Studies on the binding of a carditionic agent to human serum albumin by two-dimensional correlation fluorescence spectroscopy and molecular modeling

Evaluating binding behavior of quercetin to human serum albumin and calf thymus DNA: Insights from molecular dynamics, spectroscopy, and apoptotic pathway regulation

In this work, we sought to apprehend quercetin binding affinity and its interaction behavior in complex with human serum albumin (HSA) and calf thymus DNA (ctDNA) through multi spectroscopy and molecular dynamics and also evaluated its effects on colorectal cancer. The binding constants of ctDNA-quercetin and HSA-quercetin complexes at 298 K, which were calculated to be (2.67 ± 0.04) × 103 M-1 and (4.77 ± 0.05) × 104 M-1 respectively, denoted the strong binding of quercetin with ctDNA and HSA. The Ksv and Kb values decrease with increasing temperature, indicating that the quenching of HSA and ctDNA in the presence of quercetin is caused by the combined dynamic and static effects. The obtained thermodynamic parameters for the ctDNA-quercetin interaction represented the existence of electrostatic forces (ΔH0 < 0 and ΔS0 > 0), and the thermodynamic parameters of HSA-quercetin complex disclose the dominance of hydrogen bonds and van der Waals interactions (ΔH0 < 0 and ΔS0 < 0). Moreover, the interactions were exothermic, as evidenced by the negative ΔH0 value for both interactions. According to molecular docking and MD simulation data, quercetin was capable of placing into the site 1 of HSA and forming stable interaction plus this ligand tended to unwind DNA's strands as an intercalator ligand, which was confirmed by experimental results. The fluorescence competition studies between the two intercalator probes of ethidium bromide (EB) and acridine orange (AO), as well as the effect of ionic strength, proposed the strong tendency of quercetin to exist between the two strands of ctDNA as a sign of its intercalative property. Consequently, quercetin can be assumed as an efficient intercalator ligand carried by HSA with an anticancer property. We also conducted cell viability experiments on HT-29 and SW620 cell lines to validate the anticancer ability of quercetin, and observed its decreasing impact on the cell viability of these two cell lines. Additionally, the outcomes of Real-time qPCR proved its capability to reduce the CXCR4 expression and increase the NKD2 expression in Wnt signaling pathway. Therefore, these facts confirm the inhibiting ability of quercetin towards colorectal cancer growth via the prevention of Wnt pathway and approve its functionality as a potential anticancer agent for this cancer.

Exploring Biological Interactions: A New Pyrazoline as a Versatile Fluorescent Probe for Energy Transfer and Cell Staining Applications

Fluorescent dyes are used in biological systems, because they are highly sensitive and selective. In this work, we investigated the fluorescent probe properties of 2-(5-(pyridin-2-yl)-1H-pyrazol-3-yl) phenol (PYDP) in two media [sodium dodecyl sulfate (SDS) and human serum albumin (HSA)]. Energy transfer parameters, photophysical and thermodynamic parameters of probe were determined. We investigated cytotoxicity of PYDP against colorectal adenocarcinoma cell lines (HT-29), breast cancer cell lines (MCF-7) and 3T3-L1 adipocytes (3T3 L1) cells. The cell staining property of PYDP was monitored using a confocal microscope. The results showed that PYDP binds to HSA, bindings are due to electrostatic/ionic interactions, and the binding process is spontaneous. PYDP was found to exhibit negligible cytotoxicity at high concentrations, and confocal microscope images showed that PYDP stained the cytoplasm of MCF-7 cells.

Molecular interaction of some cardiovascular drugs with human serum albumin at physiological-like conditions: A new approach

In the present study, the interaction of human serum albumin (HSA) with some cardiovascular drugs (CARs) under physiological conditions was investigated via the fluorescence spectroscopic and Fourier transform infrared spectroscopy. The CAR included Captopril, Timolol, Propranolol, Atenolol, and Amiodarone. Cardiovascular drugs can effectively quench the endogenous fluorescence of HSA by static quenching mechanism. The fluorescence quenching of HSA is mainly caused by complex formation of HSA with CAR. The binding reaction of CAR with HSA can be concluded that hydrophobic and electrostatic interactions are the main binding forces in the CAR-HSA system. The results showed that CAR strongly quenched the intrinsic fluorescence of HSA through a static quenching procedure, and nonradiation energy transfer happened within molecules. Fourier transform infrared spectroscopy absorption studies showed that the secondary structure was changed according to the interaction of HSA and CAR. The binding reaction of CAR with HSA can be concluded that hydrophobic and electrostatic interactions are the main binding forces in the CAR-HSA system. The results obtained herein will be of biological significance in pharmacology and clinical medicines.

Fast two-dimensional fluorescence correlation spectroscopy technique for tea quality detection

A fast two-dimensional fluorescence correlation spectroscopy technique based on light emitting diodes is developed, which uses light intensity and excitation wavelength as quickly changeable and easily controllable external perturbations. A compact and automatic system is set up to detect tea quality. A partial least square regression method is used to create predictive models for tea grades. Compared to the traditional fluorescence spectroscopy method, this convenient two-dimensional correlation spectroscopy technique is more accurate according to our experimental results and is promising for practical applications.

The aggregation behavior of native collagen in dilute solution studied by intrinsic fluorescence and external probing

The aggregation behavior of type I collagen in acid solutions with the concentrations covering a range of 0.06-1.50mg/mL was studied utilizing both of the fluorescence resonance energy transfer (FRET) between the phenylalanine and tyrosine residues and the external probing of 1,8-anilinonaphthalene sulfonate (ANS). FRET at 0.30 mg/mL showed the distance among collagen monomers was within 10nm without the obvious aggregates formed. The predominance of tyrosine fluorescence in FRET in the range of 0.45-0.75 mg/mL identified the existence of collagen aggregates companied with the formation of hydrophobic microdomains revealed by the change of the fluorescence of ANS. The blue-shift of tyrosine fluorescence from 303 to 293 nm for 0.90-1.50mg/mL dedicated the formation of high order aggregates. The results from the two-phase diagrams of the intrinsic fluorescence for the guanidine hydrochloride-induced unfolding of collagen confirmed these conclusions. By the two-dimensional correlation analysis for the intrinsic fluorescence of collagen solutions of 0.45, 0.75 and 1.05 mg/mL, the probable characteristic fluorescence peaks for the interactions of proline-aromatic (CH∼π) among the collagen molecules were found at 298 and 316 nm.

Probing the interaction of human serum albumin with bilirubin in the presence of aspirin by multi-spectroscopic, molecular modeling and zeta potential techniques: insight on binary and ternary systems

Here, we report on the effect of aspirin (ASA), on the binding parameters with regard to bilirubin (BR) to human serum albumin (HSA). Two different classes of binding sites were detected. Binding to the first and second classes of the binding sites was dominated by hydrophobic forces in the case of HSA-BR, whereas in the case of the ternary system, binding to the first and second classes of the binding sites was achieved by electrostatic interaction. The binding constant (K(a)) and number of binding site (n) obtained were 1.6 × 10(6)M(-1) and 0.98, respectively, for the primary binding site in the case of HSA-BR, and 3.7 × 10(6)M(-1) and 0.84, respectively, in the presence of ASA (ternary complex) at λ(ex)= 280 nm. The progressive quenching of the protein fluorescence as the BR concentration increased indicated an arrangement of the domain IIA in HSA. Changes in the environment of the aromatic residues were also observed by synchronous fluorescence spectroscopy (SFS). Changes of the secondary structure of HSA involving a decrease of α-helical and β-sheet contents and increased amounts of turns and unordered conformations were mainly found at high concentrations of BR. For the first time, the relationship between the structural parameters of HSA-BR by RLS for determining the critical induced aggregation concentration (C(CIAC)) of BR in the absence and presence of ASA was investigated, and there was a more significant enhancement in the case of the ternary mixture as opposed to the binary one. Changes in the zeta potential of HSA and the HSA-ASA complex in the presence of BR demonstrated a hydrophobic adsorption of this anionic ligand onto the surface of HSA in the binary system as well as both electrostatic and hydrophobic adsorption in the case of the ternary complex. By performing docking experiments, it was found that the acting forces between BR and HSA were mainly hydrophobic > hydrogen bonding > electrostatic interactions, and consequently BR had a long storage time in blood plasma, especially in the presence of ASA. This was due to the electrostatic interaction force between the BR and HSA being stronger in (HSA-ASA) BR than in the HSA-BR complex. In addition, it was demonstrated that, in the presence of ASA, the first binding site of BR on HSA was altered, but the parameters of binding did not become significantly modified, and thus the affinity of BR barely changed with and without ASA.

Use of spectroscopic, zeta potential and molecular dynamic techniques to study the interaction between human holo-transferrin and two antagonist drugs: comparison of binary and ternary systems

For the first time, the binding of ropinirole hydrochloride (ROP) and aspirin (ASA) to human holo-transferrin (hTf) has been investigated by spectroscopic approaches (fluorescence quenching, synchronous fluorescence, time-resolved fluorescence, three-dimensional fluorescence, UV-vis absorption, circular dichroism, resonance light scattering), as well as zeta potential and molecular modeling techniques, under simulated physiological conditions. Fluorescence analysis was used to estimate the effect of the ROP and ASA drugs on the fluorescence of hTf as well as to define the binding and quenching properties of binary and ternary complexes. The synchronized fluorescence and three-dimensional fluorescence spectra demonstrated some micro-environmental and conformational changes around the Trp and Tyr residues with a faint red shift. Thermodynamic analysis displayed the van der Waals forces and hydrogen bonds interactions are the major acting forces in stabilizing the complexes. Steady-state and time-resolved fluorescence data revealed that the fluorescence quenching of complexes are static mechanism. The effect of the drugs aggregating on the hTf resulted in an enhancement of the resonance light scattering (RLS) intensity. The average binding distance between were computed according to the forster non-radiation energy transfer theory. The circular dichroism (CD) spectral examinations indicated that the binding of the drugs induced a conformational change of hTf. Measurements of the zeta potential indicated that the combination of electrostatic and hydrophobic interactions between ROP, ASA and hTf formed micelle-like clusters. The molecular modeling confirmed the experimental results. This study is expected to provide important insight into the interaction of hTf with ROP and ASA to use in various toxicological and therapeutic processes.

Investigation of the behavior of HSA upon binding to amlodipine and propranolol: Spectroscopic and molecular modeling approaches

The interaction between human serum albumin (HSA) and two drugs - amlodipine and propranolol - was investigated using fluorescence, UV absorption and circular dichroism (CD) spectroscopy. In addition, the binding site was established by applying molecular modeling technique. Fluorescence data suggest that amlodipine will quench the intrinsic fluorescence of HSA; whereas propranolol enhances the fluorescence of HSA. The binding constants for the interaction of amlodipine and propranolol with HSA were found to be 3.63×10(5)M(-1) and 2.29×10(4)M(-1), respectively. The percentage of secondary structure feature of each one of the HSA-bound drugs, i.e. the α-helix content, was estimated empirically by circular dichroism. The results indicated that amlodipine causes an increase, and that propranolol leads to a decrease in α-helix content of HSA. The spectroscopic analysis indicates that the binding mechanisms of the two drugs are different from each other. The data obtained by the molecular modeling study indicated that these drugs bind, with different affinity, to different sites located in subdomain IIA and IIIA.