Metabolism of ethanol and some associated adverse effects on the liver and the stomach

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

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

Prevention of alcohol-induced DNA damage by a proprietary glycyrrhizin/D-mannitol product: A randomized, placebo-controlled, cross-over human study

OBJECTIVES

The purpose of the present study was to evaluate the ability of a proprietary combination of glycyrrhizin and D-mannitol to protect against oxidative damage to DNA associated with acute alcohol consumption by human subjects in a randomized, placebo-controlled cross-over designed study. Excessive alcohol consumption is associated with numerous diseases. Alcohol has been shown to generate reactive oxygen species that can result in DNA damage, leading to genetic and epigenetic changes.

METHODS

A total of 25 subjects (13 male and 12 female) were enrolled. Alcohol intake in the form of vodka (40% ethanol) was adjusted based on 1.275 g of 100% ethanol/kg body weight for men and 1.020 g/kg body weight for women, which was consumed with and without the study product. Blood samples were drawn at 2 h after alcohol consumption, lymphocytes were isolated, and were subjected to DNA comet electrophoresis on a blinded basis.

RESULTS

Acute alcohol consumption increased lymphocyte DNA damage by approximately 8.36%. Co-consumption of the glycyrrhizin/D-mannitol study product with alcohol reduced DNA damage to baseline levels. No adverse effects were associated with use of the study product, and no differences were observed in blood alcohol concentrations in the presence or absence of the study product in males and females.

CONCLUSIONS

Acute alcohol ingestion resulted in measurable increases in DNA damage, which were prevented by the addition of the proprietary glycyrrhizin/D-mannitol (NTX^®) study product to the alcohol, suggesting that the tissue-damaging effects of alcohol consumption can be ameliorated.

Alcohol Drinking Mediates the Association between Polymorphisms of ADH1B and ALDH2 and Hepatitis B-Related Hepatocellular Carcinoma

BACKGROUND

The role of polymorphisms on ADH1B and ALDH2 in patients with chronic hepatitis B is unclear. This study aims to examine whether alcohol drinking mediates the association between two ADH1B and ALDH2 polymorphisms and the risk of hepatocellular carcinoma among chronic hepatitis B patients.

METHODS

A total of 3,824 individuals were enrolled in this study. Two SNPs, rs1229984 (ADH1B) and rs671 (ALDH2), were genotyped using the Affymetrix Axiom Genome-Wide CHB1 Array (Affymetrix, Inc). Multivariate unconditional logistic regression and mediation analyses were used, comparing CT or TT with CC for rs1229984 and GA and AA with GG for rs671.

RESULTS

There were 602 cases of hepatocellular carcinoma and 3,222 controls. Frequencies of the rs1229984 (ADH1B) T allele and rs671 (ALDH2) A allele were 72.9% and 28.8%, respectively. Individuals who carried at least one deficient allele for both SNPs were significantly less likely to become habitual alcohol drinkers, with an OR and 95% confidence interval (CI) of 0.24 (0.15-0.40). Alleles for rs1229984 (ADH1B) and rs671 (ALDH2) were not associated with hepatocellular carcinoma in multivariate analyses. However, mediation analyses showed that the rs1229984 T allele, rs671 A allele, and two SNPs combined were significantly associated with decreased hepatocellular carcinoma risk, mediated through alcohol drinking, with an OR (95% CI) of 0.87 (0.79-0.96), 0.70 (0.61-0.82), and 0.73 (0.58-0.88), respectively.

CONCLUSIONS

Polymorphisms on ADH1B and ALDH2 had significant indirect effects on hepatocellular carcinoma risk, mediated through alcohol drinking.

IMPACT

Future genetic studies of chronic hepatitis B and hepatocellular carcinoma must take mediation effects into consideration. Cancer Epidemiol Biomarkers Prev; 25(4); 693-9. ©2016 AACR.

Effect of alcohol on diethylnitrosamine-induced hepatic toxicity: Critical role of ROS, lipid accumulation, and mitochondrial dysfunction

Hepatocellular carcinoma (HCC) is the fifth most common cancer in men and the seventh in women worldwide. Chronic heavy alcohol consumption is a major risk factor for the development of HCC. However, the mechanism underlying the direct association between alcohol consumption and HCC is far from completely understood. In the present study, we investigated the effect of chronic consumption of alcohol on diethylnitrosamine (DEN)-induced cytotoxicity, which was essential for the malignant transformation. We showed that alcohol deceased survival of mice treated by DEN and promoted DEN-induced toxicity and hepatic injury. In addition, alcohol promoted DEN-induced increase of proinflammatory factors, collagen content and fibrosis-related genes, including collagen1, 3 and 4, TMIP1, TIMP2 and TGFβ1, and compensatory proliferation. Alcohol may increase alcohol dehydrogenase (ADH) and cytochrome P4502E1 (CYP2E1) expression, enhanced reactive oxygen species (ROS) generation, and resulted in a vicious circle between ROS generation, lipid accumulation, and mitochondrial dysfunction, aggravating liver injury and toxicity in DEN-treated mice. These results demonstrated that the combination of alcohol and carcinogens could aggravate carcinogen-induced cytotoxicity in the early phase of rumourigenesis through ADH and CYP2E1-generated ROS and the resultant cytotoxic process. The present study provided direct experimental evidence for alcohol-promoted toxicity and hepatic injury in carcinogen (DEN)-treated mice.

Antioxidant effects of some drugs on ethanol-induced ulcers

The aim of this work was to investigate the antioxidant potential of some commonly used drugs (bromocriptine, haloperidol and azithromycin) on alcohol-induced ulcers in the rat. The following parameters were determined: content of reduced glutathione, activities of catalase, xanthine oxidase, glutathione reductase, glutathione peroxidase, peroxidase, and lipid peroxidation intensity. A battery of biochemical assays were used and the resulting data was statistically analyzed. Alcohol stress caused gastric ulcerations and hemorrhages and changed all the examined parameters except glutathione peroxidase activity. All drugs reduced the ulcer index and hemorrhages, with azithromycin showing the strongest effects. The drugs in combination with alcohol showed different effects on biochemical parameters. Our results indicate that the gastroprotective effects of the investigated drugs on experimental lesions induced by 100% ethanol could not be correlated with their antioxidative properties.

The activity of class I, II, III, and IV alcohol dehydrogenase (ADH) isoenzymes and aldehyde dehydrogenase (ALDH) in liver cancer

BACKGROUND

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which are most abundant in the liver, are the main enzymes involved in ethanol and acetaldehyde metabolism.

AIMS

The purpose of this study was to compare the activity of ADH isoenzymes and ALDH between liver carcinoma cells and healthy hepatocytes.

PATIENTS

Samples were taken from 44 liver cancer patients (19 drinkers, 25 nondrinkers). Seventeen patients had primary liver tumors and 27 had metastatic liver tumors.

METHODS

Fluorimetric methods were used for measurement of the activity of class I and II ADH isoenzymes and ALDH activity. Total ADH activity and activity of class III and IV isoenzymes were measured by a photometric method.

RESULTS

The activities of total ADH, ALDH, and class I ADH were significantly higher in cancer cells than in healthy tissues. The other tested classes of ADH showed a tendency toward higher activity in cancer than in normal cells. The differences between enzymes of drinkers and nondrinkers in both cancer and healthy tissue, were not significant.

CONCLUSION

Differences in the activities of total ADH, ALDH and class I ADH isoenzyme between cancer liver tissues and healthy hepatocytes might be a factor in ethanol metabolism disorders, which can intensify carcinogenesis.

Molecular pathogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common life-threatening malignancies in the world. This cancer generally arises within the boundaries of well-defined causal factors, of which viral hepatitis infection, aflatoxin exposure, chronic alcohol abuse, and nonalcoholic steatohepatitis are the major risk factors. Despite the identification of these etiological agents, hepatocarcinogenesis remains poorly understood. The molecular mechanisms leading to the development of HCC appear extremely complex and only recently have begun to be elucidated. Currently, surgical resection or liver transplantation offer the best chance of cure for the patient with HCC; however, these therapies are hindered by inability of many of these patients to undergo liver resection, by tumor recurrence and by donor shortages. A lack of suitable therapeutic strategies has led to a greater focus on prevention of HCC using antiviral agents and vaccination. Overall, the current outlook for patients with HCC is bleak; however, a better understanding of the molecular and genetic basis of this cancer should lead to the development of more efficacious therapies.

Effects of the Aerial Parts of Orostachys japonicus and Its Bioactive Component on Hepatic Alcohol-Metabolizing Enzyme System

In the course of screening medicinal plants that modulate hepatic alcohol-metabolizing enzymes and lipid peroxidation, effects of the methanol extract (ME) of Orostachys japonicus and its major bioactive compound, gallic acid (GA), were investigated in rats treated with 10% ethanol solution for 6 weeks. The ME and GA greatly enhanced the activities of hepatic alcohol dehydrogenase (ADH), the microsomal ethanol-oxidizing system (MEOS), and aldehyde dehydrogenase (ALDH) in a dose-dependent manner, but had no effect on catalase. The hepatic lipid peroxide level increased by ethanol administration was moderately reduced by treatment with ME or GA. The results suggest that the detoxification of hepatic alcohol by O. japonicus ME under our experimental conditions was due to the enhanced activities of the alcohol-oxidizing enzymes, ADH, MEOS, and ALDH. In addition, GA may be partly responsible for the effects.

Alcohol and liver cancer

Hepatocellular carcinoma is the eighth most frequent cancer in the world, accounting for approximately 500,000 deaths per year. Unlike many malignancies, hepatocellular carcinoma occurs predominantly within the context of known risk factors, with hepatic cirrhosis being the most common precursor to the development of hepatocellular carcinoma. After ethanol ingestion, the liver represents the major site of metabolism. Ethanol metabolism by alcohol dehydrogenase leads to the generation of acetaldehyde and free radicals that bind rapidly to numerous cellular targets, including components of cell signaling pathways and DNA. In addition to direct DNA damage, acetaldehyde depletes glutathione, an antioxidant involved in detoxification. Chronic ethanol abuse leads to induction of hepatocyte microsomal cytochrome P450 2E1, an enzyme that metabolizes ethanol to acetaldehyde and, in doing so, causes further free radical production and aberrant cell function. Cytochrome P450 2E1-dependent ethanol metabolism is also associated with activation of procarcinogens, changes in cell cycle, nutritional deficiencies, and altered immune system responses. The identification of oxidative stress in mediating many deleterious effects of ethanol in the liver has led to renewed interest in the use of dietary antioxidants as therapeutic agents. Included in this group are S-adenosyl-L-methionine and plant-derived flavanoids.

Inhibition of alcohol dehydrogenase blocks enhanced Gi-protein expression following ethanol treatment in experimental hepatocellular carcinoma in vitro

OBJECTIVE

Chronic alcohol abuse is one of the major contributors to the onset and progression of hepatocellular carcinoma (HCC). We have previously identified increased expression and function of inhibitory guanine nucleotide regulatory proteins (Gi-proteins) in primary human and animal models of HCC. Stimulation of Gi-proteins in HCC stimulates cell mitogenesis, an effect not observed in hepatocytes. The aim of this study was to determine the effect of ethanol and ethanol metabolism on Gi-protein expression in an experimental model of HCC.

DESIGN

Pharmacological agents that inhibit alcohol metabolism were used in conjunction with ethanol or ethanol metabolites. We were also able to assess the relative contribution of alcohol and acetaldehyde, the major metabolite of alcohol, on Gi-protein expression in HCC and hepatocytes.

METHODS

These studies used the rat hepatic tumorigenic H4IIE cell line in conjunction with isolated rat hepatocytes. Cells were cultured in vitro and exposed to ethanol, ethanol in the presence of an alcohol dehydrogenase (ADH) inhibitor, or acetaldehyde for varying lengths of time. Ethanol metabolism and changes in Gi-protein expression were subsequently determined by assay.

RESULTS

Exposure to ethanol alone led to significant dose and time dependent increases in Gialpha1/2 and Gialpha3 protein and mRNA expression in HCC cells. In contrast, ethanol failed to alter Gialpha1/2, and only moderately affected Gialpha3 protein expression in isolated cultured hepatocytes. Pretreatment of HCC cells and hepatocytes with 4-methyl pyrazole (4-MP, 10 microm) significantly inhibited alcohol metabolism. Treatment of HCC cells with 4-MP inhibited changes in Gi-protein expression following exposure to ethanol (25 mm, 24 h). In addition, the increased expression of Gi-proteins observed after exposure to ethanol in HCC were mimicked by direct exposure of HCC cells to acetaldehyde in a dose and time dependent manner.

CONCLUSIONS

These data suggest that alcohol metabolites, not alcohol, lead to increased Gi-protein expression in HCC in vitro. Ethanol and ethanol metabolites, in contrast, fail to significantly alter Gialpha1/2 protein expression in hepatocytes. These data may have significant implications in HCC progression in vivo.