Nanosized bilayer disks: attractive model membranes for drug partition studies

Stable nanosized bilayer disks were prepared from either 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol, or lipid mixtures with a composition reflecting that of the porcine brush border membrane. Two different polyethylene glycol (PEG)-grafted lipids, the negatively charged 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethylene glycol)-5000] (DSPE-PEG(5000)) and the neutral N-palmitoyl-sphingosine-1-[succinyl (methoxy (polyethylene glycol) 5000] (Ceramide-PEG(5000)), were used to stabilize the disks. The disks were employed as model membranes in drug partition studies based on a fast chromatography method. Results show that the lipid composition, as well as the choice of PEG-lipid, have an important influence on the partition behavior of charged drugs. Comparative studies using multilamellar liposomes indicate that bilayer disks have the potential to generate more accurate partition data than do liposomes. Further, initial investigations using bacteriorhodopsin suggest that membrane proteins can be reconstituted into the bilayer disks. This fact further strengthens the potential of the bilayer disk as an attractive model membrane.