Pathophysiological Insights of Methylglyoxal Induced Type-2 Diabetes

Methylglyoxal induces endothelial cell apoptosis and coronary microvascular dysfunction through regulating AR-cPLA2 signaling

OBJECTIVE

Since diabetic patients with coronary microvascular dysfunction (CMD) exhibit high cardiac mortality and women have higher prevalence of non-obstructive coronary artery disease than men, we tried to expand the limited understanding about the etiology and the sex difference of diabetic CMD.

APPROACH AND RESULTS

Accumulated methylglyoxal (MGO) due to diabetes promotes vascular damage and it was used for mimicking diabetic status. Flow cytometry analysis and isometric tension measurement were performed to evaluate coronary artery endothelial injury. MGO induced apoptosis of coronary endothelial cells, accompanied by downregulation of androgen receptor (AR). Lentivirus-mediated stable expression of AR in coronary endothelial cells increased anti-apoptotic Bcl-2 expression and attenuated MGO-induced cell apoptosis. cPLA2 activation was the downstream of AR downregulation by MGO treatment. Moreover, MGO also activated cPLA2 rapidly to impair endothelium-dependent vasodilation of coronary arteries from mice. Reactive oxygen species (ROS) overproduction was demonstrated to account for MGO-mediated cPLA2 activation and endothelial dysfunction. Importantly, AR blockade increased endothelial ROS production whereas AR activation protected coronary artery endothelial vasodilatory function from the MGO-induced injury. Although galectin-3 upregulation was confirmed by siRNA knockdown in endothelial cells not to participate in MGO-induced endothelial apoptosis, pharmacological inhibitor of galectin-3 further enhanced MGO-triggered ROS generation and coronary artery endothelial impairment.

CONCLUSIONS

Our data proposed the AR downregulation-ROS overproduction-cPLA2 activation pathway as one of the mechanisms underlying diabetic CMD and postulated a possible reason for the sex difference of CMD-related angina. Meanwhile, MGO-induced galectin-3 activation played a compensatory role against coronary endothelial dysfunction.

Differential Rates of Glycation Following Exposure to Unique Monosaccharides

A complication of reducing sugars is that they can undergo Maillard chemical reactions, forming advanced glycation end-products (AGEs) that can induce oxidative stress and inflammation via engagements with the main receptor for AGEs (RAGE) in various tissues. Certain sugars, such as glucose and fructose, are well known to cause AGE formation. Recently, allulose has emerged as a rare natural sugar that is an epimer of fructose and which is of low caloric content that is minimally metabolized, leading to it being introduced as a low-calorie sugar alternative. However, the relative ability of allulose to generate AGEs compared to glucose and fructose is not known. Here we assess the accumulation of AGEs in cell-free, in vitro, and in vivo conditions in response to allulose and compare it to glycation mediated by glucose or fructose. AGEs were quantified in cell-free samples, cell culture media and lysates, and rat serum with glycation-specific ELISAs. In cell-free conditions, we observed concentration and time-dependent increases in AGEs when bovine serum albumin (BSA) was incubated with glucose or fructose and significantly less glycation when incubated with allulose. AGEs were significantly elevated when pulmonary alveolar type II-like cells were co-incubated with glucose or fructose; however, significantly less AGEs were detected when cells were exposed to allulose. AGE quantification in serum obtained from rats fed a high-fat, low-carb (HFLC) Western diet for 2 weeks revealed significantly less glycation in animals co-administered allulose compared to those exposed to stevia. These results suggest allulose is associated with less AGE formation compared to fructose or glucose, and support its safety as a low-calorie sugar alternative.

Trapping mechanism by di-d-psicose anhydride with methylglyoxal for prevention of diabetic nephropathy

Di-d-psicose anhydride (DPA), derived from functional rare saccharide as d-psicose, is investigated for its strong chelating ability. Methylglyoxal (MGO), an important precursor of advanced glycation end-products (AGEs), promotes obesity, and causes complications such as diabetic nephropathy. On mesangial cells, DPA can substantially reduce the negative effects of MGO. DPA effectively trapping MGO in mesangial cells. The bonding properties of the DPA-MGO adduct were discussed by mass spectrometry and nuclear magnetic resonance (NMR). The NMR spectra of the DPA-MGO adduct provide evidence for chelation bonding. The inhibition of AGE formation and the mass spectrometry results of the DPA-MGO adduct indicate that DPA can scavenge MGO at a molar ratio of 1:1. DPA suppressed 330 % of the up-regulated receptor for an AGEs protein expression to a normal level and restored the suppressed glyoxalase 1 level to 86 % of the normal group. This research provides important evidence and theoretical basis for the development of AGE inhibitors derived from rare saccharide.

Exploring correlations between soy sauce components and the formation of thermal contaminants during low-salt solid-state fermentation

Soy sauce is a traditional seasoning in Asia and provides a unique flavor to food. However, some harmful Maillard reaction products (MRPs) were inevitably formed during the manufacturing process. Fermentation is a critical step of soy sauce manufacturing and has a significant impact on MRPs formation. Therefore, this study investigated the formation of some characteristic MRPs (e.g., furan, carboxymethyl lysine (CML), 5-hydroxymethylfurfural (5-HMF), α-dicarbonyl compounds) and their correlation with major quality indicators (e.g., free amino acids, reducing sugar, total acid, ammonia nitrogen, total nitrogen, non-salt soluble solids) in low-salt solid-state fermentation soy sauce (LSFSS). The result showed that the levels of furan, CML, and 5-HMF continue to increase during the fermentation process, reaching a maximum after sterilization. Further testing using Person correlation showed that the formation of furan, CML, and 5-HMF in LSFSS was positively correlated with glucose, fructose, α-dicarbonyl compounds, and most of the amino acids, while it was negatively correlated with sucrose and methionine. Among them, the contribution of lysine, valine, isoleucine, leucine, and arginine to furan formation has rarely been reported. Our results provide a good theoretical basis for the control of MRPs during LSFSS fermentation.

Urocortin2 attenuates diabetic coronary microvascular dysfunction by regulating macrophage extracellular vesicles

Diabetic patients develop coronary microvascular dysfunction (CMD) and exhibit high mortality of coronary artery disease. Methylglyoxal (MGO) largely accumulates in the circulation due to diabetes. We addressed whether macrophages exposed to MGO exhibited damaging effect on the coronary artery and whether urocortin2 (UCN2) serve as protecting factors against such diabetes-associated complication. Type 2 diabetes was induced by high-fat diet and a single low-dose streptozotocin in mice. Small extracellular vesicles (sEV) derived from MGO-treated macrophages (MGO-sEV) were used to produce diabetes-like CMD. UCN2 was examined for a protective role against CMD. The involvement of arginase1 and IL-33 was tested by pharmacological inhibitor and IL-33-/- mice. MGO-sEV was capable of causing coronary artery endothelial dysfunction similar to that by diabetes. Immunocytochemistry studies of diabetic coronary arteries supported the transfer of arginase1 from macrophages to endothelial cells. Mechanism studies revealed arginase1 contributed to the impaired endothelium-dependent relaxation of coronary arteries in diabetic and MGO-sEV-treated mice. UCN2 significantly improved coronary artery endothelial function, and prevented MGO elevation in diabetic mice or enrichment of arginase1 in MGO-sEV. Diabetes caused a reduction of IL-33, which was also reversed by UCN2. IL-33-/- mice showed impaired endothelium-dependent relaxation of coronary arteries, which can be mitigated by arginase1 inhibition but can't be improved by UCN2 anymore, indicating the importance of restoring IL-33 for the protection against diabetic CMD by UCN2. Our data suggest that MGO-sEV induces CMD via shuttling arginase1 to coronary arteries. UCN2 is able to protect against diabetic CMD via modulating MGO-altered macrophage sEV cargoes.

Correlation of serum IGF-1, AGEs and their receptors with the risk of colorectal cancer in patients with type 2 diabetes mellitus

Background

According to epidemiological evidence, people with type 2 diabetes mellitus have a higher risk of developing colorectal cancer.

Objective

To examine the relationship between colorectal cancer (CRC) and serum levels of IGF-1, IGF-1R, AGEs,RAGE and sRAGE in patients with type 2 diabetes.

Methods

By using RNA-Seq data of CRC patients from The Cancer Genome Atlas (TCGA) database, we divided the patients into normal group(58 patients)and tumor group(446 patients), and analyzed the expression and prognostic value analysis of IGF-1,IGF1R and RAGE. Cox regression and the Kaplan-Meier method were used to determine the predictive value of target gene on clinical outcomes in CRC patients. In order to further combine CRC with diabetes research,one hundred forty-eight patients hospitalized in the Second Hospital of Harbin Medical University from July 2021 to July 2022 were enrolled and divided into CA and control groups. There were 106 patients in the CA group, including 75 patients with CRC and 31 patients with CRC+T2DM; the control group comprised 42 patients with T2DM. Circulating levels of IGF-1, IGF-1R, AGEs, RAGE, and sRAGE in the serum of the patients were measured using Enzyme-Linked Immunosorbnent Assay (ELISA) kits, and other clinical parameters were also measured during hospitalization. Statistical methods used were χ² test, independent samples t-test and Pearson correlation analysis were. Finally, we controlled for confounding factors and used logistic multi-factor regression analysis.

Results

Bioinformatics analysis showed that IGF-1, IGF1R and RAGE were highly expressed in CRC patients, and the patients with high expression also showed significantly lower overall survival rate. Through Cox regression analysis, IGF-1 can be used as an independent influencing factor of CRC. In the ELISA experiment, serum AGE, RAGE, IGF-1, and IGF-1R levels were higher in the CRC and CRC+T2DM groups than in the T2DM group, but the serum sRAGE concentrations in these groups were lower than those in the T2DM group (P < 0.05). Serum AGE, RAGE, sRAGE, IGF1, and IGF1R levels were higher in the CRC+T2DM group than in the CRC group (P < 0.05). In CRC+T2DM patients, serum AGEs were correlated with age (p = 0.027), and the serum AGE levels in these groups were positively correlated with RAGE and IGF-1 levels (p < 0.001) and negatively correlated with sRAGE and IGF-1R levels (p < 0.001). After correcting for confounding factors based on logistic multiple regression analysis, the effects of age, serum IGF-1 and IGF-1R on the development of CRC in patients with T2DM were statistically significant (p<0.05).

Conclusion

Serum IGF-1 and IGF-1R levels independently influenced the development of CRC in patients with T2DM. Furthermore, IGF-1 and IGF-1R were correlated with AGEs in CRC patients who also had T2DM, suggesting that AGEs may influence the development of CRC in T2DM patients. These findings suggest that we may be able to lower the risk of CRC in the clinic by regulating AGEs through the regulation of blood glucose levels, which will affect IGF-1 and its receptors.

Effects of dietary macronutrients on the hepatic transcriptome and serum metabolome in mice

Dietary macronutrient composition influences both hepatic function and aging. Previous work suggested that longevity and hepatic gene expression levels were highly responsive to dietary protein, but almost unaffected by other macronutrients. In contrast, we found expression of 4005, 4232, and 4292 genes in the livers of mice were significantly associated with changes in dietary protein (5%–30%), fat (20%–60%), and carbohydrate (10%–75%), respectively. More genes in aging‐related pathways (notably mTOR, IGF‐1, and NF‐kappaB) had significant correlations with dietary fat intake than protein and carbohydrate intake, and the pattern of gene expression changes in relation to dietary fat intake was in the opposite direction to the effect of graded levels of caloric restriction consistent with dietary fat having a negative impact on aging. We found 732, 808, and 995 serum metabolites were significantly correlated with dietary protein (5%–30%), fat (8.3%–80%), and carbohydrate (10%–80%) contents, respectively. Metabolomics pathway analysis revealed sphingosine‐1‐phosphate signaling was the significantly affected pathway by dietary fat content which has also been identified as significant changed metabolic pathway in the previous caloric restriction study. Our results suggest dietary fat has major impact on aging‐related gene and metabolic pathways compared with other macronutrients.

Self-Assembled Nanochaperones Inhibit the Aggregation of Human Islet Amyloid Polypeptide Associated with Type 2 Diabetes

Human islet amyloid polypeptide (hIAPP) aggregation is closely associated with dysfunction and apoptosis of pancreatic β-cells in type 2 diabetes (T2D). Accordingly, hIAPP amyloid inhibitors have shown promise against T2D. Here, by mimicking the function of natural molecular chaperones, nanochaperones (nChaps) based on self-assembled polymeric micelles with tunable surface microdomains for T2D treatment are reported. By capturing the aggregation-prone species of hIAPP onto the hydrophobic microdomains and segregating them by hydrophilic PEG chains, this kind of nChaps could effectively prevent hIAPP aggregation, block cell adhesion of hIAPP, facilitate hIAPP aggregates degradation and reduce hIAPP-related cytotoxicity. Therefore, our work will provide useful insights to develop a biomimetic strategy for the treatment of T2D.

Diabetic nephropathy induced by methylglyoxal: gallic acid regulates kidney microRNAs and glyoxalase1-Nrf2 in male mice

BACKGROUND

Methylglyoxal (MG) has been reported to be a toxic by-product of glycolysis and intracellular stressor compound. This study investigated the effects of gallic acid (GA) against diabetic nephropathy (DN) induced by MG in male mice.

METHODS

DN was induced by methylglyoxal (600 mg/kg/day, p.o.) treated for 28 consecutive days. The animals received GA (30 mg/kg/day, p.o.) and metformin (MT) (150 mg/kg/day, p.o.) for 7 consecutive days after diabetes induction. Biochemical assays, antioxidant evaluation, microRNAs associated with fibrosis, endoplasmic reticulum stress, and histopathological analysis were examined.

RESULTS

MG increased malondialdehyde, albuminuria, Nrf2, miR-192 and miR-204 expression in diabetic groups and GA decreased them. Superoxide dismutase, catalase, glyoxalase1, and miR-29a expression decreased in diabetic groups and increased in treatment with GA.

CONCLUSION

Our results revealed that GA has improved DN induced by MG via amelioration of biochemical indices, histopathological aspects, oxidative stress and microRNAs associated with endoplasmic reticulum stress and fibrosis.

The occurrence and stability of Maillard reaction products in various traditional Chinese sauces

Traditional Chinese sauces, especially soy sauce, vinegar, and oyster sauce, provide foods with special color, flavor, and taste. However, during their manufacturing process, Maillard reaction products (MRPs) might be formed and cause adverse effects on human health. This study detected the levels of some typical MRPs in these sauces. Results showed that dark soy sauce and some vinegar products were high in 5-hydroxymethylfurfural (HMF). Moreover, dark soy sauce was significantly higher in 5-methylfurfural (MF) and methylglyoxal (MGO) than oyster sauce but lower in glyoxal (GO) than vinegar and oyster sauce, while light soy sauce had significantly higher advanced glycation end products (AGEs) than the rest three types of sauces. Besides, storage stability results indicated that MRPs increased obviously in vinegar and dark soy sauce. Finally, concentration limits/regulations of MRPs in traditional Chinese sauces should be established in the future considering their high frequency of usage and high potential of insalubrity.

Ginsenoside Rb1 mitigates oxidative stress and apoptosis induced by methylglyoxal in SH-SY5Y cells via the PI3K/Akt pathway

Diabetic encephalopathy is a severe diabetic complication characterized by cognitive dysfunction and neuropsychiatric disability. Methylglyoxal (MGO), a highly reactive metabolite of hyperglycemia, serves as a major precursor of advanced glycation end products that play key roles in diabetic complications. Ginsenoside Rb1 (abbreviated as Rb1) has received extensive attention due to its potential therapeutic effects on diabetes and neurodegeneration. Therefore, this study aimed to investigate the effects of Rb1 on MGO-induced damage in SH-SY5Y cells and the related mechanism. SH-SY5Y cells were pretreated with Rb1 for 8 h and then exposed to MGO (0.5 mM) for 24 h. Cell survival was assessed by the MTT assay. Cell apoptosis was assessed using Hoechst 33342/propidium iodide (PI) staining and an Annexin-V/PI kit. The activities of oxidative stress markers were examined using commercial kits. Reactive oxygen species (ROS) staining and JC-1 staining were used to evaluate mitochondria injury. In addition, protein levels were measured by Western blot analysis. As a result, Rb1 alleviated the injury induced by MGO by increasing the activities of superoxide dismutase, catalase and total glutathione, decreasing the level of malondialdehyde, and alleviating mitochondrial damage and ROS production. Furthermore, Rb1 could enhance the Bcl-2/Bax ratio, inhibit the expression of cleaved caspase-3 and cleaved caspase-9, and enhance the levels of phosphorylated Akt. Moreover, the protective effects of Rb1 against MGO-induced apoptosis were partly abolished by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K) phosphorylation. Our results demonstrated that Rb1 ameliorated MGO-induced oxidative stress and apoptosis in SH-SY5Y cells via activating the PI3K/Akt signaling pathway.

The Microbiotic Highway to Health-New Perspective on Food Structure, Gut Microbiota, and Host Inflammation

This review provides evidence that not only the content of nutrients but indeed the structural organization of nutrients is a major determinant of human health. The gut microbiota provides nutrients for the host by digesting food structures otherwise indigestible by human enzymes, thereby simultaneously harvesting energy and delivering nutrients and metabolites for the nutritional and biological benefit of the host. Microbiota-derived nutrients, metabolites, and antigens promote the development and function of the host immune system both directly by activating cells of the adaptive and innate immune system and indirectly by sustaining release of monosaccharides, stimulating intestinal receptors and secreting gut hormones. Multiple indirect microbiota-dependent biological responses contribute to glucose homeostasis, which prevents hyperglycemia-induced inflammatory conditions. The composition and function of the gut microbiota vary between individuals and whereas dietary habits influence the gut microbiota, the gut microbiota influences both the nutritional and biological homeostasis of the host. A healthy gut microbiota requires the presence of beneficial microbiotic species as well as vital food structures to ensure appropriate feeding of the microbiota. This review focuses on the impact of plant-based food structures, the "fiber-encapsulated nutrient formulation", and on the direct and indirect mechanisms by which the gut microbiota participate in host immune function.

Metformin attenuates myocardium dicarbonyl stress induced by chronic hypertriglyceridemia

Reactive dicarbonyls stimulate production of advanced glycation endproducts, increase oxidative stress and inflammation and contribute to the development of vascular complications. We measured concentrations of dicarbonyls - methylglyoxal (MG), glyoxal (GL) and 3-deoxyglucosone (3-DG) - in the heart and kidney of a model of metabolic syndrome - hereditary hypertriglyceridemic rats (HHTg) and explored its modulation by metformin. Adult HHTg rats were fed a standard diet with or without metformin (300 mg/kg b.w.) and dicarbonyl levels and metabolic parameters were measured. HHTg rats had markedly elevated serum levels of triacylglycerols (p<0.001), FFA (p<0.01) and hepatic triacylglycerols (p<0.001) along with increased concentrations of reactive dicarbonyls in myocardium (MG: p<0.001; GL: p<0.01; 3-DG: p<0.01) and kidney cortex (MG: p<0.01). Metformin treatment significantly reduced reactive dicarbonyls in the myocardium (MG: p<0.05, GL: p<0.05, 3-DG: p<0.01) along with increase of myocardial concentrations of reduced glutathione (p<0.01) and glyoxalase 1 mRNA expression (p<0.05). Metformin did not have any significant effect on dicarbonyls, glutathione or on glyoxalase 1 expression in kidney cortex. Chronically elevated hypertriglyceridemia was associated with increased levels of dicarbonyls in heart and kidney. Beneficial effects of metformin on reactive dicarbonyls and glyoxalase in the heart could contribute to its cardioprotective effects.

The endothelial border to health: Mechanistic evidence of the hyperglycemic culprit of inflammatory disease acceleration

The endothelial cell (EC) layer constitutes a barrier that controls movements of fluid, solutes and cells between blood and tissue. Further, the endothelial layer regulates vascular tone and directs local humoral and cellular inflammatory processes. The strategic position makes it an important player for maintenance of health and for development of a number of diseases. Endothelial dysfunction is known to be an important component of type 2 diabetes, but is also assumed to be involved in many other diseases, for example, rheumatoid arthritis, inflammatory bowel disease, asthma, and cardiovascular diseases. We here suggest that the EC plays a pivotal role in disease pathophysiology through initiation, potentiation, and maintenance of several inflammatory mechanisms. Our contention is based on the observation that hyperglycemia-intermittent or sustained, local or systemic-is a major culprit for several endothelial dysfunctions. There is also mounting epidemiological evidence that dietary intake of refined sugars is important for the development of a number of diseases beyond obesity and type 2 diabetes. Various diseases involving inflammatory and immunological components are accelerated by hyperglycemic events because the endothelium transduces "high glucose" signaling into significant pathophysiological phenomena leading to reduced endothelial barrier function, compromised vascular tone regulation and inflammation (e.g., cytokine secretion and RAGE activation). In addition, endothelial extracellular proteins form epitopes for potential specific antibody formation upon interactions with reducing sugars. This paper reviews the endothelial metabolism, biology, inflammatory processes, physical barrier functions, and summarizes evidence that although stochastic in nature, endothelial responses to hyperglycemia are major contributors to disease pathophysiology. We present molecular and mechanistic evidence that both biological and physical barriers, protein function, specific immunity, and inflammatory processes are compromised by hyperglycemic events and thus, hyperglycemic events alone should be considered risk factors for numerous human diseases. © 2017 IUBMB Life, 69(3):148-161, 2017.

Antiamylase, Anticholinesterases, Antiglycation, and Glycation Reversing Potential of Bark and Leaf of Ceylon Cinnamon (Cinnamomum zeylanicum Blume) In Vitro

Ethanol (95%) and dichloromethane : methanol (DCM : M, 1 : 1 v/v) bark extracts (BEs) and leaf extracts (LEs) of authenticated Ceylon cinnamon (CC) were studied for antiamylase, antiglucosidase, anticholinesterases, and antiglycation and glycation reversing potential in bovine serum albumin- (BSA-) glucose and BSA-methylglyoxal models in vitro. Further, total proanthocyanidins (TP) were quantified. Results showed significant differences (p < 0.05) between bark and leaf extracts for the studied biological activities (except antiglucosidase) and TP. BEs showed significantly high (p < 0.05) activities for antiamylase (IC₅₀: 214 ± 2–215 ± 10 μg/mL), antibutyrylcholinesterase (IC₅₀: 26.62 ± 1.66–36.09 ± 0.83 μg/mL), and glycation reversing in BSA-glucose model (EC₅₀: 94.33 ± 1.81–107.16 ± 3.95 μg/mL) compared to LEs. In contrast, glycation reversing in BSA-methylglyoxal (EC₅₀: ethanol: 122.15 ± 6.01 μg/mL) and antiglycation in both BSA-glucose (IC₅₀: ethanol: 15.22 ± 0.47 μg/mL) and BSA-methylglyoxal models (IC₅₀: DCM : M: 278.29 ± 8.55 μg/mL) were significantly high (p < 0.05) in leaf. Compared to the reference drugs used some of the biological activities were significantly (p < 0.05) high (BEs: BChE inhibition and ethanol leaf: BSA-glucose mediated antiglycation), some were comparable (BEs: BSA-glucose mediated antiglycation), and some were moderate (BEs and LEs: antiamylase, AChE inhibition, and BSA-MGO mediated antiglycation; DCM : M leaf: BSA-glucose mediated antiglycation). TP were significantly high (p < 0.05) in BEs compared to LEs (BEs and LEs: 1097.90 ± 73.01–1381.53 ± 45.93 and 309.52 ± 2.81–434.24 ± 14.12 mg cyanidin equivalents/g extract, resp.). In conclusion, both bark and leaf of CC possess antidiabetic properties and thus may be useful in managing diabetes and its complications.

Unraveling the role of ER stress inhibitors in the context of metabolic diseases

ER stress is provoked by the accumulation of unfolded and misfolded proteins in the ER lumen leading to perturbations in ER homeostasis. ER stress activates a signaling cascade called the Unfolded Protein Response (UPR) which triggers a set of transcriptional and translational events that restore ER homeostasis, promoting cell survival and adaptation. If this adaptive response fails, a terminal UPR program commits such cells to apoptosis. Existing preclinical and clinical evidence testify that prolonged ER stress escalates the risk of several metabolic disorders including diabetes, obesity and dyslipidemia. There have been considerable efforts to develop small molecules that are capable of ameliorating ER stress. Few naturally occurring and synthetic molecules have already been demonstrated for their efficacy in abrogating ER stress in both in vitro and in vivo models of metabolic disorders. This review provides a broad overview of the molecular mechanisms of inhibition of ER stress and its association with various metabolic diseases.

Trapping Methylglyoxal by Genistein and Its Metabolites in Mice

Increasing evidence supports dicarbonyl stress such as methylglyoxal (MGO) as one of the major pathogenic links between hyperglycemia and diabetic complications. In vitro studies have shown that dietary flavonoids can inhibit the formation of advanced glycation end products (AGEs) by trapping MGO. However, whether flavonoids can trap MGO in vivo and whether biotransformation limits the trapping capacity of flavonoids remain virtually unknown. In this study, we investigated whether genistein (GEN), the major soy isoflavone, could trap MGO in mice by promoting the formation of MGO adducts of GEN and its metabolites. Two different mouse studies were conducted. In the acute study, a single dose of MGO and GEN were administered to mice via oral gavage. In the chronic study, MGO was given to mice in drinking water for 1 month and then GEN was given to mice for 4 consecutive days via oral gavage. Two mono-MGO adducts of GEN and six mono-MGO adducts of GEN phase I and microbial metabolites were identified in mouse urine samples from these studies using liquid chromatography/electrospray ionization tandem mass spectrometry. The structures of these MGO adducts were confirmed by analyzing their MS(n) (n = 1-4) spectra as well as by comparing them with the tandem mass spectra of authentic standards. All of the MGO adducts presented in their phase II conjugated forms in mouse urine samples in the acute and chronic studies. To our knowledge, this is the first in vivo evidence to demonstrate the trapping efficacy of GEN in mice and to show that the metabolites of GEN remain bioactive.

Defence against methylglyoxal in Group A Streptococcus: a role for Glyoxylase I in bacterial virulence and survival in neutrophils?

Methylglyoxal is a dicarbonyl compound that acts as a toxic electrophile in biological systems. Methylglyoxal is produced in certain bacteria as a byproduct of glycolysis through methylglyoxal synthase. Like many bacteria, Group A Streptococcus (GAS), a Gram-positive human pathogen responsible for a wide spectrum of diseases, uses a two-step glyoxalase system to remove methylglyoxal. However, bioinformatic analysis revealed that no homologue of methylglyoxal synthase is present in GAS, suggesting that the role of the glyoxalase system is to detoxify methylglyoxal produced by the host. In this study, we investigated the role of methylglyoxal detoxification in the pathogenesis of GAS. A mutant (5448ΔgloA), deficient in glyoxylase I (S-lactoylglutathione lyase), was constructed and tested for susceptibility to methylglyoxal, human neutrophil survival and virulence in a murine model of infection. 5448ΔgloA was more sensitive to methylglyoxal and was also more susceptible to human neutrophil killing. Inhibition of neutrophil myeloperoxidase rescued the gloA-deficient mutant indicating that this enzyme was required for methylglyoxal production. Furthermore, the 5448ΔgloA mutant was slower at disseminating into the blood in the murine model. These data suggest that neutrophils produce methylglyoxal as an antimicrobial agent during bacterial infection, and the glyoxalase system is part of the GAS defence against the innate immune system during pathogenesis.