Human cytochrome P-450 metabolism of retinals to retinoic acids.
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 b(5) (b(5)), 3A5, and 4A11, expressed individually in insect cells together with NADPH-P-450 reductase. Only CYP1A1, 1A2, 1B1, and 3A4+b(5) converted all-trans-retinal (20 microM) 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+b(5) had turnover numbers of 0.40, 0.27, and 0.41 nmol/min/nmol P-450, respectively. For CYP3A4 activities with both retinals, b(5) was required. Kinetic analyses revealed that CYP1A1, 1A2, and 3A4+b(5) with all-trans-retinal had apparent K(m) values of 55, 356, and 255 microM, and V(max) values of 2.0, 8.3, and 6.3 nmol/min/nmol P-450, respectively, and with 9-cis-retinal had K(m) values of 77, 91, and 368 microM, and V(max) 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.
Zhang
Q Y
QY
Wadsworth Center, New York State Department of Health, Albany, New York 12201-0509, USA.
Dunbar
D
D
Kaminsky
L
L
D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004224:Diterpenes; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012172:Retinaldehyde / Q000378:metabolism*; D014212:Tretinoin / Q000378:metabolism*
D001571:Benzoflavones; D004224:Diterpenes; D007527:Isoenzymes; D011994:Recombinant Proteins; C031390:9-cis-retinal; D014212:Tretinoin; C011512:alpha-naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D009251:NADPH-Ferrihemoprotein Reductase; D012172:Retinaldehyde