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Vol. 28, Issue 3, 292-297, March 2000

Human Cytochrome P-450 Metabolism of Retinals to Retinoic Acids

Qing-Yu Zhang, Deborah Dunbar, and Laurence Kaminsky

Wadsworth Center, New York State Department of Health, Albany, New York

Retinoic acids have important pleiotropic biological effects and thus the potential for human cytochrome P-450s (CYPs) to mediate retinoic acid synthesis was investigated. We examined the retinoic acid synthetic activity of human cDNA-expressed CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, 3A4+ cytochrome b5 (b5), 3A5, and 4A11, expressed individually in insect cells together with NADPH-P-450 reductase. Only CYP1A1, 1A2, 1B1, and 3A4+b5 converted all-trans-retinal (20 µM) to all-trans-retinoic acid with turnover numbers of 0.53, 0.18, 0.20, and 0.41 nmol/min/nmol P-450, respectively. With 9-cis-retinal as substrate, CYP1A2 exhibited a turnover number of 1.58 nmol/min/nmol P-450 whereas CYP1A1, 2C19, and 3A4+b5 had turnover numbers of 0.40, 0.27, and 0.41 nmol/min/nmol P-450, respectively. For CYP3A4 activities with both retinals, b5 was required. Kinetic analyses revealed that CYP1A1, 1A2, and 3A4+b5 with all-trans-retinal had apparent Km values of 55, 356, and 255 µM, and Vmax values of 2.0, 8.3, and 6.3 nmol/min/nmol P-450, respectively, and with 9-cis-retinal had Km values of 77, 91, and 368 µM, and Vmax values of 2.7, 9.7, and 7.6 nmol/min/nmol P-450, respectively. The 9-cis retinoic acid synthetic activity of a group of 12 human liver microsomes correlated only with the CYP1A2 activity (r = 0.96), implicating CYP1A2 in human liver microsomal metabolism of 9-cis- retinal to 9-cis-retinoic acid. These studies have indicated that human CYPs are capable of catalyzing retinal to retinoic acid metabolism, but the physiological relevance of this metabolism is still unclear.

Copyright © 2000 by The American Society for Pharmacology and Experimental Therapeutics


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Copyright © 2000 by the American Society for Pharmacology and Experimental Therapeutics.