Intestine-selective farnesoid X receptor inhibition improves obesity-related metabolic dysfunction

Host ALDH2 deficiency aggravates nonalcoholic steatohepatitis through gut-liver axis

Nonalcoholic steatohepatitis (NASH) is the major cause of liver dysfunction. Animal and population studies have shown that mitochondrial aldehyde dehydrogenase (ALDH2) is implicated in fatty liver disease. However, the role of ALDH2 in NASH and the underlying mechanisms remains unclear. To address this issue, ALDH2 knockout (ALDH2-/-) mice and wild-type littermate mice were fed a methionine-and choline-deficient (MCD) diet to induce a NASH model. Fecal, serum, and liver samples were collected and analyzed to investigate the impact of the gut microbiota and bile acids on this process. We found that MCD-fed ALDH2-/- mice exhibited increased serum pro-inflammation cytokines, hepatic inflammation and fat accumulation than their wild-type littermates. MCD-fed ALDH2-/- mice exhibited worsened MCD-induced intestinal inflammation and barrier damage, and gut microbiota disorder. Furthermore, mice receiving microbiota from MCD-fed ALDH2-/- mice had increased severity of NASH compared to those receiving microbiota from MCD-fed wild-type mice. Notably, the intestinal Lactobacillus was significantly reduced in MCD-fed ALDH2-/- mice, and gavage with Lactobacillus cocktail significantly improved MCD-induced NASH. Finally, we found that ALDH2-/- mice had reduced levels of bile salt hydrolase and specific bile acids, especially lithocholic acid (LCA), accompanied by downregulated expression of the intestinal FXR-FGF15 pathway. Supplementation of LCA in ALDH2-/- mice upregulated intestinal FXR-FGF15 pathway and alleviated NASH. In summary, ALDH2 plays a critical role in the development of NASH through modulation of gut microbiota and bile acid. The findings suggest that supplementing with Lactobacillus or LCA could be a promising therapeutic approach for treating NASH exacerbated by ALDH2 deficiency.

Impact of intestinal microenvironments in obesity and bariatric surgery on shaping macrophages

Obesity is associated with alterations in tissue composition, systemic cellular metabolism, and low-grade chronic inflammation. Macrophages are heterogenous innate immune cells ubiquitously localized throughout the body and are key components of tissue homeostasis, inflammation, wound healing, and various disease states. Macrophages are highly plastic and can switch their phenotypic polarization and change function in response to their local environments. Here, we discuss how obesity alters the intestinal microenvironment and potential key factors that can influence intestinal macrophages as well as macrophages in other organs, including adipose tissue and hematopoietic organs. As bariatric surgery can induce metabolic adaptation systemically, we discuss the potential mechanisms through which bariatric surgery reshapes macrophages in obesity.

New Insights into the Pathogenesis of Metabolic-Associated Fatty Liver Disease (MAFLD): Gut-Liver-Heart Crosstalk

Metabolism-associated fatty liver disease (MAFLD) is a multifaceted disease that involves complex interactions between various organs, including the gut and heart. It is defined by hepatic lipid accumulation and is related to metabolic dysfunction, obesity, and diabetes. Understanding the intricate interplay of the gut-liver-heart crosstalk is crucial for unraveling the complexities of MAFLD and developing effective treatment and prevention strategies. The gut-liver crosstalk participates in the regulation of the metabolic and inflammatory processes through host-microbiome interactions. Gut microbiota have been associated with the development and progression of MAFLD, and its dysbiosis contributes to insulin resistance, inflammation, and oxidative stress. Metabolites derived from the gut microbiota enter the systemic circulation and influence both the liver and heart, resulting in the gut-liver-heart axis playing an important role in MAFLD. Furthermore, growing evidence suggests that insulin resistance, endothelial dysfunction, and systemic inflammation in MAFLD may contribute to an increased risk of cardiovascular disease (CVD). Additionally, the dysregulation of lipid metabolism in MAFLD may also lead to cardiac dysfunction and heart failure. Overall, the crosstalk between the liver and heart involves a complex interplay of molecular pathways that contribute to the development of CVD in patients with MAFLD. This review emphasizes the current understanding of the gut-liver-heart crosstalk as a foundation for optimizing patient outcomes with MAFLD.

Recent updates on the role of the gut-liver axis in the pathogenesis of NAFLD/NASH, HCC, and beyond

The gut and the liver are anatomically and physiologically connected, and this connection is called the "gut-liver axis," which exerts various influences on liver physiology and pathology. The gut microbiota has been recognized to trigger innate immunity and modulate the liver immune microenvironment. Gut microbiota influences the physiological processes in the host, such as metabolism, by acting on various signaling receptors and transcription factors through their metabolites and related molecules. The gut microbiota has also been increasingly recognized to modulate the efficacy of immune checkpoint inhibitors. In this review, we discuss recent updates on gut microbiota-associated mechanisms in the pathogenesis of chronic liver diseases such as NAFLD and NASH, as well as liver cancer, in light of the gut-liver axis. We particularly focus on gut microbial metabolites and components that are associated with these liver diseases. We also discuss the role of gut microbiota in modulating the response to immunotherapy in liver diseases.

Lipid remodeling of adipose tissue in metabolic health and disease

Adipose tissue is a dynamic and metabolically active organ that plays a crucial role in energy homeostasis and endocrine function. Recent advancements in lipidomics techniques have enabled the study of the complex lipid composition of adipose tissue and its role in metabolic disorders such as obesity, diabetes, and cardiovascular disease. In addition, adipose tissue lipidomics has emerged as a powerful tool for understanding the molecular mechanisms underlying these disorders and identifying bioactive lipid mediators and potential therapeutic targets. This review aims to summarize recent lipidomics studies that investigated the dynamic remodeling of adipose tissue lipids in response to specific physiological changes, pharmacological interventions, and pathological conditions. We discuss the molecular mechanisms of lipid remodeling in adipose tissue and explore the recent identification of bioactive lipid mediators generated in adipose tissue that regulate adipocytes and systemic metabolism. We propose that manipulating lipid-mediator metabolism could serve as a therapeutic approach for preventing or treating obesity-related metabolic diseases.

Grape Polyphenols May Prevent High-Fat Diet-Induced Dampening of the Hypothalamic-Pituitary-Adrenal Axis in Male Mice

Context 

Chronic high-fat diet (HFD) consumption causes obesity associated with retention of bile acids (BAs) that suppress important regulatory axes, such as the hypothalamic-pituitary-adrenal axis (HPAA). HFD impairs nutrient sensing and energy balance due to a dampening of the HPAA and reduced production and peripheral metabolism of corticosterone (CORT).

Objective

We assessed whether proanthocyanidin-rich grape polyphenol (GP) extract can prevent HFD-induced energy imbalance and HPAA dysregulation.

Methods

Male C57BL6/J mice were fed HFD or HFD supplemented with 0.5% w/w GPs (HFD-GP) for 17 weeks.

Results

GP supplementation reduced body weight gain and liver fat while increasing circadian rhythms of energy expenditure and HPAA-regulating hormones, CORT, leptin, and PYY. GP-induced improvements were accompanied by reduced mRNA levels of Il6, Il1b, and Tnfa in ileal or hepatic tissues and lower cecal abundance of Firmicutes, including known BA metabolizers. GP-supplemented mice had lower concentrations of circulating BAs, including hydrophobic and HPAA-inhibiting BAs, but higher cecal levels of taurine-conjugated BAs antagonistic to farnesoid X receptor (FXR). Compared with HFD-fed mice, GP-supplemented mice had increased mRNA levels of hepatic Cyp7a1 and Cyp27a1, suggesting reduced FXR activation and more BA synthesis. GP-supplemented mice also had reduced hepatic Abcc3 and ileal Ibabp and Ostβ, indicative of less BA transfer into enterocytes and circulation. Relative to HFD-fed mice, CORT and BA metabolizing enzymes (Akr1d1 and Srd5a1) were increased, and Hsd11b1 was decreased in GP supplemented mice.

Conclusion

GPs may attenuate HFD-induced weight gain by improving hormonal control of the HPAA and inducing a BA profile with less cytotoxicity and HPAA inhibition, but greater FXR antagonism.

FXR Friend-ChIPs in the Enterohepatic System

Chronic liver diseases encompass a wide spectrum of hepatic maladies that often result in cholestasis or altered bile acid secretion and regulation. Incidence and cost of care for many chronic liver diseases are rising in the United States with few Food and Drug Administration-approved drugs available for patient treatment. Farnesoid X receptor (FXR) is the master regulator of bile acid homeostasis with an important role in lipid and glucose metabolism and inflammation. FXR has served as an attractive target for management of cholestasis and fibrosis; however, global FXR agonism results in adverse effects in liver disease patients, severely affecting quality of life. In this review, we highlight seminal studies and recent updates on the FXR proteome and identify gaps in knowledge that are essential for tissue-specific FXR modulation. In conclusion, one of the greatest unmet needs in the field is understanding the underlying mechanism of intestinal versus hepatic FXR function.

Bile acid metabolism and signaling: Emerging pharmacological targets of dietary polyphenols

Beyond their role as emulsifiers of lipophilic compounds, bile acids (BAs) are signaling endocrine molecules that show differential affinity and specificity for a variety of canonical and non-canonical BA receptors. Primary BAs (PBAs) are synthesized in the liver while secondary BAs (SBAs) are gut microbial metabolites of PBA species. PBAs and SBAs signal to BA receptors that regulate downstream pathways of inflammation and energy metabolism. Dysregulation of BA metabolism or signaling has emerged as a feature of chronic disease. Dietary polyphenols are non-nutritive plant-derived compounds associated with decreased risk of metabolic syndrome, type-2 diabetes, hepatobiliary and cardiovascular disease. Evidence suggests that the health promoting effects of dietary polyphenols are linked to their ability to alter the gut microbial community, the BA pool, and BA signaling. In this review we provide an overview of BA metabolism and summarize studies that link the cardiometabolic improvements of dietary polyphenols to their modulation of BA metabolism and signaling pathways, and the gut microbiota. Finally, we discuss approaches and challenges in deciphering cause-effect relationships between dietary polyphenols, BAs, and gut microbes.

Hepatic deletion of serine palmitoyl transferase 2 impairs ceramide/sphingomyelin balance, bile acids homeostasis and leads to liver damage in mice

Ceramides (Cer) have been shown as lipotoxic inducers, which disturb numerous cell-signaling pathways, leading to metabolic disorders such as type 2 diabetes. In this study, we aimed to determine the role of de novo hepatic ceramide synthesis in energy and liver homeostasis in mice. We generated mice lacking serine palmitoyltransferase 2 (Sptlc2), the rate limiting enzyme of ceramide de novo synthesis, in liver under albumin promoter. Liver function, glucose homeostasis, bile acid (BA) metabolism and hepatic sphingolipids content were assessed using metabolic tests and LC-MS. Despite lower expression of hepatic Sptlc2, we observed an increased concentration of hepatic Cer, associated with a 10-fold increase in neutral sphingomyelinase 2 (nSMase2) expression, and a decreased sphingomyelin content in the liver. Sptlc2ΔLiv mice were protected against obesity induced by high fat diet and displayed a defect in lipid absorption. In addition, an important increase in tauro-muricholic acid was associated with a downregulation of the nuclear BA receptor FXR target genes. Sptlc2 deficiency also enhanced glucose tolerance and attenuated hepatic glucose production, while the latter effect was dampened in presence of nSMase2 inhibitor. Finally, Sptlc2 disruption promoted apoptosis, inflammation and progressive development of hepatic fibrosis, worsening with age. Our data suggest a compensatory mechanism to regulate hepatic ceramides content from sphingomyelin hydrolysis, with deleterious impact on liver homeostasis. In addition, our results show the involvement of hepatic sphingolipid modulation in BA metabolism and hepatic glucose production in an insulin-independent manner, which highlight the still under-researched role of ceramides in many metabolic functions.

Uncovering the Gut-Liver Axis Biomarkers for Predicting Metabolic Burden in Mice

Western diet (WD) intake, aging, and inactivation of farnesoid X receptor (FXR) are risk factors for metabolic and chronic inflammation-related health issues ranging from metabolic dysfunction-associated steatotic liver disease (MASLD) to dementia. The progression of MASLD can be escalated when those risks are combined. Inactivation of FXR, the receptor for bile acid (BA), is cancer prone in both humans and mice. The current study used multi-omics including hepatic transcripts, liver, serum, and urine metabolites, hepatic BAs, as well as gut microbiota from mouse models to classify those risks using machine learning. A linear support vector machine with K-fold cross-validation was used for classification and feature selection. We have identified that increased urine sucrose alone achieved 91% accuracy in predicting WD intake. Hepatic lithocholic acid and serum pyruvate had 100% and 95% accuracy, respectively, to classify age. Urine metabolites (decreased creatinine and taurine as well as increased succinate) or increased gut bacteria (Dorea, Dehalobacterium, and Oscillospira) could predict FXR deactivation with greater than 90% accuracy. Human disease relevance is partly revealed using the metabolite-disease interaction network. Transcriptomics data were also compared with the human liver disease datasets. WD-reduced hepatic Cyp39a1 (cytochrome P450 family 39 subfamily a member 1) and increased Gramd1b (GRAM domain containing 1B) were also changed in human liver cancer and metabolic liver disease, respectively. Together, our data contribute to the identification of noninvasive biomarkers within the gut-liver axis to predict metabolic status.

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.

Lipidomics in pathogenesis, progression and treatment of nonalcoholic steatohepatitis (NASH): Recent advances

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease affecting up to 30% of the general adult population. NAFLD encompasses a histological spectrum ranging from pure steatosis to non-alcoholic steatohepatitis (NASH). NASH can progress to cirrhosis and is becoming the most common indication for liver transplantation, as a result of increasing disease prevalence and of the absence of approved treatments. Lipidomic readouts of liver blood and urine samples from experimental models and from NASH patients disclosed an abnormal lipid composition and metabolism. Collectively, these changes impair organelle function and promote cell damage, necro-inflammation and fibrosis, a condition termed lipotoxicity. We will discuss the lipid species and metabolic pathways leading to NASH development and progression to cirrhosis, as well as and those species that can contribute to inflammation resolution and fibrosis regression. We will also focus on emerging lipid-based therapeutic opportunities, including specialized proresolving lipid molecules and macrovesicles contributing to cell-to-cell communication and NASH pathophysiology.

The Gut Microbial Bile Acid Modulation and Its Relevance to Digestive Health and Diseases

The human gut microbiome has been linked to numerous digestive disorders, but its metabolic products have been much less well characterized, in part due to the expense of untargeted metabolomics and lack of ability to process the data. In this review, we focused on the rapidly expanding information about the bile acid repertoire produced by the gut microbiome, including the impacts of bile acids on a wide range of host physiological processes and diseases, and discussed the role of short-chain fatty acids and other important gut microbiome-derived metabolites. Of particular note is the action of gut microbiome-derived metabolites throughout the body, which impact processes ranging from obesity to aging to disorders traditionally thought of as diseases of the nervous system, but that are now recognized as being strongly influenced by the gut microbiome and the metabolites it produces. We also highlighted the emerging role for modifying the gut microbiome to improve health or to treat disease, including the "engineered native bacteria'' approach that takes bacterial strains from a patient, modifies them to alter metabolism, and reintroduces them. Taken together, study of the metabolites derived from the gut microbiome provided insights into a wide range of physiological and pathophysiological processes, and has substantial potential for new approaches to diagnostics and therapeutics of disease of, or involving, the gastrointestinal tract.

Glycine-β-Muricholic Acid Improves Liver Fibrosis and Gut Barrier Function by Reducing Bile Acid Pool Size and Hydrophobicity in Male Cyp2c70 Knockout Mice

Cyp2c70 knockout mice lack the enzyme that produces muricholic acids and show a "human-like" hydrophobic bile acid pool-induced hepatobiliary injury. In this study, we investigated the potential anti-cholestasis effect of glycine-conjugated β muricholic acid (G-β-MCA) in male Cyp2c70 KO mice based on its hydrophilic physiochemical property and signaling property as an farnesoid X receptor (FXR) antagonist. Our results showed that G-β-MCA treatment for 5 weeks alleviated ductular reaction and liver fibrosis and improved gut barrier function. Analysis of bile acid metabolism suggested that exogenously administered G-β-MCA was poorly absorbed in the small intestine and mostly deconjugated in the large intestine and converted to taurine-conjugated MCA (T-MCA) in the liver, leading to T-MCA enrichment in the bile and small intestine. These changes decreased the biliary and intestine bile acid hydrophobicity index. Furthermore, G-β-MCA treatment decreased intestine bile acid absorption via unknown mechanisms, resulting in increased fecal bile acid excretion and a reduction in total bile acid pool size. In conclusion, G-β-MCA treatment reduces the bile acid pool size and hydrophobicity and improves liver fibrosis and gut barrier function in Cyp2c70 KO mice.

FXR and NASH: an avenue for tissue-specific regulation

NASH is within the spectrum of NAFLD, a liver condition encompassing liver steatosis, inflammation, hepatocyte injury, and fibrosis. The prevalence of NASH-induced cirrhosis is rapidly rising and has become the leading indicator for liver transplantation in the US. There is no Food and Drug Administration (FDA)-approved pharmacological intervention for NASH. The farnesoid X receptor (FXR) is essential in regulating bile acid homeostasis, and dysregulation of bile acids has been implicated in the pathogenesis of NASH. As a result, modulators of FXR that show desirable effects in mitigating key characteristics of NASH have been developed as promising therapeutic approaches. However, global FXR activation causes adverse effects such as cholesterol homeostasis imbalance and pruritus. The development of targeted FXR modulation is necessary for ideal NASH therapeutics, but information regarding tissue-specific and cell-specific FXR functionality is limited. In this review, we highlight FXR activation in the regulation of bile acid homeostasis and NASH development, examine the current literature on tissue-specific regulation of nuclear receptors, and speculate on how FXR regulation will be beneficial in the treatment of NASH.

Discovery of the First-in-Class Intestinal Restricted FXR and FABP1 Dual Modulator ZLY28 for the Treatment of Nonalcoholic Fatty Liver Disease

The prevalence of nonalcoholic steatohepatitis (NASH) is increasing rapidly worldwide, and NASH has become a serious problem for human health. Recently, the selective activation of the intestinal farnesoid X receptor (FXR) was considered as a more promising strategy for the treatment of NASH with lesser side effects due to reduced systemic exposure. Moreover, the inhibition of intestinal fatty acid binding protein 1 (FABP1) alleviated obesity and NASH by reducing dietary fatty acid uptake. In this study, the first-in-class intestinal restricted FXR and FABP1 dual-target modulator ZLY28 was discovered by comprehensive multiparameter optimization studies. The reduced systemic exposure of ZLY28 might provide better safety by decreasing the on- and off-target side effects in vivo. In NASH mice, ZLY28 exerted robust anti-NASH effects by inhibiting FABP1 and activating the FXR-FGF15 signaling pathway in the ileum. With the above attractive efficacy and preliminary safety profiles, ZLY28 is worthy of further evaluation as a novel anti-NASH agent.

Gut microbiota-bile acids-glucagon like peptide-1 axis contributes the resistance to high fat diet-induced obesity in mice

In human and rodents, some individuals may remain lean even when they are challenged with high calorie intake. The underlying mechanism for resistance to diet-induced obesity was poorly understood. Here, we used C57BL/6J mice to establish animal models of high-fat diet (HFD) induced obesity sensitive (DIO) mice and obesity resistant (DIR) mice. We then investigated the role of gut microbiota, bile acids (BAs) and brown adipose tissue (BAT) thermogenesis in the development of DIR. Reduced fat accumulation, increased glucose tolerance and energy expenditure through BAT activation were observed in DIR mice. The plasma BAs of DIR mice especially the unconjugated BAs were significantly decreased, while intestine tauro-conjugated bile acids (T-CA, T-β-MCA, T-ω-MCA and T-UDCA) were significantly increased in DIR mice. The composition of the gut flora also changed drastically, and negative correlation was found between metabolic profiles (plasma TG, TC, LDL and body weight) and the abundance of Ruminiclostridium in DIR mice, while genus Anaerotruncus abundance in DOR mice was found to be positively correlated. After fecal microbiota transplants, HFD fed recipient mice exhibited a trend toward reduced adiposity and improved glucose tolerance, while showing increased serum tauro-conjugated BAs levels. STC-1 cell experiments confirmed tauro-conjugated BA (T-β-MCA) activated FXR/TGR5 pathway and induced the production of GLP-1, inhibiting genes that regulate the ceramide synthesis. Our results indicated that the DIR mice exhibited higher energy expenditure by activating BAT thermogenesis, which may be related altered gut microbiota-bile acids-glucagon like peptide-1 axis.

Binding, activity and risk assessment of bisphenols toward farnesoid X receptor pathway: In vitro and in silico study

Bisphenols have been identified as emerging environmental pollutants of high concern with potential adverse effects through interactions with receptor-mediated pathways. However, their potential mechanism of action and health risks through the farnesoid X receptor (FXR) pathway remain poorly understood. In the present study, we aimed to explore the potential disruption mechanism of bisphenols through the FXR signalling pathway. Receptor binding assays showed that bisphenols bound to FXR directly, with tetrabromobisphenol A (TBBPA; 34-fold), tetrachlorobisphenol A (TCBPA; 8.7-fold), bisphenol AF (BPAF; 2.0-fold), and bisphenol B (BPB; 1.9-fold) showing a significantly stronger binding potency than bisphenol A (BPA). In receptor transcriptional activity assays, bisphenols showed agonistic activity toward FXR, with BPAF, BPB, and bisphenol F (BPF) exhibiting higher activity than BPA, but TBBPA and TCBPA showing significantly weaker activity than BPA. Molecular docking results indicated that the number of hydrogen bonds dictated their binding strength. Intracellular concentrations of bisphenols were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in receptor activity assays, and it was found that the intracellular concentrations of TBBPA and TCBPA were 40-fold lower than those of BPA. Using the bioactivity concentrations in the FXR receptor activity assay, the liver concentrations of bisphenols were estimated using physiologically-based pharmacokinetic (PBPK) models through their serum concentrations, and the hazard quotient (HQ) values were calculated. The results suggest a potentially high concern for the risk of activating the FXR pathway for some populations with high exposure. Overall, these results indicate that bisphenols can bind to and activate FXR receptors, and that the activation mechanism is dependent on cellular uptake and binding strength. This study provides important information regarding the exposure risk of bisphenols, which can promote the development of environmentally friendly bisphenols.

Parabacteroides distasonis ameliorates hepatic fibrosis potentially via modulating intestinal bile acid metabolism and hepatocyte pyroptosis in male mice

Parabacteroides distasonis (P. distasonis) plays an important role in human health, including diabetes, colorectal cancer and inflammatory bowel disease. Here, we show that P. distasonis is decreased in patients with hepatic fibrosis, and that administration of P. distasonis to male mice improves thioacetamide (TAA)- and methionine and choline-deficient (MCD) diet-induced hepatic fibrosis. Administration of P. distasonis also leads to increased bile salt hydrolase (BSH) activity, inhibition of intestinal farnesoid X receptor (FXR) signaling and decreased taurochenodeoxycholic acid (TCDCA) levels in liver. TCDCA produces toxicity in mouse primary hepatic cells (HSCs) and induces mitochondrial permeability transition (MPT) and Caspase-11 pyroptosis in mice. The decrease of TCDCA by P. distasonis improves activation of HSCs through decreasing MPT-Caspase-11 pyroptosis in hepatocytes. Celastrol, a compound reported to increase P. distasonis abundance in mice, promotes the growth of P. distasonis with concomitant enhancement of bile acid excretion and improvement of hepatic fibrosis in male mice. These data suggest that supplementation of P. distasonis may be a promising means to ameliorate hepatic fibrosis.

Expanding the Library of 1,2,4-Oxadiazole Derivatives: Discovery of New Farnesoid X Receptor (FXR) Antagonists/Pregnane X Receptor (PXR) Agonists

Compounds featuring a 1,2,4-oxadiazole core have been recently identified as a new chemotype of farnesoid X receptor (FXR) antagonists. With the aim to expand this class of compounds and to understand the building blocks necessary to maintain the antagonistic activity, we describe herein the synthesis, the pharmacological evaluation, and the in vitro pharmacokinetic properties of a novel series of 1,2,4-oxadiazole derivatives decorated on the nitrogen of the piperidine ring with different N-alkyl and N-aryl side chains. In vitro pharmacological evaluation showed compounds 5 and 11 as the first examples of nonsteroidal dual FXR/Pregnane X receptor (PXR) modulators. In HepG2 cells, these compounds modulated PXR- and FXR-regulated genes, resulting in interesting leads in the treatment of inflammatory disorders. Moreover, molecular docking studies supported the experimental results, disclosing the ligand binding mode and allowing rationalization of the activities of compounds 5 and 11.

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 Impact of Phytochemicals in Obesity-Related Metabolic Diseases: Focus on Ceramide Metabolism

The prevalence of obesity and related metabolic diseases has increased dramatically worldwide. As obesity progresses, various lipid species accumulate in ectopic tissues. Amongst them, ceramides-a deleterious sphingolipid species-accumulate and cause lipotoxicity and metabolic disturbances. Dysregulated ceramide metabolism appears to be a key feature in the pathogenesis of obesity-related metabolic diseases. Notably, dietary modification might have an impact on modulating ceramide metabolism. Phytochemicals are plant-derived compounds with various physiological properties, which have been shown to protect against obesity-related metabolic diseases. In this review, we aim to examine the impact of a myriad of phytochemicals and their dietary sources in altering ceramide deposition and ceramide-related metabolism from in vitro, in vivo, and human clinical/epidemiological studies. This review discusses how numerous phytochemicals are able to alleviate ceramide-induced metabolic defects and reduce the risk of obesity-related metabolic diseases via diverse mechanisms.

Role of FXR in Renal Physiology and Kidney Diseases

Farnesoid X receptor, also known as the bile acid receptor, belongs to the nuclear receptor (NR) superfamily of ligand-regulated transcription factors, which performs its functions by regulating the transcription of target genes. FXR is highly expressed in the liver, small intestine, kidney and adrenal gland, maintaining homeostasis of bile acid, glucose and lipids by regulating a diverse array of target genes. It also participates in several pathophysiological processes, such as inflammation, immune responses and fibrosis. The kidney is a key organ that manages water and solute homeostasis for the whole body, and kidney injury or dysfunction is associated with high morbidity and mortality. In the kidney, FXR plays an important role in renal water reabsorption and is thought to perform protective functions in acute kidney disease and chronic kidney disease, especially diabetic kidney disease. In this review, we summarize the recent advances in the understanding of the physiological and pathophysiological function of FXR in the kidney.

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>.

Farnesoid X receptor is inhibited after ileum transposition in diabetic rats: its hypoglycemic effect

Background: Aim to investigate bile acid profile changes and the Farnesoid X receptor (FXR) status after ileotransposition (IT), and reveal its possible hypoglycemic mechanism. Methods: Twenty male diabetic rats were randomly assigned into the IT group and the sham IT (SH) group. Bile acid profiles were measured using an ultra-performance liquid chromatography-tandem mass spectrometry. Glucose metabolism was monitored after oral administration of FXR inhibitor and agonist. And the expression of key FXR target genes were measured. Results: The levels of β-muricholic acid (P = 0.047), tauro-α-muricholic acid and tauro-β-muricholic acid (P < 0.001) in plasma in the IT group were higher than those in the SH group, and the levels of taurocholic acid (P = 0.049) and turoursodeoxycholic acid (P = 0.030) were lower than those in the SH group. After inhibition of intestinal FXR, the glucose metabolism in the SH group was improved. When FXR agonist was given, the blood glucose level was increased in both groups. After sacrifice, the levels of glycoursodeoxycholic acid, tauro-α-muricholic acid and tauro-β-muricholic acid in liver and ileum tissues were higher than those in the SH group (P < 0.05), the level of α- muricholic acid (P < 0.001) in liver tissues were lower than that in the SH group. Moreover, the expression of CYP7A1 mRNA (P < 0.001) and FGF15 mRNA (P = 0.001) in the IT group was significantly higher, and the expression of PEPCK mRNA (P = 0.004), SREPB1c mRNA (P = 0.005) and SRB1 mRNA (P = 0.001) were significantly lower than that in the SH group. Conclusions: We demonstrate a remarkable heterogeneity of BA profiles after IT, FXR activation might has a detrimental effect on glucose metabolism.

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.

The emerging role of the small intestinal microbiota in human health and disease

The human gut microbiota continues to demonstrate its importance in human health and disease, largely owing to the countless number of studies investigating the fecal microbiota. Underrepresented in these studies, however, is the role played by microbial communities found in the small intestine, which, given the essential function of the small intestine in nutrient absorption, host metabolism, and immunity, is likely highly relevant. This review provides an overview of the methods used to study the microbiota composition and dynamics along different sections of the small intestine. Furthermore, it explores the role of the microbiota in facilitating the small intestine in its physiological functions and discusses how disruption of the microbial equilibrium can influence disease development. The evidence suggests that the small intestinal microbiota is an important regulator of human health and its characterization has the potential to greatly advance gut microbiome research and the development of novel disease diagnostics and therapeutics.

Microbiota-induced lipid peroxidation impairs obeticholic acid-mediated antifibrotic effect towards nonalcoholic steatohepatitis in mice

Obeticholic acid (OCA) has been examined to treat non-alcoholic steatohepatitis (NASH), but has unsatisfactory antifibrotic effect and deficient responsive rate in recent phase III clinical trial. Using a prolonged western diet-feeding murine NASH model, we show that OCA-shaped gut microbiota induces lipid peroxidation and impairs its anti-fibrotic effect. Mechanically, Bacteroides enriched by OCA deconjugates tauro-conjugated bile acids to generate excessive chenodeoxycholic acid (CDCA), resulting in liver ROS accumulation. We further elucidate that OCA reduces triglycerides containing polyunsaturated fatty acid (PUFA-TGs) levels, whereas elevates free PUFAs and phosphatidylethanolamines containing PUFA (PUFA-PEs), which are susceptible to be oxidized to lipid peroxides (notably arachidonic acid (ARA)-derived 12-HHTrE), inducing hepatocyte ferroptosis and activating hepatic stellate cells (HSCs). Inhibiting lipid peroxidation with pentoxifylline (PTX) rescues anti-fibrotic effect of OCA, suggesting combination of OCA and lipid peroxidation inhibitor could be a potential antifibrotic pharmacological approach in clinical NASH-fibrosis.

Limosilactobacillus reuteri and caffeoylquinic acid synergistically promote adipose browning and ameliorate obesity-associated disorders

OBJECTIVE

High intake of caffeoylquinic acid (CQA)-rich dietary supplements, such as green coffee bean extracts, offers health-promoting effects on maintaining metabolic homeostasis. Similar to many active herbal ingredients with high pharmacological activities but low bioavailability, CQA has been reported as a promising thermogenic agent with anti-obesity properties, which contrasts with its poor oral absorption. Intestinal tract is the first site of CQA exposure and gut microbes might react quickly to CQA. Thus, it is of interest to explore the role of gut microbiome and microbial metabolites in the beneficial effects of CQA on obesity-related disorders.

RESULTS

Oral CQA supplementation effectively enhanced energy expenditure by activating browning of adipose and thus ameliorated obesity-related metabolic dysfunctions in high fat diet-induced obese (DIO) mice. Here, 16S rRNA gene amplicon sequencing revealed that CQA treatment remodeled the gut microbiota to promote its anti-obesity actions, as confirmed by antibiotic treatment and fecal microbiota transplantation. CQA enriched the gut commensal species Limosilactobacillus reuteri (L. reuteri) and stimulated the production of short-chain fatty acids, especially propionate. Mono-colonization of L. reuteri or low-dose CQA treatment did not reduce adiposity in DIO mice, while their combination elicited an enhanced thermogenic response, indicating the synergistic effects of CQA and L. reuteri on obesity. Exogenous propionate supplementation mimicked the anti-obesity effects of CQA alone or when combined with L. reuteri, which was ablated by the monocarboxylate transporter (MCT) inhibitor 7ACC1 or MCT1 disruption in inguinal white adipose tissues to block propionate transport.

CONCLUSIONS

Our data demonstrate a functional axis among L. reuteri, propionate, and beige fat tissue in the anti-obesity action of CQA through the regulation of thermogenesis. These findings provide mechanistic insights into the therapeutic use of herbal ingredients with poor bioavailability via their interaction with the gut microbiota. Video Abstract.

Liver-derived metabolites as signaling molecules in fatty liver disease

Excessive fat accumulation in the liver has become a major health threat worldwide. Unresolved fat deposition in the liver can go undetected until it develops into fatty liver disease, followed by steatohepatitis, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Lipid deposition in the liver is governed by complex communication, primarily between metabolic organs. This can be mediated by hormones, organokines, and also, as has been more recently discovered, metabolites. Although how metabolites from peripheral organs affect the liver is well documented, the effect of metabolic players released from the liver during the development of fatty liver disease or associated comorbidities needs further attention. Here we focus on interorgan crosstalk based on metabolites released from the liver and how these molecules act as signaling molecules in peripheral tissues. Due to the liver's specific role, we are covering lipid and bile mechanism-derived metabolites. We also discuss the high sucrose intake associated with uric acid release from the liver. Excessive fat deposition in the liver during fatty liver disease development reflects disrupted metabolic processes. As a response, the liver secretes a variety of signaling molecules as well as metabolites which act as a footprint of the metabolic disruption. In the coming years, the reciprocal exchange of metabolites between the liver and other metabolic organs will gain further importance and will help to better understand the development of fatty liver disease and associated diseases.

Astragaloside IV ameliorates diet-induced hepatic steatosis in obese mice by inhibiting intestinal FXR via intestinal flora remodeling

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a major clinical and public health burden worldwide with no established pharmacological therapy. Changes in the intestinal flora and associated metabolite bile acids (BAs) have been described in NAFLD. Astragaloside IV (AS-IV) is a low drug permeability saponin with protective effects against multiple diseases. However, the specific mechanism underlying the involvement of AS-IV in the regulation of NAFLD is yet to be clarified.

PURPOSE

This study aimed to investigate the effect of AS-IV on NAFLD and explore whether intestinal flora was involved.

METHODS

The effect of AS-IV was evaluated on high-fat diet-fed mice. Real-time PCR, immunohistochemistry, immunofluorescence, and biochemical analyses were performed. 16S rRNA gene sequencing and UPLC-TQMS were used to determine the alterations in the intestinal flora and concentration of BAs. Fecal microbiota transplantation (FMT) and intestine-specific farnesoid X receptor (FXR) knockout were also performed.

RESULTS

AS-IV treatment alleviated diet-induced metabolic impairments, particularly hepatic steatosis. These changes occurred in the setting of decreased intestinal bile salt hydrolase (BSH)-expressing flora. Further analysis showed that the reduced BSH activity increased intestinal tauro-β-muricholic acid levels, an inhibitor of intestinal FXR. Inhibition of intestinal FXR signaling by AS-IV was accompanied by decreased expression of intestinal fibroblast growth factor 15 and subsequent hepatic FXR activation as well as increased glucagon-like peptide-1 and decreased ceramide production, all of which contribute to the inhibition of sterol regulatory element-binding protein-1c-mediated hepatic steatosis. Furthermore, intestine-specific Fxr knockout and FMT further demonstrated an FXR- and intestinal flora-dependent preventive effect of AS-IV on hepatic steatosis.

CONCLUSION

These results show that the changes in intestinal flora and BAs serve an essential role in the remission of hepatic steatosis by AS-IV, thereby suggesting that AS-IV may be used as a prebiotic agent to provide viable treatment for NAFLD.

Disulfiram ameliorates nonalcoholic steatohepatitis by modulating the gut microbiota and bile acid metabolism

Nonalcoholic steatohepatitis (NASH) has been linked with the gut-liver axis. Here, we investigate the potential for repurposing disulfiram (DSF), a drug commonly used to treat chronic alcoholism, for NASH. Using a mouse model, we show that DSF ameliorates NASH in a gut microbiota-dependent manner. DSF modulates the gut microbiota and directly inhibits the growth of Clostridium. Administration of Clostridium abolishes the ameliorating effects of DSF on NASH. Mechanistically, DSF reduces Clostridium-mediated 7α-dehydroxylation activity to suppress secondary bile acid biosynthesis, which in turn activates hepatic farnesoid X receptor signaling to ameliorate NASH. To assess the effect of DSF on human gut microbiota, we performed a self-controlled clinical trial (ChiCTR2100048035), including 23 healthy volunteers who received 250 mg-qd DSF for 7 days. The primary objective outcomes were to assess the effects of the intervention on the diversity, composition and functional profile of gut microbiota. The pilot study shows that DSF also reduces Clostridium-mediated 7α-dehydroxylation activity. All volunteers tolerated DSF well and there were no serious adverse events in the 7-day follow-up period. Transferring fecal microbiota obtained from DSF-treated humans into germ-free mice ameliorates NASH. Collectively, the observations of similar ameliorating effects of DSF on mice and humans suggest that DSF ameliorates NASH by modulating the gut microbiota and bile acid metabolism.

The role of FXR and TGR5 in reversing and preventing progression of Western diet-induced hepatic steatosis, inflammation, and fibrosis in mice

Nonalcoholic steatohepatitis (NASH) is the most common chronic liver disease in the US, partly due to the increasing incidence of metabolic syndrome, obesity, and type 2 diabetes. The roles of bile acids and their receptors, such as the nuclear receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5, on the development of NASH are not fully clear. C57BL/6J male mice fed a Western diet (WD) develop characteristics of NASH, allowing determination of the effects of FXR and TGR5 agonists on this disease. Here we show that the FXR-TGR5 dual agonist INT-767 prevents progression of WD-induced hepatic steatosis, inflammation, and fibrosis, as determined by histological and biochemical assays and novel label-free microscopy imaging techniques, including third harmonic generation, second harmonic generation, and fluorescence lifetime imaging microscopy. Furthermore, we show INT-767 decreases liver fatty acid synthesis and fatty acid and cholesterol uptake, as well as liver inflammation. INT-767 markedly changed bile acid composition in the liver and intestine, leading to notable decreases in the hydrophobicity index of bile acids, known to limit cholesterol and lipid absorption. In addition, INT-767 upregulated expression of liver p-AMPK, SIRT1, PGC-1α, and SIRT3, which are master regulators of mitochondrial function. Finally, we found INT-767 treatment reduced WD-induced dysbiosis of gut microbiota. Interestingly, the effects of INT-767 in attenuating NASH were absent in FXR-null mice, but still present in TGR5-null mice. Our findings support treatment and prevention protocols with the dual FXR-TGR5 agonist INT-767 arrest progression of WD-induced NASH in mice mediated by FXR-dependent, TGR5-independent mechanisms.

Beneficial effects of UDCA and norUDCA in a rodent model of steatosis are linked to modulation of GPBAR1/FXR signaling

Non-alcoholic steatosis (NAFLD) and steatohepatitis (NASH) are two highly prevalent human disorders for which therapy remains suboptimal. Bile acids play an essential role in regulating liver metabolism, and several bile acids-based therapy are currently investigated for their potential therapeutic efficacy in NAFLD/NASH. Bile acids exert their functions, at least in part, by modulating two main receptors the Farnesoid-x-receptor (FXR) and the G protein-coupled receptor, GPBAR1. In the present study we have compared the pharmacological effects of two bile acids, the ursodeoxycholic acid (UDCA) and its derivative norUDCA, in a model of NAFLD/NASH induced by feeding mice with a Western diet for 12 weeks. The results of these studies demonstrated that both UDCA and norUDCA protected against development of steatosis and fibrosis, but did not reduce the hepatocytes ballooning nor the development of a pro-atherogenic lipid profile. Both agents reduced liver lipogenesis and ameliorated insulin sensitivity and adipocytes signaling as shown by increased expression of adiponectin. Mechanistically, UDCA acts as weak GPBAR1 agonist, while norUDCA exerted no effect on both GPBAR1 and FXR. In vivo administration of UDCA resets bile acid synthesis and promotes a shift toward bile acids species that are GPBAR1 agonists, UDCA, TUDCA and hyodeoxycholic acid, and increases GLP1 expression in the ileum. In contrast norUDCA is poorly metabolized exerting a minimal impact on GPBAR1 signaling. Together, these data, highlight the potential role of UDCA and norUDCA in treating of NAFLD, though these beneficial effects are supported by different mechanisms.

Xanthohumol improves cognition in farnesoid X receptor-deficient mice on a high-fat diet

Xanthohumol (XN) improves cognition of wild-type rodents on a high-fat diet (HFD). Bile acids and ceramide levels in the liver and hippocampus might be linked to these effects. XN modulates activity of the nuclear farnesoid X receptor (FXR; also known as NR1H4), the primary receptor for bile acids. To determine the role of FXR in the liver and intestine in mediating the effects of XN on cognitive performance, mice with intestine- and liver-specific FXR ablation (FXRIntestine-/- and FXRLiver-/-, respectively) on an HFD or an HFD containing XN were cognitively tested. XN improved cognitive performance in a genotype- and sex-dependent manner, with improved task learning in females (specifically wild-type), reversal learning in males (specifically wild-type and FXRIntestine-/- mutant) and spatial learning (both sexes). XN increased hippocampal diacylglycerol and sphingomyelin levels in females but decreased them in males. XN increased the ratio of shorter-chain to longer-chain ceramides and hexaceramides. Higher diacylglycerol and lower longer-chain ceramide and hexaceramide levels were linked to improved cognitive performance. Thus, the beneficial sex-dependent cognitive effects of XN are linked to changes in hippocampal diacylglycerol and ceramide levels. This article has an associated First Person interview with the first author of the paper.

Bile acids-gut microbiota crosstalk contributes to the improvement of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) occurs that cannot effectively use the insulin. Insulin Resistance (IR) is a significant characteristic of T2DM which is also an essential treatment target in blood glucose regulation to prevent T2DM and its complications. Bile acids (BAs) are one group of bioactive metabolites synthesized from cholesterol in liver. BAs play an important role in mutualistic symbiosis between host and gut microbiota. It is shown that T2DM is associated with altered bile acid metabolism which can be regulated by gut microbiota. Simultaneously, BAs also reshape gut microbiota and improve IR and T2DM in the bidirectional communications of the gut-liver axis. This article reviewed the findings on the interaction between BAs and gut microbiota in improving T2DM, which focused on gut microbiota and its debinding function and BAs regulated gut microbiota through FXR/TGR5. Meanwhile, BAs and their derivatives that are effective for improving T2DM and other treatments based on bile acid metabolism were also summarized. This review highlighted that BAs play a critical role in the glucose metabolism and may serve as therapeutic targets in T2DM, providing a reference for discovering and screening novel therapeutic drugs.

Metformin alleviates irradiation-induced intestinal injury by activation of FXR in intestinal epithelia

Abdominal irradiation (IR) destroys the intestinal mucosal barrier, leading to severe intestinal infection. There is an urgent need to find safe and effective treatments to reduce IR-induced intestinal injury. In this study, we reported that metformin protected mice from abdominal IR-induced intestinal injury by improving the composition and diversity of intestinal flora. The elimination of intestinal microbiota (Abx) abrogated the protective effects of metformin on irradiated mice. We further characterized that treatment of metformin increased the murine intestinal abundance of Lactobacillus, which mediated the radioprotective effect. The administration of Lactobacillus or fecal microbiota transplantation (FMT) into Abx mice considerably lessened IR-induced intestinal damage and restored the radioprotective function of metformin in Abx mice. In addition, applying the murine intestinal organoid model, we demonstrated that IR inhibited the formation of intestinal organoids, and metformin alone bore no protective effect on organoids after IR. However, a combination of metformin and Lactobacillus or Lactobacillus alone displayed a strong radioprotection on the organoid formation. We demonstrated that metformin/Lactobacillus activated the farnesoid X receptor (FXR) signaling in intestinal epithelial cells and hence upregulated tight junction proteins and mucins in intestinal epithelia, increased the number of goblet cells, and augmented the mucus layer thickness to maintain the integrity of intestinal epithelial barrier, which eventually contributed to reduced radiation intestinal injury. In addition, we found that Lactobacillus abundance was significantly increased in the intestine of patients receiving metformin while undergoing abdominal radiotherapy and the abundance was negatively correlated with the diarrhea duration of patients. In conclusion, our results demonstrate that metformin possesses a protective effect on IR-induced intestinal injury by upregulating the abundance of Lactobacillus in the intestine.

The role of the gut microbiota in health and cardiovascular diseases

The gut microbiota is critical to human health, such as digesting nutrients, forming the intestinal epithelial barrier, regulating immune function, producing vitamins and hormones, and producing metabolites to interact with the host. Meanwhile, increasing evidence indicates that the gut microbiota has a strong correlation with the occurrence, progression and treatment of cardiovascular diseases (CVDs). In patients with CVDs and corresponding risk factors, the composition and ratio of gut microbiota have significant differences compared with their healthy counterparts. Therefore, gut microbiota dysbiosis, gut microbiota-generated metabolites, and the related signaling pathway may serve as explanations for some of the mechanisms about the occurrence and development of CVDs. Several studies have also demonstrated that many traditional and latest therapeutic treatments of CVDs are associated with the gut microbiota and its generated metabolites and related signaling pathways. Given that information, we summarized the latest advances in the current research regarding the effect of gut microbiota on health, the main cardiovascular risk factors, and CVDs, highlighted the roles and mechanisms of several metabolites, and introduced corresponding promising treatments for CVDs regarding the gut microbiota. Therefore, this review mainly focuses on exploring the role of gut microbiota related metabolites and their therapeutic potential in CVDs, which may eventually provide better solutions in the development of therapeutic treatment as well as the prevention of CVDs.

Glycine-β-muricholic acid antagonizes the intestinal farnesoid X receptor-ceramide axis and ameliorates NASH in mice

Nonalcoholic steatohepatitis (NASH) is a rapidly developing pathology around the world, with limited treatment options available. Some farnesoid X receptor (FXR) agonists have been applied in clinical trials for NASH, but side effects such as pruritus and low-density lipoprotein elevation have been reported. Intestinal FXR is recognized as a promising therapeutic target for metabolic diseases. Glycine-β-muricholic acid (Gly-MCA) is an intestine-specific FXR antagonist previously shown to have favorable metabolic effects on obesity and insulin resistance. Herein, we identify a role for Gly-MCA in the pathogenesis of NASH, and explore the underlying molecular mechanism. Gly-MCA improved lipid accumulation, inflammatory response, and collagen deposition in two different NASH models. Mechanistically, Gly-MCA decreased intestine-derived ceramides by suppressing ceramide synthesis-related genes via decreasing intestinal FXR signaling, leading to lower liver endoplasmic reticulum (ER) stress and proinflammatory cytokine production. The role of bile acid metabolism and adiposity was excluded in the suppression of NASH by Gly-MCA, and a correlation was found between intestine-derived ceramides and NASH severity. This study revealed that Gly-MCA, an intestine-specific FXR antagonist, has beneficial effects on NASH by reducing ceramide levels circulating to liver via lowering intestinal FXR signaling, and ceramide production, followed by decreased liver ER stress and NASH progression. Intestinal FXR is a promising drug target and Gly-MCA a novel agent for the prevention and treatment of NASH.

Dysregulation of secondary bile acid metabolism precedes islet autoimmunity and type 1 diabetes

The gut microbiota is crucial in the regulation of bile acid (BA) metabolism. However, not much is known about the regulation of BAs during progression to type 1 diabetes (T1D). Here, we analyzed serum and stool BAs in longitudinal samples collected at 3, 6, 12, 18, 24, and 36 months of age from children who developed a single islet autoantibody (AAb) (P1Ab; n = 23) or multiple islet AAbs (P2Ab; n = 13) and controls (CTRs; n = 38) who remained AAb negative. We also analyzed the stool microbiome in a subgroup of these children. Factor analysis showed that age had the strongest impact on both BA and microbiome profiles. We found that at an early age, systemic BAs and microbial secondary BA pathways were altered in the P2Ab group compared with the P1Ab and CTR groups. Our findings thus suggest that dysregulated BA metabolism in early life may contribute to the risk and pathogenesis of T1D.

Nuciferine Protects Against High-Fat Diet-Induced Hepatic Steatosis via Modulation of Gut Microbiota and Bile Acid Metabolism in Rats

Our previous study showed that nuciferine (NF) attenuated non-alcoholic fatty liver disease (NAFLD), which is attributed to a high-fat diet (HFD) through reinforcing intestinal barrier functions, regulating lipid metabolism, and improving inflammation. To clarify whether other mechanisms contribute to the anti-NAFLD efficacy of NF, the present study investigated the influence of NF on bile acid (BA) metabolism and gut microbiota in HFD-fed rats. The data demonstrated that NF changed the composition of colonic BA, particularly elevating conjugated BA and non-12OH BA levels. As shown by downregulated protein levels of FXR, FGF15, FGFR4, and ASBT and upregulated protein levels of CYP7A1 and CYP27A1, NF inhibited ileal FXR signaling, promoted BA synthesis, suppressed BA reabsorption, and facilitated fecal BA excretion. NF might affect hepatic FXR signaling, BA conjugation, and enterohepatic circulation by the changed mRNA levels of Fxr, Shp, Baat, Bacs, Bsep, Ntcp, Ibabp, and Ostα/β. Meanwhile, NF regulated the gut microbiota, characterized by decreased BSH-producing genus, 7α-dehydroxylation genus, and increased taurine metabolism-related genus. Spearman rank correlation analysis implied that Colidextribacter, Adlercreutzia, Family_XIII_AD3011_group, Lachnospiraceae_UCG-010, Eisenbergiella, and UCG-005 were robustly associated with particular BA monomers. In conclusion, our experiment results suggested that NF could exert a mitigating effect on NAFLD via regulating BA metabolism and modulating the gut microbiota.

Probiotics protect against hepatic steatosis in tris (2-chloroethyl) phosphate-induced metabolic disorder of mice via FXR signaling

Tris (2-chloroethyl) phosphate (TCEP), the most widely useful and most frequently detective organophosphate flame retardants in environment, has been shown potential relationship with adolescent weight. Probiotics is an effective therapy for metabolic diseases such as obesity and NAFLD with gut microbiota dysregulation. This study aims to explore the protective effects of probiotics against lipid metabolic disorder induced by chronic TCEP exposure and demonstrate the mechanism of this event. The data showed that dietary complex probiotics supplement attenuated TCEP-induced obesity, hyperlipidemia, liver dysfunction, and hepatic steatosis. In addition, dietary complex probiotics suppressed TCEP-promoted ileal FXR signaling, and upregulated hepatic FXR/SHP pathway inhibited by TCEP. Moreover, dietary complex probiotics stimulated PPARα-mediated lipid oxidation and suppressed SREBP1c/PPARγ-mediated lipid synthesis via regulation of FXR signaling. Therefore, this study indicates that dietary complex probiotics could protect against hepatic steatosis via FXR-mediated signaling pathway in TCEP-induced metabolism disorder in mice, resulting in attenuation of systemic lipid accumulation.

Ferulic acid attenuates high-fat diet-induced hypercholesterolemia by activating classic bile acid synthesis pathway

Ferulic acid (FA), a natural phenolic phytochemical abundantly present in whole grains, displays promising therapeutic effects on hypercholesterolemia while its underlying mechanism not fully elucidated. This study aimed to investigate the cholesterol-lowering effect of FA in high-fat diet (HFD)-fed mice and its potential molecular mechanism. FA supplementation alleviated HFD-induced hypercholesterolemia (–13.2%, p < 0.05), along with increased excretion of bile acids (BAs) in feces (37.0%, p < 0.05). Mechanism studies showed that FA activated the expression of cholesterol 7α hydroxylase (CYP7A1), a rate-limiting enzyme in BA biosynthesis in the liver, which increased the BAs biosynthesis from cholesterol. Surprisingly, increased excretion of BAs in feces is a consequence, not a cause, of CYP7A1 activation. Furthermore, enterohepatic farnesoid X receptor (FXR) signaling is not involved in the activation of hepatic CYP7A1 by FA. In conclusion, FA activates CYP7A1 through non-FXR signaling, which on the one hand effectively prevents hypercholesterolemia, and on the other hand leads to secondary BAs elevation in plasma. The latter may be the key to the anti-obesity and hypoglycemic effects of FA.

Bile acid metabolism and signaling, the microbiota, and metabolic disease

The diversity, composition, and function of the bacterial community inhabiting the human gastrointestinal tract contributes to host health through its role in producing energy or signaling molecules that regulate metabolic and immunologic functions. Bile acids are potent metabolic and immune signaling molecules synthesized from cholesterol in the liver and then transported to the intestine where they can undergo metabolism by gut bacteria. The combination of host- and microbiota-derived enzymatic activities contribute to the composition of the bile acid pool and thus there can be great diversity in bile acid composition that depends in part on the differences in the gut bacteria species. Bile acids can profoundly impact host metabolic and immunological functions by activating different bile acid receptors to regulate signaling pathways that control a broad range of complex symbiotic metabolic networks, including glucose, lipid, steroid and xenobiotic metabolism, and modulation of energy homeostasis. Disruption of bile acid signaling due to perturbation of the gut microbiota or dysregulation of the gut microbiota-host interaction is associated with the pathogenesis and progression of metabolic disorders. The metabolic and immunological roles of bile acids in human health have led to novel therapeutic approaches to manipulate the bile acid pool size, composition, and function by targeting one or multiple components of the microbiota-bile acid-bile acid receptor axis.

Local and systemic effects of microbiome‐derived metabolites

Commensal microbes form distinct ecosystems within their mammalian hosts, collectively termed microbiomes. These indigenous microbial communities broadly expand the genomic and functional repertoire of their host and contribute to the formation of a “meta‐organism.” Importantly, microbiomes exert numerous biochemical reactions synthesizing or modifying multiple bioactive small molecules termed metabolites, which impact their host's physiology in a variety of contexts. Identifying and understanding molecular mechanisms of metabolite–host interactions, and how their disrupted signaling can contribute to diseases, may enable their therapeutic application, a modality termed “postbiotic” therapy. In this review, we highlight key examples of effects of bioactive microbe‐associated metabolites on local, systemic, and immune environments, and discuss how these may impact mammalian physiology and associated disorders. We outline the challenges and perspectives in understanding the potential activity and function of this plethora of microbially associated small molecules as well as possibilities to harness them toward the promotion of personalized precision therapeutic interventions.

Duodenal-jejunal bypass reduces serum ceramides via inhibiting intestinal bile acid-farnesoid X receptor pathway

BACKGROUND

Bile acids play an important role in the amelioration of type 2 diabetes following duodenal-jejunal bypass (DJB). Serum bile acids are elevated postoperatively. However, the clinical relevance is not known. Bile acids in the peripheral circulation reflect the amount of bile acids in the gut. Therefore, a further investigation of luminal bile acids following DJB is of great significance.

AIM

To investigate changes of luminal bile acids following DJB.

METHODS

Salicylhydroxamic acid (SHAM), DJB, and DJB with oral chenodeoxycholic acid (CDCA) supplementation were performed in a high-fat-diet/streptozotocin-induced diabetic rat model. Body weight, energy intake, oral glucose tolerance test, luminal bile acids, serum ceramides and intestinal ceramide synthesis were analyzed at week 12 postoperatively.

RESULTS

Compared to SHAM, DJB achieved rapid and durable improvement in glucose tolerance and led to increased total luminal bile acid concentrations with preferentially increased proportion of farnesoid X receptor (FXR) - inhibitory bile acids within the common limb. Intestinal ceramide synthesis was repressed with decreased serum ceramides, and this phenomenon could be partially antagonized by luminal supplementation of FXR activating bile acid CDCA.

CONCLUSION

DJB significantly changes luminal bile acid composition with increased proportion FXR-inhibitory bile acids and reduces serum ceramide levels. There observations suggest a novel mechanism of bile acids in metabolic regulation after DJB.

Duodenal Anaerobutyricum soehngenii infusion stimulates GLP-1 production, ameliorates glycaemic control and beneficially shapes the duodenal transcriptome in metabolic syndrome subjects: a randomised double-blind placebo-controlled cross-over study

OBJECTIVE

Although gut dysbiosis is increasingly recognised as a pathophysiological component of metabolic syndrome (MetS), the role and mode of action of specific gut microbes in metabolic health remain elusive. Previously, we identified the commensal butyrogenic Anaerobutyricum soehngenii to be associated with improved insulin sensitivity in subjects with MetS. In this proof-of-concept study, we investigated the potential therapeutic effects of A. soehngenii L2-7 on systemic metabolic responses and duodenal transcriptome profiles in individuals with MetS.

DESIGN

In this randomised double-blind placebo-controlled cross-over study, 12 male subjects with MetS received duodenal infusions of A. soehngenii/ placebo and underwent duodenal biopsies, mixed meal tests (6 hours postinfusion) and 24-hour continuous glucose monitoring.

RESULTS

A. soehngenii treatment provoked a markedly increased postprandial excursion of the insulinotropic hormone glucagon-like peptide 1 (GLP-1) and an elevation of plasma secondary bile acids, which were positively associated with GLP-1 levels. Moreover, A. soehngenii treatment robustly shaped the duodenal expression of 73 genes, with the highest fold induction in the expression of regenerating islet-protein 1B (REG1B)-encoding gene. Strikingly, duodenal REG1B expression positively correlated with GLP-1 levels and negatively correlated with peripheral glucose variability, which was significantly diminished in the 24 hours following A. soehngenii intake. Mechanistically, Reg1B expression is induced upon sensing butyrate or bacterial peptidoglycan. Importantly, A. soehngenii duodenal administration was safe and well tolerated.

CONCLUSIONS

A single dose of A. soehngenii improves peripheral glycaemic control within 24 hours; it specifically stimulates intestinal GLP-1 production and REG1B expression. Further studies are needed to delineate the specific pathways involved in REG1B induction and function in insulin sensitivity.

TRIAL REGISTRATION NUMBER

NTR-NL6630.