The incretin hormone GLP-1 and mechanisms underlying its secretion

Vitamin A influences the incretin hormone profiles by activating the retinoic acid receptor β

BACKGROUND

This study aimed to investigate the impact of Vitamin A (VA) on intestinal glucose metabolic phenotypes.

METHODS

Male C57BL/6 mice were randomized assigned to a VA-normal diet (VAN) or a VA-deficient diet (VAD) for 12 weeks. After12 weeks, the VAD mice were given 30 IU/g/d retinol for 10 days and VAN diet (VADN) for 10 weeks. By using glucose tolerance tests, immunofluorescence staining, quantitative polymerase chain reaction, siRNA transduction, and enzyme-linked immunosorbent assay, the glucose metabolic phenotypes as well as secretory function and intracellular hormone changes of STC-1 were assessed.

RESULTS

VAD mice showed a decrease of glucose-stimulated insulin secretion and a loss of intestinal glucagon-like peptide-1 (GLP-1) expression. Through reintroducing dietary VA to VAD mice, the intestinal VA levels, GLP-1 expression and normal glucose can be restored. The incubation with retinol increased VA signaling factors expression within STC-1 cells, especially retinoic acid receptor β (RARβ). The activation of RARβ restored intracellular incretin hormone synthesis and secretory function.

CONCLUSIONS

VA deficiency leads to an imbalance of intestinal glucose metabolic phenotypes through a mechanism involving RARβ signaling pathway, suggesting a new method to achieve the treatment for VAD induced glucose metabolism impairment.

Lactobacillus reuteri JCM 1112 ameliorates chronic acrylamide-induced glucose metabolism disorder via the bile acid-TGR5-GLP-1 axis and modulates intestinal oxidative stress in mice

Acrylamide (AA) is a toxic food contaminant that has been reported to cause glucose metabolism disorders (GMD) at high doses. However, it is unclear whether chronic low-dose AA can induce GMD and whether probiotics can alleviate AA-induced GMD. Here, C57BL/6N mice were orally administered with 5 mg per kg bw AA for 10 weeks, followed by another 3 weeks of glucagon-like peptide-1 (GLP-1) analogue (dulaglutide) treatment. Chronic low-dose AA exposure increased the blood glucose level and decreased serum insulin and GLP-1 levels, whereas dulaglutide treatment decreased the blood glucose level and increased the serum insulin level in AA-exposed mice. Then, mice were administered with AA or AA + INT-777 (Takeda G-protein-coupled receptor 5 (TGR5) agonist) for 10 weeks. INT-777 treatment reversed AA-induced downregulation of ileal TGR5 and proglucagon (PG) gene expression and decreased the serum GLP-1 level. These findings indicated that chronic low-dose AA induced GMD via inhibiting the TGR5-GLP-1 axis. Finally, mice were administered with AA for 10 weeks, followed by another 3 weeks of Lactobacillus reuteri JCM 1112 supplementation. L. reuteri supplementation significantly increased serum glucose, insulin and GLP-1 levels, upregulated ileal TGR5 and PG gene expression, and effectively restored the imbalance of bile acid (BA) metabolism in AA-exposed mice, demonstrating that L. reuteri ameliorates chronic AA-induced GMD via the BA-TGR5-GLP-1 axis. In addition, L. reuteri significantly enhanced ileal superoxide dismutase and catalase activities and total antioxidant capacity, thereby preventing chronic AA-induced oxidative stress. Our research provides new insights into the GMD toxicity of chronic low-dose AA and confirms the role of probiotics in alleviating AA-induced GMD.

Metformin Therapy Changes Gut Microbiota Alpha-Diversity in COVID-19 Patients with Type 2 Diabetes: The Role of SARS-CoV-2 Variants and Antibiotic Treatment

The gut microbiota play a crucial role in maintaining host health and have a significant impact on human health and disease. In this study, we investigated the alpha diversity of gut microbiota in COVID-19 patients and analyzed the impact of COVID-19 variants, antibiotic treatment, type 2 diabetes (T2D), and metformin therapy on gut microbiota composition and diversity. We used a culture-based method to analyze the gut microbiota and calculated alpha-diversity using the Shannon H' and Simpson 1/D indices. We collected clinical data, such as the length of hospital stay (LoS), C-reactive protein (CRP) levels, and neutrophil-to-lymphocyte ratio. We found that patients with T2D had significantly lower alpha-diversity than those without T2D. Antibiotic use was associated with a reduction in alpha-diversity, while metformin therapy was associated with an increase. We did not find significant differences in alpha-diversity between the Delta and Omicron groups. The length of hospital stay, CRP levels, and NLR showed weak to moderate correlations with alpha diversity. Our findings suggest that maintaining a diverse gut microbiota may benefit COVID-19 patients with T2D. Interventions to preserve or restore gut microbiota diversity, such as avoiding unnecessary antibiotic use, promoting metformin therapy, and incorporating probiotics, may improve patient outcomes.

Structural characterization of pectic polysaccharides from Amaranth caudatus leaves and the promotion effect on hippocampal glucagon-like peptide-1 level

In this study, decolorized pectic polysaccharides (D-ACLP) with molecular weight (Mw) distribution of 3483- 2,023,656 Da were prepared from Amaranth caudatus leaves. Purified polysaccharides (P-ACLP) with the Mw of 152,955 Da were further isolated from D-ACLP through gel filtration. The structure of P-ACLP was analyzed by 1D and 2D NMR spectra. P-ACLP were identified as rhamnogalacturonan-I (RG-I) containing dimeric arabinose side chains. The main chain of P-ACLP was composed of →4)-α-GalpA-(1→, →2)-β-Rhap-(1→, →3)-β-Galp-(1 → and →6)-β-Galp-(1→. There was a branched chain of α-Araf-(1 → 2)-α-Araf-(1 → connected to the O-6 position of →3)-β-Galp-(1→. The GalpA residues were partially methyl esterified at O-6 and acetylated at O-3. The 28-day consecutive gavage of D-ALCP (400 mg/kg) significantly elevated the hippocampal glucagon-like peptide-1 (GLP-1) levels in rats. The concentrations of butyric acid and total short chain fatty acids in the cecum contents also increased significantly. Moreover, D-ACLP could significantly increase the gut microbiota diversity and dramatically up-regulated the abundance of Actinobacteriota (phylum) and unclassified Oscillospiraceae (genus) in intestinal bacteria. Taking together, D-ACLP might promote the hippocampal GLP-1 level through the beneficial regulation of butyric acid-producing bacteria in gut microbiota. This study contributed to making full use of Amaranth caudatus leaves for cognitive dysfunction intervention in food industry.

Resveratrol intervention attenuates chylomicron secretion via repressing intestinal FXR-induced expression of scavenger receptor SR-B1

Two common features of dietary polyphenols have hampered our mechanistic understanding of their beneficial effects for decades: targeting multiple organs and extremely low bioavailability. We show here that resveratrol intervention (REV-I) in high-fat diet (HFD)-challenged male mice inhibits chylomicron secretion, associated with reduced expression of jejunal but not hepatic scavenger receptor class B type 1 (SR-B1). Intestinal mucosa-specific SR-B1-/- mice on HFD-challenge exhibit improved lipid homeostasis but show virtually no further response to REV-I. SR-B1 expression in Caco-2 cells cannot be repressed by pure resveratrol compound while fecal-microbiota transplantation from mice on REV-I suppresses jejunal SR-B1 in recipient mice. REV-I reduces fecal levels of bile acids and activity of fecal bile-salt hydrolase. In Caco-2 cells, chenodeoxycholic acid treatment stimulates both FXR and SR-B1. We conclude that gut microbiome is the primary target of REV-I, and REV-I improves lipid homeostasis at least partially via attenuating FXR-stimulated gut SR-B1 elevation.

The Oral Delivery System of Modified GLP-1 by Probiotics for T2DM

The glucagon-like peptide-1 (GLP-1) is a peptide with incretin activity and plays an important role in glycemic control as well as the improvement of insulin resistance in type 2 diabetes mellitus (T2DM). However, the short half-life of the native GLP-1 in circulation poses difficulties for clinical practice. To improve the proteolytic stability and delivery properties of GLP-1, a protease-resistant modified GLP-1 (mGLP-1) was constructed with added arginine to ensure the structural integrity of the released mGLP-1 in vivo. The model probiotic Lactobacillus plantarum WCFS1 was chosen as the oral delivery vehicle with controllable endogenous genetic tools driven for mGLP-1 secretory constitutive expression. The feasibility of our design was explored in db/db mice which showed an improvement in diabetic symptoms related to decreased pancreatic glucagon, elevated pancreatic β-cell proportion, and increased insulin sensitivity. In conclusion, this study provides a novel strategy for the oral delivery of mGLP-1 and further probiotic transformation.

Glucagon-like peptide 1 receptor agonists and the potential risk of pancreatic carcinoma: a pharmacovigilance study using the FDA Adverse Event Reporting System and literature visualization analysis

BACKGROUND

There are increasing data on the potential risk of pancreatic carcinoma associated with glucagon-like peptide 1 receptor agonists (GLP-1RAs).

AIM

The study aimed to determine whether GLP-1RAs are associated with increased detection of pancreatic carcinoma based on the FDA Adverse Events Reporting System and clarify its potential mechanisms through keyword co-occurrence analysis from literature database.

METHOD

Disproportionality and Bayesian analyses were used for signal detection using reporting odds ratio (ROR), proportional reporting ratio (PRR), information component (IC), and empirical Bayesian geometric mean (EBGM). Mortality, life-threatening events, and hospitalizations were also investigated. VOSviewer was adopted to generate visual analysis of keyword hotspots.

RESULTS

A total of 3073 pancreatic carcinoma cases were related to GLP-1RAs. Five GLP-1RAs were detected with signals for pancreatic carcinoma. Liraglutide had the strongest signal detection (ROR 54.45, 95% CI 51.21-57.90; PRR 52.52, 95% CI 49.49-55.73; IC 5.59; EBGM 48.30). The signals of exenatide (ROR 37.32, 95% CI 35.47-39.28; PRR 36.45, 95% CI 34.67-38.32; IC 5.00; EBGM 32.10) and lixisenatide (ROR 37.07, 95% CI 9.09-151.09; PRR 36.09; 95% CI 9.20-141.64; IC 5.17, EBGM 36.09) were stronger than those of semaglutide (ROR 7.43, 95% CI 5.22-10.57; PRR 7.39; 95% CI 5.20-10.50; IC 2.88, EBGM 7.38) and dulaglutide (ROR 6.47, 95% CI 5.56-7.54; PRR 6.45; 95% CI 5.54-7.51; IC 2.67, EBGM 6.38). The highest mortality rate occurred in exenatide (63.6%). Based on the bibliometric investigation, cAMP/protein-kinase, Ca²⁺ channel, endoplasmic-reticulum stress, and oxidative stress are potential pathogenesis of pancreatic carcinoma resulting from GLP-1RAs.

CONCLUSION

Based on this pharmacovigilance study, GLP-1RAs, except albiglutide, are associated with pancreatic carcinoma.

Short-term semaglutide treatment improves FGF21 responsiveness in primary hepatocytes isolated from high fat diet challenged mice

Metabolic functions of GLP-1 and its analogues have been extensively investigated. In addition to acting as an incretin and reducing body weight, we and others have suggested the existence of GLP-1/fibroblast growth factor 21 (FGF21) axis in which liver mediates certain functions of GLP-1 receptor agonists. In a more recent study, we found with surprise that four-week treatment with liraglutide but not semaglutide stimulated hepatic FGF21 expression in HFD-challenged mice. We wondered whether semaglutide can also improve FGF21 sensitivity or responsiveness and hence triggers the feedback loop in attenuating its stimulation on hepatic FGF21 expression after a long-term treatment. Here, we assessed effect of daily semaglutide treatment in HFD-fed mice for 7 days. HFD challenge attenuated effect of FGF21 treatment on its downstream events in mouse primary hepatocytes, which can be restored by 7-day semaglutide treatment. In mouse liver, 7-day semaglutide treatment stimulated FGF21 as well as genes that encode its receptor (FGFR1) and the obligatory co-receptor (KLB), and a battery of genes that are involved in lipid homeostasis. In epididymal fat tissue, expressions of a battery genes including Klb affected by HFD challenge were reversed by 7-day semaglutide treatment. We suggest that semaglutide treatment improves FGF21 sensitivity which is attenuated by HFD challenge.

Fibroblast growth factor 21 and dietary interventions: what we know and what we need to know next

Dietary interventions include the change of dietary styles, such as fasting and dietary or nutrient restrictions; or the addition of plant-derived compounds (such as polyphenols known as curcumin, resveratrol, or anthocyanin, or other nutraceuticals) into the diet. During the past a few decades, large number of studies have demonstrated therapeutic activities of these dietary interventions on metabolic and other diseases in human subjects or various animal models. Mechanisms underlying those versatile therapeutic activities, however, remain largely unclear. Interestingly, recent studies have shown that fibroblast growth factor 21 (FGF21), a liver-derived hormone or hepatokine, mediates metabolic beneficial effects of certain dietary polyphenols as well as protein restriction. Here I have briefly summarized functions of FGF21, highlighted related dietary interventions, and presented literature discussions on role of FGF21 in mediating function of dietary polyphenol intervention and protein restriction. This is followed by presenting my perspective view, with the involvement of gut microbiota. It is anticipated that further breakthroughs in this field in the near future will facilitate conceptual merge of classical medicine and modern medicine.

Modulatory role of gut microbiota in cholesterol and glucose metabolism: Potential implications for atherosclerotic cardiovascular disease Atherosclerosis

Accumulating evidence suggests an important role of gut microbiota in physiological processes of host metabolism as well as cardiometabolic disease. Recent advances in metagenomic and metabolomic research have led to discoveries of novel pathways in which intestinal microbial metabolism of dietary nutrients is linked to metabolic profiles and cardiovascular disease risk. A number of metaorganismal circuits have been identified by microbiota transplantation studies and experimental models using germ-free rodents. Many of these pathways involve gut microbiota-related bioactive metabolites that impact host metabolism, in particular lipid and glucose homeostasis, partly via specific host receptors. In this review, we summarize the current knowledge of how the gut microbiome can impact cardiometabolic phenotypes and provide an overview of recent advances of gut microbiome research. Finally, the potential of modulating intestinal microbiota composition and/or targeting microbiota-related pathways for novel preventive and therapeutic strategies in cardiometabolic and cardiovascular diseases will be discussed.

Beneficial Influence of Exendin-4 on Specific Organs and Mechanisms Favourable for the Elderly with Concomitant Obstructive Lung Diseases

Exendin-4 (Ex-4), better known in its synthetic form and used clinically as exenatide, currently applied in the treatment of diabetes, induces a beneficial impact on nerve cells, and shows promising effects in obstructive lung diseases. At an advanced age, the development of the neurodegenerative process of brain tissue is masked by numerous concomitant diseases. The initial latent phase of neurodegenerative disease results in occurrence of manifestations at an advanced stage. To protect the brain and to simultaneously ensure proper treatment of common coexisting conditions in late life, such as diabetes, chronic obstructive pulmonary disease, or asthma, a pleiotropic medication should be chosen. Molecular mechanisms of Ex-4 exert neuroprotective effects or lead to secondary neurogenesis. Additionally, Ex-4 plays an important role in anti-inflammatory actions which are necessary both in the case of asthma and Parkinson’s disease. Specific receptors in the lungs also reduce the secretion of surfactants, which decreases the risk of exacerbation in chronic obstructive lung disease. In a great number of patients suffering from diabetes, asthma, or chronic lung disease, there is a great potential for both treatment of the main condition and protection against brain neurodegeneration.

A novel therapeutic combination of sitagliptin and melatonin regenerates pancreatic β-cells in mouse and human islets

Autoimmune-led challenge resulting in β-cell loss is responsible for the development of type 1 diabetes (T1D). Melatonin, a pineal hormone or sitagliptin, a dipeptidyl peptidase IV (DPP-IV) inhibitor, has increased β-cell mass in various diabetic models and has immunoregulatory property. Both β-cell regenerative capacity and melatonin secretion decrease with ageing. Thus, we aimed to investigate the therapeutic potential of melatonin combined with sitagliptin on β-cell regeneration under glucotoxic stress, in the streptozotocin-induced young and old diabetic mouse models, and euglycemic humanized islet transplant mouse model. Our results suggest that combination therapy of sitagliptin and melatonin show an additive effect in inducing mouse β-cell regeneration under glucotoxic stress, and in the human islet transplant mouse model. Further, in the young diabetic mouse model, the monotherapies induce β-cell transdifferentiation and reduce β-cell apoptosis whereas, in the old diabetic mouse model, melatonin and sitagliptin induce β-cell proliferation and β-cell transdifferentiation, and it also reduces β-cell apoptosis. Further, in both the models, combination therapy reduces fasting blood glucose levels, increases plasma insulin levels and glucose tolerance and promotes β-cell proliferation, β-cell transdifferentiation, and reduces β-cell apoptosis. It can be concluded that combination therapy is superior to monotherapies in ameliorating diabetic manifestations, and it can be used as a future therapy for β-cell regeneration in diabetes patients.

Identification of the DPP-IV Inhibitory Peptides from Donkey Blood and Regulatory Effect on the Gut Microbiota of Type 2 Diabetic Mice

After being treated with protease K, peptides extracted from donkey blood were separated, identified, and characterized. The results showed that Sephadex G-25 medium purified with MW < 3 kDa had the highest dipeptidyl peptidase IV (DPP-IV) inhibition capacity. Three-hundred-and-thirty-four peptides were identified with UPLC−MS/MS. Peptide Ranker and molecular docking analysis were used to screen active peptides, and 16 peptides were finalized out of the 334. The results showed that the lowest binding energy between P7(YPWTQ) and DPP-IV was −9.1, and the second-lowest binding energy between P1(VDPENFRLL) and DPP-IV was −8.7. The active peptides(MW < 3 kDa) could cause a reduction in the fasting blood glucose levels of type 2 diabetic mice, improve glucose tolerance, and facilitate healing of the damaged structure of diabetic murine liver and pancreas. Meanwhile, the peptides were found to ameliorate the diabetic murine intestinal micro-ecological environment to a certain extent.

Dietary Gamma-Aminobutyric Acid (GABA) Induces Satiation by Enhancing the Postprandial Activation of Vagal Afferent Nerves

Gamma-aminobutyric acid (GABA) is present in the mammalian brain as the main inhibitory neurotransmitter and in foods. It is widely used as a supplement that regulates brain function through stress-reducing and sleep-enhancing effects. However, its underlying mechanisms remain poorly understood, as it is reportedly unable to cross the blood–brain barrier. Here, we explored whether a single peroral administration of GABA affects feeding behavior as an evaluation of brain function and the involvement of vagal afferent nerves. Peroral GABA at 20 and 200 mg/kg immediately before refeeding suppressed short-term food intake without aversive behaviors in mice. However, GABA administration 30 min before refeeding demonstrated no effects. A rise in circulating GABA concentrations by the peroral administration of 200 mg/kg GABA was similar to that by the intraperitoneal injection of 20 mg/kg GABA, which did not alter feeding. The feeding suppression by peroral GABA was blunted by the denervation of vagal afferents. Unexpectedly, peroral GABA alone did not alter vagal afferent activities histologically. The coadministration of a liquid diet and GABA potentiated the postprandial activation of vagal afferents, thereby enhancing postprandial satiation. In conclusion, dietary GABA activates vagal afferents in collaboration with meals or meal-evoked factors and regulates brain function including feeding behavior.

The anti-inflammatory feature of glucagon-like peptide-1 and its based diabetes drugs—Therapeutic potential exploration in lung injury

Since 2005, GLP-1 receptor (GLP-1R) agonists (GLP-1RAs) have been developed as therapeutic agents for type 2 diabetes (T2D). GLP-1R is not only expressed in pancreatic islets but also other organs, especially the lung. However, controversy on extra-pancreatic GLP-1R expression still needs to be further resolved, utilizing different tools including the use of more reliable GLP-1R antibodies in immune-staining and co-immune-staining. Extra-pancreatic expression of GLP-1R has triggered extensive investigations on extra-pancreatic functions of GLP-1RAs, aiming to repurpose them into therapeutic agents for other disorders. Extensive studies have demonstrated promising anti-inflammatory features of GLP-1RAs. Whether those features are directly mediated by GLP-1R expressed in immune cells also remains controversial. Following a brief review on GLP-1 as an incretin hormone and the development of GLP-1RAs as therapeutic agents for T2D, we have summarized our current understanding of the anti-inflammatory features of GLP-1RAs and commented on the controversy on extra-pancreatic GLP-1R expression. The main part of this review is a literature discussion on GLP-1RA utilization in animal models with chronic airway diseases and acute lung injuries, including studies on the combined use of mesenchymal stem cell (MSC) based therapy. This is followed by a brief summary.

Cardiovascular effects of GLP-1 receptor agonism

Glucagon-like peptide-1 (GLP-1) receptor agonists are extensively used in type 2 diabetic patients for the effective control of hyperglycemia. It is now clear from outcomes trials that this class of drugs offers important additional benefits to these patients due to reducing the risk of developing major adverse cardiac events (MACE). This risk reduction is, in part, due to effective glycemic control in patients; however, the various outcomes trials, further validated by subsequent meta-analysis of the outcomes trials, suggest that the risk reduction in MACE is also dependent on glycemic-independent mechanisms operant in cardiovascular tissues. These glycemic-independent mechanisms are likely mediated by GLP-1 receptors found throughout the cardiovascular system and by the complex signaling cascades triggered by the binding of agonists to the G-protein coupled receptors. This heterogeneity of signaling pathways underlying different downstream effects of GLP-1 agonists, and the discovery of biased agonists favoring specific signaling pathways, may have import in the future treatment of MACE in these patients. We review the evidence supporting the glycemic-independent evidence for risk reduction of MACE by the GLP-1 receptor agonists and highlight the putative mechanisms underlying these benefits. We also comment on the different signaling pathways which appear important for mediating these effects.

Protective Effect of MFG-E8 on Necroptosis-Induced Intestinal Inflammation and Enteroendocrine Cell Function in Diabetes

Low-grade inflammation is one of the characteristics of metabolic disorders induced by diabetes mellitus. The present study explores the underlying mechanism of milk fat globule epidermal growth factor 8 (MFG-E8) on necroptosis-induced intestinal inflammation and intestinal epithelial endocrine cell dysfunction in diabetes. Compared with the normal control group, pathological changes such as blunt and shortened villus and denuded villus tips were observed in ileum tissue of streptozotocin (STZ) induced senescence-resistant 1 (SAMR1) and senescence-accelerated prone 8 (SAMP8) diabetic mice under light microscope. Western blotting and immunohistochemistry (IHC) displayed significantly decreased protein expression of MFG-E8 in SAMR1 and SAMP8 diabetic mice, accompanied by an increased expression of phosphorylated mixed lineage kinase domain-like (p-MLKL) and HMGB1. In addition, advanced glycation end products (AGEs) significantly increased the pro-inflammatory mediators (TNF-α, IL-1β, IL-6) and HMGB1 by activating the receptor-interacting protein kinase 3 (RIPK3)/MLKL signaling pathway in enteroendocrine STC-1 cells. D-pinitol pretreatment markedly attenuated the release of pro-inflammatory mediators and increased the expression of MFG-E8. MFG-E8 small interfering RNA (siRNA) promoted, while MFG-E8 overexpression inhibited, the activation of receptor-interacting proteins (RIPs) pathway and pro-inflammatory factors. Our study demonstrated that downregulation of MFG-E8 is an important phenomenon in the pathogenesis of diabetes-related intestinal inflammatory damage. MFG-E8 overexpression and D-pinitol intervention could protect against necroptosis-induced intestinal inflammation and maintain the function of enteroendocrine STC-1 cells in diabetes.

Potential roles of the gut microbiota in the manifestations of drug use disorders

Drug use disorders (DUDs) not only cause serious harm to users but also cause huge economic, security, and public health burdens to families and society. Recently, several studies have shown that gut microbiota (GM) can affect the central nervous system and brain functions. In this review, we focus on the potential role of the GM in the different stages of DUDs. First, the GM may induce individuals to seek novel substances. Second, the gut microbiota is involved in the decomposition and absorption of drugs. Symptoms of individuals who suffer from DUDs are also related to intestinal microorganisms. Third, the effects of the GM and its metabolites on drug relapse are mainly reflected in the reward effect and drug memory. In conclusion, recent studies have preliminarily explored the relationship between GM and DUDs. This review deepens our understanding of the mechanisms of DUDs and provides important information for the future development of clinical treatment for DUDs.

Potential new therapeutic target for Alzheimer's disease: Glucagon-like peptide-1

Increasing evidence shows a close relationship between Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). Recently, glucagon-like peptide-1 (GLP-1), a gut incretin hormone, has become a well-established treatment for T2DM and is likely to be involved in treating cognitive impairment. In this mini review, the similarities between AD and T2DM are summarised with the main focus on GLP-1-based therapeutics in AD.

Hepatic Fibroblast Growth Factor 21 Is Involved in Mediating Functions of Liraglutide in Mice With Dietary Challenge

BACKGROUND AND AIMS

Several studies have shown that expression of hepatic fibroblast growth factor 21 (FGF21) can be stimulated by glucagon-like peptide 1 (GLP-1)-based diabetes drugs. As GLP-1 receptor (GLP-1R) is unlikely to be expressed in hepatocytes, we aimed to compare such stimulation in mice and in mouse hepatocytes, determine the involvement of GLP-1R, and clarify whether FGF21 mediates certain functions of the GLP-1R agonist liraglutide.

APPROACH AND RESULTS

Liver FGF21 expression was assessed in mice receiving a daily liraglutide injection for 3 days or in mouse primary hepatocytes (MPHs) undergoing direct liraglutide treatment. The effects of liraglutide on metabolic improvement and FGF21 expression were then assessed in high-fat diet (HFD)-fed mice and compared with the effects of the dipeptidyl-peptidase 4 inhibitor sitagliptin. Animal studies were also performed in Glp1r^-/- mice and liver-specific FGF21-knockout (lFgf21-KO) mice. In wild-type mouse liver that underwent RNA sequencing and quantitative reverse-transcription PCR, we observed liraglutide-stimulated hepatic Fgf21 expression and a lack of Glp1r expression. In MPHs, liraglutide did not stimulate Fgf21. In mice with HFD-induced obesity, liraglutide or sitagliptin treatment reduced plasma triglyceride levels, whereas their effect on reducing body-weight gain was different. Importantly, increased hepatic FGF21 expression was observed in liraglutide-treated mice but was not observed in sitagliptin-treated mice. In HFD-fed Glp1r^-/- mice, liraglutide showed no beneficial effects and could not stimulate Fgf21 expression. In lFgf21-KO mice undergoing dietary challenge, the body-weight-gain attenuation and lipid homeostatic effects of liraglutide were lost or significantly reduced.

CONCLUSIONS

We suggest that liraglutide-stimulated hepatic Fgf21 expression may require GLP-1R to be expressed in extrahepatic organs. Importantly, we revealed that hepatic FGF21 is required for liraglutide to lower body weight and improve hepatic lipid homeostasis. These observations advanced our mechanistic understanding of the function of GLP-1-based drugs in NAFLD.

Emerging Nondopaminergic Medications for Parkinson's Disease: Focusing on A2A Receptor Antagonists and GLP1 Receptor Agonists

Parkinson's disease (PD) is a severe neurodegenerative disease characterized by classic motor features associated with the loss of dopaminergic neurons and appearance of Lewy bodies in the substantia nigra. Due to the complexity of PD, a definitive diagnosis in the early stages and effective management of symptoms in later stages are difficult to achieve in clinical practice. Previous research has shown that colocalization of A2A receptors (A2AR) and dopamine D2 receptors (D2R) may induce an antagonistic interaction between adenosine and dopamine. Clinical trials have found that the A2AR antagonist istradefylline decreases dyskinesia in PD and could be used as an adjuvant to levodopa treatment. Meanwhile, the incretin hormone glucagon-like peptide 1 (GLP1) mainly facilitates glucose homeostasis and insulin signaling. Preclinical experiments and clinical trials of GLP1 receptor (GLP1R) agonists show that they may be effective in alleviating neuroinflammation and sustaining cellular functions in the central nervous system of patients with PD. In this review, we summarize up-to-date findings on the usefulness of A2AR antagonists and GLP1R agonists in PD management. We explain the molecular mechanisms of these medications and their interactions with other neurotransmitter receptors. Furthermore, we discuss the efficacy and limitations of A2AR antagonists and GLP1R agonists in clinical practice.

Oral semaglutide in the management of type 2 DM: Clinical status and comparative analysis

BACKGROUND

In the incretin system, Glucagon-like peptide-1 (GLP-1) is a hormone that inhibits the release of glucagon and regulates glucose-dependent insulin secretion. In type 2 diabetes, correcting the impaired incretin system using GLP-1 agonist is a well-defined therapeutic strategy.

OBJECTIVES

This review article aims to discuss the mechanism of action, key regulatory events, clinical trials for glycaemic control and comparative analysis of semaglutide with the second-line antidiabetic drugs.

DESCRIPTION

Semaglutide is a glucagon-like peptide 1 (GLP 1) receptor agonist with enhanced glycaemic control in diabetes patients. In 2019, USFDA approved the first oral GLP-1 receptor agonist, semaglutide to be administered as a once-daily tablet. Further, recent studies highlight the ability of semaglutide to improve the glycaemic control in obese patients with a reduction in body weight. Still, in clinical practice, in type 2 DM treatment paradigm the impact of oral semaglutide remains unidentified. This review article discusses the mechanism of action, pharmacodynamics, key regulatory events, and clinical trials regarding glycaemic control.

CONCLUSION

The review highlights the comparative analysis of semaglutide with the existing second-line drugs for the management of type 2 diabetes mellitus by stressing on its benefits and adverse events.

Anti-inflammatory effects of GLP-1 in patients with COVID-19

Introduction

Understanding the pathogenesis and risk factors to control the coronavirus disease 2019 (COVID-19) is necessary. Due to the importance of the inflammatory pathways in the pathogenesis of COVID-19 patients, evaluating the effects of anti-inflammatory medications is important. Glucagon-like peptide 1 receptor agonist (GLP-1 RA) is awell-known glucose-lowering agent with anti-inflammatory effects.

Areas covered

Resources were extracted from the PubMed database, using keywords such as glucagon-like peptide-1, GLP-1 RA, SARS-CoV-2, COVID-19, inflammation, in April2021. In this review, the effects of GLP-1RA in reducing inflammation and modifying risk factors of COVID-19 severe complications are discussed. However, GLP-1 is degraded by DPP-4 with aplasma half-life of about 2–5 minutes, which makes it difficult to measure GLP-1 plasma level in clinical settings.

Expert opinion

Since no definitive treatment is available for COVID-19 so far, determining promising targets to design and/or repurpose effective medications is necessary.

The HIF-2α/PPARα pathway is essential for liraglutide-alleviated, lipid-induced hepatic steatosis

Liraglutide has been demonstrated to alleviate hepatic steatosis in clinical practice, but the underlying mechanism remains unclear. Our previous study indicated that the HIF-2α/PPARα pathway was involved in hepatic lipid accumulation induced by hypoxia.We aimed to investigate whether liraglutide could alleviate lipid-induced hepatic steatosis via the HIF-2α/PPARα pathway. Whole-body HIF-2α heterozygous knockout (HIF-2α^+/-) mice and littermate wild-type (WT) mice were successfully established. Male mice challenged with a high-fat diet were treated with liraglutide (0.6 mg/kg/d) or normal saline by intraperitoneal injection for 4 weeks. We observed that, compared with WT mice, many indicators of HIF-2α^+/- mice improved, including GTT, ITT, fasting blood glucose, body weight, liver weight, and lipid profile in serum or liver lipid deposition, and the expression level of PPARα, mitochondrial function genes, and fatty acid oxidation genes were upregulated, while those of HIF-2α and lipogenesis genes were downregulated significantly. After liraglutide treatment in WT mice, we found that significant improvements were observed in the fat mass, GTT, ITT, fasting blood glucose, body weight, liver weight, lipid profile in serum or liver lipid deposition; the β-oxidation genes were upregulated and the lipogenesis genes were downregulated; and the abundance of intestinal Akkermansia muciniphila increased significantly. However, the effects of liraglutide on WT mice were not observed in HIF-2α^+/- mice. In addition, in the HepG2 steatotic hepatocyte model, liraglutide alleviated lipid deposits by repressing lipid synthesis and enhancing fatty acid β-oxidation, which were substantially suppressed by the HIF-2α modulators. Therefore, the HIF-2α/PPARα pathway is essential for liraglutide-alleviated lipid-induced hepatic steatosis.

Ge-Gen-Jiao-Tai-Wan Affects Type 2 Diabetic Rats by Regulating Gut Microbiota and Primary Bile Acids

The Ge-Gen-Jiao-Tai-Wan (GGJTW) formula has been used to treat type 2 diabetes mellitus (T2DM) in China for a long time. Our previous study has proved that GGJTW could alleviate the type 2 diabetic symptoms, but the underlying mechanisms are still unclear. This study aimed to investigate the changes in gut microbiota and primary bile acids (PBAs) to determine the potential mechanisms of GGJTW in treating T2DM.The fecal transplant method and pseudogerm-free rats were used in our study.The16S rRNA gene sequencing method was used to analyze the changes in the intestinal flora, and PBAs in the colon contents were detected. Finally, the expression of farnesoid X receptor (FXR), G protein-coupled membrane receptor 5 (TGR5), and glucagon-like peptide-1 (GLP-1) was assessed. Following GGJTW treatment, we observed a decrease in blood glucose levels and improvements in glucose tolerance and serum lipid levels. Furthermore, we found that GGJTW could regulate the composition of the gut microbiota and upregulate the diabetic beneficial phylum Firmicutes and bile-acid-related genus Lactobacillus. PBAs in the colon contents were increased in the GGJTW-treated group, accompanied by upregulated expression of the bile acid receptors FXR and TGR5 and increased concentrations of GLP-1. These results indicated that GGJTW could alleviate symptoms of type 2 diabetic rats by regulating the gut microbiota, promoting the production of PBAs, and upregulating the PBA-FXR/TGR5-GLP-1 pathway.

Non-Alcoholic Fatty Liver Disease and Cardiovascular Comorbidities: Pathophysiological Links, Diagnosis, and Therapeutic Management

Non-alcoholic fatty liver disease (NAFLD) has a growing prevalence in recent years. Its association with cardiovascular disease has been intensively studied, and certain correlations have been identified. The connection between these two entities has lately aroused interest regarding therapeutic management. In order to find the best therapeutic options, a detailed understanding of the pathophysiology that links (NAFLD) to cardiovascular comorbidities is needed. This review focuses on the pathogenic mechanisms that are behind these two diseases and on the therapeutic management available at this time.

NFAT5 Is Involved in GRP-Enhanced Secretion of GLP-1 by Sodium

Gastrin, secreted by G-cells, and glucagon-like peptide-1 (GLP-1), secreted by L-cells, may participate in the regulation of sodium balance. We studied the effect of sodium in mice in vivo and mouse ileum and human L-cells, on GLP-1 secretion, and the role of NFAT5 and gastrin-releasing peptide receptor (GRPR) in this process. A high-sodium diet increases serum GLP-1 levels in mice. Increasing sodium concentration stimulates GLP-1 secretion from mouse ileum and L-cells. GRP enhances the high sodium-induced increase in GLP-1 secretion. High sodium increases cellular GLP-1 expression, while low and high sodium concentrations increase NFAT5 and GRPR expression. Silencing NFAT5 in L-cells abrogates the stimulatory effect of GRP on the high sodium-induced GLP-1 secretion and protein expression, and the sodium-induced increase in GRPR expression. GLP-1 and gastrin decrease the expression of Na⁺-K⁺/ATPase and increase the phosphorylation of sodium/hydrogen exchanger type 3 (NHE3) in human renal proximal tubule cells (hRPTCs). This study gives a new perspective on the mechanisms of GLP-1 secretion, especially that engendered by ingested sodium, and the ability of GLP-1, with gastrin, to decrease Na⁺-K⁺/ATPase expression and NHE3 function in hRPTCs. These results may contribute to the better utilization of current and future GLP-1-based drugs in the treatment of hypertension.

Friend or foe? ACE2 inhibitors and GLP-1R agonists in COVID-19 treatment

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been a pandemic since WHO made the statement on March 11, 2020. The infection is causing a high mortality in old people, especially those with obesity, type 2 diabetes (T2D) or cardiovascular diseases (CVD). Extra cautions are needed in the treatment of those patients. The CVD drugs ACEIs and ARBs, as well as the T2D drugs GLP-1R agonists, were shown to activate angiotensin-converting enzyme 2 (ACE2) expression in experimental animals. Elevated ACE2 expression may accelerate virus entrance into the host cells during the infection for its replication. However, expression of the soluble ACE2, may neutralize the virus to limit the infection and replication. Given that obese, diabetes and CVD patients often take those medicines in the treatment and prevention of blood pressure and glucose elevation, it remains to be determined whether those medicines represent friend or foe in the treatment of COVID-19. We suggest that retrospective studies should be conducted to determine the exact impact of those medicines in obese, diabetic, or CVD patients who had COVID-19. Results obtained will provide guidance whether those drugs can be utilized in COVID-19 patients with obesity, diabetic, or CVD.

Gastrointestinal Distension by Pectin-Containing Carbonated Solution Suppresses Food Intake and Enhances Glucose Tolerance via GLP-1 Secretion and Vagal Afferent Activation

Diet-induced gastrointestinal distension is known to evoke satiation and suppress postprandial hyperglycemia; however, the underlying mechanisms remain poorly understood. This study explored how gastrointestinal distension regulates energy homeostasis by using inflating stomach formulation (ISF), the carbonated solution containing pectin that forms stable gel bubbles under acidic condition in the stomach. Here we show that, in mice, oral administration of ISF induced distension of stomach and proximal intestine temporarily, stimulated intestinal glucagon-like peptide-1 (GLP-1) secretion, and activated vagal afferents and brainstem. ISF suppressed food intake and improved glucose tolerance via enhancing insulin sensitivity. The anorexigenic effect was partially inhibited, and the beneficial glycemic effect was blunted by pharmacological GLP-1 receptor blockade and chemical denervation of capsaicin-sensitive sensory nerves. In HFD-fed obese mice showing arrhythmic feeding and obesity, subchronic ISF treatment at the light period (LP) onset for 10 days attenuated LP hyperphagia and visceral fat accumulation. These results demonstrate that gastrointestinal distension by ISF stimulates GLP-1 secretion and the vagal afferent signaling to the brain, thereby regulating feeding behavior and glucose tolerance. Furthermore, subchronic ISF treatment ameliorates HFD-induced visceral obesity. We propose the diet that induces gastrointestinal distension as a novel treatment of hyperphagic obesity and diabetes.

Polyethylene Glycol Loxenatide (PEX-168) Reduces Body Weight and Blood Glucose in Simple Obese Mice

BACKGROUND

At present, there is a lack of drug treatment for obese patients, so it is needed to find a drug that is effective and has few side effects to treat obesity. PEX-168 is a novel long-acting glucagon-like peptide-1 receptor agonist for T2DM. It improves blood glucose with fewer side effects. The aim of the present study was to investigate the effect of PEX-168 on blood glucose and body weight of mice with simple obesity.

METHODS

Thirty healthy and 6-week-old C57BL/6 male mice were randomly divided into a normal control group (NC, n = 6) and obesity model group (n = 24). The obesity model mice were randomly divided into a high-fat diet group (HF) and intervention groups with different doses of PEX-168 (0.03 mg/kg, 0.1 mg/kg, and 0.3 mg/kg). Each group includes 6 mice. Body weight, food intake, and fasting blood glucose (FBG) were evaluated after intraperitoneal injection, and the intervention was performed weekly for 12 weeks. Fasting insulin (FINS) levels were measured at the 12^th week.

RESULTS

Compared with HF, the food intake of mice in the intervention groups decreased transiently, but there was no difference between different doses (P > 0.05). The body weight of mice in the middle and high dose of PEX-168 intervention groups decreased significantly, and the differences were statistically significant (P < 0.05). The administration of PEX-168 can effectively improve the blood glucose of obese mice, the difference was statistically significant (P < 0.05), but there was no difference between different doses (P > 0.05). At the 10^th week, the incidence of transient hypoglycemia was 67% and 50% in the middle- and high-dose groups, respectively. The levels of serum FINS in the intervention groups were significantly lower than those in the HF group, and the differences were statistically significant (P < 0.05), but there was no difference between different doses (P > 0.05).

CONCLUSIONS

PEX-168 showed significant improvement in the FBG and FINS levels of simple obese mice. Middle and high doses of PEX-168 could reduce the weight of simple obese mice, but there was a certain risk of hypoglycemia.

Internalization-Dependent Free Fatty Acid Receptor 2 Signaling Is Essential for Propionate-Induced Anorectic Gut Hormone Release

The ability of propionate, a short-chain fatty acid produced from the fermentation of non-digestible carbohydrates in the colon, to stimulate the release of anorectic gut hormones, such as glucagon like peptide-1 (GLP-1), is an attractive approach to enhance appetite regulation, weight management, and glycemic control. Propionate induces GLP-1 release via its G protein-coupled receptor (GPCR), free fatty acid receptor 2 (FFA2), a GPCR that activates Gαi and Gαq/11. However, how pleiotropic GPCR signaling mechanisms in the gut regulates appetite is poorly understood. Here, we identify propionate-mediated G protein signaling is spatially directed within the cell whereby FFA2 is targeted to very early endosomes. Furthermore, propionate activates a Gαi/p38 signaling pathway, which requires receptor internalization and is essential for propionate-induced GLP-1 release in enteroendocrine cells and colonic crypts. Our study reveals that intestinal metabolites engage membrane trafficking pathways and that receptor internalization could orchestrate complex GPCR pathways within the gut.

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) for the management of nonalcoholic fatty liver disease (NAFLD): A systematic review

There are no licensed drugs for nonalcoholic fatty liver disease (NAFLD), and there is a lack of consensus on the best outcome measures for controlled trials. This systematic review aimed to evaluate the efficacy of GLP-1 RAs in the management of NAFLD, the degree of heterogeneity in trial design and the robustness of conclusions drawn from these clinical trials. We searched publication databases and clinical trial registries through 2 November 2019 for clinical trials with NAFLD. We evaluated improvements in histological findings, noninvasive markers of hepatic steatosis, inflammation, and fibrosis, insulin resistance and anthropometric measures. Our final analysis included 24 clinical trials, comprising 6313 participants with a mean duration of 37 weeks. Four clinical trials, including RCT (n = 1), single-arm studies (n = 2) and case series studies (n = 1), used biopsy-confirmed liver histological change as their end-points. The remaining studies (n = 20) used surrogate end-points. GLP-1 RAs were effective for the improvement in hepatic inflammation, hepatic steatosis and fibrosis. More importantly, GLP-1 RAs showed promise in improving the histological features of NASH. In addition, 8 ongoing trials were identified. In this systematic review of published and ongoing clinical trials of the efficacy of GLP-1RAs for NAFLD, we found that GLP-1 RAs are effective for hepatic steatosis and inflammation, with the potential to reverse fibrosis. Further prospective studies of sufficient duration using histological end-points are needed to fully assess the efficacy of GLP-1 RAs in the management of NAFLD.

Recent advances in understanding the role of glucagon-like peptide 1

The discovery that glucagon-like peptide 1 (GLP-1) mediates a significant proportion of the incretin effect during the postprandial period and the subsequent observation that GLP-1 bioactivity is retained in type 2 diabetes (T2D) led to new therapeutic strategies being developed for T2D treatment based on GLP-1 action. Although owing to its short half-life exogenous GLP-1 has no use therapeutically, GLP-1 mimetics, which have a much longer half-life than native GLP-1, have proven to be effective for T2D treatment since they prolong the incretin effect in patients. These GLP-1 mimetics are a desirable therapeutic option for T2D since they do not provoke hypoglycaemia or weight gain and have simple modes of administration and monitoring. Additionally, over more recent years, GLP-1 action has been found to mediate systemic physiological beneficial effects and this has high clinical relevance due to the post-diagnosis complications of T2D. Indeed, recent studies have found that certain GLP-1 analogue therapies improve the cardiovascular outcomes for people with diabetes. Furthermore, GLP-1-based therapies may enable new therapeutic strategies for diseases that can also arise independently of the clinical manifestation of T2D, such as dementia and Parkinson's disease. GLP-1 functions by binding to its receptor (GLP-1R), which expresses mainly in pancreatic islet beta cells. A better understanding of the mechanisms and signalling pathways by which acute and chronic GLP-1R activation alleviates disease phenotypes and induces desirable physiological responses during healthy conditions will likely lead to the development of new therapeutic GLP-1 mimetic-based therapies, which improve prognosis to a greater extent than current therapies for an array of diseases.

Sennoside A Induces GLP-1 Secretion Through Activation of the ERK1/2 Pathway in L-Cells

PURPOSE

Glucagon-like peptide-1 (GLP-1) is secreted from the intestinal L-cells to stimulate insulin secretion in the blood glucose control. Our previous study indicates that Sennoside A (SA) can increase the plasma GLP-1 level in a mouse model of type 2 diabetes. However, the mechanism of SA activity remains largely unknown. This issue was explored in this study.

MATERIALS AND METHODS

C57BL/6 mice were randomly divided into four groups: a control group without drug treatment, and the other groups with different SA dosages, respectively. Blood glucose was assayed by oral glucose tolerance test (OGTT). Plasma GLP-1 and insulin were investigated. Colon tissues were collected for mRNA or Western blot analysis. Immunofluorescence staining assays were performed to evaluate the number of β-cells and L-cells. In NCI-H716 cells, extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitors were employed to investigate the SA-induced GLP-1 secretion mechanism.

RESULTS

In this work, the SA was found to improve OGTT in mice. Plasma GLP-1 and insulin were markedly elevated by SA at the dosage of 45 mg/kg/day. Meanwhile, the increased phosphorylation status of EKR1/2 and prohormone convertase 1/3 (PC1/3) proteins were observed in the colon of SA-treated mice. The number of L-cells exhibited no change in each group. In the NCI-H716 cells, GLP-1 secretion induced by SA was blocked by the ERK1/2 inhibitor.

CONCLUSION

The present study provides a direct evidence for the interaction between SA and L cells for induction of GLP-1 secretion. These data suggest that GLP-1 secretion induced by SA is dependent on the ERK1/2 signaling pathway. Therefore, the SA is a new drug candidate for the type 2 diabetes treatment by induction of GLP-1 secretion.

Black soybean seed coat polyphenols promote nitric oxide production in the aorta through glucagon-like peptide-1 secretion from the intestinal cells

Black soybean seed coat polyphenols were reported to possess various bioregulatory functions. However, the effects of black soybean seed coat polyphenols on vascular functions are unknown. Vascular dysfunction caused by aging and vascular stiffness is associated with a risk of cardiovascular disease (CVD), and a reduction in nitric oxide (NO) levels can trigger the onset of CVD. In the present study, we investigated the effect of polyphenol-rich black soybean seed coat extract (BE) on vascular functions and the underlying mechanisms involved. The oral administration of BE at 50 mg per kg body weight to Wistar rats increased NO levels as determined by eNOS phosphorylation. The administration of BE also increased GLP-1 and cAMP levels. Furthermore, the effects of BE were inhibited in the presence of a GLP-1 receptor antagonist. This suggests that GLP-1 is strongly involved in the underlying mechanism of NO production in vivo. In conclusion, BE contributes to the improvement of vascular functions by promoting NO production. Regarding the putative underlying mechanism, GLP-1 secreted from intestinal cells by the polyphenols in BE activates eNOS in vascular endothelial cells.

An Integrated In Silico and In Vitro Assays of Dipeptidyl Peptidase-4 and α-Glucosidase Inhibition by Stellasterol from Ganoderma australe

Background: Ganoderma fungus is rich in terpenoids. These compounds are known for their anti-hyperglycemic activities. However, the study of terpenoids as the secondary metabolite from Ganoderma as a dipeptidyl peptidase-4 (DPP-4) inhibitor remains unexplored. In addition, we examined the α-glucosidase inhibition activity. Objective: This study aimed to isolate the major terpenoid from non-laccate Ganoderma and examined its inhibitor activity on DPP-4 and α-glucosidase enzymes, and its interaction. Methods: The compound was isolated using column chromatography from Ganoderma australe. The structure of the isolated compound was confirmed by 1H and 13C nuclear magnetic resonance spectroscopy, while the inhibitory activity was evaluated using an enzymatic assay. The interaction of the isolated compound with DPP-4 and α-glucosidase enzymes was investigated using an in silico study. Results: The isolated compound was identified as stellasterol; IC50 values for DPP-4 and α-glucosidase inhibitor were 427.39 µM and 314.54 µM, respectively. This study revealed that the inhibitory effect of stellasterol on DPP-4 enzyme is through hydrophobic interaction, while the α-glucosidase enzyme is due to the interaction with six amino acids of the enzyme. Conclusion: Stellasterol is the major component of the steroid from G. australe. Enzyme inhibitory assay and in silico study suggest that stellasterol may contribute antidiabetic activity with a mechanism closer to acarbose rather than to sitagliptin.

Exosomes and pancreatic diseases: status, challenges, and hopes

Pancreatic disease, including pathologies such as acute pancreatitis (AP), chronic pancreatitis (CP), and pancreatic cancer (PC), is a complicated and dangerous clinical condition involving the disruption of exocrine or endocrine function. PC has one of the highest mortality rates among cancers due to insufficient diagnosis in early stages. Furthermore, efficient treatment options for the disease etiologies of AP and CP are lacking. Thus, the identification of new therapeutic targets and reliable biomarkers is required. As essential couriers in intercellular communication, exosomes have recently been confirmed to play an important role in pancreatic disease, but the specific underlying mechanisms are unknown. Herein, we summarize the current knowledge of exosomes in pancreatic disease with respect to diagnosis, molecular mechanisms, and treatment, proposing new ideas for the study of pancreatic disease.

[Effect of glucagon-like peptide 1 receptor agonists on body fat redistribution and muscle mass in overweight and obese type 2 diabetic patients]

OBJECTIVE

To investigate the effect of glucagon-like peptide 1 receptor agonists (GLP-1RAs) on body fat redistribution and muscle mass in overweight/obese patients with type 2 diabetes (T2DM).

METHODS

We retrospectively analyzed the data of 76 patients with body mass indexes (BMI)≥24 kg/m2, who had an established diagnosis of T2DM in our department between December, 2014 and September, 2015. We divided these patients according to their BMI in overweight group (BMI of 24-27.9 kg/m2, n=14), obese group (BMI of 28-31.9 kg/m2, n=35) and severely obese group (BMI≥32 kg/m2, n=27). All the patients received treatment with GLP-1RAs (Exenatide or Liraglutide) for 3.0 to 29.0 weeks (mean 8.9 weeks), and their blood glucose, HbA1c and serum lipids were analyzed. For each patient, the fat and muscle masses were analyzed using a human body composition analyzer (JAWON-IOI353, Korea) before and after GLP-1RAs treatment.

RESULTS

Treatment with GLP-1RAs significantly decreased BMI and visceral adiposity index (VAI) in all the patients in the 3 groups (P < 0.05). The treatment significantly decreased the body weight in the overweight group and obese group by 2.70 kg (0.60-4.95 kg) and 2.65 kg (1.45-6.40 kg), respectively (P < 0.05), and significantly decreased the waist-to-hip ratio (WHR) in the overweight group (P < 0.05). The obese and severely obese patients showed significantly decreased percentage body fat (including both subcutaneous and visceral fat) and increased muscle mass after the treatment (P < 0.05). Compared with those in the overweight group, the percentage body fat and VAI were significantly decreased in the obese group after the treatment (P < 0.05), and the percentage of subcutaneous fat reduced and the muscle ratio increased more obviously in the obese and severely obese patients (P < 0.05).

CONCLUSIONS

GLP-1RAs treatment can significantly lower BMI and improve body fat distribution in obese patients with T2DM, especially in patients with a greater BMI.

Alteration of GLP-1/GPR43 expression and gastrointestinal motility in dysbiotic mice treated with vancomycin

Gut microbiota plays a pivotal role in various aspects of host physiology, including metabolism, gastrointestinal (GI) motility and hormonal secretion. In the present study, we investigated the effect of antibiotic-associated dysbiosis on metabolism and GI motility in relation to colonic expression of glucagon-like peptide-1 (GLP-1) and G protein coupled receptor (GPR)43. Specific pathogen-free (SPF) mice (ICR, 6 weeks old, female) were orally administered vancomycin (0.2 mg/ml) in drinking water for 7 days. In another experiment, germ-free (GF) mice (ICR, 6 weeks old, female) were subjected to oral fecal transplantation (FT) using a fecal bacterial suspension prepared from SPF mice that had received vancomycin treatment (FT-V) or one from untreated control SPF mice (FT-C). The gastrointestinal transit time (GITT) was measured by administration of carmine red (6% w/v) solution. The expression of GLP-1 and GPR43 was examined by immunohistochemistry and realtime RT-PCR, and the plasma GLP-1 level was measured by ELISA. In vancomycin-treated SPF mice, the diversity of the gut microbiota was significantly reduced and the abundance of Lactobacillus was markedly increased. Significant increases in body weight, cecum weight, plasma GLP-1 level and colonic GLP-1/GPR43 expression were also noted relative to the controls. These alterations were reproducible in GF mice with FT-V. Moreover, FT-V GF mice showed a significantly increased food intake and a significantly prolonged GITT in comparison with FT-C GF mice. Vancomycin-induced dysbiosis promotes body weight gain and prolongs GITT, accompanied by an increase of colonic GLP-1/GPR43 expression.

Effect of the peptides Relaxin, Neuregulin, Ghrelin and Glucagon-like peptide-1, on cardiomyocyte factors involved in the molecular mechanisms leading to diastolic dysfunction and/or heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) represents an important cardiac condition because of its increasing prevalence, resistance to treatment and high associated morbidity and mortality. Two of the major mechanisms responsible for HFpEF are impaired cardiomyocyte sarcoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA2a), which is responsible for calcium reuptake into the SR, and cardiac fibroblasts/myofibroblasts that produce collagen or myocardial fibrosis. Phospholamban (PLB), in the SR and endoplasmic reticulum, is the primary regulator of SERCA2a in the heart and acts as a reversible inhibitor of SERCA2a. Glucagon-like peptide-1, a 30 amino acid peptide, improves diastolic function through increasing SERCA2a expression and activity as well as by decreasing phosphorylation of Ryanodine receptors. It also enhances collagen production through enhanced procollagen IalphaI/IIIalphaI, connective tissue growth factor, fibronectin, TGF-β3 as well as Interleukin -10, -1beta, and -6 gene expression. Relaxin-2, a two chain, 53 amino acid peptide, increases Ser16- and Thr17-phosphorylation levels of PLB, thereby relieving SERCA2a of its inhibition. H3 Relaxin inhibits TGF-β1-stimulated collagen deposition through H3 relaxin-induced increases in pSmad2. Neuregulin-1, an epidermal growth factor, induces nitric oxide and PI-3 kinase activation that enhance SERCA2 activity. Neuregulin-1 was associated with less myocardial macrophage infiltration and cytokine expression reducing collagen deposition. Ghrelin, a 28 amino acid peptide, improves SERCA2a function by inducing PLB phosphorylation. Ghrelin also reduces cardiac fibrosis. In summary, Glucagon-like peptide-1, Relaxin-2, Neuregulin-1, and Ghrelin each modify calcium dynamics, collagen expression, and myocardial fibrosis through attenuation of deleterious signaling cascades, and induction of adaptive pathways, representing potential therapeutic targets for HFpEF.

Functions and clinical implications of exosomes in pancreatic cancer

Pancreatic cancer is one of the most aggressive human malignancies and is associated with a dismal prognosis, which can be contributed to its atypical symptoms, metastatic propensity, and significant chemoresistance. Emerging evidence shows that pancreatic cancer cell-derived exosomes (PEXs) play critical roles in tumorigenesis and tumor development, as they are involved in drug resistance, immune evasion and metabolic reprograming, and distant metastasis of pancreatic cancer. Their numerous differentially expressed and functional contents make PEXs promising screening tools and therapeutic targets, which require further exploration. In this review, we focus on the functions of PEX contents and their clinical implications in pancreatic cancer.

α7 Nicotinic Acetylcholine Receptor Regulates the Function and Viability of L Cells

Enteroendocrine L cells secrete the incretin hormone glucagon-like peptide-1 (GLP-1), and they also express the α7 nicotinic acetylcholine receptor (α7nAChR), which may regulate GLP-1 secretion. Here, GTS-21, a selective α7nAChR agonist, was used to examine the effect of α7nAChR activation in L-cell lines, mouse intestinal primary cell cultures, and C57BL/6 mice. GTS-21 stimulated GLP-1 secretion in vitro, and this effect was attenuated by an α7nAChR antagonist or by α7nAChR-specific small interfering RNA. Under in vitro cell culture conditions of glucotoxicity, GTS-21 restored GLP-1 secretion and improved L-cell viability while also acting in vivo to raise levels of circulating GLP-1 in mice. To assess potential signaling mechanisms underlying these actions of GTS-21, we first monitored Ca2+, cAMP, and phosphatidylinositol 3-kinase (PI3K) activity. As expected for a GLP-1 secretagogue promoting Ca2+ influx through α7nAChR cation channels, [Ca2+]i increased in response to GTS-21, but [cAMP]i was unchanged. Surprisingly, pharmacological inhibition of growth factor signaling pathways revealed that GTS-21 also acts on the PI3K-protein kinase B-mammalian target of rapamycin pathway to promote L-cell viability. Moreover, the Ca2+ chelator BAPTA-AM counteracted GTS-21‒stimulated PI3K activity, thereby indicating unexpected crosstalk of L-cell Ca2+ and growth factor signaling pathways. Collectively, these data demonstrate that α7nAChR activation enhances GLP-1 secretion by increasing levels of cytosolic Ca2+ while also revealing Ca2+- and PI3K-dependent processes of α7nAChR activation that promote L-cell survival.

Pancreatic cancer-derived exosomes suppress the production of GIP and GLP-1 from STC-1 cells in vitro by down-regulating the PCSK1/3

One hallmark of pancreatic cancer (PC) is the high prevalence of pancreatic cancer-associated diabetes mellitus (PC-DM), but the mechanisms remain to be elucidated. Patients with PC who are diagnosed with new-onset diabetes/prediabetes have recently been shown to display significantly lower levels of glucose-dependent insulinotropic peptide (GIP) secreted mainly by enteroendocrine cells. We hypothesized that PC-derived exosomes are responsible for the decreased levels of incretins in patients with PC-DM. In this study, exosomes were successfully isolated from PANC-1, MIA PaCa-2 and SW620 cells and characterized. Only the exosomes from MIA PaCa-2 cells (Exo-Mia) reduce the production of GIP and glucagon-like peptide-1 (GLP-1) from STC-1 cells in vitro in a concentration- and time-dependent manner. Moreover, Exo-Mia increased the levels of the Gip and proglucagon mRNAs and decreased the expression of proprotein convertase subtilisin/kexin type 1/3 (PCSK1/3), which is responsible for the post-translational processing of Gip and proglucagon. Furthermore, differentially expressed exosomal miRNAs (miR-6796-3p, miR-6763-5p, miR-4750-3p and miR-197-3p) were identified and considered to be responsible for the inhibitory effects on GIP and GLP-1 production. To further determine the approach of cancer-derived exosomes reaching enteroendocrine cells, we analyzed the uptake and distribution of exosomes in animal model. It was observed that exosomes infused into the intestinal cavity were more easily internalized by the intestinal epithelium than exosomes injected into blood. In conclusion, pancreatic cancer-derived exosomes (Exo-Mia) suppress the synthesis of GIP and GLP-1 from STC-1 cells in vitro by down-regulating the PCSK1/3. Moreover, it may be the pancreatic juice that transport cancer-derived exosomes to target cells (K and L cells) in the gut.