Immunological studies on peroxynitrite modified human DNA

Deciphering the anticancer, anti-inflammatory and antioxidant potential of Ti nanoparticles fabricated using Zingiber officinale

Rapid and sustainable green technology was implemented in the current study to fabricated Ti nanoparticles. The vegetable ginger with the scientific name Zingiber officinale was employed as a biological source in the fabrication process of nanoparticles. The optical, structural, morphological, and particle size of the fabricated Ti nanoparticles were characterized with the help of UV-visible absorption spectrum, FTIR (Fourier Transform Infrared) spectrum, SEM (Scanning Electron Microscope) analysis, DLS (Dynamic Light Scattering) technique and XRD (X-ray powder diffraction) crystallography technique. The presence of spherical-shaped Ti nanoparticles with an average particle size of 93 nm was confirmed based on these characterization techniques. The anti-cancer properties of the Z. officinale mediated Ti nanoparticles were analyzed through MTT assay against cell lines MCF-7 (Human breast adenocarcinoma cell line) and concentration-dependent anti-cancer properties were observed. The anti-inflammatory capacity of the Z. officinale mediated Ti nanoparticles were examined through protein denaturation and nitric oxide scavenging assay. The antioxidant capacity of the Z. officinale mediated Ti nanoparticles were examined through DPPH assay, hydrogen peroxide radical scavenging assay, hydroxyl radical scavenging assay, and FRAP (Ferric Reducing Antioxidant Power) analysis. The fabricated Ti nanoparticles exhibited anti-inflammatory and antioxidant capacity in a concentration-dependent pattern.

Molecular docking explores heightened immunogenicity and structural dynamics of acetaldehyde human immunoglobulin G adduct

Acetaldehyde is a metabolite of ethanol, an important constituent of tobacco pyrolysis and the aldehydic product of lipid peroxidation. Acetaldehyde induced toxicity is mainly due to its binding to cellular macromolecules resulting in the formation of stable adducts accompanied by oxidative stress. The aim of this study was to characterize structural and immunological alterations in human immunoglobulin G (IgG) modified with acetaldehyde in the presence of sodium borohydride, a reducing agent. The IgG modifications were studied by various physicochemical techniques such as fluorescence and CD spectroscopy, free amino group estimation, 2,2-azobis 2-amidinopropane (AAPH) induced red blood cell hemolysis as well as transmission electron microscopy. Molecular docking was also employed to predict the preferential binding of acetaldehyde to IgG. The immunogenicity of native and acetaldehyde-modified IgG was investigated by immunizing female New Zealand white rabbits using native and modified IgG as antigens. Binding specificity and cross reactivity of rabbit antibodies was screened by competitive inhibition ELISA and band shift assays. The modification of human IgG with acetaldehyde results in quenching of the fluorescence of tyrosine residues, decrease in free amino group content, a change in the antioxidant property as well as formation of cross-linked structures in human IgG. Molecular docking reveals strong binding of IgG to acetaldehyde. Moreover, acetaldehyde modified IgG induced high titer antibodies (>1:12800) in the experimental animals. The antibodies exhibited high specificity in competitive binding assay toward acetaldehyde modified human IgG. The results indicate that acetaldehyde induces alterations in secondary and tertiary structure of IgG molecule that leads to formation of neo-epitopes on IgG that enhances its immunogenicity.

Genotoxic effect and antigen binding characteristics of SLE auto-antibodies to peroxynitrite-modified human DNA

Systemic lupus erythematosus (SLE) is an inflammatory autoimmune disease characterized by auto-antibodies against native deoxyribonucleic acid after modification and is one of the reasons for the development of SLE. Here, we have evaluated the structural perturbations in human placental DNA by peroxynitrite using spectroscopy, thermal denaturation and high-performance liquid chromatography (HPLC). Peroxynitrite is a powerful potent bi-functional oxidative/nitrative agent that is produced both endogenously and exogenously. In experimental animals, the peroxynitrite-modified DNA was found to be highly immunogenic. The induced antibodies showed cross-reactions with different types of DNA and nitrogen bases that were modified with peroxynitrite by inhibition ELISA. The antibody activity was inhibited by approximately 89% with its immunogen as the inhibitor. The antigen-antibodies interaction between induced antibodies with peroxynitrite-modified DNA showed retarded mobility as compared to the native form. Furthermore, significantly increased binding was also observed in SLE autoantibodies with peroxynitrite-modified DNA than native form. Moreover, DNA isolated from lymphocyte of SLE patients revealed significant recognition of anti-peroxynitrite-modified DNA immunoglobulin G (IgG). Our data indicates that DNA modified with peroxynitrite presents unique antigenic determinants that may induce autoantibody response in SLE.

Nonenzymatic glycosylation of human serum albumin and its effect on antibodies profile in patients with diabetes mellitus

Background

Albumin glycation and subsequent formation of advanced glycation end products (AGEs) correlate with diabetes and associated complications.

Methods

Human Serum Albumin (HSA) was modified with D-glucose for a 40 day period under sterile conditions at 37°C. Modified samples along with native HSA (unmodified) were analyzed for structural modifications by UV and fluorescence, FTIR, Liquid chromatography mass spectrometry (LCMS) and X–ray crystallography. New-Zealand white female rabbits immunized with AGEs, represent auto-antibodies formation as assessed by competitive and direct binding enzyme-linked immunosorbent assay (ELISA). Neo-epitopesagainst In-vitro formed AGEs were characterized in patients with diabetes mellitus type 2 (n = 50), type 1 (n = 50), gestational diabetes (n = 50) and type 2 with chronic kidney disease (CKD) with eGFR level 60–89 mL/min (n = 50) from serum direct binding ELISA.

Results

Glycated-HSA showed amarked increase in hyperchromicity of 65.82%,71.98%, 73.62% and 76.63% at λ_{280 nm} along with anincreasein fluorescence intensity of 65.82%, 71.98%, 73.62% and 76.63% in glycated-HSA compared to native. FTIR results showed theshifting of Amide I peak from 1656 cm^_1 to 1659 cm^_1 and Amide II peak from 1554 cm^_1 to 1564 cm^_1 in glycated-HSA, with anew peak appearance of carbonyl group at 1737 cm-1. LCMS chromatogram of glycated-HSA showed thepresence of carboxymethyl lysine (CML) at 279.1 m/z. Immunological analysis showed high antibody titre>1:12,800 in theserum of rabbits immunized with glycated-HSA (modified with 400 mg/dL glucose) and inhibition of 84.65% at anantigen concentration of 20μg/mL. Maximum serum auto-antibody titre was found in T2DM (0.517±0.086), T1DM (0.108±0.092), GDM (0.611±0.041) and T2DM+CKD (0.096±0.25) patients immunized with glycated-HSA (modified with 400 mg/dL glucose).

Conclusions

Non-enzymatic glycosylation of HSA manifests immunological complications in diabetes mellitus due to change in its structure that enhances neo-epitopes generation.

Impact of anti-peroxynitrite-damaged-thymidine-monophosphate antibodies on disease activity in patients with systemic lupus erythematosus

Present study probes the role of peroxynitrite (ONOO(-))-modified thymidine-5'-monophosphate (TMP) in SLE patients with different disease activity scores according to the SLE Disease Activity Index (SLEDAI). Serum analysis showed significant increased number of subjects positive for anti-ONOO(-)-TMP-protein antibodies in SLE patients with different SLEDAI scores. Interestingly, the levels of these antibodies were significantly higher among SLE patients, whose SLEDAI scores were ≥20. In addition, a significant correlation was observed between the levels of anti-ONOO(-)-TMP-protein antibodies and the SLEDAI score (r = 0.595, p < 0.0001). In short, this study shows a positive association between anti-ONOO(-)-TMP-protein antibodies and SLEDAI. The stronger response observed in patients with higher SLEDAI scores suggests that anti-ONOO(-)-TMP-protein antibodies may be useful in evaluating the progression of SLE and in elucidating the mechanisms of disease pathogenesis.

Role of early glycation Amadori products of lysine-rich proteins in the production of autoantibodies in diabetes type 2 patients

In 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 50 mM 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.

Fructosylation generates neo-epitopes on human serum albumin

Hyperglycemia is the defining feature of diabetes mellitus. The persistently high levels of reducing sugars like glucose and fructose cause glycation of various macromolecules in the body. Human serum albumin (HSA), the most abundant serum protein with a myriad of functions, is prone to glycation and consequent alteration in its structural and biological properties. This study aimed to assess the role of fructose-modified human serum albumin as a marker of diabetic pathophysiology. We carried out modification of HSA with fructose and the changes induced were studied by various physicochemical studies. Fructose modified-HSA showed hyperchromicity in UV spectrum and increased AGE-specific fluorescence as well as quenching of tryptophan fluorescence. In SDS-PAGE protein aggregation was seen. Amadori products were detected by NBT. The fructose modified HSA had higher content of carbonyls along with perturbations in secondary structure as revealed by CD and FT-IR. A greater hydrodynamic radius of fructose-modified HSA was evident by DLS measurement. The fructose-modified HSA induced high titre antibodies in experimental animals exhibiting high specificity towards the immunogen.

Pathophysiological Role of Peroxynitrite Induced DNA Damage in Human Diseases: A Special Focus on Poly(ADP-ribose) Polymerase (PARP)

Peroxynitrite is formed in biological systems when nitric oxide and superoxide rapidly interact at near equimolar ratio. Peroxynitrite, though not a free radical by chemical nature, is a powerful oxidant which reacts with proteins, DNA and lipids. These reactions trigger a wide array of cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. The present review outlines the various peroxynitrite-induced DNA modifications with special mention to the formation of 8-nitroguanine and 8-oxoguanine as well as the induction of DNA single strand breakage. Low concentrations of peroxynitrite cause apoptotic death, whereas higher concentrations cause necrosis with cellular energetics (ATP and NAD(+)) serving as control between the two modes of cell death. DNA damage induced by peroxynitrite triggers the activation of DNA repair systems. A DNA nick sensing enzyme, poly(ADP-ribose) polymerase-1 (PARP-1) becomes activated upon detecting DNA breakage and it cleaves NAD(+) into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins. Over-activation of PARP induced by peroxynitrite consumes NAD(+) and consequently ATP decreases, culminating in cell dysfunction, apoptosis or necrosis. This mechanism has been implicated in the pathogenesis of various diseases like diabetes, cardiovascular diseases and neurodegenerative diseases. In this review, we have discussed the cytotoxic effects (apoptosis and necrosis) of peroxynitrite in the etiology of the mentioned diseases, focusing on the role of PARP in DNA repair in presence of peroxynitrite.

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.

Human DNA damage by the synergistic action of 4-aminobiphenyl and nitric oxide: an immunochemical study

4-Aminobiphenyl (4-ABP), an aromatic amine is a major environmental carcinogen found mainly in cigarette smoke. It has been vastly implicated in mutagenesis and cancer development. In this study, commercially available human placental DNA was exposed to 4-ABP (1.3 mM) in presence of sodium nitroprusside (SNP; 8 mM) at 37°C for 3 h. The 4-ABP + SNP-mediated structural changes in human DNA were studied by ultraviolet, circular dichroism and fluorescence spectroscopy, thermal melting profile, agarose gel electrophoresis, and nuclease S1 digestibility assay. Spectroscopical analysis and melting temperature studies suggest structural perturbations in the DNA as a result of modification. This might be due to generation of single-stranded regions and destabilization of hydrogen bonds. Modification was also visualized in agarose gel electrophoresis. Furthermore, nuclease S1 digestibility confirmed the generation of single strand breaks. Rabbits challenged with 4-ABP-SNP-modified human DNA-induced high-titer immunogen-specific antibodies, which showed Cross-reaction with modified/unmodified DNA bases and ss-DNA in competitive inhibition assay. The immunogen specificity of induced antibodies against 4-ABP-SNP-modified human DNA was further confirmed in gel retardation assay. It may be concluded that induction of anti-modified DNA antibodies could be due to perturbation in the DNA structure and its subsequent recognition by immunoregulatory cells as a foreign molecule.

Genotoxicity and immunogenicity of DNA-advanced glycation end products formed by methylglyoxal and lysine in presence of Cu2+

The highly reactive electrophile, methylglyoxal (MG), a break down product of carbohydrates, is a major environmental mutagen having potential genotoxic effects. Previous studies have suggested the reaction of MG with free amino groups of proteins forming advanced glycation end products (AGEs). This results in the generation of free radicals which play an important role in pathophysiology of aging and diabetic complications. MG also reacts with free amino group of nucleic acids resulting in the formation of DNA-AGEs. While the formation of nucleoside AGEs has been demonstrated previously, no extensive studies have been performed to assess the genotoxicity and immunogenicity of DNA-AGEs. In this study we report both the genotoxicity and immunogenicity of AGEs formed by MG-Lys-Cu(2+) system. Genotoxicity of the experimentally generated AGEs was confirmed by comet-assay. Spectroscopical analysis and melting temperature studies suggest structural perturbations in the DNA as a result of modification. This might be due to generation of single-stranded regions and destabilization of hydrogen bonds. Immunogenicity of native and MG-Lys-Cu(2+)-DNA was probed in female rabbits. The modified DNA was highly immunogenic eliciting high titre immunogen specific antibodies, while the unmodified form was almost non-immunogenic. The results show structural perturbations in MG-Lys-Cu(2+)-DNA generating new epitopes that render the molecule immunogenic.

Tomato ( Lycopersicon esculentum ) seeds: new flavonols and cytotoxic effect

In this study, seeds of Lycopersicon esculentum Mill. were analyzed by HPLC/UV-PAD/MS(n)-ESI. Fourteen flavonoids were identified, including quercetin, kaempferol, and isorhamnetin derivatives, with 13 of them being reported for the first time in tomato seeds. The major identified compounds were quercetin-3-O-sophoroside, kaempferol-3-O-sophoroside, and isorhamnetin-3-O-sophoroside. A significant cell proliferation inhibition (>80%), against rat basophile leukemia (RBL-2H3) cell line, was observed with this extract (IC(50) = 5980 microg/mL). For acetylcholinesterase inhibitory activity, a concentration-dependent effect was verified (IC(20) = 2400 microg/mL). The same behavior was noted regarding antioxidant capacity, evaluated against DPPH (IC(10) = 284 microg/mL), nitric oxide (IC(25) = 396 microg/L), and superoxide radicals (IC(25) = 3 microg/mL).

Biochemical and cellular toxicology of peroxynitrite: implications in cell death and autoimmune phenomenon

Reactive nitrogen species include nitric oxide (.NO), peroxynitrite (ONOO(-)) and nitrogen dioxide radical (NO2*). Peroxynitrite is a reactive oxidant, produced from nitric oxide (*NO) and superoxide anion (O(2*-), that reacts with a variety of biological macromolecules. It is produced in the body in response to physiological stress and environmental toxins. It is a potent trigger of oxidative protein and DNA damage-including DNA strand breakage and base modification. It activates the nuclear enzyme poly-ADP ribose polymerase (PARP) resulting in energy depletion and apoptosis/necrosis of cells. Peroxynitrite generation is a crucial pathological mechanism in stroke, diabetes, inflammation, neurodegeneration, cancer, etc. Peroxynitrite modified DNA may also lead to the generation of autoantibodies in various autoimmune disorders such as systemic lupus erythematosus (SLE). In chronic inflammatory diseases, peroxynitrite formed by phagocytic cells may cause damage to DNA, generating neoepitopes leading to the production of autoantibodies. Hence, understanding the pathophysiology of peroxynitrite could lead to important therapeutic interventions.

Hydroxyl radical modification of human serum albumin generated cross reactive antibodies

Hydroxyl radical-mediated in vitro modification of human serum albumin (HSA) showed 59.2% hyperchromicity at lambdamax, 30% loss of alpha helical structure and 71.4% loss of tryptophan fluorescence. The reactive oxygen species (ROS)-modified HSA was highly immunogenic in rabbits as compare to native HSA. The antibody binding was inhibited to the extent of 97% with the immunogen as inhibitor, indicating the induction of immunogen specific antibodies. Experimentally induced antibodies against modified HSA exhibited diverse antigen binding characteristics. Native plasmid DNA, ROS-modified plasmid DNA and ROS-chromatin were found to be an effective inhibitor of induced antibody-immunogen interaction. Induced antibodies against native HSA showed negligible binding to the above mentioned nucleic acid antigens. Band shift assay reiterated the recognition towards nucleic acid antigens. Thus, the induced antibodies against *OH modified HSA resembled the diverse antigen-binding characteristics of naturally occurring systemic lupus erythematosus (SLE) anti-DNA autoantibodies.

Preferential recognition of Amadori-rich lysine residues by serum antibodies in diabetes mellitus: role of protein glycation in the disease process

This study analyzes effect of glycation on proteins rich in lysine residues as hyperglycemia induced protein glycation has been mainly reported in diabetes mellitus at the intrachain lysine residues leading to the formation of Amadori modified proteins. We have studied the effect of glucose on poly-l-lysine (PLL), a homopolymer of lysine residues. Levels of Amadori products in the glycated PLL were evaluated by fructosamine assay and the presence of 5-hydroxymethylfurfural (HMF) in the glycated PLL was analyzed by thiobarbituric acid assay. Fluorescence and FT-IR spectroscopy were applied to characterize the modified PLL. Binding characteristics of experimentally induced antibodies against glycated PLL and the presence of antibodies against glycated PLL in the sera of diabetes patients was evaluated by solid phase enzyme immunoassays. The fructosamine assay showed significantly high yield of early glycation (Amadori) products in the glycated PLL, which was confirmed by increased yield of HMF from Amadori products of glycated PLL. Loss in fluorescence intensity and appearance of a new band corresponding to Amadori products were observed in FT-IR spectrum of the glycated PLL. Glycated PLL was found to be highly immunogenic in rabbits as compared to the native form. Serum antibodies from diabetes patients showed appreciably high recognition of the glycated PLL. The results conclusively show the glycation induced damage to the lysine molecules and specific recognition of Amadori-lysine residues by serum antibodies from diabetes patients. The glycated lysine residues may serve as a diagnostic biomarker for early glycation process in diabetes mellitus.

Tronchuda cabbage (Brassica oleracea L. var. costata DC): scavenger of reactive nitrogen species

The ability of tronchuda cabbage ( Brassica oleracea L. var. costata DC) to act as a scavenger of the reactive nitrogen species nitric oxide and peroxynitrite was investigated. The aqueous extracts obtained from tronchuda cabbage seeds and from its external and internal leaves exhibited a concentration dependent scavenging capacity. The antioxidant potential observed against the two reactive species was as follows: seeds > external leaves > internal leaves. In order to establish a possible correlation with the chemical composition of the extracts, the activity of ascorbic and sinapic acids and kaempferol 3- O-rutinoside was also studied. Among the compounds tested, sinapic acid showed the strongest antioxidant activity against both species.

Enhanced recognition of reactive oxygen species damaged human serum albumin by circulating systemic lupus erythematosus autoantibodies

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with autoantibodies as a near universal feature of the disease. Earlier investigations from our laboratory revealed increased oxidative damage in SLE patients. Therefore, we hypothesized that oxidative by-products, such as hydroxyl radical (*OH), could lead to neoantigens like *OH damaged human serum albumin (HSA), which could in turn initiate autoimmunity in SLE. In the present study, the binding characteristics of SLE autoantibodies with native and *OH damaged HSA were assessed. SLE patients (n = 74) were examined by direct binding ELISA and the results were compared with healthy age- and sex-matched controls (n = 44). High degree of specific binding by 52.7% of patients sera towards *OH damaged HSA, in comparison to its native analogue (p < 0.05) was observed. Normal human sera showed negligible binding with either antigen. Competitive ELISA and gel retardation assays reiterate the direct binding results. The increase in total serum protein carbonyl levels in the SLE patients was largely due to an increase in oxidized albumin. HSA of SLE patients (SLE-HSA) and normal subjects (normal-HSA) were purified. Spectroscopic analysis confirmed that the SLE-HSA samples contained higher levels of carbonyls than normal-HSA (p < 0.01). SLE-HSA was conformationally altered, with more exposure of its hydrophobic regions. Collectively, the oxidation of plasma proteins, especially HSA, might enhance oxidative stress in SLE patients.

Peroxynitrite: biochemistry, pathophysiology and development of therapeutics

Peroxynitrite--the product of the diffusion-controlled reaction of nitric oxide with superoxide radical--is a short-lived oxidant species that is a potent inducer of cell death. Conditions in which the reaction products of peroxynitrite have been detected and in which pharmacological inhibition of its formation or its decomposition have been shown to be of benefit include vascular diseases, ischaemia-reperfusion injury, circulatory shock, inflammation, pain and neurodegeneration. In this Review, we first discuss the biochemistry and pathophysiology of peroxynitrite and then focus on pharmacological strategies to attenuate the toxic effects of peroxynitrite. These include its catalytic reduction to nitrite and its isomerization to nitrate by metalloporphyrins, which have led to potential candidates for drug development for cardiovascular, inflammatory and neurodegenerative diseases.

Binding Characteristics of SLE Anti-DNA Autoantibodies to Catecholestrogen-modified DNA

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease in which anti-double-stranded DNA antibody is a classic autoantibody that characterizes SLE. A role for oestrogens in the pathogenesis of SLE has been suspected for many years but the exact patho-aetiology remains elusive. In this study, the binding of SLE autoantibodies with native and 4-OHE(2)-NO-modified plasmid DNA were assessed. Binding specificity of antibodies was analysed by direct binding and inhibition enzyme-linked immunosorbent assay, quantitative precipitin titration and gel retardation assay. Anti-DNA IgG from SLE sera, purified on Protein A-Agarose matrix, exhibited increased recognition of 4-OHE(2)-NO-DNA than native DNA (P < 0.001). Gel retardation assay further substantiated the enhanced recognition of modified DNA by anti-DNA autoantibodies. The affinity of anti-DNA antibodies for modified polymer was found to be high as calculated by using Langmuir plot. DNA modified by 4-OHE(2)-NO presents unique neo-epitopes that might be one of the factor in antigen-driven induction of SLE autoantibodies.

Reactive oxygen species damaged human serum albumin in patients with type 1 diabetes mellitus: biochemical and immunological studies

The role of hydroxyl radical (.OH) damaged human serum albumin (HSA) in type 1 diabetes has been investigated in the present study. Hydroxyl radical induced modification on HSA has been studied by UV absorption spectroscopy, ANS fluorescence and carbonyl estimation. Hydroxyl radical modified HSA was found to be highly immunogenic in rabbits as compared to native HSA. The binding characteristics of circulating autoantibodies in type 1 diabetes patients against native and modified HSA were assessed. Diabetes patients (n=31) were examined by direct binding ELISA and the results were compared with healthy age-matched controls (n=22). High degree of specific binding by 54.8% of patients sera towards .OH modified HSA, in comparison to its native analogue (p<0.05) was observed. Sera from those type 1 diabetes patients having smoking history, high aging with high degree of disease showed substantially stronger binding to .OH modified HSA over native HSA in particular. Normal human sera showed negligible binding with either antigen. Competitive inhibition ELISA reiterates the direct binding results. Gel retardation assay further substantiated the enhanced recognition of modified HSA by circulating autoantibodies in diabetes patients. The increase in total serum protein carbonyl levels in the diabetes patients was largely due to an increase in oxidized albumin. HSA of diabetes mellitus patients (DM-HSA) and normal subjects (normal-HSA) were purified on a Sephacryl S-200 HR column. Spectroscopic analysis confirmed that the DM-HSA samples contained higher levels of carbonyls than normal-HSA (p<0.001). DM-HSA was conformationally altered, with more exposure of its hydrophobic regions. Collectively, the oxidation of plasma proteins, especially HSA, might enhance oxidative stress in type 1 diabetes mellitus patients.