Prostaglandin Endoperoxides. Novel Transformations of Arachidonic Acid in Human Platelets

Abstract

Arachidonic acid incubated with human platelets was converted into three compounds, 12L-hydroxy-5,8,10,14-eicosatetraenoic acid, 12L-hydroxy-5,8,-10-beptadecatrienoic acid, and the hemiacetal derivative of 8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid. The formation of the two latter compounds from arachidonic acid proceeded by pathways involving the enzyme, fatty acid cyclo-oxygenase, in the initial step and with the prostaglandin endoperoxide, PGG2, as an intermediate. The first mentioned compound was formed from 12L-hydroperoxy-5,8,10,14-eicosatetraenoic acid, which in turn was formed from arachidonic acid by the action of a novel lipoxygenase. Aspirin and indomethacin inhibited the fatty acid cyclo-oxygenase but not the lipoxygenase, whereas 5,8,11,14-eicosatetraynoic acid inhibited both enzymes. The almost exclusive transformation of the endoperoxide structure into nonprostaglandin derivatives supports the hypothesis that the endoperoxides can participate directly and not by way of the classical prostaglandins in regulation of cell functions. The observed transformations of arachidonic acid in platelets also explain the aggregating effect of this acid.Prostaglandins (PG) E2 and F2a are formed and released by human platelets during aggregation induced by various agents (3,4). This biosynthetic capacity has also been demonstrated with labeled precursors (5, 6).Recent work in our laboratory led to the isolation (1) of an earlier postulated (7) endoperoxide intermediate in prostaglandin biosynthesis. This finding was confirmed and extended in subsequent studies in which an additional endoperoxide derivative, carrying a hydroperoxy group at C-15, was isolated (2,8). Studies of the aggregation of human platelets also demonstrated that the biosynthetic process can stop at the endoperoxide stage resulting in release of the intermediates (PGG2 and/or PGH2) (2). Since the endoperoxides were found to be potent aggregating agents and since blockade of their formation is accompanied by inhibition of the second wave of aggregation, it was suggested that they play a physiological role in this process (2).In connection with these and other studies it became of particular interest to further investigate the transformation of arachidonic acid by human platelets. The present work demonstrates that arachidonic acid is oxygenated in this system both by the cyclo-oxygenase involved in prostaglandin [5,6,8,9,11,12,14,Arachidonic acid was prepared as described (10). 12-Hydroxyeicosanoic acid was prepared by anodic coupling of 10-acetoxyoctadecanoic acid [80 mg, prepared by acetylation of lO-hydroxyoctadecanoic acid (11)1 and methyl hydrogen succinate (300 mg). The product was hydrolyzed and subjected to silicic acid chromatography and preparative thin-layer chromatography, giving 30 mg (39%) of pure 12-hydroxyeicosanoic acid. Thin-layer chromatography of the methyl ester showed a single spot with RF = 0.57. Gasliquid chromatographic analysis of the methyl ester showed a single peak with equivalent c...

Isolation of eriocitrin (eriodictyol 7‐O‐rutinoside) as an arachidonate lipoxygenase inhibitor from Lumie fruit (Citrus lumia) and its distribution in Citrus species

“…Its molecular formula was deduced as C 27 The individual signals in the NMR spectrum of the inhibitory compound were compatible with those of eriocitrin, as reported by Miyake et al 22 In addition, Kawai et al 23 reported that eriocitrin existed but neoeriocitrin was not detectable in Lumie fruit. From these results the inhibitory compound was identified as eriocitrin (Fig.…”

“…If one enzyme is stimulated by a selective inhibitor such as indomethacin, enhanced production of the metabolite by the other enzyme is observed. 27 Eriocitrin inhibited both 12-LOX (IC 50 22.3 µmol L −1 ) and 5-LOX (IC 50 29.1 µmol L −1 ) activities at nearly the same rate (Figs 3 and 4). Eriocitrin is converted to eriodictyol and 3,4-dihydroxyhydrocinnamic acid (3,4-DHCA) by intestinal bacteria, and conjugated forms of eriodictyol, homoeriodictyol and hesperetin, and free 3,4-DHCA were detected in rat plasma.…”

Effect of Leukotrienes, 12-HETE, Histamine, Bradykinin, and 5-Hydroxytryptamine on in vivo Rabbit Cerebral Arteriolar Diameter

“…28-29. The fractions containing 12-HETE were pooled; an aliquot was evaporated, derivatized, and its 12-HETE structure confirmed by gas chromatography/ mass spectrometry (Hamberg and Samuels son, 1974). The 12-HETE was stored in methanol until used.…”

Studies on the Action Potential Originated From Nerve Elements in Guinea Pig Ureter

“…Arachidonic acid is now known to be converted by cyclo-oxygenase of the PG synthetase system to the PG endo peroxides PGG2 and PGH2 (10,11,12), precursors of PGE2 and PGF2a. The endoperoxides have contractile activity on the rat stomach fundus (13,14).…”