MANGANESE-BASED LIPOSOMES - COMPARATIVE APPROACHES

RATIONALE AND OBJECTIVES. The purpose of this study was to further dev elop and compare manganese-based liposomes prepared by two different a pproaches wherein a manganese ion was entrapped within the internal aq ueous space of the vesicles or into the bilayer surface via membrane b ound complexes. METHODS. Small unilamellar liposomes (SUVs) were prepa red entrapping manganese chloride. Alkylated complexes of manganese we re prepared and also incorporated into SUVs. The two different mangane se-based liposomes were compared for in-vitro relaxivity, stability, t oxicity, and in-vivo imaging in rats with liver tumors. RESULTS. Lipos omes entrapping manganese had a concentration-dependent change in rela xivity 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 ima ging showed greater and more specific hepatic enhancement with mangane se liposomes bearing alkylated complexes than those entrapping mangane se ion. CONCLUSIONS. Correlation effects likely explain the increased relaxivity of manganese entrapped in phospholipid vesicles. Greater ef ficacy, however, is afforded by liposomes bearing alkylated complexes.