Cyclopropylamine inactivation of cytochromes P450: role of metabolic intermediate complexes.
The inactivation of cytochrome P450 enzymes by cyclopropylamines has been attributed to a mechanism involving initial one-electron oxidation at nitrogen followed by scission of the cyclopropane ring leading to covalent modification of the enzyme. Herein, we report that in liver microsomes N-cyclopropylbenzylamine (1) and related compounds inactivate P450 to a large extent via formation of metabolic intermediate complexes (MICs) in which a nitroso metabolite coordinates tightly to the heme iron, thereby preventing turnover. MIC formation from 1 does not occur in reconstituted P450 systems with CYP2B1/2, 2C11 or 2E1, or in microsomes exposed to gentle heating to inactivate the flavin-containing monooxygenase (FMO). In contrast, N-hydroxy-N-cyclopropylbenzylamine (3) and N-benzylhydroxylamine (4) generate MICs much faster than 1 in both reconstituted and microsomal systems. MIC formation from nitrone 5 (PhCH = N(O)cPr) is somewhat faster than from 1, but very much faster than the hydrolysis of 5 to a primary hydroxylamine. Thus the major overall route from 1 to a P450 MIC complex would appear to involve FMO oxidation to 3, further oxidation by P450 and/or FMO to nitrone 5' (C2H4C = N(O)CH2Ph), hydrolysis to 4, and P450 oxidation to alpha-nitrosotoluene as the precursor to oxime 2 and the major MIC from 1.
Cerny
Matthew A
MA
Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, USA.
Hanzlik
Robert P
RP
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D003521:Cyclopropanes / Q000737:chemistry / Q000494:pharmacology*; D019362:Cytochrome P-450 CYP2B1 / Q000378:metabolism; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D000072467:Cytochrome P450 Family 2; D004583:Electrons; D005415:Flavins / Q000737:chemistry; D005559:Formamides / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D006358:Hot Temperature; D006868:Hydrolysis; D019811:Hydroxylamine / Q000737:chemistry; D007477:Ions; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D008956:Models, Chemical; D009603:Nitroso Compounds / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism; D010105:Oxygenases / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D013053:Spectrophotometry; D039181:Steroid 16-alpha-Hydroxylase / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
D003521:Cyclopropanes; D005415:Flavins; D005559:Formamides; D007477:Ions; D009603:Nitroso Compounds; D019811:Hydroxylamine; D006418:Heme; C031066:formamide; C067351:cyclopropylamine; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; D013250:Steroid Hydroxylases; D019392:Cytochrome P-450 CYP2E1; C020066:dimethylaniline monooxygenase (N-oxide forming); D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D019362:Cytochrome P-450 CYP2B1; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C025619:steroid 16-beta-hydroxylase; C035324:2-nitrosotoluene; D010100:Oxygen