Structural mechanism of ring-opening reaction of glucose by human serum albumin

Aggregation of Apo/Glycated Human Serum Albumins and Aptamer-Saturated Graphene Quantum Dot: A Simulation Study

Human serum albumin (HSA) is a protein carrier that transports a wide range of drugs and nutrients. The amount of glycated HSA (GHSA) is used as a diabetes biomarker. To quantify the GHSA amount, the fluorescent graphene-based aptasensor has been a successful method. In aptasensors, the key mechanism is the adsorption/desorption of albumin from the aptamer-graphene complex. Recently, the graphene quantum dot (GQD) has been reported to be an aptamer sorbent. Due to its comparable size to aptamers, it is attractive enough to explore the possibility of GQD as a part of an albumin aptasensor. Therefore, molecular dynamics (MD) simulations were performed here to reveal the binding mechanism of albumin to an aptamer-GQD complex in molecular detail. GQD saturated by albumin-selective aptamers (GQDA) is studied, and GHSA and HSA are studied in comparison to understand the effect of glycation. Fast and spontaneous albumin-GQDA binding was observed. While no specific GQDA-binding site on both albumins was found, the residues used for binding were confined to domains I and III for HSA and domains II and III for GHSA. Albumins were found to bind preferably to aptamers rather than to GQD. Lysines and arginines were the main contributors to binding. We also found the dissociation of GLC from all GHSA trajectories, which highlights the role of GQDA in interfering with the ligand binding affinity in Sudlow site I. The binding of GQDA appears to impair albumin structure and function. The insights obtained here will be useful for the future design of diabetes aptasensors.

Insights into the effect of glucose on the binding between human serum albumin and the nonsteroidal anti-inflammatory drug nimesulide

Glucose interacts with human serum albumin (HSA, the main protein responsible for the biodistribution of drugs in the bloodstream) and consequently affects the binding capacity of exogenous compounds. Thus, in this work, the interactive profile between HSA and the anti-inflammatory drug nimesulide (NMD, used mainly by patients with diabetic neuropathy to relieve acute or chronic pains) was characterized in nonglycemic, normoglycemic (80 mg/dL), and hyperglycemic (320 mg/dL) conditions by biophysics techniques. There is a spontaneous and ground-state association HSA:NMD under physiological conditions. Therefore, the Stern-Volmer constant (Ksv) can also be used to estimate the binding affinity. The Ksv values for nonglycemic, normoglycemic, and hyperglycemic conditions are around 104 M-1, indicating a moderate affinity of NMD to albumin that was slightly improved by glucose levels. Additionally, the binding is enthalpically and entropically driven mainly into subdomains IIA or IIIA. The binding perturbs weakly the α-helix content of albumin, however, glucose potentially stabilizes the tertiary structure, decreasing the structural perturbation upon NMD binding and improves the complex HSA:NMD stability. Overall, the biophysical characterization indicated that glucose levels might slightly positively impact the pharmacokinetic profile of NMD, allowing NMD to achieve its therapeutical potential without affecting drastically its effective dosages.

Study on the toxicity prediction model ofacetolactate synthase inhibitor herbicides based on human serum albumin and superoxide dismutase binding information

Toxicity significantly influences the successful development of drugs. Based on the toxicity prediction method (carrier protein binding information-toxicity relationship) previously established by the our group, this paper introduces information on the interaction between pesticides and environmental markers (SOD) into the model for the first time, so that the toxicity prediction model can not only predict the toxicity of pesticides to humans and animals, but also predict the toxicity of pesticides to the environment. Firstly, the interaction of acetolactate synthase inhibitor herbicides (ALS inhibitor herbicides) with human serum albumin (HSA) and superoxide dismutase (SOD) was investigated systematically from theory combined with experiments by spectroscopy methods and molecular docking, and important fluorescence parameters were obtained. Then, the fluorescence parameters, pesticides acute toxicity LD50 and structural splitting information were used to construct predictive modeling of ALS inhibitor herbicides based on the carrier protein binding information (R2 = 0.977) and the predictive modeling of drug acute toxicity based on carrier protein binding information and conformational relationship (R2 = 0.991), which had effectively predicted pesticides toxicity in humans and animals. To predict potential environmental toxicity, the predictive modeling of drug acute toxicity based on superoxide dismutase binding information was established (R2 = 0.883) by ALS inhibitor herbicides-SOD binding information, which has a good predictive ability in the potential toxicity of pesticides to the environment. This study lays the foundation for developing low toxicity pesticides.

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.

Applications of human and bovine serum albumins in biomedical engineering: A review

Serum albumin, commonly recognized as a predominant major plasma protein, is ubiquitously distributed among vertebrates, demonstrating versatility and widespread accessibility. Numerous studies have discussed the composition and attributes of human and bovine serum albumin; nonetheless, few systematic and comprehensive summaries on human and bovine serum albumin exist. This paper reviews the applications of human and bovine serum albumin in biomedical engineering. First, we introduce the differences in the structure of human and bovine serum albumin. Next, we describe the extraction methods for human and bovine serum albumin (fractionation process separation, magnetic adsorption, reverse micellar (RM) extraction, and genetic engineering) and the advantages and disadvantages of recently developed extraction methods. The characteristics of different processing forms of human and bovine serum albumin are also discussed, concomitantly elucidating their intrinsic properties, functions, and applications in biomedicine. Notably, their pivotal functions as carriers for drugs and tissue-engineered scaffolds, as well as their contributions to cell reproduction and bioimaging, are critically examined. Finally, to provide guidance for researchers in their future work, this review summarizes the current state of human and bovine serum albumin research and outlines potential future research topics.

Crystal structures of human serum albumin in complex with lysophosphatidylcholine

Lysophospholipids (lysoPLs) are crucial metabolites involved in various physiological and pathological cellular processes. Understanding their binding interactions, particularly with human serum albumin (HSA), is essential due to their role in regulating lysoPLs-induced cytotoxicity. However, the precise mechanism of lysoPLs binding to HSA remains elusive. In this study, we employed fluorescence quenching and optical interferometry assays to demonstrate direct binding between lysophosphatidylcholine (LPC) and HSA (KD = 25 μM). Furthermore, we determined crystal structures of HSA in complex with LPC, both in the absence and the presence of the endogenous fatty acid myristate (14:0). The crystal structure of binary HSA:LPC revealed that six LPC molecules are bound to HSA at the primary fatty acid binding sites. Interestingly, the ternary HSA:Myr:LPC structure demonstrated the continued binding of three LPC molecules to HSA at binding sites 1, 3, and 5 in the presence of myristate. These findings support HSA's role as a carrier protein for lysoPLs in blood plasma and provide valuable insights into the structural basis of their binding mechanisms.

Biophysical and docking study on the interaction of anticancer drugs encorafenib and binimetinib with human serum albumin

The utilization of BRAF and MEK inhibitors in combination therapy has demonstrated superior outcomes in the treatment of melanoma as compared to monotherapy. In the present scenario, the combination therapy of Encorafenib (ENC), a BRAF inhibitor, and Binimetinib (BINI), a MEK inhibitor, has been identified as one of the most efficacious treatment modalities for this malignancy. Investigations of protein binding, particularly with human serum albumin (HSA), are essential to understand drug performance and enhance therapeutic outcomes. The investigation of the interplay between small molecule drugs and HSA is of paramount importance, given that such interactions can exert a substantial influence on the pharmacokinetics of these therapeutic agents. The present study aims to bridge these lacunae by implementing a comprehensive approach that integrates fluorescence spectroscopy (FS), isothermal titration calorimetry (ITC), far-ultraviolet circular dichroism (far-UV CD), and molecular simulations. Through analysis of the fluorescence quenching of HSA at three distinct temperatures, it was ascertained that the association constants for the complexes formed between drugs and HSA were of the magnitude of 104 M-1. This suggests that the interactions between the compounds and albumin were moderate and comparable. Simultaneously, the investigation of fluorescence indicated a contrasting binding mechanism for the two inhibitors: ENC predominantly binds to HSA through enthalpic interaction, while BINI/HSA is stabilized by entropic contributions. The data obtained was confirmed through experimental procedures conducted using the ITC method. The results of ligand-competitive displacement experiments indicate that ENC and BINI can bind to HSA within subdomain IIA, specifically Sudlow site I. However, far-UV CD studies show that there are no notable alterations in the structure of HSA upon binding with either of the two inhibitors. Ultimately, the results were supported by computational molecular analysis, which identified the key interactions that contribute to the stabilization of the two ligand/HSA complexes.

A novel polysaccharide/zein conjugate as an alternative green plastic

The flax seed cake is a waste product from flax oil extraction. Adding value to this wasted material aligns with the concept of circularity. In this study, we explored zein protein conjugation with flax mucilage for packaging material development. Although both flax mucilage and zein have excellent film-forming properties, they lack the required mechanical properties for industrial processing and are sensitive to high humidity. We present a simple and non-toxic one-pot method for developing the novel flax mucilage/zein conjugate. Where the flax mucilage undergoes oxidation to form aldehyde groups, which then react with zein's amino groups in a glycation process. The conjugates were analyzed using different techniques. The flax mucilage conjugate had a water-holding capacity of 87-62%. Increasing the zein content improved the surface smoothness of the films. On the other hand, higher levels of zein led to a significant decrease in film solubility (p < 0.05). The flax mucilage conjugate exhibited thermoplastic and elastic properties; revealing Young's modulus of 1-3 GPa, glass transition temperature between 49 °C and 103 °C and excellent processability with various industrial techniques. Showing its potential as a sustainable alternative to traditional plastics.

Binding of Apo and Glycated Human Serum Albumins to an Albumin-Selective Aptamer-Bound Graphene Quantum Dot Complex

Diabetes mellitus is a chronic metabolic disease involving continued elevated blood glucose levels. It is a leading cause of mortality and reduced life expectancy. Glycated human serum albumin (GHSA) has been reported to be a potential diabetes biomarker. A nanomaterial-based aptasensor is one of the effective techniques to detect GHSA. Graphene quantum dots (GQDs) have been widely used in aptasensors as an aptamer fluorescence quencher due to their high biocompatibility and sensitivity. GHSA-selective fluorescent aptamers are first quenched upon binding to GQDs. The presence of albumin targets results in the release of aptamers to albumin and consequently fluorescence recovery. To date, the molecular details on how GQDs interact with GHSA-selective aptamers and albumin remain limited, especially the interactions of an aptamer-bound GQD (GQDA) with an albumin. Thus, in this work, molecular dynamics simulations were used to reveal the binding mechanism of human serum albumin (HSA) and GHSA to GQDA. The results show the rapid and spontaneous assembly of albumin and GQDA. Multiple sites of albumins can accommodate both aptamers and GQDs. This suggests that the saturation of aptamers on GQDs is required for accurate albumin detection. Guanine and thymine are keys for albumin-aptamer clustering. GHSA gets denatured more than HSA. The presence of bound GQDA on GHSA widens the entrance of drug site I, resulting in the release of open-chain glucose. The insight obtained here will serve as a base for accurate GQD-based aptasensor design and development.

Structural and Dynamic Alteration of Glycated Human Serum Albumin in Schiff Base and Amadori Adducts: A Molecular Simulation Study

Human serum albumin (HSA) is a protein carrier in blood transporting metabolites and drugs. Glycated HSA (GHSA) acts as a potential biomarker for diabetes. Thus, many attempts have been made to detect GHSA. Glycation was reported to damage the structure and ligand binding capability, where no molecular detail is available. Recently, the crystal structure of GHSA has been solved, where two glucose isomers (pyranose/GLC and open-chain/GLO) are located at Sudlow's site I. GLO was found to covalently bind to K195, while GLC is trapped by noncontact interactions. GHSA exists in two forms (Schiff base (SCH) and Amadori (AMA) adducts), but how both disrupt albumin activity microscopically remains unknown. To this end, molecular dynamics simulations were performed here to explore the nature of SCH and AMA. Both forms are found to alter the main protein dynamics, resulting in (i) the widening of Sudlow's site I entrance, (ii) the size reduction of nine fatty acid-binding pockets, (iii) the enlargement of Sudlow's site I and the shrinking of Sudlow's site II, (iv) the enhancement of C34 reactivity, and (v) the change in the W214 microenvironment. These unique characteristics found here can be useful for understanding the effect of glycation on the albumin function in more detail and designing specific and selective GHSA detection strategies.

Site Identification by Ligand Competitive Saturation-Biologics Approach for Structure-Based Protein Charge Prediction

Protein-based therapeutics typically require high concentrations of the active protein, which can lead to protein aggregation and high solution viscosity. Such solution behaviors can limit the stability, bioavailability, and manufacturability of protein-based therapeutics and are directly influenced by the charge of a protein. Protein charge is a system property affected by its environment, including the buffer composition, pH, and temperature. Thus, the charge calculated by summing the charges of each residue in a protein, as is commonly done in computational methods, may significantly differ from the effective charge of the protein as these calculations do not account for contributions from bound ions. Here, we present an extension of the structure-based approach termed site identification by ligand competitive saturation-biologics (SILCS-Biologics) to predict the effective charge of proteins. The SILCS-Biologics approach was applied on a range of protein targets in different salt environments for which membrane-confined electrophoresis-determined charges were previously reported. SILCS-Biologics maps the 3D distribution and predicted occupancy of ions, buffer molecules, and excipient molecules bound to the protein surface in a given salt environment. Using this information, the effective charge of the protein is predicted such that the concentrations of the ions and the presence of excipients or buffers are accounted for. Additionally, SILCS-Biologics also produces 3D structures of the binding sites of ions on the proteins, which enable further analyses such as the characterization of protein surface charge distribution and dipole moments in different environments. Notable is the capability of the method to account for competition between salts, excipients, and buffers on the calculated electrostatic properties in different protein formulations. Our study demonstrates the ability of the SILCS-Biologics approach to predict the effective charge of proteins and its applicability in uncovering protein-ion interactions and their contributions to protein solubility and function.

The first fluorescent sensor for the detection of closantel in meat

Closantel is widely used in the management of parasitic infestation in livestock, but is contraindicated in humans due to its high toxic to human retina. Thus, development of a fast and selective method for the detection of closantel residues in animal products is highly needed yet still challenging. In the present study, we report a supramolecular fluorescent sensor for closantel detection through a two-step screening process. The fluorescent sensor can detect closantel with a fast response (<10 s), high sensitivity, and high selectivity. The limit of detection is 0.29 ppm, which is much lower than the maximum residue level set by government. Moreover, the applicability of this sensor has been demonstrated in commercial drugs tablets, injection fluids, and real edible animal products (muscle, kidney, and liver). This work provides the first fluorescence analytical tool for accurate and selective determination of closantel, and may inspire more sensor design for food analysis.

Trehalose counteracts the dissociation of tetrameric rabbit lactate dehydrogenase induced by acidic pH conditions

The lactate dehydrogenase from rabbit skeletal muscle (rbLDH) is a tetrameric enzyme, known to undergo dissociation when exposed to acidic pH conditions. Moreover, it should be mentioned that this dissociation translates into a pronounced loss of enzyme activity. Notably, among the compounds able to stabilize proteins and enzymes, the disaccharide trehalose represents an outperformer. In particular, trehalose was shown to efficiently counteract quite a number of physical and chemical agents inducing protein denaturation. However, no information is available on the effect, if any, exerted by trehalose against the dissociation of protein oligomers. Accordingly, we thought it of interest to investigate whether this disaccharide is competent in preventing the dissociation of rbLDH induced by acidic pH conditions. Further, we compared the action of trehalose with the effects triggered by maltose and cellobiose. Surprisingly, both these disaccharides enhanced the dissociation of rbLDH, with maltose being responsible for a major effect when compared to cellobiose. On the contrary, trehalose was effective in preventing enzyme dissociation, as revealed by activity assays and by Dynamic Light Scattering (DLS) experiments. Moreover, we detected a significant decrease of both K_0.5 and V_max when the rbLDH activity was tested (at pH 7.5 and 6.5) as a function of pyruvate concentration in the presence of trehalose. Further, we found that trehalose induces a remarkable increase of V_max when the enzyme is exposed to pH 5. Overall, our observations suggest that trehalose triggers conformational rearrangements of tetrameric rbLDH mirrored by resistance to dissociation and peculiar catalytic features.

Nafamostat Mesylate in Combination with the Mouse Amino-Terminal Fragment of Urokinase-Human Serum Albumin Improves the Treatment Outcome of Triple-Negative Breast Cancer Therapy

Triple-negative breast cancer (TNBC) is highly aggressive and causes a higher proportion of metastatic cases. However, therapies directed to specific molecular targets have rarely achieved clinically meaningful improvements in the outcome of TNBC therapy. A urokinase-type plasminogen activator (uPA), one of the best-validated biomarkers of breast cancer, is an extracellular proteolytic serine protease involved in many pathological and physiological processes, including tumor cell invasion and metastasis. Nafamostat mesylate (NM) is a synthetic compound that inhibits various serine proteases and has been used as a therapeutic agent for the treatment of TNBC. Nevertheless, NM has poor specificity for serine proteases and is easy be hydrolyzed; moreover, the inhibitory mechanism of TNBC therapy is unclear. In this study, we combine NM with a macromolecular drug delivery vehicle, mouse amino-terminal fragment of urokinase-human serum albumin (mATF-HSA), to form a complex (mATF-HSA:NM) using the dilution-incubation-purification method. mATF specifically targets uPAR overexpressed on the surface of TNBC cells; moreover, HSA prevents NM from being hydrolyzed by numerous serine proteases. mATF-HSA:NM showed stronger inhibitory effects on the proliferation and metastasis of TNBC in vitro and in vivo without significant cytotoxicity on normal cells and tissues. In addition, we demonstrated that NM mediates metastasis of TNBC cells through inhibition of uPA using a stable uPA knockdown cell line (MDA-MB231 shuPA). Overall, we have developed a macromolecular complex targeted to treat high uPAR-expressing tumor types, and mATF-HSA can potentially be used to load other types of drugs with tumor-targeting specificity for mouse tumor models and is a promising tool to study tumor biology in mouse tumor models.

Bioinspired Polyethylene Glycol Coatings for Reduced Nanoparticle-Protein Interactions

Nanoparticles (NPs) and other engineered nanomaterials have great potential as nanodrugs or nanomedical devices for biomedical applications. However, the adsorption of proteins in blood circulation or similar physiological fluids can significantly alter the surface properties and therapeutic response induced by most nanomaterials. For example, interaction with proteins can change the bloodstream circulation time and availability of therapeutic NPs or hinder the accumulation in their desired target organs. Proteins can also trigger or prevent agglomeration. By combining experimental and computational approaches, we have developed NPs carrying polyethylene glycol (PEG) polymeric coatings that mimic the surface charge distribution of proteins typically found in blood, which are known to show low aggregation under normal blood conditions. Here, we show that NPs with coatings based on apoferritin or human serum albumin display better antifouling properties and weaker protein interaction compared to similar NPs carrying conventional PEG polymeric coatings.

Organism-specific differences in the binding of ketoprofen to serum albumin

Serum albumin is a circulatory transport protein that has a highly conserved sequence and structure across mammalian organisms. Its ligand-binding properties are of importance as albumin regulates the pharmacokinetics of many drugs. Due to the high degree of structural conservation between mammalian albumins, nonhuman albumins such as bovine serum albumin or animal models are often used to understand human albumin-drug interactions. Ketoprofen is a popular nonsteroidal anti-inflammatory drug that is transported by albumin. Here, it is revealed that ketoprofen exhibits different binding-site preferences when interacting with human serum albumin compared with other mammalian albumins, despite the conservation of binding sites across species. The reasons for the observed differences were explored, including identifying ketoprofen binding determinants at specific sites and the influence of fatty acids and other ligands on drug binding. The presented results reveal that the drug-binding properties of albumins cannot easily be predicted based only on a complex of albumin from another organism and the conservation of drug sites between species. This work shows that understanding organism-dependent differences is essential for assessing the suitability of particular albumins for structural or biochemical studies.

Crystallographic analysis of interaction between cisplatin and human serum albumin: Effect of fatty acid

Metallodrugs are important for anticancer treatments. They bind mainly to human serum albumin (HSA) in blood circulation, greatly modulating their pharmacokinetics and anticancer efficacy. Fatty acid (FA) is one of the most important endogenous ligands of HSA with tight binding to HSA and affecting its conformation. However, the effect of fatty acids on metallodrugs interaction with HSA is unknown. Here we identify the binding sites of a widely used metallodrug, cisplatin, in HSA in the presence or absence of a representative fatty acid, myristate, by X-ray crystallography. Our crystal structures indicate that the sidechain of residue Met548 becomes more exposed to solvent in the presence of fatty acid, and is the main Pt binding site together with Met329 in HSA:Myr:cisplatin ternary structure. An undoubted new Pt binding site is detected at His338 in the presence of fatty acid, and additional two sites are also identified at His146 and His440 + K436. In addition, we revealed the mechanism of cisplatin-induced HSA aggregation, which is due to the crosslinking between Met298 and His510 of two HSA molecules.

General Method for Pesticide Recognition Using Albumin-Based Host-Guest Ensembles

The massive use of pesticides nowadays has led to serious consequences for the environment and public health. Fluorescence analytical methods for pesticides are particularly advantageous with respect to simplicity and portability; however, currently available fluorescence methods (enzyme-based assays and indicator displacement assays) with poor universality are only able to detect few specific pesticides (e.g., organophosphorus). Making use of the multiple flexible and asymmetrical binding sites in albumin, we herein report a set of multicolor albumin-based host-guest ensembles. These ensembles exhibit a universal but distinctive fluorescent response to most of the common pesticides and allow array-based identification of pesticides with high accuracy. Furthermore, the simplicity, portability, and visualization of this method enable on-site determination of pesticides in a practical setting. This albumin host strategy largely expands the toolbox of traditional indicator displacement assays (synthetic macrocycles as hosts), and we expect it to inspire a series of sensor designs for pesticide detection.

Binding of the B-Raf Inhibitors Dabrafenib and Vemurafenib to Human Serum Albumin: A Biophysical and Molecular Simulation Study

Drug binding to human serum albumin (HSA) significantly affects in vivo drug transport and biological activity. To gain insight into the binding mechanism of the two B-Raf tyrosine kinase inhibitors dabrafenib and vemurafenib to HSA, in this work, we adopted a combined strategy based on fluorescence spectroscopy, isothermal titration calorimetry (ITC), circular dichroism (CD), and molecular simulations. Both anticancer drugs are found to bind spontaneously and with a 1:1 stoichiometry within the same binding pocket, located in Sudlow's site II (subdomain IIIA) of the protein with comparable affinity and without substantially perturbing the protein secondary structure. However, the nature of each drug-protein interactions is distinct: whereas the formation of the dabrafenib/HSA complex is more entropically driven, the formation of the alternative vemurafenib/HSA assembly is prevalently enthalpic in nature. Kinetic analysis also indicates that the association rate is similar for the two drugs, whereas the residence time of vemurafenib within the HSA binding pocket is somewhat higher than that determined for the alternative B-Raf inhibitor.

Changes in elastin structure and extensibility induced by hypercalcemia and hyperglycemia

Elastin is a key elastomeric protein responsible for the elasticity of many organs, including heart, skin, and blood vessels. Due to its intrinsic long life and low turnover rate, damage in elastin induced by pathophysiological conditions, such as hypercalcemia and hyperglycemia, accumulates during biological aging and in aging-associated diseases, such as diabetes mellitus and atherosclerosis. Prior studies have shown that calcification induced by hypercalcemia deteriorates the function of aortic tissues. Glycation of elastin is triggered by hyperglycemia and associated with elastic tissue damage and loss of mechanical functions via the accumulation of advanced glycation end products. To evaluate the effects on elastin's structural conformations and elasticity by hypercalcemia and hyperglycemia at the molecular scale, we perform classical atomistic and steered molecular dynamics simulations on tropoelastin, the soluble precursor of elastin, under different conditions. We characterize the interaction sites of glucose and calcium and associated structural conformational changes. Additionally, we find that elevated levels of calcium ions and glucose hinder the extensibility of tropoelastin by rearranging structural domains and altering hydrogen bonding patterns, respectively. Overall, our investigation helps to reveal the behavior of tropoelastin and the biomechanics of elastin biomaterials in these physiological environments. STATEMENT OF SIGNIFICANCE: Elastin is a key component of elastic fibers which endow many important tissues and organs, from arteries and veins, to skin and heart, with strength and elasticity. During aging and aging-associated diseases, such as diabetes mellitus and atherosclerosis, physicochemical stressors, including hypercalcemia and hyperglycemia, induce accumulated irreversible damage in elastin, and consequently alter mechanical function. Yet, molecular mechanisms associated with these processes are still poorly understood. Here, we present the first study on how these changes in elastin structure and extensibility are induced by hypercalcemia and hyperglycemia at the molecular scale, revealing the essential roles that calcium and glucose play in triggering structural alterations and mechanical stiffness. Our findings yield critical insights into the first steps of hypercalcemia- and hyperglycemia-mediated aging.

Biophysical, Biochemical, and Molecular Docking Investigations of Anti-Glycating, Antioxidant, and Protein Structural Stability Potential of Garlic

Garlic has been reported to inhibit protein glycation, a process that underlies several disease processes, including chronic complications of diabetes mellitus. Biophysical, biochemical, and molecular docking investigations were conducted to assess anti-glycating, antioxidant, and protein structural protection activities of garlic. Results from spectral (UV and fluorescence) and circular dichroism (CD) analysis helped ascertain protein conformation and secondary structure protection against glycation to a significant extent. Further, garlic showed heat-induced protein denaturation inhibition activity (52.17%). It also inhibited glycation, advanced glycation end products (AGEs) formation as well as lent human serum albumin (HSA) protein structural stability, as revealed by reduction in browning intensity (65.23%), decrease in protein aggregation index (67.77%), and overall reduction in cross amyloid structure formation (33.26%) compared with positive controls (100%). The significant antioxidant nature of garlic was revealed by FRAP assay (58.23%) and DPPH assay (66.18%). Using molecular docking analysis, some of the important garlic metabolites were investigated for their interactions with the HSA molecule. Molecular docking analysis showed quercetin, a phenolic compound present in garlic, appears to be the most promising inhibitor of glucose interaction with the HSA molecule. Our findings show that garlic can prevent oxidative stress and glycation-induced biomolecular damage and that it can potentially be used in the treatment of several health conditions, including diabetes and other inflammatory diseases.

A versatile insertion point on albumin to accommodate peptides and maintain their activities

Genetic fusion of human serum albumin to peptides is an important strategy to enhance the plasma half-life of the peptide. An inherent challenge of such method is the reduction of specific activity of the cargo peptides upon connecting at N- or C-termini of albumin. Here, we report a finding that residue 363-364 of albumin can be inserted with a peptide while maintaining the peptide activities. We insert a peptide inhibitor into this site, and at the N-terminus of albumin, for comparison. The chimeric protein displays potent inhibition (IC₅₀ value of 30 nM) to its target (uPAR), but not the N-terminally fused construct. We also study the chimera of HSA with a cyclic peptide inhibitor of murine urokinase-type plasminogen activator grafted at either the internal site or the N-terminus. The internally peptide-grafted protein possesses a much more potent inhibition compared to the N-terminally located fusion (IC₅₀ value of 32 nM vs 19 μM). We further demonstrate that such internal fusion does not affect albumin expression, secondary structure, and inherent drug binding activity. Thus, this work identifies a versatile insertion point inside albumin for maintaining fusion peptide activity, and opens a new avenue to expand the applications of albumin fusion technology.

A new method for predicting the acute toxicity of carbamate pesticides based on the perspective of binding information with carrier protein

Toxicity is one of the most important factors limiting the success of new drug development. In this paper, we built a fast and convenient new method (Carrier protein binding information-toxicity relationship, CPBITR) for predicting drug acute toxicity based on the perspective of binding information with carrier protein. First, we studied the binding information between carbamate pesticides and human serum albumin (HSA) through various spectroscopic methods and molecular docking. Then a total of 16 models were established to clarify the relationship between binding information with HSA and drug toxicity. The results showed that the binding information was related to toxicity. Finally we obtained the effective toxicity prediction model for carbamate pesticides. And the "Platform for Predicting Drug Toxicity Based on the Information of Binding with Carrier Protein" was established with the Back-propagation neural network model. We proposed and proved that it was feasible to predict drug toxicity from this new perspective: binding with carrier protein. According to this new perspective, toxicity prediction model of other drugs can also be established. This new method has the advantages of convenience and fast, and can be used to screen out low-toxic drugs quickly in the early stage. It is helpful for drug research and development.

The binding of apo and glucose-bound human serum albumins to a free graphene sheet in aqueous environment: Simulation studies

Human serum albumin (HSA) is a blood protein serving as a carrier for a wide range of drugs and nutrients. A level of glycated HSA (GHSA) is used as a diabetes biomarker. A graphene-based aptasensor is one of potential techniques to detect GHSA. Not only the interactions of albumin and aptamer, but the albumin-graphene (GRA) binding mechanism are also crucial for developing a diabetes aptasensor. In this work, Molecular Dynamics simulations (MD) were employed to explore the binding of GRA to both GHSA and HSA. The GRA binding from the back and front sides of an albumin are fast and spontaneous. The multiple GRA binding sites are identified. GRA causes more denaturation of helical characteristics in GHSA (∼12% reduction of helical structure). Both back and front GRA adhesions generate comparable degrees of helical unfolding. Importantly, the presence of bound GRA induces the release of glucose from drug sites implying the loss of ligand-binding affinity. This loss of drug site activity is independent on the GRA binding positions because all bound positions lead to the exit of sugars. The GRA binding deconstructs not only secondary structure, but also albumin function. Apparently, GRA is a non-biocompatible material for albumin. To construct a potential graphene-based aptasensor to detect GHSA, it is necessary to be certain that no free GRA surface is available because a bare GRA can bind and denature both HSA and GHSA which can cause misleading data.

Perturbing dimer interactions and allosteric communication modulates the immunosuppressive activity of human galectin-7

The design of allosteric modulators to control protein function is a key objective in drug discovery programs. Altering functionally essential allosteric residue networks provides unique protein family subtype specificity, minimizes unwanted off-target effects, and helps avert resistance acquisition typically plaguing drugs that target orthosteric sites. In this work, we used protein engineering and dimer interface mutations to positively and negatively modulate the immunosuppressive activity of the proapoptotic human galectin-7 (GAL-7). Using the PoPMuSiC and BeAtMuSiC algorithms, mutational sites and residue identity were computationally probed and predicted to either alter or stabilize the GAL-7 dimer interface. By designing a covalent disulfide bridge between protomers to control homodimer strength and stability, we demonstrate the importance of dimer interface perturbations on the allosteric network bridging the two opposite glycan-binding sites on GAL-7, resulting in control of induced apoptosis in Jurkat T cells. Molecular investigation of G16X GAL-7 variants using X-ray crystallography, biophysical, and computational characterization illuminates residues involved in dimer stability and allosteric communication, along with discrete long-range dynamic behaviors involving loops 1, 3, and 5. We show that perturbing the protein-protein interface between GAL-7 protomers can modulate its biological function, even when the overall structure and ligand-binding affinity remains unaltered. This study highlights new avenues for the design of galectin-specific modulators influencing both glycan-dependent and glycan-independent interactions.

Comprehensive overview of human serum albumin glycation in diabetes mellitus

The presence of excess glucose in blood is regarded as a sweet hurt for patients with diabetes. Human serum albumin (HSA) is the most abundant protein in human plasma, which undergoes severe non-enzymatic glycation with glucose in patients with diabetes; this modifies the structure and function of HSA. Furthermore, the advanced glycation end products produced by glycated HSA can cause pathological damage to the human body through various signaling pathways, eventually leading to complications of diabetes. Many potential glycation sites on HSA have different degrees of sensitivity to glucose concentration. This review provides a comprehensive assessment of the in vivo glycation sites of HSA; it also discusses the effects of glycation on the structure and function of HSA. Moreover, it addresses the relationship between HSA glycation and diabetes complications. Finally, it focuses on the value of non-enzymatic glycation of HSA in diabetes-related clinical applications.

Structural and Photodynamic Studies on Nitrosylruthenium-Complexed Serum Albumin as a Delivery System for Controlled Nitric Oxide Release

How to deliver nitric oxide (NO) to a physiological target and control its release quantitatively is a key issue for biomedical applications. Here, a water-soluble nitrosylruthenium complex, [(CH₃)₄N][RuCl₃(5cqn)(NO)] (H5cqn = 5-chloro-8-quinoline), was synthesized, and its structure was confirmed with ¹H NMR and X-ray crystal diffraction. Photoinduced NO release was investigated with time-resolved Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The binding constant of the [RuCl₃(5cqn)(NO)]^- complex with human serum albumin (HSA) was determined by fluorescence spectroscopy, and the binding mode was identified by X-ray crystallography of the HSA and Ru-NO complex adduct. The crystal structure reveals that two molecules of the Ru-NO complex are located in the subdomain IB, which is one of the major drug binding regions of HSA. The chemical structures of the Ru complexes were [RuCl₃(5cqn)(NO)]^- and [RuCl₃(Glycerin)NO]^-, in which the electron densities for all ligands to Ru are unambiguously identified. EPR spin-trapping data showed that photoirradiation triggered NO radical generation from the HSA complex adduct. Moreover, the near-infrared image of exogenous NO from the nitrosylruthenium complex in living cells was observed using a NO-selective fluorescent probe. This study provides a strategy to design an appropriate delivery system to transport NO and metallodrugs in vivo for potential applications.

A DS2-specific flavonoid-based probe with a unique dual-emissive response to human serum albumin

The hydroxyl substituent in flavonoids can cause the binding site to change from DS1 to DS2 and restore the ESIPT process of flavonoids, thereby leading to a unique dual-emissive response towards human serum albumin.

Glycated Hemoglobin and Methods for Its Point of Care Testing

Glycated hemoglobin (HbA1c) is a product of the spontaneous reaction between hemoglobin and elevated glucose levels in the blood. It is included among the so-called advanced glycation end products, of which is the most important for the clinical diagnosis of diabetes mellitus, and it can serve as an alternative to glycemia measurement. Compared to the diagnosis of diabetes mellitus by glycemia, the HbA1c level is less influenced by a short-term problem with diabetes compensation. Mass spectroscopy and chromatographic techniques are among the standard methods of HbA1c level measurement. Compared to glycemia measurement, there is lack of simple methods for diabetes mellitus diagnosis by means of the HbA1c assay using a point-of-care test. This review article is focused on the surveying of facts about HbA1c and its importance in diabetes mellitus diagnosis, and surveying standard methods and new methods suitable for the HbA1c assay under point-of-care conditions. Various bioassays and biosensors are mentioned and their specifications are discussed.

Monosaccharides interact weakly with human serum albumin. Insights for the functional perturbations on the binding capacity of albumin

Monosaccharides, e.g. fructose, glucose, and arabinose are present in most foods consumed daily, whether, in natural or industrialized forms, and their concentration in the human bloodstream can impact the formation of advanced glycation end-products (AGEs, prevalent in people with diabetes) impacting the profile of Human Serum Albumin (HSA) in biodistribution of endogenous and exogenous compounds. Multiple spectroscopic techniques (UV-vis, circular dichroism, steady-state, and time-resolved fluorescence) combined with molecular docking showed that carbohydrates interact weakly and spontaneously via a ground-state association with HSA. The binding is enthalpically and entropically driven in the subdomain IIA (site I) and perturb weakly the secondary structure of the albumin. Hydrogen bonding and van der Waals forces are the main intermolecular interactions involved in the ligand binding, as well as hydrophobic effects related to the release of hydration shell upon ligand binding. Overall, the results indicated that an increase in glucose, fructose or arabinose level in the human bloodstream may cause functional perturbation on the binding capacity of albumin. Therefore, there is the necessity of carbohydrate level control in the bloodstream to not compromise the interaction and distribution of exogenous and endogenous compounds by HSA.

Antiglycation Activity of Triazole Schiff's Bases Against Fructosemediated Glycation: In Vitro and In Silico Study

BACKGROUND

Advanced glycation end products (AGEs) are known to be involved in the pathophysiology of diabetic complications, neurodegenerative diseases, and aging. Preventing the formation of AGEs can be helpful in the management of these diseases.

OBJECTIVES

Two classes of previously synthesized traizole Schiff's bases (4H-1,2,4-triazole-4- Schiff's bases 1-14, and 4H-1,2,4-triazole-3-Schiff's bases 15-23) were evaluated for their in vitro antiglycation activity.

METHODS

In vitro fructose-mediated human serum albumin (HSA) glycation assay was employed to assess the antiglycation activity of triazole Schiff's bases. The active compounds were subjected to cytotoxicity analysis by MTT assay on mouse fibroblast (3T3) cell line. Molecular docking and simulation studies were carried out to evaluate the interactions and stability of compounds with HSA. Anti-hyperglycemic and antioxidant activities of selected non-cytotoxic compounds were evaluated by in vitro α-glucosidase inhibition, and DPPH free radical scavenging assays, respectively.

RESULTS

Compound 1 (IC50=47.30±0.38 µM) from 4H-1,2,4-triazole-4-Schiff's bases has exhibited antiglycation activity comparable to standard rutin (IC50=54.5±0.05 µM) along with a stable RMSD profile in MD simulation studies. Compound 1 also exhibited a potent α-glucosidase inhibitory activity, and moderate antioxidant property. Other derivatives showed a weak antiglycation activity with IC50 values between 248.1-637.7 µM. Compounds with potential antiglycation profile were found to be non-cytotoxic in a cellular assay.

CONCLUSION

The study identifies triazole Schiff's bases active against fructose-mediated glycation of HSA, thus indicates their potential against late diabetic complications due to production of advancedend products (AGEs).

3,3'-Dichlorobiphenyl Is Metabolized to a Complex Mixture of Oxidative Metabolites, Including Novel Methoxylated Metabolites, by HepG2 Cells

3,3'-Dichlorobiphenyl (PCB 11) is a byproduct of industrial processes and detected in environmental samples. PCB 11 and its metabolites are present in human serum, and emerging evidence demonstrates that PCB 11 is a developmental neurotoxicant. However, little is known about the metabolism of PCB 11 in humans. Here, we investigated the metabolism of PCB 11 and the associated metabolomics changes in HepG2 cells using untargeted high-resolution mass spectrometry. HepG2 cells were exposed for 24 h to PCB 11 in DMSO or DMSO alone. Cell culture media were analyzed with ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry. Thirty different metabolites were formed by HepG2 cells exposed to 10 μM PCB 11, including monohydroxylated, dihydroxylated, methoxylated-hydroxylated, and methoxylated-dihydroxylated metabolites and the corresponding sulfo and glucuronide conjugates. The methoxylated PCB metabolites were observed for the first time in a human-relevant model. 4-OH-PCB 11 (3,3'-dichlorobiphenyl-4-ol) and the corresponding catechol metabolite, 4,5-di-OH-PCB 11 (3',5-dichloro-3,4-dihydroxybiphenyl), were unambiguously identified based on liquid and gas chromatographic analyses. PCB 11 also altered several metabolic pathways, in particular vitamin B6 metabolism. These results demonstrate that complex PCB 11 metabolite profiles are formed in HepG2 cells that warrant further toxicological investigation, particularly since catechol metabolites are likely reactive and toxic.

Serum albumin: clinical significance of drug binding and development as drug delivery vehicle

Human serum albumin, the primary transport and reservoir protein in the human circulatory system, interacts with numerous endogenous and exogenous ligands of varying structural characteristics. The mode of binding of drugs to albumin is central to understanding their pharmacokinetic profiles and has a major influence on their in vivo efficacy. Altered drug binding to albumin due to drug-drug interactions or abnormal physiology may result in marked changes in the active drug concentration, thus affecting its pharmacokinetic and pharmacodynamic properties. The propensity of drug-drug interaction to be clinically significant as well as possible exploitation of such interactions for therapeutic purposes is reviewed. Being the major organs of albumin metabolism, any impairment in the liver and kidney functions frequently alter the level of serum albumin, which affects the pharmacokinetic profiles of drugs and may have serious clinical implications. The natural function of serum albumin as a drug carrier is facilitated by its interaction with various cellular receptors. These receptors not only promote the uptake of drugs into cells but are also responsible for the extraordinarily long circulatory half-life of albumin. This property in combination with the presence of multiple ligand binding pockets have led to the emergence of serum albumin as an attractive vehicle for novel drug delivery systems. Here, we provide an overview of various albumin-based drug delivery strategies, classified according to their methods of drug attachment, and highlight their experimental and clinical successes.

Discovery of [1,2,3]triazolo[4,5-d]pyrimidine derivatives as highly potent, selective, and cellularly active USP28 inhibitors

Ubiquitin specific peptidase 28 (USP28) is closely associated to the occurrence and development of various malignancies, and thus has been validated as a promising therapeutic target for cancer therapy. To date, only few USP28 inhibitors with moderate inhibitory activity have been reported, highly potent and selective USP28 inhibitors with new chemotypes remain to be discovered for pathologically investigating the roles of deubiquitinase. In this current study, we reported the synthesis and biological evaluation of new [1,2,3]triazolo[4,5-d]pyrimidine derivatives as potent USP28 inhibitors. Especially, compound 19 potently inhibited USP28 (IC₅₀ = 1.10 ± 0.02 μmol/L, K_d = 40 nmol/L), showing selectivity over USP7 and LSD1 (IC₅₀ > 100 μmol/L). Compound 19 was cellularly engaged to USP28 in gastric cancer cells. Compound 19 reversibly bound to USP28 and directly affected its protein levels, thus inhibiting the proliferation, cell cycle at S phase, and epithelial-mesenchymal transition (EMT) progression in gastric cancer cell lines. Docking studies were performed to rationalize the potency of compound 19. Collectively, compound 19 could serve as a new tool compound for the development of new USP28 inhibitors for exploring the roles of deubiquitinase in cancers.

Ligand binding to natural and modified human serum albumin

This paper reports evaluation of ligand binding constants for unmodified or biotinylated HSA (HSA_B) for two well-known HSA binding ligands, naproxen and bromocresol green. Results demonstrate differential scanning calorimetry (DSC) is a reliable quantitative method for straight-forward and rapid evaluation of ligand binding constants for HSA and modified derivatives. DSC measured the thermodynamic stability of free and ligand-bound HSA and HSA_B at pH = 6.0, 7.4 and 8.0. DSC analysis provided a quantitative gauge of responses of HSA and HSA_B thermodynamic stability to ligand binding. The influence of different levels of biotinylation of HSA_B on ligand binding, and how ligand binding varied as a function of pH for these molecules was also examined. In the three pH environments, biotinylation increased stability of HSA_B alone compared to free HSA at pH 7.4. Stabilities of free protein and ligand-bound complexes varied with pH in the order, pH = 6.0>7.4>8.0. Our analytical approach provided very accurate estimates for known binding constants of these ligands for HSA. Results revealed, for both ligands, extent of biotinylation of HSA_B affected binding, reducing binding constants from three to 100-fold. DSC analysis was able to delineate inter-relationships between molecular structure and thermodynamic stability of HSA and HSA_B bound by ligands; and their variations with pH.

Albumin-Based Transport of Nonsteroidal Anti-Inflammatory Drugs in Mammalian Blood Plasma

Every day, hundreds of millions of people worldwide take nonsteroidal anti-inflammatory drugs (NSAIDs), often in conjunction with multiple other medications. In the bloodstream, NSAIDs are mostly bound to serum albumin (SA). We report the crystal structures of equine serum albumin complexed with four NSAIDs (ibuprofen, ketoprofen, etodolac, and nabumetone) and the active metabolite of nabumetone (6-methoxy-2-naphthylacetic acid, 6-MNA). These compounds bind to seven drug-binding sites on SA. These sites are generally well-conserved between equine and human SAs, but ibuprofen binds to both SAs in two drug-binding sites, only one of which is common. We also compare the binding of ketoprofen by equine SA to binding of it by bovine and leporine SAs. Our comparative analysis of known SA complexes with FDA-approved drugs clearly shows that multiple medications compete for the same binding sites, indicating possibilities for undesirable physiological effects caused by drug-drug displacement or competition with common metabolites. We discuss the consequences of NSAID binding to SA in a broader scientific and medical context, particularly regarding achieving desired therapeutic effects based on an individual's drug regimen.

Covalent immobilization of delipidated human serum albumin on poly(pyrrole-2-carboxylic) acid film for the impedimetric detection of perfluorooctanoic acid

The immobilization of biomolecules at screen printed electrodes for biosensing applications is still an open challenge. To enrich the toolbox of bioelectrochemists, graphite screen printed electrodes (G-SPE) were modified with an electropolymerized film of pyrrole-2-carboxilic acid (Py-2-COOH), a pyrrole derivative rich in carboxylic acid functional groups. These functionalities are suitable for the covalent immobilization of biomolecular recognition layers. The electropolymerization was first optimized to obtain stable and conductive polymeric films, comparing two different electrolytes: sodium dodecyl sulphate (SDS) and sodium perchlorate. The G-SPE modified with Py-2-COOH in 0.1 M SDS solution showed the required properties and were further tested. A proof-of-concept study for the development of an impedimetric sensor for perfluorooctanoic acid (PFOA) was carried out using the delipidated human serum albumin (hSA) as bioreceptor. The data interpretation was supported by size exclusion chromatography and small-angle X-ray scattering (SEC-SAXS) analysis of the bioreceptor-target complex and the preliminary results suggest the possibility to further develop this biosensing strategy for toxicological and analytical studies.

H-Bonding-mediated binding and charge reorganization of proteins on gold nanoparticles

Gold nanoparticles with various functionalities interact with the human serum albumin (HSA) leading to protein structural changes. HSA-nanoparticles bioconjugates display lower toxicity and slower cell uptake rates, compared to nanoparticles in the absence of protein.

Characterization of the binding of cyanidin-3-glucoside to bovine serum albumin and its stability in a beverage model system: A multispectroscopic and chemometrics study

Anthocyanins as one of the main natural groups of food colorants undergo quick color fading, which can be diminished through protein association. The stabilization of cyanidin-3-glucoside (CYG) through binding to bovine serum albumin (BSA) was investigated at pH 3.0 using atomic force microscopy and differential scanning calorimetry along with UV-Vis absorption, steady-state fluorescence, circular dichroism, and three-dimensional emission spectral analyses merged with the multivariate curve resolution-alternative least square method. The stabilized CYG molecules were found at the site II of BSA with combined static and dynamic quenching mechanisms. Approximately 93% of the BSA binding sites were occupied in the BSA-CYG complex through hydrogen bonds and van der Waals forces with the binding constant and stoichiometry ratio of 1.88 × 10⁵ M^-1 and 1:13, respectively. The results also revealed that CYG molecules caused partial unfolding of the BSA structure, while it was not enough for significant alteration of denaturation temperature. The binding results also indicated that the reduction of H₂O₂-induced-CYG oxidation rate (34.78%) at pH 3.0 was mainly driven via the BSA-hemiketal association, although the colored species of CYG had a greater affinity towards BSA in the equilibrated system at pHs 1.0 and 5.0.

Capping gold nanoparticles with albumin to improve their biomedical properties

Nanotechnology is an emerging field which has created great opportunities either through the creation of new materials or by improving the properties of existing ones. Nanoscale materials with a wide range of applications in areas ranging from engineering to biomedicine have been produced. Gold nanoparticles (AuNPs) have emerged as a therapeutic agent, and are useful for imaging, drug delivery, and photodynamic and photothermal therapy. AuNPs have the advantage of ease of functionalization with therapeutic agents through covalent and ionic binding. Combining AuNPs and other materials can result in nanoplatforms, which can be useful for biomedical applications. Biomaterials such as biomolecules, polymers and proteins can improve the therapeutic properties of nanoparticles, such as their biocompatibility, biodistribution, stability and half-life. Serum albumin is a versatile, non-toxic, stable, and biodegradable protein, in which structural domains and functional groups allow the binding and capping of inorganic nanoparticles. AuNPs coated with albumin have improved properties such as greater compatibility, bioavailability, longer circulation times, lower toxicity, and selective bioaccumulation. In the current article, we review the features of albumin, as well as its interaction with AuNPs, focusing on its biomedical applications.