The identification and formation of 20-aldehyde leukotriene B4.

Microsomes of human polymorphonuclear leukocytes (PMN) in the presence of 100 microM NADPH converted 0.6 microM leukotriene B4 (LTB4) to 20-OH-LTB4 (retention time = 18.0 min) and to two additional compounds designated I (retention time = 16.8 min) and II (retention time = 9.6 min) as analyzed by reverse-phase high performance liquid chromatography (HPLC). Compounds I and II were also formed from the reaction of 1.0 microM 20-OH-LTB4, PMN microsomes, and 100 microM NADPH; the identity of compound II was confirmed as 20-COOH-LTB4 by gas chromatography-mass spectrometry. Equine alcohol dehydrogenase in the presence of 100 microM NAD+ in 0.2 M glycine buffer (pH 10.0) converted 20-OH-LTB4 to 20-aldehyde (CHO) LTB4, which coeluted with compound I on reverse-phase HPLC. In the presence of 100 microM NADH in 50 mM potassium phosphate buffer (pH 6.5), equine alcohol dehydrogenase reduced both 20-CHO-LTB4 and compound I to 20-OH-LTB4, indicating the identity of compound I as 20-CHO-LTB4. Gas chromatography-mass spectrometry of trideuterated O-methyl-oxime trimethylsilyl ether methyl ester derivative of 3H-labeled compound I definitively established compound I as 20-CHO-LTB4. Addition of immune IgG to cytochrome P-450 reductase or 1.0 mM SKF-525A completely inhibited the formation of 20-CHO-LTB4 from 20-OH-LTB4, indicating that the reaction was catalyzed by a cytochrome P-450. LTB5 (3.0 microM), a known substrate for cytochrome P-450LTB and a competitive inhibitor of LTB4 omega-oxidation, completely inhibited the omega-oxidation of 1.5 microM 20-OH-LTB4 to 20-CHO-LTB4, indicating that the cytochrome P-450 was P-450LTB. Conversion of 1.0 microM 20-CHO-LTB4 to 20-COOH-LTB4 by PMN microsomes was also dependent on NADPH and inhibited by antibody to cytochrome P-450 reductase, 1.0 mM SKF-525A, or 5.0 microM LTB5, indicating that this reaction was also catalyzed by cytochrome P-450LTB. These results identify the novel metabolite 20-CHO-LTB4 and indicate that cytochrome P-450LTB catalyzes three sequential omega-oxidations of LTB4 leading to the formation of 20-COOH-LTB4 via 20-OH-LTB4 and 20-CHO-LTB4 intermediates.

Isomeric prostaglandin F2 compounds arising from prostaglandin D2: a family of icosanoids produced in vivo in humans.

Prostaglandin (PG) D2 has been shown to be transformed by human 11-ketoreductase to 9 alpha,11 beta-PGF2, a biologically active metabolite that is produced in vivo. During the course of developing a mass spectrometric assay for 9 alpha,11 beta-PGF2, several compounds with characteristics similar to PGF2 were detected in both plasma and urine of normal humans by selected ion monitoring. Analysis of pooled plasma obtained from patients with mastocytosis during severe episodes of systemic mast cell activation associated with the release of markedly increased quantities of PGD2 was revealing in that all of these compounds were present in approximately 800-fold greater abundance compared to levels found in normal plasma, suggesting that these compounds arose from PGD2 metabolism. Complete electron impact mass spectra were obtained of these compounds in both plasma and urine; these spectra established that they were all isometric forms of PGF2. Approximately 16 isomeric PGF2 compounds were identified. Treatment with butylboronic acid indicated that the C-9 and C-11 hydroxyls were trans in approximately one-third of the compounds and cis in approximately two-thirds. Preliminary experiments suggest that PGD2 is a very labile compound in vivo and undergoes extensive isomerization, after which reduction by 11-ketoreductase yields a family of more stable isomeric PGF2 compounds. Elucidating the profile of biological activity of these compounds and their mechanism of formation will contribute importantly to our understanding of the biological consequences of PGD2 release in vivo. These results also bring into question the reliability of assays for PGF2 alpha and its metabolites in human biological fluids as a specific index of endogenous PGF2 alpha biosynthesis, as these assays may also measure in part isomeric PGF2 compounds arising from PGD2 metabolism.