Elucidation of structural and functional properties of albumin bound to gold nanoparticles

Nanoparticle–albumin complexes are being designed for targeted drug delivery and imaging. However, the changes in the functional properties of albumin due to adsorption on nanoparticles remain elusive. Thus, the objective of this work was to elucidate the structural and functional properties of human and bovine serum albumin bound to negatively charged gold nanoparticles (GNPs). Fluorescence data demonstrated static quenching of albumin by GNP with the quenching of buried as well as surface tryptophan in BSA. The binding process was enthalpy and entropy-driven in HSA and BSA, respectively. At lower concentrations of GNP there was a higher affinity for tryptophan, whereas at higher concentrations both tryptophan and tyrosine participated in the interaction. Synchronous fluorescence spectra revealed that the microenvironment of tryptophan in HSA turned more hydrophilic upon exposure to GNP. The α-helical content of albumin was unaltered by GNP. Approximately 37 and 23% reduction in specific activity of HSA and BSA was observed due to GNP binding. In presence of warfarin and ibuprofen the binding constants of albumin–GNP complexes were altered. A very interesting observation not reported so far is the retained antioxidant activity of albumin in presence of GNP i.e. we believe that GNPs did not bind to the free sulfhydryl groups of albumin. However enhanced levels of copper binding were observed. We have also highlighted the differential response in albumin due to gold and silver nanoparticles which could be attributed to differences in the charge of the nanoparticle.     

Probing the interaction of thionine with human serum albumin by multispectroscopic studies and its in vitro cytotoxic activity toward MCF-7 breast cancer cells

The studies on protein–dye interactions are important in biological process and it is regarded as vital step in rational drug design. The interaction of thionine (TH) with human serum albumin (HSA) was analyzed using isothermal titration calorimetry (ITC), spectroscopic, and molecular docking technique. The emission spectral titration of HSA with TH revealed the formation of HSA–TH complex via static quenching process. The results obtained from absorption, synchronous emission, circular dichroism, and three-dimensional (3D) emission spectral studies demonstrated that TH induces changes in the microenvironment and secondary structure of HSA. Results from ITC experiments suggested that the binding of TH dye was favored by negative enthalpy and a favorable entropy contribution. Site marker competitive binding experiments revealed that the binding site of TH was located in subdomain IIA (Sudlow site I) of HSA. Molecular docking study further substantiates that TH binds to the hydrophobic cavity of subdomain IIA (Sudlow site I) of HSA. Further, we have studied the cytotoxic activity of TH and TH–HSA complex on breast cancer cell lines (MCF-7) by MTT assay and LDH assay. These studies revealed that TH–HSA complex showed the higher level of cytotoxicity in cancer cells than TH dye-treated MCF-7 cells and the significant adverse effect did not found in the normal HBL-100 cells. Fluorescence microscopy analyses of nuclear fragmentation studies validate the significant reduction of viability of TH–HSA-treated human MCF-7 breast cancer cells through activation of apoptotic-mediated pathways.     

In vitro study on binding interaction of quinapril with bovine serum albumin (BSA) using multi-spectroscopic and molecular docking methods

The binding interaction between quinapril (QNPL) and bovine serum albumin (BSA) in vitro has been investigated using UV absorption spectroscopy, steady-state fluorescence spectroscopic, synchronous fluorescence spectroscopy, 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and molecular docking methods for obtaining the binding information of QNPL with BSA. The experimental results confirm that the quenching mechanism of the intrinsic fluorescence of BSA induced by QNPL is static quenching based on the decrease in the quenching constants of BSA in the presence of QNPL with the increase in temperature and the quenching rates of BSA larger than 10¹⁰ L mol^?1 s^?1, indicating forming QNPL–BSA complex through the intermolecular binding interaction. The binding constant for the QNPL–BSA complex is in the order of 10⁵ M^?1, indicating there is stronger binding interaction of QNPL with BSA. The analysis of thermodynamic parameters together with molecular docking study reveal that the main binding forces in the binding process of QNPL with BSA are van der Waal’s forces and hydrogen bonding interaction. And, the binding interaction of BSA with QNPL is an enthalpy-driven process. Based on Förster resonance energy transfer, the binding distance between QNPL and BSA is calculated to be 2.76 nm. The results of the competitive binding experiments and molecular docking confirm that QNPL binds to sub-domain IIA (site I) of BSA. It is confirmed there is a slight change in the conformation of BSA after binding QNPL, but BSA still retains its secondary structure α-helicity.     

LC–MS/MS and chiroptical spectroscopic analyses of multidimensional metabolic systems of chiral thalidomide and its derivatives

Enantiomeric thalidomide undergoes various kinds of biotransformations including chiral inversion, hydrolysis, and enzymatic oxidation, which results in several metabolites, thereby adding to the complexity in the understanding of the nature of thalidomide. To decipher this complexity, we analyzed the multidimensional metabolic reaction networks of thalidomide and related molecules in vitro . Characteristic patterns in the amount of various metabolites of thalidomide and related molecules generated during a combination of chiral inversion, hydrolysis, and hydroxylation were observed using liquid chromatography–tandem mass spectrometry and chiroptical spectroscopy. We found that monosubstituted thalidomide derivatives exhibited different time‐dependent metabolic patterns compared with thalidomide. We also revealed that monohydrolyzed and monohydroxylated metabolites of thalidomide were likely to generate mainly by a C‐5 oxidation of thalidomide and subsequent ring opening of the hydroxylated metabolite. Since chirality was conserved in most of these metabolites during metabolism, they had the same chirality as that of nonmetabolized thalidomide. Our findings will contribute toward understanding the significant pharmacological effects of the multiple metabolites of thalidomide and its derivatives.     

Mid-infrared spectroscopic analysis of saccharides in aqueous solutions with sodium chloride

The infrared spectral characteristics of three different types of disaccharides (trehalose, maltose, and sucrose) and four different types of monosaccharides (glucose, mannose, galactose, and fructose) in aqueous solutions with sodium chloride (NaCl) were determined. The infrared spectra were obtained using the FT-IR/ATR method and the absorption intensities respected the interaction between the saccharide and water with NaCl were determined. This study also focused on not only the glycosidic linkage position and the constituent monosaccharides, but also the concentration of the saccharides and NaCl and found that they have a significant influence on the infrared spectroscopic characterization of the disaccharides in an aqueous solution with NaCl. The absorption intensities representing the interaction between a saccharide and water with NaCl were spectroscopically determined. Additionally, the applications of MIR spectroscopy to obtain information about saccharide–NaCl interactions in foods and biosystems were suggested.     

Betamethasone‐based chiral electrochemical sensor coupled to chemometric methods for determination of mandelic acid enantiomers

A chiral biosensing platform was developed using betamethasone (BMZ) as chiral recognition element through multilayered electrochemical deposition of BMZ, overoxidized polypyrrole, and nanosheets of graphene (OPPy‐BMZ/GR), for enantio‐recognition of mandelic acid (MA) enantiomers. The deposited film was characterized by scanning electron microscopy, differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. It was shown that the chiral sensing platform can discriminate R‐ and S‐MA differential pulse voltammetry signals, at the voltages of 1.35 and 1.33 V (vs Ag/AgCl), respectively. To tackle the problem of highly overlapping peaks of these enantiomers, the partial least squares (PLS) regression and genetic algorithm‐PLS (GA‐PLS) were used for simultaneous quantification of MA enantiomers. Generally, variable selection by genetic algorithm provided an improvement in prediction results when compared to full‐voltammogram PLS. Good analytical performances were obtained despite the inherent complexity of the simultaneous determination.     

The impact of hyperglycemia on adhesion between endothelial and cancer cells revealed by single‐cell force spectroscopy

The impact of hyperglycemia on adhesion between lung carcinoma cells (A549) and pulmonary human aorta endothelial cells (PHAEC) was studied using the single‐cell force spectroscopy. Cancer cells were immobilized on a tipless Atomic Force Microscopy (AFM) cantilever and a single layer of endothelial cells was prepared on a glass slide. The measured force‐distance curves provided information about the detachment force and about the frequency of specific ligand‐receptor rupture events. Measurements were performed for different times of short term (up to 2 h) and prolonged hyperglycemia (3 h ‐ 24 h). Single‐cell force results were correlated with the expression of cell adhesion molecules (intercellular adhesion molecule, P‐selectin) and with the length and density of the PHAECs glycocalyx layer, which were measured by AFM nanoindentation. For short‐term hyperglycemia, we observed a statistically significant increase of the adhesion parameters that was accompanied by an increase of the glycocalyx length and expression of P‐selectin. Removal of hyaluronic acid from PHAECs glycocalyx significantly decreased the adhesion parameters, which indicates that hyaluronic acid has a strong impact on adhesion in A549/PHAEC system in short term of hyperglycemia. For prolonged hyperglycemia, the most significant increase of adhesion parameters was observed for 24 hours and this phenomenon correlated with the expression of adhesion molecules and a decrease of the glycocalyx length. Taking together, presented data indicate that both mechanical and structural properties of the endothelial glycocalyx strongly modulate the adhesion in the A549/PHAEC system.