Analysis of multi-site drug-protein interactions by high-performance affinity chromatography: Binding by glimepiride to normal or glycated human serum albumin

Generation of affinity maps for thiazolidinediones with human serum albumin using affinity microcolumns. II. Effects of advanced glycation end products on multisite drug binding

Multisite protein interactions by the thiazolidinedione-class drugs pioglitazone and rosiglitazone were examined by using high-performance affinity microcolumns that contained normal human serum albumin (HSA) vs HSA that had been modified to form advanced glycation end products by glyoxal (Go) or methylglyoxal (MGo). The results were used to generate an affinity map for these drugs at several key regions on HSA. Strong binding (∼105 M-1) by these drugs was seen at both Sudlow sites I and II. About a 50 % decrease in the affinities at Sudlow site II was observed for pioglitazone for Go-modified HSA, while either a 47 % decrease or 1.6-fold increase in affinity was seen for MGo-modified HSA, depending on the extent of modification. The binding affinity for rosiglitazone at Sudlow site II had a 40-83 % decrease for Go-modified HSA and either a non-significant change or 1.4-fold increase for MGo-modified HSA. At Sudlow site I, pioglitazone gave a 41 % decrease in affinity for either Go or MGo-modified HSA, and for rosiglitazone up to a 55 % decrease or 1.3-fold increase in affinity was noted. Positive allosteric effects were seen by these drugs with the tamoxifen site of HSA, and neither drug had any notable binding at the digitoxin site for the normal or modified forms of HSA. Rosiglitazone also had weak interactions at a site in subdomain IB, which increased in affinity by up to 5.0-fold with the Go- or MGo-modified HSA. This study illustrated how affinity microcolumns can be used to provide a detailed analysis of solute-protein systems that involve complex interactions. The data obtained should also be valuable in providing a better understanding of how drug interactions with HSA and other proteins can be altered by modifications of these binding agents in diseases such as diabetes.

Generation of affinity maps for thiazolidinediones with human serum albumin using affinity microcolumns. I. Studies of effects by glycation on multisite drug binding

Human serum albumin (HSA) is known to undergo modifications by glucose during diabetes. This process produces glycated HSA that can have altered binding to some drugs. In this study, high-performance affinity microcolumns and competition studies were used to see how glycation affects the binding by two thiazolidinedione-class drugs (i.e., pioglitazone and rosiglitazone) at specific regions of HSA. These regions included Sudlow sites I and II, the tamoxifen and digitoxin sites, and a drug-binding site located in subdomain IB. At Sudlow site II, the association equilibrium constants (or binding constants) for pioglitazone and rosiglitazone with normal HSA were 1.7 × 105 M-1 and 2.0 × 105 M-1 at pH 7.4 and 37 °C, with values that changed by up to 5.7-fold for glycated HSA. Sudlow site I of normal HSA had binding constants for pioglitazone and rosiglitazone of 3.4 × 105 M-1 and 4.6 × 105 M-1, with these values changing by up to 1.5-fold for glycated HSA. Rosiglitazone was found to also bind a second region that had a positive allosteric effect on Sudlow site I for all the tested preparations of HSA (binding affinity, 1.1-3.2 × 105 M-1; coupling constant for Sudlow site I, 1.20-1.34). Both drugs had a strong positive allosteric effect on the tamoxifen site of HSA (coupling constants, 13.7-19.9 for pioglitazone and 3.7-11.5 for rosiglitazone). Rosiglitazone also had weak interactions at a site in subdomain IB, with a binding constant of 1.4 × 103 M-1 for normal HSA and a value that was altered by up to 6.8-fold with glycated HSA. Neither of the tested drugs had any significant binding at the digitoxin site. The results were used to produce affinity maps that described binding by these thiazolidinediones with HSA and the effects of glycation on these interactions during diabetes.

Affinity Chromatographic Method for Determining Drug-Protein Interaction with Enhanced Speed Than Typical Frontal Analysis

Revealing drug-protein interaction is highly important to select a drug candidate with improved drug-like properties in the early stages of drug discovery. This highlights the urgent need to develop assays that enable the analysis of drug-protein interaction with high speed. Herein, this purpose was realized by the development of an affinity chromatographic method with a two-fold higher speed than typical assays like frontal analysis and zonal elution. The method involved synthesis of a stationary phase by immobilizing poly(ADP-ribose) polymerase-1 (PARP1) onto macroporous silica gel through a one-step bioorthogonal reaction, characterization of mutual displacement interaction of two canonical drugs to the immobilized PARP1, determination of the interaction between three (iniparib, rucaparib, and olaparib) drugs and the protein, and validation of these parameters by typical frontal analysis. The numbers of binding sites on the column were (2.85 ± 0.05) × 10-7, (1.89 ± 0.71) × 10-6, and (1.49 ± 0.06) × 10-7 M for iniparib, rucaparib, and olaparib, respectively. On these sites, the association constants of the three drugs to the protein were (9.85 ± 0.56) × 104, (2.85 ± 0.34) × 104, and (1.07 ± 0.35) × 105 M-1. The determined parameters presented a good agreement with the calculation by typical frontal analyses, which indicated that the current continuous competitive frontal analysis method was reliable for determining drug-protein interaction. Application of the methods was achieved by screening tubeimosides I and II as the bioactive compounds against breast cancer in Bolbostemma paniculatum. Their mechanism may be the interference of DNA repair via down-regulating PARP1 and meiotic recombination 11 expressions, thus leading to oncogene mutations and death of cancer cells. The method was high speed since it allowed simultaneous determination of binding parameters between two drugs and a protein with a smaller number of experiments to be performed. Such a feature made the method an attractive alternative for high-speed analysis of drug-protein interaction or the other bindings in a binary system.

Characterization of binding by repaglinide and nateglinide with glycated human serum albumin using high-performance affinity microcolumns

High-performance affinity microcolumns were used to characterize binding by the anti-diabetic drugs repaglinide and nateglinide with normal and glycated forms of human serum albumin. The microcolumns contained only nmol amounts of protein and provided a detailed analysis of these drug interactions with good precision and in a matter of minutes per experiment. The overall binding by repaglinide to normal and glycated albumin fits a model with two types of binding sites: a set of one or two moderate-to-high affinity regions and a larger set of weaker regions with association equilibrium constants of ∼10⁵ and 10³  M^-1 , respectively, at pH 7.4 and 37°C. Competition studies gave site-specific association constants for repaglinide and nateglinide at Sudlow site I of 4.2 × 10⁴ and 5.0 × 10⁴  M^-1 for normal albumin, with a decrease of 26%-30% being seen for nateglinide with glycated albumin and no significant change being noted for repaglinide. At Sudlow site II, repaglinide and nateglinide had association constants for normal albumin of 6.1 × 10⁴ and 7.1 × 10⁵  M^-1 , with glycated albumin giving an increase in the association constant at this site for repaglinide of 1.6- to 1.8-fold and a decrease for nateglinide of 51%-58%.

Two Original Experimental Setups for Staircase Frontal Affinity Chromatography at the Miniaturized Scale

Frontal affinity chromatography is a powerful, underappreciated technique for the qualitative (screening) and quantitative (K_d determination) evaluation of biological interactions. Its development has been previously hampered by its sample consumption, limited throughput, and lack of dedicated instrumentation especially at a miniaturized scale. This work describes two original experimental devices allowing nano-frontal affinity chromatography titrations (nano-FAC) to be automatically implemented in the time-saving staircase mode. The first nano-FAC system utilizes a capillary electrophoresis device (7100 CE Agilent system) in the pressurization mode with in situ UV detection. The second nano-FAC experimental setup implements a nano-LC device (Ultimate 3000 Thermo) modified with a 10-port valve equipped with two superloops (loop volume, 5 μL) operating alternatively and automatically in a single run. The benefits and drawbacks of each approach are exemplified using two model protein-ligand interactions (concanavalin A-mannose and concanavalin A-glucose). The two methods result in concordant dissociation constants (K_d) and number of active site (B_act) values, obtained in a fully automated manner, with low sample consumption and good throughput.

Hypoglycemia possibly caused by CYP2C9-mediated drug interaction in combination with bucolome: a case report

Background

Bucolome is a non-steroidal anti-inflammatory drug and uricosuric agent, currently used only in Japan. It is known to induce drug interactions by inhibiting cytochrome P450 (CYP) 2C9. It is often used to enhance the anticoagulant effect of warfarin by utilizing its drug interactions. There are only a few reports on drug interactions of bucolome and the mechanism remain poorly understood.

Case presentation

An 81-year-old woman with a history of type 2 diabetes mellitus was taking glimepiride 2 mg/day and voglibose 0.6 mg/day. After hospitalization, the patient underwent surgical aortic valve replacement surgery (day 0). Glimepiride and voglibose were resumed on the second postoperative day (day 2), and warfarin was started to prevent thromboembolism. Since the prothrombin time-international normalized ratio on day 9 was low at 1.24, 300 mg/day of bucolome was added to enhance the effect of warfarin. A gradual decrease in blood glucose levels was observed from the day after bucolome administration was initiated. Hypoglycemia in the 56–57 mg/dL range occurred before lunch and dinner on the 6th day (day 14) of bucolome administration, due to which voglibose was discontinued. Hypoglycemia below 70 mg/dL was not observed thereafter, and the general condition of the patient was stable.

Conclusions

Based on the clinical course and literature review, we believe that hypoglycemia in the present case was due to a drug interaction, caused by inhibition of CYP2C9 by bucolome and competitive inhibition of CYP2C9 by warfarin, which affected the pharmacokinetics of glimepiride. The possibility of hypoglycemia due to drug interactions should be considered by physicians, when bucolome is included to enhance the effect of warfarin, in patients taking glimepiride.

[Advances in chromatography in the study of drug-plasma protein interactions]

After entering human blood circulation, small-molecule drugs interact extensively with various plasma proteins, such as human serum albumin and α1-acid glycoprotein. These interactions profoundly affect the distribution of drugs in vivo and the binding of drugs to targets, thus affecting the efficacy of drugs. In-depth investigation of drug-plasma protein interactions is of great significance for the optimization of drug properties, the development of new drugs, risk assessment, and combination therapy of drugs. Therefore, it is essential to develop highly efficient, sensitive, and accurate methods for elucidating drug-plasma protein interactions. Chromatography is a powerful tool with high throughput, high separation performance, and high sensitivity in the characterization of drug-protein interactions. High-performance affinity chromatography (HPAC) and capillary electrophoresis (CE) have been widely utilized in this field. These methods include the determination of the effects of the posttranslational modification of proteins on binding and the competitive binding of multiple drugs. In addition, various chromatographic methods are used to obtain interaction information such as the binding constant, binding-site number, and dissociation rate constant. In this review, the common strategies and recent advances in HPAC and CE in the study of drug-plasma protein interactions are briefly reviewed. The immobilization methods of proteins, the principles and applications of frontal analysis, zonal elution, ultrafast affinity extraction, peak profiling, and peak decay analysis are discussed for HPAC and affinity capillary electrophoresis (ACE) and capillary electrophoresis frontal analysis (CE-FA) for CE. HPAC relies on the fixation of proteins on the surfaces of chromatographic stationary phases by covalent linking or physical adsorption, followed by obtaining the drug-protein interaction information through a variety of chromatographic methods. In the frontal chromatography analysis, mobile phases with different concentrations of drugs are passed through the HPAC column to obtain different breakthrough times. The process can determine the number of drug binding sites and the binding constant of each site in the affinity protein with high accuracy. The zonal elution method can detect the drug binding sites on proteins using site-specific probes to determine whether there is competition between drugs and probes. The sample consumption and analysis time of the zonal elution method are much less than those in frontal chromatography analysis. The ultrafast affinity extraction method can inject complex samples, such as serum, into affinity columns to determine the free drug components. It can measure the combination and dissociation constants of drug-protein interactions by changing the chromatography flow rate. Peak profiling and peak decay analyses are both effective methods for investigating the dissociation of drugs and proteins. In CE analysis, the drug and protein samples are dissolved in an electrophoresis buffer, and their interactions are measured during electrophoresis with high accuracy and low sample consumption. However, the adsorption of proteins on the capillary wall can compromise CE performance. Common CE methods in drug-protein interaction analysis are ACE and CE-FA. ACE is usually performed by changing the effective mobility of drugs via the addition of different concentrations of proteins. This method has been widely used, and several variant techniques have been developed recently. CE-FA involves the sampling of a drug premixed at a known concentration with a target protein. Compared with other CE methods, CE-FA exhibits the unique advantages of high throughput, automatic online analysis, and the ability to determine high-order drug-protein interactions. Finally, the shortcomings of current chromatography methods are summarized, and the application prospects and development direction of chromatography technology in the field of drug-plasma protein interaction research are discussed.

High-Performance affinity chromatographic studies of repaglinide and nateglinide interactions with normal and glyoxal- or methylglyoxal-modified human albumin serum

During diabetes human serum albumin (HSA), an important drug transport protein, can be modified by agents such as glyoxal (Go) and methylglyoxal (MGo) to form advanced glycation end-products. High-performance affinity microcolumns and zonal elution competition studies were used to compare interactions by the anti-diabetic drugs repaglinide and nateglinide with normal and Go- or MGo-modified HSA at Sudlow sites I and II of this protein. Both drugs had their strongest binding at Sudlow site II for the normal and modified forms of HSA. The association equilibrium constants at this site for repaglinide and nateglinide with normal HSA were 6.1 (± 0.2) × 10⁴ M^-1 and 7.1 (± 0.8) × 10⁵ M^-1, respectively, at pH 7.4 and 37⁰C; these values increased by up to 3.6-fold for repaglinide and decreased by up to 45-55 % for nateglinide when HSA was modified by Go or MGo at levels seen in prediabetes or diabetes. Both drugs were also found to bind at Sudlow site I, with association equilibrium constants at this site on normal HSA of 4.2 (± 0.3) × 10⁴ M^-1 for repaglinide and 5.0 (± 0.1) × 10⁴ M^-1 for nateglinide. The binding strength for repaglinide at Sudlow site I increased by 1.3- to 1.7-fold with the Go-modified HSA and decreased slightly (i.e., up to 19 %) for the MGo-modified HSA, while nateglinide showed only a small or insignificant change in binding with the same modified HSA samples. These results indicated that binding by repaglinide and nateglinide with HSA can be altered significantly by modification of this protein with Go or MGo, making these modifications of potential interest in the treatment of patients with these drugs during diabetes.

Recent Advances in Supramolecular Affinity Separations: Affinity Chromatography and Related Methods

Affinity chromatography is a technique that uses a stationary phase based on the supramolecular interactions that occur in biological systems or mimics of these systems. This method has long been a popular tool for the isolation, measurement, and characterization of specific targets in complex samples. This review discusses the basic concepts of this method and examines recent developments in affinity chromatography and related supramolecular separation methods. Topics that are examined include advances that have occurred in the types of supports, approaches to immobilization, and binding agents that are employed in this method. New developments in the applications of affinity chromatography are also summarized, including an overview on the use of this method for biochemical purification, sample preparation or analysis, chiral separations, and biointeraction studies.

Synthesis, X-ray structure, antiproliferative activity, interaction with HSA and docking studies of three novel mono and binuclear copper complexes containing the maltol ligand

The present study aims at synthesizing three new copper(ii) complexes of maltol in the presence of 1,10-phenanthroline-, 2,2′-bipyridine- and 4,4-dibromo-2,2′-bipyridine ligands.

Solid-Supported Proteins in the Liquid Chromatography Domain to Probe Ligand-Target Interactions

Ligand-target interactions play a central role in drug discovery processes because these interactions are crucial in biological systems. Small molecules-proteins interactions can regulate and modulate protein function and activity through conformational changes. Therefore, bioanalytical tools to screen new ligands have focused mainly on probing ligand-target interactions. These interactions have been evaluated by using solid-supported proteins, which provide advantages like increased protein stability and easier protein extraction from the reaction medium, which enables protein reuse. In some specific approaches, precisely in the ligand fishing assay, the bioanalytical method allows the ligands to be directly isolated from complex mixtures, including combinatorial libraries and natural products extracts without prior purification or fractionation steps. Most of these screening assays are based on liquid chromatography separation, and the binding events can be monitored through on-line or off-line methods. In the on-line approaches, solid supports containing the immobilized biological target are used as chromatographic columns most of the time. Several terms have been used to refer to such approaches, such as weak affinity chromatography, high-performance affinity chromatography, on-flow activity assays, and high-performance liquid affinity chromatography. On the other hand, in the off-line approaches, the binding event occurs outside the liquid chromatography system and may encompass affinity and activity-based assays in which the biological target is immobilized on magnetic particles or monolithic silica, among others. After the incubation step, the supernatant or the eluate from the binding assay is analyzed by liquid chromatography coupled to various detectors. Regardless of the selected bioanalytical approach, the use of solid supported proteins has significantly contributed to the development of automated and reliable screening methods that enable ligands to be isolated and characterized in complex matrixes without purification, thereby reducing costs and avoiding time-laborious steps. This review provides a critical overview of recently developed assays.

Binding studies based on ultrafast affinity extraction and single- or two-column systems: Interactions of second- and third-generation sulfonylurea drugs with normal or glycated human serum albumin

Ultrafast affinity extraction was evaluated and used with microcolumns containing human serum albumin (HSA) to measure the global affinity constants and dissociation rate constants for several second- and third-generation sulfonylurea drugs with solution-phase normal HSA or glycated HSA. Glibenclamide, glimepiride and glipizide were used as model drugs for this work. Both single- and two-column systems were considered for the analysis of global affinities for the model drugs. These methods were optimized with respect to the flow rates, column sizes and sample residence times that were employed with each drug for ultrafast affinity extraction. Data acquired with single-column systems were further utilized to estimate the dissociation rate constants for normal HSA and glycated HSA with the given drugs. The binding constants obtained by the single- and two-column systems showed good agreement with each other and with values obtained from the literature. Use of a single-column system indicated that levels of glycation found in controlled or advanced diabetes resulted in a 18-44% decrease in the overall binding strength of the model drugs with HSA. Although the two-column system allowed work with smaller free drug fractions and clinically-relevant drug/protein concentrations, the single-column system required less protein, provided better precision, and was easier to use in binding studies.

Chromatographic studies of chlorpropamide interactions with normal and glycated human serum albumin based on affinity microcolumns

Sulfonylurea drugs have significant binding to proteins in blood, with most of this binding believed to occur with human serum albumin (HSA). High performance affinity chromatography and affinity microcolumns containing immobilized HSA were used to investigate binding by the sulfonylurea drug chlorpropamide to normal HSA and glycated HSA, which is a modified form of HSA that has an increased serum concentration in diabetes. Experiments employing frontal analysis indicated that the binding by chlorpropamide gave a good fit to a two-site model for both normal HSA and glycated HSA samples that were representative of controlled or advanced diabetes. These interactions involved a set of moderate-to-high affinity sites and a set of lower affinity sites, with binding constants in the range of 6.2-9.9 × 10⁴ M^-1 and 0.18-0.57 × 10⁴ M^-1, respectively, at pH 7.4 and 37 °C. Competition studies utilizing a zonal elution format demonstrated that chlorpropamide could interact at both Sudlow sites I and II of HSA, with affinities in the range expected for the moderate-to-high affinity sites of this drug. The affinity of chlorpropamide at Sudlow site I had a small increase of up to 1.2-fold when comparing the normal HSA and glycated HSA samples. Chlorpropamide gave a larger 1.4- to over 1.5-fold increase at Sudlow site II when the affinity of this drug was compared between normal HSA and the same samples of glycated HSA. These results were compared to those obtained previously with other sulfonylurea drugs to help determine how glycation can change the overall and site-selective binding strength of these drugs with HSA at levels of protein modification that are seen in patients with diabetes.

Analysis of solute-protein interactions and solute-solute competition by zonal elution affinity chromatography

Many biological processes involve solute-protein interactions and solute-solute competition for protein binding. One method that has been developed to examine these interactions is zonal elution affinity chromatography. This review discusses the theory and principles of zonal elution affinity chromatography, along with its general applications. Examples of applications that are examined include the use of this method to estimate the relative extent of solute-protein binding, to examine solute-solute competition and displacement from proteins, and to measure the strength of these interactions. It is also shown how zonal elution affinity chromatography can be used in solvent and temperature studies and to characterize the binding sites for solutes on proteins. In addition, several alternative applications of zonal elution affinity chromatography are discussed, which include the analysis of binding by a solute with a soluble binding agent and studies of allosteric effects. Other recent applications that are considered are the combined use of immunoextraction and zonal elution for drug-protein binding studies, and binding studies that are based on immobilized receptors or small targets.

Overview of the detection methods for equilibrium dissociation constant KD of drug-receptor interaction

Drug-receptor interaction plays an important role in a series of biological effects, such as cell proliferation, immune response, tumor metastasis, and drug delivery. Therefore, the research on drug-receptor interaction is growing rapidly. The equilibrium dissociation constant (KD) is the basic parameter to evaluate the binding property of the drug-receptor. Thus, a variety of analytical methods have been established to determine the KD values, including radioligand binding assay, surface plasmon resonance method, fluorescence energy resonance transfer method, affinity chromatography, and isothermal titration calorimetry. With the invention and innovation of new technology and analysis method, there is a deep exploration and comprehension about drug-receptor interaction. This review discusses the different methods of determining the KD values, and analyzes the applicability and the characteristic of each analytical method. Conclusively, the aim is to provide the guidance for researchers to utilize the most appropriate analytical tool to determine the KD values.

High performance affinity chromatography and related separation methods for the analysis of biological and pharmaceutical agents

The last few decades have witnessed the development of many high-performance separation methods that use biologically related binding agents. The combination of HPLC with these binding agents results in a technique known as high performance affinity chromatography (HPAC). This review will discuss the general principles of HPAC and related techniques, with an emphasis on their use for the analysis of biological compounds and pharmaceutical agents. Various types of binding agents for these methods will be considered, including antibodies, immunoglobulin-binding proteins, aptamers, enzymes, lectins, transport proteins, lipids, and carbohydrates. Formats that will be discussed for these methods range from the direct detection of an analyte to indirect detection based on chromatographic immunoassays, as well as schemes based on analyte extraction or depletion, post-column detection, and multi-column systems. The use of biological agents in HPLC for chiral separations will also be considered, along with the use of HPAC as a tool to screen or study biological interactions. Various examples will be presented to illustrate these approaches and their applications in fields such as biochemistry, clinical chemistry, and pharmaceutical research.

Analysis of stereoselective drug interactions with serum proteins by high-performance affinity chromatography: A historical perspective

The interactions of drugs with serum proteins are often stereoselective and can affect the distribution, activity, toxicity and rate of excretion of these drugs in the body. A number of approaches based on affinity chromatography, and particularly high-performance affinity chromatography (HPAC), have been used as tools to study these interactions. This review describes the general principles of affinity chromatography and HPAC as related to their use in drug binding studies. The types of serum agents that have been examined with these methods are also discussed, including human serum albumin, α1-acid glycoprotein, and lipoproteins. This is followed by a description of the various formats based on affinity chromatography and HPAC that have been used to investigate drug interactions with serum proteins and the historical development for each of these formats. Specific techniques that are discussed include zonal elution, frontal analysis, and kinetic methods such as those that make use of band-broadening measurements, peak decay analysis, or ultrafast affinity extraction.

Analysis of Biological Interactions by Affinity Chromatography: Clinical and Pharmaceutical Applications

BACKGROUND

The interactions between biochemical and chemical agents in the body are important in many clinical processes. Affinity chromatography and high-performance affinity chromatography (HPAC), in which a column contains an immobilized biologically related binding agent, are 2 methods that can be used to study these interactions.

CONTENT

This review presents various approaches that can be used in affinity chromatography and HPAC to characterize the strength or rate of a biological interaction, the number and types of sites that are involved in this process, and the interactions between multiple solutes for the same binding agent. A number of applications for these methods are examined, with an emphasis on recent developments and high-performance affinity methods. These applications include the use of these techniques for fundamental studies of biological interactions, high-throughput screening of drugs, work with modified proteins, tools for personalized medicine, and studies of drug-drug competition for a common binding agent.

SUMMARY

The wide range of formats and detection methods that can be used with affinity chromatography and HPAC for examining biological interactions makes these tools attractive for various clinical and pharmaceutical applications. Future directions in the development of small-scale columns and the coupling of these methods with other techniques, such as mass spectrometry or other separation methods, should continue to increase the flexibility and ease with which these approaches can be used in work involving clinical or pharmaceutical samples.

Rapid analysis of interaction between six drugs and β2 -adrenergic receptor by injection amount-dependent method

Drug-protein interaction analysis has become a considerable topic in life science which includes clarifying protein functions, explaining drug action mechanisms and uncovering novel drug candidates. This work was to determine the association constants (K_A ) of six drugs to β₂ -adrenergic receptor by injection amount-dependent method using stationary phase containing the immobilized receptor. The values of K_A were calculated to be (25.85 ± 0.035) × 10⁴  m^-1 for clorprenaline, (42.51 ± 0.054) × 10⁴  m^-1 for clenbuterol, (6.67 ± 0.008) × 10⁴  m^-1 for terbutaline, (33.99 ± 0.025) × 10⁴  m^-1 for tulobuterol, (7.59 ± 0.011) × 10⁴  m^-1 for salbutamol and (78.52 ± 0.087) × 10⁴  m^-1 for bambuterol. This rank order agreed well with the data determined by zonal elution, frontal analysis and nonlinear chromatography, even using different batches of β₂ -AR column. A good correlation was found between the association constants by the current method and radio-ligand binding assay. Our data indicates that the injection amount-dependent method is a powerful alternative for rapid analysis of ligand-receptor interactions.

Chromatographic Studies of Protein-Based Chiral Separations

The development of separation methods for the analysis and resolution of chiral drugs and solutes has been an area of ongoing interest in pharmaceutical research. The use of proteins as chiral binding agents in high-performance liquid chromatography (HPLC) has been an approach that has received particular attention in such work. This report provides an overview of proteins that have been used as binding agents to create chiral stationary phases (CSPs) and in the use of chromatographic methods to study these materials and protein-based chiral separations. The supports and methods that have been employed to prepare protein-based CSPs will also be discussed and compared. Specific types of CSPs that are considered include those that employ serum transport proteins (e.g., human serum albumin, bovine serum albumin, and alpha1-acid glycoprotein), enzymes (e.g., penicillin G acylase, cellobiohydrolases, and α-chymotrypsin) or other types of proteins (e.g., ovomucoid, antibodies, and avidin or streptavidin). The properties and applications for each type of protein and CSP will also be discussed in terms of their use in chromatography and chiral separations.

High-Performance Affinity Chromatography: Applications in Drug-Protein Binding Studies and Personalized Medicine

The binding of drugs with proteins and other agents in serum is of interest in personalized medicine because this process can affect the dosage and action of drugs. The extent of this binding may also vary with a given disease state. These interactions may involve serum proteins, such as human serum albumin or α1-acid glycoprotein, or other agents, such as lipoproteins. High-performance affinity chromatography (HPAC) is a tool that has received increasing interest as a means for studying these interactions. This review discusses the general principles of HPAC and the various approaches that have been used in this technique to examine drug-protein binding and in work related to personalized medicine. These approaches include frontal analysis and zonal elution, as well as peak decay analysis, ultrafast affinity extraction, and chromatographic immunoassays. The operation of each method is described and examples of applications for these techniques are provided. The type of information that can be obtained by these methods is also discussed, as related to the analysis of drug-protein binding and the study of clinical or pharmaceutical samples.

Analysis of Hormone-Protein Binding in Solution by Ultrafast Affinity Extraction: Interactions of Testosterone with Human Serum Albumin and Sex Hormone Binding Globulin

Ultrafast affinity extraction was used to study hormone-protein interactions in solution, using testosterone and its transport proteins human serum albumin (HSA) and sex hormone binding globulin (SHBG) as models. Both single column and two-dimensional systems based on HSA microcolumns were utilized to measure the free fraction of testosterone in hormone/protein mixtures at equilibrium or that were allowed to dissociate for various lengths of time. These data were used to determine the association equilibrium constants (Ka) or global affinities (nKa') and dissociation rate constants (kd) for testosterone with soluble HSA and SHBG. This method was also used to measure simultaneously the free fraction of testosterone and its equilibrium constants with both these proteins in physiological mixtures of these agents. The kd and Ka values obtained for HSA were 2.1-2.2 s(-1) and 3.2-3.5 × 10(4) M(-1) at pH 7.4 and 37 °C. The corresponding constants for SHBG were 0.053-0.058 s(-1) and 0.7-1.2 × 10(9) M(-1). All of these results gave good agreement with literature values, indicating that this approach could provide information on a wide range of rate constants and binding strengths for hormone-protein interactions in solution and at clinically relevant concentrations. The same method could be extended to alternative hormone-protein systems or other solutes and binding agents.