STUDIES WITH cDNA PROBES ON THE IN VIVO EFFECT OF ETHANOL ON EXPRESSION OF THE GENES OF ALCOHOL METABOLISM

Mice (Mus musculus) from three genetic strains with variable responses to ethanol challenge (BALB/c, C57BL/6J and 129/ReJ) were used to evaluate the effect of ethanol feeding on hepatic mRNA specific to the two primary enzymes of ethanol metabolism; alcohol dehydrogenase (ADH; E.C. 1.1.1.1) and aldehyde dehydrogenase (ALDH; E.C. 1.2.1.3). Adh-1 (ADH) and Ahd-2 (ALDH) specific mRNA were evaluated on the livers of ethanol-fed mice and from their age, sex and genotype matched controls (using an isocaloric liquid diet). C57BL/6J (alcohol resistant) mice show a significant (approx. 200%) increase in ADH-1 mRNA levels after ethanol treatment, compared to their matched controls. BALB/c (alcohol sensitive) mice have approximately a 20% increase with ethanol treatment while 129/ReJ (alcohol sensitive) mice show a slight reduction in the ADH-1 specific mRNA following ethanol feeding. A strain-specific pattern is also apparent in the AHD-2 mRNA as a result of ethanol feeding in the experimental animals. C57BL/6J mice have an increase and BALB/c mice show no apparent change in the AHD-2 mRNA. 129/ReJ mice fed an ethanol diet, on the other hand, appear to have a decrease in the level of AHD-2 hepatic mRNA as compared to their matched controls. The relative mRNA levels of the two genes correlate well with the respective enzyme activity levels, but for mice on the control diet only. Ethanol feeding, which causes an apparent reduction in hepatic ADH enzyme activity in BALB/c and 129/ReJ and an apparent increase in ALDH activity in C57BL/6J (under the experimental protocols used) also alters the mRNA levels specific to the two genes. However, changes in the mRNA levels after ethanol feeding cannot be directly related to the changes seen in enzyme activity. The observed steady state level of AHD-2 mRNA and the increase in ALDH activity after ethanol feeding, which is unique to C57BL/6J mice, is expected to offer a faster clearance (metabolism) of acetaldehyde, the toxic metabolite, and may be responsible for, or contribute to, the relative resistance of this strain to ethanol.