title: Binding of methylene blue onto Langmuir monolayers representing cell membranes may explain its efficiency as photosensitizer in photodynamic therapy.
abstract: We provide evidence for the electrostatic interactions between the cationic photosensitizer methylene blue (MB) and cell membrane models represented by neat and mixed Langmuir monolayers of dioleylphosphatidylcholine (DOPC) and 1,1',2,2'-tetraoleoylcardiolipin (CL). From surface pressure measurements, MB was found to adsorb strongly and expand CL-containing monolayers, while it caused an apparent decreasing in molecular area on neat DOPC monolayer. The binding site of MB could be inferred from data with the surface-specific polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) technique, where changes induced by MB were observed in the vibrational modes of the phosphate groups of both CL and DOPC. The incorporation of MB also affected the carbonyl groups and the packing of the alkyl chains, thus indicating that MB binding site favors singlet oxygen generation close to the double bonds in the alkyl chains, an important requirement for photodynamic efficiency. Significantly, the data presented here demonstrate that MB may act in membranes composed by PCs, such as mammalian plasma membranes, and in those containing CL, as in bacterial and inner mitochondrial membranes.
authors: †Federal University of ABC (UFABC), Santo André, SP 09210-580, Brazil.
authors: Thaís F
authors: TF
authors: Schmidt
authors: ‡Institute of Environmental, Chemical, and Pharmaceutical Sciences, Federal University of São Paulo, Diadema, SP 09913-030, Brazil.
authors: Luciano
authors: L
authors: Caseli
authors: §São Carlos Institute of Physics, University of São Paulo, São Carlos, SP 13560-970, Brazil.
authors: Osvaldo N
authors: ON
authors: Oliveira
authors: ∥Institute of Physics, University of São Paulo, São Paulo, SP 05508-090, Brazil.
authors: Rosangela
authors: R
authors: Itri
mesh_terms: D002308:Cardiolipins / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D008751:Methylene Blue / Q000737:chemistry / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000737:chemistry / Q000378:metabolism*; D055672:Static Electricity
chemical_list: C519576:1,1',2,2'-tetraoleoylcardiolipin; D002308:Cardiolipins; D010713:Phosphatidylcholines; D017319:Photosensitizing Agents; C017251:1,2-oleoylphosphatidylcholine; D008751:Methylene Blue