Acquired immunogenicity of human DNA damaged by N-hydroxy-N-acetyl-4-aminobiphenyl

Identification of Glycoxidative Lesion in Isolated Low-Density Lipoproteins from Diabetes Mellitus Subjects

Methylglyoxal (MG) is a precursor for advanced glycation end-products (AGEs), which have a significant role in diabetes. The present study is designed to probe the immunological response of native and glycated low-density lipoprotein (LDL) in experimental animals. The second part of this study is to probe glycoxidative lesion detection in low-density lipoproteins (LDL) in diabetes subjects with varying disease duration. The neo-epitopes attributed to glycation-induced glycoxidative lesion of LDL in DM patients' plasma were, analyzed by binding of native and MG-modified LDL immunized animal sera antibodies using an immunochemical assay. The plasma purified human LDL glycation with MG, which instigated modification in LDL. Further, the NewZealand-White rabbits were infused with unmodified natural LDL (N-LDL) and MG-glycatedLDL to probe its immunogenicity. The glycoxidative lesion detection in LDL of DM with disease duration (D.D.) of 5-15 years and D.D. > 15 years was found to be significantly higher as compared to normal healthy subjects (NHS) LDL. The findings support the notion that prolonged duration of diabetes can cause structural alteration in LDL protein molecules, rendering them highly immunogenic in nature. The presence of LDL lesions specific to MG-associated glycoxidation would further help in assessing the progression of diabetes mellitus.

4-Chloro-orthophenylenediamine alters DNA integrity and affects cell survival: inferences from a computational, biophysical/biochemical, microscopic and cell-based study

The deleterious impact of toxic constituents of hair dyes over the human health has gained immense attention in the recent past. Their oncogenicity, mutagenicity, role in protein modification, impact on cellular metabolism has been documented. There is little information on the mechanism of reactivity of hair dye components with the nucleic acids and its implications. This work, therefore, uses computational, biophysical/biochemical, microscopic and cell-based study to analyze the interaction of monocyclic aromatic amine and a hair dye component, 4-chloro-orthophenylenediamine (4-Cl-OPD) with the DNA, its impact on DNA structure and cell survival. The results suggest that 4-Cl-OPD binds with the DNA in minor groove of the duplex involving three base pairs preferentially the G-C residues, induces strand breaks and makes DNA thermally labile through loss of hydrogen bonding/base unstacking. 4-Cl-OPD causes fragmentation of DNA, reduction in size of the molecule, alters B-DNA conformation and disrupts its secondary structure. The modified DNA gives fragmented appearance, shows broken strands and aggregation in ultra-structural analysis. 4-Cl-OPD induces ROS generation in lymphocytes, increases the comet's average tail length and reduces the viability of lymphocytes. This study forms a base for establishing the direct toxicity of 4-Cl-OPD at the molecular and cellular level through direct production of superoxide radicalCommunicated by Ramaswamy H. Sarma.

N-OH-AABP Modifications in Human DNA May Lead to Auto-Antibodies in Bladder Cancer Subjects

4-Aminobiphenyl (4-ABP) and other related arylamines have emerged to be responsible for human urinary bladder tumors and cancers. Hemoglobin-ABP adducts have been recognized in the blood of smokers, and it builds up in the circulatory system over the period of years that might lead to a bladder tumor. N-hydroxy-Acetyl 4-Aminobiphenyl (N-OH-AABP) is one of the reactive forms of 4-ABP which has a potential to initiate tumor growth and causes cancer rapidly. In the present study, commercially available human DNA was modified by N-OH-AABP, and its modifications were analyzed biophysically from fluorescence spectroscopy and thermal denaturation studies. Further, Sera and IgG from bladder cancer patients’ blood were assessed for affinity to native and N-OH-AABP modified human DNA using ELISA. The study showed N-OH-AABP caused damage in the structure of the DNA macromolecule and the perturbations resulting from damage leads to change in the Tm of the DNA molecule. Bladder cancer auto-antibodies, particularly in smoker group, showed preferential binding to N-OH-AABP modified human DNA. This study shows that N-OH-AABP modified DNA could be an antigenic stimulus for the generation of autoantibodies in the sera of bladder cancer patients.

Rosmarinic acid inhibits DNA glycation and modulates the expression of Akt1 and Akt3 partially in the hippocampus of diabetic rats

Non-enzymatic glycation of DNA and the associated effects are among pathogenic factors in diabetes mellitus. Natural polyphenols have anti-diabetic activity. Herein, the protective role of one of the phytochemicals, rosmarinic acid (RA), was evaluated in glycation (with fructose) of human DNA and expression of Akt genes in the hippocampus of diabetic rats. In-vitro studies using fluorescence, agarose gel electrophoresis, fluorescence microscopy, and thermal denaturation analyses revealed that glycation causes DNA damage and that RA inhibits it. In-vivo studies were performed by induction of diabetes in rats using streptozotocin. The diabetic rats were given RA daily through gavage feeding. The expression of Akt genes (inhibitors of apoptosis) in the hippocampus was evaluated using RT-qPCR. In diabetic rats, Akt1 and Akt3 were significantly down-regulated compared to the control group. Treating the diabetic rats with RA returned the expression of Akt1 and Akt3 relatively to the normal condition. Past studies have shown that diabetes induces apoptosis in the hippocampal neurons. Given that glycation changes the genes expression and causes cell death, apoptosis of the hippocampal neurons can be due to the glycation of DNA. The results also suggest that RA has reliable potency against the gross modification of DNA under hyperglycemic conditions.

Measurement of Advanced Glycation End Products Could Be Used as an Indicator of Unhealthy Nutrition for Colorectal Cancer Risk

The main culprit behind most cancers is the accumulation of reactive oxygen species. Glyoxal (GO) and methylglyoxal (MGO) are reactive intermediates created by food processing and they are precursors of advanced glycation end products (AGE) that cause glycative stress. We aimed to evaluate the relationship between AGE levels of healthy volunteers and treatment-naive patients diagnosed with colorectal cancer. The study consisted of patients diagnosed with colorectal cancer and healthy volunteers who underwent routine colonoscopy. The study was conducted with a total of 42 cases, 47.6% (n = 20) female. The ages of the participants in the study ranged from 41 to 82 years, and the mean was 60.57 ± 10.78 years. The GO and MGO values of the patient group were found to be significantly higher than those of the control group (p = 0.007, p = 0.001, respectively). The risk of colorectal cancer was 22 and 57 times higher in individuals with GO and MGO values above 1.25 μg/mL and 0.0095 μg/mL, respectively. The blood AGE level is closely related to diet, and it can be decreased through the appropriate improvement of diet. Thus, the measurement of AGE can be used to predict whether a person's nutrition is healthy or unhealthy and prevent increased risk of colorectal cancer.

Methylglyoxal mediated glycation leads to neo-epitopes generation in fibrinogen: Role in the induction of adaptive immune response

In diabetes mellitus, hyperglycemia mediated non-enzymatic glycosylation of proteins results in the pathogenesis of diabetes-associated secondary complications via the generation of advanced glycation end products (AGEs). The focus of this study is to reveal the immunological aspects of methylglyoxal (MG) mediated glycation of fibrinogen protein. The induced immunogenicity of modified fibrinogen is analyzed by direct binding and inhibition ELISA. Direct binding ELISA confirmed that MG glycated fibrinogen (MG-Fib) is highly immunogenic and induces a high titer of antibodies in comparison to its native analog. Cross-reactivity and antigen-binding specificity of induced antibodies were confirmed by inhibition ELISA. The enhanced affinity of immunoglobulin G (IgG) from immunized rabbits' sera and MG glycated fibrinogen is probably the aftermath of neo-epitopes generation in the native structure of protein upon modification. Thus, we deduce that under the glycative stress, MG-mediated structural alterations in fibrinogen could induce the generation of antibodies which might serve as a potential biomarker in diabetes mellitus and its associated secondary disorders.

Lycopene Triggers Nrf2-AMPK Cross Talk to Alleviate Atrazine-Induced Nephrotoxicity in Mice

Atrazine (ATR), an environmental persistent and bioaccumulative herbicide, has been associated with environmental nephrosis. Lycopene (LYC) exhibits important properties of nephroprotection, but there are limited data on the specific underlying mechanism. The primary objective of this study was to explore the therapeutic effect of LYC on ATR-induced nephrotoxicity in mice. The mice were divided randomly into 6 groups and treated as follows: control group (C), 5 mg/kg LYC group (L), 50 mg/kg ATR group (A1), 200 mg/kg ATR group (A2), 50 mg/kg ATR plus 5 mg/kg LYC group (A1+L), and 200 mg/kg ATR plus 5 mg/kg LYC group (A2+L) by oral gavage administration for 21 days. We found that pretreatment with LYC significantly suppressed the ATR-induced renal tubular epithelial cell swelling. Furthermore, LYC mitigated ATR-induced dysregulation of oxidative stress markers by reducing MDA, H₂O₂ levels, and increasing SOD, GPx, CAT concentration, and Nrf2 activation. Moreover, LYC activated the autophagic flux by a detectable change in autophagy-related genes (Beclin-1 and ATGs) and proteins (p62/SQSTM) and by the formation of autophagic vacuole (AV) and LC3 aggregation, in parallel with AMPK activation (pAMPK/AMPK). Herein, ATR-up-regulated nuclear factor erythroid 2-related factor 2 (Nrf2) expression and Nrf2-regulated redox genes, including quinoneoxidoreductase-1 (NQO1) and heme oxidase-1 (HO1), whereas LYC down-regulated those of the above genes. In addition, LYC suppressed ATR-induced activation of autophagy (increased LC3II/LC3I, ATGs, Beclin1, and p62, in parallel with increased AMPK activation). Collectively, our findings identified a cross talk between AMPK-activated autophagy and the Nrf2 signaling pathway in LYC-mediated nephroprotection against ATR-induced toxicity in mice kidney.

Glycation of hemoglobin leads to the immunogenicity as a result of neo-epitope generation

Non-enzymatic glycation occurs rapidly which ultimately leads to the formation of advanced glycation endproducts (AGEs). These AGEs have shown to associated with the development of many diseases such as diabetes-mellitus. This study is focused on immunological characterization of glycated-Hb induced by d-ribose. Here, we analysed the immunogenicity of glycated-Hb by direct binding and competitive inhibition ELISA. Direct binding ELISA confirmed that glycated-Hb was highly immunogenic and induced high titre antibodies as compared to native-Hb. The antigen binding specificity and cross reactivity of these antibodies were also screened by competitive inhibition ELISA. The IgG from rabbit sera showed enhanced binding of glycated-Hb than native-Hb. Thus, it is possible that alterations in Hb induced by d-ribose could have generated highly immunogenic neoepitopes. Moreover, induced antibodies were also found to cross-react with other modified/native proteins. On the basis of the results of this study, we presume that this type of structural perturbations in Hb in vivo by d-ribose might take place in untreated diabetic condition that could induce such type of immunogenic auto-antibodies. Furthermore, increased level of these auto-antibodies could serve as a biomarker in diabetes and its progression.

Immuno-chemistry of hydroxyl radical modified GAD-65: A possible role in experimental and human diabetes mellitus

The repertoire of known auto-antigens is limited to a very small proportion of all human proteins, and the reason why only some proteins become auto-antigens is unclear. The 65 kDa isoform of the enzyme glutamic acid decarboxylase (GAD-65) is a major auto-antigen in type I diabetes, and in various neurological diseases. Most patients with type I diabetes (70-80%) have auto-antibodies against GAD-65, which often appear years before clinical onset of the autoimmune diabetes. Thus, the aim of the study is to focus on the immunogenicity of GAD65 and its reactive oxygen species (ROS) conformer in STZ-induced diabetic rats and on human diabetic patients. In the present study, GAD-65 was modified by hydroxyl radical following Fenton's reaction. The modifications in the structure of the GAD-65 are supported by UV-vis and fluorescence spectral studies. Immunogenicity of both native and hydroxyl radical modified GAD-65 (ROS-GAD-65) was studied in experimental rabbits and was confirmed by inducing type I diabetes in experimental male albino rats using streptozotocin (45 mg/kg). We found that ROS-GAD-65 was a better immunogen as compared to the native GAD-65. A considerable high binding to ROS-GAD-65 was observed as compared to native GAD-65 in both the serum antibodies from diabetes animal models and as well as in the serum samples of type I diabetes. Hydrogen peroxide under the exposure of UV light produces hydroxyl radical (·OH) which is most potent oxidant, and could cause protein damage (GAD-65) to the extent of generating neo-epitopes on the molecule, thus making it immunogenic.

Lycopene powers the inhibition of glycation-induced diabetic nephropathy: a novel approach to halt the AGE-RAGE axis menace

There are accumulating evidences suggesting that interaction between advanced glycation end products (AGEs) and their receptors (RAGEs) induces oxidative stress and subsequently encourages inflammatory reactions, thereby resulting in progressive alteration in renal architecture and function. Interventions that reduce the tissue burden of AGEs have yielded significant positive results in inhibiting the progression of diabetic complications such as diabetic nephropathy. Lycopene, a carotenoid, plays an important role in protection against oxidative stress and hence might prove an efficient antiglycating agent. Current study investigates the effect of lycopene in downregulating the menace caused by ribose-induced glycation both in vitro and in vivo. We observed that treatment with lycopene decelerated the ribose induced AGE formation in HK-2 cells and in rat kidneys thereby downregulating the expression RAGE. HK-2 cells with decreased levels of RAGE showed a decline in nuclear factor κB (NFκB) and matrix metalloproteinase 2 (MMP 2) expressions. Administration of ribose not only induced hyperglycemia in Wistar rats but also developed diabetic nephropathy (DN). However, lycopene was found effective in relieving the biochemical symptoms of DN. Thus lycopene provides protection against development of diabetic nephropathy and ameliorates renal function by halting AGE-RAGE axis.

Glycation of H1 Histone by 3-Deoxyglucosone: Effects on Protein Structure and Generation of Different Advanced Glycation End Products

Advanced glycation end products (AGEs) culminate from the non-enzymatic reaction between a free carbonyl group of a reducing sugar and free amino group of proteins. 3-deoxyglucosone (3-DG) is one of the dicarbonyl species that rapidly forms several protein-AGE complexes that are believed to be involved in the pathogenesis of several diseases, particularly diabetic complications. In this study, the generation of AGEs (N^ε-carboxymethyl lysine and pentosidine) by 3-DG in H1 histone protein was characterized by evaluating extent of side chain modification (lysine and arginine) and formation of Amadori products as well as carbonyl contents using several physicochemical techniques. Results strongly suggested that 3-DG is a potent glycating agent that forms various intermediates and AGEs during glycation reactions and affects the secondary structure of the H1 protein. Structural changes and AGE formation may influence the function of H1 histone and compromise chromatin structures in cases of secondary diabetic complications.

Quercetin as a finer substitute to aminoguanidine in the inhibition of glycation products

Non-enzymatic glycation is the addition of a free carbonyl group of a reducing sugar to the free amino groups of proteins, which results in the formation of early and advanced glycation end-products (AGEs). Glycation reaction is profoundly associated with diabetes and its secondary complications, such as nephropathy and neuropathy. Glyoxal is a carbonyl species that reacts rapidly with the free amino groups of proteins to form AGEs. While the formation of AGEs with various glycating agents has previously been demonstrated, no extensive studies have been conducted to assess the role of quercetin in all three stages of glycation (early, intermediate and late). In this study, we report the glycation of HSA (human serum albumin) and its characterization by several spectroscopic techniques. Furthermore, inhibition of products at all stages of glycation was studied by various assays. Spectroscopic analysis suggests structural perturbations in the HSA macromolecule as a result of modification, which might be due to the generation of free radicals and the formation of AGEs. Inhibition in the formation of glycation has established that quercetin is a better and a more potent antiglycating agent than aminoguanidine at all stages of glycation.

A clinical correlation of anti-DNA-AGE autoantibodies in type 2 diabetes mellitus with disease duration

Nonenzymatic glycation of amino groups of DNA bases by reducing sugars can generate advanced glycation end products (AGEs). Cellular formation of AGEs under normal physiology is continuously scanned and removed by efficient system in the cells. However, excess formation and accumulation of AGEs may be cause or consequence of some human diseases. Mammalian DNA incubated with d-glucose for 28 days at 37°C showed structural changes in DNA as confirmed by UV, fluorescence, CD, melting temperature, S1 nuclease sensitivity and gel electrophoresis. Formation of DNA-AGE was confirmed by HPLC and LC-MS. Enzyme immunoassay and electrophoretic mobility shift assay of autoantibodies in type 2 diabetes patients' sera with disease duration of 5-15 years exhibited significantly high binding with DNA-AGE as compared to patients with 1-5 years of disease duration. Autoantibodies against aberrant DNA-AGE may be important in the assessment of initiation/progression of secondary complications in type 2 diabetes mellitus patients.

Inhibitory effect of leonurine on the formation of advanced glycation end products

Leonurine inhibits AGE formation through scavenging of the carbonyl species

Biochemical and immunological parameters as indicators of osteoarthritis subjects: role of OH-collagen in auto-antibodies generation

Osteoarthritis (OA) is characterized by inflammation of the knee joint, which is caused by accumulation of cytokines and C-reactive protein (CRP) in the extracellular matrix as an early immune response to infection. The articular cartilage destruction is discernible by elevated tumour necrosis factor-α (TNF-α). In this study, blood samples of knee osteoarthritis patients were analyzed for biochemical and physiological parameters based on the lipid profile, uric acid, total leukocyte count (TLC), hemoglobin percentage (Hb%) and absolute lymphocyte count (ALC). Furthermore, immunological parameters including TNF-α , interleukin-6 (IL-6) and CRP were analyzed. The presence of antibodies against hydroxyl radical modified collagen-II (^•OH-collagen-II) was also investigated in arthritis patients using direct binding ELISA. The uric acid and lipid profiles changed extensively. Specifically, increased uric acid levels were associated with OA in both genders, as were enhanced immunological parameters. The TNF-α level also increased in both genders suffering from OA. Finally, auto-antibodies against OH-collagen II antigen were found in the sera of arthritis patients. These results indicated that immunological parameters are better predictors or indexes for diagnosis of OA than biochemical parameters.

An immunohistochemical analysis to validate the rationale behind the enhanced immunogenicity of D-ribosylated low density lipo-protein

Advanced glycation end products (AGEs) are thought to contribute to the abnormal lipoprotein profiles and increased risk of cardiovascular disease in patients with diabetes and renal failure. D-ribose is one of the naturally occurring pentose monosaccharide present in all living cells and is a key component of numerous biomolecules involved in many important metabolic pathways. Formation of D-ribose derived glycated low density lipoprotein (LDL) has been previously demonstrated but no studies have been performed to assess the immune complex deposition in the kidney of rabbits immunized with glycated LDL. In this study, LDL was glycated with D-ribose, and it was further used as an immunogen for immunizing NZW female rabbits. The results showed that female rabbits immunized with D-ribose modified LDL induced antibodies as detected by direct binding and competitive ELISA. The modified LDL was found to be highly immunogenic eliciting high titer immunogen-specific antibodies, while the native forms were moderately immunogenic. The induced antibodies from modified LDL exhibited wide range of heterogeneity in recognizing various proteins and amino acids conformers. Furthermore, our histopathological results illustrated the deposits of immune complex in glomerular basement membrane in rabbits immunized with D-ribose-LDL.

Acquired immunogenicity of calf thymus DNA and LDL modified by D-ribose: a comparative study

Glycation of biologically important macromolecules leads to the establishment of advanced glycation end products (AGEs) having significant role in the pathophysiology of various diseases. d-Ribose, is a highly reactive pentose sugar resulting in the rapid formation of AGEs. Formation of d-ribose derived glycated DNA and LDL has been previously demonstrated; however no comparative, extensive studies have been performed to assess the immunogenicity of d-ribose glycated calf thymus DNA (CT-DNA) and LDL. In the present study, the results showed that animals immunized with d-ribose modified CT-DNA and LDL induced antibodies as detected by direct binding and competition ELISA. The modified CT-DNA and LDL were found to be highly immunogenic, eliciting high titer immunogen-specific antibodies, while the native forms of DNA was almost non-immunogenic. The induced antibodies from modified CT-DNA and LDL exhibited wide range of heterogeneity in recognizing various nucleic acid conformers, DNA bases and amino acids. Furthermore, Serum antibodies from diabetes and diabetes atherosclerosis patients were screened for their binding to native CT-DNA, LDL and glycated CT-DNA, LDL. Glycated CT-DNA showed almost equivalent binding to both diabetes and diabetic atherosclerosis group while high recognition was observed when glycated LDL was used as an antigen.

Autoimmune response to AGE modified human DNA: Implications in type 1 diabetes mellitus

Aims

Non-enzymatic glycation of DNA both in vivo and in vitro results in generation of free radicals, known as glycoxidation. Glycoxidation leads to structural perturbation of DNA resulting in generation of neo-antigenic epitopes having implication in autoimmune disorders like diabetes mellitus. In this study human placental DNA was glycated with methylglyoxal (MG) and lysine (Lys) in the presence of Cu²⁺ and its auto-antibody binding was probed in Type 1 diabetes patients.

Methods

Glycation was carried out by incubating DNA with MG, Lys and Cu²⁺ for 24 h at 37 °C. Carboxyethyl deoxyguanosine (CEdG) formed in glycation reaction was studied by LC-MS and the pathway for Amadori formation was studied by ESI-MS techniques. Furthermore, binding characteristics of auto-antibodies in diabetes patients were assessed by direct binding, competitive ELISA and band shift assay.

Results

DNA glycation with MG, Lys and Cu²⁺ results in the formation of CEdG (marker of DNA glycation) which was confirmed by LC-MS. The intermediate stages of glycation were confirmed by ESI-MS technique. Serum from diabetes patients exhibited enhanced binding and specificity for glycated DNA as compared to native form.

Conclusions

Glycation of DNA has resulted in structural perturbation causing generation of neo-antigenic epitopes thus recognizing auto-antibodies in diabetes.

Immunogenicity of DNA-advanced glycation end product fashioned through glyoxal and arginine in the presence of Fe³⁺: its potential role in prompt recognition of diabetes mellitus auto-antibodies

Glyoxal, methylglyoxal and 3-deoxyglucosones are reactive dicarbonyl compounds, which transform free amino groups of proteins and lipoproteins macromolecule into advanced glycation end-products (AGEs). AGEs play a significant role in the pathophysiology of aging and diabetic complications because of their genotoxic effect. Glyoxal also reacts with free amino group of nucleic acids resulting in the formation of DNA-AGEs. The present study reports the genotoxicity and immunogenicity of AGEs formed by Glyoxal-Arginine-Fe(3+) (G-Arg-Fe(3+)) system as a glycating agent. Immunogenicity of native and G-Arg-Fe(3+)-DNA was probed in female rabbits. Immunofluorescence suggests the presence of immune complex deposition in the kidney section of immunized rabbits. Spectroscopic analysis and melting temperature indicates the structural modification in the human DNA. The modified human DNA is found to be highly immunogenic, whereas unmodified form was simply non-immunogenic. This study shows the presence of auto-antibodies against G-Arg-Fe(3+) modified human DNA in the sera of diabetes type 1 and in few cases type 2 patients due to secondary complications of nephropathy. The glyco-oxidative lesions have also been detected in the lymphocyte DNA isolated from patients having type 1 and type 2 diabetes. The results show structural perturbations generating new epitopes in G-Arg-Fe(3+)-DNA rendering it pretty immunogenic.

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.

Inhibitory effect of metformin and pyridoxamine in the formation of early, intermediate and advanced glycation end-products

Background

Non-enzymatic glycation is the addition of free carbonyl group of reducing sugar to the free amino groups of proteins, resulting in the formation of a Schiff base and an Amadori product. Dihydroxyacetone (DHA) is one of the carbonyl species which reacts rapidly with the free amino groups of proteins to form advanced glycation end products (AGEs). The highly reactive dihydroxyacetone phosphate is a derivative of dihydroxyacetone (DHA), and a product of glycolysis, having potential glycating effects to form AGEs. The formation of AGEs results in the generation of free radicals which play an important role in the pathophysiology of aging and diabetic complications. While the formation of DHA-AGEs has been demonstrated previously, no extensive studies have been performed to assess the inhibition of AGE inhibitors at all the three stages of glycation (early, intermediate and late) using metformin (MF) and pyridoxamine (PM) as a novel inhibitor.

Methodology/Principal Findings

In this study we report glycation of human serum albumin (HSA) & its characterization by various spectroscopic techniques. Furthermore, inhibition of glycation products at all the stages of glycation was also studied. Spectroscopic analysis suggests structural perturbations in the HSA as a result of modification which might be due to generation of free radicals and formation of AGEs.

Conclusion

The inhibition in the formation of glycation reaction reveals that Pyridoxamine is a better antiglycating agent than Metformin at all stages of the glycation (early, intermediate and late stages).

Genotoxic effect of N-hydroxy-4-acetylaminobiphenyl on human DNA: implications in bladder cancer

BACKGROUND

The interaction of environmental chemicals and their metabolites with biological macromolecules can result in cytotoxic and genotoxic effects. 4-Aminobiphenyl (4-ABP) and several other related arylamines have been shown to be causally involved in the induction of human urinary bladder cancers. The genotoxic and the carcinogenic effects of 4-ABP are exhibited only when it is metabolically converted to a reactive electrophile, the aryl nitrenium ions, which subsequently binds to DNA and induce lesions. Although several studies have reported the formation of 4-ABP-DNA adducts, no extensive work has been done to investigate the immunogenicity of 4-ABP-modified DNA and its possible involvement in the generation of antibodies in bladder cancer patients.

METHODOLOGY/PRINCIPAL FINDINGS

Human DNA was modified by N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP), a reactive metabolite of 4-ABP. Structural perturbations in the N-OH-AABP modified DNA were assessed by ultraviolet, fluorescence, and circular dichroic spectroscopy as well as by agarose gel electrophoresis. Genotoxicity of N-OH-AABP modified DNA was ascertained by comet assay. High performance liquid chromatography (HPLC) analysis of native and modified DNA samples confirmed the formation of N-(deoxyguanosine-8-yl)-4-aminobiphenyl (dG-C8-4ABP) in the N-OH-AABP damaged DNA. The experimentally induced antibodies against N-OH-AABP-modified DNA exhibited much better recognition of the DNA isolated from bladder cancer patients as compared to the DNA obtained from healthy individuals in competitive binding ELISA.

CONCLUSIONS/SIGNIFICANCE

This work shows epitope sharing between the DNA isolated from bladder cancer patients and the N-OH-AABP-modified DNA implicating the role of 4-ABP metabolites in the DNA damage and neo-antigenic epitope generation that could lead to the induction of antibodies in bladder cancer patients.