Glass Microsphere‐Supported Giant Vesicles for the Observation of Self‐Reproduction of Lipid Boundaries

Growth and division experiments on phospholipid boundaries were carried out using glass microsphere‐supported phospholipid (DOPC) giant vesicles (GVs) fed with a fatty acid solution (oleic acid) at two distinct feeding rates. Both fast and slow feeding methods produced daughter GVs. Under slow feeding conditions the membrane growth process (evagination, buds, filaments) was observed in detail by fluorescence microscopy. The density difference between supported mother vesicles and newly formed daughter vesicles allowed their easy separation. Mass spectrometric analysis of the resulting mother and daughter GVs showed that the composition of both vesicle types was a mixture of original supported phospholipids and added fatty acids reflecting the total composition of amphiphiles after the feeding process. Thus, self‐reproduction of phospholipid vesicles can take place under preservation of the lipid composition but different aggregate size.     

Isolation and structural analysis of the cyclic fatty acid monomers formed from eicosapentaenoic and docosahexaenoic acids during fish oil deodorization

Long-chain polyunsaturated fatty acids (LC-PUFAs) present in fish oils are thermolabile molecules. Among the degradation reactions encountered, thermal cyclization occurs during refining or other heat treatments. Numerous studies have been carried out in the past to quantify and determine the structures of cyclic fatty acid monomers (CFAMs) formed from oleic, linoleic and linolenic acids in heated vegetable oils. Recently, much attention have been given to LC-PUFAs due to their potential health benefits. However, data on quantification of CFAMs formed from these fatty acids, such as eicosapentaenoic acid (EPA, cis-5, cis-8, cis-11, cis-14, cis-17 20:5) and docosahexaenoic acid (DHA, cis-4, cis-7, cis-10, cis-13, cis-16, cis-19 22:6), the two main LC-PUFAs in fish oils, are scarce. In the present study, structural analyses of CFAMs formed from EPA and DHA during the deodorization of fish oil are presented. Fish oil sample was deodorized at 250 degrees C for 3 h under a pressure of 1.5 mbar in a laboratory deodorizer. The CFAMs formed during heat treatment of fish oil were isolated by a combination of saponification, esterification, urea fractionations and column chromatography. Structural analyses of C20- and C22-CFAMs were achieved by gas-chromatography electronic-ionization mass-spectrometry (GC-EI-MS) of their 4,4-dimethyloxazoline (DMOX) derivatives. We identified seven out of 13 possible structures of hydrogenated CFAMs formed from EPA, and nine out of 16 possible structures of CFAM formed from DHA. Major CFAMs from both EPA and DHA were cyclohexyl isomers. All possible cyclohexyl isomers were found but only nine out of 18 of the cyclopentyl isomers were present in concentration sufficient for identification. Chemical mechanisms involved in the formation of polyunsaturated LC-PUFAs have been investigated. The results have shown that general principle involved in the cyclization of LC-PUFAs is same as that for the thermal cyclization of oleic, linoleic and alpha-linolenic acids.     

Shrink-wrap vesicles

We describe a simple approach to the controlled removal of molecules from the membrane of large unilamellar vesicles made of fatty acids. Such vesicles shrink dramatically upon mixing with micelles composed of a mixture of fatty acid and a phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)), as fatty acid molecules leave the vesicle membrane and accumulate within the mixed micelles. Vesicle shrinkage was confirmed by dynamic light scattering, fluorescence recovery after photobleaching of labeled vesicles, and fluorescence resonance energy transfer between lipid dyes incorporated into the vesicle membrane. Most of the encapsulated impermeable solute is retained during shrinkage, becoming concentrated by a factor of at least 50-fold in the final small vesicles. This unprecedented combination of vesicle shrinkage with retention of contents allows for the preparation of small vesicles containing high solute concentrations, and may find applications in liposomal drug delivery.     

Fatty acid vesicles

Results obtained from recent studies on the preparation and application of fatty acid vesicles are reviewed, focusing on some of the particular properties of fatty acid vesicles in comparison with conventional phospholipid vesicles (liposomes): (i) pH dependency which allows reversible transformations from non-vesicular to vesicular aggregates, and (ii) dynamic features that place fatty acid vesicles in between conventional vesicles formed from double-chain amphiphiles and micelles formed from single-chain surfactants. There are two main research areas in which fatty acid vesicles have been studied actively during the last years: (i) basic physico-chemical properties, and (ii) applications as protocell models. Applications of fatty acid vesicles in the fields of food additives and drug delivery are largely unexplored, which is at least partially due to concerns regarding the colloidal stability of fatty acid vesicles (pH- and divalent cation-sensitivity). Recently, fatty acid vesicles were prepared from highly unsaturated fatty acids (docosahexaenoic acid) and the pH range of vesicle formation could be extended to high or low pH values by preparing mixed vesicles through addition of a second type of single-chain amphiphile that stabilizes the vesicle bilayer but itself is not a fatty acid.     

Phospholipase D-mediated aggregation, fusion, and precipitation of phospholipid vesicles

Large unilamellar vesicles with a diameter of 100 nm were prepared from the zwitterionic phospholipid POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) at pH 8.0. After addition to these vesicles of the enzyme phospholipase D (PLD) from Streptomyces sp. AA586 at 40 degrees C, the terminal phosphate ester bond of POPC was hydrolyzed, yielding the negatively charged POPA (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidic acid) and the positively charged choline. While the reaction yield in the presence of 1 mM Ca2+ reached 100%, the yield was only approximately 68% in the absence of Ca2+. Furthermore, in the absence of Ca2+, the size of the vesicles did not change significantly with time upon PLD addition, as judged from turbidity, dynamic light scattering, and electron microscopy measurements. In the presence of 1 mM Ca2+, however, PLD addition resulted in vesicle aggregation, fusion, and precipitation, originating from the interaction of Ca2+ ions with the negatively charged phospholipids formed in the membranes. Vesicle fusion was monitored by using a novel fusion assay system involving vesicles containing entrapped trypsin and vesicles containing entrapped chymotrypsinogen A. After vesicle fusion, chymotrypsinogen A transformed into a-chymotrypsin, catalyzed by trypsin inside the fused vesicles. The alpha-chymotrypsin formed could be detected with benzoyl-L-Tyr-p-nitroanilide as a membrane permeable chymotrypsin substrate. The observed vesicle precipitation occurring after vesicle fusion in the presence of 1 mM Ca2+ was correlated with an increase of the main phase transition temperature, Tm, of POPA to values above 40 degrees C.     

Comparative quantitative fatty acid analysis of triacylglycerols using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gas chromatography.

Quantitative analyses of fatty acids from five triacylglycerol products, coconut oil, palm kernel oil, palm oil, lard and cocoa butter, were carried out using two analytical methods: matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and gas chromatography (GC), in an effort to validate the application of MALDI-TOFMS in quantitative fatty acid analysis. For the GC analysis, transmethylated products were used, whereas, for the MALDI-TOF analysis, saponified products were used. Under MALDI-TOF conditions, the acids were detected as sodiated sodium carboxylates [RCOONa + Na](+) consistent with the mode of ionization that was previously reported. Thus, the MALDI-TOF mass spectrum of saponified coconut oil showed the presence of sodiated sodium salts of caprylic acid (7.5 +/- 0.67, m/z 189), capric acid (6.9 +/- 0.83, m/z 217), lauric acid (47.8 +/- 0.67, m/z 245), myristic acid (20.4 +/- 0.51, m/z 273), palmitic acid (9.8 +/- 0.47, m/z 301), linoleic acid (0.9 +/- 0.07, m/z 325), oleic acid (4.8 +/- 0.42, m/z 327) and stearic acid (2.0 +/- 0.13, m/z 329). Saponified palm kernel oil had a fatty acid profile that included caprylic acid (3.5 +/- 0.59), capric acid (4.7 +/- 0.82), lauric acid (58.6 +/- 2.3), myristic acid (20.9 +/- 1.5), palmitic acid (7.2 +/- 1.1), oleic acid (3.8 +/- 0.62) and stearic acid (1.2 +/- 0.15). Saponified palm oil gave myristic acid (0.83 +/- 0.18), palmitic acid (55.8 +/- 1.7), linoleic acid (4.2 +/- 0.51), oleic acid (34.5 +/- 1.5), stearic acid (3.8 +/- 0.26) and arachidic acid (0.80 +/- 0.22). Saponified lard showed the presence of myristic acid (1.5 +/- 0.24), palmitic acid (28.9 +/- 1.3), linoleic acid (13.7 +/- 0.67), oleic acid (38.7 +/- 1.4), stearic acid (12.8 +/- 0.64) and arachidic acid (2.4 +/- 0.35). Finally, for saponified cocoa butter, the fatty acid distribution was: palmitic acid (32.3 +/- 1.0), linoleic acid (2.6 +/- 0.35), oleic acid (34.9 +/- 1.7) and stearic acid (30.3 +/- 1.6). Quantitative gas chromatographic analysis of the corresponding methyl esters from these triacylglycerol products yielded data that were mostly in agreement with the MALDI-TOFMS data. The MALDI-TOF experiment, however, proved to be superior to the GC experiment, particularly with regard to baseline resolution of unsaturated acids. Furthermore, the ability of MALDI-TOFMS to detect low concentrations of fatty acids rendered it more sensitive than the GC methodology.     

Temperature-sensitive nonionic vesicles prepared from Span 80 (sorbitan monooleate)

Different types of nonionic vesicles were prepared from commercial Span 80 (also called sorbitan monooleate), as an inexpensive, biocompatible alternative to conventional phospholipid-based vesicles (liposomes). The vesicles were characterized by different techniques and comparison was made with vesicles formed from POPC (1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine) or DOPC (1,2-dioleoyl- sn-glycero-3-phosphocholine). Dynamic light scattering measurements, electron microscopy analyses, and two types of fusion assays indicate that Span 80 vesicles are stable for at least 7 days at 4 or 25 degrees C, while storage at 42 degrees C causes irreversible vesicle fusion. This indicates that Span 80 vesicles are thermoresponsive with vesicle fusion occurring at elevated temperature. This property may be related to headgroup dehydration and is certainly not directly linked to the phase transition temperature (Tm) of the vesicles, since the Tm is below -30 degrees C, as determined by differential scanning calorimetry (DSC). The measured Tm value for Span 80 vesicles is lower than in the case of DOPC or POPC, correlating with a higher fluidity of Span 80 vesicles as compared to POPC or DOPC vesicles, as determined with DPH (1,6-diphenyl-1,3,5-hexatriene) as fluorescent membrane probe. High fluidity correlates with increased leakage of entrapped water-soluble dye molecules. Addition of cholesterol and soybean phosphatidylcholine lowers the extent of leakage, allowing a tuning of the bilayer permeability.     

Stabilization of phospholipid multilayers at the air-water interface by compression beyond the collapse: a BAM, PM-IRRAS, and molecular dynamics study

Compression beyond the collapse of phospholipid monolayers on a modified Langmuir trough has revealed the formation of stable multilayers at the air-water interface. Those systems are relevant new models for studying the properties of biological membranes and for understanding the nature of interactions between membranes and peptides or proteins. The collapse of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-di[cis-9-octadecenoyl]-sn-glycero-3-[phospho-l-serine] (DOPS), 1,2-di[cis-9-octadecenoyl]-sn-glycero-3-phosphocholine (DOPC), and 1,2-di[cis-9-octadecenoyl]-sn-glycero-3-[phospho-1-rac-glycerol] (DOPG) monolayers has been investigated by isotherm measurements, Brewster angle microscopy (BAM), and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). In the cases of DMPC and DOPS, the collapse of the monolayers revealed the formation of bilayer and trilayer structures, respectively. The DMPC bilayer stability has been analyzed also by a molecular dynamics study. The collapse of the DOPC and DOPG systems shows a different behavior, and the Brewster angle microscopy reveals the formation of luminous bundles, which can be interpreted as diving multilayers in the subphase.     

Spontaneous Membrane Generation and Extension in a Dipeptide Single Crystal and Phospholipid Mixed System

Self‐reproduction is one of the most important characteristics of lipid vesicles for origin of life research. Most vesicle self‐reproduction systems are based on fatty acid vesicles and spontaneous phospholipid vesicle production is difficult owing to the relatively high stability of these vesicles. Now, spontaneous phospholipid vesicle generation and extension in a dipeptide/phospholipid system is demonstrated. Dissolution of the dipeptide crystal provides both the driving force and phospholipid constituents for vesicle generation and extension. This study provides a new system to enhance the understanding of vesicle self‐reproduction mechanisms.     

Probing lipid vesicles by bimolecular association and dissociation trajectories of single molecules

Vesicles prepared by DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) and SOPC (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) lipid molecules having sizes smaller than the diffraction-limited focused laser beam have been used to confine single molecules in the laser focus. The confinement of single molecules in a volume smaller than the focused laser beam leads to a Gaussian distribution of single molecule fluorescence intensity. The interactions of single Nile Red molecules with DMPC and SOPC lipid bilayers were studied by single molecule fluorescence confocal microscopy. Nile Red molecules were observed to associate with and dissociate from individual DMPC and SOPC vesicles adsorbed on a glass surface, generating on-and-off fluctuations in a fluorescence signal representing a very low noise two-state trajectory. Off-time statistics were used to investigate the mean radius of the vesicles and the size distribution functions. The means of the on-time distributions of Nile Red in DMPC and SOPC vesicles were significantly different. The association and dissociation reactions of single Nile Red molecules with a vesicle have been studied. Features of the bimolecular interaction between the probe Nile Red and the vesicle were evaluated from the uncorrelated mean on-time and vesicle radius distributions, and the linear Nile Red concentration dependence of the mean off-time. Nile Red is shown to be a useful probe of the structural fluctuations and heterogeneity of these membrane structures, and it is a useful model with which to directly study a diffusion-influenced reversible bimolecular reaction.     

Determination of the fatty acid composition of saponified vegetable oils using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A method using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) for the determination of the fatty acid composition of vegetable oils is described and illustrated with the analysis of palm kernel oil, palm oil, olive oil, canola oil, soybean oil, vernonia oil, and castor oil. Solutions of the saponified oils, mixed with the matrix, meso-tetrakis(pentafluorophenyl)porphyrin, provided reproducible MALDI-TOF spectra in which the ions were dominated by sodiated sodium carboxylates [RCOONa + Na]+. Thus, palm kernel oil was found to contain capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid. Palm oil had a fatty acid profile including palmitic, linoleic, oleic, and stearic. The relative percentages of the fatty acids in olive oil were palmitoleic (1.2 +/- 0.5), palmitic (10.9 +/- 0.8), linoleic (0.6 +/- 0.1), linoleic (16.5 +/- 0.8), and oleic (70.5 +/- 1.2). For soybean oil, the relative percentages were: palmitoleic (0.4 +/- 0.4), palmitic (6.0 +/- 1.3), linolenic (14.5 +/- 1.8), linoleic (50.1 +/- 4.0), oleic (26.1 +/- 1.2), and stearic (2.2 +/- 0.7). This method was also applied to the analysis of two commercial soap formulations. The first soap gave a fatty acid profile that included: lauric (19.4% +/- 0.8), myristic (9.6% +/- 0.5), palmitoleic (1.9% +/- 0.3), palmitic (16.3% +/- 0.9), linoleic (5.6% +/- 0.4), oleic (37.1% +/- 0.8), and stearic (10.1% +/- 0.7) and that of the second soap was: lauric (9.3% +/- 0.3), myristic (3.8% +/- 0.5), palmitoleic (3.1% +/- 0.8), palmitic (19.4% +/- 0.8), linoleic (4.9% +/- 0.7), oleic (49.5% +/- 1.1), and stearic (10.0% +/- 0.9). The MALDI-TOFMS method described in this communication is simpler and less time-consuming than the established transesterification method that is coupled with analysis by gas chromatography/mass spectrometry (GC/MS). The new method could be used routinely to determine the qualitative fatty acid composition of vegetable oils, and, when fully validated by comparison with standard analytical methodologies, should provide a relatively fast quantitative measurement of fatty acid mixtures and/or soap formulations that contain saturated and unsaturated hydrocarbon moieties.     

Synthesis and characterization of magnetic Co nanoparticles: A comparison study of three different capping surfactants

This paper compares the performance of three long-chain acids—oleic and elaidic (both olefinic) and stearic (aliphatic)—as a capping agent in the synthesis of magnetic Co nanoparticles. The particles were formed through thermal decomposition of dicobalt octacarbonyl in toluene in the presence of the long-chain acid, and characterized by TEM, high-resolution TEM, and SQUID measurements. Infrared spectra revealed that some of the added olefinic acid was transformed from cis- to trans-configuration (for oleic acid) or from trans- to cis- (for elaidic acid) to facilitate the formation of a densely packed monolayer on the surface of Co nanoparticles. As compared to aliphatic acids, olefinic acids are advantageous for dense packing on small particles with high surface curvatures due to a bent shape of the cis-isomer. The presence of an olefinic acid is able to control particle growth, stabilize the colloidal suspension, and prevent the final product from oxidation by air. Our results indicate that oleic acid, elaidic acid, and a mixture of oleic/stearic acids or elaidic/stearic acids have roughly the same performance in serving as a capping agent for the synthesis of Co nanoparticles with a spherical shape and narrow size distribution.     

Impact of PAMAM G2 and G6 dendrimers on bovine serum albumin (fatty acids free and loaded with different fatty acids)

Dendrimers are a new class of nanotechnological polymers suitable for drug targeting, microarray systems or detoxication. The present study is devoted to a detailed analysis of binding between PAMAM dendrimers and bovine serum albumin (fatty acid free or loaded with oleic, linoleic, oleic+linoleic or oleic+linoleic+arachodonic acids) by measuring zeta-potential, fluorescence quenching, fluorescence anisotropy and electron paramagnetic resonance. Addition of PAMAM G2 and G6 dendrimers to protein solutions resulted in attachment to the protein molecule. The PAMAM dendrimers also competed with BSA for fatty acids if two or three fatty acids were loaded per protein. This can lead to the extraction of fatty acids from BSA to the PAMAM dendrimer.     

Vesicles from docosahexaenoic acid

In dilute aqueous solution and at room temperature, cis-4,7,10,13,16,19-docosahexaenoic acid (DHA) self-assembles into vesicles (self-closed bilayers), if the molar ratio of the neutral form of DHA to anionic DHA is kept between 1:1 and 1:3 (corresponding to a bulk pH between 8.5 and 9.2 for a system with 10 mM DHA). By using polycarbonate membrane extrusion, stable unilamellar DHA vesicles with an average diameter of 80 nm can be prepared at pH 8.8. Cryo-transmission electron microscopy indicates that the width of the DHA bilayers in the vesicles is clearly below twice the length of an extended DHA molecule, indicating a high conformational flexibility of DHA within the vesicle bilayer. These DHA bilayers have a similar thickness like bilayers of vesicles prepared at pH 8.5 from oleic acid (cis-9-octadecenoic acid). Using calcein as fluorescent reference compound, it is shown that water-soluble molecules can be encapsulated inside DHA vesicles which may make them interesting for medical or food applications.     

Surface thermodynamic properties of monolayers versus reconstitution of a membrane protein in solid-supported bilayers

Atomic force microscopy (AFM) was used to study the influence of a membrane protein, lactose permease of Escherichia coli (LacY), on the surface spreading behavior and the features of self-assembled phospholipids bilayers on mica. The miscibility of phospholipids used, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), was investigated by surface pressure area isotherm measurements at the air-water interface. A composition with an equimolar proportion of POPC and DMPC was used to form the liposomes. Surface layers formed with DMPC:POPC (0.5:0.5, mol/mol) or LacY reconstituted in proteoliposomes with the same phospholipid composition were imaged by using AFM. When lactose permease was reconstituted in DMPC:POPC (0.5:0.5, mol/mol), self-assembled structures that remained firmly adsorbed onto the mica surface were observed. These sheets had an irregular shape and their upper layer was more corrugated than that obtained for the phospholipid matrix.     

油松籽油脂的提取及其脂肪酸组成与含量的评价

采用索氏提取法提取油松籽中的油脂,得油率为42.9%;对油脂进行甲酯化处理后用气相色谱-质谱联用仪检测其中的脂肪酸组成及含量。实验结果表明,油松籽油中含有7种脂肪酸,分别为肉豆蔻酸10.38%、硬脂酸3.05%、油酸21.98%、亚油酸(13,16-十八碳二烯酸)3.53%、亚油酸(9,12-十八碳二烯酸)38.38%、亚麻酸20.06%和二十碳三烯酸2.62%,其中饱和脂肪酸含量为13%,不饱和脂肪酸含量为87%。     

AFM studies of solid-supported lipid bilayers formed at a Au(111) electrode surface using vesicle fusion and a combination of Langmuir-Blodgett and Langmuir-Schaefer techniques

Atomic force microscopy (AFM) has been used to characterize the formation of a phospholipid bilayer composed of 1,2-dimyristyl-sn-glycero-3-phosphocholine (DMPC) at a Au(111) electrode surface. The bilayer was formed by one of two methods: fusion of lamellar vesicles or by the combination of Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) deposition. Results indicate that phospholipid vesicles rapidly adsorb and fuse to form a film at the electrode surface. The resulting film undergoes a very slow structural transformation until a characteristic corrugated phase is formed. Force-distance curve measurements reveal that the thickness of the corrugated phase is consistent with the thickness of a bilayer lipid membrane. The formation of the corrugated phase may be explained by considering the elastic properties of the film and taking into account spontaneous curvature induced by the asymmetric environment of the bilayer, in which one side faces the gold substrate and the other side faces the solution. The effect of temperature and electrode potential on the stability of the corrugated phase has also been described.     

Directed growth of pure phosphatidylcholine nanotubes in microfluidic channels

The morphology of self-assembled phospholipid membranes (e.g., micelles, vesicles, rods, tubes, etc.) depends on the method of formation, secondary manipulation, temperature, and storage conditions. In this contribution, microfluidic systems are used to create pure phosphatidylcholine (PC) micro- and nanotubes with unprecedented lengths. Tubes up to several centimeters in length and aligned with the long axis of the microchannel were created from spots of dry films of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). These high aspect ratio structures, which, to our knowledge, represent the first examples of extended tubes formed from pure PC lipids, were examined by fluorescence microscopy, electron and optical microscopy, and optical manipulation tools (i.e., a laser trap and laser scalpel) to characterize structure and stability. In particular, the tubular structure was confirmed by observation of fluorescent dyes that were sequestered within the aqueous cavity or within the phospholipid tube. Compared to other phospholipid tubes, the tubes formed from PC lipids in microfluidic channels show high mechanical stability and rigidity that depend on tube size, age, and storage conditions.     

Compositions of the seed oil of the Borago officinalis from Iran

In order to investigate the composition of borage (Borago officinalis L.) seed oil, this research was performed under the field conditions at Shahriyar and Garmsar zones, Iran during the 2012 planting year. The oil yield of borage was 31.46% and 33.7% at Shahriyar and Garmsar zone, respectively, and nine and eight fatty acids were identified in the seed oil of borage at Shahriyar and Garmsar, respectively – palmitic, linoleic, stearic and γ-linolenic acids were dominant in the seed oil of borage from both zones. Unsaturated fatty acid content was more than the saturated fatty acids in both zones. The ratio of linoleic acid and α-linolenic acid in the borage cultivated at Shahriyar and Garmsar zones was 2.13 and 2.29. The fatty acid profile of Garmsar borage, oleic and oleic/linoleic acid ratio, increased. Locations with different ecological conditions resulted in changes in both seed oil content and fatty acid profile of borage.     

Influence of surfactant and lipid chain length on the solubilisation of phosphatidylcholine vesicles by micelles comprised of polyoxyethylene sorbitan monoesters

Photon correlation spectroscopy and freeze-fracture electron microscopy have been used to determine the ability of a range of micelle-forming, polyoxyethylene (20) sorbitan monoesters (Tweens) to solubilise vesicles prepared from phosphatidylcholines of different acyl chain lengths and degrees of saturation with a view to rationalising (in terms of their membrane toxicity) which of the micelle-forming surfactants to use as drug delivery vehicles. The phosphatidylcholines used were dimyristoyl-, dipalmitoyl-, distearoyl- and dioleoylphosphatidylcholine (DMPC, DPPC, DSPC and DOPC, respectively) while the nonionic polyoxyethylene sorbitan monoesters studied were polyoxyethylene (20) sorbitan monolaurate (Tween 20), a 9:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 40), a 1:1 weight ratio mixture of polyoxyethylene (20) sorbitan monopalmitate and monostearate (Tween 60), and polyoxyethylene (20) sorbitan monooleate (Tween 80). The ability of the Tween micelles to solubilise phospholipid vesicles was found to depend both upon the length of the surfactant acyl chain and the length of the acyl chains of the phospholipid comprising the vesicle. Vesicles composed of long saturated diacyl chain phospholipids, namely DSPC and DPPC, were the most resistant to solubilisation, while those prepared from the shorter acyl chained DMPC were more readily solubilised. In terms of their solubilisation behaviour, vesicles made from phospholipids containing long, unsaturated acyl chains, namely DOPC behaved more akin to those vesicles prepared from DMPC. None of the Tween surfactants were effective at solubilising vesicles prepared from DPPC or DSPC. In contrast, there were clear differences in the ability of the various surfactants to solubilise vesicles prepared from DMPC and DOPC, in that micelles formed from Tween 20 were the most effective solubilising agent while those formed by Tween 60 were the least effective. As a consequence of these observations it was considered that Tween 60 was the surfactant least likely to cause membrane damage in vivo and, therefore, is the most suitable surfactant for use as a micellar drug delivery vehicle.