Spectroscopic Study on the Interaction between Naphthalimide-Polyamine Conjugates and Bovine Serum Albumin (BSA)

Modulation of protein-ligand interactions in the presence of ZIF-8: Spectroscopy and molecular dynamics simulation

In this paper, we investigated the protein-ligand interactions in the presence of ZIF-8 using multi-spectroscopic approaches and molecular dynamics simulation. Fluorescence experiments and molecular docking results showed that ZIF-8 did not change the type of quenching and interaction force between ciprofloxacin (CIP) and human serum albumin (HSA), but made the binding constant of HSA-CIP to be smaller, suggesting that ZIF-8 maybe accelerate the dissociation of CIP from HSA-CIP complex. Moreover, the effect of ZIF-8 on the physiological function of HSA was explored. Multi-spectroscopic methods revealed that ZIF-8 did not significantly alter the microenvironment of amino acid groups, but cause a slight decrease in the content of α-helical conformation, and a sparse and flexible structure of the protein backbone. These peculiarities might lead to the diminution of HSA's ability to control drugs. In short, ZIF-8 might enhance drug effect due to affecting the binding of drugs to proteins. However, the present study is only a preliminary investigation of the suitability of ZIF-8 as a drug carrier in vitro, and subsequent in vivo experimental studies will be required to further confirm the idea.

Novel vanadyl complexes synthesis, characterization and interactions with bovine serum albumin-effects on STZ- diabetes rats

Drug-protein interactions are essential since most administered drugs bind abundantly and reversibly to serum albumin and are delivered mainly as a complex with protein. The nature and strength of drug-protein interactions have a big impact on how a drug works biologically. The binding parameters are useful in studying the pharmacological response of drugs and the designing of dosage forms. Serum albumin is regarded as optimal model for in vitro research on drug-protein interaction since it is the main protein that binds medicines and other physiological components. In this perspective, binary complex have been synthesized and characterized, from vanadium metal and acetylacetone(4,4,4-trifluoro-1-(2-theonyl)-1,3-butanedione). Imidazole, 2-Methyl-imidazole, and 2-Ethyl-imidazole auxiliary ligands were employed for the synthesis of ternary complexes. Additionally, UV absorption and fluorescence emission spectroscopy were used to examine the binding interactions between vanadium complexes and Bovine Serum Albumin. The outcomes of the binding studies and spectral approaches were in strong agreement with one another. These complexes upon inoculation into diabetes-induced Wistar rats stabilized their serum glucose levels within 3 days. From various studies, it was discovered that the ordering of glucose-lowering actions of these metal complexes were equivalent. The vanadium ternary metal complex derived from (4,4,4-trifluoro-1-(2-theonyl)-1,3-butanedione) and imidazole as ligands is the best among the other metal vanadium complexes.

Spectroscopic and in silico evaluation of hesperetin, aglycone flavanone, as a prospective regulatory ligand for human salivary α-amylase

The insight into the binding mechanism of hesperetin, an aglycone flavanone, with human salivary α-amylase (HSAA), simulated under physiological salivary condition, was explored using various spectroscopic approaches and in silico method. Hesperetin effectively quenched the intrinsic fluorescence of HSAA and the quenching was mixed quenching mechanism. The interaction perturbed the HSAA intrinsic fluorophore microenvironment and the enzyme global surface hydrophobicity. The negative values of ΔG for thermodynamic parameters and in silico study revealed the spontaneity of HSAA-hesperetin complex while the positive values of enthalpy change (ΔH) and entropy change (ΔS) showed noticeable involvement of hydrophobic bonding in the stabilization of the complex. Hesperetin was a mixed inhibitor for HSAA with a KI of 44.60 ± 1.63 μM and having apparent inhibition coefficient (α) of 0.26. Macromolecular crowding, given rise to microviscosity and anomalous diffusion, regulated the interaction. Sodium ion (Na+) created high ionic strength, also, modulated the interaction. The in silico study proposed the preferential binding of hesperetin at the active cleft domain of HSAA with the least energy of -8.0 kcal/mol. This work gives a novel insight on the potentials of hesperetin as a future prospective medicinal candidate in the management of postprandial hyperglycemic condition.Communicated by Ramaswamy H. Sarma.

Thermodynamic Characterization of the Interaction of Biofunctionalized Gold Nanoclusters with Serum Albumin Using Two- and Three-Dimensional Methods

Fluorescent gold nanoclusters have been successfully used as fluorescent markers for imaging of cells and tissues, and their potential role in drug delivery monitoring is coming to the fore. In addition, the development of biosensors using structure-tunable fluorescent nanoclusters is also a prominent research field. In the case of these sensor applications, the typical goal is the selective identification of, e.g., metal ions, small molecules having neuroactive or antioxidant effects, or proteins. During these application-oriented developments, in general, there is not enough time to systematically examine the interaction between nanoclusters and relevant biomolecules/proteins from a thermodynamic viewpoint. In this way, the primary motivation of this article is to carry out a series of tests to partially fill this scientific gap. Besides the well-known fluorescent probes, the mentioned interactions were investigated using such unique measurement methods as surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). These two-dimensional (at the solid/liquid interface) and three-dimensional (in the bulk phase) measuring techniques provide a unique opportunity for the thermodynamic characterization of the interaction between different gold nanoclusters containing various surface functionalizing ligands and bovine serum albumin (BSA).

2-Phenylquinoline-polyamine conjugate (QPC): Interaction with bovine serum albumin (BSA)

A novel 2-phenylquinoline-polyamine conjugate (QPC) was synthesized and characterized, its interaction with bovine serum albumin (BSA) was evaluated using UV-Vis, fluorescence and circular dichroism (CD) spectroscopy. The results showed that QPC caused a whole train of spectral variation, including enhancement of UV-vis absorption and reduction of fluorescence (FL), indicating QPC-BSA complex formed. FL results showed that the type of FL quenching waslarge static quenching, which was also accompanied with a process of dynamic quenching. Binding constants, thermodynamic parameters and docking results showed that the interaction between QPC and BSA was basically a Van der Waals, hydrogen bond and hydrophobic interaction. Synchronous and 3D-FL analysis revealed that QPC resulted in unapparent conformational alteration of BSA. The docking study suggested QPC was situated at the binding sites II of BSA, and 2-phenylquinoline moiety contributed to the hydrophobic interaction. The results of molecular dynamics revealed QPC altered the conformation of BSA, which showed that the inconsistency between experimental data and theoretical calculation results may be due to the instability of the compound.

Promising Bioactivity of Vitamin B1-Au Nanocluster: Structure, Enhanced Antioxidant Behavior, and Serum Protein Interaction

In the current work, we first present a simple synthesis method for the preparation of novel Vitamin-B1-stabilized few-atomic gold nanoclusters with few atomic layers. The formed nanostructure contains ca. eight Au atoms and shows intensive blue emissions at 450 nm. The absolute quantum yield is 3%. The average lifetime is in the nanosecond range and three main components are separated and assigned to the metal–metal and ligand–metal charge transfers. Based on the structural characterization, the formed clusters contain Au in zero oxidation state, and Vitamin B1 stabilizes the metal cores via the coordination of pyrimidine-N. The antioxidant property of the Au nanoclusters is more prominent than that of the pure Vitamin B1, which is confirmed by two different colorimetric assays. For the investigation into their potential bioactivity, interactions with bovine serum albumin were carried out and quantified. The determined stoichiometry indicates a self-catalyzed binding, which is almost the same value based on the fluorometric and calorimetric measurements. The calculated thermodynamic parameters verify the spontaneous bond of the clusters along the protein chain by hydrogen bonds and electrostatic interactions.

Mechanistic insight into differential interactions of iron oxide nanoparticles with native, glycated albumin and their effect on erythrocytes parameters

Nanoparticles and protein bioconjugates have been studied for multiple biomedical applications. We sought to investigate the interaction and structural modifications of bovine serum albumin (BSA) with iron oxide nanoparticles (IONPs). The IONPs were green synthesized using E. crassipes aqueous leaf extract following characterization using transmission electron microscopy, energy dispersive X-ray analysis and X-Ray Diffraction. Two different concentrations of native/glycated albumin (0.5 and 1.5 mg/ml) with IONPs were allowed to interact for 1 h at 37 °C. Glycation markers, protein modification markers, cellular antioxidant, and hemolysis studies showed structural modifications and conformational changes in albumin due to the presence of IONPs. UV-Visible absorbance resulted in hyperchromic and bathochromic effects of IONPs-BSA conjugates. Fluorescence measurements of tyrosine, tryptophan, advanced glycated end products, and ANS binding assay were promising and quenching effects proved IONPs-BSA conjugate formation. In FTIR of BSA-IONPs, transmittance was increased in amide A and B bands while decreased in amide I and II bands. In summary, native PAGE, HPLC, and FTIR analysis displayed a differential behaviour of IONPs with native and glycated BSA. These results provided an understanding of the interaction and structural modifications of glycated and native BSA which may provide fundamental repercussions in future studies.

A study of structure-activity relationship and anion-controlled quinolinyl Ag(I) complexes as antimicrobial and antioxidant agents as well as their interaction with macromolecules

In this communication, we feature the synthesis and in-depth characterization of a series of silver(I) complexes obtained from the complexation of quinolin-4-yl Schiff base ligands ((E)-2-((quinolin-4-ylmethylene)amino)phenol L_a, 2-(quinolin-4-yl)benzo[d]thiazole L_b, (E)-N-(2-fluorophenyl)-1-(quinolin-4-yl)methanimine L_c, (E)-N-(4-chlorophenyl)-1-(quinolin-4-yl)methanimine L_d, (E)-1-(quinolin-4-yl)-N-(p-tolyl)methanimine L_e, (E)-1-(quinolin-4-yl)-N-(thiophen-2-ylmethyl)methanimine L_f) and three different silver(I) anions (nitrate, perchlorate and triflate). Structurally, the complexes adopted different coordination geometries, which included distorted linear or distorted tetrahedral geometry. The complexes were evaluated in vitro for their potential antibacterial and antioxidant activities. In addition, their interactions with calf thymus-DNA (CT-DNA) and bovine serum albumin (BSA) were evaluated. All the complexes had a wide spectrum of effective antibacterial activity against gram-positive and gram-negative bacterial and good antioxidant properties. The interactions of the complexes with CT-DNA and BSA were observed to occur either through intercalation or through a minor groove binder, while the interaction of the complexes with BSA reveals that some of the complexes can strongly quench the fluorescence of BSA through the static mechanism. The molecular docking studies of the complexes were also done to further elucidate the modes of interaction with CT-DNA and BSA.

Influence of Low Molecular Weight Salts on the Viscosity of Aqueous-Buffer Bovine Serum Albumin Solutions

Pharmaceutical design of protein formulations aims at maximum efficiency (protein concentration) and minimum viscosity. Therefore, it is important to know the nature of protein-protein interactions and their influence on viscosity. In this work, we investigated the dependence of the viscosity of BSA in an aqueous 20 mM acetate buffer at pH = 4.3 on protein concentration and on temperature (5-45 °C). The viscosity of the solution increased with protein concentration and was 230% higher than the viscosity of the protein-free formulation at 160 mg/mL. The viscosity decreased by almost 60% in the temperature range from 5 to 45 °C. The agreement of the modified Arrhenius theory with experiment was quantitative, whereas a hard-sphere model provided only a qualitative description of the experimental results. We also investigated the viscosity of a 100 mg/mL BSA solution as a function of the concentration of added low molecular weight salts (LiCl, NaCl, KCl, RbCl, CsCl, NaBr, NaI) in the range of salt concentrations up to 1.75 mol/L. In addition, the particle size and zeta potential of BSA-salt mixtures were determined for solutions containing 0.5 mol/L salt. The trends with respect to the different anions followed a direct Hofmeister series (Cl^- > Br^- > I^-), whereas for cations in the case of viscosity the indirect Hofmeister series was observed (Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺), but the values of particle sizes and zeta potential did not show cation-specific effects. Since the protein is positively charged at pH = 4.3, anions are more attracted to the protein surface and shield its charge, while the interaction with cations is less pronounced. We hypothesize that salt surface charge shielding reduces protein colloidal stability and promotes protein aggregate formation.

Anti-polyphenol oxidase properties of total flavonoids from young loquat fruits: inhibitory activity and mechanism

This study investigated anti-polyphenol oxidase activity and mechanism of purified total flavonoids (PTF) from young loquat fruits. PTF remarkably inhibited the activity of polyphenol oxidase (PPO) with an IC₅₀ value of 21.03 ± 2.37 μg/mL. Based on enzyme kinetics, PTF was found to be a potent, mixed-type, and reversible inhibitor of PPO. The fluorescence intensity of PPO was quenched by PTF through forming a PTF-PPO complex in a static procedure. Therefore, this study authenticated PTF as an efficient PPO inhibitor, which would contribute to their utilization in food industry.

Spectroscopic and molecular modelling study of binding mechanism of bovine serum albumin with phosmet

Phosmet exerts its neurotoxicity by inhibiting acetylcholinesterase that catalyzes the degradation of acetylcholine (a neurotransmitter). Serum proteins are known to influence the biodistribution of various endogenous and exogenous compounds. In the present study, the binding interactions of phosmet with bovine serum albumin (BSA) was investigated to determine the free concentration of phosmet for its neurotoxicity. The binding mechanism was studied using fluorescence, UV-Vis absorption spectroscopy, circular dichroism (CD), and molecular docking techniques. UV-Vis absorption data showed an increase in absorbance of BSA upon binding with phosmet with a slight red-shift in the peak around 280 nm. Intrinsic fluorescence of BSA was quenched in the presence of phosmet. The quenching was observed to be inversely correlated to the temperature that indicated the formation of ground state non-fluorescent complex (static quenching). Binding constant values and n values for the binding of phosmet with BSA at three different temperatures confirmed non-covalent binding interactions with a single set of equivalent binding sites. Thermodynamic parameters ∆G (-137.40 ± 3.58 kJ mol^-1); ΔH (-16.33 ± 5.28 kJ mol^-1) and ΔS(-469 ± 12.45 kJ mol^-1) confirmed that the binding was spontaneous and non-covalent interactions like electrostatic, hydrogen bonding and van der Waals forces played an important role in the binding. The CD data indicated the conformational change in BSA upon binding with phosmet which resulted in a change in the melting temperature. Molecular docking presented the binding model for BSA-phosmet complex and displayed that non-covalent interactions played a significant role in the binding mechanism.

Investigation of the interaction of a polyamine-modified flavonoid with bovine serum albumin (BSA) by spectroscopic methods and molecular simulation

The interaction between BSA and compound 1 was studied by UV-vis, fluorescence and circular dichroism spectroscopy under physiological conditions (pH = 7.4). Molecular docking and molecular dynamics analyses were also performed. The results showed that compound 1 could bind to BSA. When compound 1 bound to BSA, there were a series of changes in the spectral properties of BSA, which were an enhancement effect of the UV-Vis spectrum of BSA, fluorescence quenching and a weak conformational change in the CD spectrum. The results of the fluorescence experiments at 298, 303 and 310 K showed that fluorescence quenching caused by the addition of compound 1 to BSA was generally static quenching accompanied by a dynamic quenching process, which was shown by the quenching constants of 2.010 × 10⁴ L∙M^-1, 1.850 × 10⁴ L∙M^-1, and 1.970 × 10⁴ L∙M^-1 at the three different temperatures, respectively. From the obtained binding constants and thermodynamic parameters, it was found that hydrophobic forces played an important role in the binding process of 1 to BSA. The results of synchronous fluorescence and three-dimensional fluorescence showed that compound 1 caused a weak conformational change in BSA. Docking results showed that compound 1 was located at binding site II of bovine serum albumin protease. In addition, the flavonoid moiety of compound 1 contributes to the hydrophobic binding of compound 1 to BSA. The results of molecular dynamics, including the root-mean-square deviation (RMSD) and RMS fluctuation (RMSF) values, showed that the binding of compound 1 to BSA did not cause a significant conformational change in BSA.

Insight into the delivery channel and selectivity of multiple binding sites in bovine serum albumin towards naphthalimide-polyamine derivatives

Naphthalimide derivatives are types of small-molecule anticancer drug candidates; however, their negative factors and potential side effects make their application limited. The pharmacophores select a direct access into the tumor cells as the first choice; this can reduce the side effect of the anti-cancer drugs on the normal cells. Herein, the delivery and binding of the naphthalimide-polyamine complex assisted by the bovine serum albumin (BSA) protein have been studied by combining several molecular dynamic simulations. The plausible transportation channels and the most favorable pathways for the delivery of the naphthalimide-polyamine complex to two drug sites (DSI and DSII), their thermodynamic and dynamic properties and the mechanisms have been discussed in detail. The residues His287 and Phe394 acted as guards in the DSI and DSII, respectively, which played a gating-switch role by flipping the ring from open to close during the compound delivery. The binding mode, binding energy and substituent effects have been also identified. The two drug sites have different preferences towards the compound with the electron-withdrawing and electron-donating substituents, and their strong interactions are more sensitive to the number of the substituent groups. The naphthalimide-polyamine complexes are more likely to choose DSI, both thermodynamically and dynamically, as compared to DSII. This selective specificity of these two drug sites manipulated by the electron-withdrawing and electron-donating substituents is quite promising for the design of new naphthalimide drugs.

Extraction of orange pectin based on the interaction between sodium caseinate and pectin

The interaction between commercial orange pectin (COP) and sodium caseinate (SC) was studied using FTIR, fluorescence spectroscopy, CD, and LSCM. The effect of different conditions on the formation and separation of COP-SC complex was determined. The extraction of the orange pectin using SC precipitation (SCOP) was performed, and the physicochemical properties of SCOP were determined and compared with the orange pectin extracted by alcohol precipitation (APOP). The results showed that the electrostatic interaction was the main interaction between these two polymers, and it was strongly dependent on pH, COP/SC ratio, and salt concentration. The mixture of COP and SC formed an electrostatic complex in the pH range of 1.5-6.8 with the absence of NaCl. The recovery rate of SCOP and precipitation rate of SC were 89.43% and 98.33% when the ratio was 1:15. The physicochemical properties of SCOP were almost the same as APOP.

Electrochemical, spectroscopic and theoretical monitoring of anthracyclines' interactions with DNA and ascorbic acid by adopting two routes: Cancer cell line studies

Pharmacodynamic interactions of three anthracycline antibiotics namely doxorubicin (DXH), epirubicin (EpiDXH) and daunorubicin (DNR) with DNA in the absence and presence of ascorbic acid (AA) as natural additive were monitored under physiological conditions (pH = 7.4, 4.7 and T = 309.5K). Route–1 (Anthracycline–AA–DNA) and Route–2 (Anthracycline–DNA–AA) were adopted to see the interactional behavior by cyclic voltammetry (CV) and UV-visible spectroscopy. In comparison to Route–2; voltammetric and spectral responses as well as binding constant (K_b) and Gibb’s free energy change (ΔG) values revealed strongest and more favorable interaction of anthracycline–AA complex with DNA via Route–1. K_b, s (binding site sizes) and ΔG evaluated from experimental (CV, UV-Vis) and theoretical (molecular docking) findings showed enhanced binding strength of tertiary complexes as compared to binary drug–DNA complexes. The results were found comparatively better at pH 7.4. Consistency was observed in binding parameters evaluated from experimental and theoretical techniques. Diffusion coefficients (D_o) and heterogeneous electron transfer rate constant (k_s,h) confirmed the formation of complexes via slow diffusion kinetics. Percent cell inhibition (%C_inh) of anthracyclines for non-small cell cancer cell lines (NSCCLs) H-1299 and H-157 were evaluated higher in the presence of AA which further complimented experimental and theoretical results.

Cytosine arabinoside prodrug designed to bind plasma serum albumin for drug delivery

Rational design of anticancer prodrugs for efficient albumin binding can show distinct advantages in drug delivery in terms of high drug availability, long systemic circulation, potential targeting effect, and enhanced chemotherapy effect. In the present study, we reported a cytosine arabinoside (Ara-C) prodrug which could well formulate in solution and instantly transform into long-circulating nanocomplexes by hitchhiking blood-circulating albumin after i.v. administration. Specifically, Ara-C was conjugated with an albumin-binding maleimide derivative, the resulting Ara-C maleimide caproic acid conjugate (AM) was well formulated in aqueous solution, conferring high albumin-binding ability in vitro albumin-binding studies. Moreover, in vivo fluorescence images of sulfo-cyanine5 maleimide indirectly demonstrated that AM showed better accumulation in tumors, exhibiting superior tumor targeting ability and antitumor activity compared to Ara-C. Such a uniquely developed strategy, integrating high albumin-binding capability, has great potential to be applied in clinical cancer therapy.

Synthetic nanoparticles of bovine serum albumin with entrapped salicylic acid

Bovine serum albumin (BSA) is highly water soluble and binds drugs or inorganic substances noncovalently for their effective delivery to various affected areas of the body. Due to the well-defined structure of the protein, containing charged amino acids, albumin nanoparticles (NPs) may allow electrostatic adsorption of negatively or positively charged molecules, such that substantial amounts of drug can be incorporated within the particle, due to different albumin-binding sites. During the synthesis procedure, pH changes significantly. This variation modifies the net charge on the surface of the protein, varying the size and behavior of NPs as the drug delivery system. In this study, the synthesis of BSA NPs, by a desolvation process, was studied with salicylic acid (SA) as the active agent. SA and salicylates are components of various plants and have been used for medication with anti-inflammatory, antibacterial, and antifungal properties. However, when administered orally to adults (usual dose provided by the manufacturer), there is 50% decomposition of salicylates. Thus, there has been a search for some time to develop new systems to improve the bioavailability of SA and salicylates in the human body. Taking this into account, during synthesis, the pH was varied (5.4, 7.4, and 9) to evaluate its influence on the size and release of SA of the formed NPs. The samples were analyzed using field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, zeta potential, and dynamic light scattering. Through fluorescence, it was possible to analyze the release of SA in vitro in phosphate-buffered saline solution. The results of chemical morphology characterization and in vitro release studies indicated the potential use of these NPs as drug carriers in biological systems requiring a fast release of SA.

Rapid Screening and Identification of BSA Bound Ligands from Radix astragali Using BSA Immobilized Magnetic Nanoparticles Coupled with HPLC-MS

Radix astragali is widely used either as a single herb or as a collection of herbs in a complex prescription in China. In this study, bovine serum albumin functionalized magnetic nanoparticles (BSA-MN) coupled with high performance liquid chromatography-mass spectrometry (HPLC-MS) were used to screen and identify bound ligands from the n-butanol part of a Radix astragali extract. The prepared BSA-MN showed sufficient magnetic response for the separation with an ordinary magnet and satisfied reusability. Fundamental parameters affecting the preparation of BSA-MN and the screening efficiency were studied and optimized. Under the optimum conditions, four bound ligands were screened out from the n-butanol part of a Radix astragali extract and identified as genistin (1), calycosin-7-O-β-d-glucoside (2), ononin (3) and formononetin (4). This effective method could be widely applied for rapid screening and identification of active compounds from complex mixtures without the need for preparative isolation.