Microfluidic preparation of drug-loaded PEGylated liposomes,and the impact of liposome size on tumour retention and penetration

Understanding the effect of liposome size on tendency for accumulation in tumour tissue requires preparation of defined populations of different sized particles. However, controlling the size distributions without changing the lipid composition is difficult, and differences in compositions itself modify distribution behaviour. Here, a commercial microfluidic format as well as traditional methods was used to prepare doxorubicin-loaded liposomes of different size distributions but with the same lipid composition, and drug retention, biodistribution and localization in tumour tissues were evaluated. The small (～50?nm diameter) liposomes prepared by microfluidics and large (～75?nm diameter) liposomes displayed similar drug retention in in vitro release studies, and similar biodistribution patterns in tumour-bearing mice. However, the extent of extravasation was clearly dependent on size of the liposomes, with the small liposomes showing tissue distribution beyond the vascular area compared to the large liposomes. The use of microfluidics to prepare smaller size distribution liposomes compared to sonication methods is demonstrated, and allowed preparation of different size distribution drug carriers from the same lipid composition to enable new understanding of tissue distribution in compositionally consistent materials is demonstrated.     

Spontaneous vesiculation of aqueous lipid dispersions

The swelling properties of lipid mixtures consisting of phosphatidylcholine and a charged single-chain detergent have been studied. The work presented here is confined to lipid mixtures forming smectic lamellar phases in H2O. These mixtures exhibit continuous swelling with increasing water content, provided the surface charge density exceeds a threshold value of about 1-2 microC/cm2. In excess H2O, such mixtures undergo spontaneous vesiculation: unilamellar vesicles form spontaneously when excess H2O or salt solutions of moderate ionic strength (I less than 0.2) are added to the dried film of such lipid mixtures. The resulting dispersion of unilamellar vesicles is usually polydisperse. Its average size depends on the detergent/phospholipid mole ratio, decreasing with increasing detergent content. It is shown that in the phase diagram of three-component systems consisting of phosphatidylcholine, a charged single-chain detergent, and excess H2O there is a compositional range, though narrow, within which the small unilamellar vesicle (diameter less than 100 nm) is the thermodynamically most stable structure. This behavior is characteristic of charged, single-chain detergents of 14 and more C atoms. Many pharmacologically active compounds are amphiphilic and surface-active, and as such, they will orient at phospholipid-water interfaces, imparting a net surface charge to neutral lipid surfaces. It is shown that such drugs exhibit detergent-like action. Mixed films of phosphatidylcholine and a pharmacologically active compound behave similarly to phosphatidylcholine-detergent mixtures: they undergo spontaneous vesiculation when excess H2O or salt solutions of moderate ionic strength are added. In this case, the drug itself induces vesiculation; possible pharmacological implications of this finding are discussed.     

Characterization of the size distribution of unilamellar vesicles by gel filtration, quasi-elastic light scattering and electron microscopy

The size and size distribution of unilamellar phospholipid vesicles present in unsonicated phosphatidic acid and mixed phosphatidic acid/phosphatidylcholine dispersions were determined by gel filtration, quasi-elastic light scattering and freeze-fracture electron microscopy. The vesiculation in these dispersions was induced by a transient increase in pH as described previously (Hauser, H. and Gains, N. (1982) Proc. Natl. Acad. Sci. USA 79, 1683–1687). The resulting phospholipid dispersions are heterogeneous consisting of small unilamellar vesicles (average radius r < 50 nm) and large unilamellar vesicles (average r ranging from about 50 to 500 nm). The smallest vesicles with r = 11 ± 2 nm are observed with dispersions of pure phosphatidic acid, the population of these vesicles amounting to about 80% of the total lipid. With increasing phosphatidylcholine content the radius of the small unilamellar vesicles increases and at the same time the population of small unilamellar vesicles decreases. The average radius of small unilamellar vesicles present in phosphatidic acid/phosphatidylcholine dispersions (mole ratio, 1:1) is 17.5 ± 2 nm, the population of these vesicles amounting to about 70% of the total lipid. By a combination of gel filtration, quasi-elastic light scattering and freeze-fracture electron microscopy it was possible to characterize the large unilamellar vesicles. This population is heterogeneous with its mean radius also increasing with increasing phosphatidylcholine content. After separating the large unilamellar vesicles from small unilamellar vesicles on Sepharose 4B it can be shown by quasi-elastic light scattering that in pure phosphatidic acid dispersions 80–90% of the large unilamellar vesicle population consist of vesicles with a mean radius of 170 nm. In mixed phosphatidic acid/phosphatidylcholine dispersions this radius increases to about 265 nm as the phosphatidylcholine content is raised to 90 mol%.     

Enhancement of oral bioavailability of pentoxifylline by solid lipid nanoparticles

Pentoxifylline (PTX) is a highly water-soluble, hemorheologic drug that undergoes first-pass effect with 20% bioavailability. The solid lipid nanoparticles (SLNs) of PTX were prepared to enhance its oral bioavailability by homogenization, followed by the sonification method. Seven different variables, each at two levels, were studied: lipid type, surfactant type and concentration, speed of homogenizer, acetone:dichloromethane (DCM) ratio, lecithin:lipid ratio, and sonication time. The mean particle size and size distribution, drug entrapment efficiency (EE%), zeta potential, and drug release of the SLNs were investigated. A pharmacokinetic study was conducted in male Wistar rats after oral administration of 10?mg kg^?1 PTX in the form of free drug or SLNs. The z-average particle size, zeta potential, and EE% of the SLNs were at least 250?nm, ?30.2 mV, and 70%, respectively. Among the studied factors, the lipid type, surfactant type, and percentage had a significant effect on the particle size. Zeta potential was more affected by lipid type, acetone:DCM ratio, and sonication time. Speed of homogenizer and acetone:DCM ratio had a significant effect on the EE%. The optimized SLN was prepared by 80?mg of cetyl alcohol, 10?mg of lecithin, acetone:DCM ratio (1:2), 30-second sonication, 3% Tween 20, and a mixing rate of 800?rpm. In vitro drug release lasted for about 5 hours. It was found that the relative bioavailability of PTX in SLNs was significantly increased, compared to that of the PTX solution. SLNs offer a promising approach to improve the oral bioavailability of PTX that is affected by a high first-pass effect.     

Characterization of liposomal systems containing doxorubicin entrapped in response to pH gradients

Studies from this laboratory (Mayer et al. (1986) Biochim. Biophys. Acta 857, 123-126) have shown that doxorubicin can be accumulated into liposomal systems in response to transmembrane pH gradients (inside acidic). Here, detailed characterizations of the drug uptake and retention properties of these systems are performed. It is shown that for egg phosphatidylcholine (EPC) vesicles (mean diameter of 170 nm) exhibiting transmembrane pH gradients (inside acidic) doxorubicin can be sequestered into the interior aqueous compartment to achieve drug trapping efficiencies in excess of 98% and drug-to-lipid ratios of 0.36:1 (mol/mol). Drug-to-lipid ratios as high as 1.7:1 (mol/mol) can be obtained under appropriate conditions. Lower drug-to-lipid ratios are required to achieve trapping efficiencies in excess of 98% for smaller (less than or equal to 100 nm) systems. Doxorubicin trapping efficiencies and uptake capacities are related ito maintenance of the transmembrane pH gradient during encapsulation as well as the interaction between doxorubicin and entrapped citrate. This citrate-doxorubicin interaction increases drug uptake levels above those predicted by the Henderson-Hasselbach relationship. Increased drug-to-lipid ratios and trapping efficiencies are observed for higher interior buffering capacities. Retention of a large transmembrane pH gradient (greater than 2 units) after entrapment reduces the rate of drug leakage from the liposomes. For example, EPC/cholesterol (55:45, mol/mol) liposomal doxorubicin systems can be achieved which released less than 5% of encapsulated doxorubicin (drug-to-lipid molar ratio = 0.33:1) over 24 h at 37 degrees C. This pH gradient-dependent encapsulation technique is extremely versatile, and well characterized liposomal doxorubicin preparations can be generated to exhibit a wide range of properties such as vesicle size, lipid composition, drug-to-lipid ratio and drug release kinetics. This entrapment procedure therefore appears well suited for use in therapeutic applications. Finally, a rapid colorimetric test for determining the amount of unencapsulated doxorubicin in liposomal systems is described.     

Brain delivery of olanzapine by intranasal administration of transfersomal vesicles

The aim of this study was to investigate the presence of a possible direct correlation between vesicle elasticity and the amount of drug reaching the brain intranasally. Therefore, transfersomes were developed using phosphatidylcholine (PC) as the lipid matrix and sodium deoxycholate (SDC), Span^® 60, Cremophor^® EL, Brij^® 58, and Brij^® 72 as surfactants. The influence of the type of surfactant and PC-to-surfactant ratio on vesicle morphology, size, membrane elasticity, drug entrapment, and in vitro drug release was studied. The prepared transfersomes were mainly spherical in shape, with diameters ranging from 310 to 885?nm. Transfersomes containing SDC and Span 60 with optimum lipid-to-surfactant molar ratio showed suitable diameters (410 and 380?nm, respectively) and deformability indices (17.68 and 20.76?mL/sec, respectively). Values for absolute drug bioavailability in rat plasma for transfersomes containing SDC and those containing Span 60 were 24.75 and 51.35%, whereas AUC_0–360min values in rat brain were 22,334.6 and 36,486.3?ng/mL/min, respectively. The present study revealed that the deformability index is a parameter having a direct relation with the amount of the drug delivered to the brain by the nasal route.     

Development and optimization of solid lipid nanoparticles of amikacin by central composite design

Solid lipid nanoparticles (SLNs) have been studied as a drug-delivery system for the controlling of drug release. These colloidal systems have many important advantages, such as biocompatibility, good tolerability, and ease of scale-up. In the preparation of SLNs, many factors are involved in the characteristics of the particles, such as particle size, drug loading, and zeta potential. In this study, fractional factorial design was applied to examine which variables affect the physicochemical properties of amikacin SLNs. Study was continued by a statistical central composite design (CCD) to minimize particle size and maximize drug-loading efficiency of particles. The results showed that three quantitative factors, including the amount of lipid phase, ratio of drug to lipid, and volume of aqueous phase, were the most important variables on studied responses. The best predicted model for particle size was the quadratic model, and for drug-loading efficiency, was the linear model without any significant lack of fit. Optimum condition was achieved when the ratio of drug to lipid was set at 0.5, the amount of lipid phase at 314?mg, and the volume of aqueous phase at 229?mL. The optimized particle size was 149?±?4?nm and the drug-loading efficiency 88?±?5%. Polydispersity index was less than 0.3. The prepared particles had spherical shape, and the drug release from nanoparticles continued for 144 hours (6 days) without significant burst effect.     

Liposomal solubilization of new 3-hydroxy-quinolinone derivatives with promising anticancer activity: a screening method to identify maximum incorporation capacity

Four new 3-hydroxy-quinolinone derivatives with promising anticancer activity could be solubilized using liposomes as vehicle to an extent that allows their in vitro and in vivo testing without use of toxic solvent(s). A screening method to identify the maximum incorporation capacity of hydrophobic drugs within liposomes was successfully applied. The compounds and lipid(s) were dissolved in methanol, and the solvent was removed by rotary evaporation. The film was resuspended with phosphate buffer (pH 7.4), and the dispersion was sonicated to reduce vesicle size. Ultracentrifugation was used to separate liposome-associated drug from free (i.e., precipitated) drug, and the amount of drug incorporated within the liposomes was quantified using high-performance liquid chromatography. All four compounds were found to be significantly incorporated within soy phosphatidylcholine (SPC) liposomes, resulting in a 200–500-fold increase in apparent solubility. Drug-to-lipid ratios in the range of 2–5 µg/mg were obtained. Interestingly, the four quinolinone derivatives have shown different association tendencies with liposomes, probably due to the physicochemical properties of the different group bonded in position 2 of the quinolinone ring. None of the alternative lipids/lipid blends tested incorporated as much drug as SPC. Photon correlation spectroscopy analyses indicated that use of ultrasounds produced an efficient reduction in liposome size. The present approach appears suitable for incorporation capacity studies of any lipophilic drug in liposomes.     

DIMENSIONAL ANALYSIS AND SCALE-UP IN THEORY AND INDUSTRIAL APPLICATION*

A comparative study between archaeosomes, lipid lamellar vesicles made from archaea polar lipids, and conventional phospholipids liposomes was carried out, aiming at evaluating the properties and the potential of archaeosomes as novel colloidal carriers for effective drug delivery to the skin. Betamethasone dipropionate (BMD)–loaded archaeosomes and conventional liposomes were prepared by the thin-lipid film and sonication procedures, using, respectively, archaeal lipids extracted from archaea Halobacterium salinarum and enriched soy phosphatidylcholine. Vesicular formulations were characterized by assessing vesicle size, zeta potential, incorporation efficiency, and morphology. In order to investigate the effect of the incorporation in the two different colloidal carrier systems on the (trans)dermal delivery of BMD, in vitro drug permeation studies through full-thickness pig skin were carried out by using Franz diffusion vertical cells by testing both archaeal and liposomal dispersions. Interestingly, archaeosomes appeared to be the most effective carriers for the model drug, achieveing a major drug penetration and accumulation in the skin strata, especially in the epidermis. This can, presumably, be due to the enhanced archaeosomal bilayer fluidity, as indicated by the rheological studies that provided insight into the viscoelastic properties of all the studied systems. The available data suggest that suitably developed archaeosomes may hold great promise as delivery vehicles for topical applications.     

Amphotericin B Formulated in Liposomes and Lipid Based Systems: A Review

Abstract

The therapeutic index (T.I.) of amphotericin B (amB) is significantly increased when the drug is formulated in a variety of liposome and lipidic systems. This increase is due to a dramatic decrease in toxicity with maintenance of antifungal activity. Three formulations are currently being commercialized: ABLC?, AmBisome and Amphocil?. ABLC? is a ribbon-type lipid complex with a diameter in the 2-5 micron range consisting of dimyristoylphosphatidylcholine, dimyristoylphosphatidylglycerol and amB (7/3/10 mole ratio). AmBisome? is a liposome with a particle diameter less than 100 nm and composed of hydrogenated soy phosphatidylcholine, cholesterol, distearoylphosphatidylglycerol and amB (2/1/0.8/0.4 mole ratio). Amphocil? is a lipidic particle with a diameter of 115 nm and consists of cholesterylsulfate and amB (1/1 mole ratio). In spite of the differences, each formulation reduces the transfer of amB into a sensitive site of toxicity while affecting transfer of the drug into the fungal target to a lesser extent. Two principal mechanisms account for this: vehicle composition decreases the transfer rate of amB into cholesterol containing mammalian membranes (sites of toxicity) more than into ergosterol containing fungal membranes (sites of efficacy). Vehicle diameter influences the pharmacokinetics and disposition of the drug into the reticuloendothelial system. Immediate toxicity is reduced because the drug is rapidly eliminated from the central compartment and directed into macrophages. Subsequent release from macrophages at sites of infection can improve die efficacy. The chapters in this volume review the current understanding of the mechanism of amB and cover in detail die biophysical, pharmaceutical and therapeutic aspects of amphotericin B lipid formulations.     

Ethanol-based proliposome delivery systems of paclitaxel for in vitro application against brain cancer cells

In this study the anticancer activity of paclitaxel-loaded nano-liposomes on glioma cell lines was investigated. Soya phosphatidylcholine:cholesterol (SPC:Chol), hydrogenated soya phosphatidylcholine:cholesterol (HSPC:Chol) or dipalmitoylphosphatidylcholine:cholesterol (DPPC:Chol) in 1:1?mole ratio were used to prepare ethanol-based proliposomes. Following hydration of proliposomes, the size of resulting vesicles was subsequently reduced to nanometer scale via probe-sonication. The resulting formulations were characterized in terms of size, zeta potential and morphology of the vesicles, and entrapment efficiency of paclitaxel (PX) as well as the final pH of the preparations. DPPC-liposomes entrapped 35–92% of PX compared to 27–74% and 25–60% entrapped by liposomes made from SPC and HSPC formulations respectively, depending on drug concentration. The entrapment efficiency of liposomes was dependent on the lipid bilayer properties and ability of PX to modify surface charge of the vesicles. In vitro cytotoxicity studies revealed that PX-liposome formulations were more selective at inhibiting the malignant cells. The cytotoxicity of PX-liposomes was dependent on their drug-entrapment efficiency. This study has shown PX-liposomes generated from proliposomes have selective activity against glioma cell lines, and the synthetic DPPC phospholipid was most suitable for maximized drug entrapment and highest activity against the malignant cells in vitro.     

Liposomes with entrapped doxorubicin exhibit extended blood residence times

The blood residence time of liposomes with entrapped doxorubicin is shown to be significantly longer than for identically prepared empty liposomes. Liposomal doxorubicin systems with a drug-to-lipid ratio of 0.2 (w/w) were administered at a dose of 100 mg lipid/kg. Both doxorubicin and liposomal lipid were quantified in order to assess in vivo stability and blood residence times. For empty vesicles composed of phosphatidylcholine (PC)/cholesterol (55:45, mole ratio) and sized through filters of 100 nm pore size, 15-25% of the administered lipid dose was recovered in the blood 24 h after i.v. injection. The percentage of the dose retained in the circulation at 24 h increased 2-3-fold when the liposomes contain entrapped doxorubicin. For 100 nm distearoyl PC/chol liposomal doxorubicin systems, as much as 80% of the injected dose of lipid and drug remain within the blood compartment 24 h after i.v. administration.     

Automated formation of multicomponent-encapuslating vesosomes using continuous flow microcentrifugation

Vesosomes – hierarchical assemblies consisting of membrane-bound vesicles of various scales – are potentially powerful models of cellular compartmentalization. Current methods of vesosome fabrication are labor intensive, and offer little control over the size and uniformity of the final product. In this article, we report the development of an automated vesosome formation platform using a microfluidic device and a continuous flow microcentrifuge. In the microfluidic device, water-in-oil droplets containing nanoscale vesicles in the water phase were formed using T-junction geometry, in which a lipid monolayer is formed at the oil/water interface. These water-in-oil droplets were then immediately transferred to the continuous flow microcentrifuge. When a water-in-oil droplet passed through a second lipid monolayer formed in the continuous flow microcentrifuge, a bilayer-encapsulated vesosome was created, which contained all of the contents of the aqueous phase encapsulated within the vesosome. Encapsulation of nanoscale liposomes within the outer vesosome membrane was confirmed by fluorescence microscopy. Laser diffraction analysis showed that the vesosomes we fabricated were uniform (coefficient of variation of 0.029). The yield of the continuous flow microcentrifuge is high, with over 60% of impinging water droplets being converted to vesosomes. Our system provides a fully automatable route for the generation of vesosomes encapsulating arbitrary contents. The method employed in this work is simple and can be readily applied to a variety of systems, providing a facile platform for fabricating multicomponent carriers and model cells.     

mRNA lipid nanoparticle phase transition

Crucial for mRNA-based vaccines are the composition, structure, and properties of lipid nanoparticles (LNPs) as their delivery vehicle. Using all-atom molecular dynamics simulations as a computational microscope, we provide an atomistic view of the structure of the Comirnaty vaccine LNP, its molecular organization, physicochemical properties, and insight in its pH-driven phase transition enabling mRNA release at atomistic resolution. At physiological pH, our simulations suggest an oil-like LNP core that is composed of the aminolipid ALC-0315 and cholesterol (ratio 72:28). It is surrounded by a lipid monolayer formed by distearoylphosphatidylcholine, ALC-0315, PEGylated lipids, and cholesterol at a ratio of 22:9:6:63. Protonated aminolipids enveloping mRNA formed inverted micellar structures that provide a shielding and likely protection from environmental factors. In contrast, at low pH, the Comirnaty lipid composition instead spontaneously formed lipid bilayers that display a high degree of elasticity. These pH-dependent lipid phases suggest that a change in pH of the environment upon LNP transfer to the endosome likely acts as trigger for cargo release from the LNP core by turning aminolipids inside out, thereby destabilizing both the LNP shell and the endosomal membrane.     

Inhibitory Effects of Sulfur Nanoparticles on Membrane Lipids of Aspergillus niger: A Novel Route of Fungistasis

Orthorhombic (spherical; ~10?nm) and monoclinic (cylindrical; ~50?nm) sulfur nanoparticles (SNPs) were synthesized and examined for their effects on the total lipid content and desaturase enzymes of Aspergillus niger. Synthesized SNPs were characterized for size with transmission electron microscopy, elemental composition with energy dispersive X-ray spectroscopy and allotropic nature with X-ray diffraction pattern. Both the SNPs considerably reduced total lipid content of the treated fungal isolates with significant down regulation of the expression of various desaturase enzymes (linoleoyl-CoA desaturase, stearoyl-CoA 9-desaturase and phosphatidylcholine desaturase). Unusual high accumulation of saturated fatty acids with depleted lipid layer can be inferred as one of the major reasons of SNPs mediated fungistasis.     

Development and characterization of phospholipid-stabilized submicron aqueous dispersions of coenzyme Q10 presenting continuous vibrating-mesh nebulization performance

Abstract

Coenzyme Q₁₀ (CoQ₁₀) is a poorly-water soluble compound that is being investigated for the treatment of carcinomas. The aim of this research was to develop a suitable formulation for pulmonary delivery of this anticancer agent. An appropriate selection of excipients (phospholipids) and a suitable device (Aeroneb Pro® vibrating-mesh nebulizer) were selected initially after reviewing the literature. After characterization of the bulk drug, a feasible manufacturing process was selected to obtain small particle size dispersions of CoQ₁₀. Following selection of an appropriate process, the parameters affecting drug particle size were studied. Using LD and gravimetrical analysis, nebulization was evaluated to assess the performance of the inhalation system triad: drug–excipients–device. CoQ₁₀ powder studied was crystalline with a melting point approximately at 51?°C and with a particle size of 30?µm. Microfluidization was found to be a suitable method to prepare submicron drug particles in aqueous dispersions. Increasing microfluidization processing to more than 50 passes did not provide further particle downsizing for both soya phosphatidylcholine (lecithin) and dipalmitoyl phosphatidylcholine (DPPC) dispersions of CoQ₁₀, presenting Z-average values of approximately 130 and 70?nm, respectively. Nebulization performance of lecithin-stabilized CoQ₁₀ dispersions varied according to number of passes in the microfluidizer. Formulations processed with 10 passes presented steadier nebulization over time and different rheological behavior compared to those processed with 30 or 50 passes. In conclusion, aqueous dispersions of CoQ₁₀ were adequately produced using a microfluidizer with characteristics that were suitable for pulmonary delivery with an Aeroneb Pro® nebulizer. Furthermore, the rheology of these dispersions appeared to play a significant role in the aerosol generation from the active vibrating-mesh nebulizer used.     

Spectrofluorometric studies of the lipid probe, nile red

We found that the dye nile red, 9-diethylamino-5H-benzo[alpha]phenoxazine-5-one, can be applied as a fluorescent vital stain for the detection of intracellular lipid droplets by fluorescence microscopy and flow cytofluorometry (J. Cell. Biol. 1985. 100: 965-973). To understand the selectivity of the staining, we examined the fluorescence properties of nile red in the presence of organic solvents and model lipid systems. Nile red was found to be both very soluble and strongly fluorescent in organic solvents. The excitation and emission spectra of nile red shifted to shorter wavelengths with decreasing solvent polarity. However, the fluorescence of nile red was quenched in aqueous medium. Nile red was observed to fluoresce intensely in the presence of aqueous suspensions of phosphatidylcholine vesicles (excitation maximum: 549 nm; emission maximum: 628 nm). When neutral lipids such as triacylglycerols or cholesteryl esters were incorporated with phosphatidylcholine to form microemulsions, nile red fluorescence emission maxima shifted to shorter wavelengths. Serum lipoproteins also induced nile red fluorescence and produced spectral blue shifts. Nile red fluorescence was not observed in the presence of either immunoglobulin G or gelatin. These results demonstrate that nile red fluorescence accompanied by a spectral blue shift reflects the presence of nile red in a hydrophobic lipid environment and account for the selective detection of neutral lipid by the dye. Nile red thus serves as an excellent fluorescent lipid probe.     

Tissue distribution of EDTA encapsulated within liposomes of varying surface properties

Liposomes containing ethylenediaminetetraacetic acid (EDTA) were prepared with different surface properties by varying the liposomal lipid constituents. Positively charged liposomes were prepared with a mixture of phosphatidylcholine, cholesterol, and stearylamine. Negatively charged liposomes were prepared with a mixture of phosphatidylcholine, cholesterol, and phosphatidylserine. Neutral liposomes were prepared with phosphatidylcholine alone, dipalmitoyl phosphatidylcholine alone, or with a mixture of phosphatidylcholine and cholesterol. Distributions of ¹⁴C-labeled EDTA were determined in mouse tissues from 5 min to 24 h after a single intravenous injection of liposome preparation. Differences in tissue distribution were produced by the different liposomal lipid compositions. Uptake of EDTA by spleen and marrow was highest from negatively charged liposomes. Uptake of EDTA by lungs was highest from positively charged liposomes; lungs and brain retained relatively high levels of EDTA from these liposomes between 1 and 6 h after injection. Liver uptake of EDTA from positively or negatively charged liposomes was similar; the highest EDTA uptake by liver was from the neutral liposomes composed of a mixture of phosphatidylcholine and cholesterol. Liposomes composed of dipalmitoyl phosphatidylcholine produced the lowest liposomal EDTA uptake observed in liver and marrow but modrate uptake by lungs. Tissue uptake and retention of EDTA from all of the liposome preparations were greater than those of non-encapsulated EDTA. The results presented demonstrate that the tissue distribution of a molecule can be modified by encapsulation of that substance into liposomes of different surface properties. Selective delivery of liposome-encapsulated drugs to specific tissues could be effectively used in chemotherapy and membrane biochemistry.     

Formulation and optimization of solid lipid nanoparticles of buspirone HCl for enhancement of its oral bioavailability

Solid lipid nanoparticles (SLNs) of buspirone HCl as a water-soluble drug were prepared by emulsification-evaporation, followed by the sonification method. A preliminary screening of the most effective parameters on the production of nanoparticles by a Taguchi L₈ orthogonal array showed that the lipid type, surfactant percentage, speed of homogenizer, and acetone:dichloromethane (DCM) ratio had a significant effect on particle size. In the next step, the lipid was fixed on cetyl alcohol, surfactant on Tween 20, lecithin:lipid weight ratio on 20:70, sonication time on 30 seconds, and the other effective, independent factors aforementioned were studied each at three levels by a three-factor, three-level Box-Behnken design. The percentage of drug entrapment, mean particle-size diameter, and zeta potential were studied as the responses. Contour plots were constructed to further elucidate the relationship between the independent and dependent variables. A pharmacokinetic study was conducted in male Wistar rats after oral administration of 15?mg.kg^?1 buspirone in the form of free drug or SLNs. The optimized SLNs had aq particle size of 345.7?nm, loading efficiency of 32.8%, and zeta potential of ?6.8?mV. Buspirone released about 90% during 4.5?hours in vitro. It was found that the relative bioavailability of the drug in SLNs was significantly increased, compared to that of the drug solution.     

Impact of Surface Active Compounds on Iron Catalyzed Oxidation of Methyl Linolenate in AOT–Water–Hexadecane Systems

Edible oils contain minor surface active components that form micro-heterogeneous environments, such as reverse micelles, which can alter the rate and direction of chemical reactions. However, little is known about the role of these micro-heterogeneous environments on lipid oxidation of bulk oil. Our objective was to evaluate the ability of water, cumene hydroperoxide, oleic acid, and phosphatidylcholine to influence the structure of reverse micelles in a model oil system: sodium bis(2-ethylhexyl) sulfosuccinate (aerosol-OT; AOT) in n-hexadecane. The influence of reverse micelle structure on iron catalyzed lipid oxidation was determined using methyl linolenate as an oxidizable substrate. The size and shape of the reverse micelle were investigated by small-angle x-ray scattering, and water contents was determined by Karl Fischer titrations. Lipid hydroperoxides and thiobarbituric acid reactive substances were used to follow lipid oxidation. Our results showed that AOT formed spherical reverse micelles in hexadecane. The size of the reverse micelles increased with increased water or phosphatidylcholine concentration, but decreased upon addition of cumene hydroperoxide or oleic acid. Iron catalyzed oxidation of methyl linolenate in the reverse micelle system decreased with increasing water concentration. Addition of phosphatidylcholine into the reverse micelle systems decreased methyl linolenate oxidation compared to control and reverse micelles with added oleic acid. These results indicate that water, cumene hydroperoxide, oleic acid, and phosphatidylcholine can alter reverse micelle size and lipid oxidation rates. Understanding how these compounds influence reverse micelle structure and lipid oxidation rates could provide information on how to modify bulk oil systems to increase oxidative stability.