Effect of Diclofenac Sodium, Tolfenamic Acid and Indomethacin on the Production of Superoxide Induced by N-Formyl-Methionyl-Leucyl-Phenylalanine in Normal Human Polymorphonuclear Leukocytes

Abstract

The effect of three non-steroidal anti-inflammatory drugs, diclofenac, indomethacin and tolfenamic acid, on the production of superoxide (O⁻2), by normal human polymorphonuclear leukocytes (PMNL) was studied, in vitro. The cells were activated with N-formyl-methionyl-leucyl-phenylalanine (FMLP) and O⁻2 production was measured as superoxide dismutase inhibitable cytochrome c reduction. Cell viability was checked with assays of liberated LDH. Concentrations of the drugs considerably higher than those of therapeutic plasma were required to inhibit O⁻2 production. The drug concentrations producing a 50% inhibition (IC₅₀) of total O⁻2 production were: diclofenac 2.7×10⁻⁴ M, indomethacin 4.0×10⁻⁴ M and tolfenamic acid 4.2×10⁻⁴ M. At drug concentrations causing a significant suppression of O⁻₂ generation, diclofenac showed a slight and tolfenamic acid a marked inhibition of [³H]FMLP binding to its cellular receptor; indomethacin has earlier been shown to inhibit FMLP-binding slightly. No dismutating activity of the drugs could be demonstrated. It is concluded that the inhibition of O⁻2 production is due to a combined effect on FMLP binding and on cellular O⁻2 metabolism. Because of the high drug concentrations required to inhibit O⁻2 production, this phenomenon is obviously of little significance for the anti-inflammatory effect obtained with therapeutic doses of the drugs studied.