Incorporation of platelet and leukocyte lipoxygenase metabolites by cultured vascular cells

When arachidonic acid metabolism is studied during platelet-endothelial interactions in vitro, the predominant cyclooxygenase end products of each cell type (thromboxane B2 and 6-keto-prostaglandin-F1 alpha, respectively) are essentially completely recovered in the cell-free supernatants of these reactions. In contrast, 50% of 12-hydroxy- 5,8,10,14-eicosatetraenoic acid (12-HETE), the major lipoxygenase metabolite from platelets, is released into the cell-free supernatant. In investigating the basis of this observation, we have found that platelet lipoxygenase metabolites were generated to the same extent during these coincubations but became rapidly incorporated into the endothelial cells. The endothelial cell-associated 12-HETE was present not only as free fatty acid, but was also incorporated into cellular phospholipids and triglycerides. When purified 3H-12-HETE, 3H-5-HETE (the major hydroxy acid lipoxygenase product of leukocytes), and 3H- arachidonic acid (the common precursor of these metabolites) were individually incubated with suspensions of cultured bovine aortic endothelial cells or smooth muscle cells, different patterns of intracellular lipid distribution were found. In endothelial cells, 12- HETE was incorporated equally into phospholipids and triglycerides, whereas 5-HETE was incorporated preferentially into triglycerides, and arachidonic acid was incorporated into phospholipids. In smooth muscle cells, both 12-HETE and 5-HETE showed more extensive incorporation into triglycerides. The rapid and characteristic incorporation and esterification of platelet and leukocyte monohydroxy fatty acid lipoxygenase products by endothelial and smooth muscle cells suggests a possible physiologic role for these processes in regulating vascular function.