Abdul Rouf Mir

Methylglyoxal mediated conformational changes in histone H2A—generation of carboxyethylated advanced glycation end products

Methylglyoxal, an oxo-aldehyde has been implicated as a potential precursor in non enzymatic glycation reactions. Its role in the modification of extra cellular proteins has been extensively reported, but little is known about its modification of nuclear proteins, like histones. Here, we report the methylglyoxal induced modification of histone H2A which forms an essential part of intact core nucleosome. In this study commercially available histone H2A was subjected to in vitro non-enzymatic glycation by methylglyoxal. The structural alterations in the histone were characterised by various biophysical and biochemical techniques. The modified histone showed hyperchromicity at 276nm, loss in intrinsic tyrosine fluorescence intensity at 305nm along with a red shift, cross linking and dimer formation in SDS PAGE, induction of α-helix in CD spectroscopy, reduced hydrophobicity in ANS binding studies, accumulation of AGE products, increased carbonyl content, and appearance of a novel peak showing carboxyethylation complemented by a shift in amide I and amide II bands in ATR-FTIR spectroscopy. The modified histone exhibited increased melting temperatures (Tm) and enhanced heat capacities (Cp) in differential scanning calorimetric analysis. The results suggest that methylglyoxal significantly altered the structure of the nuclear histone H2A by non enzymatic glycation reaction. The conformational changes in histone H2A may influence the chromatin integrity which may have implications in various pathological conditions.

Structural changes in histone H2A by methylglyoxal generate highly immunogenic amorphous aggregates with implications in auto-immune response in cancer

The role of aberrant protein modifications in cancer and its diagnosis have emerged as a promising research field. Nonenzymatic glyco-oxidation of proteins under oxidative stress has been associated with carcinogenesis through advanced glycation end products (AGE)-receptors for advanced glycation end products (RAGE) axis. Modified proteins that are immunogenic and stimulate cellular and humoral immune responses are being studied to develop early detection markers of cancer. This study has probed the structural alternations; leading to the formation of adducts and aggregates, in histone H2A upon in vitro modification by methylglyoxal (MG). The immunogenicity of modified histone H2A and its binding with cancer autoantibodies was also assessed. MG induced lysine side chain modifications, blocking of free amino groups and the formation of condensed cross structures in histone H2A; and its effect was inhibited by carbonyl scavengers. It led to the adduct formation and generation of N-epsilon-(carboxyethyl)lysine (CEL) and its decomposition forms as revealed by Matrix-assisted laser desorption ionization-mass spectrometry, high-performance liquid chromatography and LC-MS. MG-H2A showed amorphous aggregate formation under electron microscopy and altered binding with DNA in circular dichroism studies. The modified histone elicited high titer immunogen-specific antibodies in rabbits when compared with the native, thus pointing toward the generation of neo-epitopes in MG-H2A. The autoantibodies derived from cancer patients exhibited enhanced binding with MG-H2A as compared with the native histone in enzyme-linked immunosorbent assay and gel retardation assay. This reflects sharing of epitopes on MG-H2A and histones in cancer patients. The neo-epitopes on H2A may be responsible for induction and elevated levels of antibodies in cancer patients. Thus, MG-H2A may be considered as potential antigenic candidate for auto-immune response in cancer.

Immunochemical studies on HNE-modified HSA: Anti-HNE-HSA antibodies as a probe for HNE damaged albumin in SLE.

Non-enzymatic lipid peroxidation of cellular membranes occurs during periods of sustained oxidative stress. 4-Hydroxynonenal (HNE), the most reactive lipid peroxidation product, is capable of modifying and/or cross-linking proteins leading to impaired physiological functions. The formation of protein adducts produce structural modifications which generate neo-antigens and induce auto-antibodies. Enhanced oxidative stress and accumulation of HNE-modified proteins are associated with systemic lupus erythematosus (SLE) and other autoimmune diseases. This study has probed the role of lipid peroxidation derived aldehydes in SLE. We report the structural perturbations in human serum albumin (HSA) upon modification with HNE and the consequential enhanced immunogenicity. The induced antibodies were found to be highly specific for the immunogen and exhibited cross-reactivity with HNE-modified epitopes on proteins, amino acids and nucleic acid. The experimentally induced anti-HNE-HSA antibodies appreciably recognized HNE modified epitopes on the HSA obtained from SLE patients. These antibodies, therefore, form a good immunochemical probe to detect such damages in lupus patients. Possible role of anti-HNE-HSA antibodies as a marker for detection/progression of SLE has been discussed.

Glycoxidation of histone proteins in autoimmune disorders

Post translational modifications (PTMs) alter the characteristic properties of proteins by influencing the spatial orientation of amino acid residues leading to a variety of pathological complications. Among the large number of PTMs, much attention has focused on non-enzymatic glycation and oxidation of proteins that form advanced glycation end products and generate autoantibodies. Histone proteins are essential components of chromatin structure and have role in its higher order structural formation. They have abundance of lysine and arginine residues and thus are prone to glyoxidation reactions. Glyoxidation causes structural alterations in histones and consequently leads to a variety of modifications in their amino acid sequence and the secondary and tertiary structure producing new antigenic determinants that may result in cause an aggressive autoimmune response. Here we review and evaluate the field of histone glyoxidation and its role in autoimmune disorders. We explore their structural alterations and immunogenicity of histones after glycation and oxidation reactions, and their role in autoimmune disease such as systemic lupus erythematosus, rheumatoid arthritis and diabetes.

Role of Early Glycation Amadori Products of Lysine-Rich Proteins in the Production of Autoantibodies in Diabetes Type 2 Patients

AbstractIn diabetes, protein glycation mostly occurs at intrachain lysine residues resulting in the formation of early stage Amadori products which are finally converted to advance glycation end products (AGEs). Several studies have reported autoantibodies against AGEs in diabetes but not much data are found in respect of Amadori products. In this study, poly-l-lysine (PLL) was glycated with 50xa0mM glucose and the resultant Amadori products were estimated by fructosamine or nitroblue tetrazolium assay. We report high content of Amadori products in PLL upon glycation. Glycated PLL showed marked hyperchromicity in the UV spectrum, ellipticity changes in CD spectroscopy, and variations in ε-methylene protons shift in NMR. It was better recognized by autoantibodies in type 2 diabetics compared to the native PLL. Induced antibodies against glycated PLL were successfully used to probe early glycation in the IgG isolated from diabetes type 2 patients. Role of Amadori products of glycated proteins in the induction of autoantibodies in type 2 diabetes as well as in associated secondary complications has been discussed.n

Dicarbonyl Induced Structural Perturbations Make Histone H1 Highly Immunogenic and Generate an Auto-Immune Response in Cancer.

Increased oxidative stress under hyperglycemic conditions, through the interaction of AGEs with RAGE receptors and via activation of interleukin mediated transcription signalling, has been reported in cancer. Proteins modifications are being explored for their roles in the development and progression of cancer and autoantibody response against them is gaining interest as a probe for early detection of the disease. This study has analysed the changes in histone H1 upon modification by methylglyoxal (MG) and its implications in auto-immunopathogenesis of cancer. Modified histone showed modifications in the aromatic residues, changed tyrosine microenvironment, intermolecular cross linking and generation of AGEs. It showed masking of hydrophobic patches and a hypsochromic shift in the in ANS specific fluorescence. MG aggressively oxidized histone H1 leading to the accumulation of reactive carbonyls. Far UV CD measurements showed di-carbonyl induced enhancement of the alpha structure and the induction of beta sheet conformation; and thermal denaturation (Tm) studies confirmed the thermal stability of the modified histone. FTIR analysis showed amide I band shift, generation of a carboxyethyl group and N-Cα vibrations in the modified histone. LCMS analysis confirmed the formation of Nε-(carboxyethyl)lysine and electron microscopic studies revealed the amorphous aggregate formation. The modified histone showed altered cooperative binding with DNA. Modified H1 induced high titre antibodies in rabbits and the IgG isolated form sera of rabbits immunized with modified H1 exhibited specific binding with its immunogen in Western Blot analysis. IgG isolated from the sera of patients with lung cancer, prostate cancer, breast cancer and cancer of head and neck region showed better recognition for neo-epitopes on the modified histone, reflecting the presence of circulating autoantibodies in cancer. Since reports suggest a link between AGE-RAGE axis and carcinogenesis, glycoxidation of histone H1 and its immunogenicity paves ways for understanding role of glycoxidatively damaged nuclear proteins in cancer.

Circulating autoantibodies in cancer patients have high specificity for glycoxidation modified histone H2A.

BACKGROUNDnNovel immunological epitopes upon glyoxidation modified proteins have been discovered and multi-specific natural antibodies against them have been identified. The association of glyoxidation with cancer has also been reported. We probed the link of glyoxidation of histone H2A with autoimmune response in cancer.nnnMETHODSnWe report the formation of thermo stable amorphous aggregate formation in histone H2A upon methylglyoxal modification using circular dichroism (CD) analysis and transmission electron microscopy.nnnRESULTSnThe modified histone was found to be highly immunogenic that generates specific immune response in rabbits as analysed by cross reaction studies by competitive ELISA and Western blotting technique. The anti-methylglyoxal modified H2A antibodies were found in the circulating autoantibodies in various types of cancer patients by immunosorbent assay and gel retardation studies. The results clearly indicate the formation of highly specific antibodies in cancer patients against glyoxidation modified histone H2A with cross reactive tendencies with other glycated proteins and nucleic acids.nnnCONCLUSIONSnThe results are important because a link between AGE-RAGE axis (Advanced glycation end products and Receptors for AGEs) and carcinogenesis is emerging and the role of glyoxidation of proteins is expected in the development of biomarkers for the early detection of cancer.

Studies on glycoxidatively modified human IgG: Implications in immuno-pathology of type 2 diabetes mellitus

Structural rearrangements and condensations of proteins under hyperglycemic stress have been implicated in various pathological disorders. This study aims to probe the role of methylglyoxal (MG) modified human immunoglobulin G (MG-IgG) in immuno-pathology of type 2 diabetes mellitus (T2DM). MG was found to perturb the structural integrity of IgG, affect its aromatic micro-environment and cause the generation of advanced glycation end products (AGEs) and aggregate adducts. It liberated the hydrophobic pockets of the protein, reduced its β pleated sheet structure and affected its tertiary conformation. Transition from β sheet to α helix and random coil was also observed in IgG upon modification by MG. It acted with strong oxidative potential and caused oligomerisation and disordered or amorphous type aggregation in the modified protein. Modified IgG had a cytotoxic and genotoxic impact. The MG modified IgG presented novel antigenic determinants that lead to an aggressive immune response. The antibodies had high affinity towards the immunogen. Auto-antibodies derived from T2DM patients exhibited strong affinity towards the modified IgG in comparison to the unmodified protein. Specificity of serum antibodies from T2DM patients was further confirmed by competitive-inhibition ELISA. The potential role of MG-IgG in the immunopathogenesis of T2DM has been discussed.

Neo-epitopes on methylglyoxal modified human serum albumin lead to aggressive autoimmune response in diabetes

Glyco-oxidation of proteins has implications in the progression of diabetes type 2. Human serum albumin is prone to glyco-oxidative attack by sugars and methylglyoxal being a strong glycating agent may have severe impact on its structure and consequent role in diabetes. This study has probed the methylglyoxal mediated modifications of HSA, the alterations in its immunological characteristics and possible role in autoantibody induction. We observed an exposure of chromophoric groups, loss in the fluorescence intensity, generation of AGEs, formation of cross-linked products, decrease in α-helical content, increase in hydrophobic clusters, FTIR band shift, attachment of methylglyoxal to HSA and the formation of N(ε)-(carboxyethyl) lysine in the modified HSA, when compared to the native albumin. MG-HSA was found to be highly immunogenic with additional immunogenicity invoking a highly specific immune response than its native counterpart. The binding characteristics of circulating autoantibodies in type 2 diabetes mellitus (DM) patients showed the generation of anti-MG-HSA auto-antibodies in the these patients, that are preferentially recognized by the modified albumin. We propose that MG induced structural perturbations in HSA, result in the generation of neo-epitopes leading to an aggressive auto-immune response and may contribute to the immunopathogenesis of diabetes type 2 associated complications.

Peroxynitrite modified DNA presents better epitopes for anti-DNA autoantibodies in diabetes type 1 patients.

Peroxynitrite (ONOO(-)), formed by the reaction between nitric oxide (NO) and superoxide (O2(-)), has been implicated in the etiology of numerous disease processes. Peroxynitrite interacts with DNA via direct oxidative reactions or via indirect radical-mediated mechanism. It can inflict both oxidative and nitrosative damages on DNA bases, generating abasic sites, resulting in the single strand breaks. Plasmid pUC 18 isolated from Escherichiacoli was modified with peroxynitrite, generated by quenched flow process. Modifications incurred in plasmid DNA were characterized by ultraviolet and fluorescence spectroscopy, circular dichroism, HPLC and melting temperature studies. Binding characteristics and specificity of antibodies from diabetes patients were analyzed by direct binding and inhibition ELISA. Peroxynitrite modification of pUC 18 plasmid resulted in the formation of strand breaks and base modification. The major compound formed when peroxynitrite reacted with DNA was 8-nitroguanine, a specific marker for peroxynitrite induced DNA damage in inflamed tissues. The concentration of 8-nitroguanine was found to be 3.8 μM. Sera from diabetes type 1 patients from different age groups were studied for their binding to native and peroxynitrite modified plasmid. Direct binding and competitive-inhibition ELISA results showed higher recognition of peroxynitrite modified plasmid, as compared to the native form, by auto-antibodies present in diabetes patients. The preferential recognition of modified plasmid by diabetes autoantibodies was further reiterated by gel shift assay. Experimentally induced anti-peroxynitrite-modified plasmid IgG was used as a probe to detect nitrosative lesions in the DNA isolated from diabetes patients.