Genetic variation in alcohol dehydrogenase 3 and the decrease of hs-C-reactive protein levels by moderate alcohol consumption

Authors


  • K.F. current address: Department of Nephrology and Transplantology, Białystok University Medical School, Białystok, Poland.

Licia Iacoviello MD PhD, Catholic University Research Laboratories, ContradaTappino, 86100 Campobasso, Italy.
Tel.:+39 0874 312274; fax:+39 0874 312710; e-mail: licia.iacoviello@rm.unicatt.it

An inverse association between light to moderate alcohol consumption and cardiovascular disease morbidity and mortality has been shown consistently in epidemiological studies [1,2]. One mechanism for this potential protection by ethanol is the increase in HDL-cholesterol, an effect that would account, however, for only half the observed benefit [3]. Coronary atherosclerosis is largely a product of chronic inflammation in the arterial wall and recent animal and human studies suggest a direct effect of ethanol on inflammation. This may provide an additional mechanism by which alcohol protects against cardiovascular disease. Cross-sectional studies have found a J- or U-shaped relationship between alcohol intake and circulating levels of CRP, fibrinogen and other inflammatory markers [4,5]. More recently, in a randomized, crossover trial, Estruck et al. [6] showed that red wine and gin were both able to reduce fibrinogen levels, but only red wine decreased CRP and adhesion molecules of monocyte and endothelial cells.

A possible influence of genetics on the beneficial effect of ethanol has also been described. This influence was explained by changes in the rate of alcohol metabolism by a polymorphism in the gene of alcohol dehydrogenase 3 (ADH3), which is the predominant pathway for hepatic ethanol oxidation. ADH metabolizes ethanol to acetaldehyde, which is more toxic than ethanol itself. Polymorphisms have been described in the ADH3 gene, producing γ1 and γ2 variants [7]. The γ2 variant is associated to a slower rate of ethanol oxidation and lower levels of acetaldehyde, while the γ1 variant reflects the fast rate reaction. Moderate consumers of alcohol who are homozygous for the slow-oxidizing ADH3 allele (γ2) have higher high-density lipoprotein cholesterol levels and a substantially decreased risk of myocardial infarction [8].

The aim of our study was to investigate the effect of alcohol consumption on high sensitive (hs) CRP (hs-CRP), interleukin-6 (IL-6) and P-selectin in relation to ADH3 polymorphism among a healthy population living in a Central-Southern region of Italy.

One hundred and thirty-nine apparently healthy Italian subjects (50% males), aged 30–60 years, born and living in that region, whose four grandparents were also born there, were selected randomly from the general population through the national health insurance list.

Exclusion criteria included history of cardiovascular disease, diabetes, familial hypercholesterolaemia, malignancies, heart, liver or renal failure, definite coagulation deficiency, hypo/hyperthyroidism and epilepsy.

The amount of consumed alcoholic beverages was assessed by a questionnaire on the frequency (daily, weekly, monthly, yearly, never) of intake of ‘drinks’ of wine, beer or spirits. The amount of a ‘drink’ was considered equivalent to 120 mL, 200 mL and 40 mL, for wine, beer or spirits, respectively. Finally, it was assumed that wine contains 12%, beer 5% and spirit 36% ethanol. Former drinkers and abstainers were excluded from the analysis.

All study participants agreed to give blood samples for DNA analysis and biochemical measurements, by written informed consent.

Polymorphism of ADH3 was determined as described [8]. Soluble P-selectin and IL-6 from citrate plasma were determined by enzyme-linked immunosorbent assay (ELISA) kit (BMS219/2, Bender MedSystem and HS600B, R&D System). hs-CRP levels in citrate plasma were obtained by immunoturbidimetric method (Instrumentation Laboratory, Milan, Italy) using the ACL 9000 (Instrumentation Laboratory, Vienna, Austria.

The frequencies of the alleles and genotypes among groups were counted and compared by the χ2 test with the values predicted by the assumption of Hardy–Weinberg equilibrium. Continuous variables were compared using the analysis of variance or Kruskall–Wallis test, according to their observed distribution. The variables P-selectin and hs-CRP were logarithmic-transformed to remove positive skewness. Univariate correlations were assessed using Pearson's statistic. Multivariate linear regression analysis with age, sex and ADH3 genotypes as covariates was used to analyse the correlation among different variables and consumption of alcoholic beverages (SAS statistical package, version 8.2 for Windows; SAS Institute Inc., Cary, NC, 1989).

There were 72 (52%) homozygotes for the γ1 allele, 58 (42%) heterozygotes for the γ1γ2 allele and nine homozygotes for the γ2 allele (6%). Frequencies of alleles were as follows: γ1 = 0.73 (95% confidence interval: 0.67–0.78) and γ2 = 0.27 (95% confidence interval: 0.22–0.33). The distribution of genotypes was in Hardy–Weinberg's equilibrium (χ2 = 0.35; P = 0.55). Due to the small number of γ2γ2 homozygotes and the codominant effect of the γ2 allele, we grouped γ2γ2 homozygotes with γ1γ2 heterozygotes.

The mean alcohol intake was 25 ± 33 g die−1, consumed mainly as wine. There was no correlation between alcohol intake and neither IL-6 (r = 0.03; P = 0.70), P-selectin (r =− 0.01; P = 0.88) or hs-CRP levels (r = − 0.10; P = 0.22). hs-CRP were correlated positively with IL-6 (r = 0.32; P < 0.0001).

When taking into account the ADH3 genotype, a significant negative correlation between alcohol consumption and hs-CRP levels was apparent in γ2 carriers (r = − 0.37; P = 0.0023) but not in γ1 homozygotes (r = 0.09; P = 0.43; P = 0.0075 for difference of effects, after adjustment for age and sex) (Fig. 1). No significant interaction was found between alcohol intake and ADH3 genotypes on the levels of IL-6 or P-selectin.

Figure 1.

 Correlation between hs-CRP levels and alcohol intake (g/day) among all population (all), γ1 homozygotes (γ1) and γ2 carriers (γ1γ2 + γ2γ2).

Hines et al. [8] had observed, in a Northern American population, a strong interaction between the ADH3 genotype and alcohol consumption in relation to HDL levels and the risk of myocardial infarction. In a sample of apparently healthy, Central-Southern Italian people consuming wine as main source of alcohol, the present study extends to hs-CRP, an inflammatory marker, a positive association between low levels of the protein and the presence of the r2 allele of the ADH3 gene. Altogether, these findings support the hypothesis that in about half the general population, a slower alcohol clearance rate, associated with the ADH3 y2 allele, enhances the beneficial effect of moderate alcohol consumption on the risk of cardiovascular disease by improving the effect of alcohol on both lipid and inflammatory profiles.

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