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Preparation and characteristics of dichloromethylene diphosphonate-containing liposomes
1Immunocytochemistry Unit, Medical Faculty, Free University, Amsterdam, The Netherlands.
Abstract:
Dichloromethylene diphosphonate (DMDP), encapsulated in liposomes and administered intravenously in mice, will eliminate all macrophages in spleen and liver. DMDP can be incorporated in liposomes to a maximum of 15 mM, if less than 12 mM is encapsulated not all macrophages will be eliminated (since the animals could not be injected with more liposomes). To determine DMDP content of the liposomes before in vivo administration, an in vitro test system was developed. This method is based on the competition for calcium binding by either DMDP or murexide. Murexide is a metallochromatic indicator which gives a distinct wavelength shift after binding of calcium. The decrease in absorbance at 510 nm of the murexide-calcium complex, due to the addition of DMDP, was used as a reliable (s.d. 5 per cent) value for measurement of DMDP concentrations. The possible use of this system in the study of calcium binding and transport over artificial biomembranes is discussed.
Insights
Dichloromethylene diphosphonate (DMDP) liposomes effectively eliminate macrophages. A new in vitro assay accurately measures DMDP concentration in liposomes for reliable in vivo macrophage depletion.
Area of Science:
- Biochemistry
- Immunology
- Pharmacology
Background:
- Dichloromethylene diphosphonate (DMDP) is a bisphosphonate with potential for macrophage depletion.
- Encapsulation of DMDP in liposomes enables intravenous administration for targeted delivery.
- Effective macrophage elimination requires specific DMDP concentrations within liposomes.
Purpose of the Study:
- To develop an in vitro method for quantifying DMDP content in liposomes prior to in vivo administration.
- To establish a reliable system for ensuring adequate DMDP encapsulation for complete macrophage depletion.
Main Methods:
- Development of an in vitro assay based on competitive calcium binding between DMDP and murexide.
- Utilizing murexide as a metallochromatic indicator, monitoring absorbance changes at 510 nm.
- Quantifying DMDP concentration by measuring the decrease in absorbance of the murexide-calcium complex.
Main Results:
- The developed in vitro system reliably measures DMDP concentrations in liposomes with a standard deviation of 5%.
- Accurate DMDP quantification ensures optimal liposomal encapsulation for effective in vivo macrophage elimination.
- The assay provides a critical quality control measure for liposomal DMDP formulations.
Conclusions:
- An accurate and reliable in vitro assay for DMDP quantification in liposomes has been established.
- This method facilitates precise control over liposomal DMDP concentrations for consistent macrophage depletion.
- The system holds potential for studying calcium binding and transport across artificial biomembranes.