An insight into the binding of aceclofenac with bovine serum albumin at physiological condition: a spectroscopic and computational approach

The role of Maillard reaction in increasing affinity between soybean protein isolate and phloretin and its effects on protein functionality

This study investigated the effects of the Maillard reaction on the interaction between soybean protein isolate (SPI) and phloretin (PHL), along with its impact on the functional properties of soybean protein isolate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that sodium alginate (SA) was successfully grafted onto SPI. The fluorescence results indicated that the red shift and fluorescence burst of the ternary complexes were more pronounced, indicating that the proteins in the complexes had a more compact tertiary structure. The molecular docking showed that phloretin formed shorter hydrogen bonds with surrounding active amino acid residues after the Maillard reaction, suggesting that the Maillard reaction enhanced the stability of Phloretin's binding to proteins. The slight blue shifts observed in the amide I and amide II bands suggested hydrogen bonding and electrostatic interactions are also present. A decrease in α-helix and β-sheet content, along with an increase in irregular curl content, indicating protein unfolding. Also, the functional properties of SPI were improved due to the unfolding of the protein structure. These findings will provide valuable insights for the subsequent study of Maillard reaction products in the construction of nutrient delivery systems.

Interaction of plant phenol vanillin with human hemoglobin: A spectroscopic and molecular docking study

Vanillin is a phenolic aldehyde widely used as a flavouring agent in the food industry. Vanillin has many health benefits and has gained attention in pharmacological industries also, due to its antioxidant properties and non-toxic nature. The interaction of vanillin with human hemoglobin (hHb), an abundant tetrameric heme protein, was investigated by several spectroscopic techniques and molecular modeling methods. UV-visible spectra showed that the binding of vanillin to hHb induces structural changes due to alterations in the micro-environment of hHb. Vanillin quenches the intrinsic fluorescence of hHb by the dynamic mechanism, which was confirmed by both temperature dependent and time resolved fluorescence studies. Vanillin binds spontaneously to hHb at a single site and the binding is stabilized by hydrogen bonds and hydrophobic interactions. The circular dichroism spectra showed that the binding of vanillin altered the secondary structure of hHb due to change in its alpha-helical content. Molecular docking identified the amino acids of hHb involved in binding to vanillin and also that the free energy change of the binding reaction is -5.5 kcal/mol. Thus, our results indicate that vanillin binds spontaneously to hHb at a single site and alters its secondary structure. This will help in understanding the potential use of vanillin and related antioxidants as therapeutic agents in various hematological disorders.

Exploring the binding mechanism and esterase-like activity of human serum albumin with levofloxacin and its choline based conjugates: A biophysical approach

Human serum albumin (HSA) effectively binds to compounds having different molecular weight and thus facilitates their distribution in the living organisms. Thus, the binding interactions between a potential antibacterial drug (levofloxacin) and synthesized choline based levofloxacinate conjugates with HSA have been explored. The binding efficacy and mechanism were explored by utilizing different spectroscopic techniques; UV-Visible, steady state fluorescence, time resolved fluorescence and esterase-like activity. The interactions between the ligands and protein were electrostatic as well as hydrophobic in nature. The influence of different ligands having different alkyl chain shows quenching of the fluorescence emission of HSA. The spontaneous binding/quenching of HSA with ligands was static in nature, validated by steady state and time resolved fluorescence spectroscopy. Also, the impact of these ligands on the conformation of the native HSA structure was evaluated by using circular dichroism spectroscopy. In combination to the structural change study, the native protein functionality was observed (in terms of 'esterase-like activity') which has been found to be on lower side due to ligand binding. Further, we have performed the reverse study to check the impact of HSA on the fluorescent fluoroquinolone drug. The current study may prove helpful in elucidating the chemico-biological interactions which may prove useful in the pharmaceuticals, pharmacology, and different biochemistry fields.

Electrospinning of bovine serum albumin-based nano-fibers: From synthesis to medical prospects; Challenges and future directions

Bovine serum albumin (BSA) is a globular non-glycoprotein that has gotten a lot of attention because of its unique properties like biocompatibility, biodegradability, non-immunogenicity, non-toxicity, and strong resemblance to the natural extracellular matrix (ECM). Given its robust mechanical properties, such as interfacial tension, conductivity, swelling resistance, and viscoelasticity, it can be concluded that it is an appropriate matrix for producing novel BSA-based nanoconstructs. Thus, simple analytic methods are required for accurately detecting BSA as a model protein in medical sciences and healthcare. Furthermore, the characteristics mentioned above aid BSA in the electrospinning process, which results in fibers conjugated with other polymers. Electrospun synthesis has recently received much attention for its ability to produce stable, biomimicking, highly porous, 3D BSA-derived nano-fibers. As a result, BSA-based nano-fibers have achieved exclusive developments in the medical sector, such as tissue engineering for the remodeling of damaged tissue or organ repair by creating artificial ones. Meanwhile, they could be used as drug delivery systems (DDS) for target-specific drug delivery, wound dressings, and so on. This study illustrates the structural and physicochemical properties of BSA and the determination of BSA using various methods, by citing recent reports and current developments in the medical field. Furthermore, current challenges and future directions are also highlighted.

Insight into the Inhibitory Mechanisms of Hesperidin on α-Glucosidase through Kinetics, Fluorescence Quenching, and Molecular Docking Studies

The α-glucosidase inhibitor is of interest to researchers due to its association with type-II diabetes treatment by suppressing postprandial hyperglycemia. Hesperidin is a major flavonoid in orange fruit with diverse biological properties. This paper evaluates the effects of hesperidin on α-glucosidase through inhibitory kinetics, fluorescence quenching, and molecular docking methods for the first time. The inhibition kinetic analysis shows that hesperidin reversibly inhibited the α-glucosidase activity with an IC50 value of 18.52 μM and the inhibition was performed in an uncompetitive type. The fluorescence quenching studies indicate that the intrinsic fluorescence of α-glucosidase was quenched via a static quenching process and only one binding site was present between the hesperidin and α-glucosidase. The interaction between them was spontaneous and mainly driven by hydrogen bonds, as well as hydrophobic forces. Furthermore, the molecular docking results suggest that hesperidin might bond to the entrance or outlet part of the active site of α-glucosidase through a network of five hydrogen bonds formed between hesperidin and the four amino acid residues (Trp709, Arg422, Asn424, and Arg467) of α-glucosidase and the hydrophobic effects. These results provide new insight into the inhibitory mechanisms of hesperidin on α-glucosidase, supporting the potential application of a hesperidin-rich orange product as a hypoglycemic functional food.

Synergistic protection of quercetin and lycopene against oxidative stress via SIRT1-Nox4-ROS axis in HUVEC cells

Oxidative stress is a potential factor in the promotion of endothelial dysfunction. In this research, flavonoids (quercetin, luteolin) combined with carotenoids (lycopene, lutein), especially quercetin-lycopene combination (molar ratio 5:1), prevented the oxidative stress in HUVEC cells by reducing the reactive oxygen species (ROS) and suppressing the expression of NADPH oxidase 4 (Nox4), a major source of ROS production. RNA-seq analysis indicated quercetin-lycopene combination downregulated inflammatory genes induced by H₂O₂, such as IL-17 and NF-κB. The expression of NF-κB p65 was activated by H₂O₂ but inhibited by the quercetin-lycopene combination. Moreover, the quercetin and lycopene combination promoted the thermostability of Sirtuin 1 (SIRT1) and activated SIRT1 deacetyl activity. SIRT1 inhibitor EX-527 attenuated the inhibitory effects of quercetin, lycopene, and their combination on the expression of p65, Nox4 enzyme, and ROS. Quercetin-lycopene combination could interact with SIRT1 to inhibit Nox4 and prevent endothelial oxidative stress, potentially contributing to the prevention of cardiovascular disease.

Control of eriocitrin release from pH-sensitive gelatin-based microgels to inhibit α-glucosidase: an experimental and computational study

α-Glucosidase is among the intestinal epithelial enzymes that produce absorbable glucose in the final stage of glycan catabolism. It leads to an increase in blood glucose levels as a result of high glucose uptake in diabetic patients. However, inhibition of this essential biochemical process can be a useful therapeutic approach to diabetes mellitus (DM). Eriocitrin (ER) is an abundant "flavanone glycoside" in citrus fruits with rich antioxidant properties whose effects on α-Glu inhibition in the small intestine remain to be determined. Herein, pH-sensitive microgels (MGs) were designed based on cross-linked methacrylate with acrylamide (AM) and acrylic acid (AAc) (molar ratio 70 : 30 of AAc : AM) as a controlled release system for sustained delivery of ER into the small intestine. The presence of amide and acrylate in MGs and the mechanical resistance were determined using FT-IR spectroscopy, rheology, and viscoelastometry. In vitro experiments showed that MGs could protect ER against diffusion in the gastric location and adjust its release in the intestinal milieu. The intestinal α-Glu activity was inhibited by ER (IC₅₀ value of 12.50 ± 0.73 μM) in an uncompetitive dose-dependent manner. The presence of ER altered the structure of α-Glu and reduced the hydrophobic pockets of the enzyme. Molecular docking analysis along with molecular dynamics simulation displayed that ER-α-Glu formation is directed by hydrogen binding with Asp69, Asp215, Glu411, Asp307, and Tyr347 residues. Moreover, in vivo assessment showed that rat blood glucose concentration decreased after ER administration compared with the control group. The results highlight that ER-loaded-MGs can be considered as a useful releasing strategy in treating DM via α-Glu inhibition.

Exploring the binding mechanism of ferulic acid and ovalbumin: insights from spectroscopy, molecular docking and dynamics simulation

BACKGROUND

Ferulic acid (FA), a phenolic acid widely occurring in nature, has attracted extensive attention because of its biological activity. Ovalbumin (OVA) is a commonly used carrier protein. The mechanism of FA binding with OVA was investigated by utilizing a variety of spectral analyses, accompanied by computer simulation.

RESULTS

It was discovered that the fluorescence quenching mechanism of OVA by FA was a static mode as a result of the formation of an FA-OVA complex, which was verified by the concentration distributions and pure spectrum of the constituents decomposed from the high overlap spectrum signals using multivariate curve resolution-alternate least squares algorithm. Hydrogen bonds and Van der Waals forces drove the formation of FA-OVA complex with a binding constant of 1.69 × 10⁴  L mol^-1 . The presence of FA induced the loose structure of OVA with an attenuation of α-helix content and improved the thermal stability of OVA. Computer docking indicated that FA interacted with the amino acid residues Arg84, Asn88, Leu101 and Ser103 of OVA through hydrogen bonds. Molecular dynamics simulation proved that the combination of FA with OVA boosted the conformational stability of OVA and hydrogen bonds brought a crucial part in stabilizing the structure of the complex.

CONCLUSIONS

The study may supply the theoretical basis for the design of FA transport system using OVA as carrier protein to improve the instability and low bioavailability of FA. © 2021 Society of Chemical Industry.

Exploring two types of prenylated bitter compounds from hop plant (Humulus lupulus L.) against α-glucosidase in vitro and in silico

Hops are abundant in natural bioactive compounds. In this work, nine prenylated bitter compounds from hop were evaluated for their inhibitory activity against α-glucosidase. As a result, four flavonoids and one phloroglucinol (lupulone, LP) outperformed acarbose in inhibiting α-glucosidase. Isoxanthohumol (IX) and LP with two types of structures were selected for inhibition mechanism studies by spectroscopic methods and molecular dynamics simulation (MD). Results showed that IX acted as noncompetitive inhibitor and bound to α-glucosidase in allosteric sites via hydrogen bonds, hydrophobic, van der Waals (vdW), and electrostatic force, whereas LP was uncompetitive inhibitor and bound to catalytic sites via hydrophobic and vdW interactions. Notably, the conformation around binding site of α-glucosidase formed stable α-helix and tightened after binding IX and LP, respectively, which helped to elucidate noncompetitive and uncompetitive inhibitory mechanisms. This work demonstrated that two types of prenylated bitter compounds are discrepant in their mechanisms of interaction with α-glucosidase.

Characterization, biological evaluation and molecular docking of mulberry fruit pectin

Contemplating the exemplary benefits of pectin on human health, we precisely characterized and evaluated the antibacterial and anticancer activities from purified Mulberry Fruit Pectins (MFP). Here, we tested BR-2 and S-13 varieties of mulberry fruit pectins against six bacterial strains and two human cancer cell lines (HT-29 and Hep G-2), using MIC and an in vitro cell-based assay respectively. The BR-2 mulberry fruit pectin performs superior to S-13 by inhibiting strong bacterial growth (MIC = 500–1000 μg/mL) against tested bacterial strains and cytotoxic activities at the lowest concentration (10 µg/ml) against the Hep G-2 cell line. However, both tested drugs failed to exhibit cytotoxicity on the human colon cancer cell line (HT-29). Based on molecular interaction through docking, pectin binds effectively with the receptors (1e3g, 3t0c, 5czz, 6j7l, 6v40, 5ibs, 5zsy, and 6ggb) and proven to be a promising antimicrobial and anti-cancer agents. The pursuit of unexploited drugs from mulberry fruit pectin will potentially combat against bacterial and cancer diseases. Finally, future perspectives of MFP for the treatment of many chronic diseases will help immensely due to their therapeutic properties.

Development and in vitro Evaluation of Gastro-protective Aceclofenac-loaded Self-emulsifying Drug Delivery System

AIM

Chronic use of oral nonsteroidal anti-inflammatory drugs (NSAIDs) is commonly associated with gastric irritation and gastric ulceration. Therefore, the aim of study was to develop a novel oral drug delivery system with minimum gastric effects and improved dissolution rate for aceclofenac (ACF), a model BCS class-II drug.

METHODS

Self-emulsifying drug delivery systems (SEDDS) were formulated to increase the solubility and ultimately the oral bioavailability of ACF. Oleic acid was used as an oil phase, Tween 80 (T80) and Kolliphor EL (KEL) were used as surfactants, whereas, polyethylene glycol 400 (PEG 400) and propylene glycol (PG) were employed as co-surfactants. Optimized formulations (F1, F2, F3 and F4) were analyzed for droplet size, poly dispersity index (PDI), cell viability studies, in vitro dissolution in both simulated gastric fluid and simulated intestinal fluid, ex vivo permeation studies and thermodynamic stability.

RESULTS

The optimized formulations showed mean droplet sizes in the range of 111.3 ± 3.2 nm and 470.9 ± 12.52 nm, PDI from 244.6 nm to 389.4 ± 6.51 and zeta-potential from -33 ± 4.86 mV to -38.5 ± 5.15 mV. Cell viability studies support the safety profile of all formulations for oral administration. The in vitro dissolution studies and ex vivo permeation analysis revealed significantly improved drug release ranging from 95.68 ± 0.02% to 98.15 ± 0.71% when compared with control. The thermodynamic stability studies confirmed that all formulations remain active and stable for a longer period.

CONCLUSION

In conclusion, development of oral SEDDS might be a promising tool to improve the dissolution of BCS class-II drugs along with significantly reduced exposure to gastric mucosa.

Evaluation of the interaction of novel tyrosine kinase inhibitor apatinib mesylate with bovine serum albumin using spectroscopies and theoretical calculation approaches

Apatinib mesylate (APM), a novel tyrosine kinase inhibitor, has been applied in treating various cancers. In the present study, the binding mechanism of APM with bovine serum albumin (BSA) was studied by making use of various spectroscopic and theoretical calculation approaches to provide theoretical support for further studying its pharmacokinetics and metabolism. The results from fluorescence experiments showed that the quenching mechanism of BSA induced by APM was static quenching and the APM-BSA complex with the stoichiometry of 1:1 was formed during binding reaction. Moreover, the findings also showed that the binding process of APM to BSA was spontaneous and enthalpy-driven, and the mainly driving forces were hydrogen bonding, van der Waals as well as hydrophobic interactions. From the outcomes of the competitive experiments, it can be found that the binding site was primarily nestled in sub-domain IIIA of BSA (site II) which was in line with the results of molecular docking. An appreciable decline in α-helix content of BSA can be observed from the FT-IR data, meaning that the conformational change of BSA occurred after binding with APM, this phenomenon can be corroborated by the results of UV-vis, synchronous fluorescence and 3D fluorescence studies. Furthermore, the effect of some metal ions (e.g. K⁺, Co²⁺, Ni²⁺, Fe³⁺) on the binding constant of APM to BSA was explored.Communicated by Ramaswamy H. Sarma.

Monitoring biomolecular interaction between folic acid and bovine serum albumin

Folic acid is a bioactive food component whose deficiency can lead to a variety of health problems, while a high intake of folic acid can reduce the cytotoxicity of natural killer cells. The binding mechanism of folic acid to free bovine serum albumin (BSA) was studied using fluorescence, while the biomolecular interaction between confined-BSA and free folic acid was assessed by electrochemical methods and surface plasmon resonance. The fluorescence quenching mechanism of BSA by folic acid was found to have a static character. The thermodynamic parameters of the interaction were determined and indicated a spontaneous exothermic process with a binding constant of 8.72 × 10⁴ M^-1 at 25 °C. Confinement of BSA to gold surfaces occurred through different immobilization methods (static and hydrodynamic), inducing conformational changes, which influenced the orientation of BSA molecules binding sites towards free folic acid. The apparent binding constant using electrochemical methods (voltammetry and impedance spectroscopy) was only 5 times higher (41 and 37 × 10⁴ M^-1) compared to BSA free in solution, while for surface plasmon resonance, where the hydrodynamic immobilization method was used, the value was much higher (19 × 10⁶ M^-1). This work gives also an insight on the interaction of BSA with gold substrates, surface plasmon resonance enabling the calculation of the adsorbed amount. The obtained results help understanding the specific interaction between free and confined BSA with free folic acid.

Esterase activity and interaction of human hemoglobin with diclofenac sodium: A spectroscopic and molecular docking study

To get an idea about the pharmacokinetics and pharmacodynamics, it is important to study the drug-protein interaction. Therefore, herein, we studied the interaction of diclofenac sodium (DIC) with human hemoglobin. The binding study of nonsteroidal antiinflammatory drug, DIC with human hemoglobin (HHB) was done by utilizing fluorescence, UV-visible, time-resolved fluorescence and far-UV circular dichroism spectroscopy (CD). Various thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) were also calculated. CD results showed that DIC induces secondary structure change in HHB. Fluorescence resonance energy transfer was also performed. Additionally, it was also observed that DIC inhibits the esterase-like enzymatic activity of HHB via competitive inhibition.

Binding mechanism of maltol with catalase investigated by spectroscopy, molecular docking, and enzyme activity assay

Maltol is a flavor additive that is widely used in the daily diet of humans, and its biosafety attention is concomitantly increasing. Catalase (CAT) is an antioxidant enzyme to maintain homeostasis in the tissue's environment of human body and protect cells from oxidative damages. The adverse effects of maltol to CAT activity within mouse hepatocytes as well as the structural and functional changes of CAT on molecular level were investigated by multiple spectroscopy techniques, enzyme activity experiments, and molecular docking. Results suggested that when the maltol concentrations reached to 8 × 10^-5 mol L^-1 , the viability of hepatocytes decreased to 93%, and CAT activity was stimulated by maltol to 111% than the control group after exposure for 24 hours. Changes in CAT activity on molecular level were consistent with those on cellular level. The fluorescence quenching of CAT by maltol was static with the forming of maltol-CAT complex. Moreover, ultraviolet-visible (UV-visible) absorption, synchronous fluorescence, and circular dichroism (CD) spectra reflected that the presence of maltol caused conformational change of CAT and made the CAT molecule skeleton loose and increased α-helix of CAT. Maltol mainly bound with CAT through hydrogen bond, and binding site that is near the heme ring in the enzyme activity center did not interact with its main amino acid residues. This study explores the combination between maltol and CAT, providing references for evaluating health damages caused by maltol.

Inhibitory effect of corosolic acid on α-glucosidase: kinetics, interaction mechanism, and molecular simulation

BACKGROUND

The suppression of α-glucosidase activity to retard glucose absorption is an important therapy for type-2 diabetes. Corosolic acid (CRA) is a potential antidiabetic component in many plant-based foods and herbs. In this study, the interplay mechanism between α-glucosidase and corosolic acid was investigated by several methods, including three-dimensional fluorescence spectra, circular dichroism spectra, and molecular simulation.

RESULTS

Corosolic acid significantly inhibited α-glucosidase reversibly in an uncompetitive manner and its IC₅₀ value was 1.35 × 10^-5 mol L^-1 . A combination of CRA with myricetin exerted a weak synergy against α-glucosidase. The intrinsic fluorescence of α-glucosidase was quenched via a static quenching course and the binding constant was 3.47 × 10³  L mol^-1 at 298 K. The binding of CRA to α-glucosidase was mainly driven by hydrophobic forces and resulted in a partial extension of the protein polypeptide chain with a loss of α-helix content. The molecular simulation illustrated that CRA bound to the entrance part of the active center of α-glucosidase and interacted with the amino acid residues Ser157, Arg442, Phe303, Arg315, Tyr158, and Gln353, which could hinder the release of substrate and catalytic reaction product, eventually suppressing the catalytic activity of α-glucosidase.

CONCLUSIONS

These results may suggest new insights into corosolic acid from food sources as a potential α-glucosidase inhibitor that could better control diabetes. © 2019 Society of Chemical Industry.

A model to study the inhibition of nsP2B-nsP3 protease of dengue virus with imidazole, oxazole, triazole thiadiazole, and thiazolidine based scaffolds

A theoretical model was developed to allosterically inhibit the biological activity of dengue virus (DENV) by targeting the non-structural protein ns2B-nsP3 protease based on the in silico studies. The imidazole, oxazole, triazole, thiadiazole, and thiazolidine based scaffolds were imported from the ZINC database, reported by various research group with different biological activity. They were found biologically active as they contain heterocyclic fragments. Generic evolutionary based molecular docking was performed to screen the highly potent molecule. The docking results show that the molecule having ZINC ID-633972 is best inhibitor. Further, the bioavailability and other physiochemical parameters were also calculated for the top four molecule. The highly potent molecule was further refined by the density functional theory and molecular dynamic (MD) simulation. The MD analysis coroborate the successful docking of the molecule in the binding cavity of nsP2B-nsP3 protease of DENV. The Molecular Mechanics Poisson-Boltzmann Surface Area approach was also applied and result coroborate the docking and MD result.

Gallic acid influence on bovine serum albumin thermal stability

A thermoanalytical approach reveals the dual action of GA on BSA thermal stability.

Interaction of flavonols with human serum albumin: a biophysical study showing structure-activity relationship and enhancement when coated on silver nanoparticles

Binding affinities of flavonols namely quercetin, myricetin, and kaempferol to human serum albumin (HSA) were determined fluorimetrically and the order was observed to be myricetin > quercetin > kaempferol demonstrating structure-activity relationship. Quercetin-coated silver nanoparticles (AgNPs) show higher binding affinity to HSA compared to free quercetin with binding constants 6.04 × 10⁷ M^-1 and 4.2 × 10⁶ M^-1, respectively. Using site-specific markers it is concluded that free quercetin and that coated on AgNPs bind at different sites. Significant structural changes in circular dichroism (CD) spectra of HSA were recorded with quercetin-coated AgNPs compared to free quercetin. These results were further substantiated by time-resolved fluorescence spectroscopy where fluorescence life time of the tryptophan residue in HSA-quercetin-coated AgNPs complex decreased to 3.63 ns from 4.22 ns in HSA-quercetin complex. Isothermal calorimetric studies reveal two binding modes for quercetin-coated AgNPs and also higher binding constants compared to free quercetin. These higher binding affinities are attributed to altered properties of quercetin when coated on AgNPs enabling it to reach the binding sites other than site II where free quercetin mainly binds.