TGR5-mediated bile acid sensing controls glucose homeostasis

Current and Future Treatments in the Fight Against Non-Alcoholic Fatty Liver Disease

Obesity is recognised as a risk factor for many types of cancers, in particular hepatocellular carcinoma (HCC). A critical factor in the development of HCC from non-alcoholic fatty liver disease (NAFLD) is the presence of non-alcoholic steatohepatitis (NASH). Therapies aimed at NASH to reduce the risk of HCC are sparse and largely unsuccessful. Lifestyle modifications such as diet and regular exercise have poor adherence. Moreover, current pharmacological treatments such as pioglitazone and vitamin E have limited effects on fibrosis, a key risk factor in HCC progression. As NAFLD is becoming more prevalent in developed countries due to rising rates of obesity, a need for directed treatment is imperative. Numerous novel therapies including PPAR agonists, anti-fibrotic therapies and agents targeting inflammation, oxidative stress and the gut-liver axis are currently in development, with the aim of targeting key processes in the progression of NASH and HCC. Here, we critically evaluate literature on the aetiology of NAFLD-related HCC, and explore the potential treatment options for NASH and HCC.

Molecular regulators of lipid metabolism in the intestine - Underestimated therapeutic targets for obesity?

The incidence of obesity and type 2 diabetes continues to rise across the globe necessitating the need to identify new therapeutic approaches to manage these diseases. In this review, we explore the potential for therapeutic interventions focussed on the intestinal epithelium, by targeting the role of this tissue in lipid uptake, lipid-mediated cross talk and lipid oxidation. We focus initially on ongoing strategies to manage obesity by targeting the essential role of the intestinal epithelium in lipid uptake, and in mediating tissue cross talk to regulate food intake. Subsequently, we explore a previously underestimated capacity of intestinal epithelial cells to oxidize fatty acids. In this context, we describe recent findings which have unveiled a key role for the peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors and histone deacetylases (HDACs) in the regulation of lipid oxidation genes in enterocytes and how targeted genetic manipulation of these factors in enterocytes reduces weight gain, identifying intestinal PPARs and HDACs as potential therapeutic targets in the management of obesity.

The effect of exenatide on fasting bile acids in newly diagnosed type 2 diabetes mellitus patients, a pilot study

Background

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) demonstrated good glycemic efficacy in patients with type 2 diabetes mellitus (T2DM) recent years, whereas studies on GLP-1 RAs’ biliary effects were limited. Therefore, we aimed to assess the effect of exenatide on bile acids (BAs) and investigate the role of BAs in the glycemic control effect of exenatide.

Methods

Thirty-eight newly diagnosed T2DM participants without glucose-lowering drugs intake were recruited. Plasma total bile acids in fasting state (FTBAs) and other parameters were tested at baseline. Then exenatide were applied to the T2DM participants for 12 weeks. FTBAs and glycemic parameters were measured again after exenatide treatment, and correlation analysis between changes of FTBAs and glycemic parameters were conducted to investigate the role of BAs in the glycemic control effect of exenatide.

Results

The baseline FTBAs level of T2DM patients had no significance (3.84 ± 2.06 vs. 3.87 ± 2.89, P = 0.954) compared with healthy subjects. After 12-week exenatide treatment for the T2DM patients, FTBAs were decreased from 3.84 ± 2.06 μmol/L to 3.06 ± 1.27 μmol/L (P < 0.01). The correlation analysis showed that changes of FTBAs was positively correlated with changes of FPG (r = 0.355, P < 0.05).

Conclusions

Our results demonstrated a decreased FTBAs level after exenatide treatment for 12 weeks, without the interference of metformin and other glucose-lowering drugs. The reduction of FTBAs might not exert a positive role in the glycemic control effect of exenatide.

Trial registration

Trial registration number: NCT04303819. Registered in March 11, 2020 - Retrospectively registered.

Up to date on cholesterol 7 alpha-hydroxylase (CYP7A1) in bile acid synthesis

Cholesterol 7 alpha-hydroxylase (CYP7A1, EC1.14) is the first and rate-limiting enzyme in the classic bile acid synthesis pathway. Much progress has been made in understanding the transcriptional regulation of CYP7A1 gene expression and the underlying molecular mechanisms of bile acid feedback regulation of CYP7A1 and bile acid synthesis in the last three decades. Discovery of bile acid-activated receptors and their roles in the regulation of lipid, glucose and energy metabolism have been translated to the development of bile acid-based drug therapies for the treatment of liver-related metabolic diseases such as alcoholic and non-alcoholic fatty liver diseases, liver cirrhosis, diabetes, obesity and hepatocellular carcinoma. This review will provide an update on the advances in our understanding of the molecular biology and mechanistic insights of the regulation of CYP7A1 in bile acid synthesis in the last 40 years.

ID1-Mediated BMP Signaling Pathway Potentiates Glucagon-Like Peptide-1 Secretion in Response to Nutrient Replenishment

Glucagon-like peptide-1 (GLP-1) is a well-known incretin hormone secreted from enteroendocrinal L cells in response to nutrients, such as glucose and dietary fat, and controls glycemic homeostasis. However, the detailed intracellular mechanisms of how L cells control GLP-1 secretion in response to nutrients still remain unclear. Here, we report that bone morphogenetic protein (BMP) signaling pathway plays a pivotal role to control GLP-1 secretion in response to nutrient replenishment in well-established mouse enteroendocrinal L cells (GLUTag cells). Nutrient starvation dramatically reduced cellular respiration and GLP-1 secretion in GLUTag cells. Transcriptome analysis revealed that nutrient starvation remarkably reduced gene expressions involved in BMP signaling pathway, whereas nutrient replenishment rescued BMP signaling to potentiate GLP-1 secretion. Transient knockdown of inhibitor of DNA binding (ID)1, a well-known target gene of BMP signaling, remarkably reduced GLP-1 secretion. Consistently, LDN193189, an inhibitor of BMP signaling, markedly reduced GLP-1 secretion in L cells. In contrast, BMP4 treatment activated BMP signaling pathway and potentiated GLP-1 secretion in response to nutrient replenishment. Altogether, we demonstrated that BMP signaling pathway is a novel molecular mechanism to control GLP-1 secretion in response to cellular nutrient status. Selective activation of BMP signaling would be a potent therapeutic strategy to stimulate GLP-1 secretion in order to restore glycemic homeostasis.

Novel Strategies to Prevent Total Parenteral Nutrition-Induced Gut and Liver Inflammation, and Adverse Metabolic Outcomes

Total parenteral nutrition (TPN) is a life-saving therapy administered to millions of patients. However, it is associated with significant adverse effects, namely liver injury, risk of infections, and metabolic derangements. In this review, the underlying causes of TPN-associated adverse effects, specifically gut atrophy, dysbiosis of the intestinal microbiome, leakage of the epithelial barrier with bacterial invasion, and inflammation are first described. The role of the bile acid receptors farnesoid X receptor and Takeda G protein-coupled receptor, of pleiotropic hormones, and growth factors is highlighted, and the mechanisms of insulin resistance, namely the lack of insulinotropic and insulinomimetic signaling of gut-originating incretins as well as the potentially toxicity of phytosterols and pro-inflammatory fatty acids mainly released from soybean oil-based lipid emulsions, are discussed. Finally, novel approaches in the design of next generation lipid delivery systems are proposed. Propositions include modifying the physicochemical properties of lipid emulsions, the use of lipid emulsions generated from sustainable oils with favorable ratios of anti-inflammatory n-3 to pro-inflammatory n-6 fatty acids, beneficial adjuncts to TPN, and concomitant pharmacotherapies to mitigate TPN-associated adverse effects.

Modulation of the human gut microbiota by phenolics and phenolic fiber-rich foods

The gut microbiota plays a prominent role in human health. Alterations in the gut microbiota are linked to the development of chronic diseases such as obesity, inflammatory bowel disease, metabolic syndrome, and certain cancers. We know that diet plays an important role to initiate, shape, and modulate the gut microbiota. Long-term dietary patterns are shown to be closely related with the gut microbiota enterotypes, specifically long-term consumption of carbohydrates (related to Prevotella abundance) or a diet rich in protein and animal fats (correlated to Bacteroides). Short-term consumption of solely animal- or plant-based diets have rapid and reproducible modulatory effects on the human gut microbiota. These alterations in microbiota profile by dietary alterations can be due to impact of different dietary macronutrients, carbohydrates, protein, and fat, which have diverse modulatory effects on gut microbial composition. Food-derived phenolics, which encompass structural variants of flavonoids, hydroxybenzoic acids, hydroxycinnamic acids, coumarins, stilbenes, ellagitannins, and lignans can modify the gut microbiota. Gut microbes have been shown to act on dietary fibers and phenolics to produce functional metabolites that contribute to gut health. Here, we discuss recent studies on the impacts of phenolics and phenolic fiber-rich foods on the human gut microbiota and provide an insight into potential synergistic roles between their bacterial metabolic products in the regulation of the intestinal microbiota.

Treatment of Obesity in Mitigating Metabolic Risk

Through diverse mechanisms, obesity contributes to worsened cardiometabolic health and increases rates of cardiovascular events. Effective treatment of obesity is necessary to reduce the associated burdens of diabetes mellitus, cardiovascular disease, and death. Despite increasing cardiovascular outcome data on obesity interventions, only a small fraction of the population with obesity are optimally treated. This is a primary impetus for this article in which we describe the typical weight loss, as well as the associated impact on both traditional and novel cardiovascular disease risk factors, provided by the 4 primary modalities for obtaining weight loss in obesity-dietary modification, increasing physical activity, pharmacotherapy, and surgery. We also attempt to highlight instances where changes in metabolic risk are relatively specific to particular interventions and appear at least somewhat independent of weight loss. Finally, we suggest important areas for further research to reduce and prevent adverse cardiovascular consequences due to obesity.

Dietary supplementation with Lactobacillus plantarum modified gut microbiota, bile acid profile and glucose homoeostasis in weaning piglets

Bile acids (BA) have emerged as signalling molecules regulating intestinal physiology. The importance of intestinal microbiota in production of secondary BA, for example, lithocholic acid (LCA) which impairs enterocyte proliferation and permeability, triggered us to determine the effects of oral probiotics on intestinal BA metabolism. Piglets were weaned at 28 d of age and allocated into control (CON, n 14) or probiotic (PRO, n 14) group fed 50 mg of Lactobacillus plantarum daily, and gut microbiota and BA profile were determined. To test the potential interaction of LCA with bacteria endotoxins in inducing damage of enterocytes, IPEC-J2 cells were treated with LCA, lipopolysaccharide (LPS) and LCA + LPS and expressions of genes related to inflammation, antioxidant capacity and nutrient transport were determined. Compared with the CON group, the PRO group showed lower total LCA level in the ileum and higher relative abundance of the Lactobacillus genus in faeces. In contrast, the relative abundances of Bacteroides, Clostridium_sensu_stricto_1, Parabacteroides and Ruminococcus_1, important bacteria genera in BA biotransformation, were all lower in the PRO than in the CON group. Moreover, PRO piglets had lower postprandial glucagon-like peptide-1 level, while higher glucose level than CON piglets. Co-administration of LPS and LCA led to down-regulated expression of glucose and peptide transporter genes in IPEC-J2 cells. Altogether, oral L. plantarum altered BA profile probably by modulating relative abundances of gut microbial genera that play key roles in BA metabolism and might consequently impact glucose homoeostasis. The detrimental effect of LCA on nutrient transport in enterocytes might be aggravated under LPS challenge.

Hepatic lipid droplet homeostasis and fatty liver disease

In cells, lipids are stored in lipid droplets, dynamic organelles that adapt their size, abundance, lipid and protein composition and organelle interactions to metabolic changes. Lipid droplet accumulation in the liver is the hallmark of non-alcoholic fatty liver disease (NAFLD). Due to the prevalence of obesity, the strongest risk factor for steatosis, NAFLD and its associated complications are currently affecting more than 1 billion people worldwide. Here, we review how triglyceride and phospholipid homeostasis are regulated in hepatocytes and how imbalances between lipid storage, degradation and lipoprotein secretion lead to NAFLD. We discuss how organelle interactions are altered in NAFLD and provide insights how NAFLD progression is associated with changes in hepatocellular signaling and organ-crosstalk. Finally, we highlight unsolved questions in hepatic LD and lipoprotein biology and give an outlook on therapeutic options counteracting hepatic lipid accumulation.

Hepatic Bile Acid Reuptake in the Rat Depends on Bile Acid Conjugation but Not on Agonistic Properties towards FXR and TGR5

Farnesoid X receptor (FXR) and Takeda G-protein coupled receptor 5 (TGR5) are the two known bile acid (BA) sensitive receptors and are expressed in the intestine and liver as well as in extra-enterohepatic tissues. The physiological effects of extra-enterohepatic FXR/TRG5 remain unclear. Further, the extent BAs escape liver reabsorption and how they interact with extra-enterohepatic FXR/TGR5 is understudied. We investigated if hepatic BA reuptake differed between BAs agonistic for FXR and TGR5 compared to non-agonists in the rat. Blood was collected from the portal vein and inferior caval vein from anesthetized rats before and 5, 20, 30, and 40 min post stimulation with sulfated cholecystokinin-8. Plasma concentrations of 20 different BAs were assessed by liquid chromatography coupled to mass spectrometry. Total portal vein BA AUC was 3–4 times greater than in the vena cava inferior (2.7 ± 0.6 vs. 0.7 ± 0.2 mM x min, p < 0.01, n = 8) with total unconjugated BAs being 2–3-fold higher than total conjugated BAs (AUC 8–10 higher p < 0.05 for both). However, in both cases, absolute ratios varied greatly among different BAs. The average hepatic reuptake of BAs agonistic for FXR/TGR5 was similar to non-agonists. However, as the sum of non-agonist BAs in vena portae was 2–3-fold higher than the sum agonist (p < 0.05), the peripheral BA pool was composed mostly of non-agonist BAs. We conclude that hepatic BA reuptake varies substantially by type and does not favor FXR/TGR5 BAs agonists.

Capsaicin improves glucose homeostasis by enhancing glucagon-like peptide-1 secretion through the regulation of bile acid metabolism via the remodeling of the gut microbiota in male mice

Mounting evidence has linked dietary capsaicin (CAP) consumption to the improvement of glucose homeostasis; however, the underlying mechanisms still need to be further elucidated. Male mice were fed a high-fat diet (HFD) with CAP administration for 8 weeks, gut microbiota, bile acid (BA) profiles and markers for BA, and glucose metabolism were investigated. CAP improved glucose homeostasis partially by enhancing the secretion of glucagon-like peptide 1 (GLP-1). The gut microbiota was remodeled by CAP and was characterized by the increased abundance of Bacteroides genera, which is related with lithocholic acid (LCA) production. LCA is an endogenous agonist of Takeda G-protein coupled receptor 5 (TGR5); it may enhance GLP-1 secretion in intestinal L cells. Meanwhile, antibiotics experiment abolished the effects of CAP on glucose homeostasis and microbiota transplantation experiments demonstrated that the CAP-induced beneficial effects were transferable, indicating that the effects of CAP on glucose homeostasis were largely dependent on the gut microbiota. Additionally, we further identified that the improvements induced by CAP were attenuated by the antagonist of GLP-1 receptor, indicating that the activation of GLP-1 signaling contributes to the CAP-induced improvement in glucose homeostasis.

Impact of air pollution on intestinal redox lipidome and microbiome

Air pollution is a rising public health issue worldwide. Cumulative epidemiological and experimental studies have shown that exposure to air pollution such as particulate matter (PM) is linked with increased hospital admissions and all-cause mortality. While previous studies on air pollution mostly focused on the respiratory and cardiovascular effects, emerging evidence supports a significant impact of air pollution on the gastrointestinal (GI) system. The gut is exposed to PM as most of the inhaled particles are removed from the lungs to the GI tract via mucociliary clearance. Ingestion of contaminated food and water is another common source of GI tract exposure to pollutants. Recent studies have associated air pollution with intestinal diseases, including appendicitis, colorectal cancer, and inflammatory bowel disease. In addition to the liver and adipose tissue, intestine is an important organ system for lipid metabolism, and the intestinal redox lipids might be tightly associated with the intestinal and systematic inflammation. The gut microbiota modulates lipid metabolism and contributes to the initiation and development of intestinal disease including inflammatory bowel disease. Recent data support microbiome implication in air pollution-mediated intestinal and systematic effects. In this review, the associations between air pollution and intestinal diseases, and the alterations of intestinal lipidome and gut microbiome by air pollution are highlighted. The potential mechanistic aspects underlying air pollution-mediated intestinal pathology will also be discussed.

A dysregulated bile acid-gut microbiota axis contributes to obesity susceptibility

BACKGROUND

The composition of the bile acid (BA) pool is closely associated with obesity and is modified by gut microbiota. Perturbations of gut microbiota shape the BA composition, which, in turn, may alter important BA signaling and affect host metabolism.

METHODS

We investigated BA composition of high BMI subjects from a human cohort study and a high fat diet (HFD) obesity prone (HF-OP) / HFD obesity resistant (HF-OR) mice model. Gut microbiota was analysed by metagenomics sequencing. GLP-1 secretion and gene regulation studies involved ELISA, qPCR, Western blot, Immunohistochemistry, and Immunofluorescence staining.

FINDINGS

We found that the proportion of non-12-OH BAs was significantly decreased in the unhealthy high BMI subjects. The HF-OR mice had an enhanced level of non-12-OH BAs. Non-12-OH BAs including ursodeoxycholate (UDCA), chenodeoxycholate (CDCA), and lithocholate (LCA) were decreased in the HF-OP mice and associated with altered gut microbiota. Clostridium scindens was decreased in HF-OP mice and had a positive correlation with UDCA and LCA. Gavage of Clostridium scindens in mice increased the levels of hepatic non-12-OH BAs, accompanied by elevated serum 7α-hydroxy-4-cholesten-3-one (C4) levels. In HF-OP mice, altered BA composition was associated with significantly downregulated expression of GLP-1 in ileum and PGC1α, UCP1 in brown adipose tissue. In addition, we identified that UDCA attenuated the high fat diet-induced obesity via enhancing levels of non-12-OH BAs.

INTERPRETATION

Our study highlights that dysregulated BA signaling mediated by gut microbiota contributes to obesity susceptibility, suggesting modulation of BAs could be a promising strategy for obesity therapy.

Therapeutic Landscape for NAFLD in 2020

Lifestyle modifications focused on healthy eating and regular exercise are the primary recommendations for patients with nonalcoholic steatohepatitis (NASH). However, for multiple societal, psychological, physical, genetic, and epigenetic reasons, the ability of people to adopt and sustain such changes is challenging and typically not successful. To end the epidemic of NASH and prevent its complications, including cirrhosis and hepatocellular carcinoma, pharmacological interventions are now being evaluated in clinical trials. Treatments include drugs targeting energy intake, energy disposal, lipotoxic liver injury, and the resulting inflammation and fibrogenesis that lead to cirrhosis. It is likely that patients develop the phenotype of NASH by multiple mechanisms, and thus the optimal treatments of NASH will likely evolve to personalized therapy once we understand the mechanistic underpinnings of NASH in each patient. Reviewed here is the treatment landscape in this rapidly evolving field with an emphasis on drugs in Phase 2 and Phase 3 trials.

Pharmacological activation of TGR5 promotes intestinal growth via a GLP-2-dependent pathway in mice

Glucagon-like peptide (GLP)-1 and -2-secreting L cells have been shown to express the bile acid receptor Takeda G protein-receptor-5 (TGR5) and increase secretion upon receptor activation. Previous studies have explored GLP-1 secretion following acute TGR5 activation, but chronic activation and GLP-2 responses have not been characterized. In this study, we aimed to investigate the consequences of pharmacological TGR5 receptor activation on L cell hormone production in vivo using the specific TGR5 agonist RO5527239 and the GLP-2 receptor knockout mouse. Here, we show that 1) TGR5 receptor activation led to increased GLP-1 and GLP-2 content in the colon, which 2) was associated with an increased small intestinal weight that 3) was GLP-2 dependent. Additionally, we report that TGR5-mediated gallbladder filling occurred independently of GLP-2 signaling. In conclusion, we demonstrate that pharmacological TGR5 receptor activation stimulates L cells, triggering GLP-2-dependent intestinal adaption in mice.NEW & NOTEWORTHY Using the specific Takeda G protein-receptor-5 (TGR5) agonist RO5527239 and GLP-2 receptor knockout mice, we show that activation of TGR5 led to the increase in colonic GLP-1 and GLP-2 concomitant with a GLP-2 dependent growth response in the proximal portion of the small intestine.

Hepatoprotective impact of the bile acid receptor TGR5

During liver repair after injury, bile secretion has to be tightly modulated in order to preserve liver parenchyma from bile acid (BA)-induced injury. The mechanisms allowing the liver to maintain biliary homeostasis during repair after injury are not completely understood. Besides their historical role in lipid digestion, bile acids (BA) and their receptors constitute a signalling network with multiple impacts on liver repair, both stimulating regeneration and protecting the liver from BA overload. BA signal through nuclear (mainly Farnesoid X Receptor, FXR) and membrane (mainly G Protein-coupled BA Receptor 1, GPBAR-1 or TGR5) receptors to elicit a wide array of biological responses. While a great number of studies have been dedicated to the hepato-protective impact of FXR signalling, TGR5 is by far less explored in this context. Because the liver has to face massive and potentially harmful BA overload after partial ablation or destruction, BA-induced protective responses crucially contribute to spare liver repair capacities. Based on the available literature, the TGR5 BA receptor protects the remnant liver and maintains biliary homeostasis, mainly through the control of inflammation, biliary epithelial barrier permeability, BA pool hydrophobicity and sinusoidal blood flow. Mouse experimental models of liver injury reveal that in the lack of TGR5, excessive inflammation, leaky biliary epithelium and hydrophobic BA overload result in parenchymal insult and compromise optimal restoration of a functional liver mass. Translational perspectives are thus opened to target TGR5 with the aim of protecting the liver in the context of injury and BA overload.

Ileo-colonic delivery of conjugated bile acids improves glucose homeostasis via colonic GLP-1-producing enteroendocrine cells in human obesity and diabetes

Background

The bile acid (BA) pathway plays a role in regulation of food intake and glucose metabolism, based mainly on findings in animal models. Our aim was to determine whether the BA pathway is altered and correctable in human obesity and diabetes.

Methods

We conducted 3 investigations: 1) BA receptor pathways were studied in NCI-H716 enteroendocrine cell (EEC) line, whole human colonic mucosal tissue and in human colonic EEC isolated by Fluorescence-activated Cell Sorting (ex vivo) from endoscopically-obtained biopsies colon mucosa; 2) We characterized the BA pathway in 307 participants by measuring during fasting and postprandial levels of FGF19, 7αC4 and serum BA; 3) In a placebo-controlled, double-blind, randomised, 28-day trial, we studied the effect of ileo-colonic delivery of conjugated BAs (IC-CBAS) on glucose metabolism, incretins, and lipids, in participants with obesity and diabetes.

Findings

Human colonic GLP-1-producing EECs express TGR5, and upon treatment with bile acids in vitro, human EEC differentially expressed GLP-1 at the protein and mRNA level. In Ussing Chamber, GLP-1 release was stimulated by Taurocholic acid in either the apical or basolateral compartment. FGF19 was decreased in obesity and diabetes compared to controls. When compared to placebo, IC-CBAS significantly decreased postprandial glucose, fructosamine, fasting insulin, fasting LDL, and postprandial FGF19 and increased postprandial GLP-1 and C-peptide. Increase in faecal BA was associated with weight loss and with decreased fructosamine.

Interpretations

In humans, BA signalling machinery is expressed in colonic EECs, deficient in obesity and diabetes, and when stimulated with IC-CBAS, improved glucose homeostasis. ClinicalTrials.gov number, NCT02871882, NCT02033876.

Funding

Research support and drug was provided by Satiogen Pharmaceuticals (San Diego, CA). AA, MC, and NFL report grants (AA- C-Sig P30DK84567, K23 DK114460; MC- NIH R01 DK67071; NFL- R01 DK057993) from the NIH. JR was supported by an Early Career Grant from Society for Endocrinology.

Loss of Glp2r signaling activates hepatic stellate cells and exacerbates diet-induced steatohepatitis in mice

A glucagon-like peptide-2 (GLP-2) analog is used in individuals with intestinal failure who are at risk for liver disease, yet the hepatic actions of GLP-2 are not understood. Treatment of high-fat diet-fed (HFD-fed) mice with GLP-2 did not modify the development of hepatosteatosis or hepatic inflammation. In contrast, Glp2r-/- mice exhibited increased hepatic lipid accumulation, deterioration in glucose tolerance, and upregulation of biomarkers of hepatic inflammation. Both mouse and human liver expressed the canonical GLP-2 receptor (GLP-2R), and hepatic Glp2r expression was upregulated in mice with hepatosteatosis. Cell fractionation localized the Glp2r to hepatic stellate cells (HSCs), and markers of HSC activation and fibrosis were increased in livers of Glp2r-/- mice. Moreover, GLP-2 directly modulated gene expression in isolated HSCs ex vivo. Taken together, these findings define an essential role for the GLP-2R in hepatic adaptation to nutrient excess and unveil a gut hormone-HSC axis, linking GLP-2R signaling to control of HSC activation.

Leveraging the Gut to Treat Metabolic Disease

25 years ago, the future of treating obesity and diabetes focused on end organs known to be involved in energy balance and glucose regulation, including the brain, muscle, adipose tissue, and pancreas. Today, the most effective therapies are focused around the gut. This includes surgical options, such as vertical sleeve gastrectomy and Roux-en-Y gastric bypass, that can produce sustained weight loss and diabetes remission but also extends to pharmacological treatments that simulate or amplify various signals that come from the gut. The purpose of this Review is to discuss the wealth of approaches currently under development that seek to further leverage the gut as a source of novel therapeutic opportunities with the hope that we can achieve the effects of surgical interventions with less invasive and more scalable solutions.

Role of Gut Microbiota in Neuroendocrine Regulation of Carbohydrate and Lipid Metabolism via the Microbiota-Gut-Brain-Liver Axis

Gut microbiota play an important role in maintaining intestinal health and are involved in the metabolism of carbohydrates, lipids, and amino acids. Recent studies have shown that the central nervous system (CNS) and enteric nervous system (ENS) can interact with gut microbiota to regulate nutrient metabolism. The vagal nerve system communicates between the CNS and ENS to control gastrointestinal tract functions and feeding behavior. Vagal afferent neurons also express receptors for gut peptides that are secreted from enteroendocrine cells (EECs), such as cholecystokinin (CCK), ghrelin, leptin, peptide tyrosine tyrosine (PYY), glucagon-like peptide-1 (GLP-1), and 5-hydroxytryptamine (5-HT; serotonin). Gut microbiota can regulate levels of these gut peptides to influence the vagal afferent pathway and thus regulate intestinal metabolism via the microbiota-gut-brain axis. In addition, bile acids, short-chain fatty acids (SCFAs), trimethylamine-N-oxide (TMAO), and Immunoglobulin A (IgA) can also exert metabolic control through the microbiota-gut-liver axis. This review is mainly focused on the role of gut microbiota in neuroendocrine regulation of nutrient metabolism via the microbiota-gut-brain-liver axis.

Long Non-Coding RNA (lncRNA) SNHG5 Participates in Vertical Sleeve Gastrectomy for Type II Diabetes Mellitus by Regulating TGR5

BACKGROUND Due to its remarkable effect in controlling glycometabolism, relatively simple operation, and low risk of complications, sleeve gastrectomy (SG) has become the preferred surgical treatment for type II diabetes mellitus. Increased blood glucose in the body can cause damage to functional cells. MATERIAL AND METHODS Long non-coding RNA SNHG5 expression and TGR5 in serum were analyzed by real-time PCR. A diabetic cell model was established by culturing normal human intestinal epithelial cells NCM460 and DLD-1 with high-glucose and high-fat medium. CCK-8 assay, TUNEL assay, and flow cytometry were used to assess cell growth and apoptosis, respectively. The secretion of lactate dehydrogenase (LDH) was detected using the LDH Cytotoxicity Kit. lncRNA SNHG5 was downregulated by siRNA. The changes in expression of SNHG5, TGR5, Akt, p65, and Bcl-2 were analyzed by real-time PCR assay or Western blot. RESULTS In 40 type II diabetes patients who underwent sleeve gastrectomy, the expression of SNHG5 decreased and the expression of TGR5 increased compared with that before the operation. After high-glucose and high-fat culture, cell growth was inhibited and cell apoptosis increased significantly. The expression of SNHG5 was increased and TGR5 was decreased with high-glucose and high-fat culture. However, high glucose and high fat showed an opposite trend for cell growth, apoptosis, and LDH release under inhibition of SNHG5. The expression levels of TGR5 and Akt, p65, and Bcl-2 were also returned to normal by SNHG5 inhibition. CONCLUSIONS By downregulating expression of the SNHG5 gene and then altering expression of the TGR5 gene, the damage to colorectal cells induced by high glucose was alleviated. This may be one of the mechanisms underlying the effect of sleeve gastric surgery in treatment of diabetes mellitus.

L-Cell Differentiation Is Induced by Bile Acids Through GPBAR1 and Paracrine GLP-1 and Serotonin Signaling

Glucagon-like peptide 1 (GLP-1) mimetics are effective drugs for treatment of type 2 diabetes, and there is consequently extensive interest in increasing endogenous GLP-1 secretion and L-cell abundance. Here we identify G-protein-coupled bile acid receptor 1 (GPBAR1) as a selective regulator of intestinal L-cell differentiation. Lithocholic acid and the synthetic GPBAR1 agonist, L3740, selectively increased L-cell density in mouse and human intestinal organoids and elevated GLP-1 secretory capacity. L3740 induced expression of Gcg and transcription factors Ngn3 and NeuroD1 L3740 also increased the L-cell number and GLP-1 levels and improved glucose tolerance in vivo. Further mechanistic examination revealed that the effect of L3740 on L cells required intact GLP-1 receptor and serotonin 5-hydroxytryptamine receptor 4 (5-HT4) signaling. Importantly, serotonin signaling through 5-HT4 mimicked the effects of L3740, acting downstream of GLP-1. Thus, GPBAR1 agonists and other powerful GLP-1 secretagogues facilitate L-cell differentiation through a paracrine GLP-1-dependent and serotonin-mediated mechanism.

Pathophysiological connections between gallstone disease, insulin resistance, and obesity

Obesity and cholesterol gallstone disease (GSD) are frequently coexisting diseases; therefore and considering the current worldwide obesity epidemics, a precise understanding of the pathophysiological relationships between GSD and insulin resistance (IR) is important. Classically, obesity has been understood as a risk factor for GSD and the gallbladder (GB) viewed as a simple bile reservoir, with no metabolic roles whatsoever. However, consistent evidence has showed that both GSD and cholecystectomy associates with fatty liver and IR, raising the possibility that the GB is indeed an organ with metabolic regulatory roles. Herein, we review the pathophysiological mechanisms by which GSD, IR, and obesity are interconnected, with emphasis in the actions of the GB as a regulator of bile acids kinetics and a hormone secreting organ, with metabolic actions at the systemic level. We also examine the relationships between increased hepatic lipogenic in IR states and GSD pathogenesis. We propose a model in which GSD and hepatic IR mutually interact to determine a state of dysregulated lipid and energy metabolism that potentiate the metabolic dysregulation of obesity.

Biliary Jejunostomy Might Improve Glucose in Type 2 Diabetes Patients

PURPOSES

Biliopancreatic diversion could improve type 2 diabetes mellitus. Our aim was to investigate the effects of biliary jejunostomy on the improvement of glucose.

MATERIALS AND METHODS

Twenty-seven type 2 diabetes patients underwent biliary jejunostomy between January 2013 and January 2018 in our hospital and were followed up. Demographic data, operation details, body weight, food intake, effects on diabetes control, and biomedical parameters were collected and analyzed.

RESULTS

As defined previously, 3 of 27 diabetes patients were "under control," 8 patients were "in remission," and 12 patients were "improved." The fasting glucose decreased from 9.7 ± 2.1 mmol/L before surgery to 7.9 ± 1.8 mmol/L 12 months after surgery (P = 0.001). The level of hemoglobin A1c in these patients was 9.1 ± 2.3% before surgery, and it decreased to 7.2 ± 1.3% 12 months after surgery (P < 0.001). There was no significant difference in the body weight index (P = 0.78) or food intake (P = 0.18) between the time prior to surgery and 12 months afterward. The average level of total bile acids increased significantly after surgery, from 6.7 ± 2.2 μmol/L before surgery to 8.6 ± 2.9 μmol/L 12 months after surgery (P < 0.001).

CONCLUSIONS

Fasting glucose in type 2 diabetes patients was improved after biliary jejunostomy. Increasing bile acids levels might play an important role in the remission of type 2 diabetes.

Bile acid-based therapies for non-alcoholic steatohepatitis and alcoholic liver disease

Bile acids are synthesized from cholesterol only in hepatocytes. Bile acids circulating in the enterohepatic system act as physiological detergent molecules to help solubilize biliary cholesterol and emulsify dietary lipids and fat-soluble vitamins in small intestine. Bile acids are signaling molecules that activate nuclear receptor farnesoid X receptor (FXR) and cell surface G protein-coupled receptor TGR5. FXR critically regulates bile acid homeostasis by mediating bile acid feedback inhibition of hepatic bile acid synthesis. In addition, bile acid-activated cellular signaling pathways regulate metabolic homeostasis, immunity, and cell proliferation in various metabolically active organs. In the small and large intestine, gut bacterial enzymes modify primary bile acids to generate secondary bile acids to help shape the bile acid pool composition and subsequent biological effects. In turn, bile acids exhibit anti-microbial properties and modulate gut microbiota to influence host metabolism and immunity. Currently, bile acid-based therapies including systemic and intestine-restricted FXR agonists, TGR5 agonists, fibroblast growth factor 19 analogue, intestine FXR antagonists, and intestine apical sodium-bile acid transporter (ASBT) inhibitors have been developed as promising treatments for non-alcoholic steatohepatitis (NASH). These pharmacological agents improved metabolic and inflammatory disorders via distinct mechanisms of action that are subjects of extensive research interest. More recently, human and experimental alcoholic liver disease (ALD) has been associated with disrupted bile acid homeostasis. In additional, new findings showed that targeting bile acid metabolism and signaling may be promising therapeutic approaches for treating ALD.

Probiotics VSL#3 are effective in reversing non-alcoholic steatohepatitis in a mouse model

Background

Probiotic VSL#3 is used to treat ulcerative colitis. This study examines the effect of VSL#3 in non-alcoholic steatohepatitis (NASH) that has liver carcinogenic potential.

Methods

Western diet (WD)-fed wild-type (WT) mice that do not have hepatic inflammation with lymphocyte infiltration and carcinogenic potential were used for baseline comparison. Age-, sex-, and diet-matched bile acid (BA) receptor farnesoid X receptor (FXR) knockout (KO) mice, which developed severe NASH and had the potential for liver cancer development, were supplemented with and without VSL#3 for 7 months. All the mice were euthanized when they were 10 months old.

Results

Supplementation with VSL#3 completely abolished hepatic lymphocyte infiltration, reduced hepatic fat content, and improved insulin sensitivity in WD-fed FXR KO mice. In addition, VSL#3 normalized dysregulated BA homoeostasis by inhibiting the classical BA synthesis pathway, inducing the alternative BA pathway, and activating ileal G-protein coupled BA receptor 1 (GPBAR1)-regulated signaling. Moreover, VSL#3 reconstructed the gut microbiota by reducing Bacteroidaceae, Porphyromonadaceae, and Helicobacteraceae as well as increasing Lachnospiraceae. Further, VSL#3 enriched the abundance of Ruminococcus and Faecalibacterium, which generate butyrate, at the genus level. It also increased the copy number of the butyrate-producing genes bcoA and buk, suggesting their anti-inflammatory and metabolic effects.

Conclusions

VSL#3 is useful in reversing NASH that occurred due to dysregulated BA synthesis and dysbiosis, suggesting its potential in liver cancer prevention.

Gut microbiota in non-alcoholic fatty liver disease and alcohol-related liver disease: Current concepts and perspectives

The term, gut-liver axis, is used to highlight the close anatomical and functional relationship between the intestine and the liver. It has been increasingly recognized that the gut-liver axis plays an essential role in the development and progression of liver disease. In particular, in non-alcoholic fatty liver disease and alcohol-related liver disease, the two most common causes of chronic liver disease, a dysbiotic gut microbiota can influence intestinal permeability, allowing some pathogens or bacteria-derived factors from the gut reaching the liver through the enterohepatic circulation contributing to liver injury, steatohepatitis, and fibrosis progression. Pathways involved are multiple, including changes in bile acid metabolism, intestinal ethanol production, generation of short-chain fatty acids, and other by-products. Bile acids act through dedicated bile acid receptors, farnesoid X receptor and TGR5, in both the ileum and the liver, influencing lipid metabolism, inflammation, and fibrogenesis. Currently, both non-alcoholic fatty liver disease and alcohol-related liver disease lack effective therapies, and therapeutic targeting of gut microbiota and bile acids enterohepatic circulation holds promise. In this review, we summarize current knowledge about the role of gut microbiota in the pathogenesis of non-alcoholic fatty liver disease and alcohol-related liver disease, as well as the relevance of microbiota or bile acid-based approaches in the management of those liver diseases.

Soybean Oil Modulates the Gut Microbiota Associated with Atherogenic Biomarkers

During the last few decades there has been a staggering rise in human consumption of soybean-oil (SO). The microbiome and specific taxa composing it are dramatically affected by diet; specifically, by high-fat diets. Increasing evidence indicates the association between dysbiosis and health or disease state, including cardiovascular diseases (CVD) and atherosclerosis pathogenesis in human and animal models. To investigate the effects of high SO intake, C57BL/6 mice were orally supplemented with SO-based emulsion (SOE) for one month, followed by analyses of atherosclerosis-related biomarkers and microbiota profiling by 16S rRNA gene sequencing of fecal DNA. SOE-supplementation caused compositional changes to 64 taxa, including enrichment in Bacteroidetes, Mucispirillum, Prevotella and Ruminococcus, and decreased Firmicutes. These changes were previously associated with atherosclerosis in numerous studies. Among the shifted taxa, 40 significantly correlated with at least one atherosclerosis-related biomarker (FDR < 0.05), while 13 taxa positively correlated with the average of all biomarkers. These microbial alterations also caused a microbial-derived metabolic-pathways shift, including enrichment in different amino-acid metabolic-pathways known to be implicated in CVD. In conclusion, our results demonstrate dysbiosis following SOE supplementation associated with atherosclerosis-related biomarkers. These findings point to the microbiome as a possible mediator to CVD, and it may be implemented into non-invasive diagnostic tools or as potential therapeutic strategies.

Bofutsushosan improves gut barrier function with a bloom of Akkermansia muciniphila and improves glucose metabolism in mice with diet-induced obesity

Obesity and insulin resistance are associated with dysbiosis of the gut microbiota and impaired intestinal barrier function. Herein, we report that Bofutsushosan (BFT), a Japanese herbal medicine, Kampo, which has been clinically used for constipation in Asian countries, ameliorates glucose metabolism in mice with diet-induced obesity. A 16S rRNA sequence analysis of fecal samples showed that BFT dramatically increased the relative abundance of Verrucomicrobia, which was mainly associated with a bloom of Akkermansia muciniphila (AKK). BFT decreased the gut permeability as assessed by FITC-dextran gavage assay, associated with increased expression of tight-junction related protein, claudin-1, in the colon. The BFT treatment group also showed significant decreases of the plasma endotoxin level and expression of the hepatic lipopolysaccharide-binding protein. Antibiotic treatment abrogated the metabolic effects of BFT. Moreover, many of these changes could be reproduced when the cecal contents of BFT-treated donors were transferred to antibiotic-pretreated high fat diet-fed mice. These data demonstrate that BFT modifies the gut microbiota with an increase in AKK, which may contribute to improving gut barrier function and preventing metabolic endotoxemia, leading to attenuation of diet-induced inflammation and glucose intolerance. Understanding the interaction between a medicine and the gut microbiota may provide insights into new pharmacological targets to improve glucose metabolism.

Parabacteroides distasonis Alleviates Obesity and Metabolic Dysfunctions via Production of Succinate and Secondary Bile Acids

We demonstrated the metabolic benefits of Parabacteroides distasonis (PD) on decreasing weight gain, hyperglycemia, and hepatic steatosis in ob/ob and high-fat diet (HFD)-fed mice. Treatment with live P. distasonis (LPD) dramatically altered the bile acid profile with elevated lithocholic acid (LCA) and ursodeoxycholic acid (UDCA) and increased the level of succinate in the gut. In vitro cultivation of PD demonstrated its capacity to transform bile acids and production of succinate. Succinate supplementation in the diet decreased hyperglycemia in ob/ob mice via the activation of intestinal gluconeogenesis (IGN). Gavage with a mixture of LCA and UDCA reduced hyperlipidemia by activating the FXR pathway and repairing gut barrier integrity. Co-treatment with succinate and LCA/UDCA mirrored the benefits of LPD. The binding target of succinate was identified as fructose-1,6-bisphosphatase, the rate-limiting enzyme in IGN. The succinate and secondary bile acids produced by P. distasonis played key roles in the modulation of host metabolism.

A compendium of G-protein-coupled receptors and cyclic nucleotide regulation of adipose tissue metabolism and energy expenditure

With the ever-increasing burden of obesity and Type 2 diabetes, it is generally acknowledged that there remains a need for developing new therapeutics. One potential mechanism to combat obesity is to raise energy expenditure via increasing the amount of uncoupled respiration from the mitochondria-rich brown and beige adipocytes. With the recent appreciation of thermogenic adipocytes in humans, much effort is being made to elucidate the signaling pathways that regulate the browning of adipose tissue. In this review, we focus on the ligand-receptor signaling pathways that influence the cyclic nucleotides, cAMP and cGMP, in adipocytes. We chose to focus on G-protein-coupled receptor (GPCR), guanylyl cyclase and phosphodiesterase regulation of adipocytes because they are the targets of a large proportion of all currently available therapeutics. Furthermore, there is a large overlap in their signaling pathways, as signaling events that raise cAMP or cGMP generally increase adipocyte lipolysis and cause changes that are commonly referred to as browning: increasing mitochondrial biogenesis, uncoupling protein 1 (UCP1) expression and respiration.

Gut Microbiome Toxicity: Connecting the Environment and Gut Microbiome-Associated Diseases

The human gut microbiome can be easily disturbed upon exposure to a range of toxic environmental agents. Environmentally induced perturbation in the gut microbiome is strongly associated with human disease risk. Functional gut microbiome alterations that may adversely influence human health is an increasingly appreciated mechanism by which environmental chemicals exert their toxic effects. In this review, we define the functional damage driven by environmental exposure in the gut microbiome as gut microbiome toxicity. The establishment of gut microbiome toxicity links the toxic effects of various environmental agents and microbiota-associated diseases, calling for more comprehensive toxicity evaluation with extended consideration of gut microbiome toxicity.

Bile acid receptors FXR and TGR5 signaling in fatty liver diseases and therapy

Bile acid synthesis is the most significant pathway for catabolism of cholesterol and for maintenance of whole body cholesterol homeostasis. Bile acids are physiological detergents that absorb, distribute, metabolize, and excrete nutrients, drugs, and xenobiotics. Bile acids also are signal molecules and metabolic integrators that activate nuclear farnesoid X receptor (FXR) and membrane Takeda G protein-coupled receptor 5 (TGR5; i.e., G protein-coupled bile acid receptor 1) to regulate glucose, lipid, and energy metabolism. The gut-to-liver axis plays a critical role in the transformation of primary bile acids to secondary bile acids, in the regulation of bile acid synthesis to maintain composition within the bile acid pool, and in the regulation of metabolic homeostasis to prevent hyperglycemia, dyslipidemia, obesity, and diabetes. High-fat and high-calorie diets, dysbiosis, alcohol, drugs, and disruption of sleep and circadian rhythms cause metabolic diseases, including alcoholic and nonalcoholic fatty liver diseases, obesity, diabetes, and cardiovascular disease. Bile acid-based drugs that target bile acid receptors are being developed for the treatment of metabolic diseases of the liver.

Lipid and energy metabolism in Wilson disease

Copper accumulation and deficiency are reciprocally connected to lipid metabolism. In Wilson disease (WD), which is caused by a genetic loss of function of the copper-transporting P-type ATPase beta, copper accumulates mainly in the liver and lipid metabolism is dysregulated. The underlying mechanisms linking copper and lipid metabolism in WD are not clear. Copper may impair metabolic machinery by direct binding to protein and lipid structures or by generating reactive oxygen species with consequent damage to cellular organelles vital to energy metabolism. In the liver, copper overload results in mitochondrial impairment, down-regulation of lipid metabolism, and the development of steatosis with an etiology not fully elucidated. Little is known regarding the effect of copper overload on extrahepatic energy homeostasis. This review aims to discuss alterations in hepatic energy metabolism associated with WD, highlights potential mechanisms involved in the development of hepatic and systemic dysregulation of lipid metabolism, and reviews current knowledge on the effects of copper overload on extrahepatic energy metabolism.

Assessing the progression of gastric cancer via profiling of histamine, histidine, and bile acids in gastric juice using LC-MS/MS

Bile acid (BA) imbalance may be directly associated with gastric cancer and indirectly influence stomach carcinogenesis via overexpression of histidine decarboxylase (HDC), which converts histidine (His) into histamine (HIST). Moreover, the progression of gastric cancer, could change the gut microbiome, including bacteria spp. that produce secondary BAs. Gastric juice has various metabolites that could indicate gastric cancer-related stomach conditions. Therefore, profiling of HIST, His, and BAs in gastric juice is crucial for understanding the etiological mechanisms of gastric cancer. We used a profiling method to simultaneously determine targeted metabolites in gastric juice using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We successfully analyzed 70 human gastric juice samples from patients with chronic superficial gastritis (CSG, n = 20), intestinal metaplasia (IM, n = 12), and gastric cancer (n = 38). Furthermore, we investigated the relevance between BA metabolism and gastric cancer. There were statistical differences in the metabolism of cholic acid (CA) into deoxycholic acid (DCA) based on the progression of CSG into IM and gastric cancer. Hence, the progression of gastric cancer might be related to the alterations in gut microbiome composition. We provide insight into the etiological mechanisms of the progression of gastric cancer and biomarkers to diagnose and treat gastric cancer.

Nonalcoholic Fatty Liver Disease Pandemic Fuels the Upsurge in Cardiovascular Diseases

Cardiovascular diseases (CVDs) remain a leading cause of death worldwide. Among the major risk factors for CVD, obesity and diabetes mellitus have received considerable attention in terms of public policy and awareness. However, the emerging prevalence of nonalcoholic fatty liver disease (NAFLD), as the most common liver and metabolic disease and a cause of CVD, has been largely overlooked. Currently, the number of individuals with NAFLD is greater than the total number of individuals with diabetes mellitus and obesity. Epidemiological studies have established a strong correlation between NAFLD and an increased risk of CVD and CVD-associated events. Although debate continues over the causal relationship between NAFLD and CVD, many mechanistic and longitudinal studies have indicated that NAFLD is one of the major driving forces for CVD and should be recognized as an independent risk factor for CVD apart from other metabolic disorders. In this review, we summarize the clinical evidence that supports NAFLD as a risk factor for CVD epidemics and discuss major mechanistic insights regarding the acceleration of CVD in the setting of NAFLD. Finally, we address the potential treatments for NAFLD and their potential impact on CVD.

Hepatic HAX-1 inactivation prevents metabolic diseases by enhancing mitochondrial activity and bile salt export

Increasing hepatic mitochondrial activity through pyruvate dehydrogenase and elevating enterohepatic bile acid recirculation are promising new approaches for metabolic disease therapy, but neither approach alone can completely ameliorate disease phenotype in high-fat diet-fed mice. This study showed that diet-induced hepatosteatosis, hyperlipidemia, and insulin resistance can be completely prevented in mice with liver-specific HCLS1-associated protein X-1 (HAX-1) inactivation. Mechanistically, we showed that HAX-1 interacts with inositol 1,4,5-trisphosphate receptor-1 (InsP3R1) in the liver, and its absence reduces InsP3R1 levels, thereby improving endoplasmic reticulum-mitochondria calcium homeostasis to prevent excess calcium overload and mitochondrial dysfunction. As a result, HAX-1 ablation activates pyruvate dehydrogenase and increases mitochondria utilization of glucose and fatty acids to prevent hepatosteatosis, hyperlipidemia, and insulin resistance. In contrast to the reduction of InsP3R1 levels, hepatic HAX-1 deficiency increases bile salt exporter protein levels, thereby promoting enterohepatic bile acid recirculation, leading to activation of bile acid-responsive genes in the intestinal ileum to augment insulin sensitivity and of cholesterol transport genes in the liver to suppress hyperlipidemia. The dual mechanisms of increased mitochondrial respiration and enterohepatic bile acid recirculation due to improvement of endoplasmic reticulum-mitochondria calcium homeostasis with hepatic HAX-1 inactivation suggest that this may be a potential therapeutic target for metabolic disease intervention.

Mechanism of glucose-lowering by metformin in type 2 diabetes: Role of bile acids

Type 2 diabetes mellitus (T2DM) is an increasingly prevalent chronic condition, characterized by abnormally elevated blood glucose concentrations and, as a consequence, increased risk of micro- and macrovascular complications. Metformin is usually the first-line glucose-lowering medication in T2DM; however, despite being used for more than 60 years, the mechanism underlying the glucose-lowering action of metformin remains incompletely understood. Although metformin reduces hepatic glucose production, there is persuasive evidence that the gastrointestinal tract is crucial in mediating this effect, particularly via secretion of the incretin hormone glucagon-like peptide 1 (GLP-1). It is now well recognized that bile acids, in addition to their established function in fat digestion and absorption, are important regulators of glucose metabolism. Exposure of the small and large intestine to bile acids induces GLP-1 secretion, modulates the composition of the gut microbiota, and reduces postprandial blood glucose excursions in humans with and without T2DM. Metformin reduces intestinal bile acid resorption substantially, such that intraluminal bile acids may, at least in part, account for its glucose-lowering effect. The present review focuses on the conceptual shift in our understanding as to how metformin lowers blood glucose in T2DM, with a particular emphasis on the role of intestinal bile acids.

Long-Term Effects of Multi-Drug-Resistant Tuberculosis Treatment on Gut Microbiota and Its Health Consequences

Gut microbiota dysbiosis has adverse health effects on human body. Multi-drug-resistant tuberculosis (MDR-TB) treatment uses a variety of antibiotics typically for more than 20 months, which may induce gut microbiota dysbiosis. The aim of this study is to investigate the long-term effects of MDR-TB treatment on human gut microbiota and its related health consequences. A total of 76 participants were recruited at a hospital in Linyi, China. The study included one active MDR-TB treatment group, one recovered group from MDR-TB and two treatment-naive tuberculosis groups as control. The two treatment-naïve tuberculosis groups were constructed to match the sex and the age of the active MDR-TB treatment and the recovered group, respectively. The fecal and blood samples were collected and analyzed for gut microbiota and metabolic parameters. An altered gut microbiota community and a loss of richness were observed during the MDR-TB treatment. Strikingly, 3-8 years after recovery and discontinuing the treatment, the gut microbiota still exhibited an altered taxonomic composition (p = 0.001) and a 16% decrease in richness (p = 0.018) compared to the gut microbiota before the treatment. The abundance of fifty-eight bacterial genera was significantly changed in the MDR-TB recovered group versus the untreated control group. Although there were persistent and pervasive gut microbiota alterations, no gastrointestinal symptom such as abdominal pain, diarrhea, nausea, flatulence, and constipation was observed in the recovered group. However, chronic disorders may be indicated by the elevated level of low-density lipoprotein cholesterol (LDLC) (p = 0.034) and total cholesterol (TC) (p = 0.017). These adverse lipid changes were associated with the altered gut bacterial taxa, including phylum Firmicutes and Verrucomicrobia and genera Adlercreutzia, Akkermansia, Butyricicoccus, Coprococcus, Clostridioides, Eubacterium, Erysipelatoclostridium, Fusicatenibacter, Klebsiella, Psychrobacter, and Streptococcus. Collectively, MDR-TB treatment induced a lasting gut microbiota dysbiosis, which was associated with unfavorable changes in lipid profile.

Fenugreek Counters the Effects of High Fat Diet on Gut Microbiota in Mice: Links to Metabolic Benefit

Fenugreek (Trigonella foenum-graecum) is an annual herbaceous plant and a staple of traditional health remedies for metabolic conditions including high cholesterol and diabetes. While the mechanisms of the beneficial actions of fenugreek remain unknown, a role for intestinal microbiota in metabolic homeostasis is likely. To determine if fenugreek utilizes intestinal bacteria to offset the adverse effects of high fat diets, C57BL/6J mice were fed control/low fat (CD) or high fat (HFD) diets each supplemented with or without 2% (w/w) fenugreek for 16 weeks. The effects of fenugreek and HFD on gut microbiota were comprehensively mapped and then statistically assessed in relation to effects on metrics of body weight, hyperlipidemia, and glucose tolerance. 16S metagenomic analyses revealed robust and significant effects of fenugreek on gut microbiota, with alterations in both alpha and beta diversity as well as taxonomic redistribution under both CD and HFD conditions. As previously reported, fenugreek attenuated HFD-induced hyperlipidemia and stabilized glucose tolerance without affecting body weight. Finally, fenugreek specifically reversed the dysbiotic effects of HFD on numerous taxa in a manner tightly correlated with overall metabolic function. Collectively, these data reinforce the essential link between gut microbiota and metabolic syndrome and suggest that the preservation of healthy populations of gut microbiota participates in the beneficial properties of fenugreek in the context of modern Western-style diets.

Beneficial bile acid metabolism from Lactobacillus plantarum of food origin

Bile acid (BA) signatures are altered in many disease states. BA metabolism is an important microbial function to assist gut colonization and persistence, as well as microbial survival during gastro intestinal (GI) transit and it is an important criteria for potential probiotic bacteria. Microbes that express bile salt hydrolase (BSH), gateway BA modifying enzymes, are considered to have an advantage in the gut. This property is reported as selectively limited to gut-associated microbes. Food-associated microbes have the potential to confer health benefits to the human consumer. Here, we report that food associated Lactobacillus plantarum strains are capable of BA metabolism, they can withstand BA associated stress and propagate, a recognised important characteristic for GIT survival. Furthermore, we report that these food associated Lactobacillus plantarum strains have the selective ability to alter BA signatures in favour of receptor activation that would be beneficial to humans. Indeed, all of the strains examined showed a clear preference to alter human glycol-conjugated BAs, although clear strain-dependent modifications were also evident. This study demonstrates that BA metabolism by food-borne non-pathogenic bacteria is beneficial to both microbe and man and it identifies an evolutionary-conserved characteristic, previously considered unique to gut residents, among food-associated non-pathogenic isolates.

TGR5 receptor activation attenuates diabetic retinopathy through suppression of RhoA/ROCK signaling

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus. Abnormal energy metabolism in microvascular endothelium is involved in the progression of diabetic retinopathy. Bile Acid G-Protein-Coupled Membrane Receptor (TGR5) has emerged as a novel regulator of metabolic disorders. However, the role of TGR5 in diabetes mellitus-induced microvascular dysfunction in retinas is largely unknown. Herein, enzyme-linked immunosorbent assay was used for analyzing bile acid (BA) profiles in diabetic rat retinas and retinal microvascular endothelial cells (RMECs) cultured in high glucose medium. The effects of TGR5 agonist on streptozotocin (STZ)-induced diabetic retinopathy were evaluated by HE staining, TUNEL staining, retinal trypsin digestion, and vascular permeability assay. A pharmacological inhibitor of RhoA was used to study the role of TGR5 on the regulation of Rho/Rho-associated coiled-coil containing protein kinase (ROCK) and western blot, immunofluorescence and siRNA silencing were performed to study the related signaling pathways. Here we show that bile acids were downregulated during DR progression in the diabetic rat retinas and RMECs cultured in high glucose medium. The TGR5 agonist obviously ameliorated diabetes-induced retinal microvascular dysfunction in vivo, and inhibited the effect of TNF-α on endothelial cell proliferation, migration, and permeability in vitro. In contrast, knockdown of TGR5 by siRNA aggravated TNF-α-induced actin polymerization and endothelial permeability. Mechanistically, the effects of TGR5 on the improvement of endothelial function was due to its regulatory role on the ROCK signaling pathway. An inhibitor of RhoA significantly reversed the loss of tight junction protein under TNF-α stimulation. Taken together, our findings suggest that insufficient BA signaling plays an important pathogenic role in the development of DR. Upregulation or activation of TGR5 may inhibit RhoA/ROCK-dependent actin remodeling and represent an important therapeutic intervention for DR.

The nuclear receptor FXR inhibits Glucagon-Like Peptide-1 secretion in response to microbiota-derived Short-Chain Fatty Acids

The gut microbiota participates in the control of energy homeostasis partly through fermentation of dietary fibers hence producing short-chain fatty acids (SCFAs), which in turn promote the secretion of the incretin Glucagon-Like Peptide-1 (GLP-1) by binding to the SCFA receptors FFAR2 and FFAR3 on enteroendocrine L-cells. We have previously shown that activation of the nuclear Farnesoid X Receptor (FXR) decreases the L-cell response to glucose. Here, we investigated whether FXR also regulates the SCFA-induced GLP-1 secretion. GLP-1 secretion in response to SCFAs was evaluated ex vivo in murine colonic biopsies and in colonoids of wild-type (WT) and FXR knock-out (KO) mice, in vitro in GLUTag and NCI-H716 L-cells activated with the synthetic FXR agonist GW4064 and in vivo in WT and FXR KO mice after prebiotic supplementation. SCFA-induced GLP-1 secretion was blunted in colonic biopsies from GW4064-treated mice and enhanced in FXR KO colonoids. In vitro FXR activation inhibited GLP-1 secretion in response to SCFAs and FFAR2 synthetic ligands, mainly by decreasing FFAR2 expression and downstream Gαq-signaling. FXR KO mice displayed elevated colonic FFAR2 mRNA levels and increased plasma GLP-1 levels upon local supply of SCFAs with prebiotic supplementation. Our results demonstrate that FXR activation decreases L-cell GLP-1 secretion in response to inulin-derived SCFA by reducing FFAR2 expression and signaling. Inactivation of intestinal FXR using bile acid sequestrants or synthetic antagonists in combination with prebiotic supplementation may be a promising therapeutic approach to boost the incretin axis in type 2 diabetes.

Beneficial Effects of Dietary Polyphenols on High-Fat Diet-Induced Obesity Linking with Modulation of Gut Microbiota

Obesity is caused by an imbalance of energy intake and expenditure. It is characterized by a higher accumulation of body fat with a chronic low-grade inflammation. Many reports have shown that gut microbiota in the host plays a pivotal role in mediating the interaction between consumption of a high-fat diet (HFD) and onset of obesity. Accumulative evidence has suggested that the changes in the composition of gut microbiota may affect the host's energy homeostasis, systemic inflammation, lipid metabolism, and insulin sensitivity. As one of the major components in human diet, polyphenols have demonstrated to be capable of modulating the composition of gut microbiota and reducing the HFD-induced obesity. The present review summarizes the findings of recent studies on dietary polyphenols regarding their metabolism and interaction with bacteria in the intestine as well as the underlying mechanisms by which they modulate the gut microbiota and alleviate the HFD-induced obesity.