Loss of Glyoxalase 1 Induces Compensatory Mechanism to Achieve Dicarbonyl Detoxification in Mammalian Schwann Cells

Lysine L-lactylation is the dominant lactylation isomer induced by glycolysis

Lysine L-lactylation (Kl-la) is a novel protein posttranslational modification (PTM) driven by L-lactate. This PTM has three isomers: Kl-la, N-ε-(carboxyethyl)-lysine (Kce) and D-lactyl-lysine (Kd-la), which are often confused in the context of the Warburg effect and nuclear presence. Here we introduce two methods to differentiate these isomers: a chemical derivatization and high-performance liquid chromatography analysis for efficient separation, and isomer-specific antibodies for high-selectivity identification. We demonstrated that Kl-la is the primary lactylation isomer on histones and dynamically regulated by glycolysis, not Kd-la or Kce, which are observed when the glyoxalase system was incomplete. The study also reveals that lactyl-coenzyme A, a precursor in L-lactylation, correlates positively with Kl-la levels. This work not only provides a methodology for distinguishing other PTM isomers, but also highlights Kl-la as the primary responder to glycolysis and the Warburg effect.

Endogenous Cellular Metabolite Methylglyoxal Induces DNA-Protein Cross-Links in Living Cells

Methylglyoxal (MGO) is an electrophilic α-oxoaldehyde generated endogenously through metabolism of carbohydrates and exogenously due to autoxidation of sugars, degradation of lipids, and fermentation during food and drink processing. MGO can react with nucleophilic sites within proteins and DNA to form covalent adducts. MGO-induced advanced glycation end-products such as protein and DNA adducts are thought to be involved in oxidative stress, inflammation, diabetes, cancer, renal failure, and neurodegenerative diseases. Additionally, MGO has been hypothesized to form toxic DNA-protein cross-links (DPC), but the identities of proteins participating in such cross-linking in cells have not been determined. In the present work, we quantified DPC formation in human cells exposed to MGO and identified proteins trapped on DNA upon MGO exposure using mass spectrometry-based proteomics. A total of 265 proteins were found to participate in MGO-derived DPC formation including gene products engaged in telomere organization, nucleosome assembly, and gene expression. In vitro experiments confirmed DPC formation between DNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), as well as histone proteins H3.1 and H4. Collectively, our study provides the first evidence for MGO-mediated DNA-protein cross-linking in living cells, prompting future studies regarding the relevance of these toxic lesions in cancer, diabetes, and other diseases linked to elevated MGO levels.

Deletion of Glyoxalase 1 Exacerbates Acetaminophen-Induced Hepatotoxicity in Mice

Acetaminophen (APAP) overdose triggers a cascade of intracellular oxidative stress events, culminating in acute liver injury. The clinically used antidote, N-acetylcysteine (NAC), has a narrow therapeutic window, and early treatment is essential for a satisfactory therapeutic outcome. For more versatile therapies that can be effective even at late presentation, the intricacies of APAP-induced hepatotoxicity must be better understood. Accumulation of advanced glycation end products (AGEs) and the consequent activation of the receptor for AGEs (RAGE) are considered one of the key mechanistic features of APAP toxicity. Glyoxalase 1 (Glo-1) regulates AGE formation by limiting the levels of methylglyoxal (MEG). In this study, we studied the relevance of Glo-1 in the APAP-mediated activation of RAGE and downstream cell death cascades. Constitutive Glo-1-knockout mice (GKO) and a cofactor of Glo-1, ψ-GSH, were used as tools. Our findings showed elevated oxidative stress resulting from the activation of RAGE and hepatocyte necrosis through steatosis in GKO mice treated with high-dose APAP compared to wild-type controls. A unique feature of the hepatic necrosis in GKO mice was the appearance of microvesicular steatosis as a result of centrilobular necrosis, rather than the inflammation seen in the wild type. The GSH surrogate and general antioxidant ψ-GSH alleviated APAP toxicity irrespective of the Glo-1 status, suggesting that oxidative stress is the primary driver of APAP toxicity. Overall, the exacerbation of APAP hepatotoxicity in GKO mice suggests the importance of this enzyme system in antioxidant defense against the initial stages of APAP overdose.

Accumulation of Non-Pathological Liver Fat Is Associated with the Loss of Glyoxalase I Activity in Humans

The underlying molecular mechanisms for the development of non-alcoholic fatty liver (NAFL) and its progression to advanced liver diseases remain elusive. Glyoxalase 1 (Glo1) loss, leading to elevated methylglyoxal (MG) and dicarbonyl stress, has been implicated in various diseases, including obesity-related conditions. This study aimed to investigate changes in the glyoxalase system in individuals with non-pathological liver fat. Liver biopsies were obtained from 30 individuals with a narrow range of BMI (24.6-29.8 kg/m2). Whole-body insulin sensitivity was assessed using HOMA-IR. Liver biopsies were analyzed for total triglyceride content, Glo1 and Glo2 mRNA, protein expression, and activity. Liquid chromatography-tandem mass spectrometry determined liver dicarbonyl content and oxidation and glycation biomarkers. Liver Glo1 activity showed an inverse correlation with HOMA-IR and liver triglyceride content, but not BMI. Despite reduced Glo1 activity, no associations were found with elevated liver dicarbonyls or glycation markers. A sex dimorphism was observed in Glo1, with females exhibiting significantly lower liver Glo1 protein expression and activity, and higher liver MG-H1 content compared to males. This study demonstrates that increasing liver fat, even within a non-pathological range, is associated with reduced Glo1 activity.

Molecular Assessment of Methylglyoxal-Induced Toxicity and Therapeutic Approaches in Various Diseases: Exploring the Interplay with the Glyoxalase System

This comprehensive exploration delves into the intricate interplay of methylglyoxal (MG) and glyoxalase 1 (GLO I) in various physiological and pathological contexts. The linchpin of the narrative revolves around the role of these small molecules in age-related issues, diabetes, obesity, cardiovascular diseases, and neurodegenerative disorders. Methylglyoxal, a reactive dicarbonyl metabolite, takes center stage, becoming a principal player in the development of AGEs and contributing to cell and tissue dysfunction. The dual facets of GLO I-activation and inhibition-unfold as potential therapeutic avenues. Activators, spanning synthetic drugs like candesartan to natural compounds like polyphenols and isothiocyanates, aim to restore GLO I function. These molecular enhancers showcase promising outcomes in conditions such as diabetic retinopathy, kidney disease, and beyond. On the contrary, GLO I inhibitors emerge as crucial players in cancer treatment, offering new possibilities in diseases associated with inflammation and multidrug resistance. The symphony of small molecules, from GLO I activators to inhibitors, presents a nuanced understanding of MG regulation. From natural compounds to synthetic drugs, each element contributes to a molecular orchestra, promising novel interventions and personalized approaches in the pursuit of health and wellbeing. The abstract concludes with an emphasis on the necessity of rigorous clinical trials to validate these findings and acknowledges the importance of individual variability in the complex landscape of health.

Deletion of Glyoxalase 1 exacerbates acetaminophen-induced hepatotoxicity in mice

Acetaminophen (APAP) overdose triggers a cascade of intracellular oxidative stress events culminating in acute liver injury. The clinically used antidote, N-acetylcysteine (NAC) has a narrow therapeutic window and early treatment is essential for satisfactory therapeutic outcome. For more versatile therapies that can be effective even at late-presentation, the intricacies of APAP-induced hepatotoxicity must be better understood. Accumulation of advanced glycation end-products (AGEs) and consequent activation of the receptor for AGEs (RAGE) are considered one of the key mechanistic features of APAP toxicity. Glyoxalase-1 (Glo-1) regulates AGE formation by limiting the levels of methylglyoxal (MEG). In this study, we studied the relevance of Glo-1 in APAP mediated activation of RAGE and downstream cell-death cascades. Constitutive Glo-1 knockout mice (GKO) and a cofactor of Glo-1, ψ-GSH, were employed as tools. Our findings show elevated oxidative stress, activation of RAGE and hepatocyte necrosis through steatosis in GKO mice treated with high-dose APAP compared to wild type controls. A unique feature of the hepatic necrosis in GKO mice is the appearance of microvesicular steatosis as a result of centrilobular necrosis, rather than inflammation seen in wild type. The GSH surrogate and general antioxidant, ψ-GSH alleviated APAP toxicity irrespective of Glo-1 status, suggesting that oxidative stress being the primary driver of APAP toxicity. Overall, exacerbation of APAP hepatotoxicity in GKO mice suggests the importance of this enzyme system in antioxidant defense against initial stages of APAP overdose.

Methylglyoxal in Cardiometabolic Disorders: Routes Leading to Pathology Counterbalanced by Treatment Strategies

Methylglyoxal (MGO) is the major compound belonging to reactive carbonyl species (RCS) responsible for the generation of advanced glycation end products (AGEs). Its upregulation, followed by deleterious effects at the cellular and systemic levels, is associated with metabolic disturbances (hyperglycemia/hyperinsulinemia/insulin resistance/hyperlipidemia/inflammatory processes/carbonyl stress/oxidative stress/hypoxia). Therefore, it is implicated in a variety of disorders, including metabolic syndrome, diabetes mellitus, and cardiovascular diseases. In this review, an interplay between pathways leading to MGO generation and scavenging is addressed in regard to this system's impairment in pathology. The issues associated with mechanistic MGO involvement in pathological processes, as well as the discussion on its possible causative role in cardiometabolic diseases, are enclosed. Finally, the main strategies aimed at MGO and its AGEs downregulation with respect to cardiometabolic disorders treatment are addressed. Potential glycation inhibitors and MGO scavengers are discussed, as well as the mechanisms of their action.

Sex-specificities in offspring neurodevelopment and behaviour upon maternal glycation: Putative underlying neurometabolic and synaptic changes

AIM

Lactation is an important programming window for metabolic disease and neuronal alterations later in life. We aimed to study the effect of maternal glycation during lactation on offspring neurodevelopment and behaviour, assessing possible sex differences and underpinning molecular players.

METHODS

Female Wistar rats were treated with the Glyoxalase-1 inhibitor S-p-Bromobenzylguthione cyclopentyl diester (BBGC 5 mg/kg). A control and vehicle group treated with dimethyl sulfoxide were considered. Male and female offspring were tested at infancy for neurodevelopment hallmarks. After weaning, triglycerides and total antioxidant capacity were measured in breast milk. At adolescence, offspring were tested for locomotor ability, anxious-like behaviour, and recognition memory. Metabolic parameters were assessed, and the hippocampus and prefrontal cortex were collected for molecular analysis.

KEY FINDINGS

Maternal glycation reduced triglycerides and total antioxidant capacity levels in breast milk. At infancy, both male and female offspring presented an anticipation on the achievement of neurodevelopmental milestones. At adolescence, male offspring exposed to maternal glycation presented hyperlocomotion, whereas offspring of both sexes presented a risk-taking phenotype, accompanied by GABA_A receptor upregulation in the hippocampus. Females also demonstrated GABA_A and PSD-95 changes in prefrontal cortex. Furthermore, lower levels of GLO1 and consequently higher accumulation of AGES were also observed in both male and female offspring hippocampus.

SIGNIFICANCE

Early exposure to maternal glycation induces changes in milk composition leading to neurodevelopment changes at infancy, and sex-specific behavioural and neurometabolic changes at adolescence, further evidencing that lactation period is a critical metabolic programming window and in sculpting behaviour.

A glutathione-independent DJ-1/PfpI domain-containing tomato glyoxalaseIII2, SlGLYIII2, confers enhanced tolerance under salt and osmotic stresses

In plants, glyoxalase enzymes are activated under stress conditions to mitigate the toxic effects of hyperaccumulated methylglyoxal (MG), a highly reactive carbonyl compound. Until recently, a glutathione-dependent bi-enzymatic pathway involving glyoxalase I (GLYI) and glyoxalase II (GLYII) was considered the primary MG-detoxification system. Recently, a new glutathione-independent glyoxalase III (GLYIII) mediated direct route was also reported in plants. However, the physiological significance of this new pathway remains to be elucidated across plant species. This study identified the full complement of 22 glyoxalases in tomato. Based on their strong induction under multiple abiotic stresses, SlGLYI4, SlGLYII2 and SlGLYIII2 were selected candidates for further functional characterisation. Stress-inducible overexpression of both glutathione-dependent (SlGLYI4 + SlGLYII2) and independent (SlGLYIII2) pathways led to enhanced tolerance in both sets of transgenic plants under abiotic stresses. However, SlGLYIII2 overexpression (OE) plants outperformed the SlGLYI4 + SlGLYII2 OE counterparts for their stress tolerance under abiotic stresses. Further, knockdown of SlGLYIII2 resulted in plants with exacerbated stress responses than those silenced for both SlGLYI4 and SlGLYII2. The superior performance of SlGLYIII2 OE tomato plants for better growth and yield under salt and osmotic treatments could be attributed to better GSH/GSSG ratio, lower reactive oxygen species levels, and enhanced antioxidant potential, indicating a prominent role of GLYIII MG-detoxification pathway in abiotic stress mitigation in this species.

Methylglyoxal and Its Adducts: Induction, Repair, and Association with Disease

Metabolism is an essential part of life that provides energy for cell growth. During metabolic flux, reactive electrophiles are produced that covalently modify macromolecules, leading to detrimental cellular effects. Methylglyoxal (MG) is an abundant electrophile formed from lipid, protein, and glucose metabolism at intracellular levels of 1-4 μM. MG covalently modifies DNA, RNA, and protein, forming advanced glycation end products (MG-AGEs). MG and MG-AGEs are associated with the onset and progression of many pathologies including diabetes, cancer, and liver and kidney disease. Regulating MG and MG-AGEs is a potential strategy to prevent disease, and they may also have utility as biomarkers to predict disease risk, onset, and progression. Here, we review recent advances and knowledge surrounding MG, including its production and elimination, mechanisms of MG-AGEs formation, the physiological impact of MG and MG-AGEs in disease onset and progression, and the latter in the context of its receptor RAGE. We also discuss methods for measuring MG and MG-AGEs and their clinical application as prognostic biomarkers to allow for early detection and intervention prior to disease onset. Finally, we consider relevant clinical applications and current therapeutic strategies aimed at targeting MG, MG-AGEs, and RAGE to ultimately improve patient outcomes.

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

The activity of glyoxylase 1 is regulated by glucose-responsive phosphorylation on Tyr136

OBJECTIVE

Methylglyoxal (MG) is a highly reactive α-oxoaldehyde that glycates proteins. MG has been linked to the development of diabetic complications: MG is the major precursor of advanced glycation end products (AGEs), a risk marker for diabetic complications in humans. Furthermore, flies and fish with elevated MG develop insulin resistance, obesity, and hyperglycemia. MG is detoxified in large part through the glyoxalase system, whose rate-limiting enzyme is glyoxalase I (Glo1). Hence, we aimed to study how Glo1 activity is regulated.

METHODS

We studied the regulation and effect of post-translational modifications of Glo1 in tissue culture and in mouse models of diabetes.

RESULTS

We show that Glo1 activity is promoted by phosphorylation on Tyrosine 136 via multiple kinases. We find that Glo1 Y136 phosphorylation responds in a bimodal fashion to glucose levels, increasing in cell culture from 0 mM to 5 mM (physiological) glucose, and then decreasing at higher glucose concentrations, both in cell culture and in mouse models of hyperglycemia.

CONCLUSIONS

These data, together with published findings that elevated MG leads to hyperglycemia, suggest the existence of a deleterious positive feedback loop whereby hyperglycemia leads to reduced Glo1 activity, contributing to elevated MG levels, which in turn promote hyperglycemia. Hence, perturbations elevating either glucose or MG have the potential to start an auto-amplifying feedback loop contributing to diabetic complications.

Role of glyoxalase 1 in methylglyoxal detoxification-the broad player of psychiatric disorders

Methylglyoxal (MG) is a highly reactive α-ketoaldehyde formed endogenously as a byproduct of the glycolytic pathway. To remove MG, various detoxification systems work together in vivo, including the glyoxalase system, which enzymatically degrades MG using glyoxalase 1 (GLO1) and GLO2. Recently, numerous reports have shown that GLO1 expression and MG accumulation in the brain are involved in the pathogenesis of psychiatric disorders, such as anxiety disorder, depression, autism, and schizophrenia. Furthermore, it has been reported that GLO1 inhibitors may be promising drugs for the treatment of psychiatric disorders. In this review, we discuss the recent findings of the effects of altered GLO1 function on mental behavior, especially focusing on results obtained from animal models.

Differentially expressed proteins in the interaction of Paracoccidioides lutzii with human monocytes

BACKGROUND

Fungi of the genus Paracoccidioides are the etiological agents of paracoccidioidomycosis, a highly prevalent mycosis in Latin America. Infection in humans occurs by the inhalation of conidia, which later revert to the form of yeast. In this context, macrophages are positioned as an important line of defense, assisting in the recognition and presentation of antigens, as well as producing reactive oxygen species that inhibit fungal spreading.

AIMS

The objective of this study was to identify differentially expressed proteins during the interaction between Paracoccidioides lutzii Pb01 strain and human U937 monocytes.

METHODS

Two-dimensional electrophoresis, combined with mass spectrometry, was used to evaluate the differential proteomic profiles of the fungus P. lutzii (Pb01) interacting with U937 monocytes.

RESULTS

It was possible to identify 25 proteins differentially expressed by Pb01 alone and after interacting with U937 monocytes. Most of these proteins are directly associated with fungal metabolism for energy generation, such as glyceraldehyde-3-phosphate dehydrogenase, and intracellular adaptation to monocytes. Antioxidant proteins involved in the response to oxidative stress, such as peroxiredoxin, cytochrome, and peroxidase, were expressed in greater quantity in the interaction with monocytes, suggesting their association with survival mechanisms inside phagocytic cells. We also identified 12 proteins differentially expressed in monocytes before and after the interaction with the fungus; proteins involved in the reorganization of the cytoskeleton, such as vimentin, and proteins involved in the response to oxidative stress, such as glioxalase 1, were identified.

CONCLUSIONS

The results of this proteomic study of a P. lutzii isolate are novel, mimicking in vitro what occurs in human infections. In addition, the proteins identified may aid to understand fungal-monocyte interactions and the pathogenesis of paracoccidioidomycosis.

Fasting concentrations and postprandial response of 1,2-dicarbonyl compounds 3-deoxyglucosone, glyoxal and methylglyoxal are not increased in healthy older adults

Dicarbonyl stress describes the increased formation of 1,2-dicarbonyl compounds and is associated with age-related pathologies. The role of dicarbonyl stress in healthy aging is poorly understood. In a preliminary study, we analyzed 1,2-dicarbonyl compounds, namely 3-deoxyglucosone (3-DG), glyoxal (GO), and methylglyoxal (MGO) in plasma of older (25 months, n = 11) and younger (5 months, n = 14) male C57BL/6J (B6) mice via ultra performance liquid chromatography tandem mass spectrometry. Postprandial 3-DG was higher in younger compared to older mice, whereas no differences were found for GO and MGO. Subsequently, in the main study, we analyzed fasting serum of older women (OW, 72.4 ± 6.14 years, n = 19) and younger women (YW, 27.0 ± 4.42 years, n = 19) as well as older men (OM, 74.3 ± 5.20 years, n = 15) and younger men (YM, 27.0 ± 3.34, n = 15). Serum glucose, insulin, 1,2-dicarbonyl concentrations, and markers of oxidative stress were quantified. In a subgroup of this cohort, an oral dextrose challenge was performed, and postprandial response of 1,2-dicarbonyl compounds, glucose, and insulin were measured. In women, there were no age differences regarding fasting 1,2-dicarbonyl concentrations nor the response after the oral dextrose challenge. In men, fasting MGO was significantly higher in OM compared to YM (median: 231 vs 158 nM, p = .006), whereas no age differences in fasting 3-DG and GO concentrations were found. Glucose (310 ± 71.8 vs 70.8 ± 11.9 min·mmol/L) and insulin (7 149 ± 1 249 vs 2 827 ± 493 min·µIU/mL) response were higher in OM compared to YM, which did not translate into a higher 1,2-dicarbonyl response in older individuals. Overall, aging does not necessarily result in dicarbonyl stress, indicating that strategies to cope with 1,2-dicarbonyl formation can remain intact.

Glyoxalase-I Is Upregulated in Acute Cerulein-Induced Pancreatitis: A New Mechanism in Pancreatic Inflammation?

Inflammation caused by oxidative stress (ROS) demonstrates an essential mechanism in the pathogenesis of acute pancreatitis (AP). Important sources for ROS comprise the reactive compound methylglyoxal (MGO) itself and the MGO-derived formation of advanced glycation end-products (AGEs). AGEs bind to the transmembrane receptor RAGE and activate NF-κB, and lead to the production of pro-inflammatory cytokines. MGO is detoxified by glyoxalase-I (Glo-I). The importance of Glo-I was shown in different models of inflammation and carcinogenesis. Nevertheless, the role of Glo-I and MGO in AP has not been evaluated so far. This study analyzed Glo-I in cerulein-(CN)-induced AP and determined the effects of Glo-I knockdown, overexpression and pharmacological modulation. Methods: AP was induced in C57BL6/J mice by i.p. injection of CN. Glo-I was analyzed in explanted pancreata by Western Blot, qRT-PCR and immunohistochemistry. AR42J cells were differentiated by dexamethasone and stimulated with 100 nM of CN. Cells were simultaneously treated with ethyl pyruvate (EP) or S-p-bromobenzylglutathione-cyclopentyl-diester (BrBz), two Glo-I modulators. Knockdown and overexpression of Glo-I was achieved by transient transfection with Glo-I siRNA and pEGFP-N1-Glo-I-Vector. Amylase secretion, TNF-α production (ELISA) and expression of Glo-I, RAGE and NF-κB were measured. Results: Glo-I was significantly upregulated on protein and mRNA levels in CN-treated mice and AR42J cells. Dexamethasone-induced differentiation of AR42J cells increased the expression of Glo-I and RAGE. Treatment of AR42J cells with CN and EP or BrBz resulted in a significant reduction of CN-induced amylase secretion, NF-κB, RAGE and TNF-α. Overexpression of Glo-I led to a significant reduction of CN-induced amylase levels, NF-κB expression and TNF-α, whereas Glo-I knockdown revealed only slight alterations. Measurements of specific Glo-I activity and MGO levels indicated a complex regulation in the model of CN-induced AP. Conclusion: Glo-I is overexpressed in a model of CN-induced AP. Pharmacological modulation and overexpression of Glo-I reduced amylase secretion and the release of pro-inflammatory cytokines in AP in vitro. Targeting Glo-I in AP seems to be an interesting approach for future in vivo studies of AP.

Generation of a GLO-2 deficient mouse reveals its effects on liver carbonyl and glutathione levels

Objective

Hydroxyacylglutathione hydrolase (aka as GLO-2) is a component of the glyoxalase pathway involved in the detoxification of the reactive oxoaldehydes, glyoxal and methylglyoxal. These reactive metabolites have been linked to a variety of pathological conditions, including diabetes, cancer and heart disease and may be involved in the aging process. The objective of this study was to generate a mouse model deficient in GLO-2 to provide insight into the function of GLO-2 and to determine if it is potentially linked to endogenous oxalate synthesis which could influence urinary oxalate excretion.

Methods

A GLO-2 knock out mouse was generated using CRISPR/Cas 9 techniques. Tissue and 24-h urine samples were collected under baseline conditions from adult male and female animals for biochemical analyses, including chromatographic measurement of glycolate, oxalate, glyoxal, methylglyoxal, D-lactate, ascorbic acid and glutathione levels.

Results

The GLO-2 KO animals developed normally and there were no changes in 24-h urinary oxalate excretion, liver levels of methylglyoxal, glyoxal, ascorbic acid and glutathione, or plasma d-lactate levels. GLO-2 deficient males had lower plasma glycolate levels than wild type males while this relationship was not observed in females.

Conclusions

The lack of a unique phenotype in a GLO-2 KO mouse model under baseline conditions is consistent with recent evidence, suggesting a functional glyoxalase pathway is not required for optimal health. A lower plasma glycolate in male GLO-2 KO animals suggests glyoxal production may be a significant contributor to circulating glycolate levels, but not to endogenous oxalate synthesis.

Emerging Targets in Type 2 Diabetes and Diabetic Complications

Type 2 diabetes is a metabolic, chronic disorder characterized by insulin resistance and elevated blood glucose levels. Although a large drug portfolio exists to keep the blood glucose levels under control, these medications are not without side effects. More importantly, once diagnosed diabetes is rarely reversible. Dysfunctions in the kidney, retina, cardiovascular system, neurons, and liver represent the common complications of diabetes, which again lack effective therapies that can reverse organ injury. Overall, the molecular mechanisms of how type 2 diabetes develops and leads to irreparable organ damage remain elusive. This review particularly focuses on novel targets that may play role in pathogenesis of type 2 diabetes. Further research on these targets may eventually pave the way to novel therapies for the treatment-or even the prevention-of type 2 diabetes along with its complications.

The Glyoxalase System in Age-Related Diseases: Nutritional Intervention as Anti-Ageing Strategy

The glyoxalase system is critical for the detoxification of advanced glycation end-products (AGEs). AGEs are toxic compounds resulting from the non-enzymatic modification of biomolecules by sugars or their metabolites through a process called glycation. AGEs have adverse effects on many tissues, playing a pathogenic role in the progression of molecular and cellular aging. Due to the age-related decline in different anti-AGE mechanisms, including detoxifying mechanisms and proteolytic capacities, glycated biomolecules are accumulated during normal aging in our body in a tissue-dependent manner. Viewed in this way, anti-AGE detoxifying systems are proposed as therapeutic targets to fight pathological dysfunction associated with AGE accumulation and cytotoxicity. Here, we summarize the current state of knowledge related to the protective mechanisms against glycative stress, with a special emphasis on the glyoxalase system as the primary mechanism for detoxifying the reactive intermediates of glycation. This review focuses on glyoxalase 1 (GLO1), the first enzyme of the glyoxalase system, and the rate-limiting enzyme of this catalytic process. Although GLO1 is ubiquitously expressed, protein levels and activities are regulated in a tissue-dependent manner. We provide a comparative analysis of GLO1 protein in different tissues. Our findings indicate a role for the glyoxalase system in homeostasis in the eye retina, a highly oxygenated tissue with rapid protein turnover. We also describe modulation of the glyoxalase system as a therapeutic target to delay the development of age-related diseases and summarize the literature that describes the current knowledge about nutritional compounds with properties to modulate the glyoxalase system.

Combined glyoxalase 1 dysfunction and vitamin B6 deficiency in a schizophrenia model system causes mitochondrial dysfunction in the prefrontal cortex

Methylglyoxal (MG) is a reactive and cytotoxic α-dicarbonyl byproduct of glycolysis. Our bodies have several bio-defense systems to detoxify MG, including an enzymatic system by glyoxalase (GLO) 1 and GLO2. We identified a subtype of schizophrenia patients with novel mutations in the GLO1 gene that results in reductions of enzymatic activity. Moreover, we found that vitamin B6 (VB6) levels in peripheral blood of the schizophrenia patients with GLO1 dysfunction are significantly lower than that of healthy controls. However, the effects of GLO1 dysfunction and VB6 deficiency on the pathophysiology of schizophrenia remains poorly understood. Here, we generated a novel mouse model for this subgroup of schizophrenia patients by feeding Glo1 knockout mice VB6-deficent diets (KO/VB6(−)) and evaluated the combined effects of GLO1 dysfunction and VB6 deficiency on brain function. KO/VB6(−) mice accumulated homocysteine in plasma and MG in the prefrontal cortex (PFC), hippocampus, and striatum, and displayed behavioral deficits, such as impairments of social interaction and cognitive memory and a sensorimotor deficit in the prepulse inhibition test. Furthermore, we found aberrant gene expression related to mitochondria function in the PFC of the KO/VB6(−) mice by RNA-sequencing and weighted gene co-expression network analysis (WGCNA). Finally, we demonstrated abnormal mitochondrial respiratory function and subsequently enhanced oxidative stress in the PFC of KO/VB6(−) mice in the PFC. These findings suggest that the combination of GLO1 dysfunction and VB6 deficiency may cause the observed behavioral deficits via mitochondrial dysfunction and oxidative stress in the PFC.

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A combination of Glo1 KO and VB6 deficiency induces MG accumulation in the brain.

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Glo1 KO/VB6(−) mice exhibit schizophrenia-like behavioral deficits.

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Gene expression related to mitochondria is impaired in the PFC of the Glo1 KO/VB6(−).

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Mitochondria in the PFC of the Glo1 KO/VB6(−) mice show respiratory dysfunction.

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Oxidative stress is enhanced in the PFC of the Glo1 KO/VB6(−).

Phosphorylation of T107 by CamKIIδ Regulates the Detoxification Efficiency and Proteomic Integrity of Glyoxalase 1

The glyoxalase system is a highly conserved and ubiquitously expressed enzyme system, which is responsible for the detoxification of methylglyoxal (MG), a spontaneous by-product of energy metabolism. This study is able to show that a phosphorylation of threonine-107 (T107) in the (rate-limiting) Glyoxalase 1 (Glo1) protein, mediated by Ca²⁺/calmodulin-dependent kinase II delta (CamKIIδ), is associated with elevated catalytic efficiency of Glo1 (lower K_M; higher V_max). Additionally, we observe proteasomal degradation of non-phosphorylated Glo1 via ubiquitination does occur more rapidly as compared with native Glo1. The absence of CamKIIδ is associated with poor detoxification capacity and decreased protein content of Glo1 in a murine CamKIIδ knockout model. Therefore, phosphorylation of T107 in the Glo1 protein by CamKIIδ is a quick and precise mechanism regulating Glo1 activity, which is experimentally linked to an altered Glo1 status in cancer, diabetes, and during aging.

Polymorphisms in Glyoxalase I Gene Are Not Associated with Glyoxalase I Expression in Whole Blood or Markers of Methylglyoxal Stress: The CODAM Study

Glyoxalase 1 (Glo1) is the rate-limiting enzyme in the detoxification of methylglyoxal (MGO) into D-lactate. MGO is a major precursor of advanced glycation endproducts (AGEs), and both are associated with development of age-related diseases. Since genetic variation in GLO1 may alter the expression and/or the activity of Glo1, we examined the association of nine SNPs in GLO1 with Glo1 expression and markers of MGO stress (MGO in fasting plasma and after an oral glucose tolerance test, D-lactate in fasting plasma and urine, and MGO-derived AGEs CEL and MG-H1 in fasting plasma and urine). We used data of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM, n = 546, 60 ± 7 y, 25% type 2 diabetes). Outcomes were compared across genotypes using linear regression, adjusted for age, sex, and glucose metabolism status. We found that SNP4 (rs13199033) was associated with Glo1 expression (AA as reference, standardized beta AT = −0.29, p = 0.02 and TT = −0.39, p = 0.3). Similarly, SNP13 (rs3799703) was associated with Glo1 expression (GG as reference, standardized beta AG = 0.17, p = 0.14 and AA = 0.36, p = 0.005). After correction for multiple testing these associations were not significant. For the other SNPs, we observed no consistent associations over the different genotypes. Thus, polymorphisms of GLO1 were not associated with Glo1 expression or markers of MGO stress, suggesting that these SNPs are not functional, although activity/expression might be altered in other tissues.

Michaelis-Menten Kinetics Measurements of Aldo-Keto Reductases for Various Substrates in Murine Tissue

Aldo-keto reductases (AKRs) are responsible for the detoxification of harmful aldehydes. Due to the large number of isotypes, the physiological relevance of AKRs cannot be obtained using mRNA or protein quantification, but only through the use of enzymatic assays to demonstrate functionality. Here, we present a fast and simple protocol to determine the important Michaelis-Menten kinetics of AKRs, which includes various aldehyde substrates of interest such as 4-hydroxynonenal, methylglyoxal, and malondialdehyde.

For complete details on the use and execution of this protocol, please refer to Morgenstern et al. (2017) and Schumacher et al. (2018).

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Mild and efficient extraction/lysis of mouse tissue

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Monitoring of aldo-keto reductase catalyzed reactions for various substrates

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Comprehensive explanations in order to determine Michaelis-Menten kinetics

Dicarbonyl derived post-translational modifications: chemistry bridging biology and aging-related disease

In living systems, nucleophilic amino acid residues are prone to non-enzymatic post-translational modification by electrophiles. α-Dicarbonyl compounds are a special type of electrophiles that can react irreversibly with lysine, arginine, and cysteine residues via complex mechanisms to form post-translational modifications known as advanced glycation end-products (AGEs). Glyoxal, methylglyoxal, and 3-deoxyglucosone are the major endogenous dicarbonyls, with methylglyoxal being the most well-studied. There are several routes that lead to the formation of dicarbonyl compounds, most originating from glucose and glucose metabolism, such as the non-enzymatic decomposition of glycolytic intermediates and fructosyl amines. Although dicarbonyls are removed continuously mainly via the glyoxalase system, several conditions lead to an increase in dicarbonyl concentration and thereby AGE formation. AGEs have been implicated in diabetes and aging-related diseases, and for this reason the elucidation of their structure as well as protein targets is of great interest. Though the dicarbonyls and reactive protein side chains are of relatively simple nature, the structures of the adducts as well as their mechanism of formation are not that trivial. Furthermore, detection of sites of modification can be demanding and current best practices rely on either direct mass spectrometry or various methods of enrichment based on antibodies or click chemistry followed by mass spectrometry. Future research into the structure of these adducts and protein targets of dicarbonyl compounds may improve the understanding of how the mechanisms of diabetes and aging-related physiological damage occur.

Glyoxalase 1 Inhibitor Alleviates Autism-like Phenotype in a Prenatal Valproic Acid-Induced Mouse Model

Autism spectrum disorder (ASD) is a severe neurological and developmental disorder that impairs a person's ability to socialize and communicate and affects behavior. The number of patients diagnosed with ASD has risen rapidly. However, the pathophysiology of ASD is poorly understood, and drugs for ASD treatment are strikingly limited. This study aims to evaluate the roles of glyoxalase 1 (GLO1)-methylglyoxal (MG)-γ-aminobutyric acid (GABA) signaling in ASD using a valproic acid (VPA)-induced animal model of autism. The GLO1 levels were analyzed by RT-qPCR and Western blot assay, and MG levels were measured with a Methylglyoxal Assay Kit. The open-field and sniff duration tests were used to assess the interest and anxiety of VPA mice. The three-chamber, marble-burying, and tail-flick tests were applied to determine the sociability, repetitive behavior, and nociceptive threshold of VPA mice. Our results demonstrated that increased GLO1 and decreased MG were observed in VPA mice. Administration of S-p-bromobenzylglutathione cyclopentyl diester (BrBzGCp2), a GLO1 inhibitor, was beneficial for alleviating anxiety, reducing repetitive behavior, and improving the impaired sociability and nociceptive threshold of VPA mice. BrBzGCp2 treatment may be developed as a promising therapeutic strategy for patients with ASD.

A novel crosslinked type of advanced glycation end-product derived from lactaldehyde

Glycation of amino or guanidino groups of proteins with glucose and glucose-derived reactive aldehydes, such as α-hydroxyaldehydes, leads to accumulation of advanced glycation end-products (AGEs) in the body, resulting in diabetic complications and age-related pathology. Although molecular structures of glycolaldehyde- and glyceraldehyde-derived AGEs have been described in previous studies, little is known about lactaldehyde-derived AGEs of α-hydroxyaldehydes. Here, we report a novel crosslinked type of AGE, named as lactaldehyde-derived lysine dimer (LAK2), which is produced due to non-enzymatic glycation of N^α-acetyl-L-lysine with lactaldehyde under physiological conditions. We have identified the molecular structure of LAK2 by extensive mass spectrometry and nuclear magnetic resonance analyses. Furthermore, we propose a reaction pathway to produce LAK2, in which it is formed through an intermediate common with the recently reported lactaldehyde-derived pyridinium-type lysine adduct (LAPL). Since lactaldehyde is known to be produced from L-threonine in a myeloperoxidase (MPO)-mediated reaction at sites of inflammation, LAK2 has the potential to be an oxidative stress marker of MPO-mediated reactions induced in inflammation.

Glyoxalase System as a Therapeutic Target against Diabetic Retinopathy

Hyperglycemia, a defining characteristic of diabetes, combined with oxidative stress, results in the formation of advanced glycation end products (AGEs). AGEs are toxic compounds that have adverse effects on many tissues including the retina and lens. AGEs promote the formation of reactive oxygen species (ROS), which, in turn, boost the production of AGEs, resulting in positive feedback loops, a vicious cycle that compromises tissue fitness. Oxidative stress and the accumulation of AGEs are etiologically associated with the pathogenesis of multiple diseases including diabetic retinopathy (DR). DR is a devastating microvascular complication of diabetes mellitus and the leading cause of blindness in working-age adults. The onset and development of DR is multifactorial. Lowering AGEs accumulation may represent a potential therapeutic approach to slow this sight-threatening diabetic complication. To set DR in a physiological context, in this review we first describe relations between oxidative stress, formation of AGEs, and aging in several tissues of the eye, each of which is associated with a major age-related eye pathology. We summarize mechanisms of AGEs generation and anti-AGEs detoxifying systems. We specifically feature the potential of the glyoxalase system in the retina in the prevention of AGEs-associated damage linked to DR. We provide a comparative analysis of glyoxalase activity in different tissues from wild-type mice, supporting a major role for the glyoxalase system in the detoxification of AGEs in the retina, and present the manipulation of this system as a therapeutic strategy to prevent the onset of DR.

The Glyoxalase System-New Insights into an Ancient Metabolism

The glyoxalase system was discovered over a hundred years ago and since then it has been claimed to provide the role of an indispensable enzyme system in order to protect cells from a toxic byproduct of glycolysis. This review gives a broad overview of what has been postulated in the last 30 years of glyoxalase research, but within this context it also challenges the concept that the glyoxalase system is an exclusive tool of detoxification and that its substrate, methylglyoxal, is solely a detrimental burden for every living cell due to its toxicity. An overview of consequences of a complete loss of the glyoxalase system in various model organisms is presented with an emphasis on the role of alternative detoxification pathways of methylglyoxal. Furthermore, this review focuses on the overlooked posttranslational modification of Glyoxalase 1 and its possible implications for cellular maintenance under various (patho-)physiological conditions. As a final note, an intriguing point of view for the substrate methylglyoxal is offered, the concept of methylglyoxal (MG)-mediated hormesis.

Neural Glyoxalase Pathway Enhancement by Morin Derivatives in an Alzheimer's Disease Model

The glyoxalase pathway (GP) is an antioxidant defense system that detoxifies metabolic byproduct methylglyoxal (MG). Through sequential reactions, reduced glutathione (GSH), glyoxalase I (glo-1), and glyoxalase II (glo-2) convert MG into d-lactate. Spontaneous reactions involving MG alter the structure and function of cellular macromolecules through the formation of inflammatory advanced glycation endproducts (AGEs). Accumulation of MG and AGEs in neural cells contributes to oxidative stress (OS), a state of elevated inflammation commonly found in neurodegenerative diseases including Alzheimer's disease (AD). Morin is a common plant-produced flavonoid polyphenol that exhibits the ability to enhance the GP-mediated detoxification of MG. We hypothesize that structural modifications to morin will improve its inherent GP enhancing ability. Here we synthesized a morin derivative, dibromo-morin (DBM), formulated a morin encapsulated nanoparticle (MNP), and examined their efficacy in enhancing neural GP activity. Cultured mouse primary cerebellar neurons and Caenorhabditis elegans were induced to a state of OS with MG and treated with morin, DBM, and MNP. Results indicated the morin derivatives were more effective compared to the parent compound in neural GP enhancement and preventing MG-mediated OS in an AD model.

Methylglyoxal Metabolism and Aging-Related Disease: Moving from Correlation toward Causation

Methylglyoxal (MG) is a ubiquitous metabolite that spontaneously reacts with biopolymers forming advanced glycation end-products (AGEs). AGEs are strongly associated with aging-related diseases, including cancer, neurodegenerative diseases, and diabetes. As the formation of AGEs is nonenzymatic, the damage caused by MG and AGEs has been regarded as unspecific. This may have resulted in the field generally been regarded as unappealing by many researchers, as detailed mechanisms have been difficult to probe. However, accumulating evidence highlighting the importance of MG in human metabolism and disease, as well as data revealing how MG can elicit its signaling function via specific protein AGEs, could change the current mindset, accelerating the field to the forefront of future research.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Glyoxalase 1 gene improves the antistress capacity and reduces the immune inflammatory response

BACKGROUND

Fish immunity is not only affected by the innate immune pathways but is also triggered by stress. Transport and loading stress can induce oxidative stress and further activate the immune inflammatory response, which cause tissue damage and sudden death. Multiple genes take part in this process and some of these genes play a vital role in regulation of the immune inflammatory response and sudden death. Currently, the key genes regulating the immune inflammatory response and the sudden death caused by stress in Coilia nasus are unknown.

RESULTS

In this study, we studied the effects of the Glo1 gene on stress, antioxidant expression, and immune-mediated apoptosis in C. nasus. The full-length gene is 4356 bp, containing six exons and five introns. Southern blotting indicated that Glo1 is a single-copy gene in the C. nasus genome. We found two single-nucleotide polymorphisms (SNPs) in the Glo1 coding region, which affect the three-dimensional structure of Glo1 protein. An association analysis results revealed that the two SNPs are associated with stress tolerance. Moreover, Glo1 mRNA and protein expression of the heterozygous genotype was significantly higher than that of the homozygous genotype. Na+ and sorbitol also significantly enhanced Glo1 mRNA and protein expression, improved the fish's antioxidant capacity, and reduced the immune inflammatory response, thus sharply reducing the mortality caused by stress.

CONCLUSIONS

Glo1 plays a potential role in the stress response, antioxidant capacity, and immune-mediated apoptosis in C. nasus.

Role of the Glyoxalase System in Alzheimer's Disease

Alzheimer's disease (AD) is an insidious and progressive neurodegenerative disease. The main pathological features of AD are the formation of amyloid-β deposits in the anterior cerebral cortex and hippocampus as well as the formation of intracellular neurofibrillary tangles. Thus far, accumulating evidence shows that glycation is closely related to AD. As a final product resulting from the crosslinking of a reducing sugar or other reactive carbonyls and a protein, the advanced glycation end products have been found to be associated with the formation of amyloid-β and neurofibrillary tangles in AD. As a saccharification inhibitor, the glyoxalase system and its substrate methylglyoxal (MG) were certified to be associated with AD onset and development. As an active substance of AGEs, MG could cause direct or indirect damage to nerve cells and tissues. MG is converted to D-lactic acid after decomposition by the glyoxalase system. Under normal circumstances, MG metabolism is in a dynamic equilibrium, whereas MG accumulates in cells in the case of aging or pathological states. Studies have shown that increasing glyoxalase activity and reducing the MG level can inhibit the generation of oxidative stress and AGEs, thereby alleviating the symptoms and signs of AD to some extent. This paper focuses on the relevant mechanisms of action of the glyoxalase system and MG in the pathogenesis of AD, as well as the potential of inhibiting the production of advanced glycation end products in the treatment of AD.

Neutrophil-derived advanced glycation end products-Nε-(carboxymethyl) lysine promotes RIP3-mediated myocardial necroptosis via RAGE and exacerbates myocardial ischemia/reperfusion injury

Nε-(carboxymethyl) lysine (CML), the major member of advanced glycation end products, was widely studied in diabetic complications and aging-associated diseases. However, the impact of CML on myocardial ischemia/reperfusion injury (MI/RI) was rarely reported. In the present study, CML was increased in both patients with acute myocardial infarction (53.4 ± 7.8 vs. 28.1 ± 4.4 ng; P = 0.017), and mice underwent MI/RI (16.4 ± 1.4 vs. 10.8 ± 0.9 ng; P = 0.006). Depletion of neutrophils reduced CML (17.8 ± 1.0 vs. 9.9 ± 0.3 ng; P < 0.001), indicating neutrophils were the major cells contributing to CML formation during MI/RI. CML treatment exacerbated MI/RI by elevating myocardial injury marker (274.3 ± 18.0 vs. 477.2 ± 34.3 pg; P < 0.001), enlarging myocardial infarct size (32.9 ± 3.6 vs. 45.2 ± 3.8%; P = 0.03), increasing myocardial fibrosis (17.5 ± 1.6 vs. 29.7 ± 2.2%; P < 0.001) and impairing cardiac function (59.4 ± 2.4% vs. 46.0 ± 1.3%; P = 0.001). Further study revealed that CML increased the phosphorylation of receptor interacting protein (RIP) 3, an important initiator of necroptosis, and its downstream proteins. Receptor for advanced glycation end product (RAGE) deficiency effectively blocked RIP3 phosphorylation induced by CML and rescued CML-mediated MI/RI, indicating CML promoted RIP3-mediated necroptosis through RAGE. In addition, glyoxalase-1 overexpression could effectively attenuate MI/RI by reducing CML formation, providing a potential therapeutic target for MI/RI.-Yang, J., Zhang, F., Shi, H., Gao, Y., Dong, Z., Ma, L., Sun, X., Li, X., Chang, S., Wang, Z., Qu, Y., Li, H., Hu, K., Sun, A., Ge, J. Neutrophil-derived advanced glycation end products-Nε-(carboxymethyl) lysine promotes RIP3-mediated myocardial necroptosis via RAGE and exacerbates myocardial ischemia/reperfusion injury.

Inhibition of Glyoxalase-I Leads to Reduced Proliferation, Migration and Colony Formation, and Enhanced Susceptibility to Sorafenib in Hepatocellular Carcinoma

Background: Glyoxalase-I (Glo-I) is essential for detoxification of methylglyoxal (MGO), a byproduct of glycolysis. Overexpression of Glo-I has been linked to multi-drug resistance in cancer therapy. The aim of this study was to analyze Glo-I in hepatocellular carcinoma (HCC) and the effect of the multi-tyrosine kinase inhibitor sorafenib on Glo-I. Methods: Expression and specific activity of Glo-I was measured in human HCC samples, HCC-cell lines (HepG2, Huh7) and a hepatocyte cell line (AML 12). Cells were either treated with Glo-I inhibitors, ethyl pyruvate (EP, 1-20 mM) and BrBzGSHCp2 (1-10 μM), or sorafenib (2.5-10 μM) and protein expression (Western Blot), proliferation (WST-assay), migration (scratch assay), and colony formation (clonogenic assay) were assessed. Results: High expression of Glo-I was detected in human HCC tissue samples. Huh7 showed highest expression and activity of Glo-I and revealed highest proliferation compared to AML 12 and HepG2. Targeting Glo-I by EP or BrBzGSHCp₂ led to significantly reduced proliferation (20 mM EP 24 h: 57 ± 12%), migration and colony formation. Glo-I inhibition by 20 mM EP resulted in reduced expression of PDGFR-β (18 ± 10%), VEGFR2 (46 ± 11%), VEGF (61 ± 10%), pERK/ERK (62 ± 6%), NF-κB (44 ± 12%) as well as stimulation of Nrf2 (243 ± 36%). Similar results were seen with BrBzGSHCp2. Sorafenib treatment revealed elevation of Glo-I (10 μM: 209 ± 25%) and MGO. Co-treatment of EP and sorafenib led to an additional reduction of proliferation compared to sorafenib alone. Conclusion: Glo-I is positively correlated with HCC proliferation. Inhibition of Glo-I reduced proliferation, migration, and colony formation. In turn, sorafenib increases Glo-I. Co-treatment using Glo-I inhibitors could enhance susceptibility of HCC to sorafenib.

The combination of loss of glyoxalase1 and obesity results in hyperglycemia

The increased formation of methylglyoxal (MG) under hyperglycemia is associated with the development of microvascular complications in patients with diabetes mellitus; however, the effects of elevated MG levels in vivo are poorly understood. In zebrafish, a transient knockdown of glyoxalase 1, the main MG detoxifying system, led to the elevation of endogenous MG levels and blood vessel alterations. To evaluate effects of a permanent knockout of glyoxalase 1 in vivo, glo1-/- zebrafish mutants were generated using CRISPR/Cas9. In addition, a diet-induced-obesity zebrafish model was used to analyze glo1-/- zebrafish under high nutrient intake. Glo1-/- zebrafish survived until adulthood without growth deficit and showed increased tissue MG concentrations. Impaired glucose tolerance developed in adult glo1-/- zebrafish and was indicated by increased postprandial blood glucose levels and postprandial S6 kinase activation. Challenged by an overfeeding period, fasting blood glucose levels in glo1-/- zebrafish were increased which translated into retinal blood vessel alterations. Thus, the data have identified a defective MG detoxification as a metabolic prerequisite and glyoxalase 1 alterations as a genetic susceptibility to the development of type 2 diabetes mellitus under high nutrition intake.

ReactELISA method for quantifying methylglyoxal levels in plasma and cell cultures

Methylglyoxal (MG) is a toxic glycolytic by-product associated with increased levels of inflammation and oxidative stress and has been linked to ageing-related diseases, such as diabetes and Alzheimer's disease. As MG is a highly reactive dicarbonyl compound, forming both reversible and irreversible adducts with a range of endogenous nucleophiles, measuring endogenous levels of MG are quite troublesome. Furthermore, as MG is a small metabolite it is not very immunogenic, excluding conventional ELISA for detection purposes, thus only more instrumentally demanding LC-MS/MS-based methods have demonstrated convincing quantitative data. In the present work we develop a novel bifunctional MG capture probe as well as a high specificity monoclonal antibody to finally setup a robust reaction-based ELISA (ReactELISA) method for detecting the highly reactive and low-level (nM) metabolite MG in human biological specimens. The assay is tested and validated against the current golden standard LC-MS/MS method in human blood plasma and cell-culture media. Furthermore, we demonstrate the assays ability to measure small perturbations of MG levels in growth media caused by a small molecule drug buthionine sulfoximine (BSO) of current clinical relevance. Finally, the assay is converted into a homogenous (no-wash) AlphaLISA version (ReactAlphaLISA), which offers the potential for operationally simple screening of further small molecules capable of perturbing cellular MG. Such compounds could be of relevance as probes to gain insight into MG metabolism as well as drug-leads to alleviate ageing-related diseases.

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MG is challenging to quantify, here we present a simple and specific ReactELISA based approach and validate against LC-MS/MS.

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Sensitivity at low (nM) endogenous concentration in both human blood plasma and cell culture media.

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Impact of BSO treatment of HEK293 cells can be profiled in culture media.

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Potential use in cell-based phenotypic screen for small molecules modulating MG metabolism.

Identification of a novel advanced glycation end product derived from lactaldehyde

Advanced glycation end products (AGEs) are implicated in the development of diabetic complications via the receptor for AGEs (RAGE). We have reported that the 3-hydroxypyridinium (3HP)-containing AGEs derived from α-hydroxyaldehydes physically interact with RAGE and show cytotoxicity. Lactaldehyde (LA) is formed from a reaction between threonine and myeloperoxidase, but no LA-derived AGEs have been characterized. Here, we identify the structure and physiological effects of an AGE derived from LA. We isolated a novel 3HP derivative, 2-acetamido-6-(3-hydroxy-5-methyl-pyridin-1-ium-1-yl)hexanoate, named as N-acetyl-LAPL (lactaldehyde-derived pyridinium-type lysine adduct), from a mixture of LA with N^α-acetyl-L-lysine. LAPL was also detected in the LA-modified protein. LAPL elicited toxicity in PC12 neuronal cells, but the effect was suppressed by the soluble form of RAGE as a decoy receptor. Moreover, surface plasmon resonance-based analysis revealed that LAPL specifically binds to recombinant RAGE. These results indicate that LA generates an AGE containing the 3HP moiety and contributes to RAGE-dependent cytotoxicity. Abbreviations: AGEs: advanced glycation end products; RAGE: receptor for advanced glycation end products; 3HP: 3-hydroxypyridinium; LA: lactaldehyde; LAPL: lactaldehyde-derived pyridinium-type lysine adduct; BSA: bovine serum albumin; GLAP: glyceraldehyde-derived pyridinium; MPO: myeloperoxidase; HFBA: heptafluorobutyric acid; TFA: trifluoroacetic acid; HPLC: high performance liquid chromatography; LC-ESI-QTOF-MS: liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry; NMR: nuclear magnetic resonance; LA-BSA: lactaldehyde-modified bovine serum albumin; PBS: phosphate buffered saline, GST, glutathione S-transferase; SPR: surface plasmon resonance; OP-lysine: 2-ammonio-6-(3-oxidopyridinium-1-yl)hexanoate; GLO1: glyoxalase 1; MG, methylglyoxal.

Glyoxalase 1 Modulation in Obesity and Diabetes

Significance: Obesity and type 2 diabetes mellitus are increasing globally. There is also increasing associated complications, such as non-alcoholic fatty liver disease (NAFLD) and vascular complications of diabetes. There is currently no licensed treatment for NAFLD and no recent treatments for diabetic complications. New approaches are required, particularly those addressing mechanism-based risk factors for health decline and disease progression. Recent Advances: Dicarbonyl stress is the abnormal accumulation of reactive dicarbonyl metabolites such as methylglyoxal (MG) leading to cell and tissue dysfunction. It is a potential driver of obesity, diabetes, and related complications that are unaddressed by current treatments. Increased formation of MG is linked to increased glyceroneogenesis and hyperglycemia in obesity and diabetes and also down-regulation of glyoxalase 1 (Glo1)-which provides the main enzymatic detoxification of MG. Glo1 functional genomics studies suggest that increasing Glo1 expression and activity alleviates dicarbonyl stress; slows development of obesity, related insulin resistance; and prevents development of diabetic nephropathy and other microvascular complications of diabetes. A new therapeutic approach constitutes small-molecule inducers of Glo1 expression-Glo1 inducers-exploiting a regulatory antioxidant response element in the GLO1 gene. A prototype Glo1 inducer, trans-resveratrol (tRES)-hesperetin (HESP) combination, in corrected insulin resistance, improved glycemic control and vascular inflammation in healthy overweight and obese subjects in clinical trial. Critical Issues: tRES and HESP synergize pharmacologically, and HESP likely overcomes the low bioavailability of tRES by inhibition of intestinal glucuronosyltransferases. Future Directions: Glo1 inducers may now be evaluated in Phase 2 clinical trials for treatment of NAFLD and vascular complications of diabetes.

Methylglyoxal evokes acute Ca2+ transients in distinct cell types and increases agonist-evoked Ca2+ entry in endothelial cells via CRAC channels

Methylglyoxal (MG) is a by-product of glucose metabolism and its accumulation has been linked to the development of diabetic complications such as retinopathy and nephropathy by affecting multiple signalling pathways. However, its influence on the intracellular Ca²⁺ homeostasis and particularly Ca²⁺ entry, which has been reported to be mediated via TRPA1 channels in DRG neurons, has not been studied in much detail in other cell types. In this study, we report the consequences of acute and long-term MG application on intracellular Ca²⁺ levels in endothelial cells. We showed that acute MG application doesn't evoke any instantaneous changes in the intracellular Ca²⁺ concentration in immortalized mouse cardiac endothelial cells (MCECs) and murine microvascular endothelial cells (muMECs). In contrast, an MG-induced rise in intracellular Ca²⁺ level was observed in primary mouse mesangial cells within 30 s, indicating that the modulation of Ca²⁺ homeostasis by MG is strictly cell type specific. The formation of the MG-derived advanced glycation end product (AGE) MG-H1 was found to be time and concentration-dependent in MCECs. Likewise, MG pre-incubation for 6 h increased the angiotensin II-evoked Ca²⁺ entry in MCECs and muMECs which was abrogated by inhibition of Calcium release activated calcium (CRAC) channels with GSK-7975A, but unaffected by an inhibitor specific to TRPA1 channels. Quantitative PCR analysis revealed that MG pre-treatment did not affect expression of the genes encoding the angiotensin receptors AT1R (Agtr 1a & Agtr 1b), Trpa1 nor Orai1, Orai2, Orai3, Stim1, Stim2 and Saraf which operate as constituents or regulators of CRAC channels and store-operated Ca²⁺ entry (SOCE) in other cell types. Together, our results show that long-term MG stimulation leads to the formation of glycation end products, which facilitates the agonist-evoked Ca²⁺ entry in endothelial cells, and this could be a new pathway that might lead to MG-evoked vasoregression observed in diabetic vasculopathies.

Profiling of Methylglyoxal Blood Metabolism and Advanced Glycation End-Product Proteome Using a Chemical Probe

Methylglyoxal (MG) is quantitatively the most important precursor to advanced glycation end-products (AGEs), and evidence is accumulating that it is also a causally linked to diabetes and aging related diseases. Living systems primarily reside on the glyoxalase system to detoxify MG into benign d-lactate. The flux to either glycation or detoxification, accordingly, is a key parameter for how well a system handles the ubiquitous glyoxal burden. Furthermore, insight into proteins and in particular their individual modification sites are central to understanding the involvement of MG and AGE in diabetes and aging related diseases. Here, we present a simple method to simultaneously monitor the flux of MG both to d-lactate and to protein AGE formation in a biological sample by employing an alkyne-labeled methylglyoxal probe. We apply the method to blood and plasma to demonstrate the impact of blood cell glyoxalase activity on plasma protein AGE formation. We move on to isolate proteins modified by the MG probe and accordingly can present the first general inventory of more than 100 proteins and 300 binding sites of the methylglyoxal probe on plasma as well as erythrocytic proteins. Some of the data could be validated against a number of in vivo and in vitro targets for advanced glycation previously known from the literature; the majority of proteins and specific sites however were previously unknown and may guide future research into MG and AGE to elucidate how these are functionally linked to diabetic disease and aging.

Compensatory mechanisms for methylglyoxal detoxification in experimental & clinical diabetes

OBJECTIVES

The deficit of Glyoxalase I (Glo1) and the subsequent increase in methylglyoxal (MG) has been reported to be one the five mechanisms by which hyperglycemia causes diabetic late complications. Aldo-keto reductases (AKR) have been shown to metabolize MG; however, the relative contribution of this superfamily to the detoxification of MG in vivo, particularly within the diabetic state, remains unknown.

METHODS

CRISPR/Cas9-mediated genome editing was used to generate a Glo1 knock-out (Glo1-/-) mouse line. Streptozotocin was then applied to investigate metabolic changes under hyperglycemic conditions.

RESULTS

Glo1-/- mice were viable and showed no elevated MG or MG-H1 levels under hyperglycemic conditions. It was subsequently found that the enzymatic efficiency of various oxidoreductases in the liver and kidney towards MG were increased in the Glo1-/- mice. The functional relevance of this was supported by the altered distribution of alternative detoxification products. Furthermore, it was shown that MG-dependent AKR activity is a potentially clinical relevant pathway in human patients suffering from diabetes.

CONCLUSIONS

These data suggest that in the absence of GLO1, AKR can effectively compensate to prevent the accumulation of MG. The combination of metabolic, enzymatic, and genetic factors, therefore, may provide a better means of identifying patients who are at risk for the development of late complications caused by elevated levels of MG.

Age-related alteration in the distribution of methylglyoxal and its metabolic enzymes in the mouse brain

Methylglyoxal (MG) is an α-dicarbonyl compound that is naturally produced in vivo through glucose metabolism. In general, MG is metabolized by the glyoxalase 1(GLO1)/GLO2 system and aldose reductase (AR); however, excessive MG can react with proteins and nucleic acids to induce the accumulation of advanced glycation end products (AGEs). Recently, the accumulation of AGEs in the brain has been presumed to be related to neurodegenerative diseases such as Parkinson's and Alzheimer's disease, respectively. Research investigating the role of AGEs in such diseases is ongoing. However, the changes in MG concentration that occur in the brain during healthy ageing remain unclear. Therefore, we performed fractionation of the brains of aged and young mice, measured the MG concentration in each part of the brain, and then examined the distribution. We also investigated the expression levels of GLO1 and AR, the main metabolizing enzymes of MG, in various brain regions, across age groups. We show that MG concentration varies among different regions of the brain, and that MG concentration in aged mice is significantly lower than that in young mice across all regions of the brain, except the brain stem. In addition, although the expression level of the GLO1 protein in the brain did not change with ageing, the expression level of AR was higher in aged than in young mice. Moreover, although a significant positive correlation was observed between GLO1 expression and MG concentration in the brains of young mice, no significant correlations were observed in the brains of aged mice. Meanwhile, the production of protein carbonyls and the accumulation of AGEs were not observed in the brains of aged mice. These results suggest that the accumulation of MG in the brain, along with the carbonyl stress are suppressed and regionally controlled during healthy ageing. This finding is useful as the foundation for further studies to investigate the role and toxicity of MG in various age-related disease conditions.

Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model

The aim of this study was to evaluate whether damage to the neurovascular unit in diabetes depends on reactive metabolites such as methylglyoxal (MG), and to assess its impact on retinal gene expression. Male Wistar rats were supplied with MG (50 mM) by drinking water and compared with age-matched streptozotocin-diabetic animals and untreated controls. Retinal damage was evaluated for the accumulation of MG-derived advanced glycation end products, changes in hexosamine and PKC pathway activation, microglial activation, vascular alterations (pericyte loss and vasoregression), neuroretinal function assessed by electroretinogram, and neurodegeneration. Retinal gene regulation was studied by microarray analysis, and transcription factor involvement was identified by upstream regulator analysis. Systemic application of MG by drinking water increased retinal MG to levels comparable with diabetic animals. Elevated retinal MG resulted in MG-derived hydroimidazolone modifications in the ganglion cell layer, inner nuclear layer, and outer nuclear layer, a moderate activation of the hexosamine pathway, a pan-retinal activation of microglia, loss of pericytes, increased formation of acellular capillaries, decreased function of bipolar cells, and increased expression of the crystallin gene family. MG mimics important aspects of diabetic retinopathy and plays a pathogenic role in microglial activation, vascular damage, and neuroretinal dysfunction. In response to MG, the retina induces expression of neuroprotective crystallins.-Schlotterer, A., Kolibabka, M., Lin, J., Acunman, K., Dietrich, N., Sticht, C., Fleming, T., Nawroth, P., Hammes, H.-P. Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model.

Glyoxalase 1 gene is highly expressed in basal-like human breast cancers and contributes to survival of ALDH1-positive breast cancer stem cells

Glyoxalase 1 (GLO1) is a ubiquitous enzyme involved in the detoxification of methylglyoxal, a cytotoxic byproduct of glycolysis that induces apoptosis. In this study, we found that GLO1 gene expression correlates with neoplasm histologic grade (χ 2 test, p = 0.002) and is elevated in human basal-like breast cancer tissues. Approximately 90% of basal-like cancers were grade 3 tumors highly expressing both GLO1 and the cancer stem cell marker ALDH1A3. ALDH1high cells derived from the MDA-MB 157 and MDA-MB 468 human basal-like breast cancer cell lines showed elevated GLO1 activity. GLO1 inhibition using TLSC702 suppressed ALDH1high cell viability as well as the formation of tumor-spheres by ALDH1high cells. GLO1 knockdown using specific siRNAs also suppressed ALDH1high cell viability, and both TLSC702 and GLO1 siRNA induced apoptosis in ALDH1high cells. These results suggest GLO1 is essential for the survival of ALDH1-positive breast cancer stem cells. We therefore conclude that GLO1 is a potential therapeutic target for treatment of basal-like breast cancers.

Small molecule diketone flavorants diacetyl and 2,3-pentanedione promote neurotoxicity but inhibit amyloid β aggregation

We investigated the effects of the small molecule flavorants diacetyl, 2,3-pentanedione and acetoin on neuronal cell viability and β amyloid aggregation and morphology. Two neuroblastoma cell lines, SH-SY5Y and Neuro 2a (N2a) were exposed to diacetyl, 2,3-pentanedione and acetoin, while Thioflavin T fluorescence kinetics and transmission electron microscopy were used to assess effects on Aβ_1-42 fibril and aggregate formation and morphology respectively. Diacetyl was intrinsically toxic to both SH-SY5Y and N2a cells, with time and concentration-dependent reductions in cell viability occurring over 24 h and 48 h incubation periods. 2.3-Pentanedione evoked a similar concentration-dependent loss of cell viability in N2a cells at 48 h, but exhibited lessened toxicity in SH-SY5Y cells over 24 h, and minimal loss of cell viability by 48 h. Diacetyl inhibited Aβ_1-42 aggregation kinetics, reduced aggregate and fibril density and rendered Aβ_1-42 into amorphous small aggregates. 2,3-Pentanedione also reduced overall aggregate formation, but to a lesser extent than diacetyl and retaining the presence of a meshwork of Aβ_1-42 aggregates and fibrils. Acetoin was innocuous to neuronal cells and did not alter Aβ_1-42 fibril density or morphology. These findings highlight the intrinsic neurotoxicity of small molecule diketone flavorants. While providing further insight into their molecular interactions with amyloidogenic proteins, the neurotoxicity of such flavorants is a significant finding and warrants further investigation.

Discovery and Optimization of Inhibitors of the Parkinson's Disease Associated Protein DJ-1

DJ-1 is a Parkinson's disease associated protein endowed with enzymatic, redox sensing, regulatory, chaperoning, and neuroprotective activities. Although DJ-1 has been vigorously studied for the past decade and a half, its exact role in the progression of the disease remains uncertain. In addition, little is known about the spatiotemporal regulation of DJ-1, or the biochemical basis explaining its numerous biological functions. Progress has been hampered by the lack of inhibitors with precisely known mechanisms of action. Herein, we have employed biophysical methodologies and X-ray crystallography to identify and to optimize a family of compounds inactivating the critical Cys106 residue of human DJ-1. We demonstrate these compounds are potent inhibitors of various activities of DJ-1 in vitro and in cell-based assays. This study reports a new family of DJ-1 inhibitors with a defined mechanism of action, and contributes toward the understanding of the biological function of DJ-1.