Farnesoid X receptor inhibits glucagon-like peptide-1 production by enteroendocrine L cells

Obeticholic acid ameliorates sepsis-induced renal mitochondrial damage by inhibiting the NF-κb signaling pathway

Acute kidney injury (AKI), a common complication of sepsis, might be caused by overactivated inflammation, mitochondrial damage, and oxidative stress. However, the mechanisms underlying sepsis-induced AKI (SAKI) have not been fully elucidated, and there is a lack of effective therapies for AKI. To this end, this study aimed to investigate whether obeticholic acid (OCA) has a renoprotective effect on SAKI and to explore its mechanism of action. Through bioinformatics analysis, our study confirmed that the mitochondria might be a critical target for the treatment of SAKI. Thus, a septic rat model was established by cecal ligation puncture (CLP) surgery. Our results showed an evoked inflammatory response via the NF-κB signaling pathway and NLRP3 inflammasome activation in septic rats, which led to mitochondrial damage and oxidative stress. OCA, an Farnesoid X Receptor (FXR) agonist, has shown anti-inflammatory effects in numerous studies. However, the effects of OCA on SAKI remain unclear. In this study, we revealed that pretreatment with OCA can inhibit the inflammatory response by reducing the synthesis of proinflammatory factors (such as IL-1β and NLRP3) via blocking NF-κB and alleviating mitochondrial damage and oxidative stress in the septic rat model. Overall, this study provides insight into the excessive inflammation-induced SAKI caused by mitochondrial damage and evidence for the potential use of OCA in SAKI treatment.

An insoluble cellulose nanofiber with robust expansion capacity protects against obesity

An imbalance between energy intake and energy expenditure predisposes obesity and its related metabolic diseases. Soluble dietary fiber has been shown to improve metabolic homeostasis mainly via microbiota reshaping. However, the application and metabolic effects of insoluble fiber are less understood. Herein, we employed nanotechnology to design citric acid-crosslinked carboxymethyl cellulose nanofibers (CL-CNF) with a robust capacity of expansion upon swelling. Supplementation with CL-CNF reduced food intake and delayed digestion rate in mice by occupying stomach. Besides, CL-CNF treatment mitigated diet-induced obesity and insulin resistance in mice with enhanced energy expenditure, as well as ameliorated inflammation in adipose tissue, intestine and liver and reduced hepatic steatosis, without any discernible signs of toxicity. Additionally, CL-CNF supplementation resulted in enrichment of probiotics such as Bifidobacterium and decreased in the relative abundances of deleterious microbiota expressing bile salt hydrolase, which led to increased levels of conjugated bile acids and inhibited intestinal FXR signaling to stimulate the release of GLP-1. Taken together, our findings demonstrate that CL-CNF administration protects mice from diet-induced obesity and metabolic dysfunction by reducing food intake, enhancing energy expenditure and remodeling gut microbiota, making it a potential therapeutic strategy against metabolic diseases.

The role of glucagon-like peptide 1 in the postprandial effects of metformin in type 2 diabetes: a randomized crossover trial

AIMS

Although metformin is widely used for treatment of type 2 diabetes (T2D), its glucose-lowering mechanism remains unclear. Using the glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) antagonist exendin(9-39)NH2, we tested the hypothesis that postprandial GLP-1-mediated effects contribute to the glucose-lowering potential of metformin in T2D.

METHODS

In a randomized, placebo-controlled, double-blind, crossover study, 15 individuals with T2D (median HbA1c 50 mmol/mol [6.7%], body mass index 30.1 kg/m2, age 71 years) underwent, in randomized order, 14 days of metformin and placebo treatment, respectively. Each treatment period was preceded by 14 days without any glucose-lowering medicine and concluded by two 4 h mixed meal tests performed in randomized order and separated by >24 h with either continuous intravenous exendin(9-39)NH2 or saline infusion.

RESULTS

Compared to placebo, metformin treatment lowered fasting plasma glucose (mean of differences [MD] 1.4 mmol/L × min [95% CI 0.8-2.0]) as well as postprandial plasma glucose excursions during both saline infusion (MD 186 mmol/L × min [95% CI 64-307]) and exendin(9-39)NH2 infusion (MD 268 mmol/L × min [95% CI 108-427]). The metformin-induced improvement in postprandial glucose tolerance was unaffected by GLP-1R antagonization (MD 82 mmol/L × min [95% CI -6564-170]). Metformin treatment increased fasting plasma GLP-1 (MD 1.7 pmol/L × min [95% CI 0.39-2.9]) but did not affect postprandial GLP-1 responses (MD 820 pmol/L × min [95% CI -1750-111]).

CONCLUSIONS

Using GLP-1R antagonization, we could not detect GLP-1-mediated postprandial glucose-lowering effect of metformin in individuals with T2D. We show that 2 weeks of metformin treatment increases fasting plasma GLP-1, which may contribute to metformin's beneficial effect on fasting plasma glucose in T2D. Trial registration: Clinicaltrials.gov NCT03246451.

The role of botanical triterpenoids and steroids in bile acid metabolism, transport, and signaling: Pharmacological and toxicological implications

Bile acids (BAs) are synthesized by the host liver from cholesterol and are delivered to the intestine, where they undergo further metabolism by gut microbes and circulate between the liver and intestines through various transporters. They serve to emulsify dietary lipids and act as signaling molecules, regulating the host's metabolism and immune homeostasis through specific receptors. Therefore, disruptions in BA metabolism, transport, and signaling are closely associated with cholestasis, metabolic disorders, autoimmune diseases, and others. Botanical triterpenoids and steroids share structural similarities with BAs, and they have been found to modulate BA metabolism, transport, and signaling, potentially exerting pharmacological or toxicological effects. Here, we have updated the research progress on BA, with a particular emphasis on new-found microbial BAs. Additionally, the latest advancements in targeting BA metabolism and signaling for disease treatment are highlighted. Subsequently, the roles of botanical triterpenoids in BA metabolism, transport, and signaling are examined, analyzing their potential pharmacological, toxicological, or drug interaction effects through these mechanisms. Finally, a research paradigm is proposed that utilizes the gut microbiota as a link to interpret the role of these important natural products in BA signaling.

Digesting the complex metabolic effects of diet on the host and microbiome

The past 50 years of interdisciplinary research in humans and model organisms has delivered unprecedented insights into the mechanisms through which diet affects energy balance. However, translating these results to prevent and treat obesity and its associated diseases remains challenging. Given the vast scope of this literature, we focus this Review on recent conceptual advances in molecular nutrition targeting the management of energy balance, including emerging dietary and pharmaceutical interventions and their interactions with the human gut microbiome. Notably, multiple current dietary patterns of interest embrace moderate-to-high fat intake or prioritize the timing of eating over macronutrient intake. Furthermore, the rapid expansion of microbiome research findings has complicated multiple longstanding tenets of nutrition while also providing new opportunities for intervention. Continued progress promises more precise and reliable dietary recommendations that leverage our growing knowledge of the microbiome, the changing landscape of clinical interventions, and our molecular understanding of human biology.

The Potential Mechanism of Remission in Type 2 Diabetes Mellitus After Vertical Sleeve Gastrectomy

In recent years, there has been a gradual increase in the prevalence of obesity and type 2 diabetes mellitus (T2DM), with bariatric surgery remaining the most effective treatment strategy for these conditions. Vertical sleeve gastrectomy (VSG) has emerged as the most popular surgical procedure for bariatric/metabolic surgeries, effectively promoting weight loss and improving or curing T2DM. The alterations in the gastrointestinal tract following VSG may improve insulin secretion and resistance by increasing incretin secretion (especially GLP-1), modifying the gut microbiota composition, and through mechanisms dependent on weight loss. This review focuses on the potential mechanisms through which the enhanced action of incretin and metabolic changes in the digestive system after VSG may contribute to the remission of T2DM.

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

Altered bile acid and correlations with gut microbiome in transition dairy cows with different glucose and lipid metabolism status

The transition from pregnancy to lactation is critical in dairy cows. Among others, dairy cows experience a metabolic stress due to a large change in glucose and lipid metabolism. Recent studies revealed that bile acids (BA), besides being involved in both the emulsification and solubilization of fats during intestinal absorption, can also affect the metabolism of glucose and lipids, both directly or indirectly by affecting the gut microbiota. Thus, we used untargeted and targeted metabolomics and 16S rRNA sequencing approaches to investigate the concentration of plasma metabolites and BA, the composition of the rectum microbial community, and assess their interaction in transition dairy cows. In Experiment 1, we investigated BA and other blood parameters and gut microbiota in dairy cows without clinical diseases during the transition period, which can be seen as well adapted to the challenge of changed glucose and lipid metabolism. As expected, we detected an increased plasma concentration of β-hydroxybutyrate (BHBA) and nonesterified fatty acids (NEFA) but decreased concentration of glucose, cholesterol, and triglycerides (TG). Untargeted metabolomic analysis of the plasma revealed primary BA biosynthesis was one of the affected pathways, and was consistent with the increased concentration of BA in the plasma. A correlation approach revealed a complex association between BA and microbiota with the host plasma concentration of glucose and lipid metabolites. Among BA, chenodeoxycholic acid derivates such as glycolithocholic acid, taurolithocholic acid, lithocholic acid, taurochenodeoxycholic acid, and taurodeoxycholic acid were the main hub nodes connecting microbe and blood metabolites (such as glucose, TG, and NEFA). In Experiment 2, we investigated early postpartum dairy cows with or without hyperketonemia (HPK). As expected, HPK cows had increased concentration of NEFA and decreased concentrations of glucose and triglycerides. The untargeted metabolomic analysis of the plasma revealed that primary BA biosynthesis was also one of the affected pathways. Even though the BA concentration was similar among the 2 groups, the profiles of taurine conjugated BA changed significantly. A correlation analysis also revealed an association between BA and microbiota with the concentration in plasma of glucose and lipid metabolites (such as BHBA). Among BA, cholic acid and its derivates such as taurocholic acid, tauro α-muricholic acid, and taurodeoxycholic acid were the main hub nodes connecting microbe and blood metabolites. Our results indicated an association between BA, intestinal microbe, and glucose and lipid metabolism in transition dairy cows. These findings provide new insight into the adaptation mechanisms of dairy cows during the transition period.

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

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

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Metabolic Dysfunction-Associated Steatotic Liver Disease: From Pathogenesis to Current Therapeutic Options

The epidemiological burden of liver steatosis associated with metabolic diseases is continuously growing worldwide and in all age classes. This condition generates possible progression of liver damage (i.e., inflammation, fibrosis, cirrhosis, hepatocellular carcinoma) but also independently increases the risk of cardio-metabolic diseases and cancer. In recent years, the terminological evolution from "nonalcoholic fatty liver disease" (NAFLD) to "metabolic dysfunction-associated fatty liver disease" (MAFLD) and, finally, "metabolic dysfunction-associated steatotic liver disease" (MASLD) has been paralleled by increased knowledge of mechanisms linking local (i.e., hepatic) and systemic pathogenic pathways. As a consequence, the need for an appropriate classification of individual phenotypes has been oriented to the investigation of innovative therapeutic tools. Besides the well-known role for lifestyle change, a number of pharmacological approaches have been explored, ranging from antidiabetic drugs to agonists acting on the gut-liver axis and at a systemic level (mainly farnesoid X receptor (FXR) agonists, PPAR agonists, thyroid hormone receptor agonists), anti-fibrotic and anti-inflammatory agents. The intrinsically complex pathophysiological history of MASLD makes the selection of a single effective treatment a major challenge, so far. In this evolving scenario, the cooperation between different stakeholders (including subjects at risk, health professionals, and pharmaceutical industries) could significantly improve the management of disease and the implementation of primary and secondary prevention measures. The high healthcare burden associated with MASLD makes the search for new, effective, and safe drugs a major pressing need, together with an accurate characterization of individual phenotypes. Recent and promising advances indicate that we may soon enter the era of precise and personalized therapy for MASLD/MASH.

The microbial metabolite agmatine acts as an FXR agonist to promote polycystic ovary syndrome in female mice

Polycystic ovary syndrome (PCOS), an endocrine disorder afflicting 6-20% of women of reproductive age globally, has been linked to alterations in the gut microbiome. We previously showed that in PCOS, elevation of Bacteroides vulgatus in the gut microbiome was associated with altered bile acid metabolism. Here we show that B. vulgatus also induces a PCOS-like phenotype in female mice via an alternate mechanism independent of bile acids. We find that B. vulgatus contributes to PCOS-like symptoms through its metabolite agmatine, which is derived from arginine by arginine decarboxylase. Mechanistically, agmatine activates the farnesoid X receptor (FXR) pathway to subsequently inhibit glucagon-like peptide-1 (GLP-1) secretion by L cells, which leads to insulin resistance and ovarian dysfunction. Critically, the GLP-1 receptor agonist liraglutide and the arginine decarboxylase inhibitor difluoromethylarginine ameliorate ovarian dysfunction in a PCOS-like mouse model. These findings reveal that agmatine-FXR-GLP-1 signalling contributes to ovarian dysfunction, presenting a potential therapeutic target for PCOS management.

Tailoring FXR Modulators for Intestinal Specificity: Recent Progress and Insights

While FXR has shown promise in regulating bile acid synthesis and maintaining glucose and lipid homeostasis, undesired side effects have been observed in clinical trials. To address this issue, the development of intestinally restricted FXR modulators has gained attention as a new avenue for drug design with the potential for safer systematic effects. Our review examines all currently known intestinally restricted FXR ligands and provides insights into the steps taken to enhance intestinal selectivity.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

High temperature and humidity in the environment disrupt bile acid metabolism, the gut microbiome, and GLP-1 secretion in mice

High temperature and humidity in the environment are known to be associated with discomfort and disease, yet the underlying mechanisms remain unclear. We observed a decrease in plasma glucagon-like peptide-1 levels in response to high-temperature and humidity conditions. Through 16S rRNA gene sequencing, alterations in the gut microbiota composition were identified following exposure to high temperature and humidity conditions. Notably, changes in the gut microbiota have been implicated in bile acid synthesis. Further analysis revealed a decrease in lithocholic acid levels in high-temperature and humidity conditions. Subsequent in vitro experiments demonstrated that lithocholic acid increases glucagon-like peptide-1 secretion in NCI-H716 cells. Proteomic analysis indicated upregulation of farnesoid X receptor expression in the ileum. In vitro experiments revealed that the combination of lithocholic acid with farnesoid X receptor inhibitors resulted in a significant increase in GLP-1 levels compared to lithocholic acid alone. In this study, we elucidate the mechanism by which reduced lithocholic acid suppresses glucagon-like peptide 1 via farnesoid X receptor activation under high-temperature and humidity condition.

Elucidating the glucose-lowering effect of the bile acid sequestrant sevelamer

AIM

Bile acid sequestrants are cholesterol-lowering drugs, which also improve glycaemic control in people with type 2 diabetes. The mechanism behind the glucose-lowering effect is unknown but has been proposed to be mediated by increased glucagon-like peptide-1 (GLP-1) secretion. Here, we investigated the glucose-lowering effects of sevelamer including any contribution from GLP-1 in people with type 2 diabetes.

MATERIALS AND METHODS

In a randomized, double-blind, placebo-controlled, crossover study, 15 people with type 2 diabetes on metformin monotherapy underwent two 17-day treatment periods with the bile acid sequestrant sevelamer and placebo, respectively, in a randomized order and with an interposed wash-out period of minimum 6 weeks. On days 15 and 17 of each treatment period, participants underwent experimental days with 4-h liquid meal tests and application of concomitant infusion of exendin(9-39)NH2 or saline.

RESULTS

Compared with placebo, sevelamer improved insulin sensitivity (assessed by homeostatic model assessment of insulin resistance) and beta-cell sensitivity to glucose and lowered fasting and postprandial plasma glucose concentrations. In both treatment periods, exendin(9-39)NH2 increased postprandial glucose excursions compared with saline but without absolute or relative difference between the two treatment periods. In contrast, exendin(9-39)NH2 abolished the sevelamer-induced improvement in beta-cell glucose sensitivity.

CONCLUSIONS

The bile acid sequestrant sevelamer improved insulin sensitivity and beta-cell sensitivity to glucose, but using the GLP-1 receptor antagonist exendin(9-39)NH2 we were not able to detect a GLP-1-mediated glucose-lowering effect of sevelamer in individuals with type 2 diabetes. Nevertheless, the sevelamer-induced improvement of beta-cell sensitivity to glucose was shown to be GLP-1-dependent.

Gut microbiota and type 2 diabetes mellitus: a focus on the gut-brain axis

Type 2 diabetes mellitus (T2DM) has become one of the most serious public healthcare challenges, contributing to increased mortality and disability. In the past decades, significant progress has been made in understanding the pathogenesis of T2DM. Mounting evidence suggested that gut microbiota (GM) plays a significant role in the development of T2DM. Communication between the GM and the brain is a complex bidirectional connection, known as the "gut-brain axis," via the nervous, neuroendocrine, and immune systems. Gut-brain axis has an essential impact on various physiological processes, including glucose metabolism, food intake, gut motility, etc. In this review, we provide an outline of the gut-brain axis. We also highlight how the dysbiosis of the gut-brain axis affects glucose homeostasis and even results in T2DM.

The bile-gut axis and metabolic consequences of cholecystectomy

Cholelithiasis and cholecystitis affect individuals of all ages and are often treated by surgical removal of the gallbladder (cholecystectomy), which is considered a safe, low-risk procedure. Nevertheless, recent findings show that bile and its regulated storage and excretion may have important metabolic effects and that cholecystectomy is associated with several metabolic diseases postoperatively. Bile acids have long been known as emulsifiers essential to the assimilation of lipids and absorption of lipid-soluble vitamins, but more recently, they have also been reported to act as metabolic signaling agents. The nuclear receptor, farnesoid X receptor (FXR), and the G protein-coupled membrane receptor, Takeda G protein-coupled receptor 5 (TGR5), are specific to bile acids. Through activation of these receptors, bile acids control numerous metabolic functions. Cholecystectomy affects the storage and excretion of bile acids, which in turn may influence the activation of FXR and TGR5 and their effects on metabolism including processes leading to metabolic conditions such as metabolic dysfunction-associated steatotic liver disease and metabolic syndrome. Here, with the aim of elucidating mechanisms behind cholecystectomy-associated dysmetabolism, we review studies potentially linking cholecystectomy and bile acid-mediated metabolic effects and discuss possible pathophysiological mechanisms behind cholecystectomy-associated dysmetabolism.

Natural Products in the Modulation of Farnesoid X Receptor Against Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a global health concern with a high prevalence and increasing economic burden, but official medicine remains unavailable. Farnesoid X receptor (FXR), a nuclear receptor member, is one of the most promising drug targets for NAFLD therapy that plays a crucial role in modulating bile acid, glucose, and lipid homeostasis, as well as inhibits hepatic inflammation and fibrosis. However, the rejection of the FXR agonist, obecholic acid, by the Food and Drug Administration for treating hepatic fibrosis raises a question about the functions of FXR in NAFLD progression and the therapeutic strategy to be used. Natural products, such as FXR modulators, have become the focus of attention for NAFLD therapy with fewer adverse reactions. The anti-NAFLD mechanisms seem to act as FXR agonists and antagonists or are involved in the FXR signaling pathway activation, indicating a promising target of FXR therapeutic prospects using natural products. This review discusses the effective mechanisms of FXR in NAFLD alleviation, and summarizes currently available natural products such as silymarin, glycyrrhizin, cycloastragenol, berberine, and gypenosides, for targeting FXR, which can facilitate development of naturally targeted drug by medicinal specialists for effective treatment of NAFLD.

Polysaccharides from Phellinus linteus attenuate type 2 diabetes mellitus in rats via modulation of gut microbiota and bile acid metabolism

Type 2 diabetes mellitus (T2DM) is the most prevalent metabolic disorder. Polysaccharides from Phellinus linteus (PLP) have been found to have anti-diabetes effects, but the mechanism has not been elucidated. The purpose of this study was to investigate the mechanism of PLP on T2DM through the gut microbiota and bile acids metabolism. The T2DM rat model was induced by a high-fat high-carbohydrate (HFHC) diet and streptozocin (30 mg/kg). We found that PLP ameliorated diabetes symptoms. Besides, PLP intervention increased the abundance of g_Bacteroides, g_Parabacteroides, and g_Alistioes, which are associated with the biosynthesis of short-chain fatty acids (SCFAs) and bile acids (BAs) metabolism. Meanwhile, untargeted and targeted metabolomics indicated that PLP could regulate the composition of BAs and increase the levels of SCFAs. Real-time quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) were performed to analyze the expression levels of BAs metabolism enzymes in the liver. Finally, the results of correlation analysis and Glucagon-like peptide-1 (GLP-1) showed that PLP stimulated the release of GLP-1 by regulating SCFAs and BAs. In conclusion, this study demonstrated that PLP can regulate gut microbiota and BAs metabolism to promote GLP-1 secretion, thereby increasing insulin release, decreasing blood glucose and attenuating T2DM.

Revealing the Impact of Gut Microbiota on Acne Through Mendelian Randomization Analysis

Background

The association between acne and gut microbiota has garnered considerable attention; nevertheless, given the substantial diversity within gut microbiota, the precise cause-and-effect relationship linking specific microbial species to acne remains elusive. To address this gap in knowledge, our study utilized Mendelian randomization analysis to elucidate a potential causal link between gut microbiota composition and acne development while also investigating underlying mechanisms involving microbial factors associated with metabolic disorders.

Materials and Methods

The independent single nucleotide polymorphisms (SNPs) closely associated with 196 gut microbiota samples (N=18340) were selected as variable tools. The relationship between gut microbiota and acne (N=212438) was analyzed using the Twosample package in R4.3.1, employing various methods including inverse variance weighting (IVW), weighted median, MR-Egger, Simple-mode, and Weighted-mode. To ensure the stability of the estimates, a series of sensitivity analyses were conducted, such as Cochran's Q-test, MR-Egger intercept analysis, leave-one-out analysis, and funnel plots. Additionally, the impact of each instrumental variable was calculated.

Results

In the Mendelian randomization analysis, we identified twelve microbial taxa potentially associated with acne: family.Bacteroidaceae, family.Clostridiaceae1, genus.Allisonella, genus.Bacteroides, genus.Butyricimonas, genus.Clostridiumsensustricto1, and genus.Coprococcus3. These seven bacterial groups were found to be potential risk factors for acne. Conversely, family.Lactobacillaceae and genus.Ruminococcustorquesgroup along with genus.CandidatusSoleaferrea, genus.Fusicatenibacter, family.Lactobacillaceae, and genus.Lactobacillus exhibited a protective effect against acne. Furthermore, our investigation revealed that some of these microbial taxa have been implicated in metabolic diseases through previous studies. Importantly though, no causal relationship was observed in the reverse Mendelian randomization analysis.

Fecal Microbiota Transplantation: A Prospective Treatment for Type 2 Diabetes Mellitus

Purpose of Review

The aim of this review is to summarize the role of gastrointestinal microbiome (GM) in the development of type 2 diabetes mellitus (T2DM). Besides, we discuss the feasibility of applying FMT in the treatment of T2DM and propose a series of processes to refine the use of FMT in the treatment of T2DM.

Recent Findings

T2DM is a metabolic disease which is connected with the GM. According to many researches, GM can produce a variety of metabolites such as bile acid, short chain fatty acids, lipopolysaccharides and trimethylamine oxide which play an important role in metabolism. FMT is a method to regulate GM and has been observed to be effective in the treatment of metabolic diseases such as T2DM in some mouse models and people. However, there is still a lack of direct evidence for the use of FMT in the treatment of T2DM, and the process of FMT is not standardized.

Summary

Dysregulation of GM is closely related to the development of T2DM. Promoting the conversion of GM in T2DM patients to normal population through FMT can reduce insulin resistance and lower their blood glucose level, which is an optional treatment for T2DM patients in the future. At present, the feasibility and limitations of applying FMT to the treatment of T2DM need to be further studied.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

O6-methylguanine DNA methyltransferase regulates β-glucan-induced trained immunity of macrophages via farnesoid X receptor and AMPK

Trained immunity is the heightened state of innate immune memory that enhances immune response resulting in nonspecific protection. Epigenetic changes and metabolic reprogramming are critical steps that regulate trained immunity. In this study, we reported the involvement of O6-methylguanine DNA methyltransferase (MGMT), a DNA repair enzyme of lesion induced by alkylating agents, in regulation the trained immunity induced by β-glucan (BG). Pharmacological inhibition or silencing of MGMT expression altered LPS stimulated pro-inflammatory cytokine productions in BG-trained bone marrow derived macrophages (BMMs). Targeted deletion of Mgmt in BMMs resulted in reduction of the trained responses both in vitro and in vivo models. The transcriptomic analysis revealed that the dampening trained immunity in MGMT KO BMMs is partially mediated by ATM/FXR/AMPK axis affecting the MAPK/mTOR/HIF1α pathways and the reduction in glycolysis function. Taken together, a failure to resolve a DNA damage may have consequences for innate immune memory.

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.

Vancomycin relieves tacrolimus-induced hyperglycemia by eliminating gut bacterial beta-glucuronidase enzyme activity

Up to 40% of transplant recipients treated long-term with tacrolimus (TAC) develop post-transplant diabetes mellitus (PTDM). TAC is an important risk factor for PTDM, but is also essential for immunosuppression after transplantation. Long-term TAC treatment alters the gut microbiome, but the mechanisms of TAC-induced gut microbiota in the pathogenesis of PTDM are poorly characterized. Here, we showed that vancomycin, an inhibitor of bacterial beta-glucuronidase (GUS), prevents TAC-induced glucose disorder and insulin resistance in mice. Metagenomics shows that GUS-producing bacteria are predominant and flourish in the TAC-induced hyperglycemia mouse model, with upregulation of intestinal GUS activity. Targeted metabolomics analysis revealed that in the presence of high GUS activity, the hydrolysis of bile acid (BAs)-glucuronic conjugates is increased and most BAs are overproduced in the serum and liver, which, in turn, activates the ileal farnesoid X receptor (FXR) and suppresses GLP-1 secretion by L-cells. The GUS inhibitor vancomycin significantly eliminated GUS-producing bacteria and inhibited bacterial GUS activity and BAs levels, thereby enhancing L-cell GLP-1 secretion and preventing hyperglycemia. Our results propose a novel clinical strategy for inhibiting the bacterial GUS enzyme to prevent hyperglycemia without requiring withdrawal of TAC treatment. This strategy exerted its effect through the ileal bile acid-FXR-GLP-1 pathway.

Metabolic Syndrome: A Narrative Review from the Oxidative Stress to the Management of Related Diseases

Metabolic syndrome (MS) is a growing disorder affecting thousands of people worldwide, especially in industrialised countries, increasing mortality. Oxidative stress, hyperglycaemia, insulin resistance, inflammation, dysbiosis, abdominal obesity, atherogenic dyslipidaemia and hypertension are important factors linked to MS clusters of different pathologies, such as diabesity, cardiovascular diseases and neurological disorders. All biochemical changes observed in MS, such as dysregulation in the glucose and lipid metabolism, immune response, endothelial cell function and intestinal microbiota, promote pathological bridges between metabolic syndrome, diabesity and cardiovascular and neurodegenerative disorders. This review aims to summarise metabolic syndrome's involvement in diabesity and highlight the link between MS and cardiovascular and neurological diseases. A better understanding of MS could promote a novel strategic approach to reduce MS comorbidities.

Gut microbiota regulates postprandial GLP-1 response via ileal bile acid-TGR5 signaling

The gut microbiota interacts with intestinal epithelial cells through microbial metabolites to regulate the release of gut hormones. We investigated whether the gut microbiota affects the postprandial glucagon-like peptide-1 (GLP-1) response using antibiotic-treated mice and germ-free mice. Gut microbiome depletion completely abolished postprandial GLP-1 response in the circulation and ileum in a lipid tolerance test. Microbiome depletion did not influence the GLP-1 secretory function of primary ileal cells in response to stimulators in vitro, but dramatically changed the postprandial dynamics of endogenous bile acids, particularly ω-muricholic acid (ωMCA) and hyocholic acid (HCA). The bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) but not farnesoid X receptor (FXR), participated in the regulation of postprandial GLP-1 response in the circulation and ileum, and ωMCA or HCA stimulated GLP-1 secretion via TGR5. Finally, fecal microbiota transplantation or ωMCA and HCA supplementation restored postprandial GLP-1 response. In conclusion, gut microbiota is indispensable for maintaining the postprandial GLP-1 response specifically in the ileum, and bile acid (ωMCA and HCA)-TGR5 signaling is involved in this process. This study helps to understand the essential interplay between the gut microbiota and host in regulating postprandial GLP-1 response and opens the foundation for new therapeutic targets.

A Narrative Review on Strategies for the Reversion of Prediabetes to Normoglycemia: Food Pyramid, Physical Activity, and Self-Monitoring Innovative Glucose Devices

In 2019, "Nutrition Therapy for Adults with Diabetes or Prediabetes: A Consensus Report" was published. This consensus report, however, did not provide an easy way to illustrate to subjects with prediabetes (SwPs) how to follow a correct dietary approach. The purpose of this review is to evaluate current evidence on optimum dietary treatment of SwPs and to provide a food pyramid for this population. The pyramid built shows that everyday consumption should consist of: whole-grain bread or potatoes eaten with their skins (for fiber and magnesium) and low glycemic index carbohydrates (GI < 55%) (three portions); fruit and vegetables (5 portions), in particular, green leafy vegetables (for fiber, magnesium, and polyphenols); EVO oil (almost 8 g); nuts (30 g, in particular, pistachios and almonds); three portions of dairy products (milk/yogurt: 300-400 g/day); mineral water (almost 1, 5 L/day for calcium intake); one glass of wine (125 mL); and three cups of coffee. Weekly portions should include fish (four portions), white meat (two portions), protein plant-based food (four portions), eggs (egg portions), and red/processed meats (once/week). At the top of the pyramid, there are two pennants: a green one means that SwPs need some personalized supplementation (if daily requirements cannot be satisfied through diet, vitamin D, omega-3, and vitamin B supplements), and a red one means there are some foods and factors that are banned (simple sugar, refined carbohydrates, and a sedentary lifestyle). Three to four times a week of aerobic and resistance exercises must be performed for 30-40 min. Finally, self-monitoring innovative salivary glucose devices could contribute to the reversion of prediabetes to normoglycemia.

Microbial sensing in the intestine

The gut microbiota plays a key role in host health and disease, particularly through their interactions with the immune system. Intestinal homeostasis is dependent on the symbiotic relationships between the host and the diverse gut microbiota, which is influenced by the highly co-evolved immune-microbiota interactions. The first step of the interaction between the host and the gut microbiota is the sensing of the gut microbes by the host immune system. In this review, we describe the cells of the host immune system and the proteins that sense the components and metabolites of the gut microbes. We further highlight the essential roles of pattern recognition receptors (PRRs), the G protein-coupled receptors (GPCRs), aryl hydrocarbon receptor (AHR) and the nuclear receptors expressed in the intestinal epithelial cells (IECs) and the intestine-resident immune cells. We also discuss the mechanisms by which the disruption of microbial sensing because of genetic or environmental factors causes human diseases such as the inflammatory bowel disease (IBD).

Curcumin Compensates GLP-1 Deficiency via the Microbiota-Bile Acids Axis and Modulation in Functional Crosstalk between TGR5 and FXR in ob/ob Mice

SCOPE

Glucagon-like peptide-1 (GLP-1) deficiency occurs in obesity-related pathologies due to defects in the intestinal lumen. And expanding the L-cell population has emerged as a promising avenue to elevate GLP-1 secretion to tackle metabolic disorders. Curcumin (Cur), the principal active component of spice turmeric, possesses well-established anti-obesity properties. To clarify, the study investigates whether Cur promotes GLP-1 secretion built upon the L-cell expansion.

METHODS AND RESULTS

Cur (60 mg kg-1 ) is administered orally to male ob/ob mice for 8 weeks. Cur ameliorates obesity and impaires glucose tolerance through increasing energy expenditure in ob/ob mice, accompanied by the maintenance of crypt architecture and gut permeability. It refines the microbial structure and bile acid (BA) profiles, resulting in deoxycholic acid (DCA) accumulation by weakening the enrichment of Lactobacillus. Further analyses show radically different properties of Cur on the intestine function of TGR5 and FXR (i.e., activation and repression). Cur amplifies L-cell number to promote GLP-1 secretion in ob/ob mice.

CONCLUSIONS

The findings suggest that Cur may act as a natural TGR5 agonist and FXR antagonist to improve obesity by enhancing GLP-1 release from L-cell expansion via the gut microbiota-BAs-TGR5/FXR axis, and it may serve as a promising therapeutic agent to compensate obesity-related metabolic disorders.

Unveiling the potential pleiotropic effects of metformin in treating COVID-19: a comprehensive review

This review article explores the potential of metformin, a medication commonly used for type 2 diabetes, as an antiviral and anti-inflammatory agent in the context of coronavirus disease 2019 (COVID-19). Metformin has demonstrated inhibitory effects on the growth of SARS-CoV-2 in cell culture models and has shown promising results in reducing viral load and achieving undetectable viral levels in clinical trials. Additionally, metformin exhibits anti-inflammatory properties by reducing the production of pro-inflammatory cytokines and modulating immune cell function, which may help prevent cytokine storms associated with severe COVID-19. The drug's ability to regulate the balance between pro-inflammatory Th17 cells and anti-inflammatory Treg cells suggests its potential in mitigating inflammation and restoring T cell functionality. Furthermore, metformin's modulation of the gut microbiota, particularly changes in bacterial taxa and the production of short-chain fatty acids, may contribute to its therapeutic effects. The interplay between metformin, bile acids, the gut microbiome, glucagon-like peptide-1 secretion, and glycemic control has implications for the management of diabetes and potential interventions in COVID-19. By refreshing the current evidence, this review highlights the potential of metformin as a therapeutic option in the management of COVID-19, while also exploring its effects on the gut microbiome and immunometabolism.

Contribution of the microbiome for better phenotyping of people living with obesity

Obesity has reached epidemic proportion worldwide and in all ages. Available evidence points to a multifactorial pathogenesis involving gene predisposition and environmental factors. Gut microbiota plays a critical role as a major interface between external factors, i.e., diet, lifestyle, toxic chemicals, and internal mechanisms regulating energy and metabolic homeostasis, fat production and storage. A shift in microbiota composition is linked with overweight and obesity, with pathogenic mechanisms involving bacterial products and metabolites (mainly endocannabinoid-related mediators, short-chain fatty acids, bile acids, catabolites of tryptophan, lipopolysaccharides) and subsequent alterations in gut barrier, altered metabolic homeostasis, insulin resistance and chronic, low-grade inflammation. Although animal studies point to the links between an "obesogenic" microbiota and the development of different obesity phenotypes, the translational value of these results in humans is still limited by the heterogeneity among studies, the high variation of gut microbiota over time and the lack of robust longitudinal studies adequately considering inter-individual confounders. Nevertheless, available evidence underscores the existence of several genera predisposing to obesity or, conversely, to lean and metabolically health phenotype (e.g., Akkermansia muciniphila, species from genera Faecalibacterium, Alistipes, Roseburia). Further longitudinal studies using metagenomics, transcriptomics, proteomics, and metabolomics with exact characterization of confounders are needed in this field. Results must confirm that distinct genera and specific microbial-derived metabolites represent effective and precision interventions against overweight and obesity in the long-term.

THE CONNECTION BETWEEN BILE ACIDS AND TYPE 2 DIABETES MELLITUS - A REVIEW

BACKGROUND

Bile acids (BAs) are steroid molecules synthesized exclusively in the liver, being end products of cholesterol catabolism. BAs are known to be involved in several metabolic alterations, including metabolic syndrome and type 2 diabetes mellitus (DM2). DM2 is a chronic degenerative disease characterized by insulin resistance, insulin deficiency due to insufficient production of pancreatic ß-cells, and elevated serum glucose levels leading to multiple complications.

OBJECTIVE

The objective of this study is to investigate the role of BAs in the pathophysiology of DM2, highlighting the possibilities in the development of therapeutic procedures targeting BAs as an optional pathway in the treatment of DM2.

METHODS

The research was carried out through narrative review and publications on the relationship between BAs and DM2. The databases used for the search include PubMed, Scopus, and Web of Science. The keywords used for the search include bile acids, type 2 diabetes mellitus, metabolic syndrome, and metabolic disorders.

RESULTS

The studies have reported the involvement of BAs in the pathophysiology of DM2. BAs act as a ligand for the nuclear farnesoid X receptor, regulating glucose metabolism, lipid metabolism, and cellular energy production. Additionally, BAs modulate the production, elimination, and mobilization of BAs through the farnesoid X receptor. BAs also act as a signaling pathway through Takeda G protein-coupled receptor 5, further contributing to metabolic regulation. These findings suggest that targeting BAs may offer a novel therapeutic approach in the treatment of DM2.

CONCLUSION

This study highlights the important role of BAs in DM2, specifically through their interactions with key metabolic pathways. Targeting BAs may represent an innovative and effective approach to the treatment of DM2.

Serum lipidome unravels a diagnostic potential in bile acid diarrhoea

OBJECTIVE

Bile acid diarrhoea (BAD) is debilitating yet treatable, but it remains underdiagnosed due to challenging diagnostics. We developed a blood test-based method to guide BAD diagnosis.

DESIGN

We included serum from 50 treatment-naive patients with BAD diagnosed by gold standard 75selenium homotaurocholic acid test, 56 feature-matched controls and 37 patients with non-alcoholic fatty liver disease (NAFLD). Metabolomes were generated using mass spectrometry covering 1295 metabolites and compared between groups. Machine learning was used to develop a BAD Diagnostic Score (BDS).

RESULTS

Metabolomes of patients with BAD significantly differed from controls and NAFLD. We detected 70 metabolites with a discriminatory performance in the discovery set with an area under receiver-operating curve metric above 0.80. Logistic regression modelling using concentrations of decanoylcarnitine, cholesterol ester (22:5), eicosatrienoic acid, L-alpha-lysophosphatidylinositol (18:0) and phosphatidylethanolamine (O-16:0/18:1) distinguished BAD from controls with a sensitivity of 0.78 (95% CI 0.64 to 0.89) and a specificity of 0.93 (95% CI 0.83 to 0.98). The model was independent of covariates (age, sex, body mass index) and distinguished BAD from NAFLD irrespective of fibrosis stage. BDS outperformed other blood test-based tests (7-alpha-hydroxy-4-cholesten-3-one and fibroblast growth factor 19) currently under development.

CONCLUSIONS

BDS derived from serum metabolites in a single-blood sample showed robust identification of patients with BAD with superior specificity and sensitivity compared with current blood test-based diagnostics.

The Crosstalk between Gut Microbiota and Bile Acids Promotes the Development of Non-Alcoholic Fatty Liver Disease

Recently the roles of gut microbiota are highly regarded in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). The intestinal bacteria regulate the metabolism of bile acids depending on bile salt hydrolase (BSH), 7-dehydroxylation, hydroxysteroid dehydrogenase (HSDH), or amide conjugation reaction, thus exerting effects on NAFLD development through bile acid receptors such as farnesoid X receptor (FXR), Takeda G-protein-coupled bile acid protein 5 (TGR5), and vitamin D receptor (VDR), which modulate nutrient metabolism and insulin sensitivity via interacting with downstream molecules. Reversely, the composition of gut microbiota is also affected by the level of bile acids in turn. We summarize the mutual regulation between the specific bacteria and bile acids in NAFLD and the latest clinical research based on microbiota and bile acids, which facilitate the development of novel treatment modalities in NAFLD.

RISING STARS: Endocrine regulation of metabolic homeostasis via the intestine and gut microbiome

The gastrointestinal system is now considered the largest endocrine organ, highlighting the importance of gut-derived peptides and metabolites in metabolic homeostasis. Gut peptides are secreted from intestinal enteroendocrine cells in response to nutrients, microbial metabolites, and neural and hormonal factors, and they regulate systemic metabolism via multiple mechanisms. While extensive research is focused on the neuroendocrine effects of gut peptides, evidence suggests that several of these hormones act as endocrine signaling molecules with direct effects on the target organ, especially in a therapeutic setting. Additionally, the gut microbiota metabolizes ingested nutrients and fiber to produce compounds that impact host metabolism indirectly, through gut peptide secretion, and directly, acting as endocrine factors. This review will provide an overview of the role of endogenous gut peptides in metabolic homeostasis and disease, as well as the potential endocrine impact of microbial metabolites on host metabolic tissue function.

Short-chain fatty acids, secondary bile acids and indoles: gut microbial metabolites with effects on enteroendocrine cell function and their potential as therapies for metabolic disease

The gastrointestinal tract hosts the largest ecosystem of microorganisms in the body. The metabolism of ingested nutrients by gut bacteria produces novel chemical mediators that can influence chemosensory cells lining the gastrointestinal tract. Specifically, hormone-releasing enteroendocrine cells which express a host of receptors activated by these bacterial metabolites. This review will focus on the activation mechanisms of glucagon-like peptide-1 releasing enteroendocrine cells by the three main bacterial metabolites produced in the gut: short-chain fatty acids, secondary bile acids and indoles. Given the importance of enteroendocrine cells in regulating glucose homeostasis and food intake, we will also discuss therapies based on these bacterial metabolites used in the treatment of metabolic diseases such as diabetes and obesity. Elucidating the mechanisms gut bacteria can influence cellular function in the host will advance our understanding of this fundamental symbiotic relationship and unlock the potential of harnessing these pathways to improve human health.

Pharmacotherapies of NAFLD: updated opportunities based on metabolic intervention

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease that is becoming increasingly prevalent, and it ranges from simple steatosis to cirrhosis. However, there is still a lack of pharmacotherapeutic strategies approved by the Food and Drug Administration, which results in a higher risk of death related to carcinoma and cardiovascular complications. Of note, it is well established that the pathogenesis of NAFLD is tightly associated with whole metabolic dysfunction. Thus, targeting interconnected metabolic conditions could present promising benefits to NAFLD, according to a number of clinical studies. Here, we summarize the metabolic characteristics of the development of NAFLD, including glucose metabolism, lipid metabolism and intestinal metabolism, and provide insight into pharmacological targets. In addition, we present updates on the progresses in the development of pharmacotherapeutic strategies based on metabolic intervention globally, which could lead to new opportunities for NAFLD drug development.

Interactions between Intestinal Homeostasis and NAD+ Biology in Regulating Incretin Production and Postprandial Glucose Metabolism

The intestine has garnered attention as a target organ for developing new therapies for impaired glucose tolerance. The intestine, which produces incretin hormones, is the central regulator of glucose metabolism. Glucagon-like peptide-1 (GLP-1) production, which determines postprandial glucose levels, is regulated by intestinal homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT)-mediated nicotinamide adenine dinucleotide (NAD⁺) biosynthesis in major metabolic organs such as the liver, adipose tissue, and skeletal muscle plays a crucial role in obesity- and aging-associated organ derangements. Furthermore, NAMPT-mediated NAD⁺ biosynthesis in the intestines and its upstream and downstream mediators, adenosine monophosphate-activated protein kinase (AMPK) and NAD⁺-dependent deacetylase sirtuins (SIRTs), respectively, are critical for intestinal homeostasis, including gut microbiota composition and bile acid metabolism, and GLP-1 production. Thus, boosting the intestinal AMPK-NAMPT-NAD⁺-SIRT pathway to improve intestinal homeostasis, GLP-1 production, and postprandial glucose metabolism has gained significant attention as a novel strategy to improve impaired glucose tolerance. Herein, we aimed to review in detail the regulatory mechanisms and importance of intestinal NAMPT-mediated NAD⁺ biosynthesis in regulating intestinal homeostasis and GLP-1 secretion in obesity and aging. Furthermore, dietary and molecular factors regulating intestinal NAMPT-mediated NAD⁺ biosynthesis were critically explored to facilitate the development of new therapeutic strategies for postprandial glucose dysregulation.

The gut microbiome: a core regulator of metabolism

The human body is inhabited by numerous bacteria, fungi, and viruses, and each part has a unique microbial community structure. The gastrointestinal tract harbors approximately 100 trillion strains comprising more than 1000 bacterial species that maintain symbiotic relationships with the host. The gut microbiota consists mainly of the phyla Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Of these, Firmicutes and Bacteroidetes constitute 70-90% of the total abundance. Gut microbiota utilize nutrients ingested by the host, interact with other bacterial species, and help maintain healthy homeostasis in the host. In recent years, it has become increasingly clear that a breakdown of the microbial structure and its functions, known as dysbiosis, is associated with the development of allergies, autoimmune diseases, cancers, and arteriosclerosis, among others. Metabolic diseases, such as obesity and diabetes, also have a causal relationship with dysbiosis. The present review provides a brief overview of the general roles of the gut microbiota and their relationship with metabolic disorders.

Intestinal Farnesoid X Receptor Modulates Duodenal Surface Area but Does Not Control Glucose Absorption in Mice

Bile acids facilitate the intestinal absorption of dietary lipids and act as signalling molecules in the maintenance of metabolic homeostasis. Farnesoid X receptor (FXR) is a bile acid-responsive nuclear receptor involved in bile acid metabolism, as well as lipid and glucose homeostasis. Several studies have suggested a role of FXR in the control of genes regulating intestinal glucose handling. We applied a novel dual-label glucose kinetic approach in intestine-specific FXR^-/- mice (iFXR-KO) to directly assess the role of intestinal FXR in glucose absorption. Although iFXR-KO mice showed decreased duodenal expression of hexokinase 1 (Hk1) under obesogenic conditions, the assessment of glucose fluxes in these mice did not show a role for intestinal FXR in glucose absorption. FXR activation with the specific agonist GS3972 induced Hk1, yet the glucose absorption rate remained unaffected. FXR activation increased the duodenal villus length in mice treated with GS3972, while stem cell proliferation remained unaffected. Accordingly, iFXR-KO mice on either chow, short or long-term HFD feeding displayed a shorter villus length in the duodenum compared to wild-type mice. These findings indicate that delayed glucose absorption reported in whole-body FXR^-/- mice is not due to the absence of intestinal FXR. Yet, intestinal FXR does have a role in the small intestinal surface area.

The Implication of Mechanistic Approaches and the Role of the Microbiome in Polycystic Ovary Syndrome (PCOS): A Review

As a complex endocrine and metabolic condition, polycystic ovarian syndrome (PCOS) affects women's reproductive health. These common symptoms include hirsutism, hyperandrogenism, ovulatory dysfunction, irregular menstruation, and infertility. No one knows what causes it or how to stop it yet. Alterations in gut microbiota composition and disruptions in secondary bile acid production appear to play a causative role in developing PCOS. PCOS pathophysiology and phenotypes are tightly related to both enteric and vaginal bacteria. Patients with PCOS exhibit changed microbiome compositions and decreased microbial diversity. Intestinal microorganisms also alter PCOS patient phenotypes by upregulating or downregulating hormone release, gut-brain mediators, and metabolite synthesis. The human body's gut microbiota, also known as the "second genome," can interact with the environment to improve metabolic and immunological function. Inflammation is connected to PCOS and may be caused by dysbiosis in the gut microbiome. This review sheds light on the recently discovered connections between gut microbiota and insulin resistance (IR) and the potential mechanisms of PCOS. This study also describes metabolomic studies to obtain a clear view of PCOS and ways to tackle it.

Lithocholic acid promotes skeletal muscle regeneration through the TGR5 receptor

<p indent="0mm">Lithocholic acid (LCA) is a classical secondary bile acid formed by the metabolism of gut microbiota. The TGR5 receptor (also known as G protein-coupled receptor 1, GPBAR1) is an important bile acid membrane receptor that mediates a variety of metabolic processes <italic>in vivo</italic>. In recent years, most studies have focused on the role of bile acid receptors in the intestine and liver. However, there are few reports on its effect on skeletal muscle regeneration, and the specific mechanism remains unclear. Therefore, it is necessary to investigate the mechanism of the TGR5 receptor in the regulation of skeletal muscle regeneration. The results demonstrate that muscle injection with LCA significantly reduces the necrosis rate of injured muscle and improves muscle injury. Moreover, treatment of C2C12 cells with LCA significantly increases AKT/mTOR/FoxO3 phosphorylation through the TGR5 receptor, enhances MyoG transcription and reduces FBXO32 transcription. These findings indicate that LCA can activate the TGR5/AKT signaling pathway, inhibit protein degradation and promote protein synthesis to enhance the myogenic process and promote skeletal muscle regeneration. </p>.

Inulin increases the beneficial effects of rhubarb supplementation on high-fat high-sugar diet-induced metabolic disorders in mice: impact on energy expenditure, brown adipose tissue activity, and microbiota

Consumption of prebiotics and plant-based compounds have many beneficial health effects through modulation of gut microbiota composition and are considered as promising nutritional strategy for the treatment of metabolic diseases. In the present study, we assessed the separated and combined effects of inulin and rhubarb on diet-induced metabolic disease in mice. We showed that supplementation with both inulin and rhubarb abolished the total body and fat mass gain upon high-fat and high-sucrose diet (HFHS) as well as several obesity-associated metabolic disorders. These effects were associated with increased energy expenditure, lower whitening of the brown adipose tissue, higher mitochondria activity and increased expression of lipolytic markers in white adipose tissue. Despite modifications of intestinal gut microbiota and bile acid compositions by inulin or rhubarb alone, combination of both inulin and rhubarb had minor additional impact on these parameters. However, the combination of inulin and rhubarb increased the expression of several antimicrobial peptides and higher goblet cell numbers, thereby suggesting a reinforcement of the gut barrier. Together, these results suggest that the combination of inulin and rhubarb in mice potentiates beneficial effects of separated rhubarb and inulin on HFHS-related metabolic disease and could be considered as nutritional strategy for the prevention and treatment of obesity and related pathologies.

New insights into the inter-organ crosstalk mediated by ChREBP

Carbohydrate response element binding protein (ChREBP) is a glucose responsive transcription factor recognized by its critical role in the transcriptional control of glycolysis and de novo lipogenesis. Substantial advances in the field have revealed novel ChREBP functions. Indeed, due to its actions in different tissues, ChREBP modulates the inter-organ communication through secretion of peptides and lipid factors, ensuring metabolic homeostasis. Dysregulation of these orchestrated interactions is associated with development of metabolic diseases such as type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD). Here, we recapitulate the current knowledge about ChREBP-mediated inter-organ crosstalk through secreted factors and its physiological implications. As the liver is considered a crucial endocrine organ, we will focus in this review on the role of ChREBP-regulated hepatokines. Lastly, we will discuss the involvement of ChREBP in the progression of metabolic pathologies, as well as how the impairment of ChREBP-dependent signaling factors contributes to the onset of such diseases.

Caffeic acid phenethyl ester suppresses intestinal FXR signaling and ameliorates nonalcoholic fatty liver disease by inhibiting bacterial bile salt hydrolase activity

Propolis is commonly used in traditional Chinese medicine. Studies have demonstrated the therapeutic effects of propolis extracts and its major bioactive compound caffeic acid phenethyl ester (CAPE) on obesity and diabetes. Herein, CAPE was found to have pharmacological activity against nonalcoholic fatty liver disease (NAFLD) in diet-induced obese mice. CAPE, previously reported as an inhibitor of bacterial bile salt hydrolase (BSH), inhibited BSH enzymatic activity in the gut microbiota when administered to mice. Upon BSH inhibition by CAPE, levels of tauro-β-muricholic acid were increased in the intestine and selectively suppressed intestinal farnesoid X receptor (FXR) signaling. This resulted in lowering of the ceramides in the intestine that resulted from increased diet-induced obesity. Elevated intestinal ceramides are transported to the liver where they promoted fat production. Lowering FXR signaling was also accompanied by increased GLP-1 secretion. In support of this pathway, the therapeutic effects of CAPE on NAFLD were absent in intestinal FXR-deficient mice, and supplementation of mice with C16-ceramide significantly exacerbated hepatic steatosis. Treatment of mice with an antibiotic cocktail to deplete BSH-producing bacteria also abrogated the therapeutic activity of CAPE against NAFLD. These findings demonstrate that CAPE ameliorates obesity-related steatosis at least partly through the gut microbiota-bile acid-FXR pathway via inhibiting bacterial BSH activity and suggests that propolis enriched with CAPE might serve as a promising therapeutic agent for the treatment of NAFLD.

Gut microbiota: The key to the treatment of metabolic syndrome in traditional Chinese medicine - a case study of diabetes and nonalcoholic fatty liver disease

Metabolic syndrome mainly includes obesity, type 2 diabetes (T2DM), alcoholic fatty liver (NAFLD) and cardiovascular diseases. According to the ancient experience philosophy of Yin-Yang, monarch-minister compatibility of traditional Chinese medicine, prescription is given to treat diseases, which has the advantages of small toxic and side effects and quick effect. However, due to the diversity of traditional Chinese medicine ingredients and doubts about the treatment theory of traditional Chinese medicine, the mechanism of traditional Chinese medicine is still in doubt. Gastrointestinal tract is an important part of human environment, and participates in the occurrence and development of diseases. In recent years, more and more TCM researches have made intestinal microbiome a new frontier for understanding and treating diseases. Clinically, nonalcoholic fatty liver disease (NAFLD) and diabetes mellitus (DM) often co-occur. Our aim is to explain the mechanism of interaction between gastrointestinal microbiome and traditional Chinese medicine (TCM) or traditional Chinese medicine formula to treat DM and NAFLD. Traditional Chinese medicine may treat these two diseases by influencing the composition of intestinal microorganisms, regulating the metabolism of intestinal microorganisms and transforming Chinese medicinal compounds.

From fecal microbiota transplantation toward next-generation beneficial microbes: The case of Anaerobutyricum soehngenii

The commensal gut microbiota is important for human health and well-being whereas deviations of the gut microbiota have been associated with a multitude of diseases. Restoration of a balanced and diverse microbiota by fecal microbiota transplantation (FMT) has emerged as a potential treatment strategy and promising tool to study causality of the microbiota in disease pathogenesis. However, FMT comes with logistical challenges and potential safety risks, such as the transfer of pathogenic microorganisms, undesired phenotypes or an increased risk of developing disease later in life. Therefore, a more controlled, personalized mixture of cultured beneficial microbes might prove a better alternative. Most of these beneficial microbes will be endogenous commensals to the host without a long history of safe and beneficial use and are therefore commonly referred to as next-generation probiotics (NGP) or live biotherapeutic products (LBP). Following a previous FMT study within our group, the commensal butyrate producer Anaerobutyricum spp. (previously named Eubacterium hallii) was found to be associated with improved insulin-sensitivity in subjects with the metabolic syndrome. After the preclinical testing with Anaerobutyricum soehngenii in mice models was completed, the strain was produced under controlled conditions and several clinical studies evaluating its safety and efficacy in humans were performed. Here, we describe and reflect on the development of A. soehngenii for clinical use, providing practical guidance for the development and testing of NGPs and reflecting on the current regulatory framework.