Subdomain IIA Of Human Serum Albumin Research Articles

Assessment of the binding mechanism of ergothioneine to human serum albumin: Multi-spectroscopy, molecular docking and molecular dynamic simulation

Ergothioneine (EGT) has attracted great attention due to its extremely potent antioxidant properties, universally acknowledged as ‘longevity vitamin’. In order to comprehensive understanding of its pharmacodynamics and pharmacokinetics, the binding mechanism of EGT with human serum albumin (HSA) was clarified by cutting-edged multi-spectroscopic approaches and in silico molecular docking coupled with molecular dynamic simulation. Our fluorescence quenching results revealed that the binding of EGT to HSA was in a static quenching mode validated by the descending Stern–Volmer constant (Ksv) values (2.82, 2.36, 1.48 × 104 L mol−1) and biomolecular quenching rate constant (Kq) values (2.82, 2.36, 1.48 × 1012 L mol−1) at 298 K, 305 K, and 310 K, respectively. van’t Hoff criterion revealed the combination of EGT with HSA was a spontaneous exothermic process (ΔG = −24.16 kJ mol−1) via hydrogen bonding and van der Waals force interactions (ΔH = −60.25 kJ mol−1, ΔS = −129.44 J mol−1 K−1) at 310 K. The analysis of UV–vis absorption spectrum, synchronous fluorescence spectrum, three-dimensional fluorescence spectrum and circular dichroism indicated the addition of EGT affected the microenvironment of Trp214 and rearranged the structure of HSA. The binding replacement assay interpreted their binding site was near the subdomain IIA of HSA (Sudlow’s site I), which was intuitively exhibited by molecular docking. In addition of obvious van der Wall forces, attractive charge and Pi-alkyl interactions, the chiral betaine group (N+(CH3+)3) in the side chain of EGT was inclined to form hydrogen bonds with Lys199, Ser287 and Arg257 in the hydrophobic cavity of albumin. Moreover, the dynamic simulation reinforced the equilibrium and stability of formed docking complex by four indicators (RMSD, RMSF, Rg, SASA) within 100 ns.

Spectroscopic and in silico characterization of the interaction between synthetic 2-substituted-naphtho-1,4-quinones and human serum albumin

The intermolecular interaction between 2-(N-phenyl-N-methyl)aminonaphtho-1,4-quinone (1) and 2-(4-N-methylaminophenyl)naphtho-1,4-quinone (2) and human serum albumin (HSA) was investigated using spectroscopic techniques combined with in silico calculations via molecular docking. Steady-state titration of HSA fluorescence by 1 and 2 (λexc 295 nm) in PBS at 305, 310, and 315 K, as well as studies employing time-resolved fluorescence emission, demonstrated that the HSA:1 and HSA:2 interaction occurs through a static quenching mechanism. The Stern-Volmer constant (Ksv) values, (1.56 ± 0.08) and (3.05 ± 0.10) × 104 L/mol at 310 K for HSA:1 and HSA:2, respectively, indicate a moderate binding affinity. Van't Hoff plots showed that HSA:1 and HSA:2 interactions are spontaneous (negative ΔGo) with a hydrophobic character (ΔSo value of 0.00707 ± 0.00106 and 0.0392 ± 0.0062 kJ/mol K for HSA:1 and HSA:2, respectively) and specific electrostatic interactions (ΔHo value of –22.7 ± 3.3 and −14.4 ± 1.9 kJ/mol for HSA:1 and HSA:2, respectively). Synchronous fluorescence results showed significant perturbation in the microenvironment of the tryptophan residue (Trp-214). Circular dichroism indicated that after interaction with naphthoquinones 1 and 2, the HSA structure remains predominantly in the α-helix form. Finally, molecular docking revealed the formation of hydrophobic, electrostatic, and hydrogen bond interactions with the surrounding amino acid residues in subdomain IIA of HSA, which contains the Trp-214 residue, validated with the experimental drug-displacement assays. Overall, spectroscopic and in silico characterization of HSA:1 and HSA:2 might reflect in a low half-life in the human bloodstream, indicating the necessity of methods to improve the bioavailability, e.g., studies on the type of administration (oral versus intravenous).

Human Serum Albumin-Platinum(II) Agent Nanoparticles Inhibit Tumor Growth Through Multimodal Action Against the Tumor Microenvironment.

To overcome the limitations of traditional platinum (Pt)-based drugs and further improve the targeting ability and therapeutic efficacy in vivo, we proposed to design a human serum albumin (HSA)-Pt agent complex nanoparticle (NP) for cancer treatment by multimodal action against the tumor microenvironment. We not only synthesized a series of Pt(II) di-2-pyridone thiosemicarbazone compounds and obtained a Pt(II) agent [Pt(Dp44mT)Cl] with significant anticancer activity but also successfully constructed a novel HSA-Pt(Dp44mT) complex nanoparticle delivery system. The structure of the HSA-Pt(Dp44mT) complex revealed that Pt(Dp44mT)Cl binds to the IIA subdomain of HSA and coordinates with His-242. The HSA-His242-Pt-Dp44mT NPs had an obvious effect on the inhibition of tumor growth, which was superior to that of Dp44mT and Pt(Dp44mT)Cl, and they had almost no toxicity. In addition, the HSA-His242-Pt-Dp44mT NPs were found to kill cancer cells by inducing apoptosis, autophagy, and inhibiting angiogenesis.

Deciphering conformational changes in human serum albumin induced by bile salts using spectroscopic and molecular modeling approaches

Bile salts are physiologically-important natural amphiphilic biosurfactants synthesized in the liver and play a vital role in the solubilization and digestion of dietary lipids, cholesterol, and other fat-soluble compounds in the body. Bile salts also exhibit pharmacological and biological uses as carriers for transporting scarce water-soluble drugs and other chemicals owing to their unique emulsifying, solubilizing capacities and micelle forming ability. In this context, we present an endeavor towards the possibilities underlying the interaction and binding between the most abundant plasma protein namely, human serum albumin (HSA) and bile salts to demonstrate an intriguing interplay of hydrophobic, electrostatic and hydrogen bonding effects using steady state absorption, fluorescence emission, anisotropy, time-resolved emission, and molecular modelling approaches. The outcome illuminates how amphiphilic interfaces of bile salts under various physico-chemical conditions trigger the conformational changes and binding affinities of native and molten-globule forms of HSA. To elucidate non-covalent interactions during HSA-bile salt supramolecular host–guest complex formation, changes in intrinsic (tryptophan) and extrinsic (ANS) fluorescence have been investigated. The results reveal upon binding of bile salts in subdomain IIA of HSA, the protein undergoes conformational changes mediated primarily by hydrophobic interactions. Furthermore, time-resolved fluorescence measurements provide important structural and dynamical insights into the protein-bile salt supramolecular complexes. Additionally, molecular docking studies on these complexes clearly reveal spontaneous binding of bile salts into subdomain IIA of HSA while suggesting that the binding affinity decreases with the decreasing order of hydrophobicity of the bile salts (NaDC > NaC > NaTC) (ΔGdock = −29.64 kJ mol−1, −26.15 kJ mol−1, −14.35 kJ mol−1), respectively. This study exclusively highlights the molecular mechanism of conformational perturbation in the native (pH 7) and molten-globule (pH 3) forms of HSA, induced by bile salts. We believe that the results reported herein will be helpful in the design and formulation of protein-bile salt-based pharmacological carriers suitable for drug delivery.

Theoretical and experimental investigation of novel quinazoline derivatives: synthesis, photophysical, reactive properties, molecular docking and selective HSA biointeraction

Two new quinazoline derivatives (2a and 2b) were successfully synthesized in this work using the condensation technique in excellent yields. Using spectroscopic techniques and elemental analyses, the compounds were completely characterized. Density functional theory (DFT) computations have been used to examine the title compound’s reactive characteristics. Chemical reactivity was predicted using local reactive descriptors and molecule electrostatic potential. Additionally, Time dependent DFT (TD-DFT) simulations were used to examine the impact of solvents on the photophysical characteristics. The affinity of compounds 2a and 2b for human serum albumin (HSA) was further explored using several electronic spectroscopies. Through static mechanisms, both compounds reduce the intrinsic fluorescence of HSA. It is determined that the HSA-2b complex’s binding constant is significantly greater than the HSA-2a complex. The fluorescence spectrum measurements proved that the HSA underwent structural changes after interaction with these compounds. It was demonstrated by site marker competitive displacement studies that compounds 2a and 2b preferred to bind to site I in HSA subdomain IIA. Additionally, synchronised fluorescence spectra were utilized to analyze how HSA’s conformation changed after interacting with various substances. The molecular docking investigations of these compounds with the three critical HSA binding sites, comprising subdomains IIA, IIIA, and IB, further confirmed the experimental findings. The significant contact between the investigated compounds and HSA was supported by the docking simulations. Communicated by Ramaswamy H. Sarma

Developing a Multitargeted Anticancer Palladium(II) Agent Based on the His-242 Residue in the IIA Subdomain of Human Serum Albumin.

To obtain next-generation metal drugs that can overcome the deficiencies of platinum (Pt) drugs and treat cancer more effectively, we proposed to develop a multitargeted palladium (Pd) agent to the tumor microenvironment (TME) based on the specific residue(s) of human serum albumin (HSA). To this end, we optimized a series of Pd(II) 2-benzoylpyridine thiosemicarbazone compounds to obtain a Pd agent (5b) with significant cytotoxicity. The HSA-5b complex structure revealed that 5b bound to the hydrophobic cavity in the HSA IIA subdomain and then His-242 replaced a leaving group (Cl) of 5b, coordinating with the Pd center. The in vivo results showed that the 5b/HSA-5b complex had significant capacity of inhibiting tumor growth, and HSA optimized the therapeutic behavior of 5b. In addition, we confirmed that the 5b/HSA-5b complex inhibited tumor growth through multiple actions on different components of TME: killing cancer cells, inhibiting tumor angiogenesis, and activating T cells.

A comprehensive biophysical and theoretical study on the binding of dexlansoprazole with human serum albumin

Pharmacokinetics, pharmacodynamics, and therapeutic activity of drugs are defined by the affinities between the drug and biological macromolecules through molecular recognition. The present work is on the investigation of the interaction of new generation competent proton pump inhibitor dexlansoprazole (DLP) with human serum albumin (HSA). Fluorescence and UV–visible spectroscopy studies were adopted for quantification of the interaction in terms of the quenching constant (KSV), bimolecular quenching constant (Kq), equilibrium-binding constant (Kb), the number of binding sites (n), and the thermodynamic parameters. A hypochromic effect on the addition of HSA to DLP from the absorption studies shows their interaction. The quenching and binding constants from fluorescence studies were 104 and 105 M−1 order, respectively. A higher quenching constant with increasing temperature reflects a collisional-type quenching mechanism. A higher binding constant at a higher temperature shows an increase in the rate of binding, and the negative value of the free energy change shows the spontaneity of the binding. The sign and magnitude of the change in entropy (ΔS0 = 737.12 ± 2 J mol−1 K−1) and enthalpy (ΔH0 = 193.58 ± 1.7 kJ mol−1) shows that binding is an entropy-driven process with hydrophobic force as the major driving force. Site marker competitive displacement studies using 1-Anilino-8-naphthalene sulfonate (ANS), warfarin, and ibuprofen confirmed the biding of DLP in subdomain IIA of HSA. Binding-induced structural changes were evident from the changes in the circular dichroism (CD) signatures. Molecular docking of DLP in HSA showed the position of DLP in the warfarin binding site of HSA and corroborated the experimental findings.

Study on the interaction of two quinazoline derivatives as novel PI3K/mTOR dual inhibitors and anticancer agents to human serum albumin utilizing spectroscopy and docking.

Interactions of human serum albumin (HSA) with two structurally similar quinazoline derivatives, S1 and S2 , which are potential anticancer drugs acting on PI3K/mTOR targets, were investigated in vitro utilizing multiple spectroscopy as well as molecular docking. The fluorescence quenching study demonstrated that HSA fluorescence could be statically quenched by S1 and S2 through the formation of an HSA-drug complex. Furthermore, the details of the binding site number, binding constant, as well as the thermodynamic parameters, were estimated at 298, 303, and 310 K. The results revealed that hydrogen bond interactions, as well as van der Waals forces, were the predominant factors responsible for binding HSA to S1 or S2 . Synchronous fluorescence and ultraviolet (UV) absorption spectra suggested that S1 and S2 had little effect on the polarity of the microenvironment and conformation of HSA. Energy transfer from HSA to S1 or S2 most probably occurred. The docking study revealed that S1 and S2 were able to bind to the hydrophobic cavity that was located in the HSA subdomain IIA and formed varying numbers of hydrogen bonds with amino acid residues nearby. Due to the subtle difference in the chemical structure, the binding of S1 and S2 to HSA was slightly different.

Binding elucidation of azo dyes with human serum albumin via spectroscopic approaches and molecular docking techniques

The large number of synthesized azo dyes is widely applied in the food, pharmaceutical, cosmetic, textile, and leather industries. In this study, the binding mechanism of two synthesized dyes with human serum albumin (HSA); as the most abundant protein in plasma; was elucidated by fluorescence spectroscopy, Fourier-transform infrared spectroscopy and molecular modeling methods. The fluorescence quenching measurements showed that each dye can quench the intrinsic fluorescence of HSA via a dynamic quenching mechanism with an increase in concentration. From the thermodynamic data observations, revealed that the binding process is a spontaneous molecular force for each dye with HSA due to hydrophobic interactions and hydrogen bonding. FT-IR spectra showed that the secondary structure of the protein changes due to interaction of each dye with HSA. Furthermore, docking simulation demonstrated that the probable binding location of both dyes is subdomain IIA of HSA (Sudlow site I) and that complex formed is stabilized by hydrophobic interactions and hydrogen bonding. Communicated by Ramaswamy H. Sarma

Nanoplastics alter the conformation and activity of human serum albumin

Nanoplastics finds its presence in most of the consumer products. Their chance of coming in contact with human cells and components is rampant. This study focuses on the interaction of polystyrene nanoplastics (PSNPs) with human serum albumin (HSA), ultimately causing structural and functional properties of the protein. Fluorescence and UV–Visible spectroscopic studies reported that PSNPs form a spontaneous ground-state complex with HSA, by hydrogen bonding, van der waal's, and hydrophobic force of attraction. This causes changes in the environment around major aromatic amino acids, especially tryptophan-214, which has a strong affinity with PSNPs. Further docking analysis confirmed hydrophobic interactions between PSNPs and aromatic amino acids in subdomain IIA of HSA. A shift in amide bands in HSA, as determined by FTIR analysis confirmed the disturbances in its secondary structure followed by reordering which will lead to the unfolding of HSA. Besides, PSNPs reduce the esterase activity of HSA by competitive inhibition. This molecular-level information such as binding energy, binding site, binding forces, reversible or irreversible binding, and structural changes of protein will shed light on the extent of toxicity in humans. This study will emphasize the urgent need for regulation of the use of nanoplastics (NPs) in consumer products, as well as the need for more research to determine the fate of NPs in the biological system.

Study on the interaction between 2,6-dihydroxybenzoic acid nicotine salt and human serum albumin by multi-spectroscopy and molecular dynamics simulation

As a new form of nicotine introduction for novel tobacco products, the interaction of nicotine salt with biological macromolecules may differ from that of free nicotine and thus affect its transport and distribution in vivo. Hence, the mechanism underlying the interaction between 2,6-dihydroxybenzoic acid nicotine salt (DBN) and human serum albumin (HSA) was investigated by multi-spectroscopy, molecular docking, and dynamic simulation. Experiments on steady-state fluorescence and fluorescence lifetime revealed that the quenching mechanism of DBN and HSA was dynamic quenching, and binding constant was in the order of 10^4 L mol−1. Thermodynamic parameters exhibited that the binding was a spontaneous process with hydrophobic forces as the main driving force. Fluorescence competition experiments revealed that DBN bound to site I of HSA IIA subdomain. According to the results of synchronous fluorescence, 3D fluorescence, FT-IR spectroscopy, circular dichroism (CD) spectroscopy, and molecular dynamics (MD) simulation, DBN did not affect the basic skeleton structure of HSA but changed the microenvironment around the amino acid residues. Computer simulations positively corroborated the experimental results. Moreover, DBN decreased the surface hydrophobicity and weakened the esterase-like activity of HSA, leading to the impaired function of the latter. This work provides important information for studying the interaction between DBN as a nicotine substitute and biological macromolecules and contributes to the further development and application of DBN.

Biomolecular interaction mechanism of an anticancer drug, pazopanib with human serum albumin: a multi-spectroscopic and computational approach

Pazopanib (PZP) is a multi-targeting tyrosine kinase inhibitor and is currently approved by FDA for the treatment of soft tissue sarcoma and renal cancer. Molecular interaction mechanism of PZP with human serum albumin (HSA) was explored under simulated physiological conditions (pH = 7.4), using fluorescence and UV absorption spectroscopy along with computational methods. Based on the inverse correlation between the Stern-Volmer constant (Ksv ) and temperature, it was concluded that PZP quenched the protein fluorescence through static quenching mechanism. This was also confirmed from the UV-vis absorption spectral results. Moderate binding affinity between PZP and HSA was evident from the Ka values (5.51 − 1.05 × 105 M−1) while PZP-HSA complex formation was driven by hydrophobic and van der Waals interactions as well as hydrogen bonds, as revealed by positive entropy change (ΔS = +98.37 J mol−1 K−1) and negative enthalpy change (ΔH = −60.31 kJ mol−1). Three-dimensional fluorescence spectral results disclosed microenvironmental perturbations around Trp and Tyr residues of the protein upon PZP binding. Interestingly, the addition of PZP to HSA significantly protected the protein against thermal stress. Competitive drug displacement results obtained with warfarin, phenylbutazone and diazepam elucidated Sudlow's Site I, positioned in subdomain IIA of HSA, as the preferred binding site of PZP which was well supported by molecular docking analysis, while molecular dynamics simulation results suggested the stability of the PZP-HSA complex. Communicated by Vsevolod Makeev

Molecular interactions of acebutolol hydrochloride to human serum albumin: A combined calorimetric, spectroscopic and molecular modelling approach

Acebutolol hydrochloride (AH), a beta blocker is generally used in the cure of cardiovascular disorders. We have examined the interaction between AH and human serum albumin (HSA) employing UV–vis, fluorescence quenching, circular dichroism (CD), isothermal titration calorimetry and molecular docking methods. Tryptophan fluorescence intensity of HSA was strongly quenched by AH and the binding constants (K b ) were determined by fluorescence quenching indicating high affinity of AH for HSA. The negative ΔG° value for binding indicated that HSA-AH interaction was a spontaneous process. Existence of hydrophobic interactions, and hydrogen bonds were indicated from the calorimetric analysis, thus facilitating the binding of AH with HSA. Secondary structure changes were confirmed from far-UV CD studies. Further, molecular docking studies revealed AH binds with HSA, in the binding site located in Sudlow Site I of subdomain IIA of HSA. This work provides a useful experimental strategy for investigating the interactions of beta blocker AH with HSA, thus helping the activity and drug binding mechanism.

Study of conformational and functional changes caused by binding of environmental pollutant tonalide to human serum albumin

Tonalide (AHTN) is a new category of pollutants with a wide range of potential environmental and organismal hazards due to its persistence and lipophilicity, and the safety evaluation of this pollutant under physiological condition is a pressing issue. This study investigated the mechanism of interaction between AHTN and human serum albumin (HSA) that is an important transporter in plasma using multiple spectroscopic, molecular docking, and dynamics simulation methods. The steady-state fluorescence and fluorescence lifetime experiments showed that AHTN quenches the inherent fluorescence of HSA through a static quenching mechanism. Thermodynamic parameters exhibited that the binding constant of AHTN and HSA is of the order of 10^4 L/mol, and the binding is a spontaneous process of moderate strength with hydrophobic forces as the main driving force. Site competition revealed that AHTN binds to site I of HSA IIA subdomain, which was evidenced by the molecular docking results. AHTN altered the HSA amino acid microenvironment and conformation can be derived from three-dimensional fluorescence, circular dichroism spectroscopy, and molecular dynamics simulation. The computer simulations corroborate the experimental results positively. Moreover, AHTN acted as a competitive inhibitor to weaken the esterase-like activity of HSA, leading to impaired function of HSA. Results suggest that interactions between AHTN and HSA may affect the normal structure and activities of the protein, this insight will be helpful to provide some basic information to further explore the potential hazards of AHTN in humans.

Unveiling the interaction mechanism of alogliptin benzoate with human serum albumin: Insights from spectroscopy, microcalorimetry, and molecular docking and molecular dynamics analyses.

The interaction between a DPP-4 inhibitor, alogliptin benzoate (AB), and human serum albumin (HSA) was systematically investigated via spectroscopy, microcalorimetry and molecular simulations. Steady-state fluorescence and time-resolved fluorescence spectrometry illustrated that the fluorescence quenching type of AB to HSA was static and caused by the formation of ground state AB-HSA complex. Isothermal titration calorimetry (ITC) combined with fluorescence spectra revealed that the affinity of AB to the subdomain IIA of HSA was moderate with a binding constant in the order of 104. Molecular docking analysis and thermodynamic parameters demonstrated that this combination was maintained by hydrogen bonding along with van der Waals force and hydrophobic force. Circular dichroism and three-dimensional (3D) fluorescence showed that AB increased the hydrophobicity of Trp residue and the α-helix content of HSA by 1.99%. Microdifferential scanning calorimetry revealed that the addition of AB enhanced the thermal stability of HSA. The action forces, binding stability, binding sites, and protein structure of the AB-HSA system were evaluated via molecular dynamics analysis in the simulated environment. On the basis of molecular docking, MD simulation constructed a more reliable 3D model of the AB-HSA complex in terms of spatial structure.

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.

Interactions of drugs with DNA and proteins may modify their biological activities and conformations, which effect transport and biological metabolism of drugs. 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. 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. In conclusion, REG can be delivered by HSA in a circulatory system and affect DNA as potential target.

Elucidation of molecular interaction of bioactive flavonoid luteolin with human serum albumin and its glycated analogue using multi-spectroscopic and computational studies

Human serum albumin (HSA), an abundant protein in human plasma, which is associated with the transportation of numerous drugs, fatty acids to their targets and regulates the blood pH levels, is exposed to non-enzymatic glycation by reducing sugars. The existence of elevated levels of glucose during diabetes mellitus mediates the glycation of HSA which leads to structural and functional modification of the protein. The aim of our present study is to determine the effect of non-enzymatic glycation on the binding of a bioactive flavonoid luteolin to HSA using multi-spectroscopic and computational studies. The intrinsic fluorescence exhibited by the proteins (HSA and gHSA) were quenched by luteolin through static quenching mechanism. The binding constant for the interaction of HSA with luteolin was found higher as compared to that of gHSA-Luteolin at the experimental temperatures (290, 300 and 310 K). The ∆G values for the complexes formed between HSA/gHSA and luteolin were observed to be negative, indicating the spontaneity of the binding processes. Both enthalpy and entropy factors contribute to the binding of luteolin to HSA, whereas, enthalpy factors played a major role in the binding of luteolin to gHSA. A reduction in the α-helical content of HSA-Luteolin complex was observed, but no significant change was found for gHSA-Luteolin complex. Site probe displacement and related binding studies indicated that luteolin binds to both Subdomain IIA and IIIA of HSA and gHSA but with different affinities. Further molecular docking and MD simulation studies confirmed that luteolin preferably binds to the Subdomain IIA of HSA and IIIA of gHSA. These information, in turn, would give a better understanding of the functional changes occurred due to structural modification of HSA induced by glycation and may have some useful impact on the field of pharmaceutical sciences.

Ionophoric polyphenols are permeable to the blood–brain barrier, interact with human serum albumin and Calf Thymus DNA, and inhibit AChE enzymatic activity

Alzheimer’s disease (AD) is the most common form of dementia that affects more than 40 million people around the world. The incidence is expected to rapidly increase due to the lack of any effective treatment. In previous work we synthesized a family of five ionophoric polyphenols (compounds 1–5) that targeted important aspects related to AD, such as the toxic aggregation of amyloid-β peptides, the production of reactive oxygen species, or the excessive presence of Cu2+ ions. Here, in order to gain insights into their potential therapeutic value, we have tested the ability of compounds 1–5 to cross the blood–brain barrier (BBB), to interact with human serum albumin (HSA) and Calf Thymus (ct) DNA, and to inhibit acetylcholinesterase (AChE). We performed BBB permeability and efflux mechanisms studies by means of the in vitro parallel artificial membrane permeability assay (PAMPA-BBB) and several in silico methods, while fluorescence, UV–visible, and circular dichroism spectroscopies were used to determine their ability to interact with HSA and ctDNA. Our results show that all five ionophoric polyphenols can effectively cross the BBB, and can form adducts with both HSA and ctDNA through one binding site and with association constants ranging from 104 to 106 M−1, while still maintaining levels of unbound drug to protein within therapeutic range. Docking and molecular dynamics simulations show that the ionophoric polyphenols preferably bind the hydrophobic cavities of the subdomain IIA of HSA, as many other pharmaceuticals do, with predicted affinities that correlate well with experimental results obtained by spectroscopic techniques. In addition, structurally related compounds 1, 2, and 4 were found to be moderate in vitro AChE inhibitors by interacting with several residues of the active site of the enzyme, as revealed by docking and molecular dynamics simulations. Overall, our results suggest that HSA could be an efficient transport mechanism of the compounds in the bloodstream until reaching the brain, where they could effectively cross the BBB and exert their anti-AD activity, including AChE inhibition. DNA interactions similar to natural resveratrol could in part explain the previously reported nontoxic behavior of the compounds.

Deciphering the interaction of plumbagin with human serum albumin: A combined biophysical and molecular docking study

It is important to understand the nature and mechanism of interaction of drugs with serum albumins as such interactions govern their pharmacokinetics and pharmacodynamics. Plumbagin is a natural phytocompound, mainly present in the bark of Plumbaginaceae family plants and it has numerous therapeutic potentials. In this study, the interaction of plumbagin with human serum albumin (HSA) was deciphered using an array of biophysical and computational tools. The UV–vis spectroscopy established the formation of plumbagin-HSA complex with binding constant as 2.32 × 104 M−1. Fluorescence spectroscopy revealed that there was static mode of quenching of HSA’s fluorescence by plumbagin. The binding constant obtained by fluorescence spectroscopy was of the similar order as in case of UV–vis spectroscopy. The negative value of ΔH° (−3.67) indicated an endothermic nature of the reaction and negative value of ΔG° (−6.40 to −6.58) confirmed that complexation of plumbagin to HSA was spontaneous. There was nearly one binding site in HSA for plumbagin. Titration of plumbagin to HSA in presence of site-specific markers showed that plumbagin interacted at sub-domain IIA of HSA, commonly known as Sudlow’s site I. Moreover, the binding resulted in changes in microenvironment of tryptophan while of tyrosine residues remained approximately unchanged. This interaction also resulted in decrease of α-helical content of the studied serum protein. FRET calculations revealed that distance between plumbagin and HSA’s fluorophore (Trp214) was 2.27 nm. Finally, molecular docking studies substantiated the in vitro finding. Plumbagin formed hydrogen bond with Lys199 and Arg257 of HSA. Additionally, Arg222, His242, and Ala261 interacted via van der Waals forces and Leu238, Leu260, Ile264, Ile290, and Ala291 of HSA interacted with plumbagin through hydrophobic forces.

The Interaction of Temozolomide with Blood Components Suggests the Potential Use of Human Serum Albumin as a Biomimetic Carrier for the Drug.

The interaction of temozolomide (TMZ) (the main chemotherapeutic agent for brain tumors) with blood components has not been studied at the molecular level to date, even though such information is essential in the design of dosage forms for optimal therapy. This work explores the binding of TMZ to human serum albumin (HSA) and alpha-1-acid glycoprotein (AGP), as well as to blood cell-mimicking membrane systems. Absorption and fluorescence experiments with model membranes indicate that TMZ does not penetrate into the lipid bilayer, but binds to the membrane surface with very low affinity. Fluorescence experiments performed with the plasma proteins suggest that in human plasma, most of the bound TMZ is attached to HSA rather than to AGP. This interaction is moderate and likely mediated by hydrogen-bonding and hydrophobic forces, which increase the hydrolytic stability of the drug. These experiments are supported by docking and molecular dynamics simulations, which reveal that TMZ is mainly inserted in the subdomain IIA of HSA, establishing π-stacking interactions with the tryptophan residue. Considering the overexpression of albumin receptors in tumor cells, our results propose that part of the administered TMZ may reach its target bound to plasma albumin and suggest that HSA-based nanocarriers are suitable candidates for designing biomimetic delivery systems that selectively transport TMZ to tumor cells.