Alcoholism is a notorious global public health issue, which calls for evidence-based recommendations – which have been much disputed – regarding the pros and cons of alcohol consumption. Whereas its harmful effects are well known and can be devastating, in some circumstances alcohol can confer benefits. We report here how alcohol is correlated advantageously with biomarkers of blood clotting such as total and γ’ fibrinogen, as well as certain clotting properties by comparing drinkers with abstainers. More specifically, in a genetics perspective, alcohol modulated the influence of fibrinogen SNPs on total fibrinogen concentrations and the fibrinogen SNPs as well as the FXIII SNP (rs6003) on clot density. This implies that those harbouring specific genetic variants could benefit more than others in respect of alcohol consumption in their susceptibility to coagulation and fibrinolysis.
Among alcohol consumers, intake was 11.5 g/day; equal to one standard drink per day(40) – 100 ml of wine, 45 ml spirits and 350 ml beer.(41) Self-reported alcohol intake correlated positively with all its biochemical markers. The strongest correlation was with GGT-CDT, which supports the claim of its superior diagnostic accuracy.(26) Alcohol intake and its markers correlated negatively with total fibrinogen, as well as with most of the clot properties, although after additional adjustment for fibrinogen, significance remained largely for CLT only. Correlation between alcohol biomarkers for drinkers and abstainers were largely the same. However, in drinkers, fibrinogen and maximum absorbance do not appear to increase with BMI as is seen in non-drinkers, potentially due to a protective effect of alcohol. Percentage γ’ fibrinogen was positively associated with AST and inversely with alcohol intake; however, when stratifying for alcohol consumption, negative associations were also observed for %CDT, and GGT-CDT in the drinkers and the positive association with AST was present in the abstainers only, suggesting that this relationship is likely not driven by alcohol consumption.
Our results reflect those of most researchers(12–14). The inverse relationship between fibrinogen concentrations and alcohol consumption is attributed mainly to ethanol(12), but the possibility of the result being from the ingredients accompanying ethanol in alcoholic beverage, or to their synergistic effect, is plausible. Early animal studies suggested that ethanol may interfere with hepatic plasma protein synthesis.(42) Exposure of hepatoma cells to ethanol diminished fibrinogen production by 18–20% by decreasing the transcription of fibrinogen genes.(43) Both fibrinogen(44–46) and the markers of alcohol intake, are synthesised primarily by the liver.(47) Because alcohol has direct effects on the liver, the relationship between fibrinogen and liver enzymes is expected. Our report is one of the first to investigate γ’ fibrinogen in relation to alcohol consumption and to find an inverse relationship. Increased levels of γ’ fibrinogen have been related to denser blood clots resistant to lysis(33, 48, 49), thus reduced levels may provide a mechanistic pathway through which alcohol consumption can improve clot structure.
We also observed notable associations between clot properties (slope, density and lysability) and alcohol consumption. Because fibrinogen is one of the most important factors influencing clot characteristics,(50) its elevated levels result in increased clot density.(51–53) Moderate alcohol intake may also decrease clot density, due, at least in part, to the inhibitory effect of alcohol on fibrinogen concentration. Because several relationships between alcohol intake and clot properties remained after adjustment for fibrinogen concentrations, this could indicate that the relationships were not only due to the associated lower fibrinogen concentrations, but to potential direct effects of alcohol intake on these clot properties, especially CLT. It is possible that alcohol affects CLT, through other mechanisms than clot structure. Plasminogen activator inhibitor type-1 activity(54, 55), thrombin activatable fibrinolysis inhibitor(56–58), tPA(55),BMI(54, 59, 60), HbA1c(54), triglycerides(59), blood pressure(59) and CRP(59) have all been reported to affect CLT. In our study some of the strongest correlations of CLT were with BMI, triglycerides and HbA1c. Of the latter, BMI and HbA1c correlated negatively with alcohol intake and its markers whereas triglycerides correlated positively with ALT, AST and GGT, but negatively with %CDT and alcohol intake (results not shown). However, when additionally adjusting for BMI and HbA1c, the negative association between alcohol and markers thereof with CLT remained. This suggests that the negative association between alcohol consumption and CLT is likely only partly due to the decreased fibrinogen concentration, BMI and HbA1c. The exact mechanisms through which alcohol influences CLT remains to be clarified.
To our knowledge, this study is the first of its kind to investigate the associations of alcohol intake and its markers in the presence of candidate fibrinogen and FXIII genotypes on total fibrinogen, %γ’ fibrinogen and clot properties. A genome wide association study failed to detect any gene-alcohol interactions in relation to haemostasis.(13) We revealed that the relationship of certain SNPs with total fibrinogen concentration and clot properties, in particular clot density, are modulated by alcohol intake/markers, and that the relationship with clot density remained after adjustment for fibrinogen, indicating that this effect is at least partly independent of fibrinogen concentration. Total fibrinogen correlated negatively with alcohol intake and its markers, but at rs6050, rs2066865 and rs2227388 loci, homozygote minor allele carriers’ negative relationships were the strongest, whereas at rs1800791 it was the strongest in homozygote major alleles. Genetic variation in the fibrinogen genes may alter the magnitude of fibrinogen expression in response to alcohol intake. Clot density correlated negatively with alcohol intake/markers in major allele carriers at rs1800790, rs1049636, rs1800791 and rs104963 loci, whereas no associations were observed in any of the minor allele carriers. On the other hand, clot network density correlated negatively with alcohol markers in minor allele carriers at rs7439150 and rs6003, but no relationship was observed in any of the homozygote major allele carriers. Clot density was also modulated by ALT at FXIII: rs6003. Decreased FXIII levels were associated with the minor allele carriers at rs6003.(61, 62) The negative association of the clot density with ALT was strongest in the participants who inherited the minor G allele. FXIII clearly plays a role in modulating clot structure by increasing the stability of the fibrin clot by altering its structure and increasing fibre density.(10) It has furthermore been shown that FXIII is negatively associated with alcohol intake.(63) Future basic research should investigate the specific mechanisms behind the interactions we observed per loci to explain the reason behind the differences observed in total fibrinogen or clot density among the genotypes. In this respect, we know that alcohol has the ability to perturb normal patterns of DNA methylation(64) impacting epigenetics.(65) The activities of enzymes involved in DNA and histone methylation and histone acetylation, are influenced by the levels of metabolites such as nicotinamide adenine dinucleotide, adenosine triphosphate, and S-adenosylmethionine. Chronic alcohol consumption leads to reductions in S-adenosylmethionine concentrations, thereby contributing to DNA hypomethylation.(65) Ethanol metabolism alters the ratio of nicotinamide adenine dinucleotide + to reduced nicotinamide adenine dinucleotide (NADH) and promotes the formation of acetate, all of which impact epigenetic regulatory mechanisms.(65) Metabolites of ethanol can also bind to transcription factors and/or modify chromatin structure, thereby altering gene expression.(64, 65)
Even though our report is also one of the first to investigate a broad range of haemostatic markers in relation to alcohol consumption and to take genetic factors into consideration we dealt with certain limitations. Using the QFFQ method to determine alcohol intake could result in over- or under-reporting of alcohol consumption and cannot discern between binge or moderate drinkers. However, our findings are validated by also observing associations and interactions with biomarkers reflecting alcohol intake. We believe that even with the observational nature of our study design and these limitations that our results are reliable and of importance to understand further those lifestyle factors such as alcohol intake that predispose individuals to – or protect them from – unfavourable haemostatic factors that might ultimately lead to CVD.