The effect of glycation on bovine serum albumin conformation and ligand binding properties with regard to gliclazide

Insights into the conformational, secondary structural, dynamical and hydration pattern changes of glucose mediated glycated HSA: a molecular dynamics approach

The robust structural nature of human serum albumin (HSA) is responsible for its multifarious functional property. The site specific glycation of HSA due to hyperglycaemia (excess glucose) causes structural changes which have an impact on the functioning of the protein. This work investigates the effects of glucose-mediated glycation in the altered inter-domain motion, distorted binding site conformation and modified hydration patterns, Trp214 orientation, and secondary structure transition using simulation approach. Here we have observed an increase of turns in the helices of glycated HSA, which modulates the open-close conformation of Sudlow I & II. The secondary structure changes of glycated HSA indicate plausible reduction in the alpha helical content in the helices which participates in ligand binding. It also affects geometrical features of drug binding sites (Sudlow I and II) such as volume and hydration. We found that glycation disturbs domain specific mobility patterns of HSA, a substantial feature for albumin drug binding ability which is also correlated with changes in the local environment of Trp214.Communicated by Ramaswamy H. Sarma.

Antioxidant and Anti-Glycation Potential of H2 Receptor Antagonists-In Vitro Studies and a Systematic Literature Review

Background: Histamine H2 receptor antagonists are a group of drugs that inhibit gastric juice secretion in gastrointestinal diseases. However, there is evidence to suggest that H2 blockers have a broader spectrum of activity. The antioxidant properties of H2 blockers have not been fully elucidated, and their anti-glycation potential has not been studied to date. Therefore, this is the first study to compare the antioxidant and antiglycation potentials of the most popular H2 antagonists (ranitidine, cimetidine, and famotidine) on protein glycoxidation in vitro. Methods: Bovine serum albumin (BSA) was glycated using sugars (glucose, fructose, galactose, and ribose) as well as aldehydes (glyoxal and methylglyoxal). Results: In the analyzed group of drugs, ranitidine was the only H2 blocker that significantly inhibited BSA glycation in all tested models. The contents of protein carbonyls, protein glycoxidation products (↓dityrosine, ↓N-formylkynurenine), and early (↓Amadori products) and late-stage (↓AGEs) protein glycation products decreased in samples of glycated BSA with the addition of ranitidine relative to BSA with the addition of the glycating agents. The anti-glycation potential of ranitidine was comparable to those of aminoguanidine and Trolox. In the molecular docking analysis, ranitidine was characterized by the lowest binding energy for BSA sites and could compete with protein amino groups for the addition of carbonyl groups. H2 blockers also scavenge free radicals. The strongest antioxidant properties are found in ranitidine, which additionally has the ability to bind transition metal ions. The systematic literature review also revealed that the anti-glycation effects of ranitidine could be attributed to its antioxidant properties. Conclusions: Ranitidine showed anti-glycation and antioxidant properties. Further research is needed, particularly in patients with diseases that promote protein glycation.

Comparison of bovine serum albumin glycation by ribose and fructose in vitro and in vivo

Advanced glycation end products (AGEs) play a critical pathogenic role in the development of diabetic complications. Recent studies have shown that diabetes is associated with not only abnormal glucose metabolism but also abnormal ribose and fructose metabolism, although glucose is present at the highest concentration in humans. The glycation ability and contribution of ribose and fructose to diabetic complications remain unclear. Here, the glycation ability of ribose, fructose and glucose under a mimic physiological condition, in which the concentration of ribose or fructose was one-fiftieth that of glucose, was compared. Bovine serum albumin (BSA) was used as the working protein in our experiments. Ribose generated more AGEs and was markedly more cytotoxic to SH-SY5Y cells than fructose. The first-order rate constant of ribose glycation was found to be significantly greater than that of fructose glycation. LC-MS/MS analysis revealed 41 ribose-glycated Lys residues and 12 fructose-glycated residues. Except for the shared Lys residues, ribose reacted selectively with 17 Lys, while no selective Lys was found in fructose-glycated BSA. Protein conformational changes suggested that ribose glycation may induce BSA into amyloid-like monomers compared with fructose glycation. The levels of serum ribose were correlated positively with glycated serum protein (GSP) and diabetic duration in type 2 diabetes mellitus (T2DM), respectively. These results indicate that ribose has a greater glycation ability than fructose, while ribose largely contributes to the production of AGEs and provides a new insight to understand in the occurrence and development of diabetes complications.

In Vitro Investigation of Binding Interactions between Albumin–Gliclazide Model and Typical Hypotensive Drugs

Type 2 diabetes management usually requires polytherapy, which increases the risk of drug-to-drug interactions. Among the multiple diabetes comorbidities, hypertension is the most prevalent. This study aimed to investigate the binding interactions between the model protein, bovine albumin, and the hypoglycemic agent gliclazide (GLICL) in the presence of typical hypotensive drugs: quinapril hydrochloride (QUI), valsartan (VAL), furosemide (FUR), amlodipine besylate (AML), and atenolol (ATN). Spectroscopic techniques (fluorescence quenching, circular dichroism) and thermodynamic experiments were employed. The binding of the gliclazide to the albumin molecule was affected by the presence of an additional drug ligand, which was reflected by the reduced binding constant of the BSA–DRUG–GLICL system. This may indicate a possible GLICL displacement and its enhanced pharmacological effect, as manifested in clinical practice. The analysis of the thermodynamic parameters indicated the spontaneity of the reaction and emphasized the role of hydrogen bonding and van der Waals forces in these interactions. The secondary structure of the BSA remained almost unaffected.

Piperine exhibits preventive and curative effect on erythrocytes membrane modifications and oxidative stress against in vitro albumin glycation

Inhibition of non-enzymatic glycation processes is an essential aspect of treating type 2 diabetes and related complications. In this study, piperine's preventative, simultaneous and curative effect in glucose-induced albumin glycation was examined by analyzing the structural and functional markers of albumin. The protective and antioxidant influence of piperine on erythrocytes was assessed by examining cellular membrane modifications with antioxidant status. Albumin glycation was performed in three different experimental sets of 21 days at 37°C in dark conditions-using different piperine concentrations (250, 500, and 1,000 μM) and time of addition of glucose (30 mM)/piperine (1,000 μM) in a respective solution at 10th day. Piperine with glycated albumin leads to decreased fructosamine, carbonyl group, and protein-bound glucose. It had protected free amino groups, thiol group, and reduced beta-amyloid, protein aggregates formation. The presence of piperine with glycated albumin prevented erythrocytes hemolysis, membrane modifications, and maintained the antioxidant status. Piperine showed the antiglycation effects in a dose-dependent manner, additionally, its pre-treatment exhibited maximum attenuation by manifesting its primarily preventive role. PRACTICAL APPLICATIONS: Piperine is a natural alkaloid compound found in pepper, has been reported to possess anti-cancer, anti-microbial, and anti-inflammatory properties. The present study evaluated the antiglycation potential of piperine in albumin's glycation and it displayed preventive action, protected erythrocytes from oxidative damage induced by glycated albumin. We concluded that the daily intake of piperine can be adequate to prevent glycation-induced diabetic complications development in hyperglycemic conditions.

How Does Glycation Affect Binding Parameters of the Albumin-Gliclazide System in the Presence of Drugs Commonly Used in Diabetes? In Vitro Spectroscopic Study

In this research, the selected drugs commonly used in diabetes and its comorbidities (gliclazide, cilazapril, atorvastatin, and acetylsalicylic acid) were studied for their interactions with bovine serum albumin-native and glycated. Two different spectroscopic methods, fluorescence quenching and circular dichroism, were utilized to elucidate the binding interactions of the investigational drugs. The glycation process was induced in BSA by glucose and was confirmed by the presence of advanced glycosylation end products (AGEs). The interaction between albumin and gliclazide, with the presence of another drug, was confirmed by calculation of association constants (0.11-1.07 × 10⁴ M^-1). The nature of changes in the secondary structure of a protein depends on the drug used and the degree of glycation. Therefore, these interactions may have an influence on pharmacokinetic parameters.

Polyphenol binding disassembles glycation-modified bovine serum albumin amyloid fibrils

Glycation of protein results in the formation of advanced glycation end-products (AGEs) and leads to deposition as amyloid fibrils. Adhesive structural properties of polyphenols to aromatic amino acids draw significance in promoting, accelerating and/or stabilizing on-pathway and off-pathway folding intermediates, although the mechanistic action remains unclear. In this study, polyphenols remodeling mature AGEs modified amyloid fibrils were investigated through UV-visible spectroscopy, fluorescence spectroscopy, transmission electron microscopy, atomic force microscopy, circular dichroism spectroscopy, MALDI-MS/MS analysis and molecular docking studies. Our findings confirmed the glycation-mediated transformation of native protein into β-sheet rich amyloid fibrils. SDS-PAGE results suggested the presence of shorter peptide fragments ranging from ~10 kDa to ~40 kDa. MALDI-MS/MS results identified the plausible sequences to be His105-His181, Arg193-Lys242, Leu325-Tyr410, and Ala451-Tyr529. TEM and AFM results suggested that polyphenols binding mature amyloid fibrils remodel/disassemble them into distinct aggregate structures or non-amyloid fibrils. Circular dichroism studies suggested that polyphenols upon binding amyloid fibrils stabilizes and transforms the secondary structure towards helical or random coil-like conformation. Molecular modeling studies suggested high binding affinity and hydrophobic interaction to be the main driving force in remodeling perspective. Together, our findings suggest that polyphenols could differentially remodel mature AGEs-modified amyloid fibrils into distinct aggregate structures through non-covalent interactions and can alleviate AGEs-mediated amyloidosis.

Polyphenols redirects the self-assembly of serum albumin into hybrid nanostructures

Chronic hyperglycemia results in the formation of advanced glycation end-products (AGEs) and triggers amyloid fibril formation. Molecules designed to inhibit amyloid fibrils function by eliminating toxic oligomers or reducing fibril formation. Here, the bioactivity of polyphenols in redirecting the self-assembly of amyloid fibrils was reported through microscopic, spectroscopic and molecular docking studies. Our findings illustrate that glycation causes BSA to self-assemble into amyloid fibrils. 17 Lys residues had modified to carboxy methyl lysine (CML) but only Lys523 was probable of modifying into carboxy ethyl lysine (CEL). In contrast, only 6 Arg residues are identified to be modified to Argpyrimidine (Arg-p). A simple polyphenol baicalein (BLN) redirect the self-assembly of amyloid fibrils into off-pathway hybrid nanostructures. Circular dichroism spectroscopic studies suggested that in the presence of BLN helical conformation was favored. Molecular modeling studies suggested that hydrogen bonding and hydrophobic interaction of polyphenols preferentially at crucial amyloidogenic regions can hinder amyloid fibrillation (Phe133, Lys136, Tyr137, Ile141, Tyr160 and Arg185). Mass spectrometric results illustrated that the presence of a simple polyphenol BLN several residues are unmodified to CML, CEL or Arg-p. Together, our findings suggest that polyphenols could have a protective effect and the redirection can help alleviate the amyloid fibril formation.

An Electrochemical Chip to Monitor In Vitro Glycation of Proteins and Screening of Antiglycation Potential of Drugs

Hyperglycemia and the production of advanced glycation end products (AGEs) are the primary factors for the development of chronic complications in diabetes. The level of protein glycation is proportional to the glucose concentration and represents mean glycemia. In this study, we present an electrochemical chip-based method for in vitro glycation monitoring and the efficacy evaluation of an antiglycation compound. An electrochemical chip consisting of five microchambers and embedded microelectrodes was designed for parallel measurements of capacitance signals from multiple solutions at different concentrations. The feasibility of glycation monitoring was then investigated by measuring the capacitance signal at 0.13 MHz with bovine serum albumin and gelatin samples in the presence of various glucose concentrations over 28 days. A significant change in the capacitance due to protein glycation was observed through measurements conducted within 30 s and 21 days of incubation. Finally, we demonstrated that the chip-based capacitance measurement can be utilized for the selection of an antiglycation compound by supplementing the protein solution and hyperglycemic concentration of glucose with an inhibitory concentration of the standard antiglycation agent aspirin. The lack of a significant change in the capacitance over 28 days proved that aspirin is capable of inhibiting protein glycation. Thus, a strong relationship exists between glycation and capacitance, suggesting the application of an electrochemical chip for evaluating glycation and novel antiglycation agents.

Immunoassay of Glomalin by Quartz Crystal Microbalance Biosensor Containing Iron Oxide Nanoparticles

Glomalin is a soil protein resembling heat shock protein (HSP) 60 and exerting high affinity to metals, causing retention of water in the environment and improving mechanical stability of soil. Currently, glomalin is determined in the soil or other samples by combination of autoclaving extraction and total protein determination typically by the Bradford method. In this paper, a piezoelectric biosensor was prepared to determine glomalin in a label-free measurement. The biosensor contained antibodies immobilized on quartz crystal microbalance (QCM), and the recognition layer was stabilized by iron oxide nanoparticles. The assay was tested on real soil samples and compared with the standard Bradford assay. Limit of detection of the assay was equal to 2.4 µg/g for a soil extract with a volume of 50 µl. The assay takes approximately half of an hour and was fully correlated to the Bradford assay. The biosensor had significant advantages than the other methods: it worked in a label-free mode and was fully applicable for practical samples.

Studies on the antiglycating potential of zinc oxide nanoparticle and its interaction with BSA

Nanoparticles have been proven to be a great tool as bio-sensors, medical therapeutic agents and drug delivery vehicles. In this study, the chemically synthesized zinc oxide nanoparticles (ZnO NPs) have been characterized with UV-spectrophotometer, FTIR, XRD, TEM and DLS. These ZnO NPs were investigated with respect to their binding interaction with serum albumin and the thermodynamic parameters of these interactions at different temperatures. Glycation process was checked in the presence of ZnO NPs by measuring fructosamine and carbonyl content for glycated end products and aggregation by Congo red assay. The intrinsic activities of bovine serum albumin (BSA) like esterase and cysteine reactivity were also evaluated in the presence of ZnO NPs. The results indicate that the ZnO NPs showed static as well as dynamic binding interaction with BSA, reduced the content of glycation products and prevented the glycation induced aggregation and antioxidant properties. Therefore, these findings suggest that ZnO NPs may be used for drug delivery agents and antiglycating as well as an antioxidant agent.Communicated by Ramaswamy H. Sarma.

The Antiglycoxidative Ability of Selected Phenolic Compounds-An In Vitro Study

Hyperglycemia and oxidative stress may be observed in different diseases as important factors connected with their development. They often occur simultaneously and are considered together as one process: Glycoxidation. This can influence the function or structure of many macromolecules, for example albumin, by changing their physiological properties. This disturbs the homeostasis of the organism, so the search for natural compounds able to inhibit the glycoxidation process is a current and important issue. The aim of this study was the examination of the antiglycoxidative capacity of 16 selected phenolic compounds, belonging to three phenolic groups, as potential therapeutic agents. Their antiglycoxidative ability, in two concentrations (2 and 20 µM), were examined by in vitro study. The inhibition of the formation of both glycoxidative products (advanced glycation end products (AGEs) and advanced oxidation protein products (AOPPs)) were assayed. Stronger antiglycoxidative action toward the formation of both AOPPs and AGEs was observed for homoprotocatechuic and ferulic acids in lower concentrations, as well as catechin, quercetin, and 8-O-methylurolithin A in higher concentrations. Homoprotocatechuic acid demonstrated the highest antiglycoxidative capacity in both examined concentrations and amongst all of them. A strong, significant correlation between the percentage of AOPPs and AGEs inhibition by compounds from all phenolic groups, in both examined concentrations, was observed. The obtained results give an insight into the antiglycoxidative potential of phenolic compounds and indicate homoprotocatechuic acid to be the most promising antiglycoxidative agent, but further biological and pharmacological studies are needed.

Interaction of chlorpropamide with serum albumin: Effect on advanced glycated end (AGE) product fluorescence

Carrier proteins like bovine or human serum albumin (BSA and HSA, respectively) are prone to glycation as compared to the other available proteins. In this study, reducing sugars such as l-arabinose (ara), d-(-) galactose (gal) and d-(-) fructose (fru) were used to create model glycated serum albumins and binding ability of these with well-known antidiabetic drug chlorpropamide (CPM) was monitored. Fluorescence quenching experiment revealed that interaction of CPM with native as well as glycated albumins undergoes through a ground state complex formation. CPM binds strongly to glycated HSA with arabinose (gHSA_ara) as compared to other glycated systems and to the native proteins. CPM interacts through Van der Waals and hydrogen bonding interaction to glycated BSA by d-(-) fructose (gBSA_fru) and also with native HSA; whereas, it's interaction with BSA and others glycated systems like gBSA_ara, gBSA_gal and gHSA_ara occurs primarily through hydrophobic interaction. CPM showed an enhancement in the production of the advanced glycated end products (AGE) in all the glycated proteins. The difference in the binding capability of CPM to differently glycated albumins could be a major model to understand the drug carrying capacity of the glycated serum albumins.

Spectroscopic and molecular modelling studies on glycation modified bovine serum albumin with cyanidin-3-O-glucoside

In this study, we report the glycation mediated effect of bovine serum albumin (BSA) on the molecular interaction mechanism of cyanidin-3-O-glucoside (C3G) by molecular modelling, Uv-visible spectroscopy, transmission electron microscopy (TEM), fluorescence spectroscopy, and circular dichroism spectroscopy studies. The structures of advanced glycation end-products (AGEs) modified BSA were modelled, energy minimized and analyzed for binding affinity by molecular docking studies using Autodock Vina. Glycation experiments are carried out using glucose and methylglyoxal to validate the molecular modelling results on the interaction of modified BSA with C3G. The modified structures were characterized by reduction in the binding pocket volume, surface, depth, hydrophobicity, and hydrogen bond donors/acceptors. Arg-194, Arg-196, Arg-198, Arg-217, Arg-409, Lys-114, Lys-116, Lys-204, Lys 221, and Lys-439 were found to be crucial in the context of glycation of BSA. TEM images represented the formation of unique globular aggregates in the event of glycation. Uv-visible spectroscopic studies showed the formation of new chromophores between 300 and 400 nm in the event of glycation. Fluorescence quenching was observed in a differential manner in the presence of C3G on glycation modified BSA. Circular dichroism studies suggested the loss of helical structure and formation of β-sheeted structure upon glycation, but subsequent C3G binding has resulted in the increase towards helical structure. Our findings suggested that drug binding affinity has been certainly impaired due to glycation and subsequent AGE modification. Arg-p modification has more austere impact on the structure and would affect the binding properties. We conclude that C3G had differential modulation of binding properties on glycated BSA which can help to protect the stability and bioavailability that has been impaired due to glycation mediated structural changes.

Probing the binding of phenolic aldehyde vanillin with bovine serum albumin: Evidence from spectroscopic and docking approach

The interactions of bovine serum albumin (BSA) with vanillin (VAN) were studied using UV-vis absorption, fluorescence, synchronous fluorescence, three dimensional fluorescence spectroscopy (3D), Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), and molecular docking techniques. The results revealed that VAN causes the static quenching of BSA by forming BSA-VAN complex. The thermodynamic parameters obtained using isothermal titration calorimetry (ITC) showed that the interaction between BSA and VAN is spontaneous and hydrogen bonding, van der Waals forces are mainly involved in stabilizing the complex. The distance between the donor and the acceptor was analyzed using fluorescence resonance energy transfer (FRET) which showed Forster distance of 2.58 nm. Molecular docking technique was applied to study the modes of interaction between BSA-VAN system and it was found that VAN bound to the sub-domain IIA of BSA. Structural analysis using 3D, synchronous fluorescence FTIR, and CD showed that upon binding of VAN, BSA exhibits small micro-environmental changes around tryptophan amino acid residue.

Cyanidin-3-O-glucoside functions like chemical chaperone and attenuates the glycation mediated amyloid formation in albumin

In this study, chemical chaperone like function of cyanidin-3-O-glucoside (C3G) was investigated through fluorescence spectroscopy, UV-visible spectroscopy, circular dichroism spectroscopy, confocal microscopy, scanning electron microscopy and molecular docking studies. Early and advanced glycation inhibitory effect was evaluated by fluorescence spectroscopy and agarose gel electrophoresis. Amyloids were investigated based on their propensity to bind Congo Red (CR) and Thioflavin T (ThT) by multiple microscopic approaches. Circular dichroism studies were used to analyze the changes in the secondary structure due to glycation. C3G effectively inhibited early and advanced glycation by masking like function, carbonyl scavenging and chemical chaperone activity. C3G had molecular interaction with Glu186, Arg427, Ser428, Lys431, Arg435, and Arg458 of BSA. Based on the microscopic analysis, it is evident that C3G can inhibit protein aggregation and amyloid formation. Circular dichroism studies suggested that glycation had resulted in augmented β-sheet propensity, whereas C3G had a protective effect on the helical conformation of BSA. We conclude that C3G has a chemical chaperone like function on the event of glycation mediated amyloid formation in BSA.