Role of interaction between reactive oxygen species and ferroptosis pathway in methylglyoxal-induced injury in mouse embryonic osteoblasts / 南方医科大学学报

OBJECTIVE@#To explore the interaction between reactive oxygen species (ROS) and ferroptosis in methylglyoxalinduced injury of mouse embryonic osteoblasts (MC3T3-E1 cells).@*METHODS@#MC3T3-E1 cells were treated with methylglyoxal to establish a cell model of diabetic osteoporosis. CCK-8 assay was used to detect the viability of MC3T3-E1 cells. Rhodamine 123 staining followed by photofluorography was used to examine mitochondrial membrane potential (MMP). The intracellular ROS level was detected by 2', 7'-dichlorodihydrofluorescein diacetate staining with photofluorograph. Alkaline phosphatase (ALP) activity in the cells was detected using an ALP kit, the number of mineralized nodules was determined with alizarin red S staining, and the level of iron ions was detected using a detection kit. The expression level of glutathione peroxidase 4 (GPX4, a marker protein that inhibits ferroptosis) in the osteoblasts was determined using Western blotting.@*RESULTS@#Treatment of MC3T3-E1 cells with 0.6 mmol/L methylglyoxal for 24 h significantly inhibited the expression level of GPX4 (P < 0.001), increased intracellular iron ion concentration, decreased the cell viability, increased the loss of MMP and intracellular ROS level, decreased both ALP activity and the number of mineralized nodules in the cells (P < 0.001). Co-treatment of MC3T3-E1 cells with 2 mmol/L N-acetylcysteine (NAC, a ROS scavenger) and methylglyoxal significantly increased the expression level of GPX4 (P < 0.01); co-treatment with 4 mmo/L FER-1 (a ferroptosis inhibitor) and methylglyoxal obviously decreased the intracellular ROS level (P < 0.001). Co-treatment of the cells either with NAC and methylglyoxal or with FER-1 and methylglyoxal attenuated methylglyoxal-induced injuries in the osteoblasts (P < 0.001).@*CONCLUSION@#The interaction between ROS and ferroptosis pathway plays an important role in methylglyoxal-induced injury of mouse embryonic osteoblasts.

Effect of Manuka Honey on Transforming Growth Factor Beta-1-Induced Extracelluar Matrix Production in Nasal Polyp Derived Fibroblasts / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Manuka honey has anti-microbial, anti-inflammatory, and anti-proliferative action with a high concentration of methylglyoxal compound. It is also effective in killing Staphylococcus aureus biofilm and effective for the acute exacerbation of chronic rhinosinusitis. The aim of this study was to determine the anti-fibrotic effect of manuka honey in nasal polyp fibroblasts. MATERIALS AND METHOD: Primary nasal fibroblasts were isolated from nasal polyps and treated with transforming growth factor-beta 1 (TGF-β1). To determine the anti-fibrotic effect of manuka honey, fibroblasts were pre-treated with various concentration of the honey. Reverse transcription-polymerase chain reaction and western blot analysis were then performed to determine α-smooth muscle actin (α-SMA), collagen type I, and matrix metalloproteinase-9 (MMP-9) messenger ribonucleic acid (mRNA) expression and protein production in nasal polyp fibroblasts. Phosphorylated Smad (pSmad) 2/3 and phosphorylated adenosine monophosphate-activated protein kinase (pAMPK) were then determined by western blotting. RESULTS: TGF-β1 stimulation increased α-SMA, collagen type I, and MMP-9 mRNA expression and protein production in nasal polyp fibroblasts. Manuka honey effectively suppressed α-SMA, collagen type I, and MMP-9 mRNA expression and protein production. Its inhibitory role on TGF-β1 induced myofibroblast differentiation and its extracellular matrix production was associated with Smad2/3 and AMPK pathway. CONCLUSION: Manuka honey can inhibit TGF-β1 induced myofibroblast differentiation, collagen type I, and MMP-9 production in nasal fibroblasts. These results suggest that manuka honey might be a useful candidate for the inhibition of nasal polyp formation if further studies in vivo were accompanied.

Screening for active components of Sophorae Flos on inhibiting AGEs formation based on non-enzymatic glycation reaction / 中国中药杂志

Sugar-poison caused blood-heat is the pathological basis of many complications of diabetes. Advanced glycation end products( AGEs) are considered as the potential glycotoxic factor that can cause blood-heat. Sophorae Flos hold the effect of removing pathogenic heat from blood. In this study,chromatographic non-enzymatic glycation reaction system of bovine serum albumin( BSA)/methylglyoxal( MGO) and Sophorae Flos was established to identify active components in Sophorae Flos inhibiting AGEs formation. The HPLC was used to analyze chromatograms before and after the incubation of Sophorae Flos and methylglyoxal. Changes of chromatographic peaks of eight compounds was found. It is speculated that this change may be due to new substance produced by the reaction of active components in Sophorae Flos and methylglyoxal,and these active components may be flavonoid component rutin. Further investigation for the effects of rutin and MGO reaction( 1 ∶ 1,1 ∶ 3,3 ∶ 1) for 6 days on the formation of AGEs was performed. The results showed that the inhibition activity of rutin on AGEs production was most obvious when the reaction ratio was 1 ∶3,and the most inhibition was in 24 h and stabilized after 3 d. The product of the reaction of rutin with MGO was identified by LC-ESI-MS/MS,which indicated that the newly formed seven substances were the mono-and di-MGO adducts of rutin. This study showed that rutin is the active component on Sophorae Flos for removing pathogenic heat from blood by forming new compounds to inhibit the formation of sugar poison products,which provides reference for rational application of Sophorae Flos.

Expression analysis of glyoxalase I gene among patients of diabetic retinopathy

Objectives: To study expression of glyoxalase I in patients of diabetic retinopathy

Methods: This cross-sectional comparative study was conducted at Centre for Research in Experimental and Applied Medicine [CREAM], Department of Biochemistry and Molecular Biology, Army Medical College, Rawalpindi in collaboration with Armed Forces Institute of Ophthalmology [AFIO] from January 2015 to November 2015. Sampling technique was non- probability purposive sampling. Total 60 subjects were enrolled in two groups. Group-I comprised 30 patients of diabetic retinopathy and Group-II of 30 normal healthy controls. Clinical and demographic data was collected and fasting venous blood samples [2 ml] were drawn. RNA was extracted and subjected to cDNA synthesis. Expression analysis for glyoxalase I was carried out and relative quantification done by double delta Ct method

Results: Mean age of the patients was 61.30 +/- 7.06 years and mean age of controls was 59.60 +/- 6.43 years. There were 17 [56.7%] males and 13 [43.3%] females in Group-I while Group-II comprised 14 [46.7%] males and 16 [53.3%] females. There was down regulation of glyoxalase I among patients of diabetic retinopathy in comparison with controls when relative gene expression was calculated

Conclusion: Down regulation of glyoxalase I in patients of diabetic retinopathy suggests it to be a contributory factor in the development of disease

Hypericin, a Naphthodianthrone Derivative, Prevents Methylglyoxal-Induced Human Endothelial Cell Dysfunction

Methylglyoxal (MGO) is a highly reactive metabolite of glucose which is known to cause damage and induce apoptosis in endothelial cells. Endothelial cell damage is implicated in the progression of diabetes-associated complications and atherosclerosis. Hypericin, a naphthodianthrone isolated from Hypericum perforatum L. (St. John’s Wort), is a potent and selective inhibitor of protein kinase C and is reported to reduce neuropathic pain. In this work, we investigated the protective effect of hypericin on MGO-induced apoptosis in human umbilical vein endothelial cells (HUVECs). Hypericin showed significant anti-apoptotic activity in MGO-treated HUVECs. Pretreatment with hypericin significantly inhibited MGO-induced changes in cell morphology, cell death, and production of intracellular reactive oxygen species. Hypericin prevented MGO-induced apoptosis in HUVECs by increasing Bcl-2 expression and decreasing Bax expression. MGO was found to activate mitogen-activated protein kinases (MAPKs). Pretreatment with hypericin strongly inhibited the activation of MAPKs, including P38, JNK, and ERK1/2. Interestingly, hypericin also inhibited the formation of AGEs. These findings suggest that hypericin may be an effective regulator of MGO-induced apoptosis. In conclusion, hypericin downregulated the formation of AGEs and ameliorated MGO-induced dysfunction in human endothelial cells.

Rapid Identification of Methylglyoxal Trapping Constituents from Onion Peels by Pre-column Incubation Method

The methylglyoxal (MGO) trapping constituents from onion (Allium cepa L.) peels were investigated using pre-column incubation of MGO and crude extract followed by HPLC analysis. The peak areas of MGO trapping compounds decreased, and their chemical structures were identified by HPLC-ESI/MS. Among major constituents in outer scale of onion, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2) was more effective MGO scavenger than quercetin (6) and its 4′-glucoside, spiraeoside (3). After 1 h incubation, compound 2 trapped over 90% MGO at a concentration of 0.5 mM under physiological conditions, but compounds 3 and 6 scavenged 45%, 16% MGO, respectively. HPLC-ESI/MS showed that compound 2 trapped two molecules of MGO to form a di-MGO adduct and compounds 3 and 6 captured one molecule of MGO to form mono-MGO adducts, and the positions 6 and 8 of the A ring of flavonoids were major active sites for trapping MGO.

Methylglyoxal inhibits human umbilical vein cell migration in vitro by down-regulating integrinβ3 / 南方医科大学学报

<p><b>OBJECTIVE</b>To explore the effects of methylglyoxal on endothelia cell migration.</p><p><b>METHODS</b>Human umbilical vein endothelial cells (HUVECs) were stimulated by serial concentrations of methylglyoxal (MGO, 0, 25, 50, 100 and 200 µmol/L) for 24 h, and the cell migration was assessed by scratch wound and Transwell assay. The expression of integrin β3 in the treated cells was examined by immunoblotting, and the effect of an anti-β3 antibody, LM609, on cell migration was investigated.</p><p><b>RESULTS</b>Methylglyoxal significantly inhibited HUVEC migration in a concentration-dependent manner (P<0.05). Methylglyoxal decreased the expression of integrin β3 in a time- and concentration-dependent manner (P<0.05). LM609 also significantly inhibited HUVEC migration (P<0.05).</p><p><b>CONCLUSION</b>Methylglyoxal inhibits HUVEC migration in vitro by down-regulating integrin β3 expression.</p>

No short-term effects of calorie-controlled Mediterranean or fast food dietary interventions on established biomarkers of vascular or metabolic risk in healthy individuals

BACKGROUND/OBJECTIVES: This study addressed the question whether the composition of supposedly 'healthy' or 'unhealthy' dietary regimes has a calorie-independent short-term effect on biomarkers of metabolic stress and vascular risk in healthy individuals. SUBJECTS/METHODS: Healthy male volunteers (age 29.5 +/- 5.9 years, n = 39) were given a standardized baseline diet for two weeks before randomization into three groups of different dietary regimes: fast food, Mediterranean and German cooking style. Importantly, the amount of calories consumed per day was identical in all three groups. Blood samples were analyzed for biomarkers of cardiovascular risk and metabolic stress after two weeks of the baseline diet and after two weeks of the assigned dietary regime. RESULTS: No dietary intervention affected the metabolic or cardiovascular risk profile when compared in-between groups or compared to baseline. Subjects applied to the Mediterranean diet showed a statistically significant increase of uric acid compared to baseline and compared to the German diet group. Plasma concentrations of urea were significantly higher in both the fast food group and the Mediterranean group, when compared to baseline and compared to the German diet group. No significant differences were detected for the levels of vitamins, trace elements or metabolic stress markers (8-hydroxy-2-deoxyguanosine, malondialdehyde and methylglyoxal, a potent glycating agent). Established parameters of vascular risk (e.g. LDL-cholesterol, lipoprotein(a), homocysteine) were not significantly changed in-between groups or compared to baseline during the intervention period. CONCLUSIONS: The calorie-controlled dietary intervention caused neither protective nor harmful short-term effects regarding established biomarkers of vascular or metabolic risk. When avoiding the noxious effects of overfeeding, healthy individuals can possess the metabolic capacity to compensate for a potentially disadvantageous composition of a certain diet.

No short-term effects of calorie-controlled Mediterranean or fast food dietary interventions on established biomarkers of vascular or metabolic risk in healthy individuals

BACKGROUND/OBJECTIVES: This study addressed the question whether the composition of supposedly 'healthy' or 'unhealthy' dietary regimes has a calorie-independent short-term effect on biomarkers of metabolic stress and vascular risk in healthy individuals. SUBJECTS/METHODS: Healthy male volunteers (age 29.5 +/- 5.9 years, n = 39) were given a standardized baseline diet for two weeks before randomization into three groups of different dietary regimes: fast food, Mediterranean and German cooking style. Importantly, the amount of calories consumed per day was identical in all three groups. Blood samples were analyzed for biomarkers of cardiovascular risk and metabolic stress after two weeks of the baseline diet and after two weeks of the assigned dietary regime. RESULTS: No dietary intervention affected the metabolic or cardiovascular risk profile when compared in-between groups or compared to baseline. Subjects applied to the Mediterranean diet showed a statistically significant increase of uric acid compared to baseline and compared to the German diet group. Plasma concentrations of urea were significantly higher in both the fast food group and the Mediterranean group, when compared to baseline and compared to the German diet group. No significant differences were detected for the levels of vitamins, trace elements or metabolic stress markers (8-hydroxy-2-deoxyguanosine, malondialdehyde and methylglyoxal, a potent glycating agent). Established parameters of vascular risk (e.g. LDL-cholesterol, lipoprotein(a), homocysteine) were not significantly changed in-between groups or compared to baseline during the intervention period. CONCLUSIONS: The calorie-controlled dietary intervention caused neither protective nor harmful short-term effects regarding established biomarkers of vascular or metabolic risk. When avoiding the noxious effects of overfeeding, healthy individuals can possess the metabolic capacity to compensate for a potentially disadvantageous composition of a certain diet.

Aminoguanidine suppresses methylglyoxal-mediated oxygen-glucose deprivation injury in human brain microvascular endothelial cells / 浙江大学学报·医学版

<p><b>OBJECTIVE</b>To evaluate the effects of aminoguanidine on methylglyoxal-mediated oxygen-glucose deprivation (OGD) injury in the cultured human brain microvascular endothelial cells (HBMEC).</p><p><b>METHODS</b>Cultured HBMEC cells were pretreated with methylglyoxal before oxygen-glucose deprivation injury. Cell vitality was determined by MTT method, cell mortality was assessed by LDH release method, cell apoptosis was examined by Annexin V/PI formation method, and the advanced glycation end products (AGEs) were detected by Western-blot.</p><p><b>RESULTS</b>Methylglyoxal induced HBMEC injury in a dose-dependent manner. At 2 mmol/L of methylglyoxal, the cell viability was 56.1% when methylglyoxal-pretreated cells exposed to oxygen-glucose deprivation, the cell inhibition rate was 90.0%. Aminoguanidine (1 mmol/L) inhibited methylglyoxal and OGD induced LDH release and Annexin V/PI formation. Furthermore, aminoguanidine (1 mmol/L) also decreased advanced glycation end products (AGEs) formation induced by methylglyoxal and oxygen-glucose deprivation.</p><p><b>CONCLUSION</b>Aminoguanidine protected methylglyoxal mediated-oxygen-glucose deprivation injury in the cultured HBMEC, which may be associated with anti-glycation activity.</p>

Methylglyoxal level in type-2 diabetes mellitus patients: a prospective, randomized and case control study at tertiary care hospitals, Hyderabad, Pakistan

To study the methyglyoxal [MG] levels in type 2 diabetes mellitus [T2DM] subjects compared with normal controls and to evaluate relationship of MG with blood sugar, systolic and diastolic blood pressure. Comparative case control study. This study was conducted at the Diabetic clinics of Isra University Hospital for a period of six months from. Thirty normal controls [Group. I] and thirty T2DM [Group. II] were studied according to inclusion and exclusion criteria. 5.0 ml of blood was transferred into citrated bottles. Serum was obtained by centrifugation at 4000 rpm for ten minutes and were frozen at -20 Degree C. The blood glucose level was detected by glucose oxidase method. MG was measured by the ELISA assay. Student`s t-test, Chi square test and Pearson`s correlations were used for the continous and categorical variables and linear association respectively. The Data was analyzed using SPSS version 17.0. A p-value of

Accumulation of argpyrimidine, a methylglyoxal-derived advanced glycation end product, increases apoptosis of lens epithelial cells both in vitro and in vivo

The formation of advanced glycation end products (AGEs) has been considered to be a potential causative factor of injury to lens epithelial cells (LECs). Damage of LECs is believed to contribute to cataract formation. The purpose of this study was to investigate the cytotoxic effect of AGEs on LECs both in vitro and in vivo. We examined the accumulation of argpyrimidine, a methylglyoxal-derived AGE, and the expression of apoptosis-related molecules including nuclear factor-kappaB (NF-kappaB), Bax, and Bcl-2 in the human LEC line HLE-B3 and in cataractous lenses of Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes. In cataractous lenses from twenty-one-week-old ZDF rats, LEC apoptosis was markedly increased, and the accumulation of argpyrimidine as well as subsequent activation of NF-kappaB in LECs were significantly enhanced. The ratio of Bax to Bcl-2 protein levels was also increased. In addition, the accumulation of argpyrimidine triggered apoptosis in methylglyoxal-treated HLE-B3 cells. However, the presence of pyridoxamine (an AGEs inhibitor) and pyrrolidine dithiocarbamate (a NF-kappaB inhibitor) prevented apoptosis in HLE-B3 cells through the inhibition of argpyrimidine formation and the blockage of NF-kappaB nuclear translocalization, respectively. These results suggest that the cellular accumulation of argpyrimidine in LECs is NF-kappaB-dependent and pro-apoptotic.

Reactive carbonyl compounds (RCCs) cause aggregation and dysfunction of fibrinogen

Fibrinogen is a key protein involved in coagulation and its deposition on blood vessel walls plays an important role in the pathology of atherosclerosis. Although the causes of fibrinogen (fibrin) deposition have been studied in depth, little is known about the relationship between fibrinogen deposition and reactive carbonyl compounds (RCCs), compounds which are produced and released into the blood and react with plasma protein especially under conditions of oxidative stress and inflammation. Here, we investigated the effect of glycolaldehyde on the activity and deposition of fibrinogen compared with the common RCCs acrolein, methylglyoxal, glyoxal and malondialdehyde. At the same concentration (1 mmol/L), glycolaldehyde and acrolein had a stronger suppressive effect on fibrinogen activation than the other three RCCs. Fibrinogen aggregated when it was respectively incubated with glycolaldehyde and the other RCCs, as demonstrated by SDS-PAGE, electron microscopy and intrinsic fluorescence intensity measurements. Staining with Congo Red showed that glycolaldehyde- and acrolein-fibrinogen distinctly formed amyloid-like aggregations. Furthermore, the five RCCs, particularly glycolaldehyde and acrolein, delayed human plasma coagulation. Only glycolaldehyde showed a markedly suppressive effect on fibrinogenesis, none did the other four RCCs when their physiological blood concentrations were employyed, respectively. Taken together, it is glycolaldehyde that suppresses fibrinogenesis and induces protein aggregation most effectively, suggesting a putative pathological process for fibrinogen (fibrin) deposition in the blood.

Acetilação radicalar de amino ácidos, peptídeos e nucleobases pelos sistemas biacetilo/peroxinitrito e metilglioxal/peroxinitrito / Radical acetylation of aminoacids, peptides, and nucleobases by the biacetyl or methylglyoxal/peroxynitrite systems

Biacetilo (2,3-butanediona) é um contaminante de comida e cigarro, também implicado na hepatoxicidade do álcool e em doenças pulmonares. O metilglioxal (MG), um α-oxoaldeído reativo frequentemente associado ao diabetes e envelhecimento, é produto da fragmentação oxidativa de trioses fosfato, acetona e aminoacetona. Por sua vez, peroxinitrito - um potente oxidante, agente nitrante e nucleófilo formado in vivo pela reação controlada por difusão do ânion radical superóxido com o radical óxido nítrico (k ~1010 M-1s-1) é capaz de se adicionar a CO2 e compostos carbonílicos, gerando produtos potencialmente tóxicos ou sinalizadores celulares. Aminoácidos, peptídeos e nucleobases podem ser acetilados nos grupos amina e na porção desoxiribose. Relativamente ao tratamento com peroxinitrito isolado, níveis superiores de 3-nitrotirosina foram detectados quando tirosina foi tratada com peroxinitrito/biacetilo ou metilglioxal. Ambos os grupos amina de lisina (Lys) ou um deles de derivados de lisina bloqueados e um deles (Ac-Lys-OMe, Z-Lys-OMe) foram acetilados pelo sistema biacetilo ou metilglioxal/peroxinitrito. Em tetrapeptídeos sintéticos contendo lisina como aminoácido amino-terminal (H-KALA-OH, Ac-KALA-OH and H-K(Boc)ALA-OH), a lisina foi acetilada pelo sistemas dicarbonilico/peroxinitrito no grupo α-amina (em maior extensão) e/ou no ε-amina (em menor extensão). No conjunto, estes resultados podem ser interpretados à luz do mecanismo proposto para a reação de compostos α-dicarbonílicos com peroxinitrito, o qual envolve sequencialmente: (i) adição nucleofílica de peroxinitrito à carbonila; (ii) homólise do aduto peroxinitroso formado, liberando •NO2 e um radical oxila do reagente carbonílico; (iii) β-clivagem do radical oxila a um ácido carboxílico (ácido acético no caso de biacetilo e ácido fórmico, a partir de metilglioxal) e radical acetila; (iv) captação do radical acetila pelo oxigênio molecular dissolvido dando acetato, ou por aminoácido ou nucleobase...

Diacetyl (2,3-butanedione) is a food and cigarette contaminant recently implicated in alcohol hepatotoxicity and lung disease. In turn, methylglyoxal (MG) is an α-oxoaldehyde frequently associated with diabetes and aging that is putatively formed by the oxidative fragmentation of trioses phosphate, acetone and aminoacetone. Peroxynitrite - a potent oxidant, nitrating agent and nucleophile formed in vivo by the diffusion-controlled reaction of superoxide radical with nitric oxide (k ~1010 M-1s-1) - is able to form adducts with carbon dioxide and carbonyl compounds. When initially present in the reaction mixtures before addition of ONOO-, amino acids, peptides and nucleobases undergo acetylation at the amino group and purine moieties in the presence of biacetyl or methylglyoxal. Higher levels of 3-nitrotyrosine nitration were measured when peroxynitrite/biacetyl or metilglioxal was added to tyrosine, in comparison with peroxynitrite alone. Both amino groups of L-lysine or one of the amino groups of L-lysine derivatives (Z-Lys-OH and Ac-Lys-OH) were acetylated by biacetyl and methylglyoxal/peroxynitrite system. Using tetrapeptides containing lysine at the terminal amino acid (H-KALA-OH, Ac-KALA-OH and H-K(Boc)ALA-OH), the lysine residue was acetylated at both or either α-amino (major adduct) and ε-amino group (minor adduct). Altogether these data can be interpreted by the mechanism proposed to describe the reaction of α-dicarbonyls with peroxynitrite as follows: (i) nucleophilic addition of peroxynitrite to the carbonyl group of the reagent; (ii) homolysis of the formed peroxynitroso carbonyl adduct to •NO2 and a carbonyloxyl radical; (iii) β-cleavage of the oxyl radical to acetyl radical plus acetic acid (from diacetyl) or formic acid (from methylglyoxal); (iv) competitive scavenging of the acetyl radical by dissolved molecular oxygen and by added amino acid, peptide or nucleobase, ultimately yielding acetate or acetylated biomolecule. If occurring in vivo...

Preferential recognition of methylglyoxal-modified calf thymus DNA by circulating antibodies in cancer patients.

Methylglyoxal (MG) has been implicated in mutagenesis and cancer. Present study probes the antigenicity of MG damaged DNA in cancer patients. Purified calf thymus DNA was damaged by the synergistic action of MG, lysine (Lys) and CuSO4 for 24 h at 37oC. DNA modifications produced single-strand breaks, hyperchromicity in UV spectrum and increased fluorescence intensity. Binding characteristics of auto-antibodies in cancer patients were assessed by direct binding and inhibition ELISA. These antibodies exhibited enhanced binding with the modified DNA, as compared to the native form. The effect was more pronounced when affinity-purified IgG was used in place of the serum. In conclusion, MG-modified DNA presents unique epitopes which are recognized as non-self by the immune system and may, therefore, be one of the factors for the autoantibody induction in cancer patients.

Mecanismo de oxidação aeróbica de acetoacetato e 2-metilacetoacetato catalisada por mioglobina: implicações em desordens cetogênicas / Mechanism of the aerobic oxidation of acetoacetate and 2- methylacetoacetate catalyzed by Mb: implications for ketogenic disorders

Acetoacetato (AA) e 2-metilacetoacetato (MAA) são compostos β-cetoácidos acumulados em diversas desordens metabólicas como no diabetes e na isoleucinemia, respectivamente. Examinamos o mecanismo de oxidação aeróbica de AA e MAA iniciada por intermediários reativos de mioglobina de coração de cavalo (Mb) gerados pela adição de H2O2. Uma rota quimioluminescente que envolve um intermediário dioxetânico cuja termólise gera espécies α-dicarbonílicas (metilglioxal e biacetilo) foi proposta e estudada. Emissão de luz ultra fraca acompanha a reação, e sua intensidade aumenta linearmente pelo aumento da concentração tanto de Mb (10-500 µM) quando AA (10-100 mM). Estudos de consumo de oxigênio mostraram que MAA é, como esperado, quase uma ordem de grandeza mais reativo que AA. Estudos de EPR com captação de spin, utilizando MNP, possibilitaram detectar adutos de MAA atribuíveis a um radical centrado no Cα (aN = 1.55 mT) e ao radical acetila (aN = 0.83 mT). O sinal do radical acetila é totalmente suprimido por sorbato, um conhecido e eficiente supressor de espécies tripletes, o que é consistente com uma rota reacional envolvendo um intermediário dioxetânico. Clivagem-α da ligação carbonila-carbonila do produto biacetilo triplete produziria, de fato, radicais acetila. Além disso, utilizando AA como substrato para Mb/H2O2, um sinal de EPR atribuível ao aduto MNP-AA• (aN = 1.46 mT e aH = 0.34 mT) foi observado e confirmado por efeito isotópico. O consumo de oxigênio e o rendimento de compostos α-dicarbonílicos foram dose-dependentes à concentração de AA ou MAA (1-50 mM) bem como à concentração de H2O2 adicionado às misturas de reação contendo Mb (até 1:10 quando medido o consumo de oxigênio, e até 1:25 quando medido o rendimento de compostos α-dicarbonílicos) e tert-butilhidroperóxido (até 1:200). Os perfis de pH (5,8-7,8) para consumo de oxigênio e rendimento de compostos α-dicarbonílicos mostraram maiores rendimentos para baixos valores de pH, indicativo de ferrilMb...

Acetoacetate (AA) and 2-methylacetoacetate (MAA) are β-ketoacids accumulated in several metabolic disorders such as diabetes and isoleucinemia, respectively. Here we examine the mechanism of AA and MAA aerobic oxidation initiated by the reactive enzyme intermediates formed by the reaction of muscle horse myoglobin (Mb) with H2O2. A chemiluminescent route involving a dioxetane intermediate whose thermolysis yields triplet α-dicarbonyl species (methylglyoxal and diacetyl) is envisaged. Accordingly, the ultraweak light emission that accompanies the reaction increases linearly by raising the concentration of both Mb (10-500 µM) and AA (10- 100 mM). Oxygen uptake studies revealed that MAA is, expectedly, almost one order of magnitude more reactive than AA. EPR spin-trapping studies with MNP detected spin adducts from MAA attributable to an α-carbon-centered radical (aN = 1.55 mT) and to an acetyl radical (aN = 0.83 mT). As the acetyl radical signal is totally suppressed by sorbate, a well-known efficient triplet species quencher, the dioxetane hypothesis seems to be reliable. The α-cleavage of the carbonyl-carbonyl bond of a putative excited triplet diacetyl product would, in fact, leads to an acetyl radical. Furthermore, using AA as substrate for Mb/H2O2, an EPR signal assignable to a MNP-AA• adduct (aN = 1.46 mT and aH = 0.34 mT) was observed and confirmed by isotope effect. Oxygen consumption and α-dicarbonyl yield were also dependent on AA or MAA concentrations (1-50 mM) as well as on the concentration of peroxide added to the Mb-containing reaction mixtures: H2O2 (up to 1:10 when measuring oxygen uptake and up to 1:25 when measuring the α-dicarbonyl yield) and t-butOOH (up to 1:200). The pH profiles (5.8-7.8) of oxygen consumption and α-dicarbonyl yield show higher reaction rates at lower pHs, indicative of a ferrylMb intermediate. Evaluating Mb lesion, both β-ketoacids reduced disorganization of the secondary and tertiary protein structure elicited by H2O2...

Toxicidade de aminoacetona e células produtoras de insulina / Cytotoxity of aminoacetone on insulin-producing cells

Danos induzidos por hiperglicemia em tecidos no diabetes são caracterizados por quatro mecanismos conectados: aumento do fluxo metabólico através da via do poliol, ativação da proteína quinase C (PKC), aumento da atividade da via das hexosaminas e aumento da produção intracelular dos precursores dos produtos finais de glicação avançada (AGEs). Entre eles, os derivados de metilglioxal, um potente agente de modificação de proteínas e DNA, têm sido associados a complicações microvasculares no diabetes: nefropatia, retinopatia e neuropatia. O metilglioxal é produzido a partir das trioses fosfato, acetona e aminoacetona, um catabólito de treonina e glicina, gerado na matriz mitocondrial. A aminoacetona sofre oxidação enzimática, catalisada por aminoxidase sensível a semicarbazida (SSAO), ou química, catalisada por íons de cobre e ferro, produzindo metilglioxal, H2O2 e NH4 +. Sabendo que metilglioxal e H2O2 são capazes de induzir apoptose e/ou necrose em células produtoras de insulina (RINm5f) propomos uma possível atividade pró-oxidante da aminoacetona sobre células beta do pâncreas. O tratamento destas linhagens com aminoacetona/Cu(II) aumentou a morte celular, fluxo de Ca2+ intracelular, produção de NO, fragmentação do DNA, depleção dos níveis de glutationa reduzida (GSH), expressão gênica da proteína apoptótica Bax, enzimas antioxidantes - glutationa peroxidase (GPx), glutationa redutase (GRd), catalase e isoformas de superóxido dismutases (CuZnSOD e MnSOD) - e óxido nítrico sintase induzida (iNOS). Embora as concentrações normais e patológicas da aminoacetona, provavelmente seja muito menores que as usadas nos experimentos, sugerimos que, em tecidos de diabéticos, um acúmulo da aminoacetona em longo prazo pode conduzir a danos oxidativos e eventualmente morte das células beta do pâncreas.

Tissue damages induced by hyperglycemia in diabetics are characterized by four linked mechanisms: increased flux through the polyol pathway, protein kinase C (PKC) activation, increased hexosamine pathway activity and intracellular production of advanced glycation end product (AGE) precursors. The production of AGEs by modifying proteins and DNA agent, such as methylglyoxal, has been implicated in microvascular complications in diabetes: nephropathy, retinopathy and neuropathy. Methylglyoxal is putatively produced in vivo from trioses phosphate, acetone and aminoacetone, a catabolite of threonine and glycine synthesized in the mitochondrial matrix. Aminoacetone has been reported to undergo semicarbazide sensitive amine oxidase- catalyzed and copper- and iron-catalyzed oxidations by molecular oxygen to methylglyoxal, NH4 + ion and H2O2. Considering that methylglyoxal and H2O2 have been found to promote apoptosis/necrosis to insulin-producing cells (RINm5f), we propose a possible pro-oxidant role of aminoacetone in pancreatic beta-cells. Treatment of RINm5f cells with aminoacetone plus Cu(II) ion promotes an increase of non-viable cells, influx of Ca2+ ions, NO production, DNA fragmentation, depletion of reduced glutathione (GSH) levels, and increased mRNA expression of pro-apoptotic protein (Bax), antioxidant enzymes - glutathione peroxidase (GPx), glutathione reductase (GRd), MnSOD, CuZnSOD and catalase - and inducible nitric oxide synthase (iNOS). Although both normal and pathological concentrations of aminoacetone are probably much lower than those used here, it is tempting to propose that excess aminoacetone in diabetic patients, at long term, may drive oxidative damage and eventually death of pancreatic beta-cells.

Effect of Methylglyoxal on the Oxidative Stress in Trabecular Meshwork Cells

PURPOSE: To investigate the effect of methylglyoxal (MG), intermediate metabolite of advanced glycation end products(AGE), on the induction of oxidative stress in human trabecular meshwork cells (HTMC). METHODS: Primarily cultured HTMC were exposed to at concentrations of 0, 30, 100, and 300 micrometer of MG for 18 hours, with or without co-exposure to N-acetyl-cysteine. Cellular survival and apoptosis were assessed by MTT assay and flow cytometry using annexin-PI double staining. Production of nitric oxide (NO), superoxide, and reactive oxygen species (ROS) was assessed by Griess assay, cytochrome c assay, and dichlorofluorescein diacetate assay, respectively. RESULTS: MG did not affect cellular survival at concentrations under 100 micrometer, but induced apoptosis of HTMC at concentrations over 100 micrometer. MG decreased NO production, accompanied with increased superoxide production. In addition, MG increased ROS, which were abolished by N-acetylcysteine. CONCLUSIONS: MG induced oxidative stress by decreasing NO production, accompanied by increasing superoxide and ROS productions in HTMC. AGE could induce trabecular meshwork dysfunction.

Glucose Toxicity and Pancreatic Beta Cell Dysfunction in Type 2 Diabetes / 당뇨병

The adverse effects of prolonged exposure of pancreatic islets to supraphysiologic glucose concentrations (i.e. glucose toxicity) is mediated at least in part by glucose oxidation and the subsequent generation of reactive oxygen species (ROS) that can impair insulin gene expression and beta cell function. Multiple biochemical pathways and mechanisms of action for glucose toxicity have been suggested. These include glucose autoxidation, protein kinase C activation, methylglyoxal formation and glycation, hexosamine metabolism, sorbitol formation, and oxidative phosphorylation. There are many potential mechanisms whereby excess glucose metabolites traveling along these pathways might cause beta cell damage. However, all these pathways have in common the formation of reactive oxygen species that, in excess and over time, cause chronic oxidative stress, which in turn causes defective insulin gene expression and insulin secretion as well as increased apoptosis. The intracellular peroxide levels of the pancreatic islets (INS-1 cells, rat islets) by flow cytometry were increased in the high glucose media compared to 5.6 mM glucose media. The insulin, MafA, PDX-1 mRNA levels and glucose stimulated insulin secretion (GSIS) were decreased in high glucose media compared to 5.6 mM glucose media. The HO-1 seems to mediate the protective response of pancreatic islets against the oxidative stress that is due to high glucose conditions. Also, we observed decreased glutathione level, gamma-GCS expression and increased oxidized LDL, malondialdehyde level at leukocytes and mesothelial cells from patients with Korean Type 2 Diabetes (esp, poorly controlled patients). In conclusion, this pathophysiologic sequence sets the scene for considering antioxidant therapy as an adjunct in the management of diabetes, especially type 2 Diabetes.

Methylglyoxal Induces Apoptosis Mediated by Reactive Oxygen Species in Bovine Retinal Pericytes

One of the histopathologic hallmarks of early diabetic retinopathy is the loss of pericytes. Evidences suggest that the pericyte loss in vivo is mediated by apoptosis. However, the underlying cause of pericyte apoptosis is not fully understood. This study investigated the influence of methylglyoxal (MGO), a reactive -dicarbonyl compound of glucose metabolism, on apoptotic cell death in bovine retinal pericytes. Analysis of internucleosomal DNA fragmentation by ELISA showed that MGO (200 to 800 micrometer) induced apoptosis in a concentration-dependent manner. Intracellular reactive oxygen species were generated earlier and the antioxidant, N-acetyl cysteine, inhibited the MGO-induced apoptosis. NF-kB activation and increased caspase- 3 activity were detected. Apoptosis was also inhibited by the caspase-3 inhibitor, Z-DEVD-fmk, or the NF- kB inhibitor, pyrrolidine dithiocarbamate. These data suggest that elevated MGO levels observed in diabetes may cause apoptosis in bovine retinal pericytes through an oxidative stress mechanism and suggests that the nuclear activation of NF-kB are involved in the apoptotic process.