omega 10-Lipoxygenase products of alpha-linolenic acid are esterified to phospholipids in Hydra vulgaris

We have recently reported the occurrence of 9(R)-hydroxy-, 9(R)-hydroperoxy- and 9-keto-octadeca-10E,12Z,15Z-trienoic acids (9-HOTrE, 9-HPOTrE and 9-KOTrE) in Hydra vulgaris, and their biosynthesis from alpha-linolenic acid (alpha-LA) through the action of an enantioselective omega 10(R)-lipoxygenase (omega 10-LO). Here we describe the finding of these alpha-LA metabolites as esters to the 2-position of phosphatidylcholine, phosphatidylethanolamine and, in trace amounts, phosphatidylinositol. Small amounts of a compound co-eluting with an authentic standard of 9(R)-hydroxy-octadeca-10E, 12Z-dienoic acid, a metabolite potentially derived from the action of omega 10-LO on linoleic acid, were also found esterified with phospholipids. Since direct peroxidation of membrane lipids has been described, experiments were aimed at establishing whether alpha-LA metabolite-containing phospholipids could originate, in H. vulgaris, from either spontaneous or omega 10-LO-catalyzed oxidation of phospholipid-bound alpha-LA. Incubation of either unlabelled or radiolabelled PUFA-containing phosphoglycerides with H. vulgaris omega 10-LO did not result in their peroxidation. This suggests that alpha-LA and LA metabolites are incorporated into glycerophospholipids after their formation by omega 10-LO, and that, as in mammals, membrane phospholipids may serve as a reservoir for these bioactive compounds. This is the first example in an invertebrate species of lipoxygenase products esterified to phosphoglycerides.