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Uptake of h-dihydrostreptomycin by macrophages in culture
1Department of Microbiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45219.
Abstract:
Mouse peritoneal macrophages, in culture, concentrate significant amounts of (3)H-dihydrostreptomycin, provided that the incubation period is sufficiently extended. Macrophages cultured in vitro from both stimulated and unstimulated animals concentrate the antibiotic from growth or maintenance media. The increase in cell-associated radioactivity is linear for almost a week before a plateau is reached. Calculations based on intracellular volumes of the cells indicate that the intracellular concentration of dihydrostreptomycin may attain levels greater than five times that of the external milieu. No uptake is measurable at 4 C, suggesting an active mechanism of transport into the cell. Phagocytosis of killed bacteria during incubation did not increase uptake of the antibiotic nor did the addition of poly-l-ornithine to the medium augment uptake. A nonphagocytic cell line (BHK-21) concentrated (3)H-dihydrostreptomycin to a lesser extent than the macrophages. These observations suggest that a wide variety of mammalian cells may be permeable to the antibiotic, and thus potential bactericidal action on intracellular bacteria cannot be ignored.
Insights
Mouse macrophages actively concentrate the antibiotic dihydrostreptomycin in culture over extended periods. This cellular uptake suggests potential for treating intracellular bacterial infections.
Area of Science:
- Pharmacology
- Cell Biology
- Microbiology
Background:
- Dihydrostreptomycin is an antibiotic.
- Macrophages are immune cells involved in pathogen clearance.
- Understanding cellular uptake mechanisms is crucial for drug efficacy.
Purpose of the Study:
- To investigate the in vitro uptake of dihydrostreptomycin by mouse peritoneal macrophages.
- To determine the kinetics and characteristics of this cellular accumulation.
- To assess the potential of macrophages to concentrate antibiotics for intracellular bacterial infections.
Main Methods:
- Culturing mouse peritoneal macrophages in vitro.
- Incubating macrophages with radiolabeled (3H-dihydrostreptomycin) over varying durations.
- Measuring cell-associated radioactivity.
- Comparing uptake in macrophages versus a non-phagocytic cell line (BHK-21).
Main Results:
- Macrophages demonstrated significant concentration of dihydrostreptomycin over time, reaching levels >5x external milieu.
- Uptake was linear for nearly a week, indicating an active transport mechanism (no uptake at 4°C).
- Phagocytosis or poly-l-ornithine did not enhance uptake, but macrophages accumulated more than BHK-21 cells.
Conclusions:
- Mouse macrophages actively and efficiently concentrate dihydrostreptomycin via an energy-dependent process.
- This accumulation suggests macrophages could serve as delivery vehicles for antibiotics against intracellular bacteria.
- Mammalian cells exhibit permeability to dihydrostreptomycin, with implications for treating intracellular infections.
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