Uptake and metabolism of monohydroxy-eicosatetraenoic acids by macrophages

Abstract

Within 5 min, resting macrophages metabolize microM quantities of exogenous arachidonic acid (20:4) to cyclooxygenase and lipoxygenase products. Mono-HETEs represent a major class of metabolites recovered from the medium. However, the quantity of mono-Hetes progressively decreases over a 60-min incubation period, with a concomitant increase in more polar lipoxygenase products, suggesting additional metabolic fates for these hydroxy acids. This was directly confirmed by exposing resident macrophage cultures to radiolabeled 15-, 12-, and 5-HETEs (1 microM). 12-30% of the recovered HETEs were cell-associated and predominantly esterified into phospholipid. High pressure liquid chromatography analyses of medium extracts indicated that 50% of each HETE was also converted to 10 or more metabolites over a 60-min time-course, a rate slower than for 20:4. The major metabolite generated from each mono-HETE had the elution characteristics of a di-HETE. The 5-HETE product has a triene spectrum similar to that of 5(S), 12(S)-di-HETE, whereas the 15- and 12-HETE products exhibited single ultraviolet absorption maxima, indicating a metabolic pathway for 5-HETE distinct from the other mono-HETEs. None of the stable cyclooxygenase products of 20:4 (6-keto PGF1 alpha, PGF2 alpha, PGE2, TXB2) nor polar metabolites of mono-HETEs are either incorporated or metabolized. The results indicate that macrophages have the capacity to specifically metabolize 20:4 and mono-HETEs to polar oxygenated products in the absence of a discernible trigger.