INHIBITION OF 12-O-TETRADECANOYLPHORBOL-13-ACETATE-ACCELERATED PHOSPHOLIPID-METABOLISM BY 5,8,11,14-EICOSATETRAYNOIC ACID

Abstract

The tumor-promoting agent, 12-O-tetradecanoylphorbol-13-acetate (TPA), accelerates choline phospholipid synthesis in bovine lymphocytes by an oxygen-dependent mechanism. This action is prevented by high concentrations of the cyclooxygenase inhibitor, indomethacin (1-3 mM), suggesting a possible involvement of lipid oxidation in the response. The acetylenic analog of arachidonic acid, 5,8,11,14-eicosatetraynoic acid (ETYA), at concentrations in the 10-50 .mu.M range, also prevents the acceleration of the incorporation of [methyl-3H]choline hydrochloride into choline phospholipids and appears more selective in its action. This antagonistic effect of ETYA, an agent which inhibits the cyclooxygenase and lipoxygenase routes of arachidonic acid oxidation, can be precluded by arachidonic acid but not by other unsaturated or saturated fatty acids. If ETYA is added to lymphocyte cultures after 1 h of TPA treatment, the established rate of [methyl-3H]choline hydrochloride incorporation is unaffected, but further acceleration is blocked. The inhibition of ETYA cannot be counteracted by any of the prostaglandins, Types A, B, D, E and F.alpha., or by the prostacyclin compounds, PGl1 and 6,9-thiaPGl2. The thromboxane pathway appears not to be involved since 9,11-azoprosta-5,13-dienoic acid (Azo I), a selective inhibitor of thromboxane synthetase, does not affect the TPA response. TPS may activate the lipoxygenase rather than the cyclooxygenase pathway for lipid oxidation and that an arachidonic acid hydroperoxide or a subsequent metabolite plays a key role in the stimulation of the choline phospholipid synthesis by the tumor-promoting phorbol ester, TPA.