Phospholipid hydrolysis in a pharmaceutical emulsion assessed by physicochemical parameters and a new analytical method

The Chemical Reactivity of Membrane Lipids

It is well-known that aqueous dispersions of phospholipids spontaneously assemble into bilayer structures. These structures have numerous applications across chemistry and materials science and form the fundamental structural unit of the biological membrane. The particular environment of the lipid bilayer, with a water-poor low dielectric core surrounded by a more polar and better hydrated interfacial region, gives the membrane particular biophysical and physicochemical properties and presents a unique environment for chemical reactions to occur. Many different types of molecule spanning a range of sizes, from dissolved gases through small organics to proteins, are able to interact with membranes and promote chemical changes to lipids that subsequently affect the physicochemical properties of the bilayer. This Review describes the chemical reactivity exhibited by lipids in their membrane form, with an emphasis on conditions where the lipids are well hydrated in the form of bilayers. Key topics include the following: lytic reactions of glyceryl esters, including hydrolysis, aminolysis, and transesterification; oxidation reactions of alkenes in unsaturated fatty acids and sterols, including autoxidation and oxidation by singlet oxygen; reactivity of headgroups, particularly with reactive carbonyl species; and E/Z isomerization of alkenes. The consequences of reactivity for biological activity and biophysical properties are also discussed.

Surfactants for stabilization of dermal emulsions and their skin compatibility under UVA irradiation: Diacyl phospholipids and polysorbate 80 result in high viability rates of primary human skin cells

Phospholipids are versatile formulation compounds with high biocompatibility. However, no data on their effect on skin in combination with UVA radiation exist. Thus, it was the aim of this work to (i) develop o/w nanoemulsions (NEs) differing in surfactant type and to investigate their physicochemical stability at different storage temperatures, (ii) establish a standardized protocol for in vitro phototoxicity testing using primary human skin cells and (iii) investigate the phototoxicity of amphoteric phospholipids (S45, S75, E80, S100, LPC80), sodium lauryl ether sulfate (SLES) and polysorbate 80 (PS80). Satisfying systems were developed with all surfactants except S100 due to low zeta potential (-21.4 mV ± 4.69). SLES and PS80-type NEs showed the highest stability after eight weeks; temperature-dependent variations in storage stability were most noticeable for phospholipid surfactants. For phospholipid-based NEs, higher phosphatidylcholine content led to unstable formulations. Phototoxicity assays with primary skin fibroblasts confirmed the lack of UVA-related phototoxicity but revealed cytotoxic effects of LPC80 and SLES, resulting in cell viability as low as 2.7 % ±0.78 and 1.9 % ±1.57 compared to the control. Our findings suggest that surfactants S45, S75 and PS80 are the most promising candidates for skin-friendly emulsifiers in sensitive applications involving exposure to UV light.

Ultrasonication for production of nanoliposomes with encapsulated soy protein concentrate hydrolysate: Process optimization, vesicle characteristics and in vitro digestion

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Soy protein concentrate hydrolysate (SPH) has been utilized as a mixture of antioxidant peptides.

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Novel ultrasonicated hydrolysate-loaded nanoliposome carriers are developed.

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Encapsulated SPH influenced positively the liposomal nanocarriers' stability.

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Tailored release properties of SPH are shown by in vitro gastrointestinal digestion study.

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Unilamelarity and sphericity of nanoliposomes have been confirmed by TEM and SEM.

This study presents the state-of-art research about the assembly of soy proteins in nanocarriers, liposomes, and its design includes different physicochemical strategies and approaches: two-step enzymatic hydrolysis of soy concentrate, hydrolysate encapsulation by using phospholipids and cholesterol, and application of ultrasonication. Achieved results revealed that ultrasonication, together with cholesterol addition into phospholipid layers, improved the stability of nanoliposomes, and a maximum EE value of 60.5 % was obtained. Average size of peptide-loaded nanoliposomes was found to be from 191.1 to 286.7 nm, with a ζ potential of −25.5 to −34.6 mV, and a polydispersity index of 0.250–0.390. Ultrasound-assisted encapsulation process did not lead to a decrease in the antioxidant activity of the trapped peptides. FTIR has indicated an effective hydrophobic interaction between phosphatidylcholine and hydrolysate peptides. TEM and SEM have confirmed the spherical nanocarrier structure and unilamelarity. Prolonged gastrointestinal release and stability of peptides have been enabled by liposome nanocarriers.

A geniposide-phospholipid complex ameliorates posthyperuricemia chronic kidney disease induced by inflammatory reactions and oxidative stress

Hyperuricemia is a common metabolic disease and is one of the factors that could induce chronic kidney disease (CKD). Geniposide (GEN) is a typical natural iridoid glucoside compound with a series of biological activities, but the poor bioavailability of GEN limits its clinical application. In this context, the pharmacological activity of the geniposide-phospholipid complex (GEN-PLC) in ameliorating posthyperuricemia CKD was evaluated by in vitro and in vivo experiments in this study. In vitro cell experiments showed that GEN-PLC treatment markedly decreased inflammatory cytokine levels and reactive oxygen species levels compared with those of GEN in uric acid-treated HKC cells. In vivo research results confirmed that a high concentration of uric acid could cause CKD by increasing inflammatory cytokines and reactive oxygen species in hyperuricemic mice. At the same time, GEN-PLC could regulate the PI3K/AKT/NF-κB and Keap1/Nrf2/HO-1 signaling pathways to effectively inhibit the inflammatory response and oxidative stress, thereby ameliorating posthyperuricemia CKD, and the therapeutic effect was better than that of GEN. In addition, the preparation technology of GEN-PLC was optimized, and the physiochemical analysis explained the intermolecular interactions of the two components. Based on the research results, GEN-PLC could enhance the bioavailability of GEN and become a promising candidate for clinical drug development.

A Reliable HPLC-ELSD Method for Determination of Cholesterol, Phosphatidylcholine, Lysophosphatidylcholine Content and the Stability of a Liposomal Formulation

Background:

Liposomes continue to play an important role in drug delivery research due to their ability to improve transport and targeting of a wide range of active molecules. Analysis of liposomal components is a key point in the characterization and evaluation of formulation stability. The aim of this work was to develop and validate an HPLC-ELSD method for the characterization and quality control of liposomes.

Methods:

HPLC-ELSD method was validated by assessing selectivity, linearity, precision, accuracy, limit of detection and quantitation. The mobile phase consisted of a 0.1% (v/v) of trifluoroacetic acid (TFA) and methanol in gradient elution. Initial rate was 20:80 (0.1% TFA: methanol), with a ramp reaching 100% methanol. HPLC-MS/MS was used to confirm the presence of the fatty acid mixture in the analyzed lipids, as well as sub-products generated under pre-determined conditions in the stability study.

Results:

A HPLC-ELSD method has been developed to detect and measure cholesterol, phosphatidylcholine and lysophosphatidylcholine. High specificity, sensitivity and linearity within the predetermined range for all the compounds analyzed (R2>0.99) were obtained. Accuracy and precision results for all the compounds were within the acceptance limit of ≤5% and 90-110%, respectively. Mass spectrometry results showed complementary information about the phospholipid composition to evaluate the degree of degradation of liposomes over different storage conditions.

Conclusion:

The method was successfully applied as a quality control tool for the analysis of a wide range of lipids, present in liposomal formulations. HPLC-MS/MS was used to ensure complete elucidation of the lipid components and the detected lyso-forms.

Simultaneous Quantification of DPPG, DEPC and Cholesterol in Propofol Liposome by HPLC-ELSD Using Alkaline Hydrolysis

A high-performance liquid chromatography method with evaporative light-scattering detection (ELSD) was performed for simultaneous determination of dipalmitoyl phosphatidylglycerol (DPPG), dierucoyl phosphatidylcholine (DEPC) and cholesterol in propofol liposome by the pretreatment of alkaline hydrolysis (temperature, concentration of KOH anhydrous ethanol solution and reaction time were 90°C, 1 mol · L-1 and 10 min, respectively). The analysis was carried out on an Agilent TC-C18 column (4.6 mm × 250 mm, 5 μm) with isocratic elution of methanol and 0.1% acetic acid aqueous solution (95:5, v/v) at a flow rate of 1.0 mL · min-1. The column temperature was 30°C. The drift tube temperature of the ELSD system was set at 30°C, and the pressure of carrier gas was 350 KPa. The regression equation revealed a good linear relationship (r = 0.9990-0.9993) during the test ranges. The RSD of stability and repeatability (n = 6) was found to be less than 1.96 and 1.46%, respectively. The average recoveries ranged from 97.90 to 101.00%. The proposed method was validated and showed good precision, stability, repeatability and recovery, which indicated that the method could be readily utilized as a quality evaluation method for the determination of DPPG, DEPC and cholesterol in propofol liposome.

Liposomes Containing Nickel-Bis(dithiolene) Complexes for Photothermal Theranostics

New thermosensitive liposomes with a phase transition at 42 °C, containing nickel-bis(dithiolene) complexes as efficient and stable photothermal agents, have been formulated and characterized. These liposomes are highly stable and keep their contents at 37 °C for more than 30 days. On the contrary, the mild hyperthermia generated by the nickel-bis(dithiolene) complex under 940 nm NIR irradiation allows for the fine controlled release of the liposome contents, making such liposomes highly suitable for on-demand drug delivery in the human body under NIR laser irradiation. These liposomes can also be directly used, as shown here, as nanoagents for photothermal therapy. In fact, strong cell death can be generated under laser irradiation in the presence of these photothermally active nanocargos containing less than 10% w/w of metal complex. We also demonstrate, for the first time, that nickel-bis(dithiolene) complexes are good photoacoustic agents, generating easily detectable ultrasonic signals directly proportional to the concentration of complexes and the used laser power.

Development and validation of a novel UPLC-ELSD method for the assessment of lipid composition of nanomedicine formulation

Lipid nanocarriers incorporating glycerides, polyethylene glycol (PEG)-stearates and phospholipids have attracted great attention for in vivo diagnostic, in vivo imaging, activated or non-activated targeted drug delivery. For quality control purposes, the development of appropriate methods for the quantification of their lipid components is needed. In the present study, we developed an analytical method for lipid quantification in formulated nanoparticles. PEG-stearates and glycerides were analyzed in a single run by RP-UPLC-ELSD using a two-step gradient elution program, while the analysis of phospholipids was accomplished by HILIC-UPLC-ELSD after isolation using an SPE silica column. Using both isolated compounds and commercial lipid standards, calibration curves were produced using second-order polynomials to attain the quantitative evaluation of each lipid excipient. Relative standard deviation of all analytes was between 0.9% and 5.3% for intra-day precision and recovery ranged from 83.5% to 112.2%. The presented method was successfully implemented to study the manufacturing process and stability of the formulated lipid excipients during long-term storage and accelerated conditions. The formulation lipid yield was determined and found equal to 82.5%.

Microgel Particles at Interfaces: Phenomena, Principles, and Opportunities in Food Sciences

The use of soft microgel particles for stabilizing emulsions has captured increasing attention across a wide range of disciplines in the past decades. Being soft, the nanoparticles, which are spherical in solution, undergo a structure change when adsorbed at the oil-water interface. This morphology change leads to the special dynamic properties of interface layers and packing structures, which then alter the interfacial tension and rheological properties of the interface. In addition, emulsions stabilized by these particles, known as Pickering emulsions, can be triggered by changing a variety of environmental conditions, which is especially desirable in industrial applications such as oil transportation processes and biphasic catalysis, where the emulsions can be stabilized and destabilized on demand. Although many studies of the behavior of soft microgel nanoparticles at interfaces have been reported, there are still many challenges in gaining a full understanding of the structure, dynamics, and effective interactions between microgels at the interface. In this Feature Article, we address some of the most important findings and problems in the field. They include the adsorption kinetics of soft microgel particles, particle conformation at the interface, pH and thermal responsiveness, and the interfacial rheological properties of soft-particle-occupied interfaces. We also discuss some potential benefits of using emulsions stabilized by soft particles for food applications as an alternative to conventional surfactant-based systems. We hope to encourage further investigation of these problems, which would be very beneficial to extending this knowledge to all other related soft matter systems.

Sonochemistry-Assembled Stimuli-Responsive Polymer Microcapsules for Drug Delivery

Stimuli-responsive polymer microcapsules (PMs) fabricated by the sonochemical method have emerged for developing useful drug delivery systems, and the latest developments are mainly focusing on the synthetic strategies and properties such as structure, size, stability, loading capacity, drug delivery, and release. There, the primary attribution of sonochemistry is to offer a simple and practical approach for the preparation of PMs. Structure, size, stability, and properties of PMs are designed mainly according to synthetic materials, implementation schemes, or specific demands. Numerous functionalities of PMs based on different stimuli are demonstrated: targeting motion in a magnetic field or adhering to the living cells with sensitive sites through molecular recognition, and stimuli-triggered release including enzymatic catalysis, chemical reaction as well as physical or mechanical process. The current review discusses the basic principles and mechanisms of stimuli effects, and describes the progress in the application such as targeted drug systems and controlled drug systems, and also gives an outlook on the future challenges and opportunities for drug delivery and theranostics.

Improved oral bioavailability and therapeutic efficacy of erlotinib through molecular complexation with phospholipid

The current study was aimed to prepare a molecular complex of erlotinib (ERL) with phospholipid (PC) for enhancement of solubility and thus bioavailability, therapeutic efficacy and reducing the toxicity of erlotinib. Phospholipid complex of drug was prepared by solvent evaporation method and characterized by differential scanning calorimetry (DSC), Fourier transform infra-red spectroscopy (FT-IR), proton and phosphorus nuclear magnetic resonance spectroscopy (1H NMR and 31P NMR), powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which all explained the interactions of two components, validating the complexation phenomenon. In silico study also supported the phase change and molecular interactions for the establishment of ERL-PC. Spherical shaped nanostructures with 183.37±28.61nm size, -19.52±6.94mV potential and 28.59±2.66% loading efficiency were formed following dispersion of ERL-PC in aqueous media. In vitro release study revealed the higher release of ERL-PC due to amorphization and solubilization of drug. Caco-2 cell uptake resulted in ∼2 fold higher uptake of ERL-PC than free drug. In vitro cell culture studies were performed using human pancreatic adenocarcinoma cell lines, which demonstrated the higher cytotoxicity and apoptosis in case of ERL-PC. In vivo pharmacokinetics also supported the in vitro observations and showed ∼1.7 fold higher bioavailability with ERL-PC than ERL. Finally, in vivo efficacy and toxicity studies explained the superiority of ERL-PC over the free drug. Based on the results, phospholipid complex appears to be a promising tool to enhance bioavailability, efficacy, cytotoxicity and safety of erlotinib.

A versatile, quantitative analytical method for pharmaceutical relevant lipids in drug delivery systems

Over the past few years, liposomal formulations as drug carrier systems have markedly advanced in pharmaceutical research and development. Therefore, analytical methods to characterize liposome-based formulations are required. One particular issue in liposome analysis is the imbalance of lipid ratios within the vesicle formulations and the detectability of degradation products such as lysophospholipids and fatty acids caused by hydrolysis, especially in low molar ranges. Here, a highly sensitive and selective reversed-phase high-performance liquid chromatography (rp-HPLC) method is described by the combination of an organic solvent/trifluoroacetic acid (TFA) triggered gradient and the application of an evaporative light scattering detector (ELSD). Gain setting adjustments of the ELSD were applied to obtain an optimal detection profile of the analyzed substances. This optimization provides simultaneous separation and quantification of 16 components, including different phosphatidylcholines, phosphatidylglycerols and their degradation products, as well as cholesterol. Parameters such as limit of detection (LOD) and limit of quantification (LOQ) were determined for each of the components and had ranges from 0.25-1.00mg/mL (LOD) and 0.50-2.50μg/mL (LOQ), respectively. The intra-day precision for all analytes is less than 3% (RSD) and inter-day precision is about 8%. The applicability of the method was verified by analyzing two different liposome formulations consisting of DSPC:DPPC:DSPG:Chol (35:35:20:10) and DSPC:DPPC:DSPG (38:38:24). For degradation studies, both formulations were stored at 4°C and at ambient temperature. Additionally, forced degradation experiments were performed to determine hydrolysis mass balances. A total recovery of 96-102% for phospholipid compounds was found. Analytical data revealed that the sensitivity, selectivity, accuracy, and resolution are appropriate for the detection and quantification of phospholipids and their hydrolysis products. These results as well as additional preliminary analyses of other relevant components used in liposomal formulations indicate that the developed method is suitable for the development, characterization, and stability testing of liposomal based biopharmaceuticals.

Anti-aging efficacy of topical formulations containing niosomes entrapped with rice bran bioactive compounds

CONTEXT

Rice [Oryza sativa L. (Gramineae)] bran is a rich source of phytochemicals. Its oil also contains several bioactive components that exhibit antioxidative properties such as ferulic acid (F), γ-oryzanol (O), and phytic acid (P) which can be a new source of cosmetic raw materials.

OBJECTIVE

To evaluate the anti-aging effects of the gel and cream containing niosomes entrapped with the rice bran bioactive compounds.

MATERIALS AND METHODS

The semi-purified rice bran extracts containing F, O, and P which indicated the growth stimulation of human fibroblasts and the inhibition of MMP-2 by sulforhodamine B and gelatin zymography, respectively, were entrapped in niosomes by supercritical carbon dioxide fluid (scCO(2)) and incorporated in gel and cream formulations. The skin hydration, elasticity, thickness and roughness, and pigmentation in human volunteers after treated with these gel and creams were investigated by corneometer, cutometer, visiometer, and mexameter, respectively.

RESULTS

Gel and cream containing the semi-purified rice bran extracts entrapped in niosomes gave no sign of erythema and edema detected within 72 h on the shaved rabbit skin by the closed patch test investigated by mexameter and visual observation, respectively. These formulations also demonstrated higher hydration enhancement and improvement of skin lightening, thickness, roughness, and elasticity on the skin of 30 human volunteers within the 28-day treatment not more than 9, 27, 7, 3, and 3 times, respectively.

DISCUSSION AND CONCLUSIONS

The formulations containing niosomes entrapped with the rice bran bioactive compounds gave superior clinical anti-aging activity which can be applied as a novel skin product.

A new method for the determination of biogenic amines in cheese by LC with evaporative light scattering detector

This paper presents a new LC method with evaporative light scattering detection (ELSD), for the separation and determination of the biogenic amines (histamine, spermidine, spermine, tyramine, putrescine and β-phenylethylamine) which are commonly present in cheese, as their presence and relative amounts give useful information about freshness, level of maturing, quality of storage and cheese authentication. The LC-ELSD method is validated by comparison of the results with those obtained through LC-UV determination, based on a pre-column dansyl chloride derivatisation step. The obtained data demonstrate that both methods can be interchangeably used for biogenic amines determination in cheese. The new LC-ELSD method shows good precision and permits to achieve, for standard solutions, limit of detection (LOD) values ranging from 1.4 to 3.6 mg L(-1) and limit of quantitation (LOQ) values ranging from 3.6 to 9.3 mg L(-1). The whole methodology, comprehensive of the homogenization-extraction process and LC-ELSD analysis, has been applied in the analysis of a typical Calabria (Southern Italy) POD cheese, known as Caciocavallo Silano. The most aboundant amine found was histamine, followed, in decreasing order, by tyramine, spermine, putrescine, β-phenylethylamine and spermidine, for a total amount of 127 mg kg(-1). This value does not represent a possible risk for consumer health, according to the toxicity levels reported in literature and regarded as acceptable.

Comparison of the depot effect and immunogenicity of liposomes based on dimethyldioctadecylammonium (DDA), 3β-[N-(N',N'-Dimethylaminoethane)carbomyl] cholesterol (DC-Chol), and 1,2-Dioleoyl-3-trimethylammonium propane (DOTAP): prolonged liposome retention mediates stronger Th1 responses

The immunostimulatory capacities of cationic liposomes are well-documented and are attributed both to inherent immunogenicity of the cationic lipid and more physical capacities such as the formation of antigen depots and antigen delivery. Very few studies have however been conducted comparing the immunostimulatory capacities of different cationic lipids. In the present study we therefore chose to investigate three of the most well-known cationic liposome-forming lipids as potential adjuvants for protein subunit vaccines. The ability of 3β-[N-(N',N'-dimethylaminoethane)carbomyl] cholesterol (DC-Chol), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), and dimethyldioctadecylammonium (DDA) liposomes incorporating immunomodulating trehalose dibehenate (TDB) to form an antigen depot at the site of injection (SOI) and to induce immunological recall responses against coadministered tuberculosis vaccine antigen Ag85B-ESAT-6 are reported. Furthermore, physical characterization of the liposomes is presented. Our results suggest that liposome composition plays an important role in vaccine retention at the SOI and the ability to enable the immune system to induce a vaccine specific recall response. While all three cationic liposomes facilitated increased antigen presentation by antigen presenting cells, the monocyte infiltration to the SOI and the production of IFN-γ upon antigen recall was markedly higher for DDA and DC-Chol based liposomes which exhibited a longer retention profile at the SOI. A long-term retention and slow release of liposome and vaccine antigen from the injection site hence appears to favor a stronger Th1 immune response.

Simple chromatographic method for simultaneous analyses of phosphatidylcholine, lysophosphatidylcholine, and free fatty acids

This study describes a simple chromatographic method for the simultaneous analyses of phosphatidylcholine (PC) and its hydrolytic degradation products: lysophosphatidylcholine (LPC) and free fatty acids (FFA). Quantitative determination of PC, LPC, and FFA is essential in order to assure safety and to accurately assess the shelf life of phospholipid-containing products. A single-run normal-phase high-performance liquid chromatography (HPLC) with evaporative light scattering detector has been developed. The method utilizes an Allsphere silica analytical column and a gradient elution with mobile phases consisting of chloroform: chloroform-methanol (70:30%, v/v) and chloroform-methanol-water-ammonia (45:45:9.5:0.5%, v/v/v/v). The method adequately resolves PC, LPC, and FFA within a run time of 25 min. The quantitative analysis of PC and LPC has been achieved with external standard method. The free fatty acids were analyzed as a group using linoleic acid as representative standard. Linear calibration curves were obtained for PC (1.64-16.3 μg, r(2) = 0.9991) and LPC (0.6-5.0 μg, r(2) = 0.9966), while a logarithmic calibration curve was obtained for linoleic acid (1.1-5.8 μg, r(2) = 0.9967). The detection and quantification limits of LPC and FFA were 0.04 and 0.1 μg, respectively. As a means of validating the applicability of the assay to pharmaceutical products, PC liposome was subjected to alkaline hydrolytic degradation. Quantitative HPLC analysis showed that 97% of the total mass balance for PC could be accounted for in liposome formulation. The overall results show that the HPLC method could be a useful tool for chromatographic analysis, stability studies, and formulation characterization of phospholipid-based pharmaceuticals.

Effect of ultrasound parameters for unilamellar liposome preparation

In this study, it was investigated the effects of ultrasound, namely power input, distance from ultrasound tip to base of reactor and treatment time, in the formation of liposomes. Results indicate a dependence on cavitation events that are a function of power input, and consequently dependent on the position of the probe within the reaction vessel and the wave behaviour. Short treatment times are required to achieve nanosized vesicles in anti-nodal (lambda/4; 19mm) reactor geometries. In this wave point the cavitation phenomenon is more pronounced when compared with the nodal point (lambda/2; 38mm). Therefore, the consideration of the above parameters is vital if dependable and repeatable results are to be achieved.

Incorporation of peptides in phospholipid aggregates using ultrasound

This study presents the highlights of ultrasonic effects on peptides incorporated on phospholipid aggregates (liposomes). These liposomes or vesicles are known as transport agents in skin drug delivery and for hair treatment. They might be a good model to deliver larger peptides into hair to restore fibre strength after hair coloration, modelling, permanent wave and/or straightening. The preparation of liposomes 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) with peptides (LLLLK LLLLK LLLLK LLLLK; LLLLL LCLCL LLKAK AK) was made by the thin film hydration method. The LUVs (uni-lamellar vesicles) were obtained by sonication, applying different experimental conditions, such as depth (mm) and power intensity (%). Photon-correlation spectroscopy (PCS) and electronic microscopy (EM) results confirmed that the incorporation of these peptides, with different sequence of amino acids, presented differences on the diameter, zeta-potential of membrane surface and shape of liposomes. The liposomes that included peptide LLLLK LLLLK LLLLK LLLLK present an increased in zeta-potential values after using ultrasound and an "amorphous" aspect. Conversely, the liposomes that incorporated the peptide LLLLL LCLCL LLKAK AK presented a define shape (rod shape) and the potential surface of liposome did not change significantly by the use of ultrasound.

Comparison between charged aerosol detection and light scattering detection for the analysis of Leishmania membrane phospholipids

The performance of charged aerosol detection (CAD) was compared to evaporative light scattering detection (ELSD) for the analysis of Leishmania membrane phospholipid (PL) classes by NP-HPLC. In both methods, a PVA-Sil column was used for the determination of the major Leishmania membrane PLs, phosphatidic acid, phosphatidylglycerol, cardiolipin, phosphatidylinositol, phosphatidylethathanolamine, phosphatidylserine, lysophosphatidylethathanolamine, phosphatidylcholine, sphingomyelin and lysophosphatidylcholine in the same analysis. Although the response of both detection methods can be fitted to a power function, CAD response can also be described by a linear model with determination coefficients (R(2)) ranging from 0.993 to 0.998 for an injected mass of 30 ng to 20.00 microg. CAD appeared to be directly proportional when a restricted range was used and it was found to be more sensitive at lowest mass range than ELSD. With HPLC-ELSD the limits of detection (LODs) were between 71 and 1195 ng and the limits of quantification (LOQs) were between 215 and 3622 ng. With HPLC-CAD, the LODs were between 15 and 249 ng whereas the limits of quantification (LOQs) were between 45 and 707 ng. The accuracy of the methods ranged from 62.8 to 115.8% and from 58.4 to 110.5% for ELSD and CAD, respectively. The HPLC-CAD method is suitable to assess the influence of miltefosine on the composition of Leishmania membrane phospholipids.

Influence of preparation conditions and heat treatment on the properties of supercooled smectic cholesteryl myristate nanoparticles

Colloidal dispersions of cholesterol esters in the supercooled smectic state are under investigation as a novel drug carrier system in particular with respect to parenteral application. In the present study, suitable conditions for the homogenization of cholesteryl myristate dispersions stabilized with a phospholipid/bile salt blend were evaluated. For effective particle size reduction homogenization with high pressure and at temperatures above the melting temperature of the cholesterol ester (isotropic melt) is necessary. Homogenization at lower temperature where the matrix lipid is in the smectic state is less effective even when applying the highest homogenization pressure possible but still leads to dispersions with particles in the colloidal size range. Since sterility is required for parenteral medications and is usually achieved by autoclaving for aqueous systems, the physical and chemical stability of cholesteryl myristate nanoparticles stabilized with different surface active agents during heat treatment was investigated as well. The dispersions were characterized by particle size and zeta potential measurements, differential scanning calorimetry (DSC) and high performance thin layer chromatography (HPTLC). The results indicate that cholesteryl myristate nanoparticles stabilized with phospholipid/sodium glycocholate, polyvinyl alcohol, poloxamer and poloxamine can be sterilized by autoclaving. Compared to cholesterol ester free dispersions of phospholipids, the phospholipid seems to be more stable against hydrolysis during prolonged heat treatment in the phospholipid/bile salt containing cholesteryl myristate dispersions.

Study and formation of vesicle systems with low polydispersity index by ultrasound method

The formation of liposomes with low polydispersity index by application of ultrasounds was investigated considering methodology specifications such as sonication time and sonication power. Phosphatidylcholine (PC) liposomes were formed by the evaporation-hydration method. The vesicles were sonicated using several sonication conditions. The liposomes were then characterized by dynamic light scattering (DLS) and freeze-fracture electron microscopy (FFEM). Correlation functions from DLS were treated by cumulants method and GENDIST to obtain the mean radius and polydispersity index. These calculations allowed to fix an optimal sonication time (3000 s) and a useful interval of ultrasound power between 39 and 91 W. DLS and FFEM results confirmed that vesicle size, lamellarity and the polydispersity index decreased with the increase of sonication power. Thus, we propose a systematic method to form liposomes in which the physical characteristics of the vesicles may be controlled as a function of sonication time and power.