Methylglyoxal: possible link between hyperglycaemia and immune suppression?

Recent advances in the potential of Phyllanthus emblica L. and its related foods for combating metabolic diseases through methylglyoxal trapping

Methylglyoxal (MG) serves as the primary precursor for the nonenzymatic glycation of proteins and DNA, leading to advanced glycation end products (AGEs). Regular intake of dietary MG is strongly correlated with low-grade inflammation, potentially accelerating the pathogenesis of metabolic diseases, including obesity, diabetes, cancers, liver diseases, Alzheimer's disease, cardiovascular diseases, aging, and bone loss. Although pharmaceutical agents (pimagedine and candesartan) have been developed to inhibit MG formation, they often come with serious side effects (nausea, diarrhea, headache, gastrointestinal disturbance, symptomatic hypotension, abnormal renal and liver function tests, development of antinuclear antibody, pernicious-like anemia, and hyperkalemia), highlighting the need for an efficient and safe approach to scavenging MG. Phyllanthus emblica Linn fruit, a nutritious edible fruit, and medicinal plant contains over 300 bioactive compounds. Among twenty-three herbals, 100 μg/mL of the aqueous extract of Phyllanthus emblica fruit (APF) exhibits the highest potency in trapping MG, achieving an 87.3 % reduction under d-fructose induced BSA-AGEs formation. However, there are few reports detailing APF and its related foods' specific impact on disease prevention through MG trapping. This review summarizes the mechanisms through which MG is linked to the development of metabolic diseases and provides several strategies for reducing MG levels using APF and its bioactive compounds. The potential antiglycation properties of APF may offer new applications in the food industry and pharmacological research.

Anti-bacterial, anti-biofilm and anti-quorum sensing activities of honey: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Man has used honey to treat diseases since ancient times, perhaps even before the history of medicine itself. Several civilizations have utilized natural honey as a functional and therapeutic food to ward off infections. Recently, researchers worldwide have been focusing on the antibacterial effects of natural honey against antibiotic-resistant bacteria.

AIM OF THE STUDY

This review aims to summarize research on the use of honey properties and constituents with their anti-bacterial, anti-biofilm, and anti-quorum sensing mechanisms of action. Further, honey's bacterial products, including probiotic organisms and antibacterial agents which are produced to curb the growth of other competitor microorganisms is addressed.

MATERIALS AND METHODS

In this review, we have provided a comprehensive overview of the antibacterial, anti-biofilm, and anti-quorum sensing activities of honey and their mechanisms of action. Furthermore, the review addressed the effects of antibacterial agents of honey from bacterial origin. Relevant information on the antibacterial activity of honey was obtained from scientific online databases such as Web of Science, Google Scholar, ScienceDirect, and PubMed.

RESULTS

Honey's antibacterial, anti-biofilm, and anti-quorum sensing activities are mostly attributed to four key components: hydrogen peroxide, methylglyoxal, bee defensin-1, and phenolic compounds. The performance of bacteria can be altered by honey components, which impact their cell cycle and cell morphology. To the best of our knowledge, this is the first review that specifically summarizes every phenolic compound identified in honey along with their potential antibacterial mechanisms of action. Furthermore, certain strains of beneficial lactic acid bacteria such as Bifidobacterium, Fructobacillus, and Lactobacillaceae, as well as Bacillus species can survive and even grow in honey, making it a potential delivery system for these agents.

CONCLUSION

Honey could be regarded as one of the best complementary and alternative medicines. The data presented in this review will enhance our knowledge of some of honey's therapeutic properties as well as its antibacterial activities.

Diabetes mellitus: Classification, mediators, and complications; A gate to identify potential targets for the development of new effective treatments

Nowadays, diabetes mellitus has emerged as a significant global public health concern with a remarkable increase in its prevalence. This review article focuses on the definition of diabetes mellitus and its classification into different types, including type 1 diabetes (idiopathic and fulminant), type 2 diabetes, gestational diabetes, hybrid forms, slowly evolving immune-mediated diabetes, ketosis-prone type 2 diabetes, and other special types. Diagnostic criteria for diabetes mellitus are also discussed. The role of inflammation in both type 1 and type 2 diabetes is explored, along with the mediators and potential anti-inflammatory treatments. Furthermore, the involvement of various organs in diabetes mellitus is highlighted, such as the role of adipose tissue and obesity, gut microbiota, and pancreatic β-cells. The manifestation of pancreatic Langerhans β-cell islet inflammation, oxidative stress, and impaired insulin production and secretion are addressed. Additionally, the impact of diabetes mellitus on liver cirrhosis, acute kidney injury, immune system complications, and other diabetic complications like retinopathy and neuropathy is examined. Therefore, further research is required to enhance diagnosis, prevent chronic complications, and identify potential therapeutic targets for the management of diabetes mellitus and its associated dysfunctions.

Early Prediction for Persistent Inflammation-Immunosuppression Catabolism Syndrome in Surgical Sepsis Patients

Objective

To find the predictors for persistent inflammation-immunosuppression catabolism syndrome in ICU surgical septic patients.

Design

Single center observation study.

Participants

Inclusion: 1) patients ≥18, 2) admitted to the ICU after major surgery or transferred to the ICU within 48 hours after the diagnosis of sepsis following the definition of sepsis-3.0. Exclusion: 1) pregnant or lactating patients, 2) patients with severe immune deficiency, 3) patients that expired within 14 days after the diagnosis of sepsis.

Results

A total of 169 participants were included. After propensity score matching, PICS patients were found to have higher intensive care unit (ICU) mortality (32.4% vs 12.4%, p=0.046), 90-day mortality (32.4% vs 9.1%, p=0.006), and ICU-acquired infection rate (44.1% vs 12.7%, p<0.001), and longer ICU stays (29 vs 11 days, p<0.001) comparing to non-PICS patients. In multivariate logistic regression, it demonstrated that the SOFA score, Charlson co-morbidity index (CCI), albumin level on the ICU day 1, and lymphocyte count on the ICU day 3 were statistically significant. Sensitivity analysis was conducted with the receiver operating characteristic curve for a combination of the four parameters and the area under the curve was 0.838 (95% confidence interval 0.774–0.901).

Conclusion

The chronic disease condition and decreased immunity in the early course of sepsis were crucial for PICS. The combination of CCI, SOFA score, albumin level on ICU Day 1 and lymphocyte count on ICU Day 3 can be early predictor for PICS.

The Genotoxic and Pro-Apoptotic Activities of Advanced Glycation End-Products (MAGE) Measured with Micronuclei Assay Are Inhibited by Their Low Molecular Mass Counterparts

An association between the cancer invasive activities of cells and their exposure to advanced glycation end-products (AGEs) was described early in some reports. An incubation of cells with BSA-AGE (bovine serum albumin-AGE), BSA-carboxymethyllysine and BSA-methylglyoxal (BSA-MG) resulted in a significant increase in DNA damage. We examined the genotoxic activity of new products synthesized under nonaqueous conditions. These were high molecular mass MAGEs (HMW-MAGEs) formed from protein and melibiose and low molecular mass MAGEs (LMW-MAGEs) obtained from the melibiose and N-α-acetyllysine and N-α-acetylarginine. We have observed by measuring of micronuclei in human lymphocytes in vitro that the studied HMW-MAGEs expressed the genotoxicity. The number of micronuclei (MN) in lymphocytes reached 40.22 ± 5.34 promille (MN/1000CBL), compared to 28.80 ± 6.50 MN/1000 CBL for the reference BSA-MG, whereas a control value was 20.66 ± 1.39 MN/1000CBL. However, the LMW-MAGE fractions did not induce micronuclei formation in the culture of lymphocytes and partially protected DNA against damage in the cells irradiated with X-ray. Human melanoma and all other studied cells, such as bronchial epithelial cells, lung cancer cells and colorectal cancer cells, are susceptible to the genotoxic effects of HMW-MAGEs. The LMW-MAGEs are not genotoxic, while they inhibit HMW-MAGE genotoxic activity. With regard to apoptosis, it is induced with the HMW-MAGE compounds, in the p53 independent way, whereas the low molecular mass product inhibits the apoptosis induction. Further investigations will potentially indicate beneficial apoptotic effect on cancer cells.

Effects of preoperative oral single-dose and double-dose carbohydrates on insulin resistance in patients undergoing gastrectomy:a prospective randomized controlled trial

BACKGROUND & AIMS

Preoperative oral carbohydrates are strongly recommended for routine use before various elective procedures. The regimen mainly includes preoperative oral single-dose carbohydrate (2-3 h before surgery) and preoperative oral double-dose carbohydrates (10 h before surgery and 2-3 h before surgery). The choice between the two options is still controversial.

METHODS

A total of 139 patients with gastric cancer who underwent radical gastrectomy were recruited from a hospital in Sichuan Province, China. The patients were randomly assigned to a single-dose group (n = 70) or a double-dose group (n = 69). Insulin resistance indicators, subjective comfort indicators, inflammatory mediators, immunological indicators, postoperative recovery indexes, and complications were compared between the two groups.

RESULTS

There were no differences in insulin resistance indicators (fasting plasma glucose, fasting insulin, and homeostasis model assessment indexes), inflammatory mediators (C-reactive protein, interleukin-6, and tumor necrosis factor-α), immunological indicators (CD3+, CD4+, CD8+, and CD4+/CD8+) between the single-dose group and double-dose group (all P > 0.05) at preoperative day 1, preoperative 3 h, and postoperative day 1. There were no differences in subjective comfort indicators (thirst, hunger, anxiety, nausea, fatigue, and weakness) between the two groups (all P > 0.05) at preoperative day 1, preoperative 3 h, preoperative 1 h, and postoperative day 1. The postoperative recovery indexes and complications (exhaust time, liquid intake time, postoperative hospital stay, complication incidence, unplanned readmission rate, and unplanned reoperation rate 30 days after operation) did not significantly differ between the two groups (all P > 0.05). The number of preoperative nighttime urinations in the double-dose group was higher than that in the single-dose group (88.3% VS 48.5%, P < 0.001), and the number of hours of preoperative sleep in the double-dose group was lower than that in the single-dose group (4.56 ± 0.68 VS 5.71 ± 0.57, P < 0.001).

CONCLUSION

Oral carbohydrates administered the night before surgery did not enhance the effects of oral carbohydrates administered 2-3 h before surgery on insulin resistance, subjective comfort, inflammation, and immunity and might affect the patients' night rest. In making a decision between oral carbohydrate regimes, evening carbohydrates could be omitted.

TRIAL REGISTRATION

ChiCTR, ChiCTR1900020608. Registered January 10, 2019, http://www.chictr.org.cn: ChiCTR1900020608.

Associations of dicarbonyl stress with complement activation: the CODAM study

AIMS/HYPOTHESIS

Reactive α-dicarbonyl compounds are major precursors of AGEs and may lead to glycation of circulating and/or cell-associated complement regulators. Glycation of complement regulatory proteins can influence their capacity to inhibit complement activation. We investigated, in a human cohort, whether greater dicarbonyl stress was associated with more complement activation.

METHODS

Circulating concentrations of dicarbonyl stress markers, i.e. α-dicarbonyls (methylglyoxal [MGO], glyoxal [GO] and 3-deoxyglucosone [3-DG]), and free AGEs (N^ε-(carboxymethyl)lysine [CML], N^ε-(carboxyethyl)lysine [CEL] and N^δ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine [MG-H1]), and protein-bound AGEs (CML, CEL, pentosidine), as well as the complement activation products C3a and soluble C5b-9 (sC5b-9), were measured in 530 participants (59.5 ± 7.0 years [mean ± SD], 61% men) of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM) study. Multiple linear regression analyses were used to investigate the associations between dicarbonyl stress (standardised) and complement activation (standardised) with adjustment of potential confounders, including age, sex, lifestyle, use of medication and markers of obesity. In addition, the associations of two potentially functional polymorphisms (rs1049346, rs2736654) in the gene encoding glyoxalase 1 (GLO1), the rate-limiting detoxifying enzyme for MGO, with C3a and sC5b-9 (all standardized) were evaluated.

RESULTS

After adjustment for potential confounders, plasma concentration of the dicarbonyl GO was inversely associated with sC5b-9 (β -0.12 [95% CI -0.21, -0.02]) and the protein-bound AGE CEL was inversely associated with C3a (-0.17 [-0.25, -0.08]). In contrast, the protein-bound AGE pentosidine was positively associated with sC5b-9 (0.15 [0.05, 0.24]). No associations were observed for other α-dicarbonyls and other free or protein-bound AGEs with C3a or sC5b-9. Individuals with the AG and AA genotype of rs1049346 had, on average, 0.32 and 0.40 SD lower plasma concentrations of sC5b-9 than those with the GG genotype, while concentrations of C3a did not differ significantly between rs1049346 genotypes. GLO1 rs2736654 was not associated with either C3a or sC5b-9.

CONCLUSIONS/INTERPRETATION

Plasma concentrations of dicarbonyl stress markers showed distinct associations with complement activation products: some of them were inversely associated with either C3a or sC5b-9, while protein-bound pentosidine was consistently and positively associated with sC5b-9. This suggests different biological relationships of individual dicarbonyl stress markers with complement activation.

Glycation interferes with natural killer cell function

One hallmark of molecular aging is glycation, better known as formation of so-called advanced glycation end products (AGEs), where reactive carbonyls react with amino-groups of proteins. AGEs accumulate over time and are responsible for various age-dependent diseases and impairments. Two very potent dicarbonyls to generate AGEs are glyoxal (GO) and methylglyoxal (MGO). The plasma level of such dicarbonyls is higher in aging and age-related diseases. Natural killer (NK) cells are cells of the innate immune system and provide a major defense against tumor cells and virus infected cells. They are able to kill modified or infected cells and produce different cytokines to modulate the function of other immune cells. Here we investigated the effect of GO- and MGO-induced glycation on the function of NK cells. Using the human NK cell line NK-92, we could demonstrate that both GO and MGO lead to glycation of cellular proteins, but that MGO interferes much stronger with NK cell function (cytotoxicity) than GO. In addition, glycation of NK cell targets, such as K562 tumor cells, also interferes with their lysis by NK cells. From this data we conclude that glycation acts negatively on NK cells function and reduces their cytotoxic potential towards tumor cells.

Heterologous expression of a Glyoxalase I gene from sugarcane confers tolerance to several environmental stresses in bacteria

Glyoxalase I belongs to the glyoxalase system that detoxifies methylglyoxal (MG), a cytotoxic by-product produced mainly from triose phosphates. The concentration of MG increases rapidly under stress conditions. In this study, a novel glyoxalase I gene, designated as SoGloI was identified from sugarcane. SoGloI had a size of 1,091 bp with one open reading frame (ORF) of 885 bp encoding a protein of 294 amino acids. SoGloI was predicted as a Ni2+-dependent GLOI protein with two typical glyoxalase domains at positions 28-149 and 159-283, respectively. SoGloI was cloned into an expression plasmid vector, and the Trx-His-S-tag SoGloI protein produced in Escherichia coli was about 51 kDa. The recombinant E. coli cells expressing SoGloI compared to the control grew faster and tolerated higher concentrations of NaCl, CuCl2, CdCl2, or ZnSO4. SoGloI ubiquitously expressed in various sugarcane tissues. The expression was up-regulated under the treatments of NaCl, CuCl2, CdCl2, ZnSO4 and abscisic acid (ABA), or under simulated biotic stress conditions upon exposure to salicylic acid (SA) and methyl jasmonate (MeJA). SoGloI activity steadily increased when sugarcane was subjected to NaCl, CuCl2, CdCl2, or ZnSO4 treatments. Sub-cellular observations indicated that the SoGloI protein was located in both cytosol and nucleus. These results suggest that the SoGloI gene may play an important role in sugarcane's response to various biotic and abiotic stresses.

Methylglyoxal - a signaling molecule in plant abiotic stress responses

Abiotic stresses are the most common harmful factors, adversely affecting all aspects of plants' life. Plants have to elicit appropriate responses against multifaceted effects of abiotic stresses by reprogramming various cellular processes. Signaling molecules play vital roles in sensing environmental stimuli to modulate gene expression, metabolism and physiological processes in plants to cope with the adverse effects. Methylglyoxal (MG), a dicarbonyl compound, is known to accumulate in cells as a byproduct of various metabolic pathways, including glycolysis. Several works in recent years have demonstrated that MG could play signaling roles via Ca²⁺, reactive oxygen species (ROS), K⁺ and abscisic acid. Recently, global gene expression profiling has shown that MG could induce signaling cascades, and an overlap between MG-responsive and stress-responsive signaling events might exist in plants. Once overaccumulated in cells, MG can provoke detrimental effects by generating ROS, forming advanced glycation end products and inactivating antioxidant systems. Plants are also equipped with MG-detoxifying glyoxalase system to save cellular organelles from MG toxicity. Since MG has regulatory functions in plant growth and development, and glyoxalase system is an integral component of abiotic stress adaptation, an in-depth understanding on MG metabolism and glyoxalase system will help decipher mechanisms underlying plant responses to abiotic stresses. Here, we provide a comprehensive update on the current knowledge of MG production and detoxification in plants, and highlight the putative functions of glyoxalase system in mediating plant defense against abiotic stresses. We particularly emphasize on the dual roles of MG and its connection with glutathione-related redox regulation, which is crucial for plant defense and adaptive responses under changing environmental conditions.

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.

Impact of Hyperglycemia and Age on Outcomes in Patients With Acute Myeloid Leukemia

PURPOSE/OBJECTIVES

To examine the prevalence and impact of hyperglycemia on health outcomes (number of neutropenic days, infection, and hospital length of stay) in patients hospitalized for acute myeloid leukemia (AML) receiving initial induction therapy.
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DESIGN

Retrospective, descriptive study.
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SETTING

A large urban hospital in Indianapolis, Indiana.
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SAMPLE

103 patients with AML and a subset of 41 patients aged 65 years or older. 
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METHODS

Demographics and medical information were extracted from electronic health records. Serum-fasting blood glucose was used to assess glycemic status. The association of hyperglycemia with the health outcomes was analyzed. A subset of patients aged 65 years or older was also analyzed.
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MAIN RESEARCH VARIABLES

Hyperglycemia, age, and health outcomes in patients with AML.
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FINDINGS

Forty patients experienced hyperglycemia during initial induction for AML. In the larger sample, no associations were noted between hyperglycemia and health outcomes. A significant relationship (p = 0.022) was noted between hyperglycemia and infection in patients aged 65 years or older. Patients aged 65 years or older had 5.6 times the risk of developing infection as those aged younger than 65 years. Although not statistically significant, patients aged 65 years or older with hyperglycemia had 2.5 more days of neutropenia and 1.5 days longer hospital length of stay. 
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CONCLUSIONS

This study provides preliminary evidence that hyperglycemia is prevalent during initial induction for AML and may have harmful consequences, particularly for patients aged 65 years or older. More research is needed to determine clinically significant levels of hyperglycemia and their impact on health outcomes.
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IMPLICATIONS FOR NURSING

Oncology nurses can assess and proactively collaborate with members of the healthcare team to implement strategies to prevent or mitigate the harmful consequences of hyperglycemia.

Structural studies of malonaldehyde–glyoxal and malonaldehyde–methylglyoxal etheno adducts of adenine nucleosides based on spectroscopic methods and DFT-GIAO calculations

The substitution position in the etheno rings of M₁Gx-A and M₁MGx-dA was determined based on the comparison of data derived from NMR spectra with results obtained from computational calculations.

The Anti-Inflammatory and Antibacterial Action of Nanocrystalline Silver and Manuka Honey on the Molecular Alternation of Diabetic Foot Ulcer: A Comprehensive Literature Review

Honey and silver have been used since ancient times for treating wounds. Their widespread clinical application has attracted attention in light of the increasing prevalence of antibiotic-resistant bacteria. While there have been a number of studies exploring the anti-inflammatory and antibacterial effects of manuka honey and nanocrystalline silver, their advantages and limitations with regard to the treatment of chronic wounds remain a subject of debate. The aim of this paper is to examine the evidence on the use of nanocrystalline silver and manuka honey for treating diabetic foot ulcers through a critical and comprehensive review of in vitro studies, animal studies, and in vivo studies. The findings from the in vitro and animal studies suggest that both agents have effective antibacterial actions. Their anti-inflammatory action and related impact on wound healing are unclear. Besides, there is no evidence to suggest that any topical agent is more effective for use in treating diabetic foot ulcer. Overall, high-quality, clinical human studies supported by findings from the molecular science on the use of manuka honey or nanocrystalline silver are lacking. There is a need for rigorously designed human clinical studies on the subject to fill this knowledge gap and guide clinical practice.

Identification of glutathione (GSH)-independent glyoxalase III from Schizosaccharomyces pombe

BACKGROUND

Reactive carbonyl species (RCS), such as methylglyoxal (MG) and glyoxal (GO), are synthesized as toxic metabolites in living systems. Mechanisms of RCS detoxification include the glutathione (GSH)-dependent system consisting of glyoxalase I (GLO1) and glyoxalase II (GLO2), and GSH-independent system involving glyoxalase III (GLO3). Hsp31 and DJ-1 proteins are weakly homologous to each other and belong to two different subfamilies of the DJ-1/Hsp31/PfpI superfamily. Recently, the Escherichia coli Hsp31 protein and the DJ-1 proteins from Arabidopsis thaliana and metazoans have been demonstrated to have GLO3 activity.

RESULTS

We performed a systematic survey of homologs of DJ-1 and Hsp31 in fungi. We found that DJ-1 proteins have a very limited distribution in fungi, whereas Hsp31 proteins are widely distributed among different fungal groups. Phylogenetic analysis revealed that fungal and metazoan DJ-1 proteins and bacterial YajL proteins are most closely related and together form a sister clade to bacterial and fungal Hsp31 proteins. We showed that two Schizosaccharomyces pombe Hsp31 proteins (Hsp3101 and Hsp3102) and one Saccharomyces cerevisiae Hsp31 protein (ScHsp31) displayed significantly higher in vitro GLO3 activity than S. pombe DJ-1 (SpDJ-1). Overexpression of hsp3101, hsp3102 and ScHSP31 could confer MG and GO resistance on either wild-type S. pombe cells or GLO1 deletion of S. pombe. S. pombe DJ-1 and Hsp31 proteins exhibit different patterns of subcellular localization.

CONCLUSIONS

Our results suggest that fungal Hsp31 proteins are the major GLO3 that may have some role in protecting cells from RCS toxicity in fungi. Our results also support the view that the GLO3 activity of Hsp31 proteins may have evolved independently from that of DJ-1 proteins.

Uncoupling of eNOS contributes to redox-sensitive leukocyte recruitment and microvascular leakage elicited by methylglyoxal

Elevated levels of the glycolysis metabolite methylglyoxal (MG) have been implicated in impaired leukocyte-endothelial interactions and vascular complications in diabetes, putative mechanisms of which remain elusive. Uncoupling of endothelial nitric oxide synthase (eNOS) was shown to be involved in endothelial dysfunction in diabetes. Whether MG contributes to these effects has not been elucidated. By using intravital microscopy in vivo, we demonstrate that MG-triggered reduction in leukocyte rolling velocity and increases in rolling flux, adhesion, emigration and microvascular permeability were significantly abated by scavenging reactive oxygen species (ROS). In murine cremaster muscle, MG treatment reduced tetrahydrobiopterin (BH4)/total biopterin ratio, increased arginase expression and stimulated ROS and superoxide production. The latter was significantly blunted by ROS scavengers Tempol (300μM) or MnTBAP (300μM), by BH4 supplementation (100μM) or by NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 20μM). In these tissues and cultured murine and human primary endothelial cells, MG increased eNOS monomerization and decreased BH4/total biopterin ratio, effects that were significantly mitigated by supplementation of BH4 or its precursor sepiapterin but not by L-NAME or tetrahydroneopterin, indicative of MG-triggered eNOS uncoupling. MG treatment further decreased the expression of guanosine triphosphate cyclohydrolase I in murine primary endothelial cells. MG-induced leukocyte recruitment was significantly attenuated by supplementation of BH4 or sepiapterin or suppression of superoxide by L-NAME confirming the role of eNOS uncoupling in MG-elicited leukocyte recruitment. Together, our study uncovers eNOS uncoupling as a pivotal mechanism in MG-induced oxidative stress, microvascular hyperpermeability and leukocyte recruitment in vivo.

Methylglyoxal modulates endothelial nitric oxide synthase-associated functions in EA.hy926 endothelial cells

BACKGROUND

Increased levels of the sugar metabolite methylglyoxal (MG) in vivo were shown to participate in the pathophysiology of vascular complications in diabetes. Alterations of endothelial nitric oxide synthase (eNOS) activity by hypophosphorylation of the enzyme and enhanced monomerization are found in the diabetic milieu, and the regulation of this still remains undefined. Using various pharmacological approaches, we elucidate putative mechanisms by which MG modulates eNOS-associated functions of MG-stimulated superoxide O₂•⁻ production, phosphorylation status and eNOS uncoupling in EA.hy926 human endothelial cells.

METHODS

In cultured EA.hy926 endothelial cells, the effects of MG treatment, tetrahydrobiopterin (BH4; 100 μM) and sepiapterin (20 μM) supplementation, NOS inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME; 50 μM), and inhibition of peroxynitrite (ONOO⁻) formation (300 μM Tempol plus 50 μM L-NAME) on eNOS dimer/monomer ratios, Ser-1177 eNOS phosphorylation and 3-nitrotyrosine (3NT) abundance were quantified using immunoblotting. O₂•⁻-dependent fluorescence was determined using a commercially available kit and tissue biopterin levels were measured by fluorometric HPLC analysis.

RESULTS

In EA.hy926 cells, MG treatment significantly enhanced O₂•⁻ generation and 3NT expression and reduced Ser-1177 eNOS phosphorylation, eNOS dimer/monomer ratio and cellular biopterin levels indicative of eNOS uncoupling. These effects were significantly mitigated by administration of BH4, sepiapterin and suppression of ONOO⁻ formation. L-NAME treatment significantly blunted eNOS-derived O₂•⁻ generation but did not modify eNOS phosphorylation or monomerization.

CONCLUSION

MG triggers eNOS uncoupling and hypophosphorylation in EA.hy926 endothelial cells associated with O₂•⁻ generation and biopterin depletion. The observed effects of the glycolysis metabolite MG presumably account, at least in part, for endothelial dysfunction in diabetes.

Serum methylglyoxal level and its association with oxidative stress and disease severity in patients with psoriasis

Psoriasis vulgaris (PV), a chronic inflammatory skin disease, is a condition of increased oxidative stress (OxS). However, interest related to oxidative and carbonyl stress damages to proteins, such as the formation of advanced glycation end products (AGEs) and their precursor molecule methylglyoxal (MG) has been modest. The objective of this study was to compare the systemic levels of OxS markers in patients with PV and healthy controls (Co) and to investigate their correlation with the serum level of MG. Total peroxide concentration (TPX) and total antioxidant capacity (TAC) were estimated by means of spectrophotometry. The TPX and TAC ratio was regarded as OxS index (OSI). MG level was determined using ELISA. Compared to Co, patients with PV had significantly increased blood levels of TPX (P < 0.0001), OSI (P < 0.0001), and MG (P = 0.01), and lower TAC levels (P < 0.0001). Increase in body mass index (BMI) appeared to contribute to this imbalance as TAC levels decreased with increasing BMI (r = -0.252, P < 0.01). Increased TPX concentration was associated with higher serum level of MG (r = 0.610, P = 0.004), the latter being positively correlated with psoriasis area and severity index (r = 0.577, P = 0.008). In performed multivariate regression analysis, TPX, TAC, and OSI were all significant predictors of MG level. Our study gave further proof of increased systemic psoriasis-related OxS. MG serum level, reflecting simultaneously OxS as well as carbonyl stress status, could be used as a marker of disease activity in clinical trials while looking for new systemic therapies for psoriasis.

Negative regulatory responses to metabolically triggered inflammation impair renal epithelial immunity in diabetes mellitus

Diabetes mellitus is characterized by chronic inflammation and increased risk of infections, particularly of tissues exposed to the external environment. However, the causal molecular mechanisms that affect immune cells and their functions in diabetes are unclear. Here we show, by transcript and protein analyses, signatures of glucose-induced tissue damage, chronic inflammation, oxidative stress, and dysregulated expression of multiple inflammation- and immunity-related molecules in diabetic kidneys compared with non-diabetic controls. Abnormal signaling involving cytokines, G-protein coupled receptors, protein kinase C isoforms, mitogen-activated protein kinases, nuclear factor-κB (NFκB), and Toll-like receptors (TLR) were evident. These were accompanied by overexpression of negative regulators of NFκB, TLR, and other proinflammatory pathways, e.g., A20, SOCS1, IRAK-M, IκBα, Triad3A, Tollip, SIGIRR, and ST2L. Anti-inflammatory and immunomodulatory molecules, e.g., IL-10, IL-4, and TSLP that favor T_H2 responses were strongly induced. These molecular indicators of immune dysfunction led us to detect the cryptic presence of bacteria and human cytomegalovirus in more than one third of kidneys of diabetic subjects but none in non-diabetic kidneys. Similar signaling abnormalities could be induced in primary human renal tubular epithelial (but not mesangial) cell cultures exposed to high glucose, proinflammatory cytokines and methylglyoxal, and were reversed by combined pharmacological treatment with an antioxidant and a PKC inhibitor. Our results suggest that diabetes impairs epithelial immunity as a consequence of chronic and inappropriate activation of counter-regulatory immune responses, which are otherwise physiological protective mechanisms against inflammation. The immune abnormalities and cryptic renal infections described here may contribute to progression of diabetic nephropathy.

A novel source of methylglyoxal and glyoxal in retina: implications for age-related macular degeneration

Aging of retinal pigment epithelial (RPE) cells of the eye is marked by accumulations of bisretinoid fluorophores; two of the compounds within this lipofuscin mixture are A2E and all-trans-retinal dimer. These pigments are implicated in pathological mechanisms involved in some vision-threatening disorders including age-related macular degeneration (AMD). Studies have shown that bisretinoids are photosensitive compounds that undergo photooxidation and photodegradation when irradiated with short wavelength visible light. Utilizing ultra performance liquid chromatography (UPLC) with electrospray ionization mass spectrometry (ESI-MS) we demonstrate that photodegradation of A2E and all-trans-retinal dimer generates the dicarbonyls glyoxal (GO) and methylglyoxal (MG), that are known to modify proteins by advanced glycation endproduct (AGE) formation. By extracellular trapping with aminoguanidine, we established that these oxo-aldehydes are released from irradiated A2E-containing RPE cells. Enzyme-linked immunosorbant assays (ELISA) revealed that the substrate underlying A2E-containing RPE was AGE-modified after irradiation. This AGE deposition was suppressed by prior treatment of the cells with aminoguanidine. AGE-modification causes structural and functional impairment of proteins. In chronic diseases such as diabetes and atherosclerosis, MG and GO modify proteins by non-enzymatic glycation and oxidation reactions. AGE-modified proteins are also components of drusen, the sub-RPE deposits that confer increased risk of AMD onset. These results indicate that photodegraded RPE bisretinoid is likely to be a previously unknown source of MG and GO in the eye.

Methylglyoxal-induced modifications of significant honeybee proteinous components in manuka honey: Possible therapeutic implications

Methylglyoxal (MGO) is a major antibacterial component of manuka honey. Another antibacterial component found in Revamil honey, peptide defensin1, was not identified in manuka honey. The primary aim of the study was to evaluate the content of defensin1 in honeys of different botanical origins and to investigate a presumed effect of reactive MGO on defensin1 and a dominant protein of honey MRJP1 in manuka honey. Immunoblotting of honey samples showed that defensin1 was a regular but quantitatively variable component of honeys. One of the reasons of varying contents of defensin1 in different honeys seems to be constitutive but varying defensin1 expression in individual honeybees in bee populations that we documented on samples of nurse and forager bees by RT-PCR. Comparative analyses of honeys revealed a size modification of defensin1, MRJP1 and probably also α-glucosidase in manuka honey. We further showed that (i) the treatment of purified defensin1 in solution containing high amount of MGO caused a time-dependent loss of its antibacterial activity and (ii) increasing MGO concentrations in a non-manuka honey were connected with a gradual increase in the molecular weight of MRJP1. Obtained results demonstrate that MGO abrogates the antibacterial activity of defensin1 and modifies MRJP1 in manuka honey. We assume that MGO could also have negative effects on the structure and function of other proteins/peptides in manuka honey, including glucose oxidase, generating hydrogen peroxide.

Association of two glyoxalase I gene polymorphisms with nephropathy and retinopathy in Type 2 diabetes

BACKGROUND

Glyoxalase I (GLO1), which is the major enzyme that catalyzes the metabolism of methylglyoxal (MG), may play an important role in the pathogenesis of diabetic microvascular complications.

AIM

To investigate whether the C-7T and A419C polymorphisms of the GLO1 gene are associated with nephropathy and retinopathy in Chinese Type 2 diabetic patients.

SUBJECTS AND METHODS

A total of 364 Type 2 diabetic patients and 301 healthy controls were enroled in the study. Diabetic microvascular complications were determined by urinary albumin excretion measurements and ophthalmological examinations. Genetic analyses were performed using either Taqman PCR or direct sequencing. The effect of C-7T polymorphism on promoter activity was measured by reporter gene assays.

RESULTS

The albumin/ creatinine ratio (ACR) and prevalence of nephropathy and retinopathy were significantly higher in diabetic patients with GLO1 -7CC genotype than in patients with -7CT and -7TT genotypes (p=0.02, p=0.02, and p=0.04, respectively). The - 7CC genotype is independently associated with ACR (β=0.13, p=0.01) and the risk for retinopathy [odds ratio (OR): 2.30, 95% confidence interval (CI): 1.25-4.24, p<0.01]. The luciferase activity of the -7T promoter was higher than that of the -7C promoter (13.2±0.2 vs 11.7±0.8, p=0.04). No differences were found between ACR and the prevalence of nephropathy and retinopathy for A419C polymorphism in Type 2 diabetic patients.

CONCLUSIONS

GLO1 C-7T polymorphism alters promoter activity and confers susceptibility to nephropathy and retinopathy to Type 2 diabetic patients.

Characterization of the glyoxalase 1 gene TcGLX1 in the metal hyperaccumulator plant Thlaspi caerulescens

Stress tolerance is currently one of the major research topics in plant biology because of the challenges posed by changing climate and increasing demand to grow crop plants in marginal soils. Increased Zn tolerance and accumulation has been reported in tobacco expressing the glyoxalase 1-encoding gene from Brassica juncea. Previous studies in our laboratory showed some Zn tolerance-correlated differences in the levels of glyoxalase 1-like protein among accessions of Zn hyperaccumulator Thlaspi caerulescens. We have now isolated the corresponding gene (named here TcGLX1), including ca. 570 bp of core and proximal promoter region. The predicted protein contains three glyoxalase 1 motifs and several putative sites for post-translational modification. In silico analysis predicted a number of cis-acting elements related to stress. The expression of TcGLX1 was not responsive to Zn. There was no correlation between the levels of TcGLX1 expression and the degrees of Zn tolerance or accumulation among T. caerulescens accessions nor was there co-segregation of TcGLX1 expression with Zn tolerance or Zn accumulation among F3 lines derived from crosses between plants from accessions with contrasting phenotypes for these properties. No phenotype was observed in an A. thaliana T-DNA insertion line for the closest A. thaliana homolog of TcGLX1, ATGLX1. These results suggest that glyoxalase 1 or at least the particular isoform studied here is not a major determinant of Zn tolerance in the Zn hyperaccumulator plant T. caerulescens. In addition, ATGLX1 is not essential for normal Zn tolerance in the non-tolerant, non-accumulator plant A. thaliana. Possible explanations for the apparent discrepancy between this and previous studies are discussed.

Mutagenesis and repair induced by the DNA advanced glycation end product N2-1-(carboxyethyl)-2'-deoxyguanosine in human cells

Glycation of biopolymers by glucose-derived α-oxo-aldehydes such as methylglyoxal (MG) is believed to play a major role in the complex pathologies associated with diabetes and metabolic disease. In contrast to the extensive literature detailing the formation and physiological consequences of protein glycation, there is little information about the corresponding phenomenon for DNA. To assess the potential contribution of DNA glycation to genetic instability, we prepared shuttle vectors containing defined levels of the DNA glycation adduct N(2)-(1-carboxyethyl)-2'-deoxyguanosine (CEdG) and transfected them into isogenic human fibroblasts that differed solely in the capacity to conduct nucleotide excision repair (NER). In the NER-compromised fibroblasts, the induced mutation frequencies increased up to 18-fold relative to background over a range of ∼10-1400 CEdG adducts/10(5) dG, whereas the same substrates transfected into NER-competent cells induced a response that was 5-fold over background at the highest adduct density. The positive linear correlation (R(2) = 0.998) of mutation frequency with increasing CEdG level in NER-defective cells suggested that NER was the primary if not exclusive mechanism for repair of this adduct in human fibroblasts. Consistent with predictions from biochemical studies using CEdG-substituted oligonucleotides, guanine transversions were the predominant mutation resulting from replication of MG-modified plasmids. At high CEdG levels, significant increases in the number of AT → GC transitions were observed exclusively in NER-competent cells (P < 0.0001). This suggested the involvement of an NER-dependent mutagenic process in response to critical levels of DNA damage, possibly mediated by error-prone Y-family polymerases.

Methylglyoxal-a potential risk factor of manuka honey in healing of diabetic ulcers

Honey has been considered as a remedy in wound healing since ancient times. However, as yet, there are inadequate supportive robust randomized trials and experimental data to fully accept honey as an effective medical product in wound care. Manuka honey has been claimed to have therapeutic advantages over other honeys. Recently, it has been documented that the pronounced antibacterial activity of manuka honey is due, at least in part, to reactive methylglyoxal (MG). The concentration of MG in manuka honeys is up to 100-fold higher than in conventional honeys. MG is a potent protein-glycating agent and an important precursor of advanced glycation end products (AGEs). MG and AGEs play a role in the pathogenesis of impaired diabetic wound healing and can modify the structure and function of target molecules. This commentary describes the concern that MG in manuka honey may delay wound healing in diabetic patients. Further detailed research is needed to fully elucidate the participation of honey/derived MG in healing diabetic ulcers. We advocate randomized controlled trials to determine efficacy and safety of manuka honey in this population.

Monitoring nonenzymatic glycation of human immunoglobulin G by methylglyoxal and glyoxal: A spectroscopic study

The accumulation of dicarbonyl compounds, methylglyoxal (MG) and glyoxal (G), has been observed in diabetic conditions. They are formed from nonoxidative mechanisms in anaerobic glycolysis and lipid peroxidation, and they act as advanced glycation endproduct (AGE) precursors. The objective of this study was to monitor and characterize the AGE formation of human immunoglobulin G (hIgG) by MG and G using ultraviolet (UV) and fluorescence spectroscopy, circular dichroism (CD), and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). hIgG was incubated over time with MG and G at different concentrations. Formation of AGE was monitored by UV and fluorescence spectroscopy. The effect of AGE formation on secondary structure of hIgG was studied by CD. Comparison of AGE profile for MG and G was performed by MALDI-MS. Both MG and G formed AGE, with MG being nearly twice as reactive as G. The combination of these techniques is a convenient method for evaluating and characterizing the AGE proteins.

Structural characterization of bisretinoid A2E photocleavage products and implications for age-related macular degeneration

Fluorescent bisretinoids, such as A2E and all-trans-retinal dimer, form as a by-product of vitamin A cycling in retina and accumulate in retinal pigment epithelial (RPE) cells as lipofuscin pigments. These pigments are implicated in pathological mechanisms involved in several vision-threatening diseases including age-related macular degeneration. Efforts to understand damaging events initiated by these bisretinoids have revealed that photoexcitation of A2E by wavelengths in the visible spectrum leads to singlet oxygen production and photooxidation of A2E. Here we have employed liquid chromatography coupled to electrospray ionization mass spectrometry together with tandem mass spectrometry (MS/MS), to demonstrate that A2E also undergoes photooxidation-induced degradation and we have elucidated the structures of some of the aldehyde-bearing cleavage products. Studies in which A2E was incubated with a singlet oxygen generator yielded results consistent with a mechanism involving bisretinoid photocleavage at sites of singlet molecular oxygen addition. We provide evidence that one of the products released by A2E photodegradation is methylglyoxal, a low molecular weight reactive dicarbonyl with the capacity to form advanced glycation end products. Methylglyoxal is already known to be generated by carbohydrate and lipid oxidation; this is the first report of its production via bisretinoid photocleavage. It is significant that AGE-modified proteins are detected in deposits (drusen) that accumulate below RPE cells in vivo; drusen have been linked to age-related macular degeneration pathogenesis. Whereas various processes play a role in drusen formation, these findings are indicative of a contribution from lipofuscin photooxidation in RPE.