Investigations with Spectroscopy, Zeta Potential and Molecular Modeling of the Non-Cooperative Behaviour Between Cyclophosphamide Hydrochloride and Aspirin upon Interaction with Human Serum Albumin: Binary and Ternary Systems from the View Point of Multi-Drug Therapy

Structural changes and anti-hepatocellular carcinoma activity of interferon-γ after interaction with sinensetin

Exploring the interaction of small molecules with therapeutic proteins can provide useful information about development of ligand-protein complexes as synergistically therapeutic platforms. In this study, the interaction of sinensetin with human interferon gamma (IFNγ) was evaluated experimentally and theoretically. Also, the synergistic effects of IFNγ- sinensetin complex on the inhibition of hepatocellular carcinoma HepG2 cell proliferation were assessed by cell viability and quantitative real time PCR assays. It was realized that sinensetin interacts with IFNγ through a static quenching mechanism and hydrophobic forces mediated by presence of Lys55 and Lys58 amino acid residues in the binding site were the main contributing forces in the spontaneous formation of IFNγ-sinensetin complex. Also, the interaction of sinensetin with IFNγ did not induce a significant change in the secondary and tertiary structure of the protein. Cellular assays revealed a synergistic effect of sinensetin on IFNγ -triggered anticancer action in HepG2 cells through overexpression of caspase-3 mRNA and protein. In conclusion, this study may hold great promise for the development of potential ligand- protein complexes for therapeutic purposes.

New insights on the binding of butyl-paraben to trypsin: experimental and computational approaches

Butyl-paraben (BP) is one of the most widely used preservatives in numerous foodstuffs, skin care products, and a variety of drugs, and trypsin is the main digestive enzyme, the research on the binding between the two is essential for human health. In the present paper, the effect of BP on trypsin has been explored using experimental and computational techniques to evaluate BP toxicity at the protein level. The obtained results from molecular docking and kinetic assay revealed BP was embedded in the hydrophobic cavity-S1 binding pocket of the enzyme to inhibit its activity by a competitive model. Intrinsic fluorescence of trypsin after interaction with BP revealed the static mode of quenching. FRET indicated that the distance of the enzyme to BP is 1.89 nm with high energy efficiency. Thermodynamic results proved that BP spontaneously bound to trypsin in an enthalpy-driven manner, the van der Waals interactions and H-bonds serving as the predominant forces in binding processes. CD spectroscopy and molecular dynamics (MD) simulation revealed that the trypsin structure transformed from the β-Sheet structure to the unordered Coil structure upon interacting with BP. Resonance light scattering (RLS), synchronous fluorescence, and three-dimensional (3 D) spectroscopies further supported the alteration in the conformation of trypsin. Differential scanning calorimetry (DSC) showed that trypsin was somewhat destabilized in the presence of BP. Accordingly, all of the experimental data were confirmed by MD simulation.Communicated by Ramaswamy H. Sarma.

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.

The Use of Molecular Docking and Spectroscopic Methods for Investigation of The Interaction Between Regorafenib with Human Serum Albumin (HSA) and Calf Thymus DNA (Ct-DNA) In The Presence Of Different Site Markers

BACKGROUND

Interactions of drugs with DNA and proteins may modify their biological activities and conformations, which effect transport and biological metabolism of drugs.

OBJECTIVE

In this study the interaction of anticancer drug regorafenib (REG) with calf thymus-DNA (ct-DNA) and human serum albumin (HSA) has been investigated Methods: Hence, for the first time, it was discovered interaction between REG with DNA and HSA using multi-spectroscopic, zeta potential measurements and molecular docking method.

RESULTS AND DISCUSSION

DNA displacement studies showed that REG does not have any effect on acridine orange and methylene blue bound DNA, though it was substantiated by displacement studies with Hoechst (as groove binder). Furthermore, the different concentrations of REG induce slight changes in the viscosity of ct-DNA. Zeta potential parameters indicated that hydrophobic interaction plays a major role in the DNA-REG complex. Results obtained from molecular docking demonstrate that the REG prefers to bind on the minor groove of DNAs than that of the major groove. Binding properties of HSA reveal that intrinsic fluorescence of HSA could be quenched by REG in a static mode. The competitive experiments in the presence of warfarin and ibuprofen (as site markers) suggested that the binding site of REG to HSA was most probably located in the subdomain IIA. Measurements of the zeta potential indicated that REG bound to HSA mainly by both electrostatic and hydrophobic interactions. It was found on docking procedures that REG could fit well into HSA subdomain IIA, which confirmed the experimental results.

CONCLUSION

In conclusion, REG can be delivered by HSA in a circulatory system and affect DNA as potential target.

Interaction between olanzapine and human serum albumin and effect of metal ions, caffeine and flavonoids on the binding: A spectroscopic study

In this study, the binding of olanzapine (OLZ) to human serum albumin (HSA) and the influence of metal ions (Ca²⁺, Mg²⁺, Cu²⁺, Zn²⁺, Fe³⁺), caffeine (CAF) and flavonoids (diosmin (DIO), catechin (CAT), quercetin (QUE)), on their affinity, was investigated by fluorescence spectroscopy and UV-vis absorption spectroscopy. Fluorescence experiments suggest that OLZ quench the fluorescence of HSA through the mixed quenching mechanism and non-radiation energy transferring as a result of the HSA-OLZ complex formation. OLZ spontaneously bind in the site I on HSA, and according to thermodynamic parameters, the reaction was spontaneous and mainly driven by hydrogen bonds and van der Waals interactions. The presence of Mⁿ⁺ ions, CAF, DIO and CAT decreased binding affinity between OLZ and HSA which indicates that they could compete against OLZ in the site I. Contrary, in the presence of QUE the binding affinity of the HSA-OLZ system enhanced, which may be explained by conformational changes in HSA (non-competitive interference).

Mono- and bis-pyrazolophthalazines: Design, synthesis, cytotoxic activity, DNA/HSA binding and molecular docking studies

In an attempt to find new potent cytotoxic compounds, several mono- and bis-pyrazolophthalazines 4a-m and 6a-h were synthesized through an efficient, one-pot, three- and pseudo five-component synthetic approach. All derivatives were evaluated for their in vitro cytotoxic activities against four human cancer cell lines of A549, HepG2, MCF-7, and HT29. Compound 4e showed low toxicity against normal cell lines (MRC-5 and MCF 10A, IC₅₀ > 200 µM) and excellent cytotoxic activity against A549 cell line with IC₅₀ value of 1.25 ± 0.19 µM, which was 1.8 times more potent than doxorubicin (IC₅₀ = 2.31 ± 0.13 µM). In addition, compound 6c exhibited remarkable cytotoxic activity against A549 and MCF-7 cell lines (IC₅₀ = 1.35 ± 0.12 and 0.49 ± 0.01 µM, respectively), more than two-fold higher than that of doxorubicin. The binding properties of the best active mono- and bis-pyrazolophthalazine (4e and 6c) with HSA and DNA were fully evaluated by various techniques including UV-Vis absorption, circular dichroism (CD), Zeta potential and dynamic light scattering analyses indicating interaction of the compounds with the secondary structure of HSA and significant change of DNA conformation, presumably via a groove binding mechanism. Additionally, molecular docking and site-selective binding studies confirmed the fundamental interaction of compounds 4e and 6c with base pairs of DNA. Compounds 4e and 6c showed promising features to be considered as potential lead structures for further studies in cancer therapy.

Biomolecular interactions and binding dynamics of tyrosine kinase inhibitor erdafitinib, with human serum albumin

Erdafitinib is an approved tyrosine kinase inhibitor that inhibits fibroblast growth factor receptor. It has been described as one of the potent anti-tumor drugs especially for the treatment of urothelial carcinoma. In this study, we have investigated the binding dynamics of erdafitinib with human serum albumin (HSA) using multiple spectroscopic techniques. The outcome of the results suggests the occurrence of static quenching during the interaction of HSA with erdafitinib which leads to the formation of non-fluorescent HSA-erdafitinib ground state complex. Formation of HSA-erdafitinib complex was also confirmed from the findings of absorption spectral analysis. The changes in microenvironment around hydrophobic domains (especially tryptophan and tyrosine) were deciphered from fluorescence spectroscopy which was further confirmed by synchronous spectral analysis. In order to gain insight into the binding site of erdafitinib in HSA, molecular docking combined with competitive displacement assay was performed. The modified form of Stern Volmer equation was used to estimate various binding parameters including number of binding sites. The findings are indicative of a single binding site (n = 1) with binding constant in the order of 10⁴. The negative values of thermodynamic parameters like ΔG, ΔH and ΔS were suggestive of the binding reaction being spontaneous and exothermic, while the hydrogen bonds and Van der Waals interactions being the major forces present between HSA and erdafitinib. Circular dichroism spectral analysis revealed the alterations in the conformation of HSA structure and reduction in its α-helical content.Communicated by Ramaswamy H. Sarma[Formula: see text].

Synthesis, Structural, and Cytotoxic Properties of New Water-Soluble Copper(II) Complexes based on 2,9-Dimethyl-1,10-Phenanthroline and Their One Derivative Containing 1,3,5-Triaza-7-Phosphaadamantane-7-Oxide

A series of water-soluble copper(II) complexes based on 2,9-dimethyl-1,10-phenanthroline (dmphen) and mixed-ligands, containing PTA=O (1,3,5-triaza-7-phosphaadamantane-7-oxide) have been synthesized and fully characterized. Two types of complexes have been obtained, monocationic [Cu(NO₃)(O-PTA=O)(dmphen)][PF₆] (1), [Cu(Cl)(dmphen)₂][PF₆] (2), and neutral [Cu(NO₃)₂(dmphen)] (3). The solid-state structures of all complexes have been determined by single-crystal X-ray diffraction. Magnetic studies for the complex 1–3 indicated a very weak antiferromagnetic interaction between copper(II) ions in crystal lattice. Complexes were successfully evaluated for their cytotoxic activities on the normal human dermal fibroblast (NHDF) cell line and the antitumor activity using the human lung carcinoma (A549), epithelioid cervix carcinoma (HeLa), colon (LoVo), and breast adenocarcinoma (MCF-7) cell lines. Complexes 1 and 3 revealed lower toxicity to NHDF than A549 and HeLa cells, meanwhile compound 2 appeared to be more toxic to NHDF cell line in comparison to all cancer lines. Additionally, interactions between the complexes and human apo-transferrin (apo-Tf) using fluorescence and circular dichroism (CD) spectroscopy were also investigated. All compounds interacted with apo-transferrin, causing same changes of the protein conformation. Electrostatic interactions dominate in the 1/2 – apo- Tf systems and hydrophobic and ionic interactions in the case of 3.

Potentiality of using front face fluorescence spectroscopy for quantitative analysis of cow milk adulteration in buffalo milk

In current study, synchronous front-face fluorescence spectroscopy together with partial least squares regression (PLSR) is used to predict the adulteration of cow and buffalo milk quantitatively. Fresh (unprocessed milk) samples of cow and buffalo were collected from local dairy farms. Fluorescence emission from milk samples mixed in different concentrations, show intensity variations at wavelengths 370-380 nm, 410 nm, 442 nm and 520-560 nm. Among them, the emissions at band position of 442 nm and 525 nm are highly selective between the two species and could help in finding adulteration of cow milk in buffalo milk and vice versa. The emissions at these wavelength positions correspond to fat-soluble vitamin-A as well as β-carotene. PLS regression is used as a statistical prediction model, which is developed by training with the emission spectra of milk samples having known level of adulterations. The developed model predicts the unknown level of adulterations by means of their spectral data. The goodness of the model is determined by the correlation coefficient R-square (r²) value, which in our case is 0.99. Furthermore, the model root mean square error in cross validation (RMSECV) and in prediction (RMSECP) remains 1.16 and 6.24 respectively. This approach can effectively be applied to determine milk adulterations among other species as well as in detecting external agents (fraudulent) added into milk and other dairy products by further studies.

Cyclophosphamide and isophosphamide - DFT conformational studies in the gas phase and solution

Cyclophosphamide and isophosphamide have been subjected to comprehensive conformational studies in the vacuum and solution using the SMD solvation model. Vacuum calculations were conducted using the B3LYP, M05-2X, M06-2X and ωB97XD functionals. Natural bond orbital (NBO) analysis has been performed for selected geometries. A preference for a chair conformation with the axial P=O bond is shown (¹C₄). The ⁵S₀ conformation is 1.25-2.31 kcal/mol and 1.72-2.92 kcal/mol higher in energy than the global minimum conformations of cyclophosphamide and isophosphamide, respectively. In the gas phase, the chair conformation with the equatorial P=O bond (⁴C₁) is of comparable stability or less stable than the skew form, depending on the method used, while it is slightly more favored than the ⁵S₀ conformation in solution. The stereoelectronic effects do not differentiate the ring conformer stability. The steric strains between N(EtCl)_1-2 and the C4 and C6 carbon atoms mainly influence the stability of cyclophosphamide and isophosphamide conformers.

Use of spectroscopic and zeta potential techniques to study the interaction between lysozyme and curcumin in the presence of silver nanoparticles at different sizes

This article describes, for the first time, the effect of three different sizes of silver nanoparticles on the binding of curcumin to lysozyme as examined by spectroscopic and zeta potential techniques at physiological conditions. The binding constants of curcumin to lysozyme in the presence of silver nanoparticles were measured. Based on the results of synchronous fluorescence and three-dimensional fluorescence spectroscopy, the presence of the different sizes of silver nanoparticles caused conformational changes in lysozyme during the binding of curcumin. Such changes were also observed when increasing the curcumin concentration. The results of fluorescence resonance energy transfer theory indicated that different sizes of silver nanoparticles could change the binding distance between curcumin and lysozyme. Based on the red edge excitation shift approach, we concluded that the limited mobility around the Trp residues decreased in the presence of silver nanoparticles with bigger size. Under resonance light scattering, the aggregation of curcumin on lysozyme in the presence of silver nanoparticles can play a major role in functional proteins. Communicated by Ramaswamy H. Sarma.

A resonance Rayleigh scattering sensor for sensitive differentiation of telomere DNA length and monitoring special motifs (G-quadruplex and i-motif) based on the Ag nanoclusters and NAND logic gate responding to chemical input signals

Background

Differentiation of telomere length is of vital importance because telomere length is closely related with several deadly diseases such as cancer. Additionally, G-quadruplex and i-motif formation in telomeric DNA have been shown to act as a negative regulator of telomere elongation by telomerase in vivo and are considered as an attractive drug target for cancer chemotherapy.

Results

In this assay, Ag nanoclusters templated by hyperbranched polyethyleneimine (PEI–Ag NCs) are designed as a new novel resonance Rayleigh scattering (RRS) probe for sensitive differentiation of telomere length and monitoring special motifs (G-quadruplex and i-motif). In this assay, free PEI–Ag NC probe or DNA sequence alone emits low intensities of RRS, while the formation of PEI–Ag NCs/DNA complexes yields greatly enhanced RRS signals; however, when PEI–Ag NCs react with G-quadruplex or i-motif, the intensities of RRS exhibit slight changes. At the same concentration, the enhancement of RRS signal is directly proportional to the length of telomere, and the sensitivity of 64 bases is the highest with the linear range of 0.3–50 nM (limit of detection 0.12 nM). On the other hand, due to the conversion of telomere DNA molecules among multiple surrounding conditions, a DNA logic gate is developed on the basis of two chemical input signals (K⁺ and H⁺) and a change in RRS intensity as the output signal.

Conclusion

Our results indicate that PEI–Ag NCs can serve as a novel RRS probe to identify DNA length and monitor G-quadruplex/i-motif through the different increasing degrees of RRS intensity. Meanwhile, the novel attributes of the nanoprobe stand superior to those involving dyes or labeled DNA because of no chemical modification, low cost, green, and high efficiency.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0407-5) contains supplementary material, which is available to authorized users.

Identification differential behavior of Gd@C82(OH)22 upon interaction with serum albumin using spectroscopic analysis

The interaction between Gd@C₈₂(OH)₂₂ and serum albumin (HSA and BSA) were investigated by spectroscopic analysis. From the characteristic feature of fluorescence quenching spectra at different temperatures, the inherent binding information including quenching mechanism, association constants, number of binding site, fraction of initial fluorescence and basic thermodynamic parameters were calculated. The binding of Gd@C₈₂(OH)₂₂ to serum albumin caused strong quenching of protein intrinsic fluorescence and the structural changes of serum albumin. At lower concentrations, Gd@C₈₂(OH)₂₂ was likely to rise fluorescence quenching of serum albumin through individual static quenching process by forming a ground-state complex, while dynamic and static coexisting quenching mechanism occurred in high concentration. Bimolecular quenching (K_q) value is twice the diffusion-controlled quenching constant (2.0 × 10¹⁰ L mol^-1 s^-1); binding sites of BSA were slightly more than those of HAS, and all of them reached to 1; the distance r between donor and acceptor was found to be 3.1494 nm and 3.6479 nm for HSA and BSA, respectively, both of which were fewer than 7 nm. It is confirmed that binding interaction for proteins in the presence of drugs was strong, the binding ratio was 1:1, and non-radiative energy transfer from protein to drug was extremely high probability in lower density. Binding process of Gd@C₈₂(OH)₂₂-HSA was driven mainly through van der Waals forces and hydrogen bonding formation, however more likely to be electrostatic interaction involved in the Gd@C₈₂(OH)₂₂-BSA binding process; Binding sites of Gd@C₈₂(OH)₂₂ to serum albumin were near tryprophan (HSA) and tyrosine residues (BSA), respectively. Moreover, a theoretical model of predicting the binding rate of drug to serum albumin was estimated, further analyzed that the binding rate was dynamically altered in various dose of protein and drug. Overall, these results provide potentially significant information for elucidating the distribution, transportation, the apparent relationship between pharmacologic activity and total plasma drug concentration as well as anti-carcinogenic activity and mechanisms in vivo.

Human serum albumin binding and synergistic effects of gefitinib in combination with regorafenib on colorectal cancer cell lines

This study aimed to evaluate the combination effect of gefitinib (GEF) and regorafenib (REG) against HCT116, CT26 and SW948 colorectal cancer cell lines. Results showed synergistic effects on HCT116 and CT26 cells, while the additive effect was observed on SW948 cells. Combination of GEF and REG induced sub-G1 peak as the apoptotic population on HCT116 cells, through flow cytometry histogram. Downregulation of AKT1 and TGFB2 and upregulation of CASP3 were observed in the combination of GEF and REG in HCT116 cells, using quantitative real-time PCR analysis. HSA binding properties exhibit that the first drug increased binding affinity between the second drug and HSA; as a result, HSA could transport both drugs. Thus, we hope this study creates a promising strategy to treat colorectal cancer.

Multi-spectroscopic and molecular modeling approaches to elucidate the binding interaction between bovine serum albumin and darunavir, a HIV protease inhibitor

Darunavir (DRV), a second-generation HIV protease inhibitor, is widely used across the world as an important component of HIV therapy. The interaction of DRV with bovine serum albumin (BSA), a major carrier protein, has been studied under simulated physiological conditions (pH7.4) by multi-spectroscopic techniques in combination with molecular modeling. Fluorescence data revealed that the intrinsic fluorescence of BSA was quenched by DRV in terms of a static quenching procedure due to the formation of the DRV-BSA complex. The results indicated the presence of single weak affinity binding site (~10³M^-1, 310K) on protein. The thermodynamic parameters, namely enthalpy change (ΔH⁰), entropy change (ΔS⁰) and Gibbs free energy change (ΔG⁰) were calculated, which signified that the binding reaction was spontaneous, the main binding forces were hydrogen bonding and van der Waals forces. Importantly, competitive binding experiments with three site probes, phenylbutazone (in sub-domain IIA, site I), ibuprofen (in sub-domain IIIA, site II) and artemether (in the interface between sub-domain IIA and IIB, site II'), suggested that DRV was preferentially bound to the hydrophobic cavity in site II' of BSA, and this finding was validated by the docking results. Additionally, synchronous fluorescence, three-dimensional fluorescence and Resonance Rayleigh Scattering (RRS) spectroscopy gave qualitative information on the conformational changes of BSA upon adding DRV, while quantitative data were obtained with Fourier transform infrared spectroscopy (FT-IR).

Synthesis of novel coumarin nucleus-based DPA drug-like molecular entity: In vitro DNA/Cu(II) binding, DNA cleavage and pro-oxidant mechanism for anticancer action

Despite substantial research on cancer therapeutics, systemic toxicity and drug-resistance limits the clinical application of many drugs like cisplatin. Therefore, new chemotherapeutic strategies against different malignancies are needed. Targeted cancer therapy is a new paradigm for cancer therapeutics which targets pathways or chemical entities specific to cancer cells than normal ones. Unlike normal cells, cancer cells contain elevated copper which plays an integral role in angiogenesis. Copper is an important metal ion associated with chromatin DNA, particularly with guanine. Thus, targeting copper via copper-specific chelators in cancer cells can serve as an effective anticancer strategy. New pharmacophore di(2-picolyl)amine (DPA)-3(bromoacetyl) coumarin (ligand-L) was synthesized and characterized by IR, ESI-MS, 1H- and 13C-NMR. Binding ability of ligand-L to DNA/Cu(II) was evaluated using a plethora of biophysical techniques which revealed ligand-L-DNA and ligand-L-Cu(II) interaction. Competitive displacement assay and docking confirmed non-intercalative binding mode of ligand-L with ctDNA. Cyclic voltammetry confirmed ligand-L causes quasi reversible Cu(II)/Cu(I) conversion. Further, acute toxicity studies revealed no toxic effects of ligand-L on mice. To evaluate the chemotherapeutic potential and anticancer mechanism of ligand-L, DNA damage via pBR322 cleavage assay and reactive oxygen species (ROS) generation were studied. Results demonstrate that ligand-L causes DNA cleavage involving ROS generation in the presence of Cu(II). In conclusion, ligand-L causes redox cycling of Cu(II) to generate ROS which leads to oxidative DNA damage and pro-oxidant cancer cell death. These findings will establish ligand-L as a lead molecule to synthesize new molecules with better copper chelating and pro-oxidant properties against different malignancies.

Warfarin and Flavonoids Do Not Share the Same Binding Region in Binding to the IIA Subdomain of Human Serum Albumin

Human serum albumin (HSA) binds a variety of xenobiotics, including flavonoids and warfarin. The binding of another ligand to the IIA binding site on HSA can cause warfarin displacement and potentially the elevation of its free concentration in blood. Studies dealing with flavonoid-induced warfarin displacement from HSA provided controversial results: estimated risk of displacement ranged from none to serious. To resolve these controversies, in vitro study of simultaneous binding of warfarin and eight different flavonoid aglycons and glycosides to HSA was carried out by fluorescence spectroscopy as well as molecular docking. Results show that warfarin and flavonoids do not share the same binding region in binding to HSA. Interactions were only observed at high warfarin concentrations not attainable under recommended dosing regimes. Docking experiments show that flavonoid aglycons and glycosides do not bind at warfarin high affinity sites, but rather to different regions within the IIA HSA subdomain. Thus, the risk of clinically significant warfarin-flavonoid interaction in binding to HSA should be regarded as negligible.

Identification of cow and buffalo milk based on Beta carotene and vitamin-A concentration using fluorescence spectroscopy

The current study presents the application of fluorescence spectroscopy for the identification of cow and buffalo milk based on β-carotene and vitamin-A which is of prime importance from the nutritional point of view. All samples were collected from healthy animals of different breeds at the time of lactation in the vicinity of Islamabad, Pakistan. Cow and buffalo milk shows differences at fluorescence emission appeared at band position 382 nm, 440 nm, 505 nm and 525 nm both in classical geometry (right angle) setup as well as front face fluorescence setup. In front face fluorescence geometry, synchronous fluorescence emission shows clear differences at 410 nm and 440 nm between the milk samples of both these species. These fluorescence emissions correspond to fats, vitamin-A and β-carotene. Principal Component Analysis (PCA) further highlighted these differences by showing clear separation between the two data sets on the basis of features obtained from their fluorescence emission spectra. These results indicate that classical geometry (fixed excitation wavelength) as well as front face (synchronous fluorescence emission) of cow and buffalo milk nutrients could be used as fingerprint from identification point of view. This same approach can effectively be used for the determination of adulterants in the milk and other dairy products.

Biological effects of α-adrenergic phentolamine on erythrocyte hemeprotein: Molecular insights from biorecognition behavior, protein dynamics and flexibility

Phentolamine is one of the most representative nonselective α-adrenoreceptor blocking agents, which have been proved to be owned various pharmacological actions. Unfortunately, whether erythrocytes in the veins intervene in biological behaviors of such drug are largely obscured. With the aid of multiple biophysical techniques, this scenario was to detailed explore the potential biorecognition between phentolamine and the hemeprotein in the cytosol of erythrocytes, and the influences of dynamic characters of protein during the bioreaction. Steady-state and time-resolved fluorescence data manifested that the biomolecular recognition of phentolamine by hemeprotein was processed through the biopolymer-drug adduct with a moderate strength of 10⁴M^-1. Such procedure causes a reduction in fluorescence intensity of the aromatic tryptophan (Trp) residues, and the R-T transition of the globular protein occurred concurrently. Circular dichroism demonstrated the conclusions of fluorescence essays, viz. biorecognition can induce fairly structural transformation (self-regulation) of protein conformation. Furthermore, one could find that a specific domain for phentolamine is located at the polypeptide chains α₁β₂ interface, and hydrogen bonds, π-conjugated and hydrophobic effects are discovered to be held the lowest energy state of the biomacromolecule-drug biosystem, which overtly matches the outcomes of wet experiments. Meanwhile, several crucial residues such as Trp-37 and Arg-40 were confirmed to have directly noncovalent interactions with phentolamine, and the effect of the heme group on the biomolecule-drug recognition is minimal. Further analyses of molecular dynamics simulation supported that the inherent protein flexibility may notably elicit alterations in some key noncovalent bonds between biomacromolecule and drug during the dynamic biointeraction, which might primarily be attributed to the torsion of drug structure and the conformational changes of essential residues. Undoubtedly, this research will not only help to thoroughly unearth the pharmacological profiles of phentolamine, but to elaborate the impacts of the intrinsic features (i.e. dynamics and flexibility) of critically cellular proteins on the biological conducts of active α-adrenergic blockers.

Thymoquinone binds and activates human salivary aldehyde dehydrogenase: Potential therapy for the mitigation of aldehyde toxicity and maintenance of oral health

Human salivary aldehyde dehydrogenase (hsALDH) is a very important anti-oxidant enzyme present in the saliva. It is involved in the detoxification of toxic aldehydes and maintenance of oral health. Reduced level of hsALDH activity is a risk factor for oral cancer development. Thymoquinone (TQ) has many pharmacological activities and health benefits. This study aimed to examine the activation of hsALDH by TQ. The effect of TQ on the activity and kinetics of hsALDH was studied. The binding of TQ with the enzyme was examined by different biophysical methods and molecular docking analysis. TQ enhanced the dehydrogenase activity of crude and purified hsALDH by 3.2 and 2.9 fold, respectively. The K_m of the purified enzyme decreased and the V_max increased. The esterase activity also increased by 1.2 fold. No significant change in the nucleophilicity of the catalytic cysteine residue was observed. TQ forms a strong complex with hsALDH without altering the secondary structures of the enzyme. It fits in the active site of ALDH3A1 close to Cys 243 and the other highly conserved amino acid residues which lead to enhancement of substrate binding affinity and catalytic efficiency of the enzyme. TQ is expected to give better protection from toxic aldehydes in the oral cavity and to reduce the risk of oral cancer development through the activation of hsALDH. Therefore, the addition of TQ in the diet and other oral formulations is expected to be beneficial for health.

Enantioselective recognition of an isomeric ligand by a biomolecule: mechanistic insights into static and dynamic enantiomeric behavior and structural flexibility

Enantioselective biorecognition is a vital trigger that results in remarkable enantiomeric differences in the biochemical behavior of chiral substances.

Interaction of anticancer drug clofarabine with human serum albumin and human α-1 acid glycoprotein. Spectroscopic and molecular docking approach

The binding interaction between clofarabine, an important anticancer drug and two important carrier proteins found abundantly in human plasma, Human Serum Albumin (HSA) and α-1 acid glycoprotein (AAG) was investigated by spectroscopic and molecular modeling methods. The results obtained from fluorescence quenching experiments demonstrated that the fluorescence intensity of HSA and AAG is quenched by clofarabine and the static mode of fluorescence quenching is operative. UV-vis spectroscopy deciphered the formation of ground state complex between anticancer drug and the two studied proteins. Clofarabine was found to bind at 298K with both AAG and HSA with the binding constant of 8.128×10³ and 4.120×10³ for AAG and HSA, respectively. There is stronger interaction of clofarabine with AAG as compared to HSA. The Gibbs free energy change was found to be negative for the interaction of clofarabine with AAG and HSA indicating that the binding process is spontaneous. Binding of clofarabine with HSA and AAG induced ordered structures in both proteins and lead to molecular compaction. Clofarabine binds to HSA near to drug site II. Hydrogen bonding and hydrophobic interactions were the main bonding forces between HSA-clofarabine and AAG-clofarabine as revealed by docking results. This study suggests the importance of binding of anticancer drug to AAG spatially in the diseases like cancers where the plasma concentration of AAG increases many folds. Design of drug dosage can be adjusted accordingly to achieve optimal treatment outcome.

Studies on the interaction between promethazine and human serum albumin in the presence of flavonoids by spectroscopic and molecular modeling techniques

Fluorescence, absorption, time-correlated single photon counting (TCSPC), and circular dichroism (CD) spectroscopic techniques as well as molecular modeling methods were used to study the binding characterization of promethazine (PMT) to human serum albumin (HSA) and the influence of flavonoids, rutin and baicalin, on their affinity. The results indicated that the fluorescence quenching mechanism of HSA by PMT is a static quenching due to the formation of complex. The reaction was spontaneous and mainly mediated by hydrogen bonds and hydrophobic interactions. The binding distance between the tryptophan residue of HSA and PMT is less than 8nm, which indicated that the energy transfer from the tryptophan residue of HSA to PMT occurred. The binding site of PMT on HSA was located in sites I and the presence of PMT can cause the conformational changes of HSA. There was the competitive binding to HSA between PMT and flavonoids because of the overlap of binding sites in HSA. The flavonoids could decrease the association constant and increase the binding distance. In addition, their synergistic effect can further change the conformation of HSA. The decrease in the affinities of PMT binding to HSA in the presence of flavonoids may lead to the increase of free drug in blood, which would affect the transportation or disposition of drug and evoke an adverse or toxic effect. Hence, rationalising dosage and diet regimens should be taken into account in clinical application of PMT.

The increased binding affinity of curcumin with human serum albumin in the presence of rutin and baicalin: A potential for drug delivery system

The impacts of rutin and baicalin on the interaction of curcumin (CU) with human serum albumin (HSA) were investigated by fluorescence and circular dichroism (CD) spectroscopies under imitated physiological conditions. The results showed that the fluorescence quenching of HSA by CU was a simultaneous static and dynamic quenching process, irrespective of the presence or absence of flavonoids. The binding constants between CU and HSA in the absence and presence of rutin and baicalin were 2.268×10(5)M(-1), 3.062×10(5)M(-1), and 3.271×10(5)M(-1), indicating that the binding affinity was increased in the case of two flavonoids. Furthermore, the binding distance determined according to Förster's theory was decreased in the presence of flavonoids. Combined with the fact that flavonoids and CU have the same binding site (site I), it can be concluded that they may simultaneously bind in different regions in site I, and formed a ternary complex of flavonoid-HSA-CU. Meanwhile, the results of fluorescence quenching, CD and three-dimensional fluorescence spectra revealed that flavonoids further strengthened the microenvironmental and conformational changes of HSA induced by CU binding. Therefore, it is possible to develop a novel complex involving CU, flavonoid and HSA for CU delivery. The work may provide some valuable information in terms of improving the poor bioavailabiliy of CU.

Enhancement of the binding affinity of methylene blue to site I in human serum albumin by cupric and ferric ions

In this work, the binding characteristics of methylene blue (MB) to human serum albumin (HSA) and the influence of Cu(2+) and Fe(3+) on the binding affinity of MB to HSA were investigated using fluorescence, absorption, circular dichroism (CD) spectroscopy and molecular modelling. The results of competitive binding experiments using the site probes ketoprofen and ibuprofen as specific markers suggested that MB was located in site I within sub-domain IIA of HSA. The molecular modelling results agreed with the results of competitive site marker experiments and the results of CD spectra indicated that the interaction between MB and HSA caused the conformational changes in HSA. The binding affinity of MB to HSA was enhanced but to a different extent in the presence of Cu(2+) and Fe(3+), respectively, which indicated that the influence of different metal ions varied. Enhancement of the binding affinity of MB to HSA in the presence of Cu(2+) is due to the formation of Cu(2+)-HSA complex leading to the conformational changes in HSA, whereas in the presence of Fe(3+), enhancement of the binding affinity is due to the greater stability of the Fe(3+)-HSA-MB complex compared with the MB-HSA complex.

Probing the interaction of human serum albumin with DPPH in the absence and presence of the eight antioxidants

Albumin represents a very abundant and important circulating antioxidant in plasma. DPPH radical is also called 2,2-diphenyl-1-picrylhydrazyl. It has been widely used for measuring the efficiency of antioxidants. In this paper, the ability of human serum albumin (HSA) to scavenge DPPH radical was investigated using UV-vis absorption spectra. The interaction between HSA and DPPH was investigated in the absence and presence of eight popular antioxidants using fluorescence spectroscopy. These results indicate the antioxidant activity of HSA against DPPH radical is similar to glutathione and the value of IC50 is 5.200×10(-5) mol L(-1). In addition, the fluorescence experiments indicate the quenching mechanism of HSA, by DPPH, is a static process. The quenching process of DPPH with HSA is easily affected by the eight antioxidants, however, they cannot change the quenching mechanism of DPPH with HSA. The binding of DPPH to HSA primarily takes place in subdomain IIA and exists two classes of binding sites with two different interaction behaviors. The decreased binding constants and the number of binding sites of DPPH with HSA by the introduction of the eight antioxidants may result from the competition of the eight antioxidants and DPPH binding to HSA. The binding of DPPH to HSA may induce the micro-environment of the lone Trp-214 from polar to slightly nonpolar.

Spectroscopic investigation on the food components-drug interaction: the influence of flavonoids on the affinity of nifedipine to human serum albumin

Nifedipine (NDP) is used extensively for the clinical treatment of a number of cardiovascular diseases. Herein, the interaction between human serum albumin (HSA) and NDP and the influence of flavonoids, rutin and baicalin, on their binding properties were investigated in vitro by means of fluorescence and absorption spectroscopy. The fluorescence of HSA was quenched remarkably by NDP and the quenching mechanism was considered as static quenching by forming a complex. The results of thermodynamic parameters indicate that both hydrogen bonds and hydrophobic interactions play the main role in the binding process and the binding process was spontaneous. The binding distance between the amino acid residue of HSA and NDP is 2.608 nm, which indicates that the energy transfer from HSA to NDP can occur with high probability. The decreased association constants and the increased binding distance of NDP binding to HSA in the presence of flavonoids were both due to their competitive binding to the site I of HSA. The results obtained from synchronous fluorescence and three-dimensional fluorescence spectra showed that the interaction between HSA and NDP caused the conformational changes of HSA and the synergism effects of NDP and flavonoids induced the further conformational changes of HSA.

Studies on the interactions of SAP-1 (an N-terminal truncated form of cystatin S) with its binding partners by CD-spectroscopic and molecular docking methods

SAP-1 is a 113 amino acid long single-chain protein which belongs to the type 2 cystatin gene family. In our previous study, we have purified SAP-1 from human seminal plasma and observed its cross-class inhibitory property. At this time, we report the interaction of SAP-1 with diverse proteases and its binding partners by CD-spectroscopic and molecular docking methods. The circular dichroism (CD) spectroscopic studies demonstrate that the conformation of SAP-1 is changed after its complexation with proteases, and the alterations in protein secondary structure are quantitatively calculated with increase of α-helices and reduction of β-strand content. To get insight into the interactions between SAP-1 and proteases, we make an effort to model the three-dimensional structure of SAP-1 by molecular modeling and verify its stability and viability through molecular dynamics simulations and finally complexed with different proteases using ClusPro 2.0 Server. A high degree of shape complementarity is examined within the complexes, stabilized by a number of hydrogen bonds (HBs) and hydrophobic interactions. Using HB analyses in different protein complexes, we have identified a series of key residues that may be involved in the interactions between SAP-1 and proteases. These findings will assist to understand the mechanism of inhibition of SAP-1 for different proteases and provide intimation for further research.