The lipid composition of biomembranes influence the properties of the lipid bilayer as well as that of the proteins. In this study, the lipidome and the lipid/protein ratio of membranes from High FiveTM insect cells overexpressing mouse P-glycoprotein was characterized. This provides a better understanding of the lipid environment in which P-glycoprotein is embedded, and thus of its functional and structural properties. The relative abundance of the distinct phospholipid classes and their acyl chain composition was characterized. A mass ratio of 0.57 +/- 0.11 phospholipids to protein was obtained. Phosphatidylethanolamines are the most abundant phospholipids, followed by phosphatidylcholines. Membranes are also enriched in negatively charged lipids (phosphatidylserines, phosphatidylinositols and phosphatidylglycerols), and contain small amounts of sphingomyelins, ceramides and monoglycosilatedceramides. The most abundant acyl chains are monounsaturated, with significant amounts of saturated chains. The characterization of the phospholipids by HPLC-MS allowed identification of the combination of acyl chains, with palmitoyl-oleoyl being the most representative for all major phospholipid classes except for phosphatidylserines, which are mostly saturated. A mixture of POPE:POPC:POPS in the ratio 45:35:20 is proposed for the preparation of simple representative model membranes. The adequacy of the model membranes was further evaluated by characterizing their surface potential and fluidity.

Evaluation of drug permeability using cell monolayers is an important in vitro assay in the process of drug development, to identify compounds with favourable pharmacokinetics that may proceed to in vivo studies. When allowed to differentiate on permeable filters for at least 21 days, monolayers of Caco-2 cells develop morphological and functional properties similar to those of the intestinal epithelium. Permeability through Caco-2 monolayers is thus particularly relevant to assess drug absorption after oral administration. The major drawback of this assay is its very low throughput, with the cell monolayers being used in a single permeability assay. We have previously proposed a protocol to allow the re-use of the Caco-2 monolayer on additional permeability assays during the stable period and shown that cell monolayer integrity is maintained. In this work we evaluate the effect of re-use on the permeability of several reference compounds that permeate through passive pathways and show that the cell monolayers can be re-used twice in additional permeability assays. Preliminary results were also obtained regarding active transport pathways, and a new methodology is proposed to quantify the contribution from passive and active transport. This is a major step towards the full validation of the re-use methodology proposed, which at least triplicates the throughput of this important in vitro assay.