Accumulation and activity of cethromycin (ABT-773) within human polymorphonuclear leucocytes.
OBJECTIVE
To evaluate the penetration of ketolide cethromycin (ABT-773) into human polymorphonuclear leucocytes (PMNs) and its intracellular activity.


METHODS
The uptake of radiolabelled cethromycin by PMNs was determined by a velocity gradient centrifugation technique. The activity of cethromycin against intracellular Staphylococcus aureus ATCC 25923 in PMNs was also evaluated.


RESULTS
The cellular to extracellular concentration (C/E) ratio for cethromycin was >200 at an extracellular concentration of 2 mg/L. The uptake of cethromycin into PMNs was rapid and saturable. Cethromycin was slowly released from the loaded PMNs (cell associated drug>50% after 2 h of incubation). Intracellular penetration was significantly affected by the environmental temperature (C/E ratio at 4 degrees C and 37 degrees C: 13 +/- 6 and 226 +/- 31, respectively; P < 0.05), by cell viability (C/E ratio for dead and viable cells: 100 +/- 38 and 226 +/- 31, respectively; P < 0.05), by pH (C/E ratio was significantly increased at basic pH) and by the metabolic inhibitors 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone. The intracellular accumulation of cethromycin also decreased significantly when cells were activated with phorbol myristate acetate or opsonized zymosan. These data indicate that a potentially active mechanism could be involved in the uptake of cethromycin by PMNs. At high extracellular concentrations of 5 and 10 mg/L, cethromycin showed significant intracellular activity against S. aureus.


CONCLUSIONS
Cethromycin achieves high intracellular concentrations within human PMNs, remaining active intracellularly.
García
I
I
Department of Microbiology, School of Medicine, Seville, Spain. igarcia1@us.es
Pascual
A
A
Ballesta
S
S
del Castillo
C
C
Perea
E J
EJ
D019297:2,4-Dinitrophenol / Q000494:pharmacology; D000963:Antimetabolites / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002469:Cell Separation; D002470:Cell Survival / Q000502:physiology; D002499:Centrifugation, Density Gradient; D004917:Erythromycin / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D048628:Ketolides; D007700:Kinetics; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects; D013696:Temperature; D014475:Uncoupling Agents / Q000494:pharmacology
D000963:Antimetabolites; D048628:Ketolides; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D004917:Erythromycin; C405499:cethromycin; D019297:2,4-Dinitrophenol