Regulation of human class I alcohol dehydrogenases by bile acids

Spatio-temporal analysis of toxigenic genes expression in the growing Bufo gargarizans based on RNA sequencing data

BACKGROUND

Bufo gargarizans Cantor, a widely distributed amphibian species in Asia, produces and releases toxins through its retroauricular and granular glands. Although various tissues have been sequenced, the molecular mechanisms underlying the toxin production remain unclear. To elucidate these mechanisms, abdominal skin (non-toxic secretory glands) and retroauricular gland (toxic secreting glands) samples were collected at different time points (3, 6, 12, 24, and 36 months) for RNA sequencing (RNA-seq) and analysis.

RESULTS

In comparison to the S group during the same period, a total of 3053, 3026, 1516, 1028, and 2061 differentially expressed genes (DEGs) were identified across five developmental stages. Gene Ontology (GO) analysis revealed that DEGs were primarily enriched in biological processes including cellular processes, single-organism processes, metabolic processes, and biological regulation. In terms of cellular components, the DEGs were predominantly localized in the cell and cell parts, whereas molecular function indicated significant enrichment in binding and catalytic activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the metabolism and synthesis of various substances, such as lipid metabolism, cofactor and vitamin metabolism, tryptophan metabolism, steroid biosynthesis, and primary bile acid biosynthesis, were accompanied by the development of toads. Additionally, using trend analysis, we discovered candidate genes that were upregulated in the retroauricular glands during development, and the abundance of these genes in the abdominal skin was extremely low. Finally, we identified 26 genes that are likely to be involved in toxin production and that are likely to be involved in toxin anabolism.

CONCLUSION

Overall, these results provide new insights into the genes involved in toxin production in B. gargarizans, which will improve our understanding of the molecular mechanisms underlying toxigenic gene expression.

Farnesoid X Receptor Agonists: A Promising Therapeutic Strategy for Gastrointestinal Diseases

Farnesoid X receptor (FXR) agonists have emerged as a promising therapeutic strategy for the management of various gastrointestinal (GI) diseases, including primary biliary cholangitis, nonalcoholic fatty liver disease, inflammatory bowel disease, alcohol-related liver disease, and primary sclerosing cholangitis. In this review, we discuss the mechanisms of action of FXR agonists, including their metabolic and immunomodulatory effects, and provide an overview of the clinical evidence supporting their use in the treatment of GI diseases. We also highlight the safety, adverse effects, and potential drug interactions associated with FXR agonists. While these agents have demonstrated efficacy in improving liver function, reducing hepatic steatosis, and improving histological endpoints in primary biliary cholangitis and nonalcoholic fatty liver disease, further research is needed to determine their long-term safety and effectiveness in other GI diseases, such as inflammatory bowel disease, alcohol-related liver disease, and primary sclerosing cholangitis. Additionally, the development of next-generation FXR agonists with improved potency and reduced side effects could further enhance their therapeutic potential.

New insights into the bile acid-based regulatory mechanisms and therapeutic perspectives in alcohol-related liver disease

Cholestasis is a key causative factor in alcohol-related liver disease (ALD) and variable degrees of cholestasis occur in all stages of ALD. However, the pathogenetic mechanisms and biomarkers associated with cholestasis are not well characterized. Cholestatic disease is marked by the disruption of bile acids (BA) transport and homeostasis. Consequently, in both human and experimental ALD, the disease shows a direct correlation with an imbalance in BA equilibrium, which in turn may also affect the severity of the disease. Modulation of BA metabolism or signaling pathways is increasingly considered as a potential therapeutic strategy for ALD in humans. In this paper, we highlight the key advances made in the past two decades in characterizing the molecular regulatory mechanisms of BA synthesis, enterohepatic circulation, and BA homeostasis. We summarize recent insights into the nature of the linkage between BA dysregulation and ALD, including the abnormal expression of genes involved in BA metabolism, abnormal changes in receptors that regulate BA metabolism, and disturbance in the gut flora engaged in BA metabolism caused by alcohol consumption. Additionally, we provide novel perspectives on the changes in BAs in various stages of ALD. Finally, we propose potential pharmacological therapies for ALD targeting BA metabolism and signaling.

Molecular mechanisms of hepatotoxic cholestasis by clavulanic acid: Role of NRF2 and FXR pathways

Treatment of β-lactamase positive bacterial infections with a combination of amoxicillin (AMOX) and clavulanic acid (CLAV) causes idiosyncratic drug-induced liver injury (iDILI) in a relevant number of patients, often with features of intrahepatic cholestasis. This study aims to determine serum bile acid (BA) levels in amoxicillin/clavulanate (A+C)-iDILI patients and to investigate the mechanism of cholestasis by A+C in human in vitro hepatic models. In six A+C-iDILI patients, significant elevations of serum primary conjugated BA definitely demonstrated A+C-induced cholestasis. In cultured human Upcyte hepatocytes and HepG2 cells, CLAV was more cytotoxic than AMOX, and, at subcytotoxic concentrations, it altered the expression of more than 1,300 genes. CLAV, but not AMOX, downregulated the expression of key genes for BA transport (BSEP, NTCP, OSTα and MDR2) and synthesis (CYP7A1 and CYP8B1). CLAV also caused early oxidative stress, with reduced GSH/GSSG ratio, along with induction of antioxidant nuclear factor erythroid 2-related factor 2 (NRF2) target genes. Activation of NRF2 by sulforaphane also resulted in downregulation of NTCP, OSTα, ABCG5, CYP7A1 and CYP8B1. CLAV also inhibited the BA-sensor farnesoid X receptor (FXR), in agreement with the downregulation of FXR targets BSEP, OSTα and ABCG5. We conclude that CLAV, the culprit molecule in A+C, downregulates several key biliary transporters by modulating NRF2 and FXR signaling, thus likely promoting intrahepatic cholestasis. On top of that, increased ROS production and GSH depletion may aggravate the cholestatic injury by A+C.

Distinct Bile Acid Profiles in Patients With Chronic Hepatitis B Virus Infection Reveal Metabolic Interplay Between Host, Virus and Gut Microbiome

Hepatitis B virus (HBV) can hijack the host bile acids (BAs) metabolic pathway during infection in cell and animal models. Additionally, microbiome was known to play critical role in the enterohepatic cycle of BAs. However, the impact of HBV infection and associated gut microbiota on the BA metabolism in chronic hepatitis B (CHB) patients is unknown. This study aimed to unveil the distinct BA profiles in chronic HBV infection (CHB) patients with no or mild hepatic injury, and to explore the relationship between HBV, microbiome and BA metabolism with clinical implications.

Methods: Serum BA profiles were compared between CHB patients with normal ALT (CHB-NALT, n = 92), with abnormal ALT (CHB-AALT, n = 34) and healthy controls (HCs, n = 28) using UPLC-MS measurement. Hepatic gene expression in CHB patients were explored using previously published transcriptomic data. Fecal microbiome was compared between 30 CHB-NALT and 30 HCs using 16S rRNA sequencing, and key microbial function was predicted by PICRUSt analysis.

Results: Significant higher percentage of conjugated BAs and primary BAs was found in CHB patients even without apparent liver injury. Combinatory BA features can discriminate CHB patients and HCs with high accuracy (AUC = 0.838). Up-regulation of BA importer Na+ taurocholate co-transporting peptide (NTCP) and down-regulation of bile salt export pump (BSEP) was found in CHB-NALT patients. The microbial diversity and abundance of Lactobacillus, Clostridium, Bifidobacterium were lower in CHB-NALT patients compared to healthy controls. Suppressed microbial bile salt hydrolases (BSH), 7-alpha-hydroxysteroid dehydrogenase (hdhA) and 3-dehydro-bile acid Delta 4, 6-reductase (BaiN) activity were found in CHB-NALT patients.

Conclusion: This study provides new insight into the BA metabolism influenced both by HBV infection and associated gut microbiome modulations, and may lead to novel strategy for clinical management for chronic HBV infection.

Non-cytochrome P450 enzymes involved in the oxidative metabolism of xenobiotics: Focus on the regulation of gene expression and enzyme activity

Oxidative metabolism is one of the major biotransformation reactions that regulates the exposure of xenobiotics and their metabolites in the circulatory system and local tissues and organs, and influences their efficacy and toxicity. Although cytochrome (CY)P450s play critical roles in the oxidative reaction, extensive CYP450-independent oxidative metabolism also occurs in some xenobiotics, such as aldehyde oxidase, xanthine oxidoreductase, flavin-containing monooxygenase, monoamine oxidase, alcohol dehydrogenase, or aldehyde dehydrogenase-dependent oxidative metabolism. Drugs form a large portion of xenobiotics and are the primary target of this review. The common reaction mechanisms and roles of non-CYP450 enzymes in metabolism, factors affecting the expression and activity of non-CYP450 enzymes in terms of inhibition, induction, regulation, and species differences in pharmaceutical research and development have been summarized. These non-CYP450 enzymes are detoxifying enzymes, although sometimes they mediate severe toxicity. Synthetic or natural chemicals serve as inhibitors for these non-CYP450 enzymes. However, pharmacokinetic-based drug interactions through these inhibitors have rarely been reported in vivo. Although multiple mechanisms participate in the basal expression and regulation of non-CYP450 enzymes, only a limited number of inducers upregulate their expression. Therefore, these enzymes are considered non-inducible or less inducible. Overall, this review focuses on the potential xenobiotic factors that contribute to variations in gene expression levels and the activities of non-CYP450 enzymes.

The gut microbiota: A new target in the management of alcohol dependence?

The gastrointestinal tract is the natural habitat for a huge community of microorganisms, comprising bacteria, viruses, fungi and yeast. This microbial ecosystem codevelops with the host throughout life and is subject to a complex interplay that depends on multiple factors including host genetics, nutrition, life-style, stress, diseases and antibiotics use. The gut microbiota, that refers to intestinal bacteria, has profound influence on the host immune system, metabolism and nervous system. Indeed, intestinal bacteria supply the host with essential nutrients such as vitamins, metabolize bile acids and undigested compounds, defend against pathogen invasion, participate to the development of the intestinal architecture and the intestinal immune system and play an important role in the maintenance of the gut barrier function. More recently, the gut microbiota has been shown to influence brain functions, such as myelin synthesis, the blood-brain barrier permeability and neuroinflammatory responses but also mood and behavior. The cross-talk between microbes and the host implicates a vast array of signaling pathways that involve many different classes of molecules like metabolites produced by the bacteria from dietary or endogenous sources of carbohydrates and proteins (i.e. short-chain fatty acids (SCFAs), indole), neurotransmitters and inflammatory cytokines. This review will focus on the involvement of the gut microbiota in the pathophysiological aspects of alcohol dependence related to the gut barrier function, liver damage and psychological disturbances. We will also discuss the possibility to create new and realistic humanized animal models of alcohol dependence by the use of fecal transplantation.

Omics-based responses induced by bosentan in human hepatoma HepaRG cell cultures

Bosentan is well known to induce cholestatic liver toxicity in humans. The present study was set up to characterize the hepatotoxic effects of this drug at the transcriptomic, proteomic, and metabolomic levels. For this purpose, human hepatoma-derived HepaRG cells were exposed to a number of concentrations of bosentan during different periods of time. Bosentan was found to functionally and transcriptionally suppress the bile salt export pump as well as to alter bile acid levels. Pathway analysis of both transcriptomics and proteomics data identified cholestasis as a major toxicological event. Transcriptomics results further showed several gene changes related to the activation of the nuclear farnesoid X receptor. Induction of oxidative stress and inflammation were also observed. Metabolomics analysis indicated changes in the abundance of specific endogenous metabolites related to mitochondrial impairment. The outcome of this study may assist in the further optimization of adverse outcome pathway constructs that mechanistically describe the processes involved in cholestatic liver injury.

Role of the pregnane X receptor in binge ethanol-induced steatosis and hepatotoxicity

The pregnane X receptor (PXR, NR1I2) is a xenobiotic-sensing nuclear receptor that defends against toxic agents. We have shown that PXR promotes chronic ethanol (EtOH)-induced steatosis. Therefore, we examined the role of PXR in binge EtOH-induced hepatotoxicity. Male wild type (WT) and Pxr-null mice were orally administered three binge doses of EtOH (4.5 g/kg, every 12 hours) and euthanized four hours after the final dose. Pxr-null mice displayed higher basal mRNA levels of hepatic lipogenic transcription factor sterol regulatory element binding protein 1c (Srebp-1c) and its target stearoyl-CoA desaturase 1 (Scd1) and the lipid peroxide detoxifying aldo-keto reductase 1b7 (Akr1b7) and higher protein levels of EtOH-metabolizing alcohol dehydrogenase 1 (ADH1). In both genotypes, binge EtOH-induced triglyceride accumulation was associated with inhibition of fatty acid β-oxidation and upregulation of Srebp-1c- regulated lipogenic genes and hepatic CYP2E1 protein. Unexpectedly, gene expression of Cyp2b10, a constitutive androstane receptor target gene, implicated in EtOH hepatotoxicity, was PXR-dependent upregulated by binge EtOH. Also, PXR-dependent was the binge EtOH-induced inhibition of hepatic Akr1b8 mRNA, and protein levels of aldehyde dehydrogenase (ALDH) 1A1 and anti-apoptotic Bcl-2, but increased pro-apoptotic Bax protein expression, leading to increases in residual EtOH concentration and the cellular oxidative stress marker, malondialdehyde. In contrast, Pxr-null mice displayed increased Akr1b7 gene and ADH1 protein expression and hypertriglyceridemia following binge EtOH exposure. Taken together, this study demonstrates that PXR ablation prevents EtOH induced upregulation of Cyp2b10 and that PXR potentiates binge EtOH-induced oxidative stress and inhibition of EtOH catabolism, but protects against alcoholic hyperlipidemia.

Age-dependent Protein Abundance of Cytosolic Alcohol and Aldehyde Dehydrogenases in Human Liver

Hepatic cytosolic alcohol and aldehyde dehydrogenases (ADHs and ALDHs) catalyze the biotransformation of xenobiotics (e.g., cyclophosphamide and ethanol) and vitamin A. Because age-dependent hepatic abundance of these proteins is unknown, we quantified protein expression of ADHs and ALDH1A1 in a large cohort of pediatric and adult human livers by liquid chromatography coupled with tandem mass spectrometry proteomics. Purified proteins were used as calibrators. Two to three surrogate peptides per protein were quantified in trypsin digests of liver cytosolic samples and calibrator proteins under optimal conditions of reproducibility. Neonatal levels of ADH1A, ADH1B, ADH1C, and ALDH1A1 were 3-, 8-, 146-, and 3-fold lower than the adult levels, respectively. For all proteins, the abundance steeply increased during the first year of life, which mostly reached adult levels during early childhood (age between 1 and 6 years). Only for ADH1A protein abundance in adults (age > 18 year) was ∼40% lower relative to the early childhood group. Abundances of ADHs and ALDH1A1 were not associated with sex in samples with age > 1 year compared with males. Known single nucleotide polymorphisms had no effect on the protein levels of these proteins. Quantification of ADHs and ALDH1A1 protein levels could be useful in predicting disposition and response of substrates of these enzymes in younger children.

The interrelationship between bile acid and vitamin A homeostasis

Vitamin A is a fat-soluble vitamin important for vision, reproduction, embryonic development, cell differentiation, epithelial barrier function and adequate immune responses. Efficient absorption of dietary vitamin A depends on the fat-solubilizing properties of bile acids. Bile acids are synthesized in the liver and maintained in an enterohepatic circulation. The liver is also the main storage site for vitamin A in the mammalian body, where an intimate collaboration between hepatocytes and hepatic stellate cells leads to the accumulation of retinyl esters in large cytoplasmic lipid droplet hepatic stellate cells. Chronic liver diseases are often characterized by disturbed bile acid and vitamin A homeostasis, where bile production is impaired and hepatic stellate cells lose their vitamin A in a transdifferentiation process to myofibroblasts, cells that produce excessive extracellular matrix proteins leading to fibrosis. Chronic liver diseases thus may lead to vitamin A deficiency. Recent data reveal an intricate crosstalk between vitamin A metabolites and bile acids, in part via the Retinoic Acid Receptor (RAR), Retinoid X Receptor (RXR) and the Farnesoid X Receptor (FXR), in maintaining vitamin A and bile acid homeostasis. Here, we provide an overview of the various levels of "communication" between vitamin A metabolites and bile acids and its relevance for the treatment of chronic liver diseases.

Enhanced ethanol catabolism in orphan nuclear receptor SHP-null mice

Deficiency of the orphan nuclear hormone receptor small heterodimer partner (SHP, NR0B2) protects mice from diet-induced hepatic steatosis, in part, via repression of peroxisome proliferator-activated receptor (PPAR)-γ2 (Pparg2) gene expression. Alcoholic fatty liver diseases (AFLD) share many common pathophysiological features with non-AFLD. To study the role of SHP and PPARγ2 in AFLD, we used a strategy of chronic ethanol feeding plus a single binge ethanol feeding to challenge wild-type (WT) and SHP-null (SHP(-/-)) mice with ethanol. The ethanol feeding induced liver fat accumulation and mRNA expression of hepatic Pparg2 in WT mice, which suggests that a high level of PPARγ2 is a common driving force for fat accumulation induced by ethanol or a high-fat diet. Interestingly, ethanol-fed SHP(-/-) mice displayed hepatic fat accumulation similar to that of ethanol-fed WT mice, even though their Pparg2 expression level remained lower. Mortality of SHP(-/-) mice after ethanol binge feeding was significantly reduced and their acetaldehyde dehydrogenase (Aldh2) mRNA level was higher than that of their WT counterparts. After an intoxicating dose of ethanol, SHP(-/-) mice exhibited faster blood ethanol clearance and earlier wake-up time than WT mice. Higher blood acetate, the end product of ethanol metabolism, and lower acetaldehyde levels were evident in the ethanol-challenged SHP(-/-) than WT mice. Ethanol-induced inflammatory responses and lipid peroxidation were also lower in SHP(-/-) mice. The current data show faster ethanol catabolism and extra fat storage through conversion of acetate to acetyl-CoA before its release into the circulation in this ethanol-feeding model in SHP(-/-) mice.

Intestinal microbiota contributes to individual susceptibility to alcoholic liver disease

OBJECTIVE

There is substantial inter-individual diversity in the susceptibility of alcoholics to liver injury. Alterations of intestinal microbiota (IM) have been reported in alcoholic liver disease (ALD), but the extent to which they are merely a consequence or a cause is unknown. We aimed to demonstrate that a specific dysbiosis contributes to the development of alcoholic hepatitis (AH).

DESIGN

We humanised germ-free and conventional mice using human IM transplant from alcoholic patients with or without AH. The consequences on alcohol-fed recipient mice were studied.

RESULTS

A specific dysbiosis was associated with ALD severity in patients. Mice harbouring the IM from a patient with severe AH (sAH) developed more severe liver inflammation with an increased number of liver T lymphocyte subsets and Natural Killer T (NKT) lymphocytes, higher liver necrosis, greater intestinal permeability and higher translocation of bacteria than mice harbouring the IM from an alcoholic patient without AH (noAH). Similarly, CD45+ lymphocyte subsets were increased in visceral adipose tissue, and CD4(+)T and NKT lymphocytes in mesenteric lymph nodes. The IM associated with sAH and noAH could be distinguished by differences in bacterial abundance and composition. Key deleterious species were associated with sAH while the Faecalibacterium genus was associated with noAH. Ursodeoxycholic acid was more abundant in faeces from noAH mice. Additionally, in conventional mice humanised with the IM from an sAH patient, a second subsequent transfer of IM from an noAH patient improved alcohol-induced liver lesions.

CONCLUSIONS

Individual susceptibility to ALD is substantially driven by IM. It may, therefore, be possible to prevent and manage ALD by IM manipulation.

Microarray Analysis of Differentially-Expressed Genes Encoding CYP450 and Phase II Drug Metabolizing Enzymes in Psoriasis and Melanoma

Cytochrome P450 drug metabolizing enzymes are implicated in personalized medicine for two main reasons. First, inter-individual variability in CYP3A4 expression is a confounding factor during cancer treatment. Second, inhibition or induction of CYP3A4 can trigger adverse drug–drug interactions. However, inflammation can downregulate CYP3A4 and other drug metabolizing enzymes and lead to altered metabolism of drugs and essential vitamins and lipids. Little is known about effects of inflammation on expression of CYP450 genes controlling drug metabolism in the skin. Therefore, we analyzed seven published microarray datasets, and identified differentially-expressed genes in two inflammatory skin diseases (melanoma and psoriasis). We observed opposite patterns of expression of genes regulating metabolism of specific vitamins and lipids in psoriasis and melanoma samples. Thus, genes controlling the turnover of vitamin D (CYP27B1, CYP24A1), vitamin A (ALDH1A3, AKR1B10), and cholesterol (CYP7B1), were up-regulated in psoriasis, whereas melanomas showed downregulation of genes regulating turnover of vitamin A (AKR1C3), and cholesterol (CYP39A1). Genes controlling abnormal keratinocyte differentiation and epidermal barrier function (CYP4F22, SULT2B1) were up-regulated in psoriasis. The up-regulated CYP24A1, CYP4F22, SULT2B1, and CYP7B1 genes are potential drug targets in psoriatic skin. Both disease samples showed diminished drug metabolizing capacity due to downregulation of the CYP1B1 and CYP3A5 genes. However, melanomas showed greater loss of drug metabolizing capacity due to downregulation of the CYP3A4 gene.

Genetic variants in or near ADH1B and ADH1C affect susceptibility to alcohol dependence in a British and Irish population

Certain single nucleotide polymorphisms (SNPs) in genes encoding alcohol dehydrogenase (ADH) enzymes confer a significant protective effect against alcohol dependence syndrome (ADS) in East Asian populations. Recently, attention has focused on the role of these SNPs in determining ADS risk in European populations. To further elucidate these associations, SNPs of interest in ADH1B, ADH1C and the ADH1B/1C intergenic region were genotyped in a British and Irish population (ADS cases n = 1076: controls n = 1027) to assess their relative contribution to ADS risk. A highly significant, protective association was observed between the minor allele of rs1229984 in ADH1B and ADS risk [allelic P = 8.4 × 10(-6) , odds ratio (OR) = 0.26, 95 percent confidence interval, 0.14, 0.49]. Significant associations were also observed between ADS risk and the ADH1B/1C intergenic variant, rs1789891 [allelic P = 7.2 × 10(-5) , OR = 1.4 (1.2, 1.6)] and three non-synonymous SNPs rs698, rs1693482 and rs283413 in ADH1C. However, these associations were not completely independent; thus, while the ADH1B rs1229984 minor allele association was independent of those of the intergenic variant rs1789891 and the three ADH1C variants, the three ADH1C variants were not individually independent. In conclusion, the rare ADH1B rs1229984 mutation provides significant protection against ADS in this British and Irish population; other variants in the ADH gene cluster also alter ADS risk, although the strong linkage disequilibrium between SNPs at this location precluded clear identification of the variant(s) driving the associations.

Role of farnesoid X receptor and bile acids in alcoholic liver disease

Alcoholic liver disease (ALD) is one of the major causes of liver morbidity and mortality worldwide. Chronic alcohol consumption leads to development of liver pathogenesis encompassing steatosis, inflammation, fibrosis, cirrhosis, and in extreme cases, hepatocellular carcinoma. Moreover, ALD may also associate with cholestasis. Emerging evidence now suggests that farnesoid X receptor (FXR) and bile acids also play important roles in ALD. In this review, we discuss the effects of alcohol consumption on FXR, bile acids and gut microbiome as well as their impacts on ALD. Moreover, we summarize the findings on FXR, FoxO3a (forkhead box-containing protein class O3a) and PPARα (peroxisome proliferator-activated receptor alpha) in regulation of autophagy-related gene transcription program and liver injury in response to alcohol exposure.