Acetaldehyde Metabolism Research Articles

Acetaldehyde metabolism by wine lactic acid bacteria

Acetaldehyde is a volatile flavor compound present in many fermented foods and is important in the production of red and white wines. Nine strains of the genera Lactobacillus and Oenococcus were able to metabolize acetaldehyde in a resting cell system, whereas two Pediococcus strains were not. Acetic acid and ethanol were produced from its degradation. A Lactobacillus and an Oenococcus were able to degrade SO 2-bound acetaldehyde, as well. A coincubation of resting cells of Saccharomyces bayanus Première Cuvée and Oenococcus oeni Lo111 showed that strain Lo111 metabolized acetaldehyde produced by the yeast. The ability of malolactic bacteria to degrade free and SO 2-bound acetaldehyde has implications for sensory and color qualities and the use of SO 2 in wine.

Sister-chromatid Exchanges Induced by Disulfiram in Bone Marrow and Spermatogonial Cells of Mice Treated In Vivo

Disulfiram is a widely used drug to treat alcoholism due to its capacity to inhibit the metabolism of acetaldehyde; however, its genotoxic potential is not well known. Thus, the aim of this investigation was to determine whether the chemical may induce sister-chromatid exchanges (SCEs) in an in vivo study using mouse bone marrow and spermatogonial cells. We used doses of 200, 400 and 800 mg/kg body weight and compared the obtained data with the values determined in a negative control group as well as with a positive control group (cyclophosphamide, 50 mg/kg). The results in both systems indicated a weak genotoxic response by the chemical. In the case of bone marrow, a significant SCE level was achieved only with the high tested dose, but in spermatogonial cells the three doses tested showed a significant difference with respect to the negative control. No significant alterations in the mitotic index or in the cell proliferation kinetics were observed in somatic cells. Concerning the effect of cyclophosphamide, an increase in the level of SCEs was observed in both types of cells, reaching more than three times the values obtained in their respective control groups.

The structure of retinal dehydrogenase type II at 2.7 A resolution: implications for retinal specificity.

Retinoic acid, a hormonally active form of vitamin A, is produced in vivo in a two step process: retinol is oxidized to retinal and retinal is oxidized to retinoic acid. Retinal dehydrogenase type II (RalDH2) catalyzes this last step in the production of retinoic acid in the early embryo, possibly producing this putative morphogen to initiate pattern formation. The enzyme is also found in the adult animal, where it is expressed in the testis, lung, and brain among other tissues. The crystal structure of retinal dehydrogenase type II cocrystallized with nicotinamide adenine dinucleotide (NAD) has been determined at 2.7 A resolution. The structure was solved by molecular replacement using the crystal structure of a mitochondrial aldehyde dehydrogenase (ALDH2) as a model. Unlike what has been described for the structures of two aldehyde dehydrogenases involved in the metabolism of acetaldehyde, the substrate access channel is not a preformed cavity into which acetaldehyde can readily diffuse. Retinal dehydrogenase appears to utilize a disordered loop in the substrate access channel to discriminate between retinaldehyde and short-chain aldehydes.

Reduced aldehyde dehydrogenase levels in the brain of patients with Down syndrome.

Aldehyde dehydrogenase (ALDH) is a key enzyme in fructose, acetaldehyde and oxalate metabolism and represents a major detoxification system for reactive carbonyls and aldehydes. In the brain, ALDH exerts a major function in the metabolism of biogenic aldehydes, norepinephrine, dopamine and diamines and gamma-aminobutyric acid. Subtractive hybridization studies in Down Syndrome (DS) fetal brain showed that mRNA for ALDH are downregulated. Here we studied the protein levels in the brain of adult patients. The proteins from five brain regions of 9 aged patients with DS and 9 controls were analyzed by two-dimensional (2-D) gel electrophoresis and identified by matrix-assisted laser desorption ionization mass spectrometry. ALDH levels were reduced in the brain regions of at least half of the patients with Down Syndrome, as compared to controls. The decreased ALDH levels in the DS brain may result in accumulation of aldehydes which can lead to the formation of plaques and tangles reflecting abnormally cross-linked, insoluble and modified proteins, found in aged DS brain. Furthermore, we constructed a 2-Dmap including approximately 120 identified human brain proteins.

Inhibition of human mitochondrial aldehyde dehydrogenase by metabolites of disulfiram and structural characterization of the enzyme adduct by HPLC-tandem mass spectrometry.

Ingest of disulfiram blocks the metabolism of acetaldehyde, the product of ethanol metabolism, by inhibiting hepatic mitochondrial aldehyde dehydrogenase (ALDH2), a key ene by virtue of its low Km for acetaldehyde (Mascher & Kikuta, 1992; Greenfield & Pietruszko, 1977). Disulfiram is rapidly reduced in vivo to N,N-diethyldithiocarbamate (DDC) (Cobby et al., 1977) which is further metabolized as shown in Scheme 1. The general consensus is that disulfiram is too short-lived in vivo to account for the inhibition of ALDH2 that one its metabolites is the ultimate inhibitor (Yourick & Faiman, 1991; Hart & man, 1992).

Oxidation of acetaldehyde by isolated aortic rings of UChA and UChB rats

The rate of acetaldehyde metabolism was measured in aortic rings from rat strains genetically bred for high (UChB) and low (UChA) voluntary ethanol consumption. The results show that in aortic rings from naive UChB rats, acetaldehyde oxidation rates were significantly greater than the rates observed in aortic rings from naive UChA rats. These strain differences are explained by different activity of vascular low-Km aldehyde dehydrogenase (ALDH). Chronic feeding of ethanol to UChA rats did not alter their aortic ALDH activity. The results of the present study provides additional evidence that the activity variation for the low-Km ALDH between both rat strains exists in various organs and tissues.

Microsomal Acetaldehyde Oxidation is Negligible in the Presence of Ethanol

The microsomal ethanol oxidizing system (MEOS), inducible by ethanol and acetone, oxidizes ethanol to acetaldehyde, which causes many toxic effects associated with excess ethanol. Recent studies reported that rat liver microsomes also oxidize acetaldehyde, thereby challenging the validity of the assessment of MEOS activity by measuring acetaldehyde production and suggesting that MEOS activity results in the accumulation not of acetaldehyde but, rather, of its less toxic metabolite, acetate. To address these issues, we compared both metabolic rates of ethanol and acetaldehyde and the effect of ethanol on the acetaldehyde metabolism. Liver microsomes were prepared from Sprague-Dawley rats induced either with acetone for 3 days or ethanol for 3 weeks. NADPH-dependent acetaldehyde (300 microM) metabolism was measured in two ways: (1) by detection of acetaldehyde disappearance by headspace gas chromatography, and (2) by assessment of acetaldehyde oxidation by liquid scintillation counting of acetate formed from [1,2-14C]acetaldehyde. Ethanol (50 mM) oxidation was measured by gas chromatography. In acetone- and ethanol-induced rat liver microsomes, the acetaldehyde disappearance (p < 0.0001) and oxidation (p < 0.0001) rates were both significantly increased. The rates of acetaldehyde oxidation paralleled those of p-nitrophenol hydroxylation (r = 0.974, p < 0.0001), with a Km of 82+/-14 microM and a Vmax of 4.8+/-0.5 nmol/min/mg protein in acetone-induced microsomes. Acetaldehyde disappearance in acetone-induced microsomes and acetaldehyde oxidation in acetone-induced and ethanol-induced microsomes were significantly lower than the corresponding ethanol oxidation, with rates (nmol/min/mg protein) of 4.6+/-0.6 versus 9.0+/-0.8 (p < 0.005), 4.4+/-0.3 versus 9.1+/-0.5 (p < 0.0005), and 14.0+/-0.9 versus 19.5+/-1.8 (p < 0.05), respectively. The presence of 50 mM ethanol decreased this metabolism to 0.9+/-0.3 (p < 0.005), 0.5+/-0.1 (p < 0.001), and 1.8+/-0.3 (p < 0.001), resulting in rates of acetaldehyde metabolism of only 9.8+/-3.2%, 6.0+/-0.5%, and 9.5+/-1.2% (respectively) of those of ethanol oxidation. In conclusion, rat liver microsomes oxidize acetaldehyde at much lower rates than ethanol, and this acetaldehyde metabolism is strikingly inhibited by ethanol. Accordingly, acetaldehyde formation provides an accurate assessment of MEOS activity. Furthermore, because acetaldehyde production vastly exceeds its oxidation, the net result of MEOS activity is the accumulation of this toxic metabolite.

Combined use of immobilized Candida stellata cells and Saccharomyces cerevisiae to improve the quality of wines.

Grape must fermentation by the combination of immobilized Candida stellata cells and Saccharomyces cerevisiae was carried out in order to enhance the analytical profiles of wine. Batch and continuous pre-treatment of must with immobilized C. stellata cells, followed by an inoculum of S. Cerevisiae, enhanced the analytical profiles of fermentates. The metabolic interactions between the two yeast species showed a positive influence on reducing sugars, acetaldehyde and acetoin metabolism. Sequential fermentation was the best combination for improving the analytical profiles of wine but caused a loss of viability and metabolic activity of beads by limiting their successive use. Continuous pre-treatment of must on the beads of C. stellata could be a more interesting modality to improve the quality of wines. This biotechnological process could be profitably used to produce specific and special wines.

Correlation between alcohol-induced asthma and acetaldehyde dehydrogenase-2 genotype

Background: Alcohol-induced asthma, a phenomenon characteristic of Asians, is due to differences in alcohol metabolism, particularly acetaldehyde metabolism. We investigated the effect of polymorphism in acetylaldehyde dehydrogenase 2 (ALDH2) gene on the response to alcohol challenge testing in a group of Japanese asthmatic subjects and normal subjects. Methods: Subjects were 32 asthmatic subjects and 30 healthy individuals. We measured the change in FEV 1 after ingestion of 30 gm of ethanol. Blood ethanol, acetylaldehyde, and histamine concentrations were determined. ALDH2 gene type was established by polymerase chain reaction. Results: Ethanol provocation test results were positive in 15 (47% responders) asthmatic subjects. The blood ethanol concentration was similar in responders and nonresponders. The fall in FEV 1 was associated with a rise in blood acetaldehyde and histamine concentrations. The response to oral ethanol challenge was positive in three (19%) of 16 patients with normal homozygote ALDH2 genotype, 10 (71%) of 14 patients with type mutant heterozygote, and two (100%) of two patients with type mutant homozygote ALDH2 genotype. Conclusions: Alcohol-induced asthma is probably caused by increased blood acetaldehyde concentration resulting from abnormalities of ALDH2 enzyme activity based on ALDH2 genotype differences.(J Allergy Clin Immunol 1998;101:576-80).

Effects of antineoplastics, antibiotics and antidiabetics on acetaldehyde metabolism after alcohol ingestion.

The main purpose of this study was to evaluate the inhibitory effects of 5-fluorouracil antineoplastics, cephem antibiotics containing the methyltetrazolylthiol (MTT) group and antidiabetics on aldehyde dehydrogenase (ALDH) activity in vivo and in vitro. In in vivo experiments, rats were given a 100 mg/kg dose of drugs (10 mg/kg for glibenclamide) orally or intraperitoneally. When each drug was administered singly immediately after an oral administration of 1.5 g/kg ethanol, only carmofur, an antineoplastic, produced marked increases in blood acetaldehyde concentrations. This action was also noted when ethanol was ingested 15 h after administration. The remaining drugs did not increase blood acetaldehyde concentrations. When rats were treated with carmofur at 12 h intervals for 3 consecutive days and were given 1.5 g/kg ethanol after the final treatment, blood acetaldehyde concentrations were elevated more significantly than with a single administration of carmofur. Furthermore, daily administration of cephem antibiotics containing the MTT group, latamoxef, cefamandole, cefoperazone and cefbuperazone, significantly increased blood acetaldehyde concentrations. Daily administration of sulfonylurea antidiabetics, chlorpropamide and acetohexamide, slightly increased blood acetaldehyde concentrations. Drugs causing increases in blood acetaldehyde concentrations when administration was combined with ethanol ingestion also inhibited ALDH activity in vitro. The results of the in vitro experiments roughly correlated with those of the in vivo experiments. The inhibitory effects of drugs on ALDH activity were in the following order: carmofur >> cephem antibiotics containing the MTT group > sulfonylurea antidiabetics.

Ethanol-induced changes of intracellular thiol compartmentation and protein redox status in the rat liver: effect of tauroursodeoxycholate

Background/Aims: Ethanol impairs cellular antioxidant defense and protein metabolism. Hydrophilic bile acids are protective against ethanol-induced cytotoxicity. This study investigated the compartmentation of intracellular thiol and protein redox status after acute ethanol intoxication in the liver and the effect of tauroursodeoxycholate pretreatment. Methods: The concentrations of total glutathione, glutathione bound to proteins, sulfhydryl proteins, carbonyl proteins and malondialdehyde were measured in hepatic cytosol, mitochondria and nuclei after oral administration of 25% ethanol (4 g/kg) or isocaloric carbohydrate solution to rats. The metabolisms of ethanol and acetaldehyde were investigated by giving 4-methylpyrazole (1 mmol/kg i.p.) or cyanamide (15 mg/kg i.p.) 1 h prior to ethanol ingestion. One group of rats received tauroursodeoxycholate (12 mg/kg p.os) 1 h before ethanol ingestion. Results: Ethanol significantly decreased the glutathione concentrations. Significant increases in glutathione bound to proteins; carbonyl protein and malondialdehyde concentrations were also noted, especially at the mitochondrial level. Enhanced carbonyl protein formation was also observed ( p<0.01). The inhibition of acetaldehyde metabolism, but not ethanol metabolism, exaggerated the alterations produced by ethanol. Pretreatment with tauroursodeoxycholate significantly reduced lipid and protein oxidation, particularly in mitochondria. By contrast, no changes were observed in glutathione content and compartmentation. Conclusions: Ethanol intoxication differentially impairs thiol and protein redox status in the subcellular fractions of rat liver. These alterations seem dependent on acetaldehyde rather than ethanol. Tauroursodeoxycholate administration protects proteins and lipids from ethanol-induced oxidative damage without influencing the glutathione content and compartmentation.

Dosimetry, toxicity and carcinogenicity of inspired acetaldehyde in the rat

Acetaldehyde is a ubiquitous air pollutant. It is an important industrial chemical and is also produced during the combustion of wood or tobacco. In smoky indoor atmospheres concentrations of the aldehyde may reach 100 ppb. Acetaldehyde is metabolized to acetate (releasing hydrogen ion) by aldehyde dehydrogenase a process which, in most tissues, represents a detoxification pathway. In vitro, acetaldehyde forms DNA–DNA and DNA–protein crosslinks. It is a clastogen, and inducer of sister chromatid exchanges, and is, perhaps, a weak mutagen. Inhalation exposure to 1000 ppm may induce DNA–protein crosslink formation in nasal tissues in the rat in vivo. Inhalation toxicity studies have shown acetaldehyde vapor causes chronic tissue injury and tumor formation in nasal tissues at exposure concentrations of 750 ppm or higher, with nasal olfactory mucosa being more sensitive than respiratory mucosa. Dosimetric estimates suggest that marked tissue injury and carcinogenicity occurs only at inspired concentrations which are sufficiently high to overwhelm nasal aldehyde dehydrogenase detoxification capacity. The induction of squamous cell carcinomas in the respiratory mucosa by acetaldehyde displays many analogies to the induction of squamous cell carcinomas by formaldehyde. For both vapors, non-linear concentration response relationships are observed for DNA–protein crosslink formation, tissue injury, and carcinogenicity, suggesting these responses are associated. For both vapors it is possible to document an exposure concentration that produces nasal respiratory epithelial injury without increasing tumor incidence, suggesting that for respiratory mucosa-derived tumors, exposure to non-cytotoxic concentrations may pose limited carcinogenic risk. In addition to squamous cell carcinomas of the respiratory epithelium, acetaldehyde exposure also results in nasal olfactory injury and tumors (adenocarcinomas) in the rat. The studies performed to date have not demonstrated a no observable effect level for these responses, therefore, the precise role of cytotoxicity and regenerative cell proliferation in the carcinogenic process in olfactory tissues can not be evaluated. Acetaldehyde metabolism via aldehyde dehydrogenase results in the formation of two hydrogen ions. The olfactory mucosa is quite sensitive to acid and dosimetric estimates suggest that the intracellular acid production rates that may occur in olfactory mucosa during acetaldehyde exposure may be sufficiently high to cause tissue damage. Such acid-induced tissue damage may enhance the genotoxic and tumorigenic potential of acetaldehyde in olfactory mucosa, and may, therefore, represent an important process in the production of tumors in this tissue.

Pharmacokinetic interactions between alcohol and other drugs.

The frequent use of alcohol (ethanol) together with prescription drugs gives any described pharmacokinetic interaction significant clinical implications. The issue is both the effect of alcohol on the pharmacokinetics of various drugs and also the effect of those drugs on the pharmacokinetics of alcohol. This review discusses these pharmacokinetic interactions but also briefly describes some other effects of alcohol that are clinically relevant to drug prescribing. The use of several different study designs may be required before we can confidently state the presence or absence of any alcohol-drug interaction. Short term administration of alcohol in volunteers is the most common study design but studies of social drinking and prolonged moderate alcohol intake can be important in some situations. Community-based studies may illustrate the clinical relevance of any interaction. Alcohol can affect the pharmacokinetics of drugs by altering gastric emptying or liver metabolism (by inducing cytochrome P450 2E1). Drugs may affect the pharmacokinetics of alcohol by altering gastric emptying and inhibiting gastric alcohol dehydrogenase. The role of gastric alcohol dehydrogenase in the first-pass metabolism of alcohol is reviewed in this article and the arguments for and against any potential interaction between alcohol and H2 receptor antagonists are also discussed. The inhibition of the metabolism of acetaldehyde may cause disulfiram-like reactions. Pharmacodynamic interactions between alcohol and prescription drugs are common, particularly the additive sedative effects with benzodiazepines and also with some of the antihistamine drugs; other interactions may occur with tricyclic antidepressants. Alcohol intake may be a contributing factor to the disease state which is being treated and may complicate treatment because of various pathophysiological effects (e.g. impairment of gluconeogenesis and the risk of hypoglycaemia with oral hypoglycaemic agents). The combination of nonsteroidal anti-inflammatory drugs and alcohol intake increases the risk of gastrointestinal haemorrhage.

Novel prodrugs of cyanamide that inhibit aldehyde dehydrogenase in vivo.

S-Methylisothiourea (4), when administered to rats followed by a subsequent dose of ethanol, gave rise to a 119-fold increase in ethanol-derived blood acetaldehyde (AcH) levels-a consequence of the inhibition of hepatic aldehyde dehydrogenase (A1DH)-when compared to control animals not receiving 4. The corresponding O-methylisourea was totally inactive under the same conditions, suggesting that differential metabolism may be a factor in this dramatic difference between the pharmacological effects of O-methylisourea and 4 in vivo. The S-n-butyl- and S-isobutylisothioureas (8 and 9, respectively) at doses equimolar to that of 4 were nearly twice as effective in raising ethanol-derived blood AcH, while S-allylisothiourea (10) was slightly less active. However, blood ethanol levels of all experimental groups were indistinguishable from controls. Pretreatment of the animals with 1-benzylimidazole, a known inhibitor of the hepatic mixed function oxidases, followed sequentially by either 8, 9, or 10 plus ethanol, reduced blood AcH levels by 66-88%, suggesting that the latter compounds were being oxidatively metabolized to a common product that led to the inhibition of AcH metabolism. In support of this, when 8 was incubated in vitro with rat liver microsomes coupled to catalase and yeast A1DH, the requirement for microsomal activation for the inhibition of A1DH activity was clearly indicated. We suggest that S-oxidation is involved and that the S-oxides produced in vivo inhibited A1DH directly, or spontaneously released cyanamide, an inhibitor of A1DH. Indeed, incubation of 8 with rat liver microsomes and NADPH gave rise to cyanamide as metabolite, identified as its dansylated derivative. Cyanamide formation was minimal in the absence of coenzyme. Extending the side chain was detrimental, since S-benzylisothiourea (11) and S-n-hexadecylisothiourea (12) were toxic, the latter producing extensive necrosis of the liver and kidneys when administered to rats.

Co‐Metabolism of Ethanol, Ethanol‐Derived Acetaldehyde, and 4‐Hydroxynonenal in Isolated Rat Hepatocytes

Our laboratory has previously reported on the ability of 4-hydroxynonenal (4-HNE), a primary product of lipid peroxidation, to inhibit acetaldehyde metabolism in isolated mouse liver mitochondria. The purpose of the present study is to determine whether the co-metabolism of ethanol and 4-HNE compromises the elimination of either substrate in isolated rat hepatocytes. Hepatocytes were isolated and incubated with ethanol and 4-HNE. Ethanol elimination and acetaldehyde accumulation were monitored by gas chromatography, whereas 4-HNE elimination and metabolite accumulation were measured by UV detection and reversed-phase HPLC at 202 nm. In the absence of 4-HNE, hepatocytes metabolized ethanol at an initial rate of 9.4 nmol/min/million cells. Ethanol elimination was moderately inhibited by the presence of 4-HNE. Accumulation of ethanol-derived acetaldehyde was not apparent in incubations with only ethanol. In contrast, in incubations containing both substrates, ethanol-derived acetaldehyde accumulation exceeded that observed in hepatocytes exposed only to ethanol and was proportional to the 4-HNE concentration in the incubations. In all instances, the rate of 4-HNE elimination was not compromised by the presence of ethanol. Accordingly, ethanol metabolism did not alter the oxidative or conjugative metabolism of 4-HNE. However, the reductive metabolism of 4-HNE was affected by the presence of ethanol, wherein accumulation of 1,4-dihydroxy-2-nonene increased > 2-fold of that observed in incubations with only 4-HNE. To determine further if 4-HNE and ethanol are metabolized through the same metabolic pathways, cells were preincubated with either 4-methylpyrazole or cyanamide to inhibit alcohol dehydrogenase (E.C. 1.1.1.1.) and aldehyde dehydrogenase (E.C. 1.2.1.2.), respectively. Expectantly, 4-methylpyrazole blocked the formation of 1,4-dihydroxy-2-nonene, but had no effect on the rate of 4-HNE elimination. In contrast, cyanamide substantially inhibited the formation of 4-hydroxy-2-nonenoic acid, decreased the rate of 1,4-dihydroxy-2-nonene formation, but did not decrease the elimination rate of 4-HNE. Overall, these results support our previous observation that 4-HNE inhibits acetaldehyde metabolism and establish that ethanol and 4-HNE are metabolized through the same alcohol dehydrogenase- and aldehyde dehydrogenase-mediated pathways. These data continue to suggest that, as a consequence of enhanced lipid peroxidation resulting from chronic ethanol consumption, increased 4-HNE levels could compromise cellular elimination of ethanol-derived acetaldehyde and thus function in the potentiation of alcoholic liver fibrosis.

Co-Metabolism of Ethanol, Ethanol-Derived Acetaldehyde, and 4-Hydroxynonenal in Isolated Rat Hepatocytes

Our laboratory has previously reported on the ability of 4-hydroxynonenal (4-HNE), a primary product of lipid peroxidation, to inhibit acetaldehyde metabolism in isolated mouse liver mitochondria. The purpose of the present study is to determine whether the co-metabolism of ethanol and 4-HNE compromises the elimination of either substrate in isolated rat hepatocytes. Hepatocytes were isolated and incubated with ethanol and 4-HNE. Ethanol elimination and acetaldehyde accumulation were monitored by gas chromatography, whereas 4-HNE elimination and metabolite accumulation were measured by UV detection and reversed-phase HPLC at 202 nm. In the absence of 4-HNE, hepatocytes metabolized ethanol at an initial rate of 9.4 nmol/min/million cells. Ethanol elimination was moderately inhibited by the presence of 4-HNE. Accumulation of ethanol-derived acetaldehyde was not apparent in incubations with only ethanol. In contrast, in incubations containing both substrates, ethanol-derived acetaldehyde accumulation exceeded that observed in hepatocytes exposed only to ethanol and was proportional to the 4-HNE concentration in the incubations. In all instances, the rate of 4-HNE elimination was not compromised by the presence of ethanol. Accordingly, ethanol metabolism did not alter the oxidative or conjugative metabolism of 4-HNE. However, the reductive metabolism of 4-HNE was affected by the presence of ethanol, wherein accumulation of 1,4-dihydroxy-2-nonene increased >2-fold of that observed in incubations with only 4-HNE. To determine further if 4-HNE and ethanol are metabolized through the same metabolic pathways, cells were preincubated with either 4-methylpyrazole or cyanamide to inhibit alcohol dehydrogenase (E.C. 1.1.1.1.) and aldehyde dehydrogenase (E.C. 1.2.1.2.), respectively. Expectantly, 4-methylpyrazole blocked the formation of 1,4-dihydroxy-2-nonene, but had no effect on the rate of 4-HNE elimination. In contrast, cyanamide substantially inhibited the formation of 4-hydroxy-2-nonenoic acid, decreased the rate of 1,4-dihydroxy-2-nonene formation, but did not decrease the elimination rate of 4-HNE. Overall, these results support our previous observation that 4-HNE inhibits acetaldehyde metabolism and establish that ethanol and 4-HNE are metabolized through the same alcohol dehydrogenase- and aldehyde dehydrogenase-mediated pathways. These data continue to suggest that, as a consequence of enhanced lipid peroxidation resulting from chronic ethanol consumption, increased 4-HNE levels could compromise cellular elimination of ethanol-derived acetaldehyde and thus function in the potentiation of alcoholic liver fibrosis.

Daidzin inhibits mitochondrial aldehyde dehydrogenase and suppresses ethanol intake of Syrian golden hamsters.

Daidzin is the major active principle in extracts of radix puerariae, a traditional Chinese medication that suppresses the ethanol intake of Syrian golden hamsters. It is the first isoflavone recognized to have this effect. Daidzin is also a potent and selective inhibitor of human mitochondrial aldehyde dehydrogenase (ALDH-2). To establish a link between these two activities, we have tested a series of synthetic structural analogs of daidzin. The results demonstrate a direct correlation between ALDH-2 inhibition and ethanol intake suppression and raise the possibility that daidzin may, in fact, suppress ethanol intake of golden hamsters by inhibiting ALDH-2. Hamster liver contains not only mitochondrial ALDH-2 but also high concentrations of a cytosolic form, ALDH-1, which is a very efficient catalyst of acetaldehyde oxidation. Further, the cytosolic isozyme is completely resistant to daidzin inhibition. This unusual property of the hamster ALDH-1 isozyme accounts for the fact we previously observed that daidzin can suppress ethanol intake of this species without blocking acetaldehyde metabolism. Thus, the mechanism by which daidzin suppresses ethanol intake in golden hamsters clearly differs from that proposed for the classic ALDH inhibitor disulfiram. We postulate that a physiological pathway catalyzed by ALDH-2, so far undefined, controls ethanol intake of golden hamsters and mediates the antidipsotropic effect of daidzin.

Voluntary Alcohol Drinking and Acetaldehyde Metabolism in F 2 Hybrid Crosses of AA and ANA Rat Lines

Alcohol-preferring AA and alcohol-avoiding ANA rat lines differ in their acetaldehyde metabolism and this has been suggested to be one reason for their different ethanol drinking behavior. To study whether acetaldehyde accumulation is indeed associated with alcohol drinking behavior and to evaluate which enzymatic differences previously observed in these rat lines are of importance in this regard, we produced an F 2 generation from them. ADH and ALDH activities, and ALDH patterns were then assessed from these hybrids and correlated with their voluntary ethanol drinking and blood acetaldehyde concentrations measured during ethanol metabolism. A significant negative correlation between voluntary ethanol intake and blood acetaldehyde concentration was observed in F 2 females drinking less than 17% of the total fluid as ethanol. In F 2 males, hepatic microsomal high Km ALDH activities correlated negatively with blood acetaldehyde concentrations, indicating that low activity of this isoenzyme in ANA rats could be at least in part responsible for the accumulation of acetaldehyde in their blood. Finally, F 2 rats that possessed the cytosolic ALDH isoenzyme pattern most frequently found in the AA rat line drank significantly more ethanol than the animals with typical ANA pattern, suggesting that this polymorphism might also be relevant in the regulation of voluntary ethanol drinking although it is probably not associated with acetaldehyde metabolism.

Comparative Evaluation of Cytotoxicity and Metabolism of Four Aldehydes in Two Hepatoma Cell Lines

ABSTRACTThe metabolism of acetaldehyde (ACA), benzaldehyde (BA), propionaldehyde (PA) and valeraldehyde (VA) has been studied in two hepatoma cell lines, the rat HTC and mouse Hepa 1c1c7 cells. The cytotoxicity of the four aldehydes to these two cell lines has been compared. The end-points for evaluating cytotoxicity were 1) total macromolecular content (TMC) of confluent cultures, and 2) colony forming ability of dividing cells. These two assay systems had different sensitivities for the toxicity of aldehydes, probably due to different numbers of target cells.The activities of aldehyde dehydrogenases (NAD- and NADP-dependent, ALDH), alcohol dehydrogenase and aldehyde reductase were markedly greater in the HTC cell line compared to the Hepa 1c1c7 cell line, especially with BA as substrate.The cytotoxicities of aldehydes were generally stronger in the HTC cell line than in the Hepa 1c1c7 cell line, with the CF test. Particularly, BA was highly toxic to the HTC cells, which possessed the highest ALDH levels. Moreover, the treatment with (diethylamino)benzaldehyde, an ALDH inhibitor, completely abolished the toxicity of BA.Taken together, all these findings suggest that several cell lines expressing different aldehyde metabolizing activities could be used especially in the prescreening phase to distinguish the metabolism-dependent cytotoxic effects from the metabolism independent effects.

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.