MOLECULAR-BASIS OF THE DARK AGOUTI RAT DRUG OXIDATION POLYMORPHISM - IMPORTANCE OF CYP2D1 AND CYP2D2

The Dark Agouti rat has been proposed as a model for the human debriso quine 4-hydroxylase polymorphism. Earlier studies suggested that the p oor metabolizer phenotype in the Dark Agouti rat is caused by the abse nce of the expression of CYP2D1 mRNA. Although CYP2D1 is the major enz yme catalyzing debrisoquine 4-hydroxylation, other reports have indica ted the involvement of a CYP2D, purified from rat hepatic microsomes a nd presumed to be CYP2D2, which also exhibits this activity. The level s of CYP2D1 and CYP2D2 mRNAs were markedly lower in Dark Agouti as com pared to Sprague Dawley rats. Using a baculovirus expression system, r ecombinant CYP2D1 and CYP2D2 from Spodoptera frugiperda insect cells w ere examined and were found to both forms catalize debrisoquine 4-hydr oxylase activity. These results suggest that reduced debrisoquine 4-hy droxylase activity in the Dark Agouti rat is caused by the low level e xpression not only of CYP2D1, but also of CYP2D2. Interestingly, bunit rolol 4-hydroxylation was catalyzed by recombinant CYP2D2, while CYP2D 1 was inactive toward this substrate. Thus, the low bunitrolol 4-hydro xylation in Dark Agouti rats was caused by the low level of CYP2D2 exp ression in this rat strain. (C) 1998 Chapman & Hall Ltd.