Characterization of Liposomes Containing Iodine-125-Labeled Radiographic Contrast Agents

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Abstract
Multilamellar liposomes were prepared containing either iodine-125-labeled (125I) diatrizoate or 125-I labeled iotrol in their aqueous phase. The in vitro permeabilities of liposomes containing both contrast agents were measured in the presence of saline and serum at 37.degree. C. Two different phospholipid compositions were studied: (1) phosphatidylcholine/cholesterol/stearylamine (PC/C/S, 8: 1:1molar ratio) and (2) distearoylphosphatidylcholine/sphingomyelin (DSPC/SM, 5.2 mole ratio). In saline, similar permeabilities were observed for the four phospholipid-contrast agent combinations. In serum, however, leakage of 125I activity was 2 to 3 times greater from PC/C/S liposomes that contained 125I-diatrizoate were injected into rats, the clearance half-times for 125I activity from the liver, spleen, and whole body were 4.4 hours, 4.5 hours, and 2.8 hours, respectively. Liposomes composed of DSPC/SM cleared at a significantly slower rate from the liver, spleen, and whole body with half-times of 24.0 hours, 18.4 hours, and 17.2 hours observed from these tissues, respectively.