Biological inactivation of 5-oxo-6,8,11,14-eicosatetraenoic acid by human platelets

Neutrophil-derived 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a p otent activator of neutrophils and eosinophils. In the present study we exa mined the biosynthesis and metabolism of this substance by platelets. Altho ugh platelets contain an abundant amount of 5-hydroxyeicosanoid dehydrogena se, the enzyme responsible for the formation of 5-oxo-ETE, they synthesize only very small amounts of this substance from exogenous 5-hydroxyeicosatet raenoic acid (5-HETE) unless endogenous NADPH is converted to NADP(+) by ad dition of phenazine methosulfate. Similarly, relatively small amounts of 5- oxo-ETE were formed by A23187-stimulated mixtures of platelets and neutroph ils, which instead formed substantial amounts of two 12-hydroxy metabolites of this substance, 5-oxo-12-HETE and 8-trans-5-oxo-12-HETE, which were ide ntified by comparison with authentic chemically synthesized compounds. Thes e metabolites were also formed from 5-oxo-ETE by platelets stimulated with thrombin or A23187. In contrast, unstimulated platelets converted 5-oxo-ETE principally to 5-HETE. Neither 5-oxo-12-HETE nor 8-trans-5-oxo-12-HETE had appreciable effects on neutrophil calcium levels or platelet aggregation a t concentrations as high as 10 mu mol/L, but both blocked 5-oxo-ETE-induced calcium mobilization in neutrophils with IC50 values of 0.5 and 2.5 mu mol /L, respectively. We conclude that platelets can biologically inactivate 5- oxo-ETE. Unstimulated platelets convert: 5-oxo-ETE to 5-HETE, with a 99% lo ss of biological potency, whereas stimulated platelets convert this substan ce to 12-hydroxy metabolites, which possess antagonist properties. (C) 1999 by The American Society of Hematology.