Solubilisation of drugs in micellar solutions of diblock copolymers of ethylene oxide and styrene oxide

The solubilisation of two poorly soluble drugs, furosemide and nabumetone, in micellar solutions of diblock copolymers of ethylene oxide and styrene oxide has been studied at 25 and 37 degrees C and solubilisation capacities compared with published values for griseofulvin and docetaxel. Solubilisation in the micelle core, corrected for the different proportions of poly(styrene oxide) in the copolymers, was similar for all four drugs. The highest solubilisation capacities were found for a copolymer with worm-like micelles.     

Study of the solubilization of gliclazide by aqueous micellar solutions

It was of interest to increase the solubility of gliclazide in aqueous media. Therefore, solubilization of gliclazide in a variety of surfactants was investigated. Anionic and cationic surfactants exhibited dramatic solubilizing ability for gliclazide, whereas nonionic surfactants showed significantly lower solubilizing ability. It was found that gliclazide solubility increases with increasing the carbon chain length of cationic surfactants and decreases with increasing the carbon chain length of anionic surfactants. The solubilization data were analyzed on the basis of a pseudo-phase model with gliclazide exhibiting moderate partition coefficients into the micellar phase. The possible sites of solubilization of gliclazide in the micelle were examined by studying the effect of NaCl on solubilization and by comparing the absorption spectra of gliclazide in different solvents. The results obtained from these two experiments indicated that gliclazide is solubilized mainly in the inner core of the cationic surfactant micelles and in the outer regions of the anionic surfactant micelles.     

Cholesterol monohydrate dissolution rate studies in aqueous micellar sodium chenodeoxycholate solutions

The dissolution rate of cholesterol monohydrate in various concentrations of sodium chenodeoxycholate (1) was significantly influenced by the addition of strong electrolytes. The mass transfer resistances decreased with increasing electrolyte concentrations and attained an asymptotic minimum value predicted and experimentally established for the convective/diffusion-controlled situation. Reduction of the interfacial barrier to dissolution was many times more sensitive to Mg2+ than to Na+ at equimolar concentrations. Cholesterol monohydrate solubilities increased nonlinearly with increasing 1 in 0.01 M phosphate buffer at pH 8.0 and was not influenced by the presence of strong electrolytes. Measured diffusion coefficients gave supporting evidence that the effective micellar size remained the same within the various experimental systems up to 116 mM chenodeoxycholate. The experimental findings indicated that the interfacial barrier is electrostatic in character. They are consistent with the phenomenon of diffusion of negatively charged micelles toward a negatively charged cholesterol monohydrate surface and the subsequent collision complex transfer of cholesterol molecules at the crystal surface. The results and mechanistic interpretations are also in accord with the previous model studies on cholesterol monohydrate dissolution in the presence of mixed micelles composed of nonionic and ionic surfactants.     

Solubilization of valsartan by aqueous glycerol, polyethylene glycol and micellar solutions

To increase the solubility of valsartan in aqueous solutions was considered of interest. This study therefore investigated the solubilization of valsartan by cosolvency and micellization. Of the solubilization agents used, sodium lauryl sulfate was found to be the most effective. The increase in solubility at the maximum concentration studied was in the following order: sodium lauryl sulfate > polysorbate-80 > polyethylene glycol 400 > glycerol. The effect of propylene glycol on the solubility of valsartan in a 2% w/v polysorbate-80 solution was also investigated and was found that propylene glycol decreased the solubilizing power of polysorbate-80 at the concentrations studied.     

Characterization of solidified reverse micellar solutions (SRMS) and production development of SRMS-based nanosuspensions.

Solidified reverse micellar solutions (SRMS), i.e. binary mixtures of 30-60% (w/w) lecithin and two different hard fats, were investigated regarding their physicochemical properties and the influence of lecithin on solid lipids. For this purpose, the systems were characterized with X-ray and thermal analysis, transmission electron microscopy (TEM) and photon correlation spectroscopy. The melting point (m.p.) of the solid lipids, which is a crucial parameter of the solid state, was not altered up to a lecithin concentration of 50% whereas reverse micelles were likely to be frozen still in the solid state. In addition, solubilities of 17beta-oestradiol-hemihydrate, pilocarpine base and hydrochloride in the SRMS melt were studied for evaluation of the drug carrier potency. Drug solubilization in the SRMS melt increased linearly with rising amount of lecithin. SRMS-based nanosuspensions were developed with a given lecithin/hard fat ratio of 1:1 (w/w). High-pressure homogenization was applied on cold to avoid lecithin loss. Optimization of the systems in terms of a variation of the homogenizing parameters such as pressure, number of cycles and temperature resulted in nanoparticulate systems with a polysorbate 80/SRMS ratio of 1:5 (w/w), and a total amount of 5 and 15% (w/w) SRMS, respectively. Production temperatures near the lipid m.p. proved best to be maintained by varying the pressure, yielding small nanoparticles with a narrow particle size distribution. The solid lipid nanoparticles were characterized with X-ray and thermal analysis as well as TEM. The crystalline particles (beta modification) are of anisometrical shape and have transition temperatures far below the bulk m.p. due to the colloidal character of the systems.     

Drug release and permeation studies of nanosuspensions based on solidified reverse micellar solutions (SRMS)

Solidified reverse micellar solutions (SRMS), i.e. mixtures of lecithin and triglycerides, offer high solubilisation capacities for different types of drugs in contrast to simple triglyceride systems [Friedrich, I., Müller-Goymann, C.C., 2003. Characterisation of SRMS and production development of SRMS-based nanosuspensions. Eur. J. Pharm. Biopharm. 56, 111-119]. Nanosuspensions based on SRMS were prepared by homogenisation close to the melting point of the SRMS matrix. In a first step the SRMS matrices of 1:1 (w/w) ratios of lecithin and triglycerides were loaded with 17beta-estradiol-hemihydrate (EST), hydrocortisone (HC) or pilocarpine base (PB), respectively, and subsequently ground in liquid nitrogen to minimise drug diffusion later on. The powder was then dispersed in a polysorbate 80 solution using high pressure homogenisation. The drug loading capacities of the nanosuspensions were very high in the case of poorly water-soluble EST (99% of total 0.1%, w/w, EST) and HC (97% of total 0.5%, w/w, HC) but not sufficient with the more hydrophilic PB (37-40% of total 1.0%, w/w, PB). These findings suggest SRMS-based nanosuspensions to be promising aqueous drug carrier systems for poorly soluble drugs like EST and HC. Furthermore, in vitro drug permeation from the different drug-loaded nanosuspensions was performed across human cornea construct (HCC) as an organotypical cell culture model. PB permeation did not differ from the nanosuspension and an aqueous solution whereas the permeation coefficients of HC-loaded nanosuspensions were reduced in comparison to aqueous and oily solutions of HC. However, the permeated amount was higher from the nanosuspensions due to a much lower HC concentration in the solution than that in the nanosuspension (solution 0.02%, w/w, versus nanosuspension 0.5%, w/w). The high drug load of the nanoparticles provides prolonged HC release. Permeated amounts of EST were reduced in comparison to HC and only detectable with an ELISA technique. The EST release from nanosuspensions and different EST-loaded systems revealed a prolonged EST release from the nanoparticulate systems in contrast to a faster release of an oily solution of an equal EST concentration. With regard to an aqueous EST suspension of similar concentration which represents a depot system the release rate from the nanosuspensions revealed the same order of magnitude which points again to a prolonged release potential of the nanosuspensions.     

Some relations between dissolution rates and physical parameters of a drug in aqueous micellar solutions of a non-ionic surfactant.

Dissolution rates of salicylic acid from a constant surface area into a series of aqueous micellar polysorbate 20 solutions at pH 1-0 to 4-0 have been measured using two different methods; a stirred beaker and a rotating disc technique. The micellar molecular weight of polysorbate 20 has been obtained from light scattering and differential refractometry data and used with other independently determined physical data to calculate diffusion coefficients of the diffusing species. Linear multiple regression analysis was used to assess the dependence of drug dissolution rate on the diffusion coefficient and the viscosity of the dissolution medium.     

Use of block copolymers of poly(ortho esters) and poly (ethylene glycol) micellar carriers as potential tumour targeting systems

Amphiphilic AB and ABA block copolymers have been prepared from poly (ortho esters) and poly (ethylene glycol). Such block copolymers readily form micellar dispersions in water, or buffers. The CMC is in the range of 3 x 10(-4)-5 x 10(-4) g/l which is a value low enough to assure retention of micelle integrity upon intravenous injection. The size, as determined by dynamic light scattering was in the 40-70 nm range. The micelles can be stored in lyophilized form for at lest 8 months and easily reconstituted to the original properties. The micelles are stable in PBS at pH 7.4 and 37 degrees C for 3 days and in a citrate buffer at pH 5.5 and 37 degrees C for 2 h. Stability in the presence of bovine serum albumin depends on the structure of the block copolymer and especially the length of the POE block.     

Analysis of 2,2'-azobis (2-amidinopropane) dihydrochloride degradation and hydrolysis in aqueous solutions

2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), a free radical-generating azo compound, is gaining prominence as a model oxidant in small molecule and protein therapeutics, namely for its ability to initiate oxidation reactions via both nucleophilic and free radical mechanisms. To better understand its degradation pathways, AAPH was degraded at 40°C in aqueous solutions over a wide pH range. Samples were analyzed via liquid chromatography-ultraviolet spectroscopy and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The thermal decomposition rate of AAPH to form radical species averaged 2.1 × 10(-6) s(-1) and did not vary significantly with pH. The hydrolysis rate increased exponentially with pH, showing hydroxide ion dependence. A mechanism for AAPH hydrolysis is proposed. The LC-MS/MS results provided evidence that the alkoxyl radical is a major radical species in solution. The LC-MS/MS results also showed a radical disproportionation reaction and enabled the generation of an overall reaction scheme showing the various side and termination products of AAPH degradation.     

正电性多肽copoly(Lys/Tyr)与磷脂膜的相互作用研究

目的 研究正电性多肽copoly(Lys/Tyr)(CPLT)在模拟生物膜上的透过性。方法 ①配制由卵磷脂(EPC)、2-油酰基磷脂酰乙醇胺(DOPE)和大豆磷脂(SBPL)组成的二分子磷脂膜。②Zeta电位测定法(zeta potential method，ZP)测定由上述磷脂组成的脂质体在加入CPLT后的膜表面Zeta电位。③园二色谱法(circular dichroism spectrcvscopy，CD)检测CPLT分子与磷脂膜作用时的构象情况。④电生理学方法(electrophy siology tech—nique，ET)测量CPLT分子在磷脂膜上引起的跨膜电流。⑤荧光光度分析法(fluorescence spectroscopy，FS)检测CPLT分子与磷脂膜的作用过程中的荧光强度变化。⑥共焦点激光扫描显微分析法(confocal laser scanning microscopy，CLSM)研究CPLT在磷脂膜上透过及其相对透过效率。结果①随着CPLT的加入和其浓度的增加，磷脂膜Zeta电位逐渐增加并趋向饱和。②CPLT分子在水相取β-sheet构象，当与磷脂膜结合后，其β-sheet构象的波峰发生红移，但构象基本不变。③CPLT分子能在一定浓度和一定外加电压条件下，透过二分子磷脂膜引起膜电流。④CPLT与磷脂膜的作用可分为三步：第一步，CPLT分子吸附于磷脂膜上；第二步，CPLT分子通过磷脂膜的疏水区；第三步，CPLT分子从二分子膜的内膜解吸，进入膜内水相。⑤CPLT分子在磷脂膜上的透过效率主要决定于磷脂膜的组成，在磷脂膜中存在带负电性的磷脂时可降低CPLT分子在磷脂膜上的透过效率。⑥在最初的CPLT分子与磷脂膜的相互吸附过程中，CPLT分子与磷脂膜间的静电作用力起主要作用。结论copoly(Lys／Tyr)分子能透过二分子磷脂膜，其透过效率主要决定于磷脂膜的组成。在最初的肽一膜吸附过程中，当存在静电作用力时，静电力起主要作用，疏水效应次之。     

Solubilisation and immunoprecipitation of rat striatal adenosine A(2A) receptors.

In the present study, we have sought to solubilise adenosine A(2A) receptors from rat striatal membranes using a variety of different detergents. Of the detergents tested, 1% CHAPS (3-[(3-deoxycholic acid (cholamidopropyl) dimethylammonio]-1-propanesulfonate) yielded optimal conditions for solubilisation (in the presence of 3 mg/ml protein, 44% of receptor was solubilised, 50% of total protein was solubilised). An antipeptide antibody was raised against a 15 amino-acid sequence within the predicted third intracellular loop region of the human and rat adenosine A(2A) receptor. The antibody was coupled to protein A immobilised on sepharose CL-4B and used to immunoprecipitate adenosine A(2A) receptors from solubilised rat striatal preparations. Radioligand-binding studies were performed using the selective adenosine A(2) antagonist [(3)H]ZM 241385 (4-(2-[7-amino-2-(2-fury1)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol). Using [(3)H]ZM 241385, the pharmacology of immunoprecipitated adenosine A(2A) receptors was composed to striatal membrane bound adenosine A(2A) receptors and detergent solubilised adenosine A(2A) receptors. [(3)H]ZM 241385 labelled a single saturable binding site with high affinity in all three preparations (membrane bound K(d) 2.7 nM+/-1.0; solubilised K(d) 1.9 nM+/-0.3; immunoprecipitated K(d) 2.2 nM+/-0.7). Additionally, all three assays confirmed a rank order of potency for displacers consistent with adenosine A(2A) receptor pharmacology: ZM 241385>KW 6002 ((E)-8-[2-(3,4-dimethoxyphenyl)ethynyl]-1-3-diethyl-3,7-dihydro-7-methyl-1-purine 2,6 dione)>CGS 21680, (2-(4-(2 carboxyethyl)phenylethylamino)-5'-N-ethylcarboxamidoadenosine)>DPCPX (8-cyclopentyl-1,3-dipropylxanthine). We conclude that we have solubilised and immunoprecipitated adenosine A(2A) receptors from rat striatum and that their pharmacology is consistent with native striatal adenosine A(2A) receptors.     

Photo-isomerization of fluvoxamine in aqueous solutions

The hydrolysis and photolysis of fluvoxamine, a selective serotonin reuptake inhibitor, in aqueous buffer solutions (pH 5, 7, and 9), in synthetic humic water, and lake waters were investigated in the dark and in a growth chamber outfitted with fluorescent lamps simulating the UV output of sunlight at 25 degrees C. No significant hydrolytic degradation/isomerization was observed for 30 days in all aqueous solutions. However, fluvoxamine was moderately isomerized to its (Z)-isomer by simulated sunlight. The photo-isomerization occurred in two stages. The photo-isomerization occurred rapidly within the first 7 days and slowly thereafter with a rate constant of 0.12-0.19 day(-1) for the first stage and 0.04-0.05 day(-1) for the second stage. Photosensitized rate constants in synthetic humic water and in lake waters were approximately 6-7 times faster than that in pH 9 buffer with the rate constants of 1.15-1.34 day(-1) in the first stage. The (Z)-isomer of fluvoxamine was the only product detected in all aqueous solutions and was identified using LC-ESI-MS.