Enteroendocrine L Cells Sense LPS after Gut Barrier Injury to Enhance GLP-1 Secretion

Bidirectional regulation of the brain-gut-microbiota axis following traumatic brain injury

JOURNAL/nrgr/04.03/01300535-202508000-00002/figure1/v/2024-09-30T120553Z/r/image-tiff Traumatic brain injury is a prevalent disorder of the central nervous system. In addition to primary brain parenchymal damage, the enduring biological consequences of traumatic brain injury pose long-term risks for patients with traumatic brain injury; however, the underlying pathogenesis remains unclear, and effective intervention methods are lacking. Intestinal dysfunction is a significant consequence of traumatic brain injury. Being the most densely innervated peripheral tissue in the body, the gut possesses multiple pathways for the establishment of a bidirectional "brain-gut axis" with the central nervous system. The gut harbors a vast microbial community, and alterations of the gut niche contribute to the progression of traumatic brain injury and its unfavorable prognosis through neuronal, hormonal, and immune pathways. A comprehensive understanding of microbiota-mediated peripheral neuroimmunomodulation mechanisms is needed to enhance treatment strategies for traumatic brain injury and its associated complications. We comprehensively reviewed alterations in the gut microecological environment following traumatic brain injury, with a specific focus on the complex biological processes of peripheral nerves, immunity, and microbes triggered by traumatic brain injury, encompassing autonomic dysfunction, neuroendocrine disturbances, peripheral immunosuppression, increased intestinal barrier permeability, compromised responses of sensory nerves to microorganisms, and potential effector nuclei in the central nervous system influenced by gut microbiota. Additionally, we reviewed the mechanisms underlying secondary biological injury and the dynamic pathological responses that occur following injury to enhance our current understanding of how peripheral pathways impact the outcome of patients with traumatic brain injury. This review aimed to propose a conceptual model for future risk assessment of central nervous system-related diseases while elucidating novel insights into the bidirectional effects of the "brain-gut-microbiota axis."

The emerging role of gut hormones

The gut is traditionally recognized as the central organ for the digestion and absorption of nutrients, however, it also functions as a significant endocrine organ, secreting a variety of hormones such as glucagon-like peptide 1, serotonin, somatostatin, and glucocorticoids. These gut hormones, produced by specialized intestinal epithelial cells, are crucial not only for digestive processes but also for the regulation of a wide range of physiological functions, including appetite, metabolism, and immune responses. While gut hormones can exert systemic effects, they also play a pivotal role in maintaining local homeostasis within the gut. This review discusses the role of the gut as an endocrine organ, emphasizing the stimuli, the newly discovered functions, and the clinical significance of gut-secreted hormones. Deciphering the emerging role of gut hormones will lead to a better understanding of gut homeostasis, innovative treatments for disorders in the gut, as well as systemic diseases.

Silibinin, a commonly used therapeutic agent for non-alcohol fatty liver disease, functions through upregulating intestinal expression of fibroblast growth factor 15/19

BACKGROUND AND PURPOSE

Silibinin is used to treat non-alcohol fatty liver disease (NAFLD) despite having rapid liver metabolism. Therefore, we investigated the role of the intestine in silibinin mechanism of action.

EXPERIMENTAL APPROACH

NAFLD mice model was established by feeding them with a high-fat diet (HFD). Liver pathological were examined using H&E and oil red O staining. Tissue distribution of silibinin was detected by LC-MS/MS. SiRNA was employed for gene silencing and plasmid was used for gene overexpression. ChIP-qPCR assay was performed to detect the levels of histone acetylation. Recombinant adeno-associated virus 9-short hairpin-fibroblast growth factor (FGF)-15 and -farnesoid X receptor (FXR; NR1H4) were used to knockdown expression of FGF-15 and FXR.

KEY RESULTS

Oral silibinin significantly reversed NAFLD in mice, although liver concentration was insufficient for reduction of lipid accumulation in hepatocytes. Among endogenous factors capable of reversing NAFLD, the expression of Fgf-15 was selectively up-regulated by silibinin in ileum and colon of mice. When intestinal expression of Fgf-15 was knocked down, protection of silibinin against lipid accumulation and injury of livers nearly disappeared. Silibinin could reduce activity of histone deacetylase 2 (HDAC2), enhance histone acetylation in the promoter region of FXR and consequently increase intestinal expression of FGF-15/19.

CONCLUSION AND IMPLICATIONS

Oral silibinin selectively promotes expression of FGF-15/19 in ileum by enhancing transcription of FXR via reduction of HDAC2 activity, and FGF-15/19 enters into circulation to exert anti-NAFLD action. As the site of action is the intestine this would explain the discrepancy between pharmacodynamics and pharmacokinetics of silibinin.

Lipopolysaccharide accelerates peristalsis by stimulating glucagon-like peptide-1 release from L cells in the rat proximal colon

Upon epithelial barrier dysfunction, lipopolysaccharide (LPS) stimulates glucagon-like peptide-1 (GLP-1) secretion from enteroendocrine L cells by activating Toll-like receptor 4 (TLR4). Because GLP-1 accelerates peristalsis in the proximal colon, the present study aimed to explore whether LPS facilitates colonic peristalsis by stimulating L cell-derived GLP-1 release. In isolated segments of rat proximal colon that were serosally perfused with physiological salt solution and luminally perfused with 0.9% saline, peristaltic wall motion was video recorded and converted into spatio-temporal maps. Fluorescence immunohistochemistry was also carried out. Intraluminal administration of LPS (100 or 1 µg mL-1 but not 100 ng mL-1) increased the frequency of oro-aboral propagating peristaltic contractions. The LPS-induced acceleration of colonic peristalsis was blocked by TAK-242 (the TLR4 antagonist), exendin-3 (the GLP-1 receptor antagonist) or BIBN4096 (the calcitonin gene-related peptide receptor antagonist). GLP-1-positive epithelial cells co-expressed TLR4 immunoreactivity. In aspirin-pretreated preparations where epithelial barrier function had been impaired, a lower dose of LPS (100 ng mL-1) became capable of accelerating peristalsis. By contrast, luminally applied dimethyl sulphoxide, a reactive oxygen species scavenger that protects epithelial integrity, attenuated the prokinetic effects of a higher dose of LPS (100 µg mL-1). In colonic segments of a stress rat model leading to a leaky gut, LPS induced more pronounced prokinetic effects. Colonic L cells may well sense luminal LPS via TLR4 triggering the release of GLP-1 that stimulates calcitonin gene-related peptide-containing neurons. The resultant acceleration of peristalsis would facilitate excretion of Gram-negative bacteria from the intestine, and thus L cells may have a protective role against intestinal bacterial infections. KEY POINTS: Colonic epithelial cells form a barrier against bacterial invasion but also may contribute more actively to the exclusion of luminal pathogen by stimulating colonic motility. Luminal lipopolysaccharide (LPS) accelerated colonic peristalsis by stimulating calcitonin gene-related peptide-containing neurons. The prokinetic effect of LPS was mediated by the secretion of glucagon-like peptide-1 from enteroendocrine L cells in which Toll-like receptor 4 was expressed. The LPS-mediated acceleration of peristalsis depended on epithelial barrier integrity. L cells have a defensive role against Gram-negative bacterial infections by facilitating faecal excretion, and could be a potential therapeutic target for gastrointestinal infections.

Glucagon-like peptide-1 receptor: mechanisms and advances in therapy

The glucagon-like peptide-1 (GLP-1) receptor, known as GLP-1R, is a vital component of the G protein-coupled receptor (GPCR) family and is found primarily on the surfaces of various cell types within the human body. This receptor specifically interacts with GLP-1, a key hormone that plays an integral role in regulating blood glucose levels, lipid metabolism, and several other crucial biological functions. In recent years, GLP-1 medications have become a focal point in the medical community due to their innovative treatment mechanisms, significant therapeutic efficacy, and broad development prospects. This article thoroughly traces the developmental milestones of GLP-1 drugs, from their initial discovery to their clinical application, detailing the evolution of diverse GLP-1 medications along with their distinct pharmacological properties. Additionally, this paper explores the potential applications of GLP-1 receptor agonists (GLP-1RAs) in fields such as neuroprotection, anti-infection measures, the reduction of various types of inflammation, and the enhancement of cardiovascular function. It provides an in-depth assessment of the effectiveness of GLP-1RAs across multiple body systems-including the nervous, cardiovascular, musculoskeletal, and digestive systems. This includes integrating the latest clinical trial data and delving into potential signaling pathways and pharmacological mechanisms. The primary goal of this article is to emphasize the extensive benefits of using GLP-1RAs in treating a broad spectrum of diseases, such as obesity, cardiovascular diseases, non-alcoholic fatty liver disease (NAFLD), neurodegenerative diseases, musculoskeletal inflammation, and various forms of cancer. The ongoing development of new indications for GLP-1 drugs offers promising prospects for further expanding therapeutic interventions, showcasing their significant potential in the medical field.

The role of the gut microbiome in neuroinflammation and chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most debilitating adverse effects caused by chemotherapy drugs such as paclitaxel, oxaliplatin and vincristine. It is untreatable and often leads to the discontinuation of cancer therapy and a decrease in the quality of life of cancer patients. It is well-established that neuroinflammation and the activation of immune and glial cells are among the major drivers of CIPN. However, these processes are still poorly understood, and while many chemotherapy drugs alone can drive the activation of these cells and consequent neuroinflammation, it remains elusive to what extent the gut microbiome influences these processes. In this review, we focus on the peripheral mechanisms driving CIPN, and we address the bidirectional pathways by which the gut microbiome communicates with the immune and nervous systems. Additionally, we critically evaluate literature addressing how chemotherapy-induced dysbiosis and the consequent imbalance in bacterial products may contribute to the activation of immune and glial cells, both of which drive neuroinflammation and possibly CIPN development, and how we could use this knowledge for the development of effective treatment strategies.

Obesity and the gut microbiota: implications of neuroendocrine and immune signaling

Obesity is a major health challenge due to its high prevalence and associated comorbidities. The excessive intake of a diet rich in fat and sugars leads to a persistent imbalance between energy intake and energy expenditure, which increases adiposity. Here, we provide an update on relevant diet-microbe-host interactions contributing to or protecting from obesity. In particular, we focus on how unhealthy diets shape the gut microbiota and thus impact crucial intestinal neuroendocrine and immune system functions. We describe how these interactions promote dysfunction in gut-to-brain neuroendocrine pathways involved in food intake control and postprandial metabolism and elevate the intestinal proinflammatory tone, promoting obesity and metabolic complications. In addition, we provide examples of how this knowledge may inspire microbiome-based interventions, such as fecal microbiota transplants, probiotics, and biotherapeutics, to effectively combat obesity-related disorders. We also discuss the current limitations and gaps in knowledge of gut microbiota research in obesity.

Gut microbiota and eating behaviour in circadian syndrome

Eating behaviour and circadian rhythms are closely related. The type, timing, and quantity of food consumed, and host circadian rhythms, directly influence the intestinal microbiota, which in turn impacts host circadian rhythms and regulates food intake beyond homeostatic eating. This Opinion discusses the impact of food intake and circadian disruptions induced by an obesogenic environment on gut-brain axis signalling. We also explore potential mechanisms underlying the effects of altered gut microbiota on food intake behaviour and circadian rhythmicity. Understanding the crosstalk between gut microbiota, circadian rhythms, and unhealthy eating behaviour is crucial to addressing the obesity epidemic, which remains one of the biggest societal challenges of our time.

The enteroendocrine axis and its effect on gastrointestinal function, nutrition, and inflammation

PURPOSE OF REVIEW

Gastrointestinal (GI) dysfunction limits enteral nutrition (EN) delivery in critical illness and contributes to systemic inflammation. The enteroendocrine (EE) axis plays an integral role in this interface between nutrition, inflammation, and GI function in critical illness. In this review, we present an overview of the EE system with a focus on its role in GI inflammation and function.

RECENT FINDINGS

Enteroendocrine cells have been primarily described in their role in macronutrient digestion and absorption. Recent research has expanded on the diverse functions of EE cells including their ability to sense microbial peptides and metabolites and regulate immune function and inflammation. Therefore, EE cells may be both affected by and contribute to many pathophysiologic states and interventions of critical illness such as dysbiosis , inflammation, and alternative EN strategies. In this review, we present an overview of EE cells including their growing role in nonnutrient functions and integrate this understanding into relevant aspects of critical illness with a focus on EN.

SUMMARY

The EE system is key in maintaining GI homeostasis in critical illness, and how it is impacted and contributes to outcomes in the setting of dysbiosis , inflammation and different feeding strategies in critical illness should be considered.

The benefits of GLP-1 drugs beyond obesity

Glucagon-like peptide-1-based medicines have weight loss-independent actions.

Adverse effects with semaglutide: a protocol for a systematic review with meta-analysis and trial sequential analysis

INTRODUCTION

Semaglutide is increasingly used for the treatment of type 2 diabetes mellitus, overweight and other conditions. It is well known that semaglutide lowers blood glucose levels and leads to significant weight loss. Still, a systematic review has yet to investigate the adverse effects with semaglutide for all patient groups.

METHODS AND ANALYSIS

We will conduct a systematic review and search major medical databases (Cochrane Central Register of Controlled Trials, Medline, Embase, Latin American and Caribbean Health Sciences Literature, Science Citation Index Expanded, Conference Proceedings Citation Index-Science) and clinical trial registries from their inception and onwards to identify relevant randomised clinical trials. We expect to conduct the literature search in July 2024. Two review authors will independently extract data and perform risk-of-bias assessments. We will include randomised clinical trials comparing oral or subcutaneous semaglutide versus placebo. Primary outcomes will be all-cause mortality and serious adverse events. Secondary outcomes will be myocardial infarction, stroke, all-cause hospitalisation and non-serious adverse events. Data will be synthesised by meta-analyses and trial sequential analysis; risk of bias will be assessed with Cochrane Risk of Bias tool-version 2, an eight-step procedure will be used to assess if the thresholds for statistical and clinical significance are crossed, and the certainty of the evidence will be assessed by Grading of Recommendations, Assessment, Development and Evaluations.

ETHICS AND DISSEMINATION

This protocol does not present any results. Findings of this systematic review will be published in international peer-reviewed scientific journals.

PROSPERO REGISTRATION NUMBER

CRD42024499511.

Immunomodulation and inflammation: Role of GLP-1R and GIPR expressing cells within the gut

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are peptide hormones produced by enteroendocrine cells in the small intestine. Despite being produced in the gut, the leveraging of their role in potentiating glucose-stimulated insulin secretion, also known as the incretin effect, has distracted from discernment of direct intestinal signaling circuits. Both preclinical and clinical evidence have highlighted a role for the incretins in inflammation. In this review, we highlight the discoveries of GLP-1 receptor (GLP-1R)+ natural (TCRαβ and TCRγδ) and induced (TCRαβ+CD4+ cells and TCRαβ+CD8αβ+) intraepithelial lymphocytes. Both endogenous signaling and pharmacological activation of GLP-1R impact local and systemic inflammation, the gut microbiota, whole-body metabolism, as well as the control of GLP-1 bioavailability. While GIPR signaling has been documented to impact hematopoiesis, the impact of these bone marrow-derived cells in gut immunology is not well understood. We uncover gaps in the literature of the evaluation of the impact of sex in these GLP-1R and GIP receptor (GIPR) signaling circuits and provide speculations of the maintenance roles these hormones play within the gut in the fasting-refeeding cycles. GLP-1R agonists and GLP-1R/GIPR agonists are widely used as treatments for diabetes and weight loss, respectively; however, their impact on gut homeostasis has not been fully explored. Advancing our understanding of the roles of GLP-1R and GIPR signaling within the gut at homeostasis as well as metabolic and inflammatory diseases may provide targets to improve disease management.

Anti-Inflammatory Effects of Glucagon-Like Peptide-1 Receptor Agonists via the Neuroimmune Axis

Glucagon-like peptide 1 receptor agonists (GLP-1RAs) have shown efficacy in the treatment of metabolic disease-related complications, partially attributable to their anti-inflammatory properties. However, the specific cell types and pathways involved in these effects were not fully understood. A recent study by Wong et al. demonstrated the importance of the brain GLP-1R in mediating the anti-inflammatory effects of GLP-1RAs in Toll-like receptor and sepsis-mediated inflammation. In this discussion, we review the existing literature on the action of GLP-1RAs in inflammation and explore the implications of these recent findings.

Single Cell Analysis of Human Colonoids Exposed to Uranium-Bearing Dust

BACKGROUND

Uranium exposure remains an important environmental legacy and physiological health concern, with hundreds of abandoned uranium mines located in the Southwestern United States largely impacting underserved indigenous communities. The negative effects of heavy metals on barrier permeability and inhibition of intestinal epithelial healing have been described; however, transcriptomic changes within the intestinal epithelial cells and impacts on lineage differentiation are largely unknown.

OBJECTIVES

Herein, we sought to determine the molecular and cellular changes that occur in the colon in response to uranium bearing dust (UBD) exposure.

METHODS

Human colonoids from three biologically distinct donors were acutely exposed to UBD then digested for single cell RNA sequencing to define the molecular changes that occur to specific identities of colonic epithelial cells. Validation in colonoids was assessed using morphological and imaging techniques.

RESULTS

Human colonoids acutely exposed to UBD exhibited disrupted proliferation and hyperplastic differentiation of the secretory lineage cell, enteroendocrine cells (EEC). Single-cell RNA sequencing also showed more EEC subtypes present in UBD-exposed colonoids.

DISCUSSION

These findings highlight the significance of crypt-based proliferative cells and secretory cell differentiation using human colonoids to model major colonic responses to uranium-bearing particulate dust exposure. https://doi.org/10.1289/EHP13855.

The Effect of Enteric-Derived Lipopolysaccharides on Obesity

Endotoxin is a general term for toxic substances in Gram-negative bacteria, whose damaging effects are mainly derived from the lipopolysaccharides (LPS) in the cell walls of Gram-negative bacteria, and is a strong pyrogen. Obesity is a chronic, low-grade inflammatory condition, and LPS are thought to trigger and exacerbate it. The gut flora is the largest source of LPS in the body, and it is increasingly believed that altered intestinal microorganisms can play an essential role in the pathology of different diseases. Today, the complex axis linking gut flora to inflammatory states and adiposity has not been well elucidated. This review summarises the evidence for an interconnection between LPS, obesity, and gut flora, further expanding our understanding of LPS as a mediator of low-grade inflammatory disease and contributing to lessening the effects of obesity and related metabolic disorders. As well as providing targets associated with LPS, obesity, and gut flora, it is hoped that interventions that combine targets with gut flora address the individual differences in gut flora treatment.

Dietary inulin alleviated constipation induced depression and anxiety-like behaviors: Involvement of gut microbiota and microbial metabolite short-chain fatty acid

Chronic constipation has been associated with depression-like behavior. Previous study identified the crucial role of gut microbiota in the development of constipation and depression. Dietary inulin (INU) could regulate gut microbiota. Whether INU treatment could ameliorate constipation induced depression was not clear. For this purpose, male CD-1 mice were administered diphenoxylate (20 mg/kg body weight/day) to induce constipation. We found that INU (10 % in standard diet) alleviated the diphenoxylate-induced constipation, manifested as the increase weight and moisture content of feces. Furthermore, the associated depression and anxiety-like behavior disorders were improved by inhibiting neuro-inflammation and preventing synaptic ultrastructure damage under INU treatment. Moreover, INU pretreatment improved the diphenoxylate-induced gut barrier damage by upregulating tight junction protein expression. INU also reshaped gut microbiota in constipation mice by increasing the relative abundance of Bacteroides and Proteobacteria and downregulating the abundance of Muribacalum and Melaminabacteria. The effects of INU on diphenoxylate-induced depression were abolished by gut microbiota depletion via antibiotic treatment. In addition, INU increased the concentration of short chain fatty acids (SCFAs) in feces contents. Meanwhile, supplementation of SCFAs could also partly improve diphenoxylate-induced depression. In conclusion, INU intake was a potential nutritional intervention strategy to prevent constipation induced depression via microbiota-gut-SCFAs axis.

Anti-inflammatory role of glucagon-like peptide 1 receptor agonists and its clinical implications

Glucagon-like peptide 1 receptor agonists (GLP-1RAs) have emerged as promising therapeutic agents with potent anti-inflammatory properties and diverse clinical implications. This in-depth review article explores the mechanisms behind the anti-inflammatory actions of GLP-1RAs and assesses their prospective applicability in a wide range of disease scenarios. The current review establishes the significance of comprehending the anti-inflammatory role of GLP-1RAs and identifies pertinent research gaps. A concise overview of inflammation and its clinical consequences underscores the critical need for effective anti-inflammatory interventions. Subsequently, the article elucidates the intricate mechanisms through which GLP-1RAs modulate immune cell signaling and regulate the nuclear factor-kappa B (NF-κB) pathway. Detailed discussions encompass their impact on inflammatory responses, cytokine production, and attenuation of oxidative stress. The exposition is substantiated by a collection of pertinent examples and an extensive array of references from both preclinical and clinical investigations. The historical trajectory of GLP-1RA drugs, including exenatide, lixisenatide, liraglutide, and semaglutide, is traced to delineate their development as therapeutic agents. Moreover, the review emphasizes the therapeutic potential of GLP-1RAs in specific disease contexts like type 2 diabetes, a neurodegenerative disorder, and inflammatory bowel disease (IBD), shedding light on their anti-inflammatory effects through rigorous examination of preclinical and clinical studies. The article also provides an outlook on future perspectives for GLP-1RAs, encompassing the domains of diabetes, neurodegenerative diseases, and IBD. In conclusion, GLP-1RAs exhibit substantial anti-inflammatory effects, rendering them promising therapeutic agents with broad clinical implications. They are very useful in a wide variety of diseases because they regulate immunological responses, block NF-κB activation, and decrease production of pro-inflammatory cytokines. Ongoing research endeavors aim to optimize their therapeutic use, delineate patient-specific treatment paradigms, and explore novel therapeutic applications. GLP-1RAs represent a significant breakthrough in anti-inflammatory therapy, offering novel treatment options, and improved patient outcomes.

Crosstalk between glucagon-like peptide 1 and gut microbiota in metabolic diseases

Gut microbiota exert influence on gastrointestinal mucosal permeability, bile acid metabolism, short-chain fatty acid synthesis, dietary fiber fermentation, and farnesoid X receptor/Takeda G protein-coupled receptor 5 (TGR5) signal transduction. The incretin glucagon-like peptide 1 (GLP-1) is mainly produced by L cells in the gut and regulates postprandial blood glucose. Changes in gut microbiota composition and function have been observed in obesity and type 2 diabetes (T2D). Meanwhile, the function and rhythm of GLP-1 have also been affected in subjects with obesity or T2D. Therefore, it is necessary to discuss the link between the gut microbiome and GLP-1. In this review, we describe the interaction between GLP-1 and the gut microbiota in metabolic diseases. On the one hand, gut microbiota metabolites stimulate GLP-1 secretion, and gut microbiota affect GLP-1 function and rhythm. On the other hand, the mechanism of action of GLP-1 on gut microbiota involves the inflammatory response. Additionally, we discuss the effects and mechanism of various interventions, such as prebiotics, probiotics, antidiabetic drugs, and bariatric surgery, on the crosstalk between gut microbiota and GLP-1. Finally, we stress that gut microbiota can be used as a target for metabolic diseases, and the clinical application of GLP-1 receptor agonists should be individualized.

Central glucagon-like peptide 1 receptor activation inhibits Toll-like receptor agonist-induced inflammation

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) exert anti-inflammatory effects relevant to the chronic complications of type 2 diabetes. Although GLP-1RAs attenuate T cell-mediated gut and systemic inflammation directly through the gut intraepithelial lymphocyte GLP-1R, how GLP-1RAs inhibit systemic inflammation in the absence of widespread immune expression of the GLP-1R remains uncertain. Here, we show that GLP-1R activation attenuates the induction of plasma tumor necrosis factor alpha (TNF-α) by multiple Toll-like receptor agonists. These actions are not mediated by hematopoietic or endothelial GLP-1Rs but require central neuronal GLP-1Rs. In a cecal slurry model of polymicrobial sepsis, GLP-1RAs similarly require neuronal GLP-1Rs to attenuate detrimental responses associated with sepsis, including sickness, hypothermia, systemic inflammation, and lung injury. Mechanistically, GLP-1R activation leads to reduced TNF-α via α1-adrenergic, δ-opioid, and κ-opioid receptor signaling. These data extend emerging concepts of brain-immune networks and posit a new gut-brain GLP-1R axis for suppression of peripheral inflammation.

The effects of gut microbiota on appetite regulation and the underlying mechanisms

Appetite, a crucial aspect regulated by both the central nervous system and peripheral hormones, is influenced by the composition and dynamics of the intestinal microbiota, as evidenced by recent research. This review highlights the role of intestinal microbiota in appetite regulation, elucidating the involvement of various pathways. Notably, the metabolites generated by intestinal microorganisms, including short-chain fatty acids, bile acids, and amino acid derivatives, play a pivotal role in this intricate process. Furthermore, intestinal microorganisms contribute to appetite regulation by modulating nutritional perception, neural signal transmission, and hormone secretion within the digestive system. Consequently, manipulating and modulating the intestinal microbiota represent innovative strategies for ameliorating appetite-related disorders. This paper provides a comprehensive review of the effects of gut microbes and their metabolites on the central nervous system and host appetite. By exploring their potential regulatory pathways and mechanisms, this study aims to enhance our understanding of how gut microbes influence appetite regulation in the host.

Relevance and consequence of chronic inflammation for obesity development

BACKGROUND

Increasing prevalence of morbid obesity accompanied by comorbidities like type 2 diabetes mellitus (T2DM) led to a demand for improving therapeutic strategies and pharmacological intervention options. Apart from genetics, inflammation processes have been hypothesized to be of importance for the development of obesity and related aspects like insulin resistance.

MAIN TEXT

Within this review, we provide an overview of the intricate interplay between chronic inflammation of the adipose tissue and the hypothalamus and the development of obesity. Further understanding of this relationship might improve the understanding of the underlying mechanism and may be of relevance for the establishment of new treatment strategies.

Enteroendocrine cell regulation of the gut-brain axis

Enteroendocrine cells (EECs) are an essential interface between the gut and brain that communicate signals about nutrients, pain, and even information from our microbiome. EECs are hormone-producing cells expressed throughout the gastrointestinal epithelium and have been leveraged by pharmaceuticals like semaglutide (Ozempic, Wegovy), terzepatide (Mounjaro), and retatrutide (Phase 2) for diabetes and weight control, and linaclotide (Linzess) to treat irritable bowel syndrome (IBS) and visceral pain. This review focuses on role of intestinal EECs to communicate signals from the gut lumen to the brain. Canonically, EECs communicate information about the intestinal environment through a variety of hormones, dividing EECs into separate classes based on the hormone each cell type secretes. Recent studies have revealed more diverse hormone profiles and communication modalities for EECs including direct synaptic communication with peripheral neurons. EECs known as neuropod cells rapidly relay signals from gut to brain via a direct communication with vagal and primary sensory neurons. Further, this review discusses the complex information processing machinery within EECs, including receptors that transduce intraluminal signals and the ion channel complement that govern initiation and propagation of these signals. Deeper understanding of EEC physiology is necessary to safely treat devastating and pervasive conditions like irritable bowel syndrome and obesity.

Human gut homeostasis and regeneration: the role of the gut microbiota and its metabolites

The healthy human gut is a balanced ecosystem where host cells and representatives of the gut microbiota interact and communicate in a bidirectional manner at the gut epithelium. As a result of these interactions, many local and systemic processes necessary for host functionality, and ultimately health, take place. Impairment of the integrity of the gut epithelium diminishes its ability to act as an effective gut barrier, can contribute to conditions associated to inflammation processes and can have other negative consequences. Pathogens and pathobionts have been linked with damage of the integrity of the gut epithelium, but other components of the gut microbiota and some of their metabolites can contribute to its repair and regeneration. Here, we review what is known about the effect of bacterial metabolites on the gut epithelium and, more specifically, on the regulation of repair by intestinal stem cells and the regulation of the immune system in the gut. Additionally, we explore the potential therapeutic use of targeted modulation of the gut microbiota to maintain and improve gut homeostasis as a mean to improve health outcomes.

The expanding incretin universe: from basic biology to clinical translation

Incretin hormones, principally glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(GLP-1), potentiate meal-stimulated insulin secretion through direct (GIP + GLP-1) and indirect (GLP-1) actions on islet β-cells. GIP and GLP-1 also regulate glucagon secretion, through direct and indirect pathways. The incretin hormone receptors (GIPR and GLP-1R) are widely distributed beyond the pancreas, principally in the brain, cardiovascular and immune systems, gut and kidney, consistent with a broad array of extrapancreatic incretin actions. Notably, the glucoregulatory and anorectic activities of GIP and GLP-1 have supported development of incretin-based therapies for the treatment of type 2 diabetes and obesity. Here we review evolving concepts of incretin action, focusing predominantly on GLP-1, from discovery, to clinical proof of concept, to therapeutic outcomes. We identify established vs uncertain mechanisms of action, highlighting biology conserved across species, while illuminating areas of active investigation and uncertainty that require additional clarification.

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.

Severe and fatal COVID-19 is characterised by increased circulating glucagon like peptide 1 and procalcitonin modulated by type 2 diabetes

AIMS

Endotoxemia commonly occurs in severe and fatal COVID-19, suggesting that concomitant bacterial stimuli may amplify the innate immune response induced by SARS-CoV-2. We previously demonstrated that the endogenous glucagon like peptide 1 (GLP-1) system in conjunction with increased procalcitonin (PCT) is hyperactivated in patients with severe Gram-negative sepsis and modulated by type 2 diabetes (T2D). We aimed to determine the association of COVID-19 severity with endogenous GLP-1 activation upregulated by increased specific pro-inflammatory innate immune response in patients with and without T2D.

MATERIALS AND METHODS

Plasma levels of total GLP-1, IL-6, and PCT were estimated on admission and during hospitalisation in 61 patients (17 with T2D) with non-severe and severe COVID-19.

RESULTS

COVID-19 patients demonstrated ten-fold increase of IL-6 levels regardless of disease severity. Increased admission GLP-1 levels (p = 0.03) accompanied by two-fold increased PCT were found in severe as compared with non-severe patients. Moreover, GLP-1 and PCT levels were significantly increased in non-survived as compared with survived patients at admission (p = 0.01 and p = 0.001, respectively) and at 5 to 6 days of hospitalisation (p = 0.05). Both non-diabetic and T2D patients demonstrated a positive correlation between GLP-1 and PCT response (r = 0.33, p = 0.03, and r = 0.54, p = 0.03, respectively), but the intensity of this joint pro-inflammatory/GLP-1 response was modulated by T2D. In addition, hypoxaemia down-regulated GLP-1 response only in T2D patients with bilateral lung damage.

CONCLUSIONS

The persistent joint increase of endogenous GLP-1 and PCT in severe and fatal COVID-19 suggests a role of concomitant bacterial infection in disease exacerbation. Early elevation of endogenous GLP-1 may serve as a new biomarker of COVID-19 severity and fatal outcome.

Uranium-bearing dust induces differentiation and expansion of enteroendocrine cells in human colonoids

Chronic exposure to environmental toxins and heavy metals has been associated with intestinal inflammation, increased susceptibility to pathogen-induced diseases, and higher incidences of colorectal cancer, all of which have been steadily increasing in prevalence for the past 40 years. The negative effects of heavy metals on barrier permeability and inhibition of intestinal epithelial healing have been described; however, transcriptomic changes within the intestinal epithelial cells and impacts on lineage differentiation are largely unknown. Uranium exposure remains an important environmental legacy and physiological health concern, with hundreds of abandoned uranium mines located in the Southwestern United States largely impacting underserved indigenous communities. Herein, using human colonoids, we defined the molecular and cellular changes that occur in response to uranium bearing dust (UBD) exposure. We used single cell RNA sequencing to define the molecular changes that occur to specific identities of colonic epithelial cells. We demonstrate that this environmental toxicant disrupts proliferation and induces hyperplastic differentiation of secretory lineage cells, particularly enteroendocrine cells (EEC). EECs respond to UBD exposure with increased differentiation into de novo EEC sub-types not found in control colonoids. This UBD-induced EEC differentiation does not occur via canonical transcription factors NEUROG3 or NEUROD1. These findings highlight the significance of crypts-based proliferative cells and secretory cell differentiation as major colonic responses to heavy metal-induced injury.

Know your neighbors: microbial recognition at the intestinal barrier and its implications for gut homeostasis and inflammatory bowel disease

Intestinal epithelial cells (IECs) perform several physiological and metabolic functions at the epithelial barrier. IECs also play an important role in defining the overall immune functions at the mucosal region. Pattern recognition receptors (PRRs) on the cell surface and in other cellular compartments enable them to sense the presence of microbes and microbial products in the intestinal lumen. IECs are thus at the crossroads of mediating a bidirectional interaction between the microbial population and the immune cells present at the intestinal mucosa. This communication between the microbial population, the IECs and the underlying immune cells has a profound impact on the overall health of the host. In this review, we focus on the various PRRs present in different cellular compartments of IECs and discuss the recent developments in the understanding of their role in microbial recognition. Microbial recognition and signaling at the epithelial barrier have implications in the maintenance of intestinal homeostasis, epithelial barrier function, maintenance of commensals, and the overall tolerogenic function of PRRs in the gut mucosa. We also highlight the role of an aberrant microbial sensing at the epithelial barrier in the pathogenesis of inflammatory bowel disease (IBD) and the development of colorectal cancer.

Mechanisms and clinical applications of incretin therapies for diabetes and chronic kidney disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) is the leading cause of kidney failure worldwide. Development of DKD increases risks for cardiovascular events and death. Glucagon-like peptide-1 (GLP-1) receptor agonist have demonstrated improved cardiovascular and kidney outcomes in large-scale clinical trials.

RECENT FINDING

GLP-1 and dual GLP-1/glucose-depending insulinotropic polypeptide (GIP) receptor agonists have robust glucose-lowering efficacy with low risk of hypoglycemia even in advanced stages of DKD. Initially approved as antihyperglycemic therapies, these agents also reduce blood pressure and body weight. Cardiovascular outcome and glycemic lowering trials have reported decreased risks of development and progression of DKD and atherosclerotic cardiovascular events for GLP-1 receptor agonists. Kidney and cardiovascular protection is mediated partly, but not entirely, by lowering of glycemia, body weight, and blood pressure. Experimental data have identified modulation of the innate immune response as a biologically plausible mechanism underpinning kidney and cardiovascular effects.

SUMMARY

An influx of incretin-based therapies has changed the landscape of DKD treatment. GLP-1 receptor agonist use is endorsed by all major guideline forming organizations. Ongoing clinical trials and mechanistic studies with GLP-1 and dual GLP-1/GIP receptor agonists will further define the roles and pathways for these agents in the treatment of DKD.

Glucagon-like peptide 1 receptor agonists: cardiovascular benefits and mechanisms of action

Type 2 diabetes mellitus (T2DM) and obesity are metabolic disorders characterized by excess cardiovascular risk. Glucagon-like peptide 1 (GLP1) receptor (GLP1R) agonists reduce body weight, glycaemia, blood pressure, postprandial lipaemia and inflammation - actions that could contribute to the reduction of cardiovascular events. Cardiovascular outcome trials (CVOTs) have demonstrated that GLP1R agonists reduce the rates of major adverse cardiovascular events in patients with T2DM. Separate phase III CVOTs of GLP1R agonists are currently being conducted in people living with heart failure with preserved ejection fraction and in those with obesity. Mechanistically, GLP1R is expressed at low levels in the heart and vasculature, raising the possibility that GLP1 might have both direct and indirect actions on the cardiovascular system. In this Review, we summarize the data from CVOTs of GLP1R agonists in patients with T2DM and describe the actions of GLP1R agonists on the heart and blood vessels. We also assess the potential mechanisms that contribute to the reduction in major adverse cardiovascular events in individuals treated with GLP1R agonists and highlight the emerging cardiovascular biology of novel GLP1-based multi-agonists currently in development. Understanding how GLP1R signalling protects the heart and blood vessels will optimize the therapeutic use and development of next-generation GLP1-based therapies with improved cardiovascular safety.

Glucagon-like peptide-1: a multi-faceted anti-inflammatory agent

Inflammation contributes to many chronic conditions. It is often associated with circulating pro-inflammatory cytokines and immune cells. GLP-1 levels correlate with disease severity. They are often elevated and can serve as markers of inflammation. Previous studies have shown that oxytocin, hCG, ghrelin, alpha-MSH and ACTH have receptor-mediated anti-inflammatory properties that can rescue cells from damage and death. These peptides have been studied well in the past century. In contrast, GLP-1 and its anti-inflammatory properties have been recognized only recently. GLP-1 has been proven to be a useful adjuvant therapy in type-2 diabetes mellitus, metabolic syndrome, and hyperglycemia. It also lowers HbA1C and protects cells of the cardiovascular and nervous systems by reducing inflammation and apoptosis. In this review we have explored the link between GLP-1, inflammation, and sepsis.

Intestinal Enteroendocrine Cells: Present and Future Druggable Targets

Enteroendocrine cells are specialized secretory lineage cells in the small and large intestines that secrete hormones and peptides in response to luminal contents. The various hormones and peptides can act upon neighboring cells and as part of the endocrine system, circulate systemically via immune cells and the enteric nervous system. Locally, enteroendocrine cells have a major role in gastrointestinal motility, nutrient sensing, and glucose metabolism. Targeting the intestinal enteroendocrine cells or mimicking hormone secretion has been an important field of study in obesity and other metabolic diseases. Studies on the importance of these cells in inflammatory and auto-immune diseases have only recently been reported. The rapid global increase in metabolic and inflammatory diseases suggests that increased understanding and novel therapies are needed. This review will focus on the association between enteroendocrine changes and metabolic and inflammatory disease progression and conclude with the future of enteroendocrine cells as potential druggable targets.

Association between Taxonomic Composition of Gut Microbiota and Host Single Nucleotide Polymorphisms in Crohn's Disease Patients from Russia

Crohn's disease (CD) is a chronic relapsing inflammatory bowel disease of unknown etiology. Genetic predisposition and dysbiotic gut microbiota are important factors in the pathogenesis of CD. In this study, we analyzed the taxonomic composition of the gut microbiota and genotypes of 24 single nucleotide polymorphisms (SNP) associated with the risk of CD. The studied cohorts included 96 CD patients and 24 healthy volunteers from Russia. Statistically significant differences were found in the allele frequencies for 8 SNPs and taxonomic composition of the gut microbiota in CD patients compared with controls. In addition, two types of gut microbiota communities were identified in CD patients. The main distinguishing driver of bacterial families for the first community type are Bacteroidaceae and unclassified members of the Clostridiales order, and the second type is characterized by increased abundance of Streptococcaceae and Enterobacteriaceae. Differences in the allele frequencies of the rs9858542 (BSN), rs3816769 (STAT3), and rs1793004 (NELL1) were also found between groups of CD patients with different types of microbiota communities. These findings confirm the complex multifactorial nature of CD.

GLP-1 Receptor Agonists in Obese Patients with Inflammatory Bowel Disease: from Molecular Mechanisms to Clinical Considerations and Practical Recommendations for Safe and Effective Use

PURPOSE OF REVIEW

To discuss current literature and provide practical recommendations for the safe and effective use of glucagon-like peptide 1 receptor agonists (GLP-1 RA) in people with inflammatory bowel disease (IBD) and type 2 diabetes (T2D) and/or obesity. The molecular mechanisms that justify the potential benefits of GLP-1 RA in IBD and the links between IBD, obesity, and cardiovascular disease are also discussed.

RECENT FINDINGS

Preliminary data suggest that GLP-1 RA can modulate crucial pathways in the pathogenesis of IBD, such as chronic inflammation circuits, intestinal tight junctions, and gut microbiome dysbiosis, setting the stage for human trials to investigate the role of these agents in the treatment of IBD among people with or without diabetes and obesity. However, gastrointestinal side effects related to GLP-1 RA need appropriate clinical management to mitigate risks and maximize the benefits of therapy in people with IBD. GLP-1 RA originally emerged as drugs for the treatment of hyperglycemia and are currently licensed for the management of T2D and/or overweight/obesity. However, their wealth of pleiotropic actions soon raised expectations that they might confer benefits on non-metabolic disorders. Future studies are expected to clarify whether GLP-1 RA deserve an adjunct place in the arsenal of drugs against IBD.

Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP1) exhibit incretin activity, meaning that they potentiate glucose-dependent insulin secretion. The emergence of GIP receptor (GIPR)-GLP1 receptor (GLP1R) co-agonists has fostered growing interest in the actions of GIP and GLP1 in metabolically relevant tissues. Here, we update concepts of how these hormones act beyond the pancreas. The actions of GIP and GLP1 on liver, muscle and adipose tissue, in the control of glucose and lipid homeostasis, are discussed in the context of plausible mechanisms of action. Both the GIPR and GLP1R are expressed in the central nervous system, wherein receptor activation produces anorectic effects enabling weight loss. In preclinical studies, GIP and GLP1 reduce atherosclerosis. Furthermore, GIPR and GLP1R are expressed within the heart and immune system, and GLP1R within the kidney, revealing putative mechanisms linking GIP and GLP1R agonism to cardiorenal protection. We interpret the clinical and mechanistic data obtained for different agents that enable weight loss and glucose control for the treatment of obesity and type 2 diabetes mellitus, respectively, by activating or blocking GIPR signalling, including the GIPR-GLP1R co-agonist tirzepatide, as well as the GIPR antagonist-GLP1R agonist AMG-133. Collectively, we update translational concepts of GIP and GLP1 action, while highlighting gaps, areas of uncertainty and controversies meriting ongoing investigation.

Activation of TLRs Triggers GLP-1 Secretion in Mice

The gastrointestinal tract constitutes a large interface with the inner body and is a crucial barrier against gut microbiota and other pathogens. As soon as this barrier is damaged, pathogen-associated molecular patterns (PAMPs) are recognized by immune system receptors, including toll-like receptors (TLRs). Glucagon-like peptide 1 (GLP-1) is an incretin that was originally involved in glucose metabolism and recently shown to be rapidly and strongly induced by luminal lipopolysaccharides (LPS) through TLR4 activation. In order to investigate whether the activation of TLRs other than TLR4 also increases GLP-1 secretion, we used a polymicrobial infection model through cecal ligation puncture (CLP) in wild-type and TLR4-deficient mice. TLR pathways were assessed by intraperitoneal injection of specific TLR agonists in mice. Our results show that CLP induces GLP-1 secretion both in wild-type and TLR4-deficient mice. CLP and TLR agonists increase gut and systemic inflammation. Thus, the activation of different TLRs increases GLP-1 secretion. This study highlights for the first time that, in addition to an increased inflammatory status, CLP and TLR agonists also strongly induce total GLP-1 secretion. Microbial-induced GLP-1 secretion is therefore not only a TLR4/LPS-cascade.

Influence of the gut microbiota on satiety signaling

Recent studies show a link between the gut microbiota and the regulation of satiety and energy intake, processes that contribute to the development and pathophysiology of metabolic diseases. However, this link is predominantly established in animal and in vitro studies, whereas human intervention studies are scarce. In this review we focus on recent evidence linking satiety and the gut microbiome, with specific emphasis on gut microbial short-chain fatty acids (SCFAs). Based on a systematic search we provide an overview of human studies linking the intake of prebiotics with gut microbial alterations and satiety signaling. Our outcomes highlight the importance of in-depth examination of the gut microbiota in relation to satiety and provide insights into recent and future studies in this field.

Gut microbiome-brain interactions in anorexia nervosa: Potential mechanisms and regulatory strategies

Anorexia nervosa (AN) is a psychiatric disorder characterised by malnutrition, fear of weight gain, and body image disturbances. The aetiology of AN is complex, and may involve environmental factors, genetic factors, and biochemical factors, with the latter meaning that AN may be closely associated with neurons, neurotransmitters, and hormones related to appetite and emotional regulation. In addition, an increasing number of studies have shown there is a link between the intestinal microbiota and psychiatric disorders, such as depression. However, few studies and reviews have focused on AN and gut microbes. Accordingly, in this review, we examine the potential pathogenesis of AN in terms of changes in the gut microbiota and its metabolites, and their effects on AN. The neurobiological function of the nervous system in relation to AN are also been mentioned. Furthermore, we suggest future research directions for this field, and note that probiotics may be developed for use as dietary supplements to help alleviate AN in patients.

Glucagon-like Peptide-1 Receptor-based Therapeutics for Metabolic Liver Disease

Glucagon-like peptide-1 (GLP-1) controls islet hormone secretion, gut motility, and body weight, supporting development of GLP-1 receptor agonists (GLP-1RA) for the treatment of type 2 diabetes (T2D) and obesity. GLP-1RA exhibit a favorable safety profile and reduce the incidence of major adverse cardiovascular events in people with T2D. Considerable preclinical data, supported by the results of clinical trials, link therapy with GLP-RA to reduction of hepatic inflammation, steatosis, and fibrosis. Mechanistically, the actions of GLP-1 on the liver are primarily indirect, as hepatocytes, Kupffer cells, and stellate cells do not express the canonical GLP-1R. GLP-1RA reduce appetite and body weight, decrease postprandial lipoprotein secretion, and attenuate systemic and tissue inflammation, actions that may contribute to attenuation of metabolic-associated fatty liver disease (MAFLD). Here we discuss evolving concepts of GLP-1 action that improve liver health and highlight evidence that links sustained GLP-1R activation in distinct cell types to control of hepatic glucose and lipid metabolism, and reduction of experimental and clinical nonalcoholic steatohepatitis (NASH). The therapeutic potential of GLP-1RA alone, or in combination with peptide agonists, or new small molecule therapeutics is discussed in the context of potential efficacy and safety. Ongoing trials in people with obesity will further clarify the safety of GLP-1RA, and pivotal studies underway in people with NASH will define whether GLP-1-based medicines represent effective and safe therapies for people with MAFLD.

Maintenance of Enteral ACE2 Prevents Diabetic Retinopathy in Type 1 Diabetes

BACKGROUND

We examined components of systemic and intestinal renin-angiotensin system on gut barrier permeability, glucose homeostasis, systemic inflammation, and progression of diabetic retinopathy (DR) in human subjects and mice with type 1 diabetes (T1D).

METHODS

T1D individual with (n=18) and without (n=20) DR and controls (n=34) were examined for changes in gut-regulated components of the immune system, gut leakage markers (FABP2 [fatty acid binding protein 2] and peptidoglycan), and Ang II (angiotensin II); Akita mice were orally administered a Lactobacillus paracasei (LP) probiotic expressing humanized ACE2 (angiotensin-converting enzyme 2) protein (LP-ACE2) as either a prevention or an intervention. Akita mice with genetic overexpression of humanAce2 by small intestine epithelial cells (Vil-Cre.hAce2KI-Akita) were similarly examined. After 9 months of T1D, circulatory, enteral, and ocular end points were assessed.

RESULTS

T1D subjects exhibit elevations in gut-derived circulating immune cells (ILC1 cells) and higher gut leakage markers, which were positively correlated with plasma Ang II and DR severity. The LP-ACE2 prevention cohort and genetic overexpression of intestinal ACE2 preserved barrier integrity, reduced inflammatory response, improved hyperglycemia, and delayed development of DR. Improvements in glucose homeostasis were due to intestinal MasR activation, resulting in a GSK-3β (glycogen synthase kinase-3 beta)/c-Myc (cellular myelocytomatosis oncogene)-mediated decrease in intestinal glucose transporter expression. In the LP-ACE2 intervention cohort, gut barrier integrity was improved and DR reversed, but no improvement in hyperglycemia was observed. These data support that the beneficial effects of LP-ACE2 on DR are due to the action of ACE2, not improved glucose homeostasis.

CONCLUSIONS

Dysregulated systemic and intestinal renin-angiotensin system was associated with worsening gut barrier permeability, gut-derived immune cell activation, systemic inflammation, and progression of DR in human subjects. In Akita mice, maintaining intestinal ACE2 expression prevented and reversed DR, emphasizing the multifaceted role of the intestinal renin-angiotensin system in diabetes and DR.

Glucagon-like peptide-1 receptor regulates receptor of advanced glycation end products in high glucose-treated rat mesangial cells

BACKGROUND

Hyperglycemia-induced advanced glycation end products (AGEs) and receptor for AGEs (RAGEs) play major roles in diabetic nephropathy progression. In previous study, both glucagon-like peptide-1 (GLP-1) and peroxisome proliferator-activated receptors delta (PPARδ) agonists were shown to have anti-inflammatory effect on AGE-treated rat mesangial cells (RMCs). The interaction among PPARδ agonists, GLP-1, and AGE-RAGE axis is, however, still unclear.

METHODS

In this study, the individual and synergic effect of PPARδ agonist (L-165 041) and siRNA of GLP-1 receptor (GLP-1R) on the expression of GLP-1, GLP-1R, RAGE, and cell viability in AGE-treated RMCs were investigated.

RESULTS

L-165 041 enhanced GLP-1R mRNA and protein expression only in the presence of AGE. The expression of RAGE mRNA and protein was enhanced by AGE, attenuated by L-165 041, and siRNA of GLP-1R reversed L-165 041-induced inhibition. Cell viability was also inhibited by AGE. L-165 041 attenuated AGE-induced inhibition and siRNA GLP-1R diminished L-165 041 effect.

CONCLUSION

PPARδ agonists increase GLP-1R expression on RMC in the presence of AGE. PPARδ agonists also attenuate AGE-induced upregulated RAGE expression and downregulated cell viability. The effect of PPARδ agonists needs the cooperation of GLP-1R activation.

Intestinal group 1 innate lymphoid cells drive macrophage-induced inflammation and endocrine defects in obesity and promote insulinemia

Hypercaloric diets overactivate the intestinal immune system and disrupt the microbiome and epithelial cell functions, impairing glucose metabolism. The origins of this inflammatory cascade are poorly characterized. We investigated the involvement of intestinal proinflammatory group 1 innate lymphoid cells (ILC1s) in obesity progression and metabolic disruption. In obese mice, we studied longitudinally the ILC1s response to the diet and ILC1s depletion to address its role in obesity. ILC1s are required for the expansion of pro-inflammatory macrophages and ILC2s. ILC1s depletion induced the ILC3-IL-22 pathway, increasing mucin production, antimicrobial peptides, and neuroendocrine cells. These changes were translated into higher gut hormones and reduced insulinemia and adiposity. ILC1s depletion was also associated with a bloom in Akkermansia muciniphila and decreases in Bilophila spp. Intestinal-ILC1s are upstream activators of inflammatory signals, connecting immunity with the microbiome, the enteroendocrine system, and the intestinal barrier in the control of glucose metabolism and adiposity.

Polystyrene microplastics exacerbate experimental colitis in mice tightly associated with the occurrence of hepatic inflammation

The potential health effects of microplastics (MPs) have become a public concern due to their ubiquitousness in the environment and life. Numerous studies have demonstrated that a high dose of MPs can adversely affect gastrointestinal health. However, few studies have focused on the impact of microplastics on patients' health with respect to gastrointestinal diseases. Inflammatory bowel disease (IBD) has emerged as a global disease with a rapidly increasing incidence. IBD, a specific gastrointestinal illness characterized by acute, chronic inflammation and intestinal barrier dysfunction, might increase sensitivity to MPs exposure. Herein, we investigated the impact and mechanism of PS-MPs on dextran sodium sulfate (DSS)-induced colitis. The results demonstrated that gavage with PS-MPs alone caused minimal effects on the intestinal barrier and liver status of mice. For mice with colitis, additional PS-MPs exposure caused a shorter colon length, aggravated histopathological damage and inflammation, reduced mucus secretion, and increased the colon permeability. Furthermore, PS-MPs exposure also increased the risk of secondary liver injury associated with inflammatory cell infiltration. These findings provide more histopathological evidence and suggest a need for more research on the health risk of MPs for sensitive individuals.

GLP-1 and GLP-2 Orchestrate Intestine Integrity, Gut Microbiota, and Immune System Crosstalk

The intestine represents the body's largest interface between internal organs and external environments except for its nutrient and fluid absorption functions. It has the ability to sense numerous endogenous and exogenous signals from both apical and basolateral surfaces and respond through endocrine and neuronal signaling to maintain metabolic homeostasis and energy expenditure. The intestine also harbours the largest population of microbes that interact with the host to maintain human health and diseases. Furthermore, the gut is known as the largest endocrine gland, secreting over 100 peptides and other molecules that act as signaling molecules to regulate human nutrition and physiology. Among these gut-derived hormones, glucagon-like peptide 1 (GLP-1) and -2 have received the most attention due to their critical role in intestinal function and food absorption as well as their application as key drug targets. In this review, we highlight the current state of the literature that has brought into light the importance of GLP-1 and GLP-2 in orchestrating intestine-microbiota-immune system crosstalk to maintain intestinal barrier integrity, inflammation, and metabolic homeostasis.

The Molecular Determinants of Glucagon-like Peptide Secretion by the Intestinal L cell

The intestinal L cell secretes a diversity of biologically active hormones, most notably the glucagon-like peptides, GLP-1 and GLP-2. The highly successful introduction of GLP-1-based drugs into the clinic for the treatment of patients with type 2 diabetes and obesity, and of a GLP-2 analog for patients with short bowel syndrome, has led to the suggestion that stimulation of the endogenous secretion of these peptides may serve as a novel therapeutic approach in these conditions. Situated in the intestinal epithelium, the L cell demonstrates complex relationships with not only circulating, paracrine, and neural regulators, but also ingested nutrients and other factors in the lumen, most notably the microbiota. The integrated input from these numerous secretagogues results in a variety of temporal patterns in L cell secretion, ranging from minutes to 24 hours. This review combines the findings of traditional, physiological studies with those using newer molecular approaches to describe what is known and what remains to be elucidated after 5 decades of research on the intestinal L cell and its secreted peptides, GLP-1 and GLP-2.

Divergent roles for the gut intraepithelial lymphocyte GLP-1R in control of metabolism, microbiota, and T cell-induced inflammation

Gut intraepithelial lymphocytes (IELs) are thought to calibrate glucagon-like peptide 1 (GLP-1) bioavailability, thereby regulating systemic glucose and lipid metabolism. Here, we show that the gut IEL GLP-1 receptor (GLP-1R) is not required for enteroendocrine L cell GLP-1 secretion and glucose homeostasis nor for the metabolic benefits of GLP-1R agonists (GLP-1RAs). Instead, the gut IEL GLP-1R is essential for the full effects of GLP-1RAs on gut microbiota. Moreover, independent of glucose control or weight loss, the anti-inflammatory actions of GLP-1RAs require the gut IEL GLP-1R to selectively restrain local and systemic T cell-induced, but not lipopolysaccharide-induced, inflammation. Such effects are mediated by the suppression of gut IEL effector functions linked to the dampening of proximal T cell receptor signaling in a protein-kinase-A-dependent manner. These data reposition key roles of the L cell-gut IEL GLP-1R axis, revealing mechanisms linking GLP-1R activation in gut IELs to modulation of microbiota composition and control of intestinal and systemic inflammation.

Ae1/Sbe1 maize-derived high amylose improves gut barrier function and ameliorates type II diabetes in high-fat diet-fed mice by increasing Akkermansia

Type II diabetes mellitus (T2DM) has its origins in chronic inflammation due to immune dysregulation. Improving chronic inflammation can significantly reduce the probability of T2DM and the rate of disease progression. Resistance to starch 2 (RSII) high-amylose maize starch (HAMS) has been widely implicated in the improvement and regulation of T2DM. However, its exact molecular mechanisms have not been fully discovered. Here, we used CRISPR/Cas9 technology to knock out two starch-branching enzyme genes, Ae1 and Sbe1, in maize to obtain mutants containing higher levels of HAMS. In experiments in which HAMS was fed to mice on a high-fat diet (HFD), we confirmed the function of HAMS in ameliorating hyperglycemia. Mechanistically, we found that HAMS improves the gut barrier function by increasing the Akkermansia abundance in the gut. This increase led to the alleviation of chronic inflammation in mice on a HFD, resulting in improved insulin sensitivity and a decrease in blood glucose.

Gut Bacteria and Neurotransmitters

Gut bacteria play an important role in the digestion of food, immune activation, and regulation of entero-endocrine signaling pathways, but also communicate with the central nervous system (CNS) through the production of specific metabolic compounds, e.g., bile acids, short-chain fatty acids (SCFAs), glutamate (Glu), γ-aminobutyric acid (GABA), dopamine (DA), norepinephrine (NE), serotonin (5-HT) and histamine. Afferent vagus nerve (VN) fibers that transport signals from the gastro-intestinal tract (GIT) and gut microbiota to the brain are also linked to receptors in the esophagus, liver, and pancreas. In response to these stimuli, the brain sends signals back to entero-epithelial cells via efferent VN fibers. Fibers of the VN are not in direct contact with the gut wall or intestinal microbiota. Instead, signals reach the gut microbiota via 100 to 500 million neurons from the enteric nervous system (ENS) in the submucosa and myenteric plexus of the gut wall. The modulation, development, and renewal of ENS neurons are controlled by gut microbiota, especially those with the ability to produce and metabolize hormones. Signals generated by the hypothalamus reach the pituitary and adrenal glands and communicate with entero-epithelial cells via the hypothalamic pituitary adrenal axis (HPA). SCFAs produced by gut bacteria adhere to free fatty acid receptors (FFARs) on the surface of intestinal epithelial cells (IECs) and interact with neurons or enter the circulatory system. Gut bacteria alter the synthesis and degradation of neurotransmitters. This review focuses on the effect that gut bacteria have on the production of neurotransmitters and vice versa.

Crosstalk between incretin hormones, Th17 and Treg cells in inflammatory diseases

Intestinal epithelial cells constantly crosstalk with the gut microbiota and immune cells of the gut lamina propria. Enteroendocrine cells, secrete hormones, such as incretin hormones, which participate in host physiological events, such as stimulating insulin secretion, satiety, and glucose homeostasis. Interestingly, evidence suggests that the incretin pathway may influence immune cell activation. Consequently, drugs targeting the incretin hormone signaling pathway may ameliorate inflammatory diseases such as inflammatory bowel diseases, cancer, and autoimmune diseases. In this review, we discuss how these hormones may modulate two subsets of CD4 + T cells, the regulatory T cells (Treg)/Th17 axis important for gut homeostasis: thus, preventing the development and progression of inflammatory diseases. We also summarize the main experimental and clinical findings using drugs targeting the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (GLP-1) signaling pathways and their great impact on conditions in which the Treg/Th17 axis is disturbed such as inflammatory diseases and cancer. Understanding the role of incretin stimulation in immune cell activation and function, might contribute to new therapeutic designs for the treatment of inflammatory diseases, autoimmunity, and tumors.

Prolonged lipopolysaccharide-induced illness elevates glucagon-like peptide-1 and suppresses peptide YY: A human-randomized cross-over trial

Severe systemic inflammation is associated with nausea, loss of appetite, and delayed gastric emptying, which increases hospitalization admission length and mortality rate. There is a lack of human controlled studies exploring gastric emptying rates and underlying mechanisms during inflammatory conditions. We aimed to investigate if systemic inflammation in young men delays gastro-intestinal transit times, lowers motility, and affects gastrointestinal hormone secretion. This substudy of a randomized crossover trial investigated eight healthy young men on two separate occasions; (I) following an overnight fast (healthy conditions/HC) and (II) fasting and bedrest combined with two lipopolysaccharide (LPS) injections of 1 ng kg-1 following an overnight fast and 0.5 ng kg-1 following another 24 h (systemic inflammation/SI). A standardized protein beverage and a SmartPill capsule (a wireless gastrointestinal monitoring system) were swallowed during each occasion. Whole gut transit time was comparable between HC and SI. SI decreased gastric mean pressure peak amplitude (p = 0.04) and increased pH rise across the pylorus and small bowel pH (p = 0.02) compared with HC. Glucagon-like peptide-1 was elevated during SI compared with HC (p = 0.04). Peptide YY was lower during SI compared with HC (p = 0.007). Prolonged LPS exposure combined with fasting and bedrest elevated glucagon-like peptide 1 concentrations, which may play a role for the nausea and loss of appetite typically associated with SI.