In vitro interaction between spiramycin and polymorphonuclear neutrophils oxidative metabolism

PMNs are a major component of body defense against microbial invasion, involving reactive oxygen species in great quantity, which could benefit from antibiotic therapy. Recently, possible antibiotic effects on phagocyte functions (impairment or stimulation of reactive oxygen species production) were studied. In our study, an in vitro evaluation was made on macrolide activity on phagocyte respiratory burst functions, using assay of superoxide anion (O2.-) in response to four stimuli systems: N-formyl Met-Leu-Phe (fMLP), an analogue of bacterial chemotactic factors; 4 beta-phorbol 12-myristate 13-acetate (PMA), a direct activator of protein kinase C (PKC); calcium ionophore (A23187), which acts directly on calcium influx; and a bacterial strain, Staphylococcus aureus. We have shown that spiramycin, at therapeutic plasma concentrations, increased O2.- generation by bacteria and fMLP-stimulated PMNs, with rate of 26% for 1 microgram ml-1 and 34% for 5 micrograms ml-1, respectively. This pro-oxidant effect, however, weaker, was observed when PMNs were stimulated by PMA. A weak anti-oxidant effect was observed with A23187. For higher concentrations, spiramycin decreased strongly O2.- production, with IC50 values of 74 micrograms ml-1, 154 micrograms ml-1, 296 micrograms ml-1 and 400 micrograms ml-1 when PMNs were stimulated with bacteria, A23187, fMLP and PMA, respectively. The effect of spiramycin seemed to result from an intracellular mechanism by intervention of PMN oxidative metabolism (NADPH-oxidase activation), rather than a simple chemical interaction, because no effect has been observed in acellular models. For higher spiramycin concentrations, the decrease of O2.- production observed could not be taken into consideration because this concentration was not used in therapy. The enhanced of O2.- production observed could be used in therapy, so as to increase PMNs bactericidal activity.