Drug binding in plasma. A summary of recent trends in the study of drug and hormone binding

Challenges of pediatric pharmacotherapy: A narrative review of pharmacokinetics, pharmacodynamics, and pharmacogenetics

PURPOSE

Personalized pharmacotherapy, including for the pediatric population, provides optimal treatment and has emerged as a major trend owing to advanced drug therapeutics and diversified drug selection. However, it is essential to understand the growth and developmental characteristics of this population to provide appropriate drug therapy. In recent years, clinical pharmacogenetics has accumulated knowledge in pediatric pharmacotherapy, and guidelines from professional organizations, such as the Clinical Pharmacogenetics Implementation Consortium, can be consulted to determine the efficacy of specific drugs and the risk of adverse effects. However, the existence of a large knowledge gap hinders the use of these findings in clinical practice.

METHODS

We provide a narrative review of the knowledge gaps in pharmacokinetics (PK) and pharmacodynamics (PD) in the pediatric population, focusing on the differences from the perspective of growth and developmental characteristics. In addition, we explored PK/PD in relation to pediatric clinical pharmacogenetics.

RESULTS

The lack of direct and indirect biomarkers for more accurate assessment of the effects of drug administration limits the current knowledge of PD. In addition, incorporating pharmacogenetic insights as pivotal covariates is indispensable in this comprehensive synthesis for precision therapy; therefore, we have provided recommendations regarding the current status and challenges of personalized pediatric pharmacotherapy. The integration of clinical pharmacogenetics with the health care system and institution of educational programs for health care providers is necessary for its safe and effective implementation. A comprehensive understanding of the physiological and genetic complexities of the pediatric population will facilitate the development of effective and personalized pharmacotherapeutic strategies.

Unraveling the versatility of human serum albumin - A comprehensive review of its biological significance and therapeutic potential

Human serum albumin (HSA) is a multi-domain macromolecule with diverse ligand binding capability because of its ability to allow allosteric modulation despite being a monomeric protein. Physiologically, HSA act as the primary carrier for various exogenous and endogenous compounds and fatty acids, and alter the pharmacokinetic properties of several drugs. It has antioxidant properties and is utilized therapeutically to improve the drug delivery of pharmacological agents for the treatment of several disorders. The flexibility of albumin in holding various types of drugs coupled with a variety of modifications makes this protein a versatile drug carrier with incalculable potential in therapeutics. This review provides a brief outline of the different structural properties of HSA, and its various binding sites, moreover, an overview of the genetic, biomedical, and allosteric modulation of drugs and drug delivery aspects of HSA is also included, which may be helpful in guiding advanced clinical applications and further research on the therapeutic potential of this extraordinary protein.

An efficient new method of ytterbium(III) triflate catalysis approach to the synthesis of substituted pyrroles: DFT, ADMET, and molecular docking investigations

In this study, the one-pot synthetic methodology for the preparation of substituted pyrroles with diethyl acetylene-dicarboxylate is reported for the various pyrrole derivatives via the Trifimow synthesis process from oximes. This method also offers the literature as a cyclization pathway using a ytterbium triflate catalyst. Another importance of this study is the use of pyrrole derivatives in pharmaceuticals, biological processes, and agrochemicals. From this point of view, the development of a new catalyst in synthetic organic chemistry and the difference in the method is also important. The syntheses of the target substituted pyrroles are accomplished in high yields. Also, all synthesized structures were confirmed by 1H NMR, 13C NMR, and IR spectra. The DFT computations were leveraged for structural and spectroscopic validation of the compounds. Then, FMO and NBO analyses were subsequently employed to elucidate the reactivity characteristics and intramolecular interactions within these compounds. Also, ADMET indices were ascertained to assess potential pharmacokinetic properties, drug-like qualities, and possible adverse effects of these compounds. Last, optimized molecules were analyzed by molecular docking methods against crystal structures of Bovine Serum Albumin and Leukemia Inhibitory Factor, and their binding affinities, interaction details, and inhibition constants were determined.

Characterization of binding by sulfonylureas with normal or modified human serum albumin using affinity microcolumns prepared by entrapment

Modification of proteins can occur during diabetes due to the formation of advanced glycation end-products (AGEs) with reactive dicarbonyls such as glyoxal (Go) and methylglyoxal (MGo). Human serum albumin (HSA) is a serum protein that binds to many drugs in blood and that is known to be modified by Go and MGo. This study examined the binding of various sulfonylurea drugs with these modified forms of HSA by using high-performance affinity microcolumns prepared by non-covalent protein entrapment. Zonal elution experiments were employed to compare the retention and overall binding constants for the drugs with Go- or MGo-modified HSA vs normal HSA. The results were compared to values from the literature, such as measured or estimated using affinity columns containing covalently immobilized HSA or biospecifically-adsorbed HSA. The entrapment-based approach provided estimates of global affinity constants within 3-5 min for most of the tested drugs and with typical precisions of ±10-23%. Each entrapped protein microcolumn was stable for over at least 60-70 injections and one month of use. The results obtained with normal HSA agreed at the 95% confidence level with global affinity constants that have been reported for the given drugs in the literature. It was found for HSA that had been modified with clinically-relevant levels of either Go or MGo that an increase in the global affinity constant of up to 2.1-fold occurred for some of the tested drugs. The information acquired in this study can be used in the future to adapt this entrapment-based approach to study and evaluate interactions between other types of drugs and normal or modified binding agents for clinical testing and biomedical research.

Development of Oxadiazole-Sulfonamide-Based Compounds as Potential Antibacterial Agents

In this work, substituted 1,2,4-oxadiazoles (OX1-OX27) were screened against five bacterial strains, identified to be OX7 and OX11 as growth inhibitors with minimum inhibitory concentration (MIC) values of 31.25 and 15.75 μg/mL, respectively. The growth inhibitory property of OX7 and OX11 was further validated by disk diffusion, growth curve, and time kill curve assays. Both disrupted biofilm formation with 92-100% reduction examined by the XTT assay were further visualized by scanning electron microscopy analysis. These compounds in combination with ciprofloxacin also exhibit synergy against Escherichia coli cells. With insignificant cytotoxic behavior on HEK293 cells, human red blood cells, and Galleria mellonella larvae, OX11 was tested against 28 multidrug resistant environmental isolates of bacteria and showed inhibition of Kluyvera georgiana and Citrobacter werkmanii strains with 32 and 16 μg/mL MIC values, respectively. The synergistic behavior of OX11 with ampicillin showed many fold reductions in MIC values against K. georgiana and Klebsiella pneumoniae multidrug resistant strains. Further, transmission electron microscopy analysis of OX11-treated E. coli cells showed a significantly damaged cell wall, which resulted in the loss of integrity and cytosolic oozing. OX11 showed significant changes in the secondary structure of human serum albumin (HSA) in the presence of OX11, enhancing HSA stability. Overall, the study provided a suitable core for further synthetic alterations and development as an antibacterial agent.

Comparison between lab variability and in silico prediction errors for the unbound fraction of drugs in human plasma

Variability of the unbound fraction in plasma (f_u) between labs, methods and conditions is known to exist. Variability and uncertainty of this parameter influence predictions of the overall pharmacokinetics of drug candidates and might jeopardise safety in early clinical trials. Objectives of this study were to evaluate the variability of human in vitro f_u-estimates between labs for a range of different drugs, and to develop and validate an in silico f_u-prediction method and compare the results to the lab variability.A new in silico method with prediction accuracy (Q²) of 0.69 for log f_u was developed. The median and maximum prediction errors were 1.9- and 92-fold, respectively. Corresponding estimates for lab variability (ratio between max and min f_u for each compound) were 2.0- and 185-fold, respectively. Greater than 10-fold lab variability was found for 14 of 117 selected compounds.Comparisons demonstrate that in silico predictions were about as reliable as lab estimates when these have been generated during different conditions. Results propose that the new validated in silico prediction method is valuable not only for predictions at the drug design stage, but also for reducing uncertainties of f_u-estimations and improving safety of drug candidates entering the clinical phase.

Seeking Nonspecific Binding: Assessing the Reliability of Tissue Dilutions for Calculating Fraction Unbound

It has become commonplace (270+ article citations to date) to measure the fraction unbound (FrUn) of drugs in tissue homogenates and diluted plasma and then use a Correction Factor Equation (CFE) to extrapolate to the undiluted state. The CFE is based on assumptions of nonspecific binding with experimental use of very low drug concentrations. There are several possible determinants of apparent nonspecific binding as measured by methods such as equilibrium dialysis: true macromolecule binding and lipid partitioning along with receptor, enzyme, and transporter interactions. Theoretical calculations based on nonlinear protein binding indicate that the CFE will be most reliable to obtain FrUn when added drug concentration is small, binding constants are weak, protein concentrations are relatively high, and tissue dilution is minimal. When lipid partitioning is the sole factor determining apparent tissue binding, the CFE should be perfectly accurate. Use of very low drug concentrations, however, makes it more likely that specific binding to receptors and other targets may occur, and thus FrUn may reflect some binding to such components. Inclusion of trapped blood can clearly cause minor to marked discrepancies from purely tissue binding alone, which can be corrected. Furthermore, assessment of the occurrence of ionization/pH shifts, drug instability, and tissue metabolism may be necessary. Caution is needed in the use and interpretation of results from tissue dilution studies and other assessments of nonspecific binding, particularly for very strongly bound drugs with very small FrUn values and in tissues with metabolic enzymes, receptors, and trapped blood. SIGNIFICANCE STATEMENT: The use of tissue, plasma, and cell preparations to help obtain fraction unbound and tissue-to-plasma partition coefficients in pharmacokinetics has grown commonplace, especially for brain. This report examines theoretical, physiological, and experimental issues that need consideration before trusting such measurements and calculations.

Binding of levobupivacaine-loaded gold nanoparticles to human serum albumin: a simulated physiological study

Techniques such as Fourier transform infrared (FTIR), ultraviolet-visible (UV-vis) spectra, fluorescence, circular dichroism (CD) and spectroscopy were applied to elucidate the formation, structure and physicochemical properties of levobupivacaine-gold nanoparticle (LGN) binding to human serum albumin (HSA). Thermodynamic parameters (ΔG = -2.58 × 10⁴ J·mol^-1 , ΔS = -7.80 J·mol^-1 ·K^-1 , and ΔS = -2.82 × 10⁴ J·mol^-1 at 305 K) suggested one weak binding site on HSA, which was governed by van der Waals forces as well as hydrogen bonds. Moreover, the outcomes of UV-vis, CD, FTIR, synchronous and three-dimensional fluorescence suggested that the microenvironment of HSA had been changed with addition of LGN. Based on the results of fluorescence resonance energy transfer, a distance of 2.8 nm between the LGN and HSA was observed. This approach has potential value for illustrating the pharmacodynamics of LGN when in combination with transmembrane transport, biomolecular function effect, and other experiments.

Albumin-Based Transport of Nonsteroidal Anti-Inflammatory Drugs in Mammalian Blood Plasma

Every day, hundreds of millions of people worldwide take nonsteroidal anti-inflammatory drugs (NSAIDs), often in conjunction with multiple other medications. In the bloodstream, NSAIDs are mostly bound to serum albumin (SA). We report the crystal structures of equine serum albumin complexed with four NSAIDs (ibuprofen, ketoprofen, etodolac, and nabumetone) and the active metabolite of nabumetone (6-methoxy-2-naphthylacetic acid, 6-MNA). These compounds bind to seven drug-binding sites on SA. These sites are generally well-conserved between equine and human SAs, but ibuprofen binds to both SAs in two drug-binding sites, only one of which is common. We also compare the binding of ketoprofen by equine SA to binding of it by bovine and leporine SAs. Our comparative analysis of known SA complexes with FDA-approved drugs clearly shows that multiple medications compete for the same binding sites, indicating possibilities for undesirable physiological effects caused by drug-drug displacement or competition with common metabolites. We discuss the consequences of NSAID binding to SA in a broader scientific and medical context, particularly regarding achieving desired therapeutic effects based on an individual's drug regimen.

Crosstalk between zinc and free fatty acids in plasma

In mammalian blood plasma, serum albumin acts as a transport protein for free fatty acids, other lipids and hydrophobic molecules including neurodegenerative peptides, and essential metal ions such as zinc to allow their systemic distribution. Importantly, binding of these chemically extremely diverse entities is not independent, but linked allosterically. One particularly intriguing allosteric link exists between free fatty acid and zinc binding. Albumin thus mediates crosstalk between energy status/metabolism and organismal zinc handling. In recognition of the fact that even small changes in extracellular zinc concentration and speciation modulate the function of many cell types, the albumin-mediated impact of free fatty acid concentration on zinc distribution may be significant for both normal physiological processes including energy metabolism, insulin activity, heparin neutralisation, blood coagulation, and zinc signalling, and a range of disease states, including metabolic syndrome, cardiovascular disease, myocardial ischemia, diabetes, and thrombosis.

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Serum albumin binds and transports both free fatty acids and Zn²⁺ ions

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Elevated plasma free fatty acids impair Zn²⁺ binding by albumin through an allosteric mechanism

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The resulting changes in plasma zinc speciation are thought to impact blood coagulation and may promote thrombosis

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Increased free Zn²⁺ may lead to enhanced zinc export from plasma and dysregulation of zinc homeostasis in multiple tissues

Identification of Human UMP/CMP Kinase 1 as Doxorubicin Binding Target Using Protein Microarray

Doxorubicin (DOX) is a leading anthracycline drug with exceptional efficacy; however, little is known about the molecular mechanisms of its side effects, which include heart muscle damage, noncancerous cell death, and drug resistance. A total of 17,950 human proteins expressed in HEK293 cells were screened and yielded 14 hits. Competitive and binding experiments further verified the binding of DOX to UMP/CMP kinase 1 (CMPK1), and microscale thermophoresis showed that DOX binds to CMPK1 with a Kd of 1216 nM. In addition, we observed that the binding of DOX to CMPK1 activated the phosphorylation of CMP, dCMP, and UMP. A significant activation was observed at the concentration of 30 µM DOX and reached plateau at the concentration of DOX 30 µM, 150 µM, and 100 µM, respectively. DOX would add up stimulation of CMPK1 by DTT and overcome inhibition of CMPK1 by NaF, EDTA. In summary, we showed that DOX might bind to the nonactive site of CMPK1 and regulate its activity with magnesium.

Advancing In Vitro-In Vivo Extrapolations of Mechanism-Specific Toxicity Data Through Toxicokinetic Modeling

International legislation, such as the European REACH regulation (registration, evaluation, authorization, and restriction of chemicals), mandates the assessment of potential risks of an ever-growing number of chemicals to the environment and human health. Although this legislation is considered one of the most important investments in consumer safety ever, the downside is that the current testing strategies within REACH rely on extensive animal testing. To address the ethical conflicts arising from these increased testing requirements, decision-makers, such as the European Chemicals Agency (ECHA), are committed to Russel and Burch's 3R principle (i.e., reduction, replacement, refinement) by demanding that animal experiments should be substituted with appropriate alternatives whenever possible. A potential solution of this dilemma might be the application of in vitro bioassays to estimate toxic effects using cells or cellular components instead of whole organisms. Although such assays are particularly useful to assess potential mechanisms of toxic action, scientists require appropriate methods to extrapolate results from the in vitro level to the situation in vivo. Toxicokinetic models are a straightforward means of bridging this gap. The present chapter describes different available options for in vitro-in vivo extrapolation (IVIVE) of mechanism-specific effects focused on fish species and also reviews the implications of confounding factors during the conduction of in vitro bioassays and their influence on the optimal choice of different dose metrics.

Entrapment of alpha1-acid glycoprotein in high-performance affinity columns for drug-protein binding studies

A slurry-based method was developed for the entrapment of alpha1-acid glycoprotein (AGP) for use in high-performance affinity chromatography to study drug interactions with this serum protein. Entrapment was achieved based on the physical containment of AGP in hydrazide-activated porous silica supports and by using mildly oxidized glycogen as a capping agent. The conditions needed for this process were examined and optimized. When this type of AGP column was used in binding studies, the association equilibrium constant (Ka) measured by frontal analysis at pH 7.4 and 37°C for carbamazepine with AGP was found to be 1.0 (±0.5)×10(5)M(-1), which agreed with a previously reported value of 1.0 (±0.1)×10(5)M(-1). Binding studies based on zonal elution were conducted for several other drugs with such columns, giving equilibrium constants that were consistent with literature values. An entrapped AGP column was also used in combination with a column containing entrapped HSA in a screening assay format to compare the binding of various drugs to AGP and HSA. These results also agreed with previous data that have been reported in literature for both of these proteins. The same entrapment method could be extended to other proteins and to the investigation of additional types of drug-protein interactions. Potential applications include the rapid quantitative analysis of biological interactions and the high-throughput screening of drug candidates for their binding to a given protein.

Adsorption of histones on natural polysaccharides: The potential as agent for multiple organ failure in sepsis

Histones are intracellular proteins that are structural elements of nuclear chromatin and regulate gene transcription. However, the extracellular histones released in response to bacterial challenges have been identified as mediators contributing to endothelial dysfunction, organ failure, and death during sepsis. In the present study, the adsorption of histones as well as plasma proteins (α1-acid glycoprotein (AGP), albumin, and γ-globulin) on alginic acid, pectin, dextran, and chitosan was examined in order to evaluate the potential of natural polysaccharides as therapeutic agents for multiple organ failure in sepsis. Alginic acid and pectin strongly adsorbed histones, whereas the adsorption abilities of dextran and chitosan toward histones were very low or negligible. Among the natural polysaccharides examined, only alginic acid did not adsorb any of the plasma proteins. These results demonstrated that alginic acid strongly adsorbed histones, but not plasma proteins; therefore, it has potential as a candidate drug for the treatment of multiple organ failure in sepsis.

Determination of unbound fraction of pazopanib in vitro and in cancer patients reveals albumin as the main binding site

INTRODUCTION

Pazopanib exhibits wide inter-patient pharmacokinetic variability which may contribute to differences in treatment outcome. Unbound drug concentrations are believed to be more relevant to pharmacological responses than total concentrations. Thus it is desirable to evaluate pazopanib binding on plasma proteins and different factors potentially affecting this process.

METHODS

An equilibrium dialysis method coupled with UPLC-MS/MS assay has been optimized and validated for the determination of pazopanib unbound fraction (fu%) in human plasma. Pazopanib binding in the plasma of healthy volunteers and in isolated protein solutions was investigated. The unbound fraction was determined for 24 cancer patients treated daily with pazopanib.

RESULTS

We found that pazopanib was extensively bound in human plasma (>99.9 %) with a mean fu% value of 0.0106 ± 0.0013 % at 40 μg/mL. Protein binding was concentration independent over a clinically relevant range of concentrations. In isolated protein solutions, pazopanib at 40 μg/mL was mainly bound to albumin (40 g/L) and to a lesser extent to α1-acid glycoprotein (1 g/L) and low density lipoproteins (1.2 g/L), with a mean fu% of 0.0073 ± 0.0022 %, 0.992 ± 0.44 % and 7.4 ± 1.7 % respectively. Inter-patient variability (CV%) of fu% in cancer patients was limited (27.2 %). A correlation was observed between individual unbound fraction values and albuminemia.

CONCLUSIONS

Pazopanib exhibits extensive binding to plasma proteins in human plasma. Variable albumin concentrations, frequently observed in cancer patients, may affect pazopanib unbound fraction with implications for inter-patient variability in drug efficacy and toxicity.

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 free drug fractions in human serum by ultrafast affinity extraction and two-dimensional affinity chromatography

Ultrafast affinity extraction and a two-dimensional high performance affinity chromatographic system were used to measure the free fractions for various drugs in serum and at typical therapeutic concentrations. Pooled samples of normal serum or serum from diabetic patients were utilized in this work. Several drug models (i.e., quinidine, diazepam, gliclazide, tolbutamide, and acetohexamide) were examined that represented a relatively wide range of therapeutic concentrations and affinities for human serum albumin (HSA). The two-dimensional system consisted of an HSA microcolumn for the extraction of a free drug fraction, followed by a larger HSA analytical column for the further separation and measurement of this fraction. Factors that were optimized in this method included the flow rates, column sizes, and column switching times that were employed. The final extraction times used for isolating the free drug fractions were 333-665 ms or less. The dissociation rate constants for several of the drugs with soluble HSA were measured during system optimization, giving results that agreed with reference values. In the final system, free drug fractions in the range of 0.7-9.5% were measured and gave good agreement with values that were determined by ultrafiltration. Association equilibrium constants or global affinities were also estimated by this approach for the drugs with soluble HSA. The results for the two-dimensional system were obtained in 5-10 min or less and required only 1-5 μL of serum per injection. The same approach could be adapted for work with other drugs and proteins in clinical samples or for biomedical research.

A Genetic Algorithm Based Support Vector Machine Model for Blood-Brain Barrier Penetration Prediction

Blood-brain barrier (BBB) is a highly complex physical barrier determining what substances are allowed to enter the brain. Support vector machine (SVM) is a kernel-based machine learning method that is widely used in QSAR study. For a successful SVM model, the kernel parameters for SVM and feature subset selection are the most important factors affecting prediction accuracy. In most studies, they are treated as two independent problems, but it has been proven that they could affect each other. We designed and implemented genetic algorithm (GA) to optimize kernel parameters and feature subset selection for SVM regression and applied it to the BBB penetration prediction. The results show that our GA/SVM model is more accurate than other currently available log BB models. Therefore, to optimize both SVM parameters and feature subset simultaneously with genetic algorithm is a better approach than other methods that treat the two problems separately. Analysis of our log BB model suggests that carboxylic acid group, polar surface area (PSA)/hydrogen-bonding ability, lipophilicity, and molecular charge play important role in BBB penetration. Among those properties relevant to BBB penetration, lipophilicity could enhance the BBB penetration while all the others are negatively correlated with BBB penetration.

Quantum molecular modelling of ibuprofen bound to human serum albumin

The total interaction energies of the ibuprofen complexed with FA3/FA4 and FA6 binding sites of human serum albumin are in agreement with the hypothesis that the Sudlow's site II is the main binding pocket for ibuprofen.

Analysis of biomolecular interactions using affinity microcolumns: a review

Affinity chromatography has become an important tool for characterizing biomolecular interactions. The use of affinity microcolumns, which contain immobilized binding agents and have volumes in the mid-to-low microliter range, has received particular attention in recent years. Potential advantages of affinity microcolumns include the many analysis and detection formats that can be used with these columns, as well as the need for only small amounts of supports and immobilized binding agents. This review examines how affinity microcolumns have been used to examine biomolecular interactions. Both capillary-based microcolumns and short microcolumns are considered. The use of affinity microcolumns with zonal elution and frontal analysis methods are discussed. The techniques of peak decay analysis, ultrafast affinity extraction, split-peak analysis, and band-broadening studies are also explored. The principles of these methods are examined and various applications are provided to illustrate the use of these methods with affinity microcolumns. It is shown how these techniques can be utilized to provide information on the binding strength and kinetics of an interaction, as well as on the number and types of binding sites. It is further demonstrated how information on competition or displacement effects can be obtained by these methods.

Analysis of free fractions for chiral drugs using ultrafast extraction and multi-dimensional high-performance affinity chromatography

A multi-dimensional chromatographic approach was developed to measure the free fractions of drug enantiomers in samples that also contained a binding protein or serum. This method, which combined ultrafast affinity extraction with a chiral stationary phase, was demonstrated using the drug warfarin and the protein human serum albumin.

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. Sulfonylureas 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.

Dose metric considerations in in vitro assays to improve quantitative in vitro-in vivo dose extrapolations

Challenges to improve toxicological risk assessment to meet the demands of the EU chemical's legislation, REACH, and the EU 7th Amendment of the Cosmetics Directive have accelerated the development of non-animal based methods. Unfortunately, uncertainties remain surrounding the power of alternative methods such as in vitro assays to predict in vivo dose-response relationships, which impedes their use in regulatory toxicology. One issue reviewed here, is the lack of a well-defined dose metric for use in concentration-effect relationships obtained from in vitro cell assays. Traditionally, the nominal concentration has been used to define in vitro concentration-effect relationships. However, chemicals may differentially and non-specifically bind to medium constituents, well plate plastic and cells. They may also evaporate, degrade or be metabolized over the exposure period at different rates. Studies have shown that these processes may reduce the bioavailable and biologically effective dose of test chemicals in in vitro assays to levels far below their nominal concentration. This subsequently hampers the interpretation of in vitro data to predict and compare the true toxic potency of test chemicals. Therefore, this review discusses a number of dose metrics and their dependency on in vitro assay setup. Recommendations are given on when to consider alternative dose metrics instead of nominal concentrations, in order to reduce effect concentration variability between in vitro assays and between in vitro and in vivo assays in toxicology.

Development of affinity microcolumns for drug-protein binding studies in personalized medicine: interactions of sulfonylurea drugs with in vivo glycated human serum albumin

This report used high-performance affinity microcolumns to examine the changes in binding by sulfonylurea drugs to in vivo glycated HSA that had been isolated from individual patients with diabetes. An immunoextraction approach was developed to isolate HSA and glycated HSA from clinical samples, using only 20 μL of plasma or serum and 6-12 nmol of protein to prepare each affinity microcolumn. It was found that the affinity microcolumns could be used in either frontal analysis or zonal elution studies, which typically required only 4-8 min per run. The microcolumns had good stability and allowed data to be obtained for multiple drugs and experimental conditions over hundreds of sample application cycles. Both the overall binding, as measured by frontal analysis, and site-specific interactions, as examined by zonal elution, showed good agreement with previous data that had been obtained for in vitro glycated HSA with similar levels of modification. It was also possible to directly compare the changes in site-specific binding that occurred between sulfonylurea drugs or as the level of HSA glycation was varied. This method is not limited to clinical samples of glycated HSA but could be adapted for work with other modified proteins of interest in personalized medicine.

Molecular interaction of PCB153 to human serum albumin: insights from spectroscopic and molecular modeling studies

Polychlorinated biphenyls (PCBs) possessed much potential hazard to environment because of its chemical stability and biological toxicity. Here, we identified the binding mode of a representative compound, PCB153, to human serum albumin (HSA) using fluorescence and molecular dynamics simulation methods. The fluorescence study showed that the intrinsic fluorescence of HSA was quenched by addition of PCB153 through a static quenching mechanism. The thermodynamic analysis proved the binding behavior was mainly governed by hydrophobic force. Furthermore, as evidenced by site marker displacement experiments using two probe compounds, it revealed that PCB153 acted exactly on subdomain IIIA (site II) of HSA. On the other hand, the molecular dynamics studies as well as free energy calculations made another important contribution to understand the conformational changes of HSA and the stability of HSA-PCB153 system. Molecular docking revealed PCB153 can bind in a large hydrophobic activity of subdomain IIIA by the hydrophobic interaction and hydrogen bond interactions between chlorine atoms and residue ASN391. The present work provided reasonable models helping us further understand the transporting, distribution and toxicity effect of PCBs when it spread into human blood serum.

Study of the interaction of deoxynivalenol with human serum albumin by spectroscopic technique and molecular modelling

The mechanism of interaction between deoxynivalenol (DON) and human serum albumin (HSA) was studied using spectroscopic methods including fluorescence spectra, UV-VIS, Fourier transform infrared (FT-IR) and circular dichroism (CD). The quenching mechanism was investigated in terms of the association constants, number of binding sites and basic thermodynamic parameters. The distance between the HSA donor and the acceptor DON was 2.80 nm as derived from fluorescence resonance energy transfer. The secondary structure compositions of free HSA and its DON complexes were estimated by the FT-IR spectra. Alteration of the secondary protein structure in the presence of DON was confirmed by UV-VIS and CD spectroscopy. Molecular modelling revealed that a DON-protein complex was stabilised by hydrophobic forces and hydrogen bonding. It was potentially useful for elucidating the toxigenicity of DON when combined with biomolecular function effect, transmembrane transport, toxicological testing and the other experiments.

Quantifying processes determining the free concentration of phenanthrene in Basal cytotoxicity assays

Difficulties may arise when extrapolating in vitro derived toxicity data to in vivo toxicity data because of the high variability and occasional low sensitivity of in vitro results. Differences in the free concentration of a test compound between in vitro and in vivo systems and between different in vitro systems may in part explain this variability and sensitivity difference. The aim of this study was to determine what assay components influence the free concentration of phenanthrene in a Balb/c 3T3 and RTgill-W1 MTT assay. Partition coefficients of phenanthrene to serum, well plate plastic, cells, and headspace were measured and subsequently used to model the free concentration of the compound in vitro. The estimated free concentration was compared to the free concentration measured in the assays using solid phase microextraction (SPME). Results indicate that the free concentration of phenanthrene, a relatively volatile and hydrophobic compound, is significantly reduced in a typical in vitro setup as it binds to matrices such as serum protein and well plate plastic. A reduction in free concentration due to increasing serum protein levels is accompanied by an increase in the median effect concentration (EC(50)) and can be modeled, with the exception of evaporation, using the partition coefficients of the compound to assay components.

Interaction between phillygenin and human serum albumin based on spectroscopic and molecular docking

In this paper, the interaction of human serum albumin (HSA) with phillygenin was investigated by fluorescence, circular dichroism (CD), UV-vis spectroscopic and molecular docking methods under physiological conditions. The Stern-Volmer analysis indicated that the fluorescence quenching of HSA by phillygenin resulted from static mechanism, and the binding constants were 1.71×10(5), 1.61×10(5) and 1.47×10(4) at 300, 305 and 310K, respectively. The results of UV-vis spectra show that the secondary structure of the protein has been changed in the presence of phillygenin. The CD spectra showed that HSA conformation was altered by phillygenin with a major reduction of α-helix and an increase in β-sheet and random coil structures, indicating a partial protein unfolding. The distance between donor (HSA) and acceptor (phillygenin) was calculated to be 3.52nm and the results of synchronous fluorescence spectra showed that binding of phillygenin to HSA can induce conformational changes in HSA. Molecular docking experiments found that phillygenin binds with HSA at IIIA domain of hydrophobic pocket with hydrogen bond interactions. The ionic bonds were formed with the O (4), O (5) and O (6) of phillygenin with nitrogen of ASN109, ARG186 and LEU115, respectively. The hydrogen bonds are formed between O (2) of phillygenin and SER419. In the presence of copper (II), iron (III) and alcohol, the apparent association constant K(A) and the number of binding sites of phillygenin on HSA were both decreased in the range of 88.84-91.97% and 16.09-18.85%, respectively. In view of the evidence presented, it is expected to enrich our knowledge of the interaction dynamics of phillygenin to the important plasma protein HSA, and it is also expected to provide important information of designs of new inspired drugs.