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Introduction:
Alcohol is the favorite mood-altering drug in the United States
and its effects, both pleasant and unpleasant, are well-known.
What may not be well known is the fact that alcohol is a toxic
drug that produces pathological changes (cirrhosis) in liver
tissue and can cause death.
Alcohol is readily absorbed from the gastrointestinal tract;
however, alcohol cannot be stored and therefore, the body must
oxidize it to get rid of it. Alcohol can only be oxidized in
the liver, where enzymes are found to initiate the process.
In addition, alcohol directly contributes to malnutrition
since a pint of 86 proof alcohol (not an unusual daily intake
for an alcoholic) represents about half of the daily energy requirement.
However, ethanol does not have any minerals, vitamins, carbohydrates,
fats or protein associated with it. Alcohol causes inflammation
of the stomach, pancreas, and intestines which impairs the digestion
of food and absorption into blood. Moreover, the acetaldehyde
(the oxidation product) can interfere with the activation of
vitamins.
The first step in the metabolism of alcohol is the oxidation
of ethanol to acetaldehyde catalyzed by alcohol/dehydrogenase
containing the coenzyme NAD+. The acetaldehyde is
further oxidized to acetic acid and finally CO2 and
water through the citric acid cycle. A number of metabolic effects
from alcohol are directly linked to the production of an excess
of both NADH and acetaldehyde.
CH3CH2OH + NAD+ ---> CH3CH=O
+ NADH + H+
The red box shows the above reaction.
(Adapted from C.S. Lieber, Sci. Am. 234(3),
25(1976)
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