Binding of suprofen to human serum albumin. Role of the suprofen carboxyl group

Spectroscopic studies on the interaction of aspartame with human serum albumin

In this work the binding of artificial sweetener aspartame with human serum albumin (HSA) was studied at physiological pH. Binding studies of aspartame (APM) with HSA are useful to understand APM -HSA interaction, mechanism and providing guidance for the application and design of new and more efficient artificial sweeteners. The interaction was investigated by spectrophotometric, spectrofluorometric competition experiment and circular dichroism (CD) techniques. The results indicated that the binding of APM to HSA caused fluorescence quenching of HSA through static quenching mechanism with binding constant 1.42 × 10⁺⁴ M^-1 at 298 K and the number of binding sites is approximately one. Thermodynamic parameters, enthalpy changes (ΔH) and entropy changes (ΔS) were calculated to be -41.20 kJ mol^-1 and -58.19 J mol^-1 K^-1, respectively, according to van't Hoff equation, which indicated that reaction is enthalpically driven. Quenching of the fluorescence of HSA was found to be a static quenching process. The binding constants and number of binding sites were obtained at three different temperatures (298, 308 and 318 K). Combining above results and those of spectrofluorometric competition experiment and circular dichroism (CD), indicated that APM binds to HSA via Sudlow's site I. Furthermore, the study of molecular docking on HSA binding also indicated that APM can strongly bind to the site I (subdomain IIA) of HSA mainly by hydrophobic interaction and hydrogen bond interactions exist between APM and HSA.

Structural investigations of stereoselective profen binding by equine and leporine serum albumins

Serum albumin, the most abundant transport protein of mammalian blood, interacts with various nonsteroidal anti-inflammatory drugs (NSAIDs) affecting their disposition, metabolism, and excretion. A big group of chiral NSAIDs transported by albumin, profens, is created by derivatives of 2-arylpropionic acid. The chiral center in the structures of profens is adjacent to the carboxylate moiety and often determines different pharmacological properties of profen enantiomers. This study describes crystal structures of two albumins, isolated from equine and leporine serum, in complexes with three profens: ibuprofen, ketoprofen, and suprofen. Based on three-dimensional structures, the stereoselectivity of albumin is discussed and referred to the previously published albumin complexes with drugs. Drug Site 2 (DS2) of albumin, the bulky hydrophobic pocket of subdomain IIIA with a patch of polar residues, preferentially binds (S)-enantiomers of all investigated profens. Almost identical binding mode of all these drugs clearly indicates the stereoselectivity of DS2 towards (S)-profens in different albumin species. Also, the affinity studies show that DS2 is the major site that presents high affinity towards investigated drugs. Additionally, crystallographic data reveal the secondary binding sites of ketoprofen in leporine serum albumin and ibuprofen in equine serum albumin, both overlapping with previously identified naproxen binding sites: the cleft formed between subdomains IIIA and IIIB close to the fatty acid binding site 5 and the niche created between subdomains IIA and IIIA, called fatty acid site 6.

Supramolecular photochemistry of drugs in biomolecular environments

We illustrate how the interaction of drugs with proteins or DNA in supramolecular complexes can influence the reactions initiated by drug absorbed photons, evidencing the differences with respect to solution.

Controlled release of analgesic drugs from porous bioresorbable structures for various biomedical applications

Pain is one of the most common patient complaints encountered by health professionals and remains the number one cause of absenteeism and disability. In the current study, analgesic-eluting bioresorbable porous structures prepared using the freeze-drying of inverted emulsions technique were developed and studied. These drug-eluting structures can be used for coating fibers or implants, or for creating standalone films. They are ideal for forming biomedically important structures that can be used for various applications, such as wound dressings that provide controlled release of analgesics to the wound site in addition to their wound dressing role. Our investigation focused on the effects of the inverted emulsion's parameters on the shell microstructure and on the resulting drug-release profile of ibuprofen and bupivacaine. The release profiles of ibuprofen formulations exhibited a diffusion-controlled pattern, ranging from several days to 21 days, whereas bupivacaine formulations exhibited an initial burst release followed by a three-phase release pattern over a period of several weeks. Higher organic to aqueous phase ratios and higher polymer contents reduced the burst release of both drugs and prolonged their release due to lower porosity. Overall, the drug-eluting porous structures loaded with either ibuprofen or bupivacaine demonstrated a promising potential for use in various applications that require pain relief.

Study on the interaction of the epilepsy drug, zonisamide with human serum albumin (HSA) by spectroscopic and molecular docking techniques

In the present investigation, an attempt has been made to study the interaction of zonisamide (ZNS) with the transport protein, human serum albumin (HSA) employing UV-Vis, fluorometric, circular dichroism (CD) and molecular docking techniques. The results indicated that binding of ZNS to HSA caused strong fluorescence quenching of HSA through static quenching mechanism, hydrogen bonds and van der Waals contacts are the major forces in the stability of protein ZNS complex and the process of the binding of ZNS with HSA was driven by enthalpy (ΔH=-193.442 kJ mol(-1)). The results of CD and UV-Vis spectroscopy showed that the binding of this drug to HSA induced conformational changes in HSA. Furthermore, the study of molecular docking also indicated that zonisamide could strongly bind to the site I (subdomain IIA) of HSA mainly by hydrophobic interaction and there were hydrogen bond interactions between this drug and HSA, also known as the warfarin binding site.

In Silico Prediction of Interactions between Site II on Human Serum Albumin and Profen Drugs

Since binding of a drug molecule to human serum albumin (HSA) significantly affects the pharmacokinetics of the drug, it is highly desirable to predict the binding affinity of the drug. Profen drugs are a widely used class of nonsteroidal anti-inflammatory drugs and it has been reported that several members of the profen class specifically bind to one of the main binding sites named site II. The actual binding mode of only ibuprofen has been directly confirmed by X-ray crystallography. Therefore, it is of interest whether other profen drugs are site II binders. Docking simulations using multiple template structures of HSA from three crystal structures of complexes between drugs and HSA have demonstrated that most of the currently available profen drugs should be site II binders.

Interaction and photo-induced cleavage studies of a copper based chemotherapeutic drug with human serum albumin: spectroscopic and molecular docking study

The interaction of new dinuclear copper(ii) complex 1; [Cu(2)(glygly)(2)(ppz)(H(2)O)(4)]·2H(2)O, derived from dipeptide (glycyl glycine) and piperazine as a metallopeptide drug with human serum albumin (HSA) was examined by means of fluorescence spectroscopy which revealed that complex 1 has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The alterations of HSA secondary structure in the presence of complex 1 were confirmed by UV-visible, FT-IR, CD and 3D fluorescence spectroscopy. The binding constants (K), and binding site number (n), corresponding thermodynamic parameters ΔG, ΔH and ΔS at different temperatures were calculated. The molecular docking technique was utilized to ascertain the mechanism and mode of action towards the molecular target HSA indicating that complex 1 was located at the entrance of site I by electrostatic and hydrophobic forces, consistent with the corresponding experimental results. Complex 1 shows efficient photo-induced HSA cleavage activity, indicating the involvement of hydroxyl radicals as the reactive species. Furthermore, the cytotoxicity of 1 was examined on a panel of human tumor cell lines of different histological origins showing significant GI(50) values specifically towards MIAPACA2, A498 and A549 tumor cell lines. These results complement previous biological studies of new specific target metallopeptides, providing additional information about possibilities of their transport and disposition in blood plasma.

Histidine146 of human serum albumin plays a prominent role at the interface of subdomains IA and IIA in allosteric ligand binding

Fatty acids are endogenous ligands of human serum albumin (HSA) that induce conformational changes and participate in allosteric ligand binding to HSA. In a previous study, we showed that, when myristate (MYR) is present, the binding of [(14) C]ketoprofen (KP) to subdomain IA of HSA was increased, indicating that, when MYR binds to HSA, a new binding site in formed in that region. Meanwhile, an N-B transition has been reported to increase the binding of ligands at alkaline pH when the status of albumin is the B-conformer. Six histidine single mutants of HSA, H9A, H39A, H67A, H105A, H128A and H146A were produced and photolabeled with [(14) C]KP at pH 6.5, 7.4 and 8.2 and the role of each histidine in causing the N-B transition induced allosteric ligand binding was examined. Cyanogen bromide cleavage of the photolabeled native HSA showed that subdomain IA was the site of the allosteric binding of KP at pH 8.2. From the photolabeling results, H146 was found to play a prominent role whilst H128 played little or no role in the allosteric binding. However, the remaining 4 mutants did not show a clear photolabeling pattern that was similar to either native HSA or H146A and, as a result, no firm conclusions can be made. An additional histidine mutant, H146I, was produced to confirm the results for H146A. A similar experiment using H146I showed that a benzene ring-like structure at position 146 is required for the allosteric ligand binding to occur.

Characterization of the interaction between 8-bromoadenosine with human serum albumin and its analytical application

This study was designed to examine the interaction of 8-bromoadenosine with human serum albumin (HSA) by fluorescence spectroscopy in combination with molecular modeling under simulative physiological conditions. The results of fluorescence measurements indicate that 8-bromoadenosine has a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. The binding constants (K) at different temperatures and thermodynamic parameters, enthalpy changes (DeltaH) and entropy changes (DeltaS) were calculated according to the fluorescence data. The results showed that the hydrophobic force played the major role in the binding of 8-bromoadenosine to HSA. The fluorescence experimental results were in agreement with the results obtained by molecular modeling study. The effects of some normal positive and negative ions on the binding constants were also discussed. Moreover, the synchronous fluorescence technique was used to characterize the interaction of 8-bromoadenosine to HSA and successfully applied to determine the total proteins in human serum, urine and saliva samples at room temperature under the optimum conditions with a wide linear range and satisfactory results.

[Study on binding of drug to serum protein]

After being distributed in the circulating blood, drugs bind to serum proteins varying degrees. In general, such binding is reversible, and a dynamic equilibrium exists between the bound and unbound molecular species. It is believed that unless there is a specific transport system (e.g. receptor-mediated endocytosis, protein-mediated transport), only unbound drugs are able to penetrate through biomembranes, are distributed to tissues, and undergo metabolism and glomerular filtration. It is also believed that only unbound molecules present in target tissues can exert their pharmacological effects, and that the concentration of unbound molecules in tissues is in proportion to the drug serum concentration. Therefore, drug-serum protein binding is critically involved in the manifestation of the pharmacological effects of a drug as well as its pharmacokinetics. Among serum proteins, human serum albumin (HSA) and alpha(1)-acid glycoprotein (AGP) play important roles in protein binding for many drugs, which is of key importance to drug distribution in the body. In addition, they are widely used in clinical settings as blood preparations and drug delivery system carriers. It is thus of great importance from the viewpoint of pharmaceutical science to clarify the structure, function, and pharmaceutical properties of HSA and AGP. Accordingly, since starting my laboratory, the focus of my research has involved molecular pharmaceutical studies on the interactions of drugs and HSA and AGP for the purpose of applying these findings to clinical fields, such as drug treatment, diagnosis and drug discovery. In this review, the molecular properties of HSA and AGP will be briefly outlined. The static and dynamic topology of drug binding sites on these proteins, investigated by various spectroscopic techniques, X-ray crystallography, quantitative structure-activity relationships, molecular modeling, photo affinity labeling, site-directed mutagenesis etc., changes in the serum protein binding of drugs in pathological conditions, such as liver and kidney failure and various inflammation diseases and factors contributing to the changes will then be summarized. Finally, cases in which protein binding displacement can be applied to medical fields will also be introduced.

Studies on the Interaction of Cinnamic Acid with Bovine Serum Albumin

The interaction between cinnamic acid and bovine serum albumin (BSA) have been studied at three temperatures, 296, 303 and 310 K. Fluorescence quenching spectra in combination with Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy was used to investigate the drug-binding mode, the binding constant and the protein structure changes in the presence of cinnamic acid in aqueous solution at pH 7.40. The fluorescence quenching constant K(q), K(sv) and the binding constant K were calculated according to Stern-Volmer equation based on the quenching of the fluorescence of BSA in the presence of cinnamic acid. The thermodynamic parameters, the enthalpy (DeltaH) and the entropy change (DeltaS) were estimated to be -16.457 kJ mol(-1) and 38.028 J mol(-1) K(-1) according to the van't Hoff equation. The displacement experiment shows that cinnamic acid can bind to the subdomain IIA (corresponding to Sudlow's drug binding site I). The distance between the tryptophan residues in BSA and cinnamic acid bound to site I was estimated to be 1.63 nm using Föster's equation on the basis of fluorescence energy transfer. The decreased binding constant in the presence of common ions indicates that common ions have effect on drug-BSA system.

Study of the interaction of artemisinin with bovine serum albumin

The study on the interaction of artemisinin with bovine serum albumin (BSA) has been undertaken at three temperatures, 289, 296 and 303 K and investigated the effect of common ions and UV C (253.7 nm) irradiation on the binding of artemisinin with BSA. The binding mode, the binding constant and the protein structure changes in the presence of artemisinin in aqueous solution at pH 7.40 have been evaluated using fluorescence, UV-vis and Fourier transform infrared (FT-IR) spectroscopy. The quenching constant K(q), K(sv) and the association constant K were calculated according to Stern-Volmer equation based on the quenching of the fluorescence of BSA. The thermodynamic parameters, the enthalpy (DeltaH) and the entropy change (DeltaS) were estimated to be -3.625 kJ mol(-1) and 107.419 J mol(-1)K(-1) using the van't Hoff equation. The displacement experiment shows that artemisinin can bind to the subdomain IIA. The distance between the tryptophan residues in BSA and artemisinin bound to site I was estimated to be 2.22 nm using Föster's equation on the basis of fluorescence energy transfer. The decreased binding constant in the presence of enough common ions and UV C exposure, indicates that common ions and UV C irradiation have effect on artemisinin binding to BSA.

A spectroscopic study of the interaction of isoflavones with human serum albumin

Genistein and daidzein, the major isoflavones present in soybeans, possess a wide spectrum of physiological and pharmacological functions. The binding of genistein to human serum albumin (HSA) has been investigated by equilibrium dialysis, fluorescence measurements, CD and molecular visualization. One mole of genistein is bound per mole of HSA with a binding constant of 1.5 +/- 0.2 x 10(5) m(-1). Binding of genistein to HSA precludes the attachment of daidzein. The ability of HSA to bind genistein is found to be lost when the tryptophan residue of albumin is modified with N-bromosuccinimide. At 27 degrees C (pH 7.4), van't Hoff's enthalpy, entropy and free energy changes that accompany the binding are found to be -13.16 kcal x mol(-1), -21 cal x mol(-1) K(-1) and -6.86 kcal x mol(-1), respectively. Temperature and ionic strength dependence and competitive binding measurements of genistein with HSA in the presence of fatty acids and 8-anilino-1-naphthalene sulfonic acid have suggested the involvement of both hydrophobic and ionic interactions in the genistein-HSA binding. Binding measurements of genistein with BSA and HSA, and those in the presence of warfarin and 2,3,5-tri-iodobenzoic acid and Förster energy transfer measurements have been used for deducing the binding pocket on HSA. Fluorescence anisotropy measurements of daidzein bound and then displaced with warfarin, 2,3,5-tri-iodobenzoic acid or diazepam confirm the binding of daidzein and genistein to subdomain IIA of HSA. The ability of HSA to form ternery complexes with other neutral molecules such as warfarin, which also binds within the subdomain IIA pocket, increases our understanding of the binding dynamics of exogenous drugs to HSA.

Study of the Interaction of Indirubin with Bovine Serum Albumin

This study examined the interaction of indirubin with bovine serum albumin (BSA) at three temperatures (286, 297, 308 K) at pH 7.40. In the presence of indirubin, the drug-BSA binding mode, binding constant and the protein structure changes in aqueous solution were determined by fluorescence quenching methods including Fourier transform infrared (FT-IR) spectroscopy and UV-Vis spectroscopy. The FT-IR change indicates that indirubin binds to BSA. The change in protein secondary structure accompanying ligand binding has been proved by fluorescence spectra data. The thermodynamic parameters, the enthalpy change (DeltaH), and the entropy change (DeltaS) calculated by the van't Hoff equation possess small negative (-2.744 kJ.mol(-1)) and positive values (112.756 J.mol(-1).K(-1)), respectively, which indicated that hydrophobic interactions play the main role in the binding of indirubin to BSA. Furthermore, the displacement experiment shows that indirubin can bind to the subdomain IIA and the distance between the tryptophan residues in BSA and indirubin bound to site I was estimated to be 2.24 nm according to Föster's equation on the basis of fluorescence energy transfer.

Study on the interactions between anti-HIV-1 active compounds with trans-activation response RNA by affinity capillary electrophoresis

The study on the interactions between two anti-human immunodeficiency virus type 1 (anti-HIV-1) active compounds with trans-activation response (TAR) RNA by affinity capillary electrophoresis (ACE) with UV absorbance detection is presented. The results showed that the novel active molecules could interact with TAR RNA and inhibit the reproduce process of HIV-1. The binding constants were estimated by the change of migration time of the analytes through the change of concentrations of TAR RNA in the buffer solution. The yielded binding constants of 8.87 x 10(3)M(-1) for active compound C(3) and 8.42 x 10(3)M(-1) for MC(3) at 20.0 degrees C, 0.626 x 10(3)M(-1) and 0.644 x 10(3)M(-1) at 37.0 degrees C, respectively. The thermodynamic parameters Delta H and DeltaS were obtained and shown that both hydrophobic and electrostatic interaction played roles in the binding processes. The results showed that the presented method was an easy and simple method to evaluate the interaction of small molecules with some bioactive materials.

Interaction of wogonin with bovine serum albumin

The binding of wogonin with bovine serum albumin (BSA) was investigated at different temperatures by fluorescence, circular dichroism (CD) and Fourier transform infrared spectroscopy (FT-IR) at pH7.40. The association constants K were determined by Stern-Volmer equation based on the quenching of the fluorescence of BSA in the presence of wogonin, which were in agreement with the constants calculated by Scatchard plots. The thermodynamic parameters were calculated according to the Van't Hoff equation and the result indicated that DeltaH(0) and DeltaS(0) had a negative value (-12.02 kJ/mol) and a positive value (58.72 J/mol K), respectively. On the basis of the displacement experimental and the thermodynamic results, it is considered that wogonin binds to site I (subdomain IIA) of BSA mainly by hydrophobic interaction. The studied results by FT-IR and CD experiment indicated that the secondary structures of protein have been perturbed by the interaction of wogonin with BSA.

Binding of wogonin to human serum albumin: a common binding site of wogonin in subdomain IIA

The binding of wogonin to human serum albumin (HSA) has been studied by spectroscopic method including circular dichroism (CD), infrared spectra (IR) and fluorescence spectra. The fluorescence properties of HSA were examined in presence of wogonin and the fluorescence intensity of HSA was significantly decreased in the presence of wogonin. The binding parameters of wogonin were studied from the fluorescence decreasing of HSA by the fluoremetric titrations. The Stern-Volmer plots indicated that the binding of wogonin to HSA at 296, 303, 310 K is characterized by one binding site with the binding constant K(S-V) at 1.872 x 10(5), 1.561 x 10(5), 1.392 x 10(5), respectively, which are good agreement with the results from the Scatchard plots. The binding process was exothermic, enthalpy driven and spontaneous, as indicated by the thermodynamic analyses, and the major part of the binding energy is hydrophobic interaction, which were consistent with the result of molecule modelling study, and there are also a numbers of hydrogen bonds between wogonin and HSA. Furthermore, the displacement experiments indicate that wogonin can bind to the subdomain IIA, that is, the site I of HSA, which is also good agreement with the result of molecule modelling study.

Predicting plasma protein binding of drugs: a new approach

In spite of the large amount of plasma protein binding data for drugs, it is not obvious and there is no clear consensus among different disciplines how to deal with this parameter in multidimensional lead optimization strategies. In this work, we have made a comprehensive study on the importance of plasma protein binding and the influencing factors in order to get new insights for this molecular property. Our analysis of the distribution of percentage plasma protein binding among therapeutic drugs showed that no general rules for protein binding can be derived, except for the class of chemotherapeutics, where a clear trend towards lower binding could be observed. For the majority of indication areas, however, empirical rules are missing. We present here an extensive list of multiply determined primary association constants for binding to human serum albumin (HSA) for 138 compounds from the literature. Correlating these binding constants with the percentage fraction of protein bound showed that the percentage data above 90%, corresponding to a binding constant below 6 microM, are of insufficient accuracy. Furthermore, it could be demonstrated that the lipophilicity of drugs, traditionally felt to dominate binding to HSA, is not the only relevant descriptor. Here, we report a generic model for the prediction of drug association constants to HSA, which uses a pharmacophoric similarity concept and partial least square analysis (PLS) to construct a quantitative structure-activity relationship. It is able to single out the submicromolar to nanomolar binders, i.e. to differentiate between 99.0 and 99.99% plasma protein binding. Depending on the system, this can be important in medicinal chemistry programs and may together with other computed physicochemical and ADME properties assist in the prioritization of synthetic strategies.

Identification of drug-binding sites on human serum albumin using affinity capillary electrophoresis and chemically modified proteins as buffer additives

A technique based on affinity capillary electrophoresis (ACE) and chemically modified proteins was used to screen the binding sites of various drugs on human serum albumin (HSA). This involved using HSA as a buffer additive, following the site-selective modification of this protein at two residues (tryptophan 214 or tyrosine 411) located in its major binding regions. The migration times of four compounds (warfarin, ibuprofen, suprofen and flurbiprofen) were measured in the presence of normal or modified HSA. These times were then compared and the mobility shifts observed with the modified proteins were used to identify the binding regions of each injected solute on HSA. Items considered in optimizing this assay included the concentration of protein placed into the running buffer, the reagents used to modify HSA, and the use of dextran as a secondary additive to adjust protein mobility. The results of this method showed good agreement with those of previous reports. The advantages and disadvantages of this approach are examined, as well as its possible extension to other solutes.

Protective effects of suprofen and its methyl ester against inactivation of rabbit kidney carbonyl reductase by phenylglyoxal

Suprofen (SP) was little reduced by rabbit kidney carbonyl reductase, whereas its methyl ester (SPM) was an efficient substrate of the enzyme. To account for the differential catalytic activities for SP and SPM, the protective effects of these compounds against the inactivation of the enzyme by phenylglyoxal (PGO) were compared. Since the carboxyl group of SP is negatively charged and one essential arginine residue is known to be located in the NADPH-binding site of the enzyme, the protection of SP against the inactivation of the enzyme by PGO is expected to be more effective than that of SPM lacking a carboxyl group. However, the protective effects of SP and SPM were very similar. These results suggest that in spite of evidence for the binding of SP to the coenzyme-binding site, the carboxyl group of SP fails to interact with one essential arginine residue located in the site.

Role of arg-410 and tyr-411 in human serum albumin for ligand binding and esterase-like activity

Recombinant wild-type human serum albumin (rHSA), the single-residue mutants R410A, Y411A, Y411S and Y411F and the double mutant R410A/Y411A were produced using a yeast expression system. The recombinant proteins were correctly folded, as they had the same stability towards guanidine hydrochloride and the same CD spectrum as HSA isolated from serum (native HSA). Thus the global structures of the recombinant proteins are probably very similar to that of native HSA. We investigated, by ultrafiltration and CD, the high-affinity binding of two representative site II ligands, namely ketoprofen and diazepam. According to the crystal structure of HSA, the residues Arg-410 and Tyr-411 protrude into the centre of site II (in subdomain 3A), and the binding results showed that the guanidino moiety of Arg-410, the phenolic oxygen and the aromatic ring of Tyr-411 are important for ketoprofen binding. The guanidino moiety probably interacts electrostatically with the carboxy group of ketoprofen, the phenolic oxygen could make a hydrogen-bond with the keto group of the ligand, and the aromatic ring may participate in a specific stacking interaction with one of or both of the aromatic rings of ketoprofen. By contrast, Arg-410 is not important for diazepam binding. The two parts of Tyr-411 interact favourably with diazepam, and probably do so in the same way as with ketoprofen. In addition to its unique ligand binding properties, HSA also possesses an esterase-like activity, and studies with p-nitrophenyl acetate as a substrate showed that, although Arg-410 is important, the enzymic activity of HSA is much more dependent on the presence of Tyr-411. A minor activity could be registered when serine, but not alanine or phenylalanine, was present at position 411.

Helix 6 of subdomain III A of human serum albumin is the region primarily photolabeled by ketoprofen, an arylpropionic acid NSAID containing a benzophenone moiety

It is well known that the subdomain III A (site II) of human serum albumin (HSA) binds a variety of endogenous and exogenous substances. However, the nature of the microenvironment of the binding site remains unclear. Ketoprofen (KP), an arylpropionic acid NSAID which contains a benzophenone moiety, was used as a photoaffinity labeling agent to label the binding region. Subsequent CNBr cleavage of the photolabeled HSA revealed that the 11.6 kDa and 9.4 kDa fragments contained most of the incorporated radioactivity. Competition experiments showed that the 11.6 kDa fragment contains the common binding region for site II ligands. This fragment was redigested with Achromobacter lyticus protease I (AP-I) and the amino acid sequence of the photolabeled peptide was determined to be XCTESLVNRR, which corresponds to the sequence 476C-485K of HSA. The complete amino acid sequence of the corresponding AP-I digested HSA peptide encompasses residues 476 to 499, which form helices 5 and 6 of subdomain III A. The HSA-Myr X-ray crystallography data showed that helix 5 is involved to the least extent in ligand binding. A docking model provided further support that helix 6 represents the photolabeled region of KP.

Characterization of solute binding at human serum albumin site II and its geometry using a biochromatographic approach

Chiral recognition mechanism relationships for binding at site II on human serum albumin (HSA) were investigated using D, L dansyl amino acids. Sodium phosphate salt was used as a solute-HSA interaction modifier. A new model was developed using a biochromatographic approach to describe the variation in the transfer equilibrium constant with the salt concentration, i.e., the nature of the interactions. The solute binding was divided into two salt concentration ranges c. For the low c values, below 0.03 M, the nonstereoselective interactions constituted the preponderant contribution to the variation in the solute binding with the salt concentration. For the high c values, above 0.03 M, the solute binding was governed by the hydrophobic effect and the stereoselective interactions. The different contributions implied in the binding process provided an estimation of both the surface charge density (sigma/F) and the surface area of the site II binding cavity accessible to solvent, which were found to be equal to around 10.10(-7) mol/m(2) and 2 nm(2). As well, the excess of sodium ions excluded by the solute transfer from the surface area of the pocket were about(-0.7) for dansyl norvaline and (-0.8) for dansyl tryptophan.

Binding of the Promen fluorescent probe to human serum albumin: a fluorescence spectroscopic study

The binding of Promen (6-propionyl-2-methoxynapthalene) to human serum albumin (HSA) was measured by fluorescence spectroscopy, finding only one class of binding sites on the protein. Hydrophobic interactions play an important role to stabilize the complex. Attempts were made to characterize its binding site using as competitors warfarin, phenylbutazone and diazepam, which bind in a specific site or region on the HSA. Fluorescence polarization measurements and spectrofluorimetric results suggest that diazepam and Promen bind at different but interacting binding sites on the HSA. The changes in the fluorescence emission of the bound Promen in the presence of these drugs, allow to use Promen to detect unspecific interactions with the site II on the HSA.

Effect of nonenzymatic glycation of albumin and superoxide dismutase by glucuronic acid and suprofen acyl glucuronide on their functions in vitro

Acyl glucuronides bind irreversibly to plasma proteins, and one mechanism proposed for this covalent binding is similar to that for glycation of protein by reducing sugars. Because glycation of protein by glucose and other reducing sugars can alter protein function, this lead to the hypothesis that the glycation of proteins by acyl glucuronides may cause similar effects. When human serum albumin (HSA) was incubated with 0.5 M glucose for 5 days, the unbound fractions of diazepam and warfarin were increased by 41 and 35%, respectively, less than that caused by glucuronic acid which increased the unbound fractions by 90% for diazepam and 420% for warfarin. When HSA was incubated with suprofen glucuronide (SG) at a much lower concentration of 0.005 M for only 24 h, the effects on the unbound fractions of diazepam and warfarin to HSA were altered dramatically with increases of 340 and 230%, respectively. After incubation of superoxide dismutase (SOD) with 0.5 or 1 M reducing sugars for 14 days, the enzyme activity decreased to 82 and 61% of initial levels at day 14, respectively, whereas glucuronic acid almost completely inactivated the enzyme activity over the same period. Even at a very low concentration (0.005 M) of SG, SOD activity was reduced significantly to 11% of initial levels by day 14, which was comparable to the effect by 0.5 and 1.0 M concentrations of glucuronic acid. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and matrix associated laser desorption/ionization time of flight mass spectrometry indicated that several equivalents of reducing sugars or SG became attached to albumin after incubation. These results suggest that acyl glucuronides may affect the function of proteins by the formation of glycated protein in vivo and may be associated with the toxicity of xenobiotics metabolized to labile acyl glucuronides.

HSA-solute interactions, enantioselectivity, and binding site geometrical characteristics

Recently, a theoretical model was proposed to study the existence of pockets of acetonitrile (ACN) called clusters in a hydroorganic mixture. The proposal used ACN as an interaction organic modifier between D,L-dansyl amino acids and their binding site in human serum albumin at site II. This solute binding is governed by primary and secondary interactions. The primary interactions are under the dependence of the solute solvation by ACN clusters and electrostatic interactions. Following this first step, the solute engages strong short-range interactions with the residues of site II. Using a biochromatographic approach, the solute binding, i.e., the solute retention, was divided into two dielectric constant (epsilon) ranges. In the first range, epsilon > epsilon c (epsilon c is the critical dielectric constant); the primary and secondary nonstereoselective electrostatic interactions were the major contributions to the variation in the solute binding with the ACN fraction in the mixture. In the second range, epsilon < epsilon c, the solute retention variation with the ACN fraction was governed by its solvation by the ACN clusters and also by the secondary hydrophobic stereoselective interaction. The mathematical model developed provided the determination of the surface charge density of site II as well as the cluster number that solvates each solute.

Species differences of serum albumins: I. Drug binding sites

PURPOSE

The purpose of this study was the classification and identification of drug binding sites on albumins from several species in order to understand species differences of both drug binding properties and drug interaction on protein binding.

METHODS

Binding properties and types of drug-drug interaction on the different albumins were examined using typical site I binding drugs, warfarin (WF) and phenylbutazone (PBZ), and site II binding drugs, ibuprofen (IP) and diazepam (DZ) on human albumin. Equilibrium dialysis was carried out for two drugs and the free concentrations of drugs were then treated using the methods of Kragh-Hansen (Mol. Pharmacol. 34. 160-171, (1988)).

RESULTS

Binding affinities of site I drugs to bovine, rabbit and rat albumins were reasonably similar to human albumin. However, interestingly, those to dog albumin were considerably smaller than human albumin. On the other hand, binding parameters of DZ to bovine, rabbit and rat albumins were apparently different from those of human albumin. These differences are best explained by microenvironmental changes in the binding sites resulting from change of size and/or hydrophobicity of the binding pocket, rather than a variation in amino acid residues. CONCLUSIONS. We will propose herein that mammalian serum albumins used in this study contain specific drug binding sites: Rabbit and rat albumins contain a drug binding site, corresponding to site I on human albumin, and dog albumin contains a specific drug binding site corresponding to site II on the human albumin molecule.

Relationship between lipophilicity and binding to human serum albumin of arylpropionic acid non-steroidal anti-inflammatory drugs

A possible relationship between lipophilicity and binding to human serum albumin was investigated for 11 arylpropionate non-steroidal anti-inflammatory drugs. The lipophilic parameter was determined by a reversed-phase high-performance liquid chromatographic procedure as the capacity factor (k'). The binding of arylpropionic acids to human serum albumin was studied in vitro by equilibrium dialysis. For each compound, a Scatchard analysis was performed considering two classes of binding sites characterized by high- and low-affinity constants, K1 and K2, respectively. A linear relationship was found between lipophilicity and binding parameters, n1K1 (r = 0.88, P < 0.0005) and n2K2 (r = 0.96, P < 0.0002). These results suggest the role of hydrophobic interactions in the binding of arylpropionic acids to human serum albumin.

Drug-protein binding sites. New trends in analytical and experimental methodology

In the last few years, continuous progress in instrumental analytical methodology has been achieved with a substantial increase in the number of new, more specific and more flexible methods for ligand-protein assays. In general, the methods used for drug-protein binding studies can be divided into two main groups: separation methods (enabling the calculation of binding parameters, i.e. the number of binding sites and their respective affinity constants) and non-separation methods (describing predominantly qualitative parameters of the ligand-protein complex). This review will be focussed particularly on recent trends in the development of drug-protein binding methods including stereoselective and non-stereoselective aspects using chromatography, capillary electrophoresis and microdialysis as compared to the "conventional approach" using equilibrium dialysis, ultrafiltration or size exclusion chromatography. The advantages and limitations of various methods will be discussed including a focus on "optimal" experimental strategies taking into account in vitro, ex vivo and/or in vivo studies. Furthermore, the importance of some particular aspects concerning the drug binding to proteins (covalent binding of drugs and metabolites, stereoselective interactions and evaluation of binding data) will be outlined in more detail.

Location of binding sites on immobilized human serum albumin for some nonsteroidal anti-inflammatory drugs

Anti-inflammatory drugs are widely used therapeutic agents and are very often administered with various other drugs. Because they are highly bound to human serum albumin (HSA), interferences between nonsteroidal anti-inflammatory drugs (NSAIDs) and coadministered drugs may arise from their interactions at a binding site on HSA. Although the percentage of binding to HSA is generally accurately determined, the binding sites to which a particular therapeutic agent binds are often unknown. In order to clarify where different classes of NSAIDs bind on the HSA molecule, competition studies were carried out on a HSA-based HPLC column using site I and site II markers as displacing agents. Results show that all the NSAIDs included in the study were affected by site I and site II markers and that a number of drugs had (an) extra binding site(s) not affected by any of the competitors used in the study. Competition data also suggest that binding of NSAIDs at the benzodiazepine site could in fact occur at two separate subsites, as previously observed for benzodiazepines.

Idiosyncratic liver toxicity of nonsteroidal antiinflammatory drugs: molecular mechanisms and pathology

This review explores the clinical hepatic pathology associated with the use of nonsteroidal antiinflammatory drugs (NSAIDs), possible cellular and molecular mechanisms of injury, and future challenges. NSAIDs comprise a group of widely used compounds that have been associated with rare adverse reactions in the liver, including fulminant hepatitis and cholestasis. These reactions are idiosyncratic, mostly independent of the dose administered, and host-dependent. The mechanisms responsible for the initiation and perpetuation of NSAID-induced hepatotoxicity remain poorly understood and have been largely inferred from clinical manifestation. A mounting body of evidence, however, indicates that many acidic NSAIDs are metabolized to reactive acyl glucuronides that can form covalent adducts with plasma proteins and hepatocellular proteins. In hepatocytes cocultured with lymphocytes, these NSAID-altered proteins can become antigenic. Thus, long-lived, drug-altered proteins may act as immunogens and produce cytotoxic T-cell-mediated or antibody-dependent, cell-mediated toxicity in susceptible patients. Alternatively, individual abnormalities in metabolism or disposition of some NSAIDs may lead to the formation or accumulation of toxic metabolites. Additional work with transgenic animal models is needed to permit better understanding of the general and specific risk factors involved in the pathogenesis of the idiosyncratic liver injuries related to NSAIDs and other drugs.

Study of interaction of carprofen and its enantiomers with human serum albumin--I. Mechanism of binding studied by dialysis and spectroscopic methods

The binding of carprofen, a non-steroidal anti-inflammatory drug of the aryl propionic acid class [2-(6-chlorocarbazole)propionic acid], and its enantiomers to human serum albumin (HSA) has been studied by dialysis and spectroscopic methods. Binding parameters obtained by different methods were in close agreement. The binding of carprofen to HSA by both fluorescence and equilibrium dialysis (ED) methods is characterized by two sets of association constants [K1 = 5.1 x 10(6) M-1 (fluorescence) and 3.7 x 10(6) M-1 (ED), K2 = 3.7 x 10(5) M-1 (fluorescence) and 1.3 x 10(5) M-1 (ED)]. The S(+)-enantiomer of carprofen showed slightly higher affinity for HSA than its corresponding antipode by both methods. Different analyses of the binding to HSA suggested the presence of one high affinity site and five to seven low affinity sites for carprofen and its enantiomers on HSA. Fluorescence displacement data implied that carprofen primarily binds to site II, the benzodiazepine site, while the low affinity site of carprofen is site I, the warfarin site. Circular dichroism data suggested different mechanisms for the high affinity and the low affinity binding of carprofen to HSA. The data are consistent with the major part of the binding energy at site II being electrostatic and hydrophobic interactions, whereas for the low affinity binding, hydrophobic interactions. Binding was exothermic, entropy driven and spontaneous, as indicated by the thermodynamic analyses. From binding data with chemically modified HSA derivatives, it is likely that tyrosine, lysine and histidine residues are especially involved in carprofen binding to HSA, and it is most likely that the high affinity binding of carprofen is located in the N-terminal part of domain III or that section of protein plus the C-terminal part of domain II of the HSA molecule. When the binding of carprofen to HSA was compared to the binding of carprofen methyl ester to HSA (K = 0.1 x 10(6) M-1), the carboxyl group of carprofen was found to play an important role especially in the high affinity binding of carprofen to HSA. The high affinity of carprofen to HSA was independent of the conformational changes on HSA caused by N-B transition.