The impact of CYP2E1 on the development of alcoholic liver disease as studied in a transgenic mouse model

Kaempferol and nicotiflorin ameliorated alcohol-induced liver injury in mice by miR-138-5p/SIRT1/FXR and gut microbiota

Aims

Excessive alcohol consumption can lead to alcoholic liver diseases (ALDs). Tetrastigma hemsleyanum Diels et Gilg is a rare Chinese medicinal herb. Tetrastigma hemsleyanum Diels et Gilg has been validated to be highly effective for treating hepatitis. Kaempferol and nicotiflorin are two highly representative flavonoids, which have exhibit therapeutic effects on liver disease. Therefore, the protective mechanism of kaempferol and nicotiflorin on alcohol-induced liver injury were investigated.

Main methods

Forty mice were used in this study. After treatment of Kaempferol and nicotiflorin, serum and liver were collected and used for determination of biochemical indicators, H&E staining, and molecular detection. The interaction of miRNAs from serum extracellular vehicles (EVs) with mRNAs and 16S rRNA sequencing of gut microbiota were also investigated.

Key findings

The results showed that kaempferol and nicotiflorins significantly ameliorated alcohol-induced liver damage and observably regulated gut microbiota. Specifically, the levels of malondialdehyde (MDA) and CYP2E1 in the liver significantly reduced, and the activity of superoxide dismutase (SOD) and glutathione (GSH) in the liver evidently increased. They also significantly relieved liver oxidative stress and lipid accumulation by suppressing miR-138-5p expression, inversely enhancing deacetylase silencing information regulator 2 related enzyme-1 (SIRT1) levels and then decreasing farnesoid X receptor (FXR) acetylation, which then modulated Nrf2 and SREBP-1c signaling pathways to regulate oxidative stress and lipid metabolism induced by alcohol.

Significance

Kaempferol and nicotiflorin reduced alcohol-induced liver damage by enhancing alcohol metabolism and reducing oxidative stress and lipid metabolism. The intestinal microorganism disorder was also ameliorated after oral kaempferol and nicotiflorin.

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.

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.

The Influence of Arsenic Co-Exposure in a Model of Alcohol-Induced Neurodegeneration in C57BL/6J Mice

Both excessive alcohol consumption and exposure to high levels of arsenic can lead to neurodegeneration, especially in the hippocampus. Co-exposure to arsenic and alcohol can occur because an individual with an Alcohol Use Disorder (AUD) is exposed to arsenic in their drinking water or food or because of arsenic found directly in alcoholic beverages. This study aims to determine if co-exposure to alcohol and arsenic leads to worse outcomes in neurodegeneration and associated mechanisms that could lead to cell death. To study this, mice were exposed to a 10-day gavage model of alcohol-induced neurodegeneration with varying doses of arsenic (0, 0.005, 2.5, or 10 mg/kg). The following were examined after the last dose of ethanol: (1) microglia activation assessed via immunohistochemical detection of Iba-1, (2) reactive oxygen and nitrogen species (ROS/RNS) using a colorimetric assay, (3) neurodegeneration using Fluoro-Jade® C staining (FJC), and 4) arsenic absorption using ICP-MS. After exposure, there was an additive effect of the highest dose of arsenic (10 mg/kg) in the dentate gyrus of alcohol-induced FJC+ cells. This additional cell loss may have been due to the observed increase in microglial reactivity or increased arsenic absorption following co-exposure to ethanol and arsenic. The data also showed that arsenic caused an increase in CYP2E1 expression and ROS/RNS production in the hippocampus which could have independently contributed to increased neurodegeneration. Altogether, these findings suggest a potential cyclical impact of co-exposure to arsenic and ethanol as ethanol increases arsenic absorption but arsenic also enhances alcohol's deleterious effects in the CNS.

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.

USP14 governs CYP2E1 to promote nonalcoholic fatty liver disease through deubiquitination and stabilization of HSP90AA1

Nonalcoholic fatty liver disease (NAFLD) begins with excessive triglyceride accumulation in the liver, and overly severe hepatic steatosis progresses to nonalcoholic steatohepatitis (NASH), which is characterized by lipid peroxidation, inflammation, and fibrosis. Ubiquitin-specific proteinase 14 (USP14) regulates inflammation, hepatocellular carcinoma and viral infection, but the effect of USP14 on NAFLD is unknown. The aim of this study was to reveal the role of USP14 in the progression of NAFLD and its underlying mechanism. We demonstrated that hepatic USP14 expression was significantly increased in NAFLD in both humans and mice. Hepatic USP14 overexpression exacerbated diet-induced hepatic steatosis, inflammation and fibrosis in mice, in contrast to the results of hepatic USP14 knockdown. Furthermore, palmitic/oleic acid-induced lipid peroxidation and inflammation in hepatocytes were markedly increased by USP14 overexpression but decreased by USP14 knockdown. Notably, in vivo or in vitro data show that USP14 promotes NAFLD progression in a cytochrome p4502E1 (CYP2E1)-dependent manner, which exacerbates hepatocyte oxidative stress, impairs the mitochondrial respiratory chain and inflammation by promoting CYP2E1 protein levels. Mechanistically, we demonstrated by immunoprecipitation and ubiquitination analysis that USP14 inhibits the degradation of heat shock protein 90 alpha family class A member 1 (HSP90AA1) by decreasing its lysine 48-linkage ubiquitination. Meanwhile, upregulation of HAP90AA1 protein promotes CYP2E1 protein accumulation. Collectively, our data indicate that an unknown USP14-HSP90AA1-CYP2E1 axis contributes to NAFLD progression, and we propose that inhibition of USP14 may be an effective strategy for NASH treatment.

Synergistic Protective Effect of Fermented Schizandrae Fructus Pomace and Hoveniae Semen cum Fructus Extracts Mixture in the Ethanol-Induced Hepatotoxicity

Schizandrae Fructus (SF), fruits of Schisandra chinensis (Turcz.) Baill. and Hoveniae Semen cum Fructus (HSCF), the dried peduncle of Hovenia dulcis Thunb., have long been used for alcohol detoxification in the traditional medicine of Korea and China. In the current study, we aimed to evaluate the potential synergistic hepatoprotective effect of a combination mixture (MSH) comprising fermented SF pomace (fSFP) and HSCF hot water extracts at a 1:1 (w:w) ratio against ethanol-induced liver toxicity. Subacute ethanol-mediated hepatotoxicity was induced by the oral administration of ethanol (5 g/kg) in C57BL/6J mice once daily for 14 consecutive days. One hour after each ethanol administration, MSH (50, 100, and 200 mg/kg) was also orally administered daily. MSH administration significantly reduced the serum activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and γ-glutamyl transpeptidase. Histological observation indicated that MSH administration synergistically and significantly decreased the fatty changed region of hepatic parenchyma and the formation of lipid droplet in hepatocytes. Moreover, MSH significantly attenuated the hepatic triglyceride accumulation through reducing lipogenesis genes expression and increasing fatty acid oxidation genes expression. In addition, MSH significantly inhibited protein nitrosylation and lipid peroxidation by lowering cytochrome P450 2E1 enzyme activity and restoring the glutathione level, superoxide dismutase and catalase activity in liver. Furthermore, MSH synergistically decreased the mRNA level of tumor necrosis factor-α in the hepatic tissue. These findings indicate that MSH has potential for preventing alcoholic liver disease through inhibiting hepatic steatosis, oxidative stress, and inflammation.

Experimental models of fatty liver diseases: Status and appraisal

Fatty liver diseases, including alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease nonalcoholic fatty liver disease (NAFLD), affect a large number of people worldwide and become one of the major causes of end-stage liver disease, such as liver cirrhosis and hepatocellular carcinoma (HCC). Unfortunately, there are currently no approved pharmacological treatments for ALD or NAFLD. This situation highlights the urgent need to explore new intervention targets and discover effective therapeutics for ALD and NAFLD. The lack of properly validated preclinical disease models is a major obstacle to the development of clinical therapies. ALD and NAFLD models have been in the development for decades, but there are still no models that recapitulate the full spectrum of ALD and NAFLD. Throughout this review, we summarize the current in vitro and in vivo models used for research on fatty liver diseases and discuss the advantages and limitations of these models.

Synergistic effects of combined treatment of 1,2-dichloroethane and high-dose ethanol on liver damage in mice and the related mechanisms

Our previous studies have shown that the metabolism of 1,2-dichloroethane (1,2-DCE) mediated by CYP2E1 could result in oxidative damage in the liver of mice. In the current study, we further investigated the effects of combined treatment with 1,2-DCE and high dose ethanol on liver and the mechanisms since both of them can be metabolized by CYP2E1 in the liver. There are several novel findings in the current study. First, combined treatment of mice with 1,2-DCE and high-dose ethanol could synergistically upregulate both protein and mRNA levels of CYP2E1, which might aggravate liver damage through CYP2E1-mediated oxidative stress. Second, the combined treatment could also synergistically trigger NLRP3 inflammasome activation and inflammatory responses in the liver. Third, the combined treatment synergistically upregulated the antioxidant defence systems in response to oxidative stress, however the compensatory mechanisms of antioxidant defence systems appeared to be insufficient to protect liver damage in the mice. Finally, the upregulated CYP2E1 expression was confirmed by using its specific inhibitor to play the crucial roles in liver damage in the mice during the combined treatment.

Glabridin Ameliorates Alcohol-Caused Liver Damage by Reducing Oxidative Stress and Inflammation via p38 MAPK/Nrf2/NF-κB Pathway

Licorice is a traditional and versatile herbal medicine and food. Glabridin (Gla) is a kind of isoflavone extracted from the licorice root, which has anti-obesity, anti-atherosclerotic, and antioxidative effects. Alcoholic liver disease (ALD) is a widespread liver disease induced by chronic alcohol consumption. However, studies demonstrating the effect of Gla on ALD are rare. The research explored the positive effect of Gla in C57BL/6J mice fed by the Lieber-DeCarli ethanol mice diet and HepG2 cells treated with ethanol. Gla alleviated ethanol-induced liver injury, including reducing liver vacuolation and lipid accumulation. The serum levels of inflammatory cytokines were decreased in the Gla-treated mice. The reactive oxygen species and apoptosis levels were attenuated and antioxidant enzyme activity levels were restored in ethanol-induced mice by Gla treatment. In vitro, Gla reduced ethanol-induced cytotoxicity, nuclear factor kappa B (NF-κB) nuclear translocation, and enhanced nuclear factor (erythroid-derived 2)-like 2 (Nrf2) nuclear translocation. Anisomycin (an agonist of p38 MAPK) eliminated the positive role of Gla on ethanol-caused oxidative stress and inflammation. On the whole, Gla can alleviate alcoholic liver damage via the p38 MAPK/Nrf2/NF-κB pathway and may be used as a novel health product or drug to potentially alleviate ALD.

Dietary cholesterol in alcohol-associated liver disease

There is an increasing prevalence of alcohol-associated liver disease (ALD) worldwide. In addition to excessive alcohol consumption, other nutritional factors have been shown to affect the initiation and progression of ALD. The emerging role of cholesterol in exacerbating ALD has been reported recently and the underlying mechanisms are discussed. In addition, the interplay between dietary cholesterol and alcohol on cholesterol metabolism is reviewed. Furthermore, we highlight the therapeutic potential of cholesterol-lowering drugs in managing the onset and severity of ALD. Finally, we suggest the future mechanistic investigation of the effect of cholesterol on insulin resistance and intestinal inflammation in the exacerbation of alcohol-induced cellular and systemic dysfunction.

Lutein Prevents Liver Injury and Intestinal Barrier Dysfunction in Rats Subjected to Chronic Alcohol Intake

Chronic alcohol intake can affect both liver and intestinal barrier function. The goal of this investigation was to evaluate the function and mechanism of lutein administration on the chronic ethanol-induced liver and intestinal barrier damage in rats. During the 14-week experimental cycle, seventy rats were randomly divided into seven groups, with 10 rats in each group: a normal control group (Co), a control group of lutein interventions (24 mg/kg/day), an ethanol model group (Et, 8-12 mL/kg/day of 56% (v/v) ethanol), three intervention groups with lutein (12, 24 and 48 mg/kg/day) and a positive control group (DG). The results showed that liver index, ALT, AST and TG levels were increased, and SOD and GSH-Px levels were reduced in the Et group. Furthermore, alcohol intake over a long time increased the level of pro-inflammatory cytokines TNF-α and IL-1β, disrupted the intestinal barrier, and stimulated the release of LPS, causing further liver injury. In contrast, lutein interventions prevented alcohol-induced alterations in liver tissue, oxidative stress and inflammation. In addition, the protein expression of Claudin-1 and Occludin in ileal tissues was upregulated by lutein intervention. In conclusion, lutein can improve chronic alcoholic liver injury and intestinal barrier dysfunction in rats.

Molecular Changes in Relation to Alcohol Consumption and Hepatocellular Carcinoma

Alcohol is the one of the major causes of liver diseases and promotes liver cirrhosis and hepatocellular carcinoma (HCC). In hepatocytes, alcohol is converted to acetaldehyde, which causes hepatic steatosis, cellular apoptosis, endoplasmic reticulum stress, peroxidation, production of cytokines and reduces immune surveillance. Endotoxin and lipopolysaccharide produced from intestinal bacteria also enhance the production of cytokines. The development of hepatic fibrosis and the occurrence of HCC are induced by these alcohol metabolites. Several host genetic factors have recently been identified in this process. Here, we reviewed the molecular mechanism associated with HCC in alcoholic liver disease.

Effects of Different Green Tea Extracts on Chronic Alcohol Induced-Fatty Liver Disease by Ameliorating Oxidative Stress and Inflammation in Mice

Alcoholic fatty liver disease (AFLD) is a common chronic liver disease and has become a critical global public health problem. Green tea is a popular drink worldwide and contains several bioactive compounds. Different green teas could contain diverse compounds and possess distinct bioactivities. In the present study, the effects of 10 green teas on chronic alcohol induced-fatty liver disease in mice were explored and compared. The results showed that several green teas significantly reduced triacylglycerol levels in serum and liver as well as the aminotransferase activities in mice at a dose of 200 mg/kg, suggesting that they possess hepatoprotective effects. Moreover, several green teas remarkably decreased the expression of cytochrome P450 2E1, the levels of malondialdehyde and 4-hydroxynonenoic acid, and the contents of proinflammatory cytokines, indicating that they could alleviate oxidation damage and inflammation induced by chronic alcohol exposure. In addition, Seven Star Matcha Tea and Selenium-Enriched Matcha Tea could increase glutathione level. Furthermore, the main phytochemical components in green teas were determined and quantified by high-performance liquid chromatography, and the correlation analysis showed that gallic acid, gallocatechin, catechin, chlorogenic acid, and epigallocatechin gallate might at least partially contribute to protective effects on AFLD. In conclusion, Selenium-Enriched Chaoqing Green Tea, Xihu Longjing Tea, Taiping Houkui Tea, and Selenium-Enriched Matcha Tea showed the strongest preventive effects on AFLD. This research also provides the public with new insights about the effects of different green teas on AFLD.

Selenomethionine-Dominated Selenium-Enriched Peanut Protein Ameliorates Alcohol-Induced Liver Disease in Mice by Suppressing Oxidative Stress

Numerous natural compounds are considered as potential therapeutic agents against alcohol-induced liver disease (ALD). Research shows that selenium (Se) has a variety of bioactivities, including liver protecting ability. The present study based on in vitro cell culture models and in vivo mouse models was aimed at examining the contribution of selenomethionine (SeMet)-dominated Se-enriched peanut protein (SePP) to liver protection. SeMet and especially SePP reversed cell viability and cell death, inhibited ethanol induced CYP2E1 activation, decreased reactive oxygen species level, and restored GSH level. Hence, SeMet-dominated SePP alleviates alcohol-induced AML-12 cytotoxicity by suppressing oxidative stress. The p38-dependent mechanism was found to be responsible for SePP-induced Nrf-2 activation. Furthermore, supplementation with SePP and SeMet regulated lipid metabolism and reduced oxidative stress, minimizing liver damage in mice. Selenomethionine-dominated SePP possesses potential therapeutic properties and can be used to treat ALD through the suppression of oxidative stress.

Polyploidy control in hepatic health and disease

A balanced increase in DNA content (ploidy) is observed in some human cell types, including bone-resorbing osteoclasts, platelet-producing megakaryocytes, cardiomyocytes or hepatocytes. The impact of increased hepatocyte ploidy on normal physiology and diverse liver pathologies is still poorly understood. Recent findings suggest swift genetic adaptation to hepatotoxic stress and the protection from malignant transformation as beneficial effects. Herein, we discuss the molecular mechanisms regulating hepatocyte polyploidisation and its implication for different liver diseases and hepatocellular carcinoma. We report on centrosomes' role in limiting polyploidy by activating the p53 signalling network (via the PIDDosome multiprotein complex) and we discuss the role of this pathway in liver disease. Increased hepatocyte ploidy is a hallmark of hepatic inflammation and may play a protective role against liver cancer. Our evolving understanding of hepatocyte ploidy is discussed from the perspective of its potential clinical application for risk stratification, prognosis, and novel therapeutic strategies in liver disease and hepatocellular carcinoma.

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.

Natural Compounds: A Potential Treatment for Alcoholic Liver Disease?

Excessive alcohol intake is a direct cause of alcoholic liver disease (ALD). ALD usually manifests as fatty liver in the initial stage and then develops into alcoholic hepatitis (ASH), fibrosis and cirrhosis. Severe alcoholism induces extensive hepatocyte death, liver failure, and even hepatocellular carcinoma (HCC). Currently, there are few effective clinical means to treat ALD, except for abstinence. Natural compounds are a class of compounds extracted from herbs with an explicit chemical structure. Several natural compounds, such as silymarin, quercetin, hesperidin, and berberine, have been shown to have curative effects on ALD without side effects. In this review, we pay particular attention to natural compounds and developing clinical drugs based on natural compounds for ALD, with the aim of providing a potential treatment for ALD.

Pathophysiological Aspects of Alcohol Metabolism in the Liver

Alcoholic liver disease (ALD) is a globally prevalent chronic liver disease caused by chronic or binge consumption of alcohol. The liver is the major organ that metabolizes alcohol; therefore, it is particularly sensitive to alcohol intake. Metabolites and byproducts generated during alcohol metabolism cause liver damage, leading to ALD via several mechanisms, such as impairing lipid metabolism, intensifying inflammatory reactions, and inducing fibrosis. Despite the severity of ALD, the development of novel treatments has been hampered by the lack of animal models that fully mimic human ALD. To overcome the current limitations of ALD studies and therapy development, it is necessary to understand the molecular mechanisms underlying alcohol-induced liver injury. Hence, to provide insights into the progression of ALD, this review examines previous studies conducted on alcohol metabolism in the liver. There is a particular focus on the occurrence of ALD caused by hepatotoxicity originating from alcohol metabolism.

Changes in Glutathione Content in Liver Diseases: An Update

Glutathione (GSH), a tripeptide particularly concentrated in the liver, is the most important thiol reducing agent involved in the modulation of redox processes. It has also been demonstrated that GSH cannot be considered only as a mere free radical scavenger but that it takes part in the network governing the choice between survival, necrosis and apoptosis as well as in altering the function of signal transduction and transcription factor molecules. The purpose of the present review is to provide an overview on the molecular biology of the GSH system; therefore, GSH synthesis, metabolism and regulation will be reviewed. The multiple GSH functions will be described, as well as the importance of GSH compartmentalization into distinct subcellular pools and inter-organ transfer. Furthermore, we will highlight the close relationship existing between GSH content and the pathogenesis of liver disease, such as non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), chronic cholestatic injury, ischemia/reperfusion damage, hepatitis C virus (HCV), hepatitis B virus (HBV) and hepatocellular carcinoma. Finally, the potential therapeutic benefits of GSH and GSH-related medications, will be described for each liver disorder taken into account.

The History of Alcoholic Liver Disease: From an Unrecognized Disease to One of the Most Frequent Diseases in Hepatology

This review describes the history of alcoholic liver disease from the beginning of the 1950s until now. It details how the hepatotoxicity of alcohol was discovered by epidemiology and basic research primarily by using new feeding techniques in rodents and primates. The article also recognizes the pioneering work of scientists who contributed to the understanding of the pathophysiology of alcoholic liver disease. In addition, clinical aspects, such as the development of diagnostics and treatment options for alcoholic liver disease, are discussed. Up-to-date knowledge of the mechanism of the disease in 2020 is presented.

Hepatoprotection by Ginsenoside Rg1 in alcoholic liver disease

Alcoholic hepatitis (AH) has caused serious mortality to the world's population. Despite tremendous efforts to reduce disease burden, effective treatments for this disease are still lacking. Ginsenoside Rg1 (G-Rg1) has been reported to be hepatoprotective in several liver injury models. However, therapeutic potential of this drug in AH has not been tested. In this study, using a chronic ethanol-feeding model, we found that ethanol-fed mice presented clinical indicators of liver injury, such as elevated serum levels of alanine transaminase (ALT), aspartate aminotransferase (AST) and total bilirubin (Tbil), as well as development of hepatic steatosis. Upon treatment with G-Rg1, animals showed marked decreases in serum biochemical parameters, as well as improvement in liver histology. Mechanistically, G-Rg1 blocked the induction of cytochrome P4502E1 (CYP2E1), and prevented the generation of reactive oxygen species (ROS), mitochondria damage, as well as hepatocellular apoptosis. As a result, NLRP3 inflammasome activation was inhibited, which subsequently suppressed the production of active caspase-1 and inflammatory cytokines. Our data has demonstrated a hepatoprotective role for G-Rg1 in AH, and identified potential drugable pathways to improve disease outcomes. These findings may have significant implications for developing novel therapies for inflammatory liver diseases.

Autophagy mitigates ethanol-induced mitochondrial dysfunction and oxidative stress in esophageal keratinocytes

During alcohol consumption, the esophageal mucosa is directly exposed to high concentrations of ethanol (EtOH). We therefore investigated the response of normal human esophageal epithelial cell lines EPC1, EPC2 and EPC3 to acute EtOH exposure. While these cells were able to tolerate 2% EtOH for 8 h in both three-dimensional organoids and monolayer culture conditions, RNA sequencing suggested that EtOH induced mitochondrial dysfunction. With EtOH treatment, EPC1 and EPC2 cells also demonstrated decreased mitochondrial ATPB protein expression by immunofluorescence and swollen mitochondria lacking intact cristae by transmission electron microscopy. Mitochondrial membrane potential (ΔΨm) was decreased in a subset of EPC1 and EPC2 cells stained with ΔΨm–sensitive dye MitoTracker Deep Red. In EPC2, EtOH decreased ATP level while impairing mitochondrial respiration and electron transportation chain functions, as determined by ATP fluorometric assay, respirometry, and liquid chromatography-mass spectrometry. Additionally, EPC2 cells demonstrated enhanced oxidative stress by flow cytometry for mitochondrial superoxide (MitoSOX), which was antagonized by the mitochondria-specific antioxidant MitoCP. Concurrently, EPC1 and EPC2 cells underwent autophagy following EtOH exposure, as evidenced by flow cytometry for Cyto-ID, which detects autophagic vesicles, and immunoblots demonstrating induction of the lipidated and cleaved form of LC3B and downregulation of SQSTM1/p62. In EPC1 and EPC2, pharmacological inhibition of autophagy flux by chloroquine increased mitochondrial oxidative stress while decreasing cell viability. In EPC2, autophagy induction was coupled with phosphorylation of AMP activated protein kinase (AMPK), a cellular energy sensor responding to low ATP levels, and dephosphorylation of downstream substrates of mechanistic Target of Rapamycin Complex (mTORC)-1 signaling. Pharmacological AMPK activation by AICAR decreased EtOH-induced reduction of ΔΨm and ATP in EPC2. Taken together, acute EtOH exposure leads to mitochondrial dysfunction and oxidative stress in esophageal keratinocytes, where the AMPK-mTORC1 axis may serve as a regulatory mechanism to activate autophagy to provide cytoprotection against EtOH-induced cell injury.

Cryptotanshinone from the Salvia miltiorrhiza Bunge Attenuates Ethanol-Induced Liver Injury by Activation of AMPK/SIRT1 and Nrf2 Signaling Pathways

Cryptotanshinone (CT), a diterpene that is isolated from Salvia miltiorrhiza Bunge, exhibits anti-cancer, anti-oxidative, anti-fibrosis, and anti-inflammatory properties. Here, we examined whether CT administration possess a hepatoprotective effect on chronic ethanol-induced liver injury. We established a chronic alcohol feeding mouse model while using C57BL/6 mice, and examined the liver sections with hematoxylin-eosin (H&E) and Oil Red O (ORO) staining. Further, we analyzed the lipogenesis, fatty acid oxidation, oxidative stress, and inflammation genes by using quantitative polymerase chain reaction (qPCR) and immunoblotting in in vivo, and in vitro while using HepG2 and AML-12 cells. CT treatment significantly ameliorated ethanol-promoted hepatic steatosis, which was consistent with the decreased hepatic triglyceride levels. Interestingly, CT activated the phosphorylation of AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), and nuclear factor E2-related factor 2 (Nrf2) proteins. Importantly, compound C (AMPK inhibitor) significantly blocked the CT-mediated reduction in TG accumulation, but not Ex52735 (SIRT1 inhibitor), which suggested that CT countering ethanol-promoted hepatic steatosis is mediated by AMPK activation. Furthermore, CT significantly inhibited cytochrome P450 2E1 (CYP2E1) and enhanced both the expression of antioxidant genes and hepatic glutathione levels. Finally, CT inhibited the ethanol-induced inflammation in ethanol-fed mice and HepG2 cells. Overall, CT exhibits a hepatoprotective effect against ethanol-induced liver injury by the inhibition of lipogenesis, oxidative stress, and inflammation through the activation of AMPK/SIRT1 and Nrf2 and the inhibition of CYP2E1. Therefore, CT could be an effective therapeutic agent for treating ethanol-induced liver injury.

NF-κB-mediated regulation of rat CYP2E1 by two independent signaling pathways

Cytochrome P450 2E1 (CYP2E1) plays an important role in both alcohol-induced and immune-mediated liver injury. However, the mechanism underlying CYP2E1 transcriptional regulation has not been clarified. This study focused on the NF-κB-mediated transcriptional regulation of rat CYP2E1 by two independent signaling pathways in alcohol-induced and immune-mediated liver injury rat models. Male Sprague-Dawley rats were used in pharmacokinetic, molecular pharmacology, and morphology experiments. A rat model of alcohol-induced liver injury (AL) was established by feeding an ethanol-containing diet (42 g/kg/day) for 5 weeks as indicated. A rat immune-mediated liver injury (IM) model was established by the sequential injection of bacillus Calmette-Guérin (BCG, 125 mg/kg, once) via the tail vein after test day 21 and 10 μg/kg LPS 13 days later. HPLC, real-time PCR, western blot and ELISA analyses were performed. CYP2E1 expression was enhanced during the process of alcohol-induced liver injury (increased by 56%, P < 0.05) and significantly reduced during that of immune-mediated liver injury (reducedby52%, P < 0.05). NF-κB was activated in both the AL and IM groups (increased by 56% and76%, respectively, P < 0.05). Compared to those in the livers of AL model rats, the interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and iNOS levels in IM model rat livers were increased (increased by 26%, 21% and 101%, respectively, P < 0.05). The differential changes in CYP2E1 in the processes of alcohol-induced and immune-mediated liver injury may result from the differential expression of inflammatory cytokines and iNOS after NF-κB activation, leading to the NF-κB-mediated transcriptional regulation of rat CYP2E1 by two independent signaling pathways.

Free radicals, antioxidants, nuclear factor-E2-related factor-2 and liver damage

Oxidative/nitrosative stress is proposed to be a critical factor in various diseases, including liver pathologies. Antioxidants derived from medicinal plants have been studied extensively and are relevant to many illnesses, including liver diseases. Several hepatic disorders, such as viral hepatitis and alcoholic or nonalcoholic steatohepatitis, involve free radicals/oxidative stress as agents that cause or at least exacerbate liver injury, which can result in chronic liver diseases, such as liver fibrosis, cirrhosis and end-stage hepatocellular carcinoma. In this scenario, nuclear factor-E2-related factor-2 (Nrf2) appears to be an essential factor to counteract or attenuate oxidative or nitrosative stress in hepatic cells. In fact, a growing body of evidence indicates that Nrf2 plays complex and multicellular roles in hepatic inflammation, fibrosis, hepatocarcinogenesis and regeneration via the induction of its target genes. Inflammation is the most common feature of chronic liver diseases, triggering fibrosis, cirrhosis and hepatocellular carcinoma. Increasing evidence indicates that Nrf2 counteracts the proinflammatory process by modulating the recruitment of inflammatory cells and inducing the endogenous antioxidant response of the cell. In this review, the interactions between antioxidant and inflammatory molecular pathways are analyzed.

The LRP6 functional mutation rs2302685 contributes to individual susceptibility to alcoholic liver injury related to the Wnt/β-catenin-TCF1-CYP2E1 signaling pathway

Low-density lipoprotein receptor-related protein 6 (LRP6) is an important coreceptor in the Wnt/β-catenin upstream signaling pathway. Rs2302685 is a common functional mutation of LRP6 that has been previously associated with reduced alcoholic liver injury among alcoholic liver disease (ALD) patients, and the present research was designed to study the underlying mechanisms of that finding. A total of 107 ALD patients and 138 non-ALD patients were recruited from hospitalized alcoholics in China. Their venous blood samples were collected for DNA extraction and genotyped using Sequenom MassARRAY. We found that the rs2302685 mutation, which impaired the function of LRP6, was present in higher frequency among alcoholics with ALD than those without ALD. We also conducted a mouse model experiment in which LRP6^(+/-) knockdown mice and LRP6^(+/+) wild-type mice received daily intragastric doses of ethanol (2.4 g/kg) as well as a larger dose of ethanol (4 g/kg) every 7 days for 28 days. The mouse blood and liver specimens were subsequently collected for laboratory analysis, and cell experiments were performed to compare the inhibition, activation, over-expression, and siRNA of LRP6 in the treatment versus the control HL7702 cells. Expression of the targeted molecules was detected by real-time PCR or western blot analysis. Stably transfected cells with pRL3-CYP2E1 vector were used to further study the underlying mechanisms. The total bile acid (TBA), direct bilirubin, total bilirubin (TBIL), aspartate aminotransferase (AST), mitochondrial aspartate aminotransferase, and AST/ALT values were significantly lower in carriers of the rs2302685 mutation than in the wild-type patients, by 63.4, 60.6, 82.1, 44.8, 45.7, and 21.4%, respectively. Compared to the LRP6^(+/+) wild-type mice, the LRP6^(+/-) knockdown mice had lower ALT, TBIL, TBA, and ALB/GLO values, as well reduced liver tissue damage, in accordance with their reduced expressions of LRP6, β-catenin, and CYP2E1. In HL7702 cells exposed to ethanol, AST, ALT, lipid accumulation, and ROS generation decreased in cells that were treated with LRP6 inhibitors or siRNA but increased in cells treated with LRP6 activators or over-expressed LRP6. TCF1 was the transcriptional factor most likely to connect the LRP6-Wnt/β-catenin signaling pathway to the regulation of CYP2E1. We concluded that the LRP6 functional mutation rs2302685 contributes to individual differences in susceptibility to alcoholic liver injury related to the Wnt/β-catenin-TCF1-CYP2E1 signaling pathway.

The effects of non-esterified fatty acids and β-hydroxybutyrate on the hepatic CYP2E1 in cows with clinical ketosis

Dairy cows with ketosis display severe oxidative stress as well as high blood concentrations of non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB). Cytochrome P4502E1 (CYP2E1) plays an important role in the induction of oxidative stress. The aim of this study was to investigate CYP2E1 expression and activity in the liver of clinically ketotic cows (in vivo) and the effects of NEFA and BHB on CYP2E1 expression and activity in hepatocytes (in vitro). Dairy cows with clinical ketosis exhibited a low blood concentration of glucose but high concentrations of NEFA and BHB. Hepatic mRNA, protein expression, and activity of CYP2E1 were significantly higher in cows with clinical ketosis than in control cows. In vitro, both NEFA and BHB treatment markedly up-regulated the mRNA and protein expressions as well as activity of CYP2E1 in cow hepatocytes. Taken together, these results indicate that high levels of NEFA and BHB significantly up-regulate the expression and activity of hepatic CYP2E1, and may be influential in the induction of oxidative stress in cows with clinical ketosis.

Alcoholic liver disease: Utility of animal models

Alcoholic liver disease (ALD) is a major cause of acute and chronic liver injury. Extensive evidence has been accumulated on the pathological process of ALD during the past decades. However, effective treatment options for ALD are very limited due to the lack of suitable in vivo models that recapitulate the full spectrum of ALD. Experimental animal models of ALD, particularly rodents, have been used extensively to mimic human ALD. An ideal animal model should recapitulate all aspects of the ALD process, including significant steatosis, hepatic neutrophil infiltration, and liver injury. A better strategy against ALD depends on clear diagnostic biomarkers, accurate predictor(s) of its progression and new therapeutic approaches to modulate stop or even reverse the disease. Numerous models employing rodent animals have been established in the last decades to investigate the effects of acute and chronic alcohol exposure on the initiation and progression of ALD. Although significant progress has been made in gaining better knowledge on the mechanisms and pathology of ALD, many features of ALD are unknown, and require further investigation, ideally with improved animal models that more effectively mimic human ALD. Although differences in the degree and stages of alcoholic liver injury inevitably exist between animal models and human ALD, the acquisition and translational relevance will be greatly enhanced with the development of new and improved animal models of ALD.

Alcoholic Liver Disease: Alcohol Metabolism, Cascade of Molecular Mechanisms, Cellular Targets, and Clinical Aspects

Alcoholic liver disease is the result of cascade events, which clinically first lead to alcoholic fatty liver, and then mostly via alcoholic steatohepatitis or alcoholic hepatitis potentially to cirrhosis and hepatocellular carcinoma. Pathogenetic events are linked to the metabolism of ethanol and acetaldehyde as its first oxidation product generated via hepatic alcohol dehydrogenase (ADH) and the microsomal ethanol-oxidizing system (MEOS), which depends on cytochrome P450 2E1 (CYP 2E1), and is inducible by chronic alcohol use. MEOS induction accelerates the metabolism of ethanol to acetaldehyde that facilitates organ injury including the liver, and it produces via CYP 2E1 many reactive oxygen species (ROS) such as ethoxy radical, hydroxyethyl radical, acetyl radical, singlet radical, superoxide radical, hydrogen peroxide, hydroxyl radical, alkoxyl radical, and peroxyl radical. These attack hepatocytes, Kupffer cells, stellate cells, and liver sinusoidal endothelial cells, and their signaling mediators such as interleukins, interferons, and growth factors, help to initiate liver injury including fibrosis and cirrhosis in susceptible individuals with specific risk factors. Through CYP 2E1-dependent ROS, more evidence is emerging that alcohol generates lipid peroxides and modifies the intestinal microbiome, thereby stimulating actions of endotoxins produced by intestinal bacteria; lipid peroxides and endotoxins are potential causes that are involved in alcoholic liver injury. Alcohol modifies SIRT1 (Sirtuin-1; derived from Silent mating type Information Regulation) and SIRT2, and most importantly, the innate and adapted immune systems, which may explain the individual differences of injury susceptibility. Metabolic pathways are also influenced by circadian rhythms, specific conditions known from living organisms including plants. Open for discussion is a 5-hit working hypothesis, attempting to define key elements involved in injury progression. In essence, although abundant biochemical mechanisms are proposed for the initiation and perpetuation of liver injury, patients with an alcohol problem benefit from permanent alcohol abstinence alone.

Nrf2 in alcoholic liver disease

Alcoholic liver disease (ALD) is a leading cause of morbidity and mortality of liver disorders and a major health issue globally. ALD refers to a spectrum of liver pathologies ranging from steatosis, steatohepatitis, fibrosis, cirrhosis and even hepatocellular carcinoma. Various mechanisms, including oxidative stress, protein and DNA modification, inflammation and impaired lipid metabolism, have been implicated in the pathogenesis of ALD. Further, reactive oxygen species (ROS) in particular, have been identified as a key component in the initiation and progression of ALD. Nuclear factor erythroid 2 like 2 (Nrf2) is a master regulator of the intracellular adaptive antioxidant response to oxidative stress, and aids in the detoxification of a variety of toxicants. Given its cytoprotective role, Nrf2 has been extensively studied as a therapeutic target for ALD. Paradoxically, however, emerging evidence have revealed that Nrf2 may be implicated in the progression of ALD. In this review, we summarize the role of Nrf2 in the development of ALD and discuss the underlying mechanisms. Clearly, more comprehensive studies with proper animal and cell models and in human are needed to verify the potential therapeutic role of Nrf2 in ALD.

Alcoholic liver disease

Alcoholic liver disease (ALD) is the most prevalent type of chronic liver disease worldwide. ALD can progress from alcoholic fatty liver (AFL) to alcoholic steatohepatitis (ASH), which is characterized by hepatic inflammation. Chronic ASH can eventually lead to fibrosis and cirrhosis and in some cases hepatocellular cancer (HCC). In addition, severe ASH (with or without cirrhosis) can lead to alcoholic hepatitis, which is an acute clinical presentation of ALD that is associated with liver failure and high mortality. Most individuals consuming >40 g of alcohol per day develop AFL; however, only a subset of individuals will develop more advanced disease. Genetic, epigenetic and non-genetic factors might explain the considerable interindividual variation in ALD phenotype. The pathogenesis of ALD includes hepatic steatosis, oxidative stress, acetaldehyde-mediated toxicity and cytokine and chemokine-induced inflammation. Diagnosis of ALD involves assessing patients for alcohol use disorder and signs of advanced liver disease. The degree of AFL and liver fibrosis can be determined by ultrasonography, transient elastography, MRI, measurement of serum biomarkers and liver biopsy histology. Alcohol abstinence achieved by psychosomatic intervention is the best treatment for all stages of ALD. In the case of advanced disease such as cirrhosis or HCC, liver transplantation may be required. Thus, new therapies are urgently needed.

P450-Humanized and Human Liver Chimeric Mouse Models for Studying Xenobiotic Metabolism and Toxicity

Preclinical evaluation of drug candidates in experimental animal models is an essential step in drug development. Humanized mouse models have emerged as a promising alternative to traditional animal models. The purpose of this mini-review is to provide a brief survey of currently available mouse models for studying human xenobiotic metabolism. Here, we describe both genetic humanization and human liver chimeric mouse models, focusing on the advantages and limitations while outlining their key features and applications. Although this field of biomedical science is relatively young, these humanized mouse models have the potential to transform preclinical drug testing and eventually lead to a more cost-effective and rapid development of new therapies.

Cytochrome P450s and Alcoholic Liver Disease

Alcohol consumption causes liver diseases, designated as Alcoholic Liver Disease (ALD). Because alcohol is detoxified by alcohol dehydrogenase (ADH), a major ethanol metabolism system, the development of ALD was initially believed to be due to malnutrition caused by alcohol metabolism in liver. The discovery of the microsomal ethanol oxidizing system (MEOS) changed this dogma. Cytochrome P450 enzymes (CYP) constitute the major components of MEOS. Cytochrome P450 2E1 (CYP2E1) in MEOS is one of the major ROS generators in liver and is considered to be contributive to ALD. Our labs have been studying the relationship between CYP2E1 and ALD for many years. Recently, we found that human CYP2A6 and its mouse analog CYP2A5 are also induced by alcohol. In mice, the alcohol induction of CYP2A5 is CYP2E1-dependent. Unlike CYP2E1, CYP2A5 protects against the development of ALD. The relationship of CYP2E1, CYP2A5, and ALD is a major focus of this review.

Chronic Ethanol Consumption and Generation of Etheno-DNA Adducts in Cancer-Prone Tissues

Chronic ethanol consumption is a risk factor for several human cancers. A variety of mechanisms may contribute to this carcinogenic effect of alcohol including oxidative stress with the generation of reactive oxygen species (ROS), formed via inflammatory pathways or as byproducts of ethanol oxidation through cytochrome P4502E1 (CYP2E1). ROS may lead to lipidperoxidation (LPO) resulting in LPO-products such as 4-hydoxynonenal (4-HNE) or malondialdehyde. These compounds can react with DNA bases forming mutagenic and carcinogenic etheno-DNA adducts. Etheno-DNA adducts are generated in the liver (HepG2) cells over-expressing CYP2E1 when incubated with ethanol;and are inhibited by chlormethiazole. In liver biopsies etheno-DNA adducts correlated significantly with CYP2E1. Such a correlation was also found in the esophageal- and colorectal mucosa of alcoholics. Etheno-DNA adducts also increased in liver biopsies from patients with non alcoholic steatohepatitis (NASH). In various animal models with fatty liver either induced by high fat diets or genetically modified such as in the obese Zucker rat, CYP2E1 is induced and paralleled by high levels of etheno DNA-adducts which may be modified by additional alcohol administration. As elevation of adduct levels in NASH children were already detected at a young age, these lesions may contribute to hepatocellular cancer development later in life. Together these data strongly implicate CYP2E1 as an important mediator for etheno-DNA adduct formation, and this detrimental DNA damage may act as a driving force for malignant disease progression.

Carcinogenic Etheno DNA Adducts in Alcoholic Liver Disease: Correlation with Cytochrome P-4502E1 and Fibrosis

BACKGROUND

One mechanism by which alcoholic liver disease (ALD) progresses is oxidative stress and the generation of reactive oxygen species, among others due to the induction of cytochrome P-4502E1 (CYP2E1). Experimental data underline the key role of CYP2E1 because ALD could be partially prevented in rats by the administration of the specific CYP2E1 inhibitor chlormethiazole. As CYP2E1 is linked to the formation of carcinogenic etheno DNA adducts in ALD patients, a causal role of alcohol-induced CYP2E1 in hepatocarcinogenesis is implicated. The purpose of this study was to investigate CYP2E1 induction in ALD, and its correlation with oxidative DNA lesions and with hepatic histology.

METHODS

Hepatic biopsies from 97 patients diagnosed with ALD were histologically scored for steatosis, inflammation, and fibrosis. CYP2E1 and the exocyclic etheno DNA adduct 1,N⁶ -etheno-2'deoxyadenosine (εdA) were determined immunohistochemically. In addition, in 42 patients, 8-hydroxydeoxyguanosine (8-OHdG) was also evaluated using immunohistochemistry.

RESULTS

A significant positive correlation was found between CYP2E1 and εdA (p < 0.0001) as well as between CYP2E1 and 8-OHdG (p = 0.039). Both CYP2E1 (p = 0.0094) and ɛdA (p < 0.0001) also correlated significantly with the stage of hepatic fibrosis. Furthermore, a significant correlation between the fibrosis stage and the grade of lobular inflammation (p < 0.0001) was observed. However, the amount of alcohol consumed did not correlate with any of the parameters determined.

CONCLUSIONS

These data suggest an important role of CYP2E1 in the generation of εdA, in the fibrotic progression of ALD, and thus in alcohol-mediated hepatocarcinogenesis. CYP2E1 may be a target in the treatment of ALD and a potential prognostic marker for disease progression.

Antioxidant Effect of Barley Sprout Extract via Enhancement of Nuclear Factor-Erythroid 2 Related Factor 2 Activity and Glutathione Synthesis

We previously showed that barley sprout extract (BSE) prevents chronic alcohol intake-induced liver injury in mice. BSE notably inhibited glutathione (GSH) depletion and increased inflammatory responses, revealing its mechanism of preventing alcohol-induced liver injury. In the present study we investigated whether the antioxidant effect of BSE involves enhancing nuclear factor-erythroid 2 related factor 2 (Nrf2) activity and GSH synthesis to inhibit alcohol-induced oxidative liver injury. Mice fed alcohol for four weeks exhibited significantly increased oxidative stress, evidenced by increased malondialdehyde (MDA) level and 4-hydroxynonenal (4-HNE) immunostaining in the liver, whereas treatment with BSE (100 mg/kg) prevented these effects. Similarly, exposure to BSE (0.1–1 mg/mL) significantly reduced oxidative cell death induced by t-butyl hydroperoxide (t-BHP, 300 μM) and stabilized the mitochondrial membrane potential (∆ψ). BSE dose-dependently increased the activity of Nrf2, a potential transcriptional regulator of antioxidant genes, in HepG2 cells. Therefore, increased expression of its target genes, heme oxygenase-1 (HO-1), NADPH quinone oxidoreductase 1 (NQO1), and glutamate-cysteine ligase catalytic subunit (GCLC) was observed. Since GCLC is involved in the rate-limiting step of GSH synthesis, BSE increased the GSH level and decreased both cysteine dioxygenase (CDO) expression and taurine level. Because cysteine is a substrate for both taurine and GSH synthesis, a decrease in CDO expression would further contribute to increased cysteine availability for GSH synthesis. In conclusion, BSE protected the liver cells from oxidative stress by activating Nrf2 and increasing GSH synthesis.

Increased ethanol-inducible cytochrome P450-2E1 and cytochrome P450 isoforms in exosomes of alcohol-exposed rodents and patients with alcoholism through oxidative and endoplasmic reticulum stress

This study investigated the role of ethanol‐inducible cytochrome P450‐2E1 (CYP2E1) in enhancing CYP2E1 and other P450 proteins in extracellular vesicles (EVs) from alcohol‐exposed rodents and human patients with alcoholism and their effects on oxidative hepatocyte injury. Female Fischer rats and wild‐type or Cyp2e1‐null mice were exposed to three oral doses of binge ethanol or dextrose control at 12‐hour intervals. Plasma EV and hepatic proteins from alcohol‐exposed rodents, patients with alcoholism, and their respective controls were isolated and characterized. The number of EVs and the amounts of EV CYP2E1, CYP2A, CYP1A1/2, and CYP4B proteins were markedly elevated in both patients with alcoholism and alcohol‐exposed rats and mice. The number of EVs and EV P450 proteins were significantly reduced in ethanol‐exposed rats fed a diet containing polyunsaturated fatty acids. The increased number of EVs and EV CYP2E1 and other P450 isoforms in alcohol‐exposed wild types were significantly reduced in the corresponding Cyp2e1‐null mice. EV CYP2E1 amounts depended on increased oxidative and endoplasmic reticulum (ER) stress because their levels were decreased by cotreatment with the antioxidant N‐acetylcysteine or the CYP2E1 inhibitor chlormethiazole but increased by ER stress‐inducer thapsigargin, which was blocked by 4‐phenylbutyric acid. Furthermore, cell death rates were elevated when primary hepatocytes or human hepatoma cells were exposed to EVs from alcohol‐exposed rodents and patients with alcoholism, demonstrating that EVs from alcohol‐exposed rats and patients with alcoholism are functional and can promote cell death by activating the apoptosis signaling pathway, including phospho‐c‐Jun N‐terminal kinase, proapoptotic Bax, and activated caspase‐3. Conclusion: CYP2E1 has an important role in elevating EV CYP2E1 and other P450 isoforms through increased oxidative and ER stress. Elevated EV‐CYP2E1 detected after withdrawal from alcohol or exposure to the CYP2E1 inducer pyrazole can be a potential biomarker for liver injury. (Hepatology Communications 2017;1:675–690)

Dihydromyricetin modulates p62 and autophagy crosstalk with the Keap-1/Nrf2 pathway to alleviate ethanol-induced hepatic injury

Increasing evidence has demonstrated that dihydromyricetin (DMY) contains highly effective antioxidative, anti-inflammatory, anti-microbial and anti-diabetic properties. Nevertheless, the underlying hepatoprotective mechanisms of DMY have infrequently been reported thus far. In the present study, C57BL/6 mice were fed with the Lieber-DeCarli diet containing alcohol or isocaloric maltose dextrin as a control diet with or without DMY (75 and 150mg/kg/d bw) for 6 weeks. DMY significantly attenuated hepatic enzyme release, hepatic lipid peroxidation and triglyceride deposition induced by chronic alcohol exposure. In addition, DMY dramatically attenuated the alcohol-triggered elevation of the level of inflammatory cytokines and partially recovered hepatic pathological changes. Notably, DMY remarkably modified aberrant expression of CYP2E1, Keap-1 and HO-1 in the liver and simultaneously ameliorated disordered nuclear localization of NF-κB and Nrf2 to exert its hepatoprotective effects. Further mechanistic exploration suggested that DMY activated Nrf2, possibly mediated through the autophagy pathway. Analysis of the crosstalk among p62, Keap-1 and Nrf2 demonstrated that the p62 upregulation caused by DMY contributes to a positive feedback loop in Nrf2 activation. In summary, DMY likely modulates p62 and autophagy crosstalk with the Keap-1/Nrf2 pathway to alleviate liver steatosis and the inflammatory response in the pathological progression of ALD.

Liver fibrosis and hepatic stellate cells: Etiology, pathological hallmarks and therapeutic targets

Liver fibrosis is a reversible wound-healing process aimed at maintaining organ integrity, and presents as the critical pre-stage of liver cirrhosis, which will eventually progress to hepatocellular carcinoma in the absence of liver transplantation. Fibrosis generally results from chronic hepatic injury caused by various factors, mainly viral infection, schistosomiasis, and alcoholism; however, the exact pathological mechanisms are still unknown. Although numerous drugs have been shown to have antifibrotic activity in vitro and in animal models, none of these drugs have been shown to be efficacious in the clinic. Importantly, hepatic stellate cells (HSCs) play a key role in the initiation, progression, and regression of liver fibrosis by secreting fibrogenic factors that encourage portal fibrocytes, fibroblasts, and bone marrow-derived myofibroblasts to produce collagen and thereby propagate fibrosis. These cells are subject to intricate cross-talk with adjacent cells, resulting in scarring and subsequent liver damage. Thus, an understanding of the molecular mechanisms of liver fibrosis and their relationships with HSCs is essential for the discovery of new therapeutic targets. This comprehensive review outlines the role of HSCs in liver fibrosis and details novel strategies to suppress HSC activity, thereby providing new insights into potential treatments for liver fibrosis.

Liver fibrosis and hepatic stellate cells: Etiology, pathological hallmarks and therapeutic targets

Liver fibrosis is a reversible wound-healing process aimed at maintaining organ integrity, and presents as the critical pre-stage of liver cirrhosis, which will eventually progress to hepatocellular carcinoma in the absence of liver transplantation. Fibrosis generally results from chronic hepatic injury caused by various factors, mainly viral infection, schistosomiasis, and alcoholism; however, the exact pathological mechanisms are still unknown. Although numerous drugs have been shown to have antifibrotic activity in vitro and in animal models, none of these drugs have been shown to be efficacious in the clinic. Importantly, hepatic stellate cells (HSCs) play a key role in the initiation, progression, and regression of liver fibrosis by secreting fibrogenic factors that encourage portal fibrocytes, fibroblasts, and bone marrow-derived myofibroblasts to produce collagen and thereby propagate fibrosis. These cells are subject to intricate cross-talk with adjacent cells, resulting in scarring and subsequent liver damage. Thus, an understanding of the molecular mechanisms of liver fibrosis and their relationships with HSCs is essential for the discovery of new therapeutic targets. This comprehensive review outlines the role of HSCs in liver fibrosis and details novel strategies to suppress HSC activity, thereby providing new insights into potential treatments for liver fibrosis.

Murine Models of Acute Alcoholic Hepatitis and Their Relevance to Human Disease

Alcohol-induced liver damage is a major burden for most societies, and murine studies can provide a means to better understand its pathogenesis and test new therapies. However, there are many models reported with widely differing phenotypes, not all of which fully regenerate the spectrum of human disease. Thus, it is important to understand the implications of these variations to efficiently model human disease. This review critically appraises key articles in the field, detailing the spectrum of liver damage seen in different models, and how they relate to the phenotype of disease seen in patients. A range of different methods of alcohol administration have been studied, ranging from ad libitum consumption of alcohol and water to modified diets (eg, Lieber deCarli liquid diet). Other feeding regimens have taken more invasive routes using intragastric feeding tubes to infuse alcohol directly into the stomach. Notably, models using wild-type mice generally produce a milder phenotype of liver damage than those using genetically modified mice, with the exception of the chronic binge-feeding model. We recommend panels of tests for consideration to standardize end points for the evaluation of the severity of liver damage-key for comparison of models of injury, testing of new therapies, and subsequent translation of findings into clinical practice.

Myeloperoxidase formation of PAF receptor ligands induces PAF receptor-dependent kidney injury during ethanol consumption

Cytochrome P450 2E1 (CYP2E1) induction and oxidative metabolism of ethanol in hepatocytes inflame and damage liver. Chronic ethanol ingestion also induces kidney dysfunction, which is associated with mortality from alcoholic hepatitis. Whether the kidney is directly affected by ethanol or is secondary to liver damage is not established. We found that CYP2E1 was induced in kidney tubules of mice chronically ingesting a modified Lieber-deCarli liquid ethanol diet. Phospholipids of kidney tubules were oxidized and fragmented in ethanol-fed mice with accumulation of azelaoyl phosphatidylcholine (Az-PC), a nonbiosynthetic product formed only by oxidative truncation of polyunsaturated phosphatidylcholine. Az-PC stimulates the inflammatory PAF receptor (PTAFR) abundantly expressed by neutrophils and kidney tubules, and inflammatory cells and myeloperoxidase-containing neutrophils accumulated in the kidneys of ethanol-fed mice after significant hysteresis. Decreased kidney filtration and induction of the acute kidney injury biomarker KIM-1 in tubules temporally correlated with leukocyte infiltration. Genetic ablation of PTAFR reduced accumulation of PTAFR ligands and reduced leukocyte infiltration into kidneys. Loss of this receptor in PTAFR(-/-) mice also suppressed oxidative damage and kidney dysfunction without affecting CYP2E1 induction. Neutrophilic inflammation was responsible for ethanol-induced kidney damage, because loss of neutrophil myeloperoxidase in MPO(-/-) mice was similarly protective. We conclude that ethanol catabolism in renal tubules results in a self-perpetuating cycle of CYP2E1 induction, local PTAFR ligand formation, and neutrophil infiltration and activation that leads to myeloperoxidase-dependent oxidation and damage to kidney function. Hepatocytes do not express PTAFR, so this oxidative cycle is a local response to ethanol catabolism in the kidney.

Prenatal antidepressant exposure associated with CYP2E1 DNA methylation change in neonates

Some but not all neonates are affected by prenatal exposure to serotonin reuptake inhibitor antidepressants (SRI) and maternal mood disturbances. Distinguishing the impact of these 2 exposures is challenging and raises critical questions about whether pharmacological, genetic, or epigenetic factors can explain the spectrum of reported outcomes. Using unbiased DNA methylation array measurements followed by a detailed candidate gene approach, we examined whether prenatal SRI exposure was associated with neonatal DNA methylation changes and whether such changes were associated with differences in birth outcomes. Prenatal SRI exposure was first associated with increased DNA methylation status primarily at CYP2E1(β(Non-exposed) = 0.06, β(SRI-exposed) = 0.30, FDR = 0); however, this finding could not be distinguished from the potential impact of prenatal maternal depressed mood. Then, using pyrosequencing of CYP2E1 regulatory regions in an expanded cohort, higher DNA methylation status--both the mean across 16 CpG sites (P < 0.01) and at each specific CpG site (P < 0.05)--was associated with exposure to lower 3rd trimester maternal depressed mood symptoms only in the SRI-exposed neonates, indicating a maternal mood x SRI exposure interaction. In addition, higher DNA methylation levels at CpG2 (P = 0.04), CpG9 (P = 0.04) and CpG10 (P = 0.02), in the interrogated CYP2E1 region, were associated with increased birth weight independently of prenatal maternal mood, SRI drug exposure, or gestational age at birth. Prenatal SRI antidepressant exposure and maternal depressed mood were associated with altered neonatal CYP2E1 DNA methylation status, which, in turn, appeared to be associated with birth weight.

The WNT/β-catenin pathway is a transcriptional regulator of CYP2E1, CYP1A2, and aryl hydrocarbon receptor gene expression in primary human hepatocytes

The wingless-type MMTV integration site family (WNT)/β-catenin/adenomatous polyposis coli (CTNNB1/APC) pathway has been identified as a regulator of drug-metabolizing enzymes in the rodent liver. Conversely, little is known about the role of this pathway in drug metabolism regulation in human liver. Primary human hepatocytes (PHHs), which are the most physiologically relevant culture system to study drug metabolism in vitro, were used to investigate this issue. This study assessed the link between cytochrome P450 expression and WNT/β-catenin pathway activity in PHHs by modulating its activity with recombinant mouse Wnt3a (the canonical activator), inhibitors of glycogen synthase kinase 3β, and small-interfering RNA to invalidate CTNNB1 or its repressor APC, used separately or in combination. We found that the WNT/β-catenin pathway can be activated in PHHs, as assessed by universal β-catenin target gene expression, leucine-rich repeat containing G protein-coupled receptor 5. Moreover, WNT/β-catenin pathway activation induces the expression of CYP2E1, CYP1A2, and aryl hydrocarbon receptor, but not of CYP3A4, hepatocyte nuclear factor-4α, or pregnane X receptor (PXR) in PHHs. Specifically, we show for the first time that CYP2E1 is transcriptionally regulated by the WNT/β-catenin pathway. Moreover, CYP2E1 induction was accompanied by an increase in its metabolic activity, as indicated by the increased production of 6-OH-chlorzoxazone and by glutathione depletion after incubation with high doses of acetaminophen. In conclusion, the WNT/β-catenin pathway is functional in PHHs, and its induction in PHHs represents a powerful tool to evaluate the hepatotoxicity of drugs that are metabolized by CYP2E1.

Diphenyl diselenide and sodium selenite associated with chemotherapy in experimental toxoplasmosis: influence on oxidant/antioxidant biomarkers and cytokine modulation

SUMMARY The aim of this study was to assess the effect of sulfamethoxazole/trimethoprim (ST) supplemented with diphenyl diselenide and sodium selenite in experimental toxoplasmosis, on oxidant/antioxidant biomarkers and cytokine levels. Eighty-four BALB/c mice were divided in seven groups: group A (negative control), and groups B to G (infected). Blood and liver samples were collected on days 4 and 20 post infection (p.i.). Levels of thiobarbituric acid (TBA) reactive substances and advanced oxidation protein products (AOPP) were assessed in liver samples. Both biomarkers were significantly increased in infected groups on day 4 p.i., while they were reduced on day 20 p.i., compared with group A. Glutathione reductase (GR) activity significantly (P<0·01) increased on day 4 p.i., in group G, compared with group A. INF-γ was significantly increased (P<0·001) in both periods, day 4 (groups B, C, F and G) and 20 p.i. (groups C, F and G). IL-10 significantly reduced (P<0·001) on day 4 p.i. in group B; however, in the same period, it was increased (P<0·001) in groups C and G, compared with group A. On day 20 p.i., IL-10 increased (P<0·001) in groups F and G. Therefore, our results highlighted that these forms of selenium, associated with the chemotherapy, were able to reduce lipid peroxidation and protein oxidation, providing a beneficial immunological balance between the production of pro- and anti-inflammatory cytokines.

Functional roles of protein nitration in acute and chronic liver diseases

Nitric oxide, when combined with superoxide, produces peroxynitrite, which is known to be an important mediator for a number of diseases including various liver diseases. Peroxynitrite can modify tyrosine residue(s) of many proteins resulting in protein nitration, which may alter structure and function of each target protein. Various proteomics and immunological methods including mass spectrometry combined with both high pressure liquid chromatography and 2D PAGE have been employed to identify and characterize nitrated proteins from pathological tissue samples to determine their roles. However, these methods contain a few technical problems such as low efficiencies with the detection of a limited number of nitrated proteins and labor intensiveness. Therefore, a systematic approach to efficiently identify nitrated proteins and characterize their functional roles is likely to shed new insights into understanding of the mechanisms of hepatic disease pathophysiology and subsequent development of new therapeutics. The aims of this review are to briefly describe the mechanisms of hepatic diseases. In addition, we specifically describe a systematic approach to efficiently identify nitrated proteins to study their causal roles or functional consequences in promoting acute and chronic liver diseases including alcoholic and nonalcoholic fatty liver diseases. We finally discuss translational research applications by analyzing nitrated proteins in evaluating the efficacies of potentially beneficial agents to prevent or treat various diseases in the liver and other tissues.