Interaction of macrolides and ketolides with the phagocytic cell line PLB-985

Interactions between antibacterial agents and polymorphonuclear neutrophils (PMNs) are a major focus of investigation. Owing to the variable drug susceptibility of PMNs from different individuals, in vitro studies require samples from large panels of healthy volunteers to reach statistical significance. Here, we used a phagocytic cell line, PLB-985, which can differentiate into mature PMNs in vitro, for the study of cellular interactions (drug uptake and antioxidant effects) of two macrolides (azithromycin and roxithromycin) and four ketolides [HMR 3004, HMR 3647 (telithromycin), HMR 3562 and HMR 3787]. The oxidative burst of differentiated (D) cells was inhibited by macrolides and ketolides. IC50% values (concentrations impairing the oxidative burst by 50%), determined after 30 min of incubation, were as follows for azithromycin, roxithromycin, HMR 3004, telithromycin, HMR 3562 and HMR 3787, respectively: 40, 39, 15, 23, 26, and 33 mg/l (fMLP stimulation) and 37, 86, 39, 43, 14, and 31 mg/l (PMA stimulation). These values were similar to those obtained with PMNs. Uptake of the two macrolides was significantly lower in non-differentiated (ND) cells than in D cells and PMNs. The cellular/extracellular (C/E) concentration ratios at 60 min for PMNs, D and ND PLB were respectively 67, 25 and 11 (roxithromycin) and 159, 137 and 48 (azithromycin). Ketolide uptake by ND-PLB was also significantly lower than that obtained with PMNs (C/E ratios at 60 min were about 75 versus 265 (HMR 3004), 36 vs 230 (telithromycin), 75 vs 235 (HMR 3562) and 20 vs 130 (HMR 3787). Although the active carrier system seemed to be present in ND cells, its activation pathway was not functional. Thus, the PLB-985 cell line is a good in vitro model for studying drug-PMN interactions. The use of ND and D cells may shed light on the nature and activation pathways of macrolide transport systems present on the PMN membrane.