Role of bile acids in inflammatory liver diseases

Bile acid profiles and mRNA abundance of bile acid-related genes in adipose tissue of dairy cows with high versus normal body condition

Besides their lipid-digestive role, bile acids (BA) influence overall energy homeostasis, such as glucose and lipid metabolism. We hypothesized that BA along with their receptors, regulatory enzymes, and transporters are present in subcutaneous adipose tissue (scAT). In addition, we hypothesized that their mRNA abundance varies with the body condition of dairy cows around calving. Therefore, we analyzed BA in serum and scAT as well as the mRNA abundance of BA -related enzymes, transporters, and receptors in scAT during the transition period in cows with different body conditions around calving. In a previously established animal model, 38 German Holstein cows were divided into either a high (HBCS; n = 19) or normal BCS (NBCS; n = 19) group based on their body condition score (BCS) and back fat thickness (BFT). Cows were fed different diets to achieve the targeted differences in BCS and BFT (NBCS: BCS <3.5, BFT <1.2 cm; HBCS: BCS >3.75, BFT >1.4 cm) until dry-off at 7 wk ante partum. During the dry period and subsequent lactation, both groups were fed the same diets regarding their demands. Using a targeted metabolomics approach via LC-ESI-MS /MS, BA were analyzed in serum and scAT at wk -7, 1, 3, and 12 relative to parturition. In serum, 15 BA (cholic acid (CA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), taurocholic acid (TCA), glycochenodeoxycholic acid (GCDCA), taurochenodeoxycholic acid (TCDCA), deoxycholic acid (DCA), lithocholic acid (LCA), glycodeoxycholic acid (GDCA), glycolithocholic acid (GLCA), taurodeoxycholic acid (TDCA), taurolithocholic acid (TLCA), β-muricholic acid (MCA(b)), tauromuricholic acid (sum of α and β) (TMCA (a+b)), glycoursodeoxycholic acid (GUDCA)) were observed, whereas in scAT 7 BA (CA, GCA, TCA, GCDCA, TCDCA, GDCA, TDCA) were detected. In serum and scAT samples, the primary BA CA and its conjugate GCA were predominantly detected. Increasing serum concentrations of CA, CDCA, TCA, GCA, GCDCA, DCA, and MCA(b) with the onset of lactation might be related to the increasing DMI after parturition. Furthermore, serum concentrations of CA, CDCA, GCA, DCA, GCDCA, TCA, LCA, and GDCA were lower in HBCS cows compared with NBCS cows, concomitant with increased lipolysis in HBCS cows. The correlation between CA in serum and scAT may point to the transport of CA across cell membranes. Overall, the findings of the present study suggest a potential role of BA in lipid metabolism depending on the body condition of periparturient dairy cows.

Collaborative Metabolism: Gut Microbes Play a Key Role in Canine and Feline Bile Acid Metabolism

Bile acids, produced by the liver and secreted into the gastrointestinal tract, are dynamic molecules capable of impacting the overall health of dogs and cats in many contexts. Importantly, the gut microbiota metabolizes host primary bile acids into chemically distinct secondary bile acids. This review explores the emergence of new literature connecting microbial-derived bile acid metabolism to canine and feline health and disease. Moreover, this review highlights multi-omic methodologies for translational research as an area for continued growth in veterinary medicine aimed at accelerating microbiome science and medicine as it pertains to bile acid metabolism in dogs and cats.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

A study integrated metabolomics and network pharmacology to investigate the effects of Shicao in alleviating acute liver injury

ETHNOPHARMACOLOGICAL RELEVANCE

Shicao is the aerial part of Achillea alpina L., a common herb found mainly in Europe, Asia, and North America. Traditional Chinese medicine has a history of thousands of years and is widely used to treat various diseases.

AIM OF STUDY

To explore the hepatoprotective effects of Shicao on CCl4-induced acute liver injury.

METHODS

A rat model of acute liver injury was established and liver function indices were assessed to evaluate the protective effect of Shicao on the liver. Untargeted metabolomics of the serum and liver tissues was conducted using UPLC-Q-TOF/MS to identify differential metabolites related to acute liver injury. A network of metabolite-reaction-enzyme-gene constituents was constructed using network pharmacology. Hub targets and key components of the effect of Shicao on acute liver injury were screened from the network.

RESULTS

Compared to the model group, Shicao improved the degree of liver damage through the assessment of the liver index, ALT and AST levels, and hepatic pathology slices, demonstrating its hepatoprotective effect against acute liver injury in rats. 10 and 38 differential metabolites involved in acute liver injury were identified in serum and liver tissues, respectively. Most of these were regulated or restored following treatment with Shicao, which mainly consisted of bile acids, lipids, and nucleotides such as taurocholic acid, LysoPC (17:0), and adenosine diphosphate ribose. Through the network of metabolite-reaction-enzyme-gene-constituents, 10 key components and 5 hub genes, along with 7 crucial differential metabolites, were mainly involved in glycerophospholipid metabolism, purine metabolism, biosynthesis of unsaturated fatty acids, and primary bile acid biosynthesis, which may play important roles in the prevention of acute liver injury by Shicao.

CONCLUSION

This study revealed that Shicao had protective effects against CCl4-induced liver injury in rats. It was speculated that the ingredients of Shicao might be closely related to the hub targets, thereby regulating the levels of key metabolites, affecting inflammatory response and oxidative stress and attenuate the liver injury consequently. This study provides a basis for further investigation of its therapeutic potential and the mechanism of action.

Intestinal microbiota promoted NiONPs-induced liver fibrosis via effecting serum metabolism

Nickel oxide nanoparticles (NiONPs) are toxic heavy metal compounds that induce liver fibrosis and metabolic disorders. Current research shows that the intestinal microbiota regulates liver metabolism through the gut-liver axis. However, it is unclear whether NiONPs affect the intestinal microbiota and the relationship between microbiota and liver metabolic disorders. Therefore, in this study, we established liver fibrosis model by administering 0.015, 0.06 and 0.24 mg/mL NiONPs through tracheal instillation twice a week for 9 weeks in rats, then we collected serum and fecal sample for whole metabolomics and metagenomic sequencing. As the result of sequencing, we screened out seven metabolites (beta-D-glucuronide, methylmalonic acid, linoleic acid, phosphotidylcholine, lysophosphatidylinositol, docosapentaenoic acid and progesterone) that related to functional alterations (p < 0.05), and obtained a decrease of probiotics abundances (p < 0.05) as well as a variation of the microbiota enzyme activity (p < 0.05), indicating that NiONPs inhibited the proliferation of probiotics. As the result of correlation analysis, we found a positive correlation between differential metabolites and probiotics, such as lysophosphatidylinositol was positively correlated with Desulfuribacillus, Jeotgallibacillus and Rummeliibacillus (p < 0.05). We also found that differential metabolites had correlations with differential proteins and enzymes of intestinal microbiota, such as glucarate dehydratase, dihydroorotate dehydrogenase and acetyl-CoA carboxylase (p < 0.05). Finally, we screened six metabolic pathways with both differential intestinal microbiota enzymes and metabolites were involved, such as pentose and glucuronate interconversions, and linoleic acid metabolism. In vitro experiments showed that NiONPs increased the transcriptional expression of Col1A1 in LX-2 cells, while reducing the mRNA expression of serine/threonine activators, acetyl coenzyme carboxylase, and lysophosphatidylinositol synthase, and short chain fatty acid sodium butyrate can alleviate these variation trends. The results proved that the intestinal microbiota enzyme systems were associated with serum metabolites, suggesting that the disturbance of intestinal microbiota and reduction of probiotics promoted the occurrence and development of NiONPs-induced liver fibrosis by affecting metabolic pathways.

Gut microbiota and liver metabolomics reveal the potential mechanism of Lactobacillus rhamnosus GG modulating the liver toxicity caused by polystyrene microplastics in mice

Microplastics (MPs) are known to cause liver toxicity as they can spread through the food chain. Most researches on their toxicity have focused on individual organs, neglecting the crucial "gut-liver axis"-a bidirectional communication pathway between the gut and liver. Probiotics have shown promise in modulating the effects of environmental pollutants. In this study, we exposed mice to Lactobacillus rhamnosus GG (LGG, 100 mg/kg b.w./d) and/or polystyrene microplastics (PS-MPs, 5 mg/kg b.w./d) for 28 d via gavage to investigate how probiotics influence live toxicity through the gut-liver axis. Our results demonstrated that PS-MPs induced liver inflammation (increased IL-6 and TNF-α) and disrupted lipid metabolism. However, when combined with LGG, these effects were alleviated. LGG also improved colon health, rectifying ciliary defects and abnormal mucus secretion caused by PS-MPs. Furthermore, LGG improved gut microbiota dysbiosis induced by PS-MPs. Metabolomics and gene expression analysis (Cyp7a1 and Cyp7b1) indicated that LGG modulated bile acid metabolism. In summary, LGG appears to protect the liver by maintaining gut homeostasis, enhancing gut barrier integrity, and reducing the liver inflammation. These findings confirm the potential of LGG to modulate liver toxicity caused by PS-MPs through the gut-liver axis, offering insights into probiotics' application for environmental pollutant detoxification.

Mechanisms and Therapeutic Strategies for MAFLD Targeting TLR4 Signaling Pathways

BACKGROUND

Metabolic-associated fatty liver disease (MAFLD) is one of the most common chronic liver diseases. The underlying pathophysiological mechanisms are intricate and involve various factors. Unfortunately, there is currently a lack of available effective treatment options. Toll-like receptors (TLRs) are a group of pattern-recognition receptors that are responsible for activating the innate immune system. Research has demonstrated that TLR4 plays a pivotal role in the progression of MAFLD by facilitating the pathophysiological mechanisms.

SUMMARY

Lipid peroxidation, pro-inflammatory factors, insulin resistance (IR), and dysbiosis of intestinal microbiota are considered as the pathogenic mechanisms of MAFLD. This review summarizes the impact of TLR4 signaling pathways on the progression of MAFLD, specifically in relation to lipid metabolic disorders, IR, oxidative stress, and gut microbiota disorders. Additionally, we emphasize the potential therapeutic approaches for MAFLD that target TLR4 signaling pathways, including the use of plant extracts, traditional Chinese medicines, probiotics, pharmaceuticals such as peroxisome proliferator-activated receptor antagonists and farnesol X agonists, and lifestyle modifications such as dietary changes and exercise also considered. Furthermore, TLR4 signaling pathways have also been linked to the lean MAFLD.

KEY MESSAGES

TLR4 plays a crucial role in MAFLD by triggering IR, buildup of lipids, imbalance in gut microbiota, oxidative stress, and initiation of immune responses. The mitigation of MAFLD can be accomplished by suppressing the TLR4 signaling pathway. In the future, it could potentially emerge as a therapeutic target for the condition.

Combining a microphysiological system of three organ equivalents and transcriptomics to assess toxicological endpoints for cosmetic ingredients

Animal testing for cosmetic ingredients and final products has been banned in Europe and is gaining legal force worldwide. However, the need for reliable testing methodologies remains for safety assessment of cosmetic ingredients. While new approach methodologies exist for many toxicological endpoints, some complex ones lack appropriate testing methods. Microphysiological systems (MPSs) have emerged as a promising tool to address this gap in pre-clinical testing, offering higher predictivity compared to animal models due to the phylogenetic distance between humans and animals. Moreover, they provide a more physiological approach than traditional in vitro testing by mimicking interconnections between different culture compartments as seen in complex organisms. This study presents a three-organ microfluidic MPS comprising skin, liver, and intestine equivalents. Combining this model with gene expression analysis, we evaluated toxicological endpoints of chemicals, demonstrating its potential for diverse applications. Our findings highlight the MPS model as a reliable and ethical method to be applied in an integrated approach for safety assessment in the cosmetic industry. It offers a promising strategy to evaluate toxicological endpoints for cosmetic ingredients and other chemicals, supporting the elimination of animal testing while ensuring consumer safety.

The contributions of bacteria metabolites to the development of hepatic encephalopathy

Over 20% of mortality during acute liver failure is associated with the development of hepatic encephalopathy (HE). Thus, HE is a complication of acute liver failure with a broad spectrum of neuropsychiatric abnormalities ranging from subclinical alterations to coma. HE is caused by the diversion of portal blood into systemic circulation through portosystemic collateral vessels. Thus, the brain is exposed to intestinal-derived toxic substances. Moreover, the strategies to prevent advancement and improve the prognosis of such a liver-brain disease rely on intestinal microbial modulation. This is supported by the findings that antibiotics such as rifaximin and laxative lactulose can alleviate hepatic cirrhosis and/or prevent HE. Together, the significance of the gut-liver-brain axis in human health warrants attention. This review paper focuses on the roles of bacteria metabolites, mainly ammonia and bile acids (BAs) as well as BA receptors in HE. The literature search conducted for this review included searches for phrases such as BA receptors, BAs, ammonia, farnesoid X receptor (FXR), G protein-coupled bile acid receptor 1 (GPBAR1 or TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and cirrhosis in conjunction with the phrase hepatic encephalopathy and portosystemic encephalopathy. PubMed, as well as Google Scholar, was the search engines used to find relevant publications.

Bile Acids in Autoimmune Liver Disease: Unveiling the Nexus of Inflammation, Inflammatory Cells, and Treatment Strategies

As bile acids not solely play an essential role in nutrition absorption, but also in regulating metabolic functions as well as immune response, bile acids and their signaling pathways are increasingly acknowledged as potential therapeutic targets in the context of chronic liver diseases. Bile acid receptors such as G protein bile acid-activated receptor 1 and farnesoid X receptor are expressed in different immune cells engaged in innate immunity. Recently, a series of studies have revealed distinct functions of bile acids and bile acid receptors within the adaptive immune system. In addition, a variety of molecules targeting bile acid receptors and transporters are currently in advanced stages of clinical development. Autoimmune liver diseases including conditions like primary biliary cholangitis, primary sclerosing cholangitis, and autoimmune hepatitis can lead to chronic inflammation, fibrosis, and even cirrhosis and liver failure. In this review, we focus on the role of bile acids in the inflammatory aspects of autoimmune liver diseases.

Metabolomic profiles of obesity and subgingival microbiome in periodontally healthy individuals: A cross-sectional study

AIM

Since blood metabolomic profiles of obese individuals are known to be altered, our objective was to examine the association between obesity-related metabolic patterns and subgingival microbial compositions in obese and non-obese periodontally healthy individuals.

MATERIALS AND METHODS

Thirty-nine periodontally healthy subjects were enrolled. Based on body mass index scores, 20 subjects were categorized as lean and 19 as obese. A comprehensive periodontal examination was performed. Subgingival plaque and blood samples were collected. Plaque samples were analysed for bacteria using 16S rDNA sequencing. Untargeted metabolomic profiling (mass spectrometry) was used to quantify metabolites in serum.

RESULTS

Obese subjects were statistically associated with several periodontopathic taxa including Dialister invisus, Prevotella intermedia, Prevotella denticola, Fusobacterium nucleatum_subsp.vincentii, Mogibacterium diversum, Parvimonas micra and Shuttleworthia satelles. In obese individuals, an amino acid-related metabolic pattern was elevated; however, there was a decrease in metabolic patterns related to lipids and cofactor/vitamins. These metabolic perturbations were associated with multiple subgingival bacterial species that differentiated lean from obese individuals.

CONCLUSIONS

Obesity-related perturbations in circulating blood metabolites are associated with the development of periodontopathic bacterial colonization in the subgingival microbiome and consequently may increase the risk for periodontal disease in obese individuals.

Effects of dietary bile acids levels on growth performance, anti-oxidative capacity, immunity and intestinal microbiota of abalone Haliotis discus hannai

Abalone Haliotis discus hannai (initial weight: 38.79 ± 0.70 g) was used as the experimental animal in a 105-day feeding trial to investigate the influence of dietary bile acids levels on the growth, anti-oxidation, immune response and intestinal microbiota. Six isonitrogenous and isolipidic diets were prepared by adding 0 (control group), 15, 30, 60, 120 and 240 mg/kg of bile acids, respectively (named BA0, BA15, BA30, BA60, BA120 and BA240, respectively). It was found that survival of abalone between groups had no significant difference (P > 0.05). Compared to the control, significant improvements in weight gain rate (WGR) were observed in the groups of BA30 and BA60 (P < 0.05). Based on WGR, the broken line regression model analysis showed that the optimum demand for dietary bile acids for abalone was 35.47 mg/kg. Dietary bile acids increased the total anti-oxidative capacity and activities of catalase, superoxide dismutase, lysozyme and alkaline phosphatase, meanwhile decreased the content of malondialdehyde, alanine aminotransferase and aspartate aminotransferase activities in the cell-free hemolymph (P < 0.05). When bile acids were added to the diets, mRNA levels of genes related to pro-inflammatory factors and apoptosis in the digestive gland were down-regulated (P < 0.05). In contrast, the expression of genes related to anti-oxidation was significantly up-regulated (P < 0.05). The Firmicutes, Actinobacteriota and Proteobacteria were the most abundant phyla in intestine. And dietary bile acids significantly decreased the abundance of Actinobacteria and increased the abundance of Firmicutes (P < 0.05). In conclusion, supplementation of dietary bile acids within 120 mg/kg significantly increased the growth of abalone. The 34.62 mg/kg of dietary bile acids significantly increased the anti-oxidative capacity of abalone. Appropriate levels of dietary bile acids (34.62-61.75 mg/kg) promote the immunity of abalone. Application of appropriate levels of bile acids in diets (34.62 mg/kg) changed the intestinal microbiota and promoted the intestinal health of abalone.

Emerging Therapeutic Strategies in The Fight Against Primary Biliary Cholangitis

The liver has a vital role in many metabolic and regulatory processes in the body. Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is a chronic cholestatic autoimmune disease of the intrahepatic bile ducts associated with loss of tolerance to mitochondrial antigens. At this time there is no definitive cure for PBC; however, ursodeoxycholic acid (UDCA) has been shown to reduce injury when administered as the first line of treatment. Additional therapeutics can be given concurrently or as an alternative to UDCA to manage the symptoms and further curb disease progression. Currently, a liver transplant is the only potentially curative option when the patient has developed end-stage liver disease or intractable pruritus. This review aims to delineate the pathogenesis of primary biliary cholangitis and shed light on current therapeutic strategies in the treatment of PBC.

The Mechanism of Antimicrobial Activity of Conjugated Bile Acids against Lactic Acid Bacilli

The mechanism underlying antimicrobial activity of conjugated bile acids against strains of lactic acid bacilli is not well understood. The purpose of this study was to investigate two typical conjugated bile acids (glycochenodeoxycholic acid and taurochenodeoxycholic acid) for their mechanisms of antimicrobial activity against four strains of different species of lactic acid bacilli at the physiological pH of the small intestine of humans. The bacterial cell membrane integrity, transmembrane potential, and transmembrane pH gradient were examined using the fluorescence probes SYTO 9 plus propidium iodide, 3,3'-dipropylthiadicarbocyanine iodide, and 5(6)-carboxyfluorescein diacetate N-succinimidyl ester, respectively. The intracellular ATP levels were measured by the firefly luciferase-based bioluminescence method. It was found that the antimicrobial activity of conjugated bile acids against the strains of lactic acid bacilli is strain-specific, and glycochenodeoxycholic acid showed significantly greater antimicrobial activity than taurochenodeoxycholic acid against the strains of lactic acid bacilli. The conjugated bile acids inhibited the growth of strains of lactic acid bacilli by disrupting membrane integrity, dissipating transmembrane potential, reducing the transmembrane pH gradient, and depleting intracellular ATP. In conclusion, the antimicrobial activity of conjugated bile acids against lactic acid bacilli is a multifactorial phenomenon. This study will provide valuable information for developing strategies to improve the ability of lactic acid bacilli to tolerate bile in vivo.

Probiotics, prebiotics, and synbiotics in nonalcoholic fatty liver disease and alcohol-associated liver disease

The use of probiotics, prebiotics, and synbiotics has become an important therapy in numerous gastrointestinal diseases in recent years. Modifying the gut microbiota, this therapeutic approach helps to restore a healthy microbiome. Nonalcoholic fatty liver disease and alcohol-associated liver disease are among the leading causes of chronic liver disease worldwide. A disrupted intestinal barrier, microbial translocation, and an altered gut microbiome metabolism, or metabolome, are crucial in the pathogenesis of these chronic liver diseases. As pro-, pre-, and synbiotics modulate these targets, they were identified as possible new treatment options for liver disease. In this review, we highlight the current findings on clinical and mechanistic effects of this therapeutic approach in nonalcoholic fatty liver disease and alcohol-associated liver disease.

Effects of flaxseed powder in improving non-alcoholic fatty liver by regulating gut microbiota-bile acids metabolic pathway through FXR/TGR5 mediating

Non-alcoholic fatty liver disease (NAFLD) is gradually becoming one of the most common and health-endangering diseases. Flaxseed powder (FLA) is rich in α-linolenic acid, dietary fiber, lignans, and other active ingredients, which have lipid-lowering and anti-inflammatory effects. Here, we investigated whether the FLA improves host metabolism by gut bacteria modulation and further bile acid modulation in mice fed a high-fat diet. At the end of the experiment, we found that FLA can significantly reduce the body weight, body fat content, and serum TG, LDL-C, and TNF-α levels of mice, and improve liver steatosis. FLA intervention has a significant effect on preventing and regulating the gut flora disturbance caused by HFD. FLA intervention affects bile acid metabolism in the intestine and causes significant changes in functional bile acids, which can play a lipid-lowering and anti-inflammatory role by activating the intestinal Fxr- Fgfr4-Cyp7a1 and Tgr5-Tlr4-Tnfα pathways.

The secondary bile acid isoursodeoxycholate correlates with post-prandial lipemia, inflammation, and appetite and changes post-bariatric surgery

Primary and secondary bile acids (BAs) influence metabolism and inflammation, and the gut microbiome modulates levels of BAs. We systematically explore the host genetic, gut microbial, and habitual dietary contribution to a panel of 19 serum and 15 stool BAs in two population-based cohorts (TwinsUK, n = 2,382; ZOE PREDICT-1, n = 327) and assess changes post-bariatric surgery and after nutritional interventions. We report that BAs have a moderately heritable genetic component, and the gut microbiome accurately predicts their levels in serum and stool. The secondary BA isoursodeoxycholate (isoUDCA) can be explained mostly by gut microbes (area under the receiver operating characteristic curve [AUC] = ∼80%) and associates with post-prandial lipemia and inflammation (GlycA). Furthermore, circulating isoUDCA decreases significantly 1 year after bariatric surgery (β = -0.72, p = 1 × 10-5) and in response to fiber supplementation (β = -0.37, p < 0.03) but not omega-3 supplementation. In healthy individuals, isoUDCA fasting levels correlate with pre-meal appetite (p < 1 × 10-4). Our findings indicate an important role for isoUDCA in lipid metabolism, appetite, and, potentially, cardiometabolic risk.

An integrated view of anti-inflammatory and antifibrotic targets for the treatment of NASH

Successful development of treatments for non-alcoholic fatty liver disease (NAFLD) and its progressive form, non-alcoholic steatohepatitis (NASH) has been challenging. Because NASH and fibrosis lead to NAFLD progression towards cirrhosis and to clinical outcomes, approaches have either sought to attenuate metabolic dysregulation and cell injury, or directly target the inflammation and fibrosis that ensue. Targets for reducing the activation of inflammatory cascades include nuclear receptor agonists (thyroid hormone receptor-beta, e.g. resmetirom, peroxisome proliferator-activated receptor [PPAR], e.g. lanifibranor, farnesoid X receptor [FXR], e.g. obeticholic acid), modulators of lipotoxicity (e.g. aramchol, acetyl-CoA carboxylase inhibitors) or modification of genetic variants (e.g. PNPLA3 gene silencing). Extrahepatic inflammatory signals from circulation, adipose tissue or gut are targets of hormonal agonists (e.g. glucagon-like peptide-1 [GLP-1] like semaglutide, fibroblast growth factor [FGF]-19 or FGF21), microbiota or lifestyle (weight loss, diet, exercise) interventions. Stress signals and hepatocyte death activate immune responses engaging innate (macrophages, lymphocytes) and adaptive (auto-aggressive T-cells) mechanisms. Therapies seek to blunt immune cell activation, recruitment (chemokine receptor inhibitors) and responses (e.g. galectin 3 inhibition, anti-platelet drugs). The disease-driving pathways of NASH converge to elicit fibrosis, which is reversible. The activation of hepatic stellate cells (HSC) into matrix-producing myofibroblasts can be inhibited by antagonizing soluble factors (e.g. integrins, cytokines), cellular crosstalk (e.g. with macrophages), and agonizing nuclear receptor signaling (e.g. FXR or PPAR agonists). In advanced fibrosis, cell therapy with restorative macrophages or reprogrammed T-cells (e.g., CAR T) may accelerate repair through HSC deactivation or killing, or by enhancing matrix degradation. Heterogeneity of disease - either due to genetics or divergent disease drivers - is an obstacle to defining effective drugs for all patients with NASH that will be incrementally overcome.

The impact of subchronic ozone exposure on serum metabolome and the mechanisms of abnormal bile acid and arachidonic acid metabolisms in the liver

Ambient ozone (O₃) pollution can induce respiratory and cardiovascular toxicity. However, its impact on the metabolome and the underlying mechanisms remain unclear. This study first investigated the serum metabolite changes in rats exposed to 0.5 ppm O₃ for 3 months using untargeted metabolomic approach. Results showed chronic ozone exposure significantly altered the serum levels of 34 metabolites with potential increased risk of digestive, respiratory and cardiovascular disease. Moreover, bile acid synthesis and secretion, and arachidonic acid (AA) metabolism became the most prominent affected metabolic pathways after O₃ exposure. Further studies on the mechanisms found that the elevated serum toxic bile acid was not due to the increased biosynthesis in the liver, but the reduced reuptake from the portal vein to hepatocytes owing to repressed Ntcp and Oatp1a1, and the decreased bile acid efflux in hepatocytes as a results of inhibited Bsep, Ostalpha and Ostbeta. Meanwhile, decreased expressions of detoxification enzyme of SULT2A1 and the important regulators of FXR, PXR and HNF4α also contributed to the abnormal bile acids. In addition, O₃ promoted the conversion of AA into thromboxane A2 (TXA2) and 20-hydroxyarachidonic acid (20-HETE) in the liver by up-regulation of Fads2, Cyp4a and Tbxas1 which resulting in decreased AA and linoleic acid (LA), and increased thromboxane B2 (TXB2) and 20-HETE in the serum. Furthermore, apparent hepatic chronic inflammation, fibrosis and abnormal function were found in ozone-exposed rats. These results indicated chronic ozone exposure could alter serum metabolites by interfering their metabolism in the liver, and inducing liver injury to aggravate metabolic disorders.

Uncovering the protective mechanism of Pien-Tze-Huang in rat with alcoholic liver injury based on cytokines analysis and untargeted metabonomics

Pien-Tze-Huang (PTH) is a well-known traditional Chinese patent medicine with excellent liver-protection effect. However, the mechanism of hepatoprotective action has not yet been entirely elucidated. The aim of this study was to investigate the mechanism of protective effect of PTH on alcohol-induced liver injury in rats using cytokine analysis and untargeted metabolomics approaches. An alcoholic liver disease (ALD) model with SD rats was established, and PTH was administered according to the prescribed dose. The hepatoprotective effect of PTH was evaluated by pathological observation of liver tissue and changes in biochemical index activity and cytokines in serum. Serum samples were analyzed by ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS), and differentially expressed metabolites were screened by multivariate statistical analysis. KEGG combined with metabolic pathway analysis were used to evaluate the underlying metabolic pathways. Results showed liver histopathology injury was attenuated. The levels of IL-6, TNF-α and NF-κB were significantly decreased in rats intervened with PTH groups, suggesting that it may alleviate inflammation via suppressing the inflammatory cytokines signaling pathway. Eighty differentially expressed metabolites were found and identified. Pathway analysis indicated that the hepatoprotective effects of PTH occurred through the regulation of inflammatory cytokines signaling pathway, primary bile acid biosynthesis, vitamin B6 metabolism pathway, cholesterol metabolism, and tyrosine metabolism. PTH showed favorable hepatoprotective effect through multiple pathways. This study has great importance in fully revealing the mechanism of hepatoprotective action and can help improve the clinical application of PTH.

Improvement of obesity-induced fatty liver disease by intermittent hypoxia exposure in a murine model

Background: The high prevalence of non-alcoholic fatty liver disease (NAFLD) in the world raises an important concern for human health. The western diet containing high fat and fructose is the risk factor for NAFLD development. Intermittent hypoxia (IH), known as the basis of obstructive sleep apnea (OSA), normally is correlated with impaired liver function. However, the role of IH in liver injury prevention has been revealed by many other studies based on the different IH paradigms. The current study, therefore, tests the impact of IH on the liver of high-fat and high-fructose diet (HFHFD) fed mice. Material and Method: Mice were exposed to IH (2 min cycle, FiO₂ 8% for 20 s, FiO₂ 20.9% for 100 s; 12 h/day) or intermittent air (FiO₂ 20.9%) for 15 weeks, with normal diet (ND) or high-fat and high-fructose diet (HFHFD). Indices of liver injury and metabolism were measured. Results: IH causes no overt liver injury in mice fed an ND. However, HFHFD-induced lipid accumulation, lipid peroxidation, neutrophil infiltration, and apoptotic process were significantly attenuated by IH exposure. Importantly, IH exposure altered bile acids composition and shifted the hepatic bile acids towards FXR agonism, which was involved in the protection of IH against HFHFD. Conclusion: These results support that the IH pattern in our model prevents liver injury from HFHFD in experimental NAFLD.

Bile Acids in Intrahepatic Cholestasis of Pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is the most common, reversible, and closely related to pregnancy condition characterized by elevated levels of bile acids (BAs) in blood serum and an increased risk of adverse perinatal outcomes. Due to the complex interactions between the mother and the fetus in metabolism and transplacental BAs transport, ICP is classified as a fetal-maternal disease. The disease is usually mild in pregnant women, but it can be fatal to the fetus, leading to numerous complications, including intrauterine death. The pathophysiology of the disease is based on inflammatory mechanisms caused by elevated BA levels. Although ICP cannot be completely prevented, its early diagnosis and prompt management significantly reduce the risk of fetal complications, the most serious of which is unexpected intrauterine death. It is worth emphasizing that all diagnostics and management of ICP during pregnancy are based on BA levels. Therefore, it is important to standardize the criteria for diagnosis, as well as recommendations for management depending on the level of BAs, which undoubtedly determines the impact on the fetus. The purpose of this review is to present the potential and importance of BAs in the detection and rules of medical procedure in ICP.

A Comprehensive Review of the Cardioprotective Effect of Marine Algae Polysaccharide on the Gut Microbiota

Cardiovascular disease (CVD) is the number one cause of death worldwide. Recent evidence has demonstrated an association between the gut microbiota and CVD, including heart failure, cerebrovascular illness, hypertension, and stroke. Marine algal polysaccharides (MAPs) are valuable natural sources of diverse bioactive compounds. MAPs have many pharmaceutical activities, including antioxidant, anti-inflammatory, immunomodulatory, and antidiabetic effects. Most MAPs are not utilized in the upper gastrointestinal tract; however, they are fermented by intestinal flora. The relationship between MAPs and the intestinal microbiota has drawn attention in CVD research. Hence, this review highlights the main action by which MAPs are known to affect CVD by maintaining homeostasis in the gut microbiome and producing gut microbiota-generated functional metabolites and short chain fatty acids. In addition, the effects of trimethylamine N-oxide on the gut microbiota composition, bile acid signaling properties, and CVD prevention are also discussed. This review supports the idea that focusing on the interactions between the host and gut microbiota may be promising for the prevention or treatment of CVD. MAPs are a potential sustainable source for the production of functional foods or nutraceutical products for preventing or treating CVD.

Enterococcus faecium GEFA01 alleviates hypercholesterolemia by promoting reverse cholesterol transportation via modulating the gut microbiota-SCFA axis

This study aimed to identify cholesterol-lowering commensal strains from healthy lean individuals and to evaluate the cholesterol-lowering capacity of Enterococcus faecium GEFA01 in mice fed a high-cholesterol and high-fat diet. E. faecium GEFA01 was isolated from the feces of a healthy lean individual in a selective basal salt medium supplemented with cholesterol. E. faecium GEFA01 exhibited a cholesterol removal rate (CRR) of 46.13% by coprecipitation, assimilation, and degradation of cholesterol. Moreover, E. faecium GEFA01 significantly decreased the body weight of mice and the levels of serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), hepatic TC, triglycerides (TG), and LDL-C, and increased serum high-density lipoprotein cholesterol (HDL-C) levels in mice fed a high-cholesterol diet compared with the HCD group. We also observed that E. faecium GEFA01 significantly downregulated the gene expression of HMG-CoA reductase (Hmgcr), Srebp-1c, Fxr, Shp, and Fgf 15, upregulated the gene expression of low-density lipoprotein receptor (Ldlr), Abcg5/8, Abca1, cholesterol 7 alpha-hydroxylase (Cyp7a1), and Lxr in the liver of mice in relative to the HCD group, markedly increased the relative abundance of Lactobacillus, Akkermansia, Bifidobacterium, and Roseburia, and decreased the abundance of Helicobacter in the feces. Collectively, we confirmed that E. faecium GEFA01 exhibited cholesterol-lowering effects in mice fed a high-cholesterol diet, which was achieved through assimilation, coprecipitation, and degradation of cholesterol, and through modulation of the gut microbiota short-chain fatty acid (SCFA) axis that promoted reverse cholesterol transport and bile acid excretion. Our study demonstrated that E. faecium GEFA01 may be used as a probiotic candidate to lower cholesterol levels in the future.

Increased concentrations of conjugated bile acids are associated with osteoporosis in PSC patients

Primary sclerosing cholangitis (PSC) is an idiopathic cholestatic liver disease characterized by chronic inflammation and progressive fibrosis of intra- and extrahepatic bile ducts. Osteoporosis is a frequent comorbidity in PSC, and we could previously demonstrate that IL17-dependent activation of bone resorption is the predominant driver of bone loss in PSC. Since we additionally observed an unexpected heterogeneity of bone mineral density in our cohort of 238 PSC patients, the present study focused on a comparative analysis of affected individuals with diagnosed osteoporosis (PSC^OPO, n = 10) or high bone mass (PSC^HBM, n = 7). The two groups were not distinguishable by various baseline characteristics, including liver fibrosis or serum parameters for hepatic function. In contrast, quantification of serum bile acid concentrations identified significant increases in the PSC^OPO group, including glycoursodeoxycholic acid (GUDCA), an exogenous bile acid administered to both patient groups. Although cell culture experiments did not support the hypothesis that an increase in circulating bile levels is a primary cause of PSC-associated osteoporosis, the remarkable differences of endogenous bile acids and GUDCA in the serum of PSC^OPO patients strongly suggest a yet unknown impairment of biliary metabolism and/or hepatic bile acid clearance in this patient subgroup, which is independent of liver fibrosis.

Effect of theaflavin-3,3′-digallate on leptin-deficient induced nonalcoholic fatty liver disease might be related to lipid metabolism regulated by the Fads1/PPARδ/Fabp4 axis and gut microbiota

Nonalcoholic fatty liver disease (NAFLD), one of the risk factors for hepatitis, cirrhosis, and even hepatic carcinoma, has been a global public health problem. The polyphenol compound theaflavin-3,3′-digallate (TF3), mainly extracted from black tea, has been reported to produce an effect on hypoglycemic and antilipid deposition in vitro. In our study, we further investigated the function and novel mechanisms of TF3 in protecting NAFLD in vivo. By using leptin-deficient obese (ob/ob) mice with NAFLD symptoms, TF3 treatment prevented body weight and waistline gain, reduced lipid accumulation, and alleviated liver function injury, as well as decreased serum lipid levels and TG levels in livers in ob/ob mice, observing no side effects. Furthermore, the transcriptome sequencing of liver tissue showed that TF3 treatment corrected the expression profiles of livers in ob/ob mice compared with that of the model group. It is interesting to note that TF3 might regulate lipid metabolism via the Fads1/PPARδ/Fabp4 axis. In addition, 16S rRNA sequencing demonstrated that TF3 increased the abundance of Prevotellaceae_UCG-001, norank_f_Ruminococcaceae, and GCA-900066575 and significantly decreased that of Parvibacter. Taken together, the effect of TF3 on NAFLD might be related to lipid metabolism regulated by the Fads1/PPARδ/Fabp4 axis and gut microbiota. TF3 might be a promising candidate for NAFLD therapy.

FXR deficiency in hepatocytes disrupts the bile acid homeostasis and inhibits autophagy to promote liver injury in Schistosoma japonicum-infected mice

Background

Schistosomiasis, with 250 million people affected, is characterized by its serious hepatic inflammatory response and fibrosis formation, which could lead to dangerous complications, such as portal hypertension, splenomegaly and even ascites. But until now, the pathogenesis of schistosomiasis remains largely unknown. Farnesoid X Receptor (FXR), a bile acid-activated nuclear transcription factor mainly expresses in hepatocytes in the liver, can regulate liver diseases by controlling bile acid metabolism.

Methodology/Principal findings

In this study, we found that the expression of FXR was decreased in the liver of infected mice as shown by western blot and RT-qPCR assays. Furthermore, hepatocyte-specific FXR-deficient mice (FXR^flox/floxAlb^Cre, FXR-HKO) were generated and infected with ~16 cercariae of S. japonicum for five weeks. We found that FXR deficiency in hepatocytes promoted the progression of liver injury, aggravated weight loss and death caused by infection, and promoted inflammatory cytokines production, such as IL-6, IL-1β, TNF-α, IL-4, IL-10, and IL-13. Surprisingly, hepatic granulomas and fibrosis were not affected. In addition, using UPLC-MS/MS spectrometry, it was found that S. japonicum infection resulted in elevated bile acids in the liver of mice, which was more obvious in FXR-deficient mice. Meanwhile, autophagy was induced in littermate control mice due to the infection, but it was significantly decreased in FXR-HKO mice.

Conclusions/Significance

All these findings suggest that FXR deficiency in hepatocytes disrupts bile acid homeostasis and inhibits autophagy, which may aggravate the damages of hepatocytes caused by S. japonicum infection. It highlights that FXR in hepatocytes plays a regulatory role in the progression of schistosomiasis.

The liver, a critical metabolic organ, consists of approximately 80% parenchymal hepatocytes. Hepatic schistosomiasis results in inflammatory granulomas response and fibrosis formation that inevitably affects hepatocytes. However, whether and how hepatocytes involved in the progression of liver injury caused by S. japonicum is not clear. Here, we found that, the level of FXR, a key regulator of bile acid metabolism in hepatocytes, was clearly decreased in the liver of mice with this worm infection. Further, we found that FXR specifically deficient in hepatocytes increased bile acids toxicity and inhibited hepatocellular autophagy induced by worm infection, which therefore accelerated the progression of schistosomiasis by promoting hepatocyte injuries but not the formation of egg granulomas and hepatic fibrosis. Our work provides a regulatory loop of FXR/bile acids-autophagy in schistosomiasis, which suggests a role of hepatic FXR in the protection from hepatic damages caused by infection with S. japonicum.

The Role of Bile Acids in the Human Body and in the Development of Diseases

Bile acids are specific and quantitatively important organic components of bile, which are synthesized by hepatocytes from cholesterol and are involved in the osmotic process that ensures the outflow of bile. Bile acids include many varieties of amphipathic acid steroids. These are molecules that play a major role in the digestion of fats and the intestinal absorption of hydrophobic compounds and are also involved in the regulation of many functions of the liver, cholangiocytes, and extrahepatic tissues, acting essentially as hormones. The biological effects are realized through variable membrane or nuclear receptors. Hepatic synthesis, intestinal modifications, intestinal peristalsis and permeability, and receptor activity can affect the quantitative and qualitative bile acids composition significantly leading to extrahepatic pathologies. The complexity of bile acids receptors and the effects of cross-activations makes interpretation of the results of the studies rather difficult. In spite, this is a very perspective direction for pharmacology.

Bile acid and receptors: biology and drug discovery for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), a series of liver metabolic disorders manifested by lipid accumulation within hepatocytes, has become the primary cause of chronic liver diseases worldwide. About 20%-30% of NAFLD patients advance to nonalcoholic steatohepatitis (NASH), along with cell death, inflammation response and fibrogenesis. The pathogenesis of NASH is complex and its development is strongly related to multiple metabolic disorders (e.g. obesity, type 2 diabetes and cardiovascular diseases). The clinical outcomes include liver failure and hepatocellular cancer. There is no FDA-approved NASH drug so far, and thus effective therapeutics are urgently needed. Bile acids are synthesized in hepatocytes, transported into the intestine, metabolized by gut bacteria and recirculated back to the liver by the enterohepatic system. They exert pleiotropic roles in the absorption of fats and regulation of metabolism. Studies on the relevance of bile acid disturbance with NASH render it as an etiological factor in NASH pathogenesis. Recent findings on the functional identification of bile acid receptors have led to a further understanding of the pathophysiology of NASH such as metabolic dysregulation and inflammation, and bile acid receptors are recognized as attractive targets for NASH treatment. In this review, we summarize the current knowledge on the role of bile acids and the receptors in the development of NAFLD and NASH, especially the functions of farnesoid X receptor (FXR) in different tissues including liver and intestine. The progress in the development of bile acid and its receptors-based drugs for the treatment of NASH including bile acid analogs and non-bile acid modulators on bile acid metabolism is also discussed.

Bile Acid Sequestrants for Hypercholesterolemia Treatment Using Sustainable Biopolymers: Recent Advances and Future Perspectives

Bile acids, the endogenous steroid nucleus containing signaling molecules, are responsible for the regulation of multiple metabolic processes, including lipoprotein and glucose metabolism to maintain homeostasis. Within our body, they are directly produced from their immediate precursors, cholesterol C (low-density lipoprotein C, LDL-C), through the enzymatic catabolic process mediated by 7-α-hydroxylase (CYP7A1). Bile acid sequestrants (BASs) or amphiphilic resins that are nonabsorbable to the human body (being complex high molecular weight polymers/electrolytes) are one of the classes of drugs used to treat hypercholesterolemia (a high plasma cholesterol level) or dyslipidemia (lipid abnormalities in the body); thus, they have been used clinically for more than 50 years with strong safety profiles as demonstrated by the Lipid Research Council-Cardiovascular Primary Prevention Trial (LRC-CPPT). They reduce plasma LDL-C and can slightly increase high-density lipoprotein C (HDL-C) levels, whereas many of the recent clinical studies have demonstrated that they can reduce glucose levels in patients with type 2 diabetes mellitus (T2DM). However, due to higher daily dosage requirements, lower efficacy in LDL-C reduction, and concomitant drug malabsorption, research to develop an "ideal" BAS from sustainable or natural sources with better LDL-C lowering efficacy and glucose regulations and lower side effects is being pursued. This Review discusses some recent developments and their corresponding efficacies as bile removal or LDL-C reduction of natural biopolymer (polysaccharide)-based compounds.

TNF in the liver: targeting a central player in inflammation

Tumour necrosis factor-α (TNF) is a multifunctional cytokine. First recognized as an endogenous soluble factor that induces necrosis of solid tumours, TNF became increasingly important as pro-inflammatory cytokine being involved in the immunopathogenesis of several autoimmune diseases. In the liver, TNF induces numerous biological responses such as hepatocyte apoptosis and necroptosis, liver inflammation and regeneration, and autoimmunity, but also progression to hepatocellular carcinoma. Considering these multiple functions of TNF in the liver, we propose anti-TNF therapies that specifically target TNF signalling at the level of its specific receptors.

A Lard and Soybean Oil Mixture Alleviates Low-Fat-High-Carbohydrate Diet-Induced Nonalcoholic Fatty Liver Disease in Mice

Dietary habit is highly related to nonalcoholic fatty liver disease (NAFLD). Low-fat–high-carbohydrate (LFHC) diets could induce lean NAFLD in Asians. Previously, we found that a lard and soybean oil mixture reduced fat accumulation with a medium-fat diet; therefore, in this study, we evaluated the effect of a lard and soybean oil mixture (LFHC diet) on NAFLD and its underlying mechanisms. Mice in groups were fed with lard, soybean oil, or a lard and soybean oil mixture—an LFHC diet—separately. Our results showed that mixed oil significantly inhibited serum triglyceride, liver triglyceride, serum free fatty acids (FFAs), and liver FFAs compared with soybean oil or lard, and we found fewer inflammatory cells in mice fed with mixed oil. RNA-seq results indicate that mixed oil reduced FFAs transportation into the liver via decreasing liver fatty acid-binding protein 2 expression, inhibited oxidative phosphorylation via tumor necrosis factor receptor superfamily member 6 downregulation, and alleviated inflammation via downregulating inflammatory cytokine. The liquid chromatography–mass spectrometry results showed that the mixed oil promoted bile acid conjugated with taurine and glycine, thus activating G-protein-coupled bile acid receptor 1 for improved lipids metabolism. In conclusion, the lard and soybean oil mixture alleviated NAFLD.

The Synthesis of 12β-Methyl-18-nor-Avicholic Acid Analogues as Potential TGR5 Agonists†

In the quest for new modulators of the Farnesoid-X (FXR) and Takeda G-protein-coupled (TGR5) receptors, bile acids are a popular candidate for drug development. Recently, bile acids endowed with a...

UGT1A1 and UGT1A3 activity and inhibition in human liver and intestinal microsomes and a recombinant UGT system under similar assay conditions using selective substrates and inhibitors

In vitro enzyme kinetics and inhibition data was compared for UGT1A1 and UGT1A3 isoforms under similar assay conditions using human liver microsomes (HLM), human intestinal microsomes (HIM) and recombinant UGT (rUGT) enzyme systems.UGT1A1 catalysed β-estradiol 3-β-D-glucuronide formation showed allosteric sigmoidal kinetics in all enzyme systems; while UGT1A3 catalysed CDCA 24-acyl-β-D-glucuronide formation exhibited Michaelis-Menten kinetics in HLM, substrate inhibition kinetics in HIM and rUGT systems. Corresponding K_m or S₅₀ concentrations of β-estradiol and CDCA were employed in the respective UGT inhibition studies.Atazanavir inhibited the production of β-estradiol 3-β-D-glucuronide with IC50 values of 0.54 µM and 0.16 µM in HLM and rUGT1A1, respectively. But its inhibition potential was not observed in HIM, indicating potential cross-talk with other high-affinity intestinal UGT isozymes. On the other hand, zafirlukast, a pan UGT inhibitor, exhibited moderate inhibition in HIM with an IC50 value of 16.70 µM. Lithocholic acid, inhibited the production of CDCA 24-acyl-β-D-glucuronide with IC50 values of 1.68, 1.84, and 12.42 µM in HLM, rUGT1A3, and HIM, respectively.These results indicated that HLM, HIM, and rUGTs may be used as complementary in vitro systems to evaluate hepatic and intestinal UGT mediated DDIs at the screening stage.

Oxysterol 7-α Hydroxylase (CYP7B1) Attenuates Metabolic-Associated Fatty Liver Disease in Mice at Thermoneutrality

Ambient temperature is an important determinant of both the alternative bile acid synthesis pathway controlled by oxysterol 7-α hydroxylase (CYP7B1) and the progression of metabolic-associated fatty liver disease (MAFLD). Here, we investigated whether CYP7B1 is involved in the etiology of MAFLD under conditions of low and high energy expenditure. For this, Cyp7b1^−/− and wild type (WT) mice were fed a choline-deficient high-fat diet and housed either at 30 °C (thermoneutrality) or at 22 °C (mild cold). To study disease phenotype and underlying mechanisms, plasma and organ samples were analyzed to determine metabolic parameters, immune cell infiltration by immunohistology and flow cytometry, lipid species including hydroxycholesterols, bile acids and structural lipids. In WT and Cyp7b1^−/− mice, thermoneutral housing promoted MAFLD, an effect that was more pronounced in CYP7B1-deficient mice. In these mice, we found higher plasma alanine aminotransferase activity, hyperlipidemia, hepatic accumulation of potentially harmful lipid species, aggravated liver fibrosis, increased inflammation and immune cell infiltration. Bile acids and hydroxycholesterols did not correlate with aggravated MAFLD in Cyp7b1^−/− mice housed at thermoneutrality. Notably, an up-regulation of lipoprotein receptors was detected at 22 °C but not at 30 °C in livers of Cyp7b1^−/− mice, suggesting that accelerated metabolism of lipoproteins carrying lipotoxic molecules counteracts MAFLD progression.

Bile Acids Activate NLRP3 Inflammasome, Promoting Murine Liver Inflammation or Fibrosis in a Cell Type-Specific Manner

Bile acids (BA) as important signaling molecules are considered crucial in development of cholestatic liver injury, but there is limited understanding on the involved cell types and signaling pathways. The aim of this study was to evaluate the inflammatory and fibrotic potential of key BA and the role of distinct liver cell subsets focusing on the NLRP3 inflammasome. C57BL/6 wild-type (WT) and Nlrp3^−/− mice were fed with a diet supplemented with cholic (CA), deoxycholic (DCA) or lithocholic acid (LCA) for 7 days. Additionally, primary hepatocytes, Kupffer cells (KC) and hepatic stellate cells (HSC) from WT and Nlrp3^−/− mice were stimulated with aforementioned BA ex vivo. LCA feeding led to strong liver damage and activation of NLRP3 inflammasome. Ex vivo KC were the most affected cells by LCA, resulting in a pro-inflammatory phenotype. Liver damage and primary KC activation was both ameliorated in Nlrp3-deficient mice or cells. DCA feeding induced fibrotic alterations. Primary HSC upregulated the NLRP3 inflammasome and early fibrotic markers when stimulated with DCA, but not LCA. Pro-fibrogenic signals in liver and primary HSC were attenuated in Nlrp3^−/− mice or cells. The data shows that distinct BA induce NLRP3 inflammasome activation in HSC or KC, promoting fibrosis or inflammation.