Methoxyresorufin: an inappropriate substrate for cyp1a2 in the mouse

• Published in: Biochemical pharmacology Vol. 56; no. 12; pp. 1657 - 1660
• Main Authors: Hamm, Jonathan T, Ross, David G, Richardson, Vicki M, Diliberto, Janet J, Birnbaum, Linda S
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15.12.1998; Elsevier Science
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Aryl Hydrocarbon Hydroxylases - biosynthesis; Aryl Hydrocarbon Hydroxylases - metabolism; Benzofurans; Biological and medical sciences; CYP1A2; Cytochrome P-450 CYP1A1 - biosynthesis; Cytochrome P-450 CYP1A1 - metabolism; Cytochrome P-450 CYP1A2 - biosynthesis; Cytochrome P-450 CYP1A2 - metabolism; Cytochrome P-450 Enzyme System - biosynthesis; Cytochrome P-450 Enzyme System - metabolism; Enzyme Induction; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Male; methoxyresorufin; Mice; Mice, Inbred Strains; Mice, Knockout; Microsomes, Liver - drug effects; Microsomes, Liver - enzymology; mouse; Oxazines - metabolism; Oxidoreductases; Oxidoreductases - biosynthesis; Oxidoreductases - metabolism; Polychlorinated Biphenyls; Polychlorinated Dibenzodioxins; Substrate Specificity; mouse; methoxyresorufin; CYP1A2; substrate specificity; Isozyme; Cytochrome P450; Rodentia; Microsome; Metabolism; In vitro; Vertebrata; Mammalia; Enzymatic activity; Investigation method; Mouse; Animal; Substrate specificity
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(98)00241-X

Hepatic microsomes derived from Cyp1 a2(−/−) knockout (KO) and parental strains of mice, C57BL/6N and 129Sv, were used to examine the specificity of methoxyresorufin and acetanilide as substrates for CYP1A2 activity. In addition, animals from each group were exposed to CYP1-inducing compounds. As expected, microsomes from untreated 1 a2 KO mice did not have immunodetectable CYP1A2 protein; however, methoxyresorufin- O-demethylase (MROD, 25.5 ± 6.1 pmol/min/mg protein) and acetanilide-4-hydroxylation (ACOH, 0.64 ± 0.04 nmol/min/mg protein) activities were still present. Furthermore, induction of ethoxyresorufin- O-deethylase (EROD) by 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) in 1 a2 KO mice was accompanied by a greater than 70-fold increase in MROD activity. In contrast, ACOH was only induced 2-fold by TCDD. As with 1 a2 KO mice, the parental strains exposed to TCDD or 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF) showed substantial EROD and MROD induction, whereas ACOH activity was induced to a lesser degree. PCB153 (2,2′,4,4′,5,5′-hexachlorobiphenyl) resulted in low levels of both EROD and MROD induction. Results indicate that both substrates are subject to metabolism by non-CYP1A2 sources, and the apparent contribution of CYP1A1 activity to methoxyresorufin metabolism makes MROD unsuitable for differentiating CYP1A1 and CYP1A2 activities in the mouse.