Alteration of methotrexate binding to human serum albumin induced by oxidative stress. Spectroscopic comparative study

Protective effect of colchicine on albumin glycation and cellular oxidative stress: Insights into diabetic cardiomyopathy

The present work elucidates the role of colchicine (COL) on albumin glycation and cellular oxidative stress in diabetic cardiomyopathy (DCM). Human serum albumin (HSA) was glycated with methylglyoxal in the presence of COL (2.5, 3.75, and 5 µM), whereas positive and negative control samples were maintained separately. The effects of COL on HSA glycation, structural and functional modifications in glycated HSA were analyzed using different spectroscopical and fluorescence techniques. Increased fructosamine, carbonyl, and pentosidine formation in glycated HSA samples were inhibited in the presence of COL. Structural conformation of HSA and glycated HSA samples was examined by field emission scanning electron microscopy, circular dichroism, Fourier transform infrared, and proton nuclear magnetic resonance analyses, where COL maintained both secondary and tertiary structures of HSA against glycation. Functional marker assays included ABTS•+ radical scavenging and total antioxidant activities, advanced oxidative protein product formation, and turbidimetry, which showed preserved functional properties of glycated HSA in COL-containing samples. Afterward, rat cardiomyoblast (H9c2 cell line) was treated with glycated HSA-COL complex (400 μg/mL) for examining various cellular antioxidants (nitric oxide, catalase, superoxide dismutase, and glutathione) and detoxification enzymes (aldose reductase, glyoxalase I, and II) levels. All three concentrations of COL exhibited effective anti-glycation properties, enhanced cellular antioxidant levels, and detoxification enzyme activities. The report comprehensively analyzes the potential anti-glycation and properties of COL during its initial assessment.

Biophysical changes in methylglyoxal modified fibrinogen and its role in the immunopathology of type 2 diabetes mellitus

Methylglyoxal (MG), a highly reactive dicarbonyl metabolite gets generated during glucose oxidation and lipid peroxidation, which contributes to glycation. In type 2 diabetes mellitus (T2DM), non-enzymatic glycosylation of proteins mediated by hyperglycemia results in the pathogenesis of diabetes-associated secondary complications via the generation of AGEs. Under in vitro conditions, MG altered the tertiary structure of fibrinogen. High-performance liquid chromatography (HPLC) and liquid chromatography mass spectroscopy (LCMS) studies confirmed the generation of N-(carboxymethyl) lysine, N-(carboxyethyl) lysine, hydroimidazolone, pentosidine and argpyrimidine in the modified protein. The altered fibrinogen structure upon glycation was further confirmed by confocal microscopy and nuclear magnetic resonance spectra (NMR). MG-Fib was found to be more immunogenic, as compared to its native analogue, in the immunological studies conducted on experimental rabbits. Our results reflect the presence of neo-antigenic determinants on modified fibrinogen. Competitive inhibition enzyme-linked immunosorbent assay suggested the presence of neo-epitopes with marked immunogenicity eliciting specific immune response. Binding studies on purified immunoglobulin G (IgG) confirmed the enhanced and specific immunogenicity of MG-Fib. Studies on interaction of MG-Fib with the circulating auto-antibodies from T2DM patients showed high affinity of serum antibodies toward MG-Fib. This study suggests a potent role of glycoxidatively modified fibrinogen in the generation of auto-immune response in T2DM patients.

The Influence of Oxidative Stress on Serum Albumin Structure as a Carrier of Selected Diazaphenothiazine with Potential Anticancer Activity

Albumin is one of the most important proteins in human blood. Among its multiple functions, drug binding is crucial in terms of drug distribution in human body. This protein undergoes many modifications that are certain to influence protein activity and affect its structure. One such reaction is albumin oxidation. Chloramine T is a strong oxidant. Solutions of human serum albumin, both non-modified and modified by chloramine T, were examined with the use of fluorescence, absorption and circular dichroism (CD) spectroscopy. 10H-3,6-diazaphenothiazine (DAPT) has anticancer activity and it has been studied for the first time in terms of binding with human serum albumin—its potential as a transporting protein. Using fluorescence spectroscopy, in the presence of dansylated amino acids, dansyl-l-glutamine (dGlu), dansyl-l-proline (dPro), DAPT binding with two main albumin sites—in subdomain IIA and IIIA—has been evaluated. Based on the conducted data, in order to measure the stability of DAPT complexes with human (HSA) and oxidized (oHSA) serum albumin, association constant (K_a) for ligand-HSA and ligand-oHSA complexes were calculated. It has been presumed that oxidation is not an important issue in terms of 10H-3,6-diazaphenothiazine binding to albumin. It means that the distribution of this substance is similar regardless of changes in albumin structure caused by oxidation, natural occurring in the organism.

Oxidative Alteration of Trp-214 and Lys-199 in Human Serum Albumin Increases Binding Affinity with Phenylbutazone: A Combined Experimental and Computational Investigation

Human serum albumin (HSA) is a target for reactive oxygen species (ROS), and alterations of its physiological functions caused by oxidation is a current issue. In this work, the amino-acid residues Trp-214 and Lys-199, which are located at site I of HSA, were experimentally and computationally oxidized, and the effect on the binding constant with phenylbutazone was measured. HSA was submitted to two mild oxidizing reagents, taurine monochloramine (Tau-NHCl) and taurine dibromamine (Tau-NBr₂). The oxidation of Trp-214 provoked spectroscopic alterations in the protein which were consistent with the formation of N'-formylkynurenine. It was found that the oxidation of HSA by Tau-NBr₂, but not by Tau-NHCl, provoked a significant increase in the association constant with phenylbutazone. The alterations of Trp-214 and Lys-199 were modeled and simulated by changing these residues using the putative oxidation products. Based on the Amber score function, the interaction energy was measured, and it showed that, while native HSA presented an interaction energy of -21.3 kJ/mol, HSA with Trp-214 altered to N'-formylkynurenine resulted in an energy of -28.4 kJ/mol, and HSA with Lys-199 altered to its carbonylated form resulted in an energy of -33.9 kJ/mol. In summary, these experimental and theoretical findings show that oxidative alterations of amino-acid residues at site I of HSA affect its binding efficacy.

A general microwave synthesis of metal (Ni, Cu, Zn) selenide nanoparticles and their competitive interaction with human serum albumin

Simple microwave irradiation technique was used to synthesize a series of selenide nanoparticles (platelet-like NiSe nanoparticles, uniform CuSe nanorods, and distorted ZnSe nano-hexagons) and their competitive interaction with human serum albumin was studied.

In Vitro Investigation of the Interaction of Tolbutamide and Losartan with Human Serum Albumin in Hyperglycemia States

Serum albumin is exposed to numerous structural modifications which affect its stability and activity. Glycation is one of the processes leading to the loss of the original properties of the albumin and physiological function disorder. In terms of long lasting states of the hyperglycemia, Advanced Glycation End-products (AGEs) are formed. AGEs are responsible for cellular and tissue structure damage that cause the appearance of a number of health consequences and premature aging. The aim of the present study was to analyze the conformational changes of serum albumin by glycation—“fructation”—using multiple spectroscopic techniques, such as absorption (UV-Vis), fluorescence (SFM), circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy and evaluate of possible alteration of binding and competition between tolbutamide (TB, a first-generation sulfonylurea oral hypoglycemic drug) and losartan (LOS, an angiotensin II receptor (AT₁) blocker used in hypertension (1st line with a coexisting diabetes)) in binding to non-glycated (HSA) and glycated (gHSA_FRC) human serum albumin in high-affinity binding sites. The studies allowed us to indicate the structural alterations of human serum albumin as a result of fructose glycation. Changes in binding parameters, such as association (Ka) or Stern-Volmer (KSV) constants suggest that glycation increases the affinity of TB and LOS towards albumin and affects interactions between them. The process of albumin glycation influences the pharmacokinetics of drugs, thus monitored pharmacotherapy is reasonable in the case of diabetes and hypertension polypharmacy. This information may lead to the development of more effective drug treatments based on personalized medicine for patients with diabetes. Our studies suggest the validity of monitored polypharmacy of diabetes and coexisting diseases.

Quercetin as a tyrosinase inhibitor: Inhibitory activity, conformational change and mechanism

Quercetin, a flavonoid compound, was found to inhibit both monophenolase and diphenolase activities of tyrosinase, and its inhibition against diphenolase activity was in a reversible and competitive manner with an IC₅₀ value of (3.08±0.74)×10^-5molL^-1. Quercetin bound to tyrosinase driven by hydrophobic interaction, thereby resulted in a conformational change of tyrosinase and its intrinsic fluorescence quenching. Tyrosinase had one binding site for quercetin with the binding constant in the order of magnitude of 10⁴Lmol^-1. The molecular docking revealed that quercetin bound to the active site of tyrosinase and chelated a copper with the 3', 4'-dihydroxy groups. It can be deduced that the chelation may prevent the entrance of substrate and then inhibit the catalytic activity of tyrosinase. These findings may be helpful to understand the inhibition mechanism of quercetin on tyrosinase and functional research of quercetin in the treatment of pigmentation disorders.

Effect of Temperature on Tolbutamide Binding to Glycated Serum Albumin

Glycation process occurs in protein and becomes more pronounced in diabetes when an increased amount of reducing sugar is present in bloodstream. Glycation of protein may cause conformational changes resulting in the alterations of its binding properties even though they occur at a distance from the binding sites. The changes in protein properties could be related to several pathological consequences such as diabetic and nondiabetic cardiovascular diseases, cataract, renal dysfunction and Alzheimer's disease. The experiment was designed to test the impact of glycation process on sulfonylurea drug tolbutamide-albumin binding under physiological (T = 309 K) and inflammatory (T = 311 K and T = 313 K) states using fluorescence and UV-VIS spectroscopies. It was found in fluorescence analysis experiments that the modification of serum albumin in tryptophanyl and tyrosyl residues environment may affect the tolbutamide (TB) binding to albumin in subdomain IIA and/or IIIA (Sudlow's site I and/or II), and also in subdomains IB and IIB. We estimated the binding of tolbutamide to albumin described by a mixed nature of interaction (specific and nonspecific). The association constants Ka (L∙mol^-1) for tolbutamide at its high affinity sites on non-glycated albumin were in the range of 1.98-7.88 × 10⁴ L∙mol^-1 (λ_ex = 275 nm), 1.20-1.64 × 10⁴ L∙mol^-1 (λ_ex = 295 nm) and decreased to 1.24-0.42 × 10⁴ L∙mol^-1 at λ_ex = 275 nm (T = 309 K and T = 311 K) and increased to 2.79 × 10⁴ L∙mol^-1 at λ_ex = 275 nm (T = 313 K) and to 4.43-6.61 × 10⁴ L∙mol^-1 at λ_ex = 295 nm due to the glycation process. Temperature dependence suggests the important role of van der Waals forces and hydrogen bonding in hydrophobic interactions between tolbutamide and both glycated and non-glycated albumin. We concluded that the changes in the environment of TB binding of albumin in subdomain IIA and/or IIIA as well as in subdomains IB and IIB influence on therapeutic effect and therefore the studies of the binding of tolbutamide (in diabetes) to transporting protein under glycation that refers to the modification of a protein are of great importance in pharmacology and biochemistry. This information may lead to the development of more effective drug therapy in people with diabetes.

An inhibition mechanism of dihydromyricetin on tyrosinase and the joint effects of vitamins B6, D3 or E

Dihydromyricetin occupies the active site of tyrosinase to avoid the entrance of the substrate and causes the inhibition of tyrosinase activity.

Inhibitory mechanism of morin on α-glucosidase and its anti-glycation properties

It is important to investigate the inhibition of α-glucosidase due to its correlation with type 2 diabetes. Morin was found to exert significant inhibition activity on α-glucosidase in a reversible mixed-type manner with an IC50 value of (4.48 ± 0.04) μM. Analyses of fluorescence and circular dichroism spectra indicated that the formation of the morin-α-glucosidase complex was driven mainly by hydrophobic forces and hydrogen bonding, and caused the conformational changes of α-glucosidase. The phase diagrams of fluorescence showed that the conformational change process was monophasic without intermediates. Molecular docking indicated that morin mainly interacted with amino acid residues located close to the active site of α-glucosidase, which may move to cover the active pocket to reduce the binding of the substrate and then inhibit the catalytic activity. Morin was also found to exhibit inhibition in the generation of advanced glycation end products which was related to the long term complications of diabetes.