Transmucosal passage of liposomally-entrapped drugs in rat small intestine

Intestinal absorption of liposomally-entrapped drugs was investigated for egg yolk phosphatidylcholine-cholesterol (2:1 by molar ratio) liposomes (EggPC liposome) and distearoylphosphatidylcholine-cholesterol (2:1) liposomes (DSPC liposome). The release of carboxyfluorescein, an aqueous phase marker, induced by the presence of everted rat intestine was 40 % and 6 % in one hour from DSPC liposomes and EggPC liposomes, respectively, and it is suggested that EggPC liposomes are more stable in the intestinal lumen. The transport of a liposomally-entrapped drug was examined with fluoresceinisothiocyanate-conjugated dextran (FITC-D) as a model drug that has a small mucosal-to-serosal clearance because of its high average molecular weight (64200). The clearance of FITC-D entrapped in DSPC liposomes was largely reduced and could be accounted for by the clearance of the extraliposomal FITC-D concentration in the preparation. On the other hand, the calculated clearance of EggPC liposome-associated FITC-D was similar to or even higher than that of free FITC-D. The serosal appearance of the EggPC liposome-associated drug was inhibited by colchicine, cytochalasin B, and iodoacetate, suggesting that the liposome was incorporated into the epithelial cells by endocytosis. However, the observation that a lipid phase marker, (14)C-dipalmitoylphosphatidylcholine, failed to be transported into the serosal fluid indicates the absence of the penetration by an intact liposomal form.