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Purpose: The purpose of this paper was to determine 3- and 4-chloromethcathinone (3- and 4-CMC) binding degree and possible binding interaction modes with human serum albumin (HSA) using analytical and theoretical methods. Methods: Experimental determination of 3- and 4-CMC binding degree with HSA was performed using gas chromatography–tandem mass spectrometry preceded by the equilibrium dialysis (ED) and ultrafiltration (UF). Nuclear magnetic resonance (NMR) spectroscopy was used to determine 3- and 4-CMC epitope-binding maps and possible binding sites in HSA. The molecular docking and molecular dynamics were employed to obtain detailed information about binding modes of 3- and 4-CMC enantiomers in HSA. Results: As follows from the presented data, the degree of binding of 3- and 4-CMC is at a similar level of approx. 80%. This indicates a relatively strong binding of CMC to plasma proteins. The model studies employing the NMR spectroscopy and molecular simulations indicate that both CMCs bind to HSA. The whole 3- and 4-CMC molecules are embedded in the binding sites, with aromatic moieties being in the closest contact with the HSA residues. Moreover, conducted experiments show that Sudlow site II is the main binding center for 3- and 4-CMC and Sudlow site I acts as the secondary binding site. Conclusions: Although many studies describe pharmacological and toxicological properties of synthetic cathinones (SC), the data taking SCs binding in plasma into consideration are scarce. To our knowledge, this is the first report presenting comprehensive experimental and theoretical characterization of 3- and 4-CMC binding with plasma proteins. [ABSTRACT FROM AUTHOR]

Abstract Background Telmisartan (TLT) is a prototypic angiotensin receptor blocker largely used to treat hypertension worldwide. In addition to its cardioprotective effects, TLT presents pleiotropic activities and notably displays noticeable anti-inflammatory and antitumor effects. The repression of the programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint may be implicated antitumor action of TLT, as it is the case with many other compounds equipped with a biphenyl moiety. We have used molecular modeling to compare the interaction of TLT and derivatives with the PD-L1 dimer protein. Results Two molecules, TLT-dimer and TLT-acylglucuronide, were found to form more stable complexes with PD-L1 than TLT itself. In parallel, the docking analysis performed with a series of 12 sartans led to the identification of Olmesartan as a potential PD-L1 binder. The stacked biphenyl unit of Olmesartan positions the molecule along the groove delimited by the two protein monomers. The flanking tetrazole and imidazole moieties, on each side of the biphenyl unit of Olmesartan, contribute favorably to the protein interaction via specific hydrogen bonding interactions. Conclusions The computational analysis suggests a possible binding of Olmesartan to PD-L1 dimer and thus offers novel perspectives for the design of small molecules capable of interrupting the PD-1/PD-L1 immune checkpoint. Experimental studies are warranted to validate the hypothesis. Graphical abstract

Background: Telmisartan (TLT) is a prototypic angiotensin receptor blocker largely used to treat hypertension worldwide. In addition to its cardioprotective effects, TLT presents pleiotropic activities and notably displays noticeable anti-inflammatory and antitumor effects. The repression of the programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint may be implicated antitumor action of TLT, as it is the case with many other compounds equipped with a biphenyl moiety. We have used molecular modeling to compare the interaction of TLT and derivatives with the PD-L1 dimer protein. Results: Two molecules, TLT-dimer and TLT-acylglucuronide, were found to form more stable complexes with PD-L1 than TLT itself. In parallel, the docking analysis performed with a series of 12 sartans led to the identification of Olmesartan as a potential PD-L1 binder. The stacked biphenyl unit of Olmesartan positions the molecule along the groove delimited by the two protein monomers. The flanking tetrazole and imidazole moieties, on each side of the biphenyl unit of Olmesartan, contribute favorably to the protein interaction via specific hydrogen bonding interactions. Conclusions: The computational analysis suggests a possible binding of Olmesartan to PD-L1 dimer and thus offers novel perspectives for the design of small molecules capable of interrupting the PD-1/PD-L1 immune checkpoint. Experimental studies are warranted to validate the hypothesis. [ABSTRACT FROM AUTHOR]

In this study, multiple spectroscopic and computational methods were utilized to investigate the binding mechanism of doxofylline with lysozyme. The in vitro methods were used to obtain the binding kinetics and thermodynamics. UV–vis spectroscopy indicated the formation of complex between doxofylline and lysozyme. The Gibb's free energy and binding constant from UV–vis data was obtained as −7.20 kcal M−1 and 1.929 × 105 M−1, respectively. Doxofylline successfully quenched the fluorescence of lysozyme, confirming the formation of complex. The kq and Ksv values for the quenching of lysozyme's fluorescence by doxofylline were 5.74 × 1011 M−1 s−1 and 3.32 × 103 M−1, respectively. These values signified a moderate binding affinity between doxofylline and lysozyme. In synchronous spectroscopy, red shifts were observed for indicating the changes in microenvironment of lysozyme following the binding of doxofylline. The secondary structural analysis was determined using circular dichroism (CD) which revealed an increase in % α-helical as a result of doxofylline interaction. The binding affinity and flexibility of lysozyme upon complexation have been revealed via molecular docking and molecular dynamic (MD) simulations, respectively. According to the many parameters of the MD simulation, the lysozyme–doxofylline complex was stable under physiological conditions. All during the simulation time, hydrogen bonds were continuously present. The MM-PBSA binding energy for lysozyme and doxofylline binding was found to be −30.55 kcal mol−1. [ABSTRACT FROM AUTHOR]

ZnO and CdS nanoparticle (NP) doped with first row transition metal ions showed significant antibacterial activity towards Gram-negative as well as Gram-positive bacteria. While, the antibacterial activity of ZnO NPs was found to be significant in Gram-negative bacteria, the effect was comparatively less pronounced towards Gram-positive bacteria. The activity was found to increase with increasing concentration of the NPs. Doping of ZnO NP with Fe atom resulted in significant reduction in the efficacy its antimicrobial activity. In comparison, CdS quantum dot showed antibacterial activity both in Gram-negative and Gram-positive bacteria. While Co doped CdS particles did not show any modulated antibacterial activity; doping by Fe atom augments it with increasing the dopant concentration. The interaction of anti-diabetic drug chlorpropamide is significantly stronger with bovine serum albumin adsorbed on Fe-doped CdS in comparison with undoped NPs without significant alteration in the protein secondary structure. Present study reveals that the drug binding ability of proteins can be significantly modulated on judicious choice of NP system and also the dopant. The modulation in antimicrobial activity and the drug binding ability of the adsorbed protein was explained on the basis of structural parameters and different physicochemical properties of the doped NP systems. [ABSTRACT FROM AUTHOR]

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

The pseudoguaianolide-type sesquiterpene lactone (SL) britannin (BRT), found in different Inula species, has been characterized as a potent anticancer agent acting via modulation of the transcription factor NFkB and the Nrf2-Keap1 signaling pathway. In addition, a BRT-induced down-regulation of the immune checkpoint PD-L1 (programmed cell death ligand 1) expressed on cancer cells has been evidenced. Here we have performed a docking analysis of the direct binding of BRT to the PD-L1 protein, both in its monomeric and dimeric state. BRT appears to form stable complexes with PD-L1, with a preference for the dimeric form, binding at the interface of the two monomers. The calculated empirical energy of interaction (ΔE) value reaches −63.1 kcal/mol for the BRT-PD-L1 dimer complex, not far from the value calculated with the reference PD-L1 ligand BMS-202 (ΔE = −73.4 kcal/mol) under identical conditions. We also studied the potential PD-L1 dimer binding of 15 pseudoguaianolide sesquiterpene lactones analogues to BRT, including helenalin, gaillardin, bigelovin, coronopilin, and others. The docking analysis predicted that the SL chamissonolide (CHM) can also form equally stable complexes with PD-L1 dimer (ΔE = −64.8 kcal/mol). Preliminary compound structure-PD-L1 binding relationships have been delineated. This computational study supports the proposed interaction of BRT with PD-L1 and provides a guidance to the design of novel PD-L1 binders incorporating a SL-like tricyclic core unit. [ABSTRACT FROM AUTHOR]

In this study, multiple spectroscopic and computational methods were utilized to investigate the binding mechanism of doxofylline with lysozyme. The in vitro methods were used to obtain the binding kinetics and thermodynamics. UV–vis spectroscopy indicated the formation of complex between doxofylline and lysozyme. The Gibb’s free energy and binding constant from UV–vis data was obtained as −7.20 kcal M−1 and 1.929 × 105 M−1, respectively. Doxofylline successfully quenched the fluorescence of lysozyme, confirming the formation of complex. The kq and Ksv values for the quenching of lysozyme’s fluorescence by doxofylline were 5.74 × 1011 M−1 s−1 and 3.32 × 103 M−1, respectively. These values signified a moderate binding affinity between doxofylline and lysozyme. In synchronous spectroscopy, red shifts were observed for indicating the changes in microenvironment of lysozyme following the binding of doxofylline. The secondary structural analysis was determined using circular dichroism (CD) which revealed an increase in % α-helical as a result of doxofylline interaction. The binding affinity and flexibility of lysozyme upon complexation have been revealed via molecular docking and molecular dynamic (MD) simulations, respectively. According to the many parameters of the MD simulation, the lysozyme–doxofylline complex was stable under physiological conditions. All during the simulation time, hydrogen bonds were continuously present. The MM-PBSA binding energy for lysozyme and doxofylline binding was found to be −30.55 kcal mol−1.

Drugs targeting the cell division cycle kinase 7 (Cdc7) are actively searched for the treatment of different pathologies such as amyotrophic lateral sclerosis and cancer. Cdc7 interacts with multiple protein partners, including protein Dbf4 to form the Dbf4-dependent kinase (DDK) complex which regulates DNA replication initiation. Cdc7 and its activator Dbf4 are over-expressed in some cancers. The antibacterial drug clofoctol (CFT), used to treat respiratory tract infections, has been shown to block Cdc7 kinase activity, acting as a non-ATP-competitive inhibitor, capable of arresting DNA synthesis in cancer cells. We have modeled the interaction of CFT with the DDK complex and identified four potential binding sites at the interface of the Cdc7/Dbf4 heterodimer: at T109 and D128 (Cdc7), V220 and I330 (Dbf4). CFT behaves as an interfacial protein-protein inhibitor of the Cdc7/Dbf4 complex, limiting drug access to the proximal kinase site. Six CFT analogues have been tested for binding to the kinase complex. Two potent binders were analyzed in detail. The CFT structure was modulated to replace the two chlorine atoms with hydroxyl groups. The empirical potential energy of interaction (ΔE) calculated with hydroxylated compounds points to a more favorable interaction with the DDK complex, in particular at D128 site with the compound bearing two ortho-OH groups. Our work contributes to the identification of novel DDK inhibitors. [ABSTRACT FROM AUTHOR]

Drugs targeting the cell division cycle kinase 7 (Cdc7) are actively searched for the treatment of different pathologies such as amyotrophic lateral sclerosis and cancer. Cdc7 interacts with multiple protein partners, including protein Dbf4 to form the Dbf4-dependent kinase (DDK) complex which regulates DNA replication initiation. Cdc7 and its activator Dbf4 are over-expressed in some cancers. The antibacterial drug clofoctol (CFT), used to treat respiratory tract infections, has been shown to block Cdc7 kinase activity, acting as a non-ATP-competitive inhibitor, capable of arresting DNA synthesis in cancer cells. We have modeled the interaction of CFT with the DDK complex and identified four potential binding sites at the interface of the Cdc7/Dbf4 heterodimer: at T109 and D128 (Cdc7), V220 and I330 (Dbf4). CFT behaves as an interfacial protein-protein inhibitor of the Cdc7/Dbf4 complex, limiting drug access to the proximal kinase site. Six CFT analogues have been tested for binding to the kinase complex. Two potent binders were analyzed in detail. The CFT structure was modulated to replace the two chlorine atoms with hydroxyl groups. The empirical potential energy of interaction (ΔE) calculated with hydroxylated compounds points to a more favorable interaction with the DDK complex, in particular at D128 site with the compound bearing two ortho-OH groups. Our work contributes to the identification of novel DDK inhibitors. DOI: http://dx.doi.org/10.5281/zenodo.5527211

• Binding was studied for thiazolidinediones with normal or glycated human serum albumin. • Affinity microcolumns were used to measure site-specific interactions on this protein. • Affinity maps were generated and used to examine the effects of glycation at given sites. • Strong binding was seen at Sudlow sites I and II; interactions with the tamoxifen site and subdomain IB were also noted. • At some sites, changes in binding strength up to 6- to 7-fold were observed due to glycation. Human serum albumin (HSA) is known to undergo modifications by glucose during diabetes. This process produces glycated HSA that can have altered binding to some drugs. In this study, high-performance affinity microcolumns and competition studies were used to see how glycation affects the binding by two thiazolidinedione-class drugs (i.e., pioglitazone and rosiglitazone) at specific regions of HSA. These regions included Sudlow sites I and II, the tamoxifen and digitoxin sites, and a drug-binding site located in subdomain IB. At Sudlow site II, the association equilibrium constants (or binding constants) for pioglitazone and rosiglitazone with normal HSA were 1.7 × 105 M−1 and 2.0 × 105 M−1 at pH 7.4 and 37 °C, with values that changed by up to 5.7-fold for glycated HSA. Sudlow site I of normal HSA had binding constants for pioglitazone and rosiglitazone of 3.4 × 105 M−1 and 4.6 × 105 M−1, with these values changing by up to 1.5-fold for glycated HSA. Rosiglitazone was found to also bind a second region that had a positive allosteric effect on Sudlow site I for all the tested preparations of HSA (binding affinity, 1.1–3.2 × 105 M−1; coupling constant for Sudlow site I, 1.20–1.34). Both drugs had a strong positive allosteric effect on the tamoxifen site of HSA (coupling constants, 13.7–19.9 for pioglitazone and 3.7–11.5 for rosiglitazone). Rosiglitazone also had weak interactions at a site in subdomain IB, with a binding constant of 1.4 × 103 M−1 for normal HSA and a value that was altered by up to 6.8-fold with glycated HSA. Neither of the tested drugs had any significant binding at the digitoxin site. The results were used to produce affinity maps that described binding by these thiazolidinediones with HSA and the effects of glycation on these interactions during diabetes. [ABSTRACT FROM AUTHOR]

Acankoreagenin (ACK) is a lupane triterpene found in several Acanthopanax and Schefflera plant species. ACK, also known as acankoreanogenin or HLEDA, bears a major structural analogy with other lupane triterpenoids such as impressic acid (IA) and the largely used phytochemical betulinic acid (BA). These compounds display marked anti-inflammatory, anti-diabetes, and anti-cancer properties. BA can form stable complexes with the peroxisome proliferator-activated receptor gamma (PPARγ). The tridimensional structure of the BA-PPARγ complex was used to perform a molecular docking analysis of the binding of ACK and IA to the protein. The 3-hydroxyl epimers (R/S) of each natural product were also modeled to examine the role of the C3-OH stereochemistry that distinguishes BA [3(S)] from ACK and AI [3(R)]. Calculations indicate that ACK can form more stable complexes with PPARγ than BA, upon insertion of the drug into the same binding pocket. The inversion of the C3-OH stereochemistry is not an obstacle for binding and the additional carboxy group of ACK at C23 position seems to reinforce the protein interaction. The 3-hydroxyl group does not play a major role in the geometry of the protein-drug complex, which is preserved between BA and ACK. Additional structure-binding relationships are provided, through the evaluation of the PPARγ binding capacity of ACK derivatives. Binding of ACK to PPARγ would account for its marked antidiabetic effect, at least partially. ACK can be used as a platform to design new antidiabetic compounds. [ABSTRACT FROM AUTHOR]

In this work, the effect of γ-irradiated surfactants on drug-protein binding has been assessed. Irradiated aqueous solutions of Pluronic F-127, Pluronic L-35, Tween 20, and Tween 80 surfactants were used. Gamma irradiation was carried out for three different doses, to these four surfactants viz., 6, 30, and 36 kGy. Two drugs, Ornidazole (ONZ) and Telmisartan (TMS) were used for the binding study. The effect of four irradiated surfactants in the presence of drug - Bovine serum albumin (BSA) protein was analyzed. The drug solutions in methanol-aqueous media were combined with BSA in the initial step. In the next two succeeding steps, drug-BSA interaction in the presence of unirradiated and irradiated surfactants were carried out. The results of drug-BSA due to addition of irradiated and unirradiated surfactants were compared. The interaction processes were assessed through UV Spectroscopy, DLS, zeta potential, turbidity, and docking studies. Improved binding was observed for both the drugs and four surfactants for irradiated surfactants as determined from the binding constant values using UV spectroscopic studies. The DLS measurements demonstrated no general trend of increase or decrease in micellar size with absorbed dose. The binding and change in the size of micelles were observed to be highly drug and surfactant-specific. Among the four surfactants, irradiated Pluronic F-127 showed higher binding affinity. To the best of our knowledge, this is the first report on the effect of γ-irradiated surfactant on drug-BSA interaction. This can be applied to other drug-protein systems to tune their interaction to the required level.Communicated by Ramaswamy H. Sarma.

Glycyrrhizin (GLR) is triterpenoid saponin used for the treatment of various of liver and skin diseases. GLR blocks the nucleocytoplasmic translocation of the protein HMGB1, thereby inhibiting its extracellular release and its functions as a damage-associated molecular pattern molecule. Here we have analyzed the interaction with HMGB1 of GLR and its three main metabolites mono-glucuronyl-glycyrrhetinic acid (MGA), glycyrrhetinic acid (GA) and a sulfate metabolite of GA (Cpd 3). We determined the optimized binding configurations (starting from crystallographic data for HMGB1) of the bound 18α- and 18β-epimers to compare the potential energy of interaction (ΔE) and free energy of hydration (ΔG). The molecular modeling shows that GLR and MGA can form much more stable complexes with HMGB1 than the non-glycosylated molecules GA and Cpd 3. The glucuronic acid residue common to GLR and MGA directly attached to the terpenoid core contributes importantly to the protein interaction. 18α-GLR (isoglycyrrhizinate) appeared as a better binder to HMG Box B than 18β-GLR, whereas both epimers bind very well to HMG Box A. The stabilization of HMG Box A through an intramolecular cystine disulfide bond further increases the stability of the GLR-HMG Box A complexes. On the opposite GA and Cpd 3 exhibit a considerably weaker HMG binding capacity. The study provides a detailed in silico analysis of the interaction of GLR with HMGB1; the limitations and biological implications are discussed.

This article describes the synthesis of Thy-(Phe-Phe) and Thy-(Tyr-Tyr), two thymine-bearing dipeptides based on l -phenylalanine and l -tyrosine, the circular dichroism (CD), UV and dynamic light scattering (DLS) characterization of their self-assemblies, and a CD study of their interaction with nucleic acids (using homoadenine DNA and RNA) and serum proteins (utilizing BSA as a model protein). DLS studies, alongside with CD and UV investigations conducted on aqueous solutions of the derivatives under different concentration and temperature conditions, showed the formation of extensive molecular architectures with hydrodynamic mean diameters higher than 300 nm, with Thy-(Tyr-Tyr) forming at pH = 7.5 particularly large and stable networks, involving multiple units, connected by H-bonding, aromatic and hydrophobic interactions. Finally, the findings of our study suggested that Thy-(Phe-Phe) and Thy-(Tyr-Tyr), very stable in human serum, were able to bind BSA protein altering its secondary structure. [ABSTRACT FROM AUTHOR]

Odanacatib (ODN) is a selective cathepsin K inhibitor that acts as an anti-resorptive agent to treat osteoporosis. ODN is also found effective in reducing the effect of severe periodontitis. The interaction between ODN and human serum albumin (HSA) was investigated using spectroscopic, microscopic, and in silico approaches to characterize their binding. The fluorescence intensity of HSA increased upon the addition of increasing concentrations of ODN accompanied by blueshift in the fluorescence spectrum, which suggested hydrophobic formation around the microenvironment of the fluorophores upon ODN binding. A moderate binding affinity was obtained for ODN-HSA binding, with binding constant (K a) values of ∼104 M−1. Circular dichroism results suggested that the overall secondary and tertiary structures of HSA were both only slightly altered upon ODN binding. The surface morphology of HSA was also affected upon ODN binding, showing aggregate formation. Drug displacement and molecular docking results revealed that ODN preferably binds to site III in subdomain IB of HSA, while molecular dynamics simulations indicated formation of a stable protein complex when site III was occupied by ODN. The ODN-HSA complex was mainly stabilized by a combination of hydrogen bonding, hydrophobic interactions, and van der Waals forces. These findings provide additional information to understand the interaction mechanism of ODN in blood circulation and may help in future improvements on the adverse effects of ODN. The interaction of odanacatib with human serum albumin as monitored by spectroscopic methods, atomic force microscopy, and in silico simulations. [Display omitted] • Moderate binding affinity between ODN and HSA. • Surface morphology of HSA was affected upon ODN binding, showing aggregate formation. • ODN preferably binds to site III in subdomain IB of HSA. • The complex between ODN and HSA was formed via hydrogen bonding, hydrophobic forces and van der Waals forces. [ABSTRACT FROM AUTHOR]

Aim: The aim was to evaluate drug-plasma binding (DPB).by employing Hollow Fiber-in-Syringe Equilibrium Sampling Through Supported Liquid Membrane (HFiS ESTSLM) and RP-HPLC analysis. Materials & Methods: HFiS ESTSLM and RP-HPLC were used to evaluate DPB of three weak basic drugs (Metoprolol, Diphenhydramine, and Sildenafil) with differing hydrophilicity and binding ability to blood plasma. Results: The results exhibited an increasing drug-dependent magnitude of DPB for the three model drugs. This trend of DPB confirmed that HFiS ESTSLM has the required sensitivity for determining DPB of the drugs. The DPB was drug concentration-dependent within the tested drug concentration range, especially at high concentration. Conclusion: HFiS ESTSLM and RP-HPLC offered a simple, easy and cost-effective procedure to evaluate DPB of these basic drugs.

Highlights • The binding of tolazamide with albumin was examined using affinity microcolumns. • Normal human serum albumin and glycated forms of this protein were considered. • Frontal analysis was used to examine the overall changes in binding with glycation. • Zonal elution was used to examine binding of this drug at Sudlow sites I and II. • The changes in binding were compared with those seen for other sulfonylurea drugs. Abstract Sulfonylurea drugs are antidiabetic drugs that are utilized in the treatment of type II diabetes and often have significant binding with human serum albumin (HSA). Immobilized samples of normal or glycated HSA in affinity microcolumns were used to investigate interactions of these proteins with the sulfonylurea drug tolazamide. HPLC and frontal analysis were used to first examine the overall binding of this drug with these samples of HSA. It was found that tolazamide had two general classes of binding sites (i.e., high and low affinity) for normal and glycated HSA. The higher affinity sites had binding constants of around 4.3–6.0 × 104 M−1 for these interactions at pH 7.4 and 37 °C, while the lower affinity sites had binding strengths of 4.9–9.1 × 103 M−1. Zonal competition studies between tolazamide and probes for Sudlow sites I and II on HSA were also performed and used to provide site-specific affinities for tolazamide at these sites. A decrease of 22% in affinity was observed for tolazamide at Sudlow site I and an increase up to 58% was seen at Sudlow site II when comparing glycated HSA with normal HSA. These observed changes were compared to those of other first-generation sulfonylurea drugs, providing information on how glycation can alter the total and local binding strength of tolazamide and related compounds with HSA under levels of glycation seen in patients with diabetes. [ABSTRACT FROM AUTHOR]

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

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

Binding of the immunosuppressive agent mycophenolate mofetil (MMP) and its pharmacologically active metabolite mycophenolic acid (MPA) to human serum albumin (HSA) and α 1 -acid glycoprotein (HAAG) has been investigated by means of an integrated approach involving selective excitation of the drug fluorophore, following their UV-A triggered fluorescence and docking studies. The formation of the protein/ligand complexes was evidenced by a dramatic enhancement of the fluorescence intensity and a hypsochromic shift of the emission band. In HSA, competitive studies using oleic acid as site I probe revealed site I as the main binding site of the ligands. Binding constants revealed that the affinity of the active metabolite by HSA is four-fold higher than its proactive form. Moreover, the affinity of MMP by HSA is three-fold higher than by HAAG. Docking studies revealed significant molecular binding differences in the binding of MMP and MPA to sub-domain IIA of HSA (site 1). For MPA, the aromatic moiety would be in close contact to Trp214 with the flexible chain pointing to the other end of the sub-domain; on the contrary, for MMP, the carboxylate group of the chain would be fixed nearby Trp214 through electrostatic interactions with residues Arg218 and Arg222. [ABSTRACT FROM AUTHOR]

• The theory of ultrafast affinity extraction for use in binding studies was considered. • Factors affecting the robustness, precision, and accuracy of such work were examined. • The predicted results agreed with experimental data for model drug/protein systems. • The effects of solute dissociation in such work were examined as well. • The results should be valuable in examining new systems by this separation method. Ultrafast affinity extraction (UAE) is a form of microscale affinity HPLC that can be employed to quickly measure equilibrium constants for solute-binding agent interactions in solution. This study used chromatographic and equilibrium theory with universal plots to examine the general conditions that are needed in UAE to obtain accurate, precise, and robust measurements of equilibrium constants for such interactions. The predicted results were compared to those obtained by UAE in studies that examined the binding of various drugs with two transport proteins: human serum albumin and α 1 -acid glycoprotein. The most precise and robust conditions for these binding studies occurred for systems with intermediate values for their equilibrium free fraction for the solute (F 0 ≈ 0.20–0.80). These trends showed good agreement with those seen in prior studies using UAE. It was further determined how the apparent free fraction of a solute was related to the dissociation rate of this solute, the time allowed for solute dissociation during UAE, and the equilibrium free fraction for the solute. These results also agreed with experimental results, as obtained for the binding of warfarin and gliclazide with human serum albumin. The final section examined how a change in the apparent free fraction, as caused by solute dissociation, affected the accuracy of an equilibrium constant that was measured by UAE. In addition, theoretical plots were generated to allow the selection of conditions for UAE that provided a given level of accuracy during the measurement of an equilibrium constant. The equations created and trends identified for UAE were general ones that can be extended in future work to other solutes and binding agents. [ABSTRACT FROM AUTHOR]

• Protein entrapment and affinity microcolumns were used to examine drug-protein binding. • The binding of sulfonylurea drugs with modified human serum albumin (HSA) was studied. • Methylglyoxal and glyoxal were used to form advanced glycation end products on HSA. • These modifications increased the affinity of HSA by up to 2.1-fold for some sulfonylureas. • The results agreed with those obtained using data from previous methods. 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. [ABSTRACT FROM AUTHOR]

Diabetes is a health condition associated with the elevated levels of glucose in the bloodstream and affects 366 million people worldwide. Type II diabetes is often treated with sulfonylurea drugs, which are known to bind tightly in the blood to the transport protein human serum albumin (HSA). One consequence of the elevated levels of glucose in diabetes is the nonenzymatic glycation of proteins such as HSA. Several areas of HSA are now known to be affected by glycation-related modifications, which may in turn affect the binding of sulfonylurea drugs and other solutes to this protein. This review discusses some recent studies that have examined these changes in drug-protein binding by employing high-performance affinity chromatography (HPAC). A description of the theoretical and experimental techniques that were used in these studies is given. The information on drug interactions with glycated HSA, as obtained through this method, is also summarized. In addition, the potential advantages of this approach in the areas of biointeraction analysis and personalized medicine are considered.

Theophylline (THP), theobromine (THB) and caffeine (CAF) belong to the xanthine group of drugs and are principle component of tea or coffee with important pharmacological activities and clinical applications. The interaction between these drugs and serum albumin proteins obtained from bovine and human (BSA and HSA, respectively) in the presence and absence of silver as well as gold nanoparticles (Ag and AuNP, respectively) was investigated for the first time by using a series of biophysical techniques and molecular modelling calculations. Time resolved fluorescence measurements confirm that all the drugs quench the intrinsic tryptophan fluorescence of the proteins through a static mechanism irrespective of the absence or presence of NPs. However, the binding constant of the proteins towards the drugs changes considerably in presence of NPs. Addition of drugs decreases α-helicity of the proteins both in the absence and presence of NPs; however, no substantial change in protein secondary structure is perceived only with the NPs. The results show that the drug carrying capacity of the albumins can be significantly modulated with metal NPs towards desired pharmacokinetic and therapeutic applications without compromising the basic structure; and therefore, the function of the proteins. [ABSTRACT FROM AUTHOR]

The interactions of drugs with serum proteins are often stereoselective and can affect the distribution, activity, toxicity and rate of excretion of these drugs in the body. A number of approaches based on affinity chromatography, and particularly high-performance affinity chromatography (HPAC), have been used as tools to study these interactions. This review describes the general principles of affinity chromatography and HPAC as related to their use in drug binding studies. The types of serum agents that have been examined with these methods are also discussed, including human serum albumin, α 1 -acid glycoprotein, and lipoproteins. This is followed by a description of the various formats based on affinity chromatography and HPAC that have been used to investigate drug interactions with serum proteins and the historical development for each of these formats. Specific techniques that are discussed include zonal elution, frontal analysis, and kinetic methods such as those that make use of band-broadening measurements, peak decay analysis, or ultrafast affinity extraction. [ABSTRACT FROM AUTHOR]

BI-2536 is a potent Polo-like kinase inhibitor which induces apoptosis in diverse human cancer cell lines. The binding affinity of BI-2536 for human serum albumin (HSA) protein may define its pharmacokinetic and pharmacodynamic profile. We have studied the binding of BI-2536 to HSA by means of different spectroscopic techniques and docking calculations. We have experimentally observed that the affinity of BI-2536 for HSA is higher than that of other common HSA binding drugs. Therefore, it can be postulated that the drug dose should be increased to achieve a certain concentration of free drug in plasma, although BI-2536 could also reach tumour tissues by uptaking HSA/BI-2536 complex. Only a single binding site on HSA has been observed for BI-2536 which seems to correspond to the subdomain IIA pocket. The formation of the HSA/BI-2536 complex is a spontaneous and entropy-driven process that does not cause a significant change of the secondary structure of the protein. Its endothermic character could be related to proton release. Thermodynamic analysis showed that the main protein-drug interactions are of the van der Waals type although the presence of amide and ether groups in BI-2536 could also allow H-bonding with some residues in the subdomain IIA pocket. [ABSTRACT FROM AUTHOR]

Interactions with serum proteins such as alpha 1 -acid glycoprotein (AGP) can have a significant effect on the behavior and pharmacokinetics of drugs. Ultrafast affinity extraction and peak profiling were used with AGP microcolumns to examine these processes for several model drugs (i.e., chlorpromazine, disopyramide, imipramine, lidocaine, propranolol and verapamil). The association equilibrium constants measured for these drugs with soluble AGP by ultrafast affinity extraction were in the general range of 10 4 –10 6 M −1 at pH 7.4 and 37 °C and gave good agreement with literature values. Some of these values were dependent on the relative drug and protein concentrations that were present when using a single-site binding model; these results suggested a more complex mixed-mode interaction was actually present, which was also then used to analyze the data. The apparent dissociation rate constants that were obtained by ultrafast affinity extraction when using a single-site model varied from 0.14 to 7.0 s −1 and were dependent on the relative drug and protein concentrations. Lower apparent dissociation rate constants were obtained by this approach as the relative amount of drug versus protein was decreased, with the results approaching those measured by peak profiling at low drug concentrations. This information should be useful in better understanding how these and other drugs interact with AGP in the circulation. In addition, the chromatographic approaches that were optimized and used in this report to examine these systems can be adapted for the analysis of other solute-protein interactions of biomedical interest. [ABSTRACT FROM AUTHOR]

Danhong injection (DHI) is a widely used Chinese medicine injection (CMI) for the clinical treatment of cardiovascular and cerebrovascular diseases. In this study, a simple and efficient in vitro method based on ultrafiltration LC–MS and molecular modeling has been developed to study the human serum albumin (HSA) binding of the compounds in DHI. Seven major components including protocatechuic aldehyde, p -coumaric acid, salvianolic acid D, rosmarinic acid, salvianolic acid E, lithospermic acid and salvianolic acid B were identified as HSA ligands and their binding degrees in the proposed non-saturated model were 26.17, 37.69, 99.77, 91.78, 96.91, 99.42 and 98.10%, respectively. Considering the drug-HSA binding property of the compounds in DHI may change during drug combination therapy, competitive binding assay was carried out to evaluate the influence of aspirin on the DHI-HSA binding. Experimental results revealed that the salvianolic acids in DHI had stronger binding ability to HSA than sodium salicylate. To further verify the results above, molecular modeling and probe displacement assay were conducted to investigate the optimum binding site and binding affinity of the ligands on HSA. Our findings suggested that the established method could be a powerful tool to study the drug-HSA binding property of CMIs. [ABSTRACT FROM AUTHOR]

It is well-known that only the unbound (free) drug fraction can achieve a pharmacological effect. Therefore the determination of free drug concentration is a very important issue in the field of pharmacology. In this study poly-1-vinyl-2-pyrrolidone (VP) crosslinked with divinylbenzene (DVB) compared with the micellar liquid chromatography (MLC) with and without pre-made drug adsorption was used for quantitative analysis of free ampicillin concentration in the standard solution of drug-human serum albumin owing to its ability to block protein adsorption. The commonly recognized adsorption method based on drug adsorption on VP-DVB has been compared to the entirely new application of MLC with direct sample injection (DSI) not requiring pre-made adsorption. Micellar aggregates are able to solubilize various compounds therefore micellar environment can be used for direct determination of free drug concentration. The obtained results show that the free drug concentration values obtained in the micellar systems based on cetyltrimethylammonium bromide (CTAB) (93.98 μg L −1 , 78.3%) as well as on polyoxyethylene (23) lauryl ether (Brij35) (91.15 μg L −1 , 75.9%) are similar to those obtained after the drug adsorption on VP-DVB using both RP-HPLC (95.85 μg mL −1 , 79.9%) and spectrophotometry (96.47 μg mL −1 , 80.4%). However, only %PPB (% plasma protein binding) value calculated on the basis of Brij35 retention factor is similar to the literature data. The obtained results are within the analytical range of % of free drug concentration. Therefore N-vinylpyrrolidone copolymer as well as micellar system based on the non-ionic surfactant can be successfully applied for determination of free drug concentration. Moreover, the new application of MLC with DSI can be recognized as a promising, fast and simple method for quantitative determination of free drug concentration. [ABSTRACT FROM AUTHOR]

An on-column approach for protein entrapment was developed to immobilize alpha-acid glycoprotein (AGP) for drug-protein binding studies based on high-performance affinity chromatography. Soluble AGP was physically entrapped by using microcolumns that contained hydrazide-activated porous silica and by employing mildly oxidized glycogen as a capping agent. Three on-column entrapment methods were evaluated and compared to a previous slurry-based entrapment method. The final selected method was used to prepare 1.0 cm × 2.1 mm I.D. affinity microcolumns that contained up to 21 (±4) μg AGP and that could be used over the course of more than 150 sample applications. Frontal analysis and zonal elution studies were performed on these affinity microcolumns to examine the binding of various drugs with the entrapped AGP. Site-selective competition studies were also conducted for these drugs. The results showed good agreement with previous observations for these drug-protein systems and with binding constants that have been reported in the literature. The entrapment method developed in this study should be useful for future work in the area of personalized medicine and in the high-throughput screening of drug interactions with AGP or other proteins. [ABSTRACT FROM AUTHOR]

A slurry-based method was developed for the entrapment of alpha 1 -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 ( K a ) 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. [ABSTRACT FROM AUTHOR]

The primary endogenous ligands of human serum albumin (HSA) are non-esterified fatty acids, with 0.1–2 mol of fatty acids normally being bound to HSA. In type II diabetes, fatty acid levels in serum are often elevated, and the presence of high glucose results in an increase in the non-enzymatic glycation of HSA. High-performance affinity chromatography (HPAC) was used to examine the combined effects of glycation and the presence of long chain fatty acids on the binding of HSA with R -warfarin and l -tryptophan (i.e., probes for Sudlow sites I and II, the major sites for drugs on this protein). Zonal elution competition studies were used to examine the interactions of myristic acid, palmitic acid and stearic acid with these probes on HSA. It was found that all these fatty acids had direct competition with R -warfarin at Sudlow site I of normal HSA and glycated HSA, with the glycated HSA typically having stronger binding for the fatty acids at this site. At Sudlow site II, direct competition was observed for all the fatty acids with l -tryptophan when using normal HSA, while glycated HSA gave no competition or positive allosteric interactions between these fatty acids and l -tryptophan. These data indicated that glycation can alter the interactions of drugs and fatty acids at specific binding sites on HSA. The results of this study should lead to a better understanding of how these interactions may change during diabetes and demonstrate how HPAC can be used to examine drug/solute–protein interactions in complex systems. [ABSTRACT FROM AUTHOR]

In the circulatory system, many drugs are reversibly bound to serum proteins such as human serum albumin (HSA) and alpha 1 -acid glycoprotein (AGP), resulting in both free and protein-bound fractions for these drugs. This report examined the use of microcolumns containing immobilized AGP for the measurement of free drug fractions by ultrafast affinity extraction and a two-dimensional affinity system. Several drugs known to bind AGP were used as models to develop and evaluate this approach. Factors considered during the creation of this method included the retention of the drugs on the microcolumns, the injection flow rate, the microcolumn size, and the times at which a second AGP column was placed on-line with the microcolumn. The final system had residence times of only 110–830 ms during sample passage through the AGP microcolumns and allowed free drug fractions to be determined within 10–20 min when using only 3–10 μL of sample per injection. This method was used to measure the free fractions of the model drugs at typical therapeutic levels in serum, giving good agreement with the results obtained by ultrafiltration. This approach was also used to estimate the binding constants for each drug with AGP in serum, even for drugs that had significant interactions with both AGP and HSA in such samples. These results indicated that AGP microcolumns could be used with ultrafast affinity extraction to measure free drug fractions in a label-free manner and to study the binding of drugs with AGP in complex samples such as serum. [ABSTRACT FROM AUTHOR]

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. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

• The binding of warfarin with modified human serum albumin (HSA) was studied. • Methylglyoxal and glyoxal were used to form advanced glycation end products on HSA. • Ultrafast affinity extraction measured the binding of warfarin at Sudlow site I of HSA. • Warfarin binding was not affected significantly when HSA was modified by glyoxal. • Methylglyoxal-HSA had up to a 1.3- to 1.4-fold increase in binding constant for warfarin. Ultrafast affinity extraction (UAE) and affinity microcolumns containing immobilized human serum albumin (HSA) were employed to evaluate the effect of advanced stage glycation on HSA and its binding to warfarin, a common site-specific probe for Sudlow site I of this protein. The modification of HSA by glyoxal (GO) and methylglyoxal (MGO) was considered, where GO and MGO are known to be important in the formation of many types of advanced glycation end products. Free drug fractions were measured by UAE for warfarin in solutions containing normal HSA or HSA that had been modified by GO or MGO at levels seen in serum during diabetes. The free fractions measured with the GO-modified HSA gave association equilibrium constants that ranged from 2.42–2.63 × 105 M−1 at pH 7.4 and 37 °C. These values were not significantly different from a value of 2.33 (±0.15) × 105 M−1 that was determined by the same method for warfarin with normal HSA. Similar studies using MGO-modified HSA gave association equilibrium constants for warfarin in the range of 3.07–3.31 × 105 M−1, which were 1.32- to 1.42-fold higher than the value seen for normal HSA (differences that were significant at the 95% confidence level). These results will be valuable in future binding studies based on affinity chromatography or other methods that employ warfarin as a probe to examine drug interactions at Sudlow site I of HSA and modified forms of this protein. This work also illustrates how UAE can be used, with analysis times of only minutes, to detect and measure small changes in the binding by drugs with unmodified or modified forms of a soluble binding agent or protein. [ABSTRACT FROM AUTHOR]

Background: The study of the interaction of a drug with plasma protein is very important because drug-protein binding plays an important role in determination of pharmacological and toxicological properties of drugs. Our study was designed to investigate the interaction between aceclofenac and bovine serum albumin (BSA) using fluorescence spectroscopy at different temperatures (298 and 308 K). Methods: Fluorescence spectroscopy was used to carry out the study. Fluorescence quenching constant was determined from Stern-Volmer equation. Van't Hoff equation was used to determine the thermodynamic parameters such as free energy (Δ G), enthalpy (Δ H), and entropy (Δ S). Results: The experimental data showed that the quenching of BSA by aceclofenac was due to a formation of a BSA-aceclofenac complex with probable involvement of both tryptophan and tyrosine residues of BSA. Dynamic quenching was shown for BSA by aceclofenac at the experimental conditions. The values of thermodynamic parameters indicated that the hydrophobic forces played major roles for BSA-aceclofenac complexation. The binding number ( n) was found to be ≈1 indicating that 1 mol of BSA bound with 1 mol of aceclofenac. The binding affinity of aceclofenac to BSA was calculated at different temperatures. It was shown that the binding constant decreased with increasing temperatures indicating that stability of the BSA-aceclofenac complex decreased with increasing temperatures. Conclusions: The interaction of aceclofenac with BSA was successfully explored using a fluorescence spectroscopic technique. [ABSTRACT FROM AUTHOR]

A method combining on-line immunoextraction microcolumns with high-performance affinity chromatography (HPAC) was developed and tested for use in examining drug–protein interactions with normal or modified proteins. Normal human serum albumin (HSA) and glycated HSA were used as model proteins for this work. High-performance immunoextraction microcolumns with sizes of 1.0–2.0 cm × 2.1 mm i.d. and containing anti-HSA polyclonal antibodies were developed and tested for their ability to bind normal HSA or glycated HSA. These microcolumns were able to extract up to 82–93% for either type of protein at 0.05–0.10 mL/min and had a binding capacity of 0.34–0.42 nmol HSA for a 1.0 cm × 2.1 mm i.d. microcolumn. The immunoextraction microcolumns and their adsorbed proteins were tested for use in various approaches for drug binding studies. Frontal analysis was used with the adsorbed HSA/glycated HSA to measure the overall affinities of these proteins for the drugs warfarin and gliclazide, giving comparable values to those obtained previously using similar protein preparations that had been covalently immobilized within HPAC columns. Zonal elution competition studies with gliclazide were next performed to examine the specific interactions of this drug at Sudlow sites I and II of the adsorbed proteins. These results were also comparable to those noted in prior work with covalently immobilized samples of normal HSA or glycated HSA. These experiments indicated that drug–protein binding studies can be carried out by using on-line immunoextraction microcolumns with HPAC. The same method could be used in the future with clinical samples and other drugs or proteins of interest in pharmaceutical studies or biomedical research. [ABSTRACT FROM AUTHOR]

1. This study compared the extent, affinity, and kinetics of drug binding to human serum albumin (HSA) and liver fatty acid binding protein (LFABP) using ultrafiltration and surface plasmon resonance (SPR). 2. Binding of basic and neutral drugs to both HSA and LFABP was typically negligible. Binding of acidic drugs ranged from minor (fu > 0.8) to extensive (fu < 0.1). Of the compounds screened, the highest binding to both HSA and LFABP was observed for the acidic drugs torsemide and sulfinpyrazone, and for β-estradiol (a polar, neutral compound). 3. The extent of binding of acidic drugs to HSA was up to 40% greater than binding to LFABP. SPR experiments demonstrated comparable kinetics and affinity for the binding of representative acidic drugs (naproxen, sulfinpyrazone, and torsemide) to HSA and LFABP. 4. Simulations based onin vitrokinetic constants derived from SPR experiments and a rapid equilibrium model were undertaken to examine the impact of binding characteristics on compartmental drug distribution. Simulations provided mechanistic confirmation that equilibration of intracellular unbound drug with the extracellular unbound drug is attained rapidly in the absence of active transport mechanisms for drugs bound moderately or extensively to HSA and LFABP. [ABSTRACT FROM AUTHOR]

High-performance affinity chromatography (HPAC) was used in a variety of formats to examine multi-site interactions between glimepiride, a third-generation sulfonylurea drug, and normal or in vitro glycated forms of the transport protein human serum albumin (HSA). Frontal analysis revealed that glimepiride interacts with normal HSA and glycated HSA at a group of high affinity sites (association equilibrium constant, or K a , 9.2–11.8 × 10 5 M −1 at pH 7.4 and 37 °C) and a group of lower affinity regions ( K a , 5.9–16 × 10 3 M −1 ). Zonal elution competition studies were designed and carried out in both normal- and reversed-role formats to investigate the binding by this drug at specific sites. These experiments indicated that glimepiride was interacting at both Sudlow sites I and II. Allosteric effects were also noted with R -warfarin at Sudlow site I and with tamoxifen at the tamoxifen site on HSA. The binding at Sudlow site I had a 2.1- to 2.3-fold increase in affinity in going from normal HSA to the glycated samples of HSA. There was no significant change in the affinity for glimepiride at Sudlow site II in going from normal HSA to a moderately glycated sample of HSA, but a slight decrease in affinity was seen in going to a more highly glycated HSA sample. These results demonstrated how various HPAC-based methods can be used to profile and characterize multi-site binding by a drug such as glimepiride to a protein and its modified forms. The information obtained from this study should be useful in providing a better understanding of how drug–protein binding may be affected by glycation and of how separation and analysis methods based on HPAC can be employed to study systems with complex interactions or that involve modified proteins. [ABSTRACT FROM AUTHOR]

In diabetes, the elevated levels of glucose in the bloodstream can result in the nonenzymatic glycation of proteins such as human serum albumin (HSA). This type of modification has been shown to affect the interactions of some drugs with HSA, including several sulfonylurea drugs that are used to treat type II diabetes. This study used high-performance affinity chromatography (HPAC) to examine the interactions of glipizide (i.e., a second-generation sulfonylurea drug) with normal HSA or HSA that contained various levels of in vitro glycation. Frontal analysis indicated that glipizide was interacting with both normal and glycated HSA through two general groups of sites: a set of relatively strong interactions and a set of weaker interactions with average association equilibrium constants at pH 7.4 and 37 °C in the range of 2.4-6.0 × 10 and 1.7-3.7 × 10 M, respectively. Zonal elution competition studies revealed that glipizide was interacting at both Sudlow sites I and II, which were estimated to have affinities of 3.2-3.9 × 10 and 1.1-1.4 × 10 M. Allosteric effects were also noted to occur for this drug between the tamoxifen site and the binding of R-warfarin at Sudlow site I. Up to an 18 % decrease in the affinity for glipizide was observed at Sudlow site I ongoing from normal HSA to glycated HSA, while up to a 27 % increase was noted at Sudlow site II. This information should be useful in indicating how HPAC can be used to investigate other drugs that have complex interactions with proteins. These results should also be valuable in providing a better understanding of how glycation may affect drug-protein interactions and the serum transport of drugs such as glipizide during diabetes. [ABSTRACT FROM AUTHOR]

A hybrid method was examined for increasing the binding capacity and activity of protein-based affinity columns by using a combination of protein cross-linking/modification and covalent immobilization. Various applications of this approach in the study of drug–protein interactions and in use with affinity microcolumns were considered. Human serum albumin (HSA) was utilized as a model protein for this work. Bismaleimidohexane (BMH, a homobifunctional maleimide) was used to modify and/or cross-link HSA through the single free sulfhydryl group that is present on this protein. Up to a 75–113% increase in protein content was obtained when comparing affinity supports that were prepared with BMH versus reference supports that were made by using only covalent immobilization. Several drugs that are known to bind HSA (e.g., warfarin, verapamil and carbamazepine) were further found to have a significant increase in retention on HSA microcolumns that were treated with BMH (i.e., a 70–100% increase in protein-based retention). These BMH-treated HSA microcolumns were used in chiral separations and in ultrafast affinity extraction to measure free drug fractions in drug/protein mixtures, with the latter method giving association equilibrium constants that had good agreement with literature values. In addition, it was found that the reversible binding of HSA with ethacrynic acid, an agent that can combine irreversibly with the free sulfhydryl group on this protein, could be examined by using the BMH-treated HSA microcolumns. The same hybrid immobilization method could be extended to other proteins or alternative applications that may require protein-based affinity columns with enhanced binding capacities and activities. [ABSTRACT FROM AUTHOR]

The study of drug–protein interactions can reveal the corresponding binding mechanisms, providing valuable information for the early phase drug development and development of new drugs. This article reviews the methods used for obtaining the binding parameters of drug–protein systems. The methods include equilibrium dialysis, high-performance affinity chromatography, capillary electrophoresis, spectroscopy, calorimetry, competition and displacement, mass spectrometry, fluorescence resonance energy transfer, and thermal stability shift analysis. Relevant parameters include the association constant, number of binding sites, thermodynamic properties, binding force types, binding site types, binding distances, changes in protein conformation, and changes in protein stability. In addition, the review also summarizes the principles, advantages, and limitations of each method in detail. The comparison of parameter information can not only guide method selection but also provide valuable reference information for in-depth exploration of drug–protein interaction mechanisms. [Display omitted] • Methods for the investigation of drug-protein interactions are reviewed. • The process of obtaining binding parameters for each method is discussed. • The methods are classified according to binding parameters. [ABSTRACT FROM AUTHOR]

Ultrafast affinity extraction and a multi-dimensional affinity system were developed for measuring free drug fractions at therapeutic levels. This approach was used to compare the free fractions and global affinity constants of several sulfonylurea drugs in the presence of normal human serum albumin (HSA) or glycated forms of this protein, as are produced during diabetes. Affinity microcolumns containing immobilized HSA were first used to extract the free drug fractions in injected drug/protein mixtures. As the retained drug eluted from the HSA microcolumn, it was passed through a second HSA column for further separation and measurement. Items that were considered during the optimization of this approach included the column sizes and flow rates that were used, and the time at which the second column was placed on-line with the HSA microcolumn. This method required only 1.0 μL of a sample per injection and was able to measure free drug fractions as small as 0.09–2.58% with an absolute precision of ±0.02–0.5%. The results that were obtained indicated that glycation can affect the free fractions of sulfonylurea drugs at typical therapeutic levels and that the size of this effect varies with the level of HSA glycation. Global affinity constants that were estimated from these free drug fractions gave good agreement with those predicted from previous binding studies or determined through a reference method. The same approach could be utilized with other drugs and proteins or modified binding agents of clinical or pharmaceutical interest. [ABSTRACT FROM AUTHOR]

Vinblastine (VLB), a cytotoxic alkaloid is used extensively against various cancer types and the crystal structure of its tubulin complex is already known. Multitarget affinity of vinblastine has been investigated and the nature of binding with biological receptors namely, duplex DNA and Human serum albumin (HSA) has been compared to the binding characteristics of its known complex with natural high affinity receptor tubulin using molecular docking and QM–MM calculations. VLB is found to interact with DNA as well as HSA protein, though, with weaker affinity as compared to tubulin. Analysis of various docked complexes revealed that the H-bonds and cation–pi bonds do not have significant contribution to the binding interactions and despite its large size, VLB remains in relaxed conformation and fits in the hydrophobic regions on the receptors. [ABSTRACT FROM AUTHOR]

High-performance affinity chromatography (HPAC) was utilized to examine the binding of very low density lipoprotein (VLDL) with drugs, using R/ S-propranolol as a model. These studies indicated that two mechanisms existed for the binding of R- and S-propranolol with VLDL. The first mechanism involved non-saturable partitioning of these drugs with VLDL, which probably occurred with the lipoprotein's non-polar core. This partitioning was described by overall affinity constants of 1.2 (±0.3) × 10 M for R-propranolol and 2.4 (±0.6) × 10 M for S-propranolol at pH 7.4 and 37 °C. The second mechanism occurred through saturable binding by these drugs at fixed sites on VLDL, such as represented by apolipoproteins on the surface of the lipoprotein. The association equilibrium constants for this saturable binding at 37 °C were 7.0 (±2.3) × 10 M for R-propranolol and 9.6 (±2.2) × 10 M for S-propranolol. Comparable results were obtained at 20 and 27 °C for the propranolol enantiomers. This work provided fundamental information on the processes involved in the binding of R- and S-propranolol to VLDL, while also illustrating how HPAC can be used to evaluate relatively complex interactions between agents such as VLDL and drugs or other solutes. [ABSTRACT FROM AUTHOR]

In this report we have studied the interaction of sulfadiazine (SD), which has recently been found to partially protect the amyloidosis, with human serum albumin (HSA) at physiological conditions of temperature and pH. We have employed several basic and advanced spectroscopic techniques such as UV, fluorescence, circular dichroism (CD) and Fourier transform infra-red (FTIR) spectroscopies. UV spectrum of native HSA was different from the spectrum of HSA in the presence of SD due to the complex formation between albumin and drug. Fluorescence quenching of HSA by SD at 280 nm was due to the formation of HSA-SD complex. The data were analyzed using Stern-Volmer (SV) and the quenching was found to be static with 1:1 binding ratio. Synchronous fluorescence spectra have shown a red shift and revealed that hydrophobicity around both Trp and Tyr residues was decreased. CD results have shown that the conformation of macromolecule remains undisturbed at low concentrations (up to 20 µM of the SD), though, a small change in the secondary structure from 20 to 75 µM of SD was observed followed by a large change and consequent unfolding on further increase in the drug concentration. Both synchronous and CD measurements were consistent to each other. From the FTIR measurement analysis it was found that amide I band also shifted which concluded that the conformational changes take place in the presence of SD. [ABSTRACT FROM AUTHOR]

Herein, we describe the development of a fluorescence-based high throughput assay to determine the small molecule binding towards human serum albumin (HSA). This innovative competition assay is based on the use of a novel fluorescent small molecule Red Mega 500 with unique spectroscopic and binding properties. The commercially available probe displays a large fluorescence intensity difference between the protein-bound and protein-unbound state. The competition of small molecules for HSA binding in the presence of probe resulted in low fluorescence intensities. The assay was evaluated with the library of pharmacological active compounds (LOPAC) small molecule library of 1,280 compounds identifying known high protein binders. The small molecule competition of HSA−Red Mega 500 binding was saturable at higher compound concentrations and exhibited IC values between 3 and 24 μM. The compound affinity toward HSA was confirmed by isothermal titration calorimetry indicating that the new protein binding assay is a valid high throughput assay to determine plasma protein binding. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

An improved solvent bar microextraction (SBME) combined with HPLC was applied to rapidly determine oleanolic acid (OA) and ursolic acid (UA) in Chinese medicinal herbs (CMHs), and to investigate drug-protein binding. Variables influencing SBME were investigated and optimized. Under optimal conditions, the linear ranges of 3.6-1,820 ng mL for OA and 4.2-2,080 ng mL for UA were obtained with square correlation coefficients of 0.9996 and 0.9997, respectively. The detection limits were 1.3 ng mL for OA and 1.5 ng mL for UA. The relative standard deviations were lower than 9.4 %. The protein-binding rates, the numbers of binding sites, and the binding constants of OA and UA were also obtained via the method. It has been demonstrated that SBME can not only be a simple, rapid and efficient sample preparation method for determination of active components from CMHs but also be a potential research protocol for protein-binding interactions. [ABSTRACT FROM AUTHOR]