Role of lipophilic medium in the absorption of polycyclic aromatic compounds by biomembranes.

Polycyclic aromatic hydrocarbons (PAHs), before reaching DNA where they exert their activity, have to interact with the outer lipid layer of cell membranes and subsequently penetrate inside cells. Studying the interaction PAH-lipid membrane should be interesting in assessing the relevance of the medium in the absorption processes. A technique used to study such an interaction is differential scanning calorimetry (DSC) that detects the phase transition from an ordered to a disordered lipid structure, that can be affected by the presence of foreign molecules, when submitted to heating. Effects exerted by fluorene, fluoranthene and indeno(1,2,3-cd)pyrene on the thermotropic behavior of model membranes were here investigated. Aqueous dispersions of synthetic dimyristoylphosphatidylcholine (DMPC) were used as model membranes to study PAHs-membrane interaction. All the examined PAHs, dispersed in liposomes during their preparation, affect, to a different extent, the DMPC liposome transitional phase temperature. A study carried out by leaving powdered PAHs in contact with DMPC vesicles, shows that all three PAHs are almost unable to migrate through the aqueous medium. Instead, when PAH loaded liposomes were left in contact with empty ones, it appears evident that fluorene is able to migrate from a loaded membrane to an empty one. Also fluoranthene, although to a minor extent relative to fluorene, is able to migrate through the lipid environment. Indeno(1,2,3-cd)pyrene is less able to migrate through liposomes. The obtained data seem to validate the employment of the DSC technique in studying the ability of bioactive and potentially mutagenic compounds not only to interact with biological membranes but also to be adsorbed into a cell when dispersed in a lipophilic medium.