Antimicrob Agents Chemother  2003 Mar;47(3):1047-51 

Influence of p-glycoprotein inhibitors on accumulation of macrolides in j774
murine macrophages.

Seral C, Michot JM, Chanteux H, Mingeot-Leclercq MP, Tulkens PM, Van Bambeke F.

Unite de Pharmacologie Cellulaire et Moleculaire, Universite Catholique de
Louvain, Brussels, Belgium.

The influence of inhibitors of P-glycoprotein (verapamil [VE], cyclosporine
[CY], and GF120918 [GF]) on the cell handling of macrolides (erythromycin [ERY],
clarithromycin [CLR], roxithromycin [ROX], azithromycin [AZM], and telithromycin
[TEL]) was examined in J774 murine macrophages. The net influx rates of AZM and
TEL were increased from 2- to 3.5-fold in the presence of these inhibitors, but
their efflux was slowed only marginally. At 3 h, the inhibitors increased the
levels of AZM, ERY, and TEL accumulation approximately three- to fourfold (the
effect of VE, however, was lower) but did not influence CLR accumulation (the
inhibitors had an intermediate behavior on ROX accumulation). The effect was
concentration dependent (half-maximal increases in the level of accumulation of
AZM were obtained with GF, CY, and VE at 0.5, 5, and 10 micro M, respectively).
ATP depletion also caused an approximately threefold increase in the level of
accumulation of AZM. Two inhibitors of MRP (probenecid [2.5 mM] and gemfibrozil
[0.25 mM]) had no effect. Monensin (a proton ionophore) completely suppressed
the accumulation of AZM in control cells as well as in cells incubated in the
presence of VE, demonstrating that transmembrane proton gradients are the
driving force causing the accumulation of AZM in both cases. Yet, VE did not
alter the pH of the lysosomes (approximately 5) or of the cytosol (approximately
7.1). P-glycoprotein was detected by immunostaining at the cell surface as well
as in intracellular vacuoles (endosomes and lysosomes). The data suggest that
the influx of AZM, ERY, TEL, and ROX is adversely influenced by the activity of
P-glycoprotein in J774 macrophages, resulting in suboptimal drug accumulation.

PMID: 12604540 [PubMed - in process]