1H-NMR study of the effect of acetonitrile on the interaction of ibuprofen with human serum albumin

Spectroscopic and molecular docking study of three kinds of cinnamic acid interaction with pepsin

In this work, under simulated physiological conditions (pH = 2.2, glycine hydrochloric acid buffer solution), the interactions of cinnamic acid (CA), m-hydroxycinnamic acid (m-CA) and p-hydroxycinnamic acid (p-CA) with pepsin were studied by fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared spectroscopy (FTIR), molecular docking and molecular dynamic simulation (MD). The spectrogram results showed that these three kinds of CA had a strong ability to quench the intrinsic fluorescence of pepsin, and the quenching effects were obvious with the increase of concentration of these three kinds of molecules. The quenching mechanism of CA, m-CA and p-CA on the fluorescence of pepsin was static quenching. In addition, a stable complex was formed between three kinds of CA with pepsin. Thermodynamic data and docking information suggested that three kinds of CA combine with pepsin were mainly driven by electrostatic force and hydrogen bond. The binding constant and the number of binding sites were determined. The interaction of CA, m-CA and p-CA with pepsin was spontaneous, and accompanied by non-radiative energy transfer. The results from CD, FTIR, UV-Vis and synchronous fluorescence spectra measurements manifested that the secondary structure of pepsin was changed by the binding of three kinds of CA. The β-sheet of pepsin increased after the interaction with three kinds of CA. The assay results of pepsin activity showed that three kinds of CA led to a decrease in pepsin activity within the investigated concentrations. Molecular docking investigation revealed the formation of polar hydrogen bonds as well as hydrophobic interactions between three kinds of CA with pepsin, and the ligand within the binding pocket of pepsin. MD results implied the formation of a stable complex between three kinds of CA and pepsin. The research suggested that cinnamic acid and its derivatives could be a potential effect on the structure and properties of digestive enzyme.

Interaction of Ibuprofen with Partially Unfolded Bovine Serum Albumin in the Presence of Ionic Micelles and Oligosaccharides at Different λex and pH: A Spectroscopic Analysis

The interaction between the plasma protein bovine serum albumin (BSA) and the drug ibuprofen (IBU) has been investigated at three different pH values (7.4, 6.5, and 8.0) in the presence of oligosaccharides and surfactants. The interaction analysis of BSA with oligosaccharides and surfactants has also been studied in the absence of the drug ibuprofen. The results obtained give convenient and efficient access to understand the mechanism of binding of ibuprofen to BSA, and the major forces involved are found to be hydrophobic forces, hydrogen bonding and ionic interactions. In addition to that, the formation of inclusion complexes of ibuprofen with oligosaccharides (β-CD and 2-HP-β-CD) has been observed, which has depicted that due to the hydrophobic nature of ibuprofen, it becomes more soluble in the presence of oligosaccharides, but due to the larger size of the inclusion complexes, these could not be able to access the hydrophobic pocket of BSA where tryptophan-212 (Trp-212) resides. The binding interaction between BSA and ibuprofen is observed in the presence of surfactants (SDS and CTAB), which partially unfold the protein. Non-radiative fluorescence resonance energy transfer (FRET) from Trp and Tyr residues of BSA in the presence of an anionic surfactant SDS to ibuprofen has depicted that there is a possibility of drug binding even in the partially unfolded state of BSA protein. Furthermore, the distance between the protein and the drug has been calculated from the FRET efficiency, which gives a comprehensive overview of ibuprofen binding to BSA even in its partially denatured state. The hydrophobic drug binding to the partially unfolded serum albumin protein (BSA) supports the "necklace and bead structures" model and opens up a new direction of drug loading and delivery system, which will have critical therapeutic applications in the efficient delivery of pharmacologically prominent drugs.

Evaluation of Viburnum opulus L. Fruit Phenolics Cytoprotective Potential on Insulinoma MIN6 Cells Relevant for Diabetes Mellitus and Obesity

In this study, the influence of guelder rose (Viburnum opulus) fruit fresh juice (FJ) and a phenolic-rich fraction (PRF) isolated from juice on mice insulinoma MIN6 cells activities was investigated. Extracts were able to decrease intracellular oxidative stress at the highest non-cytotoxic concentrations. They induced glucagon-like peptide-1 (GLP-1) secretion in the presence of an elevated glucose concentration, and they inhibited in vitro activity of the dipeptidyl peptidase-4 (DPP4) enzyme. Nonetheless, inhibition of glucose-stimulated insulin secretion was detected, which was accompanied by a decrease of cellular membrane fluidity and hyperpolarization effect. In addition, the increase of free fatty acid uptake and accumulation of lipid droplets in MIN6 cells were observed. Elevated extract concentrations induced cell apoptosis through the intrinsic mitochondrial pathway with activation of initiatory caspase-9 and downstream caspases-3/7. The fluorescence-quenching studies indicated that PRF extract has binding affinity to human serum albumin, which is one of the factors determining drug bioavailability. Taken together, despite the cytoprotective activity against generated intracellular oxidative stress, V. opulus revealed potential toxic effects as well as decreased insulin secretion from MIN6 cells. These findings are relevant in understanding V. opulus limitations in developing diet supplements designed for the prevention and treatment of postprandial glucose elevation.

LaPO4:Eu fluorescent nanorods, synthesis, characterization and spectroscopic studies on interaction with human serum albumin

Eu³⁺ doped LaPO₄ fluorescent nanorods (LaPO₄:Eu) was successfully fabricated by a hydrothermal process. The obtained LaPO₄:Eu nanorods under the optimal conditions were characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR), UV-vis absorption and fluorescence spectroscopy. The nanorods with a length of 50-100nm and a diameter of about 10nm, can emit strong red fluorescence upon excitation at 241nm. The FTIR result confirmed that there are lots of phosphate groups on the surfaces of nanorods. In order to better understand the physiological behavior of nanorods in human body, multiple spectroscopic methods were used to study the interaction between the LaPO₄:Eu nanorods and human serum albumin (HSA) in the simulated physiological conditions. The results indicated that the nanorods can effectively quench the intrinsic fluorescence of HSA through a dynamic quenching mode with the association constants of the order of 10³Lmol^-1. The values of the thermodynamic parameters suggested that the binding of the nanorods to HSA was a spontaneous process and van der Waals forces and hydrogen bonds played a predominant role. The displacement experiments verified that the binding site of nanorods on HSA was mainly located in the hydrophobic pocket of subdomain IIA (site I) of HSA. The binding distance between nanorods and HSA was calculated to be 4.2nm according to the theory of Förster non-radiation energy transfer. The analysis of synchronous fluorescence, three-dimensional fluorescence (3D) and circular dichroism (CD) spectra indicated that there the addition of LaPO₄:Eu nanorods did not caused significant alterations in conformation of HSA secondary structure and the polarity around the amino acid residues.

Interaction between Saikosaponin D, Paeoniflorin, and Human Serum Albumin

Saikosaponin D (SSD) and paeoniflorin (PF) are the major active constituents of Bupleuri Radix and Paeonia lactiflora Pall, respectively, and have been widely used in China to treat liver and other diseases for many centuries. We explored the binding of SSD/PF to human serum albumin (HSA) by using fluorospectrophotometry, circular dichroism (CD) and molecular docking. Both SSD and PF produced a conformational change in HSA. Fluorescence quenching was accompanied by a blue shift in the fluorescence spectra. Co-binding of PF and SSD also induced quenching and a conformational change in HSA. The Stern-Volmer equation showed that quenching was dominated by static quenching. The binding constant for ternary interaction was below that for binary interaction. Site-competitive experiments demonstrated that SSD/PF bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for the binary association. Also, there was energy transfer upon binary interaction. Molecular docking supported the experimental findings in conformation, binding sites and binding forces.

Biological Activity of Japanese Quince Extract and Its Interactions with Lipids, Erythrocyte Membrane, and Human Albumin

The aim of the study was to determine in vitro biological activity of fruit ethanol extract from Chaenomeles speciosa (Sweet) Nakai (Japanese quince, JQ) and its important constituents (−)-epicatechin (EC) and chlorogenic acid (CA). The study also investigated the structural changes in phosphatidylcholine (PC) liposomes, dipalmitoylphosphatidylcholine liposomes, and erythrocyte membranes (RBC) induced by the extract. It was found that the extract effectively inhibits oxidation of RBC, induced by 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH), and PC liposomes, induced by UVB radiation and AAPH. Furthermore, JQ extract to a significant degree inhibited the activity of the enzymes COX-1 and COX-2, involved in inflammatory reactions. The extract has more than 2 times greater activity in relation to COX-2 than COX-1 (selectivity ratio 0.48). JQ extract stimulated growth of the beneficial intestinal bacteria Lactobacillus casei and Lactobacillus plantarum. In the fluorimetric method by means of the probes Laurdan, DPH and TMA-DPH, and ¹H-NMR, we examined the structural changes induced by JQ and its EC and CA components. The results show that JQ and its components induce a considerable increase of the packing order of the polar heads of lipids with a slight decrease in mobility of the acyl chains. Lipid membrane rigidification could hinder the diffusion of free radicals, resulting in inhibition of oxidative damage induced by physicochemical agents. JQ extract has the ability to quench the intrinsic fluorescence of human serum albumin through static quenching. This report thus could be of huge significance in the food industry, pharmacology, and clinical medicine.

Binding between Saikosaponin C and Human Serum Albumin by Fluorescence Spectroscopy and Molecular Docking

Saikosaponin C (SSC) is one of the major active constituents of dried Radix bupleuri root (Chaihu in Chinese) that has been widely used in China to treat a variety of conditions, such as liver disease, for many centuries. The binding of SSC to human serum albumin (HSA) was explored by fluorescence, circular dichroism (CD), UV-vis spectrophotometry, and molecular docking to understand both the pharmacology and the basis of the clinical use of SSC/Chaihu. SSC produced a concentration-dependent quenching effect on the intrinsic fluorescence of HSA, accompanied by a blue shift in the fluorescence spectra. The Stern-Volmer equation showed that this quenching was dominated by static quenching. The binding constant of SSC with HSA was 3.72 × 10³ and 2.99 × 10³ L·mol(-1) at 26 °C and 36 °C, respectively, with a single binding site on each SSC and HSA molecule. Site competitive experiments demonstrated that SSC bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for SSC-HSA association. The energy transfer efficiency and binding distance between SSC and HSA was calculated to be 0.23 J and 2.61 nm at 26 °C, respectively. Synchronous fluorescence and CD measurements indicated that SSC affected HSA conformation in the SSC-HSA complex. Molecular docking supported the experimental findings in conformational changes, binding sites and binding forces, and revealed binding of SSC at the interface between subdomains IIA-IIB.

Synthesis and physicochemical characterization of Gd-C4-thyroxin-DTPA, a potential MRI contrast agent. Evaluation of its affinity for human serum albumin by proton relaxometry, NMR diffusometry, and electrospray mass spectrometry

Gd-C(4)-thyroxin-DTPA, a potential MRI contrast agent, was synthesized from Gd-DTPA and thyroxine, which interacts strongly with human serum albumin (HSA). It was characterized in water by its relaxometric properties and its stability versus zinc transmetalation. The affinity of the complex for HSA was studied by using three different methods: proton relaxometry, NMR diffusometry, and electrospray mass spectrometry. From the results, it appears that Gd-C(4)-thyroxin-DTPA exhibits a relatively high relaxivity (r(1) = 9.01 s(-1) mM(-1) at 1.5 T and 310 K), a good stability versus zinc transmetalation, and a strong interaction with HSA (K(a) approximately 10,000 M(-1) with two binding sites). The kinetics of the exchange between the bound and the free form of the complex was evaluated by the NMR diffusometry technique. Competition experiments have allowed the assignment of the chelate's binding site on HSA.

Studies of the interaction between palmatine hydrochloride and human serum albumin by fluorescence quenching method

The interaction between palmatine hydrochloride with human serum albumin (HSA) was investigated by fluorescence quenching technique and UV/vis absorption spectroscopy. The results of fluorescence titration revealed that palmatine hydrochloride could strongly quench the intrinsic fluorescence of HSA by static quenching and nonradiative energy transferring. The electrostatic interaction plays a major role in stabilizing the complex. The binding site number n and apparent binding constant KA, corresponding thermodynamic parameters DeltaG, DeltaH and DeltaS at different temperatures were calculated. The distance r between donor (HSA) and acceptor (palmatine hydrochloride) was obtained according to fluorescence resonance energy transfer. The effect of palmatine hydrochloride on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy.

A competitive low-affinity binding model for determining the mutual and specific sites of two ligands on protein

A competitive low-affinity binding model was proposed for determining the number of mutual (overlapped) and specific binding sites of two ligands (A, B) on a protein (P). To use the model, one needs to carry out a titration experiment by adding either ligand A or B into a three-component system (A-B-P), and to monitor the spectroscopic parameter changes. Fitting the titration curve to the proposed model, one can get the mutual and specific binding sites of the two ligands on the protein. The model was examined by using human serum albumin (HSA) as a receptor and tolmetin (TOL) and salicylic acid (SAL) as ligands. Proton longitudinal relaxation rates (R1) were measured on a 500-MHz NMR spectrometer during the titration and used to derive the mutual binding sites. It was found that among the binding sites of 32+/-4 for SAL and 28+/-2 for TOL on HSA, there were 17+/-5 mutual sites for the two ligands. This result indicates that, although HSA has large binding capacities for most ligands, there are still a reasonable amount of the low-affinity binding sites that are structure selective.

Effect of metal ions on the interaction between bovine serum albumin and berberine chloride extracted from a traditional Chinese Herb coptis chinensis franch

The effect of four metal ions Cu(2+), Ni(2+), Zn(2+) and Co(2+) on the interaction between bovine serum albumin (BSA) and berberine chloride (BC) extracted from a traditional Chinese Herb coptis chinensis franch, was investigated mainly by means of UV and fluorescence spectroscopy in this paper. The four metal ions make the quenching efficacy of BC to BSA higher than that in the absence of these metal ions because of the possible transition of BSA molecular conformation caused by metal ions. It was found that the quenching mechanism is a combination of static quenching with nonradiative energy transfer. In the presence of metal ions, the apparent association constant K(A) and the number of binding sites of BC on BSA are both decreased in a range of 8-19% and 25-28%, respectively, which indicates that the metal ions decrease the binding efficacy of BC on BSA and increase the concentration of free BC simultaneously. The scheme of interaction between BC and BSA in the presence of metal ions is a strong quenching but a weak binding.