Phospholipase A 2 Is Involved in the Mechanism of Activation of Neutrophils by Polychlorinated Biphenyls

Aroclor 1242, a mixture of polychlorinated biphenyls (PCBs), activates neutrophils to produce superoxide anion (O2-) by a mechanism that involves phospholipase C-dependent hydrolysis of membrane phosphoinositides; however, subsequent signal transduction mechanisms are unknown. We undertook this study to determine whether phospholipase A2-dependent release of arachidonic acid is involved in PCB-induced O2- production. We measured O2- production in vitro in glycogen-elicited, rat neutrophils in the presence and absence of the inhibitors of phospholipase A2: quinacrine, 4-bromophenacyl bromide (BPB), and manoalide. All three agents significantly decreased the amount of O2- detected during stimulation of neutrophils with Aroclor 1242. Similar inhibition occurred when neutrophils were activated with the classical stimuli, formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate. The effects of BPB and manoalide were not a result of cytotoxicity or other nonspecific effects, although data suggest that quinacrine is an O2- scavenger. Significant release of 3H-arachidonic acid preceded O2- production in neutrophils stimulated with Aroclor 1242 or fMLP. Manoalide, at a concentration that abolished O2- production, also inhibited the release of 3H-arachidonate. Aspirin, zileuton, or WEB 2086 did not affect Aroclor 1242-induced O2- production, suggesting that eicosanoids and platelet-activating factor are not needed for neutrophil activation by PCBs. Activation of phospholipase A2 and O2- production do not appear to involve the Ah receptor because a congener with low affinity, but not one with high affinity for this receptor, stimulated the release of arachidonic acid and O2-. These data suggest that Aroclor 1242 stimulates neutrophils to produce O2- by a mechanism that involves phospholipase A2-dependent release of arachidonic acid. ImagesFigure 1. AFigure 1. BFigure 2.Figure 3.Figure 4. AFigure 4. BFigure 4. CFigure 5. AFigure 5. BFigure 5. CFigure 6. AFigure 6. BFigure 6. CFigure 6. D