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    Interação de violaceína com modelos de membranas
    (Universidade Federal de São Paulo, 2017-03-28) Souza, Karine Damaceno de [UNIFESP]; Caseli, Luciano [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Violacein is a violet pigment produced by the gram-negative bacterium Chromobacterium violaceum, which exhibits a multiplicity of biological effects, from which we can highlight bactericidal, antitumoral, antihagasic, antileishmanial and antiviral actions. However, its efficacy is still not fully proven, and the mechanisms of action and interaction of the drug with cells and biomembranes at the molecular level are not yet fully understood. In this work, Langmuir lipid films were used as cell membrane models to study at a molecular level the interactions and effects caused by violacein. First, it was observed that violacein, which is poorly soluble in water, presents superficial activity induced by the presence of a monomolecular lipid film, demonstrating that the drug has a favorable interaction with membrane models. The lipids used were dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylserine (DPPS), and cholesterol, which were dissolved in chloroform and dispersed at the air-water interface. For mixed drug-lipid monolayers, violacein was incorporated into the lipid monolayers by inserting aliquots of the compound after lipid scattering. The adsorption of the drug was evaluated by measurements of surface pressure, infrared reflection-absorption spectroscopy with polarization modulation (PM-IRRAS) and Brewster angle microscopy (BAM). The monolayers were then compressed to obtain surface-area pressure isotherms. After adsorbing to the monolayers, violacein expands them by shifting the surface-area pressure-isotherms of the lipids to higher molecular areas. The films of DPPC and violacein reached pressure values around 50mN/m and mean molecular area of 70 to 55 Å2/mol. DPPS and violacein films reached a pressure of around 55 mN/m and a mean molecular area around 55 to 60 Å2/mol. Cholesterol films reached pressure values around 50mN/m and a molecular area of 45 Å2/mol. These isotherms suggest that violacein is incorporated into the DPPC, DPPS and cholesterol monolayers between the lipid chains. PM-IRRAS spectra show that the bands attributed to vibrational transitions of chemical groups present in the lipids are altered in terms of position and relative intensity, demonstrating the violacein-lipid affinity. Images obtained by BAM showed alteration in the interfacial morphology of the lipid films after incorporation of the drug. In general, the action of violacein on monolayers is governed primarily by non-electrostatic intermolecular interactions. Violacein was added inside unilamellar vesicles (LUVs), showing that it can not easily break the lipid bilayer by moving into the extra aqueous medium.