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Penetration of macrolides into human polymorphonuclear leucocytes
1Second Department of Internal Medicine, Nagasaki University School of Medicine, Japan.
Abstract:
Five 14C-labelled macrolide antibiotics (erythromycin, josamycin, clarithromycin (TE-031), rokitamycin and roxithromycin) were studied for their transport into human polymorphonuclear leucocytes. Intracellular/extracellular concentration ratios (transport ratios) of these macrolides were quite high: erythromycin, 6.6; josamycin, 15.5; clarithromycin, 16.4; rokitamycin, 30.5; and roxithromycin, 21.9. When polymorphonuclear leucocytes were pre-treated with formaldehyde or incubated at 4 degrees C, or at low pH, transport ratios were reduced. When extracellular macrolide was removed, intracellular macrolide concentrations became as low as 30% of the pre-wash concentrations in 5 min. KF lowered the transport ratios of josamycin and rokitamycin in particular and NaCN reduced the transport ratios of erythromycin and josamycin strikingly. Ouabain slightly lowered transport ratios of all the antibiotics tested except roxithromycin, and 2, 4-dinitrophenol decreased the transport ratio of clarithromycin markedly. The addition of various amino acids or hexose did not inhibit the transfer. Adenosine, however, inhibited the transfer of these antibiotics except erythromycin and lowered transport ratios by 83 to 92%. Puromycin reduced transport ratios of the same antibiotics by 59 to 95%. With polymorphonuclear leucocytes that had phagocytosed Legionella pneumophila serogroup 1, transport ratios of all five drugs tended to decrease. However, when Staphylococcus aureus ATCC 25923 or opsonized zymosan was phagocytosed, transport ratios for macrolides, except for roxithromycin, increased.
Insights
This study investigated macrolide antibiotic transport into human white blood cells. Results show high intracellular concentrations, suggesting active transport mechanisms influenced by cell conditions and phagocytosis.
Area of Science:
- Pharmacology
- Cell Biology
- Infectious Diseases
Background:
- Macrolide antibiotics are crucial for treating bacterial infections.
- Understanding their cellular uptake is vital for optimizing therapeutic efficacy.
- Polymorphonuclear leucocytes play a key role in immune defense against pathogens.
Purpose of the Study:
- To quantify the transport of five macrolide antibiotics into human polymorphonuclear leucocytes.
- To investigate the mechanisms and factors influencing macrolide antibiotic cellular accumulation.
- To assess how phagocytosis of bacteria affects macrolide antibiotic uptake.
Main Methods:
- Utilized 14C-labelled macrolide antibiotics (erythromycin, josamycin, clarithromycin, rokitamycin, roxithromycin).
- Measured intracellular/extracellular concentration ratios (transport ratios) in human polymorphonuclear leucocytes.
- Assessed the impact of environmental factors (temperature, pH) and metabolic inhibitors (formaldehyde, KF, NaCN, ouabain, DNP, adenosine, puromycin) on transport.
- Examined macrolide transport during phagocytosis of Legionella pneumophila, Staphylococcus aureus, and opsonized zymosan.
Main Results:
- High transport ratios (6.6–30.5) were observed for all five macrolides, indicating significant intracellular accumulation.
- Transport was reduced by low temperature, low pH, formaldehyde, and specific metabolic inhibitors, suggesting an active, energy-dependent process.
- Adenosine and puromycin significantly inhibited macrolide transport, except for erythromycin.
- Phagocytosis of Legionella pneumophila decreased macrolide transport, while phagocytosis of Staphylococcus aureus or zymosan generally increased it (except for roxithromycin).
Conclusions:
- Human polymorphonuclear leucocytes actively accumulate macrolide antibiotics.
- The transport mechanisms are influenced by cellular energy status and specific molecular interactions.
- Phagocytic activity can modulate macrolide antibiotic uptake, with varying effects depending on the pathogen involved.