Oxidation of leukotrienes at the omega end: demonstration of a receptor for the 20-hydroxy derivative of leukotriene B4 on human neutrophils and implications for the analysis of leukotriene receptors.

Leukotriene B4 [LTB4; (5S,12R)-5,12-dihydroxy-6,14-cis-8,10-trans-icosatetraenoic acid] and its 20-hydroxy derivative [20-OH-LTB4; (5S,12R)-5,12,20-trihydroxy-6,14-cis-8,10-trans-icosatetraenoic acid] are principal metabolites produced when human neutrophils (hPMNs) are stimulated by the calcium ionophore A23187. These compounds were purified to homogeneity by Nucleosil C18 and silicic acid HPLC and identified by UV absorption and gas chromatographic/mass spectral analyses. 20-OH-LTB4 is considerably more polar than LTB4 and interacts weakly with the hydrophobic Nucleosil C18 resin, whereas LTB4 interacts strongly, reflecting the hydrophobic C13-C20 domain in LTB4. Specific binding of highly purified [3H]LTB4 and [3H]20-OH-LTB4 to hPMNs was assessed. Binding of [3H]20-OH-LTB4 could be largely displaced by an excess of nonlabeled LTB4 or 20-OH-LTB4 but not by 15-hydroxyicosatetraenoic acid (15-HETE), (5S,12S)-5,12-dihydroxy-6,10-trans-8,14-cis-icosatetraenoic acid [(5S,12S)-diHETE], or the 6-trans stereoisomer of LTB4 at 1 microM. In contrast, [3H]LTB4 displays a high level of nonspecific binding to human PMNs, which makes assessment of the Kd for LTB4 binding unobtainable. Binding measurements for [3H]LTB4 were performed in a buffer containing bovine serum albumin, and under these conditions significantly less nonspecific binding was observed. The apparent Kd for high-affinity binding sites on human PMNs at 0 degrees C was 31.3 X 10(-9) M for LTB4 and 14.3 X 10(-9) M for 20-OH-LTB4. In addition, we observed a saturable low-affinity receptor for 20-OH-LTB4 with a Kd of approximately 100 X 10(-9) M and 2 X 10(5) receptors per cell. The data from this study suggest that omega oxidation represents a major pathway for metabolism of LTB4 as well as other arachidonate metabolites. LTB4 and 20-OH-LTB4 express similar functional activities and share common binding properties to hPMNs but differ significantly in their physical properties. It is the unique physical characteristics of 20-OH-LTB4 that suggest that arachidonate metabolites oxidized at the omega position may be more important agents in inflammation than LTB4.