The role of ethanol metabolism in development of alcoholic steatohepatitis in the rat

The Role of Oxidative Stress in Alcoholic Fatty Liver Disease: A Systematic Review and Meta-Analysis of Preclinical Studies

Alcoholic Fatty Liver Disease (AFLD) is characterized by the accumulation of lipids in liver cells owing to the metabolism of ethanol. This process leads to a decrease in the NAD+/NADH ratio and the generation of reactive oxygen species. A systematic review and meta-analysis were conducted to investigate the role of oxidative stress in AFLD. A total of 201 eligible manuscripts were included, which revealed that animals with AFLD exhibited elevated expression of CYP2E1, decreased enzymatic activity of antioxidant enzymes, and reduced levels of the transcription factor Nrf2, which plays a pivotal role in the synthesis of antioxidant enzymes. Furthermore, animals with AFLD exhibited increased levels of lipid peroxidation markers and carbonylated proteins, collectively contributing to a weakened antioxidant defense and increased oxidative damage. The liver damage in AFLD was supported by significantly higher activity of alanine and aspartate aminotransferase enzymes. Moreover, animals with AFLD had increased levels of triacylglycerol in the serum and liver, likely due to reduced fatty acid metabolism caused by decreased PPAR-α expression, which is responsible for fatty acid oxidation, and increased expression of SREBP-1c, which is involved in fatty acid synthesis. With regard to inflammation, animals with AFLD exhibited elevated levels of pro-inflammatory cytokines, including TNF-a, IL-1β, and IL-6. The heightened oxidative stress, along with inflammation, led to an upregulation of cell death markers, such as caspase-3, and an increased Bax/Bcl-2 ratio. Overall, the findings of the review and meta-analysis indicate that ethanol metabolism reduces important markers of antioxidant defense while increasing inflammatory and apoptotic markers, thereby contributing to the development of AFLD.

Nano polystyrene microplastics could accumulate in Nile tilapia (Oreochromis niloticus): Negatively impacts on the intestinal and liver health through water exposure

Microplastics (MPs) have become a significant concern for their potential toxicity. However, the correlation between the size of plastic particles and their toxicity remains inconclusive. Here, we investigate the toxic effects of different sizes (80 nm, 800 nm, 8 µm and 80 µm) polystyrene MPs (PS-MPs) on the model organism Nile tilapia (Oreochromis niloticus). The results of bioluminescent imaging indicate that the 80 nm PS-MPs are more likely to invade the body. H&E staining shows severe damage on the intestinal villi and distinct hepatic steatosis in the 80 nm group. EdU labeling shows that the proliferation activity of intestinal and liver cells reduces significantly in the 80 nm group. The gut microbiome analysis shows a severe imbalance of gut microbiota homeostasis in the 80 nm group. The analysis of liver transcriptomics and metabolomics shows that the liver lipid metabolism is disordered in the 80 nm group. In conclusion, this study confirms that the 80 nm PS-MPs are more likely to induce intestinal and liver toxicity. All the above lay the foundation for further study on the pathological damage of MPs to other organisms.

Pathogenic mechanisms and regulatory factors involved in alcoholic liver disease

Alcoholism is a widespread and damaging behaviour of people throughout the world. Long-term alcohol consumption has resulted in alcoholic liver disease (ALD) being the leading cause of chronic liver disease. Many metabolic enzymes, including alcohol dehydrogenases such as ADH, CYP2E1, and CATacetaldehyde dehydrogenases ALDHsand nonoxidative metabolizing enzymes such as SULT, UGT, and FAEES, are involved in the metabolism of ethanol, the main component in alcoholic beverages. Ethanol consumption changes the functional or expression profiles of various regulatory factors, such as kinases, transcription factors, and microRNAs. Therefore, the underlying mechanisms of ALD are complex, involving inflammation, mitochondrial damage, endoplasmic reticulum stress, nitrification, and oxidative stress. Moreover, recent evidence has demonstrated that the gut-liver axis plays a critical role in ALD pathogenesis. For example, ethanol damages the intestinal barrier, resulting in the release of endotoxins and alterations in intestinal flora content and bile acid metabolism. However, ALD therapies show low effectiveness. Therefore, this review summarizes ethanol metabolism pathways and highly influential pathogenic mechanisms and regulatory factors involved in ALD pathology with the aim of new therapeutic insights.

Subclinical versus advanced forms of alcohol-related liver disease: Need for early detection

Alcohol-related liver disease (ALD) consists of a wide spectrum of clinical manifestations and pathological features, ranging from asymptomatic patients to decompensated cirrhosis and hepatocellular carcinoma. Patients with heavy alcohol intake and advanced fibrosis often develop a subacute form of liver failure called alcohol-induced hepatitis (AH). Globally, most patients with ALD are identified at late stages of the disease, limiting therapeutic interventions. Thus, there is a need for early detection of ALD patients, which is lacking in most countries. The identification of alcohol misuse is hampered by the existence of alcohol underreporting by many patients. There are useful biomarkers that can detect recent alcohol use. Moreover, there are several non-invasive techniques to assess the presence of advanced fibrosis among patients with alcohol misuse, which could identify patients at high risk of liver related events or early death. In this review, we discuss differences between early stages of ALD and AH as the cornerstone of advanced forms. A global overview of epidemiological, anthropometric, clinical, analytical, histological, and molecular differences is summarized in this article. We propose that campaigns aimed at identifying patients with subclinical forms can prevent the development of life-threatening forms.

Diallyl disulfide suppresses the lipopolysaccharide-driven inflammatory response of macrophages by activating the Nrf2 pathway

Lipopolysaccharide (LPS)-driven activation of Kupffer cells plays critical roles in the development of alcoholic liver disease (ALD). Accumulating evidence has revealed that nuclear factor erythroid 2-related factor 2 (Nrf2) can modulate the polarization of macrophages. The current study aimed to investigate the roles of diallyl disulfide (DADS) in LPS-driven inflammation in vitro and in vivo. We found that DADS significantly increased the nuclear translocation of Nrf2 and the transcription of Nrf2 targets, including HO1, NQO1, and γ-GCSc, and suppressed degradation of Nrf2 protein. Besides, DADS significantly inhibited LPS-induced activation of NF-κB and MAPK, secretion of NO and TNF-α, and production of reactive oxygen species (ROS) in LPS-exposed RAW264.7 cells. In vivo study demonstrated that DADS significantly ameliorated liver damage in mice challenged with LPS, as shown by the inhibition of increases in serum aminotransferase activities, neutrophil infiltration, and NF-κB and NLRP3 inflammasome activation. Finally, knockout of Nrf2 abrogated the suppression of DADS on macrophage polarization and on liver injury induced by LPS. These findings reveal that DADS suppresses LPS-driven inflammatory response in the liver by activating Nrf2, which suggests that the protective effects of DADS against ALD may be attributed to the modulation of Kupffer cell polarization in the liver.

Disrupted H2S Signaling by Cigarette Smoking and Alcohol Drinking: Evidence from Cellular, Animal, and Clinical Studies

The role of endogenous hydrogen sulfide (H₂S) as an antioxidant regulator has sparked interest in its function within inflammatory diseases. Cigarette and alcohol use are major causes of premature death, resulting from chronic oxidative stress and subsequent tissue damage. The activation of the Nrf2 antioxidant response by H₂S suggests that this novel gasotransmitter may function to prevent or potentially reverse disease progression caused by cigarette smoking or alcohol use. The purpose of this study is to review the interrelationship between H₂S signaling and cigarette smoking or alcohol drinking. Based on the databases of cellular, animal, and clinical studies from Pubmed using the keywords of H₂S, smoking, and/or alcohol, this review article provides a comprehensive insight into disrupted H₂S signaling by alcohol drinking and cigarette smoking-caused disorders. Major signaling and metabolic pathways involved in H₂S-derived antioxidant and anti-inflammatory responses are further reviewed. H₂S supplementation may prove to be an invaluable asset in treating or preventing diseases in those suffering from cigarette or alcohol addiction.

Exploring the liver fibrosis induced by deltamethrin exposure in quails and elucidating the protective mechanism of resveratrol

Deltamethrin (DLM) is widely used in agriculture and the prevention of human insect-borne diseases. However, the molecular mechanism of DLM induced liver injury remains unclear to date. This study investigated the potential molecular mechanism that DLM induced liver fibrosis in quails. Japanese quails received resveratrol (500 mg/kg) daily with or without DLM (45 mg/kg) exposure for 12 weeks. Histopathology, transmission electron microscopy, biochemical indexes, TUNEL, quantitative real-time PCR, and western blot analysis were performed. DLM exposure induced hepatic steatosis, oxidative stress, inflammation, and apoptosis. Most importantly, the Nrf2/TGF-β1/Smad3 signaling pathway played an important role on DLM-induced liver fibrosis in quails. Interestingly, the addition of resveratrol, an Nrf2 activator, alleviates oxidative stress and inflammation response by activating Nrf2, thereby inhibits the liver fibrosis induced by DLM in quails. Collectively, these findings demonstrate that chronic exposure to DLM induces oxidative stress via the Nrf2 expression inhibition and apoptosis, and then results in liver fibrosis in quails by the activation of NF-κB/TNF-α and TGF-β1/Smad3 signaling pathway.

Acetaldehyde suppresses HBV-MHC class I complex presentation on hepatocytes via induction of ER stress and Golgi fragmentation

Alcohol consumption worsens hepatitis B virus (HBV) infection pathogenesis. We have recently reported that acetaldehyde suppressed HBV peptide-major histocompatibility complex I (MHC class I) complex display on hepatocytes, limiting recognition and subsequent removal of the infected hepatocytes by HBV-specific cytotoxic T lymphocytes (CTLs). This suppression was attributed to impaired processing of antigenic peptides by the proteasome. However, in addition to proteasome dysfunction, alcohol may induce endoplasmic reticulum (ER) stress and Golgi fragmentation in HBV-infected liver cells to reduce uploading of viral peptides to MHC class I and/or trafficking of this complex to the hepatocyte surface. Hence, the aim of this study was to elucidate whether alcohol-induced ER stress and Golgi fragmentation affect HBV peptide-MHC class I complex presentation on HBV+ hepatocytes. Here, we demonstrate that, while both acetaldehyde and HBV independently cause ER stress and Golgi fragmentation, the combined exposure provided an additive effect. Thus we observed an activation of the inositol-requiring enzyme 1α-X-box binding protein 1 and activation transcription factor (ATF)6α, but not the phospho PKR-like ER kinase-phospho eukaryotic initiation factor 2α-ATF4-C/EBP homologous protein arms of ER stress in HBV-transfected cells treated with acetaldehyde-generating system (AGS). In addition, Golgi proteins trans-Golgi network 46, GM130, and Giantin revealed punctate distribution, indicating Golgi fragmentation upon AGS exposure. Furthermore, the effects of acetaldehyde were reproduced by treatment with ER stress inducers, thapsigargin and tunicamycin, which also decreased the display of this complex and MHC class I turnover in HepG2.2.15 cells and HBV-infected primary human hepatocytes. Taken together, alcohol-induced ER stress and Golgi fragmentation contribute to the suppression of HBV peptide-MHC class I complex presentation on HBV+ hepatocytes, which may diminish their recognition by CTLs and promote persistence of HBV infection in hepatocytes.NEW & NOTEWORTHY Our current findings show that acetaldehyde accelerates endoplasmic reticulum (ER) stress by activating the unfolded protein response arms inositol-requiring enzyme 1α-X-box binding protein 1 and activation transcription factor (ATF)6α but not phospho PKR-like ER kinase-p eukaryotic initiation factor 2α-ATF4-C/EBP homologous protein in hepatitis B virus (HBV)-transfected HepG2.2.15 cells. It also potentiates Golgi fragmentation, as evident by punctate distribution of Golgi proteins, GM130, trans-Golgi network 46, and Giantin. While concomitantly increasing HBV DNA and HBV surface antigen titers, acetaldehyde-induced ER stress suppresses the presentation of HBV peptide-major histocompatibility complex I complexes on hepatocyte surfaces, thereby promoting the persistence of HBV infection in the liver.

Imidacloprid-induced liver fibrosis in quails via activation of the TGF-β1/Smad pathway

Imidacloprid (IMI) is one of the most frequently used neonicotinoid insecticide, and its potential toxicity and environmental hazards have gradually attracted people's attention. Liver fibrosis caused by long-term inflammation or oxidative stress can lead to cirrhosis and liver failure, even death. However, the mechanism of liver fibrosis induced by neonicotinoid insecticide remains unclear. This study investigates whether IMI could induce liver fibrosis in quails and a potential mechanism. Our study used a quail 90-day IMI-induced liver fibrosis model. The results showed that IMI induced histopathological lesions, oxidative stress, inflammation, fibrosis, and changes in nuclear factor-kappa B (NF-κB), nuclear factor-E2-related factor-2 (Nrf2), and transforming growth factor (TGF-β1) levels. Furthermore, IMI enhanced the expression of liver fibrosis marker proteins, including collagen I, α-smooth muscle actin (α-SMA), and fibronectin 1 (FN-1), by activating the TGF-β1/Smad signaling pathway. In conclusion, our study demonstrated that IMI exposure induces liver fibrosis via activation of the TGF-β1/Smad signaling pathway in quails.

Morphoquantitative effects of oral β-carotene supplementation on liver of C57BL/6 mice exposed to ethanol consumption

Alcohol is harmful to the body, causing hepatic steatosis, alcoholic hepatitis and cirrhosis. The effects of alcohol on the liver can be offset using natural antioxidants. This study aimed to evaluate the effects of the administration of oral β-carotene on the morphoquantitative characteristics of mice livers exposed to ethanol consumption. Forty-eight male mice were used, divided into six groups: Control (C), Low-dose alcohol (LA), Moderate-dose alcohol (MA), β-carotene (B), Low-dose alcohol+β-carotene (LA+B) and Moderate-dose alcohol+β-carotene (MA+B). On day 28 the animals were euthanized and the organs were harvested. The morphoquantitative analysis, evaluation of the collagen fiber content and transmission electron microscopy were performed. A one-way ANOVA was used for statistical analysis. There were no differences between N_Vhep, V_Vhep, S_Vhep, V_Vbin, TV_hep and TM_hep in groups C and the MA+B (P < 0.001). The analysis of type I collagen fibers revealed that the MA+B group presented differences with groups C (P < 0.001), LA (P = 0.046) and LA+B (P = 0.009). The ultrastructural analysis for N_Am, N_Vm, NT_m, V_Vm, V_m, S_Vm and TS_m did not reflect any significant differences between the groups. Our results suggest that the degree of hepatic steatosis produced by different doses of alcohol can be prevented. However, the following factors should be considered: amount of alcohol consumed, exposure time, regulatory mechanisms of alcoholic liver disease and signaling pathways involved in the ingestion of both ethanol and antioxidants.

Will Studies in Nonalcoholic Steatohepatitis Help Manage Alcoholic Steatohepatitis?

Hepatic steatosis and steatohepatitis have several etiologies; the most common are alcoholic steatohepatitis (ASH) and obesity/metabolic syndrome-induced steatohepatitis, also known as nonalcoholic steatohepatitis (NASH). Although the etiology of these 2 conditions is different, they share pathways to disease progression and severity. They also have differences in physiologic pathways, and shared and divergent mechanisms can be therapeutic targets. There is no approved pharmacologic therapy for NASH, but several molecules are under study. Focus remains on modulation of insulin resistance, oxidative stress, the inflammatory cascade, hepatic fibrosis, and cell death. This review provides an overview of pathophysiologic similarities and differences between ASH and NASH.

Propyl gallate inhibits hepatocellular carcinoma cell growth through the induction of ROS and the activation of autophagy

The poor prognosis of hepatocellular carcinoma (HCC) has been attributed to a high frequency of tumor metastasis and recurrence even after successful surgical resection. With less than 30% of patients benefiting from curative treatment, alternative treatment regimens for patients with advanced HCC are needed. Propyl gallate (PG), a synthetic antioxidant used in preserving food and medicinal preparations, has been shown to induce cancer cell death, but the anticancer effects of PG in HCC are unclear. In the present study, we demonstrated that PG inhibited HCC cell proliferation in vitro and in zebrafish models in vivo in a dose- and time-dependent manner. PG also induced cell apoptosis and increased the number of necrotic cells in a time- and dose-dependent manner as determined using a high-content analysis system. We found that PG also increased the intracellular levels of superoxide and reactive oxidative stress as well as the formation of autophagosomes and lysosomes. Regarding the molecular mechanism, PG did not alter the levels of autophagy-related 5 (ATG5), ATG5/12 or Beclin-1 but increased the rate of the LC3-I to LC3-II conversion, suggesting autophagy induction. PG exposure increased the levels of the pro-apoptotic proteins cleaved caspase-3, cleaved PARP, Bax, and Bad and a decreased level of the anti-apoptotic protein Bcl-2. In conclusion, we demonstrate that PG inhibits HCC cell proliferation through enhanced ROS production and autophagy activation. Finally, PG-treated cells induced cell apoptosis and may be a new candidate for HCC therapy.

Protective effect of Letinous edodes foot peptides against ethanol‑induced liver injury in L02 cells

The aim of the present study was to evaluate the protective effect and mechanism of Letinous edodes foot peptides on ethanol‑induced L02 cells. A cell model of ethanol‑induced damage was established in vitro to study the effects of the Letinous edodes foot peptides on human L02 hepatocytes. The expression and activity of superoxide dismutase (SOD), malondialdehyde (MDA), aspartate aminotransferase (AST), alanine aminotransferase (ALT), alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH), following treatment were examined to determine the anti‑alcoholism and hepatoprotective functions of Letinous edodes foot peptides. Taking Letinous edodes foot peptides prior to ethanol exposure was more beneficial, which significantly increased SOD activity and the mRNA expression of ADH and ALDH suppressed by ethanol. In addition, the intracellular MDA content, and AST and ALT activity decreased in ethanol‑induced L02 cells pretreated with the peptides, when compared with the control. Furthermore, Letinous edodes foot peptides inhibited the ethanol‑induced activation of the proinflammatory cytokines, interleukin‑6 and tumor necrosis factor‑α, and promoted the metabolic regulation factors, AMP‑activated protein kinase‑α2 and peroxisome proliferator‑activated receptor‑α.

HIMH0021 attenuates ethanol-induced liver injury and steatosis in mice

Chronic alcohol consumption causes alcohol-induced lipogenesis and promotes hepatic injury by preventing the oxidation of hepatocellular fatty acids through the suppression of the activation of AMP-activated protein kinase (AMPK). HIMH0021, an active flavonoid compound, which is a component of the Acer tegmentosum extract, has been shown to protect against liver damage caused by alcohol consumption. Therefore, in this study, we aimed to determine whether HIMH0021 could regulate alcoholic fatty liver and liver injury in mice. Oral administration of 10 days of Lieber-DeCarli ethanol plus a single binge of 30% ethanol (chronic-plus-binge model) induced steatosis and liver injury and inflammation in mice, which appears similar to the condition observed in human patients with alcohol-related diseases. HIMH0021, which was isolated from the active methanol extract of A. tegmentosum, inhibited alcohol-induced steatosis and attenuated the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) during hepatocellular alcohol metabolism, both of which promote lipogenesis as well as liver inflammation. Treatment with HIMH0021 conferred protection against lipogenesis and liver injury, inhibited the expression of cytochrome P4502E1, and increased serum adiponectin levels in the mice subjected to chronic-plus-binge feeding. Furthermore, in hepatocytes, HIMH0021 activated fatty acid oxidation by activating pAMPK, which comprises pACC and CPT1a. These findings suggested that HIMH0021 could be used to target a TNFα-related pathway for treating patients with alcoholic hepatitis.

Impairment of Akt activity by CYP2E1 mediated oxidative stress is involved in chronic ethanol-induced fatty liver

Protein kinase B (PKB/Akt) plays important roles in the regulation of lipid homeostasis, and impairment of Akt activity has been demonstrated to be involved in the development of non-alcoholic fatty liver disease (NAFLD). Previous studies suggest that cytochrome P4502E1 (CYP2E1) plays causal roles in the pathogenesis of alcoholic fatty liver (AFL). We hypothesized that Akt activity might be impaired due to CYP2E1-induced oxidative stress in chronic ethanol-induced hepatic steatosis. In this study, we found that chronic ethanol-induced hepatic steatosis was accompanied with reduced phosphorylation of Akt at Thr308 in mice liver. Chronic ethanol exposure had no effects on the protein levels of phosphatidylinositol 3 kinase (PI3K) and phosphatase and tensin homologue deleted on chromosome ten (PTEN), and led to a slight decrease of phosphoinositide-dependent protein kinase 1 (PDK-1) protein level. Ethanol exposure resulted in increased levels of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE)-Akt adducts, which was significantly inhibited by chlormethiazole (CMZ), an efficient CYP2E1 inhibitor. Interestingly, N-acetyl-L-cysteine (NAC) significantly attenuated chronic ethanol-induced hepatic fat accumulation and the decline of Akt phosphorylation at Thr308. In the in vitro studies, Akt phosphorylation was suppressed in CYP2E1-expressing HepG2 (CYP2E1-HepG2) cells compared with the negative control HepG2 (NC-HepG2) cells, and 4-HNE treatment led to significant decrease of Akt phosphorylation at Thr308 in wild type HepG2 cells. Lastly, pharmacological activation of Akt by insulin-like growth factor-1 (IGF-1) significantly alleviated chronic ethanol-induced fatty liver in mice. Collectively, these results indicate that CYP2E1-induced oxidative stress may be responsible for ethanol-induced suppression of Akt phosphorylation and pharmacological modulation of Akt in liver may be an effective strategy for the treatment of ethanol-induced fatty liver.

Limited Excessive Voluntary Alcohol Drinking Leads to Liver Dysfunction in Mice

BACKGROUND

Liver damage is a serious and sometimes fatal consequence of long-term alcohol intake, which progresses from early-stage fatty liver (steatosis) to later-stage steatohepatitis with inflammation and fibrosis/necrosis. However, very little is known about earlier stages of liver disruption that may occur in problem drinkers, those who drink excessively but are not dependent on alcohol.

METHODS

We examined how repeated binge-like alcohol drinking in C57BL/6 mice altered liver function, as compared with a single binge-intake session and with repeated moderate alcohol consumption. We measured a number of markers associated with early- and later-stage liver disruption, including liver steatosis, measures of liver cytochrome P4502E1 (CYP2E1) and alcohol dehydrogenase (ADH), alcohol metabolism, expression of cytokine mRNA, accumulation of 4-hydroxynonenal (4-HNE) as an indicator of oxidative stress, and alanine transaminase/aspartate transaminase as a measure of hepatocyte injury.

RESULTS

Importantly, repeated binge-like alcohol drinking increased triglyceride levels in the liver and plasma, and increased lipid droplets in the liver, indicators of steatosis. In contrast, a single binge-intake session or repeated moderate alcohol consumption did not alter triglyceride levels. In addition, alcohol exposure can increase rates of alcohol metabolism through CYP2E1 and ADH, which can potentially increase oxidative stress and liver dysfunction. Intermittent, excessive alcohol intake increased liver CYP2E1 mRNA, protein, and activity, as well as ADH mRNA and activity. Furthermore, repeated, binge-like drinking, but not a single binge or moderate drinking, increased alcohol metabolism. Finally, repeated, excessive intake transiently elevated mRNA for the proinflammatory cytokine IL-1B and 4-HNE levels, but did not alter markers of later-stage liver hepatocyte injury.

CONCLUSIONS

Together, we provide data suggesting that even relatively limited binge-like alcohol drinking can lead to disruptions in liver function, which might facilitate the transition to more severe forms of liver damage.

Enzymatic Responses to Alcohol and Tobacco Nicotine-Derived Nitrosamine Ketone Exposures in Long Evans Rat Livers

BACKGROUND

Chronic feeding plus binge administration of ethanol causes very high blood alcohol concentrations. However, its co-administration with tobacco Nicotine-Derived Nitrosamine Ketone (NNK) results in somewhat lower blood alcohol levels, suggesting that NNK and therefore smoking, alters alcohol metabolism in the liver. To explore this hypothesis, we examined effects of ethanol and/or NNK exposures on the expression and activity levels of enzymes that regulate their metabolism in liver.

METHODS

This study utilized a 4-way model in which Long Evans rats were fed liquid diets containing 0% or 26% ethanol for 8 weeks, and respectively i.p injected with saline or 2 g/kg of ethanol 3 times/week during Weeks 7 and 8. The control and ethanol-exposed groups were each sub-divided and further i.p treated with 2 mg/kg of NNK or saline (3×/week) in Weeks 3-8. ADH, catalase and ALDH activities were measured using commercial kits. CYP450 mRNA levels (17 isoforms) were measured by qRT-PCR analysis.

RESULTS

Ethanol significantly increased hepatic ADH but not catalase or ALDH activity. NNK had no effect on ADH, ALDH, or catalase, but when combined with ethanol, it increased ADH activity above the levels measured in all other groups. Ethanol increased CYP2C7, while NNK increased CYP2B1 and CYP4A1mRNA levels relative to control. In contrast, dual ethanol + NNK exposures inhibited CYP2B1 and CYP4A1 expression relative to NNK. Conclusion: Dual exposures to ethanol and NNK increase hepatic ethanol metabolism, and ethanol and/or NNK exposures alter the expression of CYP450 isoforms that are utilized in NNK and fatty acid metabolism.

Critical Roles of Kupffer Cells in the Pathogenesis of Alcoholic Liver Disease: From Basic Science to Clinical Trials

Alcoholic liver disease (ALD) encompasses a spectrum of liver injury ranging from steatosis to steatohepatitis, fibrosis, and finally cirrhosis. Accumulating evidences have demonstrated that Kupffer cells (KCs) play critical roles in the pathogenesis of both chronic and acute ALD. It has become clear that alcohol exposure can result in increased hepatic translocation of gut-sourced endotoxin/lipopolysaccharide, which is a strong M1 polarization inducer of KCs. The activated KCs then produce a large amount of reactive oxygen species (ROS), pro-inflammatory cytokines, and chemokines, which finally lead to liver injury. The critical roles of KCs and related inflammatory cascade in the pathogenesis of ALD make it a promising target in pharmaceutical drug developments for ALD treatment. Several drugs (such as rifaximin, pentoxifylline, and infliximab) have been evaluated or are under evaluation for ALD treatment in randomized clinical trials. Furthermore, screening pharmacological regulators for KCs toward M2 polarization may provide additional therapeutic agents. The combination of these potentially therapeutic drugs with hepatoprotective agents (such as zinc, melatonin, and silymarin) may bring encouraging results.

Diallyl Sulfide: Potential Use in Novel Therapeutic Interventions in Alcohol, Drugs, and Disease Mediated Cellular Toxicity by Targeting Cytochrome P450 2E1

Diallyl sulfide (DAS) and other organosulfur compounds are chief constituents of garlic. These compounds have many health benefits, as they are very efficient in detoxifying natural agents. Therefore, these compounds may be useful for prevention/treatment of cancers. However, DAS has shown appreciable allergic reactions and toxicity, as they can also affect normal cells. Thus their use as in the prevention and treatment of cancer is limited. DAS is a selective inhibitor of cytochrome P450 2E1 (CYP2E1), which is known to metabolize many xenobiotics including alcohol and analgesic drugs in the liver. CYP2E1-mediated alcohol/drug metabolism produce reactive oxygen species and reactive metabolites, which damage DNA, protein, and lipid membranes, subsequently causing liver damage. Several groups have shown that DAS is not only capable of inhibiting alcohol- and drug-mediated cellular toxicities, but also HIV protein- and diabetes-mediated toxicities by selectively inhibiting CYP2E1 in various cell types. However, due to known DAS toxicities, its use as a treatment modality for alcohol/drug- and HIV/diabetes-mediated toxicity have only limited clinical relevance. Therefore, effort is being made to generate DAS analogs, which are potent and selective inhibitor of CYP2E1 and poor substrate of CYP2E1. This review summarizes current advances in the field of DAS, its anticancer properties, role as a CYP2E1 inhibitor, preventing agent of cellular toxicities from alcohol, analgesic drugs, xenobiotics, as well as, from diseases like HIV and diabetes. Finally, this review also provides insights toward developing novel DAS analogues for chemical intervention of many disease conditions by targeting CYP2E1 enzyme.

Pathogenesis and Management of Alcoholic Liver Disease

Alcoholic liver disease (ALD) is a leading cause of liver-related morbidity and mortality. ALD encompasses a spectrum of disorders ranging from asymptomatic steatosis, alcoholic steatohepatitis, fibrosis, cirrhosis and its related complications. Moreover, patients can develop an acute-on-chronic form of liver failure called alcoholic hepatitis (AH). Most patients are diagnosed at advanced stages of the disease with higher rates of complications and mortality. The mainstream of therapy of ALD patients, regardless of the disease stage, is prolonged alcohol abstinence. The current therapeutic regimens for AH (i.e. prednisolone) have limited efficacy and targeted therapies are urgently needed. The development of such therapies requires translational studies in human samples and suitable animal models that reproduce clinical and histological features of AH. In recent years, new animal models that simulate some of the features of human AH have been developed, and translational studies using human samples have identified potential pathogenic factors and histological parameters that predict survival. In this review, we discuss the pathogenesis and management of ALD, focusing on AH, its current therapies and potential treatment targets.

ALDH2 Deficiency Promotes Ethanol-Induced Gut Barrier Dysfunction and Fatty Liver in Mice

BACKGROUND

Acetaldehyde, the toxic ethanol (EtOH) metabolite, disrupts intestinal epithelial barrier function. Aldehyde dehydrogenase (ALDH) detoxifies acetaldehyde into acetate. Subpopulations of Asians and Native Americans show polymorphism with loss-of-function mutations in ALDH2. We evaluated the effect of ALDH2 deficiency on EtOH-induced disruption of intestinal epithelial tight junctions and adherens junctions, gut barrier dysfunction, and liver injury.

METHODS

Wild-type and ALDH2-deficient mice were fed EtOH (1 to 6%) in Lieber-DeCarli diet for 4 weeks. Gut permeability in vivo was measured by plasma-to-luminal flux of FITC-inulin, tight junction and adherens junction integrity was analyzed by confocal microscopy, and liver injury was assessed by the analysis of plasma transaminase activity, histopathology, and liver triglyceride.

RESULTS

EtOH feeding elevated colonic mucosal acetaldehyde, which was significantly greater in ALDH2-deficient mice. ALDH2(-/-) mice showed a drastic reduction in the EtOH diet intake. Therefore, this study was continued only in wild-type and ALDH2(+/-) mice. EtOH feeding elevated mucosal inulin permeability in distal colon, but not in proximal colon, ileum, or jejunum of wild-type mice. In ALDH2(+/-) mice, EtOH-induced inulin permeability in distal colon was not only higher than that in wild-type mice, but inulin permeability was also elevated in the proximal colon, ileum, and jejunum. Greater inulin permeability in distal colon of ALDH2(+/-) mice was associated with a more severe redistribution of tight junction and adherens junction proteins from the intercellular junctions. In ALDH2(+/-) mice, but not in wild-type mice, EtOH feeding caused a loss of junctional distribution of tight junction and adherens junction proteins in the ileum. Histopathology, plasma transaminases, and liver triglyceride analyses showed that EtOH-induced liver damage was significantly greater in ALDH2(+/-) mice compared to wild-type mice.

CONCLUSIONS

These data demonstrate that ALDH2 deficiency enhances EtOH-induced disruption of intestinal epithelial tight junctions, barrier dysfunction, and liver damage.

Pregnane X Receptor-Humanized Mice Recapitulate Gender Differences in Ethanol Metabolism but Not Hepatotoxicity

Both human and rodent females are more susceptible to developing alcoholic liver disease following chronic ethanol (EtOH) ingestion. However, little is known about the relative effects of acute EtOH exposure on hepatotoxicity in female versus male mice. The nuclear receptor pregnane X receptor (PXR; NR1I2) is a broad-specificity sensor with species-specific responses to toxic agents. To examine the effects of the human PXR on acute EtOH toxicity, the responses of male and female PXR-humanized (hPXR) transgenic mice administered oral binge EtOH (4.5 g/kg) were analyzed. Basal differences were observed between hPXR males and females in which females expressed higher levels of two principal enzymes responsible for EtOH metabolism, alcohol dehydrogenase 1 and aldehyde dehydrogenase 2, and two key mediators of hepatocyte replication and repair, cyclin D1 and proliferating cell nuclear antigen. EtOH ingestion upregulated hepatic estrogen receptor α, cyclin D1, and CYP2E1 in both genders, but differentially altered lipid and EtOH metabolism. Consistent with higher basal levels of EtOH-metabolizing enzymes, blood EtOH was more rapidly cleared in hPXR females. These factors combined to provide greater protection against EtOH-induced liver injury in female hPXR mice, as revealed by markers for liver damage, lipid peroxidation, and endoplasmic reticulum stress. These results indicate that female hPXR mice are less susceptible to acute binge EtOH-induced hepatotoxicity than their male counterparts, due at least in part to the relative suppression of cellular stress and enhanced expression of enzymes involved in both EtOH metabolism and hepatocyte proliferation and repair in hPXR females.

Alcoholic, Nonalcoholic, and Toxicant-Associated Steatohepatitis: Mechanistic Similarities and Differences

Hepatic steatosis and steatohepatitis are common histologic findings that can be caused by multiple etiologies. The three most frequent causes for steatosis/steatohepatitis are alcohol (alcoholic steatohepatitis, ASH), obesity/metabolic syndrome (nonalcoholic steatohepatitis, NASH), and environmental toxicants (toxicant-associated steatohepatitis, TASH). Hepatic steatosis is an early occurrence in all three forms of liver disease, and they often share common pathways to disease progression/severity. Disease progression is a result of both direct effects on the liver as well as indirect alterations in other organs/tissues such as intestine, adipose tissue, and the immune system. Although the three liver diseases (ASH, NASH, and TASH) share many common pathogenic mechanisms, they also exhibit distinct differences. Both shared and divergent mechanisms can be potential therapeutic targets. This review provides an overview of selected important mechanistic similarities and differences in ASH, NASH, and TASH.

Potential contributions of the tobacco nicotine-derived nitrosamine ketone (NNK) in the pathogenesis of steatohepatitis in a chronic plus binge rat model of alcoholic liver disease

AIMS

Alcoholic liver disease (ALD) is linked to binge drinking and cigarette smoking. Heavy chronic ± binge alcohol, or low-level exposures to dietary nitrosamines cause steatohepatitis with insulin resistance and oxidative stress in animal models. This study examines hepatotoxic effects of sub-mutagenic exposures to tobacco-specific nitrosamine (NNK) in relation to ALD.

METHODS

Long Evans rats were fed liquid diets containing 0 or 26% (caloric) ethanol (EtOH) for 8 weeks. In Weeks 3 through 8, rats were treated with NNK (2 mg/kg) or saline by i.p. injection, 3×/week, and in Weeks 7 and 8, EtOH-fed rats were binge-administered 2 g/kg EtOH 3×/week; controls were given saline.

RESULTS

EtOH ± NNK caused steatohepatitis with necrosis, disruption of the hepatic cord architecture, ballooning degeneration, early fibrosis, mitochondrial cytopathy and ER disruption. Severity of lesions was highest in the EtOH+NNK group. EtOH and NNK inhibited insulin/IGF signaling through Akt and activated pro-inflammatory cytokines, while EtOH promoted lipid peroxidation, and NNK increased apoptosis. O(6)-methyl-Guanine adducts were only detected in NNK-exposed livers.

CONCLUSION

Both alcohol and NNK exposures contribute to ALD pathogenesis, including insulin/IGF resistance and inflammation. The differential effects of EtOH and NNK on adduct formation are critical to ALD progression among alcoholics who smoke.

Role of Nrf2 in chronic liver disease

Nuclear erythroid 2-related factor 2 (Nrf2) is a central regulator of antioxidative response elements-mediated gene expression. It has a significant role in adaptive responses to oxidative stress by interacting with the antioxidant response element, which induces the expression of a variety of downstream targets aimed at cytoprotection. Previous studies suggested oxidative stress and associated damage could represent a common link between different forms of diseases. Oxidative stress has been implicated in various liver diseases, including viral hepatitis, nonalcoholic fatty liver disease/steatohepatitis, alcoholic liver disease and drug-induced liver injury. Nrf2 activation is initiated by oxidative or electrophilic stress, and aids in the detoxification and elimination of potentially harmful exogenous chemicals and their metabolites. The expression of Nrf2 has been observed throughout human tissue, with high expression in detoxification organs, especially the liver. Thus, Nrf2 may serve as a major regulator of several cellular defense associated pathways by which hepatic cells combat oxidative stress. We review the relevant literature concerning the crucial role of Nrf2 and its signaling pathways against oxidative stress to protect hepatic cell from oxidative damage during development of common chronic liver diseases. We also review the use of Nrf2 as a therapeutic target to prevent and treat liver diseases.

The antiapoptotic effects of different doses of β-carotene in chronic ethanol-fed rats

BACKGROUND

Ethanol consumption might induce hepatic apoptosis and cause liver damage. The study was to investigate the effects of different doses of β-carotene supplementation on the antioxidant capacity and hepatic apoptosis in chronic ethanol-fed rats.

METHODS

Rats were divided into 6 groups: C (control liquid diet), CLB [control liquid diet with β-carotene supplementation at 0.52 mg/kg body weight (BW)/day], CHB (control liquid diet with β-carotene supplementation at 2.6 mg/kg BW/day), E (ethanol liquid diet), ELB (ethanol liquid diet with β-carotene supplementation at 0.52 mg/kg BW/day), and EHB (ethanol liquid diet with β-carotene supplementation at 2.6 mg/kg BW/day). After 12 weeks, rats were sacrificed and blood and liver samples were collected for analysis.

RESULTS

Lipid peroxidation and hepatic cytochrome P450 2E1 (CYP2E1) expression had increased, and hepatic Fas ligand, caspase-8, cytochrome c, caspase-9, and -3 expressions had significantly increased in the E group. However, lipid peroxidation and CYP2E1, caspase-9, and -3 expressions were significantly lower and Bcl-xL expression was higher in the ELB group. The hepatic tumor necrosis factor (TNF)-α level, lipid peroxidation, and cytochrome c expression were significantly lower and Bcl-2 expression was significantly higher in the EHB group.

CONCLUSIONS

The results suggest that ethanol treatment causes oxidative stress and hepatic apoptosis leading to liver injury, and β-carotene supplementation (0.52 mg/kg BW/day) can prevent ethanol-induced liver damage by decreasing ethanol-induced oxidative stress and inhibiting apoptosis in the liver.

New Insights into the Pathogenesis of Alcohol-Induced ER Stress and Liver Diseases

Alcohol-induced liver disease increasingly contributes to human mortality worldwide. Alcohol-induced endoplasmic reticulum (ER) stress and disruption of cellular protein homeostasis have recently been established as a significant mechanism contributing to liver diseases. The alcohol-induced ER stress occurs not only in cultured hepatocytes but also  in vivo  in the livers of several species including mouse, rat, minipigs, zebrafish, and humans. Identified causes for the ER stress include acetaldehyde, oxidative stress, impaired one carbon metabolism, toxic lipid species, insulin resistance, disrupted calcium homeostasis, and aberrant epigenetic modifications. Importance of each of the causes in alcohol-induced liver injury depends on doses, duration and patterns of alcohol exposure, genetic disposition, environmental factors, cross-talks with other pathogenic pathways, and stages of liver disease. The ER stress may occur more or less all the time during alcohol consumption, which interferes with hepatic protein homeostasis, proliferation, and cell cycle progression promoting development of advanced liver diseases. Emerging evidence indicates that long-term alcohol consumption and ER stress may directly be involved in hepatocellular carcinogenesis (HCC). Dissecting ER stress signaling pathways leading to tumorigenesis will uncover potential therapeutic targets for intervention and treatment of human alcoholics with liver cancer.

Locally-generated Acetaldehyde Contributes to the Effects of Ethanol on Neurosteroids and LTP in the Hippocampus

BACKGROUND

As severe alcohol intoxication impairs memory function, a high concentration of ethanol (60 mM) acutely inhibits long-term potentiation (LTP), a cellular model of learning and memory, in rat hippocampal slices. Neurosteroids are involved in this LTP inhibition. We recently reported that the inhibitory effects of 60 mM ethanol are blocked by 4-methylpyrazole (4MP), an inhibitor of alcohol dehydrogenase, suggesting that acetaldehyde locally generated within the hippocampus participates in LTP inhibition.

AIM

We investigated whether acetaldehyde generated by ethanol metabolism contributes to neurosteroidogenesis and LTP inhibition.

RESULTS

Like 60 mM ethanol, we found that exogenous acetaldehyde enhanced neurosteroid immunostaining in CA1 pyramidal neurons, and that augmented neurosteroid immunostaining by high ethanol alone was blocked by 4MP but not by inhibitors of other ethanol metabolism pathways. The inhibitory effects of 60 mM ethanol on LTP were mimicked by a lower concentration of ethanol (20 mM) plus acetaldehyde (60 μM), although neither agent alone was effective at these concentrations, suggesting that 60 mM ethanol inhibits LTP via multiple actions, one of which involves acetaldehyde and the other of which requires only 20 mM ethanol. The effects of ethanol and acetaldehyde on neurosteroid staining and LTP were overcome by inhibition of neurosteroid synthesis and by blockade of N-methyl-D-aspartate receptors (NMDARs).

CONCLUSION

These observations indicate that acetaldehyde generated by local ethanol metabolism within the hippocampus serves as a signal for neurosteroid synthesis in pyramidal neurons, and participates in the synaptic dysfunction associated with severe alcohol intoxication.

Medium chain triglycerides dose-dependently prevent liver pathology in a rat model of non-alcoholic fatty liver disease

Metabolic syndrome is often accompanied by development of hepatic steatosis and less frequently by non-alcoholic fatty liver disease (NAFLD) leading to non-alcoholic steatohepatitis (NASH). Replacement of corn oil with medium chain triacylglycerols (MCT) in the diets of alcohol-fed rats has been shown to protect against steatosis and alcoholic liver injury. The current study was designed to determine if a similar beneficial effect of MCT occurs in a rat model of NAFLD. Groups of male rats were isocalorically overfed diets containing 10%, 35% or 70% total energy as corn oil or a 70% fat diet in which corn oil was replaced with increasing concentrations of saturated fat (18:82, beef tallow:MCT oil) from 20% to 65% for 21 days using total enteral nutrition (TEN). As dietary content of corn oil increased, hepatic steatosis and serum alanine amino transferases were elevated (P < 0.05). This was accompanied by greater expression of cytochrome P450 enzyme CYP2E1 (P < 0.05) and higher concentrations of polyunsaturated 18:2 and 20:4 fatty acids (FA) in the hepatic lipid fractions (P < 0.05). Keeping the total dietary fat at 70%, but increasing the proportion of MCT-enriched saturated fat resulted in a dose-dependent reduction in steatosis and necrosis without affecting CYP2E1 induction. There was no incorporation of C8-C10 FAs into liver lipids, but increasing the ratio of MCT to corn oil: reduced liver lipid 18:2 and 20:4 concentrations; reduced membrane susceptibility to radical attack; stimulated FA β- and ω-oxidation as a result of activation of peroxisomal proliferator activated receptor (PPAR)α, and appeared to increase mitochondrial respiration through complex III. These data suggest that replacing unsaturated fats like corn oil with MCT oil in the diet could be utilized as a potential treatment for NAFLD.

Locally-generated acetaldehyde is involved in ethanol-mediated LTP inhibition in the hippocampus

Consistent with the ability of severe alcohol intoxication to impair memory, high concentrations of ethanol (60mM) acutely inhibit long-term potentiation (LTP) in the CA1 region of rat hippocampal slices. To account for this, we hypothesized that local metabolism to acetaldehyde may contribute to the effects of high ethanol on synaptic function. However, sodium azide, a catalase inhibitor, and allyl sulfide, an inhibitor of cytochrome P450 2E1 (CYP2E1), failed to overcome LTP inhibition by 60mM ethanol. In contrast, LTP was successfully induced in the presence of ethanol plus 4-methylpyrazole (4MP), an inhibitor of alcohol dehydrogenase, suggesting that local metabolism via alcohol dehydrogenase contributes to synaptic effects. Furthermore, exogenously administered acetaldehyde overcame the effects of 4MP on LTP inhibition mediated by ethanol. These observations indicate that acetaldehyde generated by local metabolism within the hippocampus participates in the synaptic dysfunction associated with severe alcohol intoxication.

Cytochrome P450 2E1: its clinical aspects and a brief perspective on the current research scenario

Research on Cytochrome P450 2E1 (CYP2E1), a key enzyme in alcohol metabolism has been very well documented in literature. Besides the involvement of CYP2E1 in alcohol metabolism as illustrated through the studies discussed in the chapter, recent studies have thrown light on several other aspects of CYP2E1 i.e. its extrahepatic expression, its involvement in several diseases and pathophysiological conditions; and CYP2E1 mediated carcinogenesis and modulation of drug efficacy. Studies involving these interesting facets of CYP2E1 have been discussed in the chapter focusing on the recent observations or ongoing studies illustrating the crucial role of CYP2E1 in disease development and drug metabolism.

Inhibition of CYP2E1 attenuates chronic alcohol intake-induced myocardial contractile dysfunction and apoptosis

Alcohol intake is associated with myocardial contractile dysfunction and apoptosis although the precise mechanism is unclear. This study was designed to examine the effect of the cytochrome P450 enzyme CYP2E1 inhibition on ethanol-induced cardiac dysfunction. Adult male mice were fed a 4% ethanol liquid or pair-fed control diet for 6weeks. Following 2weeks of diet feeding, a cohort of mice started to receive the CYP2E1 inhibitor diallyl sulfide (100mg/kg/d, i.p.) for the remaining feeding duration. Cardiac function was assessed using echocardiographic and IonOptix systems. Western blot analysis was used to evaluate CYP2E1, heme oxygenase-1 (HO-1), iNOS, the intracellular Ca(2+) regulatory proteins sarco(endo)plasmic reticulum Ca(2+)-ATPase, Na(+)Ca(2+) exchanger and phospholamban, pro-apoptotic protein cleaved caspase-3, Bax, c-Jun-NH(2)-terminal kinase (JNK) and apoptosis signal-regulating kinase (ASK-1). Ethanol led to elevated levels of CYP2E1, iNOS and phospholamban, decreased levels of HO-1 and Na(+)Ca(2+) exchanger, cardiac contractile and intracellular Ca(2+) defects, cardiac fibrosis, overt O(2)(-) production, and apoptosis accompanied with increased phosphorylation of JNK and ASK-1, the effects were significantly attenuated or ablated by diallyl sulfide. Inhibitors of JNK and ASK-1 but not HO-1 inducer or iNOS inhibitor obliterated ethanol-induced cardiomyocyte contractile dysfunction, substantiating a role for JNK and ASK-1 signaling in ethanol-induced myocardial injury. Taken together, these findings suggest that ethanol metabolism through CYP2E1 may contribute to the pathogenesis of alcoholic cardiomyopathy including myocardial contractile dysfunction, oxidative stress and apoptosis, possibly through activation of JNK and ASK-1 signaling.

β-catenin is essential for ethanol metabolism and protection against alcohol-mediated liver steatosis in mice

The liver plays a central role in ethanol metabolism, and oxidative stress is implicated in alcohol-mediated liver injury. β-Catenin regulates hepatic metabolic zonation and adaptive response to oxidative stress. We hypothesized that β-catenin regulates the hepatic response to ethanol ingestion. Female liver-specific β-catenin knockout (KO) mice and wild-type (WT) littermates were fed the Lieber-Decarli liquid diet (5% ethanol) in a pairwise fashion. Liver histology, biochemistry, and gene-expression studies were performed. Plasma alcohol and ammonia levels were measured using standard assays. Ethanol-fed (EtOH) KO mice exhibited systemic toxicity and early mortality. KO mice exhibited severe macrovesicular steatosis and 5 to 6-fold higher serum alanine aminotransferase and aspartate aminotransferase levels. KO mice had a modest increase in hepatic oxidative stress, lower expression of mitochondrial superoxide dismutase (SOD2), and lower citrate synthase activity, the first step in the tricarboxylic acid cycle. N-Acetylcysteine did not prevent ethanol-induced mortality in KO mice. In WT livers, β-catenin was found to coprecipitate with forkhead box O3, the upstream regulator of SOD2. Hepatic alcohol dehydrogenase and aldehyde dehydrogenase activities and expression were lower in KO mice. Hepatic cytochrome P450 2E1 protein levels were up-regulated in EtOH WT mice, but were nearly undetectable in KO mice. These changes in ethanol-metabolizing enzymes were associated with 30-fold higher blood alcohol levels in KO mice.

CONCLUSION

β-Catenin is essential for hepatic ethanol metabolism and plays a protective role in alcohol-mediated liver steatosis. Our results strongly suggest that integration of these functions by β-catenin is critical for adaptation to ethanol ingestion in vivo.

Effects of ethanol on CYP2E1 levels and related oxidative stress using a standard balanced diet

Expression of cytochrome P4502E1 (CYP2E1) is very much influenced by nutritional factors, especially carbohydrate consumption, and various results concerning the expression of CYP2E1 were obtained with a low-carbohydrate diet. This study describes the effects of ethanol treatment on CYP2E1 levels and its relationship with oxidative stress using a balanced standard diet to avoid low or high carbohydrate consumption. Rats were fed for 1, 2, 3, or 4 weeks a commercial diet plus an ethanol-sucrose solution. The results have shown that ethanol administration was associated with CYP2E1 induction and stabilization without related oxidative stress. Our findings suggest that experimental models with a low-carbohydrate/high-fat diet produce some undesirable CYP2E1 changes that are not present when a balanced standard diet is given.

Ethanol suppresses ureagenesis in rat hepatocytes: role of acetaldehyde

We proposed previously that closure of voltage-dependent anion channels (VDAC) in the mitochondrial outer membrane after ethanol exposure leads to suppression of mitochondrial metabolite exchange. Because ureagenesis requires extensive mitochondrial metabolite exchange, we characterized the effect of ethanol and its metabolite, acetaldehyde (AcAld), on total and ureagenic respiration in cultured rat hepatocytes. Ureagenic substrates increased cellular respiration from 15.8 ± 0.9 nmol O(2)/min/10(6) cells (base line) to 29.4 ± 1.7 nmol O(2)/min/10(6) cells in about 30 min. Ethanol (0-200 mM) suppressed extra respiration after ureagenic substrates (ureagenic respiration) by up to 51% but not base line respiration. Urea formation also declined proportionately. Inhibition of alcohol dehydrogenase, cytochrome P450 2E1, and catalase with 4-methylpyrazole, trans-1,2-dichloroethylene, and 3-amino-1,2,3-triazole restored ethanol-suppressed ureagenic respiration by 46, 37, and 66%, respectively. By contrast, inhibition of aldehyde dehydrogenase with phenethyl isothiocyanate increased the inhibitory effect of ethanol on ureagenic respiration by an additional 60%. AcAld, an intermediate product of ethanol oxidation, suppressed ureagenic respiration with an apparent IC(50) of 125 μM. AcAld also inhibited entry of 3-kDa rhodamine-conjugated dextran in the mitochondrial intermembrane space of digitonin-permeabilized hepatocytes, indicative of VDAC closure. In conclusion, AcAld, derived from ethanol metabolism, suppresses ureagenesis in hepatocytes mediated by closure of VDAC.

Limited therapeutic effect of N-acetylcysteine on hepatic insulin resistance in an experimental model of alcohol-induced steatohepatitis

BACKGROUND

Alcohol-related steatohepatitis is associated with increased oxidative stress, DNA damage, lipotoxicity, and insulin resistance in liver. As inflammation and oxidative stress can promote insulin resistance, effective treatment with antioxidants, for example, N-acetylcysteine (NAC), may restore ethanol-impaired insulin signaling in the liver.

METHODS

Adult male Sprague-Dawley rats were fed for 130 days with liquid diets containing 0 or 37% ethanol by caloric content, and simultaneously treated with vehicle or NAC. Chow-fed controls were studied in parallel. Liver tissues were used for histopathology, cytokine activation, and insulin/IGF-1 signaling assays.

RESULTS

We observed significant positive trends of increasing severity of steatohepatitis (p = 0.016) with accumulation of neutral lipid (p = 0.0002) and triglycerides (p = 0.0004) from chow to control, to the ethanol diet, irrespective of NAC treatment. In ethanol-fed rats, NAC reduced inflammation, converted the steatosis from a predominantly microvesicular to a mainly macrovesicular histological pattern, reduced pro-inflammatory cytokine gene expression, ceramide load, and acid sphingomyelinase activity, and increased expression of IGF-1 receptor and IGF-2 in liver. However, NAC did not abrogate ethanol-mediated impairments in signaling through insulin/IGF-1 receptors, IRS-1, Akt, GSK-3β, or p70S6K, nor did it significantly reduce pro-ceramide or GM3 ganglioside gene expression in liver.

CONCLUSIONS

Antioxidant treatments reduce the severity of chronic alcohol-related steatohepatitis, possibly because of the decreased expression of inflammatory mediators and ceramide accumulation, but they do not restore insulin/IGF-1 signaling in liver, most likely due to persistent elevation of GM3 synthase expression. Effective treatment of alcohol-related steatohepatitis most likely requires dual targeting of oxidative stress and insulin/IGF resistance.

Influence of selenium and/or magnesium on alleviation alcohol induced oxidative stress in rats, normalization function of liver and changes in serum lipid parameters

The aim of this study was to evaluate the attenuating effect of given selenium and/or magnesium on ethanol-induced oxidative stress, disturbances of liver function and cholesterol metabolism. Forty male rats were divided into five groups: C – control, Et – intoxicated with alcohol (15% solution in drinking water), Et + Mg, Et + Se, Et + Mg + Se – intoxicated with alcohol and supplemented with selenium (0.4 mg Se/l water), magnesium (100 mg Mg/l water) and combination of Se and Mg, respectively. The experiment was carried out over the 3 months. The results show that the chronic ingestion of alcohol induces lipid peroxidation and histopathological changes in liver. Supplementation with magnesium only partially alleviates oxidative stress and damages in this tissue. The both selenium alone and combination of magnesium and selenium significantly elevated total antioxidant status (TAS) in serum, activity of glutathione peroxidase and ratio of reduced glutathione to oxidized glutathione (GSH/GSSG) in liver and retarded oxidative stress and histopathological changes in this tissue. Chronic administration of ethanol (alone and with magnesium) resulted in significant decrease in the serum total cholesterol and retardation in the body weight gain in comparison with the control group. In the groups supplemented with selenium and selenium and magnesium simultaneously, concentration of total cholesterol in serum and body gains was similar to the control group. Supplementation of Se or selenium and magnesium simultaneously significantly enhances antioxidant defence and is more effective against alcohol-induced oxidative stress, disturbance of liver function and cholesterol metabolism than the separate use of magnesium.

Elevated glutathione level does not protect against chronic alcohol mediated apoptosis in recombinant human hepatoma cell line VL-17A over-expressing alcohol metabolizing enzymes--alcohol dehydrogenase and Cytochrome P450 2E1

Chronic consumption of alcohol leads to liver injury. Ethanol-inducible Cytochrome P450 2E1 (CYP2E1) plays a critical role in alcohol mediated oxidative stress due to its ability to metabolize ethanol. In the present study, using the recombinant human hepatoma cell line VL-17A that over-expresses the alcohol metabolizing enzymes-alcohol dehydrogenase (ADH) and CYP2E1; and control HepG2 cells, the mechanism and mode of cell death due to chronic ethanol exposure were studied. Untreated VL-17A cells exhibited apoptosis and oxidative stress when compared with untreated HepG2 cells. Chronic alcohol exposure, i.e., 100 mM ethanol treatment for 72 h caused a significant decrease in viability (47%) in VL-17A cells but not in HepG2 cells. Chronic ethanol mediated cell death in VL-17A cells was predominantly apoptotic, with increased oxidative stress as the underlying mechanism. Chronic ethanol exposure of VL-17A cells resulted in 1.1- to 2.5-fold increased levels of ADH and CYP2E1. Interestingly, the level of the antioxidant GSH was found to be 3-fold upregulated in VL-17A cells treated with ethanol, which may be a metabolic adaptation to the persistent and overwhelming oxidative stress. In conclusion, the increased GSH level may not be sufficient enough to protect VL-17A cells from chronic alcohol mediated oxidative stress and resultant apoptosis.

Oxidative stress and antioxidants in hepatic pathogenesis

Long term hepatitis B virus (HBV) infection is a major risk factor in pathogenesis of chronic liver diseases, including hepatocellular carcinoma (HCC). The HBV encoded proteins, hepatitis B virus X protein and preS, appear to contribute importantly to the pathogenesis of HCC. Both are associated with oxidative stress, which can damage cellular molecules like lipids, proteins, and DNA during chronic infection. Chronic alcohol use is another important factor that contributes to oxidative stress in the liver. Previous studies reported that treatment with antioxidants, such as curcumin, silymarin, green tea, and vitamins C and E, can protect DNA from damage and regulate liver pathogenesis-related cascades by reducing reactive oxygen species. This review summarizes some of the relationships between oxidative stress and liver pathogenesis, focusing upon HBV and alcohol, and suggests antioxidant therapeutic approaches.

Rat strain differences in susceptibility to alcohol-induced chronic liver injury and hepatic insulin resistance

The finding of more severe steatohepatitis in alcohol fed Long Evans (LE) compared with Sprague Dawley (SD) and Fisher 344 (FS) rats prompted us to determine whether host factors related to alcohol metabolism, inflammation, and insulin/IGF signaling predict proneness to alcohol-mediated liver injury. Adult FS, SD, and LE rats were fed liquid diets containing 0% or 37% (calories) ethanol for 8 weeks. Among controls, LE rats had significantly higher ALT and reduced GAPDH relative to SD and FS rats. Among ethanol-fed rats, despite similar blood alcohol levels, LE rats had more pronounced steatohepatitis and fibrosis, higher levels of ALT, DNA damage, pro-inflammatory cytokines, ADH, ALDH, catalase, GFAP, desmin, and collagen expression, and reduced insulin receptor binding relative to FS rats. Ethanol-exposed SD rats had intermediate degrees of steatohepatitis, increased ALT, ADH and profibrogenesis gene expression, and suppressed insulin receptor binding and GAPDH expression, while pro-inflammatory cytokines were similarly increased as in LE rats. Ethanol feeding in FS rats only reduced IL-6, ALDH1-3, CYP2E1, and GAPDH expression in liver. In conclusion, susceptibility to chronic steatohepatitis may be driven by factors related to efficiency of ethanol metabolism and degree to which ethanol exposure causes hepatic insulin resistance and cytokine activation.