Effect of liposome type and membrane fluidity on drug–membrane partitioning analyzed by immobilized liposome chromatography

Immobilized liposome chromatography (ILC) has been proven to be a useful method for the study or rapid screening of drug–membrane interactions. To obtain an adequate liposomal membrane phase for ILC, unilamellar liposomes were immobilized in gel beads by avidin–biotin binding. The retardation of 15 basic drugs on the liposome column could be converted to membrane partitioning coefficients, KLM. The effects of small or large unilamellar liposomes and multilamellar liposomes on the drug–membrane partitioning were compared. The KLM values for both small and large liposomes were similar, but higher than those for the multilamellar liposomes. The basic drugs showed stronger partitioning into negatively charged liposomes than into either neutral liposomes or positively charged liposomes. The membrane fluidity of the immobilized liposomes was modulated by incorporating cholesterol into the liposomal membranes, by changing the acyl chain length and degree of unsaturation of the phospholipids, and by changing the temperature for ILC runs. Our data show that KLM obtained using ILC correlated well with those reported by batch studies using free liposomes. It is concluded that negatively charged or cholesterol-containing large unilamellar liposomes are suitable models for the ILC analysis of drug–membrane interactions.