Solubilization of napthalene by sodium cholate and pattern of self-association of sodium cholate in 0.15 M sodium chloride

Naphthalene solubility was determined in aqueous 0.15 M NaCl containing sodium cholate in the 0-0.05 M concentration range at 25 +/- 0.1 degrees. Sodium cholate tends to self-associate in aqueous solutions. Most often, the association pattern has been described in terms of a monomer-micellar model in which it is assumed that no association occurs below the critical micelle concentration. By comparison of the experimental solubilization curve with curves calculated on the basis of the monomer-micellar model, it was shown that this model is inappropriate for the self-association pattern of sodium cholate. The solubility data were consistent with a model that assumes that sodium cholate associates to form dimers, trimers, and higher aggregates with an average aggregation number of 7.63. Model calculations suggest that naphthalene is solubilized by dimers and higher aggregates. Solubilization of naphthalene by trimers appears to be negligible.     

Characterization of proliposomes

Photographic evidence of the process of proliposome hydration is provided together with comprehensive particle size analysis of both hydrated dimyristoylphosphatidylcholine: dimyristoylphosphatidylglycerol:ergosterol:amphotericin B proliposomes and egg lecithin:ergosterol:amphotericin B proliposomes using photon correlation spectroscopy and Coulter Counter analysis. Proliposome particle size and the temperature during hydration have been shown to have little effect on subsequent liposome size. A short term stability study of proliposomes indicated that only minor changes in the size distribution profile of the hydrated product are apparent after storage at 20 degrees C for 9 months. Furthermore, no drop in amphotericin B potency was noticed over a 6-month period.     

Chitosan‐coated antifungal formulations for nebulisation

Objectives The aim of this study was to produce and characterise amphotericin B (AmB) containing chitosan‐coated liposomes, and to determine their delivery from an air‐jet nebuliser. Methods Soya phosphatidylcholine : AmB (100 : 1) multilamellar vesicles were generated by dispersing ethanol‐based proliposomes with 0.9% sodium chloride or different concentrations of chitosan chloride. These liposomes were compared with vesicles produced by the film hydration method and micelles. AmB loading, particle size, zeta potential and antifungal activity were determined for formulations, which were delivered into a two‐stage impinger using a jet nebuliser. Key findings AmB incorporation was highest for liposomes produced from proliposomes and was greatest (approximately 80% loading) in chitosan‐coated formulations. Following nebulisation, approximately 60% of the AmB was deposited in the lower stage of the two‐stage impinger for liposomal formulations, for which the mean liposome size was reduced. Although AmB loading in deoxycholate micellar formulations was high (99%), a smaller dose of AmB was delivered to the lower stage of the two‐stage impinger compared to chitosan‐coated liposomes generated from proliposomes. Chitosan‐coated and uncoated liposomes loaded with AmB had antifungal activities against Candida albicans and C. tropicalis similar to AmB deoxycholate micelles, with a minimum inhibitory concentration of 0.5 µg/ml. Conclusions This study has demonstrated that chitosan‐coated liposomes, prepared by an ethanol‐based proliposome method, are a promising carrier system for the delivery of AmB using an air‐jet nebuliser, having a high drug‐loading that is likely to be effectively delivered to the peripheral airways for the treatment of pulmonary fungal infections.     

Preparation and <Emphasis Type="Italic">in vitro</Emphasis> evaluation of povidone-sodium cholate-phospholipid mixed micelles for the solubilization of poorly soluble drugs

Mixed micelles made of polyvinylpyrrolidone (PVP), sodium cholate, and phospholipids were prepared to improve the solubility of poorly water-soluble drugs. Sylibin, a drug used in treating liver diseases, was incorporated into the mixed micelles. The formulation of sylibin containing PVP-sodium cholate-phospholipid mixed micelles with an optimized composition (PVP/sodium cholate/phospholipid/silybin = 3:3:4:1∼2 by weight) was obtained based on the study of pseudoternary phase diagrams. The critical micelle concentration was used to evaluate the micellar stability towards dilution. The results showed that addition of PVP to sodium-cholate-phospholipid mixed micelles increased stability. The solubility of sylibin in PVP-sodium cholate-phospholipid mixed micelles was higher than that in pure water or in sodium cholate-phospholipid mixed micelles. In a stability study, we found that PVP-sodium cholate-phospholipid mixed micelles showed good stability. After 3 months storage at 40°C, just 2.6% sylibin was lost with only minor changes of the particle size when compared to a reference formulation containing sodium cholate and phospholipid mixed micelles. In addition, the developed formulation significantly improved in vitro drug release. The time required to release 50% sylibin (t50%) from sodium cholate and phospholipid mixed micelles was 326 h, while the t50% from PVP-sodium cholate-phospholipid mixed micelles was only 51.1 h. Our results suggest that these mixed micelles might have significant potential application to the biomedical field.     

Enthalpy of bile salt-lecithin mixed micelle formation.

The enthalpies for the dissolution of lecithin by sodium salts of cholic, deoxycholic, and chenodeoxycholic acids and their glycine and taurine conjugates are reported.Exothermic enthalpies were found in each case. It is suggested that heat evolution is due to a bile salt-lecithin interaction other than hydrophobic interactions. These results provide strong support for the "mixed disk" model for the complex lecithin-bile salt micelle, which requires that a substantial fraction of the bile salt molecules be incorporated within a lecithin bilayer where hydrogenbonded pair formation can occur. Calorimetric studies of the interaction between sodium cholate and nonionic, cationic, and anionic detergents yielded exothermic heats. These results suggest that these bile salt molecules partition into the detergent micelle interior as hydrogenbonded pairs.     

Physicochemical properties of liposomes incorporating hydrochlorothiazide and chlorothiazide

In an attempt to study the effect of hydrophobic drugs on liposome properties, multilamellar liposomes (MLV) consisting of phosphatidylcholine (PC) and incorporating chlorothiazide (CT) or hydrochlorothiazide (HCT), were prepared and characterized. Liposome size, surface charge, stability (in buffer, plasma and sodium cholate) and calcium-induced aggregation were studied for drug-incorporating liposomes and empty liposomes for comparison. Results show that drug incorporation affects liposome size, z-potential and stability in presence of buffer and plasma proteins. Indeed, drug-incorporating liposomes are slightly larger and have a negative surface charge, which increases with the amount of drug incorporated in the lipid membrane. The membrane integrity of drug incorporating liposomes (in absence and presence of plasma proteins) is significantly higher when compared with that of empty liposomes (for both drugs studied). On the contrary, vesicle membrane integrity in presence of sodium cholate and calcium induced vesicle aggregation, are not affected by drug incorporation. Leakage of thiazides from liposomes was demonstrated to be induced by dilution. Low amounts of thiazides (around 10-15%) are released when lipid concentration is over 0.1 mM, while further dilution increased drug leakage exponentially. Concluding, results demonstrate that the presence of HCT or CT in liposome membranes has a significant effect on main vesicle properties, which are known to influence vesicle targeting ability. Thereby, it is very interesting to continue studies in this respect, especially with more lipophilic drugs.     

In-vitro release of diclofenac diethylammonium from lipid-based formulations

This article presents the preparation and topical performance of some new lipid-based formulations of diclofenac, namely (a) a diclofenac aqueous gel containing mixed micelles (sodium cholate:egg lecithin molar ratio 0.55); (b) diclofenac lotion that contains soya lecithin, ethanol and buffer; and (c) diclofenac lipogel containing egg lecithin, isopropyl myristate, propylene glycol and ethanol. Gel formulations were prepared using Carbomer 934. Release of diclofenac from all formulations was monitored via dialysis through Spectra/por membrane into phosphate buffer (0.2 M pH=7.4) using a Franz cell. Drug release profile and diffusion coefficients were compared with brand formulation (Geigy's Vlotaren Emulgel). Statistical analysis of data show that the diffusion coefficient of the drug from these formulations rank according to the following order: Diclofenac lotion (D=5.308x10(-7) cm(2)/s) >lipogel (D=2.102 x 10(-7) cm(2)/s) >Voltaren Emulgel (1.518 x 10(-7) cm(2)/s) >aqueous gel mixed micelle (0.966 x 10(-7) cm(2)/s). These results show that diclofenac lotion and lipogel maybe more suitable formulations than the conventional topical dosage form.     

Solubilization and pharmacokinetic behaviors of sodium cholate/lecithin-mixed micelles containing cyclosporine A

The purpose of this study was to investigate the solubilization capacity of sodium cholate/lecithin-mixed micelles and to evaluate the potential of mixed micelles as a carrier of cyclosporine A for intravenous infusion. The mixed micelles were prepared by coprecipitation technique. The formulation components and preparation procedures, which may affect the solubilization of cyclosporine A, were studied. The dilution stability of cyclosporine A-containing mixed micelles was investigated. Pharmacokinetic behaviors of mixed micelles in rabbits after intravenous infusion were compared with Sandimmun. Results showed the strategies to increase the solubility of cyclosporine A include lowering the molar ratio of sodium cholate to lecithin, increasing the concentration of lecithin, and reducing the ionic strength of the dispersion medium and temperature. The largest solubility was found to be 5.42 +/- 0.16 mg/ml. The leakage of mixed micelles in 5% glucose (5.84%) was much less than that in saline solution (36.7%). The relative bioavailability of mixed micelles versus Sandimmun was 112 +/- 20%, and statistical analysis demonstrated both preparations were bioequivalent. Sodium cholate/lecithin-mixed micelles are promising carriers in the intravenous delivery of cyclosporine A, considering their capability of large-scale production and low-toxic property.     

Solubilization and Pharmacokinetic Behaviors of Sodium Cholate/Lecithin-Mixed Micelles Containing Cyclosporine A

The purpose of this study was to investigate the solubilization capacity of sodium cholate/lecithin-mixed micelles and to evaluate the potential of mixed micelles as a carrier of cyclosporine A for intravenous infusion. The mixed micelles were prepared by coprecipitation technique. The formulation components and preparation procedures, which may affect the solubilization of cyclosporine A, were studied. The dilution stability of cyclosporine A-containing mixed micelles was investigated. Pharmacokinetic behaviors of mixed micelles in rabbits after intravenous infusion were compared with Sandimmun®. Results showed the strategies to increase the solubility of cyclosporine A include lowering the molar ratio of sodium cholate to lecithin, increasing the concentration of lecithin, and reducing the ionic strength of the dispersion medium and temperature. The largest solubility was found to be 5.42 ± 0.16 mg/ml. The leakage of mixed micelles in 5% glucose (5.84%) was much less than that in saline solution (36.7%). The relative bioavailability of mixed micelles versus Sandimmun® was 112 ± 20%, and statistical analysis demonstrated both preparations were bioequivalent. Sodium cholate/lecithin-mixed micelles are promising carriers in the intravenous delivery of cyclosporine A, considering their capability of large-scale production and low-toxic property.     

A novel method to prepare liposomes containing amikacin.

This work describes a novel method to prepare liposomal amikacin composed of soyabean lecithin and cholesterol; these were also prepared using two other methods (cast film method and proliposome method). Encapsulation efficiency was evaluated. Liposomes prepared by the new method, which combines the method of preparing proliposomes with freeze-drying, had the highest encapsulation efficiency. The influence of drug to lipid ratio on the encapsulation efficiency was investigated. The in vitro efflux of amikacin from liposomes with different lecithin: cholesterol ratios was also investigated.     

胆酸钠/磷脂混合胶团对环孢素A的增溶作用研究

目的研究胆酸钠/磷脂混合胶团对难溶性多肽环孢素A(CyA)的增溶作用.方法采用共沉淀法制备胆酸钠/磷脂混合胶团,并对影响增溶作用的处方及工艺进行考查.结果相同胆酸钠浓度条件下,混合胶团对CyA的增溶能力远大于胆酸钠胶团,增大混合胶团中的磷脂用量或者降低胆酸钠/磷脂(摩尔比)均有利于提高混合胶团对药物的增溶能力.升高水合温度,增加水合介质的离子强度,加入抗氧化剂维生素E(VE)及胆固醇,均不同程度的降低了混合胶团的增溶能力.通过优化各个影响因素可获得最大的增溶量(＞5mg/mL),增加CyA溶解度100倍以上.结论胆酸钠/磷脂混合胶团可以成为CyA等难溶性多肽药物的一种新型增溶载体.     

Clinical formulations of amphotericin B]

The clinical use of amphotericin B is impaired by its poor water solubility and by the severity of its side effects. Several amphotericin B formulations have already been prepared in an attempt to overcome these disadvantages. The following methods have been proposed to solubilize amphotericin B in water: the complexation of amphotericin B with metallic ions, sodium tetraborate or gamma cyclodextrin or the synthesis of semi-synthetic derivatives. Another approach was to use a carrier (liposomes, lipoproteins, emulsions or surfactants) to target amphotericin B. This paper summarizes and criticizes these formulations.     

Lecithin vesicles for topical delivery of diclofenac.

Skin penetration of topically applied diclofenac is important for the treatment of rheumatic diseases and actinic keratoses. We have studied the permeation of diclofenac across human cadaver epidermis in-vitro from four lecithin vesicle formulations and a few marketed semi-solid preparations. The lecithin vesicle formulations were prepared by dissolving the lipid contents (lecithin and sodium cholate) in a 1:1 mixture of methanol-chloroform, evaporating the solvents under vacuum, and hydrating the lipid layer with the drug solution in water or 10% ethanol. The vesicles were sonicated for 5 min to reduce the vesicle size and their size and Zeta potential were characterized. The cumulative amount and maximum flux of diclofenac was 69.7+/-40.3 micrograms and 4.77+/-3.16 micrograms/hcm(2) from lecithin vesicles containing sodium cholate and 10% ethanol, and is the highest of all formulations studied. The cumulative amount and mean maximum flux obtained from other formulations were in the range of 2.46+/-1.98-29.9+/-10.1 micrograms and 0.53+/-0.46-3.61+/-0.86 micrograms/hcm(2). Based on the results, lecithin vesicles of diclofenac appear to be advantageous for the topical delivery of diclofenac.     

Study of partition of nitrazepam in bile salt micelles and the role of lecithin

The effect of trihydroxy (sodium cholate and sodium glycocholate) and dihydroxy (sodium deoxycholate and sodium glycodeoxycholate) bile salt micelles on the spectrophotometric properties and on the solubility of nitrazepam in aqueous solution, at 25.0 degrees C and at ionic strength 0.1 M in sodium chloride, has been assessed. From the results obtained it was possible to calculate the partition coefficients (Kp) of nitrazepam between aqueous and micellar phases. The partition coefficients of nitrazepam have also been determined in mixed micelles of cholate or deoxycholate with lecithin (egg yolk phosphatidylcholine), which were used as a model of the gastrointestinal tract. Drug partition was found to depend on the bile acid (number of hydroxyl groups and conjugation with glycine), and our data indicate further that addition of lecithin to bile salt micelles decreases the values of the partition coefficients in the mixed micelles at physiological pH.     

Mixed Micelles as Proliposomes for the Solubilization of Teniposide

The aqueous solubility of teniposide in detergent and phospholipid mixed micelles was investigated as functions of the detergents and lipids composing the mixed micelles, the molar ratio of detergent to phospholipid, and the total lipid concentration of the system. The polarity, the charge of the phospholipid, and its saturation affected the solubilization potential of the micelles. Physical chemical factors such as the pH, ionic strength, and temperature of the dispersion medium also altered the solubilization capacity of the system. The results are explained by the changes occurring in the critical micelle concentration and packing arrangements of the aggregates. The desired solubility of teniposide can be achieved by adjusting the studied parameters to the optimum values. Teniposide-containing mixed micelles were spontaneously converted to drug-containing vesicles upon aqueous dilution; therefore, the precipitation of the drug was totally eliminated. In conclusion, mixed micelles as proliposomes can be a suitable drug carrier system for insoluble compounds such as teniposide.     

Proliposomes of indomethacin for oral administration

Indomethacin, a non-steroidal anti-inflammatory drug was encapsulated into liposomes composed of soyabean lecithin, cholesterol and stearylamine for oral administration. Liposomes of homogenous size distribution and higher entrapment efficiency were derived from effervescent granule based proliposomes. The efficacy of the oral route was studied by measuring ulcerogenic index and anti-inflammatory activity using carrageenan induced paw oedema test in rats. The effervescent granule based liposomal products exhibited improved in vivo performance with reference to their cytoprotective and anti-inflammatory activities.     

The bioavailability of dipyridamole in the form of liposomes

Liposomes containing dipyridamole have been prepared by evaporating-shaking method. Phospholipid bilayer consisted of lecithin and cholesterol in three varying molar rations: 5:2, 7:2, 10:2. According to lipid layer composition the obtained liposomes varied in size and amount of dipyridamole entrapped. The suspension of liposomes in 0.9% sodium chloride prepared with lecithin and cholesterol in molar ratio 7:2 was chosen to the study in vivo. A suspension of dipyridamole in 0.9% sodium chloride was used comparatively. Particle size of dipyridamole was similar to that of liposomes with entrapped substance. Both suspensions were administrated to guinea pigs orally or intraperitoneally. The study has shown that liposomally-entrapped dipyridamole has essential and advantageous effect on its absorption after oral or intraperitoneal administration when compared with dipyridamole itself. The best bioavailability has been demonstrated by the suspension of liposomes after intraperitoneal administration.     

Improved oral delivery of resveratrol using proliposomal formulation: investigation of various factors contributing to prolonged absorption of unmetabolized resveratrol

Objectives: The objective of this study was to design lipid-based formulation to enhance the absorption of unmetabolized resveratrol (RSV) over adequate time and investigate various factors that contribute to prolonged absorption of RSV.

Methods: Proliposomal formulations containing distearoyl phosphatidyl choline (DSPC) with or without cholesterol were prepared and evaluated. The liposomes obtained from hydration of proliposomal mixture were evaluated for size, zeta, physical appearance and entrapment. The integrity of liposomes in bile salt solution and solubility of RSV in sodium taurocholate solution in the presence of various concentrations of DSPC were evaluated to assess the stability and in varied gastrointestinal conditions. Finally, oral pharmacokinetic studies of liposomal dispersions in comparison with RSV solution were evaluated.

Results: Results revealed that spontaneous formation of liposomes did not occur upon hydration of RSV: DSPC proliposomes rather showed tendency to form loose cotton-like aggregates. Cholesterol aided in the formation of stable liposomes with large negative zeta potential. Release of RSV from liposomes in the presence of taurocholate was dependent on the amount and type of total lipid. Liposomes without cholesterol showed faster release, and release increased as the amount of DSPC in the formulation increased. Solubility studies indicated that DSPC increases the solubility of RSV in the presence of sodium taurocholate, and corroborates that bilayer assembly is disrupted because of interaction between RSV and DSPC. Mixture of RSV:DSPC:Chol at 1:0.25:0.25 formed stable colloidal dispersion with zeta potential ?22 and released only 20 – 23% of entrapped RSV when incubated with 20 mM sodium taurocholate. Pharmacokinetic profile revealed that AUC and C_max were twofold higher than plain RSV.

Conclusion: The proliposomal formulation optimized by considering various physicochemical factors and simulated in vitro testing result in significant improvement rate and extent of absorption of unmetabolized RSV.     

Deformable liposomes and ethosomes as carriers for skin delivery of ketotifen

Deformable liposomes and ethosomes were investigated as carriers for skin delivery of ketotifen (KT) in terms of vesicle size, entrapment efficiency, stability, in vitro permeation and skin deposition properties. Phosphatidylcholine (PC) from soybean lecithin was used in the preparation of all vesicles. Sodium cholate, sodium deoxycholate and Tween 80 were investigated as edge activators in preparation of KT deformable liposomes. KT ethosomes were prepared in two PC concentrations, 2% and 4.25% w/v, in 30% v/v ethanol. KT deformable liposomes showed improved entrapment efficiency over KT ethosomes. KT deformable liposomes with Tween 80 as an edge activator were more stable upon storage at 5 +/- 1 degree C than those prepared using sodium cholate or sodium deoxycholate and were more stable than KT ethosomes. In vitro permeation and skin deposition studies employed only deformable liposomes with Tween 80 as an edge activator and ethosomes with 4.25% w/v PC concentration. Both of them improved skin delivery of KT over controls and over traditional liposomes, with greater improvement of KT skin deposition than KT skin permeation, hence are more useful for dermal than for transdermal delivery of KT.     

渗透促进剂对多肽类药物肺部给药促渗作用的机理

目的从肺细胞膜流动性的角度探讨渗透促进剂增加多肽类药物肺部吸收的作用机制。方法以鲑鱼降钙素(sCT)为模型药物,考查多种渗透促进剂对sCT经肺吸收的促进作用。采用电子自旋共振(ESR)技术和荧光偏振技术测定旋转相关时间(τ_C)及荧光偏振度(P),计算渗透促进剂处理前后膜脂流动性和膜蛋白构象的变化,从而考查渗透促进剂增加药物肺部吸收的原因。结果可以显著促进药物吸收的苄泽78、卵磷脂、辛酸钠均引起膜脂质流动性的增加,同时造成蛋白构象不同程度的松散;牛磺胆酸钠对膜蛋白的影响较弱;壳聚糖降低膜脂流动性,其促渗作用主要来自于改变了膜蛋白的三级结构而使细胞间紧密连接张力减小;2-羟丙基-β-环糊精对药物吸收没有明显贡献,同时其对膜通透性基本没有影响。结论考查体外细胞膜流动性的变化为研究渗透促进剂对药物肺部吸收的促进作用提供了重要依据。