PAF and LTB4 biosynthesis in the human neutrophil: effects of putative inhibitors of phospholipase A2 and specific inhibitors of 5-lipoxygenase.

The effect of several putative phospholipase A2 (PLA2) inhibitors on [3H]-acetate incorporation into platelet-activating factor (PAF) upon calcium ionophore A23187 stimulation of purified human neutrophils (PMN) were evaluated in vitro. PLA2 inhibitors such as p-bromophenacyl bromide (pBPB), ellagic acid, aristolochic acid and gossypol were without effect or only weakly inhibited PAF biosynthesis. Luffariellolide, a potent PLA2 inhibitor isolated from the marine sponge Luffariella sp., dose-dependently inhibited PAF production (IC50 = 5 microM). Due to the relationship between PAF and LTB4 biosynthesis, the effect of inhibiting LTB4 production on PAF biosynthesis was investigated. At concentrations which reduce LTB4 production by greater than 95%, Wy-50,295 tromethamine and A-64,077, specific 5-lipoxygenase (5-LO) inhibitors, did not significantly effect PAF production. In contrast, L-663,536, the 5-LO translocation inhibitor, was a potent inhibitor of PAF production (IC50 = 1 microM). This activity of L-663,536 may contribute to its pharmacological profile at higher doses. These data also suggest that PAF biosynthesis in human PMNs is not dependent on the formation or continued presence of leukotrienes.