Comparison of rat and human cytochrome P450 (CYP) sources of N-alkylprotoporphyrin IX. Formation after interaction with porphyrinogenic xenobiotics: studies with cDNA-expressed single CYP enzymes.
1. The porphyrinogenicity of certain xenobiotics is due to mechanism-based inactivation of selected cytochrome P450 (CYP) enzymes, with concurrent formation of N-alkylprotoporphyrins (N-alkylPPs), which disrupt control of haem biosynthesis. An ambiguity arises when extrapolating results obtained with such porphyrinogenic xenobiotics in animals to humans owing to species' differences in CYP enzymes. The objective was to use cDNA-expressed individual rat CYP enzyme preparations in microsomes prepared from baculovirus-infected insect cells to determine which rat CYP enzymes were the source of N-alkylPPs after interaction with three porphyrinogenic xenobiotics and to compare the results with formation of N-alkylPPs in individual human CYP enzyme orthologues. 2. A sensitive fluorometric technique was employed to quantitate N-alkylPP formation after interaction of individual CYP enzymes with a porphyrinogenic xenobiotic. 3. N-alkylPP formation was found following the interaction of three porphyrinogenic xenobiotics with CYP1A2, 2B1, 2C6, 2C11 and 3A2, in amounts ranging from 0.45 to 0.07 nmol N-alkylPP nmol(-1) CYP. The results obtained with rat CYP1A2, 2C6, 2C11 and 3A2 were compared with those previously obtained with the human CYP orthologues 1A2, 2C9 and 3A4. 4. Some results corresponded while others did not, reinforcing a previous recommendation that when dealing with xenobiotics whose porphyrinogenicity depends upon interaction with CYP enzymes resulting in N-alkylPP formation, animal experiments should be augmented with studies using human CYP preparations.
Gamble
J T
JT
Department of Pharmacology & Toxicology, Faculty of Health Sciences, Queen's University, Kingston, Ontario, Canada K7L 3N6.
Nakatsu
K
K
Marks
G S
GS
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D016367:Baculoviridae / Q000378:metabolism; D002460:Cell Line; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D019362:Cytochrome P-450 CYP2B1 / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D018076:DNA, Complementary / Q000378:metabolism; D006801:Humans; D007313:Insecta; D008565:Membrane Proteins; D008861:Microsomes / Q000378:metabolism; D009249:NADP / Q000494:pharmacology; D011524:Protoporphyrins / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D013050:Spectrometry, Fluorescence; D039181:Steroid 16-alpha-Hydroxylase / Q000378:metabolism; D013255:Steroid 21-Hydroxylase / Q000378:metabolism; D015262:Xenobiotics / Q000494:pharmacology
D018076:DNA, Complementary; D008565:Membrane Proteins; D011524:Protoporphyrins; D015262:Xenobiotics; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; C028025:protoporphyrin IX; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; C089877:Cyp2c6v1 protein, rat; C465260:Cyp3a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D019362:Cytochrome P-450 CYP2B1; D051544:Cytochrome P-450 CYP3A; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; D013255:Steroid 21-Hydroxylase