Dipalmitoylphosphatidylcholine Liposomes Research Articles

Interactions between volatile anesthetics and dipalmitoyl phosphatidylcholine liposomes as studied by fluorometry with a thiacarbocyanine dye.

The effects of volatile anesthetics on the properties of dipalmitoyl phosphatidylcholine liposome were investigated by fluorescence spectroscopy with a thiacarbocyanine dye (3,3"-dioctadecyl-2,2"-thiacarbocyanine) which is sensitive to the viscosity and the dielectric constant of the environment. Seven volatile anesthetics, halothane, enflurane, isoflurane, methoxyflurane, sevoflurane, diethylether and chloroform were used. All anesthetics decreased the phase transition temperature of the liposome and increased the effective dielectric constant of the water-liposome interface. The increase of the effective dielectric constant was attributed to the release of the hydrated water molecules from the membrane surface. The increment of the effective dielectric constant depended on the thermodynamic activity of anesthetics in the solution, and was not affected seriously by the kind of anesthetics. On the other hand, the degree of the depression of the phase transition temperature depended on the molar concentrations of anesthetics. Considering from the Ferguson's report, which is dealt with the relationship between the physiological effect and the thermodynamic activity, the effect of anesthetics on the effective dielectric constant of the membrane surface is more correlated to the anesthetic action than the effect on the phase transition temperature.

Protein adsorption on biomedical polymers with a phosphorylcholine moiety adsorbed with phospholipid

The effects of phospholipid adsorption onto the polymer surface during adsorption of plasma proteins were investigated. When a polymer with the phosphorylcholine moiety, 2-methacryloyloxyethyl phosphorylcholine (MPC) co-polymer, was treated with dipalmitoylphosphatidylcholine (DPPC) liposome solution, an organized adsorption layer of DPPC was formed on the MPC co-polymer surface, which was confirmed by differential scanning calorimetric analysis and X-ray photoelectron spectroscopy. On the other hand, an organized layer of DPPC on poly(n-butyl methacrylate) and poly(2-hydroxyethyl methacrylate) could not be found. The amount of albumin adsorbed on the polymer surfaces was decreased by pretreatment of the surface with DPPC liposome solution in every polymer case. The smallest amount of adsorbed proteins was found on the MPC co-polymer. Protein adsorption on the surface of MPC co-polymers from the plasma was also small. The difference in protein adsorption on the polymers probably reflects the difference in the orientation of the phospholipid molecules which cover the polymer surface.

Molecular Interactions between Phospholipid and Nonionic Surfactants in a Lipid Bilayer

Molecular interactions between dipalmitoylphosphatidylcholine (DPPC) and long polyoxylated nonionic surfactants in a lipid bilayer were investigated by dynamic light scattering, ultracentrifuge, differential scanning calorimetry (DSC), ζ-pontential and fluorescence.Particle size and encapsulation efficiency of the liposomes decreased rapidly with increasing concentrations of the nonionic surfactants possessing a long oxyethylene chain (C16POE20, and C16POE40), but showed virtually no change in the case of a short chain C16POE10. The cooperative effect on the physical properties of bilayer caused by interaction among DPPC molecules decreased with increasing concentration of the nonionic surfactants. Surface charge density of the liposomes also decreased following the addition of nonionic surfactants. Microviscosity of the liposome decreased with increasing concentrations of C16POE20 and C16POE40, but remained essentially unchanged in the case of C16POE10.The addition of a long polyoxylated nonionic surfactant to a solution containing DPPC molecules caused structural change of molecular aggregation and in particular, in the presence of large amounts of C16POE20 and C16POE40, the DPPC liposome with nonionic surfactants did not form. A molecular aggregate such as a micelle was obtained instead.

高圧下における生体モデル膜の機能

Phospholipid bilayers and surfactant micelles have been used as a model for biological membranes. The temperature-pressure phase diagram of dipalmitoylphosphatidylcholine (DPPC) bilayer liposomes has been constructed. Four states, i.e., liquid crystal (Lα), gel I (Pβ'), gel II (Lβ') and interdigitated (LβI) phases, were observed in the pressure range up to 200MPa. The present study proposes a novel method for the estimation of the partition coefficient of drugs between the aqueous and the lipid phases. Two kinds of partition coefficients of an inhalation anesthetic were estimated from the depression of the main- and pre-transition temperature of DPPC liposome. The Lα phase/water and Pβ' phase/water partition coefficients of halothane were 3390 and 820, respectively. The effect of pressure on the partition coefficient was determined, and then the transfer volume of halothane was estimated.The critical temperature-pressure lines for the micellar dissolution, which represent the pressure dependence of Krafft temperature, were determined for a homologous series of cationic surfactants. The depression of Krafft temperature by solubilization can be used for the estimation of the partition coefficient of solubilizate between the aqueous phase and the micellar phase.

Surface Ionization of Dipalmitoylphosphatidylcholine as Detected by the pH Dependence of the Phase Transition Temperature of Liposomes

AbstractThe surface ionization of lecithin phosphodiester has been studied following the effect of bulk pH on the increment in the gel to liquid‐crystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine (DPPC) liposomes, induced by incorporation of protonated stearylamine. At constant pHb, the increment (Δtm is a monotone increasing function of stearylamine concentration which deviates from linearity, toward lower Δtm values, at high proportions of additive. From plots of Δtm as function of the stearylamine proportion in DPPC liposomes at different pHb values, the initial slopes, as stearylamine concentration approaches zero, is obtained and interpreted as a potentiality for tm elevation of DPPC bilayers. The slope value, seems to be related to the ionization degree of the phosphate group since it increases with bulk pH and levels off above pHb 4 i.e., for zwitterionic lecithin. If the titration curve resulting from normalization of those slope values, is attributed to ionization of lecithin phosphate, an apparent pK of 1.3 is obtained. The consistency of the data analysis is supported by the good fitting found between the experimental results and a theoretical curve based on Henderson‐Hasselbach, Boltzmann, and Gouy‐Chapman equations. Best fit is obtained when the intrinsic interfacial pK, which is the pK in the absence of surface electrostatic effects, is set equal to 4. Such a high intrinsic pK value is explained in terms of the effect of the reduced dielectric constant of the lipid‐water interface, on the ionization of the phosphate group which is a molecular acid and, as such, will be stabilized in a low polarity region.

Membrane fluidity and lipid hapten structure of liposomes affect calcium signals in antigen-specific B cells

Antigen-specific B-cell clones directed against a 2,4,6-trinitrophenyl (TNP) hapten have been established [Hamano et al. (1990) J. Immunol. 144, 811-815]. We measured here the cytosolic free calcium ion concentration ([CA2+]i) in these B-cell clones after antigen stimulation. Trinitrophenylated liposomes with different length spacers between TNP and phosphatidylethanolamine (TNP-Cn-PE) increased cytosolic free calcium concentration in TNP-specific B cells (clone TP67.21). The magnitude of calcium signals depended on the length of the spacer. TNP-C6-PE in dipalmitoylphosphatidylcholine (DPPC) liposomes triggered larger calcium signals in B cells than TNP-Cn-PE with n = 0, 4, 8, or 12. The magnitude of the calcium signals was strongly dependent on the fluidity of the liposome membranes. TNP-C6-PE in the solid DPPC liposomes triggered the calcium signals in B cells 50-100 times as efficiently as TNP-C6-PE in the fluid dimyristoylphosphatidylcholine liposomes. The difference between the solid liposomes and the fluid liposomes was more pronounced in triggering calcium signals in B cells than in antibody binding to these liposomes.

Polymer-coated liposomes; stability and release of ASA from carboxymethyl chitin-coated liposomes

Liposomes of dipalmitoylphosphatidylcholine (DPPC) were coated with carboxymethyl chitin (CM-chitin), a water-soluble polysaccharide, either during the formation of reverse phase evaporation vesicles (REVs) or using preformed REVs. Acetylsalicylic acid (ASA) encapsulation efficiency was not affected by the polymer coating. Liposomes coated with CM-chitin during processing were more stable in sodium cholate solutions and yielded significantly lower release rates of ASA than preformed liposomes coated with CM-chitin-coated liposomes. The release rate reached a minimum when liposomes were coated from a 1% CM-chitin solution and was approximately one-third of that obtained from uncoated liposomes. Thus, these improvements in liposome behaviour may be beneficial for the oral administration of drugs.

Partitioning of a homologous series of alkyl p-aminobenzoates in dipalmitoylphosphatidylcholine liposomes: effect of liposome type

Abstract The partitioning of a homologous series of n -alkyl p -aminobenzoales into the lipid bilayer is dependent not only on their physicochemical properties but also on liposome type. Partitioning studies with this homologous series demonstrate the effect of alkyl chain length on partitioning in DPPC multilamellar liposomes (MLV) and DPPC MLV extruded through 1or 0.4 μm polycarbonate filters. A general trend was observed wherein increasing alkyl chain length increased partitioning of drug into the bilayer. The distribution coefficients of the esters were found to be strongly influenced by the physical structure of the membrane. Factors which decrease the surface density of the bilayer, such as temperature, will also increase solute partitioning into the bilayer. The amounts of the alkyl p -aminobenzoates included in the bilayers of DPPC multilamellar liposomes at 23° C were quite low because the high surface density of the bilayer at 23° C precludes the incorporation of solute. The extruded liposomes studied were much smaller and are believed to have greater bilayer fluidity and disorder than their MLV counterparts, thus allowing greater incorporation of the alkyl p -aminobenzoates in the extruded DPPC bilayer. Hence, higher distribution coefficients and lower free energies of partitioning are achieved with extruded liposomes. The effect of extrusion on solute partitioning was found to be similar to the effects caused by increasing temperature.

Interaction of doxorubicin with lipid systems

The action of doxorubicin, a cancer chemotherapeutic agent, on liposomes of dipalmitoylphosphatidylcholine obtained by extrusion, with or without cholesterol, and on monolayers of the same composition, was determined by photon correlation spectroscopy, penetration kinetics, and adsorption isotherms. Doxorubicin produced a wider vesicle distribution in both of liposomes, but liposomes containing cholesterol underwent an increase of mean diameter as well as polydispersity. In contrast, films containing cholesterol showed least interaction with the drug. Since both lipids are neutral, any interaction must be primarily hydrophobic.

STUDIES ON THE MECHANISM OF THE HEMATOPORPHYRIN‐SENSITIZED PHOTOOXIDATION OF 1,3‐DIPHENYLISOBENZOFURAN IN ETHANOL and UNILAMELLAR LIPOSOMES

The 5 microM hematoporphyrin-sensitized photooxidation of 1,3-diphenylisobenzofuran (DPBF) was studied in homogeneous ethanolic solutions and in aqueous dispersions of unilamellar liposomes of dipalmitoylphosphatidylcholine; both the porphyrin and DPBF are embedded in the phospholipid bilayer. The rate and quantum yield of DPBF photooxidation were found to increase upon increasing the substrate concentration and were higher in the liposome system, while they were unaffected by the fluidity of the phospholipid bilayer. Time-resolved spectroscopic measurements showed that the photooxidation of DPBF in ethanol solution proceeds by a type II O2(1 delta g)-involving mechanism. In the liposomal vesicles the high local concentration of hematoporphyrin (Hp) and DPBF in the phospholipid bilayer (ca 2000-fold higher than the stoichiometric concentration) enhances the probability of energy transfer from triplet Hp to DPBF with generation of triplet DPBF; hence O2 (1 delta g) formation can be promoted by both triplet Hp and triplet DPBF. A minor fraction of triplet DPBF quenchings appears to generate radical species which propagate DPBF damage by chain reaction.

Effect of penetration enhancers on the phase transition of multilamellar liposomes of dipalmitoylphosphatidylcholine. A study by differential scanning calorimetry

Multilamellar liposomes of dipalmitoylphosphatidylcholine were used as a simple model of lipid bilayers representing the intercellular lipid arrangement of the stratum corneum. The effect of skin penetration enhancers such as 1-dodecylazacycloheptan-2-one (Azone), oleic acid (OA), dimethyl sulphoxide (DMSO), thiamorpholine-3-one and N-dodecylthiamorpholine-3-one (C12-thiamorpholine-3-one) on the liposomal bilayer was assessed using differential scanning calorimetry. Azone, OA and C12-thia-morpholine-3-one dramatically modified the thermotropic behaviour of the phospholipid. The pretransition peak vanished at low penetration enhancer concentrations and an increase in the penetration enhancer: lipid molar ratio broadened the gel-to-liquid crystalline transition peak and shifted it to lower temperatures. For the tested concentrations, neither DMSO nor thiamorpholine-3-one changed the phase transition temperature of the liposomes.

Tumour-localising and -photosensitizing properties of liposome-delivered Ge(IV)-octabutoxy-phthalocyanine

We selected bis-(triethylsiloxy)-Ge(IV)-1,4,8,11,15,18,22,25 ― octabutoxyphthalocyanine (GePc), which has been shown to possess favourable photophysical properties, including a large quantum yield of generation of the highly cytotoxic oxygen derivative 1 O 2 (Rihter et al., 1990). The dye was administered to tumour ― bearing mice after incorporation into small unilamellar liposomes of dipalmitoyl-phosphatidylcholine (DPPC), which are known to deliver the photosensitiser selectively to serum lipoproteins (Barel et al., 1986)

Liposomes as models to study the distribution of porphyrins in cell membranes

Unilamellar liposomes of dipalmitoylphosphatidylcholine (DPPC) have been choosen as suitable models of cell membranes in studies aimed at defining the influence of specific parameters on the distribution properties of selected hydrophobic photosensitizers, namely hematoporphyrin (HP) and protoporphyrin (PP), in normal and tumour tissues. To better mimic in vivo situations, DPPC liposomes were sometimes mixed with cardiolipid (Card) or cholesterol (Chol). Two techniques were mainly used: the quenching of porphyrin fluorescence by methyl viologen, which can discriminate different dye populations inside the vesicles as well as their degree of accessibility to the external medium, and the polarization of porphyrin fluorescence, which gives information on the dye microenvironment through its degree of rotational freedom. The nature of the porphyrin binding sites in each phospholipid monolayer is found to be a function of the degree of hydrophobicity and the concentration of the dye as well as the chemical composition of the liposomes. In DPPC and DPPC-Chol liposomes, all PP molecules are deeply embedded into very rigid, hydrophobic domains of the inner lipid monolayer. Only in the presence of cardiolipin, for [PP] > 2.5 μM, a partial shift of the dye molecules towards the outer lipid monolayer is observed. HP mostly localizes at the inner lipid/water interface in all liposomes: at very low concentrations ([HP] ≊ 0.5 μM the dye is bound to the polar heads of the lipids through its car☐ylate groups, leaving the rest of the molecule dissolved in the inner aqueous pool. At higher concentrations, HP molecules change their orientation: the ionized propionic chains still interact with the polar heads while the hydrophobic core lies in the lipid phase in DPPC and DPPC-Card vesicles. HP incorporated into DPPC-Chol mixed liposomes projects from the inner lipid phase into the aqueous compartment in all the concentration range studied by us. A very small fraction of HP population (corresponding to 5–10% of the overall fluorescence) is localized at the water/lipid external interface in DPPC and DPPC-Chol liposomes. This fraction increases in the presence of cardiolipin (up to 30% of the overall fluorescence). The possible implications of these findings for the nature of the targets of photosensitization in cell membranes are discussed.

Specific interaction between water‐soluble phospholipid polymer and liposome

AbstractA water‐soluble polymer having both a phospholipid polar group and an azobenzene group, poly(2‐methacryloyloxyethyl phosphorylcholine‐co‐p‐phenylazoacrylanilide) (poly(MPC‐co‐PAAn)) was synthesized and the interaction between the liposome of the phospholipid was investigated in comparison with other water‐soluble azoaromatic polymers. When the poly(MPC‐co‐PAAn) was incubated with dipalmitoylphosphatidylcholine (DPPC) lipo‐somes above these gel‐liquid crystalline temperatures, an electronic spectrum of azobenzene moiety, which is a hydrophobic probe, showed that the a copolymer chain exists under nonpolar circumstances. Thus, poly(MPC‐co‐PAAn) interacts with DPPC liposomes. On the other hand, other copolymers do not interact with the liposomes. Moreover, heat of the gel‐liquid crystalline transition of DPPC liposomes was increased by the presence of poly(MPC‐co‐PAAn). These findings clearly indicate that the poly(MPC‐co‐PAAn) has an affinity to the DPPC liposomes and hybridizes with liposomes based on the phospholipid polar group of the copolymer.

Characteristics of the Membrane Permeability of Temperature-Sensitive Liposome

Abstract The relationship between the temperature-sensitivity of the release of an entrapped drug from liposome as well as the type of drug or liposome is discussed. The drug release from DPPC liposome (dipalmitoylphosphatidylcholine liposome) has been confirmed to increase abruptly near its phase-transition temperature for both low-molecular-weight compouds (such as calcein) and high-molecular-weight compounds (such as dextran). The amount of temperature-sensitive calcein released from the liposomes was dependent on the method of liposome preparation: that is, the release from REV (reverse phase evaporated vesicle) was the highest; next was that from LUV (large unilamellar vesicle prepered by detergent removal method), and lowest was from SUV (small unilamellar vesicle prepared by an ultrasonication method). In order to examine the size effect of liposomes on temperature-sensitive drug release, REV was fractionated into three groups according to their average sizes and calcein release for each group was investigated. The temperature at which calcein release showed a maximum was almost the same in each of three groups; while as the average liposome size of a group was larger, the initial rate of calcein release became higher and the temperature at which calcein release began became lower. The amount of release of a entrapped drug was primarily dependent on the molecular weight of the drug, in spite of the variety of drugs investigated.

The effect of blood on the uptake of liposomal lipid by perfused rat liver

Liposomes have been prepared from dipalmitoylphosphatidylcholine (DPPC) and its mixtures with phosphatidylinositol (PI) and stearylamine. The absorption of the liposomes by perfused rat liver has been studied as a function of blood level (0-7% haematocrit). It has been found that the rate constant for uptake of liposomes (perfusion constant, kp) is markedly reduced by addition of blood to the perfusate particularly in the haematocrit range 0-3%. The perfusion constant is dependent on the liposome composition and decreases with incorporation of PI and increases with incorporation of stearylamine into DPPC liposomes, but is independent of the initial size of the liposomes in the range of weight-average diameter from 40-400 nm. The possible effects of blood components on the liposomes and their subsequent absorption by the liver are discussed.

Interaction of tributylin acetate and tributyltin chloride with dipalmitoyl phosphatidylcholine model membrane

The effect of tri- n-butyltin acetate and tri- n-butyltin chloride on the thermotropic characteristics of dipalmitoyl phosphatidylcholine liposomes was studied. The study was performed by using differential scanning calorimetry and Fourier transform infrared spectroscopy. The results show that tri- n-butyltin acetate affects to a lower extent the hydrophobic core of membrane with respect tri- n-butyltin chloride. The latter considerably lowers the main lipid phase transition and induces a lipid phase separation which was observed at pesticide/lipid molar ratio ( R) of 10 -2. At this pesticide concentration the lipid main phase transition encompasses a range of temperature of about 10°C while at 4 × 10 -2 of R value the width of the main transition becomes narrow. These results suggest that, within the same series of trialkyltin compounds, the anion moiety may play an important role in the organotion toxicity

Macromolecular prodrugs interaction with mixed lipid membrane. A calorimetric study of naproxen linked to polyaspartamide interacting with phosphatidylcholine and phosphatidylcholine-phosphatidic acid vesicles

The thermal behaviour of pure dipalmitoylphosphatidylcholine (DPPC) liposomes or mixed liposomes of DPPC with charged dipalmitoylphosphatidic acid (DPPA) and interacting with polymeric prodrugs has been investigated by differential scanning calorimetry (DSC). The apolar drug was naproxen (NAP) covalently linked to a water-soluble polymer (α,β- poly(N- hydroxyethyl)- dl - aspartamide (PHEA)). Addition of increasing amounts of NAP to DPPC liposomes causes a decrease in the transition temperature if( T m) associated to the gel-to-liquid crystal phase transition with a small decrease in the enthalpy values ( ΔH), whereas a corresponding amount of drug contained in the PHEA-adduct modifies the liposome phase transition by decreasing the ΔH and broadening the peak without T m variations. These effects have been interpreted as a different interaction of free or polymer-bound drug with the lipid bilayer. The drug effect on mixed liposomes was also investigated, and evidence of improved interaction of the drug-PHEA adduct with two-component bilayers, which better mimic biological membranes, was found. In order to understand the prodrug-lipid interactions, we modulated the surface charge density of the mixed liposomes with Ca 2+, which binds strongly to the negatively charged lipid head groups. We observed lateral phase separation, induced by NAP-PHEA adduct and modulated by Ca 2+, and the phenomenon was explained in terms of different drug solubility in DPPC-poor and DPPC-rich microdomains. The results are indicative of different interactions of naproxen, either free or bound to a polymeric carrier, with phospholipid membranes and the ability of Ca 2+ to influence the adsorption of the drug.

Interaction between phospholipids and biocompatible polymers containing a phosphorylcholine moiety

Random and block copolymers containing a phospholipid polar group in their side chain were synthesized by the copolymerization between 2-methacryloyloxyethyl phosphorylcholine and styrene. These copolymers showed amphiphilic character, especially poly(methacryloyloxyethyl phosphorylcholine-block-styrene) formed stable polymer micelles in water. The interaction between natural phospholipid, dipalmitoylphosphatidylcholine and methacryloyloxyethyl phosphorylcholine copolymers was investigated. The amount adsorbed of dipalmitoylphosphatidylcholine from its liposomal solution on to the poly(methacryloyloxyethyl phosphorylcholine-co-styrene) surface increased with increase of methacryloyloxyethyl phosphorylcholine composition. Moreover, when poly(methacryloyloxyethyl phosphorylcholineblock-styrene) was added to dipalmitoylphosphatidylcholine solution, organization of dipalmitoylphosphatidylcholine molecules and stabilization of bilayer structure of dipalmitoylphosphatidylcholine liposome were found. This means that methacryloyloxyethyl phosphorylcholine moieties in the copolymer have a strong affinity to dipalmitoylphosphatidylcholine molecules. The blood compatibility of methacryloyloxyethyl phosphorylcholine copolymers was also investigated with particular attention to the aggregation ability of platelets after contacting methacryloyloxyethyl phosphorylcholine copolymers; this ability decreased when platelets were put in contact with polymers without a methacryloyloxyethyl phosphorylcholine moiety. On the other hand, aggregation ability remained at almost the same level to that of original platelets after contact with methacryloyloxyethyl phosphorylcholine copolymers. From these findings, we concluded that methacryloyloxyethyl phosphorylcholine copolymers show excellent blood compatibility due to adsorption of lipids from plasma and the formation of an organized adsorption layer of lipids on the surface of the methacryloyloxyethyl phosphorylcholine copolymers.

A new fluorescence method to detect singlet oxygen inside phospholipid model membranes

A fluorescence method for detecting singlet oxygen ( 1O 2) in model membranes is proposed. 1O 2 was generated by hydrogen peroxide/sodium hypochlorite system. 1,3-Diphenylisobenzofuran (DPBF), a specific 1O 2 trap, dissolved in organic solvents gives a strong fluorescence spectrum when excited at 410 nm. A similar spectrum, with a maximum at 455 nm, is obtained when DPBF is incorporated in unilamellar dipalmitoylphosphatidylcholine liposomes. The intensity of fluorescence spectrum decreases when DPBF-labeled liposomes are exposed to singlet oxygen. This decrease is sensitive to 1O 2 traps and quenchers like tryptophan and sodium azide, to lipid membrane fluidity and to the concentration of sodium hypochlorite and hydrogen peroxide.