Alcohol and aldehyde dehydrogenase

The enzymes mainly responsible for ethanol degradation in humans are liver alcohol dehydrogenases (ADH) and aldehyde dehydrogenases (ALDH). Polymorphisms occur in both enzymes, with marked differences in the steady-state kinetic constants. The Km-values for ethanol of ADH isoenzymes relevant for alcohol degradation range from 49 microM to 36 microM, and the Vmax-values from 0.6 to 10 U/mg. Expression of an inactive form of the ALDH2 isoenzyme, the so-called Oriental variant, results in impaired acetaldehyde metabolizing capacity. The differences in ethanol and acetaldehyde metabolizing activities of allelic enzyme forms may be responsible in part for the large variation in the alcohol metabolism rate in humans. Interindividual differences in the isoenzyme pattern may contribute to the genetically determined predisposition for excessive alcohol intake.     

CHARACTERISTICS OF ALDEHYDE DEHYDROGENASES OF CERTAIN AEROBIC BACTERIA REPRESENTING HUMAN COLONIC FLORA

We have proposed the existence of a bacteriocolonic pathwayfor ethanol oxidation resulting in high intracolonic levelsof toxic and carcinogenic acetaldehyde. This study was aimedat determining the ability of the aldehyde dehydrogenases (ALDH)of aerobic bacteria representing human colonic flora to metabolizeintracolonically derived acetaldehyde. The apparent Michaelisconstant (K_m) values for acetaldehyde were determined in crudeextracts of five aerobic bacterial strains, alcohol dehydrogenase(ADH) and ALDH activities of these bacteria at conditions prevailingin the human large intestine after moderate drinking were thencompared. The effect of cyanamide, a potent inhibitor of mammalianALDH, on bacterial ALDH activity was also studied. The apparentK_m for acetaldehyde varied from 6.8 (NADP⁺ -linked ALDH of Escherichiacoli IH 13369) to 205 µM (NAD⁺ -linked ALDH of Pseudomonasaeruginosa IH 35342), and maximal velocity varied from 6 nmol/min/mg(NAD⁺ -linked ALDH of Klebsiella pneumoniae IH 35385) to 39nmol/min/mg (NAD⁺ -linked ALDH of Pseudomonas aeruginosa IH35342). At pH 7.4, and at ethanol and acetaldehyde concentrationsthat may be prevalent in the human colon after moderate drinking,ADH activity in four out of five bacterial strains were 10–50times higher than their ALDH activity. Cyanamide inhibited onlyNAD⁺ -linked ALDH activity of Pseudomonas aeruginosa IH 35342at concentrations starting from 0.1 mM. We conclude that ALDHsof the colonic aerobic bacteria are able to metabolize endogenicacetaldehyde. However, the ability of ALDHs to metabolize intracolonicacetaldehyde levels associated with alcohol drinking is ratherlow. Large differences between ADH and ALDH activities of thebacteria found in this study may contribute to the accumulationof acetaldehyde in the large intestine after moderate drinking.ALDH activities of colonic bacteria were poorly inhibited bycyanamide. This study supports the crucial role of intestinalbacteria in the accumulation of intracolonic acetaldehyde afterdrinking alcohol. Individual variations in human colonic floramay contribute to the risk of alcohol-related gastrointestinalmorbidity.     

A physiologically based model for ethanol and acetaldehyde metabolism in human beings.

Pharmacokinetic models for ethanol metabolism have contributed to the understanding of ethanol clearance in human beings. However, these models fail to account for ethanol's toxic metabolite, acetaldehyde. Acetaldehyde accumulation leads to signs and symptoms, such as cardiac arrhythmias, nausea, anxiety, and facial flushing. Nevertheless, it is difficult to determine the levels of acetaldehyde in the blood or other tissues because of artifactual formation and other technical issues. Therefore, we have constructed a promising physiologically based pharmacokinetic (PBPK) model, which is an excellent match for existing ethanol and acetaldehyde concentration-time data. The model consists of five compartments that exchange material: stomach, gastrointestinal tract, liver, central fluid, and muscle. All compartments except the liver are modeled as stirred reactors. The liver is modeled as a tubular flow reactor. We derived average enzymatic rate laws for alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH), determined kinetic parameters from the literature, and found best-fit parameters by minimizing the squared error between our profiles and the experimental data. The model's transient output correlates strongly with the experimentally observed results for healthy individuals and for those with reduced ALDH activity caused by a genetic deficiency of the primary acetaldehyde-metabolizing enzyme ALDH2. Furthermore, the model shows that the reverse reaction of acetaldehyde back into ethanol is essential and keeps acetaldehyde levels approximately 10-fold lower than if the reaction were irreversible.     

Research on alcohol metabolism among Asians and its implications for understanding causes of alcoholism

Research into the causes of alcoholism is a relatively recent scientific endeavor. One area of study which could lead to better understanding of the disease is the possibility of a genetic predisposition to alcoholism. Recent work has demonstrated that people have varying complements of enzymes to metabolize alcohol. Current knowledge is examined about the influence of various ethanol metabolizing enzymes on alcohol consumption by Asians and members of other ethnic groups. The two principal enzymes involved in ethanol oxidative metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). ADH is responsible for the metabolism of ethanol to acetaldehyde. ALDH catalyzes the conversion of acetaldehyde to acetate. The different isozymes account for the diversity of alcohol metabolism among individuals. An isozyme of ADH (beta 2 beta 2) is found more frequently in Asians than in whites, and an ALDH isozyme (ALDH2), although present in Asians, often is in an inactive form. The presence of an inactive form of ALDH2 is thought to be responsible for an increase in acetaldehyde levels in the body. Acetaldehyde is considered responsible for the facial flushing reaction often observed among Asians who have consumed alcohol. A dysphoric reaction to alcohol, producing uncomfortable sensations, is believed to be a response to deter further consumption. Although the presence of an inactive ALDH2 isozyme may serve as a deterrent to alcohol consumption, its presence does not fully explain the levels of alcohol consumption by those with the inactive isozyme. Other conditions, such as social pressure, and yet undetermined biological factors, may play a significant role in alcohol consumption.     

Comparative analysis of hepatic ethanol metabolism in Fawn-Hooded and Wistar-Kyoto rats.

Results of a number of studies have supported the suggestion that a correlation exists between voluntary ethanol consumption and enhanced ethanol metabolism in some (but not all) rodent strains. However, as yet, the capacity for alcohol-preferring Fawn-Hooded (FH) rats to metabolize ethanol has not been investigated. Hence, the aim of the current study was to compare the activities of the major hepatic enzymes involved in ethanol metabolism--cytosolic alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH)--in the FH rat and its alcohol-nonpreferring counterpart, the Wistar-Kyoto (WKY) rat. In addition, the effect of chronic (5 weeks in vivo) ethanol pretreatment on the activity of these enzymes was investigated. Alcohol-naive FH rats were found to have significantly higher ADH activity (+61%) and no significant change in ALDH activity when compared with findings for WKY rats. In addition, chronic ethanol self-administration produced a small increase in ADH activity (+14%) in WKY rats only. Taken as a whole, these findings are the first to demonstrate an increased in vitro hepatic ethanol metabolism in alcohol-preferring FH rats and further demonstrate an association between hepatic ethanol metabolism and voluntary ethanol self-administration in rodents.     

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH beta2, encoded by the ADH2*2 gene, and the inactive ALDH2*2 gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene-environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between the ALDH2*2 allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.     

Effect of acute ethanol drinking on alcohol metabolism in subjects with different ADH and ALDH genotypes

The effect of different amounts of orally ingested ethanol on plasma alcohol dehydrogenase (ADH) and erythrocyte aldehyde dehydrogenase (ALDH), as well as on the blood ethanol and acetaldehyde levels, was examined in healthy nonalcoholic subjects. The genotypes at ADH2 and ALDH2 locus were identified in enzymatically amplified blood DNA by hybridization with allele-specific oligonucleotides. While the Japanese subject was found to be genotypically heterozygous for both ADH2 and ALDH2, the Caucasian subjects were genotypically homozygous normal for these alleles. A faster ethanol elimination associated with a higher blood acetaldehyde level was observed in the Japanese subject as compared to Caucasian subjects. However, no significant change in ADH and ALDH enzyme activities was detected as the result of acute ethanol intake.     

Inhibition of human alcohol and aldehyde dehydrogenases by acetaminophen: Assessment of the effects on first-pass metabolism of ethanol

Acetaminophen is one of the most widely used over-the-counter analgesic, antipyretic medications. Use of acetaminophen and alcohol are commonly associated. Previous studies showed that acetaminophen might affect bioavailability of ethanol by inhibiting gastric alcohol dehydrogenase (ADH). However, potential inhibitions by acetaminophen of first-pass metabolism (FPM) of ethanol, catalyzed by the human ADH family and by relevant aldehyde dehydrogenase (ALDH) isozymes, remain undefined. ADH and ALDH both exhibit racially distinct allozymes and tissue-specific distribution of isozymes, and are principal enzymes responsible for ethanol metabolism in humans. In this study, we investigated acetaminophen inhibition of ethanol oxidation with recombinant human ADH1A, ADH1B1, ADH1B2, ADH1B3, ADH1C1, ADH1C2, ADH2, and ADH4, and inhibition of acetaldehyde oxidation with recombinant human ALDH1A1 and ALDH2. The investigations were done at near physiological pH 7.5 and with a cytoplasmic coenzyme concentration of 0.5 mm NAD⁺. Acetaminophen acted as a noncompetitive inhibitor for ADH enzymes, with the slope inhibition constants (K_is) ranging from 0.90 mm (ADH2) to 20 mm (ADH1A), and the intercept inhibition constants (K_ii) ranging from 1.4 mm (ADH1C allozymes) to 19 mm (ADH1A). Acetaminophen exhibited noncompetitive inhibition for ALDH2 (K_is = 3.0 mm and K_ii = 2.2 mm), but competitive inhibition for ALDH1A1 (K_is = 0.96 mm). The metabolic interactions between acetaminophen and ethanol/acetaldehyde were assessed by computer simulation using inhibition equations and the determined kinetic constants. At therapeutic to subtoxic plasma levels of acetaminophen (i.e., 0.2–0.5 mm) and physiologically relevant concentrations of ethanol (10 mm) and acetaldehyde (10 μm) in target tissues, acetaminophen could inhibit ADH1C allozymes (12–26%) and ADH2 (14–28%) in the liver and small intestine, ADH4 (15–31%) in the stomach, and ALDH1A1 (16–33%) and ALDH2 (8.3–19%) in all 3 tissues. The results suggest that inhibition by acetaminophen of hepatic and gastrointestinal FPM of ethanol through ADH and ALDH pathways might become significant at higher, subtoxic levels of acetaminophen.     

Distribution and Kinetic Properties of Alcohol and Aldehyde-Dehydrogenase in the Rat Testis

The distribution of both alcohol (ADH) and aldehyde-dehydrogenase (ALDH) was studied in the rat testis. Testicular ADH was mainly localized into the interstitial tissue. Testicular ALDH activity was distributed between the interstitial tissue and the seminiferous tubules with greater activity measured in the former component. The apparent K_m for ADH in the whole testis was greater than that measured in the interstitial tissue. A low K_m value was determined for ALDH in the seminiferous tubules, compared to a higher mean K_m value for this enzyme in the interstitial tissue of the testis. The study shows that interstitial tissue possesses both ADH and ALDH, which are essential for the respective metabolism of ethanol and acetaldehyde, and that the seminiferous tubules possesses greater affinity for the metabolism of acetaldehyde than that of the interstitial tissue.     

Individual susceptibility and alcohol effects:biochemical and genetic aspects

The large interethnic and interindividual variability in alcohol-induced toxic effects comes from a combination of genetic and environmental factors, influencing ethanol toxicokinetics. The hepatic enzymatic systems involved in ethanol metabolism are alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH) and microsomal P4502E1 (CYP2E1). ADH oxidizes ethanol to acetaldehyde, which is very efficiently oxidized to acetate by ALDH. About 10% of moderate quantities of ethanol is metabolised by CYP2E1; the percentage increases when ADH is saturated. During ethanol metabolism reactive oxygen species and hydroxyethyl radicals are generated, causing oxidative stress, responsible for most ethanol-induced liver damage. For their critical role in detoxifying radicals, glutathione S-transferase are gaining attention in the etiology of alcoholism. All these enzymes have been shown to be polymorphic, giving rise to altered phenotypes. For this reason recent studies have looked for a correlation between metabolic variability and differences in alcohol abuse-related effects.     

INVOLVEMENT OF GENETIC POLYMORPHISM OF ALCOHOL AND ALDEHYDE DEHYDROGENASES IN INDIVIDUAL VARIATION OF ALCOHOL METABOLISM

The involvement of genetic polymorphism at the alcohol dehydrogenase2 (ADH2) and aldehyde dehydrogenase 2 (ALDH2) loci in determiningblood acetaldehyde levels and the rate of ethanol eliminationafter ethanol intake was investigated. Sixty-eight healthy subjectsingested 0.4 g of ethanol per kg of body weight over 10 min.Blood acetaldehyde levels scarcely increased in the subjectshomozygous for ALDH2^*I, regardless of their ADH2 genotypes (ADH2^*1/^*1,ADH2^*1/^*2 and ADH2^*2/^*2). The acetaldehyde levels in the subjectswith the ALDH2^*1/^*2 heterozygote increased to 23.4 µMon average, and no significant differences were observed betweenthe three ADH2 genotype groups. Subjects homozygous for ALDH2^*2showed very high levels of blood acetaldehyde, and the averagevalue was 79.3 µM. The values of Widmark's ß₆₀(mg/ml/hr)and ethanol elimination rate (mg/kg/br) showed significant differencesamong the three ALDH2 genotypes, and in decreasing order thevalues were ALDH2^*1/^*1, ALDH2^*1/^*2, ALDH2^*2 However, no significantdifferences were seen among the ADH2 genotypes.     

Effect of chronic alcohol consumption on the ethanol- and acetaldehyde-metabolizing systems in the rat gastrointestinal tract

The activities of alcohol dehydrogenase (ADH), catalase, microsomal ethanol-oxidizing system (MEOS) and aldehyde dehydrogenase (ALDH) were measured in gastric, small intestinal, colonic and rectal mucosal samples of rats fed on a liquid alcohol diet for 1 month. In the rectum and large intestine of control animals, the activities of ADH, MEOS and catalase were maximal, whereas the activity of ALDH was minimal. After chronic alcohol intoxication, MEOS activity increased significantly in the stomach. An activation of catalase and MEOS and a decrease of the low-K(M) ALDH activity were observed in the rectum of experimental animals. In rats consuming the alcohol diet, hypertrophy of crypts and an increased number of mitoses were noticed in colonic and rectal mucosa. Acute alcohol intoxication (2 g/kg, intragastrically) produced significantly higher acetaldehyde concentrations in the contents of the large intestine and rectum of rats receiving alcohol chronically compared to controls. Thus, after chronic alcohol intoxication, the large intestine regions showed a greater imbalance between the activities of acetaldehyde-producing and -oxidizing enzymes, which resulted in accumulation of acetaldehyde. This mechanism can account for the local toxicity of ethanol after its chronic consumption, and relates the development of mucosal damage and compensatory hyper-regenerative processes, and possibly carcinogenesis, in the colonic and rectal mucosae of alcoholics to the effects of acetaldehyde.     

Regulation of Alcohol and Acetaldehyde Metabolism by a Mixture of Lactobacillus and Bifidobacterium Species in Human

Excessive alcohol consumption is one of the most significant causes of morbidity and mortality worldwide. Alcohol is oxidized to toxic and carcinogenic acetaldehyde by alcohol dehydrogenase (ADH) and further oxidized to a non-toxic acetate by aldehyde dehydrogenase (ALDH). There are two major ALDH isoforms, cytosolic and mitochondrial, encoded by ALDH1 and ALDH2 genes, respectively. The ALDH2 polymorphism is associated with flushing response to alcohol use. Emerging evidence shows that Lactobacillus and Bifidobacterium species encode alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) mediate alcohol and acetaldehyde metabolism, respectively. A randomized, double-blind, placebo-controlled crossover clinical trial was designed to study the effects of Lactobacillus and Bifidobacterium probiotic mixture in humans and assessed their effects on alcohol and acetaldehyde metabolism. Here, twenty-seven wild types (ALDH2*1/*1) and the same number of heterozygotes (ALDH2*2/*1) were recruited for the study. The enrolled participants were randomly divided into either the probiotic (Duolac ProAP4) or the placebo group. Each group received a probiotic or placebo capsule for 15 days with subsequent crossover. Primary outcomes were measurement of alcohol and acetaldehyde in the blood after the alcohol intake. Blood levels of alcohol and acetaldehyde were significantly downregulated by probiotic supplementation in subjects with ALDH2*2/*1 genotype, but not in those with ALDH2*1/*1 genotype. However, there were no marked improvements in hangover score parameters between test and placebo groups. No clinically significant changes were observed in safety parameters. These results suggest that Duolac ProAP4 has a potential to downregulate the alcohol and acetaldehyde concentrations, and their effects depend on the presence or absence of polymorphism on the ALDH2 gene.     

Interaction of the Effects of Alcohol Drinking and Polymorphisms in Alcohol-Metabolizing Enzymes on the Risk of Female Breast Cancer in Japan

Background

Epidemiological studies consistently indicate that alcoholic beverages are an independent risk factor for female breast cancer. Although the mechanism underlying this effect remains unknown, the predominant hypothesis implicates mutagenesis via the ethanol metabolite acetaldehyde, whose impact on the carcinogenesis of several types of cancer has been shown in both experimental models and molecular epidemiological studies. Many of the epidemiological studies have investigated genetic polymorphisms of alcohol dehydrogenase-1B (ADH1B) His48Arg and aldehyde dehydrogenase-2 (ALDH2) Glu504Lys, because of the strong impact these polymorphisms have on exposure to and accumulation of acetaldehyde. With regard to breast cancer, however, evidence is scarce.

Methods

To clarify the impact on female breast cancer risk of the interaction of the effects of alcohol consumption and polymorphisms in the alcohol-metabolizing enzymes ADH1B and ALDH2, we conducted a case–control study of 456 newly and histologically diagnosed breast cancer cases and 912 age- and menopausal status-matched noncancer controls. Gene–gene and gene–environment interactions between individual and combined ADH1B and ALDH2 gene polymorphisms and alcohol consumption were evaluated.

Results

Despite sufficient statistical power, there was no significant impact of ADH1B and ALDH2 on the risk of breast cancer. Neither was there any significant gene–environment interactions between alcohol drinking and polymorphisms in ADH1B and ALDH2.

Conclusions

Our findings do not support the hypothesis that acetaldehyde is the main contributor to the carcinogenesis of alcohol-induced breast cancer.Key words: breast cancer, alcohol drinking, acetaldehyde, polymorphisms in alcohol-metabolizing enzyme genes, case–control study     

Lactobacilli Infection Case Reports in the Last Three Years and Safety Implications

Lactobacilli constitute the dominant microbiota in many fermented foods and comprise widely used probiotics. However, these bacteria cause rare infections mostly in diabetic and immunocompromised subjects in presence of risk factors such as prosthetic hearth valves and dental procedures or caries. The scope of this survey was re-assessing the pathogenic potential of lactobacilli based on the infection case reports published in the last three years. In 2019, 2020, and 2021, total of 17, 15, and 16 cases, respectively, including endocarditis, bacteremia, and other infections, were reported. These annual numbers are higher than those observed previously. Lacticaseibacillus rhamnosus (13 cases), comprising strain GG (ATCC 53103) with established applications in healthcare, L. paracasei (7 cases), Lactobacillus acidophilus (5 cases), L. jensenii (5 cases), Lactiplantibacillus plantarum (3 cases), L. paraplantarum, L. delbrueckii subsp. delbrueckii, L. gasseri, L. paragasseri, Limosilactobacillus fermentum, and L. reuteri (1 case each) were involved. Virulence characterization of two strains that caused infections, a derivative of L. rhamnosus GG and L. paracasei LP10266, indicated that increased biofilm-forming capacity favors pathogenicity and it is determined by variable genetic traits. This survey highlights that the strains of lactobacilli that cause infections are little characterized genetically. Instead, to avoid that these bacteria become a hazard, genetic stability should be periodically re-evaluated by whole genome sequencing (WGS) to ensure that only non-pathogenic variants are administered to vulnerable individuals.     

Use of an "acetaldehyde clamp" in the determination of low-KM aldehyde dehydrogenase activity in H4-II-E-C3 rat hepatoma cells.

The high-affinity (K(M)<1 microM) mitochondrial class 2 aldehyde dehydrogenase (ALDH2) metabolizes most of the acetaldehyde generated in the hepatic oxidation of ethanol. H4-II-E-C3 rat hepatoma cells have been found to express ALDH2. We report a method to assess ALDH2 activity in intact hepatoma cells that does not require mitochondrial isolation. To determine only the high-affinity ALDH2 activity it is necessary to keep constant low concentrations of acetaldehyde in the cells to minimize its metabolism by high-K(M) aldehyde dehydrogenases. To maintain both low and constant concentrations of acetaldehyde we used an "acetaldehyde clamp," which keeps acetaldehyde at a concentration of 4.2+/-0.4 microM. The clamp is attained by addition of excess yeast alcohol dehydrogenase, 14C-ethanol, and oxidized form of nicotinamide adenine dinucleotide (NAD(+)) to the hepatoma cell culture medium. The concentration of 14C-acetaldehyde attained follows the equilibrium constant of the alcohol dehydrogenase reaction. Thus, 14C-acetate is generated virtually by the low-K(M) aldehyde dehydrogenase activity. 14C-acetate is separated from the culture medium by an anionic resin and its radioactivity is determined. We showed that (1) acetate production is linear for 120 min, (2) addition of 160 microM cyanamide to the culture medium leads to a 75%-80% reduction of acetate generated, and (3) ALDH2 activity is dependent on cell-to-cell contact and increases after cells reach confluence. The clamp system allows the determination of ALDH2 activity in less than one million H4-II-E-C3 rat hepatoma cells. The specificity and sensitivity of the "acetaldehyde clamp" assay should be of value in evaluation of the effects of new agents that modify Aldh2 gene expression, as well as in the study of ALDH2 regulation in intact cells.     

Studies with cDNA probes on the in vivo effect of ethanol on expression of the genes of alcohol metabolism

Mice (Mus musculus) from three genetic strains with variable responses to ethanol challenge (BALB/c, C57BL/6J and 129/ReJ) were used to evaluate the effect of ethanol feeding on hepatic mRNA specific to the two primary enzymes of ethanol metabolism; alcohol dehydrogenase (ADH; E.C. 1.1.1.1) and aldehyde dehydrogenase (ALDH; E.C. 1.2.1.3). Adh-1 (ADH) and Ahd-2 (ALDH) specific mRNA were evaluated on the livers of ethanol-fed mice and from their age, sex and genotype matched controls (using an isocaloric liquid diet). C57BL/6J (alcohol resistant) mice show a significant (approx. 200%) increase in ADH-1 mRNA levels after ethanol treatment, compared to their matched controls. BALB/c (alcohol sensitive) mice have approximately a 20% increase with ethanol treatment while 129/ReJ (alcohol sensitive) mice show a slight reduction in the ADH-1 specific mRNA following ethanol feeding. A strain-specific pattern is also apparent in the AHD-2 mRNA as a result of ethanol feeding in the experimental animals. C57BL/6J mice have an increase and BALB/c mice show no apparent change in the AHD-2 mRNA. 129/ReJ mice fed an ethanol diet, on the other hand, appear to have a decrease in the level of AHD-2 hepatic mRNA as compared to their matched controls. The relative mRNA levels of the two genes correlate well with the respective enzyme activity levels, but for mice on the control diet only. Ethanol feeding, which causes an apparent reduction in hepatic ADH enzyme activity in BALB/c and 129/ReJ and an apparent increase in ALDH activity in C57BL/6J (under the experimental protocols used) also alters the mRNA levels specific to the two genes. However, changes in the mRNA levels after ethanol feeding cannot be directly related to the changes seen in enzyme activity. The observed steady state level of AHD-2 mRNA and the increase in ALDH activity after ethanol feeding, which is unique to C57BL/6J mice, is expected to offer a faster clearance (metabolism) of acetaldehyde, the toxic metabolite, and may be responsible for, or contribute to, the relative resistance of this strain to ethanol.     

Gastrointestinal Alcohol Dehydrogenase

Alcohol dehydrogenase (ADH) consists of a family of isozymes that convert alcohols to their corresponding aldehydes using NAD+ as a cofactor. The metabolism of ethanol by gastrointestinal ADH isozymes results in the production of acetaldehyde, a highly toxic compound that binds to cellular protein and DNA if not further metabolized to acetate by acetaldehyde dehydrogenase isozymes. Acetaldehyde seems to be involved in ethanol-associated cocarcinogenesis. The metabolism of retinol and the generation of retinoic acid is a function of class I and class IV ADH, and its inhibition by alcohol may lead to an alteration of epithelial cell differentiation and cell growth and may also be involved in ethanol-associated gastrointestinal cocarcinogenesis.     

Expression pattern, ethanol-metabolizing activities, and cellular localization of alcohol and aldehyde dehydrogenases in human large bowel: association of the functional polymorphisms of ADH and ALDH genes with hemorrhoids and colorectal cancer

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are principal enzymes responsible for metabolism of ethanol. Functional polymorphisms of ADH1B, ADH1C, and ALDH2 genes occur among racial populations. The goal of this study was to systematically determine the functional expressions and cellular localization of ADHs and ALDHs in human rectal mucosa, the lesions of adenocarcinoma and hemorrhoid, and the genetic association of allelic variations of ADH and ALDH with large bowel disorders. Twenty-one surgical specimens of rectal adenocarcinoma and the adjacent normal mucosa, including 16 paired tissues of rectal tumor, normal mucosae of rectum and sigmoid colon from the same individuals, and 18 surgical mixed hemorrhoid specimens and leukocyte DNA samples from 103 colorectal cancer patients, 67 hemorrhoid patients, and 545 control subjects recruited in previous study, were investigated. The isozyme/allozyme expression patterns of ADH and ALDH were identified by isoelectric focusing and the activities were assayed spectrophotometrically. The protein contents of ADH/ALDH isozymes were determined by immunoblotting using the corresponding purified class-specific antibodies; the cellular activity and protein localizations were detected by immunohistochemistry and histochemistry, respectively. Genotypes of ADH1B, ADH1C, and ALDH2 were determined by polymerase chain reaction-restriction fragment length polymorphisms. At 33 mM ethanol, pH 7.5, the activity of ADH1C*1/1 phenotypes exhibited 87% higher than that of the ADH1C*1/*2 phenotypes in normal rectal mucosa. The activity of ALDH2-active phenotypes of rectal mucosa was 33% greater than ALDH2-inactive phenotypes at 200 μM acetaldehyde. The protein contents in normal rectal mucosa were in the following order: ADH1 > ALDH2 > ADH3 ≈ ALDH1A1, whereas those of ADH2, ADH4, and ALDH3A1 were fairly low. Both activity and content of ADH1 were significantly decreased in rectal tumors, whereas the ALDH activity remained unchanged. The ADH activity was also significantly reduced in hemorrhoids. ADH4 and ALDH3A1 were uniquely expressed in the squamous epithelium of anus at anorectal junctions. The allele frequencies of ADH1C*1 and ALDH2*2 were significantly higher in colorectal cancer and that of ALDH2*2 also significantly greater in hemorrhoids. In conclusion, ADH and ALDH isozymes are differentially expressed in mucosal cells of rectum and anus. The results suggest that acetaldehyde, an immediate metabolite of ethanol, may play an etiological role in pathogenesis of large bowel diseases.     

Properties of rat retina alcohol dehydrogenase

The rat eye fraction, including retina, pigment epithelium and choroid, contains an alcohol dehydrogenase (ADH) isoenzyme that is not present in rat liver. Starch gel electrophoresis of retina ADH shows an anodic band that can be visualized by activity staining, using either ethanol or pentanol as substrates. Ethanol is a poor substrate (Km: 336 mM, at pH 10.0) for the purified retina ADH which prefers long chain, 2-unsaturated and aromatic alcohols. The enzyme has a pH optimum of 10.0 for ethanol oxidation and it is inhibited by 4-methylpyrazole (KI: 10 microM). Electrophoretic and kinetic properties clearly differentiate the retina ADH from the hepatic cathodic ADH isoenzymes and from an anodic chi-ADH-like form that we have also detected in rat liver. At the pH and ethanol concentrations found "in vivo," retina ADH can oxidize ethanol to an appreciable extent. The subsequent production of acetaldehyde and redox change may be responsible for visual disorders during alcohol intoxication.