Physical Stability Of Liposomes Research Articles

Development of skin-permeable flexible liposome using ergosterol esters containing unsaturated fatty acids

Ergosterol (Ergo) and cholesterol contribute to performances of liposomes by increasing membrane packing density and physical stability. However, as these sterols can reduce membrane flexibility, they can lower skin permeability of liposomes. We synthesized ergosterol ester (Ergo-Est) containing unsaturated fatty acid different from Ergo in size and physical properties. In this work, we investigated effects of Ergo-Est and Ergo on physical properties of liposomes. We incorporated Ergo, Ergo-oleate (EO18:1), Ergo-linoleate (EL18:2), and Ergo-linolenate (ELn18:3) into the liposomal membrane of egg phosphatidylcholine and soybean lecithin. Ergo-Est did not reduce membrane fluidity as much as Ergo. Nevertheless, Ergo-Est increased membrane packing density and physical stability of liposomes. EL18:2 and ELn18:3 almost maintained membrane flexibility and skin permeability of liposomes, while Ergo significantly reduced them. Skin permeation test demonstrated that EL18:2 and ELn18:3 liposomes permeated to the dermis, whereas Ergo liposome mostly remained in the stratum corneum. This is the first report to show that EL18:2 and ELn18:3 can be efficient sterol compounds for flexible liposome formulation.

Preparation of Berberin Proliposomes by Film Deposition on Carrier Surface Method

This study aims to formulate berberin (BBR) proliposomes by film-deposition on carrier surface to increase BBR’s solubility and permeability through biological membranes. Proliposomes were hydrated in water to form BBR liposomes for determining the size and distribution of the vesicles. Differential thermal analysis was used to evaluate the BBR proliposomes. The study results show that berberin proliposomes prepared with hydrogenated soy phosphatidylcholine: cholesterol: berberin with a molar ratio of 9:1:6 using sorbitol as carrier with a weight ratio to lipid of 10:1. The obtained BBR proliposomes in the form of a dry yellowish powder were hydrated in water to form BBR liposomes with an average diameter of about 8.41μm. The results of the differential thermal analysis show that BBR was dispersed in molecular form into proliposomes. 
 Keywords:
 Berberin, proliposomes, sorbitol, film-deposition on the carrier method.
 References
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Effect of Gamma Irradiation on the Physical Stability of DPPC Liposomes

Unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC) were prepared by the reverse-phase evaporation method and extrusion through a polycarbonate membrane filter. Liposomes at 0.7 mg/mL lipid concentration in deionized water were exposed to gamma irradiation at a dose in the range 0.5 to 25 kGy. Gamma irradiation of liposomes resulted in the degradation of DPPC lipids into free fatty acids, lysophosphatidylcholine and 1,2-palmitoyl-phosphatidic acid (DPPA). The effect of gamma irradiation towards the physical stability of liposomes was investigated by means of dynamic light scattering (DLS), transmission electron microscopy (TEM) and zeta potential analysis. From the DLS analysis, no significant changes were observed in the hydrodynamic size of liposomes. TEM images indicate that the liposomes surface became smoother and rounder as higher irradiation doses were applied. Zeta potential analysis showed that gamma irradiation of DPPC liposomes at radiation doses as low as 0.5 kGy resulted in a drastic rise in the magnitude of the zeta potential. The results also demonstrate that gamma irradiation of liposomes suspension enhanced the overall stability of liposomes. Hence, it can be concluded that gamma irradiation on DPPC liposomes may potentially produce liposomes with higher stability.

Liposils: An effective strategy for stabilizing Paclitaxel loaded liposomes by surface coating with silica

The present work aims at improving stability of paclitaxel (PTX) loaded liposomes by its coating with silica on the surface by a modified sol-gel method. Effect of various components of liposomes such as phosphatidylcholine to cholesterol ratio (PC:CH), PTX and stearylamine on entrapment efficiency (% EE) and particle size were systematically investigated and optimized using central composite design on Design-Expert®. The optimized liposomes were utilized as a template for silica coating to prepare surface coated PTX liposils. Physical stability of liposomes and liposils was evaluated with Triton X-100 and the results indicated that liposils were much more stable as compared to liposomes and the same has been reiterated in stability study performed over 6 months. In vitro cytotoxicity study on B16F10 tumor cells showed cytotoxicity of PTX liposils was not significantly different than PTX liposomes, whereas both were less cytotoxic as compared to the commercial Taxol®. In vivo pharmacokinetics on rats, exhibited increased T1/2 of liposils when compared to liposomes and Taxol®, thus releasing the drug over a longer duration. The enhanced physicochemical stability as well as controlled release of PTX in liposils developed in this study could be an effective alternative to Taxol® and PTX liposomes.

Osmotic Dehydration of Liposomal Dispersions: Influence of Particle Size and Electrostatic Deposition of Cold Water Fish Skin Gelatin

Liposomes are a promising delivery system for bioactives in food and nutraceuticals. Their practical application is limited by their physical and chemical instability caused by extrinsic factors. The physical stability of liposomes of three different sizes coated with cold water fish skin gelatin was assessed during osmotic dehydration at 2, 21 and 70 °C. Soy lecithin was used to prepare 1 % liposomal dispersions. The size distribution was controlled with high pressure homogenization (1500 bar) and extrusion through polycarbonate membrane (3 and 0.8 μm). Fish gelatin was adsorbed to the interface to make secondary liposomes. Liposomal dispersions were osmotically dehydrated while monitoring the relative weight, size and rheological properties. The primary liposomes had an initial mean volume diameter (d4,3) of 0.09, 0.40 and 2.7 μm and a ζ-potential of −55 mV. Secondary liposomes were 0.11, 0.45 and 3.4 μm with a ζ-potential of 25 mV. The size of liposomes influenced the stability of liposomes, with the smallest liposomes being stable for 30 min, corresponding to 80 % of the initial weight, while the larger liposomes were already aggregated. Secondary liposomes were stable to 120 min for the smaller liposomes and to 150 min for the largest liposomes corresponding to 40 % of the initial weight. Stability increased during dehydration at 2 °C. Coating the liposomes increased the physical stability of the liposomal dispersions at all temperatures. The results show that cold water fish skin gelatin is a viable option to coat liposomes of a wide size range.

Impact of quercetin and fish oil encapsulation on bilayer membrane and oxidation stability of liposomes

Unsaturated soy phosphatidyl choline (PC) liposomes were systematically analyzed for chemical and physical stability and for influence on membrane fluidity, when quercetin and fish oil were encapsulated. The physical stability of liposomes was lowered with loading, which is mainly due to fish oil leakage. While fish oil did not induce oxidative acceleration, quercetin did not reduce lipid-derived radical formation but it did inhibit hexanal formation. It also showed no relevant effects on membrane fluidity, polarity or partitioning of the spin probe TEMPOL-benzoate (TB), as proved by EPR measurements and simulation. However, increasing concentration of fish oil in a membrane might increase the acyl chain dynamics and therefore apply a more attractive environment for TB. In contrast to the encapsulates increasing fluidity of saturated membranes by disturbing the lipid packing, membrane properties of unsaturated systems with a Tm below 0°C were not influenced by encapsulation of quercetin or fish oil.

Physicochemical properties of WPI coated liposomes serving as stable transporters in a real food matrix

While it is widely accepted that a whey protein isolate (WPI) coating may be applied on a lipid based transporter or carrier system like an emulsion droplet, we still do not know much about coating behavior of WPI on a liposomal surface. In particular, there is lack of information on physiochemical alteration in those modified transporters in real food grade matrices and during in vitro digestion. For this reason, physicochemical and sensory properties of WPI coated and spray-dried liposomes were tested towards those of uncoated liposomes being applied as transporter in a whey drink. Liposomes were formed from highly unsaturated soy phospholipids and incorporated the flavonoid quercetin as model encapsulate. Aroma and flavor profile of the drink were characterized by descriptive analysis and proved for effectively masking of quercetin bitterness. Relative to uncoated liposomes, the WPI coating improved liposome application into a dairy drink as well as physical stability of liposomes towards osmotically active food compounds, towards different storage condition and towards simulated gastric fluid stress. These stabilizing effects arose from the reduction of semi-permeability of the membrane as the WPI coating formed a barrier on the liposomal surface.

Modulation of the carotenoid bioaccessibility through liposomal encapsulation

The low bioaccessibility of carotenoids is currently a challenge to their incorporation in pharmaceutics, nutraceuticals and functional foods. The aim of this study was to evaluate the modulating effects of liposome encapsulation on the bioaccessibility, and its relationship with carotenoid structure and incorporated concentration. The physical stability of liposomes, lipid digestibility, carotenoids release and bioaccessibility were investigated during incubation in a simulated gastrointestinal tract. Analysis on the liposome size and morphology showed that after digestion, the majority of particles maintained spherical shape with only an increase of size in liposomes loading β-carotene or lutein. However, a large proportion of heterogeneous particles were visible in the micelle phase of liposomes loading lycopene or canthaxanthin. It was also found that the release of lutein and β-carotene from liposomes was inhibited in a simulated gastric fluid, while was slow and sustained in a simulated intestinal fluid. By contrast, lycopene and canthaxanthin exhibited fast and considerable release in the gastrointestinal media. Both carotenoid bioaccessibility and micellization content decreased with the increase of incorporated concentration. Anyway, the bioaccessibility of carotenoids after encapsulated in liposomes was in the following order: lutein>β-carotene>lycopene>canthaxanthin. Bivariate correlation analysis revealed that carotenoid bioaccessibility depended strongly on the incorporating ability of carotenoids into a lipid bilayer, loading content, and nature of the system.

Determination of platinum drug release and liposome stability in human plasma by CE-ICP-MS

An in vitro method for simultaneous assessment of platinum release and liposome stability of liposomal formulations in human plasma is demonstrated. The development and assessment of the method was performed on a PEGylated liposomal formulation containing cisplatin. Complete separation of free cisplatin, encapsulated cisplatin and cisplatin bound to plasma components was achieved by capillary electrophoresis (CE) separation and simultaneous monitoring of phosphorous (phospholipid) and platinum (cisplatin) by inductively coupled plasma mass spectrometry (ICP-MS). The method allows assessment of the encapsulation efficiency of the formulation, the physical stability of liposomes as well as cisplatin leakage in human plasma. The method was applied for studying the disintegration of liposomes and the interactions of leaked cisplatin with plasma components. Triggered release of the drug into plasma by sonication was also demonstrated. Analysis of liposomal formulations with alternative phospholipid compositions containing oxaliplatin showed similar results. Thus, the present in vitro method is suitable for mimicking the in vivo drug release profile in human plasma after administration of liposomal platinum formulations to patients. This approach may be of use in early drug development as well as in quality control.

Effects of Chitosan and Rosmarinate Esters on the Physical and Oxidative Stability of Liposomes

Liposomes have substantial potential to deliver bioactive compounds in foods. However, the oxidative degradation and physical instability of liposomes limit their utilization. This research evaluated the ability of chitosan and rosmarinic acid and its esters to increase the physical and oxidative stability of liposomes. Particle size analysis studies showed that the physical stability of liposomes was enhanced by depositing a layer of cationic chitosan onto the negatively charged liposomes. The combination of octadecyl rosmarinate (40 microM) and chitosan coating resulted in significantly greater inhibition of lipid oxidation in the liposomes compared to chitoson or octadecyl rosmarinate alone. Increasing the concentrations of octadecyl rosmarinate to a concentration of 40 microM in the chitosan-coated liposomes decreased lipid oxidation. Only butyl rosmarinate exhibited stronger antioxidant activity than free rosmarinic acid. Eicosyl rosmarinate (20 carbons) had lower antioxidant activity than all other rosmarinic acid derivatives. These results suggest that by combining the inclusion of appropriate antioxidants such as rosmarinic acid and the deposition of a chitosan coating onto the surface of liposomes may significantly increase the oxidative and physical stability of liposomes.

Atomic force microscopy and photon correlation spectroscopy: Two techniques for rapid characterization of liposomes

The direct evaluation of the heterogeneity of the particle population of nanometric drug delivery systems as liposomes is difficult to achieve owing to the dimension and the carrier characteristics. The influence of the lipidic ratio and composition on the physical stability of liposomes during their storage was investigated using atomic force microscopy (AFM) and photon correlation spectroscopy (PCS). Liposomes were made by a mixture of different lipids and obtained using distinct methods of preparation. AFM images, acquired immediately after the deposition of the sample on mica surface, clearly showed the spherical shape of the lipidic vesicles. In all the 7 months of the experiment, the average sizes of the different liposomes evaluated using the two techniques were comparable. According to PCS analysis, AFM images confirmed that almost all the diversified vesicular systems tended to form aggregates during their storage; this loss of stability was strengthened by the increase of polydispersity index value. The different behaviours observed were to ascribe to the lipidic composition more than the methods of liposome preparation. In conclusion, AFM technique owing to the relative simplicity cold be useful for the technological control of size distribution profile according to the preparative factors and moreover to the batch-to-batch reproducibility.

Ferrous sulfate liposomes: preparation, stability and application in fluid milk

The effects of cholesterol and Tween 80 on the physical stability of empty liposomes were investigated. Results showed that the physical stability of liposomes, including electrostatic and steric stability, was improved by addition of cholesterol and Tween 80. Liposomes prepared by different methods, thin-film hydration, thin-film sonication, reverse-phase evaporation and freeze-thawing, were tested for their capacity to encapsulate ferrous sulfate. Technology parameters to microencapsulate ferrous sulfate, concentration of ferrous sulfate, hydrating media and sonication strength, were optimized. The concentration of ferrous sulfate and the hydrating medium had a significant effect on the amount of encapsulated ferrous ions. The encapsulation efficiency (EE) of 67% was obtained by using the reverse-phase evaporation method. In milk fortified with ferrous sulfate liposomes, the concentration of iron increased to 15 mg L −1, and it was stable to heat sterilization (100 °C, 30 min) and storage at 4 °C during one week.

Effects of calcium-induced aggregation on the physical stability of liposomes containing plant glycolipids

Membranes containing either negatively charged lipids or glycolipids can be aggregated by millimolar concentrations of Ca 2+. In the case of membranes made from the negatively charged phospholipid phosphatidylserine, aggregation leads to vesicle fusion and leakage. However, some glycolipid-containing biological membranes such as plant chloroplast thylakoid membranes naturally occur in an aggregated state. In the present contribution, the effect of Ca 2+-induced aggregation on membrane stability during freezing and in highly concentrated salt solutions (NaCl±CaCl 2) has been determined in membranes containing different fractions of uncharged galactolipids, or a negatively charged sulfoglucolipid, or the negatively charged phospholipid phosphatidylglycerol (PG), in membranes made from the uncharged phospholipid phosphatidylcholine (PC). In the case of the glycolipids, aggregation did not lead to fusion or leakage even under stress conditions, while it did lead to fusion and leakage in PG-containing liposomes. Liposomes made from a mixture of glycolipids and PG that approximates the lipid composition of thylakoids were very unstable, both during freezing and at high solute concentrations and leakage and fusion were increased in the presence of Ca 2+. Collectively, the data indicate that the effects of Ca 2+-induced aggregation of liposomes on membrane stability depend critically on the type of lipid involved in aggregation. While liposomes aggregated through glycolipids are highly stable, those aggregated through negatively charged lipids are severely destabilized.

Liposomes containing boronophenylalanine for boron neutron capture therapy

In the present work, liposomes loaded with Boronphenylalanine (BPA), with or without stabilization, were formulated for the application in boron neutron capture therapy. BPA was encapsulated into liposomes as a complex with fructose, but also as a free drug in two different pH buffers. The influence of critical variables (cholesterol content, drug:lipid molar ratio, osmotic stress of liposomes containing hyperosmotic drug solution) on liposome morphology and drug content was evaluated. The drug content and dissolution profile of different BPA loaded liposomes were also studied. The physical stability of liposomes in terms of changes in the size distribution in different osmotic pressure buffers and the chemical oxidation of phospholipids during storing conditions were investigated. The encapsulation efficiencies of all formulations were always satisfactory, being between 2M8%; even when the liposomes were exposed to high osmotic stress, the particle size was below 200 nm. The BPA-fructose complex loaded liposomes showed a slower drug release profile.

The influence of lipid composition and lamellarity of liposomes on the physical stability of liposomes upon storage

The physical stability of the four liposomal systems was determined on storage at 4 and 25°C over a 6-month period. A correlation of the mean volume diameter, zeta potential and pH lead to the conclusion that stability follows the order of egg lecithin (PC)/cholesterol (CH)/stearylamine (SA) < PC/CH/phosphatidylserine (PS) < bovine brain ceramides (CM)/CH/palmitic acid (PA)/CS < PC/CH/cholesteryl sulphate (CS) at 4°C, as well as at 25°C, after a 6-month storage period. Large unilamellar vesicles (REV) proved to be superior to multilamellar liposomes (MLV) and dehydration/rehydration liposomes (DRV) systems as far as physical stability was concerned. Instability was exaggerated in the systems stored at 25°C as compared to storage at 4°C.

Influence of One Quinolone on the Formation and the Physical Stability of Liposomes

AbstractThe influence of one quinolone on the formation and physical stability of phosphatidylcholine (PC) liposomes is described. Based on Photon Correlation Spectroscopy (PCS) measurements, namely mean diameter and polydispersity, the maximum proportion of quinolone which is compatible with liposome morphology and homogeneous population was established in 30% mole of drug in a PC matrix. This lead to a pharmaceutical formulation which includes the additive D-α-tocoferol as antioxidant, glycerol as a co-solvent and phosphatidylcholine-cholesterol (2:1, mole/mole) as the formal lipid matrix. Drug encapsualtions between 30–40% were found. The feasibility of the method to scale-up this liposome formulation is discussed in terms of PCS, efficiency of encapsulation and preliminary assays in vivo.

A theoretical approach to describe monolayer-liposome lipid interaction

It is known from several studies on the interaction between membrane models that mechanisms such as fusion or lipid exchange can play an important role in the process of internalization by cells of lipid vesicles and also in the physical stability of liposomes. In this paper it is shown that a simple monolayer-liposome model can be used to simulate experimentally observed interactions between lipid vesicles and cell surfaces. From experimental data, a simple theoretical model is formulated to interpret the variation with time of surface pressure as a function of liposome concentration. The congruency of the physico-chemical hypothesis and its validity are studied and correlated with results from experimental systems.