ISOLEUKOTRIENES ARE BIOLOGICALLY-ACTIVE FREE-RADICAL PRODUCTS OF LIPID-PEROXIDATION

The free radical oxidation of arachidonic acid esterified to glycerophospholipids is known to generate complex metabolites, termed isoprostanes, that share structural features of prostaglandins derived from prostaglandin H-2 synthase. Furthermore, certain isoprostanes have been found to exert biological activity through endogenous receptors on cell surfaces. Using mass spectrometry and ancillary techniques, the free radical oxidation of 1-hexadecanoyl-2-arachidonoyl-glycerophosphocholine was studied in the search for products of arachidonic acid isomeric to the leukotrienes that are derived from 5-lipoxygenase-catalyzed metabolism of arachidonic acid. Several conjugated triene metabolites were chromatographically separated from known 5-lipoxygenase products and structures characterized as 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid esterified to the glycerophosphocholine backbone. We have termed these products as B-4-isoleukotrienes. Following saponification some, but not all, B-4-isoleukotrienes were found to exert biological activity in elevating intracellular calcium in Indo-1-loaded human polymorphonuclear leukocytes. This activity could be blocked by a leukotriene B-4 receptor antagonist. An EC(50) of approximately 30 nM was determined for one unique B-4-isoleukotriene with a relative retention index of 2.54. We have shown that free radical processes can lead to the formation of biologically active isoleukotrienes in glycerophosphocholine liposomes, and we propose that B-4-isoleukotrienes may also be formed in membrane glycerophospholipids as a result of lipid peroxidation during tissue injury. Such B-4-isoleukotrienes could then mediate events of tissue damage through activation of leukotriene B-4 receptors on target cells.