The inactivation of the polymorphonuclear leukocyte by non-steroidal anti-inflammatory drugs

Abstract

When human neutrophils (PMNs) are activated by appropriate stimuli, they aggregate, generate Superoxide anion (O ⁻₂ ) and secrete lysosomal enzymes. Pre-incubation of PMNs in vitro with the cyclo-oxygenase (COx) inhibitor piroxicam (50μM) before stimulation with the chemotactic peptide f-met-leu-phe (FMLP, 10⁻⁷ M) inhibited all of these responses. The COx inhibitor ibuprofen inhibited FMLP-induced aggregation and lysozyme secretion, leaving O ⁻₂ generation unaffected. Binding of³H-FMLP was inhibited by piroxicam. When the plant iectin concanavalin A (Con-A, 30μg/ml) or the tumor promoter phorbol myristate acetate (PMA, 50μml) was used as a stimulus, ibuprofen had no effect on PMN response, while piroxicam inhibited only O ⁻₂ generation. To determine whether such inhibition might also occur in vivo, we tested neutrophil aggregation and O ⁻₂ generation in response to FMLP in 26 normal subjects. These subjects were then administered therapeutic doses of piroxicam (20 mg/ day), ibuprofen (2400 mg/day) or indomethacin (100 mg/day), and neutrophil functions were retested after 3 days. Piroxicam inhibited FMLP-induced aggregation by 31% (5.2 cm²/min versus 3.6cm²/min,P<0.004) and O ⁻₂ generation by 35% (15.8 nmol cytochrorae c reduced versus 10.2 nmol,P<0.002). Ibuprofen inhibited FMLP-induced aggregation by 44% (5.2 versus 3.0,P<0.03) but had no effect on O ⁻₂ production. Indomethacin inhibited FMLP-induced aggregation (6,4 versus 2.9,P<0.01) but had no effect on O ⁻₂ generation. These studies suggest that: (a) multiple pathways exist for the activation of the neutrophil, since inhibition by non-steroidal anti-inflammatory drugs (NSAIDs) is stimulus-dependent; (b) NSAIDs have cellular effects that are not dependent on COx inhibition; (c) unique effects on cellular function may account for the clinical variability in responsiveness to different NSAIDs.