Detection of methylglyoxal as a degradation product of DNA and nucleic acid components treated with strong acid

Role of methylglyoxal and redox homeostasis in microbe-mediated stress mitigation in plants

One of the general consequences of stress in plants is the accumulation of reactive oxygen (ROS) and carbonyl species (like methylglyoxal) to levels that are detrimental for plant growth. These reactive species are inherently produced in all organisms and serve different physiological functions but their excessive accumulation results in cellular toxicity. It is, therefore, essential to restore equilibrium between their synthesis and breakdown to ensure normal cellular functioning. Detoxification mechanisms that scavenge these reactive species are considered important for stress mitigation as they maintain redox balance by restricting the levels of ROS, methylglyoxal and other reactive species in the cellular milieu. Stress tolerance imparted to plants by root-associated microbes involves a multitude of mechanisms, including maintenance of redox homeostasis. By improving the overall antioxidant response in plants, microbes can strengthen defense pathways and hence, the adaptive abilities of plants to sustain growth under stress. Hence, through this review we wish to highlight the contribution of root microbiota in modulating the levels of reactive species and thereby, maintaining redox homeostasis in plants as one of the important mechanisms of stress alleviation. Further, we also examine the microbial mechanisms of resistance to oxidative stress and their role in combating plant stress.

Methylglyoxal disturbs DNA repair and glyoxalase I system in Saccharomyces cerevisiae

Methylglyoxal (MG) is a highly reactive aldehyde able to form covalent adducts with proteins and nucleic acids, disrupting cellular functions. In this study, we performed a screening of Saccharomyces cerevisiae (S. cerevisiae) strains to find out which genes of cells are responsive to MG, emphasizing genes against oxidative stress and DNA repair. Yeast strains were grown in the YPD-Galactose medium containing MG (0.5 to 12 mM). The tolerance to MG was evaluated by determining cellular growth and cell viability. The toxicity of MG was more pronounced in the strains with deletion in genes engaged with DNA repair checkpoint proteins, namely Rad23 and Rad50. MG also impaired the growth and viability of S. cerevisiae mutant strains Glo1 and Gsh1, both components of the glyoxalase I system. Differently, the strains with deletion in genes encoding for antioxidant enzymes were apparently resistant to MG. In summary, our data indicate that DNA repair and MG detoxification pathways are keys in the control of MG toxicity in S. cerevisiae.

Circulating free methylglyoxal as a metabolic tumor biomarker in a rat colon adenocarcinoma model

Since the 1956 hypothesis of Otto Warburg, aerobic glycolysis has been recognized as a metabolic hallmark of cancer. Because methylglyoxal (MG) is a naturally occurring waste metabolite of glycolysis, we measured blood levels of this molecule in colon cancer-bearing rats. To compare the blood levels of free MG in cancerous and healthy animals,the present study used a dedicated tumor graft model consisting of the subcutaneous administration in syngenic BD-IX rats of a tumorigenic cell clone (PROb) and another non-tumorigenic clone (REGb) derived from the same tumor. Rats grafted with the PROb growing tumor cell clone exhibited a statistically significant increase in free MG blood levels (P=0.003), whereas rats transplanted with the REGb non-growing tumor cell clone exhibited normal MG values. The present study (first of three parts) suggests that cancer cells can produce and release free MG at higher levels than normal cells, making MG a putative novel metabolic biomarker of cancer.

The immune receptor Tim-3 acts as a trafficker in a Tim-3/galectin-9 autocrine loop in human myeloid leukemia cells

The immune receptor Tim-3 is often highly expressed in human acute myeloid leukemia (AML) cells where it acts as a growth factor and inflammatory receptor. Recently, it has been demonstrated that Tim-3 forms an autocrine loop with its natural ligand galectin-9 in human AML cells. However, the pathophysiological functions of Tim-3 in human AML cells remain unclear. Here, we report for the first time that Tim-3 is required for galectin-9 secretion in human AML cells. However, this effect is cell-type specific and was found so far to be applicable only to myeloid (and not, for example, lymphoid) leukemia cells. We concluded that AML cells might use Tim-3 as a trafficker for the secretion of galectin-9 which can then be possibly used to impair the anticancer activities of cytotoxic T cells and natural killer (NK) cells.

Critical considerations for developing nucleic acid macromolecule based drug products

Protein expression therapy using nucleic acid macromolecules (NAMs) as a new paradigm in medicine has recently gained immense therapeutic potential. With the advancement of nonviral delivery it has been possible to target NAMs against cancer, immunodeficiency and infectious diseases. Owing to the complex and fragile structure of NAMs, however, development of a suitable, stable formulation for a reasonable product shelf-life and efficacious delivery is indeed challenging to achieve. This review provides a synopsis of challenges in the formulation and stability of DNA/m-RNA based medicines and probable mitigation strategies including a brief summary of delivery options to the target cells. Nucleic acid based drugs at various stages of ongoing clinical trials are compiled.

Extending the spectrum of α-dicarbonyl compounds in vivo

Maillard α-dicarbonyl compounds are known as central intermediates in advanced glycation end product (AGE) formation. Glucose is the primary source of energy for the human body, whereas l-threo-ascorbic acid (vitamin C) is an essential nutrient, involved in a variety of enzymatic reactions. Thus, the Maillard degradation of glucose and ascorbic acid is of major importance in vivo. To understand the complex mechanistic pathways of AGE formation, it is crucial to extend the knowledge on plasma concentrations of reactive key α-dicarbonyl compounds (e.g. 1-deoxyglucosone). With the present work, we introduce a highly sensitive LC-MS/MS multimethod for human blood plasma based on derivatization with o-phenylenediamine under acidic conditions. The impact of workup and reaction conditions, particularly of pH, was thoroughly evaluated. A comprehensive validation provided the limit of detection, limit of quantitation, coefficients of variation, and recovery rates. The method includes the α-dicarbonyls 1-deoxyglucosone, 3-deoxyglucosone, glucosone, Lederer's glucosone, dehydroascorbic acid, 2,3-diketogulonic acid, 1-deoxypentosone, 3-deoxypentosone, 3,4-dideoxypentosone, pentosone, 1-deoxythreosone, 3-deoxythreosone, threosone, methylglyoxal, glyoxal; the α-keto-carboxylic acids pyruvic acid and glyoxylic acid; and the dicarboxylic acid oxalic acid. The method was then applied to the analyses of 15 healthy subjects and 24 uremic patients undergoing hemodialysis. The comparison of the results revealed a clear shift in the product spectrum. In most cases, the plasma levels of target analytes were significantly higher. Thus, this is the first time that a complete spectrum of α-dicarbonyl compounds relevant in vivo has been established. The results provide further insights into the chemistry of AGE formation and will be helpful to find specific markers to differentiate between the various precursors of glycation.

Methylglyoxal induces oxidative stress and mitochondrial dysfunction in osteoblastic MC3T3-E1 cells

Methylglyoxal is a reactive dicarbonyl compound produced by glycolytic processing and identified as a precursor of advanced glycation end products. The elevated methylglyoxal levels in patients with diabetes are believed to contribute to diabetic complications, including bone defects. The objective of this study was to evaluate the effect of methylglyoxal on the function of osteoblastic MC3T3-E1 cells. The data indicated that methylglyoxal decreased osteoblast differentiation and induced osteoblast cytotoxicity. Pretreatment of MC3T3-E1 cells with aminoguanidine (a carbonyl scavenger), Trolox (an antioxidant), and cyclosporin A (a blocker of the mitochondrial permeability transition pore) prevented methylglyoxal-induced cytotoxicity in MC3T3-E1 cells. However, BAPTA/AM (an intracellular Ca(2+) chelator) and dantrolene (an inhibitor of endoplasmic reticulum Ca(2+) release) did not reverse the cytotoxic effect of methylglyoxal. Methylglyoxal increased the formation of intracellular reactive oxygen species, mitochondrial superoxide, and cardiolipin peroxidation in osteoblastic MC3T3-E1 cells. Methylglyoxal also decreased the mitochondrial membrane potential and intracellular ATP and nitric oxide levels, suggesting that carbonyl stress-induced loss of mitochondrial integrity contributes to the cytotoxicity of methylglyoxal. Furthermore, the results demonstrated that methylglyoxal induced protein adduct formation, inactivation of glyoxalase I, and activation of glyoxalase II. Aminoguanidine reversed all aforementioned effects of methylglyoxal. Taken together, these data support the notion that high methylglyoxal concentrations have detrimental effects on osteoblasts through a mechanism involving oxidative stress and mitochondrial dysfunction.

Chromatographic determination of methyl glyoxal in blood plasma as the test for glycotoxicity and accumulation of glycation end-products

We developed a method of measuring methyl glyoxal concentration in blood serum using HPLC with UV detection. Methyl glyoxal concentration was determined in healthy subjects. The method was developed for indirect but reliable measurement of the levels of glycation end-products in patients with diabetes, hyperlipidemia, and cardiovascular pathologies.

A quick, convenient and economical method for the reliable determination of methylglyoxal in millimolar concentrations: the N-acetyl-L-cysteine assay

The determination of methylglyoxal (MG) concentrations in vivo is gaining increasing importance as high levels of MG are linked to various health impairments including complications of diabetes. In order to standardize the measurements of MG in body fluids, it is necessary to precisely determine the concentration of MG stock solutions used as analytical standards. The "gold standard" method for the determination of MG concentration in the millimolar range is an enzyme-catalyzed endpoint assay based on the glyoxalase I catalyzed formation of S-lactoylglutathione. However, as this assay used purified glyoxalase I enzyme, it is quite expensive. Another method uses a derivation reaction with 2,4-dinitrophenylhydrazine, but this substance is explosive and needs special handling and storage. In addition, precipitation of the product methylglyoxal-bis-2,4-dinitrophenylhydrozone during the reaction limits the reliability of this method. In this study, we have evaluated a new method of MG determination based on the previously published fast reaction between MG and N-acetyl-L-cysteine at room temperature which yields an easily detectable condensation product, N-α-acetyl-S-(1-hydroxy-2-oxo-prop-1-yl)cysteine. When comparing these three different assays for the measurement of MG concentrations, we find that the N-acetyl-L-cysteine assay is the most favorable, providing an economical and robust assay without the need for the use of hazardous or expensive reagents.

Methylglyoxal mediates adipocyte proliferation by increasing phosphorylation of Akt1

Methylglyoxal (MG) is a highly reactive metabolite physiologically presented in all biological systems. The effects of MG on diabetes and hypertension have been long recognized. In the present study, we investigated the potential role of MG in obesity, one of the most important factors to cause metabolic syndrome. An increased MG accumulation was observed in the adipose tissue of obese Zucker rats. Cell proliferation assay showed that 5–20 µM of MG stimulated the proliferation of 3T3-L1 cells. Further study suggested that accumulated-MG stimulated the phosphorylation of Akt1 and its targets including p21 and p27. The activated Akt1 then increased the activity of CDK2 and accelerated the cell cycle progression of 3T3-L1 cells. The effects of MG were efficiently reversed by advanced glycation end product (AGE) breaker alagebrium and Akt inhibitor SH-6. In summary, our study revealed a previously unrecognized effect of MG in stimulating adipogenesis by up-regulation of Akt signaling pathway and this mechanism might offer a new approach to explain the development of obesity.

The glycation of albumin: structural and functional impacts

Oxidative stress and protein modifications are frequently observed in numerous disease states. Glucose constitutes a vital nutrient necessary to cellular oxygen metabolism. However, hyperglycemia-associated damage is an important factor in diabetes disorders. Albumin, the major circulating protein in blood, can undergo increased glycation in diabetes. From recent studies, it has become evident that protein glycation has important implications for protein activity, unfolding, and degradation, as well as for cell functioning. After giving a brief overview of the key role of albumin in overall antioxidant defense, this review examines its role as a target of glycation reactions. A synthesis of state of the art methods for measuring and characterizing albumin glycation is detailed. In light of recent data, we then report the impact of glycation on the structure of albumin and its various activities, especially its antioxidant and binding capacities. The biological impact of glycated albumin on cell physiology is also discussed, specifically the role of the protein as a biological marker of diabetes.

The plastid isoform of triose phosphate isomerase is required for the postgerminative transition from heterotrophic to autotrophic growth in Arabidopsis

During postgerminative seedling establishment, reserves stored during seed filling are mobilized to provide energy and carbon for the growing seedling until autotrophic growth is possible. A plastid isoform of triose phosphate isomerase (pdTPI) plays a crucial role in this transition from heterotrophic to autotrophic growth. A T-DNA insertion in Arabidopsis thaliana pdTPI resulted in a fivefold reduction in transcript, reduced TPI activity, and a severely stunted and chlorotic seedling that accumulated dihydroxyacetone phosphate (DHAP), glycerol, and glycerol-3-phosphate. Methylglyoxal (MG), a by-product of DHAP, also accumulated in the pdtpi mutant. Wild-type seed sown in the presence of any of these four metabolites resulted in a phenocopy of this pdtpi mutant, although MG and DHAP were the most effective based upon dosage. These metabolites (except MG) are by-products of triacylglycerol mobilization and precursors for glycerolipid synthesis, suggesting that lipid metabolism may also be affected. Lipid profiling revealed lower monogalactosyl but higher digalactosyl lipids. It is unclear whether the change in lipid composition is a direct or indirect consequence of the pdtpi mutation, as ribulose-1,5-bis-phosphate carboxylase/oxygenase expression, chloroplast morphology, and starch synthesis are also defective in this mutant. We propose that DHAP and MG accumulation in developing plastids delays the transition from heterotrophic to autotrophic growth, possibly due to MG toxicity.

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.

Methylglyoxal in food and living organisms

Methylglyoxal (MG) is a highly reactive alpha-oxoaldehyde formed endogenously in numerous enzymatic and nonenzymatic reactions. It modifies arginine and lysine residues in proteins forming advanced glycation end-products such as N(delta)-(5-methyl-4-imidazolon-2-yl)-L-ornithine (MG-H1), 2-amino-5-(2-amino-5-hydro-5-methyl-4-imidazolon-1-yl)pentanoic acid (MG-H2), 2-amino-5-(2-amino-4-hydro-4-methyl-5-imidazolon-1-yl)pentanoic acid (MG-H3), argpyrimidine, N(delta)-(4-carboxy-4,6-dimethyl-5,6-dihydroxy-1,4,5,6-tetrahydropyrimidine-2-yl)-L-ornithine (THP), N(epsilon)-(1-carboxyethyl)lysine (CEL), MG-derived lysine dimer (MOLD), and 2-ammonio-6-({2-[4-ammonio-5-oxido-5-oxopently)amino]-4-methyl-4,5-dihydro-1H-imidazol-5-ylidene}amino)hexanoate (MODIC), which have been identified in vivo and are associated with complications of diabetes and some neurodegenerative diseases. In foodstuffs and beverages, MG is formed during processing, cooking, and prolonged storage. Fasting and metabolic disorders and/or defects in MG detoxification processes cause accumulation of this reactive dicarbonyl in vivo. In addition, the intake of low doses of MG over a prolonged period of time can cause degenerative changes in different tissues, and can also exert anticancer activity. MG in biological samples can be quantified by HPLC or GC methods with preliminary derivatization into more stable chromophores and/or fluorophores, or derivatives suitable for determination by MS by use of diamino derivatives of benzene and naphthalene, 6-hydroxy-2,4,5-triaminopyrimidine, cysteamine, and o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine. The methods include three basic steps: deproteinization, incubation with derivatization agent, and chromatographic analysis with or without preliminary extraction of the formed products.

Metabolic flux analysis of Escherichia coli in glucose-limited continuous culture. II. Dynamic response to famine and feast, activation of the methylglyoxal pathway and oscillatory behaviour

The metabolic dynamics of the Escherichia coli K-12 strain TG1 to feast and famine were studied in glucose-limited steady-state cultures by up- and downshifts of the dilution rate, respectively. An uncoupling of anabolic and catabolic rates was observed upon dilution rate upshifts, apparent through immediately increased glucose uptake rates which were not accompanied by an immediate increase of the growth rate but instead resulted in the temporary excretion of methylglyoxal, D- and L-lactate, pyruvate and, after a delay, acetate. The energetic state of the cell during the transient was followed by measuring the adenylate energy charge, which increased within 2 min after the upshift and declined thereafter until a new steady-state level was reached. In the downshift experiment, the adenylate energy charge behaved inversely; no by-products were formed, indicating a tight coupling of anabolism and catabolism. Both dilution rate shifts were accompanied by an instantaneous increase of cAMP, presaging the subsequent changes in metabolic pathway utilization. Intracellular key metabolites of the Embden-Meyerhof-Parnas (EMP) pathway were measured to evaluate the metabolic perturbation during the upshift. Fructose 1,6-diphosphate (FDP) and dihydroxyacetone phosphate (DHAP) increased rapidly after the upshift, while glyceraldehyde 3-phosphate decreased. It is concluded that this imbalance at the branch-point of FDP induces the methylglyoxal (MG) pathway, a low-energy-yielding bypass of the lower EMP pathway, through the increasing level of DHAP. MG pathway activation after the upshift was simulated by restricting anabolic rates using a stoichiometry-based metabolic model. The metabolic model predicted that low-energy-yielding catabolic pathways are utilized preferentially in the transient after the upshift. Upon severe dilution rate upshifts, an oscillatory behaviour occurred, apparent through long-term oscillations of respiratory activity, which started when the cytotoxic compound MG reached a threshold concentration of 1.5 mg l(-1) in the medium.

A novel sensitive high-performance liquid chromatography/electrochemical procedure for measuring formaldehyde produced from oxidative deamination of methylamine and in biological samples

Formaldehyde is a well-known environmental toxic hazard. It is also a product of oxidative deamination of methylamine catalyzed by semicarbazide-sensitive amine oxidase (SSAO). Increased SSAO-mediated deamination has been implicated in some pathophysiological conditions, such as diabetic complications. The measurement of formaldehyde in the enzymatic reactions and in vivo production using conventional methods was not straightforward due to limitations of selectivity and sensitivity. A novel high-performance liquid chromatography (HPLC)/electrochemical procedure for the measurement of formaldehyde has been developed. The measurement is based on the formation of adducts between formaldehyde and dopamine. These adducts can be selectively purified and concentrated using a batch method of alumina absorption, separated by HPLC, and electrochemically quantified. The method is highly selective and substantially more sensitive, i.e., detection of picomole levels of formaldehyde, than the conventional methods. The procedure not only facilitates the assessment of SSAO activity in vitro but also is useful for assessing formaldehyde in tissues and biological fluids.

Methylglyoxal, an endogenous aldehyde, crosslinks DNA polymerase and the substrate DNA

Methylglyoxal, a known endogenous and environmental mutagen, is a reactive alpha-ketoaldehyde that can modify both DNA and proteins. To investigate the possibility that methylglyoxal induces a crosslink between DNA and DNA polymerase, we treated a 'primed template' DNA and the exonuclease-deficient Klenow fragment (KF(exo-)) of DNA polymerase I with methylglyoxal in vitro. When the reaction mixtures were analyzed by SDS-PAGE, we found that methylglyoxal induced a DNA-KF(exo-) crosslink. The specific binding complex of KF(exo-) and 'primed template' DNA was necessary for formation of the DNA-KF(exo-) crosslink. Methylglyoxal reacted with guanine residues in the single-stranded portion of the template DNA. When 2'-deoxyguanosine was incubated with Nalpha-acetyllysine or N-acetylcysteine in the presence of methylglyoxal, a crosslinked product was formed. No other amino acid derivatives tested could generate a crosslinked product. These results suggest that methylglyoxal crosslinks a guanine residue of the substrate DNA and lysine and cysteine residues near the binding site of the DNA polymerase during DNA synthesis and that DNA replication is severely inhibited by the methylglyoxal-induced DNA-DNA polymerase crosslink.

Methylglyoxal induces G:C to C:G and G:C to T:A transversions in the supF gene on a shuttle vector plasmid replicated in mammalian cells

We previously reported that the majority of base-pair substitutions induced by an endogenous mutagen, methylglyoxal, were G:C-->T:A transversions and G:C-->A:T transitions in wild-type and nucleotide excision repair (NER)-deficient (uvrA or uvrC) Escherichia coli strains. To investigate the mutation spectrum of methylglyoxal in mammalian cells and to compare the spectrum with those detected in other experimental systems, we analyzed mutations in a bacterial suppressor tRNA (supF) gene in the shuttle vector plasmid pMY189. We treated pMY189 with methylglyoxal and immediately transfected it into simian COS-7 cells. The cytotoxicity and the mutation frequency (MF) increased according to the dose of methylglyoxal. In the mutants induced by methylglyoxal, multi-base deletions were predominant (50%), followed by base-pair substitutions (35%), in which 89% of the substitutions occurred at G:C sites. Among them, G:C-->C:G and G:C-->T:A transversions were predominant. The overall distribution of methylglyoxal-induced mutations detected in the supF gene was different from that for the spontaneous mutations. These results suggest that methylglyoxal may take part in causing G:C-->C:G and G:C-->T:A transversions in vivo.

Methylglyoxal in living organisms: chemistry, biochemistry, toxicology and biological implications

Despite the growing interest towards methylglyoxal and glyoxalases their real role in metabolic network is still obscure. In the light of developments several reviews have been published in this field mainly dealing with only a narrow segment of this research area. In this article a trial is made to present a comprehensive overview of methylglyoxal research, extending discussion from chemistry to biological implications by reviewing some important characteristics of methylglyoxal metabolism and toxicity in a wide variety of species, and emphasizing the action of methylglyoxal on energy production, free radical generation and cell killing. Special attention is paid to the discussion of alpha-oxoaldehyde production in the environment as a potential risk factor and to the possible role of this a-dicarbonyl in diseases. Concerning the interaction of methylglyoxal with biological macromolecules (DNA, RNA, proteins) an earlier review (Kalapos, Toxicology Letters, 73, 1994, 3-24) means a supplementation to this paper, thus hoping the avoidance of unnecessary bombast. The paper arrives at the conclusion that since the early stage of evolution the function of methylglyoxalase pathway has been related to carbohydrate metabolism, but its significance has been changed over the thousands of years. Namely, at the beginning of evolution methylglyoxalase path was essential for the reductive citric acid cycle as an anaplerotic route, while in the extant metabolism it concerns with the detoxification of methylglyoxal and plays some regulatory role in triose-phosphate household. As there is a tight junction between methylglyoxal and carbohydrate metabolism its pathological role in the events of the development of diabetic complications emerges in a natural manner and further progress is hoped in this field. In contrast, significant advancement cannot be expected in relation to cancer research.

Deficient nucleotide excision repair increases base-pair substitutions but decreases TGGC frameshifts induced by methylglyoxal in Escherichia coli

To investigate the mutation spectrum of a well-known mutagen, methylglyoxal, and the influence of nucleotide excision repair (NER) on methylglyoxal-induced mutations, we treated wild-type and NER-deficient (uvrA or uvrC) Escherichia coli strains with methylglyoxal, and analyzed mutations in the chromosomal lacI gene. In the three strains, the cell death and the mutation frequency increased according to the dose of methylglyoxal added to the culture medium. The frequencies of methylglyoxal-induced base-pair substitutions were higher in the NER-deficient strains than in the wild-type strain, in the presence and absence of mucAB gene. Paradoxically, the frequency of methylglyoxal-induced TGGC frameshifts was higher in the wild-type strain than in the NER-deficient strains. When the methylglyoxal-induced mutation spectra in the presence and absence of mucAB gene are compared, the ratios of base-pair substitutions to frameshifts were increased by the effects of mucAB gene. In the three strains, more than 75% of the base-pair substitutions occurred at G:C sites, independent of the mucAB gene. When the mucAB gene was present, G:C-->T:A transversions were predominant, followed by G:C-->A:T transitions. When the mucAB gene was absent, the predominant mutations differed in the three strains: in the wild-type and uvrC strains, G:C-->A:T transitions were predominant, followed by G:C-->T:A transversions, while in the uvrA strains, G:C-->T:A transversions were predominant, followed by G:C-->A:T transitions. These results suggest that NER may be involved in both the repair and the fixation of methylglyoxal-induced mutations.

Deamination of methylamine and aminoacetone increases aldehydes and oxidative stress in rats

Semicarbazide-sensitive amine oxidase (SSAO)-mediated deamination of methylamine and aminoacetone in vitro produces carbonyl compounds, such as formaldehyde and methylglyoxal, which have been proposed to be cytotoxic and may be responsible for some pathological conditions. An HPLC procedure was developed to assess different aldehydes, which were derivatized with 2,4-dinitrophenylhydrazine (DNPH). We have demonstrated in vivo deamination of methylamine and aminoacetone by examining the excretion of formaldehyde and methylglyoxal, respectively, in rats. Following chronic administration of methylamine, the urinary level of malondialdehyde (MDA), an end product of lipid peroxidation, was also found to be substantially increased. A selective SSAO inhibitor blocked the increase of MDA. The results support the idea that increased SSAO-mediated deamination of methylamine and aminoacetone can be a potential cytotoxic risk factor.

Evidence of high levels of methylglyoxal in cultured Chinese hamster ovary cells

Methylglyoxal is an alpha-ketoaldehyde and dicarbonyl formed in cells as a side product of normal metabolism. Endogenously produced dicarbonyls, such as methylglyoxal, are involved in numerous pathogenic processes in vivo, including carcinogenesis and advanced glycation end-product formation; advanced glycation end-products are contributors to the pathophysiology of aging and chronic diabetes. Despite recent advances in understanding of the systemic effects of methylglyoxal, the full significance of this compound remains unknown. Herein we provide evidence that the majority of the methylglyoxal present in vivo is bound to biological ligands. The basis for our finding is an experimental approach that provides a measure of the bound methylglyoxal present in living systems, in this instance Chinese hamster ovary cells; with our approach, as much as 310 microM methylglyoxal was detected, 100- to 1,000-fold more than observed previously in biological systems. Several artifacts were considered before concluding that the methylglyoxal was associated with cellular structures, including phosphate elimination from triose phosphates, carbohydrate degradation under the assay conditions, and interference from the derivatizing agent used as part of the assay procedure. A major source of the recovered methylglyoxal is most probably modified cellular proteins. With methylglyoxal at about 300 microM, 0.02% of cellular amino acid residues could be modified. As few as one or two "hits" with methylglyoxal per protein molecule have previously been reported to be sufficient to cause protein endocytosis and subsequent degradation. Thus, 5-10% of cellular proteins may be modified to physiologically significant levels.

Incidence and potential implications of the toxic metabolite methylglyoxal in cell culture: A review

Methylglyoxal is a toxic metabolite unavoidably produced in mammalian systems as a by-product of glycolysis. Detoxification of this compound occurs principally through the glyoxalase pathway, which consists of glyoxalase I and glyoxalase II, and requires reduced glutathione as a co-enzyme. Recently, it has been demonstrated that variations in glucose, glutamine and fetal bovine serum levels can cause significant changes in the intracellular concentration of methylglyoxal. More importantly, comparative studies involving wild-type Chinese hamster ovary cells and clones overexpressing glyoxalase I indicate that glucose and glutamine, within the range normally found in cell culture media, can cause decreased cell viability mediated solely through increased production of methylglyoxal. In addition, endogenously produced methylglyoxal has been shown to cause apoptosis in cultured HL60 cells. While the exact mechanism of the impact of methylglyoxal on cultured cells is unknown, methylglyoxal is a potent protein and nucleic acid modifying agent at physiological concentrations and under physiological conditions. Protein modification occurs mainly at arginine, lysine and cysteine residues and is believed to be an important signal for the degradation of senescent proteins. Modification of arginine and lysine results in the irreversible formation of advanced glycation endproducts, whereas modification of cysteine results in the formation of a highly reversible hemithioacetal. Methylglyoxal also forms adducts with nucleic acids, principally with guanyl residues. At high extracellular concentrations, it is genotoxic to cells grown in culture. Even at physiological concentrations (100 nM free methylglyoxal), methylglyoxal can modify unprotected plasmid DNA and cause gene mutation and abnormal gene expression.

High-performance liquid chromatographic-fluorometric determination of glyoxal, methylglyoxal, and diacetyl in urine by prederivatization to pteridinic rings

A sensitive and simple liquid chromatographic method to determine glyoxal, methylglyoxal, and diacetyl is reported. The method is based on the conversion to the corresponding pteridin derivatives (pterin, 6-methylpterin, and 6,7-dimethylpterin). The proposed method using fluorometric detection has been applied to the determination of the three alpha-dicarbonyl compounds in human urine. Linearity (peak area vs concentration of alpha-dicarbonyl) was observed at least up to 43 microM. Detection limits of 32 pmol for glyoxal, 11 pmol for methylglyoxal, and 99 pmol for diacetyl were calculated (20 microliters was injected). Levels of 132 microM for glyoxal and 15 microM for methylglyoxal were determined in normal urine samples, while diacetyl was not detected.