Interaction between glycated serum albumin and AGE-receptors depends on structural changes and the glycation reagent

Probing the effect of glycation on the pseudo-esterase activity of Human Serum Albumin

Human Serum Albumin (HSA), a major protein in blood plasma, exhibits pseudo-enzymatic activity such as pseudo-esterase activity. This study explores the impact of glycation on the pseudo-esterase activity of HSA. Glycation, a non-enzymatic reaction between reducing sugars and HSA was induced using glucose, fructose, and ribose. Glycated HSA samples (gHSA, fHSA, and rHSA) were analyzed for their pseudo-esterase activity using p-nitrophenyl acetate (PNPA) as a substrate. The kinetics of the enzyme-substrate reaction were studied, and structural changes monitored through UV-Vis, fluorescence, and circular dichroism (CD) spectroscopy. Glycation was confirmed using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-ToF) mass spectrometry. Results indicated a significant reduction in the pseudo-esterase activity of glycated HSA compared to native HSA. Ribose-induced glycation exhibited the highest reduction in activity, attributed to the higher glycation efficiency of ribose. Fluorescence studies revealed changes in Trp fluorescence, suggesting conformational alterations in glycated as well as acetylated HSA. CD spectroscopy confirmed secondary structural changes upon glycation, followed by acetylation. A binding study was conducted to deduce the effect of glycation and acetylation of HSA on its binding activity. These findings highlight the significance of understanding how glycation modifies the biochemical properties of HSA, impacting its physiological roles and therapeutic applications in metabolic disorders. Our studies specifically reveal that glycation impairs the pseudo-esterase activity and alters the drug-binding properties of HSA.

Albumin Is an Integrative Protein of Blood Plasma and Beyond

Albumin is a major protein in mammalian blood plasma or serum, where its concentration in healthy organisms is about 600 μM [...].

Diabetic Glycation of Human Serum Albumin Affects Its Immunogenicity

Advanced glycation end-products (AGEs) are products of a non-enzymatic reaction between amino acids and reducing sugars. Glycated human serum albumin (HSA) increases in diabetics as a consequence of elevated blood glucose levels and glycating metabolites like methylglyoxal (MGO). The impact of different types of glycation on the immunomodulatory properties of HSA is poorly understood and is studied here. HSA was glycated with D-glucose, MGO, or glyoxylic acid (CML). Glycation-related biochemical changes were characterized using various biochemical methods. The binding of differentially glycated HSA to AGE receptors was determined with inhibition ELISAs, and the impact on inflammatory markers in macrophage cell line THP-1 and adherent monocytes isolated from human peripheral blood mononuclear cells (PBMCs) was studied. All glycation methods led to unique AGE profiles and had a distinct impact on protein structure. Glycation resulted in increased binding of HSA to the AGE receptors, with MGO modification showing the highest binding, followed by glucose and, lastly, CML. Additionally, modification of HSA with MGO led to the increased expression of pro-inflammatory markers in THP-1 macrophages and enhanced phosphorylation of NF-κB p65. The same pattern, although less prominent, was observed for HSA glycated with glucose and CML, respectively. An increase in pro-inflammatory markers was also observed in PBMC-derived monocytes exposed to all glycated forms of HSA, although HSA-CML led to a significantly higher inflammatory response. In conclusion, the type of HSA glycation impacts immune functional readouts with potential relevance for diabetes.

The Molten Globule State of a Globular Protein in a Cell Is More or Less Frequent Case Rather than an Exception

Quite a long time ago, Oleg B. Ptitsyn put forward a hypothesis about the possible functional significance of the molten globule (MG) state for the functioning of proteins. MG is an intermediate between the unfolded and the native state of a protein. Its experimental detection and investigation in a cell are extremely difficult. In the last decades, intensive studies have demonstrated that the MG-like state of some globular proteins arises from either their modifications or interactions with protein partners or other cell components. This review summarizes such reports. In many cases, MG was evidenced to be functionally important. Thus, the MG state is quite common for functional cellular proteins. This supports Ptitsyn’s hypothesis that some globular proteins may switch between two active states, rigid (N) and soft (MG), to work in solution or interact with partners.

Modulation of Fabrication and Nutraceutical Delivery Performance of Ovalbumin-Stabilized Oleogel-Based Nanoemulsions via Complexation with Gum Arabic

Protein–polysaccharide complexes, which involve Maillard-type protein–polysaccharide conjugates and electrostatic protein–polysaccharide complexes, have the potential to stabilize oleogel-based nanoemulsions for nutraceutical delivery. Here, ovalbumin (OVA) and gum arabic (GA) were used to prepare OVA–GA conjugate (OGC) and OVA–GA mixture (OGM), followed by the fabrication of astaxanthin-loaded oleogel-based nanoemulsions. Carnauba wax (5% w/w) and rice bran oil were mixed to prepare food-grade oleogel. The successful preparation of OGC was verified by means of SDS-PAGE analysis and free amino groups determination. OGC endowed oleogel-based nanoemulsions with smaller emulsion droplets and higher stability during 30-day storage, implying more outstanding emulsifying capability than OGM. Both OGC-stabilized nanoemulsions and OGM-stabilized nanoemulsions could enhance the extent of lipolysis and the bioaccessibility of astaxanthin compared with oleogel. Meanwhile, OGC exhibited significantly better than OGM, which indicated that OGC-stabilized oleogel-based nanoemulsions possessed more desirable nutraceutical delivery performance than OGM-stabilized oleogel-based nanoemulsions. This study may fill a gap in the influence of different protein–polysaccharide complexes on oleogel-based nanoemulsions and contribute to deeper insights about novel oleogel-based nanoemulsions for their applications in the food industry.

The IgE/IgG binding capacity and structural changes of Alaska Pollock parvalbumin glycated with different reducing sugars

Parvalbumin (PV) is one of the major allergens in fish. The aim of our present work was to research the influence mechanism of glycation with different reducing sugars (glucose, fructose, ribose, lactose, and galactose) on the immunoglobulin E (IgE) and immunoglobulin G (IgG) binding capacity and structure changes of PV in Alaska Pollock. PV glycated with glucose or fructose (PV-Glu/ PV-Fru) exhibited the higher IgE/IgG binding capacities than that of ribose, galactose, or lactose. During glycation, the lysine (Lyr), tyrosine (Tyr), and phenylalanine (Phe) of PV were gradually embed into core area of three-dimensional structure of protein, which reflected in the ultraviolet (UV) spectrum and fluorescence spectra. Moreover, the increase of surface hydrophobicity had confirmed the conformation alteration of glycated PV. These results suggest that there is a specific association among the change of PV in glycation and in potential allergenicity. The types and conformation of reducing sugar greatly influenced the IgE/IgG binding capacity of PV, and glycation with ribose and galactose was a promising approach for reducing the IgE/IgG binding capacity of PV from Alaska Pollock. PRACTICAL APPLICATIONS: Parvalbumin (PV), the major allergen of fish, it can not only maintain the physiological activity of cells, but also cross react with human amyloid protein to alleviate Alzheimer's disease and Parkinson's syndrome. This study revealed that the IgE/IgG binding capacity and structural changes of PV from Alaska Pollock modified by glycation with different reducing sugars. This will help us to understand the sensitization and structural change of the glycated products after the reaction of PV with different reducing sugars. It provides an effective carbonyl source for the preparation of low antigenicity PV based on glycation and lays a foundation for glycation modification of other food allergens.

Caffeic Acid Inhibits the Formation of Advanced Glycation End Products (AGEs) and Mitigates the AGEs-Induced Oxidative Stress and Inflammation Reaction in Human Umbilical Vein Endothelial Cells (HUVECs)

The advanced glycation end products (AGEs) are the compounds produced by non-enzymatic glycation reaction of proteins and sugars, which can induce the generation of free radicals and the expression of inflammatory factors, thereby playing an important role in vascular dysfunction in diabetes. To investigate the effects of caffeic acid (CA) on glycation formed by glucose and protein, various spectroscopic techniques and molecular docking methods were carried out. Furthermore, the protective effects of CA on human umbilical vein endothelial cells (HUVECs) damaged by AGEs were detected. The results indicated that CA inhibited AGEs formation in vitro, decreased the expression of IL-1β, IL-18, ICAM-1, VCAM-1, NLRP3, Caspase-1 and CRP (C-reactive protein) and reduced the ROS in HUVECs exposed to AGEs. Our findings suggested that the supplementation with dietary CA could prevent and delay the AGEs-induced vascular dysfunction in diabetes.

Advanced Glycated End Products Alter Neutrophil Effect on Regulation of CD4+ T Cell Differentiation Through Induction of Myeloperoxidase and Neutrophil Elastase Activities

CD₄⁺ T cell subset imbalance plays an important role in the development of diabetic complications. Neutrophils have recently been known as the regulator of CD₄⁺ T cell differentiation. However, whether neutrophils affect CD₄⁺ T cell population in diabetes is still elusive. In this study, we investigated the effect of neutrophils stimulated with advanced glycated end products (AGEs), the marker of diabetes, on CD₄⁺ T cell differentiation and its underlying mechanism. Our data showed that the cultural medium of healthy adult neutrophils treated with AGEs increased expressions of both Th₁ (IFN-γ) and Th₁₇ (IL-17) phenotypes and the transcription factors of Th₁ (Tbet) and Th₁₇ (RORγt) in naive CD₄⁺T cells and CD₄⁺CD₂₅⁺FoxP₃⁺ (Treg) T cells in vitro. Next, we found that AGEs induced the generations of myeloperoxidase (MPO) and neutrophil elastase (NE) in neutrophils; inhibition of MPO or NE attenuated the effect of AGE-stimulated neutrophils on CD₄⁺ T cell bias. Furthermore, receptor for AGEs (RAGE) inhibitor interrupted AGE-induced MPO and NE expressions, but MPO and NE inhibitions did not change AGE-increased RAGE gene expression. These results suggested that AGEs drive the effect of neutrophils on CD₄⁺ T cell differentiation into pro-inflammatory program through inducing MPO and NE productions in neutrophils, which is mediated by AGE-RAGE interaction.

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.

Perspective of Advanced Glycation End Products on Human Health

In the last 20 years, the effects of advanced glycation end products (AGEs) on health have received increasing attention. High AGE levels in the body correlate with the progression of many diseases, such as diabetes, cardiovascular disease, and some cancers. However, whether AGEs are a cause of these diseases or represent accompanying symptoms of these diseases still needs to be elucidated by more comprehensive research. Recently, many researchers have begun to investigate the effects of AGE intake-induced variations of gut microbiota on disease progression, which will further explain the impact of AGEs on health and open a new chapter in AGE research.

Ousting RAGE in melanoma: A viable therapeutic target?

Melanoma remains an important health concern, given the steady increase in incidence and acquisition of resistance to systemic therapies. The receptor for advanced glycation end products (RAGE) initially identified for its binding to advanced glycation end products was subsequently acknowledged as a pattern recognition receptor given its ability to recognize similar structural elements within numerous ligands. Recent studies have elucidated a plausible role of RAGE in melanoma progression through modulation of inflammatory, proliferative and invasive cellular responses. Several of its ligands including the S100 proteins and HMGB1 are being investigated for their involvement in melanoma metastasis and as potential biomarkers of the disease. Targeting RAGE signaling represents a viable therapeutic strategy which remains underexplored in cutaneous malignancies. Here we have summarized current knowledge on the functionality of RAGE with special focus on specific ligands enumerated in various in vitro and in vivo melanoma models.

Intrinsically Disordered Regions in Serum Albumin: What Are They For?

Serum albumin is a major plasma protein in mammalian blood. The importance of this protein lies in its roles in both bioregulation and transport phenomena. Serum albumin binds various metal ions and participates in the transport and storage of fatty acids, bilirubin, steroids amino acids, and many other ligands, usually with regions of hydrophobic surface. Although the primary role of serum albumin is to transport various ligand, its versatile binding capacities and high concentration mean that it can assume a number of additional functions. The major goal of this article is to show how intrinsic disorder is encoded in the amino acid sequence of serum albumin, and how intrinsic disorder is related to functions of this important serum protein.

Mechanism of increased clearance of glycated albumin by proximal tubule cells

Serum albumin is the most abundant plasma protein and has a long half-life due to neonatal Fc receptor (FcRn)-mediated transcytosis by many cell types, including proximal tubule cells of the kidney. Albumin also interacts with, and is modified by, many small and large molecules. Therefore, the focus of the present study was to address the impact of specific known biological albumin modifications on albumin-FcRn binding and cellular handling. Binding at pH 6.0 and 7.4 was performed since FcRn binds albumin strongly at acidic pH and releases it after transcytosis at physiological pH. Equilibrium dissociation constants were measured using microscale thermophoresis. Since studies have shown that glycated albumin is excreted in the urine at a higher rate than unmodified albumin, we studied glucose and methylgloxal modified albumins (21 days). All had reduced affinity to FcRn at pH 6.0, suggesting these albumins would not be returned to the circulation via the transcytotic pathway. To address why modified albumin has reduced affinity, we analyzed the structure of the modified albumins using small-angle X-ray scattering. This analysis showed significant structural changes occurring to albumin with glycation, particularly in the FcRn-binding region, which could explain the reduced affinity to FcRn. These results offer an explanation for enhanced proximal tubule-mediated sorting and clearance of abnormal albumins.

Glycation of the high affinity NGF-receptor and RAGE leads to reduced ligand affinity

AGEs are posttranslational modifications generated by irreversible non-enzymatic crosslinking reactions between sugars and proteins - a reaction referred to as glycation. Glycation, a feature of ageing, can lead to non-degradable and less functional proteins and enzymes and can additionally induce inflammation and further pathophysiological processes such as neurodegeneration. In this study we investigated the influence of glycation on the high affinity NGF-receptor TrkA and the AGE-receptor RAGE. We quantified the binding affinity of the TrkA-receptor and RAGE to their ligands by surface plasmon resonance (SPR) and compared these to the binding affinity after glycation. At the same time, we established a glycation procedure using SPR. We found that glycation of TrkA reduced the affinity to NGF by a factor of three, which could be shown to lead to a reduction of NGF-dependent neurite outgrowth in PC12 cells. Glycation of RAGE reduced binding affinity of AGEs by 10-fold.

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.

Advanced glycation endproducts increase proliferation, migration and invasion of the breast cancer cell line MDA-MB-231

Diabetic patients have increased likelihood of developing breast cancer. Advanced glycation endproducts (AGEs) underlie the pathogenesis of diabetic complications but their impact on breast cancer cells is not understood. This study aims to determine the effects of methylglyoxal-derived bovine serum albumin AGEs (MG-BSA-AGEs) on the invasive MDA-MB-231 breast cancer cell line. By performing cell counting, using wound-healing assay, invasion assay and zymography analysis, we found that MG-BSA-AGEs increased MDA-MB-231 cell proliferation, migration and invasion through Matrigel™ associated with an enhancement of matrix metalloproteinase (MMP)-9 activities, in a dose-dependent manner. Using Western blot and flow cytometry analyses, we demonstrated that MG-BSA-AGEs increased expression of the receptor for AGEs (RAGE) and phosphorylation of key signaling protein extracellular signal-regulated kinase (ERK)-1/2. Furthermore, in MG-BSA-AGE-treated cells, phospho-protein micro-array analysis revealed enhancement of phosphorylation of the ribosomal protein 70 serine S6 kinase beta 1 (p70S6K1), which is known to be involved in protein synthesis, the signal transducer and activator of transcription (STAT)-3 and the mitogen-activated protein kinase (MAPK) p38, which are involved in cell survival. Blockade of MG-BSA-AGE/RAGE interactions using a neutralizing anti-RAGE antibody inhibited MG-BSA-AGE-induced MDA-MB-231 cell processes, including the activation of signaling pathways. Throughout the study, non-modified BSA had a negligible effect. In conclusion, AGEs might contribute to breast cancer development and progression partially through the regulation of MMP-9 activity and RAGE signal activation. The up-regulation of RAGE and the concomitant increased phosphorylation of p70S6K1 induced by AGEs may represent promising targets for drug therapy to treat diabetic patients with breast cancer.

Vascular effects of advanced glycation endproducts: Clinical effects and molecular mechanisms

The enhanced generation and accumulation of advanced glycation endproducts (AGEs) have been linked to increased risk for macrovascular and microvascular complications associated with diabetes mellitus. AGEs result from the nonenzymatic reaction of reducing sugars with proteins, lipids, and nucleic acids, potentially altering their function by disrupting molecular conformation, promoting cross-linking, altering enzyme activity, reducing their clearance, and impairing receptor recognition. AGEs may also activate specific receptors, like the receptor for AGEs (RAGE), which is present on the surface of all cells relevant to atherosclerotic processes, triggering oxidative stress, inflammation and apoptosis. Understanding the pathogenic mechanisms of AGEs is paramount to develop strategies against diabetic and cardiovascular complications.