Glycation alter serum albumin binding of valsartan and nateglinide when studied contemporarily

In this research work, an attempt was made to study alteration in glycated serum albumin binding of valsartan and nateglinide using validated HPLC-UV method and ultrafiltration as in vitro protein binding study model. The chromatographic conditions involved stationary phase Kromasil-100 C18 (100?×?4.6?mm, 3.5?µm) with mobile phase of 10?mM phosphate buffer, acetonitrile, isopropyl alcohol in the ratio of 30:65:5 as isocratic mode at a flow rate of 0.8?mL/min; and the eluent was monitored at 218?nm. Protein precipitation technique was used to extract the drugs from human plasma. The calibration curve was found linear in the range from 50 to 5000?ng/mL. Glycation of human serum albumin was achieved at different concentration levels using D-(+)-glucose and glycated human serum albumin (Gly-HSA) were prepared. Valsartan and nateglinide were not affected the plasma protein binding of each other when studied using HSA. The unbound fraction of valsartan and nateglinide was increased to 10–20 times when spiked with Gly-HSA. About 20% increase in unbound fraction of valsartan was observed when spiked with 10?µg/mL of nateglinide. Furthermore, the unbound fraction of nateglinide was increased nearly to 10% more when incubated with Gly-HSA as compare to recombinant human serum albumin.     

Resonance light scattering technique for the determination of protein with rutin and cetylpyridine bromide system

A new resonance light scattering (RLS) assay of protein is presented. In Tris-NaOH (pH = 10.93) buffer, the RLS of rutin-cetylpyridine bromide (CPB) system can be greatly enhanced by protein, including bovine serum albumin (BSA) and human serum albumin (HSA). The enhanced RLS intensities are in proportion to the concentration of proteins in the range of 5 x 10(-9) to 2.5 x 10(-6) g ml(-1) for BSA and 2.5 x 10(-8) to 3.5 x 10(-6) g ml(-1) for HSA. The detection limits (S/N = 3) are 3.0 ng ml(-1) for BSA and 10.0 ng ml(-1) for HSA. Samples are determined satisfactorily.     

Spectroscopic studies on the interaction of bovine (BSA) and human (HSA) serum albumins with ionic surfactants

Bovine (BSA) and human (HSA) serum albumins are frequently used in biophysical and biochemical studies since they have a similar folding, a well known primary structure, and they have been associated with the binding of many different categories of small molecules. One important difference of BSA and HSA is the fact that bovine albumin has two tryptophan residues while human albumin has a unique tryptophan. In this work results are presented for the interaction of BSA and HSA with several ionic surfactants, namely, anionic sodium dodecyl sulfate (SDS), cationic cethyltrimethylammonium chloride (CTAC) and zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonium-1-propanesulfonate (HPS), as monitored by fluorescence spectroscopy of intrinsic tryptophans and circular dichroism spectroscopy. On the interaction of all three surfactants with BSA, at low concentrations, a quenching of fluorescence takes place and Stern-Volmer analysis allowed to estimate their 'effective' association constants to the protein: for SDS, CTAC and HPS at pH 7.0 these constants are, respectively, (1.4+/-0.1) x 10(5) M(-1), (8.9+/-0.1) x 10(3) M(-1) and (1.4+/-0.1) x 10(4) M(-1). A blue shift of maximum emission is observed from 345 to 330 nm upon surfactant binding. Analysis of fluorescence emission spectra allowed to separate three species in solution which were associated to native protein, a surfactant protein complex and partially denatured protein. The binding at low surfactant concentrations follows a Hill plot model displaying positive cooperativity and a number of surfactant binding sites very close to the number of cationic or anionic residues present in the protein. Circular dichroism data corroborated the partial loss of secondary structure upon surfactant addition showing the high stability of serum albumin. The interaction of the surfactants with HSA showed an enhancement of fluorescence at low concentrations, opposite to the effect on BSA, consistent with the existence of a unique buried tryptophan residue in this protein with considerable static quenching in the native state. The effects of surfactants at low concentrations were very similar to those of myristic acid suggesting a non specific binding through hydrophobic interaction modulated by eletrostatic interactions. The changes in the vicinity of the tryptophan residues are discussed based on the recently published crystallographic structure of HSA myristate complex (S. Curry et al., Nat. Struct. Biol. 5 (1998) 827).     

Resonance double light scattering method for the determination of proteins with morin-CTMAB

A new determination method of proteins with the limit of determination at nanogram levels is proposed by using a common spectrofluorimeter to detect intensity of resonance double line scattering (RDLS). Proteins including bovine serum albumin (BSA), human serum albumin (HSA) can combine with morin and cetyltrimethylammonium briomide (CTMAB) in the pH range 7.0-8.0 and produce enhanced RDLS signal at lambda(ex)/lambda(em) 305.0/610.0 nm. Optimization conditions for the morin-protein-CTMAB interaction were tested. In the studied system, BSA/CTMAB/morin = 1:2:3. The association constant of morin with BSA is 5.2 x 10(4). Under the optimum conditions, the linear range is 7.5 x 10(-8)-1.0 x 10(-5) g/ml for BSA, 2.5 x 10(-8)-5.0 x 10(-6) g/ml for HSA. The detection limits (S/N = 3) are 66.0 ng/ml for BSA and 23.0 ng/ml for HSA, respectively. Four synthetic samples were analyzed satisfactorily.     

毛细管电泳-迎头分析法测定血清或血浆中氯氮平的游离浓度

采用毛细管电泳-迎头分析模式体外实验测定了人血清白蛋白溶液、人血浆、兔血清和血浆样品溶液中游离氯氮平的浓度．根据前沿峰的峰高直接测定了样品溶液中的游离氯氮平浓度,并与传统超滤法进行了比较．通过考察施加的电压和运行缓冲液的组成对氯氮平电泳峰平台形成的影响确定了最优分离条件．讨论了氯氮平蛋白结合作用的选择性．     

Spectroscopic Investigation of the Interactions of Cryptotanshinone and Icariin with Two Serum Albumins

The interactions of two drugs, cryptotanshinone (CTS) and icariin, with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated using multiple spectroscopic techniques under imitated physiological conditions. CTS and icariin can quench the fluorescence intensity of BSA/HSA by a static quenching mechanism with complex formation. The binding constants of CTS–BSA, CTS–HSA, icariin–BSA and icariin–HSA complexes were observed to be 1.67 × 10⁴, 4.04 × 10⁴, 4.52 × 10⁵ and 4.20 × 10⁵ L·mol^?1, respectively at 298.15 K. The displacement experiments suggested icariin/CTS are primarily bound to tryptophan residues of the proteins within site I and site II. The thermodynamic parameters calculated on the basis of the temperature dependence of the binding constants revealed that the binding of CTS–BSA/HSA mainly depends on van der Waals interaction and hydrogen bonds, and yet the binding of icariin–HSA/BSA strongly relies on the hydrophobic interactions. The binding distances between BSA/HSA and CTS/icariin were evaluated by the Föster non-radiative energy transfer theory. The results of synchronous fluorescence, 3D fluorescence, FT-IR and CD spectra indicates that the conformations of proteins were altered with the addition of CTS or icariin. In addition, the effects of some common ions on the binding constants of CTS/icariin to proteins are also discussed.     

Albumin separation with Cibacron Blue carrying macroporous chitosan and chitin affinity membranes

Cibacron Blue F3GA, Procion Red HE-3B and Procion Blue MX-R were immobilized on macroporous chitosan and chitin membranes with concentrations as high as 10–200 μmol/ml membrane. These dyed membranes were chemically and mechanically stable, could be reproducibly prepared, and operated at high flow rates. Human serum albumin (HSA) and bovine serum albumin (BSA) were selected as model proteins, and their adsorption on and desorption from the dyed chitosan membranes investigated. The Cibacron Blue F3GA membranes had a higher protein adsorption capacity, much greater for HSA than BSA, than the other dyed membranes. About 8.4 mg HSA/ml membrane were adsorbed at saturation by Cibacron Blue F3GA–chitosan membranes from a 0.05 M Tris–HCl/0.05 M NaCl, pH 8 solution. The chitin membranes had a lower dye content and hence a lower protein adsorption capacity than the chitosan membranes. The effects of important operation parameters (flow rate, protein concentration and loading) were also investigated. Cibacron Blue F3GA–chitosan membranes were employed for the separation of HSA from human plasma and high purity HSA thus obtained. This suggests that these membranes could be used for large-scale plasma fractionation.     

Simple and Rapid Hollow Fiber Liquid Phase Microextraction Followed by High Performance Liquid Chromatography Method for Determination of Drug-protein Binding

A method was established using hollow fiber-liquid phase microextraction(HF-LPME) followed by high performance liquid chromatography(HPLC) to determine the concentration of the free(unbound) drug in the solution of the drug and protein. Measurements of drug-protein binding ratios and free drug concentrations were then analyzed with the Klotz equation to determine the equilibrium binding constant and number of binding sites for drug-protein interaction. The optimized method allows one to perform the efficient extraction and separation of free drug from protein-bound drug, protein, and other interfering substances. This approach was used to characterize the binding of the anticholinergic drugs atropine sulfate and scopolamine hydrobromide to proteins in human plasma and bovine serum albumin(BSA). The results demonstrate the utility of HF-LPME method for measuring free drug concentrations in protein-drug mixtures and determining the protein binding parameters of a pharmacologically important class of drugs.     

高效迎头分析法测定药物-人血清白蛋白混合液中游离药物浓度

 用高效迎头分析法 (HPFA)测定了药物 人血清白蛋白 (HSA)混合液中游离药物的浓度。样品溶液不经任何处理直接进样到装有内表面反相固定相的色谱柱中 ,用 67mmol/L磷酸盐缓冲液 ( pH 7 4 ,I =0 17mol/L)作流动相。当进样体积足够大时 ,游离药物以平顶峰的形式被洗脱出来 ,平顶峰区域洗脱液中的药物浓度等于样品溶液中游离药物的浓度。收集平顶峰区域的洗脱液 ,然后将一定体积的洗脱液注入到反相色谱柱中 ,测定游离药物的浓度。用该法测定酮基布洛芬 HSA和头孢哌酮 HSA两种混合液中游离药物的浓度。     

Cd（Ⅱ）与HSA或BSA的结合平衡研究

用平衡透析法详细研究了生理pH(7.43)条件下Cd(Ⅱ)与HSA或BSA的结合平衡.通过非线性最小二乘法拟合Bjerrum方程,首次报道了Cd(Ⅱ)-HSA和Cd(Ⅱ)-BSA体系的逐级稳定常数值,其K_1～K_3的数量级均为10~4;Hill系数和自由能偶合定量分析表明Cd(Ⅱ)与HSA或BSA的结合均产生在类似体系中少见的强的正协同效应,且Cd(Ⅱ)与HSA结合产生的正协同效应大于BSA;Scatchard图分析表明,Cd(Ⅱ)在HSA和BSA中均有3个强结合部位.通过Cd(Ⅱ)与Cu(Ⅱ),Zn(Ⅱ)或Ca(Ⅱ)等竞争结合HSA或BSA的结果,进一步讨论了Cd(Ⅱ)在HSA或BSA中强结合部位的可能位置和(或)配体.     

The fluorescent probe prodan characterizes the warfarin binding site on human serum albumin

Abstract— The fluorescent probe Prodan (6-propionyl-2-dimethyl-aminonaphthalene) binds with high affinity to human serum albumin (HSA). The spectral characteristics of the Prodan bound to the protein are very different from the free Prodan in solution. These differences allowed the spectra to be deconvoluted into log-normal bands in order to quantify the bound and unbound ligand and to calculate the binding constant at different temperatures. From such temperature dependence, we found the binding to be exothermic with a van't Hoff enthalpy of -22.8 kJ mol^-1. Thermodynamic analysis suggests that the in teraction may be mainly caused by hydrophobic forces and electrostatic interactions. The above analysis of the spectra and the measures of the fluorescence polarization during the successive presence of six specific drugs suggest that the Prodan binding site corresponds with the warfarin binding site on HSA, whereas under the present experimental conditions the other characteristic binding sites of HSA were not affected. Thus, this fluorescent probe provides a rapid and simple means for the characterization of a specific binding site on HSA and also for detecting potential or nonspecific drug-protein interactions.     

Macromolecule-macromolecule interaction in drug distribution: effect of alpha-globulin concentration on the hepatic uptake of fractionated 3H-heparin by perfused rat liver.

The effect of alpha-globulin, the dominant binding protein for fractionated 3H-heparin, on the hepatic uptake of 3H-heparin was studied by liver perfusion experiments in rats. Fractionated 3H-heparin concentration in the recirculated perfusate decline one-exponentially with time for each of six initial concentration levels of alpha-globulin. The hepatic uptake clearance of fractionated 3H-heparin was 0.154 ml/min/g liver in the absence of alpha-globulin, and it decreased with increasing alpha-globulin concentrations. This result indicates that the hepatic uptake rate of alpha-globulin-bound fractionated 3H-heparin is lower than that of unbound fractionated 3H-heparin. On the other hand, it was indicated that almost all fractionated 3H-heparin binds to alpha-globulin at 8 mg/ml of alpha-globulin in in vitro study. However, the hepatic uptake clearance of the heparin at the concentration was of a certain value that could not be ignored. It was suggested that alpha-globulin-bound fractionated 3H-heparin also contributed to the hepatic uptake of fractionated 3H-heparin. Therefore, a protein-mediated transport system, which has been reported for some low molecular weight drugs, may also exist in the hepatic uptake of such a high molecular weight compound as fractionated 3H-heparin.     

Protein binding of quinolonecarboxylic acids. I. Cinoxacin, nalidixic acid and pipemidic acid

Binding of cinoxain (CINX), nalidixic acid (NA) and pipemidic acid (PPA) to serum proteins was investigated by equilibrium dialysis, ultrafiltration and circular dichroism (CD) spectroscopy. CINX and NA were found to bind mainly to albumin in human serum, the latter interacting with the protein about ten times as strongly as CINX at pH 7.4 and 37 degrees C. PPA showed little or no significant binding to human serum albumin (HSA), alpha 1-acid glycoprotein, and globulins, but showed 20-30% binding to protein in human serum. The CD results were suggestive of some weak interaction of PPA with human apotransferrin. Binding of the three drugs to HSA was found to depend on the lipophilicity of their substituents at the 7-position. The degree of protein binding for human, dog and rat sera at 37 degrees C was in the order of NA (92-97%) greater than CINX (68-90%) greater than PPA (20-30%) at drug concentrations of 10-30 micrograms/ml. CINX showed relatively large species dependence in serum protein binding, which seemed to be due to different affinities of this drug to the respective albumins. CINX was found to bind to rat serum albumin as strongly as NA.     

A highly sensitive assay for protein with dibromochloro-arsenazo-Al(3+) using resonance light scattering technique and its application

A simple, sensitive and selective method has been developed for the determination of protein using resonance light scattering (RLS) technique. The method is based on the interaction of protein and arsenazo-DBC-Al(3+) in the pH range of 5.0-7.0, which causes a substantial enhancement of the resonance scattering signal of arsenazo-DBC-Al(3+) in the wavelength range of 300-550 nm with the maximum RLS platform at 405-420 nm. With this method, 2.50-50.00 mug ml(-1) of bovine serum albumin (BSA) and 2.50-60.00 mug ml(-1) of human serum albumin (HSA) can be determined, and the detection limits, calculated three times the standard deviation (S.D.) of six blank measurements, for BSA and HSA were 123.4 and 89.6 ng ml(-1), respectively. Moreover, the method is free from interference from many amino acids and metal ions. The method, with high sensitivity, selectivity and reproducibility, was satisfactorily applied to the determination of total protein in human serum samples. Mechanism studies indicated that arsenazo-DBC-Al(3+) could bind to BSA depending mainly on electrostatic forces, which results in enhanced RLS in the arsenazo-DBC-Al(3+)-protein system.     

Structural Basis of Artemisinin Binding Sites in Serum Albumin with the Combined Use of NMR and Docking Calculations

Artemisinin is known to bind to the main plasma protein carrier serum albumin (SA); however, there are no atomic level structural data regarding its binding mode with serum albumin. Herein, we employed a combined strategy of saturation transfer difference (STD), transfer nuclear Overhauser effect spectroscopy (TR-NOESY), STD–total correlation spectroscopy (STD-TOCSY), and Interligand Noes for PHArmacophore Mapping (INPHARMA) NMR methods and molecular docking calculations to investigate the structural basis of the interaction of artemisinin with human and bovine serum albumin (HSA/BSA). A significant number of inter-ligand NOEs between artemisinin and the drugs warfarin and ibuprofen as well as docking calculations were interpreted in terms of competitive binding modes of artemisinin in the warfarin (FA7) and ibuprofen (FA4) binding sites. STD NMR experiments demonstrate that artemisinin is the main analyte for the interaction of the A. annua extract with BSA. The combined strategy of NMR and docking calculations of the present work could be of general interest in the identification of the molecular basis of the interactions of natural products with their receptors even within a complex crude extract.     

Determination of association constants between steroid compounds and albumins by partial-filling ACE

ACE is a popular technique for evaluating association constants between drugs and proteins. However, ACE has not previously been applied to study the association between electrically neutral biomolecules and plasma proteins. We studied the affinity between human and bovine serum albumins (HSA and BSA, respectively) and three neutral endogenous steroid hormones (testosterone, epitestosterone and androstenedione) and two synthetic analogues (methyltestosterone and fluoxymesterone) by applying the partial-filling technique in ACE (PF-ACE). From the endocrinological point of view, the distribution of endogenous steroids among plasma components is of great interest. Strong interactions with albumins suppress the biological activity of steroids. Notable differences in the association constants were observed. In the case of the endogenous steroids, the interactions between testosterone and the albumins were strongest, and those between androstenedione and the albumins were substantially weaker. The association constants, K(b), for testosterone, epitestosterone and androstenedione and HSA at 37 degrees C were 32 100 +/- 3600, 21 600 +/- 1500 and 13 300 +/- 1300 M(-1), respectively, while the corresponding values for the steroids and BSA were 18 800 +/- 1500, 14 000 +/- 400 and 7800 +/- 900 M(-1). Methyltestosterone was bound even more strongly than testosterone, while fluoxymesterone was only weakly bound by the albumins. Finally, the steroids were separated by PF-ACE with HSA and BSA used as resolving components.     

酮咯酸、菲普拉宗与血清蛋白相互作用的研究

血清蛋白是血浆中含量最丰富的重要载体蛋白,它可与许多内源性物质和药物广泛结合［１］,酮咯酸、菲普拉宗分别为非甾类、吡唑酮类消炎镇痛新药［２］．有关酮咯酸、菲普拉宗与蛋白质相互作用的文献尚未见报道．本文研究了在人体生理条件下,酮咯酸、菲普拉宗与牛血清蛋白、人血清蛋白的相互作用,利用药物对血清蛋白荧光的猝灭求出了酮咯酸、菲普拉宗与蛋白质的结合常数和结合位置．并根据热力学参数确定了它们之间的主要作用力类型．这对于阐明不同药物对蛋白的不同作用方式及药物在人体内的作用机制都有一定的意义．１　实验部分１．１…     

芘与人血清白蛋白和牛血清白蛋白结合位点微环境极性的差异

利用芘(Pyr)的微环境极性探针性质, 采用稳态荧光光谱、 荧光共振能量转移技术结合分子对接法, 对比分析了Pyr分别与人血清白蛋白(HSA)和牛血清白蛋白(BSA)作用机制的差异. 结果表明, HSA和BSA中Pyr的I₁/I₃平均值分别为1.36和0.92; Pyr与HSA和BSA的结合常数分别为1.86×10⁷和1.71×10⁵ L/mol; Pyr与HSA和BSA中色氨酸残基表观距离分别为2.37和2.34 nm. Pyr在HSA和BSA中不同的结合位点位于ⅠB子域和ⅠA子域, 其结合位点周围氨基酸残基的极性是影响Pyr I₁/I₃值的主要原因之一. 实验证实Pyr与HSA和BSA结合作用位点处的微环境极性存在差异.     

Binding equilibrium study of phosphotungstic acid and HSA or BSA with UV spectrum, fluorescence spectrum and equilibrium dialysis

The binding equilibrium between phosphotungstic acid (H7[P(W2O7)6] · XH2O;PTA) and human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by UV-Vis, fluorescence spectroscopies and equilibrium dialysis. It has been observed that UV absorption enhanced and the fluorescence quenched as the PTA binding to HSA or BSA at physiological pH 7.43(?.02). The Scatchard analysis indicated that there exists a strong binding site of PTA in both HSA and BSA, and the successive stability constants of these two systems are obtained by nonlinear least-squares methods fitting Bjerrum formula.     

Probing three-dimensional structure of bovine serum albumin by chemical cross-linking and mass spectrometry

Serum albumin is the principal transporter of fatty acids that are otherwise insoluble in circulating plasma. While the crystal structure of human serum albumin (HSA) as well as its binding with fatty acids has been characterized, the three dimensional structure of bovine serum albumin (BSA) has not been determined although both albumins share 76% sequence homology. In this study we used mass spectrometry coupled with chemical cross-linking, to probe the tertiary structure of BSA. BSA was modified with lysine specific cross-linkers, bis(sulfosuccinimidyl) suberate (BS(3)), disuccinimidyl suberate (DSS) or disuccinimidyl glutarate (DSG), digested with trypsin and analyzed by tandem mass spectrometry. With O-18 labeling during the digestion, through-space cross-linked peptides were readily identified in mass spectra by a characteristic 8 Da shift. From the cross-linked peptides identified in this study, we found that 12 pairs of lysine residues were separated within 20 A, while 5 pairs were spaced between 20 and 24 A. The spatial distance constraints generated from five K-K pairs in BSA were consistent with the corresponding distance obtained from the crystal structure of HSA, although only six equivalent K-K pairs could be compared. According to our data, the distance between K235 of IIA and K374 of IIB domain in BSA was farther by 7-11 A than that expected from the crystal structure of HSA, suggesting structural differences between BSA and HSA in this region. The distance constraints obtained for lysine residues using various cross-linkers should be valuable in assisting the determination of the 3-D structure of BSA.