Development of a liposome formulation for D-cycloserine local delivery

Multilamellar liposomes loaded with D-cycloserine (D-CS) were prepared by a thin layer evaporation technique, followed by freezing and thawing cycles. Charged components and bioadhesive material, such as distearolylphosphatitylethanolamine covalently coupled with methoxypolyethyleneglycol, were used to prepare liposomes with different physico-chemical and technological properties. Negatively charged liposomes showed higher D-CS encapsulation efficiency (about 37%, w/w) than neutral and positively charged liposomes (about 5 and 17%, w/w, respectively). All formulations showed in vitro, after a burst effect, a prolonged release of the encapsulated drug. Lipid vesicles made of dipalmitoylphosphatidylcholine (DPPC) were used as a biomembrane model to evaluate in vitro the interaction of D-CS with biological membranes. Differential scanning calorimetry was used as a simple and noninvasive technique of analysis. D-CS was distributed in the aqueous compartments of liposomes for interaction with the phospholipid polar head-groups (enhancement of Delta H value). However, due to its high diffusibility the drug was also able to freely permeate through DPPC liposomes, altering during this passage the hydrophobic domains of the bilayers. Stability studies were performed at different temperatures and pH values to assay the integrity of the drug during the liposome production steps. D-CS was rapidly degraded at acidic pH, but no significant hydrolysis was observed at pH 7.4 after 7 days.     

Effect of the nature of the 3beta-substitution in manoyl oxides on the thermotropic behavior of DPPC lipid bilayer and on DPPC liposomes

Functionalized manoyl oxide derivatives have been proved over the years to evoke several biological responses. Among them, 3beta-hydroxy-manoyl oxide (1) and 3beta-acetoxy-manoyl oxide (2) have been shown to exhibit in vitro antimicrobial and cytotoxic activity, while N-imidazole-3 beta-thiocarbonyl ester of manoyl oxide (3) was found to exhibit potent cytotoxic effect. Their partitioning into phospholipid bilayers may lead to membrane structure modifications that are crucial in liposome development as they may influence their maintenance and integrity. DSC was used to study the modifications induced in DPPC bilayers by incorporating increasing concentrations of the three manoyl oxide derivatives. All derivatives were found to strongly affect the bilayer structural organization in terms of a decrease of the cooperativity, the fluidization and partially destabilization of the gel phase and the induction of a lateral phase separation in clustering domains. Derivatives 1 and 3 were incorporated into DPPC liposomes and their physicochemical stability was monitored at 4 degrees C. The stability of liposomes was strongly influenced by the presence of 1 and 3 at any molar ratio studied. DPPC/1 liposomes were found to retain its stability for 48 h at low concentration of 10% mol, while at higher concentrations up to 30% mol they collapsed into aggregated material. In all cases DPPC/3 liposomes were found unstable and sticky aggregated structures precipitated from the bulk suspension.     

Calorimetric study on the induction of interdigitated phase in hydrated DPPC bilayers by bioactive labdanes and correlation to their liposome stability: The role of chemical structure

Labd-7,13-dien-15-ol (1), labd-13-ene-8alpha,15-diol (2), and labd-14-ene-8,13-diol (sclareol) have been found to exhibit cytotoxic and cytostatic effects. Their partitioning into phospholipid bilayers may induce membrane structure modifications, crucial in the development of liposomes. DSC was used to elucidate the profile of modifications induced in DPPC bilayers by incorporating increasing concentrations of the labdanes. Labdanes 1, 2 and sclareol were incorporated into SUV liposomes composed of DPPC their physicochemical stability was monitored (4 degrees C) and was compared to liposomes incorporating cholesterol. All labdanes strongly affect the bilayer organization in a concentration dependent manner in terms of a decrease of the cooperativity, the fluidization and partially destabilization of the gel phase, the induction of a lateral phase separation and the possible existence of interdigitated domains in the bilayer. The physicochemical stability of liposomes was strongly influenced by the chemical features of the labdanes. The liposomal preparations were found to retain their stability at low labdane concentration (10 mol%), while at higher concentrations up to 30 mol% a profound decrease in intact liposomes occurred, and a possible existence of interdigitated sheets was concluded.     

Development of a Liposome Formulation for D-Cycloserine Local Delivery

Multilamellar liposomes loaded with D-cycloserine (D-CS) were prepared by a thin layer evaporation technique, followed by freezing and thawing cycles. Charged components and bioadhesive material, such as distearolylphosphatitylethanolamine covalently coupled with methoxypolyethyleneglycol, were used to prepare liposomes with different physico-chemical and technological properties. Negatively charged liposomes showed higher D-CS encapsulation efficiency (about 37%, w/w) than neutral and positively charged liposomes (about 5 and 17%, w/w, respectively). All formulations showed in vitro, after a burst effect, a prolonged release of the encapsulated drug.

Lipid vesicles made of dipalmitoylphosphatidylcholine (DPPC) were used as a biomembrane model to evaluate in vitro the interaction of D-CS with biological membranes. Differential scanning calorimetry was used as a simple and noninvasive technique of analysis. D-CS was distributed in the aqueous compartments of liposomes for interaction with the phospholipid polar head-groups (enhancement of Δ?H value). However, due to its high diffusibility the drug was also able to freely permeate through DPPC liposomes, altering during this passage the hydrophobic domains of the bilayers.

Stability studies were performed at different temperatures and pH values to assay the integrity of the drug during the liposome production steps. D-CS was rapidly degraded at acidic pH, but no significant hydrolysis was observed at pH 7.4 after 7 days.     

Humoral immune response against epidermal growth factor encapsulated in dehydration rehydration vesicles of different phospholipid composition

We investigated the influence of dehydration-rehydration vesicles (DRV) phospholipid composition and the addition of other components on human recombinant epidermal growth factor (hrEGF) encapsulation efficiency and its release from liposomes. Encapsulation of EGF into DRV composed of phosphatidylcholine with different unsaturation levels was around 20-35%. The best result was obtained with dipalmitoyl phosphatidylcholine: cholesterol (DPPC:Ch) liposomes (35%) corresponding to the lowest hrEGF release during one month of storage. Even with this phospholipid composition, modification of the DRV procedure by including an extrusion step did not improve hrEGF encapsulation efficiency, rendering less stable particles. The inclusion of recombinant P64k from Neisseria meningitidis (rP64k), as such or conjugated to hrEGF, decreased the encapsulation efficiency of the latter protein into DRV or freeze and thaw multilamellar vesicles (FATMLV). The hrEGF release from liposomes could be related to the interaction between this polypeptide and the bilayer, as evidenced by increased carboxyfluorescein release from hrEGF-DRV; less susceptibility to fluorescence quenching by acrylamide in the presence of liposomes; and a measurable decrease of phospholipid phase transition Delta enthalpy (DeltaH). DRV comprising saturated phospholipids (DPPC:Ch or distearoyl phosphatidylcholine [DSPC]:Ch) and containing the conjugate EGF-P64k induced a more efficient immune response against hrEGF than unsaturated phospholipid and alum in terms of total IgG, IgG(2a), and IgG(2b) subclasses and the ability of antibody to inhibit the interaction of the EGF receptor with hrEGF.     

Encapsulation of Enrofloxacin in Liposomes I: Preparation and In Vitro Characterization of LUV

Liposomes are effectively used in the treatment of microbial infections. Higher cellular uptake has been reported when antibiotics are encapsulated in liposomes. In this study, enrofloxacin (ENF) was encapsulated in large unilamellar vesicles (LUVs) and the effects of formulation variables on the liposome characteristics were investigated. Liposomes were prepared using dry lipid film method. A number of variables such as molar ratios of phospholipid (DPPC; DL‐α‐phosphatidylcholine dipalmitoyl), cholesterol, ENF and amount of α‐tocopherol and the volumes of internal (chloroform) and external phases [phosphate buffered saline PBS (pH 7.4)] were studied. In vitro characterization of the liposomes including the encapsulation capacity, size and drug release properties were carried out. Using of this method, spherical LUV liposomes with high drug content could be produced. Particle size of liposomes changed between 3.12 and 4.95 µm. The molar ratios of DPPC, cholesterol and ENF affected the size of the liposome (p < 0.05). The drug encapsulation capacities were high and changed between 37.1% and 79.5%. The highest ENF encapsulation was obtained with the highest cholesterol content. An increase in the drug encapsulation capacity of the liposome was found with increasing molar ratios of DPPC, cholesterol and ENF (p < 0.05). Furthermore, the release of ENF from the liposomes decreased as the molar ratios of DPPC, cholesterol and ENF increased (p < 0.05). In conclusion, a convenient colloidal carrier for the controlled release of ENF can be prepared by changing the formulation parameters of LUVs.     

Encapsulation of enrofloxacin in liposomes I: preparation and in vitro characterization of LUV

Liposomes are effectively used in the treatment of microbial infections. Higher cellular uptake has been reported when antibiotics are encapsulated in liposomes. In this study, enrofloxacin (ENF) was encapsulated in large unilamellar vesicles (LUVs) and the effects of formulation variables on the liposome characteristics were investigated. Liposomes were prepared using dry lipid film method. A number of variables such as molar ratios of phospholipid (DPPC; DL-alpha-phosphatidylcholine dipalmitoyl), cholesterol, ENF and amount of alpha-tocopherol and the volumes of internal (chloroform) and external phases [phosphate buffered saline PBS (pH 7.4)] were studied. In vitro characterization of the liposomes including the encapsulation capacity, size and drug release properties were carried out. Using of this method, spherical LUV liposomes with high drug content could be produced. Particle size of liposomes changed between 3.12 and 4.95 microm. The molar ratios of DPPC, cholesterol and ENF affected the size of the liposome (p < 0.05). The drug encapsulation capacities were high and changed between 37.1% and 79.5%. The highest ENF encapsulation was obtained with the highest cholesterol content. An increase in the drug encapsulation capacity of the liposome was found with increasing molar ratios of DPPC, cholesterol and ENF (p < 0.05). Furthermore, the release of ENF from the liposomes decreased as the molar ratios of DPPC, cholesterol and ENF increased (p < 0.05). In conclusion, a convenient colloidal carrier for the controlled release of ENF can be prepared by changing the formulation parameters of LUVs.     

Dye permeability at phase transitions in single and binary component phospholipid bilayers

By encapsulating a pH-sensitive dye, phenol red, in multilamellar liposomes of DMPC, DPPC and DMPC/DPPC mixtures, the permeability of these phospholipid bilayers to dye as a function of temperature has been studied. For both DMPC and DPPC liposomes, dye release begins well below the main gel-to-liquid-crystalline phase transition (24°C and 42°C, respectively) at temperatures corresponding to the onset of the pretransition (about 14°C and 36°C, respectively) with DPPC liposomes exhibiting a permeability anomaly at the main phase transition (42°C). The perturbation occurring in the bilayer structure that allows the release of encapsulated phenol red (approx. 5 Å diameter) is not sufficient to permit the release of encapsulated haemoglobin (approx. 20 Å diameter, negatively charged). In liposomes composed of a range of DMPC/DPPC mixtures, dye release commences at the onset of the pretransition range (determined by optical absorbance measurements) and increases with increasing temperature until the first appearance of liquid crystalline phase after which no further dye release occurs. Interestingly, the dye retaining properties of DMPC and DPPC liposomes well below their respective pretransition temperature regions are very different: DMPC liposomes release much encapsulated dye at incubation temperatures of 5°C whilst DPPC liposomes do not.     

Effects of phospholipid hydrolysis on the aggregate structure in DPPC/DSPE-PEG2000 liposome preparations after gel to liquid crystalline phase transition

Upon storage of phospholipid liposome samples, lysolipids, fatty acids, and glycerol-3-phosphatidylcholine are generated as a result of acid- or base-catalyzed hydrolysis. Accumulation of hydrolysis products in the liposome membrane can induce fusion, leakage, and structural transformations of the liposomes, which may be detrimental or beneficial to their performance depending on their applications as, e.g., drug delivery devices. We investigated in the present study the influence of phospholipid hydrolysis on the aggregate morphology of DPPC/DSPE-PEG2000 liposomes after transition of the phospholipid membrane from the gel phase to liquid crystalline phase using high performance liquid chromatography (HPLC) in combination with static light scattering, dynamic light scattering, and cryo-transmission electron microscopy (cryo-TEM). The rates of DPPC hydrolysis in DPPC/DSPE-PEG2000 liposomes were investigated at a pH of 2, 4, or 6.5 and temperatures of 22 degrees C or 4 degrees C. Results indicate that following phase transition, severe structural reorganizations occurred in liposome samples that were partially hydrolyzed in the gel phase. The most prominent effect was an increasing tendency of liposomes to disintegrate into membrane discs in accordance with an increasing degree of phospholipid hydrolysis. Complete disintegration occurred when DPPC concentrations had decreased by, in some cases, as little as 3.6%. After extensive phospholipid hydrolysis, liposomes and discs fused to form large bilayer sheets as well as other more complex bilayer structures apparently due to a decreased ratio of lysolipid to palmitic acid levels in the liposome membrane.     

Biophysical characterization of gold nanoparticles-loaded liposomes

Gold nanoparticles were prepared and loaded into the bilayer of dipalmitoylphosphatidylcholine (DPPC) liposomes, named as gold-loaded liposomes. Biophysical characterization of gold-loaded liposomes was studied by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy as well as turbidity and rheological measurements. FTIR measurements showed that gold nanoparticles made significant changes in the frequency of the CH₂ stretching bands, revealing that gold nanoparticles increased the number of gauche conformers and create a conformational change within the acyl chains of phospholipids. The transmission electron micrographs (TEM) revealed that gold nanoparticles were loaded in the liposomal bilayer. The zeta potential of DPPC liposomes had a more negative value after incorporating of Au NPs into liposomal membranes. Turbidity studies revealed that the loading of gold nanoparticles into DPPC liposomes results in shifting the temperature of the main phase transition to a lower value. The membrane fluidity of DPPC bilayer was increased by loading the gold nanoparticles as shown from rheological measurements. Knowledge gained in this study may open the door to pursuing liposomes as a viable strategy for Au NPs delivery in many diagnostic and therapeutic applications.     

Effect of the Nature of the 3β-Substitution in Manoyl Oxides on the Thermotropic Behavior of DPPC Lipid Bilayer and on DPPC Liposomes

Functionalized manoyl oxide derivatives have been proved over the years to evoke several biological responses. Among them, 3β-hydroxy-manoyl oxide (1) and 3β-acetoxy-manoyl oxide (2) have been shown to exhibit in vitro antimicrobial and cytotoxic activity, while N-imidazole-3 β-thiocarbonyl ester of manoyl oxide (3) was found to exhibit potent cytotoxic effect. Their partitioning into phospholipid bilayers may lead to membrane structure modifications that are crucial in liposome development as they may influence their maintenance and integrity. DSC was used to study the modifications induced in DPPC bilayers by incorporating increasing concentrations of the three manoyl oxide derivatives. All derivatives were found to strongly affect the bilayer structural organization in terms of a decrease of the cooperativity, the fluidization and partially destabilization of the gel phase and the induction of a lateral phase separation in clustering domains. Derivatives 1 and 3 were incorporated into DPPC liposomes and their physicochemical stability was monitored at 4°C. The stability of liposomes was strongly influenced by the presence of 1 and 3 at any molar ratio studied. DPPC/1 liposomes were found to retain its stability for 48 h at low concentration of 10% mol, while at higher concentrations up to 30% mol they collapsed into aggregated material. In all cases DPPC/3 liposomes were found unstable and sticky aggregated structures precipitated from the bulk suspension.     

Effects of phospholipid hydrolysis on the aggregate structure in DPPC/DSPE-PEG2000 liposome preparations after gel to liquid crystalline phase transition

Upon storage of phospholipid liposome samples, lysolipids, fatty acids, and glycerol-3-phosphatidylcholine are generated as a result of acid- or base-catalyzed hydrolysis. Accumulation of hydrolysis products in the liposome membrane can induce fusion, leakage, and structural transformations of the liposomes, which may be detrimental or beneficial to their performance depending on their applications as, e.g., drug delivery devices. We investigated in the present study the influence of phospholipid hydrolysis on the aggregate morphology of DPPC/DSPE-PEG₂₀₀₀ liposomes after transition of the phospholipid membrane from the gel phase to liquid crystalline phase using high performance liquid chromatography (HPLC) in combination with static light scattering, dynamic light scattering, and cryo-transmission electron microscopy (cryo-TEM). The rates of DPPC hydrolysis in DPPC/DSPE-PEG₂₀₀₀ liposomes were investigated at a pH of 2, 4, or 6.5 and temperatures of 22 °C or 4 °C. Results indicate that following phase transition, severe structural reorganizations occurred in liposome samples that were partially hydrolyzed in the gel phase. The most prominent effect was an increasing tendency of liposomes to disintegrate into membrane discs in accordance with an increasing degree of phospholipid hydrolysis. Complete disintegration occurred when DPPC concentrations had decreased by, in some cases, as little as 3.6%. After extensive phospholipid hydrolysis, liposomes and discs fused to form large bilayer sheets as well as other more complex bilayer structures apparently due to a decreased ratio of lysolipid to palmitic acid levels in the liposome membrane.     

Characterization of Langmuir-Blodgett films of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine and 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphat idylcholine by FTIR-ATR

Monomolecular films of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphatidylc holine (PPDPC) were transferred from an air/water interface onto a germanium attenuated total reflection crystal by the Langmuir-Blodgett (LB) technique. The assemblies were thereafter investigated by Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy. To determine the molecular organization in the deposited layers we monitored the CH2 and C = O stretching and the CH2 bending regions of the infrared spectra of these lipids in detail. Using Fourier self-deconvolution technique, the carbonyl stretching mode was resolved into two models corresponding to the conformational differences in the ester linkages of the phospholipid sn-1 and sn-2 acyl chains. By varying the temperature of the subphase and using different surface pressures, we were able to transfer different conformational states of DPPC onto a germanium ATR crystal. Deposition of DPPC at 40 mN m-1 and at 15 degrees C or at 20 mN m-1 and at 35 degrees C results in LB-assemblies in ordered or disordered states, respectively, as judged by the IR spectra. These structures in LB films correspond to the state of DPPC in liposomes below and above the temperature of the order-disorder phase transition. Irrespective of the surface pressure and subphase temperature used during the deposition, an ordering process was found in DPPC films when the number of the transferred layers was increased from one to five. The pyrene-labelled phosphatidylcholine analogue, PPDPC, behaved differently from DPPC. In the case where one to three layers of PPDPC transferred at 35 mN m-1 and at 20 degrees C only conformational structures resembling those in fully hydrated liposomes above the main transition temperature were observed.     

Thermotropic behavior and electronmicroscopic structures of mixtures of gangliosides and dipalmitoylphosphatidylcholine

The calorimetric properties and morphological structures of dispersed mixtures of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and highly purified human brain gangliosides, GM2, GM1, GD1a, GD1b, and GT1b, were studied using a high-sensitivity differential scanning calorimeter and an electron-microscope, as a function of the ganglioside molar fraction. No thermal phase transitions of pure gangliosides in aqueous dispersions could be detected. In the mixtures of DPPC and gangliosides, the gel to liquid crystalline phase transition occurred at a higher temperature than in pure DPPC dispersions and progressed over a wide temperature range. As increasing amounts of the pure ganglioside species were added to DPPC, the temperature for the main transition gradually increased. The phase transition progressed differently among different gangliosides/DPPC mixtures. The enthalpy values were found to decrease linearly as the number of sialic acid residues increased. Electron-microscopically the ganglioside/DPPC mixtures formed multilamellar structures at lower concentrations of the gangliosides, and the structures changed to cylindrical and spherical micelles as the ganglioside concentration was increased. The polysialoganglioside/DPPC mixtures showed the micellar form even at lower ganglioside concentrations, contrary to the case of the monosialoganglioside/DPPC mixtures. The morphological changes of gangliosides/DPPC mixtures corresponded with changes in the calorimetric properties. These results show that individual gangliosides have different physicochemical effects on model membranes, possibly because of the interaction of their negatively charged head groups.     

Perturbation of phospholipid membranes by juvenile hormone

The effects of juvenile hormone and its analogs Altozar 4E and ZR-777 5E on the phase properties of liposomes prepared from dipalmitoyl phosphatidyl-choline (DPPC) have been examined by differential scanning calorimetry. Each of these compounds reduced the co-operativity of the gel to liquid-crystalline phase transition, which is manifest as a distinct broadening of the main transition endotherm, and split the transition into two distinguishable components centered at 34 and 37°C. However, there was no significant change in enthalpy of the main phase transition, suggesting that juvenile hormone and its analogs perturb the bilayer primarily in the vicinity of the phospholipid headgroups. Moreover, this perturbation does not appear to influence bilayer permeability since the osmotic swelling rates of liposomes prepared from either phosphatidylcholine or dipalmitoyl phosphatidylcholine that contained up to 33 mol% juvenile hormone were not significantly different from the swelling rates of corresponding liposomes containing no juvenile hormone. Splitting of the transition endotherm into two peaks appeared to be peculiar to compounds possessing juvenile hormone activity. A mixture of fatty acid methyl esters broadened the main transition of DPPC, but did not split the endotherm or shift the transition midpoint, and the insect hormone ecdysone had no discernible effect on the DPPC transition apart from eliminating the pretransition. The data indicate that juvenile hormone and its analogs can modulate the physical properties of phospholipid bilayers, and raise the prospect that some of the physiological effects of this hormone may be achieved through its influence on the molecular organization of membrane lipid.     

Insights on calcium-independent phospholipid membrane damage by Lys49-PLA2 using tryptophan scanning mutagenesis of bothropstoxin-I from Bothrops jararacussu

Bothropstoxin-I (BthTx-I) is a homodimeric Lys49-PLA(2) from the venom of the snake Bothrops jararacussu, which lacks hydrolytic activity against phospholipid substrates, yet permeabilizes membranes by a Ca(2+)-independent mechanism. The interaction of the BthTx-I with model membranes has been studied by intrinsic tryptophan fluorescence emission (ITFE) spectroscopy. Nine separate mutants have been created each with a unique tryptophan residue located at a different position in the interfacial recognition site (IRS) of the protein. The rapid and efficient Ca(2+)-independent membrane damage against unilamellar liposomes composed of DPPC/DMPA in a 9:1 molar ratio was unaffected by these substitutions. Binding studies revealed low protein affinity for these liposomes and no changes were observed in the ITFE properties. In contrast, the binding of all mutants to DPPC/DMPA liposomes in a 1:1 molar ratio was stronger, and was correlated with altered ITFE properties. The blue-shifted emission spectra and increased emission intensity of mutants at positions 31, 67 and 115-117 in the interface recognition surface of the protein suggest these regions are partially inserted into the membrane. These results are consistent with a model for the Ca(2+)-independent membrane damaging mechanism that involves a transient interaction of the protein with the outer phospholipid leaflet of the target membrane.     

Chlorpromazine interaction with glycerophospholipid liposomes studied by magic angle spinning solid state (13)C-NMR and differential scanning calorimetry

Phosphatidylserine (PS) extracted from pig brain and synthetic dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) were used to make DPPC/DMPC and DPPC/PS large unilamellar liposomes with a diameter of approximately 1 microm. Chlorpromazine-HCl (CPZ), an amphipathic cationic psychotropic drug of the phenothiazine group, is known to partition into lipid bilayer membranes of liposomes with partition coefficients depending on the acyl chain length and to alter the bilayer structure in a manner depending on the phospholipid headgroups. The effects of adding CPZ to these membranes were studied by differential scanning calorimetry and proton cross polarization solid state magic angle spinning (13)C-nuclear magnetic resonance spectroscopy (CP-MAS-(13)C-NMR). CP-MAS-(13)C-NMR spectra of the DPPC (60%)/DMPC (40%) and the DPPC (54%)/DMPC (36%)/CPZ (10%) liposomes, show that CPZ has low or no interaction with the phospholipids of this neutral and densely packed bilayer. Conversely, the DPPC (54%)/PS (36%)/CPZ (10%) bilayer at 25 degrees C demonstrates interaction of CPZ with the phospholipid headgroups (PS). This CPZ interaction causes about 30% of the acyl chains to enter the gauche conformation with low or no CPZ interdigitation among the acyl chains at this temperature (25 degrees C). The DPPC (54%)/PS (36%)/CPZ (10%) bilayer at a sample temperature of 37 degrees C (T(C)=31.2 degrees C), shows CPZ interdigitation among the phospholipids as deduced from the finding that approximately 30% of the phospholipid acyl chains carbon resonances shift low-field by 5-15 ppm.     

Spectroscopic and calorimetric studies on trazodone hydrochloride–phosphatidylcholine liposome interactions in the presence and absence of cholesterol

The interaction of antidepressant drug trazodone hydrochloride (TRZ) with dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes (MLVs) in the presence and absence of cholesterol (CHO) was investigated as a function of temperature by using Electron Paramagnetic Resonance (EPR) spin labeling, Fourier Transform Infrared (FTIR) Spectroscopy and Differential Scanning Calorimetry (DSC) techniques. These interactions were also examined for dimyristoyl phosphatidylcholine (DMPC) multilamellar liposomes by using Electron Paramagnetic Resonance (EPR) spin labeling technique. In the EPR spin labeling studies, 5- and 16-doxyl stearic acid (5-DS and 16-DS) spin labels were used to monitor the head group and alkyl chain region of phospholipids respectively. The results indicated that TRZ incorporation causes changes in the physical properties of PC liposomes by decreasing the main phase transition temperature, abolishing the pre-transition, broadening the phase transition profile, and disordering the system around the head group region. The interaction of TRZ with unilamellar (LUV) DPPC liposomes was also examined. The most pronounced effect of TRZ on DPPC LUVs was observed as the further decrease of main phase transition temperature in comparison with DPPC MLVs. The mentioned changes in lipid structure and dynamics caused by TRZ may modulate the biophysical activity of membrane associated receptors and in turn the pharmacological action of TRZ.