Spectrofluorimetric and molecular docking investigation on the interaction of 6-azauridine, a pyrimidine nucleoside antimetabolite, with serum protein

Preparation, characterization and analysis of anthocyanin arbutin co-amorphous complexes and evaluation of the inhibition of tyrosinase

Natural phenolic compounds, such as anthocyanins and arbutin, have demonstrated significant potential as tyrosinase (TYR) inhibitors. However, the application of anthocyanins in biological systems is hindered by their instability under alkaline conditions, elevated temperatures, and light exposure. In contrast, arbutin exhibits superior stability while also functioning as a TYR inhibitor. To overcome these limitations, this study developed an Anthocyanin-α-Arbutin Co-amorphous (AAC) system aimed at enhancing both the stability of anthocyanins and their TYR inhibitory properties. Kinetic studies revealed that anthocyanins, arbutin, and AAC act as reversible mixed-type TYR inhibitors, with competitive inhibition as the predominant mechanism. Each compound exhibited distinct inhibition sites. Fluorescence analysis demonstrated that anthocyanins induce a fluorescence burst in TYR, likely attributed to Tyr residues, whereas α-arbutin and AAC enhance the fluorescence intensity of TYR. Moreover, α-arbutin and AAC were found to decrease the microenvironmental hydrophobicity surrounding tyrosine (Tyr) residues while increasing it around tryptophan (Trp) residues, suggesting potential conformational changes in tyrosinase. Molecular docking analysis indicated that hydrogen bonding and π-π stacking interactions occurred between anthocyanins and arbutin in the AAC system. Specifically, anthocyanins primarily interacted with TYR through π-π and π-alkyl interactions, while α-arbutin predominantly bound to TYR via hydrogen bonding. Consistent with the interaction study, α-arbutin was found to associate with tyrosinase mainly through hydrogen bonding and van der Waals forces. These findings provide novel insights into the interactions between anthocyanins and α-arbutin in the context of food science and lay a foundation for the development of innovative TYR inhibitors.

Extended fluorescent uridine analogues: synthesis, photophysical properties and selective interaction with BSA protein

The improvement in fluorescence properties of 2′-deoxyuridine was made possible by the introduction of (hetero)aromatic moieties at the C–5 position of uridine with alkenyl/phenyl/styryl linkers to create a library of useful fluorescent nucleosides.

Interaction of piroxicam with bovine serum albumin investigated by spectroscopic, calorimetric and computational molecular methods

The binding of drugs to serum proteins is governed by weak non-covalent forces. In this study, the nature and magnitude of the interactions between piroxicam (PRX) and bovine serum albumin (BSA) was assessed using spectroscopic, calorimetric and computational molecular methods. The fluorescence data revealed an atypical behavior during PRX and BSA interaction. The quenching process of tryptophan (Trp) by PRX is a dual one (approximately equal static and dynamic quenched components). The FRET results indicate that a non-radiative transfer of energy occurred. The association constant and the number of binding sites indicate moderate PRX and BSA binding. The competitive binding study indicates that PRX is bound to site I from the hydrophobic pocket of subdomain IIA of BSA. The synchronous spectra showed that the microenvironment around the BSA fluorophores and protein conformation do not change considerably. The Trp lifetimes revealed that PRX mainly quenches the fluorescence of Trp-213 situated in the hydrophobic domain. The CD and DSC investigation show that addition of PRX stabilizes the protein structure. ITC results revealed that BSA-PRX binding involves a combination of electrostatic, hydrophobic and hydrogen interactions. The analysis of the computational data is consistent with the experimental results. This thorough investigation of the PRX-BSA binding may provide support for other studies concerning moderate affinity drugs with serum protein.Communicated by Ramaswamy H. Sarma.

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.

Characterization of MK₈(H₂) from Rhodococcus sp. B7740 and Its Potential Antiglycation Capacity Measurements

Menaquinone (MK) has an important role in human metabolism as an essential vitamin (VK₂), which is mainly produced through the fermentation of microorganisms. MK₈(H₂) was identified to be the main menaquinone from Rhodococcus sp. B7740, a bacterium isolated from the arctic ocean. In this work, MK₈(H₂) (purity: 99.75%) was collected through a convenient and economic extraction process followed by high-speed countercurrent chromatography (HSCCC) purification. Additionally, high-resolution mass spectrometry (HRMS) was performed for further identification and the hydrogenation position of MK₈(H₂) (terminal unit) was determined using nuclear magnetic resonance (NMR) for the first time. MK₈(H₂) showed a superior antioxidant effect and antiglycation capacity compared with ubiquinone Q10 and MK₄. High-performance liquid chromatography–mass spectrometer (HPLC-MS/MS) and molecular docking showed the fine interaction between MK₈(H₂) with methylglyoxal (MGO) and bull serum albumin (BSA), respectively. These properties make MK₈(H₂) a promising natural active ingredient with future food and medicine applications.

Design of "Click" Fluorescent Labeled 2'-deoxyuridines via C5-[4-(2-Propynyl(methyl)amino)]phenyl Acetylene as a Universal Linker: Synthesis, Photophysical Properties, and Interaction with BSA

Microenvironment-sensitive fluorescent nucleosides present attractive advantages over single-emitting dyes for sensing inter-biomolecular interactions involving DNA. Herein, we report the rational design and synthesis of triazolyl push-pull fluorophore-labeled uridines via the intermediacy of C5-[4-(2-propynyl(methyl)amino)]phenyl acetylene as a universal linker. The synthesized nucleosides showed interesting solvatochromic characteristic and/or intramolecular charge transfer (ICT) features. A few of them also exhibited dual-emitting characteristics evidencing our designing concept. The HOMO-LUMO distribution showed that the emissive states of these nucleosides were characterized with more significant electron redistribution between the C5-[4-(2-propynyl(methyl)amino)]phenyl triazolyl donor moiety and the aromatic chromophores linked to it, leading to modulated emission property. The solvent polarity sensitivity of these nucleosides was also tested. The synthesized triazolyl benzonitrile (10C), naphthyl (10E), and pyrenyl (10G) nucleosides were found to exhibit interesting ICT and dual (LE/ICT) emission properties. The dual-emitting pyrenyl nucleoside maintained a good ratiometric response in the BSA protein microenvironment, enabling the switch-on ratiometric sensing of BSA as the only protein biomolecule. Thus, it is expected that the new fluorescent nucleoside analogues would be useful in designing DNA probes for nucleic acid analysis or studying DNA-protein interactions via a drastic change in fluorescence response due to a change in micropolarity.

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.

Formation of a Multiligand Complex of Bovine Serum Albumin with Retinol, Resveratrol, and (-)-Epigallocatechin-3-gallate for the Protection of Bioactive Components

Clarification of the interaction mechanisms between proteins and bioactive components is important to develop effective carriers for encapsulation and protection of bioactive components. Bovine serum albumin (BSA), a globular protein in serum and milk, contains multiple sites to bind a variety of low-molecular-weight molecules, forming protein-monoligand complexes. In this study, the interactions of BSA with retinol, resveratrol, and/or (-)-epigallocatechin-3-gallate (EGCG) were investigated by using fluorescence, circular dichroism, and molecular docking techniques. BSA-triligand complexes were successfully formed when added in the sequence of retinol, resveratrol, and EGCG. The stability of these bioactive components was improved in the complexes relative to free ones. The complexes provided a better protective effect on retinol and resveratrol than did BSA-monoligand complexes, in which the presence of EGCG played an important role.