Gut microbiota-associated bile acid deconjugation accelerates hepatic steatosis in ob/ob mice

Bile acid metabolism in health and ageing-related diseases

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

Impacts of Dietary Standardized Ileal Digestible Lysine to Net Energy Ratio on Lipid Metabolism in Finishing Pigs Fed High-Wheat Diets

The present study aimed to investigate the impacts of dietary standardized ileal digestible lysine to net energy (SID Lys:NE) ratio on lipid metabolism in pigs fed high-wheat diets. Thirty-six crossbred growing barrows (65.20 ± 0.38 kg) were blocked into two treatment groups, fed high-wheat diets with either a high SID Lys:NE ratio (HR) or a low SID Lys:NE ratio (LR). Each treatment group consisted of three replicates, with six pigs per pen in each replicate. The diminishing dietary SID Lys:NE ratio exhibited no adverse impacts on the carcass trait (p > 0.05) but increased the marbling score of the longissimus dorsi muscle (p < 0.05). Meanwhile, LR diets tended to increase the serum triglyceride concentration (p < 0.1). LR diets upregulated fatty acid transport protein 4 and acetyl-coA carboxylase α expression levels and downregulated the expression level of adipose triglyceride lipase (p < 0.05). LR diets improved energy metabolism via decreasing the expression levels of AMP-activated protein kinase (AMPK) α1, sirtuin 1 (SIRT1), and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) (p < 0.05). Additionally, LR diets stimulated hepatic bile acid synthesis via upregulating the expression levels of cytochrome P450 family 7 subfamily A member 1 and cytochrome P450 family 27 subfamily A member 1, and downregulating farnesol X receptor (FXR) and small heterodimer partner (SHP) expression levels (p < 0.05). A lowered SID Lys:NE ratio affected the colonic microbial composition, characterized by increased relative abundances of YRC22, Parabacteroides, Sphaerochaeta, and Bacteroides, alongside a decreased in the proportion of Roseburia, f_Lachnospiraceae_g_Clostridium, Enterococcus, Shuttleworthia, Exiguobacterium, Corynebacterium, Subdoligranulum, Sulfurospirillum, and Marinobacter (p < 0.05). The alterations in microbial composition were accompanied by a decrease in colonic butyrate concentration (p < 0.1). The metabolomic analysis revealed that LR diets affected primary bile acid synthesis and AMPK signaling pathway (p < 0.05). And the mantel analysis indicated that Parabacteroides, Sphaerochaeta, f_Lachnospiraceae_g_Clostridium, Shuttleworthia, and Marinobacter contributed to the alterations in body metabolism. A reduced dietary SID Lys:NE ratio improves energy metabolism, stimulates lipogenesis, and inhibits lipolysis in finishing pigs by regulating the AMPKα/SIRT1/PGC-1α pathway and the FXR/SHP pathway. Parabacteroides and Sphaerochaeta benefited bile acids synthesis, whereas f_Lachnospiraceae_g_Clostridium, Shuttleworthia, and Marinobacter may contribute to the activation of the AMPK signaling pathway. Overall, body metabolism and colonic microbiota collectively controlled the lipid metabolism in finishing pigs.

Berberine Protects against High-Energy and Low-Protein Diet-Induced Hepatic Steatosis: Modulation of Gut Microbiota and Bile Acid Metabolism in Laying Hens

Berberine (BBR) is a natural alkaloid with multiple biotical effects that has potential as a treatment for fatty liver hemorrhagic syndrome (FLHS). However, the mechanism underlying the protective effect of BBR against FLHS remains unclear. The present study aimed to investigate the effect of BBR on FLHS induced by a high-energy, low-protein (HELP) diet and explore the involvement of the gut microbiota and bile acid metabolism in the protective effects. A total of 90 healthy 140-day-old Hy-line laying hens were randomly divided into three groups, including a control group (fed a basic diet), a HELP group (fed a HELP diet), and a HELP+BBR group (high-energy, high-protein diet supplemented with BBR instead of maize). Our results show that BBR supplementation alleviated liver injury and hepatic steatosis in laying hens. Moreover, BBR supplementation could significantly regulate the gut's microbial composition, increasing the abundance of Actinobacteria and Romboutsia. In addition, the BBR supplement altered the profile of bile acid. Furthermore, the gut microbiota participates in bile acid metabolism, especially taurochenodeoxycholic acid and α-muricholic acid. BBR supplementation could regulate the expression of genes and proteins related to glucose metabolism, lipid synthesis (FAS, SREBP-1c), and bile acid synthesis (FXR, CYP27a1). Collectively, our findings demonstrate that BBR might be a potential feed additive for preventing FLHS by regulating the gut microbiota and bile acid metabolism.

Synergistic neuroprotective effects of two natural medicinal plants against CORT-induced nerve cell injury by correcting neurotransmitter deficits and inflammation imbalance

BACKGROUND

Lilium henryi Baker (Liliaceae) and Rehmannia glutinosa (Gaertn.) DC. (Plantaginaceae) were the traditional natural medicinal plants for the treatment of depression, but the antidepression mechanism of two plants co-decoction (Also known as Lily bulb and Rehmannia decoction (LBRD) drug-containing serum (LBRDDS) has not been elucidated in the in vitro model of depression.

MATERIAL AND METHODS

Here, UHPLC-Q-TOF/MS was used to identify the active components of LBRDDS and the potential effector substance was identified by bioinformatics analysis. CORT-induced nerve cells cytotoxicity was used to investigate the neuroprotection effect of LBRDDS and the underlying pharmacological mechanisms were explored by multiple experimental methods such as molecular docking, immunofluorescence, gain- or loss-of function experiments.

RESULTS

Bioactive compounds in LBRDDS absorbed from intestinal tract were transformed or metabolized by the gut microbiota including palmitic acid, adrenic acid, linoleic acid, arachidonic acid and docosapentaenoic acid. Network pharmacology analysis and molecular docking of showed fatty acid metabolism, neurotransmitter synthesis and neuroinflammation may be potential therapeutic targets of LBRDDS. LBRDDS can improve the activity of model cells, reduce cytotoxicity of lactate dehydrogenase, recover neurotransmitter imbalance, relieve inflammatory damage, down-regulate the expression of miRNA-144-3p, increase the mRNAs and protein expression level of Gad-67 and VGAT, and promote the synthesis and transport of GABA.

CONCLUSION

Therefore, LBRDDS exerts neuroprotective effects by correcting neurotransmitter deficits and inflammation imbalance in the CORT-induced nerve cell injury model.

Maternal Western diet mediates susceptibility of offspring to Crohn's-like colitis by deoxycholate generation

BACKGROUND

The Western dietary pattern, characterized by high consumption of fats and sugars, has been strongly associated with an increased risk of developing Crohn's disease (CD). However, the potential impact of maternal obesity or prenatal exposure to a Western diet on offspring's susceptibility to CD remains unclear. Herein, we investigated the effects and underlying mechanisms of a maternal high-fat/high-sugar Western-style diet (WD) on offspring's susceptibility to 2,4,6-Trinitrobenzenesulfonic acid (TNBS)-induced Crohn's-like colitis.

METHODS

Maternal dams were fed either a WD or a normal control diet (ND) for eight weeks prior to mating and continued throughout gestation and lactation. Post-weaning, the offspring were subjected to WD and ND to create four groups: ND-born offspring fed a normal diet (N-N) or Western diet (N-W), and WD-born offspring fed a normal (W-N) or Western diet (W-W). At eight weeks of age, they were administered TNBS to induce a CD model.

RESULTS

Our findings revealed that the W-N group exhibited more severe intestinal inflammation than the N-N group, as demonstrated by a lower survival rate, increased weight loss, and a shorter colon length. The W-N group displayed a significant increase in Bacteroidetes, which was accompanied by an accumulation of deoxycholic acid (DCA). Further experimentation confirmed an increased generation of DCA in mice colonized with gut microbes from the W-N group. Moreover, DCA administration aggravated TNBS-induced colitis by promoting Gasdermin D (GSDMD)-mediated pyroptosis and IL-1beta (IL-1β) production in macrophages. Importantly, the deletion of GSDMD effectively restrains the effect of DCA on TNBS-induced colitis.

CONCLUSIONS

Our study demonstrates that a maternal Western-style diet can alter gut microbiota composition and bile acid metabolism in mouse offspring, leading to an increased susceptibility to CD-like colitis. These findings highlight the importance of understanding the long-term consequences of maternal diet on offspring health and may have implications for the prevention and management of Crohn's disease. Video Abstract.

Probiotic profiling of bifidobacteria indigenous to the human intestinal mucosa shows alleviation of dysbiosis-associated pathogen biofilms

The present study was undertaken to isolate bifidobacterial probiotics and characterize the biodiversity of mucosal bacteria in the human distal gut through 16S rRNA amplicon sequencing. Bifidobacterial strains obtained by selective culturing were investigated for biofilms and probiotic characteristics. Both culture-dependent and culture-independent approaches revealed substantial microbial diversity. Bifidobacterium strains yielded robust biofilms with predominantly exopolysaccharides and eDNA matrix. Microscopy revealed species-dependent spatial arrangement of microcolonies. Following probiotic profiling and safety assessment, the inter- and intra-specific interactions in in dual strain bifidobacterial biofilms were studied. As a species, only strains of B. bifidum exhibited exclusively inductive type of interactions whereas in other species, the interactions were more varied. On the other hand, in dual species biofilms, a preponderance of inductive interactions was evident between B. adolescentis, B. thermophilum, B. bifidum, and B. longum. The strong biofilm-formers also diminished pathogenic biofilm viability, and some were proficient in cholesterol removal in vitro. None of the strains exhibited harmful enzymatic activities associated with disease pathology. Interaction between biofilm-forming bifidobacterial strains provides an understanding of their functionality and persistence in the human host, and food or medicine. Their anti-pathogenic activity represents a therapeutic strategy against drug-resistant pathogenic biofilms.

Mechanisms linking bariatric surgery to adipose tissue, glucose metabolism, fatty liver disease and gut microbiota

PURPOSE

In the last 20 years, bariatric surgery has achieved an important role in translational and clinical research because of obesity comorbidities. Initially, a tool to lose weight, bariatric surgery now has been shown to be involved in several metabolic pathways.

METHODS

We conducted a narrative review discussing the underlying mechanisms that could explain the impact of bariatric surgery and the relationship between obesity and adipose tissue, T2D, gut microbiota, and NAFLD.

RESULTS

Bariatric surgery has an impact in the relation between obesity and type 2 diabetes, but in addition  it induces the white-to-brown adipocyte trans-differentiation, by enhancing thermogenesis. Another issue is the connection of bariatric surgery with the gut microbiota and its role in the complex mechanism underlying weight gain.

CONCLUSION

Bariatric surgery modifies gut microbiota, and these modifications influence lipid metabolism, leading to improvement of non-alcoholic fatty liver disease.

Butyrate's role in human health and the current progress towards its clinical application to treat gastrointestinal disease

Butyrate is a key energy source for colonocytes and is produced by the gut microbiota through fermentation of dietary fiber. Butyrate is a histone deacetylase inhibitor and also signals through three G-protein coupled receptors. It is clear that butyrate has an important role in gastrointestinal health and that butyrate levels can impact both host and microbial functions that are intimately coupled with each other. Maintaining optimal butyrate levels improves gastrointestinal health in animal models by supporting colonocyte function, decreasing inflammation, maintaining the gut barrier, and promoting a healthy microbiome. Butyrate has also shown protective actions in the context of intestinal diseases such as inflammatory bowel disease, graft-versus-host disease of the gastrointestinal tract, and colon cancer, whereas lower levels of butyrate and/or the microbes which are responsible for producing this metabolite are associated with disease and poorer health outcomes. However, clinical efforts to increase butyrate levels in humans and reverse these negative outcomes have generated mixed results. This article discusses our current understanding of the molecular mechanisms of butyrate action with a focus on the gastrointestinal system, the links between host and microbial factors, and the efforts that are currently underway to apply the knowledge gained from the bench to bedside.

Interventions for non-alcoholic liver disease: a gut microbial metabolites perspective

Over the past two decades, non-alcoholic fatty liver disease (NAFLD) has become a leading burden of hepatocellular carcinoma and liver transplantation. Although the exact pathogenesis of NAFLD has not been fully elucidated, recent hypotheses placed more emphasis on the crucial role of the gut microbiome and its derivatives. Reportedly, microbial metabolites such as short-chain fatty acids, amino acid metabolites (indole and its derivatives), bile acids (BAs), trimethylamine N-oxide (TMAO), and endogenous ethanol exhibit sophisticated bioactive properties. These molecules regulate host lipid, glucose, and BAs metabolic homeostasis via modulating nutrient absorption, energy expenditure, inflammation, and the neuroendocrine axis. Consequently, a broad range of research has studied the therapeutic effects of microbiota-derived metabolites. In this review, we explore the interaction of microbial products and NAFLD. We also discuss the regulatory role of existing NAFLD therapies on metabolite levels and investigate the potential of targeting those metabolites to relieve NAFLD.

Prebiotic Effects of Chinese Herbal Polysaccharides on NAFLD Amelioration: The Preclinical Progress

Nonalcoholic fatty liver disease (NAFLD) is caused by fatty degeneration of liver cells, and there are currently no effective treatments. Numerous investigations have demonstrated that Chinese herbal medicines (CHMs) are effective against NAFLD. Polysaccharides (PS), the major components of most CHM, are primarily taken orally to be degraded and fermented by gut microbiota, which makes them a promising multivalent and multifunctional prebiotic candidate for NAFLD. In this review, the experimental evidence to prevent and treat NAFLD using the unique prebiotic effects of PS isolated from CHM are summarized to discuss additional treatment options for NAFLD.

Gut microbiome and microbial metabolites in NAFLD and after bariatric surgery: Correlation and causality

Non-alcoholic fatty liver disease (NAFLD) is currently related to a heavy socioeconomic burden and increased incidence. Since obesity is the most prevalent risk factor for NAFLD, weight loss is an effective therapeutic solution. Bariatric surgery (BS), which can achieve long-term weight loss, improves the overall health of patients with NAFLD. The two most common surgeries are the Roux-en-Y gastric bypass and sleeve gastrectomy. The gut-liver axis is the complex network of cross-talking between the gut, its microbiome, and the liver. The gut microbiome, involved in the homeostasis of the gut-liver axis, is believed to play a significant role in the pathogenesis of NAFLD and the metabolic improvement after BS. Alterations in the gut microbiome in NAFLD have been confirmed compared to that in healthy individuals. The mechanisms linking the gut microbiome to NAFLD have been proposed, including increased intestinal permeability, higher energy intake, and other pathophysiological alterations. Interestingly, several correlation studies suggested that the gut microbial signatures after BS become more similar to those of lean, healthy controls than that of patients with NAFLD. The resolution of NAFLD after BS is related to changes in the gut microbiome and its metabolites. However, confirming a causal link remains challenging. This review summarizes characteristics of the gut microbiome in patients with NAFLD before and after BS and accumulates existing evidence about the underlying mechanisms of the gut microbiome.

Genetics in Familial Intrahepatic Cholestasis: Clinical Patterns and Development of Liver and Biliary Cancers: A Review of the Literature

The family of inherited intrahepatic cholestasis includes autosomal recessive cholestatic rare diseases of childhood involved in bile acids secretion or bile transport defects. Specific genetic pathways potentially cause many otherwise unexplained cholestasis or hepatobiliary tumours in a healthy liver. Lately, next-generation sequencing and whole-exome sequencing have improved the diagnostic procedures of familial intrahepatic cholestasis (FIC), as well as the discovery of several genes responsible for FIC. Moreover, mutations in these genes, even in the heterozygous status, may be responsible for cryptogenic cholestasis in both young and adults. Mutations in FIC genes can influence serum and hepatic levels of bile acids. Experimental studies on the NR1H4 gene have shown that high bile acids concentrations cause excessive production of inflammatory cytokines, resistance to apoptosis, and increased cell regeneration, all risk conditions for developing hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). NR1H4 gene encodes farnesoid X-activated receptor having a pivotal role in bile salts synthesis. Moreover, HCC and CCA can emerge in patients with several FIC genes such as ABCB11, ABCB4 and TJP2. Herein, we reviewed the available data on FIC-related hepatobiliary cancers, reporting on genetics to the pathophysiology, the risk factors and the clinical presentation.

Bacillus amyloliquefaciens SC06 alleviates the obesity of ob/ob mice and improves their intestinal microbiota and bile acid metabolism

Dietary interventions with probiotics have been widely reported to be effective in regulating obesity, and the intestinal microbiota is considered to be an important environmental factor. However, few reports focus on the interactions of microbiota-metabolites-phenotypic variables in ob/ob mice, and they have not been characterized in great detail. In this study, we investigated the effects of Bacillus amyloliquefaciens SC06 on obesity, the intestinal microbiota and the bile acid metabolism of ob/ob mice using biochemical testing, histochemical staining, high-throughput sequencing of the 16S rRNA gene, LC-MS/MS analysis and qRT-PCR. The results showed that SC06 ameliorated the fat mass percentage, hepatic steatosis and liver lipid metabolism disorders and reshaped the gut microbiota and metabolites in male ob/ob mice, specifically deceasing f_S24-7, p_TM7, s_Alistipes massiliensis, f_Rikenellaceae, f_Prevotellaceae, f_Lactobacillaceae, g_Alistipes, g_Flexispira, g_Lactobacillus, g_Odoribacter, g_AF12 and g_Prevotella and increasing f_Bacteroidaceae, g_Bacteroides and f_Desulfovibrionaceae. Meanwhile, SC06 treatment groups had lower ibuprofen and higher glycodeoxycholic acid and 7-dehydrocholesterol. Correlation analysis further clarified the relationships between compositional changes in the microbiota and alterations in the metabolites and phenotypes of ob/ob mice. Moreover, SC06 downregulated bile acid synthesis, export and re-absorption in the liver and increased ileum re-absorption into the blood in ob/ob mice, which may be mediated by the FXR-SHP/FGF15 signaling pathway. These results suggest that Bacillus amyloliquefaciens SC06 can ameliorate obesity in male ob/ob mice by reshaping the intestinal microbial composition, changing metabolites and regulating bile acid metabolism via the FXR signaling pathway.

Beyond lipids: Novel mechanisms for parenteral nutrition-associated liver disease

Parenteral nutrition (PN) is a therapy that delivers essential nutrients intravenously to patients who are unable to meet their nutrition requirements via standard enteral feeding. This methodology is often referred to as PN when accompanied by minimal or no enteral nutrition (EN). Although PN is lifesaving, significant complications can arise, such as intestinal failure-associated liver disease and gut-mucosal atrophy. The exact mechanism of injury remains ill defined. This review was designed to explore the available literature related to the drivers of injury mechanisms. The Farnesoid X receptor and fibroblast growth factor 19 signaling pathway seems to play an important role in gut-systemic signaling, and its alteration during PN provides insights into mechanistic links. Central line infections also play a key role in mediating PN-associated injury. Although lipid reduction strategies, as well as the use of multicomponent lipid emulsions and vitamin E, have shown promise, the cornerstone of preventing injury is the early establishment of EN.

The Role of Gut Microbiota-Bile Acids Axis in the Progression of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD), an emerging global health problem affecting 25-30% of the total population, refers to excessive lipid accumulation in the liver accompanied by insulin resistance (IR) without significant alcohol intake. The increasing prevalence of NAFLD will lead to an increasing number of cirrhosis patients, as well as hepatocellular carcinoma (HCC) requiring liver transplantation, while the current treatments for NAFLD and its advanced diseases are suboptimal. Accordingly, it is necessary to find signaling pathways and targets related to the pathogenesis of NAFLD for the development of novel drugs. A large number of studies and reviews have described the critical roles of bile acids (BAs) and their receptors in the pathogenesis of NAFLD. The gut microbiota (GM), whose composition varies between healthy and NAFLD patients, promotes the transformation of more than 50 secondary bile acids and is involved in the pathophysiology of NAFLD through the GM-BAs axis. Correspondingly, BAs inhibit the overgrowth of GM and maintain a healthy gut through their antibacterial effects. Here we review the biosynthesis, enterohepatic circulation, and major receptors of BAs, as well as the relationship of GM, BAs, and the pathogenesis of NAFLD in different disease progression. This article also reviews several therapeutic approaches for the management and prevention of NAFLD targeting the GM-BAs axis.

The Role of Gut Microbiota on Cholesterol Metabolism in Atherosclerosis

Hypercholesterolemia plays a causal role in the development of atherosclerosis and is one of the main risk factors for cardiovascular disease (CVD), the leading cause of death worldwide especially in developed countries. Current data show that the role of microbiota extends beyond digestion by being implicated in several metabolic and inflammatory processes linked to several diseases including CVD. Studies have reported associations between bacterial metabolites and hypercholesterolemia. However, such associations remain poorly investigated and characterized. In this review, the mechanisms of microbial derived metabolites such as primary and secondary bile acids (BAs), trimethylamine N-oxide (TMAO), and short-chain fatty acids (SCFAs) will be explored in the context of cholesterol metabolism. These metabolites play critical roles in maintaining cardiovascular health and if dysregulated can potentially contribute to CVD. They can be modulated via nutritional and pharmacological interventions such as statins, prebiotics, and probiotics. However, the mechanisms behind these interactions also remain unclear, and mechanistic insights into their impact will be provided. Therefore, the objectives of this paper are to present current knowledge on potential mechanisms whereby microbial metabolites regulate cholesterol homeostasis and to discuss the feasibility of modulating intestinal microbes and metabolites as a novel therapeutic for hypercholesterolemia.

Perinatal High-Salt Diet Induces Gut Microbiota Dysbiosis, Bile Acid Homeostasis Disbalance, and NAFLD in Weanling Mice Offspring

A perinatal high-salt (HS) diet was reported to elevate plasma triglycerides. This study aimed to investigate the hypothesis that a perinatal HS diet predisposed offspring to non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of abnormal lipid metabolism, and the possible mechanism. Female C57BL/6 mice were fed a control diet (0.5% NaCl) or HS diet (4% NaCl) during pregnancy and lactation and their offspring were sacrificed at weaning. The perinatal HS diet induced greater variation in fecal microbial beta-diversity (β-diversity) and increased bacteria abundance of Proteobacteria and Bacteroides. The gut microbiota dysbiosis promoted bile acid homeostasis disbalance, characterized by the accumulation of lithocholic acid (LCA) and deoxycholic acid (DCA) in feces. These alterations disturbed gut barrier by increasing the expression of tight junction protein (Tjp) and occludin (Ocln), and increased systemic lipopolysaccharide (LPS) levels and hepatic inflammatory cytokine secretion (TNF-α and IL-6) in the liver. The perinatal HS diet also inhibited hepatic expression of hepatic FXR signaling (CYP7A1 and FXR), thus triggering increased hepatic expression of pro-inflammatory cytokines (TNF-α and IL-6) and hepatic lipid metabolism-associated genes (SREBP-1c, FAS, ACC), leading to unique characteristics of NAFLD. In conclusion, a perinatal HS diet induced NAFLD in weanling mice offspring; the possible mechanism was related to increased bacteria abundance of Proteobacteria and Bacteroides, increased levels of LCA and DCA in feces, and increased expressions of hepatic FXR signaling.

Lactobacillus casei YRL577 combined with plant extracts reduce markers of non-alcoholic fatty liver disease in mice

Probiotics and plant extracts are considered to prevent the development of non-alcoholic fatty liver disease (NAFLD). The present study explores the effects of using both probiotics and plant extracts on NAFLD. The present study evaluated the effects of plant extracts on lipid droplet accumulation and the growth of probiotics in vitro. A C57BL/6 mouse model was used to examine the effects of probiotics and plant extracts on NAFLD. Body weight and food intake were measured. The levels of serum lipids, oxidative stress and the liver injury index were determined using commercial kits. Haematoxylin and eosin staining, GC and real-time PCR were also used for analysis. The results revealed that administration of Lactobacillus casei YRL577 and L. paracasei X11 with resveratrol (RES) or tea polyphenols (TP) significantly reduced the levels of total cholesterol, TAG and LDL-cholesterol and increased the level of the HDL-cholesterol. The groups of L. casei YRL577 with RES and TP also regulated the liver structure, oxidative stress and injury. Furthermore, L. casei YRL577 with TP exhibited a more positive effect towards improving the NAFLD and increased the concentrations of the butyric acid than other three combined groups. L. casei YRL577 with TP up-regulated the mRNA levels of the farnesoid X receptor and fibroblast growth factor 15 and decreased the mRNA levels of the apical Na-dependent bile acid transporter. These findings showed that L. casei YRL577 + TP-modified genes in the intestinal bile acid pathway improved markers of NAFLD.

Characteristics of the intestinal flora in patients with peripheral neuropathy associated with type 2 diabetes

OBJECTIVE

To study the characteristics of the intestinal flora in patients with diabetic peripheral neuropathy (DPN) and analyze the association between the intestinal flora and clinical indicators.

METHODS

We classified 80 subjects into three groups: patients with DPN (n = 45), patients type 2 diabetes without DPN (n = 21), and healthy controls (n = 14). The intestinal flora composition was compared among the three groups, and the correlation between the intestinal flora and clinical indicators was analyzed.

RESULTS

At the phylum level, the richness of Firmicutes and Actinobacteria was elevated in the DN group, and that of Bacteroidetes was decreased. At the genus level, the richness of Bacteroides and Faecalibacterium was significantly decreased in the DPN group, whereas that of Escherichia-Shigella, Lachnoclostridium, Blautia, Megasphaera, and Ruminococcus torques group was increased. The homeostasis model assessment insulin resistance index was positively correlated with Megasphaera richness. Glycine ursodeoxycholic acid was positively correlated with Ruminococcus gnavus group and Phascolarctobacterium richness. Tauroursodeoxycholic acid was positively correlated with Ruminococcus gnavus group and Parabacteroides richness.

CONCLUSION

There was obvious intestinal microbiota disorder in patients with DPN, which may be related to insulin resistance. These changes may have important roles in the development of DPN.

The gut microbiome-bile acid axis in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and is a leading cause of cancer-related deaths globally, with few effective therapeutic options. Bile acids (BAs) are synthesized from cholesterol in the liver and can be modulated by farnesoid X receptor (FXR) and G-protein coupled BA receptor 1 (GPBAR1/TGR5). Alterations in BAs can affect hepatic metabolic homeostasis and contribute to the pathogenesis of liver cancer. Increasing evidence points to the key role of bacterial microbiota in the promotion and development of liver cancer. They are also involved in the regulation of BA synthesis and metabolism. The purpose of this review is to integrate related articles involving gut microbiota, BAs and HCC, and review how the gut microbiota-BA signaling axis can possibly influence the development of HCC.

Is bariatric surgery resolving NAFLD via microbiota-mediated bile acid ratio reversal? A comprehensive review

Despite the fact that there is still insufficient evidence to consider non-alcoholic fatty liver disease (NAFLD) as an stand-alone indication for bariatric surgery, many clinical and histopathological beneficial effects on both NAFLD and non-alcoholic steatohepatitis (NASH) have been shown. Although weight loss seems to be the obvious mechanism, weight-loss independent factors are also believed to be involved. Among them, changes in gut microbiota and bile acids (BA) composition may be playing an unappreciated role in the improvement of NAFLD. In this review we examine the mechanisms and interdependence of the gut microbiota and BA, and their influence on NAFLD pathogenesis and its reversal following bariatric surgery. According to the currently available evidence, gut microbiota has a major influence on BA composition. In fact, both BA and microbiome disturbances (dysbiosis) play a role in the etiopathogenesis of NAFLD and might be potential therapeutic targets. In addition, bariatric surgery can modify the intraluminal ileal environment in a way that causes significant repopulation of the gut microbiota and a reversal of the plasma primary/secondary BA ratio, which, in turn, induces weigh-independent metabolic improvements.

Mechanisms of Parenteral Nutrition-Associated Liver and Gut Injury

Parenteral nutrition (PN) has revolutionized the care of patients with intestinal failure by providing nutrition intravenously. Worldwide, PN remains a standard tool of nutrition delivery in neonatal, pediatric, and adult patients. Though the benefits are evident, patients receiving PN can suffer serious cholestasis due to lack of enteral feeding and sometimes have fatal complications from liver injury and gut atrophy, including PN-associated liver disease or intestinal failure-associated liver disease. Recent studies into gut-systemic cross talk via the bile acid-regulated farnesoid X receptor (FXR)-fibroblast growth factor 19 (FGF19) axis, gut microbial control of the TGR5-glucagon-like peptide (GLP) axis, sepsis, and role of prematurity of hepatobiliary receptors are greatly broadening our understanding of PN-associated injury. It has also been shown that the composition of ω-6/ω-3 polyunsaturated fatty acids given parenterally as lipid emulsions can variably drive damage to hepatocytes and cell integrity. This manuscript reviews the mechanisms for the multifactorial pathogenesis of liver disease and gut injury with PN and discusses novel ameliorative strategies.

Role and effective therapeutic target of gut microbiota in NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD), the most prevalent chronic liver disease in the world, is affected by numerous extrinsic and intrinsic factors, including lifestyle, environment, diet, genetic susceptibility, metabolic syndrome and gut microbiota. Accumulating evidence has proven that gut dysbiosis is significantly associated with the development and progression of NAFLD, and several highly variable species in gut microbiota have been identified. The gut microbiota contributes to NAFLD by abnormal regulation of the liver-gut axis, gut microbial components and microbial metabolites, and affects the secretion of bile acids. Due to the key role of the gut microbiota in NAFLD, it has been regarded as a potential target for the pharmacological and clinical treatment of NAFLD. The present review provides a systematic summary of the characterization of gut microbiota and the significant association between the gut microbiota and NAFLD. The possible mechanisms of how the gut microbiota is involved in promoting the development and progression of NAFLD were also discussed. In addition, the potential therapeutic methods for NAFLD based on the gut microbiota were summarized.

Diet Control More Intensively Disturbs Gut Microbiota Than Genetic Background in Wild Type and ob/ob Mice

Changes in environmental and genetic factors are vital to development of obesity and its complications. Induction of obesity and type 2 diabetes by both leptin deficiency (ob/ob) and high fat diet (HFD) has been verified in animal models. In the present experiment, three types of diets (normal diet; ND, HFD and high sucrose diet; HSD) and two types of genetic mice (Wild type: WT and ob/ob) were used to explore the relationship among diet supplements, gut microbiota, host genetics and metabolic status. HFD increased the body, fat and liver weight of both ob/ob and WT mice, but HSD did not. HFD also resulted in dyslipidemia, as well as increased serum transaminases and fasting glucose in ob/ob mice but not in WT mice, while HSD did not. Moreover, HFD led to brain BDNF elevation in WT mice and reduction in ob/ob mice, whereas HSD did not. Both HFD and HSD had a greater influence on gut microbiota than host genotypes. In detail, both of HFD and HSD alteration elucidated the majority (≥63%) of the whole structural variation in gut microbiota, however, host genetic mutation accounted for the minority (≤11%). Overall, diets more intensively disturbed the structure of gut microbiota in excess of genetic change, particularly under leptin deficient conditions. Different responses of host genotypes may contribute to the development of metabolic disorder phenotypes linked with gut microbiota alterations.

The role of gut microbiota in non-alcoholic fatty liver disease: pathways of mechanisms

Nonalcoholic fatty liver disease (NAFLD) is a hepatic manifestation of metabolic syndrome. Its prevalence increases with increasing rates of obesity, insulin resistance, and diabetes mellitus. The pathogenesis of NAFLD involves many factors, including the gastrointestinal microbiota. However, there is still debate about the impact of gut dysbiosis in the NAFLD disease progression. Therefore, this paper aims to review the relationship between gut microbiota and other risk factors for NAFLD and how gut dysbiosis plays a role in the pathogenesis of NAFLD. Hopefully, this paper can make an appropriate contribution to the development of NAFLD research in the future.

Progress in understanding relationship between bile acid metabolic disorder and gut diseases

There are a large number of microorganisms in the human intestine, which rely on the nutrition in the digestive tract to survive. At the same time, they affect the intestinal neuro-immune function through the metabolism substances produced by themselves. The enteric neuro-immune system regulates the functions of digestion and absorption so as to maintain the homeostasis in the intestine. Intestinal bile acid metabolism disorder might induce gut dysfunction or intestinal immune imbalance. This review describes the effect of intestinal microbes on the enteric nervous system or other signal molecules of the bile acid pathway linked to some intestinal disorders, with an aim to provide a theoretical basis for clinical treatment of the related diseases.

Gut Microbiota Composition and Structure of the Ob/Ob and Db/Db Mice

INTRODUCTION

Gut microbiota is involved in the progression of metabolic diseases such as obesity and type 2 diabetes. The ob/ob and db/db mice are extensively used as models in studies on the pathogenesis of these diseases. The goal of this study is to characterize the composition and structure of gut microbiota in these model mice at different ages.

MATERIALS AND METHODS

High-throughput sequencing was used to obtain the sequences of the highly variable 16S rRNA V3-V4 region from fecal samples. The taxa with high abundance in both model mice were identified by bioinformatics analysis. Moreover, the taxa with divergent abundance in one model mice at different ages or in both model mice at the same age were also recognized.

DISCUSSION AND CONCLUSION

The high abundance of Bacteroidetes and Firmicutes in microbiota composition and their imbalanced ratio in both model mice reflect the state of metabolic disorders of these mice. Differences in microbiota composition between the two model mice of the same age or in one model mice with different ages were assumed to be closely linked to the fluctuation of their blood glucose levels with age. The data on gut microbiota in ob/ob and db/db mice investigated herein has broad implications for the pathogenesis study and drug discovery on obesity and related complications.

Microbiota, Obesity and NAFLD

Non-alcoholic fatty liver disease (NAFLD) is an increasingly important cause of chronic liver disease globally. Similar to metabolic syndrome and obesity, NAFLD is associated with alternations in the gut microbiota and its related biological pathways. While the exact pathophysiology of NAFLD remains largely unknown, changes in intestinal inflammation, gut permeability, energy harvest, anaerobic fermentation and insulin resistance have been described. In this chapter, we review the relationship between the gut microbiota, obesity and NAFLD, and highlight potential ways to modify the gut microbiota to help managing NAFLD patients.

Diabetes-associated alterations in the cecal microbiome and metabolome are independent of diet or environment in the UC Davis Type 2 Diabetes Mellitus Rat model

The composition of the gut microbiome is altered in obesity and type 2 diabetes; however, it is not known whether these alterations are mediated by dietary factors or related to declines in metabolic health. To address this, cecal contents were collected from age-matched, chow-fed male University of California, Davis Type 2 Diabetes Mellitus (UCD-T2DM) rats before the onset of diabetes (prediabetic PD; n = 15), 2 wk recently diabetic (RD; n = 10), 3 mo (D3M; n = 11), and 6 mo (D6M; n = 8) postonset of diabetes. Bacterial species and functional gene counts were assessed by shotgun metagenomic sequencing of bacterial DNA in cecal contents, while metabolites were identified by gas chromatography-quadrupole time-off-flight-mass spectrometry. Metagenomic analysis showed a shift from Firmicutes species in early stages of diabetes (PD + RD) toward an enrichment of Bacteroidetes species in later stages of diabetes (D3M + D6M). In total, 45 bacterial species discriminated early and late stages of diabetes with 25 of these belonging to either Bacteroides or Prevotella genera. Furthermore, 61 bacterial gene clusters discriminated early and later stages of diabetes with elevations of enzymes related to stress response (e.g., glutathione and glutaredoxin) and amino acid, carbohydrate, and bacterial cell wall metabolism. Twenty-five cecal metabolites discriminated early vs. late stages of diabetes, with the largest differences observed in abundances of dehydroabietic acid and phosphate. Alterations in the gut microbiota and cecal metabolome track diabetes progression in UCD-T2DM rats when controlling for diet, age, and housing environment. Results suggest that diabetes-specific host signals impact the ecology and end product metabolites of the gut microbiome when diet is held constant.

Gut adaptation after metabolic surgery and its influences on the brain, liver and cancer

Metabolic surgery is the best treatment for long-term weight loss maintenance and comorbidity control. Metabolic operations were originally intended to change anatomy to alter behaviour, but we now understand that the anatomical changes can modulate physiology to change behaviour. They are no longer considered only mechanically restrictive and/or malabsorptive procedures; rather, they are considered metabolic procedures involving complex physiological changes, whereby gut adaptation influences signalling pathways in several other organs, including the liver and the brain, regulating hunger, satiation, satiety, body weight, glucose metabolism and immune functions. The integrative physiology of gut adaptation after these operations consists of a complex mechanistic web of communication between gut hormones, bile acids, gut microbiota, the brain and both enteric and central nervous systems. The understanding of nutrient sensing via enteroendocrine cells, the enteric nervous system, hypothalamic peptides and adipose tissue and of the role of inflammation has advanced our knowledge of this integrative physiology. In this Review, we focus on the adaptation of gut physiology to the anatomical alterations from Roux-en-Y gastric bypass and vertical sleeve gastrectomy and the influence of these procedures on food intake, weight loss, nonalcoholic fatty liver disease (NAFLD) and cancer. We also aim to demonstrate the underlying mechanisms that could explain how metabolic surgery could be used as a therapeutic option in NAFLD and certain obesity-related cancers.

Specific properties of probiotic strains: relevance and benefits for the host

BACKGROUND

Probiotics have tremendous potential to develop healthy diets, treatment, and prevention. Investigation of in vitro cultural properties of health-promoting microorganisms like lactic acid bacteria (LAB) and bifidobacteria is crucial to select probiotic strains for treatments based on gut microbiota modulation to justify individualized and personalized approach for nutrition and prevention of variety of diseases. The aim was to study the biological properties of LAB and bifidobacteria probiotic strains, namely adhesive properties; resistance to antibiotics; and biological fluids (gastric juice, bile, pancreatic enzymes), and to overview the literature in the field.

MATERIALS AND METHODS

We studied six LAB strains (Lactobacillus acidophilus ІМV В-7279, L. casei ІМV В-7280, L. delbrueckii subsp. bulgaricus ІМV В-7281, L. rhamnosus LB-3 VK6, L. delbrueckii LE VK8, L. plantarum LM VK7), and two bifidobacteria strains (Bifidobacterium animalis VKL, B. animalis VKB). We characterized tinctorial, culturally morphological, physiological, and biochemical properties of probiotic strains of LAB and bifidobacteria by commonly used research methods. Determination of the resistance to antibiotics was carried out using disc-diffusion method. The effects of gastric juice, bile, and pancreatin on the viability of LAB and bifidobacteria were evaluated. Adhesive properties of LAB and bifidobacteria to epithelial cells were assessed calculating three indicators: average adhesion rate (AAR), participation rate of epithelial cells (PRE), and adhesiveness index of microorganisms (AIM). Electron microscopy of LAB and bifidobacteria cells was conducted.

RESULTS

The studied strains of LAB and bifidobacteria did not form spores, were positively stained by Gram, grow on medium in a wide range of pH (1.0-9.0, optimum pH 5.5-6.5), were sensitive to a wide range of antibiotics; and showed different resistance to gastric juice, bile, and pancreatic enzymes. The most resistant to antibiotics were L. rhamnosus LB-3 VK6 and L. delbrueckii LE VK8 strains. The most susceptible to gastric juice was L. plantarum LM VK7, which stopped its growth at 8% of gastric juice; L. acidophilus IMV B-7279, B. animalis VKL, and B. animalis VKB strains were resistant even in the 100% concentration. Strains L. acidophilus IMV В-7279, L. casei IMV В-7280, B. animalis VKL, B. animalis VKB, L. rhamnosus LB-3 VK6, L. delbrueckii LE VK8, and L. delbrueckii subsp. bulgaricus IMV В-7281 were resistant to pancreatic enzymes. Adhesive properties of the strains according to AIM index were high in L. casei IMV В-7280, B. animalis VKL, and B. animalis VKB; were moderate in L. delbrueckii subsp. bulgaricus IMV В-7281; and were low in L. acidophilus IMV В-7279, L. rhamnosus LB-3 VK6, L. delbrueckii LE VK8, and L. plantarum LM VK7.

CONCLUSION

We recognized strain-dependent properties of studied LAB and bifidobacteria probiotic strains (adhesive ability, resistance to antibiotics, and gut biological fluids) and discussed potential for most effective individualized treatment for gut and distant sites microbiome modulation.

Gut Microbiota Dysbiosis Drives and Implies Novel Therapeutic Strategies for Diabetes Mellitus and Related Metabolic Diseases

Accumulating evidence over the past decade has linked the development of metabolic syndrome related to diabetes to variations in gut microbiota, an emerging, critical homeostatic regulator of host energy metabolism and immune responses. Mechanistic studies in rodent models have revealed an ever-increasing multitude of molecular mechanisms whereby the gut microbiota interacts with various host sensing and signaling pathways, leading to modulation of endocrine system, immune responses, nervous system activity, and hence, the predisposition to metabolic diseases. Remarkably, the microbiota-driven immune responses in metabolic tissues and the host nutrient-sensing mechanisms of gut microbial metabolites, in particular short-chain fatty acids, have been significantly associated with the proneness to diabetes and related disorders. This review will synthesize the recent efforts on unraveling the mediating role of gut microbiota in the pathogenesis of metabolic diseases, aiming to reveal new therapeutic opportunities.

Importance of microbial defence systems to bile salts and mechanisms of serum cholesterol reduction

An important feature of the intestinal microbiota, particularly in the case of administered probiotic microorganisms, is their resistance to conditions in the gastrointestinal tract, particularly tolerance to and growth in the presence of bile salts. Bacteria can use several defence mechanisms against bile, including special transport mechanisms, the synthesis of various types of surface proteins and fatty acids or the production of exopolysaccharides. The ability to enzymatically hydrolyse bile salts occurs in a variety of bacteria. Choloylglycine hydrolase (EC 3.5.1.24), a bile salt hydrolase, is a constitutive intracellular enzyme responsible for the hydrolysis of an amide bond between glycine or taurine and the steroid nucleus of bile acids. Its presence was demonstrated in specific microorganisms from several bacterial genera (Lactobacillus spp., Bifidobacterium spp., Clostridium spp., Bacteroides spp.). Occurrence and gene arrangement encoding this enzyme are highly variable in probiotic microorganisms. Bile salt hydrolase activity may provide the possibility to use the released amino acids by bacteria as sources of carbon and nitrogen, to facilitate detoxification of bile or to support the incorporation of cholesterol into the cell wall. Deconjugation of bile salts may be directly related to a lowering of serum cholesterol levels, from which conjugated bile salts are synthesized de novo. Furthermore, the ability of microorganisms to assimilate or to bind ingested cholesterol to the cell wall or to eliminate it by co-precipitation with released cholic acid was also documented. Some intestinal microflora produce cholesterol reductase that catalyses the conversion of cholesterol to insoluble coprostanol, which is subsequently excreted in faeces, thereby also reducing the amount of exogenous cholesterol.

Overactivation of intestinal sterol response element-binding protein 2 promotes diet-induced nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is characterized by lipid accumulation in the liver that may progress to hepatic fibrosis and nonalcoholic steatohepatitis (NASH). Mechanisms underlying NAFLD and NASH are not yet fully understood. Dietary cholesterol was recently shown to be a risk factor for the development of NASH, suggesting a role for intestinal handling of cholesterol. One important regulator of cholesterol homeostasis is the sterol response element-binding protein-2 (SREBP-2) transcription factor. We tested the hypothesis that the overactivation of intestinal SREBP-2 increases the susceptibility to diet-induced NASH. A transgenic mouse model with intestine-specific overexpression of active SREBP-2 (ISR2 mice) driven by villin promoter was used. ISR2 mice and their wild-type littermates were fed a regular chow diet or a high-fat, high-cholesterol (HFHC) diet (15% fat, 1% cholesterol) for 15 wk. Results showed that HFHC feeding to ISR2 mice caused hepatic inflammation with increased levels of proinflammatory cytokines. Histological examination demonstrated extensive fibrosis after a HFHC diet associated with a perivascular as well as pericellular collagen deposits in ISR2 mice compared with wild-type littermates. The severe hepatic inflammation and advanced fibrosis in ISR2 mice was not associated with a difference in lipid accumulation in ISR2 mice compared with wild type littermates after HFHC feeding. These data indicate that overactivation of intestinal SREBP2 promotes diet-induced hepatic inflammation with features of human NASH resulting in rapid severe fibrosis and provide a novel link between regulatory processes of intestinal cholesterol and progression of fatty liver.NEW & NOTEWORTHY The current study highlights the role of overactivation of intestinal SREBP-2 transcription factor in the progression of hepatic fibrosis associated with diet-induced NASH. Mice with intestine-specific overexpression of SREBP-2 demonstrated more inflammation and severe fibrosis in the liver in response to 15 wk of being fed a high-cholesterol, high-fat diet as compared with their wild-type littermates. These data demonstrate a novel link between intestinal regulatory processes of cholesterol metabolism and the pathogenesis of fatty liver diseases.

Non-alcoholic fatty liver disease: An update with special focus on the role of gut microbiota

Non-alcoholic fatty liver disease (NAFLD) is a significant global health burden in children, adolescents and adults with substantial rise in prevalence over the last decades. Accumulating data from manifold studies support the idea of NAFLD as a hepatic manifestation of metabolic syndrome, being rather a systemic metabolic disease than a liver confined pathology. Emerging data support that the gut microbiome represents a significant environmental factor contributing to NAFLD development and progression. Apart from other regimens, probiotics may have a positive role in the management of NAFLD through a plethora of possible mechanisms. The current review focuses on the NAFLD multifactorial pathogenesis, including mainly the role of intestinal microbiome and all relevant issues are raised. Furthermore, the clinical manifestations and appropriate diagnostic approach of the disease are discussed, with all possible therapeutic measures that can be taken, also including the potential beneficial effect of probiotics.

Role of dietary onion in modifying the faecal bile acid content in rats fed a high-cholesterol diet

The determination of faecal bile patterns offers new opportunities in the search for non-invasive biomarkers of disease status. The objective of this study was to describe the shifts in faecal bile acid (BA) composition induced by feeding a high-cholesterol/cholic acid diet (HC) over 7 weeks of experimental feeding in Wistar rats, and to evaluate the effect of onion included as a functional ingredient (HCO). A HPLC-MS/MS method allowed the detection of 29 bile acids, 10 of which were tentatively identified and 12 confirmed and quantified by means of standards and calibration curves. The excretion of bile acids revealed a discriminating bile acid profile between the HC and HCO groups compared with the C group. HCO feeding indicated significant changes in specific primary and secondary BA in both the unconjugated and conjugated forms caused by the addition of the onion ingredient to the diet. The results suggest that the induction of microbiome modifications by the HC and HCO diets acts as a critical modifier of the faecal bile acid composition. These modifications might reflect and be linked to changes in the reabsorption of BA at an intestinal level and the process of BA deconjugation in the course of hypercholesterolemia.

An Intestinal Microbiota-Farnesoid X Receptor Axis Modulates Metabolic Disease

The gut microbiota is associated with metabolic diseases including obesity, insulin resistance, and nonalcoholic fatty liver disease, as shown by correlative studies and by transplant of microbiota from obese humans and mice into germ-free mice. Modification of the microbiota by treatment of high-fat diet (HFD)-fed mice with tempol or antibiotics resulted in decreased adverse metabolic phenotypes. This was owing to lower levels of the genera Lactobacillus and decreased bile salt hydrolase (BSH) activity. The decreased BSH resulted in increased levels of tauro-β-muricholic acid (MCA), a substrate of BSH and a potent farnesoid X receptor (FXR) antagonist. Mice lacking expression of FXR in the intestine were resistant to HFD-induced obesity, insulin resistance, and nonalcoholic fatty liver disease, thus confirming that intestinal FXR is involved in the potentiation of metabolic disease. A potent intestinal FXR antagonist, glycine-β-MCA (Gly-MCA), which is resistant to BSH, was developed, which, when administered to HFD-treated mice, mimics the effect of the altered microbiota on HFD-induced metabolic disease. Gly-MCA had similar effects on genetically obese leptin-deficient mice. The decrease in adverse metabolic phenotype by tempol, antibiotics, and Gly-MCA was caused by decreased serum ceramides. Mice lacking FXR in the intestine also have lower serum ceramide levels, and are resistant to HFD-induced metabolic disease, and this was reversed by injection of C16:0 ceramide. In mouse ileum, because of the presence of endogenous FXR agonists produced in the liver, FXR target genes involved in ceramide synthesis are activated and when Gly-MCA is administered they are repressed, which likely accounts for the decrease in serum ceramides. These studies show that ceramides produced in the ileum under control of FXR influence metabolic diseases.

Understanding and modulating mammalian-microbial communication for improved human health

The molecular basis for the regulation of the intestinal barrier is a very fertile research area. A growing body of knowledge supports the targeting of various components of intestinal barrier function as means to treat a variety of diseases, including the inflammatory bowel diseases. Herein, we will summarize the current state of knowledge of key xenobiotic receptor regulators of barrier function, highlighting recent advances, such that the field and its future are succinctly reviewed. We posit that these receptors confer an additional dimension of host-microbe interaction in the gut, by sensing and responding to metabolites released from the symbiotic microbiota, in innate immunity and also in host drug metabolism. The scientific evidence for involvement of the receptors and its molecular basis for the control of barrier function and innate immunity regulation would serve as a rationale towards development of non-toxic probes and ligands as drugs.