Yolk Phosphatidylcholine Research Articles

Lipase-catalyzed enrichment of egg yolk phosphatidylcholine with conjugated linoleic acid

The investigations were carried out to elaborate an efficient process of lipase-catalyzed acidolysis of egg yolk phosphatidylcholine (PC) with conjugated linoleic acid (CLA) taking into account both a high degree of incorporation into phospholipids (PLs) as well as the high yields of modified PLs. Therefore a term of “effective incorporation of CLA” (ECLA) was proposed as the most complex criterion for the evaluation of effectiveness of the process. The best results were achieved when Lipozyme RM IM was applied and the reaction conditions were as follows: CLA/PC molar ratio 8:1; enzyme loading 24% wt. based on substrates; reaction medium heptane; temperature 45°C; time 36h. Reaction was conducted under initial aw=0.33 which was changed after 12h to aw=0.11. Under these conditions incorporation of CLA (calculated as % of total FA) into modified PC and lysophosphatidylcholine (LPC) reached 33.8% and 50.1%, respectively. The ECLA incorporation reached 39.0%. The yields of PC and LPC were 39.5% and 25.3%, respectively. The results showed the highest effective incorporation of CLA into PC in comparison to the data reported previously.

Carotenoid binding to proteins: Modeling pigment transport to lipid membranes

Carotenoid pigments play numerous important physiological functions in human organism. Very special is a role of lutein and zeaxanthin in the retina of an eye and in particular in its central part, the macula lutea. In the retina, carotenoids can be directly present in the lipid phase of the membranes or remain bound to the protein–pigment complexes. In this work we address a problem of binding of carotenoids to proteins and possible role of such structures in pigment transport to lipid membranes. Interaction of three carotenoids, beta-carotene, lutein and zeaxanthin with two proteins: bovine serum albumin and glutathione S-transferase (GST) was investigated with application of molecular spectroscopy techniques: UV–Vis absorption, circular dichroism and Fourier transform infrared spectroscopy (FTIR). Interaction of pigment–protein complexes with model lipid bilayers formed with egg yolk phosphatidylcholine was investigated with application of FTIR, Raman imaging of liposomes and electrophysiological technique, in the planar lipid bilayer models. The results show that in all the cases of protein and pigment studied, carotenoids bind to protein and that the complexes formed can interact with membranes. This means that protein–carotenoid complexes are capable of playing physiological role in pigment transport to biomembranes.

Porphyrin interaction with the membrane: the use of membrane models to elicit the diverse partition in normal and neoplastic tissue

This work presents a comparative study of the interaction of three porphyrins: the cationic meso-tetra(4-N,N,N-trimethylanilinium) porphine tetrachloride (T973); the anionic meso-tetra(4-carboxyphenyl) porphine (T790); and the neutral meso-tetra(p-hydroxyphenyl) porphine (T679) with model membranes, at two different pH values. The models for the biological membrane used were micelles of hexadecylphosphocholine and large unilamellar liposomes of egg yolk phosphatidylcholine. The liposome–buffer partition coefficients (K) were determined by derivative spectrophotometry at two different pH values (7.4 and 5.8), in order to mimic plasma and tumor tissue conditions, respectively. Different types of partition were observed for different molecules, systems and pH values. Theoretical mathematical models, which accounted for the stoichiometry of the interaction, were used to fit the experimental data and determine the value of K. The values of K obtained are important in the choosing of a promising light-sensitizing agent to be used in photodynamic therapy for cancer treatment, since this parameter governs the distribution of the drug in the organism and the amount of drug that can be found on the site of irradiation.

Biopolymer-Lipid Bilayer Interaction Modulates the Physical Properties of Liposomes: Mechanism and Structure.

This study was conducted to elucidate the conformational dependence of the modulating ability of chitosan, a positively charged biopolymer, on a new type of liposome composed of mixed lipids including egg yolk phosphatidylcholine (EYPC) and nonionic surfactant (Tween 80). Analysis of the dynamic and structure of bilayer membrane upon interaction with chitosan by fluorescence and electron paramagnetic resonance techniques demonstrated that, in addition to providing a physical barrier for the membrane surface, the adsorption of chitosan extended and crimped chains rigidified the lipid membrane. However, the decrease in relative microviscosity and order parameter suggested that the presence of chitosan coils disturbed the membrane organization. It was also noted that the increase of fluidity in the lipid bilayer center was not pronounced, indicating the shallow penetration of coils into the hydrophobic interior of bilayer. Microscopic observations revealed that chitosan adsorption not only affected the morphology of liposomes but also modulated the particle aggregation and fusion. Especially, a number of very heterogeneous particles were visualized, which tended to confirm the role of chitosan coils as a "polymeric surfactant". In addition to particle deformation, the membrane permeability was also tuned. These findings may provide a new perspective to understand the physiological functionality of biopolymer and design biopolymer-liposome composite structures as delivery systems for bioactive components.

Role of Aminophospholipids in the Formation of Lipid Rafts in Model Membranes

The phase separation of aminophospholipids in glycerophospholipid matrix and the effect of cholesterol were studied by means of fluorescence microscopy of giant unilamellar vesicles (GUV). GUVs were composed of binary mixtures, egg yolk phosphatidylcholine (eggPC)/egg yolk phosphatidylethanolamine (eggPE) and egg yolk phosphatidylcholine (eggPC)/brain phosphatidylserine (brainPS), and ternary ones with both aminophospholipids (eggPC/eggPE/brainPS). Gel/liquid-disordered phase coexistence was detected in these mixtures, where aminophospholipids segregate in gel leaf-like domains. When cholesterol (CHOL) was added, the phase separation was shifted at lower temperatures. CHOL increases miscibility of aminophospholipids in PC matrix. Addition of PE and PS to the ternary mixtures (eggPC/eggSM/CHOL) induced liquid-ordered domain formation at higher temperatures. Based on these results, one can conclude that aminophospholipids promote the formation of Lo domains.

Cholesterol protects phosphatidylcholine liposomes from N,N-dimethyldodekanamine N-oxide influence

The interaction of N,N-dimethyl-1-dodekanamine N-oxide (C12(CH3)2NO) with egg yolk phosphatidylcholine (EYPC) liposomes containing cholesterol (CHOL) was studied. The perturbation of CHOL-EYPC bilayers in unilamellar liposomes (ULL) was observed by the leakage of fluorescent probe calcein. Weak leakage is observed at low surfactant concentration cC12NO (minimal perturbation of the bilayer) followed by an intensive leakage at a middle cC12NO (creation of pores). No change in fluorescence intensity was measured at high cC12NO (calcein totally released from liposomes). The higher CHOL amount in the bilayer, the more surfactant is needed to create pores in the bilayer. Solubiliazation of CHOL-EYPC ULL induced by C12NO was studied turbidimetrically. The solubilization curve consists of three parts: saturation of bilayer at low cC12NO (liposomes are preserved), followed by solubilization (liposome - mixed micelle transition) and post-solubilization. The c12NO concentration needed for the onset of the soubilization raises with the increase of nCHOL:nEYPC. The structure of liposomes is still preserved at total calcein release for all nCHOL:nEYPC.

Kinetic and Thermodynamic Stability of Organic and Inorganic Nanocarriers

The kinetic and thermodynamic stability of organic (sodium dodecylsulfate micelles and egg-yolk phosphatidylcholine zwitterionic liposomes) and inorganic (based on GdYVO0034:Eu3+ nanoparticles) nanocarriers (NCs) was studied by the λ-ratiometric method (analysis of fluorescence intensity at two wavelengths) using non-radiative transfer of electronic excitation energy. The kinetic and thermodynamic parameters of the redistribution of dyes DiO and DiI between NCs that was associated with the destruction of NC/DiO and NC/DiI complexes and the formation of new NC/(DiO + DiI) complexes were evaluated. Rate constants for the destruction of the complexes (K), lifetimes of the complexes (τ1/2), the activation energy for the destruction (E a), the equilibrium constant (K eq), and the change of free energy (ΔG 0), enthalpy (ΔH 0), and entropy (ΔS 0) of the process were calculated. The obtained kinetic parameters pointed to high kinetic stability for all investigated complexes whereas the thermodynamic ones indicated that dye redistribution required high temperatures.

P2.06 - Curious controlled release of flutamide-related escape products under exposure to magnetic fields

ABSTRACT Introduction: Flutamide (FM: 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide) is a non-steroidal anti-cancer drug, and is widely applied to recent drug delivery technologies. Several reports also have shown the photoreactivity of FM in phospholipid bilayer vesicles (liposomal membranes). However, there are no reported studies of the application of radical pair mechanisms to drug release controlling of FM-incorporated liposomal carriers under exposure to magnetic fields. In this study, we investigated magnetic controls of the carriers for an advantageous release of flutamide-related escape products. Materials & methods: Egg yolk phosphatidylcholine (PC) or Dipalmitoylphosphatidylcholine (DPPC) was used as the lipid component of liposomes. FM-incorporated multilamellar vesicles (FM-MLVs) were prepared according to the previous method [ 1 ]. FM-incorporated small unilamellar vesicles (FM-SUVs) were prepared by the membrane filtration method [ 2 ]. All operations were carried out under nitrogen. FM-related escape products were monitored measuring the delayed fluorescence (ex. 530 nm, em. 890 nm) of the products. The magnetic field strength was set up in the range of 50–150 mT. Results: For measurements of magnetic field effects on release of FM-related escape products, the decrease in the products is due to S-T level intersystem crossing on radical pair mechanisms. When PC was used as the lipid component of the FM-SUVs, competition between magnetic field effects and the product release was observed depending on the field strength. In the case of the FM-SUVs prepared from DPPC lipid molecules, the increase in the product release was relatively faithful to S-T Intersystem. Conclusions: From these findings, the product release is deemed not to be caused by only the radical pair mechanisms. However, the tests observing the magnetic field effects might provide useful in formation on drug targeting. Acknowledgement: A Grant-in-Aid for Encouragement of Scientists (No.26930033) from the Japan Society for the Promotion of Science (JSPS).

Modulating effect of lipid bilayer–carotenoid interactions on the property of liposome encapsulation

Liposomes have become an attractive alternative to encapsulate carotenoids to improve their solubility, stability and bioavailability. The interaction mechanism of carotenoid with lipid bilayer is one of the major concerns in improving the delivery efficiency of liposomes. In this study, the microstructure and carotenoid encapsulation efficiency of liposomes composed of native phospholipid (egg yolk phosphatidylcholine, EYPC) and nonionic surfactant Tween 80 were investigated by atomic force microscopy, dynamic light scattering, and Raman spectroscopy, respectively. Subsequently, the effects of carotenoid incorporation on the physical properties of liposomal membrane were performed by Raman spectroscopy, fluorescence polarization, and electron paramagnetic resonance. Results showed that the incorporation of carotenoids affected the liposomes morphology, size and size distribution to various extents. Analysis on the Raman characteristic peaks of carotenoids revealed that lutein exhibited the strongest incorporating ability into liposomes, followed by β-carotene, lycopene, and canthaxanthin. Furthermore, it was demonstrated that carotenoids modulated the dynamics, structure and hydrophobicity of liposomal membrane, highly depending on their molecular structures and incorporated concentration. These modulations were closely correlated with the stabilization of liposomes, including mediating particle aggregation and fusion. These findings should guide the rationale designing for liposomal encapsulation technology to efficiently deliver carotenoids in pharmaceutics, nutraceuticals and functional foods.

Enhanced glutathione PEGylated liposomal brain delivery of an anti-amyloid single domain antibody fragment in a mouse model for Alzheimer's disease

Treatment of neurodegenerative disorders such as Alzheimer's disease is hampered by the blood–brain barrier (BBB). This tight cerebral vascular endothelium regulates selective diffusion and active transport of endogenous molecules and xenobiotics into and out of the brain parenchyma. In this study, glutathione targeted PEGylated (GSH-PEG) liposomes were designed to deliver amyloid-targeting antibody fragments across the BBB into the brain.Two different formulations of GSH-PEG liposomes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and egg-yolk phosphatidylcholine (EYPC) were produced. Both formulations encapsulate 15kDa amyloid beta binding llama single domain antibody fragments (VHH-pa2H).To follow the biodistribution of VHH-pa2H rather than the liposome, the antibody fragment was labeled with the radioisotope indium-111. To prolong the shelf life of the construct beyond the limit of radioactive decay, an active-loading method was developed to efficiently radiolabel the antibody fragments after encapsulation into the liposomes, with radiolabeling efficiencies of up to 68% after purification. The radiolabeled liposomes were administered via a single intravenous bolus injection to APPswe/PS1dE9 double transgenic mice, a mouse model of Alzheimer's disease, and their wildtype littermates.Both GSH-PEG DMPC and GSH-PEG EYPC liposomes significantly increased the standard uptake values (SUV) of VHH-pa2H in the blood of the animals compared to free VHH-pa2H. Encapsulation in GSH-PEG EYPC liposomes resulted in the highest increase in SUV in the brains of transgenic animals.Overall, these data provide evidence that GSH-PEG liposomes may be suitable for specific delivery of single domain antibody fragments over the BBB into the brain.

Binding interaction of differently charged fluorescent probes with egg yolk phosphatidylcholine and the effect of β-cyclodextrin on the lipid–probe complexes: A fluorometric investigation

Interaction of cationic phenosafranin (PSF), anionic 8-anilino-1-naphthalene sulfonate (ANS) and non-ionic nile red (NR) have been studied with the zwitterionic phospholipid, egg yolk L-α-phosphatidylcholine (EYPC). The study reveals discernible binding interactions of the three fluorescent probes with the EYPC lipid vesicle. Once the binding of the probes with the lipid is established, the effect of cyclic oligosaccharide, β-cyclodextrin (β-CD), on these lipid bound probes has been investigated. Different fluorometric techniques suggest that addition of β-CD to the probe–lipid complexes leads to the release of the probes from the lipid medium through the formation of probe–β-CD inclusion complexes. A competitive binding of the probes between β-cyclodextrin and the lipid is ascribed to be responsible for the effect. This provides an easy avenue for the removal of the probe molecules from the lipid environment. Extension of this work with drug molecules in cell membranes is expected to give rise to a strategy for the removal of adsorbed drugs from the cell membranes by the use of non-toxic β-cyclodextrin.

Deformable Liposomes for the Transdermal Delivery of Piroxicam

Deformable Liposomes for the Transdermal Delivery of Piroxicam Abstract Objective: Deformable liposomes have been used to improve drugs transdermal delivery. These vesicular systems were employed to deliver piroxicam through the skin as a mean to treat inflammatory diseases and avoid undesired side-effects. Methods: Deformable liposomes, composed by egg-yolk phosphatidylcholine, sodium cholate and α-tocopherol, were prepared by the thin film hydration method followed by extrusion. Piroxicam was included into the lipid bilayer or in the aqueous phase using inclusion complexes of piroxicam with β-cyclodextrin. After characterization, it was evaluated their in vitro permeation using Franz diffusion cells with polysulfone membranes or pig skin. Results: The entrapment of piroxicam in the aqueous compartment, through the use of β-cyclodextrin inclusion complexes, enabled higher entrapment efficiency (63.27% more than when entrapped in the lipid bilayer). The optimized deformable liposomes population were homogeneous (PDI < 0.1) in terms of size (108.93 ± 3.74 nm) and presented a spherical shape. Size stability studies demonstrated that the vesicles were stable along two months of storage. In vitro permeation studies using Franz diffusion cells and polysulfone membranes showed that the vesicles own enough deformability to pass through pores smaller than their own size in a percentage ≈ 45%. Furthermore, a constancy of their diameter and morphology was verified after pores passage. In the experiments performed with pig skin, the permeation of the deformable liposomes incorporating piroxicam β-cyclodextrin complexes decrease considerably. After 24 h of diffusion, only 1.1-3.2 % of the initial population reached the liquid receptor as result of the presence of the stratum corneum which is the main barrier of the skin. Nevertheless, the histological studies demonstrated that deformable liposomes were uniformly distributed on the skin structure and thus were able to achieve a percutaneous permeation of their content. Conclusion: The results support the possibility to use this formulation on the topical treatment of inflammatory conditions.

Position-Dependent Influence of the Three Trp Residues on the Membrane Activity of the Antimicrobial Peptide, Tritrpticin.

Antimicrobial peptides (AMPs) constitute promising candidates for the development of new antibiotics. Among the ever-expanding family of AMPs, tritrpticin has strong antimicrobial activity against a broad range of pathogens. This 13-residue peptide has an unusual amino acid sequence that is almost symmetrical and features three central Trp residues with two Arg residues near each end of the peptide. In this work, the role of the three sequential Trp residues in tritrpticin was studied in a systematic fashion by making a series of synthetic peptides with single-, double- and triple-Trp substitutions to Tyr or Ala. 1H NMR and fluorescence spectroscopy demonstrated the ability of all of the tritrpticin-analog peptides to interact with negatively-charged membranes. Consequently, most tritrpticin analogs exhibited the ability to permeabilize synthetic ePC:ePG (egg-yolk phosphatidylcholine (ePC), egg-yolk phosphatidylglycerol (ePG)) vesicles and live Escherichia coli bacteria. The membrane perturbation characteristics were highly dependent on the location of the Trp residue substitution, with Trp6 being the most important residue and Trp8 the least. The membrane permeabilization activity of the peptides in synthetic and biological membranes was directly correlated with the antimicrobial potency of the peptides against E. coli. These results contribute to the understanding of the role of each of the three Trp residues to the antimicrobial activity of tritrpticin.

Lipase-catalyzed interesterification of egg-yolk phosphatidylcholine and plant oils

The incorporation of polyunsaturated fatty acids into the sn -1 position of egg-yolk phosphatidylcholine (PC) in the process of lipase-catalyzed interesterification was investigated. For this purpose plant oils containing these acids in the triacylglycerol (TAG) form were used as acyl donors and three commercially available immobilized lipases were examined as biocatalysts. In all the experiments the best results were obtained using Novozym 435. After 72 h of the reaction of PC with linseed oil the maximum incorporation of α-linolenic acid into PC was 34%. The result of this reaction was also a reduction in the n -6/ n -3 ratio in egg-yolk PC from 24.5 to 0.7. The highest incorporation n -6 PUFAs into PC were obtained with evening primrose oil as the acyl donor, and in this case, 50.7% of n -6 PUFA as the sum of linoleic and γ-linolenic was achieved. The highest content of γ-linolenic acid in modified PC (7.3%) was achieved in the reaction of PC with borage oil.

Bovine serum albumin with glycated carboxyl groups shows membrane-perturbing activities

The aim of the present study aimed to investigate whether glycated bovine serum albumin (BSA) showed novel activities on the lipid–water interface. Mannosylated BSA (Man-BSA) was prepared by modification of the carboxyl groups with p-aminophenyl α-d-mannopyranoside. In contrast to BSA, Man-BSA notably induced membrane permeability of egg yolk phosphatidylcholine (EYPC)/egg yolk sphingomyelin (EYSM)/cholesterol (Chol) and EYPC/EYSM vesicles. Noticeably, Man-BSA induced the fusion of EYPC/EYSM/Chol vesicles, but not of EYPC/EYSM vesicles. Although BSA and Man-BSA showed similar binding affinity for lipid vesicles, the lipid-bound conformation of Man-BSA was distinct from that of BSA. Moreover, Man-BSA adopted distinct structure upon binding with the EYPC/EYSM/Chol and EYPC/EYSM vesicles. Man-BSA could induce the fusion of EYPC/EYSM/Chol vesicles with K562 and MCF-7 cells, while Man-BSA greatly induced the leakage of Chol-depleted K562 and MCF-7 cells. The modified BSA prepared by conjugating carboxyl groups with p-aminophenyl α-d-glucopyranoside also showed membrane-perturbing activities. Collectively, our data indicate that conjugation of carboxyl groups with monosaccharide generates functional BSA with membrane-perturbing activities on the lipid–water interface.

Synthesis of oligo(ethylene glycol)-modified hyperbranched poly(glycidol)s for dual sensitization of liposomes to pH and temperature

A new type of polymers that change characters responding to pH and temperature was synthesized by modifying biocompatible hyperbranched poly(glycidol) (HPG) with temperature-sensitive oligo(ethylene glycol)s and pH-sensitive succinyl groups. HPG with the average polymerization degree of 40 was reacted with excess succinic anhydride and then, succinylated HPG was reacted with methoxy tri(ethylene glycol), ethoxy tri(ethylene glycol) (ETEG) or their mixtures, which afforded HPGs having oligo(ethylene glycol) and succinyl groups with varying compositions. These HPG derivatives dissolved in aqueous solutions exhibited a cloud point at a specific temperature, above which these polymers became water-insoluble. Their cloud points decreased with decreasing pH, indicating that these polymers have pH- and temperature-responsive properties. Liposomes were prepared by hydrating mixtures of egg yolk phosphatidylcholine and anchor-conjugated HPG derivatives with aqueous pyranine solution. These polymer-modified liposomes were destabilized and released pyranine under weakly acidic and mildly high temperature conditions. In addition, temperature and pH regions where the liposome destabilization was induced were affected by the polymer compositions such as succinyl groups and oligo(ethylene glycol) contents. Considering biocompatible structure and dual stimuli-responding properties, the HPG derivatives might be potential usefulness for the production of functional liposomes that achieve site-specific intracellular drug delivery in combination with local hyperthermia.

Potentiation of pH-sensitive polymer-modified liposomes with cationic lipid inclusion as antigen delivery carriers for cancer immunotherapy

Cationic lipid-incorporated liposomes modified with pH-sensitive polymers were prepared by introducing 3, 5-didodecyloxybenzamidine as a cationic lipid to egg yolk phosphatidylcholine liposomes modified with 3-methylglutarylated hyperbranched poly(glycidol) (MGlu-HPG) as a pH-sensitive polymer. These liposomes were stable at neutral pH, but were destabilized below pH 6.0 because MGlu-HPG changed its characteristics from hydrophilic to hydrophobic in response to the pH decrease. Cationic lipid inclusion improved their pH sensitivity at weakly acidic pH and association of liposomes with murine dendritic cell (DC) lines. Cationic lipid-incorporated liposomes delivered entrapped ovalbumin (OVA) molecules not only to cytosol but also to endosome/lysosome. Treatment with cationic lipid-incorporated liposomes induced up-regulation of antigen presentation-involved molecules on DCs, the promotion of cytokine production, and antigen presentation via both major histocompatibility complex (MHC) class I and II molecules. Especially, antigen presentation via MHC class II was promoted by cationic lipid inclusion, which might correspond to efficient endosome/lysosome delivery of OVA. Subcutaneous administration of OVA-loaded cationic lipid-incorporated liposomes induced antigen-specific antibody production in serum and Th1-dominant immune responses in the spleen. Furthermore, administration of the cationic lipid-incorporated liposomes to mice bearing E.G7-OVA tumor more significantly reduced the tumor volume than liposomes without cationic lipids. Therefore, cationic lipid inclusion into pH-sensitive polymer-modified liposomes, which can achieve both efficient antigen intracellular delivery and activation of antigen presenting cell, is an effective approach to develop antigen carriers for efficient cancer immunotherapy.

Enzymatic modification of phosphatidylcholine with n-3 PUFA from silkworm oil fatty acids

α-Linolenic acid (ALA) containing phosphatidylcholine (PC) was prepared by an enzymatic method employing natural substrates comprising of egg and eri silkworm oil. Eri silkworm oil extracted from eri pupae was saponified to obtain the fatty acid mixture which was further subjected to urea complexation to obtain an ALA rich fraction with a purity of about 93%. Transesterification of PC with the ALA rich fraction with three immobilized lipases namely Lipozyme TL IM, Lipozyme RM IM and lipase from Candida Antarcticaz showed that only the lipase from Candida antarctica was successful for the incorporation of ALA into egg yolk PC. It was found that ALA was incorporated by up to 27% in the sn -1 position of egg PC and the positional distribution analysis of fatty acids in the modified PC showed that the sn -1 position was found to contain about 59% ALA.

Nonallergenic urushiol derivatives inhibit the oxidation of unilamellar vesicles and of rat plasma induced by various radical generators

Urushiols consist of an o-dihydroxybenzene (catechol) structure and an alkyl chain of 15 or 17 carbons in the 3-position of a benzene ring and are allergens found in the family Anacardiaceae. We synthesized various veratrole (1,2-dimethoxybenzene)-type and catechol-type urushiol derivatives that contained alkyl chains of various carbon atom lengths, including –H, –C1H3, –C5H11, –C10H21, –C15H31, and –C20H41, and investigated their contact hypersensitivities and antioxidative activities. 3-Decylcatechol and 3-pentadecylcatechol displayed contact hypersensitivity, but the other compounds did not induce an allergic reaction, when the ears of rats were sensitized by treatment with the compounds every day for 20 days. Catechol-type urushiol derivatives (CTUDs) exerted very high radical-scavenging activity on the 1,1-diphenyl-2-picrylhydrazyl radical and inhibited lipid peroxidation in a methyl linoleate solution induced by 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN). However, veratrole-type urushiol derivatives did not scavenge or inhibit lipid peroxidation. CTUDs also acted as effective inhibitors of lipid peroxidation of the egg yolk phosphatidylcholine large unilamellar vesicle (PC LUV) liposome system induced by various radical generators such as AMVN, 2,2′-azobis(2-amidino-propane) dihydrochloride, and copper ions, although their efficiencies differed slightly. In addition, CTUDs suppressed formation of cholesteryl ester hydroperoxides in rat blood plasma induced with copper ions. CTUDs containing more than five carbon atoms in the alkyl chain showed excellent lipophilicity in a n-octanol/water partition experiment. These compounds also exhibited high affinities to the liposome membrane using the ultrafiltration method of the PC LUV liposome system. Therefore, CTUDs seem to act as efficient antioxidative compounds against membranous lipid peroxidation owing to their localization in the phospholipid bilayer. These results suggest that nonallergenic CTUDs act as antioxidants to protect against oxidative damage of cellular and subcellular membranes.

Dextran derivative-based pH-sensitive liposomes for cancer immunotherapy

pH-Sensitive dextran derivatives having 3-methylglutarylated residues (MGlu-Dex) were prepared by reacting dextran with 3-methyl-glutaric anhydride. MGlu-Dex changed the protonation state and their characteristics from hydrophilic to hydrophobic in neutral and acidic pH regions. Surface modification of egg yolk phosphatidylcholine liposomes with MGlu-Dex produced highly pH-sensitive liposomes that were stable at neutral pH but which were destabilized strongly in the weakly acidic pH region. MGlu-Dex-modified liposomes were taken up efficiently by dendritic cells and delivered entrapped ovalbumin (OVA) molecules into the cytosol. When MGlu-Dex-modified liposomes loaded with OVA were administered subcutaneously to mice, the antigen-specific humoral and cellular immunity was induced more effectively than the unmodified liposomes loaded with OVA. Furthermore, administration of MGlu-Dex-modified liposomes loaded with OVA to mice bearing E.G7-OVA tumor significantly suppressed tumor growth and extended the mice survival. Results suggest that MGlu-Dex-modified liposomes are promising for the production of safe and potent antigen delivery systems that contribute to the establishment of efficient cancer immunotherapy.