Roles of 5-lipoxygenase and cyclooxygenase-2 in the biosynthesis of hemiketals E and D by activated human leukocytes.

The 2 hemiketal (HK) eicosanoids HKD and HKE are the major products of the biosynthetic crossover of the 5-lipoxygenase (5-LOX) and cyclooxygenase-2 (COX-2) pathways. HKs result from the rearrangement of a di-endoperoxide intermediate formed in the COX-2-dependent oxygenation of 5-hydroxyeicosatetraenoic acid (5-HETE). We analyzed HK biosynthesis in human leukocytes stimulated and defined the biosynthetic roles of 5-LOX and COX-2, using inhibitors and incubations with exogenous substrates. Activation of leukocytes with LPS followed by treatment with the calcium ionophore A23187 resulted in the formation of PGE, 5-HETE, and LTB as the principal metabolites of COX-2 and 5-LOX, respectively. The formation of HKD and HKE was highest after 15 min LPS treatment, and at that time, levels were similar to PGE, but less than 5-HETE and LTB The time course of HK formation paralleled that of 5-HETE and LTB, implying the availability of the 5-HETE substrate as a limiting factor in biosynthesis rather than expression levels of COX-2. Specific inhibitors of COX-2 and 5-LOX decreased formation of HKD and HKE Platelets did not form HKs from exogenous 5-HETE, implying that COX-1 is not involved. HKs are early products during an inflammatory event and require cells that express 5-LOX and COX-2 for their biosynthesis.-Giménez-Bastida, J. A., Shibata, T., Uchida, K., Schneider, C. Roles of 5-lipoxygenase and cyclooxygenase-2 in the biosynthesis of hemiketals E and D by activated human leukocytes.