Affinity For Human Serum Albumin Research Articles

In Search for Low-Molecular-Weight Ligands of Human Serum Albumin That Affect Its Affinity for Monomeric Amyloid β Peptide.

An imbalance between production and excretion of amyloid β peptide (Aβ) in the brain tissues of Alzheimer's disease (AD) patients leads to Aβ accumulation and the formation of noxious Aβ oligomers/plaques. A promising approach to AD prevention is the reduction of free Aβ levels by directed enhancement of Aβ binding to its natural depot, human serum albumin (HSA). We previously demonstrated the ability of specific low-molecular-weight ligands (LMWLs) in HSA to improve its affinity for Aβ. Here we develop this approach through a bioinformatic search for the clinically approved AD-related LMWLs in HSA, followed by classification of the candidates according to the predicted location of their binding sites on the HSA surface, ranking of the candidates, and selective experimental validation of their impact on HSA affinity for Aβ. The top 100 candidate LMWLs were classified into five clusters. The specific representatives of the different clusters exhibit dramatically different behavior, with 3- to 13-fold changes in equilibrium dissociation constants for the HSA-Aβ40 interaction: prednisone favors HSA-Aβ interaction, mefenamic acid shows the opposite effect, and levothyroxine exhibits bidirectional effects. Overall, the LMWLs in HSA chosen here provide a basis for drug repurposing for AD prevention, and for the search of medications promoting AD progression.

Effects of ultraviolet radiation and reactive oxygen species on the structure and ligand-binding ability of human serum albumin for norfloxacin

To explore the influence of ultraviolet radiation (UV) and reactive oxygen species (ROS) on the structure and ligand-binding ability of human serum albumin (HSA) for norfloxacin (NFLX), HSA was treated with UV (HSAUV) and UV/H2O2 (HSAUV/H2O2), respectively. The structure difference of HSA, HSAUV and HSAUV/H2O2 were investigated by Fourier transform infrared, fluorescence (i.e., emission fluorescence, synchronous fluorescence and fluorescence lifetime) and circular dichroism spectroscopy. The intermolecular interactions of HSA, HSAUV and HSAUV/H2O2 with NFLX were studied at pH 7.4 and temperatures 291, 310, and 318 K, using fluorescence emission and synchronous fluorescence spectroscopy, and combined with molecular docking. The results suggested that UV and ROS could destroy the α-helix of HSA and induce the loose of HSA structure, and the average fluorescence lifetimes of HSA decreased from 6.12 ns to 3.76 ns (HSAUV) and 3.40 ns (HSAUV/H2O2). The conformational changes of HSA caused by UV and ROS allowed NFLX to get access to more potential binding sites and promoted the binding affinity of HSA for NFLX, while the temperature stability of the HSA-NFLX complex significantly decreased. The results are useful and valuable for evaluating the protein damage caused by UV and ROS in organisms.

A new trivalent recombinant protein for type 2 diabetes mellitus with oral delivery potential: design, expression, and experimental validation

Glucagon-like peptide-1 (GLP-1) receptor agonists are increasingly used in clinical practice for the management of type 2 diabetes mellitus. However, the extremely short half-life of GLP-1 and the need for subcutaneous administration limit its clinical application. Thus, half-life extension and alternative delivery methods are highly desired. DARPin domains with high affinity for human serum albumin (HSA) have been selected for the half-life extension of therapeutic peptides and proteins. In the present study, novel trivalent fusion proteins as long-acting GLP-1 receptor agonists with potential for oral delivery were computationally engineered by incorporating a protease-resistant modified GLP-1, an anti-human serum albumin DARPin, and an approved cell-penetrating peptide (Penetratin, Tat, and Polyarginine) linked either by rigid or flexible linkers. Theoretical studies and molecular dynamics simulation results suggested that mGLP1-DARPin-Pen has acceptable quality and stability. Moreover, the potential affinity of the selected fusion proteins for GLP-1 receptor and human serum albumin was explored by molecular docking. The recombinant construct was cloned into the pET28a vector and expressed in Escherichia coli. SDS-PAGE analysis of the purified fusion protein matched its molecular size and was confirmed by western blot analysis. The results demonstrated that the engineered fusion protein could bind HSA with high affinity. Importantly, insulin secretion assays using a mouse pancreatic β-cell line (β-TC6) revealed that the engineered trivalent fusion protein retained the ability to stimulate cellular insulin secretion. Immunofluorescence microscopy analysis indicated the CPP-dependent cellular uptake of mGLP1-DARPin-Pen. These findings demonstrated that mGLP1-DARPin-Pen is a highly potent oral drug candidate that could be particularly useful in the treatment of type 2 diabetes mellitus. Communicated by Ramaswamy H. Sarma

The Thiol Group Reactivity and the Antioxidant Property of Human Serum Albumin Are Controlled by the Joint Action of Fatty Acids and Glucose Binding.

The binding of ubiquitous serum ligands (free fatty acids) to human serum albumin (HSA) or its glycation can affect thiol group reactivity, thus influencing its antioxidant activity. The effects of stearic acid (SA) and glucose binding on HSA structural changes and thiol group content and reactivity were monitored by fluoroscopy and the Ellman method during a 14-day incubation in molar ratios to HSA that mimic pathophysiological conditions. Upon incubation with 5 mM glucose, HSA glycation was the same as HSA without it, in three different HSA:SA molar ratios (HSA:SA-1:1-2-4). The protective effect of SA on the antioxidant property of HSA under different glucose regimes (5-10-20 mM) was significantly affected by molar ratios of HSA:SA. Thiol reactivity was fully restored with 5-20 mM glucose at a 1:1 HSA:SA ratio, while the highest thiol content recovery was in pathological glucose regimes at a 1:1 HSA:SA ratio. The SA affinity for HSA increased significantly (1.5- and 1.3-fold, p < 0.01) with 5 and 10 mM glucose compared to the control. These results deepen the knowledge about the possible regulation of the antioxidant role of HSA in diabetes and other pathophysiological conditions and enable the design of future HSA-drug studies which, in turn, is important for clinicians when designing information-based treatments.

Elucidating the influence of some metal ions on the binding of antimalarial drugs to human serum albumin: spectroscopic approach

Influence of six metal ions viz. Mg2+, K+, Ca2+, Mn2+, Cu2+ and Ba2+ on the binding affinity of human serum albumin (HSA) towards three antimalarial drugs, namely, sulfadoxine (SDN), mefloquine (MEF) and lumefantrine (LUM) was investigated using fluorescence quenching titrations. The effects of metal ions (Mn2+, Cu2+ and Ba2+) were similar on the affinity of HSA towards SDN, MEF and LUM. Values of the association constant, Ka, for SDN/MEF/LUM ̶ HSA interactions in the presence of these metal ions, decreased significantly in the order: Mn2+ &gt; Cu2+ &gt; Ba2+. On the other hand, the presence of Mg2+, K+, and Ca2+ affected the binding affinity for these drugs differently. Whereas a slight increase in the Ka value of the SDN ̶ HSA complex was seen in the presence of Mg2+, Ca2+ produced a similar effect on the LUM ̶ HSA system. For MEF ̶ HSA and LUM ̶ HSA systems, effects of K+ and Mg2+ were similar, showing a decrease in the Ka value, being more effective with K+; however, this decrease was more significant than Mn2+, Cu2+ and Ba2+. Values of ‘n’ remained approximately equal to 1, hinting at a single binding site for each drug.

Ibuprofen-Immobilized Thin Films: A Novel Approach to Improve the Clearance of Protein-Bound Uremic Toxins.

Chronic kidney disease (CKD), a pressing global health issue, affects millions and leads to end-stage renal disease (ESRD). Hemodialysis (HD) is a crucial treatment for ESRD, yet its limited efficiency in removing protein-bound uremic toxins (PBUTs) results in high morbidity and mortality rates. A high affinity of pharmaceutical drugs for human serum albumin (HSA) can be leveraged to compete effectively with PBUTs for the same HSA binding sites, thereby enabling them to be capable of displacing these toxins. One such drug is ibuprofen (IBF), known for its very high affinity for HSA and sharing the same binding site as indoxyl sulfate (IS). This study explores the development of IBF-immobilized cellulose acetate-based (CA-based) thin films. The films were created by reacting CA with IBF-modified silica precursors at varying concentrations. The presence of IBF in CA/TEOS/APTES-IBF-3 and CA/TEOS-IBF-25 films, containing 3 and 25 wt % IBF, respectively, was confirmed through 1H NMR spectra. Competitive displacement binding assays indicated that while the incorporation of 3 wt % IBF showed no significant enhancement in IS displacement, the 25 wt % IBF film increased the dialyzed IS by 1.3 when normalized to non-IBF films. Furthermore, there was a 1.2-fold decrease in the total percentage of IS, and the free percentage of IS increased 1.3 to 3.0 times. Although direct systemic infusion of IBF in HD patients achieves a 2.4 times higher removal of IS, it is impractical due to the risks it poses to ESRD patients. The IBF-immobilized films offer the advantage of localized binding, thus eliminating the need for systemic exposure. This innovative approach lays a foundation for developing more efficient HD membranes, aiming to address the challenging issue of PBUT elimination and potentially enhance the quality of life and treatment outcomes for ESRD patients.

Covalent immobilization of human serum albumin on cellulose acetate membrane for scavenging amyloid beta – A stepping extracorporeal strategy for ameliorating Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by interrupted neurocognitive functions and impaired mental development presumably caused by the accumulation of amyloid beta (Aβ) in the form of plaques. Targeting Aβ has been considered a promising approach for treating AD. In the current study, human serum albumin (HSA), a natural Aβ binder, is covalently immobilized onto the surface of a cellulose acetate (CA) membrane to devise an extracorporeal Aβ sequester. The immobilization of HSA at 3.06 ± 0.22 μg/mm2 of the CA membrane was found to be active functionally, as evidenced by the esterase-like activity converting p-nitrophenyl acetate into p-nitrophenol. The green fluorescent protein–Aβ (GFP–Aβ) fusion protein, recombinantly produced as a model ligand, exhibited characteristics of native Aβ. These features include the propensity to form aggregates or fibrils and an affinity for HSA with a dissociation constant (KD) of 0.91 μM. The HSA on the CA membrane showed concentration-dependent sequestration of GFP–Aβ in the 1–10-μM range. Moreover, it had a greater binding capacity than HSA immobilized on a commercial amine-binding plate. Results suggest that the covalent immobilization of HSA on the CA surface can be used as a potential platform for sequestering Aβ to alleviate AD.

In silico and in vitro biological evaluation: distribution of Ru(III) Schiff base complexes through the pancreatic 3D model and immersed blood vessel network

In this study, we describe the in vitro antimicrobial activity of newly synthesized Ru(III)-Schiff base complexes, [Ru(L)Cl(H2O)], where L = bis(acetylacetone)ethylendiimine (acacen, 1), bis(benzoylacetone)ethylendiimine (bzacen, 2), (acetylacetone)(benzoylaceton)ethylendiimine (acacbzacen, 3), bis(acetylacetone) propylendiimine (acacpn, 4), bis(benzoylacetone)propylendiimine (bzacpn, 5) or (acetylacetone) (benzoylaceton)propylendiimine (acacbzacpn, 6), against Bacillus subtilis, Staphylococcus aureus, Proteus mirabilis, Klebsiella pneumoniae, Escherichia coli, Fusarium solani, Trichoderma viride, Penicillium italicum, Mucor mucedo, and Aspergillus niger. The best antibacterial activity was displayed against Staphylococcus aureus for 5 and 6 with MIC of 0.014 mg/mL, while the highest antifungal activity was obtained for 5 against Penicillium italicum and Aspergillus niger (MIC of 0.234 mg/mL). In continuation of our previous study, the diffusion process of Ru(III) complexes within the pancreatic 3D model and immersed blood vessel network was monitored by comparative analysis. Furthermore, a molecular docking investigation of 1-6 with human serum albumin (HSA) was conducted and the affinity of HSA to accommodate 1-6 in a subdomain IIA follows the order 5 > 6 ≥ 2 > 3 > 4 > 1. Finally, all selected complexes exhibit marginally similar binding affinities to the protein Bcl-2.

Photochemotherapeutic Properties of Cu(II) Complexes of L‐Lysine and L‐Arginine Appended to Anthracene

AbstractCu(II) complexes of positively charged amino acids L–Lysine and L‐Arginine appended to an anthracene unit and phenanthroline bases, namely [Cu(Anth‐Lys)(L)(ClO4)] (1, 2) and [Cu(Anth‐Arg)(L)(ClO4)] (3, 4) where L is 1,10‐phenanthroline (phen, 1 and 3), dipyrido[3,2‐a : 2′,3′‐c]phenazine (dppz, 2 and 4) were synthesized and fully characterized by various spectral and analytical methods. Cu(II) centered broad and weak d‐d band in the visible region along with phenanthroline based π→π* and n→π* bands in the UV region were observed in the electronic spectra of the complexes recorded in DMF‐Tris‐HCl buffer (1 : 4 v/v) (pH 7.2). The complexes 1–4 show efficient DNA binding propensity. They also demonstrated strong binding affinity for human serum albumin (HSA). The complexes showed efficient visible light‐induced cytotoxicity against A549 (human lung carcinoma), HaCaT (human epidermal keratinocytes) and MDA‐MB‐231(human breast cancer cells) cells with low dark toxicity. They generate both singlet oxygen (1O2) and hydroxyl radical (⋅OH) as reactive oxygen species (ROS) upon excitation with visible light which is believed to be responsible for killing cancer cells. Significant changes in the nuclear morphology of the HaCaT cells were observed when treated with complexes 2 and 4 in visible light compared to the non‐irradiated cells.

Unveiling the Modification of Esterase-like Activity of Serum Albumin by Nanoplastics and Their Cocontaminants.

Nanoplastics and other cocontaminants have raised concerns due to their widespread presence in the environment and their potential to enter the food chain. The harmful effects of these particles depend on various factors, such as nanoparticle size, shape, surface charge, and the nature of the cocontaminants involved. On entering the human body, human serum albumin (HSA) molecules bind and transport these particles in the blood system. The esterase-like activity of HSA, which plays a role in metabolizing drug/toxic compounds, was taken as a representative to portray the effects of these particles on HSA. Polystyrene nanoplastics (PSNPs) with different surface functionalization (plain (PS), amine (PS-NH2), and carboxy (PS-COOH)), different sizes (100 and 500 nm), and PS with cocontaminant metformin hydrochloride (Met-HCl), a widely used antidiabetic drug, were investigated in this study. Fluorescence emission spectra of HSA revealed that PS-NH2 exhibits a greater effect on protein conformation, smaller NPs have a greater influence on protein structure than larger NPs, and Met-HCl lowers PSNPs' affinity for HSA by coating the surface of the NPs, which may result in direct NP distribution to the drug's target organs and toxicity. Circular dichroism spectra also supported these results in terms of secondary structural changes. Esterase activity of HSA was inhibited by all the particles (except Met-HCl) by competitive inhibition as concluded from constant Vmax and increasing Km. Greater reduction in enzyme activity was observed for PS-NH2 among functionalizations and for 100 nm PS among sizes. Furthermore, Met-HCl lowers the inhibitory impact of PSNPs on HSA since the drug binds weakly to HSA, and so they can serve as a vector delivering PSNPs to their target organs, resulting in serious implications.

Gd3+ Complexes for MRI Detection of Zn2+ in the Presence of Human Serum Albumin: Structure-Activity Relationships.

Zn2+-responsive magnetic resonance imaging (MRI) contrast agents are typically composed of a Gd chelate conjugated to a Zn2+-binding moiety via a linker. They allow for Zn2+ detection in the presence of human serum albumin (HSA). In order to decipher the key parameters that drive their Zn2+-dependent MRI response, we designed a pyridine-based ligand, PyAmC2mDPA, and compared the properties of GdPyAmC2mDPA to those of analogue complexes with varying Gd core, Zn-binding moiety, or linker sizes. The stability constants determined by pH potentiometry showed the good selectivity of PyAmC2mDPA for Gd3+ (log KGd = 16.27) versus Zn2+ (log KZn = 13.58), proving that our modified Zn2+-binding DPA moiety prevents the formation of previously observed dimeric species. Paramagnetic relaxation enhancement measurements indicated at least three sites that are available for GdPyAmC2mDPA binding on HSA, as well as a 2-fold affinity increase when Zn2+ is present (KD = 170 μM versus KDZn = 60 μM). Fluorescence competition experiments provided evidence of the higher affinity for site II vs site I, as well as the importance of both the Zn-binding part and the Gd core in generating enhanced HSA affinity in the presence of Zn2+. Finally, an analysis of nuclear magnetic relaxation dispersion (NMRD) data suggested a significantly increased rigidity for the Zn2+-bound system, which is responsible for the Zn2+-dependent relaxivity response.

Interaction of antidiabetic formulation with nanoplastics and its binary influence on plasma protein

Nanoplastics exposure to humans becomes inevitable due to its prevalence and permanence. Adsorption of emerging pollutant metformin hydrochloride (Met-HCl) –antidiabetic drug, on polystyrene nanoplastics (PSNPs) and influence on plasma protein binding was investigated. Fluorescence studies were carried out for human serum albumin (HSA) binding. Adsorption follows pseudo-second-order kinetics, intraparticle-diffusion, and Langmuir isotherm, undergoing both physisorption and chemisorption which was validated by FE-SEM, FTIR, and HRMS measurements. Complex, experiences static quenching mechanism by hydrogen bonding and VanderWaals force of attraction to HSA. FTIR confirms the secondary structural alteration of HSA. Since Met-HCl covers the NPs' surface, NPs' affinity for HSA is reduced and they might reach the target organs of Met-HCl, disrupt antidiabetic mechanisms and cause far-reaching implications. Results from molecular docking and simulation studies backed up these results as hydrophobic and hydrogen bonds dominate the binding process of the HSA-Met-HCl-PSNPs complex. This work will aid in understanding of the toxico-kinetics/dynamics of binary contaminants.

Design of a Dual Agonist of Exendin-4 and FGF21 as a Potential Treatment for Type 2 Diabetes Mellitus and Obesity.

Fibroblast growth factor 21 (FGF21) is a metabolic, endocrine hormone regulating insulin sensitivity, energy expenditure, and lipid metabolism. It has significant potential as a therapeutic drug for treating type 2 diabetes and obesity. However, the clinical efficacy of FGF21 analogs is limited due to their instability and short half-life. Glucagon-like peptide 1 (GLP-1) receptor agonists have been recognized as effective medications for type 2 diabetes mellitus and obesity over the past two decades. This study designed a new long-acting dual-agonist, exendin-4/FGF21, utilizing albumin-binding-designed ankyrin repeat proteins (DARPins) as carriers. The purified fusion proteins were subcutaneously injected into mice for pharmacokinetic and biological activity studies. Ex-DARP-FGF21 had a high binding affinity for human serum albumin (HSA) in vitro and a prolonged half-life of 27.6 hours in vivo. Bioactivity results reveal that Ex-DARP-FGF21 significantly reduced blood glucose levels in healthy mice. Moreover, compared to Ex-DARP alone, the Ex-DARP-FGF21 dual agonist displayed enhanced blood glucose lowering bioactivity and superior body weight management in the diet-induced obesity (DIO) mouse model. These results indicate that the long-acting dual agonist of exendin-4 and FGF21 holds considerable potential as a treatment for type 2 diabetes mellitus (T2DM) and obesity in the future.

A novel water-soluble Cu(II) gluconate complex inhibits cancer cell growth by triggering apoptosis and ferroptosis related mechanisms

Metal copper complexes have attracted extensive attention as potential alternatives to platinum-based anticancer drugs due to their possible different modes of action. Herein, a new copper(II) gluconate complex, namely [Cu(DPQ)(Gluc)]·2H2O (CuGluc, DPQ = pyrazino[2,3-f][1,10]phenanthroline), with good water-solubility and high anticancer activity was synthesized by using D-gluconic acid (Gluc-2H) as an auxiliary ligand. The complex was well characterized by single-crystal X-ray diffraction analysis, elemental analysis, molar conductivity, and Fourier transform infrared spectroscopy (FTIR). The DNA-binding experiments revealed that CuGluc was bound to DNA by intercalation with end-stacking binding. CuGluc could oxidatively cleave DNA, in which 1O2 and H2O2 were involved. In addition, CuGluc was bound to the IIA subdomain of human serum albumin (HSA) through hydrophobic interaction and hydrogen bonding, showing a good affinity for HSA. The complex showed superior anticancer activity toward several cancer cells than cisplatin in vitro. Further studies indicated that CuGluc caused apoptotic cell death in human liver cancer (HepG2) cells through elevated intracellular reactive oxygen species (ROS) levels, mitochondrial dysfunction, cell cycle arrest, and caspase activation. Interestingly, CuGluc also triggered the ferroptosis mechanism through lipid peroxide accumulation and inhibition of glutathione peroxidase 4 (GPX4) activity. More importantly, CuGluc significantly inhibited tumor growth in vivo, which may benefit from the combined effects of apoptosis and ferroptosis. This work provides a promising strategy to develop highly effective antitumor copper complexes by coordinating with the glucose metabolite D-gluconic acid and exploiting the synergistic effects of apoptosis and ferroptosis mechanisms.

Cyclodextrins and Their Polymers Affect Human Serum Albumin's Interaction with Drugs Used in the Treatment of Pulmonary Infections.

Respiratory infectious diseases have challenged medical communities and researchers. Ceftriaxone, meropenem and levofloxacin are widely used for bacterial infection treatment, although they possess severe side effects. To overcome this, we propose cyclodextrin (CD) and CD-based polymers as a drug delivery system for the drugs under consideration. CD polymers demonstrate higher binding affinity for levofloxacin (Ka ≈ 105 M) compared to drug-CD complexes. CDs slightly alter the drugs' affinity for human serum albumin (HSA), whereas CD polymers increase the drugs' binding affinity up to 100 times. The most significant effect was observed for more the hydrophilic drugs ceftriaxone and meropenem. The drug's encapsulation in CD carriers leads to a decrease in the degree of change in the protein's secondary structure. The drug-CD carrier-HSA complexes demonstrate satisfying antibacterial activity in vitro, and even a high binding affinity does not decrease the drug's microbiological properties after 24 h. The proposed carriers are promising for a drug form with a prolonged drug release.

Silver Nanoparticle Surface Chemistry Determines Interactions with Human Serum Albumin and Cytotoxic Responses in Human Liver Cells.

Engineered nanomaterials (ENMs) are synthesized with a diversity of surface chemistries that mediate biochemical interactions and physiological response to the particles. In this work, silver engineered nanomaterials (AgENMs) are used to evaluate the role of surface charge in protein interactions and cellular cytotoxicity. The most abundant protein in blood, human serum albumin (HSA), was interacted with 40 nm AgENMs with a range of surface-charged coatings: positively charged branched polyethyleneimine (bPEI), negatively charged citrate (CIT), and circumneutral poly(ethylene glycol) (PEG). HSA adsorption to AgENMs was monitored by UV-vis spectroscopy and dynamic light scattering, while changes to the protein structure were evaluated with circular dichroism spectroscopy. Binding affinity for citrate-coated AgENMs and HSA is largest among the three AgENM coatings; yet, HSA lost the most secondary structure upon interaction with bPEI-coated AgENMs compared to the other two coatings. HSA increased AgENM oxidative dissolution across all particle types, with the greatest dissolution for citrate-coated AgENMs. Results indicate that surface coating is an important consideration in transformation of both the particle and protein upon interaction. To connect results to cellular outcomes, we also performed cytotoxicity experiments with HepG2 cells across all three AgENM types with and without HSA. Results show that bPEI-coated AgENMs cause the greatest loss of cell viability, both with and without inclusion of HSA with the AgENMs. Thus, surface coatings on AgENMs alter both biophysical interactions with proteins and particle cytotoxicity. Within this study set, positively charged bPEI-coated AgENMs cause the greatest disruption to HSA structure and cell viability.

Spectroscopic and computational study of the interaction of Pt(II) pyrrole-imine chelates with human serum albumin.

Three bis(pyrrolide-imine) Pt(II) chelates were synthesised and characterized with different bridging alkyl groups, specifically 2-hydroxypropyl (1), 2,2-dimethylpropyl (2), and 1,2-(S,S)-(+)-cyclohexyl (3). Novel compounds 1 and 2 were analysed by single-crystal X-ray diffraction (space group P1̄). The asymmetric unit of 1 comprises three independent molecules linked by hydrogen bonds involving the OH groups, forming a trimeric supramolecular structure. The Pt(II) chelates were reacted with human serum albumin (HSA) to investigate how the ligand bound to the Pt(II) ion influences the compound's affinity for HSA. Fluorescence quenching data obtained for native HSA and HSA bound to site-specific probes (warfarin, subdomain IIA; ibuprofen, subdomain IIIA) indicated that the three Pt(II) chelates bind close enough (within ∼30 Å) to Trp-214 to quench its intrinsic fluorescence. The bimolecular quenching constant (kq) was 103-104 -fold higher than the maximum diffusion-controlled collision constant in water (1010 M s-1) at 310 K, while the affinity constants, Ka, ranged from ∼5 × 103 to ∼5 × 105 at 310 K, and followed the order 1 > 3 > 2. The reactions of 1 and 3 with HSA were enthalpically driven, while that for 2 was entropically driven. Macromolecular docking simulations (Glide XP) and binding site specificity assays employing site-specific probes and UV-vis CD spectroscopy indicated that 1 and 2 target Sudlow's site II in subdomain IIIA, minimally perturbing the tertiary structure of the protein. Well-resolved induced CD signals from 1 and 2 bound to HSA in subdomain IIIA were adequately simulated by hybrid QM:MM TD-DFT methods. We conclude that the structure of the bis(pyrrolide-imine) Pt(II) chelate measurably affects its uptake by HSA without detectable decomposition or demetallation. Such compounds could thus serve as metallodrug candidates capable of utilising an HSA-mediated cellular uptake pathway.

Synthesis, characterization and biological activity of novel copper complexes containing a β-carboline derivative and amino acids.

Copper complexes have long been considered as a promising class of anticancer or antibacterial therapeutics. In this paper, two novel copper(II) complexes containing a β-carboline derivative and amino acids, namely [Cu(1-Im-βc)(L-Val)]ClO4·0.5H2O (Cu1) and [Cu(1-Im-βc)(L-Phe)]ClO4·0.5H2O (Cu2), where 1-Im-βc = 1-(2-imidazolyl)-β-carboline, L-Val = L-valine, and L-Phe = L-phenylalanine, were designed and synthesized. The complexes were characterized by elemental analysis, infrared spectroscopy, molar conductivity measurements, and mass spectrometry to determine their spatial structures and compositions. Both complexes bind to DNA by insertion. The complexes also show a good affinity for human serum albumin (HSA). In addition, the antitumor activity of the two complexes against lung cancer cells (A549), cervical cancer cells (HeLa), and breast cancer cells (MBA-MD-231) is significantly superior to that of the traditional antitumor drug, cisplatin. Finally, the anticancer mechanism results show that the complexes can induce apoptosis in HeLa cells, which is associated with mitochondrial damage, oxidative stress caused by reactive oxygen species (ROS) production, and activation of the caspase protein family. This study demonstrates that the introduction of aromatic heterocyclic alkaloid ligands with a broad spectrum of biological activities and water-soluble amino acid ligands into copper complexes can regulate their amphiphilic properties and biological activity, so as to obtain highly efficient copper-based therapeutics.

Spectroscopic and molecular docking studies of the interactions of sunset yellow and allura red with human serum albumin

AbstractBinding interactions of human serum albumin (HSA) with sunset yellow (SY) and allura red (AR), two food colorants, were investigated at the molecular level through fluorescence and UV absorption as well as molecular docking. The collective results of the study under the simulated physiological conditions proposed a static type of binding occurring between the two dyes and HSA. When compared with AR (293 K: Ksv = (4.21 ± 0.36) × 104 L·mol−1; Kb = (0.30 ± 0.23) × 106 L·mol−1), SY (293 K: Ksv = (6.80 ± 0.10) × 104 L·mol−1; Kb = (3.11 ± 2.01) × 106 L·mol−1) had stronger quenching ability and higher affinity for HSA due to less steric hindrance. It can be deduced that the energy transfer from HSA to the two dyes occurred with high probability based on the Förster resonance energy transfer theory (r &lt; 7 nm, 0.5 R0 &lt; r &lt; 2.0 R0). The spectral analysis suggested that the formation of the dye‐HSA complex resulted in the change in microenvironment around Tyr and Trp residues and in the secondary structure of the protein. According to molecular docking simulation, the two structural analogs almost bound to the same site of HSA, near Sudlow's Site I, but significant difference existed in the number and location of hydrogen bond (H‐bond) formed between the dyes and HSA. From the molecular docking along with the thermodynamic parameters (AR: ΔHo = −(58.79 ± 15.24) kJ·mol−1, ΔSo = −(115.1 ± 31.10) J·mol−1·K−1; SY: ΔHo = −(52.24 ± 3.15) kJ·mol−1, ΔSo = −(50.07 ± 11.14) J·mol−1·K−1), it could be inferred that H‐bond and van der Waals forces were the major binding forces involved in formation of the dye‐HSA complexes.

Systematic search for peptide and protein ligands of human serum albumin capable of affecting its interaction with amyloid β peptide

Background. Human serum albumin (HSA) is a natural buffer of amyloid-β peptide (Aβ), a key factor in the development of Alzheimer’s disease (AD). A promising approach to the AD prevention is to reduce the concentration of free Aβ by targeted stimulation of the interaction between HSA and Aβ. This approach can be implemented by increasing the affinity of HSA to Aβ through the action of HSA ligands, which was previously demonstrated for some low molecular weight ligands. The aim of the study was to search for peptide and protein ligands of human serum albumin capable of affecting its interaction with Aβ. Materials and methods. To perform a systematic search for peptides/proteins, HSA ligands that are capable of affecting Aβ-HSA interaction, we analyzed the DrugBank, BioGRID, and IntAct databases. As criteria for selecting candidates, along with physicochemical characteristics (molecular weight, solubility, blood-brain barrier passage, molar concentration), we used the requirements of extracellular proteins localization and strict association with AD, according to the DisGeNET and Open Targets Platform databases as well as Alzforum online resource. The algorithms for searching and analyzing the obtained data were implemented using the high-level programming language Python. Results. A candidate panel of 11 peptides and 34 proteins was formed. The most promising candidates include 4 peptides (liraglutide, exenatide, semaglutide, insulin detemir) and 4 proteins (S100A8, transferrin, C1 esterase inhibitor, cystatin C). Conclusions. Selected peptide and protein candidates are subject to experimental verification regarding their effect on the HSA-Aβ interaction and can become the basis for the development of first-in-class drugs for the prevention of Alzheimer’s disease.