Oxidation of prostaglandin H-2 and prostaglandin H-2 analogues by human cytochromes P450: analysis of omega-side chain hydroxy metabolites and four steroisomers of 5-hydroxyprostaglandin I-1 by mass spectrometry

The objective was to examine the NADPH-dependent oxygenation of prostagland in H-2 (PGH(2)) and three PGH(2) analogues, 9,11-diazo-15-deoxy-PGH(2) (U51 605), 9,11-epoxymethano-PGH(2) (U44069), and 11,9-epoxymethano-PGH(2) (U466 19), by cytochromes P450, and to characterize the metabolites by mass spect rometry. CYP2C19, CYP4A11, CYP4F8, and liver and renal cortical microsomes oxidized the omega -side chain of U44069, U46619, and U51605, whereas only CYP4F8 oxidized the omega -side chain of PGH(2). PGH(2) was transformed to four stereoisomers of 5-hydroxy-PGI(1) by recombinant cytochromes P450. CYP 4F8 formed the 5-hydroxy-PGI(1) isomers in small amounts compared to the 19 -hydroxy metabolites of PGH(2). Isomers of 5-hydroxy-PGI(1) and 6-keto-PGF( 1 alpha) were detectable when PGH(2) decomposed in the presence of hemin, h emoglobin, or heat-inactivated microsomes. 5-Hydroxy-PGI(1) is likely forme d from PGH(2) in a pseudo-enzymatic reaction involving homolytic scission o f the endoperoxide and formation of an ether between C-9 and C-6 and a carb on-centered radical at C-5, which reacts with molecular oxygen. CYP1F8 cata lyzes 19-hydroxylation of PGH(2), but the absolute configuration of the 19- hydroxy group is unknown, whereas human seminal fluid contains (19R)-hydrox y-PGE(2). CYP4F8 was found to metabolize U51605 to 90% of the (19R)-hydroxy metabolite, providing further evidence in favor of a role of CYP4F8 in bio synthesis of (19R)-hydroxy PGE in human seminal vesicles. We conclude that omega -side chain hydroxylation of PGH(2) analogues may be catalyzed by man y different cytochromes P450, but only CYP4F8 oxidizes the omega -side chai n of PGH(2) efficiently. (C) 2001 Elsevier Science Inc. All rights reserved .