Bacterial metabolite indole modulates incretin secretion from intestinal enteroendocrine L cells

Gut microbiota and associated metabolites: key players in high-fat diet-induced chronic diseases

Excessive intake of dietary fats is strongly associated with an increased risk of various chronic diseases, such as obesity, diabetes, hepatic metabolic disorders, cardiovascular disease, chronic intestinal inflammation, and certain cancers. A significant portion of the adverse effects of high-fat diet on disease risk is mediated through modifications in the gut microbiota. Specifically, high-fat diets are linked to reduced microbial diversity, an overgrowth of gram-negative bacteria, an elevated Firmicutes-to-Bacteroidetes ratio, and alterations at various taxonomic levels. These microbial alterations influence the intestinal metabolism of small molecules, which subsequently increases intestinal permeability, exacerbates inflammatory responses, disrupts metabolic functions, and impairs signal transduction pathways in the host. Consequently, diet-induced changes in the gut microbiota play a crucial role in the initiation and progression of chronic diseases. This review explores the relationship between high-fat diets and gut microbiota, highlighting their roles and underlying mechanisms in the development of chronic metabolic diseases. Additionally, we propose probiotic interventions may serve as a promising adjunctive therapy to counteract the negative effects of high-fat diet-induced alterations in gut microbiota composition.

Microbial metabolites as engines of behavioral variation across animals

The microbiome, especially that present in the gut, has emerged as a key modulator of animal behavior. However, the extent of its influence across species and behavioral repertoires, as well as the underlying mechanisms, remains poorly understood. Increasing evidence suggests that microbial metabolites play an important role in driving behavioral variation. In this review, we synthesize findings from vertebrates to invertebrates, spanning both model and non-model organisms, to define key groups of microbial-derived metabolites involved in modulating seven distinct behaviors: nutrition, olfaction, circadian rhythms, reproduction, locomotion, aggression, and social interactions. We discuss how these microbial metabolites interact with host chemosensory systems, neurotransmitter signaling, and epigenetic modifications to shape behavior. Additionally, we highlight critical gaps in mechanistic understanding, including the need to map additional host receptors and signaling pathways, as well as the untapped potential of microbial biosynthetic gene clusters as sources for novel bioactive compounds. Advancing these areas will enhance understanding of the microbiome's role in behavioral modulation and open new avenues for microbiome-based interventions for behavioral disorders.

Time-restricted feeding promotes glucagon-like peptide-1 secretion and regulates appetite via tryptophan metabolism of gut Lactobacillus in pigs

Previous clinical trials have shown that time-restricted feeding can be involved in regulating the metabolic health of humans and animals. However, the underlying mechanism has not been fully explored. In this study, the pig model was employed to simulate four prevalent human eating habits, with the aim of investigating the impact of gut microbiota and microbial metabolites on gut hormone secretion and appetite regulation. Compared to the ad libitum feeding (ALF) pattern, three time-restricted feeding patterns reduced total food intake and eating time. Meanwhile, three time-restricted feeding patterns induced elevated levels of serum and hypothalamic glucagon-like peptide-1 (GLP-1), while suppressing reward-related circuits in the hypothalamus. It is noteworthy that the early time-restricted feeding (eTRF) pattern increased the number of intestinal enteroendocrine cells (EECs) compared to ALF. Metagenomic and metabonomic analyses revealed that three time-restricted feeding patterns induced colonization of Lactobacillus and significantly increased the levels of its metabolite, indole-3-lactic acid (ILA). Dietary supplementation with ILA exhibited an increasing trend in fasting serum GLP-1 level of piglets. In vitro studies with pig intestinal organoids showed the Lactobacillus metabolite ILA enhanced GLP-1 secretion through the promotion of intestinal stem cell differentiation into EECs, rather than activating the ability of EECs to secrete GLP-1. Overall, time-restricted feeding promoted GLP-1 secretion and affected long-term appetite regulation by promoting the colonization of Lactobacillus and modulating microbial tryptophan metabolism.

Microbiota-neuroepithelial signalling across the gut-brain axis

Research over the past two decades has established a remarkable ability of the gut microbiota to modulate brain activity and behaviour. Conversely, signals from the brain can influence the composition and function of the gut microbiota. This bidirectional communication across the gut microbiota-brain axis, involving multiple biochemical and cellular mediators, is recognized as a major brain-body network that integrates cues from the environment and the body's internal state. Central to this network is the gut sensory system, formed by intimate connections between chemosensory epithelial cells and sensory nerve fibres, that conveys interoceptive signals to the central nervous system. In this Review, we provide a broad overview of the pathways that connect the gut and the brain, and explore the complex dialogue between microorganisms and neurons at this emerging intestinal neuroepithelial interface. We highlight relevant microbial factors, endocrine cells and neural mechanisms that govern gut microbiota-brain interactions and their implications for gastrointestinal and neuropsychiatric health.

Theabrownin Alleviates Type 2 Diabetes Mellitus in db/db Mice via Modulating LPS/GLP-1 Levels and Restoring Islet Cells: Evidence from Gut-Pancreas Axis

Theabrownin has demonstrated metabolic-modulating effects, but the doses used in previous studies are difficult to achieve through regular tea consumption. This study reassesses its hypoglycemic effects at physiologically relevant doses in the db/db mouse model of type 2 diabetes mellitus (T2DM), with a focus on intestinal microbiota and metabolic pathways. The findings show that theabrownin delays glucose absorption by inhibiting α-glucosidase in the duodenum. It also reduces lipopolysaccharide (LPS)-producing bacteria, increases Akkermansia muciniphila abundance, lowers serum LPS levels, and alleviates β-cell dysfunction due to oxidative stress. Additionally, theabrownin promotes the microbial indole pathway of tryptophan metabolism, enhancing glucagon-like peptide-1 (GLP-1) secretion, which helps mitigate β-cell dysfunction. In conclusion, theabrownin shows potential as a dietary supplement for T2DM treatment, primarily regulating LPS/GLP-1 levels and restoring pancreatic islet function. These findings highlight the potential role of fermented tea in glucose metabolism regulation.

Molecular mechanisms of stimulus detection and secretion in enteroendocrine cells

Enteroendocrine cells (EECs) secrete over 20 different gut hormones in response to changes to the gut environment. They detect a range of nutritional stimuli through activation of a host of nutrient-sensing G-protein-coupled receptors and electrogenic nutrient cotransport. These activate intracellular signalling pathways which converge on membrane depolarisation and action potential generation, which elicit secretion. Emerging evidence has demonstrated that EECs also respond to non-nutritional stimuli, including mechanosensation, pH changes, and metabolites produced by the gut microbiome. EECs are polyhormonal cells, in which hormone expression is plastic and dependent on location in the gut. Hormones and small-molecule neurotransmitters secreted by EECs can activate extrinsic vagal afferents, modulating central processes such as appetite and food preference. While neuronal afferents are sometimes found in close proximity to EECs, the extent to which EEC/neuronal connections recapitulate traditional synaptic connections remains undefined.

Gut microbiota and the tryptophan-kynurenine pathway in anxiety: new insights and treatment strategies

Anxiety disorders are mental health disorders characterized by long-lasting fear, worry, nervousness, and alterations in gut microbiota (GM). The GM is a vital modulator of brain function through the gut-brain axis, which acts as the neural pathway between the central and peripheral nervous systems. Dysbiosis of GM plays an essential role in anxiety development because of alterations in the vagus nerve, increased intestinal permeability, and altered breakdown of tryptophan (TRP). The Kynurenine (KYN) pathway plays a crucial role in the pathogenesis of anxiety disorders, primarily through its neuroprotective (KYNA) and neurotoxic (QUIN) metabolites. Higher ratios of KYNA/QUIN result in neuroprotection, whereas higher KYN/TRP ratios indicate increased QUIN production causing neuroinflammation. Studies on germ-free models exhibit higher plasma TRP levels, which interrupt the metabolic balance of TRP-derived compounds, thus causing brain impairment. A key issue in anxiety disorders is the dysregulation of GM, which disrupts TRP metabolism and neuroinflammatory pathways, however, remains poorly understood. Hence, the proper understanding of these mechanisms is crucial for future therapeutic advancements. Here, we highlight the significance of the TRP-KYN pathway and the potential of modulating KYN pathway enzymes, such as kynurenine aminotransferases (KATs), to adjust KYNA levels and restore neurotransmitter balance. It further discusses new therapeutic methods with a particular focus on probiotics that may restore GM and modulate TRP metabolism. Advancing our understanding of the intricate relationship between GM and anxiety disorders may facilitate novel, microbiota-targeted interventions. This ultimately contributes to precision medicine approaches in mental health care, thereby enhancing treatment efficacy and patient outcomes.

Tryptophan Indole Derivatives: Key Players in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a complex clinical syndrome characterized by insulin resistance and associated with abnormal amino acid metabolism. Tryptophan is an aromatic dietary amino acid that affects T2DM by regulating glycolipid metabolism and insulin resistance. When tryptophan reaches the intestine, it is converted by gut microbiota and tryptophanase into indole derivatives such as indoleacetic acid, indolepropionic acid, and indolealdehyde. These indole derivatives may enhance insulin sensitivity, stimulate insulin secretion, and exert functions such as lowering blood glucose, regulating hepatic oxidative stress, reducing intestinal inflammation, and improving islet cell morphology by acting on the aryl hydrocarbon receptor (AHR) or Pregnane X receptor (PXR). In summary, this review aims to examine the interactions between tryptophan indole derivatives and T2DM thoroughly, elucidate potential therapeutic approaches, and pinpoint areas for further research.

A multi-omics study of the association between insomnia with objective short sleep duration phenotype and high blood pressure

STUDY OBJECTIVES

Insomnia with objective short sleep duration is associated with increased hypertension risk. We aimed to explore the mechanism underlying the association between objective short sleep duration and hypertension in patients with chronic insomnia disorder (CID) by multi-omics.

METHODS

CID was defined according to International Classification of Sleep Disorders-3, and objective short sleep duration was based on the median value of total sleep time of the overall subjects during an overnight polysomnography. We used the mean values of measured nighttime and morning systolic (SBP) and diastolic blood pressure (DBP) for analysis. Serum metabolomics and fecal 16S rDNA amplicon sequencing were used to explore characteristic metabolites and analyze gut microbiota distribution, respectively.

RESULTS

One hundred and three patients with CID and 70 normal sleepers were included. We found 52 objective short sleep duration insomnia phenotype (ISSD)-related serum metabolites. Among the 52 ISSD-related serum metabolites, indoxyl sulfate was positively correlated with BP after adjusting for confounding factors (SBP: β = 0.250, p = .028; DBP: β = 0.256, p = .030) in ISSD. In addition, the level of serum indoxyl sulfate was significantly correlated with the genera Prevotella 9 (r = .378, p = .027), CAG-56 (r = -.359, p = .037), Ruminiclostridium 9 (r = -.340, p = .049), and Ruminococcus 2 (r = -.356, p = .039) in ISSD.

CONCLUSIONS

Our study suggests that the ISSD phenotype is associated with significant changes in serum metabolic profile, including high levels of indoxyl sulfate. The latter molecule correlates both with BP and gut microbiota in patients with the ISSD phenotype, suggesting that indoxyl sulfate may be the molecular path resulting in increased hypertension risk in this phenotype.

The Obesity-Epigenetics-Microbiome Axis: Strategies for Therapeutic Intervention

Obesity (OB) has become a serious health issue owing to its ever-increasing prevalence over the past few decades due to its contribution to severe metabolic and inflammatory disorders such as cardiovascular disease, type 2 diabetes, and cancer. The unbalanced energy metabolism in OB is associated with substantial epigenetic changes mediated by the gut microbiome (GM) structure and composition alterations. Remarkably, experimental evidence also indicates that OB-induced epigenetic modifications in adipocytes can lead to cellular "memory" alterations, predisposing individuals to weight regain after caloric restriction and subsequently inducing inflammatory pathways in the liver. Various environmental factors, especially diet, play key roles in the progression or prevention of OB and OB-related disorders by modulating the GM structure and composition and affecting epigenetic mechanisms. Here, we will first focus on the key role of epigenetic aberrations in the development of OB. Then, we discuss the association between abnormal alterations in the composition of the microbiome and OB and the interplays between the microbiome and the epigenome in the development of OB. Finally, we review promising strategies, including prebiotics, probiotics, a methyl-rich diet, polyphenols, and herbal foods for the prevention and/or treatment of OB via modulating the GM and their metabolites influencing the epigenome.

IUPHAR Review: Microbiota-Gut-Brain Axis and its role in Neuropsychiatric Disorders

The human gut microbiome, composed of a vast array of microorganisms that have co-evolved with humans, is crucial for the development and function of brain systems. Research has consistently shown bidirectional communication between the gut and the brain through neuronal, endocrine, and immunological, and chemical pathways. Recent neuroscience studies have linked changes in the microbiome and microbial metabolites to various neuropsychiatric disorders such as autism, depression, anxiety, schizophrenia, eating disorders, and neurocognitive disorders. Novel metagenome-wide association studies have confirmed these microbiome variations in large samples and expanded our understanding of the interactions between human genes and the gut microbiome. The causal relationship between gut microbiota and neuropsychiatric disorders is being elucidated through the establishment of large cohort studies incorporating microbiome data and advanced statistical techniques. Ongoing animal and human studies focused on the microbiota-gut-brain axis are promising for developing new prevention and treatment strategies for neuropsychiatric conditions. The scope of these studies has broadened from microbiome-modulating therapies including prebiotics, probiotics, synbiotics and postbiotics to more extensive approaches such as fecal microbiota transplantation. Recent systematic reviews and meta-analyses have strengthened the evidence base for these innovative treatments. Despite extensive research over the past decade, many intriguing aspects still need to be elucidated regarding the role and therapeutic interventions of the microbiota-gut-brain axis in neuropsychiatric disorders.

Endogenous Metabolites in Metabolic Diseases: Pathophysiologic Roles and Therapeutic Implications

Breakthroughs in metabolomics technology have revealed the direct regulatory role of metabolites in physiology and disease. Recent data have highlighted the bioactive metabolites involved in the etiology and prevention and treatment of metabolic diseases such as obesity, nonalcoholic fatty liver disease, type 2 diabetes mellitus, and atherosclerosis. Numerous studies reveal that endogenous metabolites biosynthesized by host organisms or gut microflora regulate metabolic responses and disorders. Lipids, amino acids, and bile acids, as endogenous metabolic modulators, regulate energy metabolism, insulin sensitivity, and immune response through multiple pathways, such as insulin signaling cascade, chemical modifications, and metabolite-macromolecule interactions. Furthermore, the gut microbial metabolites short-chain fatty acids, as signaling regulators have a variety of beneficial impacts in regulating energy metabolic homeostasis. In this review, we will summarize information about the roles of bioactive metabolites in the pathogenesis of many metabolic diseases. Furthermore, we discuss the potential value of metabolites in the promising preventive and therapeutic perspectives of human metabolic diseases.

Gut microbiome research: Revealing the pathological mechanisms and treatment strategies of type 2 diabetes

The high prevalence and disability rate of type 2 diabetes (T2D) caused a huge social burden to the world. Currently, new mechanisms and therapeutic approaches that may affect this disease are being sought. With in-depth research on the pathogenesis of T2D and growing advances in microbiome sequencing technology, the association between T2D and gut microbiota has been confirmed. The gut microbiota participates in the regulation of inflammation, intestinal permeability, short-chain fatty acid metabolism, branched-chain amino acid metabolism and bile acid metabolism, thereby affecting host glucose and lipid metabolism. Interventions focusing on the gut microbiota are gaining traction as a promising approach to T2D management. For example, dietary intervention, prebiotics and probiotics, faecal microbiota transplant and phage therapy. Meticulous experimental design and choice of analytical methods are crucial for obtaining accurate and meaningful results from microbiome studies. How to design gut microbiome research in T2D and choose different machine learning methods for data analysis are extremely critical to achieve personalized precision medicine.

Microbial dipeptidyl peptidases of the S9B family as host-microbe isozymes

Human dipeptidyl peptidase 4 (hDPP-4) has been a pharmacological target for metabolic diseases, particularly diabetes, since the early 2000s. As a ubiquitous enzyme found in both prokaryotic and eukaryotic organisms, hDPP-4 plays crucial roles in host homeostasis and disease progression. While many studies have explored hDPP-4's properties, research on gut microbially derived DPP-4 (mDPP-4) remains limited. This review discusses the significance of mDPP-4 and its health implications, analyzing crystal structures of mDPP-4 in comparison to human counterparts. We examine how hDPP-4 inhibitors could influence gut microbiome composition and mDPP-4 activity. Additionally, this review connects ongoing discussions regarding DPP-4 substrate specificity and potential access routes for mDPP-4, emphasizing the urgent need for further research on mDPP-4's role in health and improve the precision of DPP-4 inhibitor therapies.

High-Coverage Metabolomics Reveals Gut Microbiota-Related Metabolic Traits of Type-2 Diabetes in Serum

Metabolic perturbations of the gut microbiome have been implicated in the pathogenesis of multiple human diseases, including type-2 diabetes (T2D). However, our understanding of the global metabolic alterations of the gut microbiota in T2D and their functional roles remains limited. To address this, we conducted a high-coverage metabolomics profiling analysis of serum samples from 1282 Chinese individuals with and without T2D. Among the 220 detected microbiota-associated compounds detected, 111 were significantly altered, forming a highly interactive regulatory network associated with T2D development. Pathway enrichment and correlation analyses revealed aberrant metabolic pathways, primarily including the activation of pyrimidine metabolism, unsaturated fatty acid biosynthesis, and diverse amino acid metabolisms such as Tryptophan metabolism, Lysine metabolism, and Branched-chain amino acid biosynthesis. A microbiota-dependent biomarker panel, comprising pipecolinic acid, methoxysalicylic acid, N-acetylhistamine, and 3-hydroxybutyrylcarnitine, was defined and validated with satisfactory sensitivity (>78%) for large-scale, population-based T2D screening. The functional role of a gut microbial product, N-acetylhistamine, was further elucidated in T2D progression through its inhibition of adenosine monophosphate-activated protein kinase phosphorylation. Overall, this study expands our understanding of gut microbiota-driven metabolic dysregulation in T2D and suggests that monitoring these metabolic changes could facilitate the diagnosis and treatment of T2D.

Gut microbiota regulates gut homeostasis, mucosal immunity and influences immune-related diseases

The intestinal microbiome constitutes a sophisticated and massive ecosystem pivotal for maintaining gastrointestinal equilibrium and mucosal immunity via diverse pathways. The gut microbiota is continuously reshaped by multiple environmental factors, thereby influencing overall wellbeing or predisposing individuals to disease state. Many observations reveal an altered microbiome composition in individuals with autoimmune conditions, coupled with shifts in metabolic profiles, which has spurred ongoing development of therapeutic interventions targeting the microbiome. This review delineates the microbial consortia of the intestine, their role in sustaining gastrointestinal stability, the association between the microbiome and immune-mediated pathologies, and therapeutic modalities focused on microbiome modulation. We emphasize the entire role of the intestinal microbiome in human health and recommend microbiome modulation as a viable strategy for disease prophylaxis and management. However, the application of gut microbiota modification for the treatment of immune-related diseases, such as fecal microbiota transplantation and probiotics, remain quite challenging. Therefore, more research is needed into the role and mechanisms of these therapeutics.

Limosilactobacillus reuteri promotes the expression and secretion of enteroendocrine- and enterocyte-derived hormones

Intestinal microbes can beneficially impact host physiology, prompting investigations into the therapeutic usage of such microbes in a range of diseases. For example, human intestinal microbe Limosilactobacillus reuteri strains ATCC PTA 6475 and DSM 17938 are being considered for use for intestinal ailments, including colic, infection, and inflammation, as well as for non-intestinal ailments, including osteoporosis, wound healing, and autism spectrum disorder. While many of their beneficial properties are attributed to suppressing inflammatory responses, we postulated that L. reuteri may also regulate intestinal hormones to affect physiology within and outside of the gut. To determine if L. reuteri secreted factors impact the secretion of enteric hormones, we treated an engineered jejunal organoid line, NGN3-HIO, which can be induced to be enriched in enteroendocrine cells, with L. reuteri 6475 or 17938 conditioned medium and performed transcriptomics. Our data suggest that these L. reuteri strains affect the transcription of many gut hormones, including vasopressin and luteinizing hormone subunit beta, which have not been previously recognized as produced in the gut epithelium. Moreover, we find that these hormones appear to be produced in enterocytes, in contrast to canonical gut hormones produced in enteroendocrine cells. Finally, we show that L. reuteri conditioned media promote the secretion of enteric hormones, including serotonin, GIP, PYY, vasopressin, and luteinizing hormone subunit beta, and identify by metabolomics metabolites potentially mediating these effects on hormones. These results support L. reuteri affecting host physiology through intestinal hormone secretion, thereby expanding our understanding of the mechanistic actions of this microbe.

Sugar-sweetened beverage intake, gut microbiota, circulating metabolites, and diabetes risk in Hispanic Community Health Study/Study of Latinos

No population-based studies examined gut microbiota and related metabolites associated with sugar-sweetened beverage (SSB) intake among US adults. In this cohort of US Hispanic/Latino adults, higher SSB intake was associated with nine gut bacterial species, including lower abundances of several short-chain-fatty-acid producers, previously shown to be altered by fructose and glucose in animal studies, and higher abundances of fructose- and glucose-utilizing Clostridium bolteae and Anaerostipes caccae. Fifty-six serum metabolites were correlated with SSB intake and a gut microbiota score based on these SSB-related species in consistent directions. These metabolites were clustered into several modules, including a glycerophospholipid module, two modules comprising branched-chain amino acid (BCAA) and aromatic amino acid (AAA) derivatives from microbial metabolism, etc. Higher glycerophospholipid and BCAA derivative levels and lower AAA derivative levels were associated with higher incident diabetes risk during follow-up. These findings suggest a potential role of gut microbiota in the association between SSB intake and diabetes.

Skin Microbiome Dynamics in Atopic Dermatitis: Understanding Host-Microbiome Interactions

Atopic dermatitis (AD) is a chronic inflammatory skin disorder affecting both children and adults, characterized by pruritus, eczematous lesions, and compromised skin barrier function. A key feature of AD is dysbiosis of the skin microbiome, marked by reduced microbial diversity and the overgrowth of Staphylococcus aureus in lesional skin. S. aureus exacerbates skin barrier dysfunction and immune dysregulation, leading to recurrent infections and disease flares. In contrast, commensal bacteria such as Staphylococcus epidermidis and Roseomonas mucosa may exert protective effects by inhibiting S. aureus colonization and modulating immune responses. Beyond microbial composition, microbial metabolites play a crucial role in AD pathophysiology. Short-chain fatty acids, indole derivatives, and other bacterial metabolites influence cutaneous immune responses, lipid metabolism, and skin barrier integrity. Altered metabolite profiles, including reduced levels of beneficial microbial metabolites, are associated with AD severity and disease progression. Notably, S. aureus overabundance correlates with disruption in lipid metabolism, further compromising the skin barrier. This review explores recent advances in understanding the relationship between microbial metabolites and AD pathogenesis and examines the therapeutic potential of microbiome-targeted interventions. Strategies such as probiotics, prebiotics, and topical microbiome transplantation aim to restore microbial diversity and rebalance metabolite production, ultimately improving clinical outcomes in AD patients. Future therapeutic approaches focusing on commensal-derived metabolites offer promising avenues for alleviating symptoms and modulating disease severity in AD.

Aryl hydrocarbon receptor (AHR) and nuclear factor erythroid-derived 2-like 2 (NRF2): An important crosstalk in the gut-liver axis

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, mainly involved in detoxification. However, in the intestine, metabolites derived from the diet, which are converted by a wide range of bacteria can also activate the AHR. This intestinal AHR activation plays a key role in maintaining the gut barrier by, for example, upregulating antimicrobial peptides and anti-inflammatory cytokines. Since the gut barrier influences the gut-liver axis by regulating the leaking of metabolites, bacteria, and endotoxins into circulation and particularly into the liver, the AHR is a key factor in the gut-liver axis. Vice versa, certain liver pathologies also influence the gut microbiome, thereby altering bacteria-derived activation of the AHR. Additionally, bile acids can impact the gut via the liver and thereby also affect the AHR. The aryl hydrocarbon receptor (AHR) interacts with several molecular factors, one of which is the nuclear factor erythroid-derived 2-like 2 (NRF2), a transcription factor primarily associated with regulating antioxidant stress responses. The interplay between AHR and NRF2 has been investigated in the context of various diseases; this review highlights the significance of this interaction within the framework of the gut-liver axis.

Influence of menstrual cycle and oral contraception on taxonomic composition and gas production in the gut microbiome

Introduction. Oral contraceptives (OCs) are widely used for birth control and offer benefits such as menstrual cycle regulation and reduced menstrual pain. However, they have also been associated with an increased risk of cancer and reduced bone mass density.Gap Statement. While the gut microbiome is known to interact with endocrine factors, the impact of hormonal OCs on its composition and function remains underexplored. Additionally, we explore the relationship of OC use and the microbiome to gas production, which can cause symptoms and be indicative of poor health.Aim. This study investigates the effects of OCs on the diversity and composition of the gut microbiome and its association with breath hydrogen (H2) and methane (CH4) levels.Methodology. We utilized 16S rRNA gene sequencing to analyse faecal samples from 65 women, comparing OC users with non-users at two menstrual cycle time points. Breath tests measured hydrogen and CH4 production. Data were analysed for microbial diversity, community composition and correlation with gas production.Results. There were no differences in overall microbial diversity between OC users and non-users in samples collected on day 2 of the menstrual cycle. However, on day 21, we found a significant difference in microbial richness, suggesting a cycle-dependent effect of OCs on gut microbiota species richness but not composition. We found a strong correlation between H2 and CH4 concentrations and an interaction between OC use and the menstrual cycle on H2 and CH4 production. We also identified several taxa associated with both high levels of H2 and CH4 production and OC use.Conclusion. Our study highlights the intricate relationships among hormonal contraceptives, the gut microbiota and gas production and connects shifts in the microbiome composition to gastrointestinal symptoms (e.g. gas production) that can impact overall health. This underscores the need for further research on the long-term effects of OCs and for the development of precise therapeutic strategies to address potential adverse effects. Our findings offer new perspectives on the microbiome-hormone-gas production nexus, potentially broadening our understanding of the systemic implications of OCs.

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 Microbiome Regulation of Gut Hormone Secretion

The gut microbiome, comprising bacteria, viruses, fungi, and bacteriophages, is one of the largest microbial ecosystems in the human body and plays a crucial role in various physiological processes. This review explores the interaction between the gut microbiome and enteroendocrine cells (EECs), specialized hormone-secreting cells within the intestinal epithelium. EECs, which constitute less than 1% of intestinal epithelial cells, are key regulators of gut-brain communication, energy metabolism, gut motility, and satiety. Recent evidence shows that gut microbiota directly influence EEC function, maturation, and hormone secretion. For instance, commensal bacteria regulate the production of hormones like glucagon-like peptide 1 and peptide YY by modulating gene expression and vesicle cycling in EE cells. Additionally, metabolites such as short-chain fatty acids, derived from microbial fermentation, play a central role in regulating EEC signaling pathways that affect metabolism, gut motility, and immune responses. Furthermore, the interplay between gut microbiota, EECs, and metabolic diseases, such as obesity and diabetes, is examined, emphasizing the microbiome's dual role in promoting health and contributing to disease states. This intricate relationship between the gut microbiome and EECs offers new insights into potential therapeutic strategies for metabolic and gut disorders.

Select microbial metabolites in the small intestinal lumen regulate vagal activity via receptor-mediated signaling

The vagus nerve is proposed to enable communication between the gut microbiome and the brain, but activity-based evidence is lacking. We find that mice reared germ-free exhibit decreased vagal tone relative to colonized controls, which is reversed via microbiota restoration. Perfusing antibiotics into the small intestines of conventional mice, but not germ-free mice, acutely decreases vagal activity which is restored upon re-perfusion with intestinal filtrates from conventional, but not germ-free, mice. Microbiome-dependent short-chain fatty acids, bile acids, and 3-indoxyl sulfate indirectly stimulate vagal activity in a receptor-dependent manner. Serial perfusion of each metabolite class activates both shared and distinct neuronal subsets with varied response kinetics. Metabolite-induced and receptor-dependent increases in vagal activity correspond with the activation of brainstem neurons. Results from this study reveal that the gut microbiome regulates select metabolites in the intestinal lumen that differentially activate vagal afferent neurons, thereby enabling the microbial modulation of chemosensory signals for gut-brain communication.

Oral Transfer of Anti-Aging Substances: Key Chemical Found in Reproductive Caste of Termites

With the rapid increase in global population aging, the incidence and mortality rates of age-related diseases are rising, becoming a worldwide issue. Therefore, researching and discovering natural compounds with anti-aging properties is crucial. Social insects such as termites exhibit significant differences in lifespan between reproductive and non-reproductive castes. Reproductive castes are exclusively fed by worker termites through trophallaxis, providing a convenient model for the discovery of natural anti-aging compounds. This thesis systematically investigates the trophallactic fluid among different caste members of termite Reticulitermes labralis. A total of 1028 metabolites were identified in the trophallactic fluid, seven of which have been validated in the KEGG database to possess anti-aging functions. This indicates that the trophallactic fluid of termites indeed contains natural compounds that promote longevity. Using the "fishing method", we successfully screened out potential life-extending compounds, including IDA (trans-3-indoleacrylic acid). Preliminary experimental results showed that IDA influences lifespan by modulating the IIS (insulin/insulin-like growth factor signaling) pathway and the RAS pathway. Notably, the modulation of the IIS pathway by IDA does not require the involvement of foxoa. Our research findings suggest that the extended lifespan of reproductive termites is diet-related and that the lifespan-extending effects of these nutritionally regulated natural compounds are conserved across different taxa.

Mechanisms and Therapeutic Potential of Key Anti-inflammatory Metabiotics: Trans-Vaccenic Acid, Indole-3-Lactic Acid, Thiamine, and Butyric Acid

Identifying metabolites produced by probiotic bacteria, also known as metabiotics, is becoming increasingly common due to their anti-inflammatory, anti-obesogenic, and immunomodulatory effects. Postbiotics alongside diet, regulate both physical and mental health, as the microbiota members can interact physically with host cells or through secretion of nutrients and metabiotics. These metabiotics also reduce the severity of certain metabolic disorders and support the proper functioning of various organs and systems. In this review, we describe the mechanisms of action of trans-vaccenic acid (TVA), indole-3-lactic acid (ILA), thiamine (vitamin B1), and butyric acid metabolites produced or induced by probiotics such as Lactobacillus and/or Bifidobacterium, among others and previously identified using analytical techniques such as mass spectrometry (LC-MS). Within their mechanisms of action, Trans-vaccenic acid exerts anti-inflammatory effects and helps alleviate complications associated with metabolic diseases. Indole metabolites promote IL-22 production and regulate epithelial cell proliferation and antimicrobial peptide production. Thiamin is essential for energy metabolism regulation, and butyric acid regulates the brain-gut axis and also regulates immune response. This review expands our understanding of the potential therapeutic use of metabiotics.

Electroacupuncture alleviates functional constipation by upregulating host-derived miR-205-5p to modulate gut microbiota and tryptophan metabolism

Electroacupuncture (EA) has shown promise as a treatment for Functional constipation (FC), with growing evidence suggesting it may enhance gut motility. MicroRNAs (miRNAs) serve as key regulatory molecules mediating host-microbiota interactions. However, the specific fecal miRNAs regulating microbiota composition and metabolism in EA-treated constipated mice, along with their key targets, remain unidentified. We examined fecal microbiome composition, metabolism, and colonic miRNA expression in loperamide-induced constipated mice and EA-treated mice to identify differentially expressed miRNAs and assess their relationships with microbial abundance, metabolism, and gut motility. An antibiotic cocktail and adeno-associated virus were employed to interfere with the gut microbiota and target miRNA in vivo, thereby validating the proposed mechanism. Our results indicate that miR-205-5p, significantly upregulated in fecal and colonic tissues of EA-treated constipated mice, promotes intestinal motility in a microbiome-dependent manner. Specifically, EA promoted the growth of Lactobacillus reuteri, enriched in the feces of constipation-recovered mice, through host-derived miR-205-5p regulation. Furthermore, Lactobacillus reuteri and its tryptophan metabolites (indole-3-acetamide, indole-3-acetic acid, and indole-3-carboxaldehyde) alleviated loperamide-induced constipation. These findings underscore the pivotal role of host-derived miR-205-5p in modulating microbial composition and tryptophan metabolites to enhance intestinal motility through EA.

Gut Bacteria-Derived Tryptamine Ameliorates Diet-Induced Obesity and Insulin Resistance in Mice

Tryptophan is an essential amino acid that is metabolized in the intestine by gut bacteria into indole derivatives, including tryptamine. However, little is known about which bacterial tryptophan metabolites directly influence obesity. In this study, we identified tryptamine as a bacterial metabolite that significantly reduced fat mass following the intraperitoneal injection of five bacterial tryptophan end-products in a diet-induced obese mouse model. Interestingly, tryptamine, a serotonin analog, inhibited both lipogenesis and lipolysis in adipose tissue, which was further confirmed in a 3T3-L1 adipocyte cell culture study. Moreover, oral tryptamine supplementation markedly reduced fat mass and improved insulin sensitivity in a long-term, high-fat-diet, pair-feeding model. These studies demonstrate the therapeutic potential of tryptamine, a bacterial tryptophan metabolite, in ameliorating obesity and insulin resistance by directly regulating lipogenesis and lipolysis in white adipose tissue.

Naturopathic Management to Taper Off Glucagon-Like Peptide-1 Receptor Agonist Therapy in Type 2 Diabetes: A Case Report

This case report presents a 46-year-old woman with type 2 diabetes mellitus (T2DM) who sought to discontinue glucagon-like peptide-1 (GLP-1) receptor agonists (RAs) therapy while maintaining her weight and metabolic health. Her desire to reduce medication dependency, combined with her apprehension about potential metabolic regression following discontinuation of the drug, highlights a challenge often faced by patients managing chronic conditions, and the value of naturopathic adjunctive therapies to support these individuals in their wellness goals. This report details a comprehensive intervention strategy combining probiotics, nutrient supplementation, and lifestyle modifications to address her concerns. Over an 8-week period post-GLP-1 RAs therapy discontinuation, she maintained weight loss, improved glycemic control and lipid profile, demonstrated improvements in micronutrient levels, and experienced improvements in her quality of life. This case contributes to the growing body of evidence suggesting that targeted naturopathic interventions can play a supportive role in managing T2DM and mitigating the reliance on pharmacotherapy without compromising health outcomes.

Biomimetic nanoplatform with microbiome modulation and antioxidant functions ameliorating insulin resistance and pancreatic β-cell dysfunction for T2DM management

Insulin resistance and pancreatic β-cell dysfunction are the main pathogenesis of type 2 diabetes mellitus (T2DM). However, insulin therapy and diabetes medications do not effectively solve the two problems simultaneously. In this study, a biomimetic oral hydrogen nanogenerator that leverages the benefits of edible plant-derived exosomes and hydrogen therapy was constructed to overcome this dilemma by modulating gut microbiota and ameliorating oxidative stress and inflammatory responses. Hollow mesoporous silica (HMS) nanoparticles encapsulating ammonia borane (A) were used to overcome the inefficiency of H2 delivery in traditional hydrogen therapy, and exosomes originating from ginger (GE) were employed to enhance biocompatibility and regulate intestinal flora. Our study showed that HMS/A@GE not only considerably ameliorated insulin resistance and liver steatosis, but inhibited the dedifferentiation of islet β-cell and enhanced pancreatic β-cell proportion in T2DM model mice. In addition to its antioxidant and anti-inflammatory effects, HMS/A@GE augmented the abundance of Lactobacilli spp. and tryptophan metabolites, such as indole and indole acetic acid, which further activated the AhR/IL-22 pathway to improve intestinal-barrier function and metabolic impairments. This study offers a potentially viable strategy for addressing the current limitations of diabetes treatment by integrating gut-microbiota remodelling with antioxidant therapies.

Gut-X axis

Recent advances in understanding the modulatory functions of gut and gut microbiota on human diseases facilitated our focused attention on the contribution of the gut to the pathophysiological alterations of many extraintestinal organs, including the liver, heart, brain, lungs, kidneys, bone, skin, reproductive, and endocrine systems. In this review, we applied the "gut-X axis" concept to describe the linkages between the gut and other organs and discussed the latest findings related to the "gut-X axis," including the underlying modulatory mechanisms and potential clinical intervention strategies.

Hunger and the transition from parenteral nutrition in hospitalized adults: A descriptive cohort study

BACKGROUND

Parenteral nutrition (PN) provides nutrition to patients who cannot use the digestive tract. Some patients experience delayed appetite recovery after PN, but the factors contributing to this remain unclear. This study aimed to investigate whether hospitalized patients receiving PN experience reduced hunger or appetite.

METHODS

A descriptive cohort study was conducted on adults who underwent PN between April 2022 and July 2023. Data on patient characteristics and nutritional support were collected from medical records. Hunger and satiety were assessed using a validated tool during three phases: clinical stability with calorie-protein targets on PN, transition to oral/enteral feeding, and PN withdrawal. The primary outcome was the absence of hunger assessed by the tool.

RESULTS

Of 231 screened patients, 102 were included. Among these, 62.7% reported hunger during PN. Lipid doses and energy reduction strategies did not affect hunger or satiety. Transition success to oral/enteral nutrition was 2.38 times higher in patients who experienced hunger compared to those who did not (95% CI: 1.59-3.54). Poisson regression identified higher age, inflammation, and metastatic cancer as independent factors associated with the absence of hunger.

CONCLUSION

This study suggests that PN does not suppress hunger and that factors other than nutritional therapy (age, inflammation, and cancer) could explain the absence of appetite. Considering individual conditions and needs, these findings could guide decision-making strategies regarding the transition from PN to oral/enteral feeding.

Probiotics Supplementation for Improving Glucolipid Parameters in Individuals with Prediabetes: A Systematic Review and Meta-Analysis of Randomized Trials

The absence of suitable intervention significantly increases the likelihood of type 2 diabetes mellitus (T2DM) development in people with prediabetes. Recent statistical findings indicate that the gut microbiome might influences the development of insulin resistance. The objective of our study was to assess the efficacy and safety of probiotic supplementation in individuals diagnosed with prediabetes. A thorough search was carried out on the Cochrane Library, Medline, Scopus, and ClinicalTrials.gov databases until September 12th, 2024, using a mix of pertinent keywords. This review incorporates randomized clinical trials (RCTs) concerning the effect of probiotics for prediabetes. We used random-effect models to examine the mean difference (MD). A total of eight RCTs were incorporated. The results of our meta-analysis indicated that probiotics supplementation was associated with higher reduction in hemoglobin A1c (HbA1c) (MD -0.07% (95% CI -0.11, -0.03), p = 0.0005, I2 = 0%) among individuals with prediabetes when compared to placebo. Other indicators such as total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and body mass index (BMI) did not differ significantly between probiotics and placebo. No significant difference was observed in the occurrence of adverse events (AEs) between the two groups. This study indicates the efficacy and safety of probiotics supplementation to improve the glycemic parameters in patients with prediabetes.

Fam3a-mediated prohormone convertase switch in α-cells regulates pancreatic GLP-1 production in an Nr4a2-Foxa2-dependent manner

BACKGROUND

Fam3a has been demonstrated to regulate pancreatic β-cell function and glucose homeostasis. However, the role and mechanism of Fam3a in regulating α-cell function remain unexplored.

METHODS

Glucagon and glucagon-like peptide-1 (GLP-1) levels in pancreas and plasma were measured in global Fam3a knockout (Fam3a-/-) mice. Human islet single-cell RNA sequencing (scRNA-seq) datasets were utilized to analyze gene expression correlations between FAM3A and PCSK1 (encoding PC1/3, which processes proglucagon into GLP-1). Mouse pancreatic α-cell line αTC1.9 cells were transfected with Fam3a siRNA or plasmid for Fam3a knockdown or overexpression to explore the effects of Fam3a on PC1/3 expression and GLP-1 production. The downstream mediator (including Nr4a2) was identified by transcriptomic analysis, and its role was confirmed by Fam3a knockdown or overexpression in αTC1.9 cells. Based on the interacted protein of Nr4a2 and the direct binding to Pcsk1 promoter, the transcription factor Foxa2 was selected for further verification. Nuclear translocation assay and dual-luciferase reporter assay were used to clarify the involvement of Fam3a-Nr4a2-Foxa2 pathway in PC1/3 expression and GLP-1 production. Moreover, α-cell-specific Fam3a knockout (Fam3aα-/-) mice were constructed to evaluate the metabolic variables and hormone levels under normoglycemic, high-fat diet (HFD)-fed and streptozotocin (STZ)-induced diabetic conditions. Exendin 9-39 (Ex9), a GLP-1 receptor antagonist, was used to investigate GLP-1 paracrine effects in Fam3aα-/- mice and in their primary islets.

RESULTS

Compared with wild-type mice, pancreatic and plasma active GLP-1 levels were increased in Fam3a-/- mice. Analysis of human islet scRNA-seq datasets showed a significant negative correction between FAM3A and PCSK1 in α-cells. Fam3a knockdown upregulated PC1/3 expression and GLP-1 production in αTC1.9 cells, while Fam3a overexpression displayed inverse effects. Transcriptomic analysis identified Nr4a2 as a key downstream mediator of Fam3a, and Nr4a2 expression in αTC1.9 cells was downregulated and upregulated by Fam3a knockdown and overexpression, respectively. Nr4a2 silencing increased PC1/3 expression, albeit Nr4a2 did not directly bind to Pcsk1 promoter. Instead, Nr4a2 formed a complex with Foxa2 to facilitate Fam3a-mediated Foxa2 nuclear translocation. Foxa2 negatively regulated PC1/3 expression and GLP-1 production. Besides, Foxa2 inhibited the transcriptional activity of Pcsk1 promoter at specific binding sites 10 and 6, and this inhibition was intensified by Nr4a2 in αTC1.9 cells. Compared with Flox/cre littermates, improved glucose tolerance, increased active GLP-1 level in pancreas and plasma, upregulated plasma insulin level in response to glucose, and decreased plasma glucagon level were observed in Fam3aα-/- mice. Primary islets isolated from Fam3aα-/- mice also showed an increase in active GLP-1 and insulin release. In addition, the insulinotropic effect of intra-islet GLP-1 was blocked by Ex9 in Fam3aα-/- mice and in their primary islets. Similarly, HFD-fed Fam3aα-/- mice also exhibited an improved glucose tolerance. Both HFD-fed and STZ-induced diabetic Fam3aα-/- mice showed an increased pancreatic active GLP-1 level, an elevated plasma insulin level and a reduced plasma glucagon level.

CONCLUSIONS

Fam3a deficiency in α-cells enhances pancreatic GLP-1 production to improve β-cell function via paracrine signaling in an Nr4a2-Foxa2-PC1/3-dependent manner. Our study unveils a novel strategy for reprogramming α-cell proglucagon processing output from glucagon to GLP-1 and deepen the understanding of crosstalk between α-cells and β-cells.

The Beneficial Effects of GLP-1 Receptor Agonists Other than Their Anti-Diabetic and Anti-Obesity Properties

As an incretin hormone, Glucagon-like peptide-1 (GLP-1) has obvious effects on blood glucose regulation and weight loss. GLP-1 receptor (GLP-1R) agonists are synthetic products that have similar effects to GLP-1 but are less prone to degradation, and they are widely used in the treatment of type 2 diabetes and obesity. In recent years, different beneficial effects of GLP-1R agonists were discovered, such as reducing ischemia-reperfusion injury, improving the function of various organs, alleviating substance use disorder, affecting tumorigenesis, regulating bone metabolism, changing gut microbiota composition, and prolonging graft survival. Therefore, GLP-1R agonists have great potential for clinical application in various diseases. Here, we briefly summarized the beneficial effects of GLP-1R agonists other than the anti-diabetic and anti-obesity effects.

The pyrethroid insecticide deltamethrin disrupts neuropeptide and monoamine signaling pathways in the gastrointestinal tract

Enteroendocrine cells (EECs) are a rare cell type of the intestinal epithelium. Various subtypes of EECs produce distinct repertoires of monoamines and neuropeptides which modulate intestinal motility and other physiologies. EECs also possess neuron-like properties, suggesting a potential vulnerability to ingested environmental neurotoxicants. One such group of toxicants are pyrethroids, a class of prevalent insecticides used residentially and agriculturally. Pyrethroids agonize voltage-gated sodium channels (VGSCs), inducing neuronal excitotoxicity, and affect the function of monoamine-producing neurons. Given their anatomical location at the interface with the environment and their expression of VGSCs, EECs likely represent a vulnerable cell-type to oral pyrethroid exposure. In this study, we used the EEC cell line, STC-1 cells, to evaluate the effects of the common pyrethroid deltamethrin on the functional status of EECs. We find that deltamethrin impacts both expression of serotonergic pathways and inhibits the adrenergic-evoked release of an EEC hormone, GLP-1, in vitro. In a mouse model of oral exposure, we found that deltamethrin induced an acute, yet transient, loss of intestinal motility, in both fed and fasted conditions. This constipation phenotype was accompanied by a significant decrease in peripheral serotonin production and an inhibition of nutrient-evoked intestinal hormone release. Together, these data demonstrate that deltamethrin alters monoaminergic signaling pathways in EECs and regulates intestinal motility. This work demonstrates a mechanistic link between pyrethroid exposure and intestinal impacts relevant to pyrethroid-associated diseases, including inflammatory bowel disease, neurodegenerative disease, and metabolic disorders.

Exploring tryptophan metabolism in cardiometabolic diseases

Tryptophan (Trp) metabolism is linked to health and disease, with indoleamine 2,3-dioxygenase 1 (IDO) being a key enzyme in its breakdown outside the liver. This process produces metabolites that influence metabolic and inflammatory responses. A distinctive feature of the gut is its involvement in three major Trp catabolic pathways: the IDO-driven kynurenine pathway, bacteria-produced indoles, and serotonin. Dysregulation of these pathways is associated with gastrointestinal and chronic inflammatory diseases. Understanding these mechanisms could reveal how gut function affects overall systemic health and disease susceptibility. Here, we review current insights into Trp metabolism, its impact on host physiology and cardiometabolic diseases, and its role in the gut-periphery connection, highlighting its relevance for therapeutic innovation.

Smart control lipid-based nanocarriers for fine-tuning gut hormone secretion

Modulating the endogenous stores of gastrointestinal hormones is considered a promising strategy to mimic gut endocrine function, improving metabolic dysfunction. Here, we exploit mouse and human knock-in and knockout intestinal organoids and show that agents used as commercial lipid excipients can activate nutrient-sensitive receptors on enteroendocrine cells (EECs) and, when formulated as lipid nanocarriers, can bestow biological effects through the release of GLP-1, GIP, and PYY from K and L cells. Studies in wild-type, dysglycemic, and gut Gcg knockout mice demonstrated that the effect exerted by lipid nanocarriers could be modulated by varying the excipients (e.g., nature and quantities), the formulation methodology, and their physiochemical properties (e.g., size and composition). This study demonstrates the therapeutic potential of using nanotechnology to modulate release of multiple endogenous hormones from the enteroendocrine system through a patient-friendly, inexpensive, and noninvasive manner.

Exploring tryptophan metabolism: The transition from disturbed balance to diagnostic and therapeutic potential in metabolic diseases

The rapidly rising prevalence of metabolic diseases has turned them into an escalating global health concern. By producing or altering metabolic products, the gut microbiota plays a pivotal role in maintaining human health and influencing disease development. These metabolites originate from the host itself or the external environment. In the system of interactions between microbes and the host, tryptophan (Trp) plays a central role in metabolic processes. As the amino acid in the human body that must be obtained through dietary intake, it is crucial for various physiological functions. Trp can be metabolized in the gut into three main products: The gut microbiota regulates the transformation of 5-hydroxytryptamine (5-HT, serotonin), kynurenine (Kyn), and various indole derivatives. It has been revealed that a substantial correlation exists between alterations in Trp metabolism and the initiation and progression of metabolic disorders, including obesity, diabetes, non-alcoholic fatty liver disease, and atherosclerosis, but Trp metabolites have not been comprehensively reviewed in metabolic diseases. As such, this review summarizes and analyzes the latest research, emphasizing the importance of further studying Trp metabolism within the gut microbiota to understand and treat metabolic diseases. This carries potential significance for improving human health and may introduce new therapeutic strategies.

Targeting gut microbiota as a therapeutic target in T2DM: A review of multi-target interactions of probiotics, prebiotics, postbiotics, and synbiotics with the intestinal barrier

The global epidemic of type 2 diabetes mellitus (T2DM) imposes a substantial burden on public health and healthcare expenditures, thereby driving the pursuit of cost-effective preventive and therapeutic strategies. Emerging evidence suggests a potential association between dysbiosis of gut microbiota and its metabolites with T2DM, indicating that targeted interventions aimed at modulating gut microbiota may represent a promising therapeutic approach for the management of T2DM. In this review, we concentrated on the multifaceted interactions between the gut microbiota and the intestinal barrier in the context of T2DM. We systematically summarized that the imbalance of beneficial gut microbiota and its metabolites may constitute a viable therapeutic approach for the management of T2DM. Meanwhile, the mechanisms by which gut microbiota interventions, such as probiotics, prebiotics, postbiotics, and synbiotics, synergistically improve insulin resistance in T2DM are summarized. These mechanisms include the restoration of gut microbiota structure, upregulation of intestinal epithelial cell proliferation and differentiation, enhancement of tight junction protein expression, promotion of mucin secretion by goblet cells, and the immunosuppressive functions of regulatory T cells (Treg) and M2 macrophages. Collectively, these actions contribute to the amelioration of the body's metabolic inflammatory status. Our objective is to furnish evidence that supports the clinical application of probiotics, prebiotics, and postbiotics in the management of T2DM.

The Gut Microbiome's Influence on Incretins and Impact on Blood Glucose Control

Obesity and type 2 diabetes mellitus (T2DM) have been increasing in prevalence, causing complications and strain on our healthcare systems. Notably, gut dysbiosis is implicated as a contributing factor in obesity, T2DM, and chronic inflammatory diseases. A pharmacology exists which modulates the incretin pathway to improve glucose control; this has proven to be beneficial in patients with obesity and T2DM. However, it is unclear how the gut microbiome may regulate insulin resistance, glucose control, and metabolic health. In this narrative review, we aim to discuss how the gut microbiome can modulate incretin pathways and related mechanisms to control glucose. To investigate this, Google Scholar and PubMed databases were searched using key terms and phrases related to the microbiome and its effects on insulin and glucose control. Emerging research has shown that several bacteria, such as Akkermansia and MN-Gup, have GLP-1-agonistic properties capable of reducing hyperglycemia. While more human research is needed to prove clinical benefit and identify long-term implications on health, the usage of pre-, pro-, and postbiotics has the potential to improve glucose control.

Incretin hormones and obesity

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) play critical roles in co-ordinating postprandial metabolism, including modulation of insulin secretion and food intake. They are secreted from enteroendocrine cells in the intestinal epithelium following food ingestion, and act at multiple target sites including pancreatic islets and the brain. With the recent development of agonists targeting GLP-1 and GIP receptors for the treatment of type 2 diabetes and obesity, and the ongoing development of new incretin-based drugs with improved efficacy, there is great interest in understanding the physiology and pharmacology of these hormones.

Targeting the Gut Microbiota for Prevention and Management of Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic metabolic disorder with a heterogeneous etiology encompassing societal and behavioral risk factors in addition to genetic and environmental susceptibility. The cardiovascular consequences of diabetes account for more than two-thirds of mortality among people with T2D. Not only does T2D shorten life expectancy, but it also lowers quality of life and is associated with extremely high health expenditures since diabetic complications raise both direct and indirect healthcare costs. An increasing body of research indicates a connection between T2D and gut microbial traits, as numerous alterations in the intestinal microorganisms have been noted in pre-diabetic and diabetic individuals. These include pro-inflammatory bacterial patterns, increased intestinal permeability, endotoxemia, and hyperglycemia-favoring conditions, such as the alteration of glucagon-like peptide-1 (GLP-1) secretion. Restoring microbial homeostasis can be very beneficial for preventing and co-treating T2D and improving antidiabetic therapy outcomes. This review summarizes the characteristics of a "diabetic" microbiota and the metabolites produced by microbial species that can worsen or ameliorate T2D risk and progression, suggesting gut microbiota-targeted strategies to restore eubiosis and regulate blood glucose. Nutritional supplementation, diet, and physical exercise are known to play important roles in T2D, and here their effects on the gut microbiota are discussed, suggesting non-pharmacological approaches that can greatly help in diabetes management and highlighting the importance of tailoring treatments to individual needs.

The microbiota: a key regulator of health, productivity, and reproductive success in mammals

The microbiota, intensely intertwined with mammalian physiology, significantly impacts health, productivity, and reproductive functions. The normal microbiota interacts with the host through the following key mechanisms: acting as a protective barrier against pathogens, maintain mucosal barrier integrity, assisting in nutrient metabolism, and modulating of the immune response. Therefore, supporting growth and development of host, and providing protection against pathogens and toxic substances. The microbiota significantly influences brain development and behavior, as demonstrated by comprehensive findings from controlled laboratory experiments and human clinical studies. The prospects suggested that gut microbiome influence neurodevelopmental processes, modulate stress responses, and affect cognitive function through the gut-brain axis. Microbiota in the gastrointestinal tract of farm animals break down and ferment the ingested feed into nutrients, utilize to produce meat and milk. Among the beneficial by-products of gut microbiota, short-chain fatty acids (SCFAs) are particularly noteworthy for their substantial role in disease prevention and the promotion of various productive aspects in mammals. The microbiota plays a pivotal role in the reproductive hormonal systems of mammals, boosting reproductive performance in both sexes and fostering the maternal-infant connection, thereby becoming a crucial factor in sustaining mammalian existence. The microbiota is a critical factor influencing reproductive success and production traits in mammals. A well-balanced microbiome improves nutrient absorption and metabolic efficiency, leading to better growth rates, increased milk production, and enhanced overall health. Additionally, it regulates key reproductive hormones like estrogen and progesterone, which are essential for successful conception and pregnancy. Understanding the role of gut microbiota offers valuable insights for optimizing breeding and improving production outcomes, contributing to advancements in agriculture and veterinary medicine. This study emphasizes the critical ecological roles of mammalian microbiota, highlighting their essential contributions to health, productivity, and reproductive success. By integrating human and veterinary perspectives, it demonstrates how microbial communities enhance immune function, metabolic processes, and hormonal regulation across species, offering insights that benefit both clinical and agricultural advancements.

Reinventing gut health: leveraging dietary bioactive compounds for the prevention and treatment of diseases

The human gut harbors a complex and diverse microbiota essential for maintaining health. Diet is the most significant modifiable factor influencing gut microbiota composition and function, particularly through bioactive compounds like polyphenols, dietary fibers, and carotenoids found in vegetables, fruits, seafood, coffee, and green tea. These compounds regulate the gut microbiota by promoting beneficial bacteria and suppressing harmful ones, leading to the production of key microbiota-derived metabolites such as short-chain fatty acids, bile acid derivatives, and tryptophan metabolites. These metabolites are crucial for gut homeostasis, influencing gut barrier function, immune responses, energy metabolism, anti-inflammatory processes, lipid digestion, and modulation of gut inflammation. This review outlines the regulatory impact of typical bioactive compounds on the gut microbiota and explores the connection between specific microbiota-derived metabolites and overall health. We discuss how dietary interventions can affect disease development and progression through mechanisms involving these metabolites. We examine the roles of bioactive compounds and their metabolites in the prevention and treatment of diseases including inflammatory bowel disease, colorectal cancer, cardiovascular diseases, obesity, and type 2 diabetes mellitus. This study provides new insights into disease prevention and underscores the potential of dietary modulation of the gut microbiota as a strategy for improving health.

Indole induces anxiety-like behaviour in mice mediated by brainstem locus coeruleus activation

The gut microbiota produces metabolites that enrich the host metabolome and play a part in host physiology, including brain functions. Yet the biological mediators of this gut-brain signal transduction remain largely unknown. In this study, the possible role of the gut microbiota metabolite indole, originating from tryptophan, was investigated. Oral administration of indole to simulate microbial overproduction of this compound in the gut consistently led to impaired locomotion and anxiety-like behaviour in both C3H/HeN and C57BL/6J mice. By employing c-Fos protein expression mapping in mice, we observed a noticeable increase in brain activation within the dorsal motor nucleus of the vagus nerve (DMX) and the locus coeruleus (LC) regions in a dose-dependent manner. Further immune co-labelling experiments elucidated that the primary cells activated within the LC were tyrosine hydroxylase positive. To delve deeper into the mechanistic aspects, we conducted chemogenetic activation experiments on LC norepinephrine neurons with two doses of clozapine N-oxide (CNO). Low dose of CNO at 0.5 mg/kg induced no change in locomotion but anxiety-like behaviour, while high dose of CNO at 2 mg/kg resulted in locomotion impairment and anxiety-like behaviour. These findings support the neuroactive roles of indole in mediating gut-brain communication. It also highlights the LC as a novel hub in the gut-brain axis, encouraging further investigations.

Polysaccharides to postbiotics: Nurturing bone health via modulating "gut-immune axis"

The increasing prevalence of individuals affected by bone pathologies globally has sparked catastrophic concerns. Ankylosing spondylitis, osteoporosis, rheumatoid arthritis, osteoarthritis, and fractures alone impact an estimated 1.71 billion people worldwide. The gut microbiota plays a crucial role in interacting with the host through the synthesis of a diverse range of metabolites called gut-associated metabolites (GAMs), which originate from external dietary substrates or endogenous host compounds. Many metabolic disorders have been linked to alterations in the gut microbiota's activity and composition. The development of metabolic illnesses has been linked to certain microbiota-derived metabolites, such as branched-chain amino acids, bile acids, short-chain fatty acids, tryptophan, trimethylamine N-oxide, and indole derivatives. Moreover, the modulation of gut microbiota through biotics (prebiotics, probiotics and postbiotics) presents a promising avenue for therapeutic intervention. Biotics selectively promote the growth of beneficial gut bacteria, thereby enhancing the production of GAMs with potential beneficial effects on bone metabolism. Understanding the intricate interplay between GAMs, and bone-associated genes through molecular informatics holds significant promise for early diagnosis, prognosis, and novel treatment strategies for various bone disorders.

Indole alleviates nonalcoholic fatty liver disease in an ACE2-dependent manner

Indole is a microbial metabolite produced by the gut microbiota through the degradation of dietary tryptophan, known for its well-established anti-inflammatory and antioxidant properties. In this study, we collected fecal samples from mice fed a high-fat diet (HFD) and those on a standard diet (SD), then conducted 16S rRNA sequencing to analyze their gut microbiota. The analysis revealed distinct differences in the dominant bacterial species between the two groups, with a significant decrease in indole-producing probiotics in the HFD mice compared to the SD group. Then we administered oral indole treatment to male C57BL/6J mice with HFD-induced NAFLD and observed a significant improvement in hepatic steatosis and inflammation. Notably, indole alleviated the HFD-induced decline in serum Angiotensin-(1-7) [Ang-(1-7)] levels and Angiotensin-Converting Enzyme 2 (ACE2) expression. To further investigate the role of indole and ACE2 in NAFLD, we conducted experiments using ACE2 knockout (ACE2KO) mice that were also induced with HFD-induced NAFLD and treated with indole. Interestingly, the protective effects of indole were compromised in the absence of ACE2. In HepG2 cells, indole similarly stimulated ACE2 expression and, in an ACE2-dependent manner, reduced ROS generation, maintained mitochondrial membrane potential stability, and increased SIRT3 expression. In summary, our results highlight the formation of a biologically active gut-liver axis between the gut microbiota and the liver through the tryptophan metabolite indole, which mitigates NAFLD in an ACE2-dependent manner. Elevating dietary tryptophan and increasing indole levels may represent an effective approach for preventing and treating NAFLD.

Metabolic mediators: microbial-derived metabolites as key regulators of anti-tumor immunity, immunotherapy, and chemotherapy

The human microbiome has recently emerged as a focal point in cancer research, specifically in anti-tumor immunity, immunotherapy, and chemotherapy. This review explores microbial-derived metabolites, emphasizing their crucial roles in shaping fundamental aspects of cancer treatment. Metabolites such as short-chain fatty acids (SCFAs), Trimethylamine N-Oxide (TMAO), and Tryptophan Metabolites take the spotlight, underscoring their diverse origins and functions and their profound impact on the host immune system. The focus is on SCFAs' remarkable ability to modulate immune responses, reduce inflammation, and enhance anti-tumor immunity within the intricate tumor microenvironment (TME). The review critically evaluates TMAO, intricately tied to dietary choices and gut microbiota composition, assessing its implications for cancer susceptibility, progression, and immunosuppression. Additionally, the involvement of tryptophan and other amino acid metabolites in shaping immune responses is discussed, highlighting their influence on immune checkpoints, immunosuppression, and immunotherapy effectiveness. The examination extends to their dynamic interaction with chemotherapy, emphasizing the potential of microbial-derived metabolites to alter treatment protocols and optimize outcomes for cancer patients. A comprehensive understanding of their role in cancer therapy is attained by exploring their impacts on drug metabolism, therapeutic responses, and resistance development. In conclusion, this review underscores the pivotal contributions of microbial-derived metabolites in regulating anti-tumor immunity, immunotherapy responses, and chemotherapy outcomes. By illuminating the intricate interactions between these metabolites and cancer therapy, the article enhances our understanding of cancer biology, paving the way for the development of more effective treatment options in the ongoing battle against cancer.