Characterization Of Drug Interactions With Serum Proteins by Using High-Performance Affinity Chromatography

The binding of drugs with serum proteins can affect the activity, distribution, rate of excretion, and toxicity of pharmaceutical agents in the body. One tool that can be used to quickly analyze and characterize these interactions is high-performance affinity chromatography (HPAC). This review shows how HPAC can be used to study drug-protein binding and describes the various applications of this approach when examining drug interactions with serum proteins. Methods for determining binding constants, characterizing binding sites, examining drug-drug interactions, and studying drug-protein dissociation rates will be discussed. Applications that illustrate the use of HPAC with serum binding agents such as human serum albumin, α1-acid glycoprotein, and lipoproteins will be presented. Recent developments will also be examined, such as new methods for immobilizing serum proteins in HPAC columns, the utilization of HPAC as a tool in personalized medicine, and HPAC methods for the high-throughput screening and characterization of drug-protein binding

Characterization Of Drug Interactions With Serum Proteins by Using High-Performance Affinity Chromatography

The binding of drugs with serum proteins can affect the activity, distribution, rate of excretion, and toxicity of pharmaceutical agents in the body. One tool that can be used to quickly analyze and characterize these interactions is high-performance affinity chromatography (HPAC). This review shows how HPAC can be used to study drug-protein binding and describes the various applications of this approach when examining drug interactions with serum proteins. Methods for determining binding constants, characterizing binding sites, examining drug-drug interactions, and studying drug-protein dissociation rates will be discussed. Applications that illustrate the use of HPAC with serum binding agents such as human serum albumin, α1-acid glycoprotein, and lipoproteins will be presented. Recent developments will also be examined, such as new methods for immobilizing serum proteins in HPAC columns, the utilization of HPAC as a tool in personalized medicine, and HPAC methods for the high-throughput screening and characterization of drug-protein binding

Pharmaceutical And Biomedical Applications Of Affinity Chromatography: Recent Trends And Developments

Affinity chromatography is a separation technique that has become increasingly important in work with biological samples and pharmaceutical agents. This method is based on the use of a biologically-related agent as a stationary phase to selectively retain analytes or to study biological interactions. This review discusses the basic principles behind affinity chromatography and examines recent developments that have occurred in the use of this method for biomedical and pharmaceutical analysis. Techniques based on traditional affinity supports are discussed, but an emphasis is placed on methods in which affinity columns are used as part of HPLC systems or in combination with other analytical methods. General formats for affinity chromatography that are considered include step elution schemes, weak affinity chromatography, affinity extraction and affinity depletion. Specific separation techniques that are examined include lectin affinity chromatography, boronate affinity chromatography, immunoaffinity chromatography, and immobilized metal ion affinity chromatography. Approaches for the study of biological interactions by affinity chromatography are also presented, such as the measurement of equilibrium constants, rate constants, or competition and displacement effects. In addition, related developments in the use of immobilized enzyme reactors, molecularly imprinted polymers, dye ligands and aptamers are briefly considered

Pharmaceutical And Biomedical Applications Of Affinity Chromatography: Recent Trends And Developments

Affinity chromatography is a separation technique that has become increasingly important in work with biological samples and pharmaceutical agents. This method is based on the use of a biologically-related agent as a stationary phase to selectively retain analytes or to study biological interactions. This review discusses the basic principles behind affinity chromatography and examines recent developments that have occurred in the use of this method for biomedical and pharmaceutical analysis. Techniques based on traditional affinity supports are discussed, but an emphasis is placed on methods in which affinity columns are used as part of HPLC systems or in combination with other analytical methods. General formats for affinity chromatography that are considered include step elution schemes, weak affinity chromatography, affinity extraction and affinity depletion. Specific separation techniques that are examined include lectin affinity chromatography, boronate affinity chromatography, immunoaffinity chromatography, and immobilized metal ion affinity chromatography. Approaches for the study of biological interactions by affinity chromatography are also presented, such as the measurement of equilibrium constants, rate constants, or competition and displacement effects. In addition, related developments in the use of immobilized enzyme reactors, molecularly imprinted polymers, dye ligands and aptamers are briefly considered

Affinity chromatographic studies of drug-protein binding in personalized medicine

In recent years there have been an increasing number of scientific advances dedicated to the transition from traditional medicine to a new era of data-driven personalized medicine. The customization of healthcare holds a great promise for providing faster diagnosis and more effective treatments for a variety of diseases and disorders, such as diabetes. The number of diabetic patients has increased at an alarming rate over the last 20 years, with an estimated 26 million children and adults in the United States suffering from this disease and related complications such as cardiovascular disease, kidney or liver damage, and blindness. Some of these complications have been associated with high levels of blood glucose and a process known as non-enzymatic glycation, which can produce structural and functional modifications of proteins in the human body. Among these proteins, human serum albumin (HSA) is an important transport protein for many drugs, hormones and fatty acids in the circulation. Therefore, a detailed discussion of the process of glycation on HSA is provided in this dissertation. One topic examined in this manuscript is the use of high-performance affinity chromatography (HPAC) and immobilized HSA microcolumns to examine the binding of various drugs to HSA as the glycation level is increased. This work was first performed by studying the binding of a number of sulfonylurea drugs to in vivo glycated HSA. Affinity microcolumns were prepared from only 20 μL of serum from individual patients with diabetes. The clinical samples were also analyzed using mass spectrometry to identify and quantify modifications of HSA that occur due to glycation. In addition, competition studies were used to investigate the effect of in vitro glycation and the presence of long chain fatty acids on the binding of drugs at the major binding sites of HSA. Frontal analysis and zonal elution experiments were also utilized to study the binding of drugs to alpha-acid glycoprotein (AGP), an acute phase protein. A novel on-column (in situ) protein entrapment approach was developed to prepare affinity microcolumns containing AGP. Lastly, the peak decay method and HPAC were used to examine the dissociation rate constants for several species of immunoglobulin G (IgG) from immobilized protein G supports. The approaches developed in this dissertation are not limited to glycated HSA and AGP but could be adapted to other modified proteins and disease states of interest to the scientific community and to the field of personalized medicine

BINDING OF TOLBUTAMIDE TO GLYCATED HUMAN SERUM ALBUMIN

The presence of elevated levels of glucose in blood during diabetes can lead to the non-enzymatic glycation of serum proteins such as human serum albumin (HSA). This study examined the changes that occur in binding of the sulfonylurea drug tolbutamide to HSA as the level of glycation for this protein was increased. High-performance affinity chromatography was used in this work along with columns containing various preparations of in vitro glycated HSA. It was found in frontal analysis experiments that the binding of tolbutamide with all of the tested preparations of glycated HSA could be described by a two-site model involving both strong and weak affinity interactions. The association equilibrium constants (Ka) for tolbutamide at its high affinity sites on glycated HSA were in the range of 0.8–1.2 × 105 M−1 and increased by 1.4-fold in going from normal HSA to mildly glycated HSA. It was found through competition studies that tolbutamide was binding at both Sudlow sites I and II on the glycated HSA, in agreement with previous studies. The Ka for tolbutamide at Sudlow site II increased by 1.1 to 1.4-fold in going from normal HSA to glycated HSA. At Sudlow site I, the Ka for tolbutamide increased by 1.2 to 1.3-fold in going from normal HSA to the glycated HSA samples. This information demonstrates the effects that glycation can have on drug interactions on HSA and should provide a better quantitative understanding of how the protein binding of tolbutamide in serum may be affected for individuals with diabetes

Effects of Fatty Acids and Glycation on Drug Interactions with Human Serum Albumin

The presence of elevated glucose concentrations in diabetes is a metabolic change that leads to an increase in the amount of non-enzymatic glycation that occurs for serum proteins. One protein that is affected by this process is the main serum protein, human serum albumin (HSA), which is also an important carrier agent for many drugs and fatty acids in the circulatory system. Sulfonylurea drugs, used to treat type 2 diabetes, are known to have significant binding to HSA. This study employed ultrafiltration and high-performance affinity chromatography to examine the effects of HSA glycation on the interactions of several sulfonylurea drugs (i.e., acetohexamide, tolbutamide and gliclazide) with fatty acids, whose concentrations in serum are also affected by diabetes. Similar overall changes in binding were noted for these drugs with normal HSA or glycated HSA and in the presence of the fatty acids. For most of the tested drugs, the addition of physiological levels of the fatty acids to normal HSA and glycated HSA produced weaker binding. At low fatty acid concentrations, many of these systems followed a direct competition model while others involved a mixed-mode interaction. In some cases, there was a change in the interaction mechanism between normal HSA and glycated HSA, as seen with linoleic acid. Systems with only direct competition also gave notable changes in the affinities of fatty acids at their sites of drug competition when comparing normal HSA and glycated HSA. This research demonstrated the importance of considering how changes in the concentrations and types of metabolites (e.g., in this case, glucose and fatty acids) can alter the function of a protein such as HSA and its ability to interact with drugs or other agents

HIGH-PERFORMANCE AFFINITY CHROMATOGRAPHY AND THE ANALYSIS OF DRUG INTERACTIONS WITH MODIFIED PROTEINS: BINDING OF GLICLAZIDE WITH GLYCATED HUMAN SERUM ALBUMIN

This study used high-performance affinity chromatography (HPAC) to examine the binding of gliclazide (i.e., a sulfonylurea drug used to treat diabetes) with the protein human serum albumin (HSA) at various stages of modification due to glycation. Frontal analysis conducted with small HPAC columns was first used to estimate the number of binding sites and association equilibrium constants (Ka) for gliclazide with normal HSA and glycated HSA. Both normal and glycated HSA interacted with gliclazide according to a two-site model, with a class of high affinity sites (average Ka, 7.1-10 × 104 M−1) and a group of lower affinity sites (average Ka, 5.7-8.9 × 103 M−1) at pH 7.4 and 37°C. Competition experiments indicated that Sudlow sites I and II of HSA were both involved in these interactions, with the Ka values for gliclazide at these sites being 1.9 × 104 M−1 and 6.0 × 104 M−1, respectively, for normal HSA. Two samples of glycated HSA had similar affinities to normal HSA for gliclazide at Sudlow site I, but one sample had a 1.9-fold increase in affinity at this site. All three glycated HSA samples differed from normal HSA in their affinity for gliclazide at Sudlow site II. This work illustrated how HPAC can be used to examine both the overall binding of a drug with normal or modified proteins and the site-specific changes that can occur in these interactions as a result of protein modification

Analysis Of Drug Interactions With Modified Proteins By High-Performance Affinity Chromatography: Binding Of Glibenclamide To Normal And Glycated Human Serum Albumin

High-performance affinity chromatography (HPAC) was used to examine the changes in binding that occur for the sulfonylurea drug glibenclamide with human serum albumin (HSA) at various stages of glycation for HSA. Frontal analysis on columns containing normal HSA or glycated HSA indicated glibenclamide was interacting through both high affinity sites (association equilibrium constant, Ka, 1.4–1.9 × 106 M−1 at pH 7.4 and 37°C) and lower affinity sites (Ka, 4.4– 7.2 × 104 M−1). Competition studies were used to examine the effect of glycation at specific binding sites of HSA. An increase in affinity of 1.7- to 1.9-fold was seen at Sudlow site I with moderate to high levels of glycation. An even larger increase of 4.3- to 6.0-fold in affinity was noted at Sudlow site II for all of the tested samples of glycated HSA. A slight decrease in affinity may have occurred at the digitoxin site, but this change was not significant for any individual glycated HSA sample. These results illustrate how HPAC can be used as tool for examining the interactions of relatively non-polar drugs like glibenclamide with modified proteins and should lead to a more complete understanding of how glycation can alter the binding of drugs in blood