A COMPARATIVE-STUDY OF CONSTITUTIVE AND INDUCED ALKOXYRESORUFIN O-DEALKYLATION AND INDIVIDUAL CYTOCHROME-P450 FORMS IN CYNOMOLGUS MONKEY (MACACA-FASCICULARIS), HUMAN, MOUSE, RAT AND HAMSTER LIVER-MICROSOMES

The expression of constitutive and inducible cytochrome P450 forms was measured in cynomolgus monkey liver and compared with man, rat, mouse and hamster. Four alkoxyresorufin O-dealkylation (AROD) activities wi dely used as indicators of P450 induction were measured: methoxy-resor ufin O-demethylation (MROD), ethoxyresorufin O-deethylation (EROD), pe ntoxyresorufin O-dealkylation (PROD) and benzyloxyresorufin O-dealkyla tion (BROD). In monkeys there were no sex-differences in untreated, ph enobarbitone (PB)- or beta-naphthoflavone (BNF)-treated animals in ARO D activities, or in individual P450 proteins detected by immunoblottin g. Basal MROD and EROD activities varied by less than 7-fold between t he five species, but the comparative pattern of basal MROD, EROD, PROD and BROD activities (the ''MEPB profile'') was very species-specific, with monkeys being similar to rats but different from man, mouse and hamster. The induction of AROD activities by PB and BNF was also highl y species-specific. Monkeys expressed constitutive proteins immunorela ted to the CYP1A, CYP2A, CYP2B, CYP2C and CYP3A sub-families (human CY P2A6 cross-reacted with the anti-rat CYP2B1 antibodies used, and so CY P2A and CYP2B forms could not be separately identified in the monkey). Single constitutive immunoblot bands were identified in monkey for CY P1A (54 kDa), CYP2A/CYP2B (51 kDa) and CYP3A (51 kDa), respectively, b ut two strong (51 and 52 kDa) plus two weak (49 and 49.5 kDa) bands we re shown for CYP2C. Human liver expressed CYP1A2 (54 kDa), CYP2A6 (51 kDa), CYP3A4 (50.5 kDa) and three CYP2C9-immunorelated protein bands ( 48, 50 and 54 kDa). In monkeys BNF induced the 54 kDa CYP1A protein an d CYP1A-dependent MROD, EROD and PROD activities (18-, 15- and 6-fold increases in activity, respectively), whereas PB strongly induced the 51 kDa CYP2A/CYP2B protein but did not induce PROD activity. PB also i nduced non-constitutive CYP2A/CYP2B protein bands at 49 and 52 kDa in some monkeys. BROD activity was induced less that four-fold by either PB or BNF in monkeys. In conclusion, cynomolgus monkeys expressed a ra nge of constitutive CYP1A, CYP2A or CYP2B, CYP2C and CYP3A proteins si milar to man, and a range of AROD monooxygenase reaction rates similar to both man and rat, but the basal MEPB profile of AROD activities in monkeys was more similar to rat than to man. MROD and EROD were good measures of CYP1A induction by polycyclic aromatic hydrocarbons in cyn omolgus monkeys, but neither PROD nor BROD were indices of CYP2B induc tion by PB.