The role of cytochrome P4502E1 in the pathogenesis of alcoholic liver disease and carcinogenesis

Alcohol-Associated Liver Disease Outcomes: Critical Mechanisms of Liver Injury Progression

Alcohol-associated liver disease (ALD) is a substantial cause of morbidity and mortality worldwide and represents a spectrum of liver injury beginning with hepatic steatosis (fatty liver) progressing to inflammation and culminating in cirrhosis. Multiple factors contribute to ALD progression and disease severity. Here, we overview several crucial mechanisms related to ALD end-stage outcome development, such as epigenetic changes, cell death, hemolysis, hepatic stellate cells activation, and hepatic fatty acid binding protein 4. Additionally, in this review, we also present two clinically relevant models using human precision-cut liver slices and hepatic organoids to examine ALD pathogenesis and progression.

Bacillus coagulans regulates gut microbiota and ameliorates the alcoholic-associated liver disease in mice

Introduction

Alcoholic-associated liver diseases (ALD) are now widespread issues worldwide. Alcoholic-induced chronic dysbiosis of the gut microbiota is one of the factors in the pathophysiology of ALD.

Methods

In this work, we employed a chronic-binge ethanol feeding mice model, as described in a previous report.

Results

Our findings demonstrate that hepatic inflammatory injury damage and accumulation of fat can be effectively reduced in mice with ALD by altering the gut microbiota utilizing Bacillus coagulans. Treatment with B. coagulans significantly modulates the levels of TNF-α, IL-1β, and IL-22 cytokines while maintaining tight junction proteins and mucin protein expressions to support intestinal barrier function restoration. Treatment with B. coagulans also alters the composition of the gut microbiota and increases the production of short-chain fatty acids (SCFAs).

Discussion

This is mostly due to B. coagulans promotes the growth of bacteria that produce SCFAs, such as Ruminococcus species and Akkermansia, while inhibiting the growth of pathogenic bacteria like Escherichia Shigella. Moreover, treatment with B. coagulans causes levels of 2-Ketobutyric acid, ketoleucine, and indoleacetic acid increase while homovanillic acid and 3'-O-Methylguanosine metabolites decrease significantly. This study facilitates the development of therapeutic and preventive strategies for ALD using lactic acid bacteria.

What are the common downstream molecular events between alcoholic and nonalcoholic fatty liver?

Liver fat storage, also called hepatic steatosis, is increasingly common and represents a very frequent diagnosis in the medical field. Excess fat is not without consequences. In fact, hepatic steatosis contributes to the progression toward liver fibrosis. There are two main types of fatty liver disease, alcoholic fatty liver disease (AFLD) and nonalcoholic fatty liver disease (NAFLD). Although AFLD and NAFLD are similar in their initial morphological features, both conditions involve the same evolutive forms. Moreover, there are various common mechanisms underlying both diseases, including alcoholic liver disease and NAFLD, which are commonalities. In this Review, the authors explore similar downstream signaling events involved in the onset and progression of the two entities but not completely different entities, predominantly focusing on the gut microbiome. Downstream molecular events, such as the roles of sirtuins, cytokeratins, adipokines and others, should be considered. Finally, to complete the feature, some new tendencies in the therapeutic approach are presented.

Contributing roles of mitochondrial dysfunction and hepatocyte apoptosis in liver diseases through oxidative stress, post-translational modifications, inflammation, and intestinal barrier dysfunction

This review provides an update on recent findings from basic, translational, and clinical studies on the molecular mechanisms of mitochondrial dysfunction and apoptosis of hepatocytes in multiple liver diseases, including but not limited to alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatotic liver disease (MASLD), and drug-induced liver injury (DILI). While the ethanol-inducible cytochrome P450-2E1 (CYP2E1) is mainly responsible for oxidizing binge alcohol via the microsomal ethanol oxidizing system, it is also responsible for metabolizing many xenobiotics, including pollutants, chemicals, drugs, and specific diets abundant in n-6 fatty acids, into toxic metabolites in many organs, including the liver, causing pathological insults through organelles such as mitochondria and endoplasmic reticula. Oxidative imbalances (oxidative stress) in mitochondria promote the covalent modifications of lipids, proteins, and nucleic acids through enzymatic and non-enzymatic mechanisms. Excessive changes stimulate various post-translational modifications (PTMs) of mitochondrial proteins, transcription factors, and histones. Increased PTMs of mitochondrial proteins inactivate many enzymes involved in the reduction of oxidative species, fatty acid metabolism, and mitophagy pathways, leading to mitochondrial dysfunction, energy depletion, and apoptosis. Unique from other organelles, mitochondria control many signaling cascades involved in bioenergetics (fat metabolism), inflammation, and apoptosis/necrosis of hepatocytes. When mitochondrial homeostasis is shifted, these pathways become altered or shut down, likely contributing to the death of hepatocytes with activation of inflammation and hepatic stellate cells, causing liver fibrosis and cirrhosis. This review will encapsulate how mitochondrial dysfunction contributes to hepatocyte apoptosis in several types of liver diseases in order to provide recommendations for targeted therapeutics.

Hydrogen Peroxide Induces Ethanol-inducible CYP2E1 via the NF-kB-classical Pathway: CYP2E1 mRNA Levels are not High in Alcoholic Hepatitis

AIMS

The aim of the present study is to elucidate the mechanism of CYP2E1 induction as a causative factor of Alcoholic Hepatitis (AH) and its relationship with inflammation.

BACKGROUND

Chronic alcohol consumption induces CYP2E1, which is involved in the development of Alcoholic Hepatitis (AH). However, the mechanisms underlying the induction of CYP2E1 by alcohol remain unclear. Therefore, we herein investigated the induction of drug-metabolizing enzymes, particularly CYP2E1, by hydrogen peroxide (H2O2), the concentration of which is elevated under inflammatory conditions.

OBJECTIVE

The mechanisms underlying the induction of CYP2E1 by H2O2 were examined with a focus on Keap1, a target factor of H2O2.

METHODS

We assessed changes in the expression of drug-metabolizing enzymes in the human hepatoma cell line, Hep3B, following treatment with H2O2, and evaluated changes in the expression of the NF-kB-related factor RelA(p65) after the knockdown of Keap1, a regulator of Nrf2 expression by reactive oxygen species. We also performed a promoter analysis using the upstream region of the CYP2E1 gene. We herein used the GSE89632 series for non-alcoholic hepatitis (NASH) and the GSE28619 series for AH.

RESULTS

The induction of CYP2E1 by H2O2 was significantly stronger than that of other drugmetabolizing enzymes. On the other hand, the knockdown of Keap1, a target of H2O2, markedly increased RelA(p65), an NFkB factor. Furthermore, the overexpression of RelA(p65) strongly induced the expression of CYP2E1. Four candidate p65-binding sequences were identified upstream of the CYP2E1 gene, and promoter activity assays showed that the third sequence was responsive to the overexpression of RelA(p65). We used the GSE89632 series for NASH and the GSE28619 series for AH in the present study. The expression of CYP2E1 mRNA in the liver was significantly lower in AH patients than in HC patients, but was similar in HC patients and NASH patients.

CONCLUSION

We herein demonstrated that the expression of CYP2E1 was induced by H2O2. The overexpression of RelA(p65) also induced CYP2E1 mRNA expression, whereas H2O2 did not after the knockdown of RelA. These results suggest that H2O2 acts on Keap1 to upregulate RelA (p65) in the NFkB system. One of the mechanisms underlying the induction of CYP2E1 was dependent on the H2O2-Keap1-RelA axis. The results of the database analysis revealed that the expression of CYP2E1 in the liver was significantly lower in AH patients than in NASH patients, suggesting that CYP2E1 is not the main cause of AH; however, CYP2E1 may exacerbate the pathogenesis of AH.

Melatonin Prevents Alcohol- and Metabolic Dysfunction- Associated Steatotic Liver Disease by Mitigating Gut Dysbiosis, Intestinal Barrier Dysfunction, and Endotoxemia

Melatonin (MT) has often been used to support good sleep quality, especially during the COVID-19 pandemic, as many have suffered from stress-related disrupted sleep patterns. It is less known that MT is an antioxidant, anti-inflammatory compound, and modulator of gut barrier dysfunction, which plays a significant role in many disease states. Furthermore, MT is produced at 400-500 times greater concentrations in intestinal enterochromaffin cells, supporting the role of MT in maintaining the functions of the intestines and gut-organ axes. Given this information, the focus of this article is to review the functions of MT and the molecular mechanisms by which it prevents alcohol-associated liver disease (ALD) and metabolic dysfunction-associated steatotic liver disease (MASLD), including its metabolism and interactions with mitochondria to exert its antioxidant and anti-inflammatory activities in the gut-liver axis. We detail various mechanisms by which MT acts as an antioxidant, anti-inflammatory compound, and modulator of intestinal barrier function to prevent the progression of ALD and MASLD via the gut-liver axis, with a focus on how these conditions are modeled in animal studies. Using the mechanisms of MT prevention and animal studies described, we suggest behavioral modifications and several exogenous sources of MT, including food and supplements. Further clinical research should be performed to develop the field of MT in preventing the progression of liver diseases via the gut-liver axis, so we mention a few considerations regarding MT supplementation in the context of clinical trials in order to advance this field of research.

Lactoferrin Alleviates Ethanol-Induced Injury via Promoting Nrf2 Nuclear Translocation in BRL-3A Rat Liver Cells

Our previous animal studies found that the preventive effects of lactoferrin (Lf) on alcoholic liver injury (ALI) are associated with nuclear factor E2-related factor 2 (Nrf2). To further explore the causality, experiments were performed using rat normal liver BRL-3A cells. Lf treatment reduced ethanol-induced death and apoptosis; meanwhile, Lf treatment alleviated excessive LDH release. These findings confirmed the protection of Lf against ethanol-induced injury in BRL-3A cells. Mechanistically, Lf treatment reversed the reduction in nuclear Nrf2 induced by ethanol without affecting the cytoplasmic Nrf2 level, which led to antioxidant enzyme activity restoration. However, the blocking of Nrf2 nuclear translocation by ML385 eliminated the protective effects of Lf. In a conclusion, Lf protects BRL-3A cells from ethanol-induced injury via promoting Nrf2 nuclear translocation.

Post-translational modifications of histone and non-histone proteins in epigenetic regulation and translational applications in alcohol-associated liver disease: Challenges and research opportunities

Epigenetic regulation is a process that takes place through adaptive cellular pathways influenced by environmental factors and metabolic changes to modulate gene activity with heritable phenotypic variations without altering the DNA sequences of many target genes. Epigenetic regulation can be facilitated by diverse mechanisms: many different types of post-translational modifications (PTMs) of histone and non-histone nuclear proteins, DNA methylation, altered levels of noncoding RNAs, incorporation of histone variants, nucleosomal positioning, chromatin remodeling, etc. These factors modulate chromatin structure and stability with or without the involvement of metabolic products, depending on the cellular context of target cells or environmental stimuli, such as intake of alcohol (ethanol) or Western-style high-fat diets. Alterations of epigenetics have been actively studied, since they are frequently associated with multiple disease states. Consequently, explorations of epigenetic regulation have recently shed light on the pathogenesis and progression of alcohol-associated disorders. In this review, we highlight the roles of various types of PTMs, including less-characterized modifications of nuclear histone and non-histone proteins, in the epigenetic regulation of alcohol-associated liver disease (ALD) and other disorders. We also describe challenges in characterizing specific PTMs and suggest future opportunities for basic and translational research to prevent or treat ALD and many other disease states.

Stereoisomers of octahydrocurcumin, the hydrogenated metabolites of curcumin, display stereoselective activity on the CYP2E1 enzyme in L-02 cells

As the final hydrogenated metabolite of curcumin, octahydrocurcumin (OHC) exhibits increased powerful bioactivities. The chiral and symmetric chemical structure indicated that there were two OHC stereoisomers, (3R,5S)-octahydrocurcumin (Meso-OHC) and (3S,5S)-octahydrocurcumin ((3S,5S)-OHC), which may induce different effects on metabolic enzymes and bioactivities. Thus, we detected OHC stereoisomers from rat metabolites (blood, liver, urine and feces) after oral administration of curcumin. In addition, OHC stereoisomers were prepared and then their different influences on cytochrome P450 enzymes (CYPs) and UDP-glucuronyltransferases (UGTs) in L-02 cells were tested to explore the potential interaction and different bioactivities. Our results proved that curcumin could be metabolised into OHC stereoisomers first. In addition, Meso-OHC and (3S,5S)-OHC exhibited slight induction or inhibition effects on CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP3A4 and UGTs. Furthermore, Meso-OHC exhibited more intensive inhibition toward CYP2E1 expression than (3S,5S)-OHC, ascribed to the different mode of binding to the enzyme protein (P < 0.05), which finally induced more effective liver protection effects in acetaminophen-induced L-02 cell injury.

Role of AMPK-SREBP Signaling in Regulating Fatty Acid Binding-4 (FABP4) Expression following Ethanol Metabolism

Fatty acid binding protein-4 (FABP4) is not normally expressed in the liver but is induced in alcohol-dependent liver disease (ALD)). This study sought to identify mechanisms whereby ethanol (EtOH) metabolism alters triglyceride accumulation and FABP4 production. Human hepatoma cells which were stably transfected to express alcohol dehydrogenase (ADH) or cytochrome P4502E1 (CYP2E1) were exposed to EtOH in the absence/presence of inhibitors of ADH (4-methylpyrazole) or CYP2E1 (chlormethiazole). Cells were analyzed for free fatty acid (FFA) content and FABP4 mRNA, then culture medium assayed for FABP4 levels. Cell lysates were analyzed for AMP-activated protein kinase-α (AMPKα), Acetyl-CoA carboxylase (ACC), sterol regulatory element binding protein-1c (SREBP-1c), and Lipin-1β activity and localization in the absence/presence of EtOH and pharmacological inhibitors. CYP2E1-EtOH metabolism led to increased FABP4 mRNA/protein expression and FFA accumulation. Analysis of signaling pathway activity revealed decreased AMPKα activation and increased nuclear-SREBP-1c localization following CYP2E1-EtOH metabolism. The role of AMPKα-SREBP-1c in regulating CYP2E1-EtOH-dependent FFA accumulation and increased FABP4 was confirmed using pharmacological inhibitors and over-expression of AMPKα. Inhibition of ACC or Lipin-1β failed to prevent FFA accumulation or changes in FABP4 mRNA expression or protein secretion. These data suggest that CYP2E1-EtOH metabolism inhibits AMPKα phosphorylation to stimulate FFA accumulation and FABP4 protein secretion via an SREBP-1c dependent mechanism.

Oxidative stress, glutathione, and CYP2E1 in 1,4-dioxane liver cytotoxicity and genotoxicity: insights from animal models

1,4-Dioxane (DX) is an emerging drinking water contaminant worldwide, which poses a threat to public health due to its demonstrated liver carcinogenicity and potential for human exposure. The lack of drinking water standards for DX is attributed to undetermined mechanisms of DX carcinogenicity. This mini-review provides a brief discussion of a series of mechanistic studies, wherein unique mouse models were exposed to DX in drinking water to elucidate redox changes associated with DX cytotoxicity and genotoxicity. The overall conclusions from these studies support a direct genotoxic effect by high dose DX and imply that oxidative stress involving CYP2E1 activation may play a causal role in DX liver genotoxicity and potentially carcinogenicity. The mechanistic data derived from these studies can serve as important references to refine the assessment of carcinogenic pathways that may be triggered at environmentally relevant low doses of DX in future animal and human studies.

Lactoferrin Prevents Chronic Alcoholic Injury by Regulating Redox Balance and Lipid Metabolism in Female C57BL/6J Mice

This study aimed to investigate the preventive effects of lactoferrin (Lf) on chronic alcoholic liver injury (ALI) in female mice. Female C57BL/6J mice were randomly divided into four groups: control group (CON), ethanol administration group (EtOH), low-dose Lf treatment group (LLf), and high-dose Lf group (HLf). In the last three groups, chronic ALI was induced by administering 20% ethanol ad libitum for 12 weeks. Mice in the CON and EtOH groups were fed with AIN-93G diet. Meanwhile, 0.4% and 4% casein in the AIN-93G diet were replaced by Lf as the diets of LLf and HLf groups, respectively. HLf significantly reduced hepatic triglyceride content and improved pathological morphology. HLf could inhibit cytochrome P450 2E1 overexpression and promote alcohol dehydrogenase-1 expression. HLf activated protein kinase B and AMP-activated protein kinase (AMPK), as well as upregulating nuclear-factor-erythroid-2-related factor-2 expression to elevate hepatic antioxidative enzyme activities. AMPK activation also benefited hepatic lipid metabolism. Meanwhile, HLf had no obvious beneficial effects on gut microbiota. In summary, Lf could alleviate chronic ALI in female mice, which was associated with redox balance and lipid metabolism regulation.

Cytochrome P450 2E1-dependent hepatic ethanol metabolism induces fatty acid-binding protein 4 and steatosis

BACKGROUND

Hepatic steatosis is an early pathology of alcohol-associated liver disease (ALD). Fatty acid-binding protein-4 (FABP4, a FABP not normally produced in the liver) is secreted by hepatocytes in ALD and stimulates hepatoma proliferation and migration. This study sought to investigate the mechanism[s] by which hepatic ethanol metabolism regulates FABP4 and steatosis.

METHODS

Human hepatoma cells (HepG2/HuH7) and cells stably transfected to express cytochrome P450 2E1 (CYP2E1), were exposed to ethanol in the absence or presence of chlormethiazole (a CYP2E1-inhibitor; CMZ) and/or EX-527 (a sirtuin-1 [SIRT1] inhibitor). The culture medium was analyzed for ethanol metabolism and FABP4 protein abundance. Cells were analyzed for FABP4 mRNA expression, SIRT1 protein abundance, and neutral lipid accumulation. In parallel, cells were analyzed for forkhead box O1 [FOXO1], β-catenin, peroxisome proliferator-activated receptor-α [PPARα], and lipin-1α protein abundance in the absence or presence of ethanol and pharmacological inhibitors of the respective target proteins.

RESULTS

CYP2E1-dependent ethanol metabolism inhibited the amount of SIRT1 protein detected, concomitant with increased FABP4 mRNA expression, FABP4 protein secretion, and neutral lipid accumulation, effects abolished by CMZ. Analysis of pathways associated with lipid oxidation revealed increased FOXO1 nuclear localization and decreased β-catenin, PPARα, and lipin-1α protein levels in CYP2E1-expressing cells in the presence of ethanol. Pharmacological inhibition of SIRT1 mimicked the effects of ethanol, while inhibition of FOXO1 abrogated the effect of ethanol on FABP4 mRNA expression, FABP4 protein secretion, and neutral lipid accumulation in CYP2E1-expressing cells. Pharmacological inhibition of β-catenin, PPARα, or lipin-1α failed to alter the effects of ethanol on FABP4 or neutral lipid accumulation.

CONCLUSION

CYP2E1-dependent ethanol metabolism inhibits SIRT1-FOXO1 signaling, which leads to increased FABP4 mRNA expression, FABP4 protein secretion, and neutral lipid accumulation. These data suggest that FABP4 released from steatotic hepatocytes could play a role in promoting tumor cell expansion in the setting of ALD and represents a potential target for therapeutic intervention.

CYP2E1 plays a suppressive role in hepatocellular carcinoma by regulating Wnt/Dvl2/β-catenin signaling

Objective

Knowledge of the role of CYP2E1 in hepatocarcinogenesis is largely based on epidemiological and animal studies, with a primary focus on the role of CYP2E1 in metabolic activation of procarcinogens. Few studies have directly assessed the effects of CYP2E1 on HCC malignant phenotypes.

Methods

The expression of CYP2E1 in HCC tissues was determined by qRT-PCR, western blotting and immunohistochemistry. Overexpression of CYP2E1 in HCC cell was achieved by lentivirus transfection. The function of CYP2E1 were detected by CCK-8, wound healing, transwell assays, xenograft models and pulmonary metastasis model. TOP/FOPFlash reporter assay, western blotting, functional rescue experiments, Co-immunoprecipitation and reactive oxygen species detection were conducted to reveal the underlying mechanism of the tumor suppressive role of CYP2E1.

Results

CYP2E1 expression is down-regulated in HCC tissues, and this downregulation was associated with large tumor diameter, vascular invasion, poor differentiation, and shortened patient survival time. Ectopic expression of CYP2E1 inhibits the proliferation, invasion and migration and epithelial-to-mesenchymal transition of HCC cells in vitro, and inhibits tumor formation and lung metastasis in nude mice. Mechanistic investigations show that CYP2E1 overexpression significantly inhibited Wnt/β-catenin signaling activity and decreased Dvl2 expression in HCC cells. An increase in Dvl2 expression restored the malignant phenotype of HCC cells. Notably, CYP2E1 promoted the ubiquitin-mediated degradation of Dvl2 by strengthening the interaction between Dvl2 and the E3 ubiquitin ligase KLHL12 in CYP2E1-stable HCC cells. CYP2E1-induced ROS accumulation was a critical upstream event in the Wnt/β-Catenin pathway in CYP2E1-overexpressing HCC cells.

Conclusions

These results provide novel insight into the role of CYP2E1 in HCC and the tumor suppressor role of CYP2E1 can be attributed to its ability to manipulate Wnt/Dvl2/β-catenin pathway via inducing ROS accumulation, which provides a potential target for the prevention and treatment of HCC.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03396-6.

Xenobiotic-Induced Aggravation of Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD), which is often linked to obesity, encompasses a large spectrum of hepatic lesions, including simple fatty liver, steatohepatitis, cirrhosis and hepatocellular carcinoma. Besides nutritional and genetic factors, different xenobiotics such as pharmaceuticals and environmental toxicants are suspected to aggravate MAFLD in obese individuals. More specifically, pre-existing fatty liver or steatohepatitis may worsen, or fatty liver may progress faster to steatohepatitis in treated patients, or exposed individuals. The mechanisms whereby xenobiotics can aggravate MAFLD are still poorly understood and are currently under deep investigations. Nevertheless, previous studies pointed to the role of different metabolic pathways and cellular events such as activation of de novo lipogenesis and mitochondrial dysfunction, mostly associated with reactive oxygen species overproduction. This review presents the available data gathered with some prototypic compounds with a focus on corticosteroids and rosiglitazone for pharmaceuticals as well as bisphenol A and perfluorooctanoic acid for endocrine disruptors. Although not typically considered as a xenobiotic, ethanol is also discussed because its abuse has dire consequences on obese liver.

Role of Mitochondrial Cytochrome P450 2E1 in Healthy and Diseased Liver

Cytochrome P450 2E1 (CYP2E1) is pivotal in hepatotoxicity induced by alcohol abuse and different xenobiotics. In this setting, CYP2E1 generates reactive metabolites inducing oxidative stress, mitochondrial dysfunction and cell death. In addition, this enzyme appears to play a role in the progression of obesity-related fatty liver to nonalcoholic steatohepatitis. Indeed, increased CYP2E1 activity in nonalcoholic fatty liver disease (NAFLD) is deemed to induce reactive oxygen species overproduction, which in turn triggers oxidative stress, necroinflammation and fibrosis. In 1997, Avadhani’s group reported for the first time the presence of CYP2E1 in rat liver mitochondria, and subsequent investigations by other groups confirmed that mitochondrial CYP2E1 (mtCYP2E1) could be found in different experimental models. In this review, we first recall the main features of CYP2E1 including its role in the biotransformation of endogenous and exogenous molecules, the regulation of its expression and activity and its involvement in different liver diseases. Then, we present the current knowledge on the physiological role of mtCYP2E1, its contribution to xenobiotic biotransformation as well as the mechanism and regulation of CYP2E1 targeting to mitochondria. Finally, we discuss experimental investigations suggesting that mtCYP2E1 could have a role in alcohol-associated liver disease, xenobiotic-induced hepatotoxicity and NAFLD.

Alcohol induced hepatic retinoid depletion is associated with the induction of multiple retinoid catabolizing cytochrome P450 enzymes

Chronic alcohol consumption leads to a spectrum of liver disease that is associated with significant global mortality and morbidity. Alcohol is known to deplete hepatic vitamin A content, which has been linked to the pathogenesis of alcoholic liver disease. It has been suggested that induction of Cytochrome P450 2E1 (CYP2E1) contributes to alcohol-induced hepatic vitamin A depletion, but the possible contributions of other retinoid-catabolizing CYPs have not been well studied. The main objective of this study was to better understand alcohol-induced hepatic vitamin A depletion and test the hypothesis that alcohol-induced depletion of hepatic vitamin A is due to CYP-mediated oxidative catabolism. This hypothesis was tested in a mouse model of chronic alcohol consumption, including wild type and Cyp2e1 -/- mice. Our results show that chronic alcohol consumption is associated with decreased levels of hepatic retinol, retinyl esters, and retinoic acid. Moreover, the depletion of hepatic retinoid is associated with the induction of multiple retinoid catabolizing CYPs, including CYP26A1, and CYP26B1 in alcohol fed wild type mice. In Cyp2e1 -/- mice, alcohol-induced retinol decline is blunted but retinyl esters undergo a change in their acyl composition and decline upon alcohol exposure like WT mice. In conclusion, the alcohol induced decline in hepatic vitamin A content is associated with increased expression of multiple retinoid-catabolizing CYPs, including the retinoic acid specific hydroxylases CYP26A1 and CYP26B1.

WGCNA-Based Identification of Hub Genes and Key Pathways Involved in Nonalcoholic Fatty Liver Disease

Background

The morbidity of nonalcoholic fatty liver disease (NAFLD) has been rising, but the pathogenesis of NAFLD is still elusive. This study is aimed at determining NAFLD-related hub genes based on weighted gene coexpression network analysis (WGCNA).

Methods

GSE126848 dataset based construction of coexpression networks was performed based on WGCNA. Database for Annotation, Visualization, and Integrated Discovery (DAVID) was utilized for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Hub genes were identified and validated in independent datasets and mouse model.

Results

We found that the steelblue module was most significantly correlated with NAFLD. Total 15 hub genes (NDUFA9, UQCRQ, NDUFB8, COPS5, RPS17, UBL5, PSMA3, PSMA1, SF3B5, MRPL27, RPL26, PDCD5, PFDN6, SNRPD2, PSMB3) were derived from both the coexpression and PPI networks and considered “true” hub genes. Functional enrichment analysis showed that the hub genes were related to NAFLD pathway and oxidative phosphorylation. Independent dataset-based analysis and the establishment of NAFLD mouse model confirmed the involvement of two hub genes NDUFA9 and UQCRQ in the pathogenesis of NAFLD.

Conclusions

Oxidative phosphorylation and NAFLD pathway may be crucially involved in the pathogenesis of NAFLD, and two hub genes NDUFA9 and UQCRQ might be diagnostic biomarkers and therapeutic targets for NAFLD.

Lactoferrin Alleviates Acute Alcoholic Liver Injury by Improving Redox-Stress Response Capacity in Female C57BL/6J Mice

Lactoferrin (Lf) can attenuate alcoholic liver injury (ALI) in male mice; however, the effects of Lf on acute ALI in female mice are still unknown. Female C57BL/6J mice were randomly divided into four groups and fed with different diets for 4 weeks: an AIN-93G diet for control (CON) and ethanol (EtOH) groups; an AIN-93G diet with 0.4 and 4% casein replaced by Lf for low-dose Lf (LLf) and high-dose Lf (HLf) groups. Acute ALI was induced by intragastric administration of ethanol (4.8 g/kgbw) every 12 h continuously for three times. HLf had obvious alleviating effects on acute ALI. Lf pretreatment did not affect hepatic alcohol metabolism key enzymes. Meanwhile, the ethanol-induced hepatic reactive oxygen species level increase was not ameliorated by Lf. Metabolomics and bioinformatics analysis results suggested an important role of redox-stress response capacity (RRC). Western blots showed HLf-promoted AKT and AMP-activated protein kinase activations and upregulated Nrf2 and LC3-II expressions, which was associated with RRC improvement. In summary, HLf could prevent acute ALI in female mice, and RRC likely played an important role.

CYP2E1 in Alcoholic and Non-Alcoholic Liver Injury. Roles of ROS, Reactive Intermediates and Lipid Overload

CYP2E1 is one of the fifty-seven cytochrome P450 genes in the human genome and is highly conserved. CYP2E1 is a unique P450 enzyme because its heme iron is constitutively in the high spin state, allowing direct reduction of, e.g., dioxygen, causing the formation of a variety of reactive oxygen species and reduction of xenobiotics to toxic products. The CYP2E1 enzyme has been the focus of scientific interest due to (i) its important endogenous function in liver homeostasis, (ii) its ability to activate procarcinogens and to convert certain drugs, e.g., paracetamol and anesthetics, to cytotoxic end products, (iii) its unique ability to effectively reduce dioxygen to radical species causing liver injury, (iv) its capability to reduce compounds, often generating radical intermediates of direct toxic or indirect immunotoxic properties and (v) its contribution to the development of alcoholic liver disease, steatosis and NASH. In this overview, we present the discovery of the enzyme and studies in humans, 3D liver systems and genetically modified mice to disclose its function and clinical relevance. Induction of the CYP2E1 enzyme either by alcohol or high-fat diet leads to increased severity of liver pathology and likelihood to develop ALD and NASH, with subsequent influence on the occurrence of hepatocellular cancer. Thus, fat-dependent induction of the enzyme might provide a link between steatosis and fibrosis in the liver. We conclude that CYP2E1 has many important physiological functions and is a key enzyme for hepatic carcinogenesis, drug toxicity and liver disease.

Biochemical Mechanisms Associating Alcohol Use Disorders with Cancers

Simple Summary

Of all yearly deaths attributable to alcohol consumption globally, approximately 12% are due to cancers, representing approximately 0.4 million deceased individuals. Ethanol metabolism disturbs cell biochemistry by targeting the structure and function of essential biomolecules (proteins, nucleic acids, and lipids) and by provoking alterations in cell programming that lead to cancer development and cancer malignancy. A better understanding of the metabolic and cell signaling realm affected by ethanol is paramount to designing effective treatments and preventive actions tailored to specific neoplasias.

Abstract

The World Health Organization identifies alcohol as a cause of several neoplasias of the oropharynx cavity, esophagus, gastrointestinal tract, larynx, liver, or female breast. We review ethanol’s nonoxidative and oxidative metabolism and one-carbon metabolism that encompasses both redox and transfer reactions that influence crucial cell proliferation machinery. Ethanol favors the uncontrolled production and action of free radicals, which interfere with the maintenance of essential cellular functions. We focus on the generation of protein, DNA, and lipid adducts that interfere with the cellular processes related to growth and differentiation. Ethanol’s effects on stem cells, which are responsible for building and repairing tissues, are reviewed. Cancer stem cells (CSCs) of different origins suffer disturbances related to the expression of cell surface markers, enzymes, and transcription factors after ethanol exposure with the consequent dysregulation of mechanisms related to cancer metastasis or resistance to treatments. Our analysis aims to underline and discuss potential targets that show more sensitivity to ethanol’s action and identify specific metabolic routes and metabolic realms that may be corrected to recover metabolic homeostasis after pharmacological intervention. Specifically, research should pay attention to re-establishing metabolic fluxes by fine-tuning the functioning of specific pathways related to one-carbon metabolism and antioxidant processes.

Translational Approaches with Antioxidant Phytochemicals against Alcohol-Mediated Oxidative Stress, Gut Dysbiosis, Intestinal Barrier Dysfunction, and Fatty Liver Disease

Emerging data demonstrate the important roles of altered gut microbiomes (dysbiosis) in many disease states in the peripheral tissues and the central nervous system. Gut dysbiosis with decreased ratios of Bacteroidetes/Firmicutes and other changes are reported to be caused by many disease states and various environmental factors, such as ethanol (e.g., alcohol drinking), Western-style high-fat diets, high fructose, etc. It is also caused by genetic factors, including genetic polymorphisms and epigenetic changes in different individuals. Gut dysbiosis, impaired intestinal barrier function, and elevated serum endotoxin levels can be observed in human patients and/or experimental rodent models exposed to these factors or with certain disease states. However, gut dysbiosis and leaky gut can be normalized through lifestyle alterations such as increased consumption of healthy diets with various fruits and vegetables containing many different kinds of antioxidant phytochemicals. In this review, we describe the mechanisms of gut dysbiosis, leaky gut, endotoxemia, and fatty liver disease with a specific focus on the alcohol-associated pathways. We also mention translational approaches by discussing the benefits of many antioxidant phytochemicals and/or their metabolites against alcohol-mediated oxidative stress, gut dysbiosis, intestinal barrier dysfunction, and fatty liver disease.

Advanced glycation end products (AGEs) and other adducts in aging-related diseases and alcohol-mediated tissue injury

Advanced glycation end products (AGEs) are potentially harmful and heterogeneous molecules derived from nonenzymatic glycation. The pathological implications of AGEs are ascribed to their ability to promote oxidative stress, inflammation, and apoptosis. Recent studies in basic and translational research have revealed the contributing roles of AGEs in the development and progression of various aging-related pathological conditions, such as diabetes, cardiovascular complications, gut microbiome-associated illnesses, liver or neurodegenerative diseases, and cancer. Excessive chronic and/or acute binge consumption of alcohol (ethanol), a widely consumed addictive substance, is known to cause more than 200 diseases, including alcohol use disorder (addiction), alcoholic liver disease, and brain damage. However, despite the considerable amount of research in this area, the underlying molecular mechanisms by which alcohol abuse causes cellular toxicity and organ damage remain to be further characterized. In this review, we first briefly describe the properties of AGEs: their formation, accumulation, and receptor interactions. We then focus on the causative functions of AGEs that impact various aging-related diseases. We also highlight the biological connection of AGE-alcohol-adduct formations to alcohol-mediated tissue injury. Finally, we describe the potential translational research opportunities for treatment of various AGE- and/or alcohol-related adduct-associated disorders according to the mechanistic insights presented.

New insight and potential therapy for NAFLD: CYP2E1 and flavonoids

Over the years, the prevalence of nonalcoholic fatty liver disease (NAFLD) has increased year by year; however, due to its complicated pathogenesis, there is no effective treatment so far. It is reported that Cytochrome P450 2E1 (CYP2E1) plays an indispensable role in the development of NAFLD, and numerous studies have shown that flavonoids have a hepatoprotective effect and can exert a beneficial effect on NAFLD by regulating the activity of CYP2E1. Therefore, flavonoids may become effective drugs for the treatment of NAFLD in the future. This prompted us to review the research progress of the pathological mechanism of NAFLD and the impact of CYP2E1 activity changes during the pathological process, and to summarize the protective effect of flavonoids against CYP2E1 activity.

Utility of Common Marmoset (Callithrix jacchus) Embryonic Stem Cells in Liver Disease Modeling, Tissue Engineering and Drug Metabolism

The incidence of liver disease is increasing significantly worldwide and, as a result, there is a pressing need to develop new technologies and applications for end-stage liver diseases. For many of them, orthotopic liver transplantation is the only viable therapeutic option. Stem cells that are capable of differentiating into all liver cell types and could closely mimic human liver disease are extremely valuable for disease modeling, tissue regeneration and repair, and for drug metabolism studies to develop novel therapeutic treatments. Despite the extensive research efforts, positive results from rodent models have not translated meaningfully into realistic preclinical models and therapies. The common marmoset Callithrix jacchus has emerged as a viable non-human primate model to study various human diseases because of its distinct features and close physiologic, genetic and metabolic similarities to humans. C. jacchus embryonic stem cells (cjESC) and recently generated cjESC-derived hepatocyte-like cells (cjESC-HLCs) could fill the gaps in disease modeling, liver regeneration and metabolic studies. They are extremely useful for cell therapy to regenerate and repair damaged liver tissues in vivo as they could efficiently engraft into the liver parenchyma. For in vitro studies, they would be advantageous for drug design and metabolism in developing novel drugs and cell-based therapies. Specifically, they express both phase I and II metabolic enzymes that share similar substrate specificities, inhibition and induction characteristics, and drug metabolism as their human counterparts. In addition, cjESCs and cjESC-HLCs are advantageous for investigations on emerging research areas, including blastocyst complementation to generate entire livers, and bioengineering of discarded livers to regenerate whole livers for transplantation.