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Manganese-based liposomes. Comparative approaches
1Department of Radiology, University of Arizona Health Sciences Center, Tucson, AZ 85724.
Rationale And Objectives:
The purpose of this study was to further develop and compare manganese-based liposomes prepared by two different approaches wherein a manganese ion was entrapped within the internal aqueous space of the vesicles or into the bilayer surface via membrane bound complexes.
Methods:
Small unilamellar liposomes (SUVs) were prepared entrapping manganese chloride. Alkylated complexes of manganese were prepared and also incorporated into SUVs. The two different manganese-based liposomes were compared for in-vitro relaxivity, stability, toxicity, and in-vivo imaging in rats with liver tumors.
Results:
Liposomes entrapping manganese had a concentration-dependent change in relaxivity that was maximal at a several-fold molar excess of phospholipid relative to manganese ion. Liposomes bearing membrane-bound complexes showed relaxivity inversely proportional to vesicle size. In-vivo imaging showed greater and more specific hepatic enhancement with manganese liposomes bearing alkylated complexes than those entrapping manganese ion.
Conclusions:
Correlation effects likely explain the increased relaxivity of manganese entrapped in phospholipid vesicles. Greater efficacy, however, is afforded by liposomes bearing alkylated complexes.