Oxidative damage of DNA induced by methylglyoxal in vitro

Oxidative and Glycation Damage to Mitochondrial DNA and Plastid DNA during Plant Development

Oxidative damage to plant proteins, lipids, and DNA caused by reactive oxygen species (ROS) has long been studied. The damaging effects of reactive carbonyl groups (glycation damage) to plant proteins and lipids have also been extensively studied, but only recently has glycation damage to the DNA in plant mitochondria and plastids been reported. Here, we review data on organellar DNA maintenance after damage from ROS and glycation. Our focus is maize, where tissues representing the entire range of leaf development are readily obtained, from slow-growing cells in the basal meristem, containing immature organelles with pristine DNA, to fast-growing leaf cells, containing mature organelles with highly-fragmented DNA. The relative contributions to DNA damage from oxidation and glycation are not known. However, the changing patterns of damage and damage-defense during leaf development indicate tight coordination of responses to oxidation and glycation events. Future efforts should be directed at the mechanism by which this coordination is achieved.

6-Formyl Umbelliferone, a Furanocoumarin from Angelica decursiva L., Inhibits Key Diabetes-Related Enzymes and Advanced Glycation End-Product Formation

Over the years, great attention has been paid to coumarin derivatives, a set of versatile molecules that exhibit a wide variety of biological activities and have few toxic side effects. In this study, we investigated the antidiabetic potential of 6-formyl umbelliferone (6-FU), a novel furanocoumarin isolated from Angelica decursiva. Numerous pharmacological activities of 6-FU have been previously reported; however, the mechanism of its antidiabetic activity is unknown. Therefore, we examined the action of 6-FU on a few candidate-signaling molecules that may underlie its antidiabetic activity, including its inhibition of protein tyrosine phosphatase 1B (PTP1B), α-glucosidase, human recombinant aldose reductase (HRAR), and advanced glycation end-product (AGE) formation (IC₅₀ = 1.13 ± 0.12, 58.36 ± 1.02, 5.11 ± 0.21, and 2.15 ± 0.13 μM, respectively). A kinetic study showed that 6-FU exhibited mixed-type inhibition against α-glucosidase and HRAR and competitive inhibition of PTP1B. Docking simulations of 6-FU demonstrated negative binding energies and close proximity to residues in the binding pockets of those enzymes. We also investigated the molecular mechanisms underlying 6-FU's antidiabetic effects. 6-FU significantly increased glucose uptake and decreased PTP1B expression in insulin-resistant C2C12 skeletal muscle cells. Moreover, 6-FU (0.8-100 μM) remarkably inhibited the formation of fluorescent AGEs in glucose-fructose-induced human serum albumin glycation over the course of 4 weeks. The findings clearly indicate that 6-FU will be useful in the development of multiple target-oriented therapeutic modalities for the treatment of diabetes and diabetes-related complications.

Glycation damage to organelles and their DNA increases during maize seedling development

Shoot development in maize begins when meristematic, non-pigmented cells at leaf base stop dividing and proceeds toward the expanded green cells of the leaf blade. During this transition, promitochondria and proplastids develop into mature organelles and their DNA becomes fragmented. Changes in glycation damage during organelle development were measured for protein and DNA, as well as the glycating agent methyl glyoxal and the glycation-defense protein DJ-1 (known as Park7 in humans). Maize seedlings were grown under normal, non-stressful conditions. Nonetheless, we found that glycation damage, as well as defenses against glycation, follow the same developmental pattern we found previously for reactive oxygen species (ROS): as damage increases, damage-defense measures decrease. In addition, light-grown leaves had more glycation and less DJ-1 compared to dark-grown leaves. The demise of maize organellar DNA during development may therefore be attributed to both oxidative and glycation damage that is not repaired. The coordination between oxidative and glycation damage, as well as damage-response from the nucleus is also discussed.

Functional compartmentalization and metabolic separation in a prokaryotic cell

The prokaryotic cell is traditionally seen as a "bag of enzymes," yet its organization is much more complex than in this simplified view. By now, various microcompartments encapsulating metabolic enzymes or pathways are known for Bacteria These microcompartments are usually small, encapsulating and concentrating only a few enzymes, thus protecting the cell from toxic intermediates or preventing unwanted side reactions. The hyperthermophilic, strictly anaerobic Crenarchaeon Ignicoccus hospitalis is an extraordinary organism possessing two membranes, an inner and an energized outer membrane. The outer membrane (termed here outer cytoplasmic membrane) harbors enzymes involved in proton gradient generation and ATP synthesis. These two membranes are separated by an intermembrane compartment, whose function is unknown. Major information processes like DNA replication, RNA synthesis, and protein biosynthesis are located inside the "cytoplasm" or central cytoplasmic compartment. Here, we show by immunogold labeling of ultrathin sections that enzymes involved in autotrophic CO₂ assimilation are located in the intermembrane compartment that we name (now) a peripheric cytoplasmic compartment. This separation may protect DNA and RNA from reactive aldehydes arising in the I. hospitalis carbon metabolism. This compartmentalization of metabolic pathways and information processes is unprecedented in the prokaryotic world, representing a unique example of spatiofunctional compartmentalization in the second domain of life.

Ginsenoside derivatives inhibit advanced glycation end-product formation and glucose-fructose mediated protein glycation in vitro via a specific structure-activity relationship

Ginseng (Panax ginseng and red ginseng) extract has been reported to inhibit the formation of advanced glycation end-products (AGEs); however, the potential inhibitory activity of its major constituents (ginsenosides) against AGE formation is still unknown. In the present study, we investigated the inhibitory effect of ginsenoside derivatives on AGE formation. Herein, we assessed the activity of 22 ginsenosides, most of which significantly inhibited fluorescent AGE formation. Notably, ginsenoside Rh2, ginsenoside Rh1, and compound K exhibited the most potent AGE inhibitory potential with IC₅₀ values of 3.38, 8.42, and 10.85 µM, respectively. The structure- activity relationship revealed that the presence of sugar moieties, hydroxyl groups, and their linkages, and the stereostructure of the ginsenoside skeleton played an important role in the inhibition of AGE formation. Furthermore, the inhibitory activity of the most active ginsenoside Rh2 on fructose-glucose-mediated protein glycation and oxidation of bovine serum albumin (BSA) was explored. Rh2 (0.1-12.5 µM) inhibited the formation of fluorescent AGE and non-fluorescent AGE, as well as the level of fructosamine and prevented protein oxidation by decreasing protein carbonyl formation and protein thiol group modification. Rh2 also suppressed the formation of the β-cross amyloid structure of BSA. Ginsenosides might be promising new anti-glycation agents for the prevention of diabetic complications via inhibition of AGE formation and oxidation-dependent protein damage.

Protective role of Clitoria ternatea L. flower extract on methylglyoxal-induced protein glycation and oxidative damage to DNA

BACKGROUND

Methylglyoxal (MG) is a highly reactive dicarbonyl precursor for the formation of advanced glycation end products (AGEs) associated with age-related diseases, including diabetes and its complications. Clitoria ternatea L. flower has been reported to possess antioxidant and antiglycating properties. Evidence indicates that the extract of Clitoria ternatea L. flower inhibits fructose-induced protein glycation and oxidative damage to bovine serum albumin (BSA). However, there is no evidence to support the inhibitory effect of CTE against MG-mediated protein glycation and oxidative damage to protein and DNA. Therefore, the aim of the present study was to investigate whether C. ternatea flower extract (CTE) prevents MG-induced protein glycation and oxidative DNA damage.

METHODS

The formation of fluorescent AGEs in BSA was evaluated using spectrofluorometer. The protein carbonyl and thiol group content were used for detecting protein oxidation. DNA strand breakage in a glycation model comprising of MG, lysine and Cu²⁺ or a free radical generator 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH) systems was investigated using gel electrophoresis. Generation of superoxide anions and hydroxyl radicals in the MG/lysine system was assessed by the cytochrome c reduction assay and thiobarbituric acid reactive substances assay, respectively. High performance liquid chromatography (HPLC) was used to measure the MG-trapping ability.

RESULTS

In the BSA/MG system, CTE (0.25-1 mg/mL) significantly inhibited the formation of fluorescent AGEs and protein oxidation by reducing protein carbonyl content as well as preventing the protein thiol depletion. The concentration of CTE at 0.125-1 mg/mL prevented oxidative DNA cleavage in MG/lysine and AAPH systems associated with the inhibition of superoxide anion and hydroxyl radical formation. It also directly trapped MG in a concentration-dependent manner, ranging from 15 to 43%.

CONCLUSIONS

The study findings suggest that the direct carbonyl trapping ability and the free radical scavenging activity of CTE are the underlying mechanisms responsible for the prevention of protein glycation and oxidative DNA damage.

Curcumin supplementation in the maturation medium improves the maturation, fertilisation and developmental competence of porcine oocytes

This study was conducted to determine the effects of supplementing the maturation medium with the antioxidant curcumin on the in vitro maturation (IVM), fertilisation and development of porcine oocytes. Curcumin supplementation was performed at concentrations of 0, 5, 10, 20, and 40 µM. At concentrations of 5-20 µM, curcumin had significant positive effects (P < 0.05) on maturation and fertilisation rates compared to the non-treated group. Of the groups cultured with 5-20 µM curcumin, the number of oocytes with DNA-fragmented nuclei after IVM was significantly lower than in groups matured without curcumin. Moreover, curcumin supplementation at 10 µM also gave a significantly higher rate of blastocyst formation compared with oocytes matured without curcumin. Increasing the curcumin concentration to 40 µM yielded negative effects on fertilisation and embryonic development compared with the groups treated with lower concentrations of curcumin. Supplementation with 10 µM curcumin had beneficial effects on the oocyte maturation rate and DNA fragmentation index compared to the non-treated group both in the presence and absence of hydrogen peroxide. These results indicate that curcumin supplementation at a suitable concentration (10 µM) is potentially useful for porcine oocyte culture systems, in terms of protecting oocytes from various forms of oxidative stress.

Poncirin, an orally active flavonoid exerts antidiabetic complications and improves glucose uptake activating PI3K/Akt signaling pathway in insulin resistant C2C12 cells with anti-glycation capacities

Poncirin, a natural flavanone glycoside present abundantly in many citrus fruits, contains an extensive range of biological activities. However, the antidiabetic mechanism of poncirin is unexplored yet. In this study, we examined the anti-diabetic prospective of poncirin by evaluating its ability to inhibit protein tyrosine phosphatase 1B (PTP1B), α-glucosidase, human recombinant AR (HRAR), rat lens aldose reductase (RLAR), and advanced glycation end-product (AGE) formation (IC₅₀ = 7.76 ± 0.21, 21.31 ± 1.26, 3.56 ± 0.33, 11.91 ± 0.21, and 3.23 ± 0.09 µM, respectively). Kinetics data and docking studies showed the lowest binding energy and highestaffinityforthemixed and competitivetypeof inhibitorsof poncirin. Moreover, the molecular mechanisms underlying the antidiabetic outcomes of poncirin in insulin resistant C2C12 skeletal muscle cells were explored, which significantly increased glucose uptake and decreased the expression of PTP1B in C2C12 cells. Consequently, poncirin increased GLUT-4 expression level by activating the IRS-1/PI3K/Akt/GSK-3 signaling pathway. Moreover, poncirin (0.5-50 µM) remarkably inhibited the formation of fluorescent AGE, nonfluorescent CML, fructosamine, and β-cross amyloid structures in glucose-fructose-induced BSA glycation during 4 weeks of study. Poncirin also notably prevented protein oxidation demonstrated with decreasing the protein carbonyl and the consumption of protein thiol in the dose-dependent manner. The results clearly expressed the promising activity of poncirin for the therapy of diabetes and its related complications.

Taurine-Containing Hot Water Extract of Octopus Ocellatus Meat Prevents Methylglyoxal-Induced Vascular Damage

Endothelial cell dysfunction (ECD) is a broad term, which implies dysregulation of endothelial cell functions. Several factors contribute to ECD including high blood pressure, high cholesterol levels, diabetes, obesity, hyperglycemia, and advanced glycation end products (AGEs). The highly reactive dicarbonyl methylglyoxal (MGO) is mainly formed as byproduct of glycolysis. Therefore, high blood glucose levels result in increased MGO accumulation. Taurine-rich foods are considered to protect against various diseases including vasculopathy and to exert anti-aging effects. Here, we investigated the protective effect of hot water extract of Octopus ocellatus meat (OOM), which contains high amounts of taurine, on MGO-induced cell damage in human umbilical vein endothelial cells and zebrafish embryos. Hot water extract of OOMinhibited MGO-induced cytotoxicity and DNA damage, as well as AGEs accumulation. In addition, hot water extract of OOM protected against vascular damage in zebrafish embryos. These results suggest that hot water extract of OOM possesses protective activity against MGO-induced cytotoxicity in both umbilical vein endothelial cells and zebrafish embryos. Therefore, it could be used as a dietary source of an agent for the prevention of vascular diseases.

Methylglyoxal displays colorectal cancer-promoting properties in the murine models of azoxymethane and CT26 isografts

Methylglyoxal (MG), a highly reactive carbonyl species (RCS) with pro-oxidant and proinflammatory properties, may be a colon tumor-promoting factor in food and biological systems. In the present study, we found that consumption of MG significantly deteriorated azoxymethane (AOM)-induced colonic preneoplastic lesions in ICR mice, in which biomarkers of oxidative stress and inflammation within the body and feces induced by MG-fueled carbonyl stress may have played important roles. Interestingly, exposure to MG also led to increases in the serum low-density lipoprotein (LDL)/high-density lipoprotein (HDL) ratio and fecal bile acid levels in mice, which may be critical factors involved in MG-induced colonic lesions. Additionally, MG treatment (50mg/kg body weight (BW); intraperitoneally) promoted tumor growth of CT26 isografts in mice partly by carbonyl stress-evoked protumorigenic responses, including low-grade inflammation and oxidative stress. Furthermore, primary tumor cells isolated from mice with MG-induced CT26 isografts had greater proliferative and migratory activities as well as stem-like properties compared to those isolated from the vehicle controls. Excitingly, enhanced expression or activation of proteins that modulate cell survival, proliferation, or migration/invasion was also observed in those cells. In conclusion, it is conceivable that MG-induced carbonyl stress may be the pivotal promoter involved in colon cancer progression.

Structural and functional studies of SAV0551 from Staphylococcus aureus as a chaperone and glyoxalase III

The DJ-1/ThiJ/PfpI superfamily of proteins is highly conserved across all biological kingdoms showing divergent multifunctions, such as chaperone, catalase, protease, and kinase. The common theme of these functions is responding to and managing various cellular stresses. DJ-1/ThiJ/PfpI superfamily members are classified into three subfamilies according to their quaternary structure (DJ-1-, YhbO-, and Hsp-types). The Hsp-type subfamily includes Hsp31, a chaperone and glyoxalase III. SAV0551, an Hsp-type subfamily member from Staphylococcus aureus, is a hypothetical protein that is predicted as Hsp31. Thus, to reveal the function and reaction mechanism of SAV0551, the crystal structure of SAV0551 was determined. The overall folds in SAV0551 are similar to other members of the Hsp-type subfamily. We have shown that SAV0551 functions as a chaperone and that the surface structure is crucial for holding unfolded substrates. As many DJ-1/ThiJ/PfpI superfamily proteins have been characterized as glyoxalase III, our study also demonstrates SAV0551 as a glyoxalase III that is independent of any cofactors. The reaction mechanism was evaluated via a glyoxylate-bound structure that mimics the hemithioacetal reaction intermediate. We have confirmed that the components required for reaction are present in the structure, including a catalytic triad for a catalytic action, His⁷⁸ as a base, and a water molecule for hydrolysis. Our functional studies based on the crystal structures of native and glyoxylate-bound SAV0551 will provide a better understanding of the reaction mechanism of a chaperone and glyoxalase III.

Antiglycating potential of acesulfame potassium: an artificial sweetener

Sweeteners have replaced the natural sugars in the food and beverage industry because of many reasons, such as hyperglycemia and cost. Saccharin, sucralose, aspartame and acesulfame-K are the most commonly used sweeteners. In the present study, the abovementioned artificial sweeteners were used to assess their glycating properties by established methods such as browning, fructosamine assay, determination of carbonyl content, protein aggregation, and measurement of fluorescence. Amadori and advanced glycation end products (AGEs) are formed as a result of the interaction between carbonyl groups of reducing sugars and amino groups of proteins and other macromolecules during glycation. The objective of this study was to investigate the influence of artificial sweeteners on the formation of AGEs and protein oxidation in an in vitro model of glucose-mediated protein glycation. The results indicated that the abovementioned artificial sweeteners do not enhance the process of glycation. On the other hand, acesulfame-K was found to have antiglycating potential as it caused decreased formation of Amadori products and AGEs. Further studies are essential in the characterization of Amadori products and AGEs produced as a result of interaction between sweeteners and proteins, which are interfered with by sweeteners. This study is significant in understanding the probable role of artificial sweeteners in the process of glycation and the subsequent effect on macromolecular alteration.

The structural damages of lens crystallins induced by peroxynitrite and methylglyoxal, two causative players in diabetic complications and preventive role of lens antioxidant components

Peroxynitrite (PON) and methylglyoxal (MGO), two diabetes-associated compounds, are believed to be important causative players in development of diabetic cataracts. In the current study, different spectroscopic methods, gel electrophoresis, lens culture and microscopic assessments were applied to examine the impact of individual, subsequent or simultaneous modification of lens crystallins with MGO and PON on their structure, oligomerization and aggregation. The protein modifications were confirmed with detection of the significantly increased quantity of carbonyl groups and decreased levels of sulfhydryl, tyrosine and tryptophan. Also, lens proteins modification with these chemical agents was accompanied with important structural alteration, oligomerization, disulfide/chromophore mediated protein crosslinking and important proteolytic instability. All these structural damages were more pronounced when the lens proteins were modified in the presence of both mentioned chemical agents, either in sequential or simultaneous manner. Ascorbic acid and glutathione, as the main components of lens antioxidant defense mechanism, were also capable to markedly prevent the damaging effects of PON and MGO on lens crystallins, as indicated by gel electrophoresis. The results of this study may highlight the importance of lens antioxidant defense system in protection of crystallins against the structural insults induced by PON and MGO during chronic hyperglycemia in the diabetic patients.

Cinnamic Acid and Its Derivatives: Mechanisms for Prevention and Management of Diabetes and Its Complications

With recent insight into the development of dietary supplements and functional foods, search of effective phytochemical compounds and their mechanisms involved in prevention and management of diabetes and its complications are now being assessed. Cinnamic acid and its derivatives occur naturally in high levels of plant-based foods. Among various biological activities, cinnamic acid and its derivatives are associated with a beneficial influence on diabetes and its complications. The aim of the review is to summarize the potential mechanisms of these compounds for prevention and management of diabetes and its complications. Based on several in vitro studies and animal models, cinnamic acid and its derivatives act on different mechanism of actions, including stimulation of insulin secretion, improvement of pancreatic β-cell functionality, inhibition of hepatic gluconeogenesis, enhanced glucose uptake, increased insulin signaling pathway, delay of carbohydrate digestion and glucose absorption, and inhibition of protein glycation and insulin fibrillation. However, due to the limited intestinal absorption being a result of low bioavailability of cinnamic acid and its derivatives, current improvement efforts with entrapping into solid and liquid particles are highlighted. Further human clinical studies are needed to clarify the effects of cinnamic acid and its derivatives in diabetic patients.

Ferulic acid prevents methylglyoxal-induced protein glycation, DNA damage, and apoptosis in pancreatic β-cells

Methylglyoxal (MG) can react with amino acids of proteins to induce protein glycation and consequently the formation of advanced glycation end-products (AGEs). Previous studies reported that ferulic acid (FA) prevented glucose-, fructose-, and ribose-induced protein glycation. In this study, FA (0.1-1 mM) inhibited MG-induced protein glycation and oxidative protein damage in bovine serum albumin (BSA). Furthermore, FA (0.0125-0.2 mM) protected against lysine/MG-mediated oxidative DNA damage, thereby inhibiting superoxide anion and hydroxyl radical generation during lysine and MG reaction. In addition, FA did not have the ability to trap MG. Finally, FA (0.1 mM) pretreatment attenuated MG-induced decrease in cell viability and prevented MG-induced cell apoptosis in pancreatic β-cells. The results suggest that FA is capable of protecting β-cells from MG-induced cell damage during diabetes.

Protective effect of cyanidin against glucose- and methylglyoxal-induced protein glycation and oxidative DNA damage

Cyanidin, a natural anthocyanin abundant in fruits and vegetables, has shown the health benefits due to its pharmacological properties. However, there was no evidence regarding anti-glycation activity of cyanidin. The aim of the study was to investigate the inhibitory effect of cyanidin on methylglyoxal (MG)- and glucose-induced protein glycation in bovine serum albumin (BSA) as well as oxidative DNA damage. Free radical scavenging activity and the MG-trapping ability of cyanidin were also investigated. The results demonstrated that cyanidin (0.125-1mM) significantly inhibited the formation of fluorescent and non-fluorescent AGEs in BSA/MG and BSA/glucose systems. There was a significantly improved protein thiol in BSA/MG and BSA/glucose when incubated with cyanidin. Correspondingly, cyanidin decreased the level of protein carbonyl content in BSA/glucose system. Moreover, cyanidin (0.5-1mM) prevented lysine/MG-mediated oxidative DNA damage in the absence or presence of copper ion. The results demonstrated that cyanidin showed the MG-trapping ability in a concentration-dependent manner. Cyanidin also reduced superoxide anion and hydroxyl radical generation in lysine/MG system. The mechanism by which cyanidin inhibited protein glycation was the MG-trapping ability and the free radical scavenging activity. The present study suggests that cyanidin might be a promising antiglycation agent for preventing or ameliorating AGEs-mediated diabetic complications.

Moringa oleifera aqueous leaf extract inhibits reducing monosaccharide-induced protein glycation and oxidation of bovine serum albumin

Advanced glycation end products (AGEs) play an important factor for pathophysiology of diabetes and its complications. Moringa oleifera is one of the medicinal plants that have anti-hyperglycemic activity. However, anti-glycation property of Moringa oleifera leaf extract on the different types of reducing monosaccharides-induced protein glycation has not been investigated. Therefore, the aim of this study was to examine the protective effect of Moringa oleifera aqueous leaf extract (MOE) on reducing sugars-induced protein glycation and protein oxidation. Total phenolic content of MOE was measured using the Folin–Ciocalteu method. Bovine serum albumin was incubated with 0.5 M of reducing sugars (glucose or fructose) with or without MOE (0.5–2.0 mg/mL) for 1, 2, 3 and 4 weeks. The results found that total phenolic content was 38.56 ± 1.50 mg gallic acid equivalents/g dry extract. The formation of fluorescent and non-fluorescent AGEs [N^ε-(carboxymethyl) lysine (CML)] and the level of fructosamine were determined to indicate protein glycation, whereas the level of protein carbonyl content and thiol group were examined for protein oxidation. MOE (0.5–2.0 mg/mL) significantly inhibited the formation of fluorescent, N^ε-CML and markedly decreased fructosamine level (P < 0.05). Moreover, MOE significantly prevented protein oxidation manifested by reducing protein carbonyl and the depletion of protein thiol in a dose-dependent manner (P < 0.05). Thus, the findings indicated that polyphenols containing in MOE have high potential for decreasing protein glycation and protein oxidation that may delay or prevent AGE-related diabetic complications.

Cyanidin-3-rutinoside attenuates methylglyoxal-induced protein glycation and DNA damage via carbonyl trapping ability and scavenging reactive oxygen species

BACKGROUND

Advanced glycation end-products (AGEs) play a significant role in the development and progression of vascular complication in diabetes. Anthocyanin has been recently reported to possess antiglycating activity. This study aimed to determine whether a naturally occurring anthocyanin, cyanidin-3-rutinoside (C3R) inhibits methylglyoxal (MG) induced protein glycation and oxidative protein and DNA damage.

METHODS

C3R (0.125-1 mM) was incubated with bovine serum albumin and MG (1 mM) for 2 weeks. The formation of fluorescent AGEs was measured by using spectrofluorometer and thiol group content were used to detect protein oxidative damage. Gel electrophoresis was used to determine whether C3R (0.125-1 mM) reduced DNA strand breakage in a glycation model comprising lysine, MG and/or Cu(2+). The generation of superoxide anions and hydroxyl radicals were detected by the cytochrome c reduction assay and the thiobarbituric acid reactive substances assay. MG-trapping capacity was assessed by high performance liquid chromatography (HPLC).

RESULTS

C3R (0.25-1 mM) reduced the formation of fluorescent AGEs and depleted protein thiol groups in bovine serum albumin mediated by MG. At 1 mM C3R inhibited oxidative DNA damage in the glycation model (p < 0.05) and at 0.5-1 mM prevented Cu(2+) induced DNA strand breakage in the presence of lysine and MG. The findings showed that C3R reduced the formation of superoxide anion and hydroxyl radicals during the glycation reaction of MG with lysine. C3R directly trapped MG in a concentration and time dependent manner (both p < 0.001).

CONCLUSIONS

These findings suggest that C3R protects against MG-induced protein glycation and oxidative damage to protein and DNA by scavenging free radicals and trapping MG.

Inhibitory effect of herbal medicines and their trapping abilities against methylglyoxal-derived advanced glycation end-products

Background

Methylglyoxal (MG) is one of the most reactive glycating agents, which result the formation of advanced glycation end-products (AGEs) that have been implicated in the progression of age-related diseases. Inhibition of MG-induced AGE formation is the imperative approach for alleviating diabetic complications. The objective of this study was to investigate the MG-trapping abilities of herbal medicines and their inhibitory activities on the formation of MG-derived AGEs.

Methods

The aqueous extract of herbal medicines was measured for the content of total phenolic compounds and the antioxidant activity by Folin-Ciocalteu assay and the 1,1-diphenyl 2-picrylhydrazyl (DPPH) radical scavenging activity, respectively. The extracts were investigated the MG-trapping ability by high performance liquid chromatography (HPLC). The extracts were incubated with BSA and MG at 37 °C for 1 day. The formation of MG-derived AGEs was measured.

Results

Total phenolic compounds of eleven herbal medicines showed marked variations, ranging from 12.16 to 272.36 mg gallic acid equivalents/g extract. All extracts (1 mg/mL) markedly exhibited the DPPH radical scavenging activity (0.31–73.52 %) and the MG-trapping abilities (13.97–58.97 %). In addition, they also inhibited the formation of MG-derived AGEs by 4.01–79.98 %. The results demonstrated that Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus were the potent inhibitors against the formation of MG-derived AGEs. The positive correlations between the contents of phenolics and % MG trapping (r = 0.912, p < 0.01) and % inhibition of MG-derived AGEs (r = 0.716, p < 0.01) were observed in the study. Furthermore, there was a moderate positive correlation between % MG trapping and % inhibition of MG-derived AGEs (r =0.584, p < 0.01).

Conclusions

Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus could reduce the formation of MG-derived AGEs through their MG-trapping abilities. These findings are relevant for focusing on potential herbal medicines to prevent or ameliorate AGE-mediated diabetic complications.

Isoferulic acid prevents methylglyoxal-induced protein glycation and DNA damage by free radical scavenging activity

BACKGROUND

Isoferulic acid (IFA), a naturally occurring cinnamic acid derivative, is a main active ingredient of the rhizoma of Cimicifuga dahurica. It has been shown various pharmacological activities. The aim of the study was to investigate the effect of IFA against MG-induced protein glycation and oxidative DNA damage. Free radical scavenging activity and the MGO-trapping abilities of IFA were also investigated.

METHODS

The fluorescent MG-derived AGEs and non-fluorescent N(ε)-(carboxymethyl) lysine (N(ε)-CML) was measured using a spectrofluorometer and an enzyme linked immunosorbant assay (ELISA). Protein carbonyl content was used to detect protein oxidation. Gel electrophoresis was used to determine DNA damage. Superoxide anion radicals and hydroxyl radicals were determined using cytochrome c reduction assay and thiobarbituric acid reactive 2-deoxy-D-ribose oxidation products, respectively. The MG-trapping capacity was performed by HPLC.

RESULTS

IFA (1.25-5 mM) inhibited the formation of fluorescent MG-derived AGEs, and N(ε)-CML, and protein carbonyl in bovine serum albumin. In addition, IFA (0.1-1 mM) also prevented MG/lysine-mediated oxidative DNA damage in the presence and absence of copper ion. The protective ability of IFA was directly correlated to inhibition of hydroxyl and superoxide anion radical generation during the reaction of MG and lysine. Most notably, IFA had no the directly trapping ability to MG.

CONCLUSIONS

The present results highlighted that free radical scavenging activity, but not the MG-trapping ability, is the mechanism of IFA for preventing MG-induced protein glycation and DNA damage.

The temporal and spatial dynamics of glyoxalase I following excitoxicity and brain ischaemia

MG (methylglyoxal) is an inevitable metabolite derived from glycolysis leading to protein modification, mitochondrial dysfunction and cell death. The ubiquitous glyoxalase system detoxifies MG under GSH consumption by mean of Glo1 (glyoxalase I) as the rate-limiting enzyme. Neurons are highly vulnerable to MG, whereas astrocytes seem less susceptible due to their highly expressed glyoxalases. In neurodegenerative diseases, MG and Glo1 were found to be pivotal players in chronic CNS (central nervous system) diseases. Comparable results obtained upon MG treatment and NMDA (N-methyl-D-aspartate) receptor activation provided evidence of a possible link. Additional evidence was presented by alterations in Glo1 expression upon stimulation of excitotoxicity as an event in the aftermath of brain ischaemia. Glo1 expression was remarkably changed following ischaemia, and beneficial effects were found after exogenous application of Tat (transactivator of transcription)-Glo1. In summary, there are strong indications that Glo1 seems to be a suitable target to modulate the consequences of acute neuronal injury.

Inhibitory effect of Clitoria ternatea flower petal extract on fructose-induced protein glycation and oxidation-dependent damages to albumin in vitro

BACKGROUND

The accumulation of advanced glycation end products (AGEs) in body tissue has been implicated in the progression of age-related diseases. Inhibition of AGE formation is the imperative approach for alleviating diabetic complications. Clitoria ternatea extract (CTE) has been demonstrated to possess anti-diabetic activity. However, there is no scientific evidence supporting its anti-glycation activity. The objective of this study was to determine the inhibitory effect of CTE on fructose-induced formation of AGEs and protein oxidation. Antioxidant activity of CTE was also assessed by various methods.

METHODS

The aqueous extract of CTE (0.25-1.00 mg/ml) was measured for the content of total phenolic compounds, flavonoid, and anthocyanin by Folin-Ciocalteu assay, AlCl3 colorimetric method, and pH differential method, respectively. The various concentrations of CTE were incubated with BSA and fructose at 37°C for 28 days. The formation of fluorescent AGEs, the level of fructosamine, protein carbonyl content, and thiol group were measured. The in vitro antioxidant activity was measured by the 1,1-diphenyl 2-picrylhydrazyl (DPPH) scavenging activity, trolox equivalent antioxidant capacity (TEAC), ferric reducing antioxidant power (FRAP), hydroxyl radical scavenging activity (HRSA), superoxide radical scavenging activity (SRSA), and ferrous ion chelating power (FICP).

RESULTS

The results demonstrated that the content of total phenolics, flavonoids and total anthocyanins in CTE was 53 ± 0.34 mg gallic acid equivalents/g dried extract, 11.2 ± 0.33 mg catechin equivalents/g dried extract, and 1.46 ± 0.04 mg cyanidin-3-glucoside equivalents/g dried extract, respectively. Moreover, CTE (0.25-1.00 mg/ml) significantly inhibited the formation of AGEs in a concentration-dependent manner. CTE also markedly reduced the levels of fructosamine and the oxidation of protein by decreasing protein carbonyl content and preventing free thiol depletion. In the DPPH radical scavenging activity and SRSA, CTE had the IC50 values of 0.47 ± 0.01 mg/ml and 0.58 ± 0.04 mg/ml. Furthermore, the FRAP and TEAC values of CTE were 0.38 ± 0.01 mmol FeSO4 equivalents/mg dried extract and 0.17 ± 0.01 mg trolox equivalents/mg dried extract. However, CTE showed weak scavenging activity on hydroxyl radical and a weak antioxidant iron chelator.

CONCLUSIONS

The results showed that CTE has strong antiglycation and antioxidant properties and might have therapeutic potentials in the prevention of AGE-mediated diabetic complications.

Lactoylglutathione lyase, a critical enzyme in methylglyoxal detoxification, contributes to survival of Salmonella in the nutrient rich environment

Glyoxalase I which is synonymously known as lactoylglutathione lyase is a critical enzyme in methylglyoxal (MG) detoxification. We assessed the STM3117 encoded lactoylglutathione lyase (Lgl) of Salmonella Typhimurium, which is known to function as a virulence factor, due in part to its ability to detoxify methylglyoxal. We found that STM3117 encoded Lgl isomerises the hemithioacetal adduct of MG and glutathione (GSH) into S-lactoylglutathione. Lgl was observed to be an outer membrane bound protein with maximum expression at the exponential growth phase. The deletion mutant of S. Typhimurium (Δlgl) exhibited a notable growth inhibition coupled with oxidative DNA damage and membrane disruptions, in accordance with the growth arrest phenomenon associated with typical glyoxalase I deletion. However, growth in glucose minimal medium did not result in any inhibition. Endogenous expression of recombinant Lgl in serovar Typhi led to an increased resistance and growth in presence of external MG. Being a metalloprotein, Lgl was found to get activated maximally by Co(2+) ion followed by Ni(2+), while Zn(2+) did not activate the enzyme and this could be attributed to the geometry of the particular protein-metal complex attained in the catalytically active state. Our results offer an insight on the pivotal role of the virulence associated and horizontally acquired STM3117 gene in non-typhoidal serovars with direct correlation of its activity in lending survival advantage to Salmonella spp.

Quercetin inhibits advanced glycation end product formation by trapping methylglyoxal and glyoxal

Methylglyoxal (MGO) and glyoxal (GO) not only are endogenous metabolites but also exist in exogenous resources, such as foods, beverages, urban atmosphere, and cigarette smoke. They have been identified as reactive dicarbonyl precursors of advanced glycation end products (AGEs), which have been associated with diabetes-related long-term complications. In this study, quercetin, a natural flavonol found in fruits, vegetables, leaves, and grains, could effectively inhibit the formation of AGEs in a dose-dependent manner via trapping reactive dicarbonyl compounds. More than 50.5% of GO and 80.1% of MGO were trapped at the same time by quercetin within 1 h under physiological conditions. Quercetin and MGO (or GO) were combined at different ratios, and the products generated from this reaction were analyzed with LC-MS. Both mono-MGO and di-MGO adducts of quercetin were detected in this assay using LC-MS, but only tiny amounts of mono-GO adducts of quercetin were found. Additionally, di-MGO adducts were observed as the dominant product with prolonged incubation time. In the bovine serum albumin (BSA)-MGO/GO system, quercetin traps MGO and GO directly and then significantly inhibits the formation of AGEs.

Temporal dynamics of glyoxalase 1 in secondary neuronal injury

Background

Enhanced glycolysis leads to elevated levels of the toxic metabolite methylglyoxal which contributes to loss of protein-function, metabolic imbalance and cell death. Neurons were shown being highly susceptible to methylglyoxal toxicity. Glyoxalase 1 as an ubiquitous enzyme reflects the main detoxifying enzyme of methylglyoxal and underlies changes during aging and neurodegeneration. However, little is known about dynamics of Glyoxalase 1 following neuronal lesions so far.

Methods

To determine a possible involvement of Glyoxalase 1 in acute brain injury, we analysed the temporal dynamics of Glyoxalase 1 distribution and expression by immunohistochemistry and Western Blot analysis. Organotypic hippocampal slice cultures were excitotoxically (N-methyl-D-aspartate, 50 µM for 4 hours) lesioned in vitro (5 minutes to 72 hours). Additionally, permanent middle cerebral artery occlusion was performed (75 minutes to 60 days).

Results

We found (i) a predominant localisation of Glyoxalase 1 in endothelial cells in non-lesioned brains (ii) a time-dependent up-regulation and re-distribution of Glyoxalase 1 in neurons and astrocytes and (iii) a strong increase in Glyoxalase 1 dimers after neuronal injury (24 hours to 72 hours) when compared to monomers of the protein.

Conclusions

The high dynamics of Glyoxalase 1 expression and distribution following neuronal injury may indicate a novel role of Glyoxalase 1.

Resveratrol protects mouse oocytes from methylglyoxal-induced oxidative damage

Methylglyoxal, a reactive dicarbonyl compound, is mainly formed from glycolysis. Methylglyoxal can lead to the dysfunction of mitochondria, the depletion of cellular anti-oxidation enzymes and the formation of advanced glycation ends. Previous studies showed that the accumulation of methylglyoxal and advanced glycation ends can impair the oocyte maturation and reduce the oocyte quality in aged and diabetic females. In this study, we showed that resveratrol, a kind of phytoalexin found in the skin of grapes, red wine and other botanical extracts, can alleviate the adverse effects caused by methylglyoxal, such as inhibition of oocyte maturation and disruption of spindle assembly. Besides, methylglyoxal-treated oocytes displayed more DNA double strands breaks and this can also be decreased by treatment of resveratrol. Further investigation of these processes revealed that methylglyoxal may affect the oocyte quality by resulting in excessive reactive oxygen species production, aberrant mitochondrial distribution and high level lipid peroxidation, and resveratrol can block these cytotoxic changes. Collectively, our results showed that resveratrol can protect the oocytes from methylglyoxal-induced cytotoxicity and this was mainly through the correction of the abnormity of cellular reactive oxygen species metabolism.

Methylglyoxal-induced stomatal closure accompanied by peroxidase-mediated ROS production in Arabidopsis

Methylglyoxal (MG) is an oxygenated short aldehyde and a glycolytic intermediate that accumulates in plants under environmental stresses. Being a reactive α-oxoaldehyde, MG may act as a signaling molecule in plants during stresses. We investigated whether MG induces stomatal closure, reactive oxygen species (ROS) production, and cytosolic free calcium concentration ([Ca²⁺](cyt)) to clarify roles of MG in Arabidopsis guard cells. MG induced production of ROS and [Ca²⁺](cyt) oscillations, leading to stomatal closure. The MG-induced stomatal closure and ROS production were completely inhibited by a peroxidase inhibitor, salicylhydroxamic acid (SHAM), but were not affected by an NAD(P)H oxidase mutation, atrbohD atrbohF. Furthermore, the MG-elicited [Ca²⁺](cyt) oscillations were significantly suppressed by SHAM but not by the atrbohD atrbohF mutation. Neither endogenous abscisic acid nor endogenous methyl jasmonate was involved in MG-induced stomatal closure. These results suggest that intrinsic metabolite MG can induce stomatal closure in Arabidopsis accompanied by extracellular ROS production mediated by SHAM-sensitive peroxidases, intracellular ROS accumulation, and [Ca²⁺](cyt) oscillations.

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

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

Aminoacetone, a putative endogenous source of methylglyoxal, causes oxidative stress and death to insulin-producing RINm5f cells

Aminoacetone (AA), triose phosphates, and acetone are putative endogenous sources of potentially cytotoxic and genotoxic methylglyoxal (MG), which has been reported to be augmented in the plasma of diabetic patients. In these patients, accumulation of MG derived from aminoacetone, a threonine and glycine catabolite, is inferred from the observed concomitant endothelial overexpression of circulating semicarbazide-sensitive amine oxidases. These copper-dependent enzymes catalyze the oxidation of primary amines, such as AA and methylamine, by molecular oxygen, to the corresponding aldehydes, NH4(+) ion and H2O2. We recently reported that AA aerobic oxidation to MG also takes place immediately upon addition of catalytic amounts of copper and iron ions. Taking into account that (i) MG and H2O2 are reportedly cytotoxic to insulin-producing cell lineages such as RINm5f and that (ii) the metal-catalyzed oxidation of AA is propagated by O2(*-) radical anion, we decided to investigate the possible pro-oxidant action of AA on these cells taken here as a reliable model system for pancreatic beta-cells. Indeed, we show that AA (0.10-5.0 mM) administration to RINm5f cultures induces cell death. Ferrous (50-300 microM) and Fe(3+) ion (100 microM) addition to the cell cultures had no effect, whereas Cu(2+) (5.0-100 microM) significantly increased cell death. Supplementation of the AA- and Cu(2+)-containing culture medium with antioxidants, such as catalase (5.0 microM), superoxide dismutase (SOD, 50 U/mL), and N-acetylcysteine (NAC, 5.0 mM) led to partial protection. mRNA expression of MnSOD, CuZnSOD, glutathione peroxidase, and glutathione reductase, but not of catalase, is higher in cells treated with AA (0.50-1.0 mM) plus Cu(2+) ions (10-50 microM) relative to control cultures. This may imply higher activity of antioxidant enzymes in RINm5f AA-treated cells. In addition, we have found that AA (0.50-1.0 mM) plus Cu(2+) (100 microM) (i) increase RINm5f cytosolic calcium; (ii) promote DNA fragmentation; and (iii) increase the pro-apoptotic (Bax)/antiapoptotic (Bcl-2) ratio at the level of mRNA expression. In conclusion, although both normal and pathological concentrations of AA are probably much lower than those used here, it is tempting to propose that excess AA in diabetic patients may drive oxidative damage and eventually the death of pancreatic beta-cells.

Genistein protects methylglyoxal-induced oxidative DNA damage and cell injury in human mononuclear cells

Methylglyoxal (MG) is a reactive dicarbonyl compound produced mainly from glycolytic intermediates in the cell and often found at high level in the blood from the diabetic patients. Glycation reactions of MG with amino acids can induce oxidative stress and free radical generation, leading to subsequent cytotoxicity and apoptosis. Recently, studies have demonstrated that high level MG may be the main cause of immune dysfunction in diabetic patients. Here, we examined the effects of genistein, an antioxidant isoflavone compound, on MG-induced effects in vitro and in human mononuclear cells. We first monitored DNA strand breakage to examine the effect of 12.5-100 microM genistein on the ROS generation and oxidative DNA damage induced in vitro by a 50 microM MG/lysine glycation reaction (3h). Our results revealed that genistein concentrations higher than 25 microM decreased the oxidative stress and DNA damage induced by 50 microM MG/lysine. In mononuclear cells, pretreatment with 8-16 microM genistein for 1h followed by co-incubation with genistein and 50 microM MG for an additional 36 h inhibited MG-induced reactive oxygen species (ROS) generation and apoptosis. Finally, animal model experiments showed that dietary genistein effectively blocks MG-induced apoptosis in mononuclear cells. These results collectively suggest that oxidative stress plays a role in MG-induced cell injury, and that genistein blocks these effects by virtue of its antioxidant properties, consequently preventing cell apoptosis.

Genomic Damage and Malignancy in End-Stage Renal Failure: Do Advanced Glycation End Products Contribute?

In end-stage renal disease (ESRD) there is not only excessive morbidity and mortality due to cardiovascular disease but also an enhanced occurrence of various types of cancer. Both are characterized by oxidative stress and inflammation as two of the central underlying causes of the disease states. In cancer, genomic damage has been demonstrated to be of high pathogenetic relevance. DNA lesions may induce mutations of oncogenes and tumor-suppressor genes which, in the long-run, may lead to malignancies if mutagenicity is not mitigated by repair mechanisms. A high incidence of genomic damage in ESRD patients has been validated by various biomarkers of DNA lesions. We reviewed the mechanisms of DNA damage, focusing in particular on the role of advanced glycation end products (AGEs) which accumulate markedly in renal insufficiency. Considering the in vitro and in vivo findings to date, one has to assume a significant role of AGEs in DNA damage and the potential development of cancer.

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.

Protective effects of curcumin on methylglyoxal-induced oxidative DNA damage and cell injury in human mononuclear cells

AIM

To examine the effect of curcumin on oxidative DNA damage and cell apoptosis and injury caused by the reaction of methylglyoxal(MG) with amino acids.

METHODS

We used DNA strand breaks to examine the effect of curcumin on oxidative DNA damage. In addition, reactive oxygen species(ROS) formation occurs in MG-treated mononuclear cells, so the effect of curcumin on ROS generation was measured using 2',7'-dichlorofluorescin diacetate(DCF-DA) as the detection reagent. Moreover, the impact effects of curcumin on MG-induced cell apoptosis and ROS injury were analyzed by TUNEL and ELISA assay. The collagen I attachment ability of mononuclear cells was examined by trypan blue staining.

RESULTS

Our results revealed that curcumin prevented MG/lysine-induced oxidative stress and DNA damage. Curcumin also inhibited MG-induced apoptosis and generation of ROS in mononuclear cells. MG-treated mononuclear cells displayed a lower degree of attachment to collagen (the major component of the vessel wall subendo-thelium), whereas cells pretreated with curcumin before MG treatment exhibited restored affinities for collagen.

CONCLUSION

These results demonstrated that oxidative stress plays a role in MG-induced cell injury and alterations in attachment ability, and that curcumin blocks these effects by virtue of its antioxidant properties.

On the mechanisms of ageing suppression by dietary restriction-is persistent glycolysis the problem?

The mechanism(s) by which dietary restriction (DR) suppresses ageing and onset of age-related pathologies are discussed in relation to frequency of glycolysis, and the reactivity of glycolytic intermediates. Most glycolytic intermediates are potentially toxic and readily modify (i.e. glycate) proteins and other macromolecules non-enzymically. Attention is drawn to the reactivity of methyglyoxal (MG) which is formed predominantly from the glycolytic intermediates dihydroxyacetone- and glyceraldehyde-3-phosphates. MG rapidly glycates proteins, damages mitochondria and induces a pro-oxidant state, similar to that observed in aged cells. It is suggested that because DR animals' energy metabolism is less glycolytic than in those fed ad libitum, intracellular MG levels are lowered by DR The decreased glycolysis during DR may delay senescence by lowering intracellular MG concentration compared to ad libitum-fed animals. Because of the reactivity MG and glycolytic intermediates, occasional glycolysis could be hormetic where glyoxalase, carnosine synthetase and ornithine decarboxylase are upregulated to control cellular MG concentration. It is suggested that in ad libitum-fed animals persistent glycolysis permanently raises MG levels which progressively overwhelm protective processes, particularly in non-mitotic tissues, to create the senescent state earlier than in DR animals. The possible impact of diet and intracellular glycating agents on age-related mitochondrial dysfunction is also discussed.