Interaction of Human Serum Albumin with Indomethacin: Spectroscopic and Molecular Modeling Studies

Spectroscopic and Molecular Docking Studies of the Interaction of Non-steroidal Anti-inflammatory Drugs with a Carrier Protein: an Interesting Case of Inner Filter Effect and Intensity Enhancement in Protein Fluorescence

Interaction of diclofenac and indomethacin with lysozyme was studied using several spectroscopic and molecular docking methods. Difference UV-visible spectra showed that the absorption profile of lysozyme changed when both diclofenac and indomethacin were mixed with the former. The sequential addition of both drugs to the lysozyme solution caused the decrease of the intrinsic fluorescence of the latter, however, when the data were corrected for inner filter effect, an enhancement in the fluorescence of lysozyme was detected. Accordingly, the fluorescence enhancement data were analyzed using Benesi-Hildebrand equation. Both, diclofenac and indomethacin showed good interaction with lysozyme, although, the association constants of indomethacin were nearly two-fold higher as compared to that of diclofenac. The binding was slightly more spontaneous in case of indomethacin and the major forces involved in the binding of both drugs with lysozyme were hydrogen bonding and hydrophobic interactions. Secondary structural analysis revealed that both drugs partially unfolded lysozyme. Results obtained through molecular docking were also in good agreement with the experimental outcomes. Both, diclofenac and indomethacin, are bounded at the same site inside lysozyme which is located in the big hydrophobic cavity of the protein.

A fluorescent probe for bioimaging of GSH in cancer cells

A fluorescent probe CTP2-IMC was designed for bioimaging of glutathione (GSH) in cancer cells with indomethacin (IMC), coumarin and bromide as the targeting group, fluorophore and receptor, respectively. Due to the π-π interaction between coumarin and IMC, CTP2-IMC mainly exists in the form of folded state in aqueous solution. The non-radiative transitions caused by the photo-induced electron transfer (PET) process from IMC to the fluorophore as well as the heavy-atom effect led to non-fluorescent of CTP2-IMC. The substitution of Br by GSH and unfolded conformation induced by IMC acceptor on cancer cells resulted in significant fluorescence enhancement, which enabled CTP2-IMC to bioimage GSH in cancer cells rather than in normal one.

Detailed Experimental and In Silico Investigation of Indomethacin Binding with Human Serum Albumin Considering Primary and Secondary Binding Sites

The interaction of indomethacin with human serum albumin (HSA) has been studied here considering the primary and secondary binding sites. The Stern–Volmer plots were linear in the lower concentration range of indomethacin while a downward curvature was observed in the higher concentration range, suggesting the presence of more than one binding site for indomethacin inside HSA due to which the microenvironment of the fluorophore changed slightly and some of its fraction was not accessible to the quencher. The Stern–Volmer quenching constants (KSV) for the primary and secondary sites were calculated from the two linear portions of the Stern–Volmer plots. There was around a two-fold decrease in the quenching constants for the low-affinity site as compared to the primary binding site. The interaction takes place via a static quenching mechanism and the KSV decreases at both primary and secondary sites upon increasing the temperature. The binding constants were also evaluated, which show strong binding at the primary site and fair binding at the secondary site. The binding was thermodynamically favorable with the liberation of heat and the ordering of the system. In principle, hydrogen bonding and Van der Waals forces were involved in the binding at the primary site while the low-affinity site interacted through hydrophobic forces only. The competitive binding was also evaluated using warfarin, ibuprofen, hemin, and a warfarin + hemin combination as site markers. The binding profile remained unchanged in the presence of ibuprofen, whereas it decreased in the presence of both warfarin and hemin with a straight line in the Stern–Volmer plots. The reduction in the binding was at a maximum when both warfarin and hemin were present simultaneously with the downward curvature in the Stern–Volmer plots at higher concentrations of indomethacin. The secondary structure of HSA also changes slightly in the presence of higher concentrations of indomethacin. Molecular dynamics simulations were performed at the primary and secondary binding sites of HSA which are drug site 1 (located in the subdomain IIA of the protein) and the hemin binding site (located in subdomain IB), respectively. From the results obtained from molecular docking and MD simulation, the indomethacin molecule showed more binding affinity towards drug site 1 followed by the other two sites.

Indomethacin-induced spectral responses of naphthalimide-based dyes to serum albumin: effects of substituent and spacer

Four indomethacin-naphthalimide binaries with different proton receptors at 4-position of naphthalimide were designed and synthesized. N,N-Dimethylethylenediamine and N-methyl piperazine were served as proton receptors as well as solubility regulators. Indomethacin, an inhibitor for cyclooxygenase-2 overexpressed on cancer cells, was connected at the imine N through different spacers. The attachment of indomethacin significantly quenched the fluorescence of all compounds with obvious red-shift in the absorption maxima due to the strong photo-induced electron transfer process of the folded-state. Human serum albumin (HSA) triggered about 15-fold fluorescence enhancements of DMN-IMC-5 with 30 nm blue-shift. However, it caused much smaller fluorescence increments of other compounds, suggesting that indomethacin, the linker and proton receptor play critical roles in HSA identification. Fluorescence bioimaging results show that indomethacin enables the naphthalimide-based compounds to fluorescent imaging living cells. Molecular docking reveals that the introduction of indomethacin improved the binding affinity of the dyes to HSA.

Lysine reactivity profiling reveals molecular insights into human serum albumin-small-molecule drug interactions

Human serum albumin (HSA) is one of the most important serum carrier proteins that deliver small-molecule drugs to their specific targets. Clarifying the molecular mechanism of the interaction between natural HSA and drugs in an aqueous solution has been a hot topic in pharmaceutical chemistry, clinical medicine, and biochemistry in recent years, but it is still challenging. In this paper, the details of molecular interactions of HSA with a variety of therapeutic drugs including ibuprofen, indomethacin, phenylbutazone, and warfarin are systematically investigated using a mass spectrometry (MS)-based lysine reactivity profiling (LRP) strategy. The results reaffirm that the major ligand binding sites (including Sites I and II) of HSA are located in subdomains IIA and IIIA, while several potential drug-binding areas at subdomain IIIB and α helix IIB-IIIA are newly characterized. The MS-LRP strategy may have important application prospects in pharmacodynamics, pharmacokinetics, and safety evaluation of small-molecule drugs.

Selective bioimaging of cancer cells and detection of HSA with indomethacin-based fluorescent probes

Two fluorescent probes were designed by connecting indomethacin to coumarin through different linkers. The introduction of indomethacin quenched the fluorescence of coumarin-based probes with apparent red-shifts in the absorption and emission maxima, probably due to the photoinduced electron transfer (PET) from the indomethacin to the fluorophore and the formation of folding conformation. The addition of human serum albumin (HSA) triggered about 40-fold fluorescence enhancements of ADC-IMC-2 and ADC-IMC-6 with 85 nm blue-shifts. The probe with longer spacer ADC-IMC-6 exhibited ratiometric fluorescent response toward HSA, and that with shorter linker showed "off-on" fluorescence response to HSA. However, insignificant spectral changes of the reference compounds (ADC-6 and ADC-2) initiated by HSA implied that indomethacin played critical role in the identification of HSA. The competitive assays and molecular docking results reveal that the indomethacin in ADC-IMC-6 could tightly combine at drug site I of HSA. Fluorescence bio-imaging experiments show that both probes could distinguish cancer cells from normal cells.

Physiological changes in the albumin-bound non-esterified free fatty acids critically influence heme/bilirubin binding properties of the protein: A comparative, in vitro, spectroscopic study using the endogenous biomolecules

Heme and bilirubin (BR), as by-products of red blood cells (and hemoglobin) degradation, show increased plasma concentrations in some diseases. These two toxic hydrophobic molecules are mainly transported in the blood-stream by human serum albumin (HSA) that carries a wide variety of ligands. Under normal physiological conditions, ~3 fatty acid (FA) molecules are bound to each HSA; and its possible effect on BR/heme binding remains to be more clarified. In the present study, to provide deeper insight on this issue, we purified albumin from healthy individuals (as purified non-defatted albumin or PA) with normal plasma levels of FA, then defatted some of the purified protein (as defatted-HSA; or DA). In the next step, using various spectroscopic methods, their interactions with heme and BR were investigated. By 1: 1 binding of the ligands, quenching and thermodynamic analysis of parameters indicated that binding constants (K_b) values of bilirubin and heme for PA and DA are different. It could be perceived that the presence of FAs in high-affinity FA binding sites (FABSs) exerted considerable conformational changes in the structure followed by an improved BR binding while hindered heme interaction. The data was confirmed by determining surface hydrophobicity of the purified albumin (PA) and DA, and then supported by bioinformatics analyses. The physiological and clinical relevance of the observed dynamic interactions is also discussed. This study, also, re-confirmed that the primary BR binding site is subdomain IIA not subdomain IB.

Study on the interaction of anti-inflammatory drugs with human serum albumin using molecular docking, quantitative structure-activity relationship, and fluorescence spectroscopy

The interaction of 14 anti-inflammatory drugs with human serum albumin (HSA) was investigated using fluorescence quenching, molecular docking studies, and quantitative structure-activity relationship (QSAR) methodology. Binding of anti-inflammatory drugs to HSA plays a fundamental role in their transport, distribution, delivery, and elimination. Binding constants of these drugs to HSA, obtained using the fluorescence quenching method, were within the range 0.01 × 10⁴  M^-1 (acetaminophen) to 1881.05 × 10⁴  M^-1 (meloxicam). Binding sites and binding constants of these anti-inflammatory drugs were estimated using molecular docking. Inspection of the obtained values for docking score, logK_b and K_b , showed that the drugs in this data set have a relatively strong binding constant for HSA. QSAR modelling was applied for binding constants obtained from fluorescence quenching and theoretical molecular descriptors. This modelling led to a linear two-parameter model with a correlation coefficient of 0.95 and adequate robustness. The descriptor results showed the importance of a bonding network and electronegativity as the discriminative structural factors in binding affinity for the HSA molecule.

Molecular spectroscopic studies examining the interactions between phenobarbital and human serum albumin in alcohol consumption

BACKGROUND

Alcohol dependence is associated with a wide range of serious mental, physical, and social consequences and is one of the most common chronic diseases worldwide. Barbiturates, which are a first-line treatment in the clinic for alcohol withdrawal, may result in combined barbiturate and alcohol use. Their co-use abuse may promote synergistic effects between barbiturates and alcohol in vivo.

OBJECTIVE

To investigate the effects of different alcohol concentrations on the synergistic effects of phenobarbital and alcohol.

METHODS

The interactions between phenobarbital and human serum albumin (HSA) and the effects of different alcohol concentrations on the binding behaviors of the phenobarbital-HSA system were investigated by molecular docking and spectroscopic methods, including fluorescence spectroscopy and UV-visible absorption spectroscopy.

RESULTS

Experimental results revealed that phenobarbital can be stored and carried by HSA. The presence of alcohol (≤1.96 × 10^-2 M) can increase the proportion of free phenobarbital and shorten the half-life and storage time of phenobarbital in the blood, thereby enhancing its bioactive efficacy. The binding constants (K_b) of the phenobarbital-HSA system decrease in the presence of alcohol (≥2.61 × 10^-2 M), which suggests that phenobarbital should be quickly cleared from blood, thereby decreasing the activity of phenobarbital.

CONCLUSIONS

The effects of alcohol on the transposition of phenobarbital by HSA at the beginning of the barbiturate metabolic process play an important role in the synergistic effects of phenobarbital and alcohol. This mechanism may be significant for the clinical dosage of patients with alcohol dependence.

Biophysical insights into the interaction of hen egg white lysozyme with therapeutic dye clofazimine: modulation of activity and SDS induced aggregation of model protein

The present study details the binding process of clofazimine to hen egg white lysozyme (HEWL) using spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), and molecular docking techniques. Clofazimine binds to the protein with binding constant (K_b) in the order of 1.57 × 10⁴ at 298 K. Binding process is spontaneous and exothermic. Molecular docking results suggested the involvement of hydrogen bonding and hydrophobic interactions in the binding process. Bacterial cell lytic activity in the presence of clofazimine increased to more than 40% of the value obtained with HEWL only. Interaction of the drug with HEWL induced ordered secondary structure in the protein and molecular compaction. Clofazimine also effectively inhibited the sodium dodecyl sulfate (SDS) induced amyloid formation in HEWL and caused disaggregation of preformed fibrils, reinforcing the notion that there is involvement of hydrophobic interactions and hydrogen bonding in the binding process of clofazimine with HEWL and clofazimine destabilizes the mature fibrils. Further, TEM images confirmed that fibrillar species were absent in the samples where amyloid induction was performed in the presence of clofazimine. As clofazimine is a drug less explored for the inhibition of fibril formation of the proteins, this study reports the inhibition of SDS-induced amyloid formation of HEWL by clofazimine, which will help in the development of clofazimine-related molecules for the treatment of amyloidosis.

Investigation on the protein-binding properties of icotinib by spectroscopic and molecular modeling method

Icotinib is a highly-selective epidermal growth factor receptor tyrosine kinase inhibitor with preclinical and clinical activity in non-small cell lung cancer, which has been developed as a new targeted anti-tumor drug in China. In this work, the interaction of icotinib and human serum albumin (HSA) were studied by three-dimensional fluorescence spectra, ultraviolet spectra, circular dichroism (CD) spectra, molecular probe and molecular modeling methods. The results showed that icotinib binds to Sudlow's site I in subdomain IIA of HSA molecule, resulting in icotinib-HSA complexes formed at ground state. The number of binding sites, equilibrium constants, and thermodynamic parameters of the reaction were calculated at different temperatures. The negative enthalpy change (ΔH(θ)) and entropy change (ΔS(θ)) indicated that the structure of new complexes was stabilized by hydrogen bonds and van der Waals power. The distance between donor and acceptor was calculated according to Förster's non-radiation resonance energy transfer theory. The structural changes of HSA caused by icotinib binding were detected by synchronous spectra and circular dichroism (CD) spectra. Molecular modeling method was employed to unfold full details of the interaction at molecular level, most of which could be supported by experimental results. The study analyzed the probability that serum albumins act as carriers for this new anticarcinogen and provided fundamental information on the process of delivering icotinib to its target tissues, which might be helpful in understanding the mechanism of icotinib in cancer therapy.

Interaction of new kinase inhibitors cabozantinib and tofacitinib with human serum alpha-1 acid glycoprotein. A comprehensive spectroscopic and molecular Docking approach

In the current study we have investigated the interaction of newly approved kinase inhibitors namely Cabozantinib (CBZ) and Tofacitinib (TFB) with human Alpha-1 acid glycoprotein (AAG) under simulated physiological conditions using fluorescence quenching measurements, circular dichroism, dynamic light scattering and molecular docking methods. CBZ and TFB binds to AAG with significant affinity and the calculated binding constant for the drugs lie in the order of 10(4). With the increase in temperature the binding constant values decreased for both CBZ and TFB. The fluorescence resonance energy transfer (FRET) from AAG to CBZ and TFB suggested the fluorescence intensity of AAG was quenched by the two studied drugs via the formation of a non-fluorescent complex in the static manner. The molecular distance r value calculated from FRET is around 2 nm for both drugs, fluorescence spectroscopy data was employed for the study of thermodynamic parameters, standard Gibbs free energy change at 300 K was calculated as -5.234 kcal mol(-1) for CBZ-AAG interaction and -6.237 kcal mol(-1) for TFB-AAG interaction, standard enthalpy change and standard entropy change for CBZ-AAG interaction are -9.553 kcal mol(-1) and -14.618 cal mol(-1) K(-1) respectively while for AAG-TFB interaction, standard enthalpy and standard entropy change was calculated as 4.019 kcal mol(-1) and 7.206 cal mol(-1) K(-1) respectively. Protein binding of the two drugs caused the tertiary structure alterations. Dynamic light scattering measurements demonstrated the reduction in the hydrodynamic radii of the protein. Furthermore molecular docking results suggested the Hydrophobic interaction and hydrogen bonding were the interactive forces in the binding process of CBZ to AAG while in case of TFB only hydrophobic interactions were found to be involved, overlap of the binding site for two studied drugs on the AAG molecule was revealed by docking results.

In vitro interaction investigation between three Ru(ii) arene complexes and human serum albumin: structural influences

In vitro interactions between three Ru(ii) arene complexes and human serum albumin were systematically investigated by multi-spectroscopic techniques.

Protein-binding properties of a designed steroidal lactam compound

Introducing amide bonds into a steroid nucleus or its side chain may reduce the acute toxicity and enhance the pharmaceutical activity. In this work, a designed steroidal amide compound, named 3β-hydroxy-17-aza-d-homo-5-androsten-17-one (HAAO), was synthesized and identified. The interactions between HAAO and human serum albumin (HSA) were studied by multiple spectroscopic methods and molecular modeling procedures. It was found that HAAO locates in Sudlow's site I in subdomain IIA of HSA molecules, relying on hydrogen bonds and van der Waals power to form HAAO-HSA complexes at ground state. The number of binding sites, binding constants, enthalpy change (ΔH(θ)), Gibbs free energy change (ΔG(θ)) and entropy change (ΔS(θ)) were calculated at different temperatures based on fluorescence quenching theory and classical thermodynamic equation. The percentages content of the HSA's secondary structures in presence of HAAO were detected by circular dichroism (CD) spectra and compared with those in no presence of HAAO. In addition, the experimental results of both binding site and conformational change were further confirmed by molecular modeling investigation, in which more details of the binding were visually unfolded. The information provided by the study may be useful for designing novel chemotherapeutic drugs and be helpful both in the early stages of drug discovery and in clinical practice.

Fluorescence spectroscopy of osthole binding to human serum albumin

The interaction of human serum albumin (HSA) with osthole was investigated by fluorescence spectroscopy. Osthole can quench the fluorescence of HSA and the quenching mechanism is a static process. The binding site number n and apparent binding constant K were measured at different temperatures. The thermodynamic parameters ΔH⁰, ΔG⁰ and ΔS⁰ were calculated at different temperatures. The results indicated that electrostatic forces played a major role in the interaction of osthole with HSA. Results of osthole synchronous fluorescence and UV absorption spectra showed that the microenvironment and conformation of HSA were changed.