Phospholipase A 2-mediated superoxide production of murine peritoneal macrophages induced by chrysotile stimulation

Abstract

In the present study, we investigated how chrysotile-stimulated macrophages generate superoxide using murine peritoneal macrophages, with special attention to the modulatory role of phospholipase A 2 (PLA 2). We examined the effects of the following inhibitors and antagonists for signaling molecules on the superoxide anion (O − 2) production of chrysotile-stimulated macrophages: p-bromophenacyl bromide (pBPB) and mepacrine for PLA 2; islet-activating protein (IAP) for G-protein; H-7 for protein kinase C (PKC); AA861 for 5-lipoxygenase (5-LO); indomethacin for cyclo-oxygenase (COX); ETYA for both 5-LO and COX; hexanolamine PAF for platelet-activating factor (PAF). The PLA 2 and PKC inhibitors effectively inhibited the chrysotile-induced superoxide anion production of macrophages, but not the G-protein inhibitor, the 5-LO and COX inhibitors, and the PAF antagonist. We also examined the effects of the PLA 2 inhibitors on macrophages stimulated by phorbol 12-myristate 13-acetate (PMA) which directly activates PKC. The two structurally different PLA 2 inhibitors showed differential effects on the PMA-induced superoxide generation: pBPB inhibited it but mepacrine did not. These results suggested that (1) PLA 2 and PKC modulate the chrysotile-induced O 2 production, and (2) two different kinds of PLA 2 work upstream and downstream of PKC, but (3) G-protein, 5-LO and COX metabolites, and PAF have no modulatory role in the reaction.