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Thomas C, Byer-Alcorace A, Wang T. Human Serum Albumin Immobilized On Magnetizable Beads: A Rapid Method for Compound HSA Binding Study. J Pharm Sci 2024; 113:1359-1367. [PMID: 38325737 DOI: 10.1016/j.xphs.2024.01.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 01/30/2024] [Accepted: 01/30/2024] [Indexed: 02/09/2024]
Abstract
Immobilized human serum albumin (HSA) was developed by coupling His-tagged HSA onto Ni2+-coupled magnetizable beads (HSA-beads), allowing the HSA to be easily removed from incubation components. The HSA-beads system provides a rapid and convenient method to study HSA compound binding. In this study, the HSA-beads system was characterized and evaluated as a tool for assessing compound HSA binding properties. The free fraction (fu) values of test compounds measured using HSA-beads were comparable to those determined by equilibrium dialysis (ED), which is commonly used to evaluate albumin binding in vitro. The equilibrium dissociation constant (Kd) values determined for a series of compounds using the HSA-beads method demonstrated good correlation with literature data. This good correlation also suggests that the binding of His-HSA to the beads does not impact the conformations of the two compound binding sites of HSA, as the range of compounds tested encompassed binding to both sites. Furthermore, the Kd values of representative compounds itraconazole and BIRT2584 that were difficult to assess using ED, due to significant cellulose membrane adsorption, were successfully determined. The HSA-beads provide several advantages over ED, such as simple preparation, short assay incubation duration, and the ability to quantify both free and HSA-bound species of the test compound, facilitated by the simple separation of HSA-beads from the solution phase using a magnetic field. These properties render the HSA-beads method suitable for high-throughput studies on compound HSA binding.
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Affiliation(s)
- Cody Thomas
- Department of Drug Metabolism and Pharmacokinetics, Boehringer Ingelheim Pharmaceuticals, Inc., 900 Ridgebury Rd., Ridgefield, CT 06877, USA
| | - Alexander Byer-Alcorace
- Department of Drug Metabolism and Pharmacokinetics, Boehringer Ingelheim Pharmaceuticals, Inc., 900 Ridgebury Rd., Ridgefield, CT 06877, USA
| | - Ting Wang
- Department of Drug Metabolism and Pharmacokinetics, Boehringer Ingelheim Pharmaceuticals, Inc., 900 Ridgebury Rd., Ridgefield, CT 06877, USA.
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2
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Fortuna A, Alves G, Falcão A, Soares-da-Silva P. Binding of licarbazepine enantiomers to mouse and human plasma proteins. Biopharm Drug Dispos 2010; 31:362-6. [PMID: 20578208 DOI: 10.1002/bdd.716] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Racemic licarbazepine (Lic) is the active metabolite of oxcarbazepine (OXC) and eslicarbazepine acetate (ESL), appearing in human plasma as S-licarbazepine (S-Lic) and R-licarbazepine (R-Lic). However, human metabolism of OXC and ESL to Lic differs in the S-Lic/R-Lic enantiomeric ratio observed in plasma. S-Lic appears in higher proportion after ESL administration than after OXC (95% versus 80%). Enantioselective pharmacokinetics of Lic enantiomers have been found in mice after their separate administration and in humans following OXC treatment. Since protein binding of drugs may be enantioselective and a determining factor of pharmacokinetics, the binding of S-Lic and R-Lic to mouse and human total plasma proteins and, specifically, to human serum albumin (HSA) and alpha(1)-acid glycoprotein (AGP) were herein investigated for the first time. Free and bound fractions of S-Lic and R-Lic were separated by ultrafiltration after previous in vitro incubation of spiked plasma samples and protein solutions with each enantiomer at 10, 25 and 50 microg/ml. The results revealed that the extent of binding of Lic enantiomers to total plasma proteins was 30% and independent of the drug concentration and species considered. The data also suggest that the binding of Lic enantiomers to HSA is greater than that to AGP. Moreover, absence of enantioselectivity in the binding of Lic enantiomers to mouse and human plasma proteins and to HSA and AGP is evident. In conclusion, these findings suggest that the enantioselectivity observed in vivo in the biodisposition of S-Lic and R-Lic is not dependent on their affinity to plasma proteins.
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Affiliation(s)
- Ana Fortuna
- Pharmacology Department, University of Coimbra, Portugal
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3
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Vaz-da-Silva M, Almeida L, Falcão A, Soares E, Maia J, Nunes T, Soares-da-Silva P. Effect of eslicarbazepine acetate on the steady-state pharmacokinetics and pharmacodynamics of warfarin in healthy subjects during a three-stage, open-label, multiple-dose, single-period study. Clin Ther 2010; 32:179-92. [DOI: 10.1016/j.clinthera.2010.01.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/17/2009] [Indexed: 10/19/2022]
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4
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Escuder-Gilabert L, Martínez-Gómez MA, Villanueva-Camañas RM, Sagrado S, Medina-Hernández MJ. Microseparation techniques for the study of the enantioselectivity of drug-plasma protein binding. Biomed Chromatogr 2009; 23:225-38. [DOI: 10.1002/bmc.1134] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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5
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Zimmerman JJ, Raible DG, Harper DM, Matschke K, Speth JL. Evaluation of a Potential Tigecycline-Warfarin Drug Interac. Pharmacotherapy 2008; 28:895-905. [DOI: 10.1592/phco.28.7.895] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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6
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Abstract
Stereoselectivity in binding can have a significant effect on the drug disposition such as first-pass metabolism, metabolic clearance, renal clearance, and protein and tissue binding. Human serum albumin (HSA) is able to stereoselectively bind a great number of various endogenous and exogenous compounds. Various experimental data suggested that the two major drug-binding cavities, namely, site I and site II, do not seem to be the stereoselective binding sites of HSA. Stereoselective binding of HSA under disease conditions such as renal and hepatic diseases was found to be enhanced. In addition, site-to-site displacement of a site II-specific drug by another site II-specific drug was found to be stereoselective, too. Endogenous compounds such as long-chain fatty acids and uremic toxins are likely to cause combined direct and cascade effects that contribute to the preferential binding of a particular drug enantiomer. Taking together the findings of other studies, it is highly possible that the stereoselective binding site exists at the interface of the subdomains.
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Affiliation(s)
- Victor Tuan Giam Chuang
- Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto, Japan
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7
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André C, Jacquot Y, Truong TT, Thomassin M, Robert JF, Guillaume YC. Analysis of the progesterone displacement of its human serum albumin binding site by beta-estradiol using biochromatographic approaches: effect of two salt modifiers. J Chromatogr B Analyt Technol Biomed Life Sci 2004; 796:267-81. [PMID: 14581067 DOI: 10.1016/s1570-0232(03)00563-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The mechanisms of (i) the binding of two sex-hormones (i.e. progesterone and beta-estradiol) to human serum albumin (HSA) and (ii) the progesterone displacement of its HSA binding cavity by beta-estradiol were studied by biochromatography using three different methods. In the first time, zonal elution method was used to prove the direct competition effect between the two sex-hormone. In the second time, the competition effect between beta-estradiol and progesterone to bound on the same HSA site was analysed by the competitive bi-Langmuir approach. Finally, the thermodynamic data of these two binding processes were studied. The Gibbs free energy value (Delta(approximately)G degrees) of the displacement equilibrium was negative demonstrating that beta-estradiol displaced progesterone of its HSA binding cavity. Moreover, the effect of two chloride modifiers (i.e. Na(+), Mg(2+)) on these two binding processes were analysed. Results showed that in the salt biological concentration ranges, the Mg(2+) cation enhanced strongly the bioavailable progesterone, whereas the Na(+) cation interacted slowly on the progesterone displacement of its HSA binding site by beta-estradiol. This study showed that it must be useful to carry out more in vivo test on the magnesium supplementation effect for women who suffer from estrogen dominance syndrome.
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Affiliation(s)
- C André
- Equipe des Sciences Séparatives et Biopharmaceutiques (2SB), Laboratoire de Chimie Analytique, Place Saint-Jacques, 25030 Besançon Cedex, France
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8
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Li F, Qiao M, Guo X. Specific determination of unbound oxacillin in protein solution with cefoperazone by high-performance frontal analysis with chemiluminescence detection. Biomed Chromatogr 2003; 17:53-7. [PMID: 12583007 DOI: 10.1002/bmc.213] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Unbound oxacillin concentrations in human serum albumin (HSA) solutions in the presence or absence of cefoperazone were determined using high-performance frontal analysis coupled with chemiluminescence detection (HPFA-CL). The HPFA was performed on an ISRP column with 67 mM potassium phosphate buffer of pH 7.4 and ionic strength of 0.17 as the mobile phase. The luminol-H(2)O(2)-Co(2+) system was employed in the chemiluminescence detection. The detection was highly specific for oxacillin in the presence of cefoperazone. Although both drugs in HSA solutions co-eluted in the same region in HPFA, cefoperazone did not interfere with the determination of unbound concentration of oxacillin. In the solution of 100 microM HSA and 11.33 micro M oxacillin the bound percentage of oxacillin to HSA was estimated as 80.5%. Addition of 30.98 micro M cefoperazone into the HSA-equilibrated solution produced little effect on the protein binding of oxacillin. In the presence of 154.9 micro M cefoperazone, however, the bound percentage of oxacillin was significantly reduced. This specific method could be applied to the investigation of drug-drug interaction in protein binding.
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Affiliation(s)
- Famei Li
- Department of Analytical Chemistry, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang 110016, People's Republic of China.
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Machtejevas E, Maruška A. A new approach to human serum albumin chiral stationary phase synthesis and its use in capillary liquid chromatography and capillary electrochromatography. J Sep Sci 2002. [DOI: 10.1002/1615-9314(20021101)25:15/17<1303::aid-jssc1303>3.0.co;2-w] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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10
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Fitos I, Visy J, Kardos J. Stereoselective kinetics of warfarin binding to human serum albumin: effect of an allosteric interaction. Chirality 2002; 14:442-8. [PMID: 11984760 DOI: 10.1002/chir.10113] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Kinetic and equilibrium binding studies were performed on the interaction of warfarin enantiomers with human serum albumin (HSA) in the absence and presence of lorazepam acetate (LoAc) enantiomers. Binding kinetics were followed by recording changes in the fluorescence of warfarin upon binding to HSA using the stopped-flow technique. The binding of (R)-warfarin displayed an exponentially increasing fluorescence, satisfying the two-step mechanism reported previously for the racemate, i.e., a diffusion controlled pre-equilibrium is followed by a slower rearrangement of the complex. In the case of (S)-warfarin, the signal was biphasic: a fast fluorescence enhancement was followed by a slow decline. The different kinetic features indicate that the equilibrium conformations of the [(S)-warfarin-HSA] and [(R)-warfarin-HSA] complexes are achieved via different mechanisms. The phenomenon was seen in buffers of different pH and compositions. Equilibrium binding measurements indicated significantly lower molar intrinsic fluorescence for the (S)-warfarin complex, suggesting differences in the microenvironments of the bound enantiomers. In the presence of (S)-LoAc, the allosterically enhanced binding of (S)-warfarin manifested itself in accelerated relaxation kinetics. In accordance with the low molar intrinsic fluorescence determined for the stable ternary complex, the amplitude of the decline in fluorescence became larger.
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Affiliation(s)
- Ilona Fitos
- Department of Molecular Pharmacology, Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary.
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Qiao M, Guo X, Li F. Chemiluminescence detection coupled to high-performance frontal analysis for the determination of unbound concentrations of drugs in protein binding equilibrium. J Chromatogr A 2002; 952:131-8. [PMID: 12064525 DOI: 10.1016/s0021-9673(02)00086-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
High-performance frontal analysis coupled with chemiluminescence detection (HPFA-CL) was developed for the determination of unbound oxacillin concentration in human serum albumin solution. The HPFA system consisted of an ISRP column and a mobile phase of 67 mM potassium phosphate buffer of pH 7.4 and ionic strength of 0.17. The luminol-H2O2-Co2+ system was used in the chemiluminescence detection. An enhancement of luminol chemiluminescence by oxacillin was investigated and employed for determining the concentration of oxacillin in the HPFA eluate. Sample solutions were directly injected onto the column; the drug was eluted as a zonal peak with a plateau region. The unbound drug concentrations were determined by using the height of the plateau. The results agreed with those obtained with conventional ultrafiltration-HPLC method. Good reproducibility was confirmed by the within run and between run RSD < or = 7.4%. HPFA-CL provided a selective method for determination of unbound drug concentration in protein binding equilibrium.
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Affiliation(s)
- Mingxi Qiao
- Department of Analytical Chemistry, Shenyang Pharmaceutical University, China
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12
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Shibukawa A, Ishizawa N, Kimura T, Sakamoto Y, Ogita K, Matsuo Y, Kuroda Y, Matayatsu C, Nakagawa T, Wainer IW. Plasma protein binding study of oxybutynin by high-performance frontal analysis. J Chromatogr B Analyt Technol Biomed Life Sci 2002; 768:177-88. [PMID: 11939551 DOI: 10.1016/s0378-4347(01)00497-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Plasma protein binding of oxybutynin (OXY) was investigated quantitatively and enantioselectively using high-performance frontal analysis (HPFA). An on-line HPLC system which consists of HPFA column, extraction column and analytical column was developed to determine the unbound concentrations of OXY enantiomers in human plasma, in human serum albumin (HSA) solutions, and in human alpha1-acid glycoprotein (AGP) solutions. OXY is bound in human plasma strongly and enantioselectively. The bound drug fraction in human plasma containing 2-10 microM (R)- or (S)-OXY was higher than 99%, and the unbound fraction of (R)-OXY was 1.56 times higher than that of (S)-isomer. AGP plays the dominant role in this strong and enantioselective plasma protein binding. The total binding affinities (nK) of (R)- and (S)-OXY to AGP were 6.86 x 10(6) and 1.53 x 10(7) M(-1), respectively, while the nK values of (R)- and (S)-OXY to HSA were 2.64 x 10(4) and 2.19 x 10(-4) M(-1), respectively. The binding affinity of OXY to AGP is much higher than that to HSA, and shows high enantioselectivity (SIR ratio of nK values is 2.2). It was found that both enantiomers are bound competitively at the same binding site on an AGP molecule. The binding property between OXY and low density lipoprotein (LDL) was investigated by using the frontal analysis method incorporated in high-performance capillary electrophoresis (HPCE/FA). It was found the binding is non-saturable and non-enantioselective.
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Affiliation(s)
- Akimasa Shibukawa
- Graduate School of Pharmaceutical Sciences, Kyoto University, Japan.
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13
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Chapter 9 Recent developments in liquid chromatographic enantioseparation. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s1567-7192(00)80012-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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14
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Rodriguez Rosas ME, Shibukawa A, Yoshikawa Y, Kuroda Y, Nakagawa T. Binding study of semotiadil and levosemotiadil with alpha(1)-acid glycoprotein using high-performance frontal analysis. Anal Biochem 1999; 274:27-33. [PMID: 10527493 DOI: 10.1006/abio.1999.4266] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
High-performance frontal analysis (HPFA) was used to investigate the binding properties of human alpha(1)-acid glycoprotein (AGP) with semotiadil ((R)-isomer, Ca-channel blocker) and its antipode levosemotiadil ((S)-isomer, Ca- and Na-channel blockers). An on-line HPLC system consisting of a HPFA column, an extraction column, and an analytical HPLC column was used to determine the unbound concentrations of these enantiomers, and the experimental data were subsequently subjected to the Scatchard analyses to estimate their binding parameters. The binding affinity of the (R)-isomer (K = 3.17 x 10(7) M, n = 0.74) is approximately 1.2 times stronger than that of (S)-isomer (K = 2.59 x 10(7) M, n = 0.74). An enantioselective competitive binding study indicated that both enantiomers are bound at the same site on AGP molecules.
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Affiliation(s)
- M E Rodriguez Rosas
- Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan
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Shibukawa A, Kuroda Y, Nakagawa T. Development of high-performance frontal analysis and the application to the study of drug–plasma protein binding. Trends Analyt Chem 1999. [DOI: 10.1016/s0165-9936(99)00136-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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16
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Abstract
The aim of this work was to provide a short overview of existing methods for the determination of free drug concentration and protein-drug binding fraction in plasma. Various methods have been described in terms of principles, evaluation of methods, and applications in recent years, with an emphasis on the chromatographic method, i.e. high-performance frontal analysis (HPFA).
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Affiliation(s)
- Z Liu
- Department of Analytical Chemistry, Shenyang Pharmaceutical University, People's Republic of China
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17
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Shibukawa A, Kuroda Y, Nakagawa T. High-performance frontal analysis for drug-protein binding study. J Pharm Biomed Anal 1999; 18:1047-55. [PMID: 9925341 DOI: 10.1016/s0731-7085(98)00201-5] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
High-performance frontal analysis (HPFA) is a novel analytical method which enables simultaneous determination of total and unbound drug concentrations under drug-plasma protein binding condition. HPFA can be achieved using separation systems such as HPLC and CE. This paper deals with the principle and feature of HPFA method and its application to the stereoselective protein binding study. HPFA allows a simple analysis following direct sample injection, and does not suffer from undesirable drug adsorption on membrane nor leakage of bound drug through the membrane which are often encountered in conventional ultrafiltration and dialysis methods. HPFA can be easily incorporated into on-line HPLC system. By coupling HPFA with a chiral HPLC column, the unbound concentration of a racemic drug can be determined enantioselectively. The detection limit can be improved by coupling of HPFA with a preconcentration column. High-performance capillary electrophoresis/frontal analysis (HPCE/FA) enables to determine unbound concentrations enantioselectively with ultramicro injection volume, and is hence useful especially for the binding study of proteins which are scarce and difficult to obtain.
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Affiliation(s)
- A Shibukawa
- Graduate School of Pharmaceutical Sciences, Kyoto University, Japan.
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18
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ROSAS MER, SHIBUKAWA A, YOSHIKAWA Y, KURODA Y, NAKAGAWA T. Binding Study of Semotiadil and Levosemotiadil with Human Serum Albumin Using High-Performance Frontal Analysis. ANAL SCI 1999. [DOI: 10.2116/analsci.15.217] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
| | | | - Yuki YOSHIKAWA
- Graduate School ofPharmaceutical Sciences, Kyoto University
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Zhivkova ZD, Russeva VN. Stereoselective binding of ketoprofen enantiomers to human serum albumin studied by high-performance liquid affinity chromatography. JOURNAL OF CHROMATOGRAPHY. B, BIOMEDICAL SCIENCES AND APPLICATIONS 1998; 714:277-83. [PMID: 9766867 DOI: 10.1016/s0378-4347(98)00211-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
A chiral stationary phase based on immobilized human serum albumin (HSA) was used to study the stereoselective binding of ketoprofen enantiomers by means of high-performance liquid affinity chromatography. The technique of zonal elution was applied together with a novel mathematical approach describing attachment to more than one type of binding site. Phenylbutazon (PBZ) and diazepam (DAZ) were used as markers for the major believed binding regions on HSA. Both R- and S-ketoprofen (KTR and KTS) display high affinity to the primary PBZ- and DAZ-binding sites and low-affinity to the secondary DAZ sites. The binding to high-affinity regions is accepted to be a stepwise process initiated by the binding to the primary DAZ sites and followed by the attachment to the primary PBZ sites. The chiral recognition is attributed to the high-affinity PBZ-binding sites and to the low-affinity DAZ-binding sites.
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Affiliation(s)
- Z D Zhivkova
- Department of Chemistry, Faculty of Pharmacy, Medical University, Sofia, Bulgaria
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Zhivkova Z, Russeva V. New mathematical approach for the evaluation of drug binding to human serum albumin by high-performance liquid affinity chromatography. JOURNAL OF CHROMATOGRAPHY. B, BIOMEDICAL SCIENCES AND APPLICATIONS 1998; 707:143-9. [PMID: 9613943 DOI: 10.1016/s0378-4347(97)00586-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A novel mathematical approach for investigation of drug-human serum albumin (HSA) interactions by means of high-performance liquid affinity chromatography is developed. The model is based on the assumption that two types of competitive binding sites exist on the HSA molecule. The widely used single-site binding equation is extended and a proper mathematical analysis is proposed allowing the determination of the major parameters characterizing the multisite binding (cobinding) process. The utility of the new approach is proved by competitive studies on HSA binding of two model drugs, diazepam and diclofenac.
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Affiliation(s)
- Z Zhivkova
- Department of Chemistry, Faculty of Pharmacy, Medical University, Solia, Bulgaria
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