Biodistribution studies of liposome encapsulated hemoglobin (LEH) studied with a newly developed 99m-technetium liposome label.

A new method has been developed to label preformed liposomes with 99m-Technetium (99mTc) using hexamethylpropylenamine oxime (HMPAO). 99mTc is an ideal isotope for performing non-invasive dynamic biodistribution studies. This labeling method results in a high labeling efficiency (greater than 95%) and is stable as determined by both in vitro and in vivo studies. In vitro studies indicated that glutathione encapsulated in the LEH is important in the labeling process with 99mTc-HMPAO. In vivo studies with LEH were performed on 7 rabbits with dynamic scintigraphic 1 minute images performed from 1-120 minutes. Delayed images were performed at 20 hours followed by sacrifice and organ counting. Dynamic images reveal a gradual deposition of the LEH in the liver and spleen. Twenty hour biodistributions revealed 50% of the LEH remaining in the blood, 15% in the liver, 14% in the spleen, 3% in lungs, 3% in muscle with trace amounts in the brain, kidneys, and heart. Doses per gram were highest in the spleen with 12.5% of the injected dose per gram of spleen vs. 0.2% per gram of liver. This labeling technique is an effective method for non-invasively monitoring dynamic changes in liposome biodistribution and can be used to study the effects of various liposome modifications on biodistribution.