Inhibition of neutrophil phospholipase A2 by p-bromophenylacyl bromide, nordihydroguaiaretic acid, 5,8,11,14-eicosatetraynoic acid and quercetin.

The lipoxygenase and/or cyclooxygenase inhibitors nordihydroguaiaretic acid (NDGA), 4,8,11,14-eicosatetraynoic acid (ETYA) and the bioflavonoid, quercetin, also inhibit phospholipase A2 (phosphatidase 2-acyl hydrolase; EC 3.1.1.4) activity of neutrophil acid extracts and sonicates. The IC50 are 13 microM for NDGA, 22 microM for ETYA, and 100 microM for quercetin when measured on the neutrophil acid extracts; the IC50 obtained with the sonicates are 11 microM, 12 microM and 57 microM, respectively. p-Bromophenylacyl bromide (BPB) inhibits the phospholipase A2 activity of neutrophil acid extracts with an IC50 of 10 microM. In contrast, intact neutrophils incubated for up to 1 h with BPB, washed to remove the drug, and sonicated to expose the phospholipase A2, lose less than 20% of their activity. This strongly suggests that BPB does not inhibit neutrophil function by preventing phospholipase action.