Ethanol-inducible cytochrome P-450 activity and increase in acetaldehyde bound to microsomes after chronic administration of acetaldehyde or ethanol.

Chronic ethanol consumption results in acetaldehyde adduct formation with proteins such as haemoglobin and liver proteins in vivo. Our purpose was to study the binding of acetaldehyde to liver microsomal proteins, a site of ethanol oxidation via cytochrome P-450 (especially P-450 II E1), after chronic administration of ethanol or acetaldehyde for 21 days to rats. The liver microsomal oxidation of 1-butanol by the ethanol-inducible P-450 also was examined. Acetaldehyde bound to liver microsomal proteins was higher in ethanol-fed rats compared with acetaldehyde-treated rats (0.735 vs 0.413 nmol/mg of protein respectively). The biotransformation of n-butanol to butyraldehyde by liver microsomes was increased (by 136%) in ethanol-fed rats vs controls, whereas in acetaldehyde-treated rats this increase was much lower (only 27%). However, in this last group, a significant negative relationship between the quantity of acetaldehyde bound to microsomal proteins and the monooxygenase-catalyzed transformation of butanol by liver microsomes was demonstrated (r = -0.79, P less than 0.01). These results suggest that proteins of liver microsomes are a target for acetaldehyde binding during ethanol oxidation and such adduct formation could impair the oxidative properties of the alcohol-inducible cytochrome P-450.