Separation of agonist-stimulated arachidonate mobilization from subsequent leukotriene B4 synthesis in human neutrophils: Different effects of oleoylacetylglycerol and phorbol myristate acetate as priming agents

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Abstract
Preincubation of human neutrophils with phorbol esters or soluble diglycerides enhances subsequent f‐Met‐Leu‐Phe (fMLP)‐stimulated arachidonate mobilization and leukotriene B4 (LTB4) synthesis. We have recently reported that 1,3‐dioctanoylglycerol (1,3‐diC8) is equipotent with 1,2‐sn‐dioctanoylglycerol (1,2‐diC8) as a priming agent, thus suggesting that the priming effects of diacylglycerols are protein kinase C (PKC) independent (Rosenthal et al., 1993, Biochim. Biophys. Acta 1177:79–86). In order to further investigate this question, the present study has directly compared the effects of oleoylacetylglycerol (OAG) and the PKC activator, phorbol 12‐myristate 13‐acetate (PMA), on agonist‐stimulated lipid metabolism. The results indicate that both OAG and PMA dose dependently enhance f‐Met‐Leu‐Phe (fMLP)‐stimulated release of [3H]arachidonate. Optimal concentrations of OAG (5 μm) and PMA (10 nM) are equipotent in increasing fMLP‐stimulated arachidonate mobilization as quantitated either with total radioactivity or by mass measurements of free arachidonate. By contrast OAG is sixfold more effective than PMA in enhancing synthesis of 5‐lipoxygenase (5‐LO) metabolites by mass and two to threefold more effective than PMA in enhancing synthesis of [3H]eicosanoids. Furthermore, OAG, but not PMA, enhances fMLP‐stimulated synthesis of platelet‐activating factor. By contrast, PMA directly stimulates [3H]arachidonate mobilization, while OAG (20 μM) does not; despite these differences, the combined effects of PMA + OAG on subsequent agonist‐stimulated arachidonate release are not greater than those of PMA alone. In cells challenged with subthreshold concentrations (3H]arachidonate release but not [3H]LTB4 synthesis. These findings suggest that OAG does not directly activate 5‐LO, but instead couples arachidonate mobilization to leukotriene synthesis in a PKC‐independent manner.

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