Studies on the interaction of caffeic acid with human serum albumin in membrane mimetic environments

Effect of the presence of berberine/curcumin on the binding of limonin to human serum albumin and antitumor activity in vitro

The competition among drugs for binding to plasma proteins is regarded as a pharmacokinetic drug interaction. Competition between antitumor agents and other drugs for plasma protein binding can alter the free concentration of the drug, potentially impacting its efficacy and increasing the risk of toxic side effects. Through a range of spectroscopic techniques, this study examined the interaction between limonin and human serum albumin (HSA) in the context of berberine (Ber) and curcumin (Cur) under physiological conditions to clarify the binding mechanisms of binary and ternary systems at the molecular level. As demonstrated by fluorescence quenching experiments, Static quenching was identified as the mechanism of interaction between HSA and limonin. The results of site competition experiments indicated that the binding site between limonin and HSA was site I, a result further supported by molecular docking simulations. Through the use of thermodynamic data calculations, it was determined that limonin forms a stable complex with HSA by establishing hydrogen bonds and van der Waals forces. Circular dichroism (CD) spectroscopy, three-dimensional (3D) fluorescence spectroscopy, and synchronous fluorescence spectroscopy (SFS) employed to validate the notion that limonin perturbed the microenvironment of amino acids and induced conformational changes in HSA. What's more, the presence of Ber or Cur was found to have further modified the alterations observed in the interaction between the original HSA-limonin binary system. In vitro cellular experiments showed that interaction with HSA reduced the antitumor activity of limonin. In contrast, adding Ber or Cur increased the inhibition rate of tumor cells. The coexistence of both Ber and Cur significantly diminished limonin's binding affinity to HSA. The current investigation enhances comprehension regarding the binding characteristics and interaction mechanisms involving limonin, Ber, Cur, and HSA. It explores the potential of HSA as a versatile drug carrier and furnishes theoretical underpinnings for co-administrative strategies.

Phytoferritin functions in two interface-loading of natural pigment betanin and caffeic acid with enhanced color stability and the sustained release of betanin

Betanin, a natural red pigment, is sensitive and prone to fading and discoloration, affecting its stability and bioavailability. Phytoferritin is a nano-diameter protein with unique interior-/exterior-interfaces. By the unique interfaces and pH-induced self-assembly of ferritin, a ferritin-betanin complex (FB) with an encapsulation efficiency of 17.66 ± 1.24% was prepared. The caffeic acid-FB (CFB) was further fabricated by attaching ferritin with caffeic acid, and the binding number n of caffeic acid was 88.47 ± 9.49, with a binding constant K of (1.63 ± 0.33) × 104 M-1. Fluorescence and Fourier transform infrared analysis indicated that the encapsulation of betanin and the binding of caffeic acid influenced the ferritin structure. The interaction between caffeic acid and ferritin was mainly through van der Waals forces and hydrogen bonds. TEM and DLS showed that the globular structure and diameter (12 nm) remained in CFB. Furthermore, the ferritin and caffeic acid exhibited a synergistic effect in enhancing thermal, light, and ferric ion stabilities, and controlled the betanin release in a more sustained manner in the simulated gastrointestinal tract. In addition, the antioxidant capacity of CFB was enhanced compared with free betanin. This study promotes the bioavailability of betanin by two interface-loading of ferritin, and guides the use of ferritin nanoparticles as a nanocarrier for pigment stabilization.

Food Antioxidants and Their Interaction with Human Proteins

Common to all biological systems and living organisms are molecular interactions, which may lead to specific physiological events. Most often, a cascade of events occurs, establishing an equilibrium between possibly competing and/or synergistic processes. Biochemical pathways that sustain life depend on multiple intrinsic and extrinsic factors contributing to aging and/or diseases. This article deals with food antioxidants and human proteins from the circulation, their interaction, their effect on the structure, properties, and function of antioxidant-bound proteins, and the possible impact of complex formation on antioxidants. An overview of studies examining interactions between individual antioxidant compounds and major blood proteins is presented with findings. Investigating antioxidant/protein interactions at the level of the human organism and determining antioxidant distribution between proteins and involvement in the particular physiological role is a very complex and challenging task. However, by knowing the role of a particular protein in certain pathology or aging, and the effect exerted by a particular antioxidant bound to it, it is possible to recommend specific food intake or resistance to it to improve the condition or slow down the process.

Insight into the Interaction Mechanism of HSA with Aztreonam: A Multispectroscopic and Computational Approach

Aztreonam is a Gram-negative bacteria-targeting synthetic monobactam antibiotic. Human serum albumin (HSA) plays an important role in the transference of pharmaceuticals, hormones, and fatty acids, along with other compounds, determining their biodistribution and physiological fate. Using several biophysical and in silico approaches, we studied the interaction of aztreonam with HSA under physiological environments in this study. Results confirm the formation of HSA-aztreonam complex where aztreonam showed moderate affinity towards HSA. A static mode of quenching was confirmed from the steady state fluorescence data. FRET findings also showed that there was a significant feasibility of energy transfer between HSA and aztreonam. Site marker displacement experimental conclusion suggested the binding site of aztreonam was the sub-domain IB of HSA. Circular dichroic spectroscopic analysis suggested that aztreonam interaction decreases the α-helical content of HSA. Changes in microenvironment were studied through synchronous fluorescence data. According to molecular docking results, the HSA-aztreonam complex is mostly maintained by non-covalent forces, with a binding energy of 7.7 kcal mol^-1. The presence of a hydrogen bond, van der Waal interaction, and pi-anion interaction in the binding process, as well as conformational changes in HSA after binding with aztreonam, are all confirmed by molecular dynamic simulation.

Multispectroscopic and synergistic antioxidant study on the combined binding of caffeic acid and (-)-epicatechin gallate to lysozyme

The binding of caffeic acid (CA) and/or (-)-epicatechin gallate (ECG) to lysozyme was investigated by multispectroscopic methods and molecular docking. The effects of the single and combined binding on the structure, activity and stability of lysozyme and the synergistic antioxidant activity of CA and ECG were also studied. Fluorescence quenching spectra, time-resolved fluorescence spectra, and UV-vis absorption difference spectra all ascertained the static quenching mechanism of lysozyme by CA/ECG. Thermodynamic parameters indicated that CA and ECG competitively bound to lysozyme, and CA had a stronger binding affinity, which was consistent with the results of molecular docking. Hydrogen bonding, van der Waals' force and electrostatic interaction were the main driving forces for the binding process. Synchronous fluorescence spectra displayed that the interaction of CA/ECG exposed the tryptophan residues of lysozyme to a more hydrophilic environment. Circular dichroism spectroscopy, Fourier transform infrared spectroscopy and dynamic light scattering indicated that the binding of CA and/or ECG to lysozyme resulted in the change of the secondary structure and increased the particle size of lysozyme. The binding of CA and/or ECG to lysozyme inhibited the enzyme activity and enhanced the thermal stability of lysozyme. The combined application of CA and ECG showed antioxidant synergy which was influenced by the encapsulation of lysozyme and cellular uptake. In summary, this work provides theoretical guidance for lysozyme as a carrier for the combined application of CA and ECG.

Insight on the microscopic binding mechanism of bisphenol compounds (BPs) with transthyretin (TTR) based on multi-spectroscopic methods and computational simulations

Thyroid hormones are involved in numerous physiological processes as regulators of metabolism, regulating organ growth, and mental state. Bisphenol compounds (BPs) are recognized as chemicals that interfere with endocrine balance. Because BPs have a similar structure to thyroxine, they can compete for binding to thyroid protein and disrupt the normal physiological activity of the thyroid system. In this study, three typical bisphenol compounds were selected to explore the interaction between BPs and TTR by computer simulations and multi-spectroscopic methods. The results revealed that BPs quenched the endogenous fluorescence of TTR via the combination of static quenching and non-radiative energy transfer, and the van der Waals forces and hydrogen bonding played a synergistic role in the binding process of BPs and TTR. Furthermore, the three-dimensional fluorescence spectroscopy, UV-vis spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, which were employed to determine the conformation of protein, revealed that binding of BPs with TTR could induce conformational changes in TTR. In addition, the binding sites and the residues surrounding the BPs within the TTR were determined through molecular docking and molecular dynamics simulation. Therefore, this work provides new insights into the interaction between BPs and TTR to evaluate the potential toxicity of BPs.

Unveiling the interaction profile of rosmarinic acid and its bioactive substructures with serum albumin

Rosmarinic acid, a phytochemical compound, bears diverse pharmaceutical profile. It is composed by two building blocks: caffeic acid and a salvianic acid unit. The interaction profile, responsible for the delivery of rosmarinic acid and its two substructure components by serum albumin remains unexplored. To unveil this, we established a novel low-cost and efficient method to produce salvianic acid from the parent compound. To probe the interaction profile of rosmarinic acid and its two substructure constituents with the different serum albumin binding sites we utilised fluorescence spectroscopy and competitive saturation transfer difference NMR experiments. These studies were complemented with transfer NOESY NMR experiments. The thermodynamics of the binding profile of rosmarinic acid and its substructures were addressed using isothermal titration calorimetry. In silico docking studies, driven by the experimental data, have been used to deliver further atomic details on the binding mode of rosmarinic acid and its structural components.

Novel Fluorescent Microemulsion: Probing Properties, Investigating Mechanism, and Unveiling Potential Application

Nanoscale microemulsions have been utilized as delivery carriers for nutraceuticals and active biological drugs. Herein, we designed and synthesized a novel oil in water (O/W) fluorescent microemulsion based on isoamyl acetate, polyoxyethylene castor oil EL (CrEL), and water. The microemulsion emitted bright blue fluorescence, thus exhibiting its potential for active drug detection with label-free strategy. The microemulsion exhibited excitation-dependent emission and distinct red shift with longer excitation wavelengths. Lifetime and quantum yield of fluorescent microemulsion were 2.831 ns and 5.0%, respectively. An excellent fluorescent stability of the microemulsion was confirmed by altering pH, ionic strength, temperature, and time. Moreover, we proposed a probable mechanism of fluorochromic phenomenon, in connection with the aromatic ring structure of polyoxyethylene ether substituent in CrEL. Based on our findings, we concluded that this new fluorescent microemulsion is a promising drug carrier that can facilitate active drug detection with a label-free strategy. Although further research is required to understand the exact mechanism behind its fluorescence property, this work provided valuable guidance to develop new biosensors based on fluorescent microemulsion.

Interaction rule and mechanism of perfluoroalkyl sulfonates containing different carbon chains with human serum albumin

All three PFASs bind to HSA mainly through electrostatic forces and the toxicity decreases with the shortening of the carbon chain.

Study on acute toxicity and structure-activity relationship of zebrafish (Danio rerio) exposed to naphthoquinones

In this paper, we evaluated the acute toxicity of five naphthoquinone compounds, expressed as median lethal concentration at 96 h (LC(50)) using zebrafish as a model. The five compounds were classified as harmful or very toxic. The Gaussian method was used to calculate the quantitative-chemical parameters of each compound. Based on the structure-activity relationship analysis, the interaction between the naphthoquinones and the target is likely mediated by 1-carbonyl and the hydrophobic fraction substituted in alpha -position of naphthoquinone via hydrogen bonding and hydrophobic interactions. Our results provide a foundation for evaluating the aquatic ecological risk and the mode of action of naphthoquinones in the environment.