16( R)-hydroxy-5,8,11,14-eicosatetraenoic acid, a new arachidonate metabolite in human polymorphonuclear leukocytes

Abstract

Intact human polymorphonuclear leukocytes (PMNL) incubated with substimulatory amounts of arachidonic acid in the absence of a calcium ionophore formed four metabolites that were isolated by reverse-phase HPLC and characterized structurally by GC/MS. A major metabolite eluting as the most abundant peak of radioactivity lacked UV chromophores above 215 nm, and its formation was sensitive to 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF525A) but not 3-amino-1-[ m(trifluoromethyl)phenyl]-2-pyrazoline (BW755C), suggesting that it was likely to be a product of cytochrome P450. The GC/MS analysis revealed the presence of two components: 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) and 16-hydroxy-5,8,11,14-eicosatetraenoic acid (16-HETE) in an approximate ratio of 4:1. The minor metabolites were identified as 15-HETE and 5-HETE. Although 20-HETE has been observed previously as a product of arachidonic acid metabolism in PMNL, the occurrence of 16-HETE was a novel finding. The stereochemistry of the hydroxyl group in PMNL-derived 16-HETE was established by analysis of 1-pentafluorobenzyl-16-naphthoyl derivatives on a chiral-phase chromatographic column and comparison with authentic synthetic stereoisomers. The PMNL-derived radioactive metabolite co-eluted with the synthetic 16( R)-HETE stereoisomer. Analysis of the total lipid extracts from intact PMNL followed by mild alkaline hydrolysis resulted in detectable amounts of 16-HETE (108 ± 26 pg/10 8 cells) and 20-HETE (341 ± 69 pg/10 8 cells), which suggested that these HETEs were formed from endogenous arachidonic acid and esterified within PMNL lipids. Thus, in contrast to calcium ionophore-stimulated neutrophils that generate large amounts of 5-lipoxygenase products, the intact PMNL generate 20-HETE and 16( R)-HETE via a cytochrome P450 ω- and ω-4 oxygenase(s).