Optimizing Biological Activity of Lipophilic Compounds in Cultured Cells by Improving Delivery: Theoretical and Practical Considerations

Abstract

The use of lipophilic compounds in the study of signal transduction and other cellular processes is often complicated by the need to deliver compounds that are minimally soluble in water to cells in culture. A typical approach is to dissolve the lipophilic compound at high concentration in organic solvent and then to dilute the solvent in aqueous medium. However, such an approach usually results in precipitation of the compound in the aqueous medium and may minimize delivery of the compound to cells. Three techniques to keep the lipophilic compound In a nonprecipitated and stable form that will be readily available to the cells are described. They involve the use of protein carriers, liposomes, and emulsions. Particular attention is given to the use of emulsions, since this technique combines the advantages of a high capacity for lipophilic compounds, ease of assembly, and minimum contact between the lipophilic compound and water. Although the techniques differ with respect to the mechanics of combining the compound and the carrier, they all consist of a two-phase system dependent on partitioning between the carrier and the cells. Due to the need to take partitioning into account, all of these techniques differ from homogeneous solution-phase delivery. Therefore, in addition to descriptions of the techniques, criteria for both experimental design and analysis of data generated using two-phase systems are presented. In combination, the use of methods appropriate for delivery of lipophilic compounds to cells and the application of relevant calculations and analytical procedures provide the means necessary for design and Interpretation of experiments using lipophilic compounds.