ISSN:
1432-0827
Keywords:
Bisphosphonates
;
Diphosphonates
;
Ultrafiltration-Chromatography
;
Protein-binding
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
,
Physics
Notes:
Summary Ultrafiltration and gel filtration were used to study the behavior of pyrophosphate (PPi), 1-hydroxyethylidene-1,1-bisphosphonate (HEBP), and dichloromethylenebisphosphonate (Cl2MBP) in aqueous buffer and in human blood plasma. In aqueous buffer, pH 7.4, at a 10'000 dalton molecular cut-off, 4µM HEBP and Cl2MBP were only 45% and 4µM PPi 70% ultrafiltrable, much less than expected for such low molecular weight compounds. At a 50'000 dalton cut-off, ultrafiltrability approached 100%. The ultrafiltrability of HEBP and PPi, but not of Cl2MBP was reduced by 1 mM Ca and 5 mM Pi at a 50'000 dalton cut-off. The ultrafiltrability of HEBP was higher at acid pH and in the presence of 1 M NaClO4, suggesting a dependence of the apparent molecular size on the hydration of the molecule. In plasma, HEBP was 70% and Cl2MBP 73% ultrafiltrable at a 50'000 dalton cut-off. In dialyzed Ca-free plasma the ultrafiltrability of HEBP was 79%, and addition of 2.5 mM Ca reduced it to 70%, suggesting a role for Ca in the binding of HEBP to plasma protein. Chromatography of HEBP with Sephadex G 25 showed two peaks. In the presence of 1 M NaClO4, however, there was only one peak, suggesting that HEBP might be present in several differently hydrated forms. Cl2MBP and PPi were eluted as a single peak. Our results suggest thatin vivo HEBP and Cl2MBP should diffuse easily into the extravascular space. Since only about one-fourth of the drugs is protein-bound in the blood, it should be possible to achieve pharmacologically effective concentrations in a majority of tissues, not only in the skeleton.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02405066
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