Molecular Physiology of Bile Acid Signaling in Health, Disease, and Aging

Characterization of the mechanism of bile salt hydrolase substrate specificity by experimental and computational analyses

Bile salt hydrolases (BSHs) are currently being investigated as target enzymes for metabolic regulators in humans and as growth promoters in farm animals. Understanding structural features underlying substrate specificity is necessary for inhibitor design. Here, we used a multidisciplinary workflow including mass spectrometry, mutagenesis, molecular dynamic simulations, machine learning, and crystallography to demonstrate substrate specificity in Lactobacillus salivarius BSH, the most abundant enzyme in human and farm animal intestines. We show the preference of substrates with a taurine head and a dehydroxylated sterol ring for hydrolysis. A regression model that correlates the relative rates of hydrolysis of various substrates in various enzyme mutants with the residue-substrate interaction energies guided the identification of structural determinants of substrate binding and specificity. In addition, we found T208 from another BSH protomer regulating the hydrolysis. The designed workflow can be used for fast and comprehensive characterization of enzymes with a broad range of substrates.

Expression characteristics of Hsd3b7 in the gonads of Paralichthys olivaceus

Steroidogenesis is an important biological process for gonadal differentiation and development. In mammals, 3β-hydroxysteroid dehydrogenase 7 (HSD3B7) could convert 3β-hydroxy of 7α-hydroxycholesterol into a ketone and form 7α-hydroxy-4-cholesten-3-one, which may affect steroidogenesis. However, in fish, the study of Hsd3b7 is still lacking. In this study, Hsd3b7 was identified in the olive flounder Paralichthys olivaceus, an important mariculture fish. According to bioinformatics analysis, Hsd3b7 belongs to a Rossmann-fold NAD(P)(+)-binding protein and can interact in a predictable manner with Hsd17b2, -3, and - 4, which play a role in steroidogenesis. In the adult flounder, Hsd3b7 was expressed in various tissues, at particularly high level in male muscle. The expression levels of Hsd3b7 at gonadal development stages I-V initially increased and then decreased, with an inflection point in the ovary at stage III and in the testis at stage IV. At stage III, the expression level of Hsd3b7 was significantly higher in the ovary than in the testis (P < 0.01). The results of in situ hybridization (ISH) revealed that it was mainly expressed in oocytes of phases I-IV or around oocytes of phases IV-V in the ovaries and around spermatid lobules at stages IV-V in the testes. Three regulatory sites of SRY-box transcription factor 9 (Sox9), a transcription factor involved in steroidogenesis and gonadal differentiation, were predicted in the promoter of Hsd3b7. After intraperitoneal injection with the recombination flounder Sox9a, the expression of Hsd3b7 was significantly up-regulated (P < 0.01). During the flounder gonadal differentiation, 17β-estradiol (E2, 5 μg/g feed) and 17α-methyltestosterone (T, 5 μg/g feed) were used to obtain the phenotypic female or male flounder, and the results showed that in the E2 group, Hsd3b7 expression was highest at 2 cm TL, the primordial gonad stage, which was significantly higher than that at 12 cm TL (P < 0.05). In the T group, Hsd3b7 expression level was also highest at 2 cm TL and significantly higher than at 10 and 12 cm TL (P < 0.05). Moreover, Hsd3b7 was detected to be localized mainly around oogonia and spermatogonia during the differentiated gonads with ISH. These findings first introduce the expression characteristics of Hsd3b7 and the effect of Sox9a on its expression, which contribute to our understanding of the function of Hsd3b7 in fish gonads.

Combination of Lactobacillus plantarum improves the effects of tacrolimus on colitis in a mouse model

The gut microbiome has been considered to play an important role in inflammatory bowel disease (IBD). Our previous study reported that tacrolimus-altered gut microbiota elicited immunoregulatory effects in both colonic mucosa and circulation, contributing to an increased allograft survival rate in mice. Here, we aimed to observe the changes in the tacrolimus-induced microbiome in a dextran sulfate sodium (DSS)-induced colitis mouse model and explore the possibility and efficacy of combination therapy with tacrolimus and the microbiome on colitis. Mice were divided into the control, DSS, tacrolimus monotherapy and tacrolimus plus Lactobacillus plantarum 550 (Lacto)-treated groups. The body weight, stool consistency, hematochezia and survival of mice were observed daily. Total RNA from colonic mucosa was extracted and subjected to transcriptome sequencing. Cecal contents were collected and the 16S rRNA sequencing was performed to characterize the gut microbiome and the ultrahigh- performance liquid chromatography-MS/MS (UHPLC-MS/MS) was used for targeted quantification of bile acids. The results confirmed that tacrolimus significantly ameliorated DSS-induced colitis in mice. Beneficial alterations of the gut microbiome characterized by a remarkable expansion of the genus Lactobacillus were induced by tacrolimus treatment. Oral supplementation with Lacto further improved the tacrolimus-mediated suppression of body weight loss in colitis, while the survival time of mice was further prolonged and the inflammation of colonic mucosa was obviously relieved. The immune and inflammation-related signaling pathways, including IFN-γ and IFN-α response, allograft rejection, IL2 STAT5 signaling and the inflammatory response pathways, were further downregulated in the tacrolimus plus Lacto cotreatment group. Cotreatment also improved the diversity of the gut microbiome and rescued the concentration of taurochenodeoxycholic acid (TCDCA) in colitis. The latter was positively correlated with the abundance of Lactobacillus but negatively related to the disease activity index score. Overall, our results indicated that Lactobacillus plantarum promoted the therapeutic effect of tacrolimus in experimental colitis, offering a promising strategy to combine tacrolimus and Lactobacillus in the treatment of colitis patients.

Small Intestinal Bacterial Overgrowth and Non-Alcoholic Fatty Liver Disease: What Do We Know in 2023?

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease associated with the pathological accumulation of lipids inside hepatocytes. Untreated NAFL can progress to non-alcoholic hepatitis (NASH), followed by fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). The common denominator of the above-mentioned metabolic disorders seems to be insulin resistance, which occurs in NAFLD patients. Obesity is the greatest risk factor for lipid accumulation inside hepatocytes, but a part of the NAFLD patient population has a normal body weight according to the BMI index. Obese people with or without NAFLD have a higher incidence of small intestinal bacterial overgrowth (SIBO), and those suffering from NAFLD show increased intestinal permeability, including a more frequent presence of bacterial overgrowth in the small intestine (SIBO). The health consequences of SIBO are primarily malabsorption disorders (vitamin B12, iron, choline, fats, carbohydrates and proteins) and bile salt deconjugation. Undetected and untreated SIBO may lead to nutrient and/or energy malnutrition, thus directly impairing liver function (e.g., folic acid and choline deficiency). However, whether SIBO contributes to liver dysfunction, decreased intestinal barrier integrity, increased inflammation, endotoxemia and bacterial translocation is not yet clear. In this review, we focus on gut–liver axis and discuss critical points, novel insights and the role of nutrition, lifestyle, pre- and probiotics, medication and supplements in the therapy and prevention of both SIBO and NAFLD.

Inhibition of microtubule affinity regulating kinase 4 by an acetylcholinesterase inhibitor, Huperzine A: Computational and experimental approaches

Microtubule affinity regulating kinase 4 (MARK4), 752 amino acids long, belonging to the AMPK superfamily, plays a vital role in regulating microtubules due to its potential to phosphorylate microtubule-associated proteins (MAP's) and thus, MARK4 plays a key role in Alzheimer's disease (AD) pathology. MARK4 is a druggable target for cancer, neurodegenerative diseases, and metabolic disorders. In this study, we have evaluated the MARK4 inhibitory potential of Huperzine A (HpA), an acetylcholinesterase inhibitor (AChEI), a potential AD drug. Molecular docking revealed the key residues governing the MARK4-HpA complex formation. The structural stability and conformational dynamics of the MARK4-HpA complex was assessed by employing Molecular dynamics (MD) simulation. The results suggested that the binding of HpA with MARK4 leads to minimal structural alterations in the native conformation of MARK4, implying the stability of the MARK4-HpA complex. Isothermal titration calorimetry (ITC) studies deciphered that HpA binds to MARK4 spontaneously. Moreover, the kinase assay depicted significant inhibition of MARK by HpA (IC₅₀ = 4.91 μM), implying it to be a potent MARK4 inhibitor that can be implicated in the treatment of MARK4-directed diseases.

Gut microbiome is linked to functions of peripheral immune cells in transition cows during excessive lipolysis

BACKGROUND

Postpartum dairy cows experiencing excessive lipolysis are prone to severe immunosuppression. Despite the extensive understanding of the gut microbial regulation of host immunity and metabolism, its role during excessive lipolysis in cows is largely unknown. Herein, we investigated the potential links between the gut microbiome and postpartum immunosuppression in periparturient dairy cows with excessive lipolysis using single immune cell transcriptome, 16S amplicon sequencing, metagenomics, and targeted metabolomics.

RESULTS

The use of single-cell RNA sequencing identified 26 clusters that were annotated to 10 different immune cell types. Enrichment of functions of these clusters revealed a downregulation of functions in immune cells isolated from a cow with excessive lipolysis compared to a cow with low/normal lipolysis. The results of metagenomic sequencing and targeted metabolome analysis together revealed that secondary bile acid (SBA) biosynthesis was significantly activated in the cows with excessive lipolysis. Moreover, the relative abundance of gut Bacteroides sp. OF04 - 15BH, Paraprevotella clara, Paraprevotella xylaniphila, and Treponema sp. JC4 was mainly associated with SBA synthesis. The use of an integrated analysis showed that the reduction of plasma glycolithocholic acid and taurolithocholic acid could contribute to the immunosuppression of monocytes (CD14⁺MON) during excessive lipolysis by decreasing the expression of GPBAR1.

CONCLUSIONS

Our results suggest that alterations in the gut microbiota and their functions related to SBA synthesis suppressed the functions of monocytes during excessive lipolysis in transition dairy cows. Therefore, we concluded that altered microbial SBA synthesis during excessive lipolysis could lead to postpartum immunosuppression in transition cows. Video Abstract.

6α-hydroxylated bile acids mediate TGR5 signalling to improve glucose metabolism upon dietary fiber supplementation in mice

OBJECTIVE

Dietary fibres are essential for maintaining microbial diversity and the gut microbiota can modulate host physiology by metabolising the fibres. Here, we investigated whether the soluble dietary fibre oligofructose improves host metabolism by modulating bacterial transformation of secondary bile acids in mice fed western-style diet.

DESIGN

To assess the impact of dietary fibre supplementation on bile acid transformation by gut bacteria, we fed conventional wild-type and TGR5 knockout mice western-style diet enriched or not with cellulose or oligofructose. In addition, we used germ-free mice and in vitro cultures to evaluate the activity of bacteria to transform bile acids in the caecal content of mice fed with western-style diet enriched with oligofructose. Finally, we treated wild-type and TGR5 knockout mice orally with hyodeoxycholic acid to assess its antidiabetic effects.

RESULTS

We show that oligofructose sustains the production of 6α-hydroxylated bile acids from primary bile acids by gut bacteria when fed western-style diet. Mechanistically, we demonstrated that the effects of oligofructose on 6α-hydroxylated bile acids were microbiota dependent and specifically required functional TGR5 signalling to reduce body weight gain and improve glucose metabolism. Furthermore, we show that the 6α-hydroxylated bile acid hyodeoxycholic acid stimulates TGR5 signalling, in vitro and in vivo, and increases GLP-1R activity to improve host glucose metabolism.

CONCLUSION

Modulation of the gut microbiota with oligofructose enriches bacteria involved in 6α-hydroxylated bile acid production and leads to TGR5-GLP1R axis activation to improve body weight and metabolism under western-style diet feeding in mice.

Primary biliary cholangitis as a roadmap for the development of novel treatments for cholestatic liver diseases†

The discovery of nuclear receptors and transporters has contributed to the development of new drugs for the treatment of cholestatic liver diseases. Particular progress has been made in the development of second-line therapies for PBC. These new drugs can be separated into compounds primarily targeting cholestasis, molecules targeting fibrogenesis and molecules with immune-mediated action. Finally, drugs aimed at symptom relief (pruritus and fatigue) are also under investigation. Obeticholic acid is currently the only approved second-line therapy for PBC. Drugs in the late phase of clinical development include peroxisome proliferator-activated receptor agonists, norursodeoxycholic acid and NADPH oxidase 1/4 inhibitors.

Sex, puberty, and the gut microbiome

In brief

Sex differences in the gut microbiome may impact multiple aspects of human health and disease. In this study, we review the evidence for microbial sex differences in puberty and adulthood and discuss potential mechanisms driving differentiation of the sex-specific gut microbiome.

Abstract

In humans, the gut microbiome is strongly implicated in numerous sex-specific physiological processes and diseases. Given this, it is important to understand how sex differentiation of the gut microbiome occurs and how these differences contribute to host health and disease. While it is commonly believed that the gut microbiome stabilizes after 3 years of age, our review of the literature found considerable evidence that the gut microbiome continues to mature during and after puberty in a sex-dependent manner. We also review the intriguing, though sparse, literature on potential mechanisms by which host sex may influence the gut microbiome, and vice versa, via sex steroids, bile acids, and the immune system. We conclude that the evidence for the existence of a sex-specific gut microbiome is strong but that there is a dearth of research on how host-microbe interactions lead to this differentiation. Finally, we discuss the types of future studies needed to understand the processes driving the maturation of sex-specific microbial communities and the interplay between gut microbiota, host sex, and human health.

Circulating Bile Acids as Biomarkers for Disease Diagnosis and Prevention

CONTEXT

Bile acids (BAs) are pivotal signaling molecules that regulate energy metabolism and inflammation. Recent epidemiological studies have reported specific alterations in circulating BA profiles in certain disease states, including obesity, type 2 diabetes mellitus (T2DM), nonalcoholic fatty liver disease (NAFLD), and Alzheimer disease (AD). In the past decade, breakthroughs have been made regarding the translation of BA profiling into clinical use for disease prediction. In this review, we summarize and synthesize recent data on variation in circulating BA profiles in patients with various diseases to evaluate the value of these biomarkers in human plasma for early diagnosis.

EVIDENCE ACQUISITION

This review is based on a collection of primary and review literature gathered from a PubMed search for BAs, obesity, T2DM, insulin resistance (IR), NAFLD, hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), colon cancer, and AD, among other keywords.

EVIDENCE SYNTHESIS

Individuals with obesity, T2DM, HCC, CCA, or AD showed specific alterations in circulating BA profiles. These alterations may have existed long before the initial diagnosis of these diseases. The intricate relationship between obesity, IR, and NAFLD complicates the establishment of clear and independent associations between BA profiles and nonalcoholic steatohepatitis. Alterations in the levels of total BAs and several BA species were seen across the entire spectrum of NAFLD, demonstrating significant increases with the worsening of histological features.

CONCLUSIONS

Aberrant circulating BA profiles are an early event in the onset and progression of obesity, T2DM, HCC, and AD. The pleiotropic effects of BAs explain these broad connections. Circulating BA profiles could provide a basis for the development of biomarkers for the diagnosis and prevention of a wide range of diseases.

Effects of thiacloprid exposure on microbiota-gut-liver axis: Multiomics mechanistic analysis in Japanese quails

Neonicotinoid insecticides (NNIs) are the most widely used class of pesticides globally. However, NNIs may cause adverse health effects, including chronic liver disease, and perturbation of the gut microbiota. Thiacloprid (THI) is one of the NNIs widely used in agriculture. Therefore, it is essential to elucidate effects of THI on the microbiota-gut-liver axis to assess the risk of chronic liver disease following exposure to NNIs. This study aimed at investigating whether THI exposure promoted liver injury by altering the gut microbiota and related metabolites. In this study, healthy male quails were exposed to 2 or 4 mg/kg THI or 0.75 % (w/v) saline once daily for 6 weeks, respectively. Metabolomics, 16S rRNA sequencing, and transcriptomic methods were performed to analyze the toxic mechanisms of THI in Japanese quails. We found that THI evoked damage and disruption to intestinal barrier function, leading to increased harmful substances such as lipopolysaccharide (LPS) and phenylacetic acid entering the liver. Besides, our results showed significantly altered hepatic bile acid and cholesterol metabolism in THI-exposed quails, with abnormal liver lipid metabolism, showing severe liver injury, fibrosis, and steatosis compared with the control quails. In conclusion, THI exposure aggravates liver injury via microbiota-gut-liver axis.

Biological tuners to reshape the bile acid pool for therapeutic purposes in non-alcoholic fatty liver disease

Bile acids synthesized within the hepatocytes are transformed by gut microorganisms and reabsorbed into the portal circulation. During their enterohepatic cycling, bile acids act as signaling molecules by interacting with receptors to regulate pathways involved in many physiological processes. The bile acid pool, composed of a variety of bile acid species, has been shown to be altered in diseases, hence contributing to disease pathogenesis. Thus, understanding the changes in bile acid pool size and composition in pathological processes will help to elaborate effective pharmacological treatments. Five crucial steps along the enterohepatic cycle shape the bile acid pool size and composition, offering five possible targets for therapeutic intervention. In this review, we provide an insight on the strategies to modulate the bile acid pool, and then we discuss the potential benefits in non-alcoholic fatty liver disease.

Dysregulation of Bile Acids, Lipids, and Nucleotides in Psoriatic Arthritis Revealed by Unbiased Profiling of Serum Metabolites

OBJECTIVE

The transition from psoriasis to psoriatic arthritis (PsA) occurs in 20-30% of patients; however, the mechanisms underlying the emergence of musculoskeletal disease are not well understood. Metabolic disease is prevalent in psoriasis patients, but whether metabolic factors, other than obesity, increase arthritis risk in psoriasis patients is not known. This study was undertaken to investigate the link between metabolic changes and disease progression in psoriasis patients.

METHODS

To characterize the metabolic alterations during the progression of arthritis in psoriasis patients, we analyzed cross-sectional healthy controls and PsA samples and longitudinal psoriasis serum samples, before and after PsA onset. Nontargeted metabolomic profiling was performed using liquid chromatography mass spectrometry.

RESULTS

We identified several serum metabolites that differed between PsA patients, psoriasis patients, and healthy controls. Differentially abundant bile acids, purines, pyrimidines, glutathione, lipids, and amino acid metabolites were noted in these 3 groups. We also noted differences between psoriasis patients who progressed and those who did not progress to PsA. Bile acid and butyrate levels were depressed in those who progressed to PsA compared to those who did not, and the level of inflammatory lipid mediators increased following PsA diagnosis. In particular, the combination of leukotriene B4 and glycoursodeoxycholic acid sulfate were sensitive and specific predictors of PsA progression.

CONCLUSION

We observed notable differences in bile acid, purine, lipid, and amino acid-derived metabolites, among the healthy controls, psoriasis patients, and PsA patients and identified changes during the transition from psoriasis to PsA. The decreased bile acid and butyrate levels and elevated guanine levels in psoriasis patients at risk for PsA were particularly striking and may reflect gut microbial dysbiosis and dysregulated hepatic metabolism, leading to altered proliferation of immune cells and enhanced cytokine expression.

Mechanisms of pruritus in cholestasis: understanding and treating the itch

Pruritus in cholestatic liver diseases can be a major burden and dramatically impair the quality of life of those affected. Here, we provide an update on the latest insights into the molecular pathogenesis of and novel therapeutic approaches for cholestasis-associated itch. Endogenous and exogenous small-molecule pruritogen candidates bind to their receptors on unmyelinated itch C-fibres in the skin. Candidate pruritogens in cholestasis include certain lysophospholipids and sulfated progesterone metabolites, among others, whereas total bile acid or bilirubin conjugates seem unlikely to have a dominant role in the pathogenesis of cholestasis-associated pruritus. Transmission of itch signals via primary, secondary and tertiary itch neurons to the postcentral gyrus and activation of scratch responses offer various targets for therapeutic intervention. At present, evidence-based treatment options for pruritus in fibrosing cholangiopathies, such as primary biliary cholangitis and primary sclerosing cholangitis, are the peroxisome proliferator-associated receptor (PPAR) agonist bezafibrate and the pregnane X receptor (PXR) agonist rifampicin. In pruritus of intrahepatic cholestasis of pregnancy, ursodeoxycholic acid is recommended and might be supported in the third trimester by rifampicin if needed. Alternatively, non-absorbable anion exchange resins, such as cholestyramine, can be administered, albeit with poor trial evidence. Liver transplantation for intolerable refractory pruritus has become an extremely rare therapeutic strategy.

Polysaccharide from aerial part of Chuanminshen violaceum alleviates oxidative stress and inflammatory response in aging mice through modulating intestinal microbiota

Aging is a biological process of progressive deterioration of physiological functions, which poses a serious threat to individual health and a heavy burden on public health systems. As population aging continues, research into anti-aging drugs that prolong life and improve health is of particular importance. In this study, the polysaccharide from stems and leaves of Chuanminshen violaceum was obtained with water extraction and alcohol precipitation, and then separated and purified with DEAE anion exchange chromatography and gel filtration to obtain CVP-AP-I. We gavaged natural aging mice with CVP-AP-I and performed serum biochemical analysis, histological staining, quantitative real-time PCR (qRT-PCR) and ELISA kit assays to analyze inflammation and oxidative stress-related gene and protein expression in tissues, and 16SrRNA to analyze intestinal flora. We found that CVP-AP-I significantly improved oxidative stress and inflammatory responses of the intestine and liver, restored the intestinal immune barrier, and balanced the dysbiosis of intestinal flora. In addition, we revealed the potential mechanism behind CVP-AP-I to improve intestinal and liver function by regulating intestinal flora balance and repairing the intestinal immune barrier to regulate the intestinal-liver axis. Our results indicated that C. violaceum polysaccharides possessed favorable antioxidant, anti-inflammatory and potentially anti-aging effects in vivo.

Anti-infective bile acids bind and inactivate a Salmonella virulence regulator

Bile acids are prominent host and microbiota metabolites that modulate host immunity and microbial pathogenesis. However, the mechanisms by which bile acids suppress microbial virulence are not clear. To identify the direct protein targets of bile acids in bacterial pathogens, we performed activity-guided chemical proteomic studies. In Salmonella enterica serovar Typhimurium, chenodeoxycholic acid (CDCA) most effectively inhibited the expression of virulence genes and invasion of epithelial cells and interacted with many proteins. Notably, we discovered that CDCA can directly bind and inhibit the function of HilD, an important transcriptional regulator of S. Typhimurium virulence and pathogenesis. Our characterization of bile acid-resistant HilD mutants in vitro and in S. Typhimurium infection models suggests that HilD is one of the key protein targets of anti-infective bile acids. This study highlights the utility of chemical proteomics to identify the direct protein targets of microbiota metabolites for mechanistic studies in bacterial pathogens.

Chemoproteomic Analysis of Microbiota Metabolite-Protein Targets and Mechanisms

The microbiota have emerged as an important factor in host physiology, disease, and response to therapy. These diverse microbes (bacteria, virus, fungi, and protists) encode unique functions and metabolites that regulate intraspecies and interspecies interactions. While the mechanisms of some microbiota species and metabolites have been elucidated, the diversity and abundance of different microbiota species and their associated pathways suggest many more metabolites and mechanisms of action remain to be discovered. In this Perspective, we highlight how the advances in chemical proteomics have provided new opportunities to elucidate the molecular targets of specific microbiota metabolites and reveal new mechanisms of action. The continued development of specific microbiota metabolite reporters and more precise proteomic methods should reveal new microbiota mechanisms of action, therapeutic targets, and biomarkers for a variety of human diseases.

Intestinal Stem Cells Damaged by Deoxycholic Acid via AHR Pathway Contributes to Mucosal Barrier Dysfunction in High-Fat Feeding Mice

High-fat exposure leads to impaired intestinal barrier function by disrupting the function of intestinal stem cells (ISCs); however, the exact mechanism of this phenomenon is still not known. We hypothesize that high concentrations of deoxycholic acid (DCA) in response to a high-fat diet (HFD) affect aryl hydrocarbon receptor (AHR) signalling in ISCs and the intestinal barrier. For this purpose, C57BL/6J mice feeding on a low-fat diet (LFD), an HFD, an HFD with the bile acid binder cholestyramine, and a LFD with the DCA were studied. We found that high-fat feeding induced an increase in faecal DCA concentrations. An HFD or DCA diet disrupted the differentiation function of ISCs by downregulating AHR signalling, which resulted in decreased goblet cells (GCs) and MUC2, and these changes were reversed by cholestyramine. In vitro experiments showed that DCA downregulated the differentiation function of ISCs, which was reversed by the AHR agonist 6-formylindolo [3,2-b]carbazole (FICZ). Mechanistically, DCA caused a reduction in indoleamine 2,3-dioxygenase 1 (IDO1) in Paneth cells, resulting in paracrine deficiency of the AHR ligand kynurenine in crypts. We demonstrated for the first time that DCA disrupts intestinal mucosal barrier function by interfering with AHR signalling in ISCs. Supplementation with AHR ligands may be a new therapeutic target for HFD-related impaired intestinal barrier function.

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.

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.

Bile acids and neurological disease

This review will focus on how bile acids are being used in clinical trials to treat neurological diseases due to their central involvement with the gut-liver-brain axis and their physiological and pathophysiological roles in both normal brain function and multiple neurological diseases. The synthesis of primary and secondary bile acids species and how the regulation of the bile acid pool may differ between the gut and brain is discussed. The expression of several bile acid receptors in brain and their currently known functions along with the tools available to manipulate them pharmacologically are examined, together with discussion of the interaction of bile acids with the gut microbiome and their lesser-known effects upon brain glucose and lipid metabolism. How dysregulation of the gut microbiome, aging and sex differences may lead to disruption of bile acid signalling and possible causal roles in a number of neurological disorders are also considered. Finally, we discuss how pharmacological treatments targeting bile acid receptors are currently being tested in an array of clinical trials for several different neurodegenerative diseases.

Role of the Gut Microbiome in Skeletal Muscle Physiology and Pathophysiology

PURPOSE OF REVIEW

This review aims to summarize the recent findings about the contribution of the gut microbiome to muscle pathophysiology and discuss molecular pathways that may be involved in such process. Related findings in the context of cancer cachexia are outlined.

RECENT FINDINGS

Many bacterial metabolites have been reported to exert a beneficial or detrimental impact on muscle physiology. Most of the evidence concentrates on short-chain fatty acids (SCFAs), with an emerging role for bile acids, bacterial amino acid metabolites (bAAms), and bacterial polyphenol metabolites. Other molecular players worth considering include cytokines, hormones, lipopolysaccharides, and quorum sensing molecules. The current literature clearly establishes the ability for the gut microbiome to modulate muscle function and mass. The understanding of the mechanisms underlying this gut-muscle axis may lead to the delivery of novel therapeutic tools to tackle muscle wasting in cancer cachexia, chronic kidney disease, liver fibrosis, and age-related sarcopenia.

The association of serum total bile acid with new-onset hypertension during pregnancy

Background

There has been considerable interest in the interrelationship between the liver and hypertension. The relationship between serum total bile acid (TBA) and hypertension has been reported. Moreover, intrahepatic cholestasis of pregnancy was correlated to gestation hypertension. However, the association between maternal serum TBA level in the normal range and new-onset hypertension disorders during pregnancy remains unclear. The present study aimed to evaluate the relationship between maternal serum TBA level in the normal range and the risk, disease severity and adverse pregnancy outcomes of new-onset hypertension during pregnancy.

Method

Using the electronic medical records on all pregnant women from the Department of Obstetrics and Gynecology, Third Affiliated Hospital of Guangzhou Medical University, between 2014 and 2020, we conducted a retrospective cohort study of 2581 singleton pregnant women with maternal serum TBA levels in the normal range. Patients were grouped into the non-hypertension during pregnancy (1071), gestational hypertension (480) and preeclampsia (1030) groups.

Result

We found that maternal serum TBA levels were significantly higher in the preeclampsia and gestational hypertension groups than in the non-hypertension group (p < 0.01). Multiple logistic regression analysis showed that TBA level was independently and significantly associated with preeclampsia and gestational hypertension (odds ratio: 1.37, 95% confidence interval [CI]: 1.27–1.48, p = 0.001, odds ratio: 1.34, 95% confidence interval [CI]: 1.24–1.46, p = 0.005, respectively). Moreover, elevated TBA level was positively associated with the risk of severe PE and negatively with mild PE (p < 0.01). In addition, maternal serum TBA levels were negatively related to birth weight (p < 0.001).

Conclusions

These results suggest that maternal serum TBA in the normal range also might be a valuable biomarker for disease severity in preeclampsia and gestational hypertension. Additionally, our results also indicate associations of serum total bile acid levels in the normal range with an increased risk of fetal growth restriction and low birth weight among offspring. These results suggest that TBA could serve as a prognostic biomarker for new-onset hypertension during pregnancy.

Gut-liver axis: Pathophysiological concepts and clinical implications

Bidirectional crosstalk along the gut-liver axis controls gastrointestinal health and disease and exploits environmental and host mediators. Nutrients, microbial antigens, metabolites, and bile acids regulate metabolism and immune responses in the gut and liver, which reciprocally shape microbial community structure and function. Perturbation of such host-microbe interactions is observed in a variety of experimental liver diseases and is facilitated by an impaired intestinal barrier, which is fueling hepatic inflammation and disease progression. Clinical evidence describes perturbation of the gut-liver crosstalk in non-alcoholic fatty liver disease, alcoholic liver disease, and primary sclerosing cholangitis. In liver cirrhosis, a common sequela of these diseases, the intestinal microbiota and microbial pathogen-associated molecular patterns constitute liver inflammation and clinical complications, such as hepatic encephalopathy. Understanding the intricate metabolic interplay between the gut and liver in health and disease opens an avenue for targeted therapies in the future, which is probed in controlled clinical trials.

Changes in circulating bile acid subtypes in response to weight-loss diets are associated with improvements in glycemic status and insulin resistance: The POUNDS Lost trial

OBJECTIVE

Various primary and secondary bile acids (BAs) may play pivotal roles in glucose/insulin metabolism. We investigated whether changes in specific BA subtypes were associated with long-term changes in glucose and insulin sensitivity.

METHODS

This study included 515 adults with overweight or obesity who participated in a 2-year intervention study of weight-loss diets with different macronutrient intakes. Circulating primary and secondary unconjugated BAs and their taurine-/glycine-conjugates were measured at baseline and 6 months after the interventions. We analyzed associations of changes in BA subtypes with two-year changes in fasting glucose, insulin, and insulin resistance (HOMA-IR).

RESULTS

Greater decreases in primary and secondary BA subtypes induced by the interventions were significantly associated with greater reductions of fasting insulin and HOMA-IR at 6 months, showing various effects across the BA subtypes. The reductions of specific BA subtypes (chenodeoxycholate [CDCA], taurocholate [TCA], taurochenodeoxycholate [TCDCA], and taurodeoxycholate [TDCA]) were significantly related to improved glucose levels at 6 months. The initial (6-month) decreases in primary and secondary BA subtypes (glycochenodeoxycholate [GCDCA], TCDCA, and glycoursodeoxycholate [GUDCA]) were also significantly associated with long-term improvements in glucose and insulin metabolism over 2 years. We found significant interactions between dietary fat intake and changes in the BA subtypes for changes in glucose metabolism (Pinteraction < 0.05).

CONCLUSIONS

Weight-loss diet-induced changes in distinct subtypes of circulating BAs were associated with improved glucose metabolism and insulin sensitivity in adults with overweight or obesity. Dietary fat intake may modify the associations of changes in BA metabolism with glucose metabolism.

Serum Metabolomic Profiling in Aging Mice Using Liquid Chromatography-Mass Spectrometry

BACKGROUND

The process of aging and metabolism are intricately linked, thus rendering the identification of reliable biomarkers related to metabolism crucial for delaying the aging process. However, research of reliable markers that reflect aging profiles based on machine learning is scarce.

METHODS

Serum samples were obtained from aged mice (18-month-old) and young mice (3-month-old). LC-MS was used to perform a comprehensive analysis of the serum metabolome and machine learning was used to screen potential aging-related biomarkers.

RESULTS

In total, aging mice were characterized by 54 different metabolites when compared to control mice with criteria: VIP ≥ 1, q-value < 0.05, and Fold-Change ≥ 1.2 or ≤0.83. These metabolites were mostly involved in fatty acid biosynthesis, cysteine and methionine metabolism, D-glutamine and D-glutamate metabolism, and the citrate cycle (TCA cycle). We merged the comprehensive analysis and four algorithms (LR, GNB, SVM, and RF) to screen aging-related biomarkers, leading to the recognition of oleic acid. In addition, five metabolites were identified as novel aging-related indicators, including oleic acid, citric acid, D-glutamine, trypophol, and L-methionine.

CONCLUSIONS

Changes in the metabolism of fatty acids and conjugates, organic acids, and amino acids were identified as metabolic dysregulation related to aging. This study revealed the metabolic profile of aging and provided insights into novel potential therapeutic targets for delaying the effects of aging.

Bile Acids-A Peek Into Their History and Signaling

Bile acids wear many hats, including those of an emulsifier to facilitate nutrient absorption, a cholesterol metabolite, and a signaling molecule in various tissues modulating itching to metabolism and cellular functions. Bile acids are synthesized in the liver but exhibit wide-ranging effects indicating their ability to mediate organ-organ crosstalk. So, how does a steroid metabolite orchestrate such diverse functions? Despite the inherent chemical similarity, the side chain decorations alter the chemistry and biology of the different bile acid species and their preferences to bind downstream receptors distinctly. Identification of new modifications in bile acids is burgeoning, and some of it is associated with the microbiota within the intestine. Here, we provide a brief overview of the history and the various receptors that mediate bile acid signaling in addition to its crosstalk with the gut microbiota.

Integrative systems analysis identifies genetic and dietary modulators of bile acid homeostasis

Bile acids (BAs) are complex and incompletely understood enterohepatic-derived hormones that control whole-body metabolism. Here, we profiled postprandial BAs in the liver, feces, and plasma of 360 chow- or high-fat-diet-fed BXD male mice and demonstrated that both genetics and diet strongly influence BA abundance, composition, and correlation with metabolic traits. Through an integrated systems approach, we mapped hundreds of quantitative trait loci that modulate BAs and identified both known and unknown regulators of BA homeostasis. In particular, we discovered carboxylesterase 1c (Ces1c) as a genetic determinant of plasma tauroursodeoxycholic acid (TUDCA), a BA species with established disease-preventing actions. The association between Ces1c and plasma TUDCA was validated using data from independent mouse cohorts and a Ces1c knockout mouse model. Collectively, our data are a unique resource to dissect the physiological importance of BAs as determinants of metabolic traits, as underscored by the identification of CES1C as a master regulator of plasma TUDCA levels.

Hepatocellular carcinoma: Novel understandings and therapeutic strategies based on bile acids (Review)

Bile acids (BAs) are the major components of bile and products of cholesterol metabolism. Cholesterol is catalyzed by a variety of enzymes in the liver to form primary BAs, which are excreted into the intestine with bile, and secondary BAs are formed under the modification of the gut microbiota. Most of the BAs return to the liver via the portal vein, completing the process of enterohepatic circulation. BAs have an important role in the development of hepatocellular carcinoma (HCC), which may participate in the progression of HCC by recognizing receptors such as farnesoid X receptor (FXR) and mediating multiple downstream pathways. Certain BAs, such as ursodeoxycholic acid and obeticholic acid, were indicated to be able to delay liver injury and HCC progression. In the present review, the structure and function of BAs were introduced and the metabolism of BAs and the process of enterohepatic circulation were outlined. Furthermore, the mechanisms by which BAs participate in the development of HCC were summarized and possible strategies for targeting BAs and key sites of their metabolic processes to treat HCC were suggested.

Multiple Timescale Dynamic Analysis of Functionally-Impairing Mutations in Human Ileal Bile Acid-Binding Protein

Human ileal bile acid-binding protein (hI-BABP) has a key role in the enterohepatic circulation of bile salts. Its two internal binding sites exhibit positive cooperativity accompanied by a site-selectivity of glycocholate (GCA) and glycochenodeoxycholate (GCDA), the two most abundant bile salts in humans. To improve our understanding of the role of dynamics in ligand binding, we introduced functionally impairing single-residue mutations at two key regions of the protein and subjected the mutants to NMR relaxation analysis and MD simulations. According to our results, mutation in both the vicinity of the C/D (Q51A) and the G/H (Q99A) turns results in a redistribution of motional freedom in apo hI-BABP. Mutation Q51A, deteriorating the site-selectivity of GCA and GCDA, results in the channeling of ms fluctuations into faster motions in the binding pocket hampering the realization of key side chain interactions. Mutation Q99A, abolishing positive binding cooperativity for GCDA, leaves ms motions in the C-terminal half unchanged but by decoupling βD from a dynamic cluster of the N-terminal half displays an increased flexibility in the vicinity of site 1. MD simulations of the variants indicate structural differences in the portal region and mutation-induced changes in dynamics, which depend on the protonation state of histidines. A dynamic coupling between the EFGH portal, the C/D-region, and the helical cap is evidenced highlighting the interplay of structural and dynamic effects in bile salt recognition in hI-BABP.

Melatonin relieves hepatic lipid dysmetabolism caused by aging via modifying the secondary bile acid pattern of gut microbes

It has been reported that aging-generated gut microecosystem may promote host hepatic lipid dysmetabolism through shaping the pattern of secondary bile acids (BAs). Then as an oral drug, melatonin (Mel)-mediated beneficial efforts on the communication between gut microbiota and aging host are still not clearly. Here, we show that aging significantly shapes the pattern of gut microbiota and BAs, whereas Mel treatment reverses these phenotypes (P < 0.05), which is identified to depend on the existence of gut microbiota. Mechanistically, aging-triggered high-level expression of ileac farnesoid X receptor (FXR) is significantly decreased through Mel-mediated inhibition on Campylobacter jejuni (C. jejuni)-induced deconjugation of tauroursodeoxycholic acid (TUDCA) and glycoursodeoxycholic acid (GUDCA) (P < 0.05). The aging-induced high-level of serum taurine chenodeoxycholic acid (TCDCA) activate trimethylamine-N-oxide (TMAO)-triggered activating transcriptional factor 4 (ATF4) signaling via hepatic FXR, which further regulates hepatic BAs metabolism, whereas TUDCA inhibits aging-triggered high-level of hepatic ATF4. Overall, Mel reduces C. jejuni-mediated deconjugation of TUDCA to inhibit aging-triggered high-level expression of hepatic FXR, which further decreases hepatic TMAO production, to relieve hepatic lipid dysmetabolism.

Maternal Treatment with Metformin Persistently Ameliorates High-Fat Diet-Induced Metabolic Symptoms and Modulates Gut Microbiota in Rat Offspring

A maternal high-fat (HF) diet has long-term deleterious effect on offspring. This study aims to evaluate whether maternal metformin (MT) treatment ameliorates the adverse effects of maternal HF diet on offspring and the role of gut microbiota in it. Pregnant Sprague-Dawley rats were randomly assigned to a HF diet (60% fat) or a standard chow diet (11.8% fat) group, and part of the HF diet group rats were co-treated with MT via drinking water (300 mg/kg/day), resulting in three groups according to maternal diet and MT treatment during gestation and lactation. All offspring were weaned on a chow diet. A maternal HF diet showed a significant deleterious effect on offspring’s metabolic phenotype and induced colonic inflammation and gut-barrier disruption through the reshaped gut microbiota. The daily oral administration of MT to HF-fed dams during gestation and lactation reversed the dysbiosis of gut microbiota in both dams and adult offspring. The hypothalamic TGR5 expression and plasma bile acids composition in adult male offspring was restored by maternal MT treatment, which could regulate hypothalamic appetite-related peptides expression and alleviate inflammation, thereby improving male offspring’s metabolic phenotype. The present study indicates that targeting the gut–brain axis through the mother may be an effective strategy to control the metabolic phenotype of offspring.

Age-dependent effects of gut microbiota metabolites on brain resident macrophages

In recent years, development of age-related diseases, such as Alzheimer's and Parkinson's disease, as well as other brain disorders, including anxiety, depression, and schizophrenia have been shown to be associated with changes in the gut microbiome. Several factors can induce an alteration in the bacterial composition of the host's gastrointestinal tract. Besides dietary changes and frequent use of antibiotics, the microbiome is also profoundly affected by aging. Levels of microbiota-derived metabolites are elevated in older individuals with age-associated diseases and cognitive defects compared to younger, healthy age groups. The identified metabolites with higher concentration in aged hosts, which include choline and trimethylamine, are known risk factors for age-related diseases. While the underlying mechanisms and pathways remain elusive for the most part, it has been shown, that these metabolites are able to trigger the innate immunity in the central nervous system by influencing development and activation status of brain-resident macrophages. The macrophages residing in the brain comprise parenchymal microglia and non-parenchymal macrophages located in the perivascular spaces, meninges, and the choroid plexus. In this review, we highlight the impact of age on the composition of the microbiome and microbiota-derived metabolites and their influence on age-associated diseases caused by dysfunctional brain-resident macrophages.

Dynamics and determinants of human plasma bile acid profiles during dietary challenges

In recent years, bile acids (BA) have received great interest due to their pleiotropic biological activity and the presence of plasma membrane-bound and nuclear receptors. Moreover, BA in blood have been identified by metabolite screening approaches as biomarkers that are associated with various diseases and even with a human longevity phenotype. With the growing interest in the microbiota contribution to the health-disease trajectory, BA that undergo deconjugation and other modifications by bacteria in the large intestine have become a prime target as a microbiome diversity modifier. We here profiled BA by a quantitative and a semiquantitative approach in 15 healthy and phenotypically very similar young individuals for over a 36-h fasting period, an oral glucose tolerance test (OGTT), and an oral lipid tolerance test (OLTT). We demonstrate a remarkable heterogeneity of the responses and describe the different dynamics of the plasma changes that likely originate from different routes by which BA enters the peripheral blood, and that may represent a direct secretion from the liver into the blood and a route that reaches the blood as a spill-over after passing from the gallbladder through the intestine and the portal system. We discuss the finding that an individual transport process involved in the passage of BA could be a critical determinant in the kinetics of plasma appearance and the overall phenotypic variability found.

5-Aminosalicylic acid ameliorates dextran sulfate sodium-induced colitis in mice by modulating gut microbiota and bile acid metabolism

Colitis develops via the convergence of environmental, microbial, immunological, and genetic factors. The medicine 5-aminosalicylic acid (5-ASA) is widely used in clinical practice for colitis (especially ulcerative colitis) treatment. However, the significance of gut microbiota in the protective effect of 5-ASA on colitis has not been explored. Using a dextran sulfate sodium (DSS)-induced colitis mouse model, we found that 5-ASA ameliorated colitis symptoms in DSS-treated mice, accompanied by increased body weight gain and colon length, and a decrease in disease activity index (DAI) score and spleen index. Also, 5-ASA alleviated DSS-induced damage to colonic tissues, as indicated by suppressed inflammation and decreased tight junction, mucin, and water-sodium transport protein levels. Moreover, the 16S rDNA gene sequencing results illustrated that 5-ASA reshaped the disordered gut microbiota community structure in DSS-treated mice by promoting the abundance of Bifidobacterium, Lachnoclostridium, and Anaerotruncus, and reducing the content of Alloprevotella and Desulfovibrio. Furthermore, 5-ASA improved the abnormal metabolism of bile acids (BAs) by regulating the Farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5) signaling pathways in DSS-treated mice. In contrast, 5-ASA did not prevent the occurrence of colitis in mice with gut microbiota depletion, confirming the essential role of gut microbiota in colitis treatment by 5-ASA. In conclusion, 5-ASA can ameliorate DSS-induced colitis in mice by modulating gut microbiota and bile acid metabolism. These findings documented the new therapeutic mechanisms of 5-ASA in clinical colitis treatment.

Dietary compounds in modulation of gut microbiota-derived metabolites

Gut microbiota, a group of microorganisms that live in the gastrointestinal tract, plays important roles in health and disease. One mechanism that gut microbiota in modulation of the functions of hosts is achieved through synthesizing and releasing a series of metabolites such as short-chain fatty acids. In recent years, increasing evidence has indicated that dietary compounds can interact with gut microbiota. On one hand, dietary compounds can modulate the composition and function of gut microbiota; on the other hand, gut microbiota can metabolize the dietary compounds. Although there are several reviews on gut microbiota and diets, there is no focused review on the effects of dietary compounds on gut microbiota-derived metabolites. In this review, we first briefly discussed the types of gut microbiota metabolites, their origins, and the reasons that dietary compounds can interact with gut microbiota. Then, focusing on gut microbiota-derived compounds, we discussed the effects of dietary compounds on gut microbiota-derived compounds and the following effects on health. Furthermore, we give our perspectives on the research direction of the related research fields. Understanding the roles of dietary compounds on gut microbiota-derived metabolites will expand our knowledge of how diets affect the host health and disease, thus eventually enable the personalized diets and nutrients.

Lithocholic Acid Alleviates Deoxynivalenol-Induced Lethal Cholesterol Metabolic Abnormalities in IPI-2I Cells

Deoxynivalenol (DON) is a secondary metabolite of fungi. Ingestion of feed containing DON causes severe intestinal damage in humans and animals, possibly due to cholesterol-enriched lipid raft abnormalities. Cholic acid (CA) and lithocholic acid (LCA) are metabolites of cholesterol transformation, which have been proven to benefit epithelial cell proliferation and reduce intestinal inflammation and lesions. Therefore, we aimed to study the protective roles of CA and LCA administration on the DON-exposed intestinal epithelial cells (IPI-2I) and the underlying mechanisms involved in cholesterol metabolism. We found that LCA pretreatment, but not CA, alleviated the reduction of cell numbers caused by DON exposure. Furthermore, we demonstrate that LCA restored the DON-induced cell apoptosis by reducing the cleaved caspase 3 and cleaved PARP-1 expression. DON-increased cellular cholesterol and bile acid contents were significantly reduced when LCA was co-treated. Further transcriptomic analysis revealed that the aberrant cholesterol homeostasis genes profile was observed in the cells exposed to DON or pretreated with LCA. We also validated that the key genes involved in cholesterol biosynthesis and transformation (cholesterol to bile acids) were strongly inhibited by the LCA treatment in the DON-exposed cells. Together, this study demonstrated that LCA ameliorated DON-caused toxic apoptosis in IPI-2I cells by maintaining cholesterol metabolism. We suggest that as an endogenous metabolite, LCA may be used as a therapeutic and/or integrated into a dietary intervention against mycotoxin toxicity.

Functions of Gut Microbiota Metabolites, Current Status and Future Perspectives

Gut microbiota, a collection of microorganisms that live within gastrointestinal tract, provides crucial signaling metabolites for the physiological of hosts. In healthy state, gut microbiota metabolites are helpful for maintaining the basic functions of hosts, whereas disturbed production of these metabolites can lead to numerous diseases such as metabolic diseases, cardiovascular diseases, gastrointestinal diseases, neurodegenerative diseases, and cancer. Although there are many reviews about the specific mechanisms of gut microbiota metabolites on specific diseases, there is no comprehensive summarization of the functions of these metabolites. In this Opinion, we discuss the knowledge of gut microbiota metabolites including the types of gut microbiota metabolites and their ways acting on targets. In addition, we summarize their physiological and pathologic functions in health and diseases, such as shaping the composition of gut microbiota and acting as nutrition. This paper can be helpful for understanding the roles of gut microbiota metabolites and thus provide guidance for developing suitable therapeutic strategies to combat microbial-driven diseases and improve health.

Quantitative Profiling of Bile Acids in Feces of Humans and Rodents by Ultra-High-Performance Liquid Chromatography–Quadrupole Time-of-Flight Mass Spectrometry

A simple, sensitive, and reliable quantification and identification method was developed and validated for simultaneous analysis of 58 bile acids (BAs) in human and rodent (mouse and rat) fecal samples. The method involves an extraction step with a 5% ammonium–ethanol aqueous solution; the BAs were quantified by high-resolution mass spectrometry (ultra-high-performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry, UPLC–Q-TOF). The recoveries were 80.05–120.83%, with coefficient variations (CVs) of 0.01–9.82% for three biological species. The limits of detection (LODs) were in the range of 0.01–0.24 μg/kg, and the limits of quantification (LOQs) ranged from 0.03 to 0.81 μg/kg. In addition, the analytical method was used to identify and quantify BAs in end-stage renal disease (ESRD) patients, C57BL/6 mice, and Sprague-Dawley (SD) rats. The fecal BA profile and analysis of BA indices in these samples provide valuable information for further BA metabolic disorder research.

MiR-203 is an anti-obese miRNA by targeting ASBT

Obesity is characterized by excessive fat deposition within the body. Bile acids (BA) are important regulators for controlling the absorption of lipid. Here we show that miR-203 exerts weight-loss and lipid-lowering effects by increasing total BA excretion in obese rodents. miR-203 overexpression transgenic mice are resistant to high-fat diet (HFD)-induced obesity and dyslipidemia. Moreover, the knockdown of miR-203 deteriorates metabolic disorders. ASBT plays important role in regulating BA homeostasis and is a direct target of miR-203. In human intestinal epithelial cells, overexpression of miR-203 decreases the cellular uptake of BA by inhibiting ASBT. Furthermore, TCF7L2 is downregulated in obese mice and acts as a transcription factor of miR-203. The ASBT mRNA level was positively correlated with the body mass index (BMI) of population, while the miR-203 level was negatively associated with BMI. Taken together, these data suggest miR-203 could be a new therapeutic BA regulator for obesity and dyslipidemia.

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miR-203 is downregulated in obese rodents and overweight/obese population

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ASBT is a direct target of miR-203 in obesity

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TCF7L2 acts as an upstream activator of miR-203 in obesity

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miR-203 ameliorates obesity and dyslipidemia by increasing TBAs and lipids excretion

Quinoa Reduces High-Fat Diet-Induced Obesity in Mice via Potential Microbiota-Gut-Brain-Liver Interaction Mechanisms

The gut microbiota is important in the occurrence and development of obesity. It can not only via its metabolites, but also through microbiota-gut-brain-liver interactions, directly or indirectly, influence obesity. Quinoa, known as one kind of pseudocereals and weight loss food supplements, has been high-profile for its high nutritional value and broad applications. In this context, we produced high-fat diet-induced (HFD) obese mouse models and assessed the efficacy of quinoa with saponin and quinoa without saponin on obesity. We explored the potential therapeutic mechanisms of quinoa using methods such as 16S rRNA, Western blotting, Immunohistochemical (IHC). Our results indicated that quinoa can improve the obese symptoms significantly on HFD mice, as well as aberrant glucose and lipid metabolism. Further analyses suggest that quinoa can regulate microbiota in the colon and have predominantly regulation on Bacteroidetes, Actinobacteria and Desulfovibrio, meanwhile can decrease the F/B ratio and the abundance of Blautia. Contemporaneously, quinoa can upregulate the expression of TGR5 in the colon and brain, as well as GLP-1 in the colon, liver and brain. while downregulate the expression of TLR4 in the colon and liver, as well as markers of ER stress and oxidative stress in livers and serums. Beyond this, tight junctional proteins in colons and brains are also increased in response to quinoa. Therefore, quinoa can effectively reduce obesity and may possibly exert through microbiota-gut-brain-liver interaction mechanisms. IMPORTANCE Gut microbiota has been investigated extensively, as a driver of obesity as well as a therapeutic target. Studies of its mechanisms are predominantly microbiota-gut-brain axis or microbiota-gut-liver axis. Recent studies have shown that there is an important correlation between the gut-brain-liver axis and the energy balance of the body. Our research focus on microbiota-gut-brain-liver axis, as well as influences of quinoa in intestinal microbiota. We extend this study to the interaction between microbiota and brains, and the result shows obvious differences in the composition of the microbiome between the HFD group and others. These observations infer that besides the neurotransmitter and related receptors, microbiota itself may be a mediator for regulating bidirectional communication, along the gut-brain-liver axis. Taken together, these results also provide strong evidence for widening the domain of applicability of quinoa.

Serum Total Bile Acids in Relation to Gastrointestinal Cancer Risk: A Retrospective Study

Background

Bile acids (BAs) have been proposed to promote gastrointestinal cells carcinogenesis. However, studies on serum total bile acid (TBA) levels and gastrointestinal cancers (GICs) risk are rare.

Methods

We conducted a retrospective case-control study from 2015 to 2019 at the First Affiliated Hospital of Air Force Military Medical University, in which 4,256 GICs cases and 1,333 controls were recruited. Patients' demographic, clinical and laboratory data were collected. The odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using binary logistic regression models.

Results

Positive associations were observed between serum TBA levels and risks of esophageal cancer (EC), gastric cancer (GC) and colorectal cancer (CRC). Overall, ORs of EC, GC and CRC risk rose with the TBA levels increasing. After adjustment for potential confounders, the OR of TBA-positive for EC risk was 4.89 (95% CI: 3.20-7.49), followed by GC (OR: 3.92, 95% CI: 2.53-6.08), and CRC (OR: 3.32, 95% CI: 2.04-5.11). Patients aged 60 years or older have a higher risk of GICs, especially for EC patients. Males are associated with a higher risk of GC, while females are associated with a higher risk of CRC. Preoperative serum TBA positive and negative was significantly different in the presence or absence of hematogenous metastasis among EC patients (P=0.014), and lymph node metastasis among GC patients (P=0.018).

Conclusions

This retrospective study showed positive associations between serum TBA level and GICs risk, and a higher serum TBA level constitutes a risk factor for GICs.

Gut microbiota, bile acids, and nature compounds

Natural compounds (NPs) have historically made a major contribution to pharmacotherapy in various diseases and drug discovery. In the past decades, studies on gut microbiota have shown that the efficacy of NPs can be affected by the interactions between gut microbiota and NPs. On one hand, gut microbiota can metabolize NPs. On the other hand, NPs can influence the metabolism and composition of gut microbiota. Among gut microbiota metabolites, bile acids (BAs) have attracted widespread attention due to their effects on the body homeostasis and the development of diseases. Studies have also confirmed that NPs can regulate the metabolism of BAs and ultimately regulate the physiological function of the body and disease progresses. In this review, we comprehensively summarize the interactions among NPs, gut microbiota, and BAs. In addition, we also discuss the role of microbial BAs metabolism in understanding the toxicity and efficacy of NPs. Furthermore, we present personal insights into the future research directions of NPs and BAs.

Plasma Metabolic Signatures of Healthy Overweight Subjects Challenged With an Oral Glucose Tolerance Test

Insulin secretion following ingestion of a carbohydrate load affects a multitude of metabolic pathways that simultaneously change direction and quantity of interorgan fluxes of sugars, lipids and amino acids. In the present study, we aimed at identifying markers associated with differential responses to an OGTT a population of healthy adults. By use of three metabolite profiling platforms, we assessed these postprandial responses of a total of 202 metabolites in plasma of 72 healthy volunteers undergoing comprehensive phenotyping and of which half enrolled into a weight-loss program over a three-month period. A standard oral glucose tolerance test (OGTT) served as dietary challenge test to identify changes in postprandial metabolite profiles. Despite classified as healthy according to WHO criteria, two discrete clusters (A and B) were identified based on the postprandial glucose profiles with a balanced distribution of volunteers based on gender and other measures. Cluster A individuals displayed 26% higher postprandial glucose levels, delayed glucose clearance and increased fasting plasma concentrations of more than 20 known biomarkers of insulin resistance and diabetes previously identified in large cohort studies. The volunteers identified by canonical postprandial responses that form cluster A may be called pre-pre-diabetics and defined as “at risk” for development of insulin resistance. Moreover, postprandial changes in selected fatty acids and complex lipids, bile acids, amino acids, acylcarnitines and sugars like mannose revealed marked differences in the responses seen in cluster A and cluster B individuals that sustained over the entire challenge test period of 240 min. Almost all metabolites, including glucose and insulin, returned to baseline values at the end of the test (at 240 min), except a variety of amino acids and here those that have been linked to diabetes development. Analysis of the corresponding metabolite profile in a fasting blood sample may therefore allow for early identification of these subjects at risk for insulin resistance without the need to undergo an OGTT.

Comparison of bile acids profiles in the enterohepatic circulation system of mice and rats

Bile acids (BAs) were selected as biomarkers for the diagnosis and prevention of multiple liver diseases, and they were also considered as an important signal transductor via "liver-gut" axis. As important factors for maintaining the normal function and tissue morphology, BA homeostasis throughout the enterohepatic circulation system was guaranteed by BA synthases and transporters, nuclear receptors (NRs) and gut microbiota, all of which presented significant species differences. Thus, we simultaneously quantify BA profiles in the enterohepatic circulation of SD rats and C57BL/6 mice to reveal the species differences of BA homeostasis between these two main rodents of preclinical studies. Our results showed that BA profiles of mice plasma, bile and liver were most dissimilar from these of rats. Meanwhile, BAs profiles also presented obvious species differences in the intestine of mice and rats, especially small intestine. Unlike rats, taurine-conjugated bile acids (T-BAs) were predominant in mice small intestine content and tissue, in which taurocholic acid (TCA) was the most prominent BAs. BAs dynamic analysis showed that compared with rats, mice showed stranger taurine and glycine de-conjugations in lager intestine. However, both the ratios of unconjugated bile acids (Un-BAs) to conjugated BAs, and secondary BAs to primary BAs in mice small content and tissue were all much lower than these in rats. Furthermore, ileum BAs profiles also showed significantly separation trend between rats and mice, whether content or tissue. Our data revealed that the patterns of BAs homeostasis in mice enterohepatic circulation system were significantly different from these in rats (especially in intestine), suggesting that more cautious should be paid to the selection of BAs as biomarkers for disease diagnosis or/and drug induced toxicity, and the certain role and mechanism of individual BA in the pathological process of BA-related diseases via "liver-gut" axis should be verified by using of multiple species.