calcimycin and 1-3-dicapryloylglycerol

In the present study, we investigated the effects of different diacylglycerols in comparison with phorbol 12-myristate 13-acetate (PMA) on eicosanoid-independent phospholipase A2 (PLA2) activation in human platelets and neutrophils. Eicosanoid-independent PLA2 activation was measured under conditions where both cyclooxygenase and lipoxygenases were blocked by BW755C. In the presence of PMA (50 nM), the amount of mass arachidonic acid (AA) released represented 400 and 257% of control (without PMA) in A23187-stimulated platelets and neutrophils, respectively, while 1,2-dioctanoylglycerol (1,2-DiC8) and 1-oleoyl-2-acetyl-sn-glycerol (OAG) had increased the eicosanoid-independent AA release by 150 and 117-134% of control, in platelets and neutrophils, respectively. Our results further demonstrate that 1,3-dioctanoylglycerol (1,3-DiC8), a poor activator of protein kinase C (PKC), is nearly as effective as diacylglycerols, such as OAG and 1,2-DiC8 (activators of PKC) in priming PLA2 activation, but is less effective than PMA as a priming agent. However, all three diacylglycerols were less effective than PMA as priming agents. Furthermore, diacylglycerols including 1,3-DiC8 exerted a much greater effect on PLA2 activation in platelets than in neutrophils. Neither 1,3-DiC8 nor 1,2-DiC8 and OAG had any significant priming effect on the accumulation of palmitic and stearic acids, while PMA caused a substantial accumulation of these fatty acids in platelets, but not in neutrophils. We also found that exogenously added OAG underwent significant hydrolysis even in unstimulated platelets, but not in neutrophils, suggesting that exogenously added OAG may be readily accessible for diacylglycerol (DAG) lipase/PLA1 in platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Arachidonic Acid; Blood Platelets; Calcimycin; Diglycerides; Enzyme Activation; Humans; Neutrophils; Phospholipases A; Phospholipases A1; Phospholipases A2; Protein Kinase C; Tetradecanoylphorbol Acetate

Preincubation of human neutrophils with 1-oleoyl-2-acetylglycerol (OAG) enhances subsequent f-Met-Leu-Phe (fMLP)-stimulated arachidonate mobilization. We have recently demonstrated that preincubation of neutrophils with OAG also reverses inhibition of A23187 stimulated [3H]arachidonate mobilization by the phospholipase A2 inhibitors, PGBx and aristolochic acid. The present study has compared the effects of 1,2-sn-dioctanoylglycerol (1,2-diC8) and 1,3-dioctanoylglycerol (1,3-diC8) on these cellular events. Dose-dependent priming (ED50 < 2.5 microM) of fMLP-stimulated [3H]arachidonate mobilization is obtained with both 1,2-diC8 and 1,3-diC8. Both diC8s also enhance fMLP-stimulated synthesis of leukotriene B4, 5-hydroxyeicosatetraenoic acid and platelet-activating factor, and generation of superoxide. Furthermore, both 1,2-diC8 and 1,3-diC8 reverse the effects of PGBx on A23187-stimulated [3H]arachidonate mobilization and platelet-activating factor synthesis. By contrast, higher concentrations (5-10 microM) of 1,2-diC8, but not 1,3-diC8, directly stimulate both [3H] arachidonate mobilization and superoxide generation. Since 1,3-diC8 does not activate protein kinase C (PKC), these results suggest that PKC is involved in direct activation of neutrophils by diacylglycerols but not in priming. Furthermore, reversal of the inhibitory effects of PGBx by diacylglycerols also appears to involve a PKC-independent mechanism.

Topics: Arachidonic Acid; Calcimycin; Diglycerides; Dose-Response Relationship, Drug; Humans; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Platelet Activating Factor; Polymers; Prostaglandins B; Protein Kinase C; Signal Transduction; Superoxides