Review article: therapeutic aspects of bile acid signalling in the gut-liver axis

Bile acid metabolism and signalling in liver disease

Bile acids (BAs) serve as signalling molecules, efficiently regulating their own metabolism and transport, as well as key aspects of lipid and glucose homeostasis. BAs shape the gut microbial flora and conversely are metabolised by microbiota. Disruption of BA transport, metabolism and physiological signalling functions contribute to the pathogenesis and progression of a wide range of liver diseases including cholestatic disorders and MASLD (metabolic dysfunction-associated steatotic liver disease), as well as hepatocellular and cholangiocellular carcinoma. Additionally, impaired BA signalling may also affect the intestine and kidney, thereby contributing to failure of gut integrity and driving the progression and complications of portal hypertension, cholemic nephropathy and the development of extrahepatic malignancies such as colorectal cancer. In this review, we will summarise recent advances in the understanding of BA signalling, metabolism and transport, focusing on transcriptional regulation and novel BA-focused therapeutic strategies for cholestatic and metabolic liver diseases.

Regulation of bile acids and their receptor FXR in metabolic diseases

High sugar, high-fat diets and unhealthy lifestyles have led to an epidemic of obesity and obesity-related metabolic diseases, seriously placing a huge burden on socio-economic development. A deeper understanding and elucidation of the specific molecular biological mechanisms underlying the onset and development of obesity has become a key to the treatment of metabolic diseases. Recent studies have shown that the changes of bile acid composition are closely linked to the development of metabolic diseases. Bile acids can not only emulsify lipids in the intestine and promote lipid absorption, but also act as signaling molecules that play an indispensable role in regulating bile acid homeostasis, energy expenditure, glucose and lipid metabolism, immunity. Disorders of bile acid metabolism are therefore important risk factors for metabolic diseases. The farnesol X receptor, a member of the nuclear receptor family, is abundantly expressed in liver and intestinal tissues. Bile acids act as endogenous ligands for the farnesol X receptor, and erroneous FXR signaling triggered by bile acid dysregulation contributes to metabolic diseases, including obesity, non-alcoholic fatty liver disease and diabetes. Activation of FXR signaling can reduce lipogenesis and inhibit gluconeogenesis to alleviate metabolic diseases. It has been found that intestinal FXR can regulate hepatic FXR in an organ-wide manner. The crosstalk between intestinal FXR and hepatic FXR provides a new idea for the treatment of metabolic diseases. This review focuses on the relationship between bile acids and metabolic diseases and the current research progress to provide a theoretical basis for further research and clinical applications.

Gut Microbiota and Liver Regeneration: A Synthesis of Evidence on Structural Changes and Physiological Mechanisms

Liver regeneration (LR) is a unique biological process with the ability to restore up to 70% of the organ. This allows for the preservation of liver resections for various liver tumors and for living donor liver transplantation (LDLT). However, in some cases, LR is insufficient and interventions that can improve LR are urgently needed. Gut microbiota (GM) is one of the factors influencing LR, as the liver and intestine are intimately connected through the gut-liver axis. Thus, healthy GM facilitates normal LR, whereas dysbiosis leads to impaired LR due to imbalance of bile acids, inflammatory cytokines, microbial metabolites, signaling pathways, etc. Therefore, GM can be considered as a new possible therapeutic target to improve LR. In this review, we critically observe the current knowledge about the influence of gut microbiota (GM) on liver regeneration (LR) and the possibility to improve this process, which may reduce complication and mortality rates after liver surgery. Although much research has been done on this topic, more clinical trials and systemic reviews are urgently needed to move this type of intervention from the experimental phase to the clinical field.

Oral-gut microbiome interactions in advanced cirrhosis: characterisation of pathogenic enterotypes and salivatypes, virulence factors and antimicrobial resistance

BACKGROUND & AIMS

Cirrhosis complications are often triggered by bacterial infections with multidrug-resistant organisms. Alterations in the gut and oral microbiome in decompensated cirrhosis (DC) influence clinical outcomes. We interrogated: (i) gut and oral microbiome community structures, (ii) virulence factors (VFs) and antimicrobial resistance genes (ARGs) and (iii) oral-gut microbial overlap in patients with differing cirrhosis severity.

METHODS

Fifteen healthy controls (HCs), as well as 26 patients with stable cirrhosis (SC), 46 with DC, 14 with acute-on-chronic liver failure (ACLF) and 14 with severe infection without cirrhosis participated. Metagenomic sequencing was undertaken on paired saliva and faecal samples. 'Salivatypes' and 'enterotypes' based on genera clustering were assessed against cirrhosis severity and clinical parameters. VFs and ARGs were evaluated in oral and gut niches, and distinct resistotypes identified.

RESULTS

Salivatypes and enterotypes revealed a greater proportion of pathobionts with concomitant reduction in autochthonous genera with increasing cirrhosis severity and hyperammonaemia. Increasing overlap between oral and gut microbiome communities was observed in DC and ACLF vs. SC and HCs, independent of antimicrobial, beta-blocker and gastric acid-suppressing therapies. Two distinct gut microbiome clusters harboured genes encoding for the PTS (phosphoenolpyruvate:sugar phosphotransferase system) and other VFs in DC and ACLF. Substantial ARGs (oral: 1,218 and gut: 672) were detected (575 common to both sites). The cirrhosis resistome was distinct, with three oral and four gut resistotypes identified, respectively.

DISCUSSION

The degree of oral-gut microbial community overlap, frequency of VFs and ARGs all increase significantly with cirrhosis severity, with progressive dominance of pathobionts and loss of commensals. Despite similar antimicrobial exposure, patients with DC and ACLF have reduced microbial richness compared to patients with severe infection without cirrhosis, supporting the additive pathobiological effect of cirrhosis.

IMPACT AND IMPLICATIONS

This research underscores the crucial role of microbiome alterations in the progression of cirrhosis in an era of escalating multidrug resistant infections, highlighting the association and potential impact of increased oral-gut microbial overlap, virulence factors, and antimicrobial resistance genes on clinical outcomes. These findings are particularly significant for patients with decompensated cirrhosis and acute-on-chronic liver failure, as they reveal the intricate relationship between microbiome alterations and cirrhosis complications. This is relevant in the context of multidrug-resistant organisms and reduced oral-gut microbial diversity that exacerbate cirrhosis severity, drive hepatic decompensation and complicate treatment. For practical applications, these insights could guide the development of targeted microbiome-based therapeutics and personalised antimicrobial regimens for patients with cirrhosis to mitigate infectious complications and improve clinical outcomes.

Prevalence and prognostic value of zinc and selenium deficiency in advanced chronic liver disease

BACKGROUND AND AIMS

Zinc and selenium are essential trace elements involved in important (patho)physiological processes. The prevalence and prognostic implications of zinc and selenium deficiency in patients with advanced chronic liver disease (ACLD) remain unknown.

METHODS

We determined serum zinc and selenium concentrations in 309 patients with ACLD undergoing hepatic venous pressure gradient (HVPG) measurement between 2019 and 2022. We evaluated the prevalence of zinc/selenium deficiency and assessed its association with severity of ACLD and liver-related events (LRE, i.e. first/further hepatic decompensation/liver-related death).

RESULTS

Among 309 ACLD patients (median: age: 57 [IQR: 50-64], MELD: 11 [IQR: 9-16], HVPG: 17 [IQR: 11-20]), 73% (227) and 63% (195) were deficient in zinc and selenium, respectively. Decompensated (dACLD) patients showed significantly lower serum zinc (median: 48 [IQR: 38-59] vs. compensated, cACLD: 65 [IQR: 54-78], p < 0.001) and selenium levels (median: 4.9 [IQR 4.0-6.2] vs. cACLD: 6.1 [IQR 5.1-7.3], p < 0.001). Significant correlations of zinc/selenium levels were found with MELD (zinc: ρ = -0.498, p < 0.001; selenium: ρ = -0.295, p < 0.001), HVPG (zinc: ρ = -0.400, p < 0.001; selenium: ρ = -0.157, p = 0.006) and liver disease-driving mechanisms (IL6, bile-acid homeostasis). On multivariable analysis, low zinc/selenium levels, age and MELD remained independently associated with LRE.

CONCLUSION

Zinc and selenium deficiencies are common in ACLD patients especially with higher MELD and HVPG. Low zinc and selenium levels independently predicted hepatic decompensation and liver-related death. The effect of zinc/selenium supplementation in ACLD should be investigated in future trials.

Metabolic-associated fatty liver disease and pregnancy complications: new challenges and clinical perspectives

The term metabolic-associated fatty liver disease (MAFLD), with a global prevalence estimated at 38.77%, has gradually replaced the traditional concept of non-alcoholic fatty liver disease (NAFLD). Compared to the general population, the incidence of MAFLD is notably higher among pregnant women, posing potential risks to both maternal and neonatal health. This review summarizes the latest research on MAFLD, focusing on its association with pregnancy complications. Additionally, it provides a comparative analysis with previous studies on NAFLD, presenting a comprehensive perspective for clinical management. Findings suggest that pregnant women with MAFLD face a higher risk of gestational hypertension and cesarean delivery compared to those with NAFLD, while the risk for gestational diabetes mellitus remains similar between the two conditions. Additionally, MAFLD is associated with an increased likelihood of delivering large-for-gestational-age infants and heightened risks of preterm birth and low birth weight. Current treatment strategies for MAFLD focus on lifestyle modifications, such as dietary adjustments and increased physical activity. However, there is an urgent need for the development of safe and effective pharmacological treatments, particularly tailored toward pregnant women. Future research should delve deeper into the causal relationships between MAFLD and pregnancy complications and explore optimal therapeutic approaches to improve outcomes for mothers and their infants.

Recent Advances in Gut- and Gut-Organ-Axis-on-a-Chip Models

The human gut extracts nutrients from the diet while forming the largest barrier against the outer environment. In addition, the gut actively maintains homeostasis through intricate interactions with the gut microbes, the immune system, the enteric nervous system, and other organs. These interactions influence digestive health and, furthermore, play crucial roles in systemic health and disease. Given its primary role in absorbing and metabolizing orally administered drugs, there is significant interest in the development of preclinical in vitro model systems that can accurately emulate the intestine in vivo. A gut-on-a-chip system holds great potential as a testing and screening platform because of its ability to emulate the physiological aspects of in vivo tissues and expandability to incorporate and combine with other organs. This review aims to identify the key physiological features of the human gut that need to be incorporated to build more accurate preclinical models and highlights the recent progress in gut-on-a-chip systems and competing technologies toward building more physiologically relevant preclinical model systems. Furthermore, various efforts to construct multi-organ systems with the gut, called gut-organ-axis-on-a-chip models, are discussed. In vitro gut models with physiological relevance can provide valuable platforms for bridging the gap between preclinical and clinical studies.

The gut microbiota-bile acid axis in cholestatic liver disease

Cholestatic liver diseases (CLD) are characterized by impaired normal bile flow, culminating in excessive accumulation of toxic bile acids. The majority of patients with CLD ultimately progress to liver cirrhosis and hepatic failure, necessitating liver transplantation due to the lack of effective treatment. Recent investigations have underscored the pivotal role of the gut microbiota-bile acid axis in the progression of hepatic fibrosis via various pathways. The obstruction of bile drainage can induce gut microbiota dysbiosis and disrupt the intestinal mucosal barrier, leading to bacteria translocation. The microbial translocation activates the immune response and promotes liver fibrosis progression. The identification of therapeutic targets for modulating the gut microbiota-bile acid axis represents a promising strategy to ameliorate or perhaps reverse liver fibrosis in CLD. This review focuses on the mechanisms in the gut microbiota-bile acids axis in CLD and highlights potential therapeutic targets, aiming to lay a foundation for innovative treatment approaches.

Yinchenhao Decoction Protects Against Acute Liver Injury in Mice With Biliary Acute Pancreatitis by Regulating the Gut Microflora-Bile Acids-Liver Axis

Background and Aims: Acute liver injury (ALI) often follows biliary acute pancreatitis (BAP), but the exact cause and effective treatment are unknown. The aim of this study was to investigate the role of the gut microflora-bile acids-liver axis in BAP-ALI in mice and to assess the potential therapeutic effects of Yinchenhao decoction (YCHD), a traditional Chinese herbal medicine formula, on BAP-ALI. Methods: Male C57BL/6 mice were allocated into three groups: negative control (NC), BAP model, and YCHD treatment groups. The severity of BAP-ALI, intrahepatic bile acid levels, and the gut microbiota were assessed 24 h after BAP-ALI induction in mice. Results: Our findings demonstrated that treatment with YCHD significantly ameliorated the severity of BAP-ALI, as evidenced by the mitigation of hepatic histopathological changes and a reduction in liver serum enzyme levels. Moreover, YCHD alleviated intrahepatic cholestasis and modified the composition of bile acids, as indicated by a notable increase in conjugated bile acids. Additionally, 16S rDNA sequencing analysis of the gut microbiome revealed distinct alterations in the richness and composition of the microbiome in BAP-ALI mice compared to those in control mice. YCHD treatment effectively improved the intestinal flora disorders induced by BAP-ALI. Spearman's correlation analysis revealed a significant association between the distinct compositional characteristics of the intestinal microbiota and the intrahepatic bile acid concentration. Conclusions: These findings imply a potential link between gut microbiota dysbiosis and intrahepatic cholestasis in BAP-ALI mice and suggest that YCHD treatment may confer protection against BAP-ALI via the gut microflora-bile acids-liver axis.

Obeticholic acid attenuates the intestinal barrier disruption in a rat model of short bowel syndrome

BACKGROUND

Short bowel syndrome (SBS) features nutrients malabsorption and impaired intestinal barrier. Patients with SBS are prone to sepsis, intestinal flora dysbiosis and intestinal failure associated liver disease. Protecting intestinal barrier and preventing complications are potential strategies for SBS treatment. This study aims to investigate the effects of farnesoid X receptor (FXR) agonist, obeticholic acid (OCA), have on intestinal barrier and ecological environment in SBS.

METHODS AND RESULTS

Through testing the small intestine and serum samples of patients with SBS, impaired intestinal barrier was verified, as evidenced by reduced expressions of intestinal tight junction proteins (TJPs), increased levels of apoptosis and epithelial cell damage. The intestinal expressions of FXR and related downstream molecules were decreased in SBS patients. Then, global FXR activator OCA was used to further dissect the potential role of the FXR in a rat model of SBS. Low expressions of FXR-related molecules were observed on the small intestine of SBS rats, along with increased proinflammatory factors and damaged barrier function. Furthermore, SBS rats possessed significantly decreased body weight and elevated death rate. Supplementation with OCA mitigated the damaged intestinal barrier and increased proinflammatory factors in SBS rats, accompanied by activated FXR-related molecules. Using 16S rDNA sequencing, the regulatory role of OCA on gut microbiota in SBS rats was witnessed. LPS stimulation to Caco-2 cells induced apoptosis and overexpression of proinflammatory factors in vitro. OCA incubation of LPS-pretreated Caco-2 cells activated FXR-related molecules, increased the expressions of TJPs, ameliorated apoptosis and inhibited overexpression of proinflammatory factors.

CONCLUSIONS

OCA supplementation could effectively ameliorate the intestinal barrier disruption and inhibit overexpression of proinflammatory factors in a rat model of SBS and LPS-pretreated Caco-2 cells. As a selective activator of FXR, OCA might realize its protective function through FXR activation.

FXR-FGF19 signaling in the gut-liver axis is dysregulated in patients with cirrhosis and correlates with impaired intestinal defence

BACKGROUND AND AIMS

Experimental studies linked dysfunctional Farnesoid X receptor (FXR)-fibroblast growth factor 19 (FGF19) signaling to liver disease. This study investigated key intersections of the FXR-FGF19 pathway along the gut-liver axis and their link to disease severity in patients with cirrhosis.

METHODS

Patients with cirrhosis undergoing hepatic venous pressure gradient measurement (cohort-I n = 107, including n = 53 with concomitant liver biopsy; n = 5 healthy controls) or colonoscopy with ileum biopsy (cohort-II n = 37; n = 6 controls) were included. Hepatic and intestinal gene expression reflecting FXR activation and intestinal barrier integrity was assessed. Systemic bile acid (BA) and FGF19 levels were measured.

RESULTS

Systemic BA and FGF19 levels correlated significantly (r = 0.461; p < 0.001) and increased with cirrhosis severity. Hepatic SHP expression decreased in patients with cirrhosis (vs. controls; p < 0.001), indicating reduced FXR activation in the liver. Systemic FGF19 (r = -0.512, p < 0.001) and BA (r = -0.487, p < 0.001) levels correlated negatively with hepatic CYP7A1, but not SHP or CYP8B1 expression, suggesting impaired feedback signaling in the liver. In the ileum, expression of FXR, SHP and FGF19 decreased in patients with cirrhosis, and interestingly, intestinal FGF19 expression was not linked to systemic FGF19 levels. Intestinal zonula occludens-1, occludin, and alpha-5-defensin expression in the ileum correlated with SHP and decreased in patients with decompensated cirrhosis as compared to controls.

CONCLUSIONS

FXR-FGF19 signaling is dysregulated at essential molecular intersections along the gut-liver axis in patients with cirrhosis. Decreased FXR activation in the ileum mucosa was linked to reduced expression of intestinal barrier proteins. These human data call for further mechanistic research on interventions targeting the FXR-FGF19 pathway in patients with cirrhosis.

CLINICAL TRIAL NUMBER

NCT03267615.

Effects of Saponins on Lipid Metabolism: The Gut-Liver Axis Plays a Key Role

Unhealthy lifestyles (high-fat diet, smoking, alcohol consumption, too little exercise, etc.) in the current society are prone to cause lipid metabolism disorders affecting the health of the organism and inducing the occurrence of diseases. Saponins, as biologically active substances present in plants, have lipid-lowering, inflammation-reducing, and anti-atherosclerotic effects. Saponins are thought to be involved in the regulation of lipid metabolism in the body; it suppresses the appetite and, thus, reduces energy intake by modulating pro-opiomelanocortin/Cocaine amphetamine regulated transcript (POMC/CART) neurons and neuropeptide Y/agouti-related peptide (NPY/AGRP) neurons in the hypothalamus, the appetite control center. Saponins directly activate the AMP-activated protein kinase (AMPK) signaling pathway and related transcriptional regulators such as peroxisome-proliferator-activated-receptors (PPAR), CCAAT/enhancer-binding proteins (C/EBP), and sterol-regulatory element binding proteins (SREBP) increase fatty acid oxidation and inhibit lipid synthesis. It also modulates gut-liver interactions to improve lipid metabolism by regulating gut microbes and their metabolites and derivatives-short-chain fatty acids (SCFAs), bile acids (BAs), trimethylamine (TMA), lipopolysaccharide (LPS), et al. This paper reviews the positive effects of different saponins on lipid metabolism disorders, suggesting that the gut-liver axis plays a crucial role in improving lipid metabolism processes and may be used as a therapeutic target to provide new strategies for treating lipid metabolism disorders.

Efficacy of Shu-yi-ning-chang decoction on IBS-D: Modulating Nr4a3 pathway to reduce visceral hypersensitivity

AIM OF THE STUDY

To evaluate the therapeutic effect of SYNC in diarrhea irritable bowel syndrome (IBS-D) and explore its underlying mechanism through transcriptomic sequencing (RNA-Seq).

MATERIALS AND METHODS

A rat model of IBS-D was constructed to elucidate the effects of SYNC. Abdominal withdrawal reflex (AWR), fecal water content (FWC), and recording body weight were calculated to assess visceral sensitivity in rats. Histopathological changes in the colon and alterations in mast cell (MC) count were determined. Immunohistochemistry was employed to assess mast cell tryptase (MCT) expression in rat colons. Serum levels of corticotropin-releasing Hormone (CRH), interleukin-6 (IL-6), calcitonin gene-related peptide (CGRP), and 5-hydroxytryptamine (5-HT) were quantified using ELISA. RNA-Seq of colon tissue was performed, followed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. Western blot analysis was conducted to quantify the expression levels of key proteins in the Nr4a3 pathway in the colon and hypothalamus tissues of rats.

RESULTS

SYNC alleviated visceral hypersensitivity and mood disorders in rats with IBS-D. Moreover, it was positively correlated with its dosage and the observed effects, such as the enhancement of the colon's mucosal lining condition and reduction in the number and activation of MCs within the model group. SYNC reduced the expression levels of factors related to the brain-gut axis and inflammatory markers in the bloodstream. RNA-Seq analysis indicated that SYNC down-regulated the expression of Nr4a3 and PI3K. These SYNC-targeted genes primarily played roles in immune regulation and inflammatory responses, correlating with the modulation of Nr4a3 and the PI3K/AKT pathway. Western blot analysis further confirmed SYNC's influence on inflammation-related MC activation by downregulating key proteins in the Nr4a3/PI3K pathway.

CONCLUSIONS

SYNC inhibited mast cell activation and attenuated visceral hypersensitivity in the colon tissues of IBS-D rats. These effects were mediated by the Nr4a3/PI3K signaling pathway.

Impact of Drug-Mediated Inhibition of Intestinal Transporters on Nutrient and Endogenous Substrate Disposition…an Afterthought?

A large percentage (~60%) of prescription drugs and new molecular entities are designed for oral delivery, which requires passage through a semi-impervious membrane bilayer in the gastrointestinal wall. Passage through this bilayer can be dependent on membrane transporters that regulate the absorption of nutrients or endogenous substrates. Several investigations have provided links between nutrient, endogenous substrate, or drug absorption and the activity of certain membrane transporters. This knowledge has been key in the development of new therapeutics that can alleviate various symptoms of select diseases, such as cholestasis and diabetes. Despite this progress, recent studies revealed potential clinical dangers of unintended altered nutrient or endogenous substrate disposition due to the drug-mediated disruption of intestinal transport activity. This review outlines reports of glucose, folate, thiamine, lactate, and bile acid (re)absorption changes and consequent adverse events as examples. Finally, the need to comprehensively expand research on intestinal transporter-mediated drug interactions to avoid the unwanted disruption of homeostasis and diminish therapeutic adverse events is highlighted.

Traditional Chinese Medicine formula Dai-Zong-Fang alleviating hepatic steatosis in db/db mice via gut microbiota modulation

Introduction: Hepatic steatosis is a hepatic pathological change closely associated with metabolic disorders, commonly observed in various metabolic diseases such as metabolic syndrome (MetS), with a high global prevalence. Dai-Zong-Fang (DZF), a traditional Chinese herbal formula, is widely used in clinical treatment for MetS, exhibiting multifaceted effects in reducing obesity and regulating blood glucose and lipids. This study aims to explore the mechanism by which DZF modulates the gut microbiota and reduces hepatic steatosis based on the gut-liver axis. Methods: This study utilized db/db mice as a disease model for drug intervention. Body weight and fasting blood glucose were monitored. Serum lipid and transaminase levels were measured. Insulin tolerance test was conducted to assess insulin sensitivity. Hematoxylin and eosin (HE) staining was employed to observe morphological changes in the liver and intestine. The degree of hepatic steatosis was evaluated through Oil Red O staining and hepatic lipid determination. Changes in gut microbiota were assessed using 16S rRNA gene sequencing. Serum lipopolysaccharide (LPS) levels were measured by ELISA. The expression levels of intestinal tight junction proteins, intestinal lipid absorption-related proteins, and key proteins in hepatic lipid metabolism were examined through Western blot and RT-qPCR. Results: After DZF intervention, there was a decrease in body weight, alleviation of glucose and lipid metabolism disorders, reduction in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, and mitigation of insulin resistance in mice. DZF significantly modulated the diversity of the gut microbiota, with a notable increase in the abundance of the Bacteroidetes phylum. PICRUSt indicated that DZF influenced various functions in gut microbiota, including carbohydrate and amino acid metabolism. Following DZF intervention, serum LPS levels decreased, intestinal pathological damage was reduced, and the expression of intestinal tight junction protein occludin was increased, while the expression of intestinal lipid absorption-related proteins cluster of differentiation 36 (CD36) and apolipoprotein B48 (ApoB48) were decreased. In the liver, DZF intervention resulted in a reduction in hepatic steatosis and lipid droplets, accompanied by a decrease fatty acid synthase (FASN) and stearoyl-CoA desaturase 1 (SCD1) and fatty acid transport protein 2 (FATP2). Conversely, there was an increase in the expression of the fatty acid oxidation-related enzyme carnitine palmitoyltransferase-1𝛂 (CPT-1𝛂). Conclusion: DZF can regulate the structure and function of the intestinal microbiota in db/db mice. This ameliorates intestinal barrier damage and the detrimental effects of endotoxemia on hepatic metabolism. DZF not only inhibits intestinal lipid absorption but also improves hepatic lipid metabolism from various aspects, including de novo lipogenesis, fatty acid uptake, and fatty acid oxidation. This suggests that DZF may act on the liver and intestine as target organs, exerting its effects by improving the intestinal microbiota and related barrier and lipid absorption functions, ultimately ameliorating hepatic steatosis and enhancing overall glucose and lipid metabolism.

Splenectomy ameliorates liver cirrhosis by restoring the gut microbiota balance

BACKGROUND

Dysbiosis of gut microbiota is frequent in liver cirrhosis (LC) patients, and splenectomy (SP) has been reported to improve LC. Herein, we report the effects of SP on gut microbiota, especially on Veillonella parvula, a Gram-negative coccus of the gastrointestinal tract, in LC mice, and the underlying mechanism.

METHODS

LC mice models were induced by tail vein injection of concanavalin A (ConA), followed by SP. 16 s rRNA sequencing was conducted to analyze the effects of ConA induction and SP on mouse gut microbiota and the gene expression affected by gut microbiota. LC mice receiving SP were gavaged with Veillonella parvula. Likewise, hepatic stellate cells (HSC) and hepatocytes (HC) were induced with conditioned medium (CM) of Veillonella parvula.

RESULTS

SP alleviated LC in mice by restoring gut barrier function and maintaining gut microbiota balance, with Veillonella as the key genus. The Veillonella parvula gavage on LC mice reversed the ameliorative effect of SP. The CM of Veillonella parvula promoted the activation of HSC and the release of IL-6, IL-1β, and TNF-α. Also, the CM of Veillonella parvula induced HC pyroptosis and the release of ALT and AST. Veillonella parvula represented an imbalance in the gut microbiota, thus enhancing gut-derived endotoxins in the liver with the main target being Tlr4/Nlrp3. Inhibition of Tlr4 blocked Veillonella parvula-induced HC damage, HSC activation, and subsequent LC progression.

CONCLUSION

SP-mediated gut microbiota regulation ameliorates ConA-related LC progression by inhibiting Tlr4/Nlrp3 in the liver.

Astragalus saponins protect against extrahepatic and intrahepatic cholestatic liver fibrosis models by activation of farnesoid X receptor

ETHNOPHARMACOLOGICAL RELEVANCE

Cholestatic Liver Fibrosis (CLF) is a hepatobiliary disease that typically arises as a late-stage complication of cholestasis, which can have multiple underlying causes. There are no satisfactory chemical or biological drugs for CLF. Total Astragalus saponins (TAS) are considered to be the main active constituents of the traditional Chinese herb Astragali Radix (AR), which has the obvious improvement effects for treating CLF. However, the mechanism of anti-CLF effects of TAS is still unclear.

AIM OF THE STUDY

The present study was undertaken to investigate the therapeutic effects of TAS against bile duct ligation (BDL) and 3, 5-diethoxycarbonyl-1,4-dihydroxychollidine (DDC) -induced CLF models and to reveal the potential mechanism to support its clinic use with scientific evidence.

MATERIALS AND METHODS

In this study, BDL-induced CLF rats were treated with TAS (20 mg/kg, 40 mg/kg) and DDC-induced CLF mice were treated with 56 mg/kg TAS. The therapeutic effects of TAS on extrahepatic and intrahepatic CLF models were evaluated by serum biochemical analysis, liver histopathology and hydroxyproline (Hyp). Thirty-nine individual bile acids (BAs) in serum and liver were quantified by using UHPLC-Q-Exactive Orbitrap HRMS. qRT-PCR, Western blot and immunohistochemistry analysis were used to measure the expression of liver fibrosis and ductular reaction markers, inflammatory factors and BAs related metabolic transporters, along with nuclear receptor farnesoid X receptor (FXR).

RESULTS

The serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bilirubin (TBiL), direct bilirubin (DBiL) and contents of liver Hyp were dose-dependently improved after treatment for TAS in BDL and DDC- induced CLF models. And the increased levels of ALT and AST were significantly improved by total extract from Astragali radix (ASE) in BDL model. The liver fibrosis and ductular reaction markers, α-smooth muscle actin (α-SMA) and cytokeratin 19 (CK19), were significantly ameliorated in TAS group. And the liver expression of inflammatory factors: interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin 1β (IL-1β) were significantly decreased after TAS treatment. In addition, TAS significantly ameliorated taurine-conjugated BAs (tau-BAs) levels, particularly α-TMCA, β-TMCA and TCA contents in serum and liver, which correlated with induced expressions of hepatic FXR and BAs secretion transporters. Furthermore, TAS significantly improved short heterodimer partner (SHP), cholesterol 7α-hydroxylase (Cyp7a1), Na+ taurocholate cotransport peptide (NTCP) and bile-salt export pump (BSEP) mRNA and protein expression.

CONCLUSIONS

TAS exerted a hepatoprotective effect against CLF by ameliorating liver injury, inflammation and restoring the altered tau-BAs metabolism to produce a positive regulatory effect on FXR-related receptors and transporters.

Viral Liver Disease and Intestinal Gut–Liver Axis

The intestinal microbiota is closely related to liver diseases via the intestinal barrier and bile secretion to the gut. Impairment of the barrier can translocate microbes or their components to the liver where they can contribute to liver damage and fibrosis. The components of the barrier are discussed in this review along with the other elements of the so-called gut–liver axis. This bidirectional relation has been widely studied in alcoholic and non-alcoholic liver disease. However, the involvement of microbiota in the pathogenesis and treatment of viral liver diseases have not been extensively studied, and controversial data have been published. Therefore, we reviewed data regarding the integrity and function of the intestinal barrier and the changes of the intestinal microbioma that contribute to progression of Hepatitis B (HBV) and Hepatitis C (HCV) infection. Their consequences, such as cirrhosis and hepatic encephalopathy, were also discussed in connection with therapeutic interventions such as the effects of antiviral eradication and the use of probiotics that may influence the outcome of liver disease. Profound alterations of the microbioma with significant reduction in microbial diversity and changes in the abundance of both beneficial and pathogenic bacteria were found.

Review on chronic metabolic diseases surrounding bile acids and gut microbiota: What we have explored so far

Bile acid, the final product of cholesterol breakdown, functions as a complex regulator and signaling factor in human metabolism. Chronic metabolic diseases pose significant medical challenges. Growing research underscores bile acids' capacity to enhance metabolism via diverse pathways, regulating disorders and offering treatment potential. Numerous bile-acid-triggered pathways have become treatment targets. This review outlines bile acid synthesis, its role as a signal in chronic metabolic diseases, and highlights its interaction with gut microbiota in different metabolic conditions. Exploring host-bacteria-bile acid links emerges as a valuable future research direction with clinical implications.

Loss of SLC27A5 Activates Hepatic Stellate Cells and Promotes Liver Fibrosis via Unconjugated Cholic Acid

Although the dysregulation of bile acid (BA) composition has been associated with fibrosis progression, its precise roles in liver fibrosis is poorly understood. This study demonstrates that solute carrier family 27 member 5 (SLC27A5), an enzyme involved in BAs metabolism, is substantially downregulated in the liver tissues of patients with cirrhosis and fibrosis mouse models. The downregulation of SLC27A5 depends on RUNX family transcription factor 2 (RUNX2), which serves as a transcriptional repressor. The findings reveal that experimental SLC27A5 knockout (Slc27a5-/- ) mice display spontaneous liver fibrosis after 24 months. The loss of SLC27A5 aggravates liver fibrosis induced by carbon tetrachloride (CCI4 ) and thioacetamide (TAA). Mechanistically, SLC27A5 deficiency results in the accumulation of unconjugated BA, particularly cholic acid (CA), in the liver. This accumulation leads to the activation of hepatic stellate cells (HSCs) by upregulated expression of early growth response protein 3 (EGR3). The re-expression of hepatic SLC27A5 by an adeno-associated virus or the reduction of CA levels in the liver using A4250, an apical sodium-dependent bile acid transporter (ASBT) inhibitor, ameliorates liver fibrosis in Slc27a5-/- mice. In conclusion, SLC27A5 deficiency in mice drives hepatic fibrosis through CA-induced activation of HSCs, highlighting its significant implications for liver fibrosis treatment.

Gut liver brain axis in diseases: the implications for therapeutic interventions

Gut-liver-brain axis is a three-way highway of information interaction system among the gastrointestinal tract, liver, and nervous systems. In the past few decades, breakthrough progress has been made in the gut liver brain axis, mainly through understanding its formation mechanism and increasing treatment strategies. In this review, we discuss various complex networks including barrier permeability, gut hormones, gut microbial metabolites, vagus nerve, neurotransmitters, immunity, brain toxic metabolites, β-amyloid (Aβ) metabolism, and epigenetic regulation in the gut-liver-brain axis. Some therapies containing antibiotics, probiotics, prebiotics, synbiotics, fecal microbiota transplantation (FMT), polyphenols, low FODMAP diet and nanotechnology application regulate the gut liver brain axis. Besides, some special treatments targeting gut-liver axis include farnesoid X receptor (FXR) agonists, takeda G protein-coupled receptor 5 (TGR5) agonists, glucagon-like peptide-1 (GLP-1) receptor antagonists and fibroblast growth factor 19 (FGF19) analogs. Targeting gut-brain axis embraces cognitive behavioral therapy (CBT), antidepressants and tryptophan metabolism-related therapies. Targeting liver-brain axis contains epigenetic regulation and Aβ metabolism-related therapies. In the future, a better understanding of gut-liver-brain axis interactions will promote the development of novel preventative strategies and the discovery of precise therapeutic targets in multiple diseases.

Impact of elobixibat on liver tumors, microbiome, and bile acid levels in a mouse model of nonalcoholic steatohepatitis

BACKGROUND

Elevated bile acid levels have been associated with liver tumors in fatty liver. Ileal bile acid transporter inhibitors may inhibit bile acid absorption in the distal ileum and increase bile acid levels in the colon, potentially decreasing the serum and hepatic bile acid levels. This study aimed to investigate the impact of these factors on liver tumor.

METHODS

C57BL/6J mice received a one-time intraperitoneal injection of 25-mg/kg diethylnitrosamine. They were fed a choline-deficient high-fat diet for 20 weeks starting from 8 weeks of age, with or without elobixibat (EA Pharma, Tokyo, Japan).

RESULTS

Both groups showed liver fat accumulation and fibrosis, with no significant differences between the two groups. However, mice with elobixibat showed fewer liver tumors. The total serum bile acid levels, including free, tauro-conjugated, glyco-conjugated, and tauro-α/β-muricholic acids in the liver, were noticeably reduced following elobixibat treatment. The proportion of gram-positive bacteria in feces was significantly lower in the group treated with elobixibat (5.4%) than in the group without elobixibat (33.7%).

CONCLUSION

Elobixibat suppressed tumor growth by inhibiting bile acid reabsorption, and decreasing total bile acid and primary bile acid levels in the serum and liver. Additionally, the presence of bile acids in the colon may have led to a significant reduction in the proportion of gram-positive bacteria, potentially resulting in decreased secondary bile acid synthesis.

The regulation of tissue-specific farnesoid X receptor on genes and diseases involved in bile acid homeostasis

Bile acids (BAs) facilitate the absorption of dietary lipids and vitamins and have also been identified as signaling molecules involved in regulating their own metabolism, glucose and lipid metabolism, as well as immunity. Disturbances in BA homeostasis are associated with various enterohepatic and metabolic diseases, such as cholestasis, nonalcoholic steatohepatitis, inflammatory bowel disease, and obesity. As a key regulator, the nuclear orphan receptor farnesoid X receptor (FXR, NR1H4) precisely regulates BA homeostasis by transcriptional regulation of genes involved in BA synthesis, metabolism, and enterohepatic circulation. FXR is widely regarded as the most potential therapeutic target. Obeticholic acid is the only FXR agonist approved to treat patients with primary biliary cholangitis, but its non-specific activation of systemic FXR also causes high-frequency side effects. In recent years, developing tissue-specific FXR-targeting drugs has become a research highlight. This article provides a comprehensive overview of the role of tissue-specific intestine/liver FXR in regulating genes involved in BA homeostasis and briefly discusses tissue-specific FXR as a therapeutic target for treating diseases. These findings provide the basis for the development of tissue-specific FXR modulators for the treatment of enterohepatic and metabolic diseases associated with BA dysfunction.

FXR agonists in NASH treatment

The farnesoid X receptor (FXR), a bile acid (BA)-activated nuclear receptor highly expressed in the liver and intestine, regulates the expression of genes involved in cholesterol and bile acid homeostasis, hepatic gluconeogenesis, lipogenesis, inflammation and fibrosis, in addition to controlling intestinal barrier integrity, preventing bacterial translocation and maintaining gut microbiota eubiosis. Non-alcoholic steatohepatitis (NASH), an advanced stage of non-alcoholic fatty liver disease, is characterized by hepatic steatosis, hepatocyte damage (ballooning) and inflammation, leading to fibrosis, cirrhosis and hepatocellular carcinoma. NASH represents a major unmet medical need, but no pharmacological treatments have yet been approved. The pleiotropic mechanisms involved in NASH development offer a range of therapeutic opportunities and among them FXR activation has emerged as an established pharmacological target. Various FXR agonists with different physicochemical properties, which can be broadly classified as BA derivatives, non-BA-derived steroidal FXR agonists, non-steroidal FXR agonists, and partial FXR agonists, are in advanced clinical development. In this review we will summarize key preclinical and clinical features of the most advanced FXR agonists and critically evaluate their potential in NASH treatment.

Targeting gut-liver axis by dietary lignans ameliorate obesity: evidences and mechanisms

An imbalance between energy consumption and energy expenditure causes obesity. It is characterized by increased adipose accumulation and accompanied by chronic low-grade inflammation. Many studies have suggested that the gut microbiota of the host mediates the relationship between high-fat diet consumption and the development of obesity. Diet and nutrition of the body are heavily influenced by gut microbiota. The alterations in the microbiota in the gut may have effects on the homeostasis of the host's energy levels, systemic inflammation, lipid metabolism, and insulin sensitivity. The liver is an important organ for fat metabolism and gut-liver axis play important role in the fat metabolism. Gut-liver axis is a bidirectional relationship between the gut and its microbiota and the liver. As essential plant components, lignans have been shown to have different biological functions. Accumulating evidences have suggested that lignans may have lipid-lowering properties. Lignans can regulate the level of the gut microbiota and their metabolites in the host, thereby affecting signaling pathways related to fat synthesis and metabolism. These signaling pathways can make a difference in inhibiting fat accumulation, accelerating energy metabolism, affecting appetite, and inhibiting chronic inflammation. It will provide the groundwork for future studies on the lipid-lowering impact of lignans and the creation of functional meals based on those findings.

Gut microbiota disorder induces liver dysfunction in polycystic ovary syndrome rats' model by regulating metabolite rosmarinic acid

AIMS

The present study aims to investigate the impact of the gut microbiota and serum metabolites on the regulation of liver dysfunction in PCOS.

MATERIALS AND METHODS

PCOS rat models were established by treating Sprague Dawley (SD) rats with DHEA (an androgen, 60 mg/kg) and LET (a nonsteroidal aromatase inhibitor, 1 mg/kg) for 90 days. Hematoxylin and eosin staining (H&E), Western blotting, and radioimmunoassay were employed to test ovarian and liver functions. Gut microbiome and serum metabolites were assessed using 16S rRNA amplicon sequencing and non-targeted metabolomics, respectively. The association between gut microbiota and serum metabolites was examined using Spearman analysis. Finally, using HepG2 cells to investigate the function of the serum metabolite rosmarinic acid (RA).

KEY FINDINGS

Both Dehydroepiandrosterone (DHEA) and letrozole (LET) treatments induced a PCOS phenotype and liver dysfunction. However, LET resulted in more severe lipid accumulation and liver cell apoptosis than DHEA. 16S rRNA sequencing and non-targeted metabolomics analysis revealed significant differences in beta diversity and serum metabolite profiles among the three groups. Furthermore, among the significantly changed metabolites, RA was found to have a significant correlation with the levels of serum aspartate transaminase (AST) and lactate dehydrogenase (LDH) and could promote HepG2 cell apoptosis.

SIGNIFICANCE

Restoring gut microbiota, altering serum metabolites and/or decreasing RA may provide a new insight to treat this complication.

The molecular insights of bile acid homeostasis in host diseases

Bile acids (BAs) function as detergents promoting nutrient absorption and as hormones regulating nutrient metabolism. Most BAs are key regulatory factors of physiological activities, which are involved in the regulation of glucose, lipid, and drug metabolisms. Hepatic and intestinal diseases have close connections with the systemic cycling disorders of BAs. The abnormal in BA absorption came up with overmuch BAs could be involved in the pathophysiology of liver and bowel and metabolic disorders such as fatty liver diseases and inflammatory bowel diseases. The primary BAs (PBAs), which are synthesized in the liver, can be transformed into the secondary BAs (SBAs) by gut microbiota. The transformation processes are tightly associated with the gut microbiome and the host endogenous metabolism. The BA biosynthesis gene cluster bile-acid-inducible operon is essential for modulating BA pool, gut microbiome composition, and the onset of intestinal inflammation. This forms a bidirectional interaction between the host and its gut symbiotic ecosystem. The subtle changes in the composition and abundance of BAs perturb the host physiological and metabolic activity. Therefore, maintaining the homeostasis of BAs pool contributes to the balance of the body's physiological and metabolic system. Our review aims to dissect the molecular mechanisms underlying the BAs homeostasis, assess the key factors sustaining the homeostasis and the role of BA acting on host diseases. By linking the BAs metabolic disorders and their associated diseases, we illustrate the effects of BAs homeostasis on health and potential clinical interventions can be taken under the latest research findings.

Long-term benefit of DAAs on gut dysbiosis and microbial translocation in HCV-infected patients with and without HIV coinfection

Long-term effect of Direct-acting antivirals (DAAs) on gut microbiota, short-chain fatty acids (SCFAs) and microbial translocation in patients with hepatitis C virus (HCV) infection who achieve sustained virological response (SVR) were limited. A longitudinal study of 50 patients with HCV monoinfection and 19 patients with HCV/HIV coinfection received DAAs were conducted. Fecal specimens collected at baseline and at week 72 after treatment completion (FUw72) were analyzed for 16S rRNA sequencing and the butyryl-CoA:acetateCoA transferase (BCoAT) gene expression using real-time PCR. Plasma lipopolysaccharide binding protein (LBP) and intestinal fatty acid binding protein (I-FABP) were quantified by ELISA assays. SVR rates in mono- and coinfected patients were comparable (94% vs. 100%). The improvement of gut dysbiosis and microbial translocation was found in responders but was not in non-responders. Among responders, significant restoration of alpha-diversity, BCoAT and LBP were observed in HCV patients with low-grade fibrosis (F0-F1), while HCV/HIV patients exhibited partial improvement at FUw72. I-FABP did not decline significantly in responders. Treatment induced microbiota changes with increasing abundance of SCFAs-producing bacteria, including Blautia, Fusicatenibacter, Subdoligranulum and Bifidobacterium. In conclusion, long-term effect of DAAs impacted the restoration of gut dysbiosis and microbial translocation. However, early initiation of DAAs required for an alteration of gut microbiota, enhanced SCFAs-producing bacteria, and could reduce HCV-related complications.

Non-alcoholic fatty liver disease: pathophysiological concepts and treatment options

The prevalence of non-alcoholic fatty liver disease (NAFLD) is continually increasing due to the global obesity epidemic. NAFLD comprises a systemic metabolic disease accompanied frequently by insulin resistance and hepatic and systemic inflammation. Whereas simple hepatic steatosis is the most common disease manifestation, a more progressive disease course characterized by liver fibrosis and inflammation (i.e. non-alcoholic steatohepatitis) is present in 10-20% of affected individuals. NAFLD furthermore progresses in a substantial number of patients towards liver cirrhosis and hepatocellular carcinoma. Whereas this disease now affects almost 25% of the world's population and is mainly observed in obesity and type 2 diabetes, NAFLD also affects lean individuals. Pathophysiology involves lipotoxicity, hepatic immune disturbances accompanied by hepatic insulin resistance, a gut dysbiosis, and commonly hepatic and systemic insulin resistance defining this disorder a prototypic systemic metabolic disorder. Not surprisingly many affected patients have other disease manifestations, and indeed cardiovascular disease, chronic kidney disease, and extrahepatic malignancies are all contributing substantially to patient outcome. Weight loss and lifestyle change reflect the cornerstone of treatment, and several medical treatment options are currently under investigation. The most promising treatment strategies include glucagon-like peptide 1 receptor antagonists, sodium-glucose transporter 2 inhibitors, Fibroblast Growth Factor analogues, Farnesoid X receptor agonists, and peroxisome proliferator-activated receptor agonists. Here, we review epidemiology, pathophysiology, and therapeutic options for NAFLD.

Bacterial translocation occurs early in cirrhosis and triggers a selective inflammatory response

BACKGROUND

Experimental data suggest that bacterial translocation (BT) promotes systemic inflammation, portal hypertension, and circulatory dysfunction in advanced chronic liver disease (ACLD).

METHODS

Patients with ACLD undergoing hepatic venous pressure gradient (HVPG) measurement and absence of acute decompensation or infections were included (n = 249). Serum biomarkers of BT (lipopolysaccharide [LPS], lipoteichoic acid [LTA], bacterial DNA [bactDNA]), systemic inflammation and markers of circulatory dysfunction were assessed. T-cell subsets in intestinal biopsies (n = 7 ACLD, n = 4 controls) were analyzed by flow cytometry.

RESULTS

Patients had a median HVPG of 18 (12-21) mmHg and 56% had decompensated ACLD. LPS (0.04 [0.02-0.06] vs. 0.64 [0.30-1.06] EU/mL), LTA (4.53 [3.58-5.97] vs. 43.2 [23.2-109] pg/mL), and detection of bactDNA (≥ 5 pg/mL; 5% vs. 41%) were markedly higher in patients with ACLD than healthy controls (n = 40; p < 0.001) but were similar between different clinical stages of compensated and decompensated ACLD and displayed no meaningful correlation with HVPG and systemic hemodynamics. TNF-α and IL-10 correlated with LPS (Spearman's rs = 0.523, p < 0.001/rs = 0.143, p = 0.024) but not with LTA. Presence of bactDNA was associated with higher LPS (0.54 [0.28-0.95] vs. 0.88 [0.32-1.31] EU/mL, p = 0.001) and TNF-α (15.3 [6.31-28.1] vs. 20.9 [13.8-32.9] pg/mL). Patients with ACLD exhibited a decreased CD4:CD8-ratio and increased TH1-cells in the intestinal mucosa as compared to controls. During a median FU of 14.7 (8.20-26.5) months, bacterial antigens did not predict decompensation or liver-related death (in contrast to HVPG, IL-6, and MAP) as well as infections at 24 months.

CONCLUSION

BT occurs already in early ACLD stages and triggers a systemic inflammatory response via TNF-α and IL-10. Interestingly, BT markers showed no clear correlation with portal hypertension and circulatory dysfunction in patients with stable ACLD.

CLINICAL TRIAL NUMBER

NCT03267615.

The Effect of MSTN Mutation on Bile Acid Metabolism and Lipid Metabolism in Cattle

Myostatin (MSTN) is a negative regulator of skeletal muscle genesis during development. MSTN mutation leads to increased lean meat production and reduced fat deposition in livestock. However, the mechanism by which MSTN promotes myogenesis by regulating metabolism is not clear. In this study, we compared the metabolomics of the livers of wild-type (WT) and MSTN mutation cattle (MT), and found changes in the content and proportion of fatty acids and bile acids in MT cattle. The differential metabolites were enriched in sterol synthesis and primary bile acid synthesis. We further analyzed the expression of genes involved in the regulation of lipid and bile acid metabolism, and found that the loss of MSTN may alter lipid synthesis and bile acid metabolism. This study provides new basic data for MSTN mutations in beef cattle breeding.

The regulatory role of bile acid microbiota in the progression of liver cirrhosis

Bile acids (BAs) are synthesized in liver tissue from cholesterol and are an important endocrine regulator and signaling molecule in the liver and intestine. It maintains BAs homeostasis, and the integrity of intestinal barrier function, and regulates enterohepatic circulation in vivo by modulating farnesoid X receptors (FXR) and membrane receptors. Cirrhosis and its associated complications can lead to changes in the composition of intestinal micro-ecosystem, resulting in dysbiosis of the intestinal microbiota. These changes may be related to the altered composition of BAs. The BAs transported to the intestinal cavity through the enterohepatic circulation are hydrolyzed and oxidized by intestinal microorganisms, resulting in changes in their physicochemical properties, which can also lead to dysbiosis of intestinal microbiota and overgrowth of pathogenic bacteria, induction of inflammation, and damage to the intestinal barrier, thus aggravating the progression of cirrhosis. In this paper, we review the discussion of BAs synthesis pathway and signal transduction, the bidirectional regulation of bile acids and intestinal microbiota, and further explore the role of reduced total bile acid concentration and dysregulated intestinal microbiota ratio in the development of cirrhosis, in order to provide a new theoretical basis for the clinical treatment of cirrhosis and its complications.

Metabolic-Associated Fatty Liver Disease and Insulin Resistance: A Review of Complex Interlinks

Metabolic-associated fatty liver disease (MAFLD) has now surpassed alcohol excess as the most common cause of chronic liver disease globally, affecting one in four people. Given its prevalence, MAFLD is an important cause of cirrhosis, even though only a small proportion of patients with MAFLD ultimately progress to cirrhosis. MAFLD suffers as a clinical entity due to its insidious and often asymptomatic onset, lack of an accurate and reliable non-invasive diagnostic test, and lack of a bespoke therapy that has been designed and approved for use specifically in MAFLD. MAFLD sits at a crossroads between the gut and the periphery. The development of MAFLD (including activation of the inflammatory cascade) is influenced by gut-related factors that include the gut microbiota and intactness of the gut mucosal wall. The gut microbiota may interact directly with the liver parenchyma (through translocation via the portal vein), or indirectly through the release of metabolic metabolites that include secondary bile acids, trimethylamine, and short-chain fatty acids (such as propionate and acetate). In turn, the liver mediates the metabolic status of peripheral tissues (including insulin sensitivity) through a complex interplay of hepatokines, liver-secreted metabolites, and liver-derived micro RNAs. As such, the liver plays a key central role in influencing overall metabolic status. In this concise review, we provide an overview of the complex mechanisms whereby MAFLD influences the development of insulin resistance within the periphery, and gut-related factors impact on the development of MAFLD. We also discuss lifestyle strategies for optimising metabolic liver health.

Association between Intestinal Microecological Changes and Atherothrombosis

Atherosclerosis (AS) is a chronic inflammatory disease of large- and medium-sized arteries that causes ischemic heart disease, strokes, and peripheral vascular disease, collectively called cardiovascular disease (CVD), and is the leading cause of CVD resulting in a high rate of mortality in the population. AS is pathological by plaque development, which is caused by lipid infiltration in the vessel wall, endothelial dysfunction, and chronic low-grade inflammation. Recently, more and more scholars have paid attention to the importance of intestinal microecological disorders in the occurrence and development of AS. Intestinal G-bacterial cell wall lipopolysaccharide (LPS) and bacterial metabolites, such as oxidized trimethylamine (TMAO) and short-chain fatty acids (SCFAs), are involved in the development of AS by affecting the inflammatory response, lipid metabolism, and blood pressure regulation of the body. Additionally, intestinal microecology promotes the progression of AS by interfering with the normal bile acid metabolism of the body. In this review, we summarize the research on the correlation between maintaining a dynamic balance of intestinal microecology and AS, which may be potentially helpful for the treatment of AS.

Dysregulated biomarkers of innate and adaptive immunity predict infections and disease progression in cirrhosis

Background & Aims

Cirrhosis-associated immune dysfunction (CAID) affects both innate and adaptive immunity. This study investigated the complement system, immunoglobulins, and acute-phase proteins and their prognostic relevance in patients with advanced chronic liver disease (ACLD).

Methods

Patients with ACLD (hepatic venous pressure gradient [HVPG] ≥6 mmHg) but without acute decompensation/infections were characterised by HVPG and by clinical EASL stages: compensated (cACLD; S0-2) vs. decompensated ACLD (dACLD) with previous variceal bleeding (S3), non-bleeding decompensation (S4), or further decompensation (S5). Complement factors (C3c, C4, CH50), immunoglobulins (IgA, IgM, IgG, IgG1-4), acute-phase proteins and systemic inflammation biomarkers (white blood cells, C-reactive protein, IL-6, procalcitonin) were measured.

Results

A total of 245 patients (median model for end-stage liver disease score: 11 [9-15], median HVPG: 17 [12-21] mmHg) were included with 150 (61%) presenting dACLD. Complement levels and activity significantly decreased in dACLD substages S4 and S5 (p <0.001). Total IgA/IgM/IgG and IgG1-4 subtype levels increased in patients with dACLD (all p <0.05). Complement and immunoglobulin levels correlated negatively and positively, respectively, with systemic inflammation (all p <0.05). High IgG-1 (adjusted hazard ratio per 100 mg/dl: 1.12, 1.04-1.19, p = 0.002) and IL-6 (adjusted hazard ratio: 1.03, 1.00-1.05, p = 0.023) levels predicted the development of infections during follow-up. High IgA (stratified by median; log-rank p <0.001), high IgG1 (log-rank p = 0.043) and low C3c (log-rank p = 0.003) indicated a higher risk of first/further decompensation or liver-related death (composite endpoint). Next to HVPG and IL-6, low C3c (adjusted hazard ratio per mg/dl: 0.99, 0.97-0.99, p = 0.040) remained independently associated with the composite endpoint on multivariate Cox regression analysis.

Conclusions

Complement levels and immunoglobulins may serve as surrogates of cirrhosis-associated immune dysfunction and associate with cirrhosis severity and systemic inflammation. Low complement C3c predicted decompensation and liver-related death, whereas high IgG-1 indicated an increased risk for infections.

Impact and Implications

Patients with cirrhosis are at increased risk for infections, which worsen their prognosis. We found a significant dysregulation of several essential components of the immune system that was linked to disease severity and indicated a risk for infections and other complications. Simple blood tests identify patients at particularly high risk, who may be candidates for preventive measures.

Clinical Trials Registration

This study is registered at ClinicalTrials.gov (NCT03267615).

Gut-liver axis: barriers and functional circuits

The gut and the liver are characterized by mutual interactions between both organs, the microbiome, diet and other environmental factors. The sum of these interactions is conceptualized as the gut-liver axis. In this Review we discuss the gut-liver axis, concentrating on the barriers formed by the enterohepatic tissues to restrict gut-derived microorganisms, microbial stimuli and dietary constituents. In addition, we discuss the establishment of barriers in the gut and liver during development and their cooperative function in the adult host. We detail the interplay between microbial and dietary metabolites, the intestinal epithelium, vascular endothelium, the immune system and the various host soluble factors, and how this interplay establishes a homeostatic balance in the healthy gut and liver. Finally, we highlight how this balance is disrupted in diseases of the gut and liver, outline the existing therapeutics and describe the cutting-edge discoveries that could lead to the development of novel treatment approaches.

Impact of ammonia levels on outcome in clinically stable outpatients with advanced chronic liver disease

Background & Aims

Ammonia levels predicted hospitalisation in a recent landmark study not accounting for portal hypertension and systemic inflammation severity. We investigated (i) the prognostic value of venous ammonia levels (outcome cohort) for liver-related outcomes while accounting for these factors and (ii) its correlation with key disease-driving mechanisms (biomarker cohort).

Methods

(i) The outcome cohort included 549 clinically stable outpatients with evidence of advanced chronic liver disease. (ii) The partly overlapping biomarker cohort comprised 193 individuals, recruited from the prospective Vienna Cirrhosis Study (VICIS: NCT03267615).

Results

(i) In the outcome cohort, ammonia increased across clinical stages as well as hepatic venous pressure gradient and United Network for Organ Sharing model for end-stage liver disease (2016) strata and were independently linked with diabetes. Ammonia was associated with liver-related death, even after multivariable adjustment (adjusted hazard ratio [aHR]: 1.05 [95% CI: 1.00-1.10]; p = 0.044). The recently proposed cut-off (≥1.4 × upper limit of normal) was independently predictive of hepatic decompensation (aHR: 2.08 [95% CI: 1.35-3.22]; p <0.001), non-elective liver-related hospitalisation (aHR: 1.86 [95% CI: 1.17-2.95]; p = 0.008), and - in those with decompensated advanced chronic liver disease - acute-on-chronic liver failure (aHR: 1.71 [95% CI: 1.05-2.80]; p = 0.031). (ii) Besides hepatic venous pressure gradient, venous ammonia was correlated with markers of endothelial dysfunction and liver fibrogenesis/matrix remodelling in the biomarker cohort.

Conclusions

Venous ammonia predicts hepatic decompensation, non-elective liver-related hospitalisation, acute-on-chronic liver failure, and liver-related death, independently of established prognostic indicators including C-reactive protein and hepatic venous pressure gradient. Although venous ammonia is linked with several key disease-driving mechanisms, its prognostic value is not explained by associated hepatic dysfunction, systemic inflammation, or portal hypertension severity, suggesting direct toxicity.

Impact and implications

A recent landmark study linked ammonia levels (a simple blood test) with hospitalisation/death in individuals with clinically stable cirrhosis. Our study extends the prognostic value of venous ammonia to other important liver-related complications. Although venous ammonia is linked with several key disease-driving mechanisms, they do not fully explain its prognostic value. This supports the concept of direct ammonia toxicity and ammonia-lowering drugs as disease-modifying treatment.

Metabolic-Associated Fatty Liver Disease and the Gut Microbiota

As an important sequela of the burgeoning global obesity problem, metabolic-associated fatty liver disease (MAFLD) has gained increasing prominence recently. The gut-liver axis (GLA) provides a direct conduit to the liver for the gut microbiota and their metabolic by-products (including secondary bile acids, ethanol, and trimethylamine). These GLA-related factors, including the host inflammatory response and integrity of the gut mucosal wall, likely contribute to the pathogenesis of MAFLD. Accordingly, these GLA-related factors are targets for possible preventive and treatment strategies for MAFLD, and include probiotics, prebiotics, bile acids, short-chain fatty acids, fecal microbiota transplantation, carbon nanoparticles, and bacteriophages.

Enhancing intestinal barrier efficiency: A novel metabolic diseases therapy

Physiologically, the intestinal barrier plays a crucial role in homeostasis and nutrient absorption and prevents pathogenic entry, harmful metabolites, and endotoxin absorption. Recent advances have highlighted the association between severely damaged intestinal barriers and diabetes, obesity, fatty liver, and cardiovascular diseases. Evidence indicates that an abated intestinal barrier leads to endotoxemia associated with systemic inflammation, insulin resistance, diabetes, and lipid accumulation, accelerating obesity and fatty liver diseases. Nonetheless, the specific mechanism of intestinal barrier damage and the effective improvement of the intestinal barrier remain to be explored. Here, we discuss the crosstalk between changes in the intestinal barrier and metabolic disease. This paper also highlights how to improve the gut barrier from the perspective of natural medicine, gut microbiota remodeling, lifestyle interventions, and bariatric surgery. Finally, potential challenges and prospects for the regulation of the gut barrier-metabolic disease axis are discussed, which may provide theoretical guidance for the treatment of metabolic diseases.

Diosgenin alleviates nonalcoholic steatohepatitis through affecting liver-gut circulation

Nonalcoholic steatohepatitis (NASH), as the aggressive form of nonalcoholic fatty liver disease (NAFLD), rapidly becomes the leading cause of end-stage liver disease or liver transplantation. Nowadays, there has no approved drug for NASH treatment. Diosgenin possesses multiple beneficial effects towards inhibition of lipid accumulation, cholesterol metabolism, fibrotic progression and inflammatory response. However, there has been no report concerning its effects on NASH so far. Using methionine and choline-deficient (MCD) feeding mice, we evaluated the anti-NASH effects of diosgenin. 16 S rDNA was used to investigate gut microbiota composition. Transcriptome sequencing, LC/MS and GC/MS analysis were used to evaluate bile acids (BAs) metabolism and their related pathway. Compared with the MCD group, diosgenin treatment improved the hepatic dysfunction, especially decreased the serum and hepatic TC, TG, ALT, AST and TBA to nearly 50%. Content of BAs, especially CA and TCA, were decreased from 59.30 and 26.00-39.71 and 11.48 ng/mg in liver and from 0.96 and 2.1-0.47 and 1.13 μg/mL in serum, and increased from 7.01 and 11.08-3.278 and 5.11 ng/mg in feces, respectively. Antibiotic and fecal microbiota transplantation (FMT) treatment further confirmed the therapeutic effect of diosgenin on gut microbiota, especially Clostridia (LDA score of 4.94), which regulated BAs metabolism through the hepatic FXR-SHP and intestinal FXR-FGF15 pathways. These data indicate that diosgenin prevents NASH by altering Clostridia and BAs metabolism. Our results shed light on the mechanisms of diosgenin in treating NASH, which pave way for the design of novel clinical therapeutic strategies.

Structural Characterization and Anti-Nonalcoholic Fatty Liver Effect of High-Sulfated Ulva pertusa Polysaccharide

The high-sulfated derivative of Ulva pertusa polysaccharide (HU), with unclear structure, has better anti-hyperlipidmia activity than U pertusa polysaccharide ulvan (U). In this study, we explore the main structure of HU and its therapeutic effect against nonalcoholic fatty liver disease (NAFLD). The main structure of HU was elucidated using FT-IR and NMR (13C, 1H, COSY, HSQC, HMBC). The anti-NAFLD activity of HU was explored using the high-fat diet mouse model to detect indicators of blood lipid and liver function and observe the pathologic changes in epididymal fat and the liver. Results showed that HU had these main structural fragments: →4)-β-D-Glcp(1→4)-α-L-Rhap2,3S(1→; →4)-α-L-Rhap3S(1→4)-β-D-Xylp2,3S(1→; →4)-α-L-Rhap3S(1→4)-β-D-Xylp(1→; →4)-α-L-IdopA3S(1→4)-α-L-Rhap3S(1→; →4)-β-D-GlcpA(1→3)-α-L-Rhap(1→; →4)-α-L-IdopA3S(1→4)-β-D-Glcp3Me(1→; →4)-β-D-Xylp2,3S(1→4)-α-L-IdopA3S(1→; and →4)-β-D-Xylp(1→4)-α-L-IdopA3S(1→. Treatment results indicated that HU markedly decreased levels of TC, LDL-C, TG, and AST. Furthermore, lipid droplets in the liver were reduced, and the abnormal enlargement of epididymal fat cells was suppressed. Thus, HU appears to have a protective effect on the development of NAFLD.

Liver Steatosis and Steatohepatitis Alter Bile Acid Receptors in Brain and Induce Neuroinflammation: A Contribution of Circulating Bile Acids and Blood-Brain Barrier

A tight relationship between gut-liver diseases and brain functions has recently emerged. Bile acid (BA) receptors, bacterial-derived molecules and the blood-brain barrier (BBB) play key roles in this association. This study was aimed to evaluate how non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) impact the BA receptors Farnesoid X receptor (FXR) and Takeda G-protein coupled receptor 5 (TGR5) expression in the brain and to correlate these effects with circulating BAs composition, BBB integrity and neuroinflammation. A mouse model of NAFLD was set up by a high-fat and sugar diet, and NASH was induced with the supplementation of dextran-sulfate-sodium (DSS) in drinking water. FXR, TGR5 and ionized calcium-binding adaptor molecule 1 (Iba-1) expression in the brain was detected by immunohistochemistry, while Zonula occludens (ZO)-1, Occludin and Plasmalemmal Vesicle Associated Protein-1 (PV-1) were analyzed by immunofluorescence. Biochemical analyses investigated serum BA composition, lipopolysaccharide-binding protein (LBP) and S100β protein (S100β) levels. Results showed a down-regulation of FXR in NASH and an up-regulation of TGR5 and Iba-1 in the cortex and hippocampus in both treated groups as compared to the control group. The BA composition was altered in the serum of both treated groups, and LBP and S100β were significantly augmented in NASH. ZO-1 and Occludin were attenuated in the brain capillary endothelial cells of both treated groups versus the control group. We demonstrated that NAFLD and NASH provoke different grades of brain dysfunction, which are characterized by the altered expression of BA receptors, FXR and TGR5, and activation of microglia. These effects are somewhat promoted by a modification of circulating BAs composition and by an increase in LBP that concur to damage BBB, thus favoring neuroinflammation.

Systemic inflammation is linked to liver fibrogenesis in patients with advanced chronic liver disease

BACKGROUND & AIMS

Experimental evidence indicates that systemic inflammation (SI) promotes liver fibrogenesis. This study investigated the potential link between SI and fibrogenesis in patients with advanced chronic liver disease (ACLD).

METHODS

Serum biomarkers of SI (CRP, IL-6, procalcitonin [PCT]) and extracellular matrix (ECM) turnover (i.e., fibrogenesis/fibrolysis) were analysed in 215 prospectively recruited patients with ACLD (hepatic venous pressure gradient [HVPG] ≥6 mm Hg) undergoing hepatic vein catheterization. Patients with non-elective hospitalization or bacterial infection were excluded. Histological alpha-smooth muscle actin (α-SMA) area was quantified on full biopsy scans by automated morphometric quantification in a subset of 34 patients who underwent concomitant transjugular liver biopsy.

RESULTS

Histological α-SMA proportionate area correlated with enhanced liver fibrosis (ELF) score (Spearman's ρ = 0.660, p < .001), markers of collagen formation (PRO-C3, ρ = 0.717, p < .001; PRO-C6, ρ = 0.526, p = .002) and tissue inhibitor of metalloproteinases-1 (TIMP1; ρ = 0.547, p < .001), indicating that these blood biomarkers are capable of reflecting the dynamic process of ECM turnover. CRP, IL-6 and PCT levels correlated with ELF, biomarkers of collagen synthesis/degradation and TIMP1, both in compensated and decompensated patients. Multivariate linear regression models (adjusted for HVPG) confirmed that CRP, IL-6 and PCT were independently linked to markers of liver fibrogenesis and ECM turnover.

CONCLUSION

Systemic inflammation is linked to both liver fibrogenesis and ECM turnover in ACLD and this association is not confounded by the severity of liver disease, as evaluated by HVPG. Our study confirms experimental data on the detrimental impact of SI on ECM deposition and fibrosis progression in a thoroughly characterized cohort of patients with ACLD.

A new perspective on NAFLD: Focusing on the crosstalk between peroxisome proliferator-activated receptor alpha (PPARα) and farnesoid X receptor (FXR)

Nonalcoholic fatty liver disease (NAFLD) is primarily caused by abnormal lipid metabolism and the accumulation of triglycerides in the liver. NAFLD is also associated with hepatic steatosis and nutritional and energy imbalances and is a chronic liver disease associated with a number of factors. Nuclear receptors play a key role in balancing energy and nutrient metabolism, and the peroxisome proliferator-activated receptor alpha (PPARα) and farnesoid X receptor (FXR) regulate lipid metabolism genes, controlling hepatocyte lipid utilization and regulating bile acid (BA) synthesis and transport. They play an important role in lipid metabolism and BA homeostasis. At present, PPARα and FXR are the most promising targets for the treatment of NAFLD among nuclear receptors. This review focuses on the crosstalk mechanisms and transcriptional regulation of PPARα and FXR in the pathogenesis of NAFLD and summarizes PPARα and FXR drugs in clinical trials, laying a theoretical foundation for the targeted treatment of NAFLD and the development of novel therapeutic strategies.

The gut-liver axis in immune remodeling of hepatic cirrhosis

In healthy settings, the gut-liver axis allows host-microbiota communications and mediates immune homeostasis through bidirectional regulation. Meanwhile, in diseases, gut dysbiosis, combined with an impaired intestinal barrier, introduces pathogens and their toxic metabolites into the system, causing massive immune alternations in the liver and other extrahepatic organs. Accumulating evidence suggests that these immune changes are associated with the progression of many liver diseases, especially hepatic cirrhosis. Pathogen-associated molecular patterns that originated from gut microbes directly stimulate hepatocytes and liver immune cells through different pattern recognition receptors, a process further facilitated by damage-associated molecular patterns released from injured hepatocytes. Hepatic stellate cells, along with other immune cells, contribute to this proinflammatory and profibrogenic transformation. Moreover, cirrhosis-associated immune dysfunction, an imbalanced immune status characterized by systemic inflammation and immune deficiency, is linked to gut dysbiosis. Though the systemic inflammation hypothesis starts to link gut dysbiosis to decompensated cirrhosis from a clinical perspective, a clearer demonstration is still needed for the role of the gut-liver-immune axis in cirrhosis progression. This review discusses the different immune states of the gut-liver axis in both healthy and cirrhotic settings and, more importantly, summarizes the current evidence about how microbiota-derived immune remodeling contributes to the progression of hepatic cirrhosis via the gut-liver axis.

Recent advances on FXR-targeting therapeutics

The bile acid receptor FXR has emerged as a bona fide drug target for chronic cholestatic and metabolic liver diseases, ahead of all non-alcoholic fatty liver disease (NAFLD). FXR is highly expressed in the liver and intestine and activation at both sites differentially contributes to its desired metabolic effects. Unrestricted FXR activation, however, also comes along with undesired effects such as a pro-atherogenic lipid profile, pruritus and hepatocellular toxicity under certain conditions. Several pre-clinical studies have confirmed the potency of FXR activation for cholestatic and metabolic liver diseases, but overall it remains still open whether selective activation of intestinal FXR is advantageous over pan-FXR activation and whether restricted or modulated FXR activation can limit some of the side effects. Even more, FXR antagonist also bear the potential as intestinal-selective drugs in NAFLD models. In this review we will discuss the molecular prerequisites for FXR activation, pan-FXR activation and intestinal FXR in/activation from a therapeutic point of view, different steroidal and non-steroidal FXR agonists, ways to restrict FXR activation and finally what we have learned from pre-clinical models and clinical trials with different FXR therapeutics.

Forsythiaside A alleviated carbon tetrachloride-induced liver fibrosis by modulating gut microbiota composition to increase short-chain fatty acids and restoring bile acids metabolism disorder

Liver fibrosis is a chronic and progressive disease with complex pathogenesis related to bile acids (BAs) and gut microbiota. Forsythiaside A (FTA), isolated from the traditional Chinese medicine Forsythiae Fructus (Lian Qiao), is a natural hepatoprotective agent. The purpose of this study was to investigate the protective effect of FTA on carbon tetrachloride (CCl₄)-induced liver fibrosis in mice. Liver fibrosis was induced in mice by intraperitoneal injection of 2 mL/kg CCl₄ three times a week for 4 weeks. FTA attenuated CCl₄-induced liver fibrosis in mice, which was proved by the results of Masson and Sirius red staining, liver hydroxyproline, hyaluronic acid, laminin, type III procollagen, and type IV collagen assays. FTA inhibited hepatic stellate cell activation, and reduced hepatic inflammation and oxidative stress in mice treated with CCl₄. What's more, FTA ameliorated CCl₄-induced gut dysbiosis, maintained intestinal barrier function, increased the production of short-chain fatty acids (SCFAs), and improved endotoxemia, as manifested by decreased serum lipopolysaccharide levels and increased expression of ileal tight junction proteins. Besides, FTA can modulate the genes related to bile acid metabolism to alter the distribution of fecal BAs in fibrotic mice. In a word, FTA can improve liver fibrosis by inhibiting inflammation and oxidative stress, regulating gut microbiota and BA metabolism, and increasing the content of SCFAs. The results of this study provided an important reference for the study on the mechanisms by which natural products prevent liver fibrosis.

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.