Differences in the serum protein binding of prazosin in man and rat

The serum protein binding of prazosin in man and rat has been studied in vitro by equilibrium dialysis. Prazosin was more extensively bound in human serum than in rat serum with binding ratios (B/F) of 14.3 +/- 3.4 and 4.4 +/- 0.2 (corresponding to 93.4 and 81.4% bound), respectively. This difference in binding between the species was partly due to qualitative differences between human and rat serum albumin, but also to the lower concentration of albumin in rat serum. Rat serum albumin (RSA) apparently showed two different classes of binding sites for prazosin, one with high (KD = 5.78 X 10(-6) M) and one with low (KD = 1.1 X 10(-4) M) affinity; the former is suggested as representing alpha 1-acid glycoprotein (alpha 1-AGP) with one binding site for prazosin per molecule, the latter as representing RSA with 0.28 binding sites per molecule. Human serum albumin (HSA) and human alpha 1-AGP both showed one class of binding sites with KD values of 2.7 X 10(-5) and 1.95 X 10(-6) M, respectively. HSA possessed 0.5 and human alpha 1-AGP 1 binding site for prazosin per molecule. The binding parameters obtained for the isolated serum proteins overestimated to some degree the total serum protein binding of prazosin in man. This was explained by a specific deviation from the law of mass action. HSA was the major binding protein in human serum at therapeutic concentrations, with ca. 60% of the total binding, the remaining 40% being bound to alpha 1-AGP. Anticipating that the high affinity binding site on the RSA preparation represents the binding of prazosin to alpha 1-AGP, then this protein accounts for 70% of the binding in rat serum, while rat serum albumin accounts for approximately 23%. The binding of prazosin to lipoproteins was insignificant in both species. The observed differences between man and rat in the serum protein binding of prazosin implicate differences in the two species with respect to prazosin pharmacokinetics and the pharmacological effect.     

Investigating noncovalent interactions of rutin-serum albumin by capillary electrophoresis-frontal analysis

The application of capillary electrophoresis-frontal analysis (CE-FA) to study noncovalent interaction between rutin and serum albumin (bovine serum albumin, BSA and human serum albumin, HSA) in phosphate buffer solution (67 mM, pH 7.4) at 37 degrees C is presented. Using fixed HSA or BSA concentration and increasing rutin concentration, the number of primary binding sites per HSA or BSA molecules, and the affinity constants were obtained. Both affinity constants are in a comparable range suggesting the similarity of affinity properties of HSA and BSA towards rutin. The proposed CE-FA method is simple, rapid and cost-effective which may be useful in further high-throughput protein binding studies of multi-components in traditional herbal medicines for pharmacological effect evaluations.     

阿司匹林与人血清白蛋白的相互作用研究

目的以光谱技术研究阿司匹林分子与人血清白蛋白(HSA)间结合作用机制。方法通过荧光光谱法确定阿司匹林对HSA的荧光猝灭机制。由Lineweaver-Burk双倒数作图法确定反应的解离常数。根据热力学方程讨论两者间主要的作用力类型。结合同步荧光技术考察阿司匹林对人血清白蛋白构象的影响。结果阿司匹林对HSA的荧光猝灭机制为静态猝灭。在37℃和25℃时阿司匹林与HSA的解离常数分别为KD37=1.44×10-3mol.L-1,KD25=1.96×10-3mol.L-1。结合反应热力学参数为ΔH=-19.73kJ.mol-1,△G=-16.21kJ.mol-1,ΔS=-11.77kJ.mol-1。结论两者结合的主要作用力类型是范德华力。阿司匹林与白蛋白结合后使蛋白质构象发生变化。     

In-vitro study on the competitive binding of diflunisal and uraemic toxins to serum albumin and human plasma using a potentiometric ion-probe technique

The competitive binding of diflunisal and three well-known uraemic toxins (3-indoxyl sulfate, indole-3-acetic acid and hippuric acid) to bovine serum albumin (BSA), human serum albumin (HSA) and human plasma was studied by direct potentiometry. The method used the potentiometric drug ion-probe technique with a home-made ion sensor (electrode) selective to the drug anion. The site-oriented Scatchard model was used to describe the binding of diflunisal to BSA, HSA and human plasma, while the general competitive binding model was used to calculate the binding parameters of the three uraemic toxins to BSA. Diflunisal binding parameters, number of binding sites, n(i) and association constants for each class of binding site, K(i), were calculated in the absence and presence of uraemic toxins. Although diflunisal exhibits high binding affinity for site I of HSA and the three uraemic toxins bind primarily to site II, strong interaction was observed between the drug and the three toxins, which were found to affect the binding of diflunisal on its primary class of binding sites on both BSA and HSA molecules and on human plasma. These results are strong evidence that the decreased binding of diflunisal that occurs in uraemic plasma may not be solely attributed to the lower albumin concentration observed in many patients with renal failure. The uraemic toxins that accumulate in uraemic plasma may displace the drug from its specific binding sites on plasma proteins, resulting in increased free drug plasma concentration in uraemic patients.     

Stereoselective binding properties of naproxen glucuronide diastereomers to proteins

The stability of naproxen glucuronide (NAP-G) diastereomers was investigated in buffer, 0.3% and 3% human serum albumin (HSA) solutions, and human plasma.R-NAP-G was found to be less stable in phosphate buffer than itsS-diastereomer, whereas incubation media containing protein in general increased the degradation rate of NAP-G but also caused a change of the stereoselective stability where theR-NAP-G was more stable thanS-NAP-G. Reversible binding of NAP-Gs to HSA (0.3%) was investigated and compared with the corresponding properties of naproxen (NAP) enantiomers. NAP-G diastereomers exibited a considerable and stereoselective affinity to HSA, although less than that observed for the NAP enantiomers.In vitro irreversible binding of NAP-Gs to HSA, human and rat plasma proteins was also investigated. Irreversible binding was higher forR-NAP-G (50 μM) than forS-NAP-G (50 μM) in all incubation media. This stereoselective difference was observed with HSA containing medium as well as in rat and human plasma. Incubation with unconjugated NAP did not lead to irreversible binding. Preincubation of HSA with acetylsalicylic acid (≈ 11 mM) and glucuronic acid (50 mM) decreased the extent of irreversible binding suggesting involvement of lysine residues for covalent binding. Preincubation withS-NAP also decreased the irreversible binding yield. This paper is dedicated to Professor Richard Neidlein, Pharmaceutical Chemistry Institute, Heidelberg, in commemoration of his 65th birthday. Supported in part by National Institutes of Health Grants GM 36633 and DK 26307.     

Binding Study of the Fluorescence Probe l-Anilino-8-naphthalenesulfonate to Human Plasma and Human and Bovine Serum Albumin Using Potentiometric Titration

The binding of l-anilino-8-naphthalenesulfonate (ANS) to bovine serum albumin (BSA), human serum albumin (HSA), and human plasma has been studied by potentiometric titration utilizing a laboratory constructed ion selective electrode (ISE) of ANS. Three classes of ANS binding sites were found on BSA, HSA, and plasma at 25 and 37°C. Computer analysis of the data resulted in estimates for the association constants, number of binding sites (HSA, BSA), and binding capacity of each class. The association constants for the first class of binding sites at 25°C were found to be 7.53 (±0.59) × 10⁵, 2.70 (±0.20) × 10⁵, and 2.64 (±0.26) × 10⁵ M ^–l for BSA, HSA, and plasma, respectively. Lower values for the association constants of all binding classes were estimated at the higher temperature (37°C). The binding capacity for ANS decreased in the order BSA, plasma, HSA.     

Kinetics of the binding of salicylazosulfapyridine to human serum albumin.

In order to elucidate the possibility of the dissociation rate of drugs from plasma proteins presenting a rate limiting step in the elimination of drugs by secretion (renal or biliary) and metabolism, the kinetics of salicylazosulfapyridine (SASP) binding to human serum albumin (HSA) has been investigated by stopped-flow photometry. Equilibrium dialysis showed that HSA has three classes of binding sites for SASP with 0.93, 2.3 and 8.4 sites, respectively, and association constants of 2.1.10(6), 1.4.10(5) and 3.0.10(3) M-1, respectively. The association rate constants for the first and second classes are 4.4.10(6) and 1.5.10(7) M-1 sec.-1, and the dissociation rate constants are 2.1 and 109 sec.-1. At SASP concentrations resulting from the usual therapeutic doses about 83% will bind to the first class binding sites. The dissociation "half time" for this class being 0.34 sec., leads to the conclusion that dissociation rates of this order of magnitude are unlikely to reduce the rate of metabolism or biliary secretion whereas it may reduce renal tubular secretion. Whether this is the case depends on the intrinsic rate constant of secretion.     

Protein binding of diazepam and digitoxin in uremic and normal serum.

The protein binding of diazepam and digitoxin in serum from uremie patients has been studied by equilibrium dialysis and compared to that in normal serum. Comparisons have also been made with isolated human serum albumin (HSA) from uremie and normal individuals. Diazepam and digitoxin are bound to different sites on HSA. Their binding was impaired in the serum from the patients when compared to that in the normal serum owing to decreased affinity constants for the binding to the primary sites on albumin. In the uremic serum the number of binding sites for diazepam is increased compared with the number in normal serum and HSA. For digitoxin the number of binding sites is larger both in the normal and the patient serum than that obtained with HSA. The fact that apparently an increased number of binding sites is made use of, is probably due to the presence of substances which inhibit the binding to the primary sites. The binding of the drugs was improved after charcoal-treatment of the uremie albumin at pH 3.0.     

Binding of prazosin to alpha 1-acid glycoprotein and albumin: effect of protein purity and concentrations

Prazosin is extensively bound in human serum/plasma. In the present study a bound fraction of 93-95% was observed at 37 degrees for therapeutic drug concentrations. Both alpha 1-acid glycoprotein (AAG) and albumin (HSA) are established as transport proteins for prazosin, but their individual contribution to the extent and variability of protein binding in serum/plasma is unclear. The present study showed that AAG possesses one binding site per molecule with high affinity (Kd approximately 0.8 microM) for prazosin. HSA, essentially globulin-free, bound prazosin with lower affinity (Kd approximately 30 microM) with an average of 0.3 binding sites per molecule. However, less purified HSA, containing globulins, exhibited apparently higher affinity (Kd approximately 8 microM), but lower binding capacity (0.07 sites per molecule) for prazosin. In mixtures of highly purified proteins, the concentrations of AAG, and not HSA, determined the extent and variability of prazosin binding.     

The binding of physostigmine to human serum albumin

The binding of [3H]physostigmine to crystallized human serum albumin (HSA) has been investigated using equilibrium dialysis. The percentage bound to 1% (w/v) HSA decreased from 18 to 4% as the total concentration of physostigmine increased from 3.3 nM to 2.7 microM (0.9 to 750 ng mL-1). A single class of specific binding sites with a large affinity constant, K = 8 x 10(7) L mol-1, was identified. The concentration of binding sites was approximately 3 nM. The Michaelis constants for human serum cholinesterase and albumin were the same; an explanation for these results is that the drug is binding to a trace cholinesterase, in the albumin.     

Kinetics of the Binding of Salicylazosulfapyridine to Human Serum Albumin

Abstract In order to elucidate the possibility of the dissociation rate of drugs from plasma proteins presenting a rate limiting step in the elimination of drugs by secretion (renal or biliary) and metabolism, the kinetics of salicylazosulfa-pyridine (SASP) binding to human serum albumin (HSA) has been investigated by stopped-flow photometry. Equilibrium dialysis showed that HSA has three classes of binding sites for SASP with 0.93, 2.3 and 8.4 sites, respectively, and association constants of 2.1 · 10⁶, 1.4 · 10⁵ and 3.0 · 10³ M^-1, respectively. The association rate constants for the first and second classes are 4.4 · 10⁶ and 1.5 · 10⁷ M^-1 sec.^-1, and the dissociation rate constants are 2.1 and 109 sec.^-1. At SASP concentrations resulting from the usual therapeutic doses about 83 % will bind to the first class binding sites. The dissociation “half time” for this class being 0.34 sec., leads to the conclusion that dissociation rates of this order of magnitude are unlikely to reduce the rate of metabolism or biliary secretion whereas it may reduce renal tubular secretion. Whether this is the case depends on the intrinsic rate constant of secretion.     

The energetics of the interaction of piroxicam with plasma albumin

The thermodynamics of the binding of piroxicam to human and bovine plasma albumins revealed the reactions to be spontaneous and exothermic with bond strengths indicating the involvement of hydrogen and hydrophobic bonds. The association constants (K) decreased as temperature increased for both human serum albumin (HSA) and bovine serum albumin (BSA); and at all the temperatures in this study, K values obtained for BSA were higher (except at 36 degrees C) but not the bound fraction of piroxicam (beta) and the quantity of binding (V). Scatchard plots of the data indicated at least two classes of binding sites.     

Binding of Prazosin to α1-Acid Glycoprotein and Albumin: Effect of Protein Purity and Concentrations

Abstract: Prazosin is extensively bound in human serum/plasma. In the present study a bound fraction of 93–95% was observed at 37° for therapeutic drug concentrations. Both α₁-acid glycoprotein (AAG) and albumin (HSA) are established as transport proteins for prazosin, but their individual contribution to the extent and variability of protein binding in serum/plasma is unclear. The present study showed that AAG possesses one binding site per molecule with high affinity (Kd≈0.8 μM) for prazosin. HSA, essentially globulin-free, bound prazosin with lower affinity (Kd≈30 μM) with an average of 0.3 binding sites per molecule. However, less purified HSA, containing globulins, exhibited apparently higher affinity (Kd≈8 μM), but lower binding capacity (0.07 sites per molecule) for prazosin. In mixtures of highly purified proteins, the concentrations of AAG, and not HSA, determined the extent and variability of prazosin binding.     

Displacement by uricosuric agents of sodium urate bound to human serum albumin

The displacement of sodium urate by uricosuric agents from binding sites on human serum albumin (HSA) and normal serum has been demonstrated under physiological conditions in vitro (pH 7.4, ionic strength 0.16) over he oncentration range 1–13 mg/100 ml. At 37°, 0.5 mM sodium salicylate reduced urate bound to 5 g/100 ml of HSA from 19.6 to 9.7 per cent. At 22.5°, 22.6 per cent urate was bound to 5 g/100 ml of HSA, and this was reduced to 12.3 per cent by 0.5 mM salicylate, to 9.2 per cent by 0.5 mM phenylbutazone, to 14.6 per cent by 0.2 mM diflumidone, and to 17.9 per cent by 0.2 mM sulfaethidole. At 22.5°, pooled normal human serum (4.8 g/100 ml of albumin) bound 23.5 per cent urate; with 0.5 mM salicylate present 12.6 per cent urate was bound.     

荧光光谱法研究顺铂对表柔比星与人血白蛋白结合作用的影响

目的研究顺铂对表柔比星与人血清白蛋白(HSA)结合作用的影响。方法通过荧光光谱法研究顺铂和表柔比星对HSA的荧光猝灭光谱,同步荧光光谱。由Lineweaver-Burk双倒数作图法确定反应的解离常数,根据热力学方程讨论两者间主要的作用力类型。结果荧光猝灭光谱显示,顺铂和表柔比星与HSA都有荧光猝灭作用。顺铂、表柔比星对HSA的猝灭过程为静态猝灭。表柔比星与HSA的结合点数为1,主要作用力为疏水作用力。顺铂不影响表柔比星对HSA的内源荧光猝灭作用,但能增加表柔比星与HSA的结合常数(KA)。结论顺铂不影响表柔比星的血药浓度,但能增加表柔比星与HSA的结合力。     

Plasma protein binding of the reversible type A MAO inhibitor cimoxatone (MD 780515)

Binding of a new selective reversible type A MAO inhibitor cimoxatone (MD 780515) to plasma proteins was studied in vitro by equilibrium dialysis. Binding to 580 microM human serum albumin (HSA) and to total plasma proteins was 93-96% and independent of cimoxatone concentration (0.15-207 microM). The drug was mainly bound to HSA with two binding sites and a moderate association constant (K = 2.9 X 10(4) M-1). Free fatty acids did not modify cimoxatone binding to HSA. Cimoxatone was also moderately bound to isolated lipoprotein fractions; alpha 1-acid glycoprotein and gamma-globulins did not play an important role in the binding of cimoxatone. MD 770222, the O-demethyl metabolite, appeared to be bound to HSA at the same binding sites as cimoxatone. However, no interaction occurred between the two compounds for 580 microM HSA. L-Tryptophan, bilirubin, the benzodiazepines flunitrazepam and oxazepam, imipramine and aspirin, did not displace cimoxatone from its binding sites. On the other hand, warfarin and phenylbutazone decreased cimoxatone binding to 29 microM HSA but no interaction occurred with 580 microM HSA.     

99mTc-neoglycoalbumin (NGA)-binding to human hepatic binding protein (HBP) in vitro.

1 Neoglycoalbumin (NGA) was synthesised by covalent coupling of 2-imino-2-methoxyethyl-1-thio-beta-D-galactopyranoside (IME-thiogalactose) to the primary amino groups of human serum albumin (HSA). NGA was purified by ultrafiltration and size exclusion h.p.l.c. (SEC). 99mTc-labelling was performed with and without SEC purification. 2 Estimation of 99mTc-NGA-binding to human hepatic binding protein (HBP) revealed a complex behaviour indicating saturable high- and low-affinity sites. The high-affinity binding capacity was 1.1 +/- 0.4 pmol mg-1 human liver plasma membrane protein, the low-affinity binding capacity was 6.2 +/- 1.8 pmol mg-1 liver plasma membrane protein. The apparent equilibrium dissociation constants were 2.4 +/- 1.2 and 18.4 +/- 4.8 nM, respectively. 3 Specific binding of 99mTc-NGA to human HBP in the presence of 100 microM unlabelled NGA, Ca++ and Mg++ at pH 7.5 and 37 degrees C reached 85 +/- 5% at equilibrium. The amount of ligand specifically bound increased with the amount of human liver membrane protein added. The concentration of unlabelled agonist necessary to displace 50% of ligand bound amounted to 100 nM.     

Binding of two anthranilic acid derivatives to human albumin, erythrocytes, and lipoproteins: evidence for glafenic acid high affinity binding

The binding of two anthranilic acid derivatives, glafenic and floctafenic acids, to human erythrocytes and plasma proteins has been investigated in vitro by equilibrium dialysis. Despite their close chemical structures it was shown that the binding of the two compounds to serum albumin, lipoproteins, and erythrocytes was dramatically different both in quality and quantity. Using various techniques including fluorometry and circular dichroism, it was shown that glafenic acid binds to the human serum albumin (HSA) warfarin/azapropazone site and that floctafenic acid binds to both warfarin/azapropazone and benzodiazepine sites. Glafenic acid is strongly bound to HSA with n = 1, k = 2.4 X 10(6) liters/mol and to erythrocytes with N = 12.4 mumol/liter, K = 1.7 X 10(6) liters/mol. Floctafenic acid is bound with a weaker affinity to HSA, n = 2, k = 0.3 X 10(6) liters/mol and to erythrocytes, N = 2900 mumol/liter and K = 0.007 X 10(6) liters/mol.     

Interaction of benzodiazepine derivatives with bovine serum albumin-I Gel filtration studies.

The binding of eleven benzodiazepine derivatives to bovine serum albumin was determined by means of Sephadex gel filtration. The albumin binding of the substances was characterized by the percentage of drug bound, the binding constants k⁺, K₁, and m, the number of binding sites per albumin molecule, and the free binding energy. The binding of the benzodiazepines to bovine serum albumin (BSA) is discussed in respect to the binding of these drugs to human serum albumin (HSA). The following great differences in the binding behaviour of both albumins for the benzodiaze-pines have been found: (1) The affinities of the binding of most of the drugs to BSA are exceptionally smaller than those to HSA. (2) Two benzodiazepines, lorazepam and clonazepam, are bound to BSA in a higher extent than to HSA. (3) Most of the benzodiazepines have two or three binding sites on the BSA molecule, in contrast to the single binding site on the HSA molecule. The binding of the benzodiazepines to BSA is positively influenced by the pH-value of the solution in a similar way as found for HSA. The benzodiazepines are the first group of drugs known in which binding to both albumins differs so fundamentally. The reason for these large differences and their pharmacological significance are discussed.     

Fluorescence spectroscopy studies on 5-aminosalicylic acid and zinc 5-aminosalylicylate interaction with human serum albumin

The interaction between 5-aminosalicylic acid (5-ASA) or zinc 5-aminosalylicylate (5-ASZ) and human serum albumin (HSA) was studied by fluorescence spectroscopic technique. The binding constants of 5-ASA or 5-ASZ with HSA were determined at different temperatures under the optimum conditions. The binding sites were obtained and the acting force were suggested to be mainly hydrophobic. The effect of common ions on the binding constants was also investigated. A fluorescence spectroscopy assay of the proteins is presented in the paper. The determination results of the proteins in human serum by this method are very close to those obtained using Coomassie Brilliant Blue G-250 colorimetry, with relative standard deviations of 0.8-2.9%. A practical method was proposed for the determination of 5-ASA or 5-ASZ in human serum samples.