PubMed · 15172158
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Kenji Kono, Toru Takagishi. 2004. Temperature-sensitive liposomes.. https://doi.org/10.1016/s0076-6879(04)87005-8
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The interactions of the bile salts sodium cholate (NaC) and sodium deoxycholate (NaDC) in 0.1 M NaCl (pH 7.4) with membranes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol (DPPG) and mixtures of DPPC and DPPG at molar ratios of 3:1 and 1:1 were studied by means of high-sensitivity isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and differential scanning calorimetry (DSC). The partition coefficients and the transfer enthalpies for the incorporation of bile salt molecules into the phospholipid membranes were determined by ITC. The vesicle-to-micelle transition was investigated by ITC, DLS, and DSC. The phase boundaries for the saturation of the vesicles and their complete solubilization established by ITC were in general agreement with DLS data, but systematic differences could be seen due to the difference in detected physical quantities. Electrostatic repulsion effects between the negatively charged bile salt molecules and the negatively charged membrane surfaces are not limiting factors for the vesicle-to-micelle transition. The membrane packing constraints of the phospholipid molecules and the associated spontaneous curvature of the vesicles play the dominant role. DPPG vesicles are transformed by the bile salts into mixed micelles more easily or similarly compared to DPPC vesicles. The saturation of mixed DPPC/DPPG vesicles requires less bile salt, but to induce the solubilization of the liposomes, significantly higher amounts of bile salt are needed compared to the concentrations required for the solubilization of the pure phospholipid systems. The different solubilization behavior of DPPC/DPPG liposomes compared to the pure liposomes could be due to a specific "extraction" of DPPG into the mixed micelles in the coexistence region.
Coexisting liquid phases of model membrane systems are chemically identified using imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS). The systems studied were Langmuir-Blodgett (LB) model membranes of cholesterol (CH) with two different phospholipids, one a major component in the outer plasma membrane bilayer leaflet (dipalmitoylphosphatidylcholine (PC)) and the other a major component in the inner leaflet (dipalmitoylphosphatidylethanolamine (PE)). Binary mixtures of CH with each of the phospholipids were investigated, as well as a ternary system. A single homogeneous phase is evident for PC/CH, whereas both systems containing PE show lateral heterogeneity with phospholipid-rich and CH-rich regions. The interaction between CH and the two phospholipids differs due to the disparity between the phospholipid headgroups. Imaging TOF-SIMS offers a novel opportunity to chemically identify and differentiate the specific membrane locations of CH and phospholipid in membrane regions without the use of fluorescent dyes. This unique imaging method has been used to demonstrate the formation of micrometer-size CH domains in phosphatidylethanolamine-rich systems and is further evidence suggesting that CH may facilitate transport and signaling across the two leaflets of the plasma membrane.
2-(2,4-Dihydroxyphenylo)-5,6-dichlorobenzthiazole (dHBBT) is a new drug from the group of chemical compounds characterized by documented antifungal, antibacterial, cytostatic as well as antitumour activity. Despite general knowledge regarding pharmacological importance of dHBBT its interaction to biomembranes has not been investigated. In this work, we present the electronic absorption spectroscopic study on molecular organization of dHBBT in organic solvents and on its localization and molecular organization within model lipid membranes formed with dipalmitoylphosphatidylcholine (DPPC). The spectroscopic measurements are interpreted within the framework of the exciton splitting theory. It is concluded that complex absorption spectrum of dHBBT both in the organic solvents and incorporated to DPPC represents superposition of two spectral forms: representing monomers and hypsochromically shifted spectrum representing molecular dimers. Analysis of the temperature dependencies of the absorption spectra of dHBBT incorporated to DPPC liposomes suggests localization of the drug in the polar head-group region of the membrane or in the region of the polar-nonpolar interface. Linear dichroism measurements of dHBBT incorporated to DPPC multibilayers reveal roughly vertical orientation of the drug molecules with respect to the plane of the membrane. A model is presented of molecular organization of dHBBT in lipid membranes. Potential effects of dHBBT on membrane physical properties is briefly discussed.