Manganese-based liposomes. Comparative approaches.
OBJECTIVE
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.
Unger
E
E
Department of Radiology, University of Arizona Health Sciences Center, Tucson, AZ 85724.
Fritz
T
T
Shen
D K
DK
Wu
G
G
D000818:Animals; D002712:Chlorides / Q000008:administration & dosage / Q000633:toxicity; D003287:Contrast Media / Q000008:administration & dosage* / Q000633:toxicity; D008081:Liposomes; D008114:Liver Neoplasms, Experimental / Q000175:diagnosis; D008279:Magnetic Resonance Imaging; D008345:Manganese / Q000008:administration & dosage*; D017895:Manganese Compounds / Q000008:administration & dosage; D020149:Manganese Poisoning; D008567:Membranes, Artificial; D051379:Mice; D008807:Mice, Inbred BALB C; D051381:Rats; D011916:Rats, Inbred F344
D002712:Chlorides; D003287:Contrast Media; D008081:Liposomes; D017895:Manganese Compounds; D008567:Membranes, Artificial; D008345:Manganese; C025340:manganese chloride