Pharmacogenetics of alcohol metabolism and alcoholism.

The pharmacogenetic differences among individuals in their capacity to metabolize ingested alcohol are possibly responsible for the large inter-individual and inter-ethnic variations observed in the outcome of alcohol use and misuse. Based on results of adoption, twin, and family studies it is now widely accepted that the vulnerability to alcoholism is determined by genetic factors as well as by environment. There is a constant search for biological markers and specific genes which could identify individuals genetically predisposed to alcohol abuse and alcoholism. Numerous 'candidate genes' for alcoholism have been suggested including the alcohol metabolizing enzymes, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Both ADH and ALDH exhibit genetic heterogeneity. An atypical form of ADH (ADH2), which contains a variant beta 2 subunit instead of the usual beta 1 subunit, differs substantially from the usual form in its kinetic properties and is found more frequently among the Japanese, Chinese and other Mongoloid populations than in Caucasoids and Negroids. A widely prevalent genetic polymorphism has been observed for ALDH; about 50% of Japanese and Chinese livers possess an inactive ALDH (ALDH2 isozyme) whereas none of the Caucasian or Negroid populations show this isozyme abnormality. These metabolic polymorphisms seem to contribute to differences in the in vivo elimination rate of ethanol and acetaldehyde, and may explain differences in alcohol-related behaviour and its disease outcome. Taken together, Orientals who possess an atypical ALDH2 gene are more sensitive to acute responses to alcohol, tend to be discouraged from drinking alcohol, and consequently are at lower risk of developing alcohol-related disorders. However, more work is needed to support these findings. Recent advances in molecular genetics have made it possible to analyze directly the human genome. This may help in a better understanding of the complex genetic and environmental factors in alcohol abuse by providing prospects for identification of gene loci which may be responsible for predisposition to, and protection from, alcoholism.

Evidence for a signal peptide at the amino-terminal end of human mitochondrial aldehyde dehydrogenase.

A full-length cDNA clone coding for human mitochondrial aldehyde dehydrogenase (ALDH I) was isolated from a human fetal muscle cDNA library. Sequence analysis revealed structural similarities between the amino-terminal end of ALDH I and other known targeting sequences responsible for protein uptake into the mitochondria.

Detoxification of cyclophosphamide by human aldehyde dehydrogenase isozymes.

In in vitro studies, no turnover of aldophosphamide and mafosfamide was observed with the tumor-specific aldehyde dehydrogenase 3 isozyme (ALDH3) isolated from human stomach mucosa as well as from lung (A549) and pharynx (UMSCC2) carcinoma cell lines. Only the human liver cytosolic ALDH preparation (ALDH1) showed any significant oxidation of aldophosphamide and mafosfamide.

Apolipoprotein C3 SstI polymorphism and triglyceride levels in Asian Indians.

BACKGROUND: A close association between Sst I polymorphism in the 3' untranslated region of the apolipoproteinC3 (APOC3) gene and levels of plasma triglycerides (TG) had been reported by different investigators. Hypertriglyceridemia(HTG) is a known risk factor for coronary artery disease (CAD) in the context of Asian Indians. We conducted a study on the relationship between APOC3 SstI polymorphism (S1S1, S1S2 and S2S2 genotypes) and plasma TG levels in a group of 139 male healthy volunteers from Northern India. METHODS: DNA samples were analyzed by polymerase chain reaction (PCR) followed by SstI digestion. Digested PCR products were run on 3% agarose gel and visualized by ethidium bromide staining. RESULTS: Rare S2 allele was highly prevalent in our study population (0.313) as compared to the Caucasians (0.00-0.11). The genotypic distribution was in agreement with Hardy-Weinberg equilibrium. S2 allele was almost two times more prevalent in the HTG group (N = 34) as compared to NTG group (N = 105) (p = 0.001). Multiple logistic regression revealed S1S2 individuals had age-adjusted odds ratio of 2.43 (95%CI = 0.99-6.01, p = 0.054) and S2S2 had 9.9 (95%CI = 2.66-37.29, p = 0.0006) for developing HTG in comparison to S1S1 genotype. CONCLUSIONS: Our study shows a significant association between rare S2 allele and HTG in Asian Indians.

Platelet monoamine oxidase and erythrocyte catechol-o-methyltransferase activity in alcoholism and controlled abstinence.

This study substantiates previous reports that low platelet monoamine oxidase (MAO) activity is associated with alcoholism. Catechol-o-methyltransferase (COMT) activity in erythrocytes of alcoholics did not differ from that of controls. In 20 male alcoholics low platelet MAO activity was found during the first 3 days after hospitalization. The MAO activity increased in the next 2 weeks of abstinence and then tended to decrease again.

Isolation of repetitive clones from human muscle cDNA library.

Human fetal muscle cDNA library was screened with a beta-myosin heavy chain gene fragment containing Alu sequences. Two cDNA clones AI and BII with 1.8 and 3 kb inserts respectively were chosen for further characterization by means of RNA and DNA hybridization procedures and sequencing. The clones appeared to contain repetitive sequences as well as single copy regions. They are actively transcribed in different stages of myogenic development but not in the liver. DNA sequence analysis of short stretches from both clones revealed no sequence homology to any other published DNA sequences.

Pharmacogenetics of alcohol sensitivity.

The metabolism of acetaldehyde has received considerable attention in the past few years due to its toxic effects and possible importance in pharmacogenetics. Recent studies have demonstrated rapid progress concerning the multiple molecular forms of ADH and ALDH and their genetic variants. The isozymes of ALDH may play an important role in the biological sensitivity to alcohol in certain ethnic groups and also in the pathogenesis of alcohol related organ damage. A protective effect of ALDH I deficiency against alcoholism seems to exist in Japanese.

Blood ethanol and acetaldehyde levels in Japanese alcoholics and controls.

Aldehyde dehydrogenase (ALDH) isozyme I deficiency in hair root samples from 105 healthy individuals and 72 alcoholics was determined using isoelectric focusing. From these individuals, 12 male alcoholics (2 with ALDH isozyme I deficiency and 10 normal) and 45 healthy controls (18 with ALDH isozyme I deficiency and 27 normal) were investigated for their blood ethanol and acetaldehyde levels by gas chromatography after an acute dose of alcohol (0.5 g ethanol/kg body wt.). Peak blood ethanol values of about 10 mmol/l were attained after 1 hour both in alcoholics and normal controls irrespective of their ALDH type. There was no significant difference in the blood ethanol level during the 5 hr post-drinking period in both the groups. Peak blood acetaldehyde concentration was significantly higher in healthy controls and alcoholics deficient in ALDH isozyme I after alcohol drinking (about 30 micro-mmol/l) than in individuals with normal ALDH isozyme I (3 micro-mmol/l). However, no significant difference in blood acetaldehyde was observed between alcoholics and controls.

Aldehyde dehydrogenase isozyme variation and alcoholism in Japan.

Aldehyde dehydrogenase (ALDH) isozyme composition in hair roots was determined using isoelectric focusing in 105 healthy individuals, 175 alcoholics, 86 schizophrenics and 47 drug dependents. The incidence of ALDH isozyme I deficiency in healthy populations in Japan was found to be about 40%. Among alcoholics, however, only 2.3% individuals had the isozyme deficiency. There was no difference between normal controls, schizophrenics and drug dependents regarding the incidence of ALDH isozyme I deficiency. These observations indicate a possible protective role of ALDH isozymes against alcoholism. The higher frequency of ALDH isozyme I deficiency in Japanese may explain why alcoholism in Japan has been less frequent than in European and North American countries. ALDH isozyme II was found in most of the tissues and erythrocytes. A higher frequency of individuals possessing lower ALDH activity in hemolysates was observed in alcoholics than that in controls. The activity of acid phosphatase was also reduced in alcoholics. Alcohol abuse might result in disturbed protein synthesis in the erythrocytes.

Comparative study of erythrocyte aldehyde dehydrogenase in alcoholics and control subjects.

Human erythrocyte aldehyde dehydrogenase (ALDH, EC 1.2.1.3) shows a single activity band on starch gel electrophoresis and isoelectric focusing in polyacrylamide gel (pI = 5.0-5.3). The erythrocyte enzyme is identical with the slower migrating, disulfiram-sensitive human liver ALDH isozyme II. Significantly decreased activity of erythrocyte ALDH was observed in chronic alcoholics when compared with healthy controls and non-alcoholic psychiatric and gastrointestinal patients. The measurement of ALDH in erythrocyte lysates may offer yet another sensitive and specific biochemical marker of alcoholism.

Human aldehyde dehydrogenases: their role in alcoholism.

This article surveys the state of our knowledge concerning the biochemical and genetic variations in aldehyde dehydrogenases (ALDHs) in humans and their role in alcohol sensitivity, alcohol drinking habits, and alcoholism. Variations in acetaldehyde metabolism via genetically determined polymorphisms in ALDH enzymes seem to play an important role in individual and racial differences in acute and chronic effects of alcohol drinking as well as towards vulnerability to organ damage after chronic alcohol abuse. Alcohol sensitivity and associated discomfort symptoms accompanying alcohol ingestion may be determinantal for the significantly low incidence of alcoholism among Japanese, Chinese and other Orientals of Mongoloid origin. An abnormal ALDH isozyme has been found to be widely prevalent among individuals of Mongoloid race, and is mainly responsible for the acute sensitivity to alcohol commonly observed in this race. Persons sensitive to alcohol by virtue of their genetically controlled ALDH isozyme deficiency may be discouraged from drinking large amounts of alcohol in their daily life due to the initial adverse reaction experienced after drinking alcohol, and thus are protected against alcoholism.

Human brain aldehyde dehydrogenase: activity with DOPAL and isozyme distribution.

Aldehyde dehydrogenase (ALDH, EC 1.2.1.3), has been shown to be the most important enzyme for DOPAL metabolism in human brain (Agarwal et al.). In the present investigation cerebellum, corpus striatum and pons showed the highest ALDH activity. Most of the enzyme activity was found in the mitochondrial and microsomal fractions. Two activity bands on IEF gels and dual Km values indicate the presence of two distinct isozymes in all the fractions. Two cerebella from alcoholics yielded the same results as the control group regarding their total ALDH activity, subcellular distribution pattern and protein content. The presence of DOPAC (acid metabolite of DOPAL), pargyline, pyrazole or ethanol in the assay mixture did not alter the ALDH activity significantly.

Aldehyde dehydrogenase polymorphism and alcohol metabolism in alcoholics.

Significant differences in the incidence of aldehyde dehydrogenase isozyme I deficiency were observed between healthy controls and alcoholics in Japan. Only about 5% of alcoholics were found deficient as compared to about 42% in the normal healthy population. Blood acetaldehyde level after alcohol drinking was also found significantly higher in deficient subjects than in individuals without deficiency. Among alcoholics, deficient subjects showed relatively less elevated blood acetaldehyde levels. When two districts in Japan were compared, per capita alcohol consumption correlated with the frequency of isozyme deficiency. Higher percentage of aldehyde dehydrogenase isozyme deficiency was associated with lower per capita alcohol consumption. Thus, individuals deficient in aldehyde dehydrogenase isozyme may consume less alcohol.

Quantitative and qualitative biochemical parameters for alcohol abuse.

Blood from alcoholics, non-alcoholic patients and healthy controls were analyzed for various biochemical markers. Follow-up measurements were made during about 3 months of abstention. While a gradual increase in aldehyde dehydrogenase activity (ALDH) in red cell was noted in alcoholic patients serum alpha 1-acid glycoprotein (AAG) values returned to normal range within 8 weeks during abstinence. An additional minor band for alpha 1-antitrypsin (AAT) was observed after isoelectric focusing of sera from alcoholics; this band disappeared after 3 weeks of abstinence. However, no such unusual AAT band was found in non-alcoholic patients with liver disorders.

Population genetic and family studies on aldehyde dehydrogenase deficiency and alcohol sensitivity.

Population genetic studies on the prevalence of aldehyde dehydrogenase isozyme I (ALDH I) deficiency in various Caucasian, Oriental, African, and American Indian subjects were carried out using hair roots as peripheral source of the enzyme activity. While a very high percentage of Orientals with Mongoloid origin were found deficient in ALDH I activity, no deficiency was detected in Caucasian and African populations. Native American Indians showed a relatively low incidence of ALDH I deficiency. A genetic model based on the phenotype determination using antisera against purified human liver ALDH I is proposed. Pedigree analysis of Japanese families suggests an autosomal codominant mode of inheritance.

Basis of aldehyde dehydrogenase deficiency in Orientals: immunochemical studies.

While most Caucasians have two main isozymes of liver aldehyde dehydrogenase, in about 50% of Orientals the ALDH I isozyme is missing. This isozyme, which has a faster electrophoretic mobility, is predominantly present in mitochondria and has a relatively low Km for acetaldehyde. The inherent deficiency of ALDH I is responsible for the impaired acetaldehyde oxidation leading to facial flushing and other cardiovascular symptoms of alcohol sensitivity commonly observed in Japanese and Chinese. Antibodies raised against apparently homogeneous liver ALDH I and ALDH II isozymes did not show an immunological similarity between the two isozymes which do not share common subunits. While erythrocyte ALDH II is also immunologically distinct from hepatic ALDH I, it showed an immunological similarity with hepatic ALDH II. On isoelectric focusing in agarose gel followed by immunoelectrophoresis, at least 4 components with an anti-ALDH I antibody were detected in extracts from Caucasian and Oriental livers. In Japanese livers deficient in ALDH I activity, the prominent ALDH component was missing. Apparently, more than one gene is responsible for the synthesis of ALDH isozymes reacting with an antibody against ALDH I. A deletion in one of the genes may be responsible for the loss of ALDH I enzyme activity and altered antigenic properties. However, at this stage, a point mutation in a structural gene coding for ALDH I resulting in a defective protein with altered electrophoretic and enzymatic properties is not ruled out.

Human liver aldehyde dehydrogenase: subcellular distribution in alcoholics and nonalcoholics.

Activity assay and isoelectric focusing analysis of human biopsy and autopsy liver specimens showed the existence of two major aldehyde dehydrogenases (ALDH I, ALDH II). Subcellular distribution of these isozymes was determined in autopsy livers from alcoholics and nonalcoholics. Nearly 70% of the total ALDH activity was recovered in the cytosol which contained both the major isozymes. Densitometric evaluation of isozyme bands showed that about 65% of the cytosolic enzyme activity was due to ALDH II and the rest due to ALDH I isozyme. Only about 5% of the total ALDH activity was found in the mitochondrial fraction (70% ALDH I and 30% ALDH II). Significantly reduced total and specific ALDH activities were noted in all the subcellular fractions from cirrhotic liver specimens. Apparently, ALDH I isozyme from cytosol and mitochondria is primarily responsible for the oxidation of small amounts of acetaldehyde normally found in the blood of nonalcoholics after drinking moderate amounts of alcohol. However, in alcoholics who exhibit higher blood acetaldehyde concentrations after drinking alcohol, ALDH II isozyme may be of greater physiological significance.

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

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

13C-ethanol and 13C-acetate breath tests in normal and aldehyde dehydrogenase deficient individuals.

Four normal and five aldehyde dehydrogenase (ALDH) isozyme I deficient individuals were subsequently loaded with (1-13C)ethanol and (1-13C)sodium acetate and the conversion of the label to 13CO2 was determined in expired air by isotope ratio mass spectrometry. In the 13C-acetate breath test, both groups showed virtually identical recovery of the label in expired air, namely 48.5 +/- 2.3% (mean +/- S.D.) for normal and 46.8 +/- 5.7% for deficient individuals. However, in the 13C-ethanol breath test, both the groups performed differently. On average, although a certain overlap of the single data was observed, the recovery of the label after four hours was 43.4 +/- 3.8% for the normal and 35.6 +/- 6.8% for the ALDH deficient subjects. These findings suggest a slower conversion of ethanol to carbon dioxide in aldehyde dehydrogenase deficient individuals, which may be another consequence of this deficiency besides the higher plasma acetaldehyde levels observed after ethanol loading in comparison to individuals with normal aldehyde dehydrogenase activity.

Does moderate alcohol intake protect against coronary heart disease?

There is abundant epidemiological and clinical evidence to show that light-to-moderate drinking is associated with a reduced risk of coronary heart disease (CHD), total and ischemic stroke, and total mortality in middle-aged and elderly men and women. The evidence suggests a J- or U-shaped relationship between alcohol and CHD. Alcohol reduces the risk of coronary heart disease both by inhibiting the formation of atheroma and by decreasing the rate of blood coagulation. It appears that for most conditions, other than cardiovascular diseases and cholelithiasis, moderate alcohol consumption has either none or only an intermediate type of risk as compared with the risk of either abstinence or excessive drinking. It is now fully recognized and accepted that drinking alcohol regularly for years is toxic to almost every tissue of the body. However, most people who choose to drink alcohol have little or no problem limiting their consumption to amounts that do not generally cause serious health or social consequences. Moreover, a given dose of alcohol may affect different people differently. It is, therefore, imperative that a critical evaluation, based on the observations made hitherto, be done of both the harmful and the protective effects of alcohol consumption on various organs/systems of the body. This article reviews epidemiological evidence for the protective effects of alcohol on the cardiovascular system and discusses how alcohol might lower the risk of CHD.