/release than by changes in degradation capacity and might be associated with inflammatory responses. Their close association with circulating markers of lipid metabolism and insufficient hepatic regeneration after liver surgery suggest a critical involvement during these processes in humans.

Regulation of Human Sortilin Alternative Splicing by Glucagon-like Peptide-1 (GLP1) in Adipocytes.

Type 2 diabetes mellitus is a chronic metabolic disease with no cure. Adipose tissue is a major site of systemic insulin resistance. Sortilin is a central component of the glucose transporter -Glut4 storage vesicles (GSV) which translocate to the plasma membrane to uptake glucose from circulation. Here, using human adipocytes we demonstrate the presence of the alternatively spliced, truncated sortilin variant (Sort_T) whose expression is significantly increased in diabetic adipose tissue. Artificial-intelligence-based modeling, molecular dynamics, intrinsically disordered region analysis, and co-immunoprecipitation demonstrated association of Sort_T with Glut4 and decreased glucose uptake in adipocytes. The results show that glucagon-like peptide-1 (GLP1) hormone decreases Sort_T. We deciphered the molecular mechanism underlying GLP1 regulation of alternative splicing of human sortilin. Using splicing minigenes and RNA-immunoprecipitation assays, the results show that GLP1 regulates Sort_T alternative splicing via the splice factor, TRA2B. We demonstrate that targeted antisense oligonucleotide morpholinos reduces Sort_T levels and improves glucose uptake in diabetic adipocytes. Thus, we demonstrate that GLP1 regulates alternative splicing of sortilin in human diabetic adipocytes.

Novel luciferase-based glucagon-like peptide 1 reporter assay reveals naturally occurring secretagogues.

Glucagon-like peptide 1 (GLP-1) is a hormone derived from preproglucagon. It is secreted by enteroendocrine cells in response to feeding and, in turn, acts as a critical regulator of insulin release. Modulating GLP-1 secretion holds promise as a strategy for controlling blood glucose levels. To dissect GLP-1 regulation and discover specific secretagogues, we engineered a reporter cell line introducing a luciferase within the proglucagon sequence in GLUTag cells. The assay was validated using western blotting and ELISA. A focused natural compounds library was screened. We measured luminescence, glucose uptake and ATP to investigate the mechanism by which newly found secretagogues potentiate GLP-1 secretion. The newly created reporter cell line is ideal for the rapid, sensitive and quantitative assessment of GLP-1 secretion. The small molecule screen identified non-toxic GLP-1 modulators. Quercetin is the most potent newly found GLP-1 secretagogue, while other flavonoids also potentiate GLP-1 secretion. Quercetin requires glucose and extracellular calcium to act as GLP-1 secretagogue. Our results support a mechanism whereby flavonoids cause GLUTag cells to utilize glucose more efficiently, leading to elevated ATP levels, followed by KATP channel blockade and GLP-1 exocytosis. Our methodology enabled finding of new GLP-1 secretagogues. Quercetin is a potent, naturally occurring GLP-1 secretagogue. Mechanistic studies of newly found secretagogues are possible in newly created reporter cell line. Further validation in more physiological systems, such as primary L-cells or whole organisms, is needed. GLP-1 secretagogues might serve as leads for developing alternative glucose-lowering therapies.

366-OR: 14-3-3-ζ Contributes to Effect of ß-Cell GLP1 Receptor Signaling to Alter a-Cell Proglucagon Processing

Glucagon like peptide 1 (GLP1) , a classically gut derived hormone, potentiates insulin secretion. New evidence suggests that α cells can produce GLP1 under certain conditions, which may offer a novel therapeutic modality for treating diabetes; however, the mechanisms regulating α cell GLP1 production are unknown. We previously found that enhanced β cell GLP1 receptor (GLP1R) signaling activates α cell GLP1 by activating prohormone convertase 1/3 (Pcsk1) expression. We tested the hypothesis that enhanced β cell GLP1R signaling activates α cell GLP1 production through paracrine factors. We studied the impact of conditioned media (CM) generated from β cell GLP1R WT and KO islets of saline (CTRL) and liraglutide (LIRA) treated mice on α cell gene expression and function. CM from LIRA treated islets increased α cell Pcsk1 expression and active GLP-1 secretion only if β cells expressed the GLP1R (Pcsk1 expression (AU) : CTRL WT=1.0±0.1, LIRA WT=2.0±0.3, CTRL KO=1.1±0.2, LIRA KO=1.1±0.2, P<0.01; active GLP-1 (pg/mL) : CTRL WT=124±44, LIRA WT=682±247, CTRL KO=173±101, LIRA KO=116±30, P<0.05) . Subsequent identification of the proteome secreted by mouse and human islets in response to LIRA and CTRL revealed 14-3-3-ζ as a lead candidate in the regulation of α cell Pcsk1 expression. To assess the role of 14-3-3-ζ, islets from LIRA treated mice were treated with and without 14-3-3-ζ, and islets from CTRL treated mice were treated with and without the 14-3-3 inhibitor, R18. Addition of 14-3-3-ζ ablated the effect of CM from LIRA treated islets to increase α cell Pcsk1 expression, while inhibition of 14-3-3 with R18 in CTRL islets resulted in CM that mimicked the effect of CM from LIRA treated islets to stimulate α cell Pcsk1 expression (Pcsk1 expression: CTRL=1.1±0.2, R18=2.0±0.2, LIRA=2.4±0.3, LIRA+14-3-3-ζ=1.3±0.1, P<0.05) . These data refine our understanding of α cell GLP1 regulation and identify 14-3-3-ζ as a potential target with which to enhance α cell GLP1 production for diabetes treatment. Disclosure M.Holter: None. B.Cummings: None. D.Phuong: None. I.S.H.Lee: None. M.Saikia: None. L.A.Weikert: Stock/Shareholder; Merck & Co., Inc., Oramed Pharmaceuticals. E.T.Anderson: None. Q.Fu: None. S.Zhang: None. K.Sloop: Employee; Eli Lilly and Company. Funding NIH/NIDDK (F30 DK126538) Department of Defense (W81XWH-18-1-0206) The Hartwell Foundation NIH/NIDDK (R56DK124853)

Regulation of peripheral expression of glucagon-like peptide 1 receptors in a rat streptozotocin-model of sporadic Alzheimer's disease.

Our previous research indicated incretin dysregulation in a rat model of sporadic Alzheimer's disease (sAD) induced by intracerebroventricular streptozotocin (STZ-icv) and improvement of cognitive decline following oral galactose-induced potentiation of endogenous glucagon-like peptide 1 (GLP-1). This study explored peripheral GLP-1 receptors (GLP-1R) in STZ-icv rats following the acute inhibition of cerebral GLP-1 signaling and additional acute oral galactose administration. 1 month following STZ-icv treatment, male Wistar rats were acutely icv-treated with GLP-1R antagonist Exendin9-39 (85ug/kg; /EXE-icv/) (Experiment I), and 1 hour after EXE-icv additionally with D-galactose (200mg/kg, single oral dose) (Experiment II). Total/active GLP-1 levels were analyzed in plasma and cerebrospinal fluid (CSF) by ELISA. GLP-1R distribution in paraffin embedded duodenal/mesenteric adipose tissue was examined using catalyzed deposition of fluorescent reporters, and analyzed by hierarchical mixed-effect modelling. Baseline plasma level of active GLP-1 was increased in STZ-icv group (vs controls) while EXE-icv treatment decreased it in the STZ-icv and increased in the control group. In CSF, EXE-icv induced a trend of GLP-1 increment both in STZ-icv and control group. Following acute oral galactose treatment, the same trend was observed in plasma of controls, but EXE-icv didn't exhibit a reduction in STZ-icv animals, and CSF level remained unchanged in both. The GLP-1R expression in periduodenal mesenteric adipose tissue of STZ-icv rats was increased following EXE-icv but decreased following additional acute oral galactose treatment. Acute galactose treatment unmasked the effect of EXE-icv on duodenal regulation of GLP-1 as lacteal GLP-1R signal was decreased both in STZ-icv and control group following EXE-icv. Our preliminary results support the existence of dysregulated GLP-1 brain-periphery axis in the STZ-icv rat model of sAD, and additionally indicate that incretin dysregulation is localized both in the brain and the peripheral tissues of STZ-icv rats, and that brain GLP-1 seems to be involved in regulation of the peripheral GLP-1R distribution. Funded by the Croatian Science Foundation (IP-2018-01-8938). Co-financed by the Scientific Centre of Excellence for Basic, Clinical and Translational Neuroscience (project "Experimental and clinical research of hypoxic-ischemic damage in perinatal and adult brain"; GA KK01.1.1.01.0007 funded by the European Union through the European Regional Development Fund).

The Effect of Standard Versus Longer Intestinal Bypass on GLP-1 Regulation and Glucose Metabolism in Patients With Type 2 Diabetes Undergoing Roux-en-Y Gastric Bypass: The Long-Limb Study.

OBJECTIVERoux-en-Y gastric bypass (RYGB) characteristically enhances postprandial levels of glucagon-like peptide 1 (GLP-1), a mechanism that contributes to its profound glucose-lowering effects. This enhancement is thought to be triggered by bypass of food to the distal small intestine with higher densities of neuroendocrine L-cells. We hypothesized that if this is the predominant mechanism behind the enhanced secretion of GLP-1, a longer intestinal bypass would potentiate the postprandial peak in GLP-1, translating into higher insulin secretion and, thus, additional improvements in glucose tolerance. To investigate this, we conducted a mechanistic study comparing two variants of RYGB that differ in the length of intestinal bypass.RESEARCH DESIGN AND METHODSA total of 53 patients with type 2 diabetes (T2D) and obesity were randomized to either standard limb RYGB (50-cm biliopancreatic limb) or long limb RYGB (150-cm biliopancreatic limb). They underwent measurements of GLP-1 and insulin secretion following a mixed meal and insulin sensitivity using euglycemic hyperinsulinemic clamps at baseline and 2 weeks and at 20% weight loss after surgery.RESULTSBoth groups exhibited enhancement in postprandial GLP-1 secretion and improvements in glycemia compared with baseline. There were no significant differences in postprandial peak concentrations of GLP-1, time to peak, insulin secretion, and insulin sensitivity.CONCLUSIONSThe findings of this study demonstrate that lengthening of the intestinal bypass in RYGB does not affect GLP-1 secretion. Thus, the characteristic enhancement of GLP-1 response after RYGB might not depend on delivery of nutrients to more distal intestinal segments.

(-)-Epicatechin and Anthocyanins Modulate GLP-1 Metabolism: Evidence from C57BL/6JMice and GLUTag Cells.

Generated in intestinal L cells through cleavage of proglucagon (Gcg), glucagon-like peptide 1 (GLP-1) is secreted and rapidly inactivated by dipeptidyl peptidase IV (DPP-IV). GLP-1 regulates insulin secretion and overall glucose homeostasis. The capacity of dietary bioactives to increase GLP-1 circulating levels, and therefore increase insulin secretion and glucose metabolism, has gained significant interest of late. We evaluated the effects of (-)-epicatechin (EC) and different anthocyanins (ACs) and AC metabolites on GLP-1 metabolism in mice and on GLUTag cells. We fed 6-week-old C57BL/6Jmale mice a control diet or a control diet supplemented with either 40mg AC or 20mg EC/kg body weight for 14 weeks (AC) or 15 weeks (EC). Intestinal mRNA levels of Gcg and Dpp-iv were measured. In vitro, GLUTag cells were incubated in the presence or absence of different ACs, the AC metabolite protocatechuic acid (PCA), and EC. GLP-1 secretion and the main pathways involved in its release were assessed. Long-term supplementation with EC or AC increased mouse GLP-1 plasma concentrations (55% and 98%, respectively; P<0.05). In mice, 1) EC and AC increased Gcg mRNA levels in the ileum (91%) and colon (41%), respectively (P<0.05); and 2) AC lowered ileum Dpp-iv mRNA levels (35%), while EC decreased plasma DPP-IV activity (15%; P<0.05). In GLUTag cells, 1) cyanidin, delphinidin, PCA, and EC increased GLP-1 secretion (53%, 33%, 53%, and 68%, respectively; P<0.05); and 2) cyanidin, delphinidin, EC, and PCA increased cyclin adenosine monophosphate levels (25-50%; P<0.05) and activated protein kinase A (PKA; 100%, 50%, 80%, and 86%, respectively; P<0.05). In mice, EC and ACs regulated different steps in GLP-1 regulation, leading to increased plasma GLP-1. Cyanidin, delphinidin, PCA, and EC promoted GLP-1 secretion from GLUTag cells by activating the PKA-dependent pathway. These findings support the beneficial actions of these flavonoids in sustaining intestinal and glucose homeostasis through the modulation of the GLP-1 metabolism.

Glucagon-like peptide-1 regulation by food proteins and protein hydrolysates.

Glucagon-like peptide-1 (GLP-1) is an enterohormone with a key role in several processes controlling body homeostasis, including glucose homeostasis and food intake regulation. It is secreted by the intestinal cells in response to nutrients, such as glucose, fat and amino acids. In the present review, we analyse the effect of protein on GLP-1 secretion and clearance. We review the literature on the GLP-1 secretory effects of protein and protein hydrolysates, and the mechanisms through which they exert these effects. We also review the studies on protein from different sources that has inhibitory effects on dipeptidyl peptidase-4 (DPP4), the enzyme responsible for GLP-1 inactivation, with particular emphasis on specific sources and treatments, and the gaps there still are in knowledge. There is evidence that the protein source and the hydrolytic processing applied to them can influence the effects on GLP-1 signalling. The gastrointestinal digestion of proteins, for example, significantly changes their effectiveness at modulating this enterohormone secretion in both in vivo and in vitro studies. Nevertheless, little information is available regarding human studies and more research is required to understand their potential as regulators of glucose homeostasis.

Updating the Role of α-Cell Preproglucagon Products on GLP-1 Receptor-Mediated Insulin Secretion.

While the field of islet biology has historically focused its attention on understanding β-cell function and the mechanisms by which these cells become dysfunctional with diabetes, there has been a scientific shift toward greater understanding of other endocrine cells of the islet and their paracrine role in regulating the β-cell. In recent years, many questions and new data have come forward regarding the paracrine role of the α-cell and specifically preproglucagon peptides in regulating insulin secretion. The role of intestinally secreted glucagon-like peptide 1 (GLP-1) in regulation of insulin secretion has been questioned, and a physiological role of pancreatic GLP-1 in regulation of insulin secretion has been proposed. In addition, in the last 2 years, a series of studies demonstrated a physiological role for glucagon, acting via the GLP-1 receptor, in paracrine regulation of insulin secretion. Altogether, this work challenges the textbook physiology of both GLP-1 and glucagon and presents a critical paradigm shift for the field. This article addresses these new findings surrounding α-cell preproglucagon products, with a particular focus on GLP-1, in the context of their roles in insulin secretion and consequently glucose metabolism.

The Role of the Bacterial Muramyl Dipeptide in the Regulation of GLP-1 and Glycemia.

The host’s intestinal microbiota contributes to endocrine and metabolic responses, but a dysbiosis in this environment can lead to obesity and insulin resistance. Recent work has demonstrated a role for microbial metabolites in the regulation of gut hormones, including the metabolic hormone, glucagon-like peptide-1 (GLP-1). Muramyl dipeptide (MDP) is a bacterial cell wall component which has been shown to improve insulin sensitivity and glucose tolerance in diet-induced obese mice by acting through the nucleotide oligomerization domain 2 (NOD2) receptor. The purpose of this study was to understand the effects of MDP on GLP-1 secretion and glucose regulation. We hypothesized that MDP enhances glucose tolerance by inducing intestinal GLP-1 secretion through NOD2 activation. First, we observed a significant increase in GLP-1 secretion when murine and human L-cells were treated with a fatty acid MDP derivative (L18-MDP). Importantly, we demonstrated the expression of the NOD2 receptor in mouse intestine and in L-cells. In mice, two intraperitoneal injections of MDP (5 mg/kg body weight) caused a significant increase in fasting total GLP-1 in chow-fed mice, however this did not lead to an improvement in oral glucose tolerance. When mice were exposed to a high-fat diet, they eventually lost this MDP-induced GLP-1 release. Finally, we demonstrated in L-cells that hyperglycemic conditions reduce the mRNA expression of NOD2 and GLP-1. Together these findings suggest MDP may play a role in enhancing GLP-1 during normal glycemic conditions but loses its ability to do so in hyperglycemia.

MiR-7 Regulates GLP-1-Mediated Insulin Release by Targeting β-Arrestin 1.

Glucagon-like peptide-1 (GLP-1) has been shown to potentiate glucose-stimulated insulin secretion binding GLP-1 receptor on pancreatic β cells. β-arrestin 1 (βARR1) is known to regulate the desensitization of GLP-1 receptor. Mounting evidence indicates that microRNAs (miRNAs, miRs) are fundamental in the regulation of β cell function and insulin release. However, the regulation of GLP-1/βARR1 pathways by miRs has never been explored. Our hypothesis is that specific miRs can modulate the GLP-1/βARR1 axis in β cells. To test this hypothesis, we applied a bioinformatic approach to detect miRs that could target βARR1; we identified hsa-miR-7-5p (miR-7) and we validated the specific interaction of this miR with βARR1. Then, we verified that GLP-1 was indeed able to regulate the transcription of miR-7 and βARR1, and that miR-7 significantly regulated GLP-1-induced insulin release and cyclic AMP (cAMP) production in β cells. Taken together, our findings indicate, for the first time, that miR-7 plays a functional role in the regulation of GLP-1-mediated insulin release by targeting βARR1. These results have a decisive clinical impact given the importance of drugs modulating GLP-1 signaling in the treatment of patients with type 2 diabetes mellitus.

2308-PUB: A Protective Role of H2S from Obesity-Associated Metabolic Stress in GLP-1 Regulation

Background: Obesity is a risk factor in the development of a variety of diseases including cardiovascular disease and type 2 diabetes. Circulating fatty acids (including palmitate) and protein glycation are both increased in obesity and diabetes and are known to cause metabolic stress. This includes the impairment of the glucoregulatory hormone glucagon-like peptide-1 (GLP-1) secreted from intestinal L-cells. Recently, the gastrointestinal microbiome has been implicated in the regulation of GLP-1. We believe that the bacterial metabolite hydrogen sulfide (H2S) can play a protective role in L-cell metabolic stress. Methods: Our study was conducted on both human NCI H716 and mouse GLUTag GLP-1 secreting L-cells. L-cell stress was assessed using the total reactive oxygen species (ROS) dye DCF-DA. ROS levels were examined during incubation with palmitate (PA), glycated albumin (GA), and the bacterial gas donor GYY4137(H2S). Next, GLP-1 secretion was measured after treating cells with PA and GA, along with H2S using a GLP-1 ELISA. Results: We have demonstrated that elements of the obese physiological environment: PA and GA, cause an increase of reactive oxygen species (ROS) in L-cells. Specifically, 500μm PA and 200μg/mL GA caused a 75% and 50% increase in ROS generation, respectively. Furthermore, these treatments led to a 25% reduction of GLP-1 secretion in human L-cells. Finally, the microbial gas H₂S reduced basal and PA-induced ROS by nearly half. Conclusion: The microbial gas H2S reduces metabolic stress in GLP-1 cells. This study will lay the foundation for future work exploring how bacterial products such as prebiotics and probiotics may be used as a treatment for complications associated with obesity and diabetes. Disclosure A. Mezouari: None. J. Gagnon: None. R. Nangia: None. Funding Natural Sciences and Engineering Research Council of Canada (RGPIN-2016-05905)

2301-PUB: The Role of Muramyl Dipeptide in Glucagon-Like Peptide-1 Regulation

The host’s intestinal microbiota contributes to endocrine and metabolic responses, but a dysbiosis in this environment can lead to obesity and insulin resistance. A new area a research is focused on understanding how bacterial metabolites contribute to intestinal glucagon-like peptide-1 (GLP-1) release. Muramyl dipeptide (MDP) is a bacterial cell wall component which has been shown to improve insulin sensitivity and glucose tolerance in diet-induced obese mice. The purpose of this study was to understand MDP’s mechanism of action in glucose regulation. We hypothesized that MDP enhances glucose tolerance by inducing intestinal GLP-1 secretion. We observed a significant increase (P&amp;lt;0.001, n=7) in GLP-1 secretion when mouse L-cells were treated with an MDP derivative at 10ug/ml. Using fluorescent immunohistochemistry and RT-PCR we located MDP’s receptor, nucleotide oligomerizing domain 2 (NOD2), in mouse intestine and mouse L-cells. In mice, two intraperitoneal injections of MDP (5mg/kg body weight) or PBS caused a significant increase (P=0.0009, n=15-19) in fasting total GLP-1. Understanding how bacterial products influence GLP-1 secretion and subsequent insulin release, could be translated into novel treatments options for improving glucose regulation in metabolic disease. Disclosure L. Williams: None. A. Alshehri: None. S. Mustafa: None. J. Gagnon: None. Funding Natural Sciences and Engineering Research Council of Canada (2016-05905)

GLP-1 secretion is regulated by IL-6 signalling: a randomised, placebo-controlled study.

IL-6 is a cytokine with various effects on metabolism. In mice, IL-6 improved beta cell function and glucose homeostasis via upregulation of glucagon-like peptide 1 (GLP-1), and IL-6 release from muscle during exercise potentiated this beneficial increase in GLP-1. This study aimed to identify whether exercise-induced IL-6 has a similar effect in humans. In a multicentre, double-blind clinical trial, we randomly assigned patients with type 2 diabetes or obesity to intravenous tocilizumab (an IL-6 receptor antagonist) 8mg/kg every 4weeks, oral sitagliptin (a dipeptidyl peptidase-4 inhibitor) 100mg daily or double placebos (a placebo saline infusion every 4weeks and a placebo pill once daily) during a 12week training intervention. The primary endpoints were the difference in change of active GLP-1 response to an acute exercise bout and change in the AUC for the concentration-time curve of active GLP-1 during mixed meal tolerance tests at baseline and after the training intervention. Nineteen patients were allocated to tocilizumab, 17 to sitagliptin and 16 to placebos. During the acute exercise bout active GLP-1 levels were 26% lower with tocilizumab (multiplicative effect: 0.74 [95% CI 0.56, 0.98], p = 0.034) and 53% higher with sitagliptin (1.53 [1.15, 2.03], p = 0.004) compared with placebo. After the 12week training intervention, the active GLP-1 AUC with sitagliptin was about twofold that with placebo (2.03 [1.56, 2.62]; p < 0.001), while GLP-1 AUC values showed a small non-significant decrease of 13% at 4weeks after the last tocilizumab infusion (0.87 [0.67, 1.12]; p = 0.261). IL-6 is implicated in the regulation of GLP-1 in humans. IL-6 receptor blockade lowered active GLP-1 levels in response to a meal and an acute exercise bout in a reversible manner, without lasting effects beyond IL-6 receptor blockade. Clinicaltrials.gov NCT01073826. Danish National Research Foundation. Danish Council for Independent Research. Novo Nordisk Foundation. Danish Centre for Strategic Research in Type 2 Diabetes. European Foundation for the Study of Diabetes. Swiss National Research Foundation.

Qing-Hua Granule induces GLP-1 secretion via bitter taste receptor in db/db mice.

Qing-Hua Granule (QHG), the modified formulation of a classical Chinese prescription named Gegen Qinlian Decoction, was clinically employed to treat type 2 diabetes mellitus (T2DM) through regulation of glucagon-like peptide-1 (GLP-1). However, the potential mechanism is unknown. We investigate whether QHG induces GLP-1 secretion via activation of bitter taste receptor (TAS2R) pathway in the gastrointestinal tract of db/db mice. The db/db mice were intragastrically (i.g.) administered QHG (low/medium/high dose) once daily for 8 weeks. GLP-1 secretion was evaluated. The bitter receptor signaling pathway, which regulates GLP-1 secretion, including TAS2R5 (a subtype of TAS2R), α-gustducin (Gαgust), 1-phosphatidylinositol-4, 5-bisphosphate phosphodiesterase beta-2 (PLCβ2), transient receptor potential cation channel subfamily M member 5 (TRPM5), was assessed by quantitative real-time polymerase chain reaction (qRT-PCR), Western blot and immunohistochemistry (IHC). The biochemical observations of ileum and pancreas tissue were detected histopathologically. Acquity Ultra Performance LCTM - Micromass ZQ 2000 (UPLC-MS) was used for the phytochemical analysis. QHG exhibited significant and dose-dependent effect on GLP-1 secretion in db/db mice, along with significant up-regulation of TAS2R5 mRNA level and activation of TAS2R pathway (p<0.05). In addition, QHG improved the histopathological structure of ileum and pancreatic tissue. Seventeen compounds were identified in QHG. In conclusion, QHG induces GLP-1 secretion in db/db mice, most likely through the bitter taste receptor pathway.