Detection of DNA-bound advanced glycation end-products by immunoaffinity chromatography coupled to HPLC-diode array detection

Fructosylation induced structural changes in mammalian DNA examined by biophysical techniques

Glycosylation of DNA, proteins, lipids, etc. by reducing sugars, can lead to the formation of advanced glycation end products (AGEs). These products may accumulate and involve in the pathogenesis of a number of diseases, contributing to tissue injury via several mechanisms. In this study, fructosylation of calf thymus dsDNA was carried out with varying concentrations of fructose. The neo-structure of fructosylated-DNA was studied by various biophysical techniques and morphological characterization. Fructosylated-DNA showed hyperchromicity, increase in fluorescence intensity and decrease in melting temperature. The CD signal of modified-DNA shifted in the direction of higher wavelength indicative of structural changes in DNA. FTIR results indicated shift in specific band positions in fructosylated-DNA. Morphological characterization of fructosylated-DNA exhibited strand breakage and aggregation. The results suggest that the structure and conformation of DNA may be altered under high concentrations of fructose.

The glyoxalase pathway: the first hundred years... and beyond

The discovery of the enzymatic formation of lactic acid from methylglyoxal dates back to 1913 and was believed to be associated with one enzyme termed ketonaldehydemutase or glyoxalase, the latter designation prevailed. However, in 1951 it was shown that two enzymes were needed and that glutathione was the required catalytic co-factor. The concept of a metabolic pathway defined by two enzymes emerged at this time. Its association to detoxification and anti-glycation defence are its presently accepted roles, since methylglyoxal exerts irreversible effects on protein structure and function, associated with misfolding. This functional defence role has been the rationale behind the possible use of the glyoxalase pathway as a therapeutic target, since its inhibition might lead to an increased methylglyoxal concentration and cellular damage. However, metabolic pathway analysis showed that glyoxalase effects on methylglyoxal concentration are likely to be negligible and several organisms, from mammals to yeast and protozoan parasites, show no phenotype in the absence of one or both glyoxalase enzymes. The aim of the present review is to show the evolution of thought regarding the glyoxalase pathway since its discovery 100 years ago, the current knowledge on the glyoxalase enzymes and their recognized role in the control of glycation processes.

Endogenous mitochondrial oxidative stress in MnSOD-deficient mouse embryonic fibroblasts promotes mitochondrial DNA glycation

The accumulation of somatic mutations in mitochondrial DNA (mtDNA) induced by reactive oxygen species (ROS) is regarded as a major contributor to aging and age-related degenerative diseases. ROS have also been shown to facilitate the formation of certain advanced glycation end-products (AGEs) in proteins and DNA and N(2)-carboxyethyl-2'-deoxyguanosine (CEdG) has been identified as a major DNA-bound AGE. Therefore, the influence of mitochondrial ROS on the glycation of mtDNA was investigated in primary embryonic fibroblasts derived from mutant mice (Sod2(-/+)) deficient in the mitochondrial antioxidant enzyme manganese superoxide dismutase. In Sod2(-/+) fibroblasts vs wild-type fibroblasts, the CEdG content of mtDNA was increased from 1.90 ± 1.39 to 17.14 ± 6.60 pg/μg DNA (p<0.001). On the other hand, the CEdG content of nuclear DNA did not differ between Sod2(+/+) and Sod2(-/+) cells. Similarly, cytosolic proteins did not show any difference in advanced glycation end-products or protein carbonyl contents between Sod2(+/+) and Sod2(-/+). Taken together, the data suggest that mitochondrial oxidative stress specifically promotes glycation of mtDNA and does not affect nuclear DNA or cytosolic proteins. Because DNA glycation can change DNA integrity and gene functions, glycation of mtDNA may play an important role in the decline of mitochondrial functions.

Intracellular glycation of nuclear DNA, mitochondrial DNA, and cytosolic proteins during senescence-like growth arrest

To investigate the accumulation of intracellular advanced glycation end products (AGEs), a method was established for the simultaneous analysis of glycation products of cytosolic proteins, nuclear DNA, and mitochondrial DNA (mtDNA). Nuclear DNA, mtDNA, and cytosolic proteins were simultaneously isolated from one cell lysate by differential centrifugation and combined mechanical and chemical cell disruption methods. The major DNA-AGE N(2)-carboxyethyl-2'-deoxyguanosine (CEdG) was quantified in nuclear DNA and mtDNA by ELISA, whereas the protein-AGEs N(ɛ)-(carboxymethyl)lysine (CML) and N(ɛ)-(carboxyethyl)lysine (CEL) were determined by western blot. The method was used to analyze NIH3T3 fibroblasts. In untreated cells, CEdG levels of mtDNA (14.84 ± 3.07 pg CEdG/μg mtDNA) were significantly higher compared with nuclear DNA (4.40 ± 0.64 pg CEdG/μg DNA; p < 0.001). Then, fibroblasts were analyzed after 7 days of senescence-like growth arrest. In senescent fibroblasts, the CEdG content of nuclear DNA significantly increased by 25%. However, the CEdG level of mtDNA significantly decreased to 52%; in parallel, an increase in mitochondrial mass and mtDNA was observed. Senescence did not lead to general accumulation of protein-AGEs, but two protein bands at 32 and 34 kDa showed a significant increase in the CML/CEL modification rate (208%, p < 0.001; 196%, p = 0.0016) in senescent fibroblasts compared with control cells.

Advanced glycation end products of DNA: quantification of N2-(1-Carboxyethyl)-2'-deoxyguanosine in biological samples by liquid chromatography electrospray ionization tandem mass spectrometry

Methylglyoxal (MG) and related alpha-oxoaldehydes react with proteins, lipids, and DNA to give rise to covalent adducts known as advanced glycation end products (AGEs). Elevated levels of AGEs have been implicated in the pathological complications of diabetes, uremia, Alzheimer's disease, and possibly cancer. There is therefore widespread interest in developing sensitive methods for the in vivo measurement of AGEs as prognostic biomarkers and for treatment monitoring. The two diastereomeric MG-DNA adducts of N(2)-(1-carboxyethyl)-2'-deoxyguanosine (CEdG) are the primary glycation products formed in DNA; however, accurate assessment of their distribution in vivo has not been possible since there is no readily available quantitative method for CEdG determination in biological samples. To address these issues, we have developed a sensitive and quantitative liquid chromatography electrospray ionization tandem mass spectrometry assay using the stable isotope dilution method with an (15)N(5)-CEdG standard. Methods for CEdG determination in urine or tissue extracted DNA are described. Changes in urinary CEdG in diabetic rats in response to oral administration of the AGE inhibitor LR-90 are used to demonstrate the potential utility of the method for treatment monitoring. Both stereoisomeric CEdG adducts were detected in a human breast tumor and normal adjacent tissue at levels of 3-12 adducts/10(7) dG, suggesting that this lesion may be widely distributed in vivo. Strategies for dealing with artifactual adduct formation due to oxoaldehyde generation during DNA isolation and enzymatic workup procedures are described.

Stereospecific synthesis and characterization of oligodeoxyribonucleotides containing an N2-(1-carboxyethyl)-2'-deoxyguanosine

Methylglyoxal is a highly reactive alpha-ketoaldehyde that is produced endogenously and present in the environment and foods. It can modify DNA and proteins to form advanced glycation end products (AGEs). Emerging evidence has shown that N2-(1-carboxyethyl)-2'-deoxyguanosine (N2-CEdG) is a major marker for AGE-linked DNA adducts. Here, we report, for the first time, the preparation of oligodeoxyribonucleotides (ODNs) containing individual diastereomers of N2-CEdG via a postoligomerization synthesis method, which provided authentic substrates for examining the replication and repair of this lesion. In addition, thermodynamic parameters derived from melting temperature data revealed that the two diastereomers of N2-CEdG destabilized significantly the double helix as represented by a 4 kcal/mol increase in Gibbs free energy for duplex formation at 25 degrees C. Primer extension assay results demonstrated that both diastereomers of N2-CEdG could block considerably the replication synthesis mediated by the exonuclease-free Klenow fragment of Escherichia coli DNA polymerase I. Strikingly, the polymerase incorporated incorrect nucleotides, dGMP and dAMP, opposite the lesion more preferentially than the correct nucleotide, dCMP.

Analysis of DNA-bound advanced glycation end-products by LC and mass spectrometry

Sugars and sugar degradation products readily react in vitro with guanine derivatives, resulting in the formation of DNA-bound advanced glycation end-products (DNA-AGEs). The two diastereomers of N(2)-(1-carboxyethyl)-2'-deoxyguanosine (CEdG(A,B)) and the cyclic adduct of methylglyoxal and 2'-deoxyguanosine (mdG) (N(2)-7-bis(1-hydroxy-2-oxopropyl)-2'-deoxyguanosine have also been detected in cultured cells and/or in vivo. LC-MS/MS methods have been developed to analyze sensitively DNA adducts in vitro and in vivo. In this paper, the chemical structures of possible DNA-AGEs and the application of LC-MS/MS to measure DNA-AGEs are reviewed.

The effect of nonenzymatic glycation on the stability and conformation of two deoxyoligonucleotide duplexes: a spectroscopic analysis by circular dichroism

Advanced glycation end products (AGEs) play a significant role in the pathophysiology of diabetes leading to such conditions as atherosclerosis, cataract formation, and renal dysfunction. While the formation of nucleoside AGEs was previously demonstrated, no extensive studies have been performed to assess the effect of AGEs on DNA structure and folding. The objective of this study was to investigate the nonenzymatic glycation of two DNA oligonucleotide duplexes with one duplex consisting of deoxy-poly(A)15 and deoxy-poly(T)15 and the other consisting of deoxy-poly(GA)15 and deoxy-poly(CT)15. With D-glucose, D-galactose, D/L-glyceraldehyde, and D-glucosamine serving as the model glycating carbohydrates, D-glucosamine was found to exhibit the greatest effect on the stability and structure of the oligonucleotide duplexes, a finding that was confirmed by circular dichroism. The nonenzymatic glycation of deoxy-poly(AT) by D-glucosamine destabilized the deoxy-poly(AT) structure and changed its conformation from A form to X form. D-glucosamine also altered the conformation of deoxy-poly(GA)15 and deoxy-poly(CT)15 from A form to B form. Capillary electrophoresis and ultraviolet and fluorescence spectroscopy revealed that, of the various purines and pyrimidines, 2'-deoxyguanosine and guanine were most reactive with D-glucosamine. The nonenzymatic modification of nucleic acids warrants further investigation because this phenomenon may occur in vivo, altering DNA structure and/or function.