Beta-blockers and benzodiazepines location in SDS and bile salt micellar systems. An ESR study

The work here described aimed to find out the location of the different species of two families of pharmaceutical substances, namely two beta-blockers (atenolol and nadolol) and two benzodiazepines (midazolam and nitrazepam) in synthetic (sodium dodecyl sulphate, SDS) and natural (bile salts-sodium cholate and sodium deoxycholate) micellar aggregate solutions. Electronic spin resonance spectroscopy studies were carried out, at 25 degrees C and at an ionic strength of 0.10 M in NaCl, using 5-, 12- and 16-doxylstearic acid probes (AS). The immobilization degree of solubilized stearic acid spin probes was found to vary with the position of the nitroxide group in the sequence 5-doxylstearic acid>12-doxylstearic acid>16-doxylstearic acid for SDS and 12-doxylstearic acid>5-doxylstearic acid>16-doxylstearic acid for both bile salts investigated. Therefore, from the rotational correlational time values obtained, it can be inferred that the structure of bile salt micelles is markedly different from that of SDS micelles and the results suggest that the bile salt micelles studied have similar structure independently of differences in the molecular structure of the respective bile salts. Drug location studies were performed at pH 4.0 (SDS solutions) or 7.0 (bile salt solutions) and 10.8 in order to study the effect of the drug ionisation on its relative position on micelles. The results have shown that drug location is controlled by the (i) drug hydrophilicity and acid/base properties, with the more soluble compound in water (atenolol) exhibiting smaller variation of rotational correlational time (in SDS and bile salts solutions), and with both beta-blockers exhibiting smaller deviations in the protonated forms and (ii) the bile salt monomers, with the dihydroxylic bile salt (deoxycholate) producing larger differences. The work described herein allow us to conclude that the (protonated) beta-blockers are probably located on the surface of the detergent micelles, and linked to them by means of essentially electrostatic forces, while the (neutral) benzodiazepines are probably located deeper in the interior of the micelles.     

Examination of the solubilization of drugs by bile salt micelles

The purpose of this review is to provide a critical examination of the reported solubilization of drugs by bile salt micelles. The underlying premise is that with better information regarding the inherent biological complexity, efforts to predict the oral bioavailability of drug will be enhanced. The common means of comparing the reported values was chosen to be the solubilization ratio. This is equal to the moles of drug solubilized per mole of bile salt. The values were segregated according to bile salt type, temperature, ionic strength, and the presence and absence of added lipids. Only segregation by bile salt type was pairwise statistically significant. From the solubilization ratios and the reported values of the aqueous solubility, the logarithms of the mole fraction micelle partition coefficients, log K(m/a), were calculated. The log K(m/w) was found to be correlated with the reported logarithm of the octanol/water partition coefficient. The rank order of slopes of the log K(m/a) as a function of log K(o/w) was cholate approximately taurodeoxycholate > glycocholate approximately taurocholate approximately glycodeoxycholate, with deoxycholate not being statistically different from the other data sets. The slope and intercept for the bile salt mixed micelle systems were 0.600 and 2.44, respectively, which were statistically indistinguishable from glycocholate, taurocholate, and glycodeoxycholate bile salt data. The existence of statistically significant correlations suggests that predicting the solubilization in the intestine may be possible with in vitro measurements if additional information is gathered in the appropriate micellar solutions.     

Solubilization of vitamin K1 by bile salts and phosphatidylcholine-bile salts mixed micelles

The solubilization of vitamin K1 by bile salts (sodium deoxycholate, sodium cholate and their corresponding glycine conjugates) and phosphatidylcholine (egg)-bile salt mixed micelles has been investigated. The solubilization curves were not always linear with increasing bile salts, but the vitamin was appreciably solubilized in the region below their CMCs. In the bile salt solutions (20 mM, phosphate buffered saline, pH 7.5, ions strength 0.2), the solubilized vitamin ranged from 0.3 to 0.9 mM. With increasing phosphatidylcholine, the amount of vitamin solubilized was dramatically increased; at the molar ratio of 1:1 (both 20 mM), the amount of vitamin solubilized was about 25-30 times more than by the corresponding bile salts alone. There is a possibility that exogenous phospholipid given orally as liposomal forms assists the solubilization of vitamin K1, in the intestine. This characteristic is suggested as being responsible, in part, for the enhanced recovery of blood coagulation after oral administration of liposomal vitamin K1 to warfarin-treated rabbits.     

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.     

Lecithin in mixed micelles attenuates the cytotoxicity of bile salts in Caco-2 cells

This study was designed to investigate the cytotoxicity of bile salt–lecithin mixed micelles on the Caco-2 cell model. Cell viability and proliferation after mixed micelles treatments were evaluated with the MTT assay, and the integrity of Caco-2 cell monolayer was determined by quantitating the transepithelial electrical resistance and the flux of tracer, FITC-dextran 4400. The apoptosis induced by mixed micelles treatments was investigated with the annexin V/PI protocol. The particle size of mixed micelles was all smaller than 100 nm. The mixed micelles with lower than 0.2 mM sodium deoxycholate (SDC) had no significant effects on cell viability and proliferation. When the level of SDC was higher than 0.4 mM and the lecithin/SDC ratio was lower than 2:1, the mixed micelles caused significant changes in cell viability and proliferation. Furthermore, the mixed micelles affected tight junctions in a composition-dependent manner. Specifically, the tight junctions were transiently opened rather than damaged by the mixed micelles with SDC of between 0.2 and 0.6 mM. The mixed micelles with more lecithin also induced less apoptosis. These results demonstrate that relatively higher concentrations of mixed micelles are toxic to Caco-2 cells, while phospholipids can attenuate the toxicity of the bile salts.     

Biorelevant dissolution media: aggregation of amphiphiles and solubility of estradiol

Biorelevant dissolution media containing bile salt and lecithin at concentrations appropriate for fed and fasted state are useful when testing oral solid formulations of poorly water-soluble drugs. Dilution of amphiphile solutions affects the aggregation state of the amphiphiles because bile salt is partitioned between the aqueous phase and the aggregates. The aim of the investigation was to study the effect of dilution on the size distribution of aggregates and its effect on the solubilization capacity. Clear buffered solutions of four intestinal amphiphiles (sodium glycocholate, lecithin, monoolein, and oleic acid) and a combination of these were prepared at high bile salt concentration. Micelles in the glycocholate solutions decreased in size when diluted. The addition of insoluble amphiphiles led to bigger micelles with no clear correlation between size of the micelles and amphiphile concentration. Dilution of the two- and four component media caused enlargement of the mixed micelles and formation of vesicles. The solubility of estradiol in the buffer solution was increased with addition of the amphiphiles. A good correlation (R(2) = 0.987) was found between estradiol solubility and mass concentration of the amphiphiles. The results demonstrate that, in the case of estradiol, the concentration of amphiphiles rather than the aggregation state determines the solubilization capacity of the medium.     

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.     

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.     

Effect of mixed micelle formulations including terpenes on the transdermal delivery of diclofenac

The significant inhibitory action of diclofenac formulated in mixed micelles of lecithin with cholate or deoxycholate was observed on the rat hind paw edema induced by carrageenan. In the primary stage, mixed micelle formulation of deoxycholate was more effective compared with that of cholate. However, in the final term, the inhibitory action was similar in both formulations. In a previous study, the flux of diclofenac was greater in the mixed micelle formulation of deoxycholate compared with that of cholate. It was suggested that the permeation rate of diclofenac through skin was proportional to the pharmacological activity. The hind paw edema was quickly inhibited when cyclic monoterpene such as d-limonene or l-menthol was included in the formulations. All the micelle formulations significantly decreased the value of AUC estimated the hind paw thickness-time profile. This suggests that the micelle formulation of cholate in addition to deoxycholate showed significant anti-inflammatory activity to hind paw edema of rats. Incorporation of d-limonene or l-menthol was more effective on the decrease of AUC. A pharmacological study revealed that micelle formulations were able to reduce the skin irritation of chemicals.     

A comparison of the permeation enhancement potential of simple bile salt and mixed bile salt:fatty acid micellar systems using the CaCo-2 cell culture model

The aim of this study was to compare the permeation enhancing potential and toxicity of simple bile salt and bile salt:fatty acid mixed micellar systems using the CaCo-2 cell culture model. The effects of micellar systems of sodium cholate, (NaC), and sodium taurocholate, (NaTC), on the permeability of the hydrophilic markers, mannitol (182) and polyethylene glycols (PEGS) 900 and 4000, were assessed. Simple micelle systems of the unconjugated bile salt, NaC, caused greater enhancement of the hydrophilic markers than the conjugated bile salt, NaTC. In the case of NaC systems the enhancement was coincident with excess membrane disruption and toxicity as indicated by altered TEERs, TEMs, MTT values, and, the lack of recovery following removal of the enhancer. In contrast, the NaTC systems were less toxic, and, in the simple micelle form the likely mechanism of enhancement of the hydrophilic markers is via a transient effect on the tight junctions. Formation of mixed micellar systems with linoleic acid (LA) accentuated the toxic effects of NaC. In comparison, NaTC:LA mixed micelles showed superior permeability enhancement versus simple micelles without increasing membrane toxicity. The mechanism of enhancement of NaTC:LA appears more complex and involves a possible combination effect on both the paracellular and transcellular routes.     

混合胶团增溶的环孢素A经小鼠皮肤的渗透作用

目的研究由不同表面活性剂和磷脂所组成的混合胶团(mixedmicelles)对环孢素A经小鼠皮肤给药的渗透促进作用。方法将含药混合胶团溶液封闭性应用于离体或在体小鼠皮肤,测定接收介质和血液中环孢素A含量。结果离体条件下,不同表面活性剂和磷脂所形成的混合胶团的皮肤渗透作用强度为:胆酸钠-磷脂混合胶团>脱氧胆酸钠-磷脂混合胶团>TritonX-100-磷脂混合胶团>Tween-20-磷脂混合胶团。在体条件下,用胆酸钠-磷脂混合胶团后,5h血药浓度达峰值,随后血药浓度缓慢下降。结论混合胶团在水溶液状态下对大分子难溶药物环孢素A具有一定的皮肤促渗效果。     

Mixed micelle proliposomes for preparation of liposomes containing amphotericin B, in-vitro and ex-vivo studies

The aim of this work was to produce a form of injectable liposomes containing amphotericin B derived from mixed micelle proliposomes. Mixed micelles were derived from a mixture of lecithin/sodium cholate in aqueous media. The solubility of amphotericin B in proliposomes was studied as a function of lipid composition (total lipid concentration, molar ratio of lecithin/sodium cholate), and the dispersion media (pH, ionic strength, presence or absence of human serum albumin), and the temperature. The data show that micelle-->liposome transformation occurs during the dilution of proliposomes containing amphotericin B. These transformations could be followed via transmission electron microscopy (TEM). Data related to dilution of proliposomes as well, show that under no circumstance there occurs any precipitation that might be assigned to the decreased solubility of amphotericin B. These indicate that the incorporated drug also participates during the transformation of the proliposomes into liposomes. It is thus concluded that mixed micelle proliposomes are prime candidates for the production of a form of injectable amphotericin B in liposomes.     

Bile salt composition is secondary to bile salt concentration in determining hydrocortisone and progesterone solubility in intestinal mimetic fluids

Simulated intestinal fluids (SIFs) used to assay the solubility of orally administered drugs are typically based on a single bile salt; sodium taurocholate (STC). The aim of this study was to develop mimetic intestinal fluids with a closer similarity to physiological fluids than those reported to date by developing a mixed bile salt (MBS) system (STC, sodium glycodeoxycholate, sodium deoxycholate; 60:39:1) with different concentrations of lecithin, the preponderant intestinal phospholipid. Hydrocortisone and progesterone were used as model drugs to evaluate systematically the influence of SIF composition on solubility. Increasing total bile salt concentration from 0 to 30 mM increased hydrocortisone and progesterone solubility by 2- and ～25-fold, respectively. Accordingly, higher solubilities were measured in the fed-state compared to the fasted-state SIFs. Progesterone showed the greatest increases in solubility in STC and MBS systems (2-7-fold) compared to hydrocortisone (no significant change; P>0.05) as lecithin concentration was increased. Overall, MBS systems gave similar solubility profiles to STC. In conclusion, the addenda of MBS and lecithin were found to be secondary to the influence of BS concentration. These data provide a foundation for the design of more bio-similar media for pivotal decision-guiding assays in drug development and quality control settings.     

大豆磷脂脂质载体与胆酸盐表面活性剂的体外相互作用

采用旋转薄膜蒸发法结合挤压过滤工艺制备大豆磷脂脂质体,所制得脂质体的平均粒径为217nm,跨距0．838,负染色脂质体经透射电镜观察,呈明显的双层膜圆球型结构。以胆酸钠盐和脱氧胆酸钠盐研究其与脂质体之间的相互作用,将500nm波长处的可见光吸收值评价胆盐-脂质体混悬液的浊度,测定脂质体的粒径变化情况。在胆酸盐加入的初期,由于胆酸盐和脂质体形成混合胶团,致使脂质体的粒径和浊度值稍有增加,进一步加入的胆酸盐使脂质体的粒径和浊度值下降。胆盐和脂质体问的相互作用经历了数个重排现象,使脂质体的粒径发生规律性的变化,这与脂质体的体内稳定性密切相关,也可反映脂质体的载药和释药特性。     

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.     

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.     

Silicone polymer uptake method for determination of cholesterol thermodynamic activity in model bile systems

Cholesterol in bile has been linked to the incidence of gallstone disease through the concept of supersaturation as measured by the cholesterol saturation index (CSI). The latter is a linear function of cholesterol concentration and is based on the assumption that all cholesterol in bile is solubilized and transported in bile salt-lecithin (BS-L) mixed micelles, as well as in bile salt simple micelles. In light of the discovery of the cholesterol-lecithin vesicles as significant cholesterol carriers, there is a need to re-evaluate this old concept. This study examined the feasibility of the silicone polymer uptake method for the direct determination of the cholesterol thermodynamic activity (AT) in model bile systems. In cases of unsaturation and near saturation, a linear relationship was observed between CSP,Eq, the cholesterol concentration in the silicone polymer at equilibrium, and CAq,Eq/Cs,Aq for taurocholate (TC), taurochenodeoxycholate (TCDC), and tauroursodeoxycholate (TUDC) systems either containing or not containing lecithin. Here, CAq,Eq is the cholesterol concentration in the aqueous micellar solution at equilibrium, and Cs,Aq is the cholesterol monohydrate solubility of the same medium. In TC-L solutions supersaturated with cholesterol, the linear relationship continued to hold up to the point where vesicles started to form. Vesicle formation initiated a negative deviation from linearity. At constant lecithin concentration, the CSP,Eq value, or the cholesterol thermodynamic activity at which vesicle formation began, was a function of the TC:L ratio; the larger the TC:L ratio, the higher the cholesterol thermodynamic activity for the onset of vesicle formation.(ABSTRACT TRUNCATED AT 250 WORDS)     

A dynamic in vitro lipolysis model. II: Evaluation of the model.

A lipolysis model was characterised and evaluated by investigating the composition of the aqueous phase and the concentration of probucol and danazol in the aqueous phase. Effects of bile salt levels at 5, 10, 20, and 30 mM were investigated. Samples were taken at 0%, 50%, 75% and 95% hydrolysis of the triglycerides, and the aqueous phases were isolated by ultra-centrifugation, whereby the concentrations of bile salts, fatty acids, mono-, di-, triglycerides, and drug substances were measured. At high Ca(2+)-concentrations, bile salts were believed to precipitate with Ca(2+). The concentration of lipolytic products (fatty acids + monoglycerides) was dependent on the bile salt concentration. The ratio between lipolytic product and bile salts was 1.55+/-0.09 (S.D.). This ratio is equivalent to mixed bile salt micelles and vesicles in equilibrium. The aqueous solubility of probucol and danazol was increased in the presence of bile salts. The concentration of danazol in the aqueous phase was dependent on the solubilisation capacity of the aqueous phase. In the case of probucol, the concentration in the aqueous phase was dependent on the partition of probucol between the aqueous phase and the remaining triglyceride phase. This difference between danazol and probucol was attributed to the effect of different lipophilicity.     

Improvement of absolute bioavailability of normally poorly absorbed drugs: inducement of the intestinal absorption of streptomycin and gentamycin by lipid-bile salt mixed micelles in rat and rabbit

The effect of lipid—bile salt mixed micelles on the intestinal absorption of streptomycin and gentamycin was investigated in the loop of small and large intestine of rat. While bile salts micellar solutions did not enhance the absorption of aminoglycosides, their mixed micellar solutions including monoolein, oleic or lauric acid markedly enhanced their absorption. However, lecithin—bile salt mixed micellar solution did not affect the absorption. Pretreatment with mixed micellar solutions showed neither a direct action on the mucosal membrane nor a transient increase in permeability to aminoglycosides.Improvement of bioavailability in the rabbit was evaluated using various formulations and different routes of administration. In the rectal administration, not only mixed micellar solutions but also lyophilized mixed micelles powder improved bioavailability. The duodenal administration of mixed micellar solution, however, was not effective, indicating that enhanced absorption of drugs by mixed micelles may be more pronounced with rectal administration.