Mechanism evaluation of the interactions between flavonoids and bovine serum albumin based on multi-spectroscopy, molecular docking and Q-TOF HR-MS analyses

Revealing binding mechanism of β-casein to chrysin, apigenin, and luteolin and locating its binding pockets by molecular docking and molecular dynamics

Revealing the interaction mechanism of proteins with bioactive molecules and the location of their binding pockets is crucial for predicting the structure-function relationship of proteins in drug discovery and design. Despite some published papers on the interaction of β-casein with small bioactive molecules, the ambiguity of the location and constituent amino acids of β-casein binding pockets prompted us to identify them by in silico simulation of its interaction with three polyphenols, chrysin, apigenin, and luteolin. Molecular docking revealed that the primary β-casein binding pocket for chrysin consists of five nonpolar amino acids (Leu73, Phe77, Pro80, Ile89, and Pro196), three polar neutral amino acids (Ser137, Gln138, and Gln197), and two polar charged amino acids (Glu136, and Arg198). For β-casein/apigenin and β-casein/luteolin complexes, Asn83 also contributes to forming the pocket. Molecular dynamics provided more details, such as the relative contribution of determinative amino acids and the role of various forces. For example, we found that Glu210, Glu132, and Glu35 are the most destructive residues in the binding of chrysin, apigenin, and luteolin to β-casein, respectively. Also, we observed that hydrophobic forces mainly stabilize β-casein/chrysin and β-casein/apigenin, and polar solvation (including hydrogen bonds) stabilizes β-casein/luteolin, all by spontaneous processes.

Study on the effects of endogenous polyphenols on the structure, physicochemical properties and in vitro digestive characteristics of Euryales Semen starch based on multi-spectroscopies, enzyme kinetics, molecular docking and molecular dynamics simulation

Euryales Semen (ES) is a highly nutritious food with low digestibility, which is closely associated with its endogenous phenolic compounds. In this study, five phenolic compounds (naringenin, isoquercitrin, gallic acid, epicatechin and quercetin) with high concentrations in ES were selected to prepare starch-polyphenol complexes. Subsequently, the effects of endogenous polyphenols on the structure, physicochemical properties and digestion characteristics of ES starch were studied using multiple techniques. The addition of phenolic compounds markedly reduced the in vitro digestibility, swelling power, gelatinization enthalpy, while increased the solubility of ES starch. Fourier-transform infrared spectroscopy and X-ray diffraction analysis showed that phenolic compounds interacted with the starch through non-covalent bonds. Five phenolic compounds inhibited α-amylase activity through a mixed competitive inhibition mechanism, with the inhibition potency ranked as follows: quercetin > epicatechin > gallic acid > isoquercitrin > naringenin. The spectroscopic analysis and molecular dynamics simulations confirmed that five phenolic compounds interacted with the amino acid residues of α-amylase through hydrogen bonding and hydrophobic interactions, caused α-amylase static fluorescence quenching, and altered its conformation and microenvironment. This study provides a better understanding of the interaction mechanisms between ES starch and polyphenols, and supports the development of ES as a food that lowers sugar levels.

In Vitro and In Silico Analysis of the Bindings between Legacy and Novel Per- and Polyfluoroalkyl Substances and Human Serum Albumin

Per- and polyfluoroalkyl substances (PFASs) are emerging contaminants of concern that can enter the human body through a variety of pathways and thereby cause harmful effects. Exposure of pregnant women to PFASs could even affect both the mother and the child. Human serum albumin (HSA) is considered to be the primary transport protein for a variety of substances in body fluids. It can be bound to different contaminants and might result in possible effects on human health. Yet, few studies are available on the binding affinity of legacy PFASs and their novel alternatives to HSA. In this study, the binding mechanisms of HSA to both legacy PFASs and their novel alternatives were investigated using fluorescence spectroscopy, together with further molecular docking. The results show that all the target PFASs were statically quenched against HSA with binding ratios of 1:1. The binding constants of long-chain PFASs and novel alternatives of perfluoroalkanesulfonic acids (PFSAs) were greater than 102, whereas those of short-chain PFASs alternatives and novel alternatives of perfluorocarboxylic acids (PFCAs) were less than 102. In general, the binding affinities of PFCAs on HSA were less than that of PFSAs, while the binding affinities of short-chain PFASs alternatives on HSA were smaller than those of long-chain PFASs and their novel alternatives. Therefore, bindings to HSA could be considered as an important influencing factor for the bioaccumulation of legacy and novel PFASs in the human body.

Comparative Analysis of Chemical Composition of Zanthoxylum myriacanthum Branches and Leaves by GC-MS and UPLC-Q-Orbitrap HRMS, and Evaluation of Their Antioxidant Activities

Zanthoxylum myriacanthum Wall. ex Hook. f., a plant belonging to the Rutaceae family and the Zanthoxylum genus, is extensively utilized for its medicinal properties and as a culinary seasoning in China and Southeast Asian countries. However, the chemical composition and biological activities of Z. myriacanthum branches and leaves remain insufficiently explored. In this study, the volatile and non-volatile components of Z. myriacanthum branches and leaves were analyzed using GC-MS and UPLC-Q-Orbitrap HRMS techniques. A total of 78 volatile compounds and 66 non-volatile compounds were identified. The volatile compounds were predominantly terpenoids and aliphatic compounds, while the non-volatile compounds were primarily flavonoids and alkaloids. The branches contained 52 volatile compounds and 33 non-volatile compounds, whereas the leaves contained 48 volatile compounds and 40 non-volatile compounds. The antioxidant activities of the methanol extracts from Z. myriacanthum branches and leaves were evaluated using ABTS and DPPH free-radical-scavenging assays, both of which demonstrated certain antioxidant activity. The methanol extract of leaves demonstrated significantly higher antioxidant activity compared to that of the branches, possibly due to the higher presence of flavonoids and phenols in the leaves, with IC50 values of 7.12 ± 0.257 μg/mL and 1.22 × 102 ± 5.01 μg/mL for ABTS and DPPH, respectively. These findings enhance our understanding of the chemical composition and antioxidant potential of Z. myriacanthum. The plant holds promise as a natural source of antioxidants for applications in pharmaceuticals, cosmetics, and functional foods. Further research can explore its broader biological activities and potential applications.

Probing the binding of morin with alpha-2-macroglobulin using multi-spectroscopic and molecular docking approach : Interaction of morin with α2M

Alpha-2-macroglobulin (α2M) is an essential antiproteinase that is widely distributed in human plasma. The present study was aimed at investigating the binding of a potential therapeutic dietary flavonol, morin, with human α2M using a multi-spectroscopic and molecular docking approach. Recently, flavonoid-protein interaction has gained significant attention, because a majority of dietary bioactive components interact with proteins, thereby altering their structure and function. The results of the activity assay exhibited a 48% reduction in the antiproteolytic potential of α2M upon interaction with morin. Fluorescence quenching tests unequivocally confirmed quenching in the fluorescence of α2M in the presence of morin, conforming complex formation and demonstrating that the binding mechanism involves a dynamic mode of interaction. Synchronous fluorescence spectra of α2M with morin showed perturbation in the microenvironment around tryptophan residues. Furthermore, structural changes were observed through CD and FT-IR, showing alterations in the secondary structure of α2M induced by morin. FRET further supports the results of the dynamic mode of quenching. Moderate interaction is shown by binding constant values using Stern-Volmer's fluorescence spectroscopy. Morin binds to α2M at 298 K with a binding constant of 2.7 × 104 M-1, indicating the strength of the association. The α2M-morin system was found to have negative ΔG values, which suggests that the binding process was spontaneous. Molecular docking also reveals the different amino acid residues involved in this binding process, revealing that the binding energy is -8.1 kcal/mol.

Pulsed electric field improves the EGCG binding ability of pea protein isolate unraveled by multi-spectroscopy and computer simulation

Understanding molecular mechanisms during protein modification is critical for expanding the application of plant proteins. This study investigated the conformational change and molecular mechanism of pea protein isolate (PPI) under pulsed electric field (PEF)-assisted (-)-Epigallocatechin-Gallate (EGCG) modification. The flexibility of PPI was significantly enhanced after PEF treatment (10 kV/cm) with decrease (23.25 %) in α-helix and increase (117.25 %) in random coil. The binding constant and sites of PEF-treated PPI with EGCG were increased by 2.35 times and 10.00 % (308 K), respectively. Molecular docking verified that PEF-treated PPI had more binding sites with EGCG (from 4 to 10). The number of amino acid residues involved in hydrophobic interactions in PEF-treated PPI-EGCG increased from 5 to 13. PEF-treated PPI-EGCG showed a significantly increased antioxidant activity compared to non-PEF-treated group. This work revealed the molecular level of PEF-assisted EGCG modification of PPI, which will be significant for the application of PPI in food industry.

Exploration of binding mechanism of apigenin to pepsin: Spectroscopic analysis, molecular docking, enzyme activity and antioxidant assays

Pepsin plays an important role in nutrient metabolism. Apigenin (AP) is a beneficial polyphenol to human health. To enhance the bioavailability of AP and elucidate the inhibitory effect of AP on pepsin, the interaction mechanism of AP with pepsin was investigated using spectroscopic analysis and molecular docking, and the activity of pepsin and antioxidant activity of AP was also evaluated. Specifically, AP performed static quenching of pepsin and had only one binding site on pepsin. More interestingly, the interaction between AP and pepsin was spontaneous, while hydrogen bonds and van der Waals forces were the main binding forces. Generally, synchronous and three-dimensional fluorescence confirmed that AP induced the conformational changes of pepsin, and molecular docking proved the above results and illustrated the specific binding patterns. Specifically, AP inhibited the activity of pepsin, while pepsin decreased the antioxidant activity of AP. These results provided useful information for elucidating the interactions between AP and pepsin.

Double-Site Binding and Anti-/Pro-oxidation of Luteolin on Bovine Serum Albumin Mediated by Copper(II) Coordination

The interactions of luteolin (Lut) with bovine serum albumin (BSA) mediated by Cu(II) were investigated by spectroscopic, calorimetric, and molecular dynamic (MD) methods. Fluorescence studies showed that the binding of Lut to BSA was significantly enhanced by Cu(II) coordination with the number of binding sites and binding constant increasing from n = 1 and K _a = 3.2 × 10⁵ L·mol^-1 for Lut to n = 2 and K _a = 7.1 × 10⁵ L·mol^-1 for a 1:1 Cu(II)-luteolin complex, in agreement with the results from isothermal titration calorimetry (ITC). Site-specific experiments with warfarin and ibuprofen and MD confirmed that two binding sites of BSA were sequentially occupied by two Cu(II)-luteolin complexes. Cu(II) coordination increased the antioxidant activity of luteolin by 60% in the inhibition of carbonyl formation from the oxidation of amino groups in the side chain of BSA induced by the peroxyl radical ROO^•; however, it counteracted the antioxidant effects of luteolin and played pro-oxidative roles in BSA aggregation induced by ^•OH.

Chemical aspects of polyphenol-protein interactions and their antibacterial activity

The hunt for novel antibiotics has become a global public health imperative due to the rise in multidrug-resistant microorganisms, untreatable infection cases, overuse, and inefficacy of modern antibiotics. Polyphenols are getting much attention in research due to their multiple biological effects; their use as antimicrobial agents is attributed to their activity and that microbes have a hard time developing resistance to these natural compounds. Polyphenols are secondary metabolites produced in higher plants. They are known to possess various functional properties in the human body. Polyphenols also exhibit antibacterial activities against foodborne pathogens. Their antibacterial mechanism is based on inhibiting bacterial biofilm formation or inactivating enzymes. This review focused on polyphenol-protein interactions and the creation of this complex as a possible antibacterial agent. Also, different phenolic interactions on bacterial proteins, efflux pump, cell membrane, bacterial adhesion, toxins, and other bacterial proteins will be explored; these interactions can work in a synergic combination with antibiotics or act alone to assure bacterial inhibition. Additionally, our review will focus on polyphenol-protein interaction as a possible strategy to eradicate bacteria because polyphenols have shown a robust enzyme-inhibitory characteristic and a high tendency to complex with proteins, a response that neutralizes any bactericidal potential.

Biofortified Whey/Deglycosylated Whey and Chickpea Protein Matrices: Functional Enrichment by Black Mulberry Polyphenols

Morus nigra L. (black mulberry-BM) is a promising nutraceutical fruit containing biologically active polyphenols like anthocyanins, proanthocyanidins, catechins, and stilbenes, with well-established anti-inflammatory, antidiabetic, anti-obesity, and anticancer biofunctions. However, these health-promoting properties in raw fruit are greatly masked due to the presence of soluble and insoluble carbohydrates in excess amounts restricting daily intake of the required dose to achieve targeted effects. In the current study, different protein sources (defatted whey and chickpea flours) were optimized through different conditions to capture polyphenols from BM juice while diminishing its glucose content. To optimize polyphenol-protein interactions, various pHs (3.7, 4.2, and 4.7), matrix concentrations (20, 50, and 80 g protein/L), and incubation times (5, 20, and 45 min) were tested. In the present work, optimized BM polyphenol enriched whey matrix inhibited pro-inflammatory mediators and promoted Nrf-2 dependent cytoprotective enzyme expressions in lipopolysaccharide (LPS) induced macrophages at low doses. In addition, whey proteins were also subjected to an enzymatic deglycosylation process by using recently identified EndoBI-1 enzyme for the specific cleavage of N-glycan core in all glycan types including high mannoses, hybrids as well as complex glycans found on defatted whey proteins. After this process, the polyphenol sorption capacity of deglycosylated whey proteins was found to be significantly higher (37%) than the capacity of non-treated normal whey protein under optimized conditions. In conclusion, deglycosylation of protein matrices could be a novel strategy for efficient sorption/concentration of polyphenols from fruits and vegetables, however, more detailed studies are needed to understand this effect.

MOFs and PDA-supported immobilization of BSA in open tubular affinity capillary electrochromatography: Prediction and study on drug-protein interactions

Owing to the satisfactory properties such as high specific surface area, finely tunable chemical composition, large yet adjustable pore sizes, and diverse architecture, metal-organic frameworks (MOFs) have the potential to be used as a stable, efficient, reusable and protective biomacromolecule immobilization carrier in capillary electrophoresis. Herein, a novel immobilized receptor open-tubular affinity capillary electrochromatography (OT-ACEC) strategy was developed for the first time to rapidly investigate the interactions between a set of drugs and bovine serum albumin (BSA). To further increase the amount of immobilized BSA and maintain the bioactivity of BSA, BSA was immobilized on the inner capillary surface by using polydopamine (PDA) as the adhesion layer and surface functionalization agent, a MOF namely dresden university of technology-5 (DUT-5) as supporting platform and biomacromolecule immobilization carrier, respectively. The amount of immobilized BSA on the capillary surface of the BSA@capillary and the PDA/MOFs/BSA@capillary column are separately calculated as 0.00756 nmol and 0.01812 nmol. Besides, the PDA/MOFs/BSA@capillary column was applied to investigate the interactions between BSA and flavonoids, fluoroquinolones. Under the optimal interaction conditions, three flavonoids and three fluoroquinolones are able to achieve baseline separation in the PDA/MOFs/BSA@capillary column (with resolution values of three flavonoids, 5.78 and 4.13; three fluoroquinolones, 1.72 and 1.68). The PDA/MOFs/BSA@capillary column shows good stability and reproducibility over 100 runs (relative standard deviation (RSD)＜5%). In addition, the normalized capacity factor (K_RCE) in this method replaced the binding constant and was used as an evaluation index to fast predict the activities of 20 drugs, some of which have not yet been reported for their interactions with BSA. Spectroscopy and molecular docking further illuminated the binding mechanism.

A Comprehensive Review on the Interaction of Milk Protein Concentrates with Plant-Based Polyphenolics

Functional properties and biological activities of plant-derived polyphenolic compounds have gained great interest due to their epidemiologically proven health benefits and diverse industrial applications in the food and pharmaceutical industry. Moreover, the food processing conditions and certain chemical reactions such as pigmentation, acylation, hydroxylation, and glycosylation can also cause alteration in the stability, antioxidant activity, and structural characteristics of the polyphenolic compounds. Since the (poly)phenols are highly reactive, to overcome these problems, the formulation of a complex of polyphenolic compounds with natural biopolymers is an effective approach. Besides, to increase the bioavailability and bioaccessibility of polyphenolic compounds, milk proteins such as whey protein concentrate, sodium caseinate, and milk protein concentrate act as natural vehicles, due to their specific structural and functional properties with high nutritional value. Therefore, milk proteins are suitable for the delivery of polyphenols to parts of the gastrointestinal tract. Therefore, this review reports on types of (poly)phenols, methods for the analysis of binding interactions between (poly)phenols-milk proteins, and structural changes that occur during the interaction.

A Review on Drug Delivery System for Tumor Therapy

In recent years, with the development of nanomaterials, the research of drug delivery systems has become a new field of cancer therapy. Compared with conventional antitumor drugs, drug delivery systems such as drug nanoparticles (NPs) are expected to have more advantages in antineoplastic effects, including easy preparation, high efficiency, low toxicity, especially active tumor-targeting ability. Drug delivery systems are usually composed of delivery carriers, antitumor drugs, and even target molecules. At present, there are few comprehensive reports on a summary of drug delivery systems applied for tumor therapy. This review introduces the preparation, characteristics, and applications of several common delivery carriers and expounds the antitumor mechanism of different antitumor drugs in delivery carriers in detail which provides a more theoretical basis for clinical application of personalized cancer nanomedicine in the future.

Optimization and Development of Albumin-Biopolymer Bioconjugates with Solubility-Improving Properties

Bioconjugation is an emerging field in the food and pharmaceutical industry. Due to its biocompatibility and high ligand binding capacity, albumin is widely used in modern drug delivery systems. However, the protein is sensitive to environmental stresses; albumin conjugates, on the other hand, have improved functional properties. Biopolymers are gaining interest due to their biodegradability and safety, compared to synthetic polymers. In this study, albumin–biopolymer bioconjugates were prepared by nonenzymatic Maillard reaction at 60 °C and 80% relative humidity. This nonenzymatic conjugation takes place between reducing sugars and available amino groups of a protein in certain conditions. The optimal molar ratio and time for the conjugation were studied by several investigation methods, including circular dichroism and fluorescence spectroscopy, sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), and determination of available amino groups with ortho-phthaldialdehyde (OPA) assay. All of the measurements provided evidence for the covalent bonding of albumin and biopolymers, resulting in bioconjugates. Based on the results, a higher molar ratio and longer time are necessary to complete the reaction with the available amino groups. However, the optimal parameters are specific to each given biopolymer. The rheological behavior of the conjugates is characteristic of the initial biopolymer, which can be useful in drug development. Moreover, both the physical characteristics of albumin and the solubility-improving capacity were enhanced. Therefore, the potential use of albumin–biopolymer bioconjugates in the pharmaceutical industry could be considered.

Three flavanols delay starch digestion by inhibiting α-amylase and binding with starch

The study aimed to reveal the different mechanisms of delaying starch digestion by ECG, EGCG and Procyanidin based on the perspective of α-amylase-flavanol interaction and starch-flavanol interaction. The interaction characteristics of flavanols with α-amylase were studied from five aspects: enzyme inhibition, kinetics, fluorescence quenching, circular dichroism (CD) and computer simulation. The IC50 of flavanols (ECG, EGCG and Procyanidin) against α-amylase were 172.21 ± 0.22, 732.15 ± 0.13 and 504.45 ± 0.19 μg/mL according to the results of α-amylase inhibition experiment, respectively. ECG and Procyanidin showed mixed inhibition against α-amylase, while EGCG showed non-competition against α-amylase. However, thermodynamic parameters，computer-based docking and dynamic simulation proved that ECG and EGCG-α-amylase complexs were mainly driven by van der Waals and hydrogen bonds, while Procyanidin-α-amylase complexs was driven by hydrophobic interaction. In addition, it was indicated, by means of starch‑iodine complex spectroscopy, that flavanols inhibited the digestion of starch not only through bind with α-amylase but also through bind with starch. Thus, flavanols as a starch-based food additive have the potential to be employed as adjuvant therapy for diabetes.

Screening and analysis of xanthine oxidase inhibitors in jute leaves and their protective effects against hydrogen peroxide-induced oxidative stress in cells

Jute (Corchorus capsularis L.) is an annual herb of the bast fiber plant and has great potentials in food and medicinal usages because of its various bioactivities. In this study, ultrafiltration coupled with high-performance liquid chromatography-mass spectrometry was established for screening xanthine oxidase inhibitors from the jute leaves extract. Under the optimum screening conditions, three inhibitors were successfully screened and identified as chlorogenic acid, echinacoside, and isorhamnetin-rutinoside with UV and MS data. The fluorescent quenching analysis showed that three inhibitors quenched the fluorescence intensities of enzyme with different binding capacities. For further exploring the bioactivity of three inhibitors, the protective effects on hydrogen peroxide-induced oxidative stress was investigated using human normal liver cell (LO2), human gastric mucosal epithelial cell (GES-1), and human umbilical vein endothelial cell (HUVEC). As a result, they exhibited protective effects on three injured cells in dose-dependent manners without cytotoxicity. To evaluate the difference among different jute species obtained in our laboratories, the amounts of three compounds in ten samples were assessed and analyzed. The results showed that it could be divided into three groups. The jute leaves showed nutrient and medical potentials and deserved further research on pharmaceutical and biochemical utilization in future.

Interaction of flavonoids with serum albumin: A review

Flavonoids are plant products abundant in every day diet and claimed to be beneficial for human health. After absorption, flavonoids are transported by the serum albumin (SA), the most abundant carrier blood protein, through formation of flavonoids-SA complex. This review deals with the current state of knowledge on flavonoids-SA complex over the past 10 years, mainly involved multi-spectroscopic techniques and molecular dynamics simulation studies to explore the binding mechanism, thermodynamics and structural aspects of flavonoids binding to SA. Especially, the novel method, capillary electrophoresis, high performance affinity chromatography approach, native mass spectrometry and microscale thermophoresis used in characterization of the interaction between flavonoids and SA as well as flavonoid-based fluorescent probe for SA measurement are also included in this review.

Comparative studies on the interaction of nine flavonoids with trypsin

In this study, the interaction between nine classic flavonoids (including baicalin, quercetin, myricetin, rutin, puerarin, daidzein, liquiritin and isoliquiritin) and trypsin was investigated by fluorescence spectroscopy and molecular modeling methods. The results reveal that all flavonoids can interact with trypsin to form flavonoid-trypsin complexes. The binding parameters obtained from the data at different temperatures indicate that all flavonoids can spontaneously bind with trypsin with one binding site. The binding constants of trypsin with nine classic flavonoids are in the following order as: baicalin > myricetin > rutin > isoliquiritin > hesperidin > puerarin > quercetin > daidzein > liquiritin. The interaction forces between flavonoids and trypsin may be electrostatic forces (except for rutin/puerarin/daidzein), hydrophobic interactions as well as van der Waals forces. Synchronous fluorescence spectroscopy shows that the interaction between flavonoids and trypsin changes the hydrophobicity of the microenvironment of tryptophan (Trp) residues. All flavonoids close to tyrosine (Tyr) residues but have no effect on the microenvironment around Tyr residues except for hesperidin and liquiritin. Molecular modeling displays that all flavonoids bind directly into trypsin cavity site and lead to a decrease in enzyme activity.

Evaluation of Intestinal Absorption Mechanism and Pharmacokinetics of Curcumin-Loaded Galactosylated Albumin Nanoparticles

Background

Most of the oral drugs have the properties of weak intestinal absorption and low bioavailability, which leads to little treatment to diseases. By nanotechnology, these drugs can be efficiently delivered to pass biological barriers and promote the cell uptake ability for the enhancement of the oral bioavailability.

Methods

The present work chose the prepared curcumin-loaded galactosylated albumin nanoparticles (Gal-BSA NPs) as the nano-drug samples to study the intestinal capacity and the oral bioavailability.

Results

The cell uptake assay showed that the Gal-BSA NPs could promote the internalization of more curcumin into the Caco-2 cells. Moreover, the cell uptake mechanism of Gal-BSA-Cur NPs depended on the clathrin-mediated endocytosis transport. The intestinal permeation assay using one Ussing chamber exhibited that the absorptive amounts of curcumin in Gal-BSA-Cur NPs group were 1.5-fold of pure curcumin group. Meanwhile, the permeation mechanism of Gal-BSA-Cur NPs across the intestine mainly depended on the passive transport. The pharmacokinetics study in vivo suggested that the oral bioavailability of Gal-BSA-Cur NPs was improved by 1.4-fold compared with pure curcumin.

Conclusion

All results demonstrated that Gal-BSA NPs could improve the intestinal absorption capacity and oral bioavailability of curcumin through the double absorption mechanisms of the clathrin-mediated endocytosis and the passive transport.

Toxic effects of Cr(VI) on the bovine hemoglobin and human vascular endothelial cells: Molecular interaction and cell damage

Hexavalent chromium [Cr(VI)] is the main harmful component in the atmosphere released by chemical industry. The study was conducted to assess Cr(VI) inducing cardiovascular diseases (CVDs) in vitro by investigating the effects of Cr(VI) on bovine hemoglobin (BHb) and human umbilical vein endothelial cells (HUVECs). Multi-spectroscopic techniques and molecular docking method were used to determine the interaction of Cr(VI) and BHb. Fluorescence spectra results showed that the quenching constant (K_sv) decreased with temperature raise, indicating that Cr(VI) quenches BHb fluorescence through static quenching mechanism. The number of binding sites was 1.14 (310 K), enthalpy and entropy changes revealed the interaction of Cr(VI) and BHb was driven by hydrogen bonds. The results of synchronous fluorescence and circular dichroism (CD) spectra suggested that Cr(VI) could change BHb conformation and influence the microenvironment of Trp and Tyr residues. Moreover, in order to study Cr(VI) induced HUVECs damage, inflammatory factors were detected at the mRNA level, JNK and p38 MAPK pathways were analyzed. The results shown that Cr(VI) could induce mRNA expression of NLRP3, ICAM-1, VCAM-1, TNF-α and IL-1β, and increased intracellular ROS. Furthermore, Cr(VI) could induce oxidative stress in HUVECs, and then activate JNK and p38 MAPK pathways, ultimately lead to apoptosis of HUVECs by activating mitochondrial apoptosis pathways. These results suggested that Cr(VI) might bring about CVDs by both changing the BHb conformation and inducing HUVECs damage.

Curcumin-loaded galactosylated BSA nanoparticles as targeted drug delivery carriers inhibit hepatocellular carcinoma cell proliferation and migration

Background

The main objective of this study was to develop novel BSA nanoparticles (BSA NPs) for improving the bioavailability of curcumin as an anticancer drug, and those BSA NPs were galactosylated for forming the curcumin-loaded galactosylated BSA nanoparticles (Gal-BSA-Cur NPs), thus enhancing their ability to target asialoglycoprotein receptor (ASGPR) overexpressed on hepatocellular carcinoma (HCC) cells.

Materials and methods

Gal-BSA-Cur NPs were prepared by the desolvation method and showed a spherical shape and well distribution with the average particle size of 116.24 nm.

Results

In vitro drug release assay exhibited that Gal-BSA-Cur NPs had higher release rates and improved the curcumin solubility. Cell uptake studies confirmed that Gal-BSA-Cur NPs could selectively recognize receptors on the surface of HCC (HepG2) cells and improve internalization ability of drug compared with BSA NPs-loaded curcumin (BSA-Cur NPs), which might be due to high affinity to galactose. Further, the effects of Gal-BSA-Cur NPs were evaluated by cytotoxicity assay, crystal violet assay, cell apoptosis assay, and wound healing assay, respectively, which revealed that Gal-BSA-Cur NPs could inhibit HepG2 cells proliferation, induce cell apoptosis, and inhibit cell migration.

Conclusion

Immunofluorescence staining has proved that the effects of Gal-BSA-Cur NPs related to the suppression of the nuclear factor κB-p65 (NF-κB-p65) expression in HepG2 cell nucleus. Therefore, these results indicate that novel Gal-BSA-Cur NPs are potential candidates for targeted curcumin delivery to HCC cells.

Structure-affinity relationship of the binding of phenolic acids and their derivatives to bovine serum albumin

Phenolic acids perform biological effects which are largely influenced by their binding to serum albumin. Therefore, investigating structure-affinity relationship of binding between phenolic acids and serum albumin is important. In this study, 114 phenolic acids and their derivatives, sharing the benzoic acid core with different substituents groups, were selected to investigate structure-affinity relationships with bovine serum albumin. The binding constants were obtained through fluorescence quenching, and a comprehensive mathematical model with inner-filter effect correction was applied. The results showed that the hydroxy group at the 2-position led to stronger binding affinity, while it had a negative influence at the 4-position. Substituting hydroxy groups with methoxy groups at 4-position and with methyl groups at 3-position both strengthened the binding affinity, respectively. Hydrogen bonding was one of the key binding forces for this binding interaction. Our findings provide a fundamental insight on the binding mechanism of phenolic acids to bovine serum albumin.

Inhibitory kinetics and mechanism of flavonoids from lotus (Nelumbo nucifera Gaertn.) leaf against pancreatic α-amylase

In this study, lotus leaf flavonoids (LLF) were found to show a notable inhibition activity on α-amylase in a mixed-type manner with IC₅₀ value of (5.58 ± 0.10) mg/mL. The intrinsic fluorescence of α-amylase was quenched by the interaction with LLF through a static quenching mechanism, and LLF-α-amylase complex was spontaneously formed mainly driven by the hydrophobic interaction and hydrogen bonding. Multispectroscopic analyses (synchronous fluorescence, three-dimensional fluorescence, circular dichroism (CD) and fourier transform infrared spectra (FT-IR)) comprehensively demonstrated that the binding of LLF to α-amylase would change the conformation and microenvironment of α-amylase, resulting in inhibiting the enzyme activity. The present study indicated that LLF had potential to be as an ingredient in functional food for the prevention of type-2 diabetes.

Rapid Investigation and Screening of Bioactive Components in Simo Decoction via LC-Q-TOF-MS and UF-HPLC-MD Methods

Simo decoction (SMD), as a traditional medicine, is widely used in the treatment of gastrointestinal dysmotility in China. In this study, a combined method of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) and ultrafiltration high-performance liquid chromatography molecular docking (UF-HPLC-MD) was efficiently employed to identify and screen bioactive ingredients in SMD. Ninety-four major constituents were identified or tentatively characterized by comparing their retention times and mass spectra with standards or literature data by using LC-Q-TOF-MS, and the ascription of those compounds were classified for the first time. Among them, 13 bioactive ingredients, including norisoboldine, eriocitrin, neoeriocitrin, narirutin, hesperidin, naringin, neohesperidin, hesperitin-7-O-glucoside, linderane, poncirin, costunolide, nobiletin, and tangeretin, were primarily identified as the human serum albumin (HSA) ligands at a range of docking scores from −29.7 to −40.6 kJ/mol by UF-HPLC-MD. The results indicate the systematic identification and screening of HSA ligands from Simo decoction guided by LC-Q-TOF-MS and UF-HPLC-MD represents a feasible and efficient method that could be extended for the identification and screening of other bioactive ingredients from natural medicines.

Characterization of interaction between scoparone and bovine serum albumin: spectroscopic and molecular docking methods

Scoparone is a major biological active substance derived from the traditional Chinese herbal medicine called Artemisia capillaris. It has been confirmed that scoparone has anti-inflammatory, anti-tumor, hepatoprotective and antioxidant effects. However, the binding interaction of scoparone with bovine serum albumin (BSA) still remains unknown. Therefore, the present study was conducted to clarify the binding interaction of scoparone with BSA under simulated physiological conditions (pH = 7.4) by utilizing spectroscopic and molecular docking methods. The formation of the scoparone–BSA complex was identified by UV-vis absorption spectroscopy experiment results. The fluorescence experiment results revealed that the quenching mechanism was static quenching and the binding procedure was spontaneous mainly driven by hydrophobic interaction. At 310 K, the number of binding sites was approximately equal to 1 and the binding constant was 6.79 × 10⁵ mol L⁻¹. The binding distance (4.81 nm) between scoparone and BSA was determined by Förster's non-radiative energy transfer theory. Molecular docking and site marker competitive experiment results verified that scoparone was more likely to be located in site I of BSA. In addition, the results of synchronous fluorescence spectroscopy and circular dichroism spectroscopy experiments proved that scoparone slightly changed the conformation of BSA by binding interaction with BSA. These findings would be useful for understanding the pharmacokinetics of scoparone in vivo, including scoparone transport, distribution, metabolism and excretion.

The interaction of scoparone with bovine serum albumin (BSA) was studied by utilizing spectroscopic and molecular docking methodologies.

Characterizing the binding interaction of astilbin with bovine serum albumin: a spectroscopic study in combination with molecular docking technology

Astilbin (ASN) is a flavonoid compound isolated from the rhizome of Smilax china L. (Smilacaceae). It has many bioactivities, such as selective immunosuppression, antioxidant, anti-hepatic injury, etc., and is widely used in traditional Chinese medical treatments. The interaction of ASN with bovine serum albumin (BSA) was studied in a physiological buffer (pH = 7.40) using multi-spectroscopic techniques in combination with molecular docking methods. UV-vis absorption measurements proved that a ASN–BSA complex could be formed. Fluorescence data revealed that ASN could strongly quench the intrinsic fluorescence of BSA in terms of a static quenching procedure. The process of binding was spontaneous and the binding occurred mainly through hydrogen bonding and van der Waals forces. The distance r between donor (BSA) and acceptor (ASN) was calculated to be 4.80 nm based on Förster's non-radiative energy transfer theory. The binding constant (K_a = 7.31 × 10⁴ mol L⁻¹) and the number of binding sites (n ≈ 1) at 298 K suggested that ASN only occupied one site in BSA with high affinity. Moreover, the results of molecular docking indicated that ASN was more likely to be located in site I (sub-domain IIA) of BSA. The results of synchronous fluorescence and three-dimensional fluorescence spectra showed that ASN induced conformational changes of BSA. The findings would be beneficial for research on the transportation, distribution and some important bioactivities of ASN in the human body.

The interaction of astilbin with bovine serum albumin was confirmed by multi-spectroscopic techniques and molecular docking methods.

Molecular Structure-Affinity Relationship of Flavonoids in Lotus Leaf (Nelumbo nucifera Gaertn.) on Binding to Human Serum Albumin and Bovine Serum Albumin by Spectroscopic Method

Lotus leaf has gained growing popularity as an ingredient in herbal formulations due to its various activities. As main functional components of lotus leaf, the difference in structure of flavonoids affected their binding properties and activities. In this paper, the existence of 11 flavonoids in lotus leaf extract was confirmed by High Performance Liquid Chromatography (HPLC) analysis and 11 flavonoids showed various contents in lotus leaf. The interactions between lotus leaf extract and two kinds of serum albumins (human serum albumin (HSA) and bovine serum albumin (BSA)) were investigated by spectroscopic methods. Based on the fluorescence quenching, the interactions between these flavonoids and serum albumins were further checked in detail. The relationship between the molecular properties of flavonoids and their affinities for serum albumins were analyzed and compared. The hydroxylation on 3 and 3’ position increased the affinities for serum albumins. Moreover, both of the methylation on 3’ position of quercetin and the C₂=C₃ double bond of apigenin and quercetin decreased the affinities for HSA and BSA. The glycosylation lowered the affinities for HSA and BSA depending on the type of sugar moiety. It revealed that the hydrogen bond force played an important role in binding flavonoids to HSA and BSA.

Analysis of the Total Biflavonoids Extract from Selaginella doederleinii by HPLC-QTOF-MS and Its In Vitro and In Vivo Anticancer Effects

Selaginella doederleinii Hieron has been traditionally used as a folk antitumor herbal medicine in China. In this paper, the phytochemical components of the total biflavonoids extract from S. doederleinii were studied by using high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF MS/MS) in negative ion mode, and their in vitro and in vivo anticancer effects were evaluated. Four types of biflavonoids from S. doederleinii, including IC3′–IIC8′′, IC3′–IIC6′′, IC3′–IIC3′′′, and C–O linked biflavonoids were examined originally using QTOF MS/MS. The fragmentation behavior of IC3′–IIC3′′′ linked biflavonoids was reported for the first time. A total of twenty biflavonoids were identified or tentatively characterized and eight biflavonoids were found from S. doederleinii for the first time. Furthermore, the 3-(4,5-Dimethyl-2-thizolyl)-2,5-diphenyltertazolium bromide (MTT) assay and xenograft model of mouse lewis lung cancer(LLC) in male C57BL/6 mice revealed favorable anticancer properties of the total biflavonoids extracts from S. doederleinii. The results of this work could provide useful knowledge for the identification of biflavonoids in herbal samples and further insights into the chemopreventive function of this plant.

Comparative study of the binding of 3 flavonoids to the fat mass and obesity-associated protein by spectroscopy and molecular modeling

This study aims to investigate the interaction between 3 flavonoids (quercetin, apigenin, and naringenin) and fat mass and obesity-associated protein by fluorescence, ultraviolet-visible absorption spectroscopy, and molecular modeling. Results indicate that the intrinsic fluorescence of fat mass and obesity-associated protein can be quenched by the 3 flavonoids through a static quenching procedure. Thermodynamic analysis and molecular modeling results suggest that hydrophobic interaction and hydrogen bond forces play the major roles in the binding process. Moreover, results also show that the rank order of quenching constant and binding constant is quercetin > apigenin > naringenin.

Fe3O4@PVIM@Zn(ii) magnetic microspheres for luteolin recognition via combined reflux-precipitation polymerization and metal-ion affinity strategy

Mild ploy base on acid response affinity of Fe₃O₄@PVIM@Zn(ii) for luteolin extraction.