Showing papers on "Methylglyoxal published in 2011"

Nitric oxide modulates antioxidant defense and the methylglyoxal detoxification system and reduces salinity-induced damage of wheat seedlings

Abstract: The present study investigates the possible regulatory role of exogenous nitric oxide (NO) in antioxidant defense and methylglyoxal (MG) detoxification systems of wheat seedlings exposed to salt stress (150 and 300 mM NaCl, 4 days). Seedlings were pre-treated for 24 h with 1 mM sodium nitroprusside, a NO donor, and then subjected to salt stress. The ascorbate (AsA) content decreased significantly with increased salt stress. The amount of reduced glutathione (GSH) and glutathione disulfide (GSSG) and the GSH/GSSG ratio increased with an increase in the level of salt stress. The glutathione S-transferase (GST) activity increased significantly with severe salt stress (300 mM). The ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT) and glutathione peroxidase (GPX) activities did not show significant changes in response to salt stress. The glutathione reductase (GR), glyoxalase I (Gly I), and glyoxalase II (Gly II) activities decreased upon the imposition of salt stress, especially at 300 mM NaCl, with a concomitant increase in the H2O2 and lipid peroxidation levels. Exogenous NO pre-treatment of the seedlings had little influence on the non-enzymatic and enzymatic components compared to the seedlings of the untreated control. Further investigation revealed that NO pre-treatment had a synergistic effect; that is, the pre-treatment increased the AsA and GSH content and the GSH/GSSG ratio, as well as the activities of MDHAR, DHAR, GR, GST, GPX, Gly I, and Gly II in most of the seedlings subjected to salt stress. These results suggest that the exogenous application of NO rendered the plants more tolerant to salinity-induced oxidative damage by enhancing their antioxidant defense and MG detoxification systems.

Genome-wide analysis of rice and Arabidopsis identifies two glyoxalase genes that are highly expressed in abiotic stresses

Abstract: Glyoxalase pathway, ubiquitously found in all organisms from prokaryotes to eukaryotes, consists of glyoxalase I (GLY I) and glyoxalase II (GLY II) enzymes, which detoxify a cytotoxic molecule, methylglyoxal (MG). Increase in MG has been correlated with various diseases in humans and different abiotic stresses in plants. We have previously shown that overproduction of GLY I and/or GLY II enzymes in transgenic plants provide tolerance towards salinity and heavy metal stresses. We have identified nineteen potential GLY I and four GLY II proteins in rice and twenty two GLY I and nine GLY II proteins in Arabidopsis. An analysis of complete set of genes coding for the glyoxalase proteins in these two genomes is presented, including classification and chromosomal distribution. Expression profiling of these genes has been performed in response to multiple abiotic stresses, in different tissues and during various stages of vegetative and reproductive development using publicly available databases (massively parallel signature sequencing and microarray). AtGLYI8, OsGLYI3, and OsGLYI10 expresses constitutively high in seeds while AtGLYI4, AtGLYI7, OsGLYI6, and OsGLYI11 are highly stress inducible. To complement this analyses, qRT-PCR is performed in two contrasting rice genotypes, i.e., IR64 and Pokkali where OsGLYI6 and OsGLYI11 are found to be highly stress inducible.

Fisetin lowers methylglyoxal dependent protein glycation and limits the complications of diabetes

Abstract: The elevated glycation of macromolecules by the reactive dicarbonyl and α-oxoaldehyde methylglyoxal (MG) has been associated with diabetes and its complications. We have identified a rare flavone, fisetin, which increases the level and activity of glyoxalase 1, the enzyme required for the removal of MG, as well as the synthesis of its essential co-factor, glutathione. It is shown that fisetin reduces two major complications of diabetes in Akita mice, a model of type 1 diabetes. Although fisetin had no effect on the elevation of blood sugar, it reduced kidney hypertrophy and albuminuria and maintained normal levels of locomotion in the open field test. This correlated with a reduction in proteins glycated by MG in the blood, kidney and brain of fisetin-treated animals along with an increase in glyoxalase 1 enzyme activity and an elevation in the expression of the rate-limiting enzyme for the synthesis of glutathione, a co-factor for glyoxalase 1. The expression of the receptor for advanced glycation end products (RAGE), serum amyloid A and serum C-reactive protein, markers of protein oxidation, glycation and inflammation, were also increased in diabetic Akita mice and reduced by fisetin. It is concluded that fisetin lowers the elevation of MG-protein glycation that is associated with diabetes and ameliorates multiple complications of the disease. Therefore, fisetin or a synthetic derivative may have potential therapeutic use for the treatment of diabetic complications.

Genistein inhibits advanced glycation end product formation by trapping methylglyoxal.

Abstract: Methylglyoxal (MGO) is a highly reactive endogenous metabolite derived from several nonenzymatic and enzymatic reactions, and identified as a well-known precursor of advanced glycation end products (AGEs). In the present study, genistein, a naturally occurring isoflavone derived from soy products, demonstrated significant trapping effects of MGO and consequently formed mono- and di-MGO adducts under physiological conditions (pH 7.4, 37 °C). More than 80.0% of MGO was trapped within 4 h, and the trapping efficiency could be up to 97.7% at 24 h. The reaction adducts formed from genistein and MGO under different ratios were analyzed using LC/MS. We also successfully purified and identified the major mono- and di-MGO conjugated adducts of genistein. The NMR data showed that positions 6 and 8 of the A ring of genistein were the major active sites for trapping MGO. We further demonstrated that genistein could effectively inhibit the formation of AGEs in the human serum albumin (HSA)-MGO assay. Two mono-MGO adducts and one di-MGO adduct of genistein were detected in this assay using LC/MS. The di-MGO adduct of genistein became the dominant reaction product during prolonged incubation. Results from this study, as well as our previous findings on (-)-epigallocatechin 3-gallate (EGCG), phloridzin and phloretin, indicate that dietary flavonoids that have the same A ring structure as genistein, EGCG, phloridzin, and phloretin may have the potential to inhibit the formation of AGEs by trapping reactive dicarbonyl species.

Overproduction of a rice aldo-keto reductase increases oxidative and heat stress tolerance by malondialdehyde and methylglyoxal detoxification.

Abstract: The accumulation of toxic compounds generated by the interaction between reactive oxygen species and polyunsaturated fatty acids of membrane lipids can significantly damage plant cells. A plethora of enzymes act on these reactive carbonyls, reducing their toxicity. Based on the chromosomal localization and on their homology with other stress-induced aldo–keto reductases (AKRs) we have selected three rice AKR genes. The transcription level of OsAKR1 was greatly induced by abscisic acid and various stress treatments; the other two AKR genes tested were moderately stress-inducible. The OsAKR1 recombinant protein exhibited a high nicotinamide adenine dinucleotide phosphate-dependent catalytic activity to reduce toxic aldehydes including glycolysis-derived methylglyoxal (MG) and lipid peroxidation-originated malondialdehyde (MDA). The function of this enzyme in MG detoxification was demonstrated in vivo in E. coli and in transgenic plants overproducing the OsAKR1 protein. Heterologous synthesis of the OsAKR1 enzyme in transgenic tobacco plants resulted in increased tolerance against oxidative stress generated by methylviologen (MV) and improved resistance to high temperature. In these plants lower levels of MDA were detected both following MV and heat treatment due to the activity of the OsAKR1 enzyme. The transgenic tobaccos also exhibited higher AKR activity and accumulated less MG in their leaves than the wild type plants; both in the presence and absence of heat stress. These results support the positive role of OsAKR1 in abiotic stress-related reactive aldehyde detoxification pathways and its use for improvement of stress tolerance in plants.

Manuka honey inhibits cell division in methicillin-resistant Staphylococcus aureus

Abstract: Objectives: The aim of this study was to investigate the effect of manuka honey, artificial honey and an antibacterial component (methylglyoxal) on cell division in methicillin-resistant Staphylococcus aureus (MRSA). Methods: Viability of epidemic MRSA-15 NCTC 13142 incubated with manuka honey, artificial honey and methylglyoxal was determined, and structural effects monitored by electron microscopy. Activity of murein hydrolase (a peptidoglycan-degrading enzyme implicated in cell separation, encoded by atl) was estimated by cell wall hydrolysis and zymography; expression of atl was quantified by real-time PCR. Results: Growth of MRSA was inhibited by 5%, 10% and 20% (w/v) manuka honey and 10% (w/v) artificial honey containing methylglyoxal, but not 10% (w/v) artificial honey. Statistically significantly increased numbers of cells containing septa and increased cell diameter (P,0.001 and P,0.001, respectively) were found in MRSA exposed to 5%, 10% or 20% (w/v) manuka honey, but not 10% (w/v) artificial honey with and without methylglyoxal. Intracellular activity of murein hydrolase was elevated in MRSA grown in 10% (w/v) artificial honey and at undetectable levels in MRSA treated with 10% (w/v) manuka honey. Increased atl expression was found in MRSA treated with 10% (w/v) manuka honey and 10% artificial honey containing methylglyoxal. Conclusions: Enlarged cells containing septa were observed in MRSA exposed to inhibitory concentrations of manuka honey, suggesting that cell division was interrupted. These changes were not caused by either the sugars or methylglyoxal in honey and indicate the presence of additional antibacterial components in manuka honey.

Hsp31 of Escherichia coli K-12 is glyoxalase III.

Abstract: Summary Hsp31 encoded by hchA is known as a heat-inducible molecular chaperone. Although structure studies revealed that Hsp31 has a putative catalytic triad consisting of Asp-214, His-186 and Cys-185, its enzymatic function, besides weak amino-peptidase activity, is still unknown. We found that Hsp31 displays glyoxalase activity that catalyses the conversion of methylglyoxal (MG) to d-lactate without an additional cofactor. The glyoxalase activity was completely abolished in the hchA-deficient strain, confirming the relationship between the hchA gene and its enzymatic activity in vivo. Hsp31 exhibits Michaelis–Menten kinetics for substrates MG with Km and kcat of 1.43 ± 0.12 mM and 156.9 ± 5.5 min−1 respectively. The highest glyoxalase activity was found at 35–40°C and pH of 6.0–8.0, and the activity was significantly inhibited by Cu2+, Fe3+ and Zn2+. Mutagenesis studies based on our evaluation of conserved catalytic residues revealed that the Cys-185 and Glu-77 were essential for catalysis, whereas His-186 was less crucial for enzymatic function, although it participates in the catalytic process. The stationary-phase Escherichia coli cells became more susceptible to MG when hchA was deleted, which was complemented by an expression of plasmid-encoded hchA. Furthermore, an accumulation of intracellular MG was observed in hchA-deficient strains.

Role of the Glyoxalase System in Astrocyte-Mediated Neuroprotection

Abstract: The glyoxalase system is the most important pathway for the detoxification of methylglyoxal (MG), a highly reactive dicarbonyl compound mainly formed as a by-product of glycolysis. MG is a major precursor of advanced glycation end products (AGEs), which are associated with several neurodegenerative disorders. Although the neurotoxic effects of MG and AGEs are well characterized, little is known about the glyoxalase system in the brain, in particular with regards to its activity in different neural cell types. Results of the present study reveal that both enzymes composing the glyoxalase system [glyoxalase-1 (Glo-1) and Glo-2] were highly expressed in primary mouse astrocytes compared with neurons, which translated into higher enzymatic activity rates in astrocytes (9.9- and 2.5-fold, respectively). The presence of a highly efficient glyoxalase system in astrocytes was associated with lower accumulation of AGEs compared with neurons (as assessed by Western blotting), a sixfold greater resistance to MG toxicity, and the capacity to protect neurons against MG in a coculture system. In addition, Glo-1 downregulation using RNA interference strategies resulted in a loss of viability in neurons, but not in astrocytes. Finally, stimulation of neuronal glycolysis via lentiviral-mediated overexpression of 6-phosphofructose-2-kinase/fructose-2,6-bisphosphatase-3 resulted in increased MG levels and MG-modified proteins. Since MG is largely produced through glycolysis, this suggests that the poor capacity of neurons to upregulate their glycolytic flux as compared with astrocytes may be related to weaker defense mechanisms against MG toxicity. Accordingly, the neuroenergetic specialization taking place between these two cell types may serve as a protective mechanism against MG-induced neurotoxicity.

Formation of Carcinogenic 4(5)-Methylimidazole in Maillard Reaction Systems

Abstract: 4(5)-Methylimidazole has received the attention of federal and state regulatory agencies because of its carcinogenicity and common presence in foods and beverages. In the present study, the formation of 4(5)-methylimidazole in Maillard reaction model systems consisting of d-glucose/NH3, l-rhamnose/NH3, methylglyoxal/NH3, and methylglyoxal/formaldehyde/NH3 was investigated. 4(5)-Methylimidazole was formed at levels ranging from 0.49 to 0.71 mg/mL in the d-glucose/NH3 model system. The formation of 4(5)-methylimidazole was slightly higher in the l-rhamnose/NH3 system (0.91 mg/mL) than in the d-glucose/NH3 system (0.71 mg/mL) under the conditions used in the present study. A methylglyoxal/NH3 system produced significantly higher levels of 4(5)-methylimidazole (5.70 mg/mL), suggesting that methylglyoxal is an important precursor of 4(5)-methylimidazole. Ammonolysis of methylglyoxal, which is one of the glucose degradation products, was proposed to form formamide, which subsequently reacted with 2-aminopropana...

Methylglyoxal impairs insulin signalling and insulin action on glucose-induced insulin secretion in the pancreatic beta cell line INS-1E

Abstract: Aims/hypothesis Chronic hyperglycaemia aggravates insulin resistance, at least in part, by increasing the formation of advanced glycation end-products (AGEs). Methylglyoxal (MGO) is the most reactive AGE precursor and its abnormal accumulation participates in damage in various tissues and organs. Here we investigated the ability of MGO to interfere with insulin signalling and to affect beta cell functions in the INS-1E beta cell line.

Transgenic potato overproducing L-ascorbic acid resisted an increase in methylglyoxal under salinity stress via maintaining higher reduced glutathione level and glyoxalase enzyme activity.

Abstract: Salt-tolerance was studied in transgenic potato. It was conferred by overexpression of ascorbate pathway enzyme (d-galacturonic acid reductase, GalUR). As genetic engineering of the GalUR gene in potato enhances its ascorbic acid content (l-AsA), and subsequently plants suffered minimal oxidative stress-induced damage, we now report on the comprehensive aptness of this engineering approach for enhanced salt tolerance in transgenic potato (Solanum tuberosum L. cv. Taedong Valley). Potatoes overexpressing GalUR grew and tuberized in continuous presence of 200 mM of NaCl. The transgenic plants maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio together with enhanced activity of glutathione dependent antioxidative and glyoxalase enzymes under salinity stress. The transgenics resisted an increase in methylglyoxal that increased radically in untransformed control plants under salinity stress. This is the first report of genetic engineering of ascorbate pathway gene in maintaining higher level of GSH homeostasis along with higher glyoxalase activity inhibiting the accumulation in methylglyoxal (a potent cytotoxic compound) under salt stress. These results suggested the engineering of ascorbate pathway enzymes as a major step towards developing salinity tolerant crop plants.

Insulin glycation by methylglyoxal results in native-like aggregation and inhibition of fibril formation

Abstract: Insulin is a hormone that regulates blood glucose homeostasis and is a central protein in a medical condition termed insulin injection amyloidosis. It is intimately associated with glycaemia and is vulnerable to glycation by glucose and other highly reactive carbonyls like methylglyoxal, especially in diabetic conditions. Protein glycation is involved in structure and stability changes that impair protein functionality, and is associated with several human diseases, such as diabetes and neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Familiar Amyloidotic Polyneuropathy. In the present work, methylglyoxal was investigated for their effects on the structure, stability and fibril formation of insulin. Methylglyoxal was found to induce the formation of insulin native-like aggregates and reduce protein fibrillation by blocking the formation of the seeding nuclei. Equilibrium-unfolding experiments using chaotropic agents showed that glycated insulin has a small conformational stability and a weaker dependence on denaturant concentration (smaller m-value). Our observations suggest that methylglyoxal modification of insulin leads to a less compact and less stable structure that may be associated to an increased protein dynamics. We propose that higher dynamics in glycated insulin could prevent the formation of the rigid cross-β core structure found in amyloid fibrils, thereby contributing to the reduction in the ability to form fibrils and to the population of different aggregation pathways like the formation of native-like aggregates.

Efficiency of trapping methylglyoxal by phenols and phenolic acids

Abstract: The carbonyl stress that leads to the formation of advanced glycation end products (AGEs) has drawn much attention recently because of its micro- and macrovascular implications. During monitoring of methylglyoxal (MG), the efficiency of phenolics to directly trap MG can be demonstrated. Twenty compounds consisting of a single benzene ring structure with the addition of at least one hydroxyl group were allowed to react with MG at 37 °C for 1 h under physiological conditions in pH 7.4 phosphate buffer solution. Compounds composed of a benzene structure with a mono-hydroxyl substitute cannot react with MG. Among benzenediols and di-hydroxyl benzoic acids, only hydroquinone reacted with MG and showed a 13% decrease in MG. Nevertheless, high reactivity was shown for 3 benzenetriols. The percentages of MG remaining were 45%, 51%, and 36% for pyrogallol, 1,2,4-trihydroxybenzene, and 1,3,5-trihydroxybenzene, respectively. When a carboxyl group is added to the benzenetriols, steric hindrance and carbon electron charges on benzene ring are the influential factors in reactivity. Using computational chemistry calculations, a carbon electron charge of -0.24 was the minimum value for high reactivity.

Alpha-synuclein deficiency leads to increased glyoxalase I expression and glycation stress

Abstract: The presynaptic protein alpha-synuclein has received much attention because its gain-of-function is associated with Parkinson’s disease. However, its physiological function is still poorly understood. We studied brain regions of knock-out mice at different ages with regard to consistent upregulations of the transcriptome and focused on glyoxalase I (GLO1). The microarray data were confirmed in qPCR, immunoblot, enzyme activity, and behavior analyses. GLO1 induction is a known protective cellular response to glucose stress, representing efforts to decrease toxic levels of methylglyoxal (MG), glyoxal and advanced glycation endproducts (AGEs). Mass spectrometry quantification demonstrated a ubiquitous increase in MG and fructosyl-lysine as consequences of glucose toxicity, and consistent enhancement of certain AGEs. Thus, GLO1 induction in KO brain seems insufficient to prevent AGE formation. In conclusion, the data demonstrate GLO1 expression and glycation damage to be induced by alpha-synuclein ablation. We propose that wild-type alpha-synuclein modulates brain glucose metabolism.

Coordinate induction of antioxidant defense and glyoxalase system by exogenous proline and glycinebetaine is correlated with salt tolerance in mung bean

Abstract: The purpose of this study was to assess the synergistic effects of exogenously applied proline and glycinebetaine (betaine) in antioxidant defense and methylglyoxal (MG) detoxification system in mung bean seedlings subjected to salt stress (200 mmol·L−1 NaCl, 48 h). Seven-day-old mung bean seedlings were exposed to salt stress after pre-treatment with proline or betaine. Salt stress caused a sharp increase in reduced glutathione (GSH) and oxidized glutathione (GSSG) content in leaves, while the GSH/GSSG ratio and ascorbate (AsA) content decreased significantly. The glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST) and glyoxalase II (Gly II) activities were increased in response to salt stress, while the monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT) and glyoxalase I (Gly I) activities sharply decreased with an associated increase in hydrogen peroxide (H2O2) and lipid peroxidation level (MDA). Proline or betaine pre-treatment had little influence on nonenzymatic and enzymatic components as compared to those of the untreated control. However, proline or betaine pre-treated salt-stressed seedlings showed an increase in AsA, GSH content, GSH/GSSG ratio and maintained higher activities of APX, DHAR, GR, GST, GPX, CAT, Gly I and Gly II involved in ROS and MG detoxification system as compared to those of the untreated control and mostly also salt-stressed plants with a simultaneous decrease in GSSG content, H2O2 and MDA level. These results together with our previous results suggest that coordinate induction of antioxidant defense and glyoxalase system by proline and betaine rendered the plants tolerant to salinity-induced oxidative stress in a synergistic fashion.

Chlorogenic acid inhibits the formation of advanced glycation end products and associated protein cross-linking

Abstract: Advanced glycation end products (AGEs) play an important role in the development of chronic diabetic complications. Chlorogenic acid (CGA) is a phenolic compound formed by the esterification of caffeic and quinic acids. In this study, we evaluated the inhibitory effects of CGA against the formation of AGEs and AGEs protein cross-linking in vitro. An in vitro assay for glycation of bovine serum albumin by high glucose showed that CGA inhibited AGEs formation with an IC(50) value of 148.32 μM and was found to be more effective than aminoguanidine, a well-known AGEs inhibitor (IC(50); 807.67 μM). In an indirect AGE-ELISA assay, the CGA exhibited more potent inhibitory activity on the cross-linking of AGEs to collagen than aminoguanidine. In addition, the inhibitory effects of CGA on AGEs formation and on its cross-linking with collagen might be caused by its interactions with reactive decarbonyl compounds, such as methylglyoxal. These results suggest that CGA could be beneficial in the prevention of AGEs progression in patients with diabetes because CGA can attenuate AGEs deposition in glucose.

Role of Advanced Glycation on Aggregation and DNA Binding Properties of α-Synuclein

Abstract: Parkinson's disease (PD) is a neurodegenerative disease with multiple etiologies Advanced glycation end products (AGEs) accumulate in the aging brain and could be one of the reasons for age-related diseases like PD Oxidative stress also leads to the formation of AGEs and may be involved in neurodegeneration by altering the properties of proteins α-Synuclein is involved in pathogenesis of PD and there are limited studies on the role of AGE-α-synuclein in neurodegeneration We studied the aggregation and DNA binding ability of AGE-α-synuclein in vitro α-Synuclein is glycated using methylglyoxal and formation of AGE-α-synuclein is characterized using fluorescence studies, intrinsic tyrosine fluorescence, and fructosamine estimation The results indicated that AGE-α-synuclein aggregates into smaller globular-like aggregates compared to fibrils formed with native α-synuclein Further, it is found that AGE-α-synuclein induced conformational changes in scDNA from B-form to B-C-A mixed conformation Additionally, AGE-α-synuclein altered DNA integrity as evidenced by the melting temperature, ethidium bromide, and DNAse I sensitivity studies AGE-α-synuclein converted biphasic Tm to higher monophasic Tm The Tm of AGE-α-synuclein-scDNA complex is more than that of native α-synuclein-scDNA complex, indicating that AGE-α-synuclein stabilized the uncoiled scDNA AGE-α-synuclein could stabilize the uncoiled scDNA, as shown by the decrease in the number of ethidium bromide binding molecules per base pair of DNA DNAse I sensitive studies indicated that both AGE-α-synuclein-scDNA and α-synuclein-scDNA are resistant to DNAse I digestion The relevance of these findings to neuronal cell death is discussed

Formation of arginine modifications in a model system of Nα-tert-butoxycarbonyl (Boc)-arginine with methylglyoxal.

Abstract: The present study deals with the mechanistic reaction pathway of the α-dicarbonyl compound methylglyoxal with the guanidino group of arginine. Eight products were formed from the reaction of methylglyoxal with Nα-tert-butoxycarbonyl (Boc)-arginine under physiological conditions (pH 7.4 and 37 °C). Isolation and purification of substances were achieved using cation-exchange chromatography and preparative high-performance liquid chromatography (HPLC). Structures were verified by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry. 2-Amino-5-(2-amino-4-hydro-4-methyl-5-imidazolinone-1-yl)pentanoic acid (3) was determined as the key intermediate precursor within the total reaction scheme. Kinetic studies identified Nδ-(5-methyl-4-oxo-5-hydroimidazolinone-2-yl)-l-ornithine and N7-carboxyethylarginine as thermodynamically more stable products from compound 3. Further mechanistic investigations revealed an acidic hydrogen at C-8 of compound 3 to trigger aldol condensations. This reactivity of ...

Upregulation of aldolase B and overproduction of methylglyoxal in vascular tissues from rats with metabolic syndrome

Abstract: Aims Methylglyoxal (MG) overproduction has been reported in metabolic syndrome with hyperglycaemia (diabetes) or without hyperglycaemia (hypertension), and the underlying mechanism was investigated. Methods and results Contributions of different pathways or enzymes to MG formation were evaluated in aorta or cultured vascular smooth muscle cells (VSMCs). In all four animal models of metabolic syndrome, i.e. chronically fructose-fed hypertensive Sprague–Dawley rats, spontaneously hypertensive rats, obese non-diabetic Zucker rats, and diabetic Zucker rats, serum and aortic MG and fructose levels were increased, and the expression of GLUT5 (transporting fructose) and aldolase B (converting fructose to MG) in aorta were up-regulated. Aortic expressions of aldolase A, semicarbazide-sensitive amine oxidase (SSAO), and cytochrome P450 2E1 (CYP 2E1), accounting for MG formation during glycolysis, protein, and lipid metabolism, respectively, was unchanged/reduced. Fructose (25 mM) treatment of VSMCs up-regulated the expression of GLUT5 and aldolase B and accelerated MG formation. Insulin (100 nM) increased GLUT5 expression and augmented fructose-increased cellular fructose accumulation and MG formation. Glucose (25 mM) treatment activated the polyol pathway and enhanced fructose formation, leading to aldolase B upregulation and MG overproduction. Inhibition of the polyol pathway reduced the glucose-increased aldolase B expression and MG generation. The excess formation of MG in under these conditions was eliminated by knock-down of aldolase B, but not by knock-down of aldolase A or inhibition of SSAO or CYP 2E1. Conclusion Upregulation of aldolase B by accumulated fructose is a common mechanism for MG overproduction in VSMCs and aorta in different models of metabolic syndrome.

Dehydratase mediated 1-propanol production in metabolically engineered Escherichia coli

Abstract: With the increasing consumption of fossil fuels, the question of meeting the global energy demand is of great importance in the near future. As an effective solution, production of higher alcohols from renewable sources by microorganisms has been proposed to address both energy crisis and environmental concerns. Higher alcohols contain more than two carbon atoms and have better physiochemical properties than ethanol as fuel substitutes. We designed a novel 1-propanol metabolic pathway by expanding the well-known 1,2-propanediol pathway with two more enzymatic steps catalyzed by a 1,2-propanediol dehydratase and an alcohol dehydrogenase. In order to engineer the pathway into E. coli, we evaluated the activities of eight different methylglyoxal synthases which play crucial roles in shunting carbon flux from glycolysis towards 1-propanol biosynthesis, as well as two secondary alcohol dehydrogenases of different origins that reduce both methylglyoxal and hydroxyacetone. It is evident from our results that the most active enzymes are the methylglyoxal synthase from Bacillus subtilis and the secondary alcohol dehydrogenase from Klebsiella pneumoniae, encoded by mgsA and budC respectively. With the expression of these two genes and the E. coli ydjG encoding methylglyoxal reductase, we achieved the production of 1,2-propanediol at 0.8 g/L in shake flask experiments. We then characterized the catalytic efficiency of three different diol dehydratases on 1,2-propanediol and identified the optimal one as the 1,2-propanediol dehydratase from Klebsiella oxytoca, encoded by the operon ppdABC. Co-expressing this enzyme with the above 1,2-propanediol pathway in wild type E. coli resulted in the production of 1-propanol at a titer of 0.25 g/L. We have successfully established a new pathway for 1-propanol production by shunting the carbon flux from glycolysis. To our knowledge, it is the first time that this pathway has been utilized to produce 1-propanol in E. coli. The work presented here forms a basis for further improvement in production. We speculate that dragging more carbon flux towards methylglyoxal by manipulating glycolytic pathway and eliminating competing pathways such as lactate generation can further enhance the production of 1-propanol.

Cranberry phytochemicals inhibit glycation of human hemoglobin and serum albumin by scavenging reactive carbonyls

Abstract: Protein glycation caused by sugars and reactive carbonyls is a contributing factor to diabetic complications, aging, and other chronic diseases. The objective of this study was to investigate the inhibitory effects of cranberry phytochemicals on protein glycation. Cranberries, purified to yield sugar-free phytochemical powder, were fractionated into ethyl acetate and water fractions. Water fraction was further separated into water fraction I, II, and III on a Sephadex LH-20 column. Cranberry phytochemical powder and its fractions significantly inhibited the formation of glycated hemoglobin. The concentrations of cranberry phytochemicals required to inhibit 50% of albumin glycation (EC50) in albumin-glucose assay were lower than that of aminoguanidine except for water fraction I. Cranberry phytochemicals inhibited glycation of human serum albumin mediated by methylglyoxal, but the EC50 were higher than that of aminoguanidine. Carbonyl scavenging assay showed that water fraction II scavenged 89.3% of methylglyoxal at 6 h of reaction. Fractions enriched with procyanidins showed higher antiglycation activities, suggesting procyanidins were the major active components. The hypothesis whether cranberry procyanidins scavenged reactive carbonyls by forming adducts was tested. Epicatechin was used as a model compound to react with methylglyoxal and glyoxal at pH 7.4. Five adducts were detected and their structures were tentatively identified using HPLC-ESI-MS/MS.