The role of stem cells

Le rôle des cellules souches

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An important recent study reported that the acetaldehyde formed by oxidation of the alcohol causes significant damage to the DNA of the stem cells, which promotes the development of cancer.

Production of acetaldehyde

Alcohol is classified by the international agency for research on cancer (IARC) as a carcinogen of group 1, that is to say, a substance known to induce cancer in humans. This classification is the result of a multitude of studies showing that consumption of high amounts of alcohol is associated with an increased risk of several cancers, particularly those of the mouth, larynx, esophagus, colon, liver, and breast.

In the majority of cases, the increased risk of cancer, however, is not due to alcohol as such, but rather by molecules that are produced by its metabolism. After absorption, the alcohol is oxidized to acetaldehyde, a molecule that is highly toxic which can cause huge damage to the genetic material of cells. This amount of acetaldehyde-toxic can even be increased to 700 % in people who smoke while drinking, a phenomenon that contributes to the strong synergy that exists between the consumption of alcohol and smoking for cancers of the digestive system, the upper (mouth, larynx, esophagus). For example, the great drinkers (6 glasses of alcohol or more per day) who smoked daily more than a pack of cigarettes have up to 40 times higher risk of cancer of the oral cavity than those who drink moderately and do not smoke.

Stem cells targeted

The results of a british study recently published in the journal Nature allow us to better understand the mechanisms responsible for this action carcinogenic acetaldehyde (1). After having administered a dose of ethyl alcohol to mice, the scientists observed that the acetaldehyde formed caused major changes in the structure of the genetic material of cells of the animal, including the appearance of breaks in the DNA and a rearrangement of the chromosomes. Further analysis revealed that the damage occurred preferentially in the stem cells (the cells that give rise to a multitude of cell types), and that these mutations would thus be at the origin of the carcinogenic effect of acetaldehyde.

Defense mechanisms

In another part of the study, the authors examined the impact of natural defense mechanisms against the toxic effects of acetaldehyde on these damage to the DNA of the stem cells. The first line of defense is an enzyme called aldehyde dehydrogenase (ALDH), which converts acetaldehyde into acetate, a molecule harmless and that the cells can use as energy source. In the world, over 500 million people have a deficiency in ALDH (especially in the South-East asia), and this deficiency causes an accumulation of acetaldehyde so important that it can cause redness, tachycardia, severe nausea and vomiting (the famous “flush” asian “). Using mice lacking this enzyme, the scientists observed that the absence of ALDH causes a 4-fold increase of the levels of damage to the DNA of the stem cells, confirming the same time that the carcinogenic effects of alcohol result really is a infringement of these cells by acetaldehyde.

Focus on the red wine

These results come to remind us that alcohol is far from being a harmless substance, and it’s really necessary to show moderation. Even if most of us possess detoxification enzymes are functional, the effectiveness of these mechanisms is not perfect and fails to eliminate completely the adverse effects of alcohol. In addition, some liquors contain large amounts of acetaldehyde formed during their production and, therefore, exposed the cells to high amounts of this toxic, even when ingested in small sips (2). Conversely, large population-based studies show that red wine is less damaging, not only because this drink contains two times less acetaldehyde than other sources of alcohol, but also because it contains significant amounts of polyphenols (resveratrol, among others), which are known to have positive effects on human health, particularly in terms of prevention of cardiovascular diseases. By focusing on the red wine, so we can take advantage of the benefits of alcohol on reducing the risk of heart disease and premature mortality, while minimizing its negative effects on the risk of cancer.

(1) Garaycoechea JI et al. “Alcohol and endogenous aldehydes damage chromosomes and mutate stem cells “. Nature 2018 ; 553 : 171-177.

(2) Linderborg K, et al. “A single sip of a strong alcoholic beverage causes exposure to carcinogenic concentrations of acetaldehyde in the oral cavity “. Food and Chemical Toxicology 2011 ; 49 : 2103-2106.