Hypothesis: alcoholic liver injury and the covalent binding of acetaldehyde

Disposition of d-penicillamine, a promising drug for preventing alcohol-relapse. Influence of dose, chronic alcohol consumption and age: studies in rats

Pharmacokinetic studies concerning d-penicillamine (an acetaldehyde sequestering agent) are scarce and have not evaluated the influence of chronic ethanol consumption and age on its disposition. Since recent preclinical studies propose d-penicillamine as a promising treatment for alcohol relapse, the main aim of the present work was to evaluate the influence of these two factors on d-penicillamine disposition in order to guide future clinical studies on the anti-relapse efficacy of this drug in alcoholism. Additionally, the effect of the administered dose was also evaluated. To this end, three studies were carried out. Study 1 assessed the influence of dose on d-penicillamine disposition, whereas studies 2 and 3 evaluated, respectively, the influence of chronic alcohol consumption and age. Rapid intravenous administrations of 2, 10 and 30 mg/kg of d-penicillamine were performed using young or adult ethanol-naïve rats or adult ethanol-experienced (subjected to a long-term ethanol self-administration protocol) rats. Pharmacokinetic parameters were derived from the biexponential model. Statistical analysis of CL, normalized AUC0 (∞) , V1 and k10 revealed that disposition, in the range plasma concentrations assayed, is non-linear both in young ethanol-naïve and in adult ethanol-experienced rats. Notably, no significant changes in t1/2 were detected. Chronic ethanol consumption significantly reduced CL values by 35% without affecting t1/2 . d-Penicillamine disposition was equivalent in young and adult animals. In conclusion, although DP pharmacokinetics is non-linear, the lack of significant alterations of the t1/2 would potentially simplify the clinical use of this drug. Chronic consumption of ethanol also alters d-penicillamine disposition but, again, does not modify t1/2.

Inhibition of CYP2E1 leads to decreased malondialdehyde-acetaldehyde adduct formation in VL-17A cells under chronic alcohol exposure

AIM

Ethanol metabolism leads to the formation of acetaldehyde and malondialdehyde. Acetaldehyde and malondialdehyde can together form malondialdehyde-acetaldehyde (MAA) adducts. The role of alcohol dehydrogenase (ADH) and cytochrome P4502E1 (CYP2E1) in the formation of MAA-adducts in liver cells has been investigated.

MAIN METHODS

Chronic ethanol treated VL-17A cells over-expressing ADH and CYP2E1 were pretreated with the specific CYP2E1 inhibitor - diallyl sulfide or ADH inhibitor - pyrazole or ADH and CYP2E1 inhibitor - 4-methyl pyrazole. Malondialdehyde, acetaldehyde or MAA-adduct formation was measured along with assays for viability, oxidative stress and apoptosis.

KEY FINDINGS

Inhibition of CYP2E1 with 10 μM diallyl sulfide or ADH with 2mM pyrazole or ADH and CYP2E1 with 5mM 4-methyl pyrazole led to decreased oxidative stress and toxicity in chronic ethanol (100 mM) treated VL-17A cells. In vitro incubation of VL-17A cell lysates with acetaldehyde and malondialdehyde generated through ethanol led to increased acetaldehyde (AA)-, malondialdehyde (MDA)-, and MAA-adduct formation. Specific inhibition of CYP2E1 or ADH and the combined inhibition of ADH and CYP2E1 greatly decreased the formation of the protein aldehyde adducts. Specific inhibition of CYP2E1 led to the greatest decrease in oxidative stress, toxicity and protein aldehyde adduct formation, implicating that CYP2E1 accelerates the formation of protein aldehyde adducts which can be an important mechanism for alcohol mediated liver injury.

SIGNIFICANCE

CYP2E1-mediated metabolism of ethanol leads to increased AA-, MDA-, and MAA-adduct formation in liver cells which may aggravate liver injury.

Alcohol metabolism

This article describes the pathways and factors that modulate blood alcohol levels and metabolism and describes how the body disposes of alcohol. The various factors that play a role in the distribution of alcohol in the body, influence the absorption of alcohol, and contribute to first-pass metabolism of alcohol are described. Most alcohol is oxidized in the liver, and general principles and overall mechanisms for alcohol oxidation are summarized. The kinetics of alcohol elimination in-vivo and the various genetic and environmental factors that can modify the rate of alcohol metabolism are discussed.

Immunoproteomic identification of biotransformed self-proteins from the livers of female Balb/c mice following chronic ethanol administration

Chronic alcohol consumption culminates in alcoholic hepatitis which is characterized by ballooning degeneration of hepatocytes and perivenous inflammation. The aldehydes produced by ethanol oxidation and lipid peroxidation form adducts with the hepatic proteins rendering them immunogenic and initiating an autoimmune response. The present study was designed to identify these immunoreactive hepatic proteins in ethanol-treated Balb/c mice. Liver cytosolic, mitochondrial, and microsomal proteins from the ethanol-treated and control female Balb/c mice were size fractionated on SDS-PAGE and immunoblotted with the sera from the individual animal. The immunoreactive proteins were identified using antimouse IgG antibody and characterized by MALDI-TOF. It is the first report demonstrating that 15 hepatic proteins show immunoreactivity following alcohol administration. The identified autoreactive proteins ranged in function from metabolism to cytoskeletal support. Remarkably, three key enzymes of ethanol metabolism, namely alcohol dehydrogenase, aldehyde dehydrogenase I and III as well as important antioxidant enzyme glutathione S-transferase were found to be autoreactive upon ethanol treatment. We conclude that ethanol treatment induces biotransformation of host proteins from almost every compartment of the cell, especially the enzymes involved in the detoxification of ethanolic insult being the major target for biotransformation. Hence, we propose that these proteins can be the potential candidates for the biomarker studies.

Cyanamide potentiates the ethanol-induced impairment of receptor-mediated endocytosis in a recombinant hepatic cell line expressing alcohol dehydrogenase activity

Ethanol administration has been shown to alter receptor-mediated endocytosis in the liver. We have developed a recombinant hepatic cell line stably transfected with murine alcohol dehydrogenase cDNA to serve as an in vitro model to investigate these ethanol-induced impairments. In the present study, transfected cells were maintained in the absence or presence of 25 mM ethanol for 7 days, and alterations in endocytosis by the asialoglycoprotein receptor were determined. The role of acetaldehyde in this dysfunction was also examined by inclusion of the aldehyde dehydrogenase inhibitor, cyanamide. Our results showed that ethanol metabolism impaired internalization of asialoorosomucoid, a ligand for the asialoglycoprotein receptor. The addition of cyanamide potentiated the ethanol-induced defect in internalization and also impaired degradation of the ligand in the presence of ethanol. These results indicate that the ethanol-induced impairment in endocytosis is exacerbated by the inhibition of aldehyde dehydrogenase, suggesting the involvement of acetaldehyde in this dysfunction.

Impact of asialoglycoprotein receptor deficiency on the development of liver injury

The asialoglycoprotein (ASGP) receptor is a well-characterized hepatic receptor that is recycled via the common cellular process of receptor-mediated endocytosis (RME). The RME process plays an integral part in the proper trafficking and routing of receptors and ligands in the healthy cell. Thus, the mis-sorting or altered transport of proteins during RME is thought to play a role in several diseases associated with hepatocyte and liver dysfunction. Previously, we examined in detail alterations that occur in hepatocellular RME and associated receptor functions as a result of one particular liver injury, alcoholic liver disease (ALD). The studies revealed profound ethanol-mediated impairments to the ASGP receptor and the RME process, indicating the importance of this receptor and the maintenance of proper endocytic events in normal tissue. To further clarify these observations, studies were performed utilizing knockout mice (lacking a functional ASGP receptor) to which were administered several liver toxicants. In addition to alcohol, we examined the effects following administration of anti-Fas (CD95) antibody, carbon tetrachloride (CCl(4)) and lipopolysaccharide (LPS)/galactosamine. The results of these studies demonstrated that the knockout mice sustained enhanced liver injury in response to all of the treatments, as shown by increased indices of liver damage, such as enhancement of serum enzyme levels, histopathological scores, as well as hepatocellular death. Overall, the work completed to date suggests a possible link between hepatic receptors and liver injury. In particular, adequate function and content of the ASGP receptor may provide protection against various toxin-mediated liver diseases.

An in vitro method of alcoholic liver injury using precision-cut liver slices from rats

Alcohol abuse results in liver injury, but investigations into the mechanism(s) for this injury have been hampered by the lack of appropriate in vitro culture models in which to conduct in depth and specific studies. In order to overcome these shortcomings, we have developed the use of precision-cut liver slices (PCLS) as an in vitro culture model in which to investigate how ethanol causes alcohol-induced liver injury. In these studies, it was shown that the PCLS retained excellent viability as determined by lactate dehydrogenase and adenosine triphosphate (ATP) levels over a 96-h period of incubation. More importantly, the major enzymes of ethanol detoxification; alcohol dehydrogenase, aldehyde dehydrogenase, and cytochrome P4502E1, remained active and PCLS readily metabolized ethanol and produced acetaldehyde. Within 24 h and continuing up to 96h the PCLS developed fatty livers and demonstrated an increase in the redox state. These PCLS secreted albumin, and albumin secretion was decreased by ethanol treatment. All of these impairments were reversed following the addition of 4-methylpyrazole, which is an inhibitor of ethanol metabolism. Therefore, this model system appears to mimic the ethanol-induced changes in the liver that have been previously reported in human and animal studies, and may be a useful model for the study of alcoholic liver disease.

Hepatic expression of gamma-glutamyltranspeptidase in the human liver of patients with alcoholic liver disease

BACKGROUND

Gamma-glutamyltranspeptidase (GGT) has been recognized as an enzyme that converts glutathione into cysteine, and it is localized predominantly within the liver. Serum GGT is clinically recognized as the most useful marker for diagnosis of alcoholic liver disease (ALD).

METHODS

GGT localization within the liver was examined immunohistochemically using an anti-GGT antibody and was visualized by confocal laser scanning microscopy in ALD and normal livers. Double immunostaining for GGT and dipeptidylpeptidase-IV (DPP-IV) was carried out to evaluate GGT localization in greater detail.

RESULTS

Expression of GGT protein and mRNA was studied with immunoblot analysis and in situ hybridization, respectively. Immunohistochemically, the expression of GGT in the normal liver was faintly demonstrated in the bile canaliculi of hepatocytes and in biliary epithelial cells. In ALD livers, GGT was clearly demonstrated at the same sites. Double immunostaining demonstrated that GGT and DPP-IV were colocalized in hepatocytes in the ALD liver. In situ hybridization clearly demonstrated GGT-mRNA within the cytoplasm of hepatocytes and biliary epithelial cells. Immunoblot analysis revealed that GGT protein expression was increased in the ALD livers compared with that seen in the normal livers.

CONCLUSION

These findings indicate that GGT in control and alcoholic livers is synthesized in hepatocytes and biliary epithelial cells, and is localized within the bile canalicular membrane and the luminal membrane in those cells, respectively. In conclusion, GGT synthesis and protein expression are increased in ALD livers, leading to the elevation of serum levels of GGT that are commonly noted in patients with the disease.

Effect of ethanol on pro-apoptotic mechanisms in polarized hepatic cells

Chronic ethanol consumption is associated with serious and potentially fatal alcohol-related liver injuries such as hepatomegaly, alcoholic hepatitis and cirrhosis. Moreover, it has been documented that the clinical progression of alcohol-induced liver damage may be associated with an increase in hepatocellular death that involves apoptotic mechanisms. Although much information has been learned about the clinical manifestations associated with alcohol-related diseases, the search continues for a better understanding of the molecular and/or cellular mechanisms by which ethanol exerts its deleterious effects such as the induction of pro-apoptotic mechanisms and related cell damaging events. As part of the effort to enhance our understanding of those particular cellular pathways and mechanisms associated with ethanol toxicity, researchers over the years have utilized a variety of model systems. Recently, work has come forth demonstrating the utility of a hybrid cell line (WIF-B) as a cell culture model system for the study of alcohol-associated alterations in hepatocellular mechanisms. Success with such emerging model systems could aid in the development of potential therapeutic treatments for the prevention of alcohol-induced apoptotic cell death that may ultimately serve as a significant target in delaying the onset and/or progression of clinical symptoms of alcohol-mediated liver disease. This review article summarizes the current understanding of ethanol-mediated modifications in cell survival and thus the promotion of pro-apoptotic events with emphasis on analyses made in various experimental model systems, particularly the more recently characterized WIF-B cell system.

Ethanol-induced apoptosis in polarized hepatic cells possibly through regulation of the Fas pathway

BACKGROUND

It has been noted that alcohol-related liver diseases can be associated with an increase in apoptotic hepatocellular death. Moreover, the promotion of hepatocyte apoptosis may be linked to signals emanating from death receptors, particularly Fas [CD95/apoptosis-inducing protein 1 (APO-1)]. In the present study, we utilized an in vitro hepatic culture model [hybrid of human fibroblast (WI 38) and rat hepatoma (Fao) cells, WIF-B cells] to study potential contributing mechanisms involved in hepatocellular apoptosis following ethanol administration.

METHODS

WIF-B cultures (differentiated hepatic cells that efficiently metabolize alcohol) were treated with or without ethanol and specific inhibitors of alcohol metabolism and cysteine protease activity, followed by morphological and biochemical examination of proapoptotic parameters.

RESULTS

The results of this work demonstrated that ethanol administration leads to an increase (45%-60%) in caspase-3 activity and that the induction of apoptosis was found to be linked to the metabolism of alcohol. Additionally, increases were observed in the activity of upstream initiator caspases (caspase-2 and caspase-8) that are directly related to membrane signaling events of death receptors such as Fas. Moreover, it was determined that the activation of caspase-3 could be blocked by the presence of a specific caspase-8 inhibitor, again linking death receptor-associated proteases to downstream effector caspase activity in alcohol-related death. Finally, ethanol administration was found to result in an increase in the amount of Fas protein present in the membrane fraction of the cell. The increase in membrane Fas protein indicates ligand-independent membrane targeting of Fas in the alcohol-treated cells that could potentially be a key signaling event in the induction of the proapoptotic caspase cascade.

CONCLUSIONS

The data presented here indicate that alcohol metabolism induces apoptosis in WIF-B cells that occurs, in part, by mechanisms involving signals emanating from death receptors.

Meta-analyses of ALDH2 and ADH1B with alcohol dependence in Asians

Meta-analyses were conducted to determine the magnitude of relationships between polymorphisms in 2 genes, ALDH2 and ADH1B, with alcohol dependence in Asians. For each gene, possession of 1 variant *2 allele was protective against alcohol dependence, and possession of a 2nd *2 allele did not offer significant additional protection. The protective effects of these 2 gene polymorphisms were independent. Diagnostic criteria, recruitment strategy, and Japanese ethnicity moderated the effect of ALDH2*2. Recruitment strategy and gender moderated the effect of ADH1B*2. These findings highlight the importance of methodological issues and potential gene-gene and gene-environment interactions that must be considered when examining relationships between genetic polymorphisms and phenotypes.

Inhibition of alcohol dehydrogenase by bismuth

Bismuth compounds have been widely used for the treatment of ulcers and Helicobacter pylori infection, and enzyme inhibition was thought to be crucial for bismuth anti-microbial activity. We have investigated the interaction of colloidal bismuth subcitrate (CBS) with alcohol dehydrogenase and our results demonstrate that bismuth can effectively inhibit the enzyme. Kinetic analysis revealed that CBS acted as a non-competitive inhibitor of yeast alcohol dehydrogenase. Both UV-vis and fluorescence data show that interaction of CBS with the enzyme exhibits biphasic processes. Bismuth can replace only half of Zn(II) from the enzyme (i.e., about one Zn(II) per monomer). Surprisingly, binding of CBS also induces the enzyme dissociation from its native form, tetramer into dimers. The inhibition of Bi(III) on the enzyme is probably due to its direct interference with the zinc sites. This study is likely to provide an insight into the mechanism of action of bismuth drugs.

WIF-B cells as a model for alcohol-induced hepatocyte injury

A potential in vitro model for studying the mechanisms of alcohol-induced hepatocyte injury is the WIF-B cell line. It has many hepatocyte-like features, including a differentiated, polarized phenotype resulting in formation of bile canaliculi. The aim of this study was to examine the effects of ethanol treatment on this cell line. WIF-B cells were cultured up to 96 h in the absence or presence of 25 mM ethanol and subsequently were analyzed for ethanol-induced physiological and morphological changes. Initial studies revealed WIF-B cells exhibited alcohol dehydrogenase (ADH) activity, expressed cytochrome p4502E1 (CYP2E1), and efficiently metabolized ethanol in culture. This cell line also produced the ethanol metabolite acetaldehyde and exhibited low K(m) aldehyde dehydrogenase (ALDH) activity, comparable to hepatocytes. Ethanol treatment of the WIF-B cells for 48 h led to significant increases in the lactate/pyruvate redox ratio and cellular triglyceride levels. Ethanol treatment also significantly altered WIF-B morphology, decreasing the number of bile canaliculi, increasing the number of cells exhibiting finger-like projections, and increasing cell diameter. The ethanol-induced changes occurring in this cell line were negated by addition of the ADH inhibitor, 4-methylpyrazole (4-MP), indicating the effects were due to ethanol metabolism. In summary, the WIF-B cell line metabolizes ethanol and exhibits many ethanol-induced changes similar to those found in hepatocytes. Because of these similarities, WIF-B cells appear to be a suitable model for studying ethanol-induced hepatocyte injury.

The evaluation of reno- and hepatoprotective effects of huai-shan-yao (Rhizome Dioscoreae)

Huai-shan-yao (Chinese yam; Rhizome Dioscoreae) is a common food in China. In the present study, we evaluated the protective effects of the crude extract of huai-shan-yao on acute kidney and liver injuries in rats induced by ethanol. Results of pharmacological, biochemical and pathologic observations all showed that rats treated with the extract of huai-shan-yao had decreased damage in renal tubules as well as decreased inflammation in the central vein and necrosis in the liver tissue.

Experimental studies on the relationship between immune responses and liver damage induced by ethanol after immunization with homologous acetaldehyde adducts

BACKGROUND

It has been considered that acetaldehyde (AcH) adducts induce liver injury through an immune response. Previous experimental studies showed that hepatic necrosis, inflammatory cell infiltration, and hepatic fibrosis were induced in guinea pigs immunized with heterologous human AcH adducts and ethanol feeding. AcH modification of foreign protein may markedly increase immunogenicity of the protein itself, leading to enhanced formation of immune complex and possible liver injury. The present study investigated whether immune responses and alcoholic liver disease would be induced in mice by immunization with mouse albumin-AcH adducts and ethanol feeding.

METHODS

6B6 mice were divided into six groups with or without immunization and ethanol feeding. Mice were immunized with mouse albumin-AcH adducts three times at 2-week intervals and fed ethanol for 10 weeks. The stimulation index of [(3)H]thymidine uptake into lymphocytes cultured with mouse albumin or mouse albumin-AcH adducts was measured. Histologic findings of the liver were examined, and the plasma levels of aspartate transaminase and alanine aminotransferase were also measured.

RESULTS

The stimulation index was increased remarkably in ethanol-fed mice that were immunized with mouse albumin-AcH adducts. However, neither inflammatory cell infiltration nor hepatic necrosis was observed in the liver. There were also no differences in the plasma activities of aspartate transaminase and alanine aminotransferase between the group of mice regardless of ethanol feeding or immunization.

CONCLUSION

Although marked immune responses were observed, no liver damage was induced by long-term ethanol feeding in our mouse model using AcH-homologous albumin adducts. These results suggest that homologous protein adducts may not induce liver injury by long-term ethanol feeding or may have lower immunogenicity than heterologous protein adducts. These results also suggest that nonreduced AcH adducts and/or a larger amount of ethanol may be needed for liver injury in this model.

Binding of acetaldehyde to human and Guinea pig placentae in vitro

BACKGROUND

Significant interindividual variability exists following maternal alcohol consumption; not all children born to alcoholic women manifest the symptoms associated with foetal alcohol spectrum disorder (FASD).

OBJECTIVE

To investigate the potential role of the placenta as a source of variability by determining if interindividual variability exists in the binding of acetaldehyde to human placenta.

METHODS

Acetaldehyde was added to ten different human placental homogenates and subjected to equilibrium dialysis. Homogenates of placentae obtained from guinea pigs chronically exposed to ethanol throughout gestation were also dialysed in the presence of acetaldehyde to look for alterations in binding after chronic alcohol exposure. Nonlinear least-squares regression analysis was used to characterize the binding system involved.

RESULTS

It was found that the amount of acetaldehyde bound to human placentae varied by as much as 3-fold among placentae. The binding profile of acetaldehyde was characterized as a two site binding system (Ka(1)=9.8 x 10(5)+/-0.7 x 10(5)l/mol, N(1)=1.1 x 10(-8)+/-0.7 x 10(-8)mol/g tissue; Ka(2)=1.6 x 10(4)+/-0.9 x 10(4)l/mol, N(2)=1.7 x 10(-7)+/-0.4 x 10(-7)mol/g tissue). Chronic alcohol exposure had no effect on the degree of acetaldehyde binding.

CONCLUSION

This previously unidentified source of variability may partially explain why some foetuses are adversely affected by prenatal alcohol exposure while others are not.

Gender differences in alcohol metabolism. Physiological responses to ethanol

A gender difference in alcohol pharmacokinetics has been suggested to explain why women are more vulnerable to ethanol's toxic effects. The results of animal experiments suggest that females exhibit higher alcohol metabolic rates than males as a result of hormonal differences. Experimental results examining gender differences in human alcohol metabolism have been inconsistent; the diversity of experimental protocols and variety of pharmacokinetic parameters reported have made comparisons of these studies very difficult. Variability in alcohol metabolic rate between individuals of the same sex is often significant, preventing an assessment of gender differences in some studies. This chapter attempts to summarize the findings of studies from the last decade that examined the role of gender and sex hormone differences on ethanol metabolism in men and women. The role of body composition, genetic factors, gastric and hepatic alcohol dehydrogenase, and gastric absorption in creating gender differences in alcohol metabolism is discussed. Suggestions are offered that may result in better cross-study comparisons and more consistent experimental results.

Hypochlorhydria induced by a proton pump inhibitor leads to intragastric microbial production of acetaldehyde from ethanol

BACKGROUND

Acetaldehyde, produced locally in the digestive tract, has recently been shown to be carcinogenic in humans.

AIM

To examine the effect of iatrogenic hypochlorhydria on intragastric acetaldehyde production from ethanol after a moderate dose of alcohol, and to relate the findings to the changes in gastric flora.

METHODS

Eight male volunteers ingested ethanol 0.6 g/kg b.w. The pH, acetaldehyde level and microbial counts of the gastric juice were then determined. The experiment was repeated after 7 days of lansoprazole 30 mg b.d.

RESULTS

The mean (+/- S.E.M.) pH of the gastric juice was 1.3 +/- 0.06 and 6.1 +/- 0.5 (P < 0.001) before and after lansoprazole, respectively. This was associated with a marked overgrowth of gastric aerobic and anaerobic bacteria (P < 0. 001), by a 2.5-fold (P=0.003) increase in gastric juice acetaldehyde level after ethanol ingestion, and with a positive correlation (r=0. 90, P < 0.001) between gastric juice acetaldehyde concentration and the count of aerobic bacteria.

CONCLUSIONS

Treatment with proton pump inhibitors leads to hypochlorhydria, which associates with intragastric overgrowth of aerobic bacteria and microbially-mediated acetaldehyde production from ethanol. Since acetaldehyde is a local carcinogen in the concentrations found in this study, long-term use of gastric acid secretory inhibitors is a potential risk-factor for gastric and cardiac cancers.

N-Terminal dipeptides of D(-)-penicillamine as sequestration agents for acetaldehyde

Since acetaldehyde (AcH), a toxic oxidation product of ethanol, may play an etiologic role in the initiation of alcoholic liver disease, we had earlier pioneered the development of beta, beta-disubstituted-beta-mercapto-alpha-amino acids as AcH-sequestering agents. We now report the synthesis of a series of N-terminal dipeptides of D(-)-penicillamine, prepared from the synthon 3-formyl-2,2,5,5-tetramethylthiazolidine-4S-carboxylic acid (3), a cyclized N-protected derivative of D(-)-penicillamine. These dipeptides were equally or more effective than penicillamine in trapping AcH in a cell-free system. In experiments using a hepatocyte culture system, two of the dipeptides, D-penicillamylglycine (6a) and D-penicillamyl-beta-alanine (6d), at 1/20 the molar concentration of ethanol, lowered the concentration of ethanol-derived AcH by 79% and 84%, respectively, at 2 h. The presence of cyanamide (an inhibitor of aldehyde dehydrogenase) in the incubation medium resulted in a 45-fold increase in ethanol-derived AcH; nevertheless, dipeptides 6a and 6c (D-penicillamyl-alpha-aminoisobutyric acid) were able to reduce this AcH level by approximately one-third.

Relationship between serum levels of anti-low-density lipoprotein-acetaldehyde-adduct antibody and aldehyde dehydrogenase 2 heterozygotes in patients with alcoholic liver injury

We prepared low-density lipoprotein (LDL)-acetaldehyde-adduct (hereafter abbreviated as LDL-adduct) and anti-LDL-adduct antibody by using Watanabe hyperlipidemic rabbits, and determined values of serum anti-LDL-adduct antibody levels by the ELISA method in healthy adults and patients with alcoholic liver injury. In the nondrinking group in healthy adults, values of anti-LDL-adduct antibody levels were 25 +/- 13 microg/ml, and there was no significant difference between moderate drinkers without diseases and the nondrinking group in healthy adults. Values of anti-LDL-adduct antibody in alcoholic disease groups, 17 +/- 9 microg/ml for the patients with the fatty liver group, 21 +/- 14 microg/ml for the hepatic fibrosis group, 70 +/- 21 microg/ml for the alcoholic hepatitis group, 41 +/- 50 microg/ml for the alcoholic cirrhosis group, and 19 +/- 18 microg/ml for the alcoholic pancreatitis group. Examinations of aldehyde dehydrogenase 2 (ALDH2) genetic variations by the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) method in the healthy group and the liver injury group revealed a tendency for patients with ALDH2(1)/2(2) in the liver injury group to have relatively mild liver lesions. When comparing anti-LDL-adduct antibody levels between ALDH2 genetic variations, those for the patients with ALDH2(1)/2(2) (36 +/- 40 microg/ml) were significantly higher than those for patients with ALDH2(1)/2(2) (11 +/- 5 microg/ml). Results of the present study suggest that genetic variation may influence the progression of liver injury.

Inhibition of advanced glycation endproduct formation by acetaldehyde: role in the cardioprotective effect of ethanol

Epidemiological studies suggest that there is a beneficial effect of moderate ethanol consumption on the incidence of cardiovascular disease. Ethanol is metabolized to acetaldehyde, a two-carbon carbonyl compound that can react with nucleophiles to form covalent addition products. We have identified a biochemical modification produced by the reaction of acetaldehyde with protein-bound Amadori products. Amadori products typically arise from the nonenzymatic addition of reducing sugars (such as glucose) to protein amino groups and are the precursors to irreversibly bound, crosslinking moieties called advanced glycation endproducts, or AGEs. AGEs accumulate over time on plasma lipoproteins and vascular wall components and play an important role in the development of diabetes- and age-related cardiovascular disease. The attachment of acetaldehyde to a model Amadori product produces a chemically stabilized complex that cannot rearrange and progress to AGE formation. We tested the role of this reaction in preventing AGE formation in vivo by administering ethanol to diabetic rats, which normally exhibit increased AGE formation and high circulating levels of the hemoglobin Amadori product, HbA1c, and the hemoglobin AGE product, Hb-AGE. In this model study, diabetic rats fed an ethanol diet for 4 weeks showed a 52% decrease in Hb-AGE when compared with diabetic controls (P < 0.001). Circulating levels of HbA1c were unaffected by ethanol, pointing to the specificity of the acetaldehyde reaction for the post-Amadori, advanced glycation process. These data suggest a possible mechanism for the so-called "French paradox," (the cardioprotection conferred by moderate ethanol ingestion) and may offer new strategies for inhibiting advanced glycation.

Early alcoholic liver injury: formation of protein adducts with acetaldehyde and lipid peroxidation products, and expression of CYP2E1 and CYP3A

The formation of protein adducts with reactive aldehydes resulting from ethanol metabolism and lipid peroxidation has been suggested to play a role in the pathogenesis of alcoholic liver injury. To gain further insight on the contribution of such aldehydes in alcoholic liver disease, we have compared the appearance of acetaldehyde, malondialdehyde, and 4-hydroxynonenal adducts with the expression of cytochrome P-450IIE1, and cytochrome P-4503A enzymes in the liver of rats fed alcohol with a high-fat diet for 2 to 4 weeks according to the Tsukamoto-French procedure and in control rats (high-fat liquid diet or no treatment). Urine alcohol and serum aminotransferase levels were recorded, and the liver pathology was scored from 0 to 10 according to the presence of steatosis, inflammation, necrosis, and fibrosis. The ethanol treatment resulted in the accumulation of fat, mild necrosis and inflammation, and a mean liver pathology score of 3 (range: 1 to 5). Liver specimens from the ethanol-fed animals with early alcohol-induced liver injury were found to contain perivenular, hepatocellular acetaldehyde adducts. Malondialdehyde and 4-hydroxynonenal adducts were also present showing a more diffuse staining pattern with occasional sinusoidal reactions. In the control animals, a faint positive reaction for the hydroxynonenal adduct occurred in some of the animals fed the high fat diet, whereas no specific staining was observed in the livers from the animals receiving no treatment. Expression of both CYP2E1 and CYP3A correlated with the amount of protein adducts in the liver of alcohol-treated rats. Distinct CYP2E1-positive immunohistochemistry was seen in 3 of 7 of the ethanol-fed animals. In 5 of 7 of the ethanol-fed animals, the staining intensities for CYP3A markedly exceeded those obtained from the controls. The present findings indicate that acetaldehyde and lipid peroxidation-derived adducts are generated in the early phase of alcohol-induced liver disease. The formation of protein adducts appears to be accompanied by induction of both CYP2E1 and CYP3A.

Quantitative analysis of acetaldehyde in whole blood from human and various animals by gas chromatography

Acetaldehyde present in the blood of bull, chicken, hamster, horse, human, monkey, pig, rabbit, rat and sheep, was quantitatively analyzed by a newly developed gas chromatographic method. Acetaldehyde in a blood sample was reacted with cysteamine to give 2-methylthiazolidine, which was extracted with dichloromethane and subsequently analyzed by gas chromatography with a fused-silica capillary column and a nitrogen-phosphorus detector. The quantities of acetaldehyde found in blood ranged from 2.04 micromol/ml (hamster) to 14.8 micromol/ml (pig). The quantity of acetaldehyde recovered from human blood was 6.17 micromol/ml.

Ethanol metabolism, toxicity and genetic polymorphism

The relationships between the individual (and racial) differences in alcohol metabolism and toxicity, and the genetic polymorphism of alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and cytochrome P-4502E1(CYPIIE1) were reviewed. In recent studies involving DNA analysis, it was found that a deficiency of the ALDH2 isozyme (ALDH2*2) was responsible for the flushing symptoms as well as other vasomotor symptoms caused by a higher acetaldehyde level after alcohol consumption. Deficiency of ALDH2 activity has been found prevalently only among people of Mongoloid origin, and the deficiency of ALDH2 prevents them from developing alcohol dependence due to the unpleasant physical effects of the flushing symptom. It was reported that Mongoloids such as Japanese and Chinese people carry the enzymatically active (ALDH2*1) subunit and/or the inactive (ALDH2*2) one, and that a low proportion of ALDH2 deficiency (ALDH2*2 allele frequency) was found in alcoholics compared with healthy controls. It was also reported that polymorphism of ALDH2 and/or CYP2E1 may be associated with the susceptibility to alcohol-induced liver injury. Concerning blood ethanol elimination kinetics, it was reported that the c2 gene of CYP2E1 and the ALDH2*1 gene may have greater effects on ethanol and acetaldehyde elimination than the other genotypes, when the blood ethanol level is below 20 m M.

An enzyme immune assay for serum anti-acetaldehyde adduct antibody using low-density lipoprotein adduct and its significance in alcoholic liver injury

An acetaldehyde (AcH) adduct was prepared using rabbit low-density lipoprotein as carrier proteins. An antibody against this adduct was raised in Watanabe heritable hyperlipidemic rabbits and cross-reacted with human low-density lipoprotein and bovine serum albumin adducts. Using this antibody, serum anti-AcH-adduct antibody levels were measured by a direct ELISA method in 56 Japanese adults (healthy adults and patients with nonalcoholic gastrointestinal diseases, alcoholic liver injury, or alcoholic pancreatitis). The antibody level (mean +/- SD) was 22 +/- 10 microg/ml in healthy adults, 22 +/- 11 microg/ml in nonalcoholic gastrointestinal diseases, and 16 +/- 13 microg/ml in alcoholic pancreatitis. These antibody levels tended to increase with the progression of alcoholic liver injury, starting from fatty liver via hepatitis to cirrhosis, 29 +/- 24 microg/ml in fatty liver, 35 +/- 29 microg/ml in alcoholic hepatitis, and 46 +/- 54 microg/ml in alcoholic cirrhosis. The antibody level in patients taking 100 g or more of ethanol per day tended to be higher, compared with those in people taking less ethanol. A follow-up observation revealed that alcohol abstinence after hospitalization raised serum anti-AcH-adduct antibody level in some patients and kept it constantly low in other patients. The immunohistochemical study using the anti-AcH-adduct antibody revealed the presence of adduct-like substance in hepatocytes of liver biopsy specimens obtained from patients with alcoholic liver disease. The results indicate that the anti-AcH-adduct antibody may be associated with the progress of alcoholic liver diseases.

Microbial metabolism of ethanol and acetaldehyde and clinical consequences

Many bacteria possess marked alcohol dehydrogenase activity and in the presence of ethanol they produce reactive and toxic acetaldehyde. Acetaldehyde production mediated by microbial alcohol dehydrogenases has been demonstrated in the oropharynx and bronchopulmonary washings. Also the most important gastric pathogen, Helicobacter pylori, and many skin bacteria associating with pathological dermatological conditions, possess alcohol dehydrogenase activity and produce acetaldehyde from ethanol. The most richly colonized site of the human body, however, is the large intestine, and therefore bacterial acetaldehyde production is most important in this organ. Alcohol ingested orally is transported to the colon by blood circulation and, after the distribution phase, intracolonic ethanol levels are equal to those in the blood. In the large bowel ethanol is oxidized by a bacteriocolonic pathway. In this pathway intracolonic ethanol is at first oxidized by bacterial alcohol dehydrogenase to acetaldehyde. Then acetaldehyde is oxidized either by colonic mucosal or bacterial aldehyde dehydrogenase to acetate. Part of intracolonic acetaldehyde may also be absorbed via the portal vein and metabolized in the liver. Bacteriocolonic pathway offers a new explanation for the disappearance of a part of ethanol calories. Due to the low aldehyde dehydrogenase activity of colonic mucosa acetaldehyde accumulates in the colon. Accordingly, during ethanol oxidation highest acetaldehyde levels of the body are found in the colon and not in the liver. High intracolonic acetaldehyde may contribute to the pathogenesis of alcohol-induced diarrhoea. Acetaldehyde has been proven to be a carcinogen in experimental animals. It may therefore contribute to the increased risk of colon polyps and colon cancer found to be associated with heavy alcohol consumption in man. Intracolonic acetaldehyde may also be an important determinant of blood acetaldehyde level and a possible hepatotoxin. In addition to acetaldehyde, gut-derived endotoxin is another potential candidate in the pathogenesis of alcohol-related liver injury.

Increased acetaldehyde production by mouthwashings from patients with oral cavity, laryngeal, or pharyngeal cancer

Excessive ethanol consumption is associated with an increased risk of oral cavity, laryngeal, and pharyngeal cancer. Ethanol has been shown to be oxidized to acetaldehyde by microflora of the upper respiratory tract. As a highly toxic and reactive compound, acetaldehyde of microbial origin has been incriminated as a possible carcinogenic factor behind alcohol-associated malignancies of the upper respiratory tract. The aim of the present in vitro study was to compare the acetaldehyde producing capacity of mouthwashings obtained from patients with oral cavity, laryngeal, or pharyngeal cancer to that of mouthwashings from controls. The ability of mouthwashings to produce acetaldehyde from ethanol in vitro was determined by incubating them in closed vials containing various concentrations of ethanol (0-44 mM) at 37 degrees C for 1 hr. Acetaldehyde formed during the incubation was then analyzed by head space gas chromatography. Acetaldehyde production by mouthwashings increased with raising ethanol concentration in both groups. Acetaldehyde production by mouthwashings from patients with oral cavity, laryngeal, or pharyngeal cancer was significantly (p < 0.01) higher than that of the controls. Increased acetaldehyde formation from ethanol in the upper respiratory tract could thus contribute to the pathogenesis of alcohol-associated oral cavity, laryngeal, and pharyngeal cancers.

In vitro alcohol dehydrogenase-mediated acetaldehyde production by aerobic bacteria representing the normal colonic flora in man

Excessive ethanol consumption has been related with the development of liver cirrhosis, as well as with rapid intestinal transit time and diarrhea. Moreover, heavy drinking is associated with an increased incidence of cancer of the oropharynx, larynx, esophagus, and colorectum. Acetaldehyde of microbial origin has recently been suggested as a possible pathogenic factor behind this alcohol-associated gastrointestinal morbidity. The present in vitro study was aimed to investigate alcohol dehydrogenase activity and acetaldehyde formation capacity of some major aerobic bacteria representing the normal colonic flora in man. Cytosolic alcohol dehydrogenase activity and cytosolic protein concentration were determined spectrophotometrically. Alcohol dehydrogenase activity was then calculated as nmoles of reduced substrate produced by milligrams of protein per minute. The ability of different bacteria to produce acetaldehyde was determined by incubating the intact bacterial suspension in closed vials containing ethanol (final concentration 22 mM) for 1 hr at 37 degrees C. The acetaldehyde formed during the incubation was analyzed by headspace gas chromatography. Marked differences in the alcohol dehydrogenase activity and acetaldehyde forming capacity were found among the strains tested. The alcohol dehydrogenase activity varied from 606 +/- 91 nmol/min/mg protein (Escherichia coli IH 50546) to 1 +/- 0.2 nmol/min/mg protein (E. coli IH 50817), and acetaldehyde formation varied from 1,717 +/- 2 nmol acetaldehyde/10(9) colony-forming units (Klebsiella oxytoca IH 35403) to 5 +/- 2 nmol acetaldehyde/10(9) colony-forming units (Pseudomonas aeruginosa ATCC 27853). There was a statistically significant correlation (r = 0.77; p < 0.001) between alcohol dehydrogenase activity and acetaldehyde production from ethanol, strongly suggesting the catalytic role of bacterial alcohol dehydrogenase in this reaction.

High intracolonic acetaldehyde values produced by a bacteriocolonic pathway for ethanol oxidation in piglets

BACKGROUND

Human colonic contents and many colonic microbes produce considerable amounts of acetaldehyde from ethanol in vitro.

AIMS

To examine in piglets if acetaldehyde is produced in the colon also in vivo, and if so, what is the fate of intracolonically formed acetaldehyde.

ANIMALS

Seventeen native, non-fasted female piglets (20-25 kg) were used.

METHODS

Six piglets received either 1.5 g/kg bw or 2.5 g/kg bw of ethanol intravenously. In seven piglets, 0.7 g or 1.75 g of ethanol/kg bw was administered intravenously, followed by a subsequent intragastric ethanol infusion of 1.8 g/kg bw and 4.5 g/kg bw, respectively. The samples of colonic contents for the assessment of ethanol and acetaldehyde concentrations were obtained up to seven hours. In four additional piglets, the intracolonic values of ethanol, acetaldehyde, and acetate were observed for 60 minutes after an intracolonic infusion of acetaldehyde solution.

RESULTS

A raised intracolonic, endogenous acetaldehyde concentration (mean (SEM); 36 (9) microM) was found in all piglets before ethanol infusion. After the infusion of ethanol, intracolonic ethanol and acetaldehyde values increased in parallel, reaching the peak values 57 (4) mM of ethanol and 271 (20) microM of acetaldehyde in the group that received the highest dose of ethanol. A positive correlation (r = 0.45; p < 0.001) was found between intracolonic ethanol and acetaldehyde values. Acetaldehyde administered intracolonically was mainly metabolised to acetate but also to ethanol in the colon.

CONCLUSIONS

Significant endogenous intracolonic acetaldehyde values can be found in the normal porcine colon. Furthermore, our results suggest the existence of a bacteriocolonic pathway for ethanol oxidation. Increased amounts of acetaldehyde are formed intracolonically from ingested ethanol by this pathway.

Bacteriocolonic pathway for ethanol oxidation: characteristics and implications

Alcohol ingested orally is transported to the colon by blood circulation, and after the distribution phase, intracolonic ethanol levels are equal to those in the blood. Recent studies in our laboratory suggest that in the large bowel ethanol is oxidized by a bacteriocolonic pathway. In this pathway intracolonic ethanol is at first oxidized by bacterial alcohol dehydrogenase to acetaldehyde. Then acetaldehyde is oxidized either by colonic mucosal or bacterial aldehyde dehydrogenase to acetate. Part of intracolonic acetaldehyde may also be absorbed to portal vein and be metabolized in the liver. The bacteriocolonic pathway offers a new explanation for the disappearance of a part of ethanol calories. Due to the low aldehyde dehydrogenase activity of colonic mucosa, acetaldehyde accumulates in the colon. Accordingly during ethanol oxidation highest acetaldehyde levels of the body are found in the colon and not in the liver. High intracolonic acetaldehyde may contribute to the pathogenesis of alcohol-induced diarrhoea. Because acetaldehyde is a carcinogen in experimental animals, it may also contribute to the increased risk of colon polyps and colon cancer, which have been found to be associated with heavy alcohol consumption. Intracolonic acetaldehyde may also be an important determinant of the blood acetaldehyde level and a possible hepatotoxin. In addition to acetaldehyde, gut-derived endotoxin is another potential candidate in the pathogenesis of alcohol-related liver injury. Experimental alcoholic liver injury has recently been prevented by antibiotics, and this effect was related to the prevention of endotoxin-induced activation of Kupffer's cells.

Hepatotoxicity and absorption of extrahepatic acetaldehyde in rats

Acetaldehyde, the first metabolite of ethanol oxidation, has been proposed as a major initiating factor in ethanol-induced liver injury. The aims of this study were to examine whether acetaldehyde is absorbable from the digestive tract and whether, when delivered chronically in drinking water, it is capable of inducing liver injury in rats. Acetaldehyde concentrations in the rat portal and peripheral blood were measured by head space gas chromatography after intragastric (5 ml) and intracolonic (3 ml) administration of 20 mM acetaldehyde solution. In the hepatotoxicity study, rats were exposed to acetaldehyde (20 and 120 mM) delivered in drinking water for 11 weeks and histopathological changes in the liver were morphometrically assessed. Peak blood acetaldehyde levels were found at 5 min after acetaldehyde infusion and were 235 +/- 11 microM (mean +/- SE) after intragastric and 344 +/- 83 microM after intracolonic infusion of 20 mM acetaldehyde solution. The exposure of rats to 120 mM acetaldehyde solution for 11 weeks resulted in the development of fatty liver and inflammatory changes. Morphometric analysis showed significantly more fat accumulation in rats receiving 120 mM acetaldehyde solution (85 +/- 2 per cent of hepatocytes occupied by fat) than in rats receiving 20 mM acetaldehyde solution (38 +/- 11 per cent) or in controls (36 +/- 10 per cent). The dose of extrahepatic acetaldehyde (500 mg/kg per day) producing liver injury corresponds to only around 3 per cent of that derived from hepatic ethanol oxidation in animals receiving an ethanol-containing totally liquid diet (15 g/kg per day). These results indicate that acetaldehyde delivered via the digestive tract can reach the liver by the portal circulation and that acetaldehyde of extrahepatic origin appears to be more hepatotoxic than acetaldehyde formed during ethanol oxidation within the liver.

CYP2E1 genotypes and serum LAP in Japanese alcoholics

The genotypes of the ALDH2 and CYP2E1 loci of Japanese alcoholic patients were determined to investigate the susceptibility to alcoholic liver injury. In alcoholics with a liver-function disorder, a significant association was observed between the genotypes of the CYP2E1 loci and the serum level of a liver-derived enzyme, LAP. However, there was no significant association between the ALDH2 genotypes and liver dysfunction.

Polymorphism at the P450IIE1 locus is not associated with alcoholic liver disease in Caucasian men

Because alcoholic hepatitis and cirrhosis, well-known complications of alcohol abuse, do not occur in all alcoholics, genetic factors such as differences in alcohol-metabolizing enzymes may play a role in the development of alcoholic liver disease. Cytochrome P450IIE1 catalyzes the oxidation of ethanol, producing acetaldehyde and free radicals capable of reacting with and peroxidizing cell membranes. Polymorphisms have been identified in the 5'-flanking region of the P450IIE1 gene that may alter the transcriptional activity of the gene. In this study, we analyzed the P450IIE1 genotypes at the polymorphic PstI and RsaI restriction enzyme sites in 53 Caucasians with severe alcoholic liver disease to determine if there is an association between these polymorphisms and alcoholic liver disease. Subjects that tested positive for the hepatitis C virus were eliminated from the study. To identify the type A (homozygous for the c1 gene), type B (heterozygous for the c1 and c2 genes), and type C (homozygous for the c2 gene) genotypes at the P450IIE1 locus, DNA encompassing the polymorphisms was amplified by polymerase chain reaction, slot-blotted, and probed with allele-specific oligonucleotides. Allele frequencies for the c1 allele were 0.95 for alcoholics with severe liver disease, 0.95 for alcoholics without liver disease, and 0.98 for the general population. No differences in allele frequencies between alcoholic patients with severe liver disease and alcoholics without liver disease were observed.

Effects of ethanol feeding on the interaction of rat hepatocytes with laminin peptides

Laminin, a complex glycoprotein of the extracellular matrix, contains a number of biologically active sites. These sites are involved in cell growth, attachment, differentiation, and gene expression. Our previous studies have shown that chronic ethanol consumption by rats impairs hepatocyte attachment to various components of the extracellular matrix including laminin. In this study, three synthetic peptides (PA22-2, YIGSR, and RGD) that correspond to three distinct functional sites on the laminin molecule were used to investigate the effect of ethanol consumption on their cognate receptors. Initially, varying concentrations of each peptide were incubated with isolated hepatocytes from ethanol-fed and pair-fed control rats. These hepatocytes were then assayed for the ability to attach to laminin. The results indicated that all three peptides effectively inhibited laminin-mediated cell adhesion: the degree of inhibition appeared similar between pair-fed controls and ethanol-fed animals. Of the three peptides, PA22-2 showed the most dramatic inhibition of attachment. Therefore, we investigated the ability of hepatocytes to attach directly to PA22-2 itself. Attachment of hepatocytes from ethanol-fed animals to PA22-2 was impaired by 30% after 4 days and 90% by 14 days. Conversely, no significant difference in attachment to the entire laminin molecule was observed in ethanol-fed animals at these early time points. These results indicated that the ethanol-induced impairment of hepatocyte attachment to laminin may be caused by the decreased interaction of hepatocytes with specific functional sites on the laminin molecule and that specific receptors on the hepatocyte may be affected differently.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro acetaldehyde formation by human colonic bacteria

Incubation of human colonic contents with various ethanol concentrations (2.75-44 mM) in vitro at 37 degrees C resulted in significant accumulation of acetaldehyde--a toxic and highly reactive compound. At pH 9.6, all samples produced notable acetaldehyde concentrations (58 (13) microM; mean (SEM)) even from the lowest (2.75 mM) ethanol concentration, and the production of acetaldehyde increased lin-early with rising ethanol concentration (r = 0.97; p < 0.005), reaching a peak concentration of 238 (37) microM at 44 mM ethanol. The formation of acetaldehyde took place rapidly, as almost 50% of acetaldehyde formed during the total eight hour incubation was detectable after one hour, and 75% of the total after four hours. Maximal acetaldehyde production from 22 mM ethanol occurred at pH 9.6 (160 (35) microM) but appreciable concentrations were also seen at pH 7.4 (110 (38) microM) and pH 6.0 (63 (19) microM). At pH 4.0, by contrast, acetaldehyde formation was negligible (17 (5) microM). 4-Methylpyrazole, a potent inhibitor of alcohol dehydrogenase, showed a decreasing effect on acetaldehyde production in vitro but first at a concentration of 100 mM. Considerable acetaldehyde production by human colonic bacteria--if it occurs also in vivo--could constitute a risk factor for rectal cancer in heavy drinkers and also provide a pathogenetic mechanism for alcohol induced diarrhoea.

Acetaldehyde exposure causes growth inhibition in a Chinese hamster ovary cell line that expresses alcohol dehydrogenase

Chronic ethanol exposure causes many pathophysiological changes in cellular function due to ethanol itself and/or the effects of its metabolism (i.e., generation of acetaldehyde and redox equivalents). However, the role of each of these effects remains controversial. To address these questions, we have developed a cell line that expresses alcohol dehydrogenase. This cell line permits separate examination of the effects of ethanol and its metabolite acetaldehyde on cell function. An expression vector for the mouse liver alcohol dehydrogenase was constructed and transfected into Chinese hamster ovary cells. Cells expressing alcohol dehydrogenase were identified by screening with allyl alcohol, which is metabolized by alcohol dehydrogenase to the toxic aldehyde acrolein. A number of cell lines were identified that expressed alcohol dehydrogenase. A-10 cells were selected for further study because of their high sensitivity to allyl alcohol, suggesting a high level of alcohol dehydrogenase expression. These cells expressed a mRNA that hybridizes with the alcohol dehydrogenase cDNA and had an alcohol dehydrogenase activity comparable to murine liver. When cultures of these cells were exposed to ethanol, acetaldehyde was detected in both the medium and cells. The acetaldehyde concentration in the medium remained constant for at least 1 week in culture and was a function of the added ethanol concentration. Chronic exposure of A-10 cells to ethanol resulted in a dose-dependent reduction in the number of cells that accumulated over 7 days. Ethanol-treated cells remained viable, and growth inhibition was reversible. Growth inhibition was blocked by the alcohol dehydrogenase inhibitor 4-methylpyrazole, suggesting that acetaldehyde and not ethanol was responsible for growth inhibition in these cells.

Helicobacter pylori alcohol dehydrogenase

We have recently shown that 34 different Helicobacter pylori strains of human and three of animal origin contain alcohol dehydrogenase (ADH). Isoelectric focusing of the enzyme showed activity bands with pI at 7.1-7.3, a pattern different from that of gastric mucosal ADHs. The Km value of H. pylori ADH for ethanol oxidation ranges from 64 to 104 mM. Although H. pylori ADH was capable of utilizing both NADP and NAD as cofactors in alcohol oxidation, it showed a strong preference for NADP over NAD. At neutral pH H. pylori ADH was more effective in aldehyde reduction than in alcohol oxidation. Distinct findings suggest that H. pylori ADH could be a metabolic enzyme taking part in ethanol production by fermentation. It is a rather abundant enzyme comprising approx. 0.5% of all bacterial cytosolic proteins. Therefore, the enzyme presumably has a basic role in the functions and maintenance of H. pylori. 4-methylpyrazole inhibits H. pylori ADH, and suppresses its growth during culture. Bismuth compounds that are commonly used in the treatment of H. pylori associated gastric diseases appeared to be potent inhibitors of H. pylori ADH. Owing to its high specific activity for ethanol (14 U mg-1) under physiological conditions H. pylori ADH can also effectively produce acetaldehyde at moderate ethanol levels. This reversed function of the enzyme and the production of the toxic and reactive acetaldehyde could account for at least some of the gastrointestinal morbidity associated with H. pylori infection. H. pylori lacks aldehyde dehydrogenase activity and can therefore not remove acetaldehyde at least by this pathway.

Association of restriction fragment length polymorphism in alcohol dehydrogenase 2 gene with alcohol induced liver damage

OBJECTIVE

To investigate the role of genetically determined differences in the enzymes of alcohol metabolism in susceptibility to liver damage from misusing alcohol.

DESIGN

Use of pADH36 probe to study PVU II restriction length fragment polymorphism in alcohol dehydrogenase 2 gene in white alcohol misusers and controls.

SETTING

Teaching hospital referral centres for liver disease and alcohol misuse.

SUBJECTS

45 white alcohol misusers (38 with alcoholic liver disease) and 23 healthy controls.

MAIN OUTCOME MEASURES

Alcohol misuse, the presence and severity of alcoholic liver disease, alcohol dependency, and family history of alcohol misuse.

RESULTS

A two allele polymorphism (A and B) was identified. In control subjects the allele frequencies were 85% for A and 15% for B compared with 37% and 63% respectively in alcohol misusers (p < 0.001). B allele was significantly associated with severe liver damage (p < 0.05) as well as alcohol dependency and family history of alcohol misuse compared with controls.

CONCLUSION

Inherited variation in enzymes of ethanol metabolism may contribute to the pathogenesis of alcohol induced liver damage. This supports the presence of a genetic component in alcohol misuse.