Phosphatidylcholine Liposomal Membranes Research Articles

Radical reactions induced by ketoprofen in phospholipid membranes under ultraviolet light irradiation

2-(3-Benzoylphenyl)propanoic acid (ketoprofen), one of the nonsteroidal anti-inflammatory drugs, causes photocontact dermatitis by ultraviolet (UV) light as a side effect. In this study, we examined radical reactions induced by ketoprofen in the lipid membranes under UV irradiation using egg yolk phosphatidylcholine (egg-PC) liposomal membranes containing 5- or 16-doxyl stearic acid (5- or 16-DSA), which carry nitroxyl radical at the 5- or 16-position of the fatty acid chain, respectively. When the suspension of liposomal membrane was mixed with ketoprofen and irradiated with UV, electron spin resonance signal of 5- and 16-DSA in the membrane decreased. The decay consisted of fast decay and subsequent slow decay. The overall decay for 5-DSA was faster than that for 16-DSA. The rate of slower decay of 16-DSA increased with ketoprofen concentration. The bulk lipid in the membrane affected the rate of slower decay of 5-DSA; the rate increased with the amount of egg-PC and decreased in the rigid membrane composed of dipalmitoylphosphatidylcholine. When spin trapping studies with α-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimetyl-1-pyrroline-N-oxide (DMPO) were performed in ketoprofen solution, C-centered radical adducts of POBN and superoxide anion radical adducts of DMPO were detected after UV irradiation. POBN suppressed the signal decay of 5-DSA in the liposomal membrane, whereas superoxide dismutase accelerated it. These results support that ketoprofen penetrates the lipid membrane and induces a radical reaction near the polar region in the membrane, and that ketoprofen-related C-centered radical is involved in the radical reaction.

Вивчення спорідненості до мембран допоміжних речовин й фармакологічно активних інгредієнтів методами флуоресцентних і спінових зондів

Мета дослідження – порівняльне вивчення спорідненості до ліпосом з фосфатидилхоліну низки гідрофільних неводних розчинників пропіленгліколю (ПГ), поліетиленгліколей (ПЕГ) з молекулярною масою 400 і 1500 (ПЕГ­400 і ПЕГ­1500), що успішно застосовуються за створення м’яких лікарських форм як допоміжні речовини. Проведено аналіз результатів, отриманих за допомогою методу флуоресцентних зондів, і розрахунок константи дисоціації (Кд) неводних розчинників ПГ, ПЕГ­400 і ПЕГ­1500 з мембранами ліпосом з фосфатидилхоліну графічним методом у зворотних координатах. Показано, що Кд = 2,5 моль/л для ПГ і Кд = 4 • 10 ­1 моль/л для ПЕГ­400. Аналіз спектрів електронно­парамагнітного резонансу (ЕПР) у зворотних координатах дозволив оцінити Кд для ПЕГ­1500, що дорівнює 10­1 моль/л. Досліджено вплив ПГ і ПЕГ­400 на мембрани ліпосом. ПГ і ПЕГ­400 ефективно зв’язуються з мембраною ліпосом, витісняючи флуоресцентний зонд з мембрани в воду. Це може бути одним із механізмів впливу ПГ і ПЕГ­400 на біодоступність, коли фармакологічно активні інгредієнти (ФАІ) можуть витиснятися в воду молекулами допоміжних речовин, сповільнюючи процес всмоктування ФАІ. Введення ПЕГ­400 у суспензію ліпосом призводить до розпушення мембран, тобто, до зменшення щільності упаковки фосфоліпідів у мембранах, що може призводити до зміни їхньої проникності та підвищенню біодоступності. Дія ПГ на мембрани є більш м’якою, ніж ПЕГ­400. Вочевидь у зоні всмоктування ФАІ на мембрані паралельно відбувається процес всмоктування низькомолекулярних допоміжних речовин, наприклад, неводних розчинників. Причому всмоктування ліпофільних ФАІ може відбуватися в оточенні розчинників (допоміжних речовин), що призводить до збільшення біодоступності ФАІ. У разі конкуренції за місця зв’язування на мембранах клітин біоповерхонь між ФАІ і неводними розчинниками більш низька (на кілька порядків) спорідненість розчинників до мембран компенсується значною кількістю розчинників у м’якій лікарській формі порівняно з ФАІ. Механізмом підвищення біосумісності за допомогою ПЕГ є здатність їхніх молекул за рахунок компактизації (спіралізації) або розпушення приймати оптимальну конформацію структури, надаючи свої гідрофобні або полярні групи для оптимального зв’язування з наночастинками, лікарськими речовинами та біооб’єктами.

Binding of trivalent metal ions (Al3+, In3+, La3+) with phosphatidylcholine liposomal membranes investigated by microelectrophoresis

.Interactions between trivalent metal ions (Al3+, In3+, La3+) and phosphatidylcholine (PC) liposomes are studied by microelectrophoresis. The dependence of the PC membrane surface charge density and zeta potential on p{rm H} (p{rm H} range from 2 to 10) of the aqueous metal chloride solutions is determined. The obtained results indicate the adsorption of Al3+, In3+ and La3+ ions on phosphatidylcholine model membranes, leading to changes in the electrical properties of the membranes. The theoretical considerations on equilibria occurring between phosphatidylcholine liposomal membrane and trivalent metal ions are presented. A mathematical model describing the interactions in a quantitative way is proposed.Graphical abstract

Interaction of Selected Phenylpropenes with Dipalmitoylphosphatidylcholine Membrane and Their Relevance to Antibacterial Activity.

The effect of structurally closely related phenylpropenes (PPs), estragole, anethole, eugenol, and isoeugenol, on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membrane was investigated by DSC, Raman, and fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH). Liposomes were prepared by thin-film hydration method at various DPPC:PP molar ratios. The DPH anisotropy measurements of blank and PP-loaded liposomes were performed at 28, 41, and 50°C, which correspond, respectively, to gel phase, main transition temperature of DPPC, and liquid phase. The Raman images showed the formation of nano- and micrometric spherical multi-lamellar vesicles. All studied PPs exhibited a membrane fluidizing effect which was reinforced by the presence of phenolic hydroxyl group in eugenol and isoeugenol. The PPs interacted with the choline head group and the alkyl chains of DPPC membrane, wherein isoeugenol and anethole possessing the same C7-C8 position of the double bond in the propenyl side chain, incorporated deeply in the bilayer. Additionally, the PPs were analyzed for antibacterial activity against E. coli by macrobroth dilution method. Anethole and estragole were more efficient in inhibiting the bacterial growth than eugenol and isoeugenol. We conclude that the fluidizing effect of PPs on the membrane is a common mechanism that is not related to the hydrophobicity of the PP molecule. Besides, other target sites may be involved in PP antibacterial activity against Gram-negative bacteria. The greater hydrophobicity of these PPs may contribute to their penetrability through the outer bacterial membrane.

Association of alkali metal cations with phosphatidylcholine liposomal membrane surface

Interactions of alkali metal cations (Li+, Na+, K+, Cs+) with phosphatidylcholine (PC) liposomal membranes were investigated through experimental studies and theoretical considerations. Using a microelectrophoresis technique, charge densities of experimental membrane surfaces were measured as a function of the pH of electrolyte solutions. Equilibria between the PC liposomal membranes and monovalent ions were mathematically analyzed and described quantitatively through a previously proposed theoretical model. Association constants between functional groups of PC and the studied ions were determined and used to define theoretical curves of membrane surface charge density versus pH. Theoretical and experimental data were compared to verify the model. The PC membrane was found to have the highest affinity for lithium ions, among the ions tested.

Tetra- and Penta-Cyclic Triterpenes Interaction with Lipid Bilayer Membrane: A Structural Comparative Study.

The effect of tetracyclic (cortisol, prednisolone, and 9-fluorocortisol acetate) and pentacyclic (uvaol and erythrodiol) triterpenes (TTPs) on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membrane was investigated by differential scanning calorimetry, Raman spectroscopy, and fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Liposomes were prepared in the absence and presence of TTPs at molar ratios DPPC:TTP 100:1, 100:2.5, and 100:10. All the studied TTPs abolished the pre-transition and modified the intensity of the Raman peak at 715cm(-1) proving the interaction of TTP molecules with the choline head group of phospholipids. An increase in the Raman height intensity ratios of the peaks I 2935/2880, I 2844/2880, and I 1090/1130, giving information about the ratio disorder/order of the alkyl chains, and a decrease of the main transition temperature demonstrated the interaction of TTPs with the alkyl chains. The tetracyclic TTPs produced broadening of the phase transition profile. Besides, a scarcely splitting of the main transition peak was obtained with prednisolone and 9-fluorocortisol acetate. The results of fluorescence depolarization of DPH showed that the studied molecules fluidized the liposomal membrane at 25, 41, and 50°C. Pentacyclic TTPs, being more hydrophobic than tetracyclic ones, demonstrated higher fluidizing effect than tetracyclic TTPs in the liquid crystalline phase suggesting a deeper incorporation in the lipid bilayer. The presence of a free polar head group at the ring D seems to control the TTP incorporation in the bilayer and consequently its effect on the membrane fluidity.

Influence of iron oxide nanoparticles on bending elasticity and bilayer fluidity of phosphotidylcholine liposomal membranes

Iron oxide nanoparticles with improved surface characteristics have tremendous applications in various biomedical fields such as magnetic resonance imaging, hyperthermia, immunoassay and targeted drug delivery. The aim of this work was to study the influence of iron oxide (γ-Fe2O3) nanoparticles on the bilayer fluidity and bending elasticity of zwitterionic phosphatidylcholine liposomal membranes. Small unilamellar vesicles prepared with l-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine lipids were encapsulated with uncoated iron oxide nanoparticles and silica coated iron oxide nanoparticles to study their effect on bilayer fluidity. Anisotropy measurements using the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene and N,N,N-trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl) phenylammonium p-toluensufonate did not show a significant difference in the lipid ordering and bilayer fluidity. Thermally induced shape fluctuations of the giant quasi-spherical lipid vesicles were used to study the influence of both types of iron oxide nanoparticles on the bending elasticity modulus kc of the lipid membrane. The results showed that in the case of uncoated iron oxide (in the studies concentration) the obtained value for the bending elasticity modulus does not differ in the frames of the experimental error from that of pure phospholipid membrane. In the case of silica coated iron oxide nanoparticles the bending elasticity modulus of the membrane decreased by 25%.

On the structure and function of the phytoene desaturase CRTI from Pantoea ananatis, a membrane-peripheral and FAD-dependent oxidase/isomerase.

CRTI-type phytoene desaturases prevailing in bacteria and fungi can form lycopene directly from phytoene while plants employ two distinct desaturases and two cis-tans isomerases for the same purpose. This property renders CRTI a valuable gene to engineer provitamin A-formation to help combat vitamin A malnutrition, such as with Golden Rice. To understand the biochemical processes involved, recombinant CRTI was produced and obtained in homogeneous form that shows high enzymatic activity with the lipophilic substrate phytoene contained in phosphatidyl-choline (PC) liposome membranes. The first crystal structure of apo-CRTI reveals that CRTI belongs to the flavoprotein superfamily comprising protoporphyrinogen IX oxidoreductase and monoamine oxidase. CRTI is a membrane-peripheral oxidoreductase which utilizes FAD as the sole redox-active cofactor. Oxygen, replaceable by quinones in its absence, is needed as the terminal electron acceptor. FAD, besides its catalytic role also displays a structural function by enabling the formation of enzymatically active CRTI membrane associates. Under anaerobic conditions the enzyme can act as a carotene cis-trans isomerase. In silico-docking experiments yielded information on substrate binding sites, potential catalytic residues and is in favor of single half-site recognition of the symmetrical C40 hydrocarbon substrate.

Kinetic of Transport of Technogenic Ecotoxicants through Model Membranes

The kinetics of ecotoxicant transport through the membrane was studied. The ecotoxicants studied were pecticides widely used in agriculture: lontrel (clopyralid), sencor (metribuzin), basagran (bentazon), roundup (glyphosate), kusagard (alloxydim sodium), and sethoxydim, as well as lontrel complexes with cobalt and copper. All compounds considered penetrate through the model phosphatidylcholine liposomal membranes. The transfer rate was monitored by fluorescence quenching of ?-ATP inside the liposomes. The mathematical model for the process was proposed, and the mass transfer rates were calculated. The octanol/water partition constants were determined. All the compounds con- sidered were shown to accumulate in the fatty layer. The kinetics of their accumulation was studied, and the rates of accumulation in the nonpolar phase were calculated, which correlate with the complexation constants of the same compounds. Bioaccumulation of the toxicants is caused by the formation of complexes with the fatty phase (lipid part) of the cellular membranes. The toxicants under study transferred into the nonpolar phase with a considerable rate dur- ing the whole observation time, namely, 18 months.

Comparative study on determination of antioxidant and membrane activities of propofol and its related compounds

Certain anesthetics have been suggested to protect against the pathological states associated with oxidative stress. We compared the antioxidant and membrane activities of propofol (2,6-diisopropylphenol) and its related compounds to address the structure–activity relationship especially in a lipid membrane phase. They were studied for the effects on 1,1-diphenyl-2-picrylhydrazyl radicals, nitro blue tetrazolium reduction by superoxide anions and membrane lipid peroxidation by peroxynitrite, and also for the induced changes in membrane fluidity of liposomes. 2-Isopropylphenols scavenged free radicals with the potency being propofol > 2,5-diisopropylphenol > 2-isopropylphenol > 2,4-diisopropylphenol, but not 3- and 4-isopropylphenols and 1,3- and 1,4-diisopropylbenzenes. The tested compounds showed no significant superoxide dismutase-like effects. Propofol inhibited membrane lipid peroxidation more intensively than 2,5-diisopropylphenol, 2,4-diisopropylphenol and 2-isopropylphenol. Despite structurally resembling antioxidant α-tocopherol, 2,6-dimethylphenol was less potent than propofol. Propofol produced 50% inhibition of the lipid peroxidation in unsaturated phosphatidylcholine liposomal membranes and cell-mimetic membranes at 4.0 and 10.1 μM, respectively. Propofol and 2-alkylphenolic compounds interacted with membranes to increase their fluidity with the potency correlating with lipid peroxidation inhibiting activity. The 2-isopropylphenol structure is a requisite for both lipid peroxidation inhibition and membrane fluidity modification. The structure-specific membrane interactivity appears to be one of possible antioxidant mechanisms for propofol.

Aβ/Cu-catalyzed oxidation of cholesterol in 1,2-dipalmitoyl phosphatidylcholine liposome membrane

The amyloid beta protein with 42 amino acid residues (Abeta), which is a causative protein of Alzheimer's disease (AD), forms the complex with copper (II) to induce the cholesterol oxidase-like activity by the proton transfer from the cholesterol. In this study, the oxidation of cholesterol by Abeta/Cu complex was investigated on the surface of the zwitterionic phospholipid liposome including the bound water advantageous for the enhancement of the proton transfer. The bound water was pooled by the formation of cholesterol-rich domain within liposomes. The resulting reactivity was enhanced by the proton transfer mediated by the bound water.

Spin-labelled lutein as a new antioxidant in protection against lipid peroxidation

A new potentially antioxidant compound, spin-labelled lutein (SL-lut), was synthesized and incorporated into egg yolk phosphatidylcholine (EYPC) liposome membrane. The approximate location of nitroxide free radical groups of SL-lut was determined based on electron paramagnetic resonance (EPR) spectra. Then the ability of SL-lut to protect EYPC liposomes against lipid peroxidation (LPO) was compared to the antioxidant effects of lutein and a nitroxide spin label 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy (3-CP). Two free radical generation systems were used—a thermal decomposition of 2,2′-azobis (2,4 dimethyl-valeronitrile) (AMVN) and a modified Fenton reaction using ferric-8-hydroxyquinoline (Fe(HQ)3). Determination of the amount of thiobarbituric acid reactive species (TBARS) was used as a measure of LPO. SL-lut was the most powerful antioxidant, reducing LPO by about 6-times in AMVN-treated liposomes and 7-times in Fe(HQ)3-treated liposomes. Lutein alone gave only a moderate protection in both systems, while 3-CP was as efficient as SL-lut in the presence of AMVN, but not efficient whatsoever in the presence of Fe(HQ)3. The results suggest that a nitroxide part of SL-lut plays an important role in enhancing the antioxidant activity of lutein and makes SL-lut a powerful antioxidant efficient under different conditions.

Antioxidative Effect of Quercetin and Its Equimolar Mixtures with Phenyltin Compounds on Liposome Membranes

Our earlier studies have shown that the compounds diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) in the presence of UVC radiation enhanced the degree of phosphatidylcholine liposome membrane oxidation (J. Agric. Food Chem. 2005, 53, 76-83). The prooxidative behavior of the compounds has now been confirmed with the electron paramagnetic resonance method, which proved the possibility that the studied compounds can exist in free radical forms. The present work investigates the possibility of the protective action of quercetin on phosphatidylcholine liposome membranes exposed to the prooxidative action of DPhT and TPhT induced by UV radiation (lambda = 253.7 nm). The concentrations of quercetin and its equimolar mixtures with DPhT and TPhT were determined (and compared with well-known antioxidants as standards-trolox and butylated hydroxytoluene, also in the presence of phenyltins) as those that induce 50% inhibition in oxidation of liposomes radiated with UV. They are 5.1 +/- 0.10, 2.9 +/- 0.12, and 1.9 +/- 0.08 microM (differences between the values are statistically significant), constituting the following sequence of antioxidative activity: quercetin:TPhT > quercetin:DPhT > quercetin. This relation is confirmed by the results on the antiradical ability of quercetin and its mixtures with DPhT and TPhT toward the free radical 1,1-diphenyl-2-pricrylhydrazil. Similar sequences obtained in both studies suggest a possible mechanism of the antiradical action of the mixtures as free radical scavengers. We suggested that (i) quercetin's ability, documented by spectrophotometric, infrared attenuated total reflectance spectroscopy, (1)H NMR, and molecular modeling methods, to form complexes with phenyltins indicates a possible way of protection against the peroxidation caused by the free radical forms of phenyltins and (ii) the differentiation in the action of the quercetin/TPhT and quercetin/DPhT associates (statisticaly significant) may result from a different localization in the liposome membrane, which is indicated by the results of the fluorimetric studies.

Antioxidative Effect of Kaempferol and Its Equimolar Mixture with Phenyltin Compounds on UV-Irradiated Liposome Membranes

The work investigates the possibility of the protective action of kaempferol on phosphatidylcholine liposome membranes exposed to the pro-oxidative action of diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) induced by UV radiation (lambda = 253.7 nm). The concentrations of kaempferol and its equimolar mixtures with DPhT and TPhT were determined so that they induce 50% inhibition in oxidation of liposomes irradiated with UV. They are 11.6, 10.0, and 4.5 microM/L, which constitute the following sequence of antioxidative activity: kaempferol/triphenyltin > kaempferol/diphenyltin > kaempferol. This relationship is confirmed by the results on the antiradical ability of kaempferol and its mixtures with DPhT and TPhT toward the free radical 2,2-diphenyl-1-picrylhydrazyl. Similar sequences obtained in both studies suggest a possible mechanism of the antiradical action of the mixtures as free radical scavengers. Kaempferol's ability, then documented, to form complexes with phenyltins indicates (a) a possible way to liquidate the peroxidation caused by the free radical forms of phenyltins and (b) the stabilizing role of chelating in the antioxidative action of the kaempferol/phenyltins. The differentiation in the action of the compounds studied may, among others, result from different localizations in the liposome membrane, which is indicated by the results of the fluorometric studies.

Quantification of lipid bilayer effective microviscosity and fluidity effect induced by propofol

Electron spin resonance (ESR) spectroscopy with nitroxide spin probes was used as a method to probe the liposome microenvironments. The effective microviscosities have been determined from the calibration of the ESR spectra of the probes in solvent mixtures of known viscosities. In the first time, by measuring ESR order parameter ( S) and correlation time ( τ c) of stearic spin probes, we have been able to quantify the value of effective microviscosity at different depths inside the liposome membrane. At room temperature, local microviscosities measured in dimyristoyl- l-α phosphatidylcholine (DMPC) liposome membrane at the different depths of 7.8, 16.95, and 27.7 Å were 222.53, 64.09, and 62.56 cP, respectively. In the gel state (10 °C), those microviscosity values increased to 472.56, 370.61, and 243.37 cP. In a second time, we have applied this technique to determine the modifications in membrane microviscosity induced by 2,6-diisopropyl phenol (propofol; PPF), an anaesthetic agent extensively used in clinical practice. Propofol is characterized by a unique phenolic structure, absent in the other conventional anaesthetics. Indeed, given its lipophilic property, propofol is presumed to penetrate into and interact with membrane lipids and hence to induce changes in membrane fluidity. Incorporation of propofol into dimyristoyl- l-α phosphatidylcholine liposomes above the phase-transition temperature (23.9 °C) did not change microviscosity. At 10 °C, an increase of propofol concentration from 0 to 1.0×10 −2 M for a constant lipid concentration mainly induced a decrease in microviscosity. This fluidity effect of propofol has been qualitatively confirmed using merocyanine 540 (MC540) as lipid packing probe. Above 10 −2 M propofol, no further decrease in microviscosity was observed, and the microviscosity at the studied depths (7.8, 16.95, and 27.7 Å) amounted 260.21, 123.87, and 102.27 cP, respectively. The concentration 10 −2 M was identified as the saturation limit of propofol in dimyristoyl- l-α phosphatidylcholine liposomes.

The effect of cholesterol on the adsorption of phenyltin compounds onto phosphatidylcholine and sphingomyelin liposome membranes

AbstractOrganometallic compounds are widely spread in the human environment sometimes, causing a substantial health risk. Their amphiphilic character enables them to intercalate and penetrate cell membranes, potentially affecting various vital cell functions. Compound adsorption onto the membrane depends on the compound properties, as well as on the membrane composition and state. When adsorbing onto the lipidic surface, phenyltins localize at areas where lipid bilayer organization is compatible with compound spatial requirements. The lipid bilayer is a dynamic and laterally nonuniform structure with complex local and global architecture correlated with a variety of cell functions. The selective binding of a toxic compound to selected membrane areas may, therefore, interfere with some types of cellular process. We present experimental results concerning phenyltin adsorption onto the lipid bilayer surface measured with the fluorescent probe fluorescein‐PE. Model lipid bilayers were formed from lipid mixtures mimicking various plasma membrane regions. The adsorption of Ph3SnCl and P2SnCl2 onto the phosphatidylcholine–cholesterol bilayer was qualitatively different from sphingomyelin–cholesterol. The results presented indicate that phenyltins are likely to accumulate in areas containing phosphatidylcholine, outside of lipid rafts. Copyright © 2004 John Wiley & Sons, Ltd.

Antioxidant effects of phytosterol and its components.

Phytosterol contained in vegetable oils is known to exert a hypocholesterolemic function. In the present study, the antioxidant effects of phytosterol and its components, beta-sitosterol, stigmasterol, and campesterol, against lipid peroxidation were examined by making a comparison with 2,2,5,7,8-pentamethyl-6-chromanol (PMC). It was found that these compounds exerted antioxidant effects on the oxidation of methyl linoleate in solution and its effect decreased in the order of: PMC >> phytosterol approximately campesterol approximately beta-sitosterol > stigmasterol. Phytosterol also suppressed the oxidation and consumption of alpha-tocopherol in beta-linoleoyl-gamma-palmitoyl phosphatidylcholine (PLPC) liposomal membranes, the effects being more significant than dimyristoyl PC of the same concentration. Stigmasterol accelerated the oxidation of both methyl linoleate in solution and PLPC liposomal membranes in aqueous dispersions, which was ascribed to the oxidation of allylic hydrogens at the 21- and 24-positions. Taken together, the present study shows that phytosterol chemically acts as an antioxidant, a modest radical scavenger, and physically as a stabilizer in the membranes.

Microcalorimetric studies on the physical stability of poly-ethylene glycol-grafted liposome

Abstract Liposomes were prepared from mixtures of egg-PC, cholesterols and distearoyl-phosphatidyl-ethanolamine covalently attached poly-ethylene glycol (PEG) with a molecular of weight 2000 (DSPE–PEG2000). In this work examines how PEG2000-grafted lipids affect the surface properties of the egg phosphatidylcholine (egg-PC) liposomal bilayer membrane through zeta potential and interaction potential measurements using microcalorimetry. Experimental results demonstrate that the absolute value of the zeta potential of PEG2000-grafted PC liposomes decreased from −19 to −8 mV when increasing DSPE–PEG2000 from 0 to 7 mol fraction, and the repulsive interaction potential of PEG2000-grafted PC liposomes decreased compared with those liposomes without PEG-grafting. However, the phenomenon of fusion between the liposomes incorporated with PEG-grafted PC was reduced. In brief, this result of fusion is contrary to the expectation of the interaction potential measurement; therefore, we believe that the steric hindrance of the grafted PEG2000 molecules on the liposomal surface contribute to a major imposition on the approach between liposomal surface and the formation of inverted micelles which are suggested as the necessary steps of liposome fusion.

Antioxidant effect of capsaicin on lipid peroxidation in homogeneous solution, micelle dispersions and liposomal membranes

The antioxidant activity of capsaicin (CAP) was measured in the oxidation of methyl linoleate (ML) in homogeneous solution, of ML micelles in aqueous dispersions and also of soybean phosphatidylcholine liposomal membrane, and was compared to that of -tocopherol (-TOH) which is one of the most important antioxidants in vivo. The reactivity of CAP toward galvinoxyl (a model phenoxyl radical) in acetonitrile solution was found to be much smaller than that of -TOH, suggesting that the radical scavenging activity of CAP is much weaker than that of -TOH. In fact, in homogeneous acetonitrile solution where the antioxidant activity is determined primarily by the chemical activity of the antioxidant toward peroxyl radicals, CAP inhibited the oxidation of ML much less efficiently than -TOH and a clear induction period was not observed. The antioxidant activity of CAP was found to be about 60 times smaller than that of -TOH in homogeneous solution. However, in micelle oxidation, the difference in antioxidant activity of the two antioxidants was much smaller than in homogeneous solution. Furthermore, in the membrane, CAP inhibited the oxidation almost as effectively as -TOH. These results suggest that CAP can act as an antioxidant in the biomembrane.

Evaluation of the antioxidant activity and partial characterisation of extracts from browned yam flour diet

The antioxidant activity of the ethyl acetate extract of browned yam flour, a diet widely consumed in West Africa especially in southern part of Nigeria, was examined in β-carotene linoleate system and egg yolk phosphatidyl choline (EYPC) liposomal membrane exposed to the lipid soluble 2,2-azobis (2-amidinopropane) hydrochloride (AAPH) generated peroxyl radicals. Total antioxidant activity (TAA) of crude ethyl acetate extract was determined using 2,2′ azinobis- (3-ethyl benzothiazoline-6-sulfonic acid) (ABTS) and Horseradish peroxidase as enzyme source. TAA of the extract was estimated to be 7.5 measured as mM of Vitamin C equivalent. The crude extract was fractionated on a sephadex LH-20 column using methanol as eluant at a flow rate of 1.8 ml/min. Fractions 1, 2 and 3 showed similar absorption maxima in the range of 190–230 and 240–269. Fractions 4–7 produced absorption maxima in the range of 270–280. Although, the crude extract showed a higher antioxidant effect than butylated hydroxyanisole (BHA), all the isolated fractions exhibited a lower antioxidant activity than BHA in the β-carotene linoleate model system. Compared to control, fractions 2, 3, 5 and 6 showed good antioxidant effect against the bleaching of β-carotene. Incorporation of the fractions into EYPC liposomes retarded the lipid peroxidation caused by AAPH derived peroxyl radicals to varying extents. Fractions 2, 3, 5 and 6 significantly ( P<0.001) reduced AAPH mediated thiobarbituric acid reactive substances (TBARS) formation. Partial characterisation of this extract by TLC on silica gel plates showed that fractions 5 and 6 contain several phenolic compounds. TLC and UV/visible data suggest that fractions 2 and 3 may contain browning reaction products such as pyrazines and acetylfurans. The results of the present investigation suggest that browned yam flour contains natural antioxidants and as such may mediate in oxidative damage and diseases caused by environmental chemicals.