Biophysical Insight into Furosemide Binding to Human Serum Albumin: A Study To Unveil Its Impaired Albumin Binding in Uremia

Spectroscopic study on volasertib: Highly stable complexes with albumin and encapsulation into alginate/montmorillonite bionanocomposites

In the present work, we study different physicochemical properties related to LADME processes of volasertib, a Polo-like kinase 1 inhibitor in advanced clinical trials. Firstly, the protonation equilibria, the extent of ionization at the physiological pH and pKa values of this drug are studied combining spectroscopic techniques and computational calculations. Secondly, the binding process of volasertib to the human serum albumin (HSA) protein is analyzed by fluorescence spectroscopy. We report a high binding constant to HSA (Ka = 4.10 × 106 M-1) and their pharmacokinetic implications are discussed accordingly. The negative enthalpy and entropy (ΔH0 = -54.49 kJ/mol; ΔS0 = -58.90 J K-1 mol-1) determined for the binding process suggests the implication of hydrogen bonds and van der Waals interactions in the formation of the HSA-volasertib complex. Additionally, volasertib is encapsulated in an alginate/montmorillonite bionanocomposite as a proof of concept for an oral delivery nanocarrier. The physical properties of that nanocomposite as well as volasertib delivery kinetics are analyzed.

Biomacromolecular carriers based hydrophobic natural products for potential cancer therapy

Cancer is the second leading cause of death worldwide. It was estimated that 90 % of cancer-related deaths were attributable to the development of multi-drug resistance (MDR) during chemotherapy, which results in ineffective chemotherapy. Hydrophobic natural products plays a pivotal role in the field of cancer therapy, with the potential to reverse MDR in tumor cells, thereby enhancing the efficacy of tumor therapy. However, their targeted delivery is considered a major hurdle in their application. The advent of numerous approaches for encapsulating bioactive ingredients in the nanodelivery systems has improved the stability and targeted delivery of these biomolecules. The manuscript comprehensively analyses the nanodelivery systems of bioactive compounds with potential cancer therapy applications, including liposomes, emulsions, solid lipid nanoparticles (NPs), and polymeric NPs. Then, the advantages and disadvantages of various nanoagents in the treatment of various cancer types are critically discussed. Further, the application of multiple-compbine delivery methods to overcome the limitations of single-delivery have need critically analyzed, which thus could help in the designing nanodrug delivery systems for bioactive compounds in clinical settings. Therefore, the review is timely and important for development of efficient nanodelivery systems involving hydrophobic natural products to improve pharmacokinetic properties for effective cancer treatment.

Furosemide Derails Human Lysozyme Fibrillation by Interacting with Aggregation Hot Spots: A Biophysical Comprehension

Kidney-associated human lysozyme amyloidosis leads to renal impairments;thus, patients are often prescribed furosemide. Based on this fact, the effect of furosemide on induced human lysozyme fibrillation, in vitro, is evaluated by spectroscopic, calorimetric, computational, and cellular-based assays/methods. Results show that furosemide increases the lag phase and decreases the apparent rate of aggregation of human lysozyme, thereby decelerating the nucleation phase and amyloid fibril formation, as confirmed by the decrease in the level of Thioflavin-T fluorescence. Fewer entities of hydrodynamic radii of ∼171 nm instead of amyloid fibrils (∼412 nm) are detected in human lysozyme in the presence of furosemide by dynamic light scattering. Moreover, furosemide decreases the extent of conversion of the α/β structure of human lysozyme into a predominant β-sheet. The isothermal titration calorimetry established that furosemide forms a complex with human lysozyme, which was also confirmed through fluorescence quenching and computational studies. Also, human lysozyme lytic activity is inhibited competitively by furosemide due to the involvement of amino acid residues of the active site in catalysis, as well as complex formation. Conclusively, furosemide interacts with Gln58, Ile59, Asn60, Ala108, and Trp109 of aggregation-prone regions 2 and 4 of human lysozyme, thereby masking its sites of aggregation and generating only lower-order entities that are less toxic to red blood cells than the fibrils. Thus, furosemide slows the progression of amyloid fibrillation in human lysozyme.

Displacing the Burden: A Review of Protein-Bound Uremic Toxin Clearance Strategies in Chronic Kidney Disease

Uremic toxins (UTs), particularly protein-bound uremic toxins (PBUTs), accumulate in chronic kidney disease (CKD) patients, causing significant health complications like uremic syndrome, cardiovascular disease, and immune dysfunction. The binding of PBUTs to plasma proteins such as albumin presents a formidable challenge for clearance, as conventional dialysis is often insufficient. With advancements in the classification and understanding of UTs, spearheaded by the European Uremic Toxins (EUTox) working group, over 120 molecules have been identified, prompting the development of alternative therapeutic strategies. Innovations such as online hemodiafiltration aim to enhance the removal process, while novel adsorptive therapies offer a means to address the high affinity of PBUTs to plasma proteins. Furthermore, the exploration of molecular displacers, designed to increase the free fraction of PBUTs, represents a cutting-edge approach to facilitate their dialytic clearance. Despite these advancements, the clinical application of displacers requires more research to confirm their efficacy and safety. The pursuit of such innovative treatments is crucial for improving the management of uremic toxicity and the overall prognosis of CKD patients, emphasizing the need for ongoing research and clinical trials.

Elucidating the significance of molecular interaction between sulphur doped zinc oxide nanoparticles and serum albumin using multispectroscopic approach

Ingenious nanomaterials with improved biocompatibility and multifunctional properties are gaining vital significance in biomedical applications, including advanced drug delivery and nanotheranostics. In a biological system, these nanoparticles interact with serum proteins forming a dynamic corona that affects their biological or toxicological properties producing undesirable effects. Thus, the current study focuses on the synthesis of sulphur-doped zinc oxide nanoparticles (ZnO/S NPs) and characterizing their mechanism of interaction with serum proteins using multispectroscopic approach. ZnO/S NPs were synthesized by employing a co-precipitation approach and characterized using various analytical techniques. The results of interaction studies demonstrated that ZnO/S NPs interact with serum albumins via the static quenching process. Analysis of thermodynamic parameters (ΔG, ΔH and ΔS) revealed that the binding process is spontaneous, exothermic and van der Waals force or hydrogen bonding plays a major role. The interaction of ZnO/S NPs with tyrosine residue in bovine serum albumin was established by synchronous fluorescence spectroscopy. In addition, the results of UV-visible, circular dichroism, Fourier transform infrared, Forster's resonance energy transfer theory and dynamic light scattering spectroscopic studies revealed that the ZnO/S NPs interact with albumin by inducing the conformational changes in secondary structure and reducing the α-helix content.

Spectroscopic investigations on the interaction between nano plastic and catalase on molecular level

As an emerging pollutant that is easily bonded with some functional proteins and the effects of their physiological expressions, nano plastics (NPs) have been widely detected in various environmental mediums, even in human blood. Compared to microplastics, less information on the interactions between NPs and proteins has been reported. Here, the interaction mechanism between common polystyrene nano plastics (PSNPs) and catalase (CAT) under two typical physiological conditions, pH 7.4 and 4.0, was investigated by UV-visible spectroscopy, circular dichroism (CD), and dynamic light scattering (DLS). Compared with the enhanced catalytic effects when increasing PSNPs at pH 7.4, a trend of initial inhibition and enhanced activity was observed at pH 4.0. Spectroscopic analysis and calculation results indicated that their binding was static, with only one binding site and stronger interactions under acidic conditions. UV-visible and CD spectra analysis demonstrated that the difference in enzymatic activity could be mainly attributed to the conformational alternation of CAT in the presence of PSNPs, which is obviously affected by solution chemistry. The change was also revealed by the hydrodynamic diameter and zeta potentials of the complexes supplied by DLS analysis. This study will help understand the health risks of nano plastic pollution and provide a theoretical basis for studying their toxicological effects.

Unusually High Affinity of the PLK Inhibitors RO3280 and GSK461364 to HSA and Its Possible Pharmacokinetic Implications

The binding processes of two Polo-like kinase inhibitors, RO3280 and GSK461364, to the human serum albumin (HSA) protein as well as the protonation equilibria of both compounds have been studied combining absorbance and fluorescence spectroscopy experiments together with density functional theory calculations. We found that the charge states of RO3280 and GSK461364 are +2 and +1, respectively, at the physiological pH. Nevertheless, RO3280 binds to HSA in the charge state +1 prior to a deprotonation pre-equilibrium. Binding constants to site I of HSA of 2.23 × 10⁶ and 8.80 × 10⁴ M^-1 were determined for RO3280 and GSK461364, respectively, at 310 K. The binding processes of RO3280 and GSK461364 to HSA are entropy- and enthalpy-driven, respectively. The positive enthalpy found for the RO3280-HSA complex formation could be related to a proton pre-equilibrium of RO3280.

Molecular interaction of di-ester bonded cationic Gemini surfactants with pepsin: in vitro and in silico perspectives

The implications of surfactant-enzyme/protein interactions in a variety of fields, including biotechnology, cosmetics, paints and pharmaceuticals, have attracted a lot of attention in contemporary studies. Herein, we have employed several in vitro and in silico techniques such as excitation and absorption spectroscopies, circular dichroism and FT-IR spectroscopies, density functional and molecular dynamics simulations to understand the interaction behavior of oxy-diester-based green cationic Gemini surfactants, N1,N1,N14,N14-tetramethyl-2,13-dioxo-N1,N14-dialkyl-3,6,12-tetraoxateradecane-1,14-diaminiumdichloride (abbreviated as Cm-E2O2-Cm, where 'm' stands for alkyl chain length, m = 12 and 14) with one of the main digestive proteins, pepsin. The spectroscopic techniques confirm the static quenching effect of surfactants on pepsin. The calculated physical parameters (Ksv, Kb and ΔG) and their order reveal the distinguished implications for the surfactants' chain lengths. The spontaneity of interaction was also confirmed by negative Gibbs free energy change values. The extrinsic spectroscopic study with pyrene as fluorescence probe, FT-IR and CD techniques indicated a potential conformational change in pepsin induced by the Gemini surfactants. DFT, docking and MD simulations provided the theoretical understanding regarding the quantum mechanical environment, location of binding and stability of the protein-surfactant complexation in energy terms. We believe this study will be a humble addition to our existing knowledge in the field of protein-surfactant interactions.Communicated by Ramaswamy H. Sarma.

Impact of Albumin Binding Function on Pharmacokinetics and Pharmacodynamics of Furosemide

Background and Objectives: Albumin binding of the loop diuretic furosemide forms the basis for its transport to the kidney and subsequent tubular secretion, which is a prerequisite for its therapeutic effects. Accordingly, high albumin concentrations should result in higher efficacy of furosemide. However, study results on the combination of furosemide in conjunction with albumin, and on the efficacy of furosemide in hypoalbuminemia, did not confirm this hypothesis. The aim of this study was to determine the efficacy of furosemide not only in relation to albumin concentration, but also taking albumin function into account. Materials and Methods: In a prospective and non-interventional clinical observational trial, blood and urine samples from 50 intensive care patients receiving continuous intravenous furosemide therapy were evaluated. Albumin binding capacity (ABiC) determination allowed conclusions to be drawn about the binding site-specific loading state of albumin, by quantifying the unbound fraction of the fluorescent marker dansylsarcosine. In addition, assessment of the total concentration of furosemide in plasma and urine, as well as the concentration of free furosemide fraction in plasma, was performed by HPLC−MS. The efficacy of furosemide was evaluated by the ratio of urine excretion to fluid intake. Results: In patients with an ABiC ≥ 60% free furosemide fraction was significantly lower compared to patients with a lower ABiC (p < 0.001), urinary furosemide concentration was higher (p = 0.136), and a significantly higher proportion of infused furosemide was excreted renally (p = 0.010). ABiC was positively correlated (r = 0.908, p = 0.017) with increase in the urine excretion to fluid input ratio after initiation of furosemide therapy. Conclusions: ABiC could serve as a marker for individual response to furosemide and could be used to generate patient-specific therapeutic regimens. In view of the relatively low number of patients in this study, the relationship between furosemide efficacy and albumin function should be investigated in larger studies in the future.

Spectroscopic Analysis of an Antimalarial Drug’s (Quinine) Influence on Human Serum Albumin Reduction and Antioxidant Potential

Quinine (Qi) is a well-known drug used in malaria therapy; it is also a potential anti-arrhythmic drug used in the treatment of calf cramps, rheumatoid arthritis, colds, and photodermatitis. Moreover, it is used in the food industry for the production of tonics. This study aimed to analyze the interaction between quinine and a transporting protein—human serum albumin (HSA)—as well as the influence of Qi on both protein reduction and antioxidant potential. It was found that Qi (via spectrofluorometric measurements and circular dichroism spectroscopy) binds to HSA with a low affinity and slightly affects the secondary structure of albumin. As demonstrated by the use of ABTS and FRAP assays, HSA has a higher antioxidant and reduction potential than Qi, while their mutual interaction results in a synergistic effect in antioxidant activity and reduction potential.

α-Crystallin chaperone mimetic drugs inhibit lens γ-crystallin aggregation: potential role for cataract prevention

Γ-Crystallins play a major role in age-related lens transparency. Their destabilization by mutations and physical chemical insults are associated with cataract formation. Therefore, drugs that increase their stability should have anticataract properties. To this end, we screened 2560 Federal Drug Agency–approved drugs and natural compounds for their ability to suppress or worsen H₂O₂ and/or heat-mediated aggregation of bovine γ-crystallins. The top two drugs, closantel (C), an antihelminthic drug, and gambogic acid (G), a xanthonoid, attenuated thermal-induced protein unfolding and aggregation as shown by turbidimetry fluorescence spectroscopy dynamic light scattering and electron microscopy of human or mouse recombinant crystallins. Furthermore, binding studies using fluorescence inhibition and hydrophobic pocket–binding molecule bis-8-anilino-1-naphthalene sulfonic acid revealed static binding of C and G to hydrophobic sites with medium-to-low affinity. Molecular docking to HγD and other γ-crystallins revealed two binding sites, one in the “NC pocket” (residues 50–150) of HγD and one spanning the “NC tail” (residues 56–61 to 168–174 in the C-terminal domain). Multiple binding sites overlap with those of the protective mini αA-crystallin chaperone MAC peptide. Mechanistic studies using bis-8-anilino-1-naphthalene sulfonic acid as a proxy drug showed that it bound to MAC sites, improved T_m of both H₂O₂ oxidized and native human gamma D, and suppressed turbidity of oxidized HγD, most likely by trapping exposed hydrophobic sites. The extent to which these drugs act as α-crystallin mimetics and reduce cataract progression remains to be demonstrated. This study provides initial insights into binding properties of C and G to γ-crystallins.

Multi-Spectroscopic, thermodynamic and molecular docking studies to investigate the interaction of eplerenone with human serum albumin

The binding of small molecular drugs with human serum albumin (HSA) has a crucial influence on their pharmacokinetics. The binding interaction between the antihypertensive Eplerenone (EPL)and HSA was investigated using multi-spectroscopic techniques for the first time. These techniques include UV-Vis spectroscopy, Fourier Transform Infrared (FT-IR), native fluorescence spectroscopy, synchronous fluorescence spectroscopy and molecular docking approach. The fluorescence spectroscopic study showed that EPL quenched HSA inherent fluorescence. The mechanism for quenching of HSA by EPL has been determined to be static in nature and confirmed by UV absorption and fluorescence spectroscopy. The modified Stern-Volmer equation was used to estimate the binding constant (K_b ) as well as the number of bindings (n). The results indicated that the binding occurs at a single site (Kb;2.238 x 10³ L mol^-1 at 298 K). The enthalpy and entropy changes (∆H and ∆S) were 58.061 and 0.258 K J mol^-1 , respectively, illustrating that the principal intermolecular interactions stabilizing the EPL-HSA system are hydrophobic forces. Synchronous fluorescence spectroscopy revealed that EPL binding to HSA occurred around the tyrosine residue (Tyr) and this agreed with the molecular docking study. The FRET analysis confirmed the static quenching mechanism. The esterase enzyme activity of HSA was also evaluated showing its decrease in the presence of EPL. Furthermore, docking analysis and site-specific markers experiment revealed that EPL binds with HSA at subdomain IB (site III).

Comparison of Losartan and Furosemide Interaction with HSA and Their Influence on HSA Antioxidant Potential

Serum albumin (HSA) is the most important protein in human body. Due to the antioxidant activity, HSA influences homeostasis maintenance and transport of drugs as well as other substances. It is noteworthy that ligands, such as popular drugs, modulate the antioxidant activity of HSA. The aim of this study was to analyze the influence of losartan (LOS) and furosemide (FUR) on HSA antioxidant properties as well as the interaction between these drugs and protein using calorimetric and spectroscopic methods. LOS and FUR showed the high affinity for human serum albumin, and the binding reactions between them were spontaneous and exothermic. LOS and FUR, separately and together in the system, have no significant impact on the secondary HSA structure; however they have significant impact on the tertiary HSA structure. LOS and FUR mixed with HSA have the ability to scavenge free radicals, and the ligand(s)-HSA interactions were synergistic.

Mechanistic In Vitro Dissection of the Inhibition of Amyloid Fibrillation by n-Acetylneuraminic Acid: Plausible Implication in Therapeutics for Neurodegenerative Disorders

A variety of neurodegenerative disorders including Parkinson's disease are due to fibrillation in amyloidogenic proteins. The development of therapeutics for these disorders is a topic of extensive research as effective treatments are still unavailable. The present study establishes that n-acetylneuraminic acid (Neu5ac) inhibits the amyloid fibrillation of hen egg-white lysozyme (HEWL) and α-synuclein (SYN), as observed using various biophysical techniques and cellular assays. Neu5ac inhibits the amyloid formation in both proteins, as suggested from the reduction in the ThT fluorescence and remnant structures in transmission electron microscopy micrographs observed in its presence. In HEWL fibrillation, Neu5ac decreases the hydrophobicity and resists the transition of the α-helix to a β-sheet, as observed by an ANS binding assay, circular dichroism (CD) spectra, and Fourier transform infrared measurements, respectively. Neu5ac stabilizes the states that facilitate the amyloid formation in HEWL and SYN, as demonstrated by an enhanced intrinsic fluorescence in its presence, which is further confirmed by an increase in T_m obtained from differential scanning calorimetry thermograms and an increase in the near-UV CD signal for HEWL with Neu5ac. However, the increase in stability is not a manifestation of Neu5ac binding to amyloid facilitating (partially folded or native) states of both proteins, as verified by isothermal titration calorimetry and fluorescence binding measurements. Besides, Neu5ac also attenuates the cytotoxicity of amyloid fibrils, as evaluated by a cell toxicity assay. These findings provide mechanistic insights into the Neu5ac action against amyloid fibrillation and may establish it as a plausible inhibitor molecule against neurodegenerative disorders.

On the binding reaction of loratadine with human serum acute phase protein alpha 1-acid glycoprotein

Loratadine is an important anti-allergic drug. It is a second generation antihistamine drug used to treat allergic rhinitis, hay fever and urticaria. Human serum alpha 1-acid glycoprotein (AG) is an important acute phase protein and its serum concentration is found to increase in inflammation and acute response.The binding interaction between loratadine and AG is studied using spectroscopy and molecular docking techniques. The results obtained from fluorescence quenching experiments demonstrated that the fluorescence intensity of AG is quenched by loratadine. Loratadine was found to bind AG with the binding constant of ≈10⁴ at 298 K. The Gibb's free energy change was found to be negative for the interaction of loratadine with AG indicating the binding process is spontaneous. Binding of loratadine with AG induced ordered structures in the protein. Hydrogen bonding and hydrophobic interactions were the main bonding forces between AG-loratadine as revealed by molecular docking results. This study suggests the importance of binding of anti-allergic drug to AG spatially in the diseases where the plasma concentration of AG increases many folds and interaction with this protein becomes significant. This study will help in design of drug dosage and adjustment accordingly to achieve optimal treatment outcome. Communicated by Ramaswamy H. Sarma.

Multi-spectroscopic and molecular docking studies for binding interaction between fluvoxamine and human serum albumin

In the present study, different spectroscopic techniques have been used to study the binding interaction between the antidepressant drug fluvoxamine and human serum albumin under simulated physiological conditions (pH 7.4). The utilized spectroscopic techniques include fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, UV-Vis absorption spectroscopy, Fourier Transform Infrared spectroscopy (FT-IR), and molecular modeling methods. The obtained results revealed that the formation of a complex between human serum albumin and fluvoxamine was responsible for quenching the native fluorescence of human serum albumin. The results indicated that the quenching mechanism between human serum albumin and fluvoxamine was static. Besides, the binding constant (K), number of binding sites (n), thermodynamic parameters (ΔH, ΔS, and ΔG), and binding forces were calculated at three different temperatures (298, 310, and 318 K). These data proposed that hydrophobic forces were the principal intermolecular forces stabilizing the complex. From the molecular docking results, it could be deduced that fluvoxamine was inserted into sub-domain II A (site I) of human serum albumin and led to a slight change in human serum albumin conformation.

Self-Immolative Difluorophenyl Ester Linker for Affinity-Based Fluorescence Turn-on Protein Detection

Currently most fluorogenic probes are developed for the analysis of enzymes, where a bond breaking or rearrangement reaction is required to transform a nonfluorescent enzymatic substrate into a fluorescent product. However, this approach cannot be used for proteins that do not possess enzymatic activities. In this article, we show that fluorogenic probes with a self-immolative difluorophenyl ester linker can mimic the bond disassembly processes of fluorogenic enzyme substrates for the rapid analysis of nonenzymatic proteins. Although numerous self-immolative reagents have shown promising applications in sensors, drug delivery systems, and material chemistry, all of them are triggered by either enzymes or small reactive molecules. In our strategy, the probe binds to the protein via a specific protein-ligand interaction, inducing a chemical reaction between the self-immolative linker and an amino acid of the protein, thereby triggering a cascade reaction that leads to the activation and release of the fluorogenic reporter. In contrast, a phenyl ester linker without the difluoro substituent cannot be triggered to release the fluorogenic reporter. With this probe design, live-cell imaging of extracellular and intracellular endogenous tumor marker proteins can be achieved with high selectivity and sensitivity.

Ribosylation induced structural changes in Bovine Serum Albumin: understanding high dietary sugar induced protein aggregation and amyloid formation

Non-enzymatic glycation of proteins is believed to be the root cause of high dietary sugar associated pathophysiological maladies. We investigated the structural changes in protein during progression of glycation using ribosylated Bovine Serum Albumin (BSA). Non enzymatic attachment of about 45 ribose molecules to BSA resulted in gradual reduction of hydrophobicity and aggregation as indicated by red-shifted tryptophan fluorescence, reduced ANS binding and lower anisotropy of FITC-conjugated protein. Parallely, there was a significant decrease of alpha helicity as revealed by Circular Dichroism (CD) and Fourier transformed-Infra Red (FT-IR) spectra. The glycated proteins assumed compact globular structures with enhanced Thioflavin-T binding resembling amyloids. The gross structural transition affected by ribosylation led to enhanced thermostability as indicated by melting temperature and Transmission Electron Microscopy. At a later stage of glycation, the glycated proteins developed non-specific aggregates with increase in size and loss of amyloidogenic behaviour. A parallel non-glycated control incubated under similar conditions indicated that amyloid formation and associated changes were specific for ribosylation and not driven by thermal denaturation due to incubation at 37 °C. Functionality of the glycated protein was significantly altered as probed by Isothermal Titration Calorimetry using polyphenols as substrates. The studies demonstrated that glycation driven globular amyloids form and persist as transient intermediates during formation of misfolded glycated adducts. To the best of our knowledge, the present study is the first systematic attempt to understand glycation associated changes in a protein and provides important insights towards designing therapeutics for arresting dietary sugar induced amyloid formation.

Probing the interaction of ciprofloxacin and E. coli by electrochemistry, spectroscopy and atomic force microscopy

Under the present investigation, effect of ciprofloxacin (CIP) on Escherichia coli has been investigated using electrochemical, spectroscopic and atomic force microscope (AFM) measurements. Investigation reveals the interaction pattern of CIP with E. coli. The CIP essentially interacts with the outer membrane protein F (OmpF), the formation constant of the complex forms between CIP and the OmpF active sites over E. coli is obtained as log K_f of 12.1. Spectroscopic measurements are carried out, which supports the electrochemical measurements on the interaction between CIP and E. coli, at a higher concentration, CIP induces lysis of the E. coli cell membrane. Spectroscopic investigations further reveals that the FeS containing proteins present inside the E. coli cells released out through the ruptured cell membrane of E. coli. Different degrees of detrimental effects on E. coli has been observed when exposed to different concentrations of the drugs. The microscopic images obtained from the AFM scans of E. coli in presence of CIP shows deformation of the E. coli cell wall and its rupture with increasing concentrations of CIP.

Biophysical insight into the interaction of levocabastine with human serum albumin: spectroscopy and molecular docking approach

Interaction of levocabastine with human serum albumin (HSA) is investigated by applying fluorescence spectroscopy, circular dichroism spectroscopy and molecular docking methods. Levocabastine is an important drug in treatment of allergy and currently a target drug for drug repurposing to treat other diseases like vernal keratoconjuctivitis. Fluorescence quenching data revealed that levocabastine bind weakly to protein with binding constant in the order of 10³ M^-1. Förster resonance energy transfer results indicated the binding distance of 2.28 nm for levocabastine. Synchronous fluorescence result suggest slight blue shift for tryptophan upon levocabastine binding, binding of levocabastine impelled rise in α-helical structure in protein, while there are minimal changes in tertiary structure in protein. Moreover, docking results indicate levocabastine binds to pocket near to the drug site-I in HSA via hydrogen bonding and hydrophobic interactions. Understanding the interaction of levocabastine with HSA is significant for the advancement of therapeutic and diagnostic strategies for optimal treatment results.Communicated by Ramaswamy H. Sarma.

Esterase activity and interaction of human hemoglobin with diclofenac sodium: A spectroscopic and molecular docking study

To get an idea about the pharmacokinetics and pharmacodynamics, it is important to study the drug-protein interaction. Therefore, herein, we studied the interaction of diclofenac sodium (DIC) with human hemoglobin. The binding study of nonsteroidal antiinflammatory drug, DIC with human hemoglobin (HHB) was done by utilizing fluorescence, UV-visible, time-resolved fluorescence and far-UV circular dichroism spectroscopy (CD). Various thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) were also calculated. CD results showed that DIC induces secondary structure change in HHB. Fluorescence resonance energy transfer was also performed. Additionally, it was also observed that DIC inhibits the esterase-like enzymatic activity of HHB via competitive inhibition.

Studies on conformational changes induced by binding of pendimethalin with human serum albumin

Pendimethalin (PND) is a widely used herbicide in modern means of agricultural practices. So, its toxic residues exist extensively in the environment and can enter human body. Therefore, the in vitro interaction of PND with human serum albumin (HSA) has been explored by employing various biophysical, molecular docking and dynamics simulation studies as well as enzyme kinetics to unravel its binding mechanism. The binding constant of the PND-HSA complex was about 10⁴ M^-1 using Fluorescence quenching spectra. The negative value of Gibbs free energy change (ΔG⁰ = -32.0 kJ mol^-1) indicates this interaction is a spontaneous process. A large negative ΔH⁰ and positive ΔS⁰ suggests that hydrophobic interactions and H-bonding are involved in the binding process of PND with HSA. The binding of PND can cause conformational and micro-environmental changes in HSA molecule, as shown by various biophysical and molecular dynamics simulation studies. The site marker competition and molecular docking and simulation experiments affirmed that the binding of PND to HSA occurs at or near site I. Esterase-like activity of HSA exhibited decline in the presence of PND revealed the direct involvement of Lys199 of subdomain IIA (Sudlow's site I) in the binding process.

Probing the Nongeneralized Amyloid Inhibitory Mechanism of Hydrophobic Chaperone

Increasing prevalence of protein misfolding disorders urges the search for effective therapies. Although several antiaggregation molecules have been identified, their molecular process of aggregation and clinical trials are underway. The present study is focused on the mechanism through which phenyl butyrate (PB), a chemical chaperone, triggers inhibition of human serum albumin (HSA) fibrillation. Turbidity and Rayleigh light scattering (RLS) measurements reveal the marked presence of aggregates in HSA that were confirmed as amyloid fibrils by thioflavin T (ThT) and Congo red (CR) and were subsequently inhibited by PB in a dose dependent manner. ThT fluorescence kinetics reveals a decrease in the apparent rate constant, K_app, in the presence of PB without triggering a lag phase in HSA suggesting PB's interference with the elongation phase. Dynamic light scattering (DLS) results display a reduction in the aggregate size in the presence of PB. Isothermal titration calorimetry (ITC) data reveals strong binding of PB at site II both at 25 °C (K_b ≈ 1.94 × 10⁵ M^-1) and 65 °C (K_b ≈ 2.90 × 10⁴ M^-1), mediated by hydrogen bonding. Overall, our finding establishes that PB stabilizes partially unfolded HSA molecules through hydrogen bonding, thereby preventing establishment of hydrogen bonds between them and hindering their progression into amyloid fibrils. This is in contrast to its chaperone effect manifested with other proteins.

Details of the cooperative binding of piperlongumine with rat serum albumin obtained by spectroscopic and computational analyses

Piperlongumine (PPL) has presented a variety of important pharmacological activities. In recent pharmacokinetics studies in rats, this molecule reached 76.39% of bioavailability. Although PPL is present in the bloodstream, no information is found on the interaction between PPL and rat serum albumin (RSA), the most abundant protein with the function of transporting endo/exogenous molecules. In this sense, the present study elucidated the mechanism of interaction between PPL and RSA, using in conjunction spectroscopic and computational techniques. This paper shows the importance of applying inner filter correction over the entire fluorescence spectrum prior to any conclusion regarding changes in the polarity of the fluorophore microenvironment, also demonstrates the convergence of the results obtained from the treatment of fluorescence data using the area below the spectrum curve and the intensity in a single wavelength. Thermodynamic parameters revealed that PPL binds to RSA spontaneously (ΔG < 0) and the process is entropically driven. Interaction density function method (IDF) indicated that PPL accessed two cooperative sites in RSA, with moderate binding constants (2.3 × 105 M-1 and 1.3 × 105 M-1). The molecular docking described the microenvironment of the interaction sites, rich in apolar residues. The stability of the RSA-PPL complex was checked by molecular dynamics.

The displacement study of 99m Tc-DTPA-Human serum albumin binding in presence of furosemide and metformin by using equilibrium dialysis and molecular docking

The ^99m Tc-DTPA (Technetium^99m diethylenetriaminepentaacetic acid), is a radiopharmaceutical used in renal scintigraphy. The human serum albumin (HSA) binding site(s) for the ^99m Tc-DTPA have never been characterized. This study will cover in vitro the binding rates of ^99m Tc-DTPA on HSA and the ^99m Tc-DTPA competition interactions with two drugs having known human serum albumin binding sites. Furosemide (FUR) and metformin (MET) were added to ^99m Tc-DTPA solution (weight ratios 1/1 vol:vol) followed by the quantification of ^99m Tc-DTPA binding rates to HSA (40 g/L) using equilibrium dialysis and the qualification of this binding using Molecular Modeling methods. The ^99m Tc-DTPA binding rates to human serum albumin increased with the highest concentration. Both drugs FUR and MET displaced ^99m Tc-DTPA binding. ^99m Tc-DTPA could bind to human serum albumin in many locations in site I and I-II, but strongly bound to site I through hydrogen bonds.

Electrochemical synthesis of carbon nano spheres and its application for detection of ciprofloxacin

Carbon nano spheres (CNSs) were synthesized by single step electrochemical synthesis route in ultra-pure water as a medium of synthesis. Characterization of synthesized CNSs was carried out using atomic force microscope (AFM), particle size analyzer, zeta potential analyzer and Fourier Transform Infrared (FTIR) measurements, from which the information about the morphology and functional groups present on the surface of the particles are obtained. The particle size of the CNSs was found to be 6 nm. FTIR spectrum shows the presence of functional groups such as -OH, C≡C, C = C and on the CNSs. Electrochemical and spectroscopic experiments were conducted to determine the interaction of the drug molecule ciprofloxacin (Cf) with CNSs, strong interaction between Cf and CNSs leads to the development of analytical method of detection of Cf using CNSs as the pre-concentrating agent. The detection of limit of the present method is obtained as 0.15 μM at (S/N) ratio of 3. CNSs can be considered as a potential candidate for the fabrication of sensor for high sensitive determination of Cf.

An investigation into the interaction between piplartine (piperlongumine) and human serum albumin

Piplartines are alkaloid amides present in the roots and stems of different pepper species which have promising pharmacological properties including cancer prevention. Some recent studies have determined pharmacokinetic parameters of piplartine in rat blood plasma but without pointing to any molecular target or describing the physicochemical forces of the interaction. The present study investigated the interaction between piplartine and human serum albumin (HSA) the predominant protein in blood plasma. Fluorescence spectroscopy was utilized to observe the complex HSA-piplartine formation. Thermodynamic parameter analysis indicates that the process occurs spontaneously and is enthalpically driven; the affinity constant suggests that this interaction is reversible. This was reinforced by the binding density function method and by the displacement analysis that the piplartine binds on HSA at a single site, which was determined to be the IIA sub-domain. In silico analysis (molecular docking) identified the main residues involved in binding and the corresponding forces, which corroborates well with the experimental results.

Curious Results in the Prospective Binding Interactions of the Food Additive Tartrazine with β-Lactoglobulin

The detailed characterizations of the binding interactions between food additive tartrazine (TZ) and β-lactoglobulin (β-LG) have been investigated through spectroscopic techniques combined with a molecular modeling study. A series of analyses, such as hyperchromic change in the UV-visible spectra, temperature-dependent quenching constant, time-resolved fluorescence, and Rayleigh scattering measurements, show that quenching of β-LG proceeds by a static quenching mechanism. TZ specifically binds with β-LG in a stoichiometry ratio of 1:1, and the observed binding constants (10⁴, K) are 7.64, 9.13, 9.72, and 10.79 at 293, 298, 303, and 308 K, respectively. However, the curious results of binding constants (K) with temperature, encountered in the static quenching, have been well explained on the basis of Le Chatelier's principle. Thermodynamic data and pH-dependent studies along with the surface hydrophobicity binding displacement assay reveal that the durable mode of binding is chiefly entropy-driven, revealing noteworthy interactions of such ionic molecules with the hydrophobic part of β-LG. The modulation of protein conformation has been investigated through steady-state absorption spectroscopy, synchronous emission spectroscopy, circular dichroism, and dynamic light scattering studies. TZ acts as a potential inhibitor in fibrillogenesis. Furthermore, the molecular docking study offers accurate insights about the binding of TZ with β-LG, in consistence with the experimental results. This study would be helpful in pharmaceutical, food, and industrial engineering chemistry research.

Interaction of piroxicam with bovine serum albumin investigated by spectroscopic, calorimetric and computational molecular methods

The binding of drugs to serum proteins is governed by weak non-covalent forces. In this study, the nature and magnitude of the interactions between piroxicam (PRX) and bovine serum albumin (BSA) was assessed using spectroscopic, calorimetric and computational molecular methods. The fluorescence data revealed an atypical behavior during PRX and BSA interaction. The quenching process of tryptophan (Trp) by PRX is a dual one (approximately equal static and dynamic quenched components). The FRET results indicate that a non-radiative transfer of energy occurred. The association constant and the number of binding sites indicate moderate PRX and BSA binding. The competitive binding study indicates that PRX is bound to site I from the hydrophobic pocket of subdomain IIA of BSA. The synchronous spectra showed that the microenvironment around the BSA fluorophores and protein conformation do not change considerably. The Trp lifetimes revealed that PRX mainly quenches the fluorescence of Trp-213 situated in the hydrophobic domain. The CD and DSC investigation show that addition of PRX stabilizes the protein structure. ITC results revealed that BSA-PRX binding involves a combination of electrostatic, hydrophobic and hydrogen interactions. The analysis of the computational data is consistent with the experimental results. This thorough investigation of the PRX-BSA binding may provide support for other studies concerning moderate affinity drugs with serum protein.Communicated by Ramaswamy H. Sarma.

Spectroscopic and computational exploration of hypoxanthine riboside interacting with plasma albumin

Hypoxanthine riboside (HXR) is a nucleoside essential for wobble base pairs to translate the genetic code. In this work, an absorption and luminescence study showed that HXR and human serum albumin (HSA) formed a new complex through hydrogen bonds and van der Waals forces at ground state. Fluorescence probe experiments indicated that HXR entered the first subdomain of domain II in HSA and was fixed by amino acid residues in site I defined by Sudlow, and after competing with a known site marker. The recognition interaction featured negative ΔH^ϴ , ΔS^ϴ and ΔG^ϴ thermodynamic parameters. Fluorescence and circular dichroism spectra described the polarity of residues and α-helix and β-strand content changed because of HXR binding. The most rational structure for the HXR-HSA complex was recommended by the molecular docking method, in which the binding location, molecular orientation, adjacent amino acid residues, and hydrogen bonds were included. In addition, the influence of β-cyclodextrin and some essential metal ions on the balance of the HSA-HXR system interaction was measured. The study gained comprehensive information on the transportation mechanism for HXR in blood, and was of great significance in understanding the theory of HXR biotransformation and in discussing its clinical in vivo half-life.

Study of the Interaction of Ciprofloxacin and Sparfloxacin with Biomolecules by Spectral, Electrochemical and Molecular Docking Methods

Interactions of ciprofloxacin and sparfloxacin with different biomolecules (DNA, RNA and BSA) are investigated by UV–Visible spectroscopy, fluorescence spectroscopy, cyclic voltammetry and molecular docking methods. Upon increasing the concentration of the biomolecules, the absorption maxima of ciprofloxacin and sparfloxacin are red shifted in the aqueous solutions whereas red or blue shift noticed in the fluorescence spectra. The negative free energy changes suggest that the interaction processes are spontaneous. Cyclic voltammetry results suggested that when the drug concentration is increased, the anodic electrode potential increased. Molecular docking results showed that hydrophobic forces, electrostatic interactions, and hydrogen bonds played vital roles in the interaction drugs with biomolecules. The molecular docking calculation clarifies the binding mode and the binding sites are in good accordance with the experiment results.

Deciphering the complexation process of a fluoroquinolone antibiotic, levofloxacin, with bovine serum albumin in the presence of additives

The current work aims to explore the thermodynamic and conformational aspects for the binding of fluoroquinolone antibacterial drug, levofloxacin (LFC), with bovine serum albumin (BSA) using calorimetric, spectroscopic (UV-visible, fluorescence, circular dichroism, and ¹H NMR), dynamic light scattering (DLS) and computational methods (molecular docking). The binding of LFC with BSA at two sequential sites with higher affinity (~10³M^-1) at the first site has been explored by calorimetry whereas the binding at a single site with affinity of the order of ~10⁴M^-1 has been observed from fluorescence spectroscopy. The calorimetric study in the presence of additives along with docking analysis reveals the significant role of electrostatic, hydrogen bonding, and hydrophobic interactions in the association process. The slight conformational changes in protein as well as the changes in the water network structure around the binding cavity of protein have been observed from spectroscopic and DLS measurements. The LFC induced quenching of BSA fluorescence was observed to be initiated mainly through the static quenching process and this suggests the formation of ground state LFC-BSA association complex. The stronger interactions of LFC in the cavity of Sudlow site I (subdomain IIA) of protein have been explored from site marker calorimetric and molecular docking study.

Exploration of ligand-induced protein conformational alteration, aggregate formation, and its inhibition: A biophysical insight

The association of protein aggregates with plentiful human diseases has fascinated studies regarding the biophysical characterization of protein misfolding and ultimately their aggregate formation mechanism. Protein-ligand interaction, their mechanism, conformational changes by ligands, and protein aggregate formation have been studied upon exploiting experimental techniques and computational methodologies. Such studies for the exploration of ligand-induced conformational changes in protein, misfolding and aggregation, has confirmed drastic progresses in the study of aggregate formation pathways. This review comprises of an inclusive description of contemporary experimental techniques as well as theoretical improvements in the interpretation of the conformational properties of protein. We have also discussed various factors responsible for the microenvironment change around protein that sequentially causes amyloidoses. Biophysical techniques and cell-based assays to gain comprehensive understandings of protein-ligand interaction, protein folding, and aggregation pathways have also been described. The promising therapeutic methods used to inhibit the protein fibrillogenesis have also been discussed.