Bile Acids, Gut Microbiome and the Road to Fatty Liver Disease

Another renaissance for bile acid gastrointestinal microbiology

The field of bile acid microbiology in the gastrointestinal tract is going through a current rebirth after a peak of activity in the late 1970s and early 1980s. This renewed activity is a result of many factors, including the discovery near the turn of the century that bile acids are potent signalling molecules and technological advances in next-generation sequencing, computation, culturomics, gnotobiology, and metabolomics. We describe the current state of the field with particular emphasis on questions that have remained unanswered for many decades in both bile acid synthesis by the host and metabolism by the gut microbiota. Current knowledge of established enzymatic pathways, including bile salt hydrolase, hydroxysteroid dehydrogenases involved in the oxidation and epimerization of bile acid hydroxy groups, the Hylemon-Bjӧrkhem pathway of bile acid C7-dehydroxylation, and the formation of secondary allo-bile acids, is described. We cover aspects of bile acid conjugation and esterification as well as evidence for bile acid C3-dehydroxylation and C12-dehydroxylation that are less well understood but potentially critical for our understanding of bile acid metabolism in the human gut. The physiological consequences of bile acid metabolism for human health, important caveats and cautionary notes on experimental design and interpretation of data reflecting bile acid metabolism are also explored.

The potential of the nutraceutical berberine in the treatment of hepatocellular carcinoma and other liver diseases such as NAFLD and NASH

Hepatocellular carcinoma (HCC) is a common cancer which unfortunately has poor outcomes. Common anti-cancer treatments such as chemotherapy and targeted therapy have not increased patient survival significantly. A common treatment for HCC patients is transplantation, however, it has limitations and complications. Novel approaches are necessary to more effectively treat HCC patients. Berberine (BBR) is a nutraceutical derived from various fruits and trees, which has been used for centuries in traditional medicine to treat various diseases such as diabetes and inflammation. More recently, the anti-proliferation effects of BBR have been investigated in the treatment of patients with various cancers, especially colorectal cancer, and in non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). In this review, we will focus on studies with BBR in liver diseases.

Reversal of cholestatic liver disease by the inhibition of sphingosine 1-phosphate receptor 2 signaling

Aims

The objective of this study is to examine the impact of inhibiting Sphingosine 1-phosphate receptor 2 (S1PR2) on liver inflammation, fibrogenesis, and changes of gut microbiome in the context of cholestasis-induced conditions.

Methods

The cholestatic liver injury model was developed by common bile duct ligation (CBDL). Sprague-Dawley rats were randomly allocated to three groups, sham operation, CBDL group and JTE-013 treated CBDL group. Biochemical and histological assessments were conducted to investigate the influence of S1PR2 on the modulation of fibrogenic factors and inflammatory infiltration. We conducted an analysis of the fecal microbiome by using 16S rRNA sequencing. Serum bile acid composition was evaluated through the utilization of liquid chromatography-mass spectrometry techniques.

Results

In the BDL rat model, the study findings revealed a significant increase in serum levels of conjugated bile acids, accompanied by an overexpression of S1PR2. Treatment with the specific inhibitor of S1PR2, known as JTE-013, resulted in a range of specific effects on the BDL rats. These effects included the improvement of liver function, reduction of liver inflammation, inhibition of hepatocyte apoptosis, and suppression of NETosis. These effects are likely mediated through the TCA/S1PR2/NOX2/NLRP3 pathway. Furthermore, the administration of JTE-013 resulted in an augmentation of the diversity of the bacterial community's diversity, facilitating the proliferation of advantageous species while concurrently inhibiting the prevalence of detrimental bacteria.

Conclusions

The results of our study suggest that the administration of JTE-013 may have a beneficial effect in alleviating cholestatic liver disease and restoring the balance of intestinal flora.

The role of bile acid metabolism in the occurrence and development of NAFLD

Non-alcoholic fatty liver disease (NAFLD) has become one of the important causes of cirrhosis and liver cancer, resulting in a huge medical burden worldwide. Currently, effective non-invasive diagnostic indicators and drugs for NAFLD are still lacking. With the development of metabolomics technology, the changes in metabolites during the development of NAFLD have been gradually revealed. Bile acid (BA) is the main endpoint of cholesterol metabolism in the body. In addition, it also acts as a signaling factor to regulate metabolism and inflammation in the body through the farnesyl X receptor and G protein-coupled BA receptor. Studies have shown that BA metabolism is associated with the development of NAFLD, but a large number of animal and clinical studies are still needed. BA homeostasis is maintained through multiple negative feedback loops and the enterohepatic circulation of BA. Recently, treatment of NAFLD by interfering with BA synthesis and metabolism has become a new research direction. Here, we review the changes in BA metabolism and its regulatory mechanisms during the development of NAFLD and describe the potential of studies exploring novel non-invasive diagnostic indicators and therapeutic targets for NAFLD based on BA metabolism.

RNA binding protein HuR protects against NAFLD by suppressing long noncoding RNA H19 expression

BACKGROUND

NAFLD has become the most common chronic liver disease worldwide. Human antigen R (HuR), an RNA-binding protein, is an important post-transcriptional regulator. HuR has been reported as a key player in regulating lipid homeostasis in the liver and adipose tissues by using tissue-specific HuR knockout mice. However, the underlying mechanism by which hepatocyte-specific HuR regulates hepatic lipid metabolism under metabolic stress remains unclear and is the focus of this study.

METHODS

Hepatocyte-specific HuR deficient mice (HuRhKO) and age-/gender-matched control mice, as well as long-noncoding RNA H19 knockout mice (H19-/-), were fed a Western Diet plus sugar water (WDSW). Hepatic lipid accumulation, inflammation and fibrosis were examined by histology, RNA transcriptome analysis, qRT-PCR, and Western blot analysis. Bile acid composition was measured using LC-MS/MS.

RESULTS

Hepatocyte-specific deletion of HuR not only significantly increased hepatic lipid accumulation by modulating fatty acid synthesis and metabolism but also markedly induced inflammation by increasing immune cell infiltration and neutrophil activation under metabolic stress. In addition, hepatic deficiency of HuR disrupted bile acid homeostasis and enhanced liver fibrosis. Mechanistically, HuR is a repressor of H19 expression. Analysis of a recently published dataset (GSE143358) identified H19 as the top-upregulated gene in liver-specific HuR knockout mice. Similarly, hepatocyte-specific deficiency of HuR dramatically induced the expression of H19 and sphingosine-1 phosphate receptor 2 (S1PR2), but reduced the expression of sphingosine kinase 2 (SphK2). WDSW-induced hepatic lipid accumulation was alleviated in H19-/- mice. Furthermore, the downregulation of H19 alleviated WDSW-induced NAFLD in HuRhKO mice.

CONCLUSIONS

HuR not only functions as an RNA binding protein to modulate post-transcriptional gene expression but also regulates H19 promoter activity. Hepatic HuR is an important regulator of hepatic lipid metabolism via modulating H19 expression.

Ring Trial on Quantitative Assessment of Bile Acids Reveals a Method- and Analyte-Specific Accuracy and Reproducibility

(1) Background: Bile acids are a key mediator of the molecular microbiome-host interaction, and various mass spectrometry-based assays have been developed in the recent decade to quantify a wide range of bile acids. We compare existing methodologies to harmonize them. (2) Methods: Methodology for absolute quantification of bile acids from six laboratories in Europe were compared for the quantification of the primary bile acids cholic acid (CA) and chenodeoxycholic acid (CDCA) and conjugated products glycocholic acid (GCA) and taurocholic acid (TCA). For the bacterially modified secondary bile acids, the quantification of deoxycholic acid (DCA) and lithocholic acid (LCA) was compared. For the murine bile acids, we used the primary muricholic acids (α-MCA and, β-MCA) and the intestinally produced secondary bile acid muricholic (ω-MCA). The standards were spiked into methanol:water (1:1) mix as well as in human and murine serum at either low concentration range (150–3000 nM) or high concentration range (1500–40,000 nM). (3) Results: The precision was better for higher concentrations. Measurements for the hydrophobic unconjugated bile acids LCA and ω-MCA were the most challenging. (4) Conclusions: The quality assessments were generally very similar, and the comprehensive analyses demonstrated that data from chosen locations can be used for comparisons between studies.

Bile acids and sphingolipids in non-alcoholic fatty liver disease

ABSTRACT

Non-alcoholic fatty liver disease (NAFLD) is one of the fastest-growing diseases, and its global prevalence is estimated to increase >50% by 2030. NAFLD is comorbid with metabolic syndrome, obesity, type 2 diabetes, and insulin resistance. Despite extensive research efforts, there are no pharmacologic or biological therapeutics for the treatment of NAFLD. Bile acids and sphingolipids are well-characterized signaling molecules. Over the last few decades, researchers have uncovered potential mechanisms by which bile acids and sphingolipids regulate hepatic lipid metabolism. Dysregulation of bile acid and sphingolipid metabolism has been linked to steatosis, inflammation, and fibrosis in patients with NAFLD. This clinical observation has been recapitulated in animal models, which are well-accepted by experts in the hepatology field. Recent transcriptomic and lipidomic studies also show that sphingolipids are important players in the pathogenesis of NAFLD. Moreover, the identification of bile acids as activators of sphingolipid-mediated signaling pathways established a novel theory for bile acid and sphingolipid biology. In this review, we summarize the recent advances in the understanding of bile acid and sphingolipid-mediated signaling pathways as potential contributors to NAFLD. A better understanding of the pathologic effects mediated by bile acids and sphingolipids will facilitate the development of new diagnostic and therapeutic strategies for NAFLD.

Multi-target regulation of intestinal microbiota by berberine to improve type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) and its complications are major public health problems that seriously affect the quality of human life. The modification of intestinal microbiota has been widely recognized for the management of diabetes. The relationship between T2DM, intestinal microbiota, and active ingredient berberine (BBR) in intestinal microbiota was reviewed in this paper. First of all, the richness and functional changes of intestinal microbiota disrupt the intestinal environment through the destruction of the intestinal barrier and fermentation/degradation of pathogenic/protective metabolites, targeting the liver, pancreas, visceral adipose tissue (VAT), etc., to affect intestinal health, blood glucose, and lipids, insulin resistance and inflammation. Then, we focus on BBR, which protects the composition of intestinal microbiota, the changes of intestinal metabolites, and immune regulation disorder of the intestinal environment as the therapeutic mechanism as well as its current clinical trials. Further research can analyze the mechanism network of BBR to exert its therapeutic effect according to its multi-target compound action, to provide a theoretical basis for the use of different phytochemical components alone or in combination to prevent and treat T2DM or other metabolic diseases by regulating intestinal microbiota.