Competitive binding of phenylbutazone and colchicine to serum albumin in multidrug therapy: A spectroscopic study

Human Serum Albumin Immobilized On Magnetizable Beads: A Rapid Method for Compound HSA Binding Study

Immobilized human serum albumin (HSA) was developed by coupling His-tagged HSA onto Ni2+-coupled magnetizable beads (HSA-beads), allowing the HSA to be easily removed from incubation components. The HSA-beads system provides a rapid and convenient method to study HSA compound binding. In this study, the HSA-beads system was characterized and evaluated as a tool for assessing compound HSA binding properties. The free fraction (fu) values of test compounds measured using HSA-beads were comparable to those determined by equilibrium dialysis (ED), which is commonly used to evaluate albumin binding in vitro. The equilibrium dissociation constant (Kd) values determined for a series of compounds using the HSA-beads method demonstrated good correlation with literature data. This good correlation also suggests that the binding of His-HSA to the beads does not impact the conformations of the two compound binding sites of HSA, as the range of compounds tested encompassed binding to both sites. Furthermore, the Kd values of representative compounds itraconazole and BIRT2584 that were difficult to assess using ED, due to significant cellulose membrane adsorption, were successfully determined. The HSA-beads provide several advantages over ED, such as simple preparation, short assay incubation duration, and the ability to quantify both free and HSA-bound species of the test compound, facilitated by the simple separation of HSA-beads from the solution phase using a magnetic field. These properties render the HSA-beads method suitable for high-throughput studies on compound HSA binding.

A flaw in applying the FRET technique to evaluate the distance between ligands and tryptophan residues in human serum albumin: Proposal of correction

Due to its primordial function as a drug carrier, human serum albumin (HSA) is extensively studied regarding its binding affinity with developing drugs. Förster resonance energy transfer (FRET) is frequently applied as a spectroscopic molecular ruler to measure the distance between the binding site and the ligand. In this work, we have shown that most of the published results that use the FRET technique to estimate the distance from ligands to the binding sites do not corroborate the crystallography data. By comparing the binding affinity of dansyl-proline with HSA and ovotransferrin, we demonstrated that FRET explains the quenching provoked by the interaction of ligands in albumin. So, why does the distance calculation via FRET not corroborate the crystallography data? We have shown that this inconsistency is related to the fact that a one-to-one relationship between donor and acceptor is not present in most experiments. Hence, the quenching efficiency used for calculating energy transfer depends on distance and binding constant, which is inconsistent with the correct application of FRET as a molecular ruler. We have also shown that the indiscriminate attribution of 2/3 to the relative orientation of transition dipoles of the acceptor and donor (κ²) generates inconsistencies. We proposed corrections based on the experimental equilibrium constant and theoretical orientation of transition dipoles to correct the FRET results.

Investigation of the separate and simultaneous bindings of warfarin and fenofibrate to bovine serum albumin

Lipid-lowering drugs are often taken with anticoagulant drugs in hyperlipidemia patients. Fenofibrate (FNBT) and warfarin (WAR) are common clinical lipid-lowering drugs and anticoagulant drugs, respectively. A study of binding affinity, binding force, binding distance, and binding sites was performed to determine the interaction mechanism between drugs and carrier proteins (bovine serum albumin, BSA), as well as their effects on BSA conformation. Both FNBT and WAR can form complexes with BSA by van der Waals force and hydrogen bonds. WAR had a stronger fluorescence quenching effect on BSA, a stronger binding affinity, and greater effects on BSA conformation than FNBT. According to fluorescence spectroscopy and cyclic voltammetry, co-administration of drugs decreased one drug's binding constant to BSA and increased its binding distance. This suggested that each drug's binding to BSA was disturbed by each other, as well as each drug's binding ability to BSA was altered by the other. It was demonstrated that co-administration of drugs had greater effects on the secondary structure of BSA and microenvironment polarity surrounding amino acid residues, using multiple spectroscopy techniques, such as ultraviolet spectroscopy, Fourier transform infrared spectroscopy, and synchronous fluorescence spectroscopy.

Interaction of acridinedione dye with a globular protein in the presence of site selective and site specific binding drugs: Photophysical techniques assisted by molecular docking methods

Photophysical investigations and molecular docking studies of photoinduced electron transfer (PET) based fluorophores of acridine family with a globular protein, Bovine Serum Albumin (BSA) bound to non-narcotic drugs like phenylbutazone (PB) and flufenamic acid (FA) were carried out in aqueous solution. PB and FA are site specific and site selective drugs, wherein PB predominantly binds at the site (I) whereas FA selectively orients towards site (II) of BSA. Acridinedione (AD) dyes, both resorcinol and dimedone based are hydrophobic in nature and exhibits a combination of both hydrophobic and hydrogen-bonding interactions that are based on the binding sites in BSA. The extent of displacement of AD from the binding sites of BSA by PB and FA are elucidated and established from variation in the fluorescence lifetime and relative amplitude distribution of free and dye bound in site (I) and site (II). The extent of binding affinity of PB-BSA and FA-BSA in the presence of AD is minimal when compared to other site I and II drugs. This is attributed to AD dye bound to several amino acid residues present in BSA such that the dye prefers multiple binding sites in BSA even in the presence of FA and PB. Further, the dye bound to several amino acid residues of BSA ascertains the combination of hydrogen-bonding, hydrophobic interactions, pi-pi and pi-alkyl interaction apart from the binding through sites (I) and (II) from molecular docking methods. The combination of fluorescence tools with molecular modelling techniques provides an excellent approach in determining the stability of these complexes containing competitive guest molecules in the presence of a fluorescence probe and the binding characteristics of dye in a micro heterogeneous environment.

Spectroscopic Studies of Quinobenzothiazine Derivative in Terms of the In Vitro Interaction with Selected Human Plasma Proteins. Part 1

Plasma proteins play a fundamental role in living organisms. They participate in the transport of endogenous and exogenous substances, especially drugs. 5-alkyl-12(H)-quino[3,4-b][1,4]benzothiazinium salts, have been synthesized as potential anticancer substances used for cancer treatment. Most anticancer substances generate a toxic effect on the human body. In order to check the toxicity and therapeutic dosage of these chemicals, the study of ligand binding to plasma proteins is very relevant. The present work presents the first comparative analysis of the binding of one of the 5-alkyl-12(H)-quino[3,4-b][1,4]benzothiazinium derivatives (Salt1) with human serum albumin (HSA), α-1-acid glycoprotein (AGP) and human gamma globulin (HGG), assessed using fluorescence, UV-Vis and CD spectroscopy. In order to mimic in vivo ligand-protein binding, control normal serum (CNS) was used. Based on the obtained data, the Salt1 binding sites in the tertiary structure of all plasma proteins and control normal serum were identified. Both the association constants (Ka) and the number of binding site classes (n) were calculated using the Klotz method. The strongest complex formed was Salt1-AGPcomplex (Ka = 7.35·104 and 7.86·104 mol·L-1 at excitation wavelengths λex of 275 and 295 nm, respectively). Lower values were obtained for Salt1-HSAcomplex (Ka = 2.45·104 and 2.71·104 mol·L-1) and Salt1-HGGcomplex (Ka = 1.41·104 and 1.33·104 mol·L-1) at excitation wavelengths λex of 275 and 295 nm, respectively, which is a positive phenomenon and contributes to the prolonged action of the drug. Salt1 probably binds to the HSA molecule in Sudlow sites I and II; for the remaining plasma proteins studied, only one binding site was observed. Moreover, using circular dichroism (CD), fluorescence and UV-Vis spectroscopy, no effect on the secondary and tertiary structures of proteins in the absence or presence of Salt1 has been demonstrated. Despite the fact that the conducted studies are basic, from the scientific point of view they are novel and encourage further in vitro and in vivo investigations. As a next part of the study (Part 2), the second new synthetized quinobenzothiazine derivative (Salt2) will be analyzed and published.

Interaction of Conazole Pesticides Epoxiconazole and Prothioconazole with Human and Bovine Serum Albumin Studied Using Spectroscopic Methods and Molecular Modeling

The interactions of epoxiconazole and prothioconazole with human serum albumin and bovine serum albumin were investigated using spectroscopic methods complemented with molecular modeling. Spectroscopic techniques showed the formation of pesticide/serum albumin complexes with the static type as the dominant mechanism. The association constants ranged from 3.80 × 104-6.45 × 105 L/mol depending on the pesticide molecule (epoxiconazole, prothioconazole) and albumin type (human or bovine serum albumin). The calculated thermodynamic parameters revealed that the binding of pesticides into serum albumin macromolecules mainly depended on hydrogen bonds and van der Waals interactions. Synchronous fluorescence spectroscopy and the competitive experiments method showed that pesticides bind to subdomain IIA, near tryptophan; in the case of bovine serum albumin also on the macromolecule surface. Concerning prothioconazole, we observed the existence of an additional binding site at the junction of domains I and III of serum albumin macromolecules. These observations were corroborated well by molecular modeling predictions. The conformation changes in secondary structure were characterized by circular dichroism, three-dimensional fluorescence, and UV/VIS absorption methods.

Influence of antioxidant flavonoids quercetin and rutin on the in-vitro binding of neratinib to human serum albumin

This study was designed to examine the interaction of neratinib (NRB) with human serum albumin (HSA) in presence of flavonoids quercetin and rutin. Both quercetin and rutin can compete with NRB to bind to HSA and displace NRB from its binding site. The interaction mechanism was studied with several spectroscopic techniques and molecular docking. Static fluorescence quenching mechanism was observed on interaction of HSA with NRB. van der Waals force and hydrogen bond were involved in the HSA-NRB interaction as per the results of thermodynamic parameters. Further, the conformational changes were observed in the HSA on its interaction with NRB. Interaction of NRB with HSA in presence of quercetin and rutin resulted in changes in the binding constants of HSA-NRB suggesting some impact on the binding of NRB in the presence of flavonoids.

Spectrofluorimetric analysis of the binding of a target molecule to serum albumin: tricky aspects and tips

Protein binding heavily modulates drug activity. Therefore, the binding features need to be elucidated when chemistry researchers study new molecules (metal complexes) to be used as drugs. This paper concerns the experimental and data treatment aspects of the mechanistic analysis of the binding to a fluorescent protein (the golden standard serum albumin) by using direct fluorescence titrations. Fluorescence data are not rarely only qualitatively used, neglecting further treatments which could offer a precious detailed picture of the behavior of the drug. We aim to spread a mechanistic approach, discussing the critical aspects for correctly designing the experiments and treating the data. The researcher may confirm adduct formation and evaluate binding constants (Stern-Volmer K_SV or other types of K). Also, we discuss here, with the help of literature examples, the correct use of temperature dependence of K to extract thermodynamic parameters, comment on enthalpy-entropy compensation, together with the use of synchronous spectra and exchange experiments to gain information on the binding type and site. We think that this tutorial/critical synopsis can be of help for the increasing community dealing with these experiments, which are valuable but often much more tricky than it might appear at first sight.

Characterizing the Binding of Angiotensin Converting Enzyme I Inhibitory Peptide to Human Hemoglobin: Influence of Electromagnetic Fields

Background:

Drug-protein complexes is one of the crucial factors when analyzing the pharmacokinetics and pharmacodynamics of a drug because they can affect the excretion, distribution, metabolism and interaction with target tissues.

Objectives:

The aim of this study was to investigate the interaction of human hemoglobin (Hb) and angiotensin I converting enzyme inhibitory peptide (ACEIP) in the absence and presence of different- frequency electromagnetic fields (EMF).

Methods:

Various spectroscopic methods like fluorescence spectroscopy, ultraviolet, circular dichroism and conductometry techniques were applied to investigate Hb-ACEIP interaction in the absence and presence of EMF.

Result:

The presented spectroscopic studies indicated that EMF changed the interaction between Hb and ACEIP. The a-helix content of Hb decreased upon binding to ACEIP and conductivity of the solution enhanced upon binding. Based on Stern-Volmer equations, it could be stated that the Hb-ACEIP affinity was higher in the presence of EMF.

Conclusion:

It can be concluded that for patients who use the drug to control blood pressure, a low-frequency electromagnetic field would have a positive effect on the uptake of the drug.

Poziotinib and bovine serum albumin binding characterization and influence of quercetin, rutin, naringenin and sinapic acid on their binding interaction

Serum albumin is the major transporter protein present in systemic circulation and the ability to transport ligands can be influenced in presence of other ligands. This interaction can influence the pharmacodynamic and pharmacokinetic property of certain ligands. Spectroscopic and molecular docking studies were conducted to understand the poziotinib binding interaction to bovine serum albumin (BSA). Further, influence of different flavonoids (quercetin, rutin, naringenin and sinapic acid) on displacing poziotinib from BSA binding sites was also studied. The BSA and poziotinib followed a static quenching mechanism as the Stern-Volmer constant showed decrease (7.6 × 10⁴-6.0 × 10⁴) when the temperature increased from 298 K to 310 K. The BSA and poziotinib interaction was spontaneous and enthalpy driven. Involvement of Van der Waals forces and hydrogen bonding in the binding interaction was suggested on the basis of thermodynamic study results. Conformational changes were suggested in the BSA on its interaction with poziotinib based on fluorescence experimental data. The binding constant for BSA-poziotinib showed a maximum decrease in presence of quercetin followed by naringenin, rutin and sinapic acid respectively. Site displacement studies suggested binding of poziotinib site I of BSA.

Induced CD of iron(ii) clathrochelates: sensing of the structural and conformational alterations of serum albumins

An ability of inherently achiral macrobicyclic metal complexes iron(ii) clathrochelates to acquire an induced CD (ICD) output in the visible spectral range upon interaction with bovine serum albumin (BSA) was recently discovered. In the present work, the CD-reporting properties of iron(ii) clathrochelates to proteins and the thermodynamic parameters of their binding to albumins are evaluated. It is shown that iron(ii) clathrochelates functionalized by six ribbed carboxyphenylsulfide groups are able to discriminate between serum albumins of relative structure (here human and bovine albumins) by giving distinct ICD spectra. Besides, by the variation of the shape and intensity of CD bands, these cage metal complexes reflect the pH-triggered alterations of the tertiary structure of albumins. The constitutional isomerism (ortho-, meta- or para-isomers) of terminal carboxyphenylsulfide groups of iron(ii) clathrochelates strongly affects both the character of their ICD output upon binding with proteins and the parameters of the formed guest-host associates. Using isothermal titration calorimetry, it was determined that cage metal complexes bearing meta- and ortho-isomers of carboxyphenylsulfide groups possess higher association constants (Ka ∼ 2 × 104 M-1) and clathrochelate-to-BSA binding ratios (n = 2) than the para-isomer (Ka ∼ 5 × 103 M-1, n = 1). The iron(ii) clathrochelates are suggested to be potential molecular three-dimensional scaffolds for the design of CD-sensitive reporters able to recognize specific elements of protein surfaces.

Chemotaxonomic studies on natural population of Gloriosa superba (L.) collected from Gangetic plain (India) and their invitro antigout activity for the identification of elite germplasm(s)

ETHNOPHARMACOLOGICAL RELEVANCE

Gloriosa superba L. (Colchicaceae) is used in the treatment of gout and rheumatism as a traditional medicine dates back to 1810. It has also been used as ethnobotanical and folklore medicine to induce abortion/vaginal poison.

AIM OF STUDY

The present study was carried out to identify the chemical variation existing in the major alkaloid metabolite (colchicine) in a threatened species, Gloriosa superba L. and is correlated with invitro antigout activity.

MATERIAL AND METHOD

The samples (tuber) were collected from their natural locations in Gangetic plain of India. HPLC-PDA quantification of colchicine was done on C₁₈ column at 245 nm and invitro antigout activity was analyzed by inhibition of protein denaturation, DPPH and Hydroxyl radical scavenging assay.

RESULTS

The colchicine content within the 29 samples ranges from 0.021 to 0.665% and the maximum contents was in NBG-10 from Kanth (U.P). Such high colchicine (0.665%) containing natural population of G. superba is reported for the first time in Indian population. Four chemotypes viz. NBG-10, NBG-120, NBG-126 and NBG-88 were selected on the basis of colchicine content for invitro antigout activity. NBG-10 was separated from rest of the population exhibiting the most promising activity with high colchicine content.

CONCLUSION

The outcomes will be helpful in the identification of elite chemotype for herbal product development and quality check of metabolites in raw material. The study will also support the site-specific commercial cultivation to meet out the industrial demand as well as income generation to farmers.

Evaluation of competitive binding interaction of neratinib and tamoxifen to serum albumin in multidrug therapy

Co-administration of two drugs to obtain a therapeutic goal is a common practice clinically and for effective use of drug therapy. However, the co-administration can sometimes cause adverse effects due to pharmacokinetic drug interactions. Breast Cancer treatment regimen include tyrosine kinase inhibitor neratinib (NRB) and/or tamoxifen (TMX). In this study neratinib and tamoxifen interaction with bovine serum albumin (BSA) and human serum albumin (HSA) individually and in combination using fluorescence spectroscopy was studied. The aim of this study was to find out whether there is a possibility of either of the two drugs interfering in the plasma protein binding of the other drug. Subdomain IIA of both the BSA and HSA was found to bind tamoxifen and neratinib. The λ_ex = 280 nm and 295 nm were used for the analysis of neratinib-SA, tamoxifen-SA, neratinib: SA in presence of constant concentration of tamoxifen and similarly tamoxifen-SA in presence of constant concentration of neratinib. The interaction study of the binary and the ternary systems suggest that neratinib doesn't affect the interaction between SA and tamoxifen. In contrast, the interaction between neratinib and SA was affected by tamoxifen. The binding constant and quenching constant values suggest that tamoxifen dislodges neratinib from its serum albumin complex whereas neratinib doesn't affect the interaction between SA and tamoxifen. Thus, it was concluded from the results the study that during simultaneous administration of neratinib and tamoxifen, their competition for the SA binding sites should be taken into account.

A critical view on the analysis of fluorescence quenching data for determining ligand-protein binding affinity

The past decade has seen an increase in the number of research papers on ligand binding to proteins based on fluorescence spectroscopy. In most cases, determination of the binding affinity is made by analyzing the quenching of protein fluorescence induced by the ligand. However, many such articles, even those published in reputed journals, suffer from several mistakes with regard to analysis of fluorescence quenching data. Using the binding of phenylbutazone to human serum albumin as a model, we consider some of these mistakes and show how they affect the values of the association constant. In particular, the failure to correct for the inner filter effect and the use of unsuitable equations are discussed. Ligand binding data presented in these articles should be treated with caution, especially in the absence of data from complementary techniques.

Study on the interaction of anti-inflammatory drugs with human serum albumin using molecular docking, quantitative structure-activity relationship, and fluorescence spectroscopy

The interaction of 14 anti-inflammatory drugs with human serum albumin (HSA) was investigated using fluorescence quenching, molecular docking studies, and quantitative structure-activity relationship (QSAR) methodology. Binding of anti-inflammatory drugs to HSA plays a fundamental role in their transport, distribution, delivery, and elimination. Binding constants of these drugs to HSA, obtained using the fluorescence quenching method, were within the range 0.01 × 10⁴  M^-1 (acetaminophen) to 1881.05 × 10⁴  M^-1 (meloxicam). Binding sites and binding constants of these anti-inflammatory drugs were estimated using molecular docking. Inspection of the obtained values for docking score, logK_b and K_b , showed that the drugs in this data set have a relatively strong binding constant for HSA. QSAR modelling was applied for binding constants obtained from fluorescence quenching and theoretical molecular descriptors. This modelling led to a linear two-parameter model with a correlation coefficient of 0.95 and adequate robustness. The descriptor results showed the importance of a bonding network and electronegativity as the discriminative structural factors in binding affinity for the HSA molecule.

Fungicide Tebuconazole Influences the Structure of Human Serum Albumin Molecule

Studies of interactions between pesticides and target mammalian proteins are important steps toward understanding the pesticide's toxicity. Using calorimetric and spectroscopic methods, the interaction between triazole fungicide tebuconazole and human serum albumin has been investigated. The spectroscopic techniques showed that fluorescence quenching of human serum albumin by tebuconazole was the result of the formation of tebuconazole/human serum albumin complex with the static type as the dominant mechanism. The association constant was found to be 8.51 × 103 L/mol. The thermodynamic parameters were obtained as ΔH = -56.964 kJ/mol, ΔS = -115.98 J/mol·K. The main active interactions forming the tebuconazole/human serum albumin complex were identified as the interplay between hydrogen bonds and/or van der Waals forces, based on thermodynamic experiments. These binding modes were corroborated well by the predictions of molecular modeling. Hydrogen bonding of tebuconazole with Arg222, Ala215 and Ala291 of human serum albumin played a relevant role in binding. The conformation changes in secondary structure were characterized by circular dichroism and 3D fluorescence spectra.

New insights into the binding behavior of lomefloxacin and human hemoglobin using biophysical techniques: binary and ternary approaches

Demonstrates the overlap that had been induced between the fluorescence emission spectrum of Hb and the absorption spectrum of drugs, which has proved that there is a high probability to the occurrence of energy transfer from Hb and LMF in the absence and presence of NRF.

Interaction of the Fungicide Tebuconazole with Human Serum Albumin: A Preliminary Study

The interactions between the fungicide tebuconazole and human serum albumin were investigated using fluorescence and circular dichroism spectroscopies. The experimental results showed that the fluorescence quenching of the protein by the tebuconazole molecule was a result of the formation of a ligand-protein complex with a binding constant of 8.51×103 l.mol−1 and the number of binding sites in the macromolecule was close to 1. These findings demonstrated the fact that although the binding affinity of tebuconazole to the protein may be slight, it was very similar to other triazole fungicides. In addition, tebuconazole stabilized the α-helical secondary structure of the human serum albumin due to the increase of the α-content in the protein macromolecule.

The role of topically applied l-ascorbic acid in ex-vivo examination of burn-injured human skin

Wound treatment and healing is complex and is comprised of an elaborate set of processes including cellular, spectroscopic and biochemical ones as well as the "reaction" of local tissue to thermal injury. Vitamin C as l-ascorbic acid (LA) prevents injurious effects of oxidants because it reduces reactive oxygen species to stable molecules, it becomes oxidized to the short-lived ascorbyl radical. As a result, antioxidant treatment may contribute to minimizing injury in burn patients. The aim of this study is to assess changes in molecular structure of collagen extracted from human epidermis burn wound scab during incubation of the epidermis in l-ascorbic acid solution. The study will be performed using FTIR and FT Raman spectroscopies. During this research it was observed that the intensity of Raman peaks increased where healing was being modified by LA. The intensity of the amide III band at 1247cm^-1 relative to the intensity at 1326cm^-1 was used to test tissue repair degree at the incision site. FTIR spectra were recorded from frozen specimens of serum modified by LA; an analysis of shifts in the amide I band position was conducted. The appearance of a new band for frozen samples modified by LA was observed around 1149-1220cm^-1. The above conclusions confirmed the creation of hydrogen bonds between NH stretch and CO. Samples being incubated in solutions of l-ascorbic acid demonstrated the absence of electrophoretic bands of albumin. Alterations in the surface of the skin incubated in l-ascorbic acid were investigated with the use of Scanning Electron Microscopy (SEM). A decrease in external symptoms of burn injury was noted in the damaged epidermis incubated in l-ascorbic acid.

Competitive binding of (-)-epigallocatechin-3-gallate and 5-fluorouracil to human serum albumin: A fluorescence and circular dichroism study

Combination therapy with more than one therapeutic agent can improve therapeutic efficiency and decrease drug resistance. In this study, the interactions of human serum albumin (HSA) with individual or combined anticancer drugs, (-)-epigallocatechin-3-gallate (EGCG) and 5-fluorouracil (FU), were investigated by fluorescence and circular dichroism (CD) spectroscopy. The results demonstrated that the interaction of EGCG or FU with HSA is a process of static quenching and EGCG formed a more stable complex. The competitive experiments of site markers suggested that both anti-carcinogens mainly bound to site I (subdomain IIA). The interaction forces which play important roles in the binding process were discussed based on enthalpy and entropy changes. Moreover, the competition binding model for a ternary system was proposed so as to precisely calculate the binding parameters. The results demonstrated that one drug decreased the binding affinity of another drug with HSA, resulting in the increasing free drug concentration at the action sites. CD studies indicated that there was an alteration in HSA secondary structure due to the binding of EGCG and FU. It can be concluded that the combination of EGCG with FU may enhance anticancer efficacy. This finding may provide a theoretical basis for clinical treatments.

Effects of non-enzymatic glycation in human serum albumin. Spectroscopic analysis

Human serum albumin (HSA), transporting protein, is exposed during its life to numerous factors that cause its functions become impaired. One of the basic factors --glycation of HSA--occurs in diabetes and may affect HSA-drug binding. Accumulation of advanced glycation end-products (AGEs) leads to diseases e.g. diabetic and non-diabetic cardiovascular diseases, Alzheimer disease, renal disfunction and in normal aging. The aim of the present work was to estimate how non-enzymatic glycation of human serum albumin altered its tertiary structure using fluorescence technique. We compared glycated human serum albumin by glucose (gHSA(GLC)) with HSA glycated by fructose (gHSA(FRC)). We focused on presenting the differences between gHSA(FRC) and nonglycated (HSA) albumin used acrylamide (Ac), potassium iodide (KI) and 2-(p-toluidino)naphthalene-6-sulfonic acid (TNS). Changes of the microenvironment around the tryptophan residue (Trp-214) of non-glycated and glycated proteins was investigated by the red-edge excitation shift method. Effect of glycation on ligand binding was examined by the binding of phenylbutazone (PHB) and ketoprofen (KP), which a primary high affinity binding site in serum albumin is subdomain IIA and IIIA, respectively. At an excitation and an emission wavelength of λex 335nm and λem 420nm, respectively the increase of fluorescence intensity and the blue-shift of maximum fluorescence was observed. It indicates that the glycation products decreases the polarity microenvironment around the fluorophores. Analysis of red-edge excitation shift method showed that the red-shift for gHSA(FRC) is higher than for HSA. Non-enzymatic glycation also caused, that the Trp residue of gHSA(FRC) becomes less accessible for the negatively charged quencher (I(-)), KSV value is smaller for gHSA(FRC) than for HSA. TNS fluorescent measurement demonstrated the decrease of hydrophobicity in the glycated albumin. KSV constants for gHSA-PHB systems are higher than for the unmodified serum albumin, while KSV values for gHSA-KP systems are only slightly lower than that obtained for HSA-KP. The affinity of PHB to the glycated HSA is stronger than to the non-glycated in the first class binding sites within subdomain IIA, in the vicinity of Trp-214. Ketoprofen bound to unmodified human serum albumin stronger than for glycated albumin and one class of binding sites is observed (Scatchard linear plots).

Systematic investigation of the toxic mechanism of PFOA and PFOS on bovine serum albumin by spectroscopic and molecular modeling

Perfluorinated compounds (PFCs), an emerging class of globally environmental contaminations, pose a great threat to humans with wide exposure from food and other potential sources. The effects of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on bovine serum albumin (BSA) under normal physiological conditions were characterized by fluorescence, UV-Vis absorption, Fourier transform infrared (FT-IR) spectroscopy and molecular docking methods. The fluorescence study suggested that the fluorescence quenching of BSA by PFCs was a static procedure forming a PFCs-BSA complex. The negative values of enthalpy change (ΔH) and entropy change (ΔS) indicated that van der Waals forces and hydrogen bonds were the dominant intermolecular forces in the binding of PFCs to BSA. The displacement experiments of site markers and molecular docking revealed that the binding of PFOA to BSA took place in sub-domain IIA (Sudlow site I) whereas PFOS was mainly located in the sub-domain IIIA (Sudlow site II) and partially bound into site I. Furthermore, the results of UV-Vis and FT-IR spectra demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of PFCs. These results indicated that PFCs indeed impact the conformation of BSA and PFOS was more toxic than PFOA, which were supported by theoretical molecular modeling methods.

Supramolecular interaction of 6-shogaol, a therapeutic agent of Zingiber officinale with human serum albumin as elucidated by spectroscopic, calorimetric and molecular docking methods

BACKGROUND

6-Shogaol, one of the main bioactive constituents of Zingiber officinale has been shown to possess various therapeutic properties. Interaction of a therapeutic compound with plasma proteins greatly affects its pharmacokinetic and pharmacodynamic properties.

PURPOSE

The present investigation was undertaken to characterize the interaction between 6-shogaol and the main in vivo transporter, human serum albumin (HSA).

METHODS

Various binding characteristics of 6-shogaol-HSA interaction were studied using fluorescence spectroscopy. Thermal stability of 6-shogaol-HSA system was determined by circular dichroism (CD) and differential scanning calorimetric (DSC) techniques. Identification of the 6-shogaol binding site on HSA was made by competitive drug displacement and molecular docking experiments.

RESULTS

Fluorescence quench titration results revealed the association constant, Ka of 6-shogaol-HSA interaction as 6.29 ± 0.33 × 10(4) M(-1) at 25 ºC. Values of the enthalpy change (-11.76 kJ mol(-1)) and the entropy change (52.52 J mol(-1) K(-1)), obtained for the binding reaction suggested involvement of hydrophobic and van der Waals forces along with hydrogen bonds in the complex formation. Higher thermal stability of HSA was noticed in the presence of 6-shogaol, as revealed by DSC and thermal denaturation profiles. Competitive ligand displacement experiments along with molecular docking results suggested the binding preference of 6-shogaol for Sudlow's site I of HSA.

CONCLUSION

All these results suggest that 6-shogaol binds to Sudlow's site I of HSA through moderate binding affinity and involves hydrophobic and van der Waals forces along with hydrogen bonds.

Biophysical study on the interaction of etomidate and the carrier protein in vitro

Etomidate is a unique drug used for induction of general anesthesia and sedation, and is usually used through intravenous injection clinically. Before targeting to the receptor, etomidate binds proteins in blood when it comes into veins. Thus to study the interaction of etomidate and serum albumin would be of great toxicological and pharmacological importance. In this study, the interaction between etomidate and human serum albumin (HSA) was studied using fluorescence spectroscopy, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), circular dichroism (CD) spectroscopy, site maker displacement and molecular modeling methods. Investigations of the binding constant (K = 3.55 × 10(5 )M(-1), 295 K), the number of binding sites (n = 1.16), thermodynamic parameters (ΔG = 3.13 × 10(4 )J·mol(-1), ΔS = 364 J·mol(-1)·K(-1) and ΔH = -6.85 × 10(5 )J·mol(-1)) for the reaction and changes to the binding sites and conformation in HSA in response to etomidate were presented. Results show that etomidate can bind HSA tightly through electrostatic forces, and the protein skeleton conformation and secondary structure changes thereby. This is the first spectroscopic report for etomidate-HSA interactions which illustrates the complex nature of this subject.

Tyrosine fluorescence probing of the surfactant-induced conformational changes of albumin

Tyrosine fluorescence in native proteins is known to be effectively quenched, whereas its emission increases upon proteins’ unfolding.

An investigation on new ruthenium(II) hydrazone complexes as anticancer agents and their interaction with biomolecules

A new set of ruthenium(II) hydrazone complexes [Ru(H)(CO)(PPh3)2(L)] (1) and [RuCl2(DMSO)2(HL)] (2), with triphenyl phosphine or DMSO as co-ligands was synthesized by reacting benzoyl pyridine furoic acid hydrazone (HL) with [Ru(H)(Cl)(CO)(PPh3)3] and [RuCl2(DMSO)4]. The single crystal X-ray data of complexes 1 and 2 revealed an octahedral geometry around the ruthenium ion in which the hydrazone is coordinated through ON and NN atoms in complexes 1 and 2 respectively. The interaction of the compounds with calf thymus DNA (CT-DNA) has been estimated by absorption and emission titration methods which indicated that the ligand and the complexes interacted with CT-DNA through intercalation. In addition, the DNA cleavage ability of these newly synthesized ruthenium complexes assessed by an agarose gel electrophoresis method demonstrated that complex 2 has a higher DNA cleavage activity than that of complex 1. The binding properties of the free ligand and its complexes with bovine serum albumin (BSA) protein have been investigated using UV-visible, fluorescence and synchronous fluorescence spectroscopic methods which indicated the stronger binding nature of the ruthenium complexes to BSA than the free hydrazone ligand. Furthermore, the cytotoxicity of the compounds examined in vitro on a human cervical cancer cell line (HeLa) and a normal mouse embryonic fibroblasts cell line (NIH 3T3) revealed that complex 2 exhibited a superior cytotoxicity than complex 1 to the cancer cells but was less toxic to the normal mouse embryonic fibroblasts under identical conditions.

The Spectroscopy Study of the Binding of an Active Ingredient of Dioscorea Species with Bovine Serum Albumin with or without Co(2+) or Zn(2+)

Diosgenin (DIO) is the active ingredient of Dioscorea species. The interaction of DIO with bovine serum albumin (BSA) was investigated through spectroscopic methods under simulated physiological conditions. The fluorescence quenching data revealed that the binding of DIO to BSA without or with Co(2+) or Zn(2+) was a static quenching process. The presence of Co(2+) or Zn(2+) both increased the static quenching constants K SV and the binding affinity for the BSA-DIO system. In the sight of the competitive experiment and the negative values of ΔH (0) and ΔS (0), DIO bound to site I of BSA mainly through the hydrogen bond and Van der Waals' force. In addition, the conformational changes of BSA were studied by Raman spectra, which revealed that the secondary structure of BSA and microenvironment of the aromatic residues were changed by DIO. The Raman spectra analysis indicated that the changes of conformations, disulfide bridges, and the microenvironment of Tyr, Trp residues of BSA induced by DIO with Co(2+) or Zn(2+) were different from that without Co(2+) or Zn(2+).

Natural occurrence of organofluorine and other constituents from Streptomyces sp. TC1

Antioxidant-directed fractionation of an ethyl acetate extract of Streptomyces sp. TC1 resulted in the isolation of a novel secondary metabolite with an aromatic organofluorine scaffold (1), an atypical tripod-type triallyl phenol (2), and a leucine residue comprised polyamine (3). Their structures were established by comprehensive spectroscopic analysis of 1D and 2D NMR data, and compound 1 was confirmed by (19)F NMR and single-crystal X-ray diffraction studies. The absolute configuration of compound 3 was assigned by comparison of its ECD spectra and quantum chemical ECD calculations. Of these, compound 1 displayed antioxidant and DNA and protein binding properties.

Axially chiral biscarbazoles and biological evaluation of the constituents from Murraya koenigii

Chemical investigation of the fruit pulp of Murraya koenigii resulted in the identification of two new dimeric carbazole alkaloids, bisgerayafoline D (1) and bismahanimbinol (2) along with four known alkaloids, bispyrayafoline (3), O-methyl mahanine (4), O-methyl mukonal (5), and mahanine (6). Structures of 1-6 were determined with the aid of UV, IR, Mass and extensive NMR spectroscopic studies. Absolute configurations of biaryls in 1 and 2 were assigned using a combination of computational Circular Dichroism (CD) and experimental electronic CD spectroscopic data. Compounds 1-6 were evaluated for anti-oxidant, anti-α-glucosidase, DNA binding, protein interactions and cytotoxic activities. Among all the isolates, mahanine (6) was found to exhibit significant radical scavenging and α-glucosidase inhibitory activities. Compound 6 was also found to be active in cytotoxicity assay against three human cancer cell lines HeLa, HCT116, AGS and this compound was weakly active against normal mouse embryonic fibroblasts (NIH3T3).

Effects of etravirine on the pharmacokinetics and pharmacodynamics of warfarin in rats

BACKGROUND AND PURPOSE

Warfarin is often used with etravirine (ETV) to prevent HIV-related thromboembolic events. As both warfarin and ETV bind to plasma proteins and are metabolized by hepatic cytochrome P450s, they are likely to interact. Hence, we evaluated the effect of ETV on the pharmacokinetics and blood clotting time of racemic warfarin in rats.

EXPERIMENTAL APPROACH

Two groups of male Sprague-Dawley rats, in which the jugular vein had been cannulated, were studied. The control group (n = 10) received 1 mg·kg(-1) racemic warfarin i.v., and the test group (n = 13) 1 mg·kg(-1) of racemic warfarin followed by 25 mg·kg(-1) ETV i.v. Serial blood samples were collected for up to 144 h and the blood clotting time (calculated as international normalized ratio [INR]) measured in blood plasma at each sample point. Plasma concentrations of R-warfarin, S-warfarin, R-7-hydroxywarfarin and S-7-hydroxywarfarin were measured by a LC/MS/MS method using a chiral lux cellulose-1 column. Pharmacokinetic parameters were analysed using non-compartmental methods.

KEY RESULTS

ETV significantly increased, by threefold, the systemic clearance and volume of distribution of S-warfarin, but not those of R-warfarin. ETV decreased the total AUC of warfarin, but had no effect on its elimination half-life. ETV also increased the systemic clearance of both R-7-hydroxywarfarin and S-7-hydroxywarfarin but only increased the volume of distribution of R-7-hydroxywarfarin. Interestingly, the effect of warfarin on blood clotting time (INR) was significantly increased in the presence of etravirine.

CONCLUSION AND IMPLICATIONS

Our data suggest that etravirine may potentiate the anticoagulant effect of warfarin and this could have clinical significance.

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

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