Methylglyoxal Research Articles

Pyridoxamine reduces methylglyoxal and markers of glycation and endothelial dysfunction, but does not improve insulin sensitivity or vascular function in abdominally obese individuals: A randomized double-blind placebo-controlled trial.

To investigate the effects of pyridoxamine (PM), a B6 vitamer and dicarbonyl scavenger, on glycation and a large panel of metabolic and vascular measurements in a randomized double-blindplacebo-controlled trial in abdominally obese individuals. Individuals (54% female; mean age 50 years; mean body mass index 32 kg/m2 ) were randomized to an 8-week intervention with either placebo (n=36), 25 mg PM (n=36) or 200 mg PM (n=36). We assessed insulin sensitivity, β-cell function, insulin-mediated microvascular recruitment, skin microvascular function, flow-mediated dilation, and plasma inflammation and endothelial function markers. PM metabolites, dicarbonyls and advanced glycation endproducts (AGEs) were measured using ultra-performance liquid chromatography tandem mass spectrometry. Treatment effects were evaluated by one-way ANCOVA. In the high PM dose group, we found a reduction of plasma methylglyoxal (MGO) and protein-bound Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine(MG-H1), as compared to placebo. We found a reduction of the endothelial dysfunction marker soluble vascular celladhesion molecule-1 (sVCAM-1) in the low and high PM dose group and of soluble intercellularadhesion molecule-1(sICAM-1) in the high PM dose, as compared to placebo. We found no treatment effects on insulin sensitivity, vascular function or other functional outcome measurements. This study shows that PM is metabolically active and reduces MGO, AGEs, sVCAM-1 and sICAM-1, but does not affect insulin sensitivity and vascular function in abdominally obese individuals. The reduction in adhesion markers is promising because these are important in the pathogenesis of endothelial damage and atherosclerosis.

Methylglyoxal-mediated Gpd1 activation restores the mitochondrial defects in a yeast model of mitochondrial DNA depletion syndrome

Human MPV17, an evolutionarily conserved mitochondrial inner-membrane channel protein, accounts for the tissue-specific mitochondrial DNA depletion syndrome. However, the precise molecular function of the MPV17 protein is still elusive. Previous studies showed that the mitochondrial morphology and cristae organization are severely disrupted in the MPV17 knockout cells from yeast, zebrafish, and mammalian tissues. As mitochondrial cristae morphology is strictly regulated by the membrane phospholipids composition, we measured mitochondrial membrane phospholipids (PLs) levels in yeast Saccharomyces cerevisiae MPV17 ortholog, SYM1 (Stress-inducible Yeast MPV17) deleted cells. We found that Sym1 knockout decreases the mitochondrial membrane PL, phosphatidyl ethanolamine (PE), and inhibits respiratory growth at 37 ̊C on rich media. Both the oxygen consumption rate and the steady state expressions of mitochondrial complex II and super-complexes are compromised. Apart from mitochondrial PE defect a significant depletion of mitochondrial phosphatidyl-choline (PC) was noticed in the sym1∆ cells grown on synthetic media at both 30 ̊C and 37 ̊C temperatures. Surprisingly, exogenous supplementation of methylglyoxal (MG), an intrinsic side product of glycolysis, rescues the respiratory growth of Sym1 deficient yeast cells. Using a combination of molecular biology and lipid biochemistry, we uncovered that MG simultaneously restores both the mitochondrial PE/PC levels and the respiration by enhancing cytosolic NAD-dependent glycerol-3-phosphate dehydrogenase 1 (Gpd1) enzymatic activity. Further, MG is incapable to restore respiratory growth of the sym1∆gpd1∆ double knockout cells. Thus, our work provides Gpd1 activation as a novel strategy for combating Sym1 deficiency and PC/PE defects.

Nicosulfuron stress on the glyoxalase system and endogenous hormone content in sweet maize seedlings.

To reduce the harmful effects of nicosulfuron on sweet corn, the physiological regulation mechanism of sweet corn detoxification was studied. This study analyzed the effects of nicosulfuron stress on the glyoxalase system, hormone content, and key gene expression of nicosulfuron-tolerant "HK301" and nicosulfuron-sensitive "HK320" sweet corn seedling sister lines. After spraying nicosulfuron, the methylglyoxal (MG) content in HK301 increased first and then decreased. Glyoxalase I (GlyI) and glyoxalase II (GlyII) activities, non-enzymatic glutathione (GSH), and the glutathione redox state glutathione/(glutathione + glutathione disulfide) (GSH/(GSH + GSSG)) showed a similar trend as the MG content. Abscisic acid (ABA), gibberellin (GA), and zeatin nucleoside (ZR) also increased first and then decreased, whereas the auxin (IAA) increased continuously. In HK301, all indices after spraying nicosulfuron were significantly greater than those of the control. In HK320, MG accumulation continued to increase after nicosulfuron spraying and GlyI and GlyII activities, and GSH first increased and then decreased after 1day of stress. The indicators above were significantly greater than the control. The GSH/(GSH + GSSG) ratio showed a decreasing trend and was significantly smaller than the control. Furthermore, ABA and IAA continued to increase, and the GA and ZR first increased and then decreased. Compared with HK320, HK301 significantly upregulated the transcription levels of GlyI and GlyII genes in roots, stems, and leaves. Comprehensive analysis showed that sweet maize seedlings improved their herbicide resistance by changing the glyoxalase system and regulating endogenous hormones. The results provide a theoretical basis for further understanding the response mechanism of the glyoxalase system and the regulation characteristics of endogenous hormones in maize under nicosulfuron stress.

Effect of exogenous taurine on pea (Pisum sativum L.) plants under salinity and iron deficiency stress

Soil salinity and Fe deficiency affect plant growth and survival by changing nutrient availability and disrupting water balance. Natural and human activities, such as evaporation and deforestation, can intensify these soil conditions. Taurine, a novel growth regulator, holds promise in mediating plant defense responses. Its effects on defense responses are still unclear. Previously, taurine showed potential in improving clover tolerance to alkaline stress and manganese toxicity. Taurine impact on plant growth under Fe deficiency and salinity stress remains uninvestigated. A pot experiment was conducted to evaluate the effects of taurine on pea plant growth, ion uptake, and defense strategies in response to salt stress and Fe deficiency. Iron deficiency was established by substituting 0.1 mM FeSO4 for 0.1 mM Fe-EDTA in the nutrient solution. Salinity stress was induced by incorporating a mixture of NaCl, MgCl2, KCl, Na2SO4, Na2CO3, NaHCO3 and CaCl2 in a 1:1:1:1:1:1:1 ratio to produce a salinity concentration of 100 mM. The simultaneous imposition of salinity and Fe deficiency significantly exacerbated oxidative stress, as evidenced by elevated levels of relative membrane permeability, hydrogen peroxide (H2O2), superoxide radical (O2•−), methylglyoxal (MG), malondialdehyde (MDA), and increased activity of lipoxygenase (LOX). Salinity stress alone and the combination of salinity and Fe deficiency resulted in substantial accumulation of Na+ ions that impeded acquisition of essential nutrients. Taurine (100 and 200 mg L−1) notably improved osmotic adjustment and oxidative defense to diminish water imbalance and oxidative injury in plants under stress. These results suggest that exogenous taurine may serve as a promising means of mitigating the detrimental effects of salt stress and Fe deficiency in plants.

BIOACCESSIBILITY OF ?-DICARBONYL COMPOUNDS IN BREADS AND OTHER BAKERY PRODUCTS USING AN IN VITRO STIMULATED GASTROINTESTINAL DIGESTIVE SYSTEMS

Digestive system conditions may increase or decrease the formation ?-dicarbonyl compounds. This study aims to determine the bioaccessibility of glyoxal (GO) and methylglyoxal (MGO) in bakery products under in vitro gastrointestinal conditions. For this purpose breads and bakery products were obtained from bakehouse in Istanbul, Turkey. The amount of GO and MGO in samples ranged between 54.8 to 180.4 µg /100 g and 45.8 to 220.3 µg / 100g respectively. After in vitro digestion GO and MGO levels were increased to between 170.4 to 656.8 µg / 100g and 105.6 to 1220.9 µg/100 g, respectively. Bioaccessibility of GO and MGO increased up to 727% and 1351% respectively. High increase rates were observed in samples that contain high fat and low moisture contents. We demonstrated that formation of GO and MGO increase under in vitro digestive system conditions. Further studies are needed to extensively investigate the formation mechanism in such foods.

Milk-derived exosomes carrying siRNA-KEAP1 promote diabetic wound healing by improving oxidative stress.

Diabetic wounds are a serious complication of diabetes mellitus (DM) that can lead to persistent infection, amputation, and even death. Prolonged oxidative stress has been widely recognized as a major instigator in the development of diabetic wounds; therefore, oxidative stress is considered a promising therapeutic target. In the present study, Keap1/Nrf2 signaling was confirmed to be activated in streptozotocin (STZ)-induced diabetic mice and methylglyoxal (MGO)-treated human umbilical vein endothelial cells (HUVECs). Knockdown of Keap1 by siRNA reversed the increase in Keap1 levels, promoted the nuclear translocation of Nrf2, and increased the expression of HO-1, an antioxidant protein. To explore therapeutic delivery strategies, milk-derived exosomes (mEXOs) were developed as a novel, efficient, and non-toxic siRNA carrier. SiRNA-Keap1 (siKeap1) was loaded into mEXOs by sonication, and the obtained mEXOs-siKeap1 were found to promote HUVEC proliferation and migration while relieving oxidative stress in MGO-treated HUVECs. Meanwhile, in a mouse model of diabetic wounds, injection of mEXOs-siKeap1 significantly accelerated diabetic wound healing with enhanced collagen formation and neovascularization. Taken together, these data support the development of Keap1 knockdown as a potential therapeutic strategy for diabetic wounds and demonstrated the feasibility of mEXOs as a scalable, biocompatible, and cost-effective siRNA delivery system. The therapeutic effect of siKeap1-loaded mEXOs on diabetic wound healing was assessed. First, we found that the expression of Keap1 was upregulated in the wounds of diabetic mice and in human umbilical vein endothelial cells (HUVECs) pretreated with methylglyoxal (MGO). Next, we extracted exosomes from raw milk by differential centrifugation and loaded siKeap1 into milk-derived exosomes by sonication. The in vitro application of the synthetic complex (mEXOs-siKeap1) was found to increase the nuclear localization of Nrf2 and the expression of the antioxidant protein HO-1, thus reversing oxidative stress. Furthermore, in vivo mEXOs-siKeap1 administration significantly accelerated the healing rate of diabetic wounds (Scheme 1). Scheme 1 Schematic diagram. A Synthesis of mEXOs-siKeap1 complex. B Mechanism of mEXOs-siKeap1 in vitro. C The treatment effect of mEXOs-siKeap1 on an in vivo mouse model of diabetic wounds.

Ethanol Extract of Passiflora cincinnata Seeds Posses Antidiabetic, Antiglycant, and Antioxidant Activities in vitro

This work aimed to investigate the antidiabetic, antiglycation, and antioxidant potentials of the ethanol extract of seeds of Passiflora cincinnata (EPCIN) in vitro. The EPCIN was evaluated from the following assays: total phenolic content (TPC – mg of Gallic Acid Equivalents (GAE)/g of dry extract), Radical Scavenging Assays (DPPH•, HOCl-scavenging assay), and protective effects against glycation of bovine serum albumin (BSA) with methylglyoxal (MGO) or a mixture of reducing sugars, fructose and glucose, as well as the potential for MGO capture by derivatization with ortho-phenylenediamine (OPD). To evaluate the antidiabetic activity of EPCIN in vitro, we used the assays of enzymes α-amylase (4 U/mL), α-glucosidase (0.25 U/mL), and dipeptidyl peptidase-4 (DPP-4 – 3.125 mU). The cell viability of EPCIN-pretreated normal human bronchial epithelial cells (BEAS-2B) alone or in the presence of the carcinogen 4-[(acetoxymethyl)nitrosamine]-1-(3-pyridyl)-1-butanone (NNKOAc) was measured using MTS assay. Quercetin (QCT), piceatannol (PIC), acarbose (ACB), and sitagliptin (STG) were used for comparison purposes. EPCIN had an average of TPC 157.0 ± 1.5 mg of GAE/g of dry extract, exhibited IC50 for DPPH• and HOCl of 11.9 ± 1.8 μg/mL and 6.9 ± 0.9 μg/mL, respectively. EPCIN and AMG inhibited the formation of advanced glycation end-products (AGE) with IC50 of 574 ± 8.7 and 31.9 ± 2.7 μg/mL for the initial stage and 542.6 ± 2.7 and 52.8 ± 8.1 μg/mL for the intermediate stage of glycation, respectively. EPCIN showed IC50 for α-amylase and α-glucosidase of 218.2 ± 15.9 μg/mL (p<0,05) and 242.0 ± 25 μg/mL (p<0,05), respectively. EPCIN did not show cytotoxicity for BEAS-2B cells at 10 and 50 μg/mL concentrations. In addition, it was also able to protect cultured human cells from oxidative stress caused by the NNKOAc at 100 μM. The in vitro evidence of the potential antioxidant, antiglycant, and antidiabetic effects warrants further investigation of the antidiabetic potential of Passiflora cincinnata seeds.

Ethanol Extract of Passiflora cincinnata Seeds Posses Antidiabetic, Antiglycant, and Antioxidant Activities in vitro

This work aimed to investigate the antidiabetic, antiglycation, and antioxidant potentials of the ethanol extract of seeds of Passiflora cincinnata (EPCIN) in vitro. The EPCIN was evaluated from the following assays: total phenolic content (TPC – mg of Gallic Acid Equivalents (GAE)/g of dry extract), Radical Scavenging Assays (DPPH•, HOCl-scavenging assay), and protective effects against glycation of bovine serum albumin (BSA) with methylglyoxal (MGO) or a mixture of reducing sugars, fructose and glucose, as well as the potential for MGO capture by derivatization with ortho-phenylenediamine (OPD). To evaluate the antidiabetic activity of EPCIN in vitro, we used the assays of enzymes α-amylase (4 U/mL), α-glucosidase (0.25 U/mL), and dipeptidyl peptidase-4 (DPP-4 – 3.125 mU). The cell viability of EPCIN-pretreated normal human bronchial epithelial cells (BEAS-2B) alone or in the presence of the carcinogen 4-[(acetoxymethyl)nitrosamine]-1-(3-pyridyl)-1-butanone (NNKOAc) was measured using MTS assay. Quercetin (QCT), piceatannol (PIC), acarbose (ACB), and sitagliptin (STG) were used for comparison purposes. EPCIN had an average of TPC 157.0 ± 1.5 mg of GAE/g of dry extract, exhibited IC50 for DPPH• and HOCl of 11.9 ± 1.8 μg/mL and 6.9 ± 0.9 μg/mL, respectively. EPCIN and AMG inhibited the formation of advanced glycation end-products (AGE) with IC50 of 574 ± 8.7 and 31.9 ± 2.7 μg/mL for the initial stage and 542.6 ± 2.7 and 52.8 ± 8.1 μg/mL for the intermediate stage of glycation, respectively. EPCIN showed IC50 for α-amylase and α-glucosidase of 218.2 ± 15.9 μg/mL (p<0,05) and 242.0 ± 25 μg/mL (p<0,05), respectively. EPCIN did not show cytotoxicity for BEAS-2B cells at 10 and 50 μg/mL concentrations. In addition, it was also able to protect cultured human cells from oxidative stress caused by the NNKOAc at100 μM. The in vitro evidence of the potential antioxidant, antiglycant, and antidiabetic effects warrants further investigation of the antidiabetic potential of Passiflora cincinnata seeds.

Exogenous hydrogen sulfide and methylglyoxal alleviate cadmium-induced oxidative stress in Salix matsudana Koidz by regulating glutathione metabolism

BackgroundCadmium (Cd) is a highly toxic element for plant growth. In plants, hydrogen sulfide (H2S) and methylglyoxal (MG) have emerged as vital signaling molecules that regulate plant growth processes under Cd stress. However, the effects of sodium hydrosulfide (NaHS, a donor of H2S) and MG on Cd uptake, physiological responses, and gene expression patterns of Salix to Cd toxicity have been poorly understood. Here, Salix matsudana Koidz. seedlings were planted in plastic pot with applications of MG (108 mg kg− 1) and NaHS (50 mg kg− 1) under Cd (150 mg kg− 1) stress.ResultsCd treatment significantly increased the reactive oxygen species (ROS) levels and malondialdehyde (MDA) content, but decreased the growth parameters in S. matsudana. However, NaHS and MG supplementation significantly decreased Cd concentration, ROS levels, and MDA content, and finally enhanced the growth parameters. Cd stress accelerated the activities of antioxidative enzymes and the relative expression levels of stress-related genes, which were further improved by NaHS and MG supplementation. However, the activities of monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) were sharply decreased under Cd stress. Conversely, NaHS and MG applications restored the MDHAR and DHAR activities compared with Cd-treated seedlings. Furthermore, Cd stress decreased the ratios of GSH/GSSG and AsA/DHA but considerably increased the H2S and MG levels and glyoxalase I-II system in S. matsudana, while the applications of MG and NaHS restored the redox status of AsA and GSH and further improved glyoxalase II activity. In addition, compared with AsA, GSH showed a more sensitive response to exogenous applications of MG and NaHS and plays more important role in the detoxification of Cd.ConclusionsThe present study illustrated the crucial roles of H2S and MG in reducing ROS-mediated oxidative damage to S. matsudana and revealed the vital role of GSH metabolism in regulating Cd-induced stress.

Inhibitory effect of Ginkgo biloba seeds peptides on methylglyoxal-induced glycations.

The aim of this study was to investigate the antiglycation activity and mechanism of two identified peptides, Valine-Valine-Phenylalanine-Proline-Glycine-Cysteine-Proline-Glutamic acid (VVFPGCPE) and Serine-Valine-Aspartic acid-Aspartic acid-Proline-Arginine-Threonine-Lysine (SVDDPRTL), from Ginkgo biloba seeds protein hydrolysates. Both VVFPGCPE and SVDDPRTL were efficient in bovine serum albumin (BSA)-methylglyoxal (MGO) model to inhibit BSA glycation, while VVFPGCPE showed higher antiglycation activity than SVDDPRTL. In antioxidant assays, VVFPGCPE scavenged more hydroxyl and super anion radicals, and chelated more Fe2+. Moreover, VVFPGCPE was more efficient in alleviating glycoxidation since it retained higher content of tryptophan and reduced dityrosine and kynurenine generation. Compared with SVDDPRTL, VVFPGCPE showed better performance in inhibiting protein aggregation and amyloid-like fibrillation formation. Therefore, VVFPGCPE was selected for further mechanism study. The circular dichroism analysis suggested VVFPGCPE could preserve α-helix structure and stabilize protein structure. The MGO trapping assay indicated VVFPGCPE (5mg/mL) could capture 66.25% MGO within 24h, and the mass spectrometry revealed VVFPGCPE could trap MGO by forming VVFPGCPE-mono-MGO adducts. Besides, molecular simulations suggested VVFPGCPE could interact with key glycation residues, arginine and lysine residues, of BSA mainly through van der Waals and hydrogen bonds. This study might supply a theoretical basis for the development of VVFPGCPE as an effective antiglycation agent.

Pyrolysis and characterization of poplar mixed nanometal oxide catalysts

Poplar is an important wood bioresource and is one of the most dominant plantations in the world with high content of cellulose (52.99%). However, the pyrolytic products produced from poplar pyrolysis are not well studied and applied. In this study, pyrolysis of poplar mixed with different types and the ratio of nanometal oxide catalyst (NiO: 0.50 g, NiO–Ag: 0.25 + 0.25 g, Ag: 0.50 g, Fe2O3: 0.50 g, and Fe2O3–Ag: 0.25 + 0.25 g) were performed to identify the catalyst showing desirable performance in poplar pyrolysis. The thermogravimetry (TG) analysis revealed that adding Fe2O3 in pyrolysis has enhanced the decomposition of poplar where most of the weight loss (71.61 wt%) was in the temperature range of 25–780 °C. The results of the gas chromatography/mass spectrometry (GC/MS) analysis showed that the primary components of the produced bio-oil are acetaldehyde, methyl glyoxal, furfural, d-allose, and acetic acid, which can be used as raw materials in pharmaceuticals, industrial processes, and agricultural endeavours.

Modulating Morphological and Redox/Glycative Alterations in the PCOS Uterus: Effects of Carnitines in PCOS Mice

(1) Background: Polycystic ovarian syndrome (PCOS) is a common and multifactorial disease affecting reproductive-age women. Although PCOS ovarian and metabolic features have received extensive research, uterine dysfunction has been poorly investigated. This research aims to investigate morphological and molecular alterations in the PCOS uterus and search for modulating effects of different carnitine formulations. (2) Methods: CD1 mice were administered or not with dehydroepiandrosterone (DHEA, 6 mg/100 g body weight) for 20 days, alone or with 0.40 mg L-carnitine (LC) and 0.20 mg acetyl-L-carnitine (ALC) in the presence or absence of 0.08 mg propionyl-L-carnitine (PLC). Uterine horns from the four groups were subjected to histology, immunohistochemistry and immunoblotting analyses to evaluate their morphology, collagen deposition, autophagy and steroidogenesis. Oxidative-/methylglyoxal (MG)-dependent damage was investigated along with the effects on the mitochondria, SIRT1, SOD2, RAGE and GLO1 proteins. (3) Results: The PCOS uterus suffers from tissue and oxidative alterations associated with MG-AGE accumulation. LC-ALC administration alleviated PCOS uterine tissue alterations and molecular damage. The presence of PLC prevented fibrosis and maintained mitochondria content. (4) Conclusions: The present results provide evidence for oxidative and glycative damage as the main factors contributing to PCOS uterine alterations and include the uterus in the spectrum of action of carnitines on the PCOS phenotype.

Salt stress-induced chloroplastic hydrogen peroxide stimulates pdTPI sulfenylation and methylglyoxal accumulation.

High salinity, an adverse environmental factor affecting about 20% of irrigated arable land worldwide, inhibits plant growth and development by causing oxidative stress, damaging cellular components, and disturbing global metabolism. However, whether and how reactive oxygen species disturb the metabolism of salt-stressed plants remain elusive. Here, we report that salt-induced hydrogen peroxide (H2O2) inhibits the activity of plastid triose phosphate isomerase (pdTPI) to promote methylglyoxal (MG) accumulation and stimulates the sulfenylation of pdTPI at cysteine 74. We also show that MG is a key factor limiting the plant growth, as a decrease in MG levels completely rescued the stunted growth and repressed salt stress tolerance of the pdtpi mutant. Furthermore, targeting CATALASE 2 into chloroplasts to prevent salt-induced overaccumulation of H2O2 conferred salt stress tolerance, revealing a role for chloroplastic H2O2 in salt-caused plant damage. In addition, we demonstrate that the H2O2-mediated accumulation of MG in turn induces H2O2 production, thus forming a regulatory loop that further inhibits the pdTPI activity in salt-stressed plants. Our findings, therefore, illustrate how salt stress induces MG production to inhibit the plant growth.

Cysteine-Induced pH-Dependent Formation of Thiols and Sulfides or 2-Acetylthiazole and Pyrazines during Thermal Treatment of N-(1-Deoxy-d-xylulos-1-yl)-alanine

The influence of pH was studied on volatile flavor formation during thermal treatment of an Amadori rearrangement product (ARP) with or without the addition of cysteine (Cys). The formation of thiols and sulfides or 2-acetylthiazole and pyrazines induced by Cys during thermal degradation of ARP was pH-dependent. At low pH levels, the hydrolysis of Cys to hydrogen sulfide (H2S) was promoted, giving rise to the increase of thiols and sulfides with an obvious meaty aroma. However, alkaline conditions were beneficial for enhancing the cyclization or transformation of imine to the enol structure, which strengthened the formation of 2-acetylthiazole and pyrazines with a roasted and nutty aroma. The imine was derived from the nucleophilic addition of Cys and methylglyoxal (MGO) and subsequent decarboxylation. At pH 8, Cys-induced variation of the flavor profile was weakened during thermal degradation of ARP. Accordingly, the combinational effect of pH and added Cys could be beneficial for achieving the desirable flavors during thermal processing of ARP.

Study on the Mechanism of Phenylacetaldehyde Formation in a Chinese Water Chestnut-Based Medium during the Steaming Process.

The white pulp of the Chinese water chestnut (CWC) is crisp and sweet with delicious flavours and is an important ingredient in many Chinese dishes. Phenylacetaldehyde is a characteristic flavoured substance produced in the steaming and cooking process of CWC. The steaming process and conditions were simulated to construct three Maillard reaction systems which consisted of glucose and phenylalanine, and of both alone. The simulation results showed that glucose and phenylalanine were the reaction substrates for the formation of phenylacetaldehyde. The intermediate α-dicarbonyl compounds (α-DCs) and the final products of the simulated system were detected by solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) methods. Through the above methods the formation mechanism of phenylacetaldehyde is clarified; under the conditions of the steaming process, glucose is caramelized to produce Methylglyoxal (MGO), 2,3-Butanedione (BD), Glyoxal (GO) and other α-DCs. α-DCs and phenylalanine undergo a Strecker degradation reaction to generate phenylacetaldehyde. The optimal ratio of the amount of substance of glucose to phenylalanine for Maillard reaction is 1:4. The results can provide scientific reference for the regulation of flavour substances and the evaluation of flavour quality in the steaming process of fruits and vegetables.

Methylglyoxal products in pre-symptomatic type 1 diabetes.

Progression to type 1 diabetes has emerged as a complex process with metabolic alterations proposed to be a significant driver of disease. Monitoring products of altered metabolism is a promising tool for determining the risk of type 1 diabetes progression and to supplement existing predictive biomarkers. Methylglyoxal (MG) is a reactive product produced from protein, lipid, and sugar metabolism, providing a more comprehensive measure of metabolic changes compared to hyperglycemia alone. MG forms covalent adducts on nucleic and amino acids, termed MG-advanced glycation end products (AGEs) that associate with type 1 diabetes. We tested their ability to predict risk of disease and discriminate which individuals with autoimmunity will progress to type 1 diabetes. We measured serum MG-AGEs from 141 individuals without type 1 diabetes and 271 individuals with type 1 diabetes enrolled in the Fr1da cohort. Individuals with type 1 diabetes were at stages 1, 2, and 3. We examined the association of MG-AGEs with type 1 diabetes. MG-AGEs did not correlate with HbA1c or differ between stages 1, 2, and 3 type 1 diabetes. Yet, RNA MG-AGEs were significantly associated with the rate of progression to stage 3 type 1 diabetes, with lower serum levels increasing risk of progression. MG-AGEs were able to discriminate which individuals with autoantibodies would progress at a faster rate to stage 3 type 1 diabetes providing a potential new clinical biomarker for determining rate of disease progression and pointing to contributing metabolic pathways.

Carnosine increases insulin-stimulated glucose uptake and reduces methylglyoxal-modified proteins in type-2 diabetic human skeletal muscle cells

Type-2 diabetes (T2D) is characterised by a dysregulation of metabolism, including skeletal muscle insulin resistance, mitochondrial dysfunction, and oxidative stress. Reactive species, such as methylglyoxal (MGO) and 4-hydroxynonenal (4-HNE), positively associate with T2D disease severity and can directly interfere with insulin signalling and glucose uptake in skeletal muscle by modifying cellular proteins. The multifunctional dipeptide carnosine, and its rate-limiting precursor β-alanine, have recently been shown to improve glycaemic control in humans and rodents with diabetes. However, the precise mechanisms are unclear and research in human skeletal muscle is limited. Herein, we present novel findings in primary human T2D and lean healthy control (LHC) skeletal muscle cells. Cells were differentiated to myotubes, and treated with 10 mM carnosine, 10 mM β-alanine, or control for 4-days. T2D cells had reduced ATP-linked and maximal respiration compared with LHC cells (p = 0.016 and p = 0.005). Treatment with 10 mM carnosine significantly increased insulin-stimulated glucose uptake in T2D cells (p = 0.047); with no effect in LHC cells. Insulin-stimulation increased MGO-modified proteins in T2D cells by 47%; treatment with carnosine attenuated this increase to 9.7% (p = 0.011). There was no effect treatment on cell viability or expression of other proteins. These findings suggest that the beneficial effects of carnosine on glycaemic control may be explained by its scavenging actions in human skeletal muscle.

Pyridoxamine prevents increased atherosclerosis by intermittent methylglyoxal spikes in the aortic arches of ApoE-/- mice

Methylglyoxal (MGO) is a reactive glucose metabolite linked to diabetic cardiovascular disease (CVD). MGO levels surge during intermittent hyperglycemia. We hypothesize that these MGO spikes contribute to atherosclerosis, and that pyridoxamine as a MGO quencher prevents this injury. To study this, we intravenously injected normoglycemic 8-week old male C57Bl6 ApoE-/- mice with normal saline (NS, n = 10) or 25 µg MGO for 10 consecutive weeks (MGOiv, n = 11) with or without 1 g/L pyridoxamine (MGOiv+PD, n = 11) in the drinking water. We measured circulating immune cells by flow cytometry. We quantified aortic arch lesion area in aortic roots after Sudan-black staining. We quantified the expression of inflammatory genes in the aorta by qPCR. Intermittent MGO spikes weekly increased atherosclerotic burden in the arch 1.8-fold (NS: 0.9 ± 0.1 vs 1.6 ± 0.2 %), and this was prevented by pyridoxamine (0.8 ± 0.1 %). MGOiv spikes increased circulating neutrophils and monocytes (2-fold relative to NS) and the expression of ICAM (3-fold), RAGE (5-fold), S100A9 (2-fold) and MCP1 (2-fold). All these changes were attenuated by pyridoxamine. This study suggests that MGO spikes damages the vasculature independently of plasma glucose levels. Pyridoxamine and potentially other approaches to reduce MGO may prevent excess cardiovascular risk in diabetes

Protective effects of crocin and gallic acid on the liver damage induced by methylglyoxal in male mice: role of inflammatory factors.

This study aims to evaluate whether biochemical alterations caused by methylglyoxal (MG), improves by the administration of gallic acid (GA), crocin (Cr), and metformin (MT) in the liver. MG is produced naturally through various physiological processes, but high levels of MG cause inflammation in hepatocytes. Normal liver function is essential for maintaining glucose homeostasis. Gallic acid and crocin can reduce inflammation. This experiment was done in 5 weeks. 50 male NMRI mice were randomly divided into 5 groups (n=10): 1) Control, 2) MG (600 mg/Kg/d, p.o.), 3) MG+GA (30 mg/kg/day, p.o.), 4) MG+Cr (60 mg/kg/day, p.o.), 5) MG+MT (150 mg/kg/day, p.o.). After one week of habituation, MG was administered for four weeks. Gallic acid, crocin, and metformin were administered in the last two weeks. Biochemical and histologic evaluations were assessed after plasma collection and tissue sample preparation. Gallic acid and crocin-received groups significantly reduced fasting blood glucose, total cholesterol, triglyceride levels, and elevated insulin sensitivity. Administration of MG exerted a marked increase in the levels of hepatic enzymes. Treatment with gallic acid, crocin, and metformin significantly decreased them. The altered levels of inflammatory factors in the diabetic group were significantly improved in the diabetic-treated groups. High levels of steatosis and red blood cells (RBCs) accumulation in the MG group markedly recovered in other treated mice. Harmful effects of accumulated MG in the liver of diabetic mice were effectively attenuated by using gallic acid and crocin.

Formation of Maillard Reaction Products in Aged Sorghum Vinegar during Ageing and Protective Effects of Pure Vinegar Melanoidin Against CCl4-Induced Rat Hepatic Damage.

The processing method generally affects the toxicity and biological activity of aged sorghum vinegar. This study investigates the changes in the intermediate Maillard reaction products of sorghum vinegar during ageing and the in vivo hepatoprotective effects of pure melanoidin obtained from it. High-performance liquid chromatography (HPLC) and fluorescence spectrophotometry were utilized to quantify intermediate Maillard reaction products. The CCl4-induced liver damage in rats was used to evaluate the protective role of pure melanoidin in rat liver. Compared with the initial concentration, the 18-month ageing process caused a 1.2- to 3.3-fold increase in the concentrations of intermediate Maillard reaction products, i.e. 5-hydroxymethylfurfural (HMF), 5-methylfurfural (MF), methyglyoxal (MGO), glyoxal (GO) and advanced glycation end products (AGEs). The concentrations of HMF in the aged sorghum vinegar were 6.1-fold higher than the 450 μM limit standard for honey, implying the need for shortening the ageing of the vinegar in practice for safety concerns. Pure melanoidin (Mr>3.5 kDa) demonstrated significant protective effects against CCl4-induced rat liver damage, as evidenced by normalized serum biochemical parameters (transaminases and total bilirubin), suppressing hepatic lipid peroxidation and reactive oxygen species, as well as increasing glutathione amount and restoring antioxidant enzyme activities. Histopathological analysis revealed that melanoidin in vinegar reduced cell infiltration and vacuolar hepatocyte necrosis in rat liver. The findings demonstrated that a shortened ageing process should be considered in practice to ensure the safety of aged sorghum vinegar. Vinegar melanoidin is a potential alternative for the prevention of hepatic oxidative damage. This study demonstrates that the manufacturing process had a profound influence on the generation of vinegar intermediate Maillard reaction products. In particular, it revealed the in vivo hepatoprotective effect of pure melanoidin from aged sorghum vinegar, and provides insight into the in vivo biological activity of melanoidin.