Metabolism of linoleic and arachidonic acids in VX2 carcinoma tissue: identification of monohydroxy octadecadienoic acids and monohydroxy eicosatetraenoic acids.

Abstract

The metabolism of arachidonic and linoleic acids by VX2 carcinoma tissue in vitro was determined. Prostaglandin E2 was the major metabolic product of arachidonic acid in the neoplastic tissue. Minor products accounting for 3- 8% of arachidonic acid metabolism were II-hydroxy-5, 8, 12, 14-eicosatetraenoic acid (II-HETE) and 15-hydroxy-5, 8, 11, 13-eicosatetraenoic acid (15-HETE). Linoleic acid was converted to a mixture of 9-hydroxy-10, 12-octadecadienoic acid (9-HODD) and 13-hydroxy-9, 11-octadecadienoic acid (13-HODD). The conversion of linoleic acid to monohydroxy C-18 fatty acids varied from 40-80% 9-HODD and 20-60% 13-HODD in tumor tissue harvested from different animals. The quantity of monohydroxy C-18 fatty acids biosynthesized by VX2 carcinoma tissue from endogenous linoleic acid equals or exceeds that of prostaglandin E2 biosynthesis from endogenous arachidonic acid. The presence of a hydroxyl group adjacent to a conjugated diene suggest that the monohydroxy C-18 and monohydroxy C-20 fatty acids were formed via the action of lipoxygenase-like enzymes. These lipoxygenase-like reactions are inhibited by indomethacin in a concentration-dependent fashion similar to the inhibition of prostaglandin E2 biosynthesis. The enzymes catalyzing the lipoxygenase-like reactions of linoleic and arachidonic acids are localized in the microsomal fraction of VX2 carcinoma tissue. These data suggest that the lipoxygenase-like reactions are catalyzed by fatty acid cyclooxygenase and that there are two major pathways of fatty acid cyclooxygenase metabolism of polyenoic fatty acids in the neoplastic tissue. One pathway involves the formation of prostaglandin E2 via cyclic endoperoxy intermediates. The second pathway involves the formation of monohydroxy C-18 fatty acids from linoleic acid via lipoxygenase-like reactions.