Cellular uptake, localization and activity of fluoroquinolones in uninfected and infected macrophages

Abstract

Pefloxacin, like other fluoroquinolones, accumulates in macrophages and several other types of nucleated cells (but not in erythrocytes). Upon fractionation of macrophage homogenates by isopycnic centrifugation in sucrose gradients, fluoroquinolones are not found associated with any specific cellular structure. We have compared the activities of pefloxacin and roxithromycin against intracellular Staphylococcus aureus in mouse J774 macrophages. Pefloxacin was significantly more active for equivalent intracellular drug concentrations (i.e. expressed by reference to the respective MICs of the drugs as determined in broth), suggesting differences in intracellular availability and/or capacity of the drugs to express their activity in the intracellular environment. The difference was enhanced by incubating the cells in acidic medium. We have also examined the cellular pharmacokinetics and intracellular distribution of pefloxacin in uninfected and Legionella pneumophila infected guinea pig macrophages. In contrast to uninfected cells from which pefloxacin was quickly released, macrophages infected with legionella retained approximately 20-30% of the accumulated pefloxacin after a 60-min wash-out. Cell fractionation studies indicated that the drug remaining in cells was associated with components of high buoyant density. These fractions also contained [3H] if cells had been incubated with [3H] labelled legionella (by in-vitro exposure to [3H]-thymidine, before phagocytosis). These results suggest that part of the intracellular pefloxacin becomes associated with legionella, or with legionella-containing cytoplasmic structures.

Contrasting Effects of Acidic pH on the Extracellular and Intracellular Activities of the Anti-Gram-Positive Fluoroquinolones Moxifloxacin and Delafloxacin againstStaphylococcus aureus

“…The same reasoning can be applied to explain the effect of extracellular pH on fluoroquinolone accumulation in eukaryotic cells. It is also interesting to note that both moxifloxacin and delafloxacin are found in the soluble fraction of the cells, with only a minimal amount detected in the organelles, as already observed for other fluoroquinolones (12,41). This is in opposition to what is seen with weak bases like macrolides or the biaryloxazolidinone radezolid, which are associated in large proportion with acidic vacuoles such as lysosomes (13,25).…”

Quinolones: a class of antimicrobial agents

“…Apart from nasal secretions (Dobbs et al, 1988) and ejaculate, body fluid concentrations of fluoroquinolones rarely reach plasma concentrations (Sorgel et al, 1989). Thus, the high tissue concentrations are a result of sequestration onto, or within, cells or cellular components of a tissue, although Carlier et al (1990) found no specific subcellular structure affinity to pefloxacin. As an example, the intracellular concentrations of fluoroquinolones in polymorphonuclear leukocytes are 7-14 times higher than those found in the extracellular fluid (Zweerink and Edison, 1988).…”

“…Fluoroquinolones are known to gain entry into phagocytic cells and remain microbiologically active inside the cells against bacterial pathogens such as Legionella pneumophyla (Carlier et al, 1990).…”

Intracellular pharmacodynamics of antibiotics

“…Efflux of fluoroquinolones is faster than uptake and is probably mediated by an efflux transporter, which can be inhibited by probenecid [43] and has been provisionally identified as an multiple resistance-related protein (MRP) efflux transporter. Cell-associated fluoroquinolones have been consistently recovered in the final supernate after cell fractionation studies [35,44]. This can be interpreted in two different ways: efflux from a specific subcellular compartment is fast; or fluoroquinolones are genuinely localized in the cytosol, but probably able to diffuse in the various subcellular compartments as they do through the various organs of the body.…”

“…Fluoroquinolones have long been known to accumulate in eucaryotic cells [15,[33][34][35][36][37][38][39][40]. The cellular concentrations of fluoroquinolones are generally 4-to 10-fold larger than the extracellular.…”