Alcohol metabolism

Alcohol metabolismGenetic testing and alcohol metabolism

Have you ever wondered why some people's faces become red and they experience headaches, nausea and increased heart rate after consuming the slightest amount of alcohol? Well, scientists have succeeded in clarifying this phenomenon on a molecular level. Namely, the reason for this is the defect of the gene which codes for the enzyme ALDH2. This enzyme is responsible for the breakdown of acetaldehyde – an intermediate product in ethanol metabolism, which is even more toxic than ethanol itself. In people with a defect of the ALDH2 gene, acetaldehyde accumulates, and this is the reason why they usually avoid drinking. Despite the fact that this defect is more characteristic of Asians, it does occur in other peoples as well.

Also enzyme ADH1 is important for alcohol metabolism as it is responsible for the first stage of the metabolism of ethanol into acetaldehyde. Researchers have discovered that a mutation can occur also in the genes that encode enzyme ADH1 and this influences greatly the efficiency of ethanol conversion. These mutations are actually not as defining as the one in the ALDH2 gene, but they still greatly determine alcohol sensitivity.

About metabolism of alcohol

Alcohol in alcoholic beverages is, chemically speaking, ethanol. Ethanol enters from the digestive system into the blood and has numerous toxic effects. As a result cells have mechanisms, which degrade ethanol into acetic acid, carbon dioxide and water. The first step in the metabolism of alcohol is the transformation of ethanol to acetaldehyde. This compound is even more toxic than ethanol itself and the negative consequences of drinking alcohol originate mostly from the toxic effects of this compound. It is thus important for cells to have mechanisms that can quickly transform it into acetic acid. Two enzymes perform this function. The first one is ALDH1 (acetaldehyde dehydrogenises 1) and the second one is ALDH2 (acetaldehyde dehydrogenises 2). In the third step the acetic acid transforms into acetyl-CoA, which becomes part of the further metabolic processes in the cell.

Scientists have discovered that a defect in the enzyme ALDH2 is responsible for the over sensitivity towards alcohol. The improper functioning of this enzyme causes acetaldehyde not to be removed from cells fast enough. The majority of Asians, who have a less active form of the enzyme, have guanine (G) switched in the same locus with adenine (A) in the ALDH2 gene. As a result there is amino acid switch, which disables functioning. Mutation can occur also in one of three ALDH1 genes, but fortunately the errors in these genes are not as crucial as one in the ALDH2 gene.