ω-Hydroxylation of lipoxin B₄ by human neutrophil microsomes: Identification of ω-hydroxy metabolite of lipoxin B₄ and catalysis by leukotriene B₄ ω-hydroxylase (cytochrome P-450LTBω)

Lipoxin B₄ (LXB₄) is metabolized either by human neutrophils or by the neutrophil microsomes to a polar compound on a reverse-phase high-performance liquid chromatography. The metabolite is identified as 20-hydroxy-lipoxin B₄ (20-OH-LXB₄), a novel member in the arachidonic acid cascade, on the basis of ultraviolet spectrometry and gas chromatography-mass spectrometry. The neutrophil microsomes convert LXB₄ to its 20-hydroxy derivative under aerobic condition in the presence of NADPH. The reaction is inhibited by carbon monoxide, an inhibitor of cytochrome P-450 (P-450), and by antibodies raised against NADPH-P-450 reductase. A P-450 is thus involved in the ω-hydroxylation of LXB₄. The P-450 appears to be the one responsible for leukotriene B₄ (LTB₄) ω-hydroxylation, P-450LTBω, based on the following observations. The formation of 20-OH-LXB₄ is inhibited solely by substrates of P-450LTBω such as LTB₄ and leukotriene B₅ among various fatty acids including prostaglandins. The order of the inhibitory potencies of these substances on the LXB₄ ω-hydroxylation is the same as that of their affinities for LTB₄ ω-hydroxylase. LTB₄ inhibits the reaction in a competitive manner with the K_i value of 0.2 μM, which agrees with the K_m value for the LTB₄ ω-hydroxylation (0.3 μM).