Volume of distribution and transcapillary passage of small unilamellar vesicles

This study investigated the biodistribution of bovine brain sphingomyelin (SM)/cholesterol (CH) (2/1; M/M) small unilamellar vesicles (SUV) in mice, addressing specifically the volume of distribution and transcapillary passage of the SUV. The complex of nitrilotriacetic acid with In-111 or Ga-67 ions was encapsulated in the SUV as the radioactive marker for various studies. The structural integrity of liposomes in vitro and in vivo was monitored by the technique of gamma ray perturbed angular correlation. Our data suggested that initially the SM/CH SUV remained within the vascular system and occupied a volume of distribution approximately 1.28 times larger than that of erythrocytes in the vascular system of mice. However, our data also indicated that with time the SM/CH SUV could get out of the vascular system of mice and were taken up by surrounding tissues over a period of 24 hours.