Phenobarbital inducibility and differences in protein expression of an animal model

Aldehyde dehydrogenases (ALDHs) are a group of enzymes which catalyze the c onversion of aldehydes to the corresponding carboxylic acids in a NAD(P)(+) -dependent reaction. In mammals, different ALDHs are constitutively express ed in liver, stomach, eye and skin. In addition, inducible ALDH-isoenzymes are detectable in many tissues; apart from other physico- and immuno-chemic al differences, two cytosolic ALDHs (ALDH1A3 and ALDH3A1) are known to be a ctivated in rat liver, by different types of inducers of drug metabolism. P henobarbital-type inducers increase the ALDH1A3, while polycyclic hydrocarb ons (such as BaP and TCDD) increase the expression of the two members of AL DB3A subfamily (3A1 and 3A2). In this study, we used two Wistar rat substra ins which have been well-characterized for different inducibility of ALDH1A 3 enzyme activity after treatment with phenobarbital. Animals that respond (RR) or do not respond (rr) to treatment have been inbred for almost 25 yea rs, offering a useful experimental model. Apart from the level of ALDH1A3 i nduced enzyme expression after phenobarbital treatment, no other difference s between the two substrains have been noticed, as far as drug metabolizing enzyme activities (like the pentoxy- and ethoxy-O-dealkylation rate) are c oncerned. According to the present results, the ALDH1A3 expression is still the only difference between the two substrains. Immunoblotting experiments with polyclonal antibodies raised against CYP2B1 or/and CYP1A1/1A2 showed no differences between the two substrains. Additionally, data concerning ti me- and dose-response induction of ALDH1A3 after phenobarbital and griseofu lvin treatment are presented. It is concluded that these two Wistar rat sub strains represent a unique animal model for studying what seems to be the o nly difference between these substrains - the genetic basis of the phenobar bital induction. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved .