Effects of (+)-totarol, a diterpenoid antibacterial agent, on phospholipid model membranes |
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Authors: | Micol V Mateo C R Shapiro S Aranda F J Villalaín J |
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Institution: | Centro de Biologia Molecular y Celular, Universidad Miguel Hernandez, E-0302 Elche, Spain. |
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Abstract: | (+)-Totarol, a highly hydrophobic diterpenoid isolated from Podocarpus spp., is inhibitory towards the growth of diverse bacterial species. (+)-Totarol decreased the onset temperature of the gel to liquid-crystalline phase transition of DMPC and DMPG membranes and was immiscible with these lipids in the fluid phase at concentrations greater than 5 mol%. Different (+)-totarol/phospholipid mixtures having different stoichiometries appear to coexist with the pure phospholipid in the fluid phase. At concentrations greater than 15 mol% (+)-totarol completely suppressed the gel to liquid-crystalline phase transition in both DMPC and DMPG vesicles. Incorporation of increasing amounts of (+)-totarol into DEPE vesicles induced the appearance of the H(II) hexagonal phase at low temperatures in accordance with NMR data. At (+)-totarol concentrations between 5 and 35 mol% complex thermograms were observed, with new immiscible phases appearing at temperatures below the main transition of DEPE. Steady-state fluorescence anisotropy measurements showed that (+)-totarol decreased and increased the structural order of the phospholipid bilayer below and above the main gel to liquid-crystalline phase transition of DMPC respectively. The changes that (+)-totarol promotes in the physical properties of model membranes, compromising the functional integrity of the cell membrane, could explain its antibacterial effects. |
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