Uptake and intracellular activity of moxifloxacin in human neutrophils and tissue-cultured epithelial cells

Abstract

The penetration by moxifloxacin of human neutrophils (polymorphonuclear leukocytes [PMN]) and tissue-cultured epithelial cells (McCoy cells) was evaluated by a fluorometric assay. At extracellular concentrations of 5 mg/liter, the cellular-to-extracellular concentration ratios (C/E) of moxifloxacin in PMN and McCoy cells were 10.9 +/- 1.0 and 8.7 +/- 1.0, respectively (20 min; 37 degrees C). The uptake of moxifloxacin by PMN was rapid, reversible, nonsaturable (at extracellular concentrations ranging from 1 to 50 microg/ml), and not affected by cell viability. The uptake of moxifloxacin was affected by external pH and the environmental temperature. The incubation of PMN in the presence of sodium fluoride, sodium cyanide, and carbonyl cyanide m-chlorophenylhydrazone significantly decreased the C/E of this agent. Neither PMN stimulation nor phagocytosis of opsonized Staphylococcus aureus significantly affected the uptake of moxifloxacin by human PMN. This agent, at concentrations of 0.5, 1, and 5 mg/liter, induced a significant reduction in the survival of intracellular S. aureus in human PMN. In summary, moxifloxacin reaches much higher intracellular concentrations within phagocytic and nonphagocytic cells than extracellular ones, remaining active inside the neutrophils.

FIG. 1

Moxifloxacin uptake by both human PMN and McCoy cells and efflux of cell-associated moxifloxacin after the removal of the extracellular drug (n = 5). The extracellular concentration was 5 mg/liter.

FIG. 2

Effect of extracellular concentrations on the intracellular penetration of moxifloxacin in human PMN (n = 5).

FIG. 3

Intracellular activity of moxifloxacin against S. aureus in human PMN in a 3-h assay (n = 5). Data are expressed as percentages of intracellular surviving staphylococci compared to controls without antimicrobial agents (100%). ∗, P ≤ 0.05 compared with control without antimicrobial agent. CPX, ciprofloxacin; OFX, ofloxacin; MFX, moxifloxacin.