Determination of glyoxal and methylglyoxal in the serum of diabetic patients by MEKC using stilbenediamine as derivatizing reagent

Highly sensitive spectrofluorimetric method for the determination of the genotoxic methylglyoxal in glycerol-containing pharmaceuticals and dietary supplements

Methylglyoxal (MGO) is a genotoxic α-dicarbonyl compound. Recently, it was found to be formed in glycerol preparations during storage through auto-oxidation. A simple fluorimetric determination of the carcinogenic degradation product of glycerol, MGO, was developed and validated. The proposed method is based on the derivatization of MGO with 4-carbomethoxybenzaldehyde (CMBA) and ammonium acetate to yield a fluorescent imidazole derivative that can be measured at 415 nm after excitation at 322 nm. The optimized conditions were determined to be 0.2 M CMBA, 1.0 M ammonium acetate and a reaction time of 40 min at 90°C using ethanol as diluting solvent. The linear range was 10.0-200.0 ng/ml. Detection and quantification limits were 2.22 and 6.72 ng/ml, respectively. The proposed method was validated according to International Council for Harmonisation (ICH) guidelines and compared with the reported method and no significant difference was found. It was successfully applied for the determination of MGO in six different glycerol-containing pharmaceutical preparations and dietary supplements.

NIR-I fluorescence imaging tumorous methylglyoxal by an activatable nanoprobe based on peptide nanotubes by FRET process

Methylglyoxal (MGO), a glycolysis metabolite with high reactivity, can nonenzymatically modify proteins, lipids and nucleic acids etc., and it is closely related to the development of tumors. The accurate detection and high-performance optical imaging of MGO from deep tumor issues is of great significance for understanding their roles in tumor initiation and progression. Herein, we have presented a nanoprobe D/I-PNTs with emission in the first near infrared (NIR-I) region by employing a fluorescence resonance energy transfer (FRET) process between a far-red emission MGO probe and IR783 based on peptide nanotubes. The nanoplatform extended the emission range of MGO probe through FRET process and avoided complex molecular design and synthesis. The biocompatible peptide nanotubes improved the water solubility of MGO probe. D/I-PNTs was sensitive to MGO with a detection limit of 272 nM and enabled high-resolution NIR-I fluorescence imaging of MGO induced by glyoxalase I (GLO1) inhibitor in tumor with higher penetration depth (∼4 mm) than that in visible (Vis) region (∼3 mm). Most importantly, the FRET process based on the structure characteristics of peptide nanotubes can be a universal approach to realize the extension of emission wavelength and ratio detection of target analytes, which will be a promising strategy for bioimaging in deep tissue with high contrast.

Determination of glyoxal and methylglyoxal in serum by UHPLC coupled with fluorescence detection

Glyoxal (GO) and methylglyoxal (MGO) are two important biomarkers in diabetes. Analytical methods for determination of GO and MGO in serum samples are either HPLC with UV-Vis (low sensitivity) or MS/MS (expensive) detection. These disadvantages have hampered the introduction of these biomarkers as a routine analyte for diabetes diagnostics into the clinical laboratory. In this study, we introduce a UHPLC method with fluorescence detection for the measurement of GO and MGO in serum samples by pre-column derivatization at neutral pH with 5, 6-diamino-2,4-dihydroxypyrimidine sulfate (DDP) to form lumazines. The method was validated as per FDA guidelines. Using this method, we have determined GO and MGO in a variety of animal serum samples, and for example, determined the GO and MGO concentration in adult bovine serum to be 852 ± 27 and 192 ± 10 nmol/L, respectively. In human serum, GO and MGO levels in non-diabetic subjects (n = 14) were determined to be 154 ± 88 and 98 ± 27 nmol/L, and in serum samples from subjects with diabetes (n = 14) 244 ± 137 and 190 ± 68 nmol/L, respectively. In addition, interference studies showed that physiological serum components did not lead to an artificial increase in the levels of GO and MGO.

Elevated levels of α-dicarbonyl compounds in the plasma of type II diabetics and their relevance with diabetic nephropathy

The presence of α‑dicarbonyl compounds (α-DCs) in vivo has been associated with the development of complications of diabetes mellitus (DM) and also with other chronic diseases. Therefore, quantitative analysis of α-DCs in body fluids is crucial to understand their roles in the formation of these chronic diseases. We established in this study a practical HPLC-UV method to measure 3‑deoxyglucosone (3-DG), glyoxal (GO), methylglyoxal (MGO), diacetyl (DA), and pentane‑2,3‑dione (PD) in blood plasma using 4‑(2,3‑dimethyl‑6‑quinoxalinyl)‑1,2‑benzenediamine (DQB) as a derivatizing reagent. The derivatizing reaction could be carried out quickly under mild conditions and the HPLC determination is simple, sensitive, and easy to operate. The recoveries of the α-DCs are between 85.26% and 110.20% (intra-day) and 87.25% and 103.18% (inter-day); the RSDs are between 1.28% and 5.69% (intra-day) and 2.26% and 6.34% (inter-day). We found the plasma levels of 3-DG, GO, and MGO in the diabetic patients are all significantly higher than those in healthy subjects. The results also show that the contents of GO and MGO in diabetic nephropathy (DN) patients are both significantly higher than those in simple T2DM patients. Moreover, it is found for the first time that the plasma level of GO might be a potential predictor of DN. The developed method would be useful for the measurements of the plasma α-DCs and the data acquired could be informative in the diagnosis of DM complications.

Methylglyoxal-induced apoptosis is dependent on the suppression of c-FLIPL expression via down-regulation of p65 in endothelial cells

Methylglyoxal (MGO) is a reactive dicarbonyl metabolite of glucose, and its plasma levels are elevated in patients with diabetes. Studies have shown that MGO combines with the amino and sulphhydryl groups of proteins to form stable advanced glycation end products (AGEs), which are associated with vascular endothelial cell (EC) injury and may contribute to the progression of atherosclerosis. In this study, MGO induced apoptosis in a dose-dependent manner in HUVECs, which was attenuated by pre-treatment with z-VAD, a pan caspase inhibitor. Treatment with MGO increased ROS levels, followed by dose-dependent down-regulation of c-FLIP_L . In addition, pre-treatment with the ROS scavenger NAC prevented the MGO-induced down-regulation of p65 and c-FLIP_L , and the forced expression of c-FLIP_L attenuated MGO-mediated apoptosis. Furthermore, MGO-induced apoptotic cell death in endothelium isolated from mouse aortas. Finally, MGO was found to induce apoptosis by down-regulating p65 expression at both the transcriptional and posttranslational levels, and thus, to inhibit c-FLIP_L mRNA expression by suppressing NF-κB transcriptional activity. Collectively, this study showed that MGO-induced apoptosis is dependent on c-FLIP_L down-regulation via ROS-mediated down-regulation of p65 expression in endothelial cells.

LR-90 prevents methylglyoxal-induced oxidative stress and apoptosis in human endothelial cells

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound known to induce cellular injury and cytoxicity, including apoptosis in vascular cells. Vascular endothelial cell apoptosis has been implicated in the pathophysiology and progression of atherosclerosis. We investigated whether the advanced glycation end-product inhibitor LR-90 could prevent MGO-induced apoptosis in human umbilical vascular endothelial cells (HUVECs). HUVECs were pre-treated with LR-90 and then stimulated with MGO. Cell morphology, cytotoxicity and apoptosis were evaluated by light microscopy, MTT assay, and Annexin V-FITC and propidium iodide double staining, respectively. Levels of Bax, Bcl-2, cytochrome c, mitogen-activated protein kinases (MAPKs) and caspase activities were assessed by Western blotting. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. LR-90 dose-dependently prevented MGO-associated HUVEC cytotoxicity and apoptotic biochemical changes such as loss of MMP, increased Bax/Bcl-2 protein ratio, mitochondrial cytochrome c release and activation of caspase-3 and 9. Additionally, LR-90 blocked intracellular ROS formation and MAPK (p44/p42, p38, JNK) activation, though the latter seem to be not directly involved in MGO-induced HUVEC apoptosis. LR-90 prevents MGO-induced HUVEC apoptosis by inhibiting ROS and associated mitochondrial-dependent apoptotic signaling cascades, suggesting that LR-90 possess cytoprotective ability which could be beneficial in prevention of diabetic related-atherosclerosis.

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.

Chromatographic determination of low-molecular mass unsaturated aliphatic aldehydes with peroxyoxalate chemiluminescence detection after fluorescence labeling with 4-(N,N-dimethylaminosulfonyl)-7-hydrazino-2,1,3-benzoxadiazole

A highly sensitive, selective and reproducible chromatographic method is described for determination of low-molecular mass unsaturated aliphatic aldehydes in human serum. The method combines fluorescent labeling using 4-(N,N-Dimethylaminosulfonyl)-7-hydrazino-2,1,3-benzoxadiazole with peroxyoxalate chemiluminescence. The derivatives were separated on a reversed-phase column C8 isocratically using a mixture of acetonitrile and 90mM imidazole-HNO3 buffer (pH 6.4, 1:1, % v/v). The calibration ranges were: 20-420nM for methylglyoxal, 16-320nM for acrolein, 15-360nM for crotonaldehyde and 20-320nM for trans-2-hexenal. The detection limits were ranged from 4.4 to 6.5nM (88-130fmol/injection), the recovery results were within the range of 87.4-103.8% and the intra and inter-day precision results were lower than 5.5%. The proposed validated method has been successfully applied to healthy, diabetic and rheumatic arthritis patients' sera with simple pretreatment method. In conclusion, this new method is suitable for routine analysis of large numbers of clinical samples for assessment of the oxidative stress state in patients.

High throughput assay for evaluation of reactive carbonyl scavenging capacity

Many carbonyl species from either lipid peroxidation or glycoxidation are extremely reactive and can disrupt the function of proteins and enzymes. 4-hydroxynonenal and methylglyoxal are the most abundant and toxic lipid-derived reactive carbonyl species. The presence of these toxics leads to carbonyl stress and cause a significant amount of macromolecular damages in several diseases. Much evidence indicates trapping of reactive carbonyl intermediates may be a useful strategy for inhibiting or decreasing carbonyl stress-associated pathologies. There is no rapid and convenient analytical method available for the assessment of direct carbonyl scavenging capacity, and a very limited number of carbonyl scavengers have been identified to date, their therapeutic potential being highlighted only recently. In this context, we have developed a new and rapid sensitive fluorimetric method for the assessment of reactive carbonyl scavengers without involvement glycoxidation systems. Efficacy of various thiol- and non-thiol-carbonyl scavenger pharmacophores was tested both using this screening assay adapted to 96-well microplates and in cultured cells. The scavenging effects on the formation of Advanced Glycation End-product of Bovine Serum Albumin formed with methylglyoxal, 4-hydroxynonenal and glucose-glycated as molecular models were also examined. Low molecular mass thiols with an α-amino-β-mercaptoethane structure showed the highest degree of inhibitory activity toward both α,β-unsaturated aldehydes and dicarbonyls. Cysteine and cysteamine have the best scavenging ability toward methylglyoxal. WR-1065 which is currently approved for clinical use as a protective agent against radiation and renal toxicity was identified as the best inhibitor of 4-hydroxynonenal.

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We describe a rapid method for assessment of reactive carbonyl scavengers.

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We evaluated the carbonyl scavenger activity of various pharmacophores.

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α-amino-β-mercaptoethane structure showed the highest degree of activity.

High-performance liquid chromatography determination of glyoxal, methylglyoxal, and diacetyl in urine using 4-methoxy-o-phenylenediamine as derivatizing reagent

Bioanalytical relevance of glyoxal (Go) and methylglyoxal (MGo) arises from their role as biomarkers of glycation processes and oxidative stress. The third compound of interest in this work is diacetyl (DMGo), a component of different food products and alcoholic beverages and one of the small α-ketoaldehydes previously reported in urine. The original idea for the determination of the above compounds by reversed phase high-performance liquid chromatography (HPLC) with fluorimetric detection was to use 4-methoxy-o-phenylenediamine (4MPD) as a derivatizing reagent and diethylglyoxal (DEGo) as internal standard. Acetonitrile was added to urine for matrix precipitation, and derivatization reaction was carried out in the diluted supernatant at neutral pH (40 °C, 4 h); after acidification, salt-induced phase separation enabled recovery of the obtained quinoxalines in the acetonitrile layer. The separation was achieved within 12 min using a C18 Kinetex column and gradient elution. The calibration detection limits for Go, MGo, and DMGo were 0.46, 0.39, and 0.28 μg/L, respectively. Within-day precision for real-world samples did not exceed 6%. Several urine samples from healthy volunteers, diabetic subjects, and juvenile swimmers were analyzed. The sensitivity of the procedure proposed here enabled detection of differences between analyte concentrations in urine from patients at different clinical or exposure-related conditions.

Glycolaldehyde induces cytotoxicity and increases glutathione and multidrug-resistance-associated protein levels in Schwann cells

Schwann cell injury is observed in diabetic neuropathy. It is speculated that glycolaldehyde (GA), a precursor of advanced glycation end products (AGEs), contributes to the pathogenesis and development of diabetic neuropathy. Here, we demonstrated for the first time that GA at near-physiological concentration decreased the viability of rat Schwann cells. In contrast, methylglyoxal, glyoxal, and 3-deoxyglucosone, all of which are AGE precursors, had no effects on cell viability. It is well known that methylglyoxal causes oxidative damage. In the present study, however, GA failed to induce reactive oxygen species production in Schwann cells. The addition of glutathione (GSH) or N-acetyl-L-cysteine protected Schwann cells from the loss of viability induced by GA. Moreover, GA increased intracellular GSH level and γ-glutamylcysteine synthetase mRNA level. Flow cytometric analysis revealed that GA increased multidrug-resistance-associated protein 1 (MRP1) level as well. Moreover, we demonstrated that the knockdown of MRP1 with small interfering RNA (siRNA) enhanced the loss of cell viability induced by GA. Taken together, these findings suggest that MRP1, together with GSH, plays an important role in the GA-induced toxicity in Schwann cells.

Methylglyoxal has deleterious effects on thioredoxin in human aortic endothelial cells

Methylglyoxal (MG), a precursor of advanced glycation end products (AGEs), is elevated in diabetic patient's plasma. Some studies have demonstrated that MG induces oxidative stress and apoptosis. Thioredoxin (Trx) is a cytoprotective protein with anti-oxidative and anti-apoptosis functions. In this study, we examined the effects of MG on Trx in human aortic endothelial cells (HAECs). MG increased oxidized-hydroethidine fluorescence intensity, suggesting intracellular accumulation of reactive oxygen species. Flow cytometric analyses with annexin-V/propidium iodide double staining revealed that cells incubated with MG displayed features characteristic of apoptosis. The condensation of chromatin, the release of cytochrome c into cytosol, and the collapse of mitochondrial membrane potential by MG were observed. The exposure to MG decreased Trx protein levels through transcription regulation. MG induced the oxidative damage of peroxiredoxin, a Trx-dependent peroxidase. These results suggest that MG has deleterious effects on Trx in HAECs, which may be contribute to oxidative stress and apoptosis.

Role of advanced glycation endproducts and glyoxalase I in diabetic peripheral sensory neuropathy

Diabetic neuropathy is the most common and debilitating complication of diabetes mellitus with more than half of all patients developing altered sensation as a result of damage to peripheral sensory neurons. Hyperglycemia results in altered nerve conduction velocities, loss of epidermal innervation, and development of painful or painless signs and symptoms in the feet and hands. Current research has been unable to determine whether a patient will develop insensate or painful neuropathy or be protected from peripheral nerve damage all together. One mechanism that has been recognized to have a role in the pathogenesis of sensory neuron damage is the process of reactive dicarbonyls forming advanced glycation endproducts (AGEs) as a direct result of hyperglycemia. The glyoxalase system, composed of the enzymes glyoxalase I (GLO1) and glyoxalase II, is the main detoxification pathway involved in breaking down toxic reactive dicarbonyls before producing carbonyl stress and forming AGEs on proteins, lipids, or nucleic acids. This review discusses AGEs, GLO1, their role in diabetic neuropathy, and potential therapeutic targets of the AGE pathway.

Glucose metabolite glyoxal induces senescence in telomerase-immortalized human mesenchymal stem cells

BACKGROUND

Various by-products of the cellular metabolism, such as reactive carbonyl species (RCS) are potentially harmful to cells and tissues, and play a role in many physiological and pathological processes. Among various RCS is the highly reactive dicarbonyl glyoxal (GO), which is a natural physiological metabolite produced by the auto-oxidation of glucose, and can form covalent adducts known as advanced glycation endproducts (AGE). We have previously reported that GO accelerates ageing and causes premature senescence in normal human skin fibroblasts.

RESULTS

Using a bone marrow-derived telomerase-immortalised mesenchymal stem cell line hMSC-TERT we have observed that an exposure of cells to 0.75 mM and 1 mM GO induces irreversible cellular senescence within 3 days. Induction of senescence in hMSC-TERT was demonstrated by a variety of markers, including characteristic cell morphology and enlargement, vacuolisation, multinucleation, induction of senescence associated β-galactosidase, cell cycle arrest, and increased levels of a cell cycle inhibitor p16. These changes were accompanied by increased extent of DNA breaks as measured by the comet assay, and increased levels of the AGE product, carboxymethyl-lysine (CML). Furthermore, the in vitro differentiation potential of hMSC-TERT to become functional osteoblasts was highly reduced in GO-treated stem cells, as determined by alkaline phosphatase (ALP) activity and mineralized matrix (MM) formation.

CONCLUSIONS

The results of our study imply that an imbalanced glucose metabolism can reduce the functioning ability of stem cells in vivo both during ageing and during stem cell-based therapeutic interventions.

Molecular basis of maillard amide-advanced glycation end product (AGE) formation in vivo

The Maillard reaction in vivo entails alteration of proteins or free amino acids by non-enzymatic glycation or glycoxidation. The resulting modifications are called advanced glycation end products (AGEs) and play a prominent role in various pathologies, including normoglycemic uremia. Recently, we established a new class of lysine amide modifications in vitro. Now, human plasma levels of the novel amide-AGEs N(6)-acetyl lysine, N(6)-formyl lysine, N(6)-lactoyl lysine, and N(6)-glycerinyl lysine were determined by means of LC-MS/MS. They were significantly higher in uremic patients undergoing hemodialysis than in healthy subjects. Model reactions with N(1)-t-butoxycarbonyl-lysine under physiological conditions confirmed 1-deoxy-d-erythro-hexo-2,3-diulose as an immediate precursor. Because formation of N(6)-formyl lysine from glucose responded considerably to the presence of oxygen, glucosone was identified as another precursor. Comparison of the in vivo results with the model experiments enabled us to elucidate possible formation pathways linked to Maillard chemistry. The results strongly suggest a major participation of non-enzymatic Maillard mechanisms on amide-AGE formation pathways in vivo, which, in the case of N(6)-acetyl lysine, parallels enzymatic processes.

MEKC as a powerful growing analytical technique

This review summarizes the principle and the developments in MEKC in terms of separation power, sensitivity, and detection approaches more than 25 years after its appearance. Newly used surfactants are mentioned. Classical and new sample concentration techniques in MEKC are described. The different detection approaches in MEKC with advantages, limitations, and future prospects are also discussed. This review highlights the wider application of MEKC in different analytical fields. Various recent selected applications of this technique in different analytical fields are reported.

Buthionine sulfoximine promotes methylglyoxal-induced apoptotic cell death and oxidative stress in endothelial cells

Methylglyoxal (MG), a reactive dicarbonyl produced during glucose metabolism, is found at high levels in the blood of diabetic patients. MG induces oxidative stress and apoptosis. There is evidence that MG causes glutathione (GSH) depletion. However, it remains unknown whether GSH plays a protective role against the cytotoxic effect of MG. We examined the effect of DL-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of glutathione (GSH) biosynthesis, on the viability of bovine aortic endothelial cells (BAECs) exposed to MG. BAECs pretreated with BSO showed reduced ability to survive MG exposure. Flow cytometric analyses with annexin V and propidium iodide double staining revealed that BAECs exposed to MG after BSO pretreatment displayed features characteristic of apoptosis. Caspase-3 activation induced by MG was increased by BSO. Moreover, measurement of protein carbonyl levels showed that BSO promoted MG-induced oxidative stress. Taken together, these findings suggest that the depletion of GSH via BSO pretreatment promoted MG-induced apoptotic cell death and oxidative stress in BAECs.

Methylglyoxal increases cardiomyocyte ischemia-reperfusion injury via glycative inhibition of thioredoxin activity

Diabetes mellitus (DM) is closely related to cardiovascular morbidity and mortality, but the specific molecular basis linking DM with increased vulnerability to cardiovascular injury remains incompletely understood. Methylglyoxal (MG), a precursor to advanced glycation end products (AGEs), is increased in diabetic patient plasma, but its role in diabetic cardiovascular complications is unclear. Thioredoxin (Trx), a cytoprotective molecule with antiapoptotic function, has been demonstrated to be vulnerable to glycative inhibition, but whether Trx is glycatively inhibited by MG, thus contributing to increased cardiac injury, has never been investigated. Cultured H9c2 cardiomyocytes were treated with MG (200 muM) for 6 days. The following were determined pre- and post-simulated ischemia-reperfusion (SI-R; 8 h of hypoxia followed by 3 h of reoxygenation): cardiomyocyte death/apoptosis, Trx expression and activity, AGE formation, Trx-apoptosis-regulating kinase-1 (Trx-ASK1) complex formation, and p38 mitogen-activated protein kinase (MAPK) phosphorylation and activity. Compared with vehicle, MG significantly increased SI-R-induced cardiomyocyte LDH release and apoptosis (P < 0.01). Prior to SI-R, Trx activity was reduced in MG-treated cells, but Trx expression was increased moderately. Moreover, Trx-ASK1 complex formation was reduced, and both p38 MAPK activity and phosphorylation were increased. To investigate the effects of MG on Trx directly, recombinant human Trx (hTrx) was incubated with MG in vitro. Compared with vehicle, MG incubation markedly increased CML formation (a glycation footprint) and inhibited Trx activity. Finally, glycation inhibitor aminoguanidine administration during MG treatment of cultured cells reduced AGE formation, increased Trx activity, restored Trx-ASK1 interaction, and reduced p38 MAPK phosphorylation and activity, caspase-3 activation, and LDH release (P < 0.01). We demonstrated for the first time that methylglyoxal sensitized cultured cardiomyocytes to SI-R injury by posttranslational modification of Trx via glycation. Therapeutic interventions scavenging AGE precursors may attenuate ischemic-reperfusion injury in hyperglycemic state diseases such as diabetes.

Kinetic characterization and comparison of various protein crosslinking reagents for matrix modification

We have characterized the relative efficacies of a number of protein crosslinking agents that have the potential for use in the crosslinking of proteinaceous matrices both in vitro and in vivo. The crosslinkers tested were; L: -threose (LT), Genipin (GP), Methylglyoxal (MG), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), proanthrocyanidin (PA) and glutaraldehyde (GA). The relative effectiveness of the crosslinkers with regard to their saturating concentrations was: GA > PA > EDC > MG = GP >> LT. Most of the crosslinkers displayed a pH dependence and were more effective at more alkaline pH. At optimal pH and saturating conditions, the relative reaction rates of the crosslinkers were: PA = GA > EDC > GP > MG >> LT.

Methylglyoxal causes dysfunction of thioredoxin and thioredoxin reductase in endothelial cells

Methylglyoxal (MG), a reactive dicarbonyl produced during glucose metabolism, induces oxidative stress and apoptosis. Under hyperglycemic conditions, the abnormal accumulation of MG is related to the development of diabetic complications. We examined the effects of MG on thioredoxin (Trx) and glutaredoxin (Grx) systems, two thiol-disulfide oxidoreductase systems that protect against oxidative damage of proteins, in bovine aortic endothelial cells (BAECs). The levels of protein carbonyls as markers of protein oxidation increased in BAECs exposed to MG at 5 mM, resulting in the loss of cell viability. Western blot analysis demonstrated that Trx protein level decreased when BAECs were exposed to 5 mM MG. MG also inactivated Trx reductase, which maintains Trx in the reduced/active state. Moreover, peroxiredoxin, which is dependent on Trx and Trx reductase to maintain its reduced state, was oxidized by 5 mM MG. No significant difference in the levels of Trx, Trx reductase, or peroxiredoxin was observed in BAECs exposed to MG at 1 mM; this concentration had little effect on protein carbonyl formation and cell viability. MG failed to decrease Grx activity, indicating that Trx is more susceptible to MG than Grx. Taken together, these findings suggest that MG causes dysfunction of the Trx system, including Trx and Trx reductase, in BAECs.

Carnosine and its possible roles in nutrition and health

The dipeptide carnosine has been observed to exert antiaging activity at cellular and whole animal levels. This review discusses the possible mechanisms by which carnosine may exert antiaging action and considers whether the dipeptide could be beneficial to humans. Carnosine's possible biological activities include scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS), chelator of zinc and copper ions, and antiglycating and anticross-linking activities. Carnosine's ability to react with deleterious aldehydes such as malondialdehyde, methylglyoxal, hydroxynonenal, and acetaldehyde may also contribute to its protective functions. Physiologically carnosine may help to suppress some secondary complications of diabetes, and the deleterious consequences of ischemic-reperfusion injury, most likely due to antioxidation and carbonyl-scavenging functions. Other, and much more speculative, possible functions of carnosine considered include transglutaminase inhibition, stimulation of proteolysis mediated via effects on proteasome activity or induction of protease and stress-protein gene expression, upregulation of corticosteroid synthesis, stimulation of protein repair, and effects on ADP-ribose metabolism associated with sirtuin and poly-ADP-ribose polymerase (PARP) activities. Evidence for carnosine's possible protective action against secondary diabetic complications, neurodegeneration, cancer, and other age-related pathologies is briefly discussed.