The effect of ethanol on drug oxidations in vitro and the significance of ethanol–cytochrome P-450 interaction

Abstract

The effect of ethanol on N-demethylation of aminopyrine in rat liver slices and in the microsomal fraction and on microsomal hydroxylation of pentobarbital and aniline was studied. With liver slices N-demethylation of aminopyrine was stimulated by 35-40% at low ethanol concentrations (2mm), whereas no stimulation occurred at high concentrations (100mm). With the liver microsomal fraction, an inhibitory effect was observed only at high ethanol concentrations (100mm). This was also observed with the other drugs studied. In agreement with these results, only at a high concentration did ethanol interfere with the binding of drug substrates to cytochrome P-450. Further, as previously reported, ethanol produced a reverse type I spectral change when added to the liver microsomal fraction. Evidence that this spectral change is due to removal of substrate, endogenously bound to cytochrome P-450, is reported. A dual effect of ethanol is assumed to explain the present findings; in liver slices, at a low ethanol concentration, the enhanced rate of drug oxidation is the result of an increased NADH concentration, whereas the inhibitory effect observed with the microsomal fraction at high ethanol concentration is due to the interference by ethanol with the binding of drug substrates to cytochrome P-450.

Interaction between Antipyrine and the Microsomal Ethanol Oxidation in Rat Liver

“…In liver slices, Cinti et al (1973) observed at low ethanol concentrations an enhanced rate of drug oxidation, probably as a result of increased NADH con centration. The same authors report an inhibition of microsomal drug metab olism in microsomal suspensions at high ethanol concentrations and attributed this to interference of ethanol with binding of drug substrates to cytochrome P-450.…”

The Effect of Chronic Alcohol Intake Upon the Hepatic Microsomal Carcinogen-activation System

“…This could be explained by the fact that in this experiment larger quantities of ethanol were administered, and, according to Cinti el al. [12], low doses of ethanol stimulate, whereas higher doses inhibit microsomal enzymes. Any dose level above 5 % v/v in water is regarded as producing liver damage [7] and this could explain the decrease in aryl hydrocarbon hydroxylase observed here.…”

“…Following intraperitoneal injection the microsomal protein and, correspondingly, the levels of the various components of the MEOS arc reduced. After oral in take the protein, initially lowered, recovers -presumably by the induction of the MEOS which has been reported for lower ethanol concentrations [12). The level to which the MEOS can be induced will be greatly influenced by the diet, especially the amount of lipid present [7j.…”

PROCEEDINGS OF THE British Pharmacological Society

“…The levels of ethanol required to inhibit the metabolism of most drugs by the hepatic microsomal fraction, around 100 mM (Rubin et al, 1970;Cinti, Grundin & Orrenius, 1973), are in general higher than those encountered except under cases of severe intoxication. It was of interest therefore to examine in vivo drug clearances several hours after a single dose of ethanol, when the ethanol had been completely removed from the blood.…”