Methylglyoxal, obesity, and diabetes

Effect of pH on the reaction between naringenin and methylglyoxal: A kinetic study

Methylglyoxal (MGO) is a highly reactive ɑ-dicarbonyl compound that may adversely impact food quality and human health by modifying proteins. The kinetics of the reaction of naringenin with MGO was studied at pH 6-8 and 37 °C by UV-Vis spectrophotometry and reaction products were characterized by liquid chromatography-mass spectrometry (LC-MS/MS). The apparent second order rate constant (k₂) increased at pH above the lowest pKa value of naringenin, indicating deprotonated naringenin as the main reactant. A Lederer-Manasse type reaction mechanism is suggested, with dehydration of the MGO-dihydrate as a rate determining step. The quantitative data obtained in the present study was used to simulate the competitive reaction between MGO and nucleophilic amino acid residues (Lys, Arg and Cys) and naringenin in milk. It is predicted that naringenin will be able to efficiently trap MGO during storage of milk, although the reversible trapping of MGO by Cys residues is initially kinetically favourable.

2-Iodo-4'-Methoxychalcone Attenuates Methylglyoxal-Induced Neurotoxicity by Activation of GLP-1 Receptor and Enhancement of Neurotrophic Signal, Antioxidant Defense and Glyoxalase Pathway

Methylglyoxal (MG) acts as a reactive precursor of advanced glycation end products (AGEs). This compound is often connected with pathologies such as diabetes, neurodegenerative processes and diseases of aging. 2-iodo-4'-methoxychalcone (CHA79), a synthetic halogen-containing chalcone derivative, has been reported its anti-diabetic activity. This study aims to investigate the potential protective capability of CHA79 against MG-mediated neurotoxicity in SH-SY5Y cells. Results indicated CHA79 increased viability of cells and attenuated the rate of apoptosis in MG-exposed SH-SY5Y. CHA79 up-regulated expression of anti-apoptotic protein (Bcl-2) and down-regulated apoptotic proteins (Bax, cytochrome c, caspase-3, caspase-9). Moreover, CHA79 significantly up-regulated expression of neurotrophic factors, including glucagon-like peptide-1 receptor (GLP-1R), brain derived neurotrophic factor (BDNF), p75NTR, p-TrkB, p-Akt, p-GK-3β and p-CREB. CHA79 attenuated MG-induced ROS production and enhanced the antioxidant defense including nuclear factor erythroid 2-related factor 2 (Nrf2), HO-1, SOD and GSH. Furthermore, CHA79 attenuated MG-induced reduction of glyoxalase-1 (GLO-1), a vital enzyme on removing AGE precursors. In conclusion, CHA79 is the first novel synthetic chalcone possessing the GLP-1R and GLO-1 activating properties. CHA 79 also exhibits neuroprotective effects against MG toxicity by enhancing neurotrophic signal, antioxidant defense and anti-apoptosis pathway.

Glycated Insulin Exacerbates the Cytotoxicity of Human Islet Amyloid Polypeptides: a Vicious Cycle in Type 2 Diabetes

The aggregation of human islet amyloid polypeptide (hIAPP) is one of the triggering factors of type 2 diabetes mellitus (T2DM). hIAPP is cosynthesized, costored, and cosecreted with insulin in pancreatic β-cells, and insulin inhibits hIAPP aggregation. In T2DM patients, long-term hyperglycemia causes glycation of near 10% of total insulin. The glycation not only modifies insulin but also cross-links insulin into oligomers. However, the effect of glycated human insulin on hIAPP aggregation is unknown. In this study, four physiologically relevant monosaccharides, methylglyoxal, glucose, fructose, and ribose were used to glycate human insulin and two C-terminus truncated insulin analogues. Glycated insulin monomers or low molecular weight oligomers such as dimers significantly exacerbated the cytotoxicity of hIAPP. Notably, glycation-induced cross-linking of insulin inhibited the aggregation, membrane disruption, and cytotoxicity of hIAPP, which was corroborated by a control study using EGS-induced cross-linking of insulin or lysozyme. Removal of B29^Lys on the C terminus of the insulin B chain not only abolished glycation-induced cross-linking but also attenuated the aggravation effect of glycated insulin on hIAPP cytotoxicity. Taken together, this study reveals a vicious cycle in T2DM, that hyperglycemia-driven insulin glycation exacerbates the cytotoxicity of hIAPP, which accelerates β-cells death and further deteriorates T2DM.

Determinants of the urinary and serum metabolome in children from six European populations

BACKGROUND

Environment and diet in early life can affect development and health throughout the life course. Metabolic phenotyping of urine and serum represents a complementary systems-wide approach to elucidate environment-health interactions. However, large-scale metabolome studies in children combining analyses of these biological fluids are lacking. Here, we sought to characterise the major determinants of the child metabolome and to define metabolite associations with age, sex, BMI and dietary habits in European children, by exploiting a unique biobank established as part of the Human Early-Life Exposome project ( http://www.projecthelix.eu ).

METHODS

Metabolic phenotypes of matched urine and serum samples from 1192 children (aged 6-11) recruited from birth cohorts in six European countries were measured using high-throughput ¹H nuclear magnetic resonance (NMR) spectroscopy and a targeted LC-MS/MS metabolomic assay (Biocrates AbsoluteIDQ p180 kit).

RESULTS

We identified both urinary and serum creatinine to be positively associated with age. Metabolic associations to BMI z-score included a novel association with urinary 4-deoxyerythreonic acid in addition to valine, serum carnitine, short-chain acylcarnitines (C3, C5), glutamate, BCAAs, lysophosphatidylcholines (lysoPC a C14:0, lysoPC a C16:1, lysoPC a C18:1, lysoPC a C18:2) and sphingolipids (SM C16:0, SM C16:1, SM C18:1). Dietary-metabolite associations included urinary creatine and serum phosphatidylcholines (4) with meat intake, serum phosphatidylcholines (12) with fish, urinary hippurate with vegetables, and urinary proline betaine and hippurate with fruit intake. Population-specific variance (age, sex, BMI, ethnicity, dietary and country of origin) was better captured in the serum than in the urine profile; these factors explained a median of 9.0% variance amongst serum metabolites versus a median of 5.1% amongst urinary metabolites. Metabolic pathway correlations were identified, and concentrations of corresponding metabolites were significantly correlated (r > 0.18) between urine and serum.

CONCLUSIONS

We have established a pan-European reference metabolome for urine and serum of healthy children and gathered critical resources not previously available for future investigations into the influence of the metabolome on child health. The six European cohort populations studied share common metabolic associations with age, sex, BMI z-score and main dietary habits. Furthermore, we have identified a novel metabolic association between threonine catabolism and BMI of children.

Methylglyoxal: A newly detected and potentially harmful metabolite in the blood of ketotic dairy cows

Ketosis causes serious economic losses for the modern dairy industry because it is a highly prevalent metabolic disease among cows in high-producing herds during the transition period. Due to some striking similarities between diabetes in humans and ketosis in dairy cows, there is potential for the use of methylglyoxal (MGO)-commonly used in human diabetics-as a biomarker in dairy cattle. However, currently no data are available about the presence of MGO in the serum of dairy cattle or about the characteristics of its production or its potential contribution in the pathogenesis of ketosis. To determine the potential origin and pathway of formation of MGO, cows in different metabolic conditions [i.e., non-subclinically ketotic dairy cows in early lactation (n = 7), subclinically ketotic dairy cows in early lactation (n = 8), overconditioned dry cows (BCS >4.25, n = 6), and nonlactating heifers (n = 6)] were selected. Serum MGO concentrations were determined and correlated with indicators of the glucose and lipid metabolism and with haptoglobin (Hp) as an inflammatory marker. The serum MGO concentrations in subclinically ketotic cows (712.60 ± 278.77 nmol/L) were significantly greater than in nonlactating heifers (113.35 ± 38.90 nmol/L), overconditioned dry cows (259.71 ± 117.97 nmol/L), and non-subclinically ketotic cows (347.83 ± 63.56 nmol/L). In serum of lactating cows, concentrations of glucose and fructosamine were lower than in heifers and were negatively correlated with MGO concentrations. Even so, concentrations of metabolic and inflammatory markers such as dihydroxyacetone phosphate, nonesterified fatty acids, β-hydroxybutyrate, acetone, and Hp were remarkably higher in subclinically ketotic cows compared with nonlactating heifers; these metabolites were also positively correlated with MGO. In human diabetics elevated MGO concentrations are stated to originate from both hyperglycemia and the enhanced lipid metabolism, whereas higher MGO concentrations in subclinically ketotic cows were not associated with hyperglycemia. Therefore, our data suggest MGO in dairy cows to be a metabolite produced from the metabolization of acetone within the lipid metabolization pathway and from the metabolization of dihydroxyacetone phosphate. Furthermore, the highly positive correlation between MGO and Hp suggests that this reactive compound might be involved in the proinflammatory state of subclinical ketosis in dairy cows. However, more research is needed to determine the potential use of MGO as a biomarker for metabolic failure in dairy cows.

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

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

Methylglyoxal produces more changes in biochemical and biophysical properties of human IgG under high glucose compared to normal glucose level

Hyperglycaemia triggers increased production of methylglyoxal which can cause gross modification in proteins’ structure vis-a-vis function though advanced glycation end products (AGEs). The AGEs may initiate vascular and nonvascular pathologies. In this study, we have examined the biochemical and biophysical changes in human IgG under normal and high glucose after introducing methylglyoxal into the assay mixture. This non-enzymatic reaction mainly engaged lysine residues as indicated by TNBS results. The UV results showed hyperchromicity in modified-IgG samples while fluorescence data supported AGEs formation during the course of reaction. Shift in amide I and amide II band position indicated perturbations in secondary structure. Increase carbonyl content and decrease in sulfhydryl suggests that the modification is accompanied by oxidative stress. All modified-IgG samples showed more thermostability than native IgG; the highest Tm was shown by IgG-high glucose-MGO variant. Results of ANS, Congo red and Thioflavin T dyes clearly suggest increase in hydrophobic patches and aggregation, respectively. SEM and TEM images support aggregates generation in modified-IgG samples.

Endothelial Cell Metabolism

Endothelial cells (ECs) are more than inert blood vessel lining material. Instead, they are active players in the formation of new blood vessels (angiogenesis) both in health and (life-threatening) diseases. Recently, a new concept arose by which EC metabolism drives angiogenesis in parallel to well-established angiogenic growth factors (e.g., vascular endothelial growth factor). 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3-driven glycolysis generates energy to sustain competitive behavior of the ECs at the tip of a growing vessel sprout, whereas carnitine palmitoyltransferase 1a-controlled fatty acid oxidation regulates nucleotide synthesis and proliferation of ECs in the stalk of the sprout. To maintain vascular homeostasis, ECs rely on an intricate metabolic wiring characterized by intracellular compartmentalization, use metabolites for epigenetic regulation of EC subtype differentiation, crosstalk through metabolite release with other cell types, and exhibit EC subtype-specific metabolic traits. Importantly, maladaptation of EC metabolism contributes to vascular disorders, through EC dysfunction or excess angiogenesis, and presents new opportunities for anti-angiogenic strategies. Here we provide a comprehensive overview of established as well as newly uncovered aspects of EC metabolism.

Do all roads lead to the Rome? The glycation perspective!

Oxidative, carbonyl, and glycative stress have gained substantial attention recently for their alleged influence on cancer progression. Oxidative stress can trigger variable transcription factors, such as nuclear factor erythroid-2-related factor (Nrf2), nuclear factor kappa B (NF-κB), protein-53 (p-53), activating protein-1 (AP-1), hypoxia-inducible factor-1α (HIF-1α), β-catenin/Wnt and peroxisome proliferator-activated receptor-γ (PPAR-γ). Activated transcription factors can lead to approximately 500 different alterations in gene expression, and can alter expression patterns of inflammatory cytokines, growth factors, regulatory cell cycle molecules, and anti-inflammatory molecules. These alterations of gene expression can induce a normal cell to become a tumor cell. Glycative stress resulting from advanced glycation end products (AGEs) and reactive dicarbonyls can significantly affect cancer progression. AGEs are fashioned from the multifaceted chemical reaction of reducing sugars with a compound containing an amino group. AGEs bind to and trigger the receptor for AGEs (RAGE) through AGE-RAGE interaction, which is a major modulator of inflammation allied tumors. Dicarbonyls like, GO (glyoxal), MG (methylglyoxal) and 3-DG (3-deoxyglucosone) fashioned throughout lipid peroxidation, glycolysis, and protein degradation are viewed as key precursors of AGEs. These dicarbonyls lead to the carbonyl stress in living organisms, possibly resulting in carbonyl impairment of proteins, carbohydrates, DNA, and lipoproteins. The damage caused by carbonyls results in numerous lesions, some of which are involved in cancer pathogenesis. In this review, the effects of oxidative, carbonyl and glycative stress on cancer initiation and progression are thoroughly discussed, including probable signaling pathways and the effects on tumorigenesis.

Ketone Body Acetoacetate Buffers Methylglyoxal via a Non-enzymatic Conversion during Diabetic and Dietary Ketosis

The α-oxoaldehyde methylglyoxal is a ubiquitous and highly reactive metabolite known to be involved in aging- and diabetes-related diseases. If not detoxified by the endogenous glyoxalase system, it exerts its detrimental effects primarily by reacting with biopolymers such as DNA and proteins. We now demonstrate that during ketosis, another metabolic route is operative via direct non-enzymatic aldol reaction between methylglyoxal and the ketone body acetoacetate, leading to 3-hydroxyhexane-2,5-dione. This novel metabolite is present at a concentration of 10%-20% of the methylglyoxal level in the blood of insulin-starved patients. By employing a metabolite-alkyne-tagging strategy it is clarified that 3-hydroxyhexane-2,5-dione is further metabolized to non-glycating species in human blood. The discovery represents a new direction within non-enzymatic metabolism and within the use of alkyne-tagging for metabolism studies and it revitalizes acetoacetate as a competent endogenous carbon nucleophile.

Phosphatidylinositol 3,5-bisphosphate is involved in methylglyoxal-induced activation of the Mpk1 mitogen-activated protein kinase cascade in Saccharomyces cerevisiae

Methylglyoxal (MG) is a natural metabolite derived from glycolysis, and this 2-oxoaldehyde has been implicated in some diseases including diabetes. However, the physiological significance of MG for cellular functions is yet to be fully elucidated. We previously reported that MG activates the Mpk1 (MAPK) cascade in the yeast Saccharomyces cerevisiae To gain further insights into the cellular functions and responses to MG, we herein screened yeast-deletion mutant collections for susceptibility to MG. We found that mutants defective in the synthesis of phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P₂) are more susceptible to MG. PtdIns(3,5)P₂ levels increased following MG treatment, and vacuolar morphology concomitantly changed to a single swollen shape. MG activated the Pkc1-Mpk1 MAPK cascade in which a small GTPase Rho1 plays a crucial role, and the MG-induced phosphorylation of Mpk1 was impaired in mutants defective in the PtdIns(3,5)P₂ biosynthetic pathway. Of note, heat shock-induced stress also provoked Mpk1 phosphorylation in a Rho1-dependent manner; however, PtdIns(3,5)P₂ was dispensable for the heat shock-stimulated activation of this signaling pathway. Our results suggest that PtdIns(3,5)P₂ is specifically involved in the MG-induced activation of the Mpk1 MAPK cascade and in the cellular adaptation to MG-induced stress.

Glyoxalase 1 expression is associated with an unfavorable prognosis of oropharyngeal squamous cell carcinoma

Background

Glyoxalase 1 is a key enzyme in the detoxification of reactive metabolites such as methylglyoxal and induced Glyoxalase 1 expression has been demonstrated for several human malignancies. However, the regulation and clinical relevance of Glyoxalase 1 in the context of head and neck squamous cell carcinoma has not been addressed so far.

Methods

Argpyrimidine modification as a surrogate for methylglyoxal accumulation and Glyoxalase 1 expression in tumor cells was assessed by immunohistochemical staining of tissue microarrays with specimens from oropharyngeal squamous cell carcinoma patients (n = 154). Prognostic values of distinct Glyoxalase 1 staining patterns were demonstrated by Kaplan-Meier, univariate and multivariate Cox proportional hazard model analysis. The impact of exogenous methylglyoxal or a Glyoxalase 1 inhibitor on the viability of two established tumor cell lines was monitored by a colony-forming assay in vitro.

Results

Glyoxalase 1 expression in tumor cells of oropharyngeal squamous cell carcinoma patients was positively correlated with the presence of Argpyrimidine modification and administration of exogenous methylglyoxal induced Glyoxalase 1 protein levels in FaDu and Cal27 cells in vitro. Cal27 cells with lower basal and methylglyoxal-induced Glyoxalase 1 expression were more sensitive to the cytotoxic effect at high methylgyoxal concentrations and both cell lines showed a decrease in colony formation with increasing amounts of a Glyoxalase 1 inhibitor. A high and nuclear Glyoxalase 1 staining was significantly correlated with shorter progression-free and disease-specific survival, and served as an independent risk factor for an unfavorable prognosis of oropharyngeal squamous cell carcinoma patients.

Conclusions

Induced Glyoxalase 1 expression is a common feature in the pathogenesis of oropharyngeal squamous cell carcinoma and most likely represents an adaptive response to the accumulation of cytotoxic metabolites. Oropharyngeal squamous cell carcinoma patients with a high and nuclear Glyoxalase 1 staining pattern have a high risk for treatment failure, but might benefit from pharmacological targeting Glyoxalase 1 activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3367-5) contains supplementary material, which is available to authorized users.

New Role for Interleukin-13 Receptor α1 in Myocardial Homeostasis and Heart Failure

BACKGROUND

The immune system plays a pivotal role in myocardial homeostasis and response to injury. Interleukins-4 and -13 are anti-inflammatory type-2 cytokines, signaling via the common interleukin-13 receptor α1 chain and the type-2 interleukin-4 receptor. The role of interleukin-13 receptor α1 in the heart is unknown.

METHODS AND RESULTS

We analyzed myocardial samples from human donors (n=136) and patients with end-stage heart failure (n=177). We found that the interleukin-13 receptor α1 is present in the myocardium and, together with the complementary type-2 interleukin-4 receptor chain Il4ra, is significantly downregulated in the hearts of patients with heart failure. Next, we showed that Il13ra1-deficient mice develop severe myocardial dysfunction and dyssynchrony compared to wild-type mice (left ventricular ejection fraction 29.7±9.9 versus 45.0±8.0; P=0.004, left ventricular end-diastolic diameter 4.2±0.2 versus 3.92±0.3; P=0.03). A bioinformatic analysis of mouse hearts indicated that interleukin-13 receptor α1 regulates critical pathways in the heart other than the immune system, such as extracellular matrix (normalized enrichment score=1.90; false discovery rate q=0.005) and glucose metabolism (normalized enrichment score=-2.36; false discovery rate q=0). Deficiency of Il13ra1 was associated with reduced collagen deposition under normal and pressure-overload conditions.

CONCLUSIONS

The results of our studies in humans and mice indicate, for the first time, a role of interleukin-13 receptor α1 in myocardial homeostasis and heart failure and suggests a new therapeutic target to treat heart disease.

Methylglyoxal-induced glycation changes adipose tissue vascular architecture, flow and expansion, leading to insulin resistance

Microvascular dysfunction has been suggested to trigger adipose tissue dysfunction in obesity. This study investigates the hypothesis that glycation impairs microvascular architecture and expandability with an impact on insulin signalling. Animal models supplemented with methylglyoxal (MG), maintained with a high-fat diet (HFD) or both (HFDMG) were studied for periepididymal adipose (pEAT) tissue hypoxia and local and systemic insulin resistance. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to quantify blood flow in vivo, showing MG-induced reduction of pEAT blood flow. Increased adipocyte size and leptin secretion were observed only in rats feeding the high-fat diet, without the development of hypoxia. In turn, hypoxia was only observed when MG was combined (HFDMG group), being associated with impaired activation of the insulin receptor (Tyr1163), glucose intolerance and systemic and muscle insulin resistance. Accordingly, the adipose tissue angiogenic assay has shown decreased capillarization after dose-dependent MG exposure and glyoxalase-1 inhibition. Thus, glycation impairs adipose tissue capillarization and blood flow, hampering its expandability during a high-fat diet challenge and leading to hypoxia and insulin resistance. Such events have systemic repercussions in glucose metabolism and may lead to the onset of unhealthy obesity and progression to type 2 diabetes.

Methylglyoxal-Derived Advanced Glycation Endproducts in Multiple Sclerosis

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS). The activation of inflammatory cells is crucial for the development of MS and is shown to induce intracellular glycolytic metabolism in pro-inflammatory microglia and macrophages, as well as CNS-resident astrocytes. Advanced glycation endproducts (AGEs) are stable endproducts formed by a reaction of the dicarbonyl compounds methylglyoxal (MGO) and glyoxal (GO) with amino acids in proteins, during glycolysis. This suggests that, in MS, MGO-derived AGEs are formed in glycolysis-driven cells. MGO and MGO-derived AGEs can further activate inflammatory cells by binding to the receptor for advanced glycation endproducts (RAGE). Recent studies have revealed that AGEs are increased in the plasma and brain of MS patients. Therefore, AGEs might contribute to the inflammatory status in MS. Moreover, the main detoxification system of dicarbonyl compounds, the glyoxalase system, seems to be affected in MS patients, which may contribute to high MGO-derived AGE levels. Altogether, evidence is emerging for a contributing role of AGEs in the pathology of MS. In this review, we provide an overview of the current knowledge on the involvement of AGEs in MS.

The Link Between Angiogenesis and Endothelial Metabolism

Angiogenesis has traditionally been viewed from the perspective of how endothelial cells (ECs) coordinate migration and proliferation in response to growth factor activation to form new vessel branches. However, ECs must also coordinate their metabolism and adapt metabolic fluxes to the rising energy and biomass demands of branching vessels. Recent studies have highlighted the importance of such metabolic regulation in the endothelium and uncovered core metabolic pathways and mechanisms of regulation that drive the angiogenic process. In this review, we discuss our current understanding of EC metabolism, how it intersects with angiogenic signal transduction, and how alterations in metabolic pathways affect vessel morphogenesis. Understanding EC metabolism promises to reveal new perspectives on disease mechanisms in the vascular system with therapeutic implications for disorders with aberrant vessel growth and function.

All-Trans Retinoic Acid supplementation prevents cardiac fibrosis and cytokines induced by Methylglyoxal

Methylglyoxal (MG), a metabolic intermediate of glycolysis is a precursor for endogeneous production of advanced glycation end-products. The increased production of MG have negative influence over the structure and function of different biomolecules and thus plays an important role in the pathogenesis of diabetic cardiac complications. Retinoic acid (RA), an active metabolite of vitamin A, has a major role in preventing cardiac remodeling and ventricular fibrosis. Hence, the objective of the present study was to determine whether rats administered with all-trans retinoic acid (RA) could attenuate MG induced pathological effects. Wistar rats were divided into 4 groups. Group 1 rats were kept as control; Group 2 rats were administrated with MG (75 mg/kg/day) for 8 weeks. Group 3 rats were given RA (Orally, 1.0 mg/kg/day) along with MG; Group 4 rats received RA alone. Cardiac antioxidant status, induction of fibrosis, AGE receptor (RAGE) and cytokines expression was evaluated in the heart tissues. Administration of MG led to depletion of antioxidant enzymes, induction of fibrosis (p < 0.001), up-regulated expression of RAGE (3.5 fold), TGF-β (4.4 fold), SMAD2 (3.7 fold), SMAD3 (6.0 fold), IL-6 (4.3 fold) and TNF-α (5.5 fold) in the heart tissues compared to control rats. Moreover, the exogenous administration of MG caused significant (p < 0.001) increase in the circulating CML levels. Whereas, RA treatment prevented the induction of fibrosis and restored the levels of cytokines and RAGE expression. Methylglyoxal-induced fibrosis can lead to pathological effects in the heart tissues. RA attenuates the effects of MG in the heart, suggesting that it can be of added value to usual diabetic therapy.

Isoferulic Acid Action against Glycation-Induced Changes in Structural and Functional Attributes of Human High-Density Lipoprotein

Glycation-induced high-density lipoprotein (HDL) modification by aldehydes can result in loss of its antiinflammatory/antioxidative properties, contributing to diabetes-associated cardiovascular diseases. Isoferulic acid, a major active ingredient of Cimicifuga heracleifolia, shows antiinflammatory, antiviral, antioxidant, and antidiabetic properties. Thus, this study investigated the antiglycation effect of isoferulic acid against compositional modifications of HDL and loss of biological activity of HDL-paraoxonase induced on incubation with different aldehydes. Protective effect of isoferulic acid was assessed by subjecting purified HDL from human plasma to glycation with methylglyoxal, glyoxal, or glycolaldehyde and varying concentrations of isoferulic acid. The effect of isoferulic acid was analyzed by determining amino group number, tryptophan and advanced glycation end-product fluorescence, thermal denaturation studies, carboxymethyl lysine content, and activity of HDL-paraoxonase. Concentration-dependent inhibitory action of isoferulic acid was observed against extensive structural perturbations, decrease in amino group number, increase in carboxymethyl lysine content, and decrease in the activity of HDL-paraoxonase caused by aldehyde-associated glycation in the HDL molecule. Isoferulic acid, when taken in concentration equal to that of aldehydes, was most protective, as 82-88% of paraoxonase activity was retained for all studied aldehydes. Isoferulic acid shows antiglycation action against aldehyde-associated glycation in HDL, which indicates its therapeutic potential for diabetic patients, especially those with micro-/macrovascular complications.

The ethyl acetate fraction of corn silk exhibits dual antioxidant and anti-glycation activities and protects insulin-secreting cells from glucotoxicity

Background

In this study, we aimed to develop a Stigmata Maydis (corn silk) fraction with dual bio-activities against oxidative stress and protein glycation to protect β-cells from diabetes-induced failure.

Methods

Corn silk fractions were prepared by partition and chemically characterised by thin-layer chromatography. Free radical scavenging assay, glycation assay, and cell-based viability test (neutral red) were employed to decide the best fraction. Cell death analysis was executed by annexin V/ Propidium iodide staining. Cell proliferation was measured by WST-1. Finally, β-cell function was evaluated by β-cell marker gene expression (RT-PCR) and acute insulin secretion test.

Results

Four corn silk fractions were prepared from an ethanolic crude extract of corn silk. In vitro assays indicate ethyl acetate fraction (YMS-EA) was the most potent fraction. YMS-EA also attenuated the hydrogen peroxide- or methylglyoxal-induced induction of reactive oxygen species, reduction of cell viability, and inhibition of cell proliferation. However, YMS-EA was unable to prevent hydrogen peroxide-induced apoptosis or advanced glycation end-products-induced toxicity. Under hyperglycemic conditions, YMS-EA effectively reduced ROS levels, improved mRNA expression of insulin, glucokinase, and PDX-1, and enhanced glucose-stimulated insulin secretion. The similarity of bioactivities among apigenin, luteolin, and YMS-EA indicated that dual activities of YMS-EA might be derived from those compounds.

Conclusions

We concluded that YMS-EA fraction could be developed as a preventive food agent against the glucotoxicity to β-cells in Type 2 diabetes.

Fructose during pregnancy provokes fetal oxidative stress: The key role of the placental heme oxygenase-1

SCOPE

One of the features of metabolic syndrome caused by liquid fructose intake is an impairment of redox status. We have investigated whether maternal fructose ingestion modifies the redox status in pregnant rats and their fetuses.

METHODS AND RESULTS

Fructose (10% wt/vol) in the drinking water of rats throughout gestation, leads to maternal hepatic oxidative stress. However, this change was also observed in glucose-fed rats and, in fact, both carbohydrates produced a decrease in antioxidant enzyme activity. Surprisingly, mothers fed carbohydrates displayed low plasma lipid oxidation. In contrast, fetuses from fructose-fed mothers showed elevated levels of plasma lipoperoxides versus fetuses from control or glucose-fed mothers. Interestingly, a clearly augmented oxidative stress was observed in placenta of fructose-fed mothers, accompanied by a lower expression of the transcription factor Nuclear factor-erythroid 2-related factor-2 (Nrf2) and its target gene, heme oxygenase-1 (HO-1), a potent antioxidant molecule. Moreover, histone deacetylase 3 (HDAC3) that has been proposed to upregulate HO-1 expression by stabilizing Nrf2, exhibited a diminished expression in placenta of fructose-supplemented mothers.

CONCLUSIONS

Maternal fructose intake provoked an imbalanced redox status in placenta and a clear diminution of HO-1 expression, which could be responsible for the augmented oxidative stress found in their fetuses.

Dicarbonyls and glyoxalase in disease mechanisms and clinical therapeutics

The reactive dicarbonyl metabolite methylglyoxal (MG) is the precursor of the major quantitative advanced glycation endproducts (AGEs) in physiological systems - arginine-derived hydroimidazolones and deoxyguanosine-derived imidazopurinones. The glyoxalase system in the cytoplasm of cells provides the primary defence against dicarbonyl glycation by catalysing the metabolism of MG and related reactive dicarbonyls. Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in ageing and disease. It is produced endogenously by increased formation and/or decreased metabolism of dicarbonyl metabolites. Dicarbonyl stress contributes to ageing, disease and activity of cytotoxic chemotherapeutic agents. It contributes to ageing through age-related decline in glyoxalase 1 (Glo-1) activity. Glo-1 has a dual role in cancer as a tumour suppressor protein prior to tumour development and mediator of multi-drug resistance in cancer treatment, implicating dicarbonyl glycation of DNA in carcinogenesis and dicarbonyl-driven cytotoxicity in mechanism of action of anticancer drugs. Glo-1 is a driver of cardiovascular disease, likely through dicarbonyl stress-driven dyslipidemia and vascular cell dysfunction. Dicarbonyl stress is also a contributing mediator of obesity and vascular complications of diabetes. There are also emerging roles in neurological disorders. Glo-1 responds to dicarbonyl stress to enhance cytoprotection at the transcriptional level through stress-responsive increase of Glo-1 expression. Small molecule Glo-1 inducers are in clinical development for improved metabolic, vascular and renal health and Glo-1 inhibitors in preclinical development for multidrug resistant cancer chemotherapy.

Methylglyoxal suppresses human colon cancer cell lines and tumor growth in a mouse model by impairing glycolytic metabolism of cancer cells associated with down-regulation of c-Myc expression

Methylglyoxal (MG) is a highly reactive dicarbonyl compound exhibiting anti-tumor activity. The anti-tumor effects of MG have been demonstrated in some types of cancer, but its role in colon cancer and the mechanisms underlying this activity remain largely unknown. We investigated its role in human colon cancer and the underlying mechanism using human colon cancer cells and animal model. Viability, proliferation, and apoptosis were quantified in DLD-1 and SW480 colon cancer cells by using the Cell Counting Kit-8, plate colony formation assay, and flow cytometry, respectively. Cell migration and invasion were assessed by wound healing and transwell assays. Glucose consumption, lactate production, and intracellular ATP production also were assayed. The levels of c-Myc protein and mRNA were quantitated by western blot and qRT-PCR. The anti-tumor role of MG in vivo was investigated in a DLD-1 xenograft tumor model in nude mice. We demonstrated that MG inhibited viability, proliferation, migration, and invasion and induced apoptosis of DLD-1 and SW480 colon cancer cells. Treatment with MG reduced glucose consumption, lactate production, and ATP production and decreased c-Myc protein levels in these cells. Moreover, MG significantly suppressed tumor growth and c-Myc expression in vivo. Our findings suggest that MG plays an anti-tumor role in colon cancer. It inhibits cancer cell growth by altering the glycolytic pathway associated with downregulation of c-Myc protein. MG has therapeutic potential in colon cancer by interrupting cancer metabolism.

Nutraceutical Bioactive Compounds Promote Healthspan Counteracting Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the leading cause of mortality in the Western world. Multiple factors are involved in CVD, including genetic factors and modifiable factors such as diet, physical activity, and smoking. CVD incidence and prevalence increase progressively with age, and it is estimated that over 80% of men and women older than 75 years have clinically manifest CVD. To reduce the gap between life expectancy (LE) and healthy life expectancy is one of the main challenges of the 21st century. Lifestyle improvement appears to be the only sustainable approach to face the dramatic chronic-degenerative disease burden of an aging population. A healthy lifestyle, represented by avoiding smoking, following a healthy diet, and practicing physical activity, protects from chronic-degenerative disease onset and progression. A healthy dietetic approach specifically formulated for elderly people, with a defined pattern of nutraceutical bioactive compounds, may represent a key strategy to improve the aging process and increase the life span. This short review summarizes the biochemical mechanisms underpinning the cardiovascular protective effects of some nutraceutical compounds such as quercetin and sulforaphane.

High serum level of methylglyoxal-derived AGE, Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine, independently relates to renal dysfunction

BACKGROUND

The dicarbonyl methylglyoxal reacts primarily with arginine residues to form advanced glycation end products, including Nδ-(5-hydro-5-methyl-4 -imidazolone-2-yl)-ornithine (MG-H1), which are risk factors for not only diabetic complications but also lifestyle-related disease including renal dysfunction. However, the data on serum level and clinical significance of this substance in chronic kidney disease are limited.

METHODS

Serum levels of MG-H1 and Nε-(carboxymethyl) lysine (CML) in 50 patients with renal dysfunction were measured by liquid chromatography/triple-quadruple mass spectrometry.

RESULTS

The median serum MG-H1 levels in patients with estimated glomerular filtration rate (eGFR) of ≥30, 15-30, and <15 ml/min/1.73 m² was 4.16, 12.58, and 14.66 mmol/mol Lys, respectively (p > 0.05). On the other hand, MG-H1 levels in patients with HbA1c of <6 and ≥6 % was 12.85 and 10.45 mmol/mol Lys, respectively, the difference between which is not significant. In logistic regression analysis, decreased renal function (eGFR <15 ml/min/1.73 m²) significantly associated with high serum levels of MG-H1 [odds ratio: 9.39 (95 % confidence interval 1.528-57.76), p = 0.015; Spearman rank correlation: MG-H1 vs. eGFR, r = -0.691, p < 0.01]. In contrast, the serum level of CML did not correlate with eGFR, but correlated with systolic blood pressure [odds ratio 16.17 (95 % confidence interval 1.973-132.5), p = 0.010; Spearman rank correlation coefficient: CML vs. eGFR, r = 0.454, p < 0.01].

CONCLUSION

These results showed that the serum concentration of MG-H1 was strongly related to renal function rather than to DM.

Sestrin2: A Promising Therapeutic Target for Liver Diseases

Sestrin2 (Sesn2), a highly conserved antioxidant protein, is induced by various stresses, including oxidative and energetic stress, and protects cells against those stresses. In normal physiological conditions, redox-homeostasis plays an essential role in cell survival and performs the cellular functions to protect the cells against oxidative damage. The liver is susceptible to oxidative stress, since it is responsible for xenobiotic detoxification and energy metabolism. For this reason, oxidative stress is associated with the pathogenesis of liver diseases. Recently, the role of Sesn2 has been investigated in liver injury and related diseases. In this paper, we review the role of Sesn2 in the pathophysiology of liver diseases and the potential clinical applications of Sesn2 as a therapeutic target to prevent/treat liver diseases. This article promotes our understanding of liver disease progression and advances the development of strategies for pharmacological intervention.

Hormetic and regulatory effects of lipid peroxidation mediators in pancreatic beta cells

Nutrient sensing mechanisms of carbohydrates, amino acids and lipids operate distinct pathways that are essential for the adaptation to varying metabolic conditions. The role of nutrient-induced biosynthesis of hormones is paramount for attaining metabolic homeostasis in the organism. Nutrient overload attenuate key metabolic cellular functions and interfere with hormonal-regulated inter- and intra-organ communication, which may ultimately lead to metabolic derangements. Hyperglycemia and high levels of saturated free fatty acids induce excessive production of oxygen free radicals in tissues and cells. This phenomenon, which is accentuated in both type-1 and type-2 diabetic patients, has been associated with the development of impaired glucose tolerance and the etiology of peripheral complications. However, low levels of the same free radicals also induce hormetic responses that protect cells against deleterious effects of the same radicals. Of interest is the role of hydroxyl radicals in initiating peroxidation of polyunsaturated fatty acids (PUFA) and generation of α,β-unsaturated reactive 4-hydroxyalkenals that avidly form covalent adducts with nucleophilic moieties in proteins, phospholipids and nucleic acids. Numerous studies have linked the lipid peroxidation product 4-hydroxy-2E-nonenal (4-HNE) to different pathological and cytotoxic processes. Similarly, two other members of the family, 4-hydroxyl-2E-hexenal (4-HHE) and 4-hydroxy-2E,6Z-dodecadienal (4-HDDE), have also been identified as potential cytotoxic agents. It has been suggested that 4-HNE-induced modifications in macromolecules in cells may alter their cellular functions and modify signaling properties. Yet, it has also been acknowledged that these bioactive aldehydes also function as signaling molecules that directly modify cell functions in a hormetic fashion to enable cells adapt to various stressful stimuli. Recent studies have shown that 4-HNE and 4-HDDE, which activate peroxisome proliferator-activated receptor δ (PPARδ) in vascular endothelial cells and insulin secreting beta cells, promote such adaptive responses to ameliorate detrimental effects of high glucose and diabetes-like conditions. In addition, due to the electrophilic nature of these reactive aldehydes they form covalent adducts with electronegative moieties in proteins, phosphatidylethanolamine and nucleotides. Normally these non-enzymatic modifications are maintained below the cytotoxic range due to efficient cellular neutralization processes of 4-hydroxyalkenals. The major neutralizing enzymes include fatty aldehyde dehydrogenase (FALDH), aldose reductase (AR) and alcohol dehydrogenase (ADH), which transform the aldehyde to the corresponding carboxylic acid or alcohols, respectively, or by biding to the thiol group in glutathione (GSH) by the action of glutathione-S-transferase (GST). This review describes the hormetic and cytotoxic roles of oxygen free radicals and 4-hydroxyalkenals in beta cells exposed to nutritional challenges and the cellular mechanisms they employ to maintain their level at functional range below the cytotoxic threshold.

Methylglyoxal activates NF-κB nuclear translocation and induces COX-2 expression via a p38-dependent pathway in synovial cells

AIMS

There is growing evidence of an increased prevalence of osteoarthritis (OA) among people with diabetes. Synovial inflammation and increased expression of cyclooxygenase-2 (COX-2) are two key features of patients with OA. Methylglyoxal (MGO) is a common intermediate in the formation of advanced glycation end-products, and its concentration is also typically higher in diabetes. In this study, we investigated the effects of the treatment of different MGO concentrations to rabbit HIG-82 synovial cells on COX-2 expression.

MAIN METHODS

The MGO induced COX-2 mRNA expression was detected by quantitative polymerase chain reaction. The MGO induced COX-2 protein production and its signaling pathways were detected by western blotting. The nuclear factor-kappa B (NF-κB) nuclear translocation by MGO was examined by immunofluorescence.

KEY FINDINGS

In the present study, we find that MGO has no toxic effects on rabbit synovial cells under the experimental conditions. Our analysis demonstrates that MGO induced COX-2 mRNA and protein production. Moreover, MGO induces p38-dependent COX-2 protein expression as well as the phosphorylations of extracellular signal-regulated kinase, c-Jun N-terminal kinase (JNK), and Akt/mammalian target of rapamycin (mTOR)/p70S6K; however, inhibition of JNK and Akt/mTOR/p70S6K phosphorylations further activates COX-2 protein expression. Furthermore, MGO is shown to activate of nuclear factor-kappa B (NF-κB) nuclear translocation.

SIGNIFICANCE

Our results suggest that MGO can induce COX-2 expression via a p38-dependent pathway and activate NF-κB nuclear translocation in synovial cells. These results provide insight into the pathogenesis of the synovial inflammation under the diabetic condition associated with higher MGO levels.

In situ clicking methylglyoxal for hierarchical self-assembly of nanotubes in supramolecular hydrogel

Methylglyoxal (MGO) is a toxic, dicarbonyl metabolite in all living cells and its detoxification is regulated by glyoxalase I (GLOI). Herein, we rationally designed a precursor o-phenylenediamine-Phe-Phe-OH (1) which “click” reacts with MGO to yield amphiphilic methylquinoxaline-Phe-Phe-OH (2) to self-assemble into supramolecular hydrogel II (Gel II). Cryo-TEM images of Gel II suggested that there existed two orders of self-assembly to form the 32.8 nm width-nanotubes in the hydrogel. The hypothesis was validated with the analyses of the fluorescence, transmittance, and circular dichroism data of the serial dilutions of Gel II. Interference tests indicated that hydrogelation of 1 with MGO would not be affected by nitric oxide (NO). Our results suggest that 1 could be applied for specific hydrogelation with MGO, and potentially the removal of MGO in vitro.

Glabridin Alleviates the Toxic Effects of Methylglyoxal on Osteoblastic MC3T3-E1 Cells by Increasing Expression of the Glyoxalase System and Nrf2/HO-1 Signaling and Protecting Mitochondrial Function

Methylglyoxal (MG) contributes to the pathogenesis of age- and diabetes-associated complications. The present study investigated the effects of glabridin on MG-induced cytotoxicity in MC3T3-E1 osteoblastic cells. MC3T3-E1 cells were treated with glabridin in the presence of MG, and markers of mitochondrial function and oxidative damage were examined. Pretreatment of MC3T3-E1 osteoblastic cells with glabridin prevented MG-induced cell death, the production of intracellular reactive oxygen species and mitochondrial superoxides, cardiolipin peroxidation, and the production of inflammatory cytokines. The soluble form of receptor for advanced glycation end products (sRAGEs)/RAGE ratio increased upon MG treatment, but less so after pretreatment with glabridin, which also increased the level of reduced glutathione and the activities of glyoxalase I and heme oxygenase-1, all of which were reduced by MG. In addition, glabridin elevated the level of nuclear factor erythroid 2-related factor 2. These findings suggest that glabridin protects against MG-induced cell damage by inhibiting oxidative stress and increasing MG detoxification. Pretreatment of MC3T3-E1 osteoblastic cells with glabridin reduced MG-induced mitochondrial dysfunction. Additionally, the nitric oxide level significantly increased upon glabridin pretreatment. Together, these data show that glabridin may potentially serve to prevent the development of diabetic bone disease associated with MG-induced oxidative stress.

Methylglyoxal, the foe and friend of glyoxalase and Trx/TrxR systems in HT22 nerve cells

Methylglyoxal (MGO) is a major glycating agent that reacts with basic residues of proteins and promotes the formation of advanced glycation end products (AGEs) which are believed to play key roles in a number of pathologies, such as diabetes, Alzheimer's disease, and inflammation. Here, we examined the effects of MGO on immortalized mouse hippocampal HT22 nerve cells. The endpoints analyzed were MGO and thiol status, the glyoxalase system, comprising glyoxalase 1 and 2 (GLO1/2), and the cytosolic and mitochondrial Trx/TrxR systems, as well as nuclear Nrf2 and its target genes. We found that nuclear Nrf2 is induced by MGO treatment in HT22 cells, as corroborated by induction of the Nrf2-controlled target genes and proteins glutamate cysteine ligase and heme oxygenase 1. Nrf2 knockdown prevented MGO-dependent induction of glutamate cysteine ligase and heme oxygenase 1. The cystine/glutamate antiporter, system xc(-), which is also controlled by Nrf2, was also induced. The increased cystine import (system xc(-)) activity and GCL expression promoted GSH synthesis, leading to increased levels of GSH. The data indicate that MGO can act as both a foe and a friend of the glyoxalase and the Trx/TrxR systems. At low concentrations of MGO (0.3mM), GLO2 is strongly induced, but at high MGO (0.75 mM) concentrations, GLO1 is inhibited and GLO2 is downregulated. The cytosolic Trx/TrxR system is impaired by MGO, where Trx is downregulated yet TrxR is induced, but strong MGO-dependent glycation may explain the loss in TrxR activity. We propose that Nrf2 can be the unifying element to explain the observed upregulation of GSH, GCL, HO1, TrxR1, Trx2, TrxR2, and system xc(-) system activity.

The role of methylglyoxal and the glyoxalase system in diabetes and other age-related diseases

The formation and accumulation of advanced glycation endproducts (AGEs) are related to diabetes and other age-related diseases. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is the major precursor in the formation of AGEs. MGO is mainly formed as a byproduct of glycolysis. Under physiological circumstances, MGO is detoxified by the glyoxalase system into D-lactate, with glyoxalase I (GLO1) as the key enzyme in the anti-glycation defence. New insights indicate that increased levels of MGO and the major MGO-derived AGE, methylglyoxal-derived hydroimidazolone 1 (MG-H1), and dysfunctioning of the glyoxalase system are linked to several age-related health problems, such as diabetes, cardiovascular disease, cancer and disorders of the central nervous system. The present review summarizes the mechanisms through which MGO is formed, its detoxification by the glyoxalase system and its effect on biochemical pathways in relation to the development of age-related diseases. Although several scavengers of MGO have been developed over the years, therapies to treat MGO-associated complications are not yet available for application in clinical practice. Small bioactive inducers of GLO1 can potentially form the basis for new treatment strategies for age-related disorders in which MGO plays a pivotal role.

Residual Cardiovascular Risk in Chronic Kidney Disease: Role of High-density Lipoprotein

Although reducing low-density lipoprotein-cholesterol (LDL-C) levels with lipid-lowering agents (statins) decreases cardiovascular disease (CVD) risk, a substantial residual risk (up to 70% of baseline) remains after treatment in most patient populations. High-density lipoprotein (HDL) is a potential contributor to residual risk, and low HDL-cholesterol (HDL-C) is an established risk factor for CVD. However, in contrast to conventional lipid-lowering therapies, recent studies show that pharmacologic increases in HDL-C levels do not bring about clinical benefits. These observations have given rise to the concept of dysfunctional HDL where increases in serum HDL-C may not be beneficial because HDL loss of function is not corrected by or even intensified by the therapy. Chronic kidney disease (CKD) increases CVD risk, and patients whose CKD progresses to end-stage renal disease (ESRD) requiring dialysis are at the highest CVD risk of any patient type studied. The ESRD population is also unique in its lack of significant benefit from standard lipid-lowering interventions. Recent studies indicate that HDL-C levels do not predict CVD in the CKD population. Moreover, CKD profoundly alters metabolism and composition of HDL particles and impairs their protective effects on functions such as cellular cholesterol efflux, endothelial protection, and control of inflammation and oxidation. Thus, CKD-induced perturbations in HDL may contribute to the excess CVD in CKD patients. Understanding the mechanisms of vascular protection in renal disease can present new therapeutic targets for intervention in this population.

Metabolic adaptations in diabetic endothelial cells

In healthy individuals, the endothelium plays a fundamental role in normal health in the maintenance of vascular homeostasis. Endothelial cell (EC) dysfunction results in the development of several pathologies. In diabetes, in particular, sustained hyperglycemia, a characteristic of diabetes, contributes to EC dysfunction and consequently mediates the pathogenesis of diabetes-associated micro- and macrovasculopathies. Hyperglycemia-induced EC dysfunction is triggered by elevated levels of oxidative stress derived from several mechanisms, with the mitochondria as a key source, and is exacerbated by a subsequent hyperglycemia-induced self-perpetuating cycle of oxidative stress and aberrant metabolic memory. Recent reports have highlighted the importance of metabolic pathways in EC and suggested the therapeutic potential of targeting EC metabolism. This review focuses on the current knowledge regarding differences in the metabolism of healthy ECs vs. diabetes-associated dysfunctional ECs, and outlines how EC metabolism may be targeted for therapeutic benefit.

Mucosal-associated invariant T cell alterations in obese and type 2 diabetic patients

Obesity and type 2 diabetes (T2D) are associated with low-grade inflammation, activation of immune cells, and alterations of the gut microbiota. Mucosal-associated invariant T (MAIT) cells, which are innate-like T cells that recognize bacterial ligands, are present in blood and enriched in mucosal and inflamed tissues. Here, we analyzed MAIT cells in the blood and adipose tissues of patients with T2D and/or severe obesity. We determined that circulating MAIT cell frequency was dramatically decreased in both patient groups, and this population was even undetectable in some obese patients. Moreover, in both patient groups, circulating MAIT cells displayed an activated phenotype that was associated with elevated Th1 and Th17 cytokine production. In obese patients, MAIT cells were more abundant in adipose tissue than in the blood and exhibited a striking IL-17 profile. Bariatric surgery in obese patients not only improved their metabolic parameters but also increased circulating MAIT cell frequency at 3 months after surgery. Similarly, cytokine production by blood MAIT cells was strongly decreased after surgery. This study reveals profound MAIT cell abnormalities in patients harboring metabolic disorders, suggesting their potential role in these pathologies.

Protective effect of liquiritigenin against methylglyoxal cytotoxicity in osteoblastic MC3T3-E1 cells

Methylglyoxal (MG), a reactive dicarbonyl compound, is a metabolic byproduct of glycolysis and elevated MG levels contribute to diabetic complications. Glycation reactions of MG with amino acids can induce oxidative stress, leading to subsequent cytotoxicity. In the present study, the effect of liquiritigenin on MG-induced cytotoxicity was investigated using osteoblastic MC3T3-E1 cells. Pretreatment of MC3T3-E1 cells with liquiritigenin prevented the MG-induced cell death and production of protein adduct, intracellular reactive oxygen species, mitochondrial superoxide, cardiolipin peroxidation, and TNF-α in osteoblastic MC3T3-E1 cells. In addition, liquiritigenin increased the activity of glyoxalase I inhibited by MG. These findings suggest that liquiritigenin provides a protective action against MG-induced cell damage by reducing oxidative stress and by increasing MG detoxification. Pretreatment with liquiritigenin prior to MG exposure reduced MG-induced mitochondrial dysfunction by preventing mitochondrial membrane potential dissipation and adenosine triphosphate loss. Additionally, the nitric oxide and PGC-1α levels were significantly increased by liquiritigenin, suggesting that liquiritigenin may induce mitochondrial biogenesis. Our findings indicate that liquiritigenin might exert its therapeutic effects via enhancement of glyoxalase I activity and mitochondrial function, and anti-oxidant and anti-inflammatory activities. Taken together, liquiritigenin has potential as a preventive agent against the development of diabetic osteopathy related to MG-induced oxidative stress in diabetes.

Scopoletin protects against methylglyoxal-induced hyperglycemia and insulin resistance mediated by suppression of advanced glycation endproducts (AGEs) generation and anti-glycation

Recently, several types of foods and drinks, including coffee, cream, and cake, have been found to result in high methylglyoxal (MG) levels in the plasma, thus causing both nutritional and health concerns. MG can be metabolized by phase-II enzymes in liver through the positive regulation of nuclear factor-erythroid 2-related factor 2 (Nrf2). In this study, we investigated the ability of scopoletin (SP) to protect against MG-induced hyperglycemia and insulin resistance. Recently, SP was shown to be a peroxisome proliferator-activated receptor-γ activator to elevate insulin sensitivity. We investigated the effects of oral administration of SP on the metabolic, biochemical, and molecular abnormalities characteristic of type 2 diabetes in MG-treated Wistar rats to understand the potential mechanism of scopoletin for diabetes protection. Our results suggested that SP activated Nrf2 by Ser40 phosphorylation, resulting in the metabolism of MG into d-lactic acid and the inhibition of AGEs generation, which reduced the accumulation of AGEs in the livers of MG-induced rats. In this manner, SP improved the results of the oral glucose tolerance test and dyslipidemia. Moreover, SP also increased the plasma translocation of glucose transporter-2 and promoted Akt phosphorylation caused by insulin treatment in MG-treated FL83B hepatocytes. In contrast, SP effectively suppressed protein tyrosine phosphatase 1B (PTP1B) expression, thereby alleviating insulin resistance. These findings suggest that SP acts as an anti-glycation and anti-diabetic agent, and thus has therapeutic potential for the prevention of diabetes.

Methylglyoxal activates the target of rapamycin complex 2-protein kinase C signaling pathway in Saccharomyces cerevisiae

Methylglyoxal is a typical 2-oxoaldehyde derived from glycolysis. We show here that methylglyoxal activates the Pkc1-Mpk1 mitogen-activated protein (MAP) kinase cascade in a target of rapamycin complex 2 (TORC2)-dependent manner in the budding yeast Saccharomyces cerevisiae. We demonstrate that TORC2 phosphorylates Pkc1 at Thr(1125) and Ser(1143). Methylglyoxal enhanced the phosphorylation of Pkc1 at Ser(1143), which transmitted the signal to the downstream Mpk1 MAP kinase cascade. We found that the phosphorylation status of Pkc1(T1125) affected the phosphorylation of Pkc1 at Ser(1143), in addition to its protein levels. Methylglyoxal activated mammalian TORC2 signaling, which, in turn, phosphorylated Akt at Ser(473). Our results suggest that methylglyoxal is a conserved initiator of TORC2 signaling among eukaryotes.