The dominance of the ALDH2 mutation, however, does not seem to be complete; phenotypic differences are associated with the three ALDH2 genotypes. Asians who are homozygous for ALDH2*2 drink very little alcohol [3], and no studies have found alcoholic persons with this genotype [4-8]. Asians who are heterozygous for ALDH2*2 drink less alcohol and are also less likely to be alcoholic compared with Asians with ALDH2*1 alleles, but they are not fully protected from alcoholism. Approximately 12% of alcoholic Asians have the ALDH2*1/2*2 genotype [5]. In the context of alcoholism or lower alcohol intake, Asian persons who are heterozygous for ALDH2*2 may be more vulnerable to alcohol-associated conditions, including liver disease [6-9], asthma [9], and esophageal cancer [10].

The three ALDH2 genotypes are also associated with variability in response to alcohol [11]. Asians who are homozygous for ALDH2*2 are very sensitive to alcohol and have tachycardia, hypotension, and vomiting after ingesting a moderate amount of alcohol. Asians who are heterozygous for ALDH2*2 are more sensitive to alcohol than Asians with ALDH2*1 alleles, although the response of the former is not necessarily aversive.

Among Asians with an ALDH2 deficiency, differences in sensitivity to alcohol may be mediated by differences in alcohol metabolism, slower elimination of alcohol, or accumulation of acetaldehyde in the blood [12]. Some studies [13-17] have measured blood levels of alcohol or acetaldehyde after ingestion of alcohol in Asians who were known to have ALDH2 genotypes, but these studies had an inadequate sample size, did not include a placebo control, or did not control for use of alcohol and cigarettes (which can alter alcohol metabolism). We measured blood levels of alcohol and acetaldehyde after ingestion of alcoholic or placebo beverages in Asian-American men who underwent genotyping at the ALDH2 locus. Particular attention was given to matching the groups for age, height, weight, history of alcohol use, and history of smoking.

Methods

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Asian-American men 21 to 25 years of age were recruited from advertisements in university newspapers for our randomized, double-blind, crossover study. They completed a questionnaire that solicited information on demographic characteristics; patterns of and problems with alcohol and drug use; and family history of alcohol, drug, and psychiatric problems. We excluded persons who completely abstained from alcohol, persons who had consumed more than 60 standard alcoholic drinks per month during the previous 6 months, and persons who reported that either biological parent was not of Chinese, Japanese, or Korean descent. Thirty-five men who did not have a personal or family history of alcohol dependence and who had no evidence of other substance dependence, major psychiatric disorders, or medical disorders gave informed consent to participate in two test sessions. The study was approved by the institutional review board at the Scripps Clinic and Research Foundation.

Participants were asked to refrain from using alcohol, cigarettes, and other drugs (including aspirin, nonsteroidal anti-inflammatory agents, and anti-histamines) that might alter alcohol metabolism for 3 days before testing. On test days, each participant arrived at the clinic at 7:30 a.m. after an overnight fast. He then ate a low-fat breakfast (two slices of dry toast and juice), and an indwelling heparin lock was inserted for drawing blood. At the first session, blood was drawn and genotyping at the ALDH2 locus was done by using polymerase chain reaction of DNA and allele-specific oligonucleotide probes [1]. At 9:00 a.m., each participant was given a placebo beverage (3 mL of 95% alcohol in a reservoir on top of noncaffeinated, sugar-free soda) or 0.75 mL of 95% alcohol (0.56 g/kg of body weight) as a 20%-by-volume solution in the same mixer. The alcohol and placebo were ingested over 7 minutes through a placebo alcohol apparatus [18]. Blood was drawn to determine levels of alcohol and acetaldehyde before beverage ingestion and 15, 30, 45, 60, 90, 120, and 150 minutes after beverage ingestion. Blood alcohol concentrations were determined by using a modified alcohol dehydrogenase assay [19]. The rate of alcohol elimination (mg/kg per hour) was calculated from the slope of the pseudolinear decline of the blood alcohol concentration-time curve (usually from the 90-, 120-, and 150- minute samples) by using linear least-squares regression. Blood acetaldehyde levels were determined by using a modified fluorigenic high-performance liquid chromatographic assay [20] that had a detection sensitivity in the picomole range and intra-assay and interassay precisions of 2.4% and 3.7%, respectively.

Statistical analyses, done by using SYSTAT software (SYSTAT, Inc., Evanston, Illinois), focused on differences between participants with ALDH2*1/2*1 and those with ALDH2*1/2*2. Demographic information, data on recent alcohol and cigarette use, peak blood alcohol concentration, time to peak blood alcohol concentration, volume of distribution, and rate of alcohol elimination were analyzed by using one-way analysis of variance; ALDH2 genotype was a between-participant variable. Data on blood alcohol concentration and acetaldehyde level were analyzed by using separate 2 x 8 analysis of variance for alcohol and placebo sessions; ALDH2 genotype was a between-participant variable, and time was a repeated measurement. Significant interactions were then analyzed by using post hoc comparisons with contrast matrices. The Bonferroni correction was used to limit the familywise error rate to 0.05 for comparisons among the placebo session time points and among the alcohol session time points.

Results

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Genotyping for ALDH2 revealed 20 participants who had ALDH2*1/2*1 genotype, 13 who had ALDH2*1/2*2 genotype, and 2 who had ALDH2*2/2*2 genotype. Three participants (1 with ALDH2*1/2*2 genotype and the 2 with ALDH2*2/2*2 genotype) became ill after ingesting alcohol and were excluded from analyses because of missing data. One participant with ALDH2*1/2*2 genotype whose acetaldehyde levels exceeded 4 SDs from the mean (most likely as a result of instrumentation error) was also excluded from data analyses.

The Table 1 shows demographic information and patterns of recent alcohol and cigarette use for the remaining 31 men. The ALDH2 genotype groups did not differ significantly for any of these variables; this reflects participant selection.

Mean peak blood alcohol concentration ±SD was 81.3 ± 12.48 mg/dL; the peak occurred 43.1 ± 15.85 minutes after ingestion of alcohol. Mean volume of distribution was 0.718 ± 0.1124 L/kg of body weight, and the mean rate of alcohol elimination was 97.8 ± 33.97 mg/kg per hour. The ALDH2 genotype groups did not differ significantly for any of these variables. Mean blood alcohol concentrations for the alcohol session and mean acetaldehyde levels for the placebo and alcohol sessions, measured over time according to ALDH2 genotype, are shown in the (Figure 1).

View larger version (19K): [in this window] [in a new window]   Figure 1. Mean (±SD) blood levels of alcohol and acetaldehyde before and after ingestion of a placebo beverage containing 3 mL of 95% alcohol and an alcoholic beverage (0.56 g of alcohol per kg of body weight) in Asian-American men with ALDH2*1/2*1 genotype (n = 20) and ALDH2*1/2*2 genotype (n = 11). Blood alcohol concentrations measured after administration of placebo were not detectable and thus are not shown. Significant interactions between ALDH2 genotype and time were followed by post hoc tests with Bonferroni corrections. An asterisk indicates significant differences between the ALDH2 genotype groups (P < 0.006).

Analysis of variance revealed that the main effects for ALDH2 genotype and the interaction between ALDH2 genotype and time were not significant for the data on blood alcohol concentration from the alcohol session. Analysis of variance also revealed that the main effects for ALDH2 genotype and the interaction between ALDH2 genotype and time were significant for the data on acetaldehyde levels from the placebo sessions (ALDH2 genotype, P < 0.005; interaction between ALDH2 genotype and time, P < 0.013) and the alcohol sessions (ALDH2 genotype, P < 0.002; interaction between ALDH2 genotype and time, P < 0.001). Post hoc analyses with Bonferroni corrections revealed significant group differences 30, 45, and 60 minutes after placebo ingestion and 60, 90, 120, and 150 minutes after alcohol ingestion.

Discussion

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We found that Asian-American men who were heterozygous for the ALDH2*2 allele did not differ from carefully matched men who were homozygous for the ALDH2*1 allele in measures of blood alcohol concentration overall or at any time after alcohol ingestion. These findings are consistent with the results of one study [14] but differ from those of other studies [15-17] in which persons with ALDH2*2 alleles had significantly slower rates of alcohol elimination than did persons with ALDH2*1 alleles. These discrepancies may result from group differences on important variables, especially history of alcohol use, that we controlled for.

We also found that, despite equivalent blood alcohol concentrations, participants with ALDH2*1/2*2 genotype had significantly higher blood acetaldehyde levels after ingesting the alcohol beverage than did participants with ALDH2*1/2*1 genotype. These findings suggest that blood acetaldehyde levels rather than blood alcohol concentrations may mediate enhanced sensitivity to alcohol among persons with ALDH2*1/2*2 genotype [11], contribute to lower alcohol intake [3], and provide some protection against alcoholism [4, 5] in Asians with this genetic polymorphism.

In addition, Asian men who were heterozygous for ALDH2*2 had slightly but significantly higher blood acetaldehyde levels after ingesting the placebo beverage. In participants with ALDH2*1/2*2 genotype, the small amount of alcohol (3 mL) that was used to mask the placebo resulted in undetectable blood alcohol concentrations but significantly higher acetaldehyde levels. These results are consistent with those of a study that evaluated acetaldehyde levels in persons with different ALDH2 genotypes after a low dose of alcohol (0.1 g/kg) [14]. These findings suggest that the toxic effects of elevated acetaldehyde levels rather than blood alcohol concentrations may also contribute to increased vulnerability to alcohol-associated conditions (such as liver disease, asthma, and esophageal cancer) among persons with ALDH2*2 alleles, even with a relatively low intake of alcohol [6-10]. Consequently, Asians with ALDH2*2 alleles who drink alcoholic beverages may be at lower risk for alcoholism but may be more vulnerable to organ damage caused by acetaldehyde.

Dr. C. Peterson: Sansum Medical Research Foundation, 2219 Bath Street, Santa Barbara, CA 93105.

Dr. K. Peterson: Matech Biomedical Technologies, 31304 Via Colinas, Suite 102, Westlake Village, CA 92362.

Dr. Thomasson: Lilly Laboratory for Clinical Research, Wishard Memorial Hospital, 1001 West Tenth Street, Indianapolis, IN 46202.

Mr. Cole and Dr. Ehlers: The Scripps Research Institute, Department of Neuropharmacology, 10666 North Torrey Pines Road, La Jolla, CA 92037.