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Binding of aminoglycoside antibiotics by degranulating mast cells
G Decorti1, L Candussio, F B Klugmann
1Department of Biomedical Sciences, Faculty of Medicine, Trieste, Italy.
Abstract:
The aminoglycoside antibiotics are polycationic at physiological pH and hence do not enter most cells. Indeed, when intact mast cells were incubated with gentamicin or tobramycin, extremely low concentrations of the two drugs could be measured. In contrast, when a controlled, specific degranulation of mast cells was induced by treating the cells with compound 48/80, Adriamycin or concanavalin A, a dose-dependent histamine release was observed and a significant increase of the intracellular concentrations of the aminoglycosides resulted. The uptake of gentamicin and tobramycin was not dependent on the type of stimulus, but was proportional to the quantity of histamine release. The aminoglycoside binding to granular material obtained from sonicated cells was similar to that of degranulating mast cells. These data suggest the occurrence of ionic interactions between the positively charged groups of the aminoglycosides and the negatively charged groups of granular matrix that are exposed as a consequence of exocytosis. The significant of this phenomenon is at present unclear but studies are in progress to clarify the fate of the aminoglycosides bound to mast cells.
Insights
Aminoglycoside antibiotics like gentamicin do not enter most cells. However, mast cell degranulation exposes binding sites, increasing aminoglycoside uptake via ionic interactions with granular matrix.
Area of Science:
- Pharmacology
- Cell Biology
- Immunology
Background:
- Aminoglycoside antibiotics are polycationic and exhibit poor cell penetration at physiological pH.
- Previous studies show limited intracellular concentrations of aminoglycosides in intact cells.
Purpose of the Study:
- To investigate the uptake mechanism of aminoglycosides in mast cells.
- To determine the relationship between mast cell degranulation and aminoglycoside intracellular concentrations.
Main Methods:
- Incubation of intact mast cells with gentamicin and tobramycin.
- Induction of mast cell degranulation using compound 48/80, Adriamycin, or concanavalin A.
- Measurement of intracellular aminoglycoside concentrations and histamine release.
- Analysis of aminoglycoside binding to isolated granular material.
Main Results:
- Intact mast cells showed extremely low intracellular aminoglycoside concentrations.
- Degranulation induced dose-dependent histamine release and significantly increased intracellular aminoglycoside levels.
- Aminoglycoside uptake was proportional to histamine release, irrespective of the stimulus type.
- Aminoglycoside binding to granular material mimicked binding in degranulating mast cells.
Conclusions:
- Aminoglycoside uptake into mast cells is facilitated by degranulation.
- Ionic interactions between aminoglycosides and exposed granular matrix components drive this uptake.
- Further studies are needed to elucidate the functional significance of this phenomenon.