SEPARATION OF AGONIST-STIMULATED ARACHIDONATE MOBILIZATION FROM SUBSEQUENT LEUKOTRIENE B-4 SYNTHESIS IN HUMAN NEUTROPHILS - DIFFERENT EFFECTS OF OLEOYLACETYLGLYCEROL AND PHORBOL-MYRISTATE ACETATE AS PRIMING AGENTS
Md. Rosenthal et Rc. Franson, SEPARATION OF AGONIST-STIMULATED ARACHIDONATE MOBILIZATION FROM SUBSEQUENT LEUKOTRIENE B-4 SYNTHESIS IN HUMAN NEUTROPHILS - DIFFERENT EFFECTS OF OLEOYLACETYLGLYCEROL AND PHORBOL-MYRISTATE ACETATE AS PRIMING AGENTS, Journal of cellular physiology, 160(3), 1994, pp. 522-530
Preincubation of human neutrophils with phorbol esters or soluble digl
ycerides enhances subsequent f-Met-Leu-Phe (fMLP)-stimulated arachidon
ate mobilization and leukotriene B-4 (LTB(4)) synthesis. We have recen
tly reported that 1,3-dioctanoylglycerol (1,3-diC8) is equipotent with
1,2-sn-dioctanoylglycerol (1,2-diC8) as a priming agent, thus suggest
ing 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 stu
dy 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 P
MA dose dependently enhance f-Met-Leu-Phe (fMLP)-stimulated release of
[H-3]arachidonate. Optimal concentrations of OAG (5 mu m) and PMA (10
nM) are equipotent in increasing fMLP-stimulated arachidonate mobiliz
ation as quantitated either with total radioactivity or by mass measur
ements 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 synt
hesis of [H-3]eicosanoids. Furthermore, OAG, but not PMA, enhances fML
P-stimulated synthesis of platelet-activating factor. By contrast, PMA
directly stimulates [H-3]arachidonate mobilization, while OAG (20 mu
M) does not; despite these differences, the combined effects of PMA OAG on subsequent agonist-stimulated arachidonate release are not grea
ter than those of PMA alone. In cells challenged with subthreshold con
centrations (<0.1 mu M) Of the calcium ionophore A23187, both OAG and
PMA stimulate [(3)Harachidonate release but not [H-3]LTB(4) 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. (C) 1994 Wiley-Liss, Inc.