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Antibiotic entry into human polymorphonuclear leukocytes
Abstract:
Since bacteria which survive within phagocytes may produce serious infection, antibiotics which inactivate these intracellular organisms are needed. To establish those factors which mediate entry of antimicrobial agents into human phagocytes, we studied the uptake of 13 radiolabeled antibiotics by peripheral blood polymorphonuclear leukocytes (PMN). At intervals during a 2-h incubation period, antibiotic uptake by PMN was determined by means of velocity gradient centrifugation, which separates the cell-associated antibiotic from the extracellular antibiotic. Penicillin G and three cephalosporin antibiotics penetrated PMN poorly. The ratio of cellular concentration to extracellular concentration (C/E) of these drugs was less than 0.01 to 0.5. For gentamicin and isoniazid, the C/E values were approximately 0.8 to 1.0. Chloramphenicol, rifampin, and lincomycin, antibiotics with good lipid solubility, were concentrated twofold (C/E = 2) in PMN. Ethambutol (C/E = 5), clindamycin (C/E = 11), and two erythromycin preparations (C/E = 10 to 13) were markedly concentrated within PMN. Clindamycin uptake was rapid: greater than 70% of the total drug entry occurred within the first minute. Accumulation of clindamycin and erythromycin was an active, energy-requiring process, dependent at least in part upon glycolysis. Clindamycin entered PMN by means of an active membrane transport system which was saturable and had a high binding affinity (Km = 2 mM) and maximum velocity of uptake (Vmax = 5 nmol/45 s per 10(6) cells). These observations, together with studies of the biological consequences of intracellular antibiotics, should lead to more effective therapy for infection due to intracellular pathogens..
Insights
Certain antibiotics effectively penetrate human phagocytes, crucial for treating intracellular bacterial infections. Clindamycin and erythromycin show high uptake via active transport, indicating potential for enhanced intracellular pathogen therapy.
Area of Science:
- Pharmacology
- Microbiology
- Cell Biology
Background:
- Intracellular bacteria pose treatment challenges as they survive within host phagocytes.
- Effective antimicrobial agents are needed to target these intracellular pathogens.
Purpose of the Study:
- To investigate factors influencing antimicrobial agent entry into human phagocytes.
- To quantify the uptake of various antibiotics by polymorphonuclear leukocytes (PMN).
Main Methods:
- Studied the uptake of 13 radiolabeled antibiotics by human peripheral blood PMN.
- Used velocity gradient centrifugation to differentiate cell-associated from extracellular antibiotics.
- Measured antibiotic concentrations over a 2-hour incubation period.
Main Results:
- Penicillin G and cephalosporins showed poor PMN penetration (C/E < 0.5).
- Gentamicin and isoniazid had C/E ratios near 1.0.
- Chloramphenicol, rifampin, and lincomycin were concentrated twofold (C/E = 2).
- Ethambutol (C/E = 5), clindamycin (C/E = 11), and erythromycin (C/E = 10-13) were markedly concentrated.
- Clindamycin uptake was rapid and energy-dependent, mediated by a saturable active transport system (Km = 2 mM, Vmax = 5 nmol/45 s/10^6 cells).
Conclusions:
- Antibiotic uptake by PMN varies significantly, with lipid solubility and active transport playing key roles.
- Clindamycin and erythromycin demonstrate substantial intracellular accumulation.
- Understanding these uptake mechanisms can guide the development of more effective therapies for intracellular bacterial infections.