Interaction of violacein in models for cellular membranes: Regulation of the interaction by the lipid composition at the air-water interface.

Some biological properties of violacein are believed to be associated with their interactions with lipid surfaces, encouraging research on the identification of membrane sites capable of drug binding. In this study, we investigated the interaction of violacein with cell membrane models represented by Langmuir monolayers of selected lipids: one representing healthy cellular membranes: dipalmitoylphosphatidylcholine, DPPC, and the other one representing tumorigenic cellular membranes, dipalmitoylphosphatidylserine, DPPS. It is shown that even small amounts of the compound affect the surface pressure-area isotherms as well as the surface vibrational spectra of the lipid monolayers, which points to a significant interaction. Such effects depend on the electrical charge of the monolayer-forming molecules, with the drug activity being particularly distinctive for negatively charged lipids in relation to zwitterionic lipids. Morphological analysis also suggests that violacein at the air-water interface is homogenized when incorporated in both lipids. Although the interaction of violacein with the lipids affects viscoelastic and structural properties of the Langmuir monolayer, it is not present permeability through lipid bilayers, as investigated using liposomes. These results therefore may have important implications in understanding how violacein acts on specific sites of the cellular membrane, and evidence the fact that the lipid composition of the monolayer modulates the interaction with the lipophilic drug.