Activities of human alcohol dehydrogenases in the metabolic pathways of ethanol and serotonin

Alcohol-Metabolizing Enzymes, Liver Diseases and Cancer

Alcohol is generally believed to be metabolized in the liver by alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and to a much lesser extent cytochrome P450 2E1 (CYP2E1) and other enzymes. Recent studies suggest that gut also play important roles in the promotion of alcohol metabolism. ADH, ALDH, and CYP2E1 have several polymorphisms that markedly impact alcohol metabolism. These alcohol-metabolizing enzymes not only affect alcohol-associated liver disease (ALD), but may also modulate the pathogenesis of other liver diseases and cancer in the absence of alcohol consumption. In this review, we discuss alcohol metabolism and the roles of alcohol-metabolizing enzymes in the pathogenesis of ALD, metabolic dysfunction-associated steatotic liver disease, metabolic dysfunction and alcohol-associated liver disease, viral hepatitis, and liver cancer. We also discuss how alcohol-metabolizing enzymes may affect endogenous ethanol production, and how ethanol metabolism in the gut affects liver disease and cancer. Directions for future research on the roles of alcohol-metabolizing enzymes in liver disease and cancer are also elaborated.

A genetically encoded tool to increase cellular NADH/NAD+ ratio in living cells

Impaired redox metabolism is a key contributor to the etiology of many diseases, including primary mitochondrial disorders, cancer, neurodegeneration and aging. However, mechanistic studies of redox imbalance remain challenging due to limited strategies that can perturb redox metabolism in various cellular or organismal backgrounds. Most studies involving impaired redox metabolism have focused on oxidative stress; consequently, less is known about the settings where there is an overabundance of NADH reducing equivalents, termed reductive stress. Here we introduce a soluble transhydrogenase from Escherichia coli (EcSTH) as a novel genetically encoded tool to promote reductive stress in living cells. When expressed in mammalian cells, EcSTH, and a mitochondrially targeted version (mitoEcSTH), robustly elevated the NADH/NAD+ ratio in a compartment-specific manner. Using this tool, we determined that metabolic and transcriptomic signatures of the NADH reductive stress are cellular background specific. Collectively, our novel genetically encoded tool represents an orthogonal strategy to promote reductive stress.

In vitro and in vivo metabolism of psilocybin's active metabolite psilocin

In vivo, psilocybin is rapidly dephosphorylated to psilocin which induces psychedelic effects by interacting with the 5-HT2A receptor. Psilocin primarily undergoes glucuronidation or conversion to 4-hydroxyindole-3-acetic acid (4-HIAA). Herein, we investigated psilocybin's metabolic pathways in vitro and in vivo, conducting a thorough analysis of the enzymes involved. Metabolism studies were performed using human liver microsomes (HLM), cytochrome P450 (CYP) enzymes, monoamine oxidase (MAO), and UDP-glucuronosyltransferase (UGT). In vivo, metabolism was examined using male C57BL/6J mice and human plasma samples. Approximately 29% of psilocin was metabolized by HLM, while recombinant CYP2D6 and CYP3A4 enzymes metabolized nearly 100% and 40% of psilocin, respectively. Notably, 4-HIAA and 4-hydroxytryptophol (4-HTP) were detected with HLM but not with recombinant CYPs. MAO-A transformed psilocin into minimal amounts of 4-HIAA and 4-HTP. 4-HTP was only present in vitro. Neither 4-HIAA nor 4-HTP showed relevant interactions at assessed 5-HT receptors. In contrast to in vivo data, UGT1A10 did not extensively metabolize psilocin in vitro. Furthermore, two putative metabolites were observed. N-methyl-4-hydroxytryptamine (norpsilocin) was identified in vitro (CYP2D6) and in mice, while an oxidized metabolite was detected in vitro (CYP2D6) and in humans. However, the CYP2D6 genotype did not influence psilocin plasma concentrations in the investigated study population. In conclusion, MAO-A, CYP2D6, and CYP3A4 are involved in psilocin's metabolism. The discovery of putative norpsilocin in mice and oxidized psilocin in humans further unravels psilocin's metabolism. Despite limitations in replicating phase II metabolism in vitro, these findings hold significance for studying drug-drug interactions and advancing research on psilocybin as a therapeutic agent.

The 5HTOL/5HIAA Ratio as a Biomarker of Alcohol Hangover

Assessment of the presence and severity of alcohol hangovers relies on the subjective method of self-report. Therefore, there is a need of adequate biomarkers that (1) correlate significantly with hangover severity, and (2) correspond to the level of hangover-related performance impairment objectively. In this naturalistic study, n = 35 social drinkers participated. Urine samples were obtained the morning after alcohol consumption and after an alcohol-free control day. Concentrations of 5-hydroxytryptophol (5-HTOL), 5-hydroxyindoleacetic acid (5-HIAA) and the 5-HTOL/5-HIAA ratio were determined. The results confirm previous findings that 5-HTOL and the 5HTOL/5-HIAA ratio are useful biomarkers of recent alcohol consumption. Significant correlations were found with the amount of alcohol consumed, total drink time, and estimated BAC. However, urine concentrations of 5-HTOL and 5-HIAA (and their ratio 5HTOL/5-HIAA) did not significantly correlate with hangover severity. In conclusion, urine 5-HTOL, 5-HIAA, and the 5HTOL/5-HIAA ratio cannot be considered to be suitable biomarkers of alcohol hangover.

Determination of serotonin metabolites in urine sample by liquid chromatography-mass spectrometry as biomarkers of recent alcohol intake: Implication for aircraft accident investigation

Background

Determination of ethanol levels in aircraft accident victims constitutes an important part of investigation. However, postmortem production of alcohol by microbial fermentation is known to interfere with the results. Distinguishing postmortem produced alcohols from antemortem ingested is very important in interpretation of results. Ratio of 5-hydroxytryptophol (5-HTOL) and 5-hydroxyindole-3-acetic acid (5-HIAA) metabolites of serotonin, has known to provide a convenient, rapid, and reliable solution as antemortem ethanol leads to an elevation in the 5-HTOL/5-HIAA ratio after ingestion of alcohol (5-HTOL/5-HIAA = >15 pm/nm).

Methods

Triple quadruple (QQQ) liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization positive mode has been used for development of single tube multiple reaction monitoring (MRM) method for simultaneous quantification of 5-HTOL and 5-HIAA in urine. Deglucuronidation of 5-HTOL glucuronide in urine by beta-glucuronidase followed by simple sample preparation has been adopted. Examination of the ratio on urine samples from 15 individuals after consumption of 60 and 90 ml of whiskey has been carried out at different time interval.

Results

A single method for analysis of both the analytes was developed with sensitivity of 50 ppb and recovery of around 80-90%. Examination of the ratio on urine samples revealed that the ratio was >15 in all groups consuming 60 ml and 90-ml whiskey up to 12 h after alcohol ingestion.

Conclusion

This is a unique highly sensitive single LC-MS method, which has been developed for simultaneous estimation of both 5-HTOL and 5-HIAA on same instrument for proving antemortem alcohol ingestion with high degree of sensitivity and specificity.

Alcohol Metabolizing Enzymes, Microsomal Ethanol Oxidizing System, Cytochrome P450 2E1, Catalase, and Aldehyde Dehydrogenase in Alcohol-Associated Liver Disease

Once ingested, most of the alcohol is metabolized in the liver by alcohol dehydrogenase to acetaldehyde. Two additional pathways of acetaldehyde generation are by microsomal ethanol oxidizing system (cytochrome P450 2E1) and catalase. Acetaldehyde can form adducts which can interfere with cellular function, leading to alcohol-induced liver injury. The variants of alcohol metabolizing genes encode enzymes with varied kinetic properties and result in the different rate of alcohol elimination and acetaldehyde generation. Allelic variants of these genes with higher enzymatic activity are believed to be able to modify susceptibility to alcohol-induced liver injury; however, the human studies on the association of these variants and alcohol-associated liver disease are inconclusive. In addition to acetaldehyde, the shift in the redox state during alcohol elimination may also link to other pathways resulting in activation of downstream signaling leading to liver injury.

Active immunization against serum alcohol dehydrogenase normalizes brain dopamine metabolism disturbed during chronic alcohol consumption

Chronic ethanol consumption in high doses is associated with constitutively elevated activity of the serum alcohol dehydrogenase I (ADH I) isoform, which demonstrates a high affinity not only for ethanol but also for a number of bioamine metabolites. Such excessive ADH activity is probably associated with disruptions in the metabolism of neurotransmitters (dopamine, serotonin, and norepinephrine) and subsequent long-term changes in the activity of their receptors. Ultimately, a stable depressive-like condition contributes to the development of patients' craving for ethanol intake, frequent disruptions during therapy, and low efficacy of treatment. We applied active immunization against ADH to investigate its efficacy in the reduction of excessive serum ADH activity and regulation of ethanol consumption by chronically ethanol-fed Wistar rats (15% ethanol, 4 months, free-choice method), and we analyzed its ability to influence the levels of bioamines in the brain. Immunization (2 injections, 2-week intervals) was performed using a combination of recombinant horse ADH isozyme as an antigen and 2% aluminum hydroxide-based adjuvant. The efficacy of immunization was demonstrated by the production of high titers of ADH-specific antibodies, which was consistent with the significantly reduced ADH activity in the serum of chronically ethanol-fed rats. On the 26th day after the first vaccine injection, we registered significantly lower levels of alcohol consumption compared to ethanol-fed control animals, and the difference reached 16% on the 49th day of the experiment. These observations were accompanied by data that showed reduced levels of ethanol preference in immunized rats. Chronic alcohol drinking led to a decrease in dopamine and DOPAL (a direct dopamine metabolite and a high-affinity ADH substrate) levels in the striatum,while immunization neutralized this effect. Additionally, we observed that inhibition of serum ADH activity caused a decrease in peak dopamine levels during acute alcohol intake in chronically ethanol-fed rats during ethanol withdrawal that was associated with reduced tyrosine hydroxylase activity in the striatum. The obtained data suggest a significant contribution of ADH to the changes in neurotransmitter systems during chronic alcohol consumption and make available new prospects for developing innovative strategies for treatment of excessive alcohol intake.

Association between alcohol dehydrogenase-2 gene polymorphism and esophageal cancer risk: a meta-analysis

BACKGROUND

It has been shown that gene polymorphisms may play an important role in the carcinogenesis of esophageal cancer. This study is to investigate the role of alcohol dehydrogenase 1B (ADH1B) gene Arg47His polymorphism in esophageal cancer susceptibility.

METHODS

Case-control studies published between January 2000 and June 2015 were searched to retrieve relevant articles. The pooled odds ratio (OR) and 95 % confidence interval (CI) were employed to calculate the strength of association.

RESULTS

A total of 23 relevant articles were finally selected for the analysis, including 9338 esophageal cancer patients and 14,896 matched controls. Overall, we found that the 47His allele was significant associated with the decreased risk of esophageal cancer when compared with the 47Arg allele in total populations (A vs. G: OR = 0.67, 95 % CI = 0.59-0.76, P < 0.00001). This protective relationship was observed under other genetic models as well (P < 0.00001). Subgroup analysis by ethnicity showed that ADH1B Arg47His variant was associated with the decreased esophageal cancer risk under all the genetic models (P < 0.00001) among Asians, especially in Chinese and Japanese; while in non-Asians, no significant correlation was detected in any genetic models (P > 0.05). Furthermore, Arg/Arg genotype of ADH1B Arg47His variant combined with drinking, smoking and males appeared to show a high risk in patients with esophageal cancer.

CONCLUSIONS

Our results suggested that ADH1B gene Arg47His variant was associated with the decreased esophageal cancer risk. Genetic-environmental interaction should be further considered in the future researches.

Effects of methylmercury and alcohol exposure in Drosophila melanogaster: Potential risks in neurodevelopmental disorders

Extensive evidence suggests the role of oxidative stress in autism and other neurodevelopmental disorders. In this study, we investigated whether methylmercury (MeHg) and/or alcohol exposure has deleterious effects in Drosophila melanogaster (fruit flies). A diet containing different concentrations of MeHg in Drosophila induced free radical generation and increased lipid peroxidation (markers of oxidative stress) in a dose-dependent manner. This effect of MeHg on oxidative stress was enhanced by further exposure to alcohol. It was observed that alcohol alone could also induce free radical generation in flies. After alcohol exposure, MeHg did not affect the immobilization of flies, but it increased the recovery time in a concentration-dependent manner. MeHg significantly inhibited the activity of alcohol dehydrogenase (ADH) in a dose-dependent manner. Linear regression analysis showed a significant negative correlation between ADH activity and recovery time upon alcohol exposure in the flies fed a diet with MeHg. This relationship between ADH activity and recovery time after alcohol exposure was confirmed by adding 4-methyl pyrazole (an inhibitor of ADH) to the diet for the flies. These results suggest that consumption of alcohol by pregnant mothers who are exposed to MeHg may lead to increased oxidative stress and to increased length of time for alcohol clearance, which may have a direct impact on the development of the fetus, thereby increasing the risk of neurodevelopmental disorders.

Association between common alcohol dehydrogenase gene (ADH) variants and schizophrenia and autism

Humans express at least seven alcohol dehydrogenase (ADH) isoforms that are encoded by ADH gene cluster (ADH7-ADH1C-ADH1B-ADH1A-ADH6-ADH4-ADH5) at chromosome 4. ADHs are key catabolic enzymes for retinol and ethanol. The functional ADH variants (mostly rare) have been implicated in alcoholism risk. In addition to catalyzing the oxidation of retinol and ethanol, ADHs may be involved in the metabolic pathways of several neurotransmitters that are implicated in the neurobiology of neuropsychiatric disorders. In the present study, we comprehensively examined the associations between common ADH variants [minor allele frequency (MAF) >0.05] and 11 neuropsychiatric and neurological disorders. A total of 50,063 subjects in 25 independent cohorts were analyzed. The entire ADH gene cluster was imputed across these 25 cohorts using the same reference panels. Association analyses were conducted, adjusting for multiple comparisons. We found 28 and 15 single nucleotide polymorphisms (SNPs), respectively, that were significantly associated with schizophrenia in African-Americans and autism in European-Americans after correction by false discovery rate (FDR) (q < 0.05); and 19 and 6 SNPs, respectively, that were significantly associated with these two disorders after region-wide correction by SNPSpD (8.9 × 10(-5) ≤ p ≤ 0.0003 and 2.4 × 10(-5) ≤ p ≤ 0.0003, respectively). No variants were significantly associated with the other nine neuropsychiatric disorders, including alcohol dependence. We concluded that common ADH variants conferred risk for both schizophrenia in African-Americans and autism in European-Americans.

The ADH1B and DRD2 gene polymorphism may modify the protective effect of the ALDH2 gene against heroin dependence

Understanding the influences of genes involved in dopamine and serotonin metabolism, such as the aldehyde dehydrogenase 2 (ALDH2) and alcohol dehydrogenase 1B (ADH1B) genes, is critical for understanding addictive behavior. In addition, dopamine D2 receptor (DRD2) gene may also interact with the dopamine metabolizing genes and link to addiction. Therefore, we investigated the association between the ALDH2, ADH1B and DRD2 polymorphisms and heroin dependence. Heroin-dependent Han Chinese patients (n=304) and healthy controls (n=335) were recruited. Genotypes of ALDH2, ADH1B and DRD2 polymorphisms were analyzed using a polymerase chain reaction with restriction fragment length polymorphism. The frequency of the ALDH2*1/*1 genotype was significantly lower in heroin-dependent patients than in controls, but the frequency of ADH1B and DRD2 genotypes was not significantly different. Further stratification of the ALDH2 gene with the ADH1B gene showed that the protective effect of ALDH2*1/*1 existed only in patients who also carried the ADH1B*1/*1 and ADH1B*1/*2 genotype. Logistic regression analysis showed a significant interaction between ALDH2 and ADH1B (P=0.022) and DRD2, ALDH2 and ADH1B in patients (P=0.037). The ALDH2*1/*1, ADH1B*1/*1, and ADH1B*1/*2 genotypes may interact and protect their carriers against heroin dependence and the protective effect may be varied by the DRD2 gene polymorphism. We conclude that the protective effect of the ALDH2 polymorphism against heroin dependence may be modified by the ADH1B and DRD2 polymorphism.

Phytoconstituents and therapeutic uses of Rheum emodi wall. ex Meissn

Rhubarb (Rheum emodi, family Polygonaceae) has been traditionally used as diuretic, liver stimulant, purgative/cathartic, stomachic, anticholesterolaemic, antitumour, antiseptic and tonic. A number of anthraquinone derivatives including emodin, aloe-emodin, physcion, chrysophanol, rhein, emodin glycoside and chrysophanol glycoside occur as the main chemical constituents. In the past few years, new components such as sulfemodin 8-O-β-d-glucoside, revandchinone-1, revandchinone-2, revandchinone-3, revandchinone-4, 6-methyl-rhein and 6-methyl aloe-emodin have been reported from the same species. Anthraquinone derivatives show evidence of antifungal, anti-microbial, anti-Parkinson’s, anti-proliferative, immuno-enhancing, antiviral and antioxidant activities. This review covers published work on botany, chemistry and therapeutic uses of different components from rhubarb.

Behavioral outcomes of monoamine oxidase deficiency: preclinical and clinical evidence

Monoamine oxidase (MAO) isoenzymes A and B are mitochondrial-bound proteins, catalyzing the oxidative deamination of monoamine neurotransmitters as well as xenobiotic amines. Although they derive from a common ancestral progenitor gene, are located at X-chromosome and display 70% structural identity, their substrate preference, regional distribution, and physiological role are divergent. In fact, while MAO-A has high affinity for serotonin and norepinephrine, MAO-B primarily serves the catabolism of 2-phenylethylamine (PEA) and contributes to the degradation of other trace amines and dopamine. Convergent lines of preclinical and clinical evidence indicate that variations in MAO enzymatic activity--due to either genetic or environmental factors--can exert a profound influence on behavioral regulation and play a role in the pathophysiology of a large spectrum of mental and neurodegenerative disorders, ranging from antisocial personality disorder to Parkinson's disease. Over the past few years, numerous advances have been made in our understanding of the phenotypical variations associated with genetic polymorphisms and mutations of the genes encoding for both isoenzymes. In particular, novel findings on the phenotypes of MAO-deficient mice are highlighting novel potential implications of both isoenzymes in a broad spectrum of mental disorders, ranging from autism and anxiety to impulse-control disorders and ADHD. These studies will lay the foundation for future research on the neurobiological and neurochemical bases of these pathological conditions, as well as the role of gene × environment interactions in the vulnerability to several mental disorders.

Hepatoprotective activity of Sapindus mukorossi and Rheum emodi extracts: In vitro and in vivo studies

AIM: To study the hepatoprotective capacity of Sapindus mukorossi (S. mukorossi) and Rheum emodi (R. emodi) extracts in CCl₄ treated male rats.

METHODS: The dried powder of S. mukorossi and R. emodi was extracted successively with petroleum ether, benzene, chloroform, and ethanol and concentrated in vacuum. Primary rat hepatocyte monolayer cultures were used for in vitro studies. In vivo, the hepatoprotective capacity of the extract of the fruit pericarp of S. mukorossi and the rhizomes of R. emodi was analyzed in liver injured CCl₄-treated male rats.

RESULTS: In vitro: primary hepatocytes monolayer cultures were treated with CCl₄ and extracts of S. mukorossi & R. emodi. A protective activity could be demonstrated in the CCl₄ damaged primary monolayer culture. In vivo: extracts of the fruit pericarp of S. mukorossi (2.5 mg/mL) and rhizomes of R. emodi (3.0 mg/mL) were found to have protective properties in rats with CCl₄ induced liver damage as judged from serum marker enzyme activities.

CONCLUSION: The extracts of S. mukorossi and R. emodi do have a protective capacity both in vitro on primary hepatocytes cultures and in in vivo in a rat model of CCl₄ mediated liver injury.

Mechanistic considerations for formaldehyde-induced bronchoconstriction involving S-nitrosoglutathione reductase

Inhalation of formaldehyde vapor has long been suspected of producing airway pathophysiology such as asthma and hyperresponsivity, presumably via irritant mechanisms. Recent studies on asthma and airway biology implicate changes in nitric oxide (NO) disposition in the adverse effects of formaldehyde, principally because enzymatic reduction of the endogenous bronchodilator S-nitrosoglutathione (GSNO) is dependent upon GSNO reductase (formally designated as alcohol dehydrogenase-3, ADH3), which also serves as the primary enzyme for cellular detoxification of formaldehyde. Considering recent evidence that regulation of bronchodilators like GSNO might play a more important role in asthma than inflammation per se, formaldehyde also needs to be considered as influencing ADH3-mediated GSNO catabolism. This is due to changes in ADH3 cofactors and thiol redox state among several potential mechanisms. Data suggest that deregulation of GSNO turnover provides a plausible, enzymatically based mechanism by which formaldehyde might exacerbate asthma and induce bronchoconstriction.

Neurotoxicity and metabolism of the catecholamine-derived 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde: the role of aldehyde dehydrogenase

Aldehydes are highly reactive molecules formed during the biotransformation of numerous endogenous and exogenous compounds, including biogenic amines. 3,4-Dihydroxyphenylacetaldehyde is the aldehyde metabolite of dopamine, and 3,4-dihydroxyphenylglycolaldehyde is the aldehyde metabolite of both norepinephrine and epinephrine. There is an increasing body of evidence suggesting that these compounds are neurotoxic, and it has been recently hypothesized that neurodegenerative disorders may be associated with increased levels of these biogenic aldehydes. Aldehyde dehydrogenases are a group of NAD(P)+ -dependent enzymes that catalyze the oxidation of aldehydes, such as those derived from catecholamines, to their corresponding carboxylic acids. To date, 19 aldehyde dehydrogenase genes have been identified in the human genome. Mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria, and pyridoxine-dependent seizures, most of which are characterized by neurological abnormalities. Several pharmaceutical agents and environmental toxins are also known to disrupt or inhibit aldehyde dehydrogenase function. It is, therefore, possible to speculate that reduced detoxification of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde from impaired or deficient aldehyde dehydrogenase function may be a contributing factor in the suggested neurotoxicity of these compounds. This article presents a comprehensive review of what is currently known of both the neurotoxicity and respective metabolism pathways of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde with an emphasis on the role that aldehyde dehydrogenase enzymes play in the detoxification of these two aldehydes.

Comparison of self-reported alcohol intake with the urinary excretion of 5-hydroxytryptophol:5-hydroxyindole-3-acetic acid, a biomarker of recent alcohol intake

Under-reporting of alcohol intake has been frequently reported. However, due to the lack of an objective reference method, e.g. a biomarker, information about the extent of under-reporting of alcohol intake obtained with dietary assessment instruments is not available. The objective of this study was to compare reported alcohol intake data derived from a 24 h recall with a biomarker of recent alcohol intake, the urinary excretion of 5-hydroxytryptophol (5-HTOL):5-hydroxyindole-3-acetic acid (5-HIAA). Embedded into the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study, Germany, a validation study that collected 24 h recall data and 24 h urine samples was conducted. Cohort study participants (n107) volunteered to participate in this validation study. Among them were five subjects who reported no consumption of alcoholic beverages but had a 5-HTOL:5-HIAA ratio that indicated recent alcohol intake when the clinical cut-off point was taken as a judging criterion. After exclusion of these under-reporters, the Pearson's correlation coefficient between reported alcohol intake and the 5-HTOL:5-HIAA ratio was 0.92 (P<0.0001). Except for low alcohol intake of <0.1 g/kg body mass, a significant increase in 5-HTOL:5-HIAA excretion was observed with increasing amounts of alcohol intake. In conclusion, the 5-HTOL:5-HIAA excretion ratio appears to be a valuable quantitative biomarker of recent alcohol consumption. Denial of alcohol intake can be detected, but for the quantification of under-reporting of alcohol intake 24 h reference data are not yet available. With these data at hand, however, 5-HTOL:5-HIAA could become a biomarker for validation purposes in nutritional epidemiology.

Multiple ADH genes modulate risk for drug dependence in both African- and European-Americans

Drug dependence (DD) is commonly co-morbid with alcohol dependence (AD). Many studies have also shown common genetic risk factors for these disorders. We previously reported associations of AD with seven alcohol dehydrogenase (ADH) genes. The present study examines the relationship between these genes and DD. We genotyped 16 markers within the ADH gene cluster and 38 unlinked ancestry-informative markers in a case-control sample of 718 individuals. All markers were consistent with Hardy-Weinberg equilibrium in controls, but some markers showed Hardy-Weinberg disequilibrium in cases (minimal P = 0.002). Genotypes of many markers were associated with DD, both before and after controlling for admixture effects (minimal P < 1.0 x 10(-6)). Diplotype trend regression analysis showed that ADH5 and ADH6 genotypes, and diplotypes at ADH1A, ADH1B, ADH1C and ADH7 (minimal P = 0.002), were associated with DD in European-Americans and/or African-Americans. This first report of an allelic association of these loci with DD provides new insight into the mechanism of genetic risk for DD. These findings, obtained using a series of powerful and reliable analytic methods, may also help to explain the high rate of co-morbidity between AD and DD.

Genome scans and gene expression microarrays converge to identify gene regulatory loci relevant in schizophrenia

Multiple linkage regions have been reported in schizophrenia, and some appear to harbor susceptibility genes that are differentially expressed in postmortem brain tissue derived from unrelated individuals. We combined traditional genome-wide linkage analysis in a multiplex family with lymphocytic genome-wide expression analysis. A genome scan suggested linkage to a chromosome 4q marker (D4S1530, LOD 2.17, theta = 0) using a dominant model. Haplotype analysis using flanking microsatellite markers delineated a 14 Mb region that cosegregated with all those affected. Subsequent genome-wide scan with SNP genotypes supported the evidence of linkage to 4q33-35.1 (LOD = 2.39) using a dominant model. Genome-wide microarray analysis of five affected and five unaffected family members identified two differentially expressed genes within the haplotype AGA and GALNT7 (aspartylglucosaminidase and UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyltransferase 7) with nominal significance; however, these genes did not remain significant following analysis of covariance. We carried out genome-wide linkage analyses between the quantitative expression phenotype and genetic markers. AGA expression levels showed suggestive linkage to multiple markers in the haplotype (maximum LOD = 2.37) but to no other genomic region. GALNT7 expression levels showed linkage to regulatory loci at 4q28.1 (maximum LOD = 3.15) and in the haplotype region at 4q33-35.1 (maximum LOD = 2.37). ADH1B (alcohol dehydrogenase IB) was linked to loci at 4q21-q23 (maximum LOD = 3.08) and haplotype region at 4q33-35.1 (maximum LOD = 2.27). Seven differentially expressed genes were validated with RT-PCR. Three genes in the 4q33-35.1 haplotype region were also differentially expressed in schizophrenia in postmortem dorsolateral prefrontal cortex: AGA, HMGB2, and SCRG1. These results indicate that combining differential gene expression with linkage analysis may help in identifying candidate genes and potential regulatory sites. Moreover, they also replicate recent findings of complex trans- and cis- regulation of genes.

Aldehyde sources, metabolism, molecular toxicity mechanisms, and possible effects on human health

Aldehydes are organic compounds that are widespread in nature. They can be formed endogenously by lipid peroxidation (LPO), carbohydrate or metabolism ascorbate autoxidation, amine oxidases, cytochrome P-450s, or myeloperoxidase-catalyzed metabolic activation. This review compares the reactivity of many aldehydes towards biomolecules particularly macromolecules. Furthermore, it includes not only aldehydes of environmental or occupational concerns but also dietary aldehydes and aldehydes formed endogenously by intermediary metabolism. Drugs that are aldehydes or form reactive aldehyde metabolites that cause side-effect toxicity are also included. The effects of these aldehydes on biological function, their contribution to human diseases, and the role of nucleic acid and protein carbonylation/oxidation in mutagenicity and cytotoxicity mechanisms, respectively, as well as carbonyl signal transduction and gene expression, are reviewed. Aldehyde metabolic activation and detoxication by metabolizing enzymes are also reviewed, as well as the toxicological and anticancer therapeutic effects of metabolizing enzyme inhibitors. The human health risks from clinical and animal research studies are reviewed, including aldehydes as haptens in allergenic hypersensitivity diseases, respiratory allergies, and idiosyncratic drug toxicity; the potential carcinogenic risks of the carbonyl body burden; and the toxic effects of aldehydes in liver disease, embryo toxicity/teratogenicity, diabetes/hypertension, sclerosing peritonitis, cerebral ischemia/neurodegenerative diseases, and other aging-associated diseases.

Genetic time-series analysis identifies a major QTL for in vivo alcohol metabolism not predicted by in vitro studies of structural protein polymorphism at the ADH1B or ADH1C loci

After ingestion of a standardized dose of ethanol, alcohol concentrations were assessed, over 3.5 hours from blood (six readings) and breath (10 readings) in a sample of 412 MZ and DZ twins who took part in an Alcohol Challenge Twin Study (ACTS). Nearly all participants were subsequently genotyped on two polymorphic SNPs in the ADH1B and ADH1C loci known to affect in vitro ADH activity. In the DZ pairs, 14 microsatellite markers covering a 20.5 cM region on chromosome 4 that includes the ADH gene family were assessed, Variation in the timed series of autocorrelated blood and breath alcohol readings was studied using a bivariate simplex design. The contribution of a quantitative trait locus (QTL) or QTL's linked to the ADH region was estimated via a mixture of likelihoods weighted by identity-by-descent probabilities. The effects of allelic substitution at the ADH1B and ADH1C loci were estimated in the means part of the model simultaneously with the effects sex and age. There was a major contribution to variance in alcohol metabolism due to a QTL which accounted for about 64% of the additive genetic covariation common to both blood and breath alcohol readings at the first time point. No effects of the ADH1B*47His or ADH1C*349Ile alleles on in vivo metabolism were observed, although these have been shown to have major effects in vitro. This implies that there is a major determinant of variation for in vivo alcohol metabolism in the ADH region that is not accounted for by these polymorphisms. Earlier analyses of these data suggested that alcohol metabolism is related to drinking behavior and imply that this QTL may be protective against alcohol dependence.

Determination of urinary 5-hydroxytryptophol glucuronide by liquid chromatography–mass spectrometry

5-Hydroxytryptophol glucuronide (GTOL) is the major excretion form of 5-hydroxytryptophol (5-HTOL), a minor serotonin metabolite under normal conditions. Because the concentration of 5-HTOL is markedly increased following consumption of alcohol, measurement of 5-HTOL is used as a sensitive biomarker for detection of recent alcohol intake. This study describes the development and evaluation of a liquid chromatography-electrospray ionization mass spectrometry (LC-MS) procedure for direct quantification of GTOL in human urine. Deuterium labelled GTOL (GTOL-(2)H(4)) was used as internal standard. GTOL was isolated from urine by solid-phase extraction on a C(18) cartridge prior to injection onto a gradient eluted Hypurity C(18) reversed-phase HPLC column. The detection limit of the method was 2.0 nmol/L and the measuring range 6-8500 nmol/L. The intra- and inter-assay coefficients of variation were <3.5% (n=10) and <6.0% (n=9), respectively. The new LC-MS method was highly correlated with an established GC-MS method for urinary 5-HTOL (r(2)=0.99, n=70; mean 5-HTOL/GTOL ratio=1.10). This is the first direct assay for quantification of GTOL in urine. The method is suitable for routine application.

Functional analysis of the ALD gene family of Saccharomyces cerevisiae during anaerobic growth on glucose: the NADP+-dependent Ald6p and Ald5p isoforms play a major role in acetate formation

In Saccharomyces cerevisiae, acetate is formed by acetaldehyde dehydrogenase (ACDH), a key enzyme of the pyruvate dehydrogenase (PDH) bypass, which fulfils the essential task of generating acetyl-CoA in the cytosol. The role of the five members of the ACDH family (ALD genes) was investigated during anaerobic growth on glucose. Single and multiple ald Delta mutants were generated in the wine-yeast-derived V5 and laboratory CEN.PK strains and analysed under standard (YPD 5 % glucose) and wine (MS 20 % glucose) fermentation conditions. The deletion of ALD6 and ALD5 decreased acetate formation in both strains, demonstrating for the first time that the mitochondrial Ald5p isoform is involved in the biosynthesis of acetate during anaerobic growth on glucose. Acetate production of the ald4 Delta mutant was slightly decreased in the CEN.PK strain during growth on YPD only. In contrast, the deletion of ALD2 or ALD3 had no effect on acetate production. The absence of Ald6p was compensated by the mitochondrial isoforms and this involves the transcriptional activation of ALD4. Consistent with this, growth retardation was observed in ald6 Delta ald4 Delta, and this effect was amplified by the additional deletion of ALD5. A ald Delta null mutant, devoid of ACDH activity, was viable and produced similar levels of acetate to the ald6 Delta ald4 Delta ald5 Delta strain, excluding a role of Ald2p and Ald3p. Thus, acetate is mainly produced by the cytosolic PDH bypass via Ald6p and by a mitochondrial route involving Ald5p. An unknown alternative pathway can compensate for the loss of Ald6p, Ald4p and Ald5p.

Evaluation of 5-hydroxytryptophol and other endogenous serotonin (5-hydroxytryptamine) analogs as substrates for UDP-glucuronosyltransferase 1A6

Serotonin is a specific in vitro substrate for human UDP-glucuronosyltransferase (UGT) 1A6. In this study, the contribution of UGT1A6 to the glucuronidation of endogenous structural analogs of serotonin, including 5-hydroxytryptophol, N-acetylserotonin, and 6-hydroxymelatonin, was evaluated using available recombinant human UGT isoforms, human liver microsomes, and liver microsomes from animals that do not express functional UGT1A6 (Gunn rats and cats). Only UGT1A6 and UGT1A9 were found to glucuronidate 5-hydroxytryptophol at a concentration of 2 mM, although the glucuronidation rate with UGT1A6 was over 10 times that of UGT1A9. K(m) values for human liver microsomes (156, 141, and 134 microM) were most similar to that of expressed UGT1A6 (135 microM) but vastly different from that of UGT1A9 (3674 microM). 5-Hydroxytryptophol glucuronidation by human liver microsomes (n = 54) correlated well with serotonin glucuronidation (R(s) = 0.83) and UGT1A6 protein content (R(s) = 0.85). 5-Hydroxytryptophol also competitively inhibited serotonin glucuronidation by human liver microsomes (K(i) = 291 microM) and UGT1A6 (K(i) = 200 microM). N-acetylserotonin was glucuronidated most extensively by UGT1A6, although UGT1A9 and UGT1A10 showed moderate catalysis. 6-Hydroxymelatonin was glucuronidated largely by UGT1A9 and UGT1A10 but not at all by UGT1A6. Gunn rat liver glucuronidation rates for serotonin, 5-hydroxytryptophol, N-acetylserotonin, and 6-hydroxymelatonin were 11, 5, 32, and 3%, respectively, of that of normal rat liver. Cat liver microsomes did not glucuronidate serotonin, whereas relatively low activities were observed for the other indole substrates. In conclusion, these results indicate that human UGT1A6 plays a predominant role in the glucuronidation of 5-hydroxytryptophol and N-acetylserotonin, whereas 6-hydroxymelatonin is not a substrate for this enzyme.

Accurate assignment of ethanol origin in postmortem urine: liquid chromatographic–mass spectrometric determination of serotonin metabolites

Toxicological examination of fatal aviation accident victims routinely includes analysis of ethanol levels. However, distinguishing between antemortem ingestion and postmortem microbial formation complicates all positive ethanol results. Development of a single analytical approach to determine concentrations of 5-hydroxytryptophol (5-HTOL) and 5-hydroxyindole-3-acetic acid (5-HIAA), two well-known metabolites of serotonin, has provided a convenient, rapid and reliable solution to this problem. Antemortem ethanol leads to an elevation in the 5-HTOL/5-HIAA ratio for 11-19 h after acute ingestion. The liquid-liquid extracts of postmortem urine samples were subjected to liquid chromatography-mass spectrometry (LC-MS) for the simultaneous quantitation of these two analytes, yielding detection limits of 0.1 ng/ml for each. Examination of the 5-HTOL/5-HIAA ratio was undertaken for 44 urine samples known to be antemortem ethanol-positive or antemortem ethanol-negative. Recent ethanol ingestion was conveniently and accurately separated using a 5-HTOL/5-HIAA ratio of 15 pmol/nmol, a value previously suggested using human volunteers. All 21 ethanol-negative postmortem samples were below this cutoff, while all 23 ethanol-positive postmortem samples were above this cutoff. Thus, we recommend the employment of this cutoff value, established using this straightforward LC-MS procedure, to confirm or deny recent antemortem ethanol ingestion in postmortem urine samples.

Biological markers in alcoholism

Alcohol biomarkers include tests indicative of acute or chronic alcohol consumption (state markers), and markers of a genetic predisposition to develop alcohol dependence after chronic exposure (trait markers). While a comprehensive trait marker for alcohol dependence has not been identified, a number of successful state markers for monitoring drinking status are used clinically. These tests provide direct or indirect ways to estimate the amounts of alcohol consumed and the duration of ingestion, and to detect any harmful effects on body functions resulting from long-term misuse. The most obvious method to prove recent drinking is by demonstrating the presence of ethanol in body fluids or breath, but, because ethanol is cleared fairly rapidly from the body, this method is limited to detect only very recent drinking. Measurement of urinary 5-hydroxytryptophol or ethyl glucuronide provide more sensitive methods to disclose recent drinking, because their washout constants are much longer than for ethanol. The liver functions test (GGT, AST and ALT in serum) and the mean corpuscular volume of erythrocytes (MCV) are among the standard diagnostic tools used to identify chronic alcohol exposure. The main disadvantage with these measures is that they have low sensitivity for recent excessive intake, and that raised levels may result from several causes besides heavy drinking, implying a low specificity for alcohol. Carbohydrate-deficient transferrin (CDT), which refers to changes in the carbohydrate composition of serum transferrin, is a more specific marker for identifying excessive alcohol consumption and monitoring abstinence during outpatient treatment. The alcohol biomarkers improves knowledge of drinking patterns in both individuals and populations, and they are also valuable tools for the objective evaluation of treatment efforts. Alcohol markers have, for example, found uses in early identification of at-risk and harmful drinking, and they help to monitor abstinence and relapse in response to outpatient treatment.

5-hydroxytryptophol as a marker for recent alcohol intake

AIMS

To review the mechanism behind the alcohol-induced shift in serotonin metabolism, and the use of urinary 5-hydroxytryptophol (5-HTOL) as a biochemical marker of acute alcohol consumption.

BACKGROUND

The serotonin metabolite 5-HTOL is a normal, minor constituent of urine and is excreted mainly in conjugated form with glucuronic acid. The formation of 5-HTOL increases dramatically after alcohol intake, due to a metabolic interaction, and the elevated urinary excretion remains for some time (>5-15 hours depending on dose) after ethanol has been eliminated. This biochemical effect can be used for detection of recent alcohol intake.

RESULTS

5-HTOL is determined by the gas chromatography-mass spectrometry (GC-MS) or liquid chromatography and mass spectrometry (LC-MS) techniques. A new ELISA method for 5-HTOL glucuronide provides a promising clinical assay. The most robust way to use the marker is by measuring the ratio of 5-HTOL to 5-hydroxyindoleacetic acid, because this compensates for urine dilution and dietary intake of serotonin. 5-HTOL is a very sensitive and specific indicator of recent alcohol consumption and, as such, a valuable complement to self-report. In clinical use, 5-HTOL is effective for monitoring lapses into drinking during out-patient treatment and for objective evaluation of treatment efforts. Other applications include detection of high-risk patients in elective surgery, monitoring of disulfiram treatment and a method to rule out artefactual ethanol formation in forensic toxicology. 5-HTOL can also be used as a sensitive reference method for validation of self-report data in clinical alcohol research.

CONCLUSIONS

An elevated urinary 5-HTOL level can serve as a sensitive and reliable marker for recent alcohol intake with a number of clinical and forensic applications.

The effect of metal ions on the binding of ethanol to human alcohol dehydrogenase beta2beta2

Molecular docking simulations were performed in this study to investigate the importance of both structural and catalytic zinc ions in the human alcohol dehydrogenase beta(2)beta(2) on substrate binding. The structural zinc ion is not only important in maintaining the structural integrity of the enzyme, but also plays an important role in determining substrate binding. The replacement of the catalytic zinc ion or both catalytic and structural zinc ions with Cu(2+) results in better substrate binding affinity than with the wild-type enzyme. The width of the bottleneck formed by L116 and V294 in the substrate binding pocket plays an important role for substrate entrance. In addition, unfavorable contacts between the substrate and T48 and F93 prevent the substrate from moving too close to the metal ion. The optimal binding position occurs between 1.9 and 2.4 A from the catalytic metal ion.

Reduction of S-nitrosoglutathione by human alcohol dehydrogenase 3 is an irreversible reaction as analysed by electrospray mass spectrometry

Human alcohol dehydrogenase 3/glutathione-dependent formaldehyde dehydrogenase was shown to rapidly and irreversibly catalyse the reductive breakdown of S-nitrosoglutathione. The steady-state kinetics of S-nitrosoglutathione reduction was studied for the wild-type and two mutated forms of human alcohol dehydrogenase 3, mutations that have previously been shown to affect the oxidative efficiency for the substrate S-hydroxymethylglutathione. Wild-type enzyme readily reduces S-nitrosoglutathione with a kcat/Km approximately twice the kcat/Km for S-hydroxymethylglutathione oxidation, resulting in the highest catalytic efficiency yet identified for a human alcohol dehydrogenase. In a similar manner as for S-hydroxymethylglutathione oxidation, the catalytic efficiency of S-nitrosoglutathione reduction was significantly decreased by replacement of Arg115 by Ser or Lys, supporting similar substrate binding. NADH was by far a better coenzyme than NADPH, something that previously has been suggested to prevent reductive reactions catalysed by alcohol dehydrogenases through the low cytolsolic NADH/NAD+ ratio. However, the major products of S-nitrosoglutathione reduction were identified by electrospray tandem mass spectrometry as glutathione sulfinamide and oxidized glutathione neither of which, in their purified form, served as substrate or inhibitor for the enzyme. Hence, the reaction products are not substrates for alcohol dehydrogenase 3 and the overall reaction is therefore irreversible. We propose that alcohol dehydrogenase 3 catalysed S-nitrosoglutathione reduction is of physiological relevance in the metabolism of NO in humans.

The mammalian alcohol dehydrogenases interact in several metabolic pathways

Mammalian alcohol dehydrogenases (ADHs), including ADH1-ADH5/6, interact extensively in the oxidation and reduction of alcohols and aldehydes. ADH1 and ADH2 are involved in several metabolic pathways besides the oxidation of ethanol and have also been shown to be involved in drug transformations. The ADH2 enzymes show further complexity among the species, e.g. in enzymatic characteristics where the rodent forms essentially lack ethanol-oxidizing capacity. ADH3 (glutathione-dependent formaldehyde dehydrogenase) has been shown to catalyze the reductive breakdown of S-nitrosoglutathione, indicating involvement in nitric oxide metabolism. Mass spectrometry identified the major enzymatic product as glutathione sulfinamide. This reductive breakdown directly interferes with the formaldehyde scavenging that has been proposed to be the physiological action of ADH3. The human ADH5 and rodent ADH6 seem to be the corresponding enzymes due to their similar behavior. None of these latter ADHs have so far been assigned to any function. They can be expressed as recombinant proteins but no enzymatic activity has been detected.

The metabolic activation of abacavir by human liver cytosol and expressed human alcohol dehydrogenase isozymes

Abacavir (ZIAGEN) is a reverse transcriptase inhibitor marketed for the treatment of HIV-1 infection. A small percentage of patients experience a hypersensitivity reaction indicating immune system involvement and bioactivation. A major route of metabolism for abacavir is oxidation of a primary betagamma unsaturated alcohol to a carboxylic acid via an aldehyde intermediate. This process was shown to be mediated in vitro by human cytosol and NAD, and subsequently the alphaalpha and gamma2gamma2 human isoforms of alcohol dehydrogenase (ADH). The alphaalpha isoform effected two sequential oxidation steps to form the acid metabolite and two isomers, qualitatively reflective of in vitro cytosolic profiles. The gamma2gamma2 isozyme generated primarily an isomer of abacavir, which was minor in the alphaalpha profiles. The aldehyde intermediate could be trapped in incubations with both isozymes as an oxime derivative. These metabolites can be rationalized as arising via the aldehyde which undergoes isomerization and further oxidation by the alphaalpha enzyme or reduction by the gamma2gamma2 isozyme. Non-extractable abacavir protein residues were generated in cytosol, and with alphaalpha and gamma2gamma2 incubations in the presence of human serum albumin (HSA). Metabolism and residue formation were blocked by the ADH inhibitor 4-methyl pyrazole (4-MP). The residues generated by the alphaalpha and gamma2gamma2 incubations were analyzed by SDS-PAGE with immunochemical detection. The binding of rabbit anti-abacavir antibody to abacavir-HSA was shown to be dependent on metabolism (i.e. NAD-dependent and 4-MP sensitive). The mechanism of covalent binding remains to be established, but significantly less abacavir-protein residue was detected with an analog of abacavir in which the double bond was removed, suggestive of a double bond migration and 1,4 addition process.

Urinary excretion patterns of 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophol in various animal species: implications for studies on serotonin metabolism and turnover rate

The concentrations of the serotonin metabolites 5-hydroxyindole-3-acetic acid (5HIAA) and 5-hydroxytryptophol (5HTOL) were determined in spot urine samples of 12 mammalian and one fish species (cat, cow, dog, ferret, golden hamster, guinea pig, horse, monkey, mouse, rabbit, rainbow trout, rat, sheep) and compared with human data. The highest urinary concentrations of 5HTOL were found in the Sprague-Dawley rat (mean 9.5 micromol/L) and NMRI mouse (8.2 micromol/L), and the lowest in rainbow trout, cynomolgus macaque, and human urine (approximately 0.1 micromol/L). The highest 5HIAA concentrations were found in hamster (89.3 micromol/L) and mouse (85.2 micromol/L), and the lowest in rainbow trout, horse and sheep (range 2.0-3.7 micromol/L). Several species showed 5HIAA concentrations similar to that normally observed in human urine (approximately 5-40 micromol/L). This study demonstrated wide inter- and intra-species variations in the urinary concentrations of 5HIAA and 5HTOL, both separately and in the sum of concentrations. The 5HTOL/5HIAA ratio, which is used as an easily accessible index of the relative importance of the reductive and oxidative pathways for serotonin metabolism, also varied considerably between different species. This observation confirms that the much higher urinary 5HTOL/5HIAA ratio in rats (mean 0.35) compared with humans (< 0.01) is due to a higher baseline formation of 5HTOL in the rat. The monkey, ferret, hamster, and rabbit most closely resembled humans in this respect, and at least the two latter species appear to be more suitable than rats as animal models for studying serotonin metabolism and turnover rate, and the metabolic interaction with ethanol.

Mammalian alcohol dehydrogenase of higher classes: analyses of human ADH5 and rat ADH6

Alcohol dehydrogenases (ADH) of classes V and VI, ADH5 and ADH6, have been defined in man and rodents, respectively. Sequence data have been obtained at cDNA and genomic levels, but limited data are available for functionality and substrate repertoire. The low positional identity (65%) between the two ADHs, place them into separate classes. We have shown that the ADH5 gene yields two differently processed mRNAs and harbors a gene organization identical to other mammalian ADHs. This is probably due to an alternative splicing in the eighth intron that results in a shorter message missing the ninth exon or a normal message with the expected number of codons. The isolated rat ADH6 cDNA was found to be fused to ADH2 at the 5'-end. The resulting main open reading frame translates into an N-terminally extended polypeptide. In vitro translation results in a polypeptide of about 42 kDa and further, protein was possible to express in COS cells as a fusion product with Green Fluorescent Protein. Both ADH5 and ADH6 show genes and gene products that are processed comparably to other mammalian ADHs and the deduced amino acid sequences indicate a lack of ethanol dehydrogenase activity that probably explains why no corresponding proteins have been isolated. The functionality of these ADHs is therefore still an enigma.

Mammalian alcohol dehydrogenase - functional and structural implications

Mammalian alcohol dehydrogenase (ADH) constitutes a complex system with different forms and extensive multiplicity (ADH1-ADH6) that catalyze the oxidation and reduction of a wide variety of alcohols and aldehydes. The ADH1 enzymes, the classical liver forms, are involved in several metabolic pathways beside the oxidation of ethanol, e.g. norepinephrine, dopamine, serotonin and bile acid metabolism. This class is also able to further oxidize aldehydes into the corresponding carboxylic acids, i.e. dismutation. ADH2, can be divided into two subgroups, one group consisting of the human enzyme together with a rabbit form and another consisting of the rodent forms. The rodent enzymes almost lack ethanol-oxidizing capacity in contrast to the human form, indicating that rodents are poor model systems for human ethanol metabolism. ADH3 (identical to glutathione-dependent formaldehyde dehydrogenase) is clearly the ancestral ADH form and S-hydroxymethylglutathione is the main physiological substrate, but the enzyme can still oxidize ethanol at high concentrations. ADH4 is solely extrahepatically expressed and is probably involved in first pass metabolism of ethanol beside its role in retinol metabolism. The higher classes, ADH5 and ADH6, have been poorly investigated and their substrate repertoire is unknown. The entire ADH system can be seen as a general detoxifying system for alcohols and aldehydes without generating toxic radicals in contrast to the cytochrome P450 system.

Cyclic expression of class I alcohol dehydrogenase in male rats treated with ethanol

Continuous infusion of ethanol-containing diets has been demonstrated to generate well-defined pulses in blood and urine ethanol concentrations that occur with a frequency of approximately 6 days. The present study aimed to determine if hepatic class I alcohol dehydrogenase was the cause of these cycles. Adult male rats were fed an ethanol-containing diet by continuous intragastric infusion. Hepatic ADH activity, class I ADH mRNA level and rate of class I ADH gene transcription fluctuated in a cyclic pattern that positively correlated with UECs, and inhibition of ADH with 4-methylpyrazole abolished the UEC pulses. These data demonstrate for the first time an ethanol-dependent regulation of rat hepatic class I ADH. The cyclic behavior of the ethanol levels correlates with changes in class I ADH expression and implies adaptability of the ethanol eliminating system to high concentrations of alcohol.

Studies on the interaction between ethanol and serotonin metabolism in rat, using deuterated ethanol and 4-methylpyrazole

The metabolic interaction between ethanol and serotonin (5-hydroxytryptamine) via alcohol dehydrogenase (ADH; EC 1.1.1.1) was studied in tissue homogenates of Sprague-Dawley rats by following the transfer of deuterium from deuterated ethanol over endogenous NADH to 5-hydroxytryptophol (5HTOL). Homogenates of whole brain, lung, spleen, kidney, liver, stomach, jejunum, ileum, colon, and caecum were incubated in the presence of [2H2]ethanol and 5-hydroxyindole-3-acetaldehyde (5HIAL), and the [2H]5HTOL formed was identified and quantified using gas chromatography-mass spectrometry. ADH activity was most abundant in liver, kidney, and within the gastrointestinal tract. The highest incorporation of deuterium was obtained in homogenates of kidney, lung, and colon, whereas in brain, which contains very low ADH activity, no incorporation could be demonstrated. Addition of extra NAD+ (2.4 mM) increased the formation of [2H]5HTOL 2.6-fold in liver homogenates, but only 1.2-fold in kidney homogenates. 4-Methylpyrazole, a potent inhibitor of class I ADH, inhibited the 5HIAL reduction in homogenates of lung, kidney, jejunum, ileum, and colon, and caused a marked drop in 5HTOL oxidation in all tissues except stomach and spleen. These results demonstrate that in the rat a metabolic interaction between ethanol and serotonin via the ADH pathway may take place in several tissues besides the liver, which is the main tissue for ethanol detoxification.