Immobilized artificial membrane (IAM) chromatography: An in vitro screen for predicting drug-membrane interactions

Immobilized artificial membranes (IAMs) are a model of liposome membranes. Drug membrane interactions were studied by IAM high-performance liquid chromatography as described in the following paragraphs.;Lipid heterogeneity prevents the development of a single membrane surface from characterizing the binding of compounds to tissue membranes in different organs. Thus, carboxyl phospholipid analogs of several membrane lipids were made to expand our abilities to measure biological relevant drug-lipid interactions. Efficient synthetic strategies were developed to prepare carboxyl analogs of membrane phospholipids for immobilization that bear interfacial functional groups identical to PC, PG, PA, PE, and PS membrane phospholipids forming the cell membranes.;The IAM methodology was established to evaluate drug-membrane interaction using chromatographic retention time data. The experimental data indicates that solute partitioning between the IAM bonded phase and the aqueous mobile phase is similar to the solute partitioning between liposomes and the aqueous phase.;IAMs also predict oral drug absorption in mice and drug permeability through Caco-2 cells. In addition to the IAM.PC surfaces used in the drug-membrane interaction studies, two other surfaces with polar headgroups were made as controls to understand the mechanism responsible for predicting drug-membrane interactions. The surfaces were 12-OH-silica and 12-MO-silica. As expected, improved correlations of predicting solute-membrane interactions were found for the chromatographic surfaces containing the PC polar head-group because the PC headgroup is endogenous to natural cell membranes.;IAM chromatography was at first time developed as a convenient and accurate method to measure pKa values at membrane interface. Membrane interfacial pKa is highly dependent on physico-chemical properties such as interfacial electrostatics, hydration, ligand packing, and polarity, which means that for pKliposomea being equal to pKIAMa the interfacial physico-chemical properties of IAM surfaces must be similar if not identical to fluid liposome membranes. This project therefore represents a critical test of the ability of IAMs to model interfacial properties of biological membranes.;In addition to the drug-IAM binding studies, IAM surfaces were used to purify rat liver Aldolase B in a single chromatographic step. Since tissue preparation involved only homogenization and centrifugation, the single step purification of Aldolase B using IAM chromatography is a very convenient method.