5(S),15(S)-DIHYDROXYEICOSATETRAENOIC ACID AND LIPOXIN GENERATION IN HUMAN POLYMORPHONUCLEAR CELLS - DUAL-SPECIFICITY OF 5-LIPOXYGENASE TOWARDS ENDOGENOUS AND EXOGENOUS PRECURSORS

5-Lipoxygenase activation of human blood polymorphonuclear cells (PMN) from asthmatic patients (asthmatics) was studied to investigate wheth er differences may exist with healthy subjects (controls). The respect ive cell capacities to produce lipoxins (LXs), leukotrienes, and 5(S), 15(S)-dihydroxyeicosatetraenoic acid [5(S),15(S)-diHETE] were compared under in vitro stimulation by ionophore A23187, with or without exoge nous 15(S)-hydoxyeicosatetraenoic acid [15(S)-HETE]. Eicosanoids were analyzed by elution with an isocratic reverse-phase high performance L iquid chromatography system, and their profiles, detected by simultane ous monitoring at 302, 280, and 246 nm, were evaluated on the basis of chromatographic behavior: UV spectral characteristics and coelution w ith synthetic standards. In the presence of exogenous 15(S)-HETE, huma n PMN were able to produce LXs and 5(S),15(S)-diHETE, Moreover, the to tal amount of LXs biosynthesized by PMN from asthmatics was twofold hi gher than that biosynthesized by PMN from controls. In the absence of exogenous 15(S)-HETE, PMN from asthmatics were able to produce 5(S),15 (S)-diHETE, and LXs from endogenous sources, whereas in the same exper imental conditions, no detectable amounts of these compounds were rele ased by PMN from controls. The levels of 5(S),15(S)-diHETE, and LXs bi osynthesized from endogenous arachidonic acid were highly correlated. Two different LX patterns were observed involving two possible metabol ic pathways: (a) via the intermediate 5,6-epoxytetraene alone for LXs generation from exogenous 15(S)-HETE; and (5) via 5,6- and/or 14,15-ep oxytetraenes leading to the formation of an enzyme-bound delocalized c arbocation for LXs generation from endogenous arachidonate, respective ly. The enhanced 5-lipoxygenase activation of blood PMN from asthmatic s and the metabolism of exogenous 15(S)-HETE may reflect a priming ind uced by various mediators released from environmental cells, and could be considered as a model of transcellular signalization between PMN a nd endothelial cells.