Application of synthetic liposomes based on acyl amino acids or acyl peptides as drug carriers. I. Their preparation and transport of glutathione into the liver.

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Abstract
Palmitoyl amino acids and palmitoyl glutathione were synthesized. Liposome-like vesicles based on these compounds were prepared and their barrier functions were examined. These vesicles showed encapsulated efficiencies for aqueous solute comparable to that of conventional phosphatidylcholine liposomes (PC-liposomes). They were also stable in fresh rat plasma at 37.degree. C. The biological behavior (blood clearance, urinary excretion and tissue distribution) of the vesicles based on palmitoyl serine (PSer-liposomes) of palmitoyl glutathione (PGSH-liposomes) was examined after intravenous injection in rats. The synthetic liposomes were cleared very rapidly from the blood compared with PC-liposomes. PSer-Liposomes showed a large amount of urinary excretion of aqueous marker ([3H]inulin), suggesting that the mechanisms of vesicle degradation in vivo and in vitro are different. These synthetic liposomes showed low affinity to the spleen and high affinity to the liver in the tissue distribution study, and thus they may be expected to be a useful drug carrier which is targetable to the liver. A suppressing effect of PGSH-liposomes on the increase of plasma glutamate oxaloacetate transaminase (GOT) induced by a high dose of acetaminophen in mice was observed, and transport of glutathione into the liver cells apparently occurred. The suppressing effect was greater than that of free glutathione or PC-liposomes containing free glutathione. However, the effect was not observed in the case of PGSH-liposomes without phosphatidylcholine, which appears to have an important role in the liposome-cell interaction.