Stereospecificity of leukotriene B4 and structure-function relationships for chemotaxis of human neutrophils

The chemotactic activity of leukotriene B4 (5S, 12R Dihydroxy 6, 14 cis, 8, 10 trans eicosatetraenoic acid) (LTB4) was examined by using a sensitive Boyden-chamber assay. The activity of LTB4 was compared to other biosynthetic stereoisomers: 5S, 12R Dihydroxy 6, 8, 10 trans 14 cis eicosatetraenoic acid (6-trans LTB4); 5S, 12S Dihydroxy 6, 8, 10 trans 14 cis eicosatetraenoic acid (12-epi-6-trans LTB4), 5S, 12S DiHETE; the metabolic product 20-Hydroxy LTB4 (20-OH LTB4); methylated LTB4 (Methyl-LTB4), and the related monoHETE 5-HETE and 12-HETE. The compounds were purified by several steps of reverse phase and straight phase HPLC. The LTB4 exhibits measurable chemotactic activity at 10(-9) M with maximal activity at 10(-7) M and an ED50 of 10(-8) M. The LTB4 isomers and monoHETE were less chemotactic than previously reported. The monoHETE (5-HETE and 12-HETE), the isomer 12-epi-6-trans LTB4, and 5S, 12S DiHETE fail to attract neutrophils at levels between 10(-6) and 10(-5) M. If these compounds are chemotactic, then activity is at least four orders of magnitude less than that of LTB4. The isomer 6-trans LTB4 at 10(-6) to 10(-5) M induced chemotaxis with an extrapolated ED50 value of 10(-5) M, indicating that a trans for cis change in configuration at position 6 reduces the chemotactic activity of LTB4 by 1000-fold. Conversely, the metabolic product 20-OH LTB4 is at least as active as the native compound LTB4. Methylation of the carboxyl group of LTB4 reduces its chemotactic activity by two orders of magnitude. These results indicate a high degree of stereospecificity for the LTB4 receptor with strict dependence on hydroxyl group, and triene configuration and considerable dependence on the carboxyl group. Modification at the aliphatic omega end of the LTB4 molecule has a minimal effect on function, suggesting that the hydrophobicity of this portion of the molecule is not important for optimal activity. Furthermore, we propose that metabolic products of LTB4 may be of greater importance than LTB4 as physiologic inflammatory mediators in vivo.