Humoral methylglyoxal level reflects glycemic fluctuation

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

Type 2 Diabetes and Parkinson's Disease: A Focused Review of Current Concepts

Highly reproducible epidemiological evidence shows that type 2 diabetes (T2D) increases the risk and rate of progression of Parkinson's disease (PD), and crucially, the repurposing of certain antidiabetic medications for the treatment of PD has shown early promise in clinical trials, suggesting that the effects of T2D on PD pathogenesis may be modifiable. The high prevalence of T2D means that a significant proportion of patients with PD may benefit from personalized antidiabetic treatment approaches that also confer neuroprotective benefits. Therefore, there is an immediate need to better understand the mechanistic relation between these conditions and the specific molecular pathways affected by T2D in the brain. Although there is considerable evidence that processes such as insulin signaling, mitochondrial function, autophagy, and inflammation are involved in the pathogenesis of both PD and T2D, the primary aim of this review is to highlight the evidence showing that T2D-associated dysregulation of these pathways occurs not only in the periphery but also in the brain and how this may facilitate neurodegeneration in PD. We also discuss the challenges involved in disentangling the complex relationship between T2D, insulin resistance, and PD, as well as important questions for further research. © 2022 International Parkinson and Movement Disorder Society.

Modulation of 1,2-Dicarbonyl Compounds in Postprandial Responses Mediated by Food Bioactive Components and Mediterranean Diet

Glycoxidative stress with the consequent generation of advanced glycation end products has been implied in the etiology of numerous non-communicable chronic diseases. During the postprandial state, the levels of 1,2-dicarbonyl compounds can increase, depending on numerous factors, including characteristics of the subjects mainly related to glucose metabolism disorders and nutritional status, as well as properties related to the chemical composition of meals, including macronutrient composition and the presence of dietary bioactive molecules and macromolecules. In this review, we examine the chemical, biochemical, and physiological pathways that contribute to postprandial generation of 1,2-dicarbonyl compounds. The modulation of postprandial 1,2-dicarbonyl compounds is discussed in terms of biochemical pathways regulating the levels of these compounds, as well as the effect of phenolic compounds, dietary fiber, and dietary patterns, such as Mediterranean and Western diets.

Methylglyoxal Drives a Distinct, Nonclassical Macrophage Activation Status

Metabolic complications in diabetic patients are driven by a combination of increased levels of nutrients and the presence of a proinflammatory environment. Methylglyoxal (MG) is a toxic byproduct of catabolism and has been strongly associated with the development of such complications. Macrophages are key mediators of inflammatory processes and their contribution to the development of metabolic complications has been demonstrated. However, a direct link between reactive metabolites and macrophage activation has not been demonstrated yet. Here, we show that acute MG treatment activated components of the p38 MAPK pathway and enhanced glycolysis in primary murine macrophages. MG induced a distinct gene expression profile sharing similarities with classically activated proinflammatory macrophages as well as metabolically activated macrophages usually found in obese patients. Transcriptomic analysis revealed a set of 15 surface markers specifically upregulated in MG-treated macrophages, thereby establishing a new set of targets for diagnostic or therapeutic purposes under high MG conditions, including diabetes. Overall, our study defines a new polarization state of macrophages that may specifically link aberrant macrophage activation to reactive metabolites in diabetes.

Investigating the Glycating Effects of Glucose, Glyoxal and Methylglyoxal on Human Sperm

Glycation is the non-enzymatic reaction between reducing sugars, such as glucose, and proteins, lipids or nucleic acids, producing Advanced Glycation End (AGE) products. AGEs, produced during natural senescence as well as through lifestyle factors such as diet and smoking, are key pathogenic compounds in the initiation and progression of diabetes. Importantly, many of these factors and conditions also have influence on male fertility, affecting sperm count and semen quality, contributing to the decreasing trend in male fertility. This study investigated the impact of AGEs on sperm damage. In vitro sperm glycation assays were used to determine the levels and localization of the potent AGE compound, carboxymethyl-lysine (CML) in response to treatment with the glycating compounds glucose, glyoxal and methylglyoxal. Sperm function assays were then used to assess the effects of glycation on motility and hyaluronan binding, and levels of oxidative DNA damage were analyzed through measurement of the marker, 8-oxoguanine. Results showed that glyoxal, but not glucose or methylglyoxal, induced significant increases in CML levels on sperm and this correlated with an increase in 8-oxoguanine. Immunocytochemistry revealed that AGEs were located on all parts of the sperm cell and most prominently on the head region. Sperm motility and hyaluronidase activity were not adversely affected by glycation. Together, the observed detrimental effects of the increased levels of AGE on DNA integrity, without an effect on motility and hyaluronidase activity, suggest that sperm may retain some fertilizing capacity under these adverse conditions.

Deleterious Effect of Advanced CKD on Glyoxalase System Activity not Limited to Diabetes Aetiology

Methylglyoxal production is increased in diabetes. Methylglyoxal is efficiently detoxified by enzyme glyoxalase 1 (GLO1). The aim was to study the effect of diabetic and CKD milieu on (a) GLO1 gene expression in peripheral blood mononuclear cells; (b) GLO1 protein levels in whole blood; and (c) GLO1 activity in RBCs in vivo in diabetic vs. non-diabetic subjects with normal or slightly reduced vs. considerably reduced renal function (CKD1-2 vs. CKD3-4). A total of 83 subjects were included in the study. Gene expression was measured using real-time PCR, and protein levels were quantified using Western blotting. Erythrocyte GLO1 activity was measured spectrophotometrically. GLO1 gene expression was significantly higher in subjects with CKD1-2 compared to CKD3-4. GLO1 protein level was lower in diabetics than in non-diabetics. GLO1 activity in RBCs differed between the four groups being significantly higher in diabetics with CKD1-2 vs. healthy subjects and vs. nondiabeticsfig with CKD3-4. GLO1 activity was significantly higher in diabetics compared to nondiabetics. In conclusion, both diabetes and CKD affects the glyoxalase system. It appears that CKD in advanced stages has prevailing and suppressive effects compared to hyperglycaemia. CKD decreases GLO1 gene expression and protein levels (together with diabetes) without concomitant changes of GLO1 activity.

N-acetylcysteine attenuates systemic platelet activation and cerebral vessel thrombosis in diabetes

Objective

We previously demonstrated that diabetes exacerbates stroke-induced brain injury, and that this correlates with brain methylglyoxal (MG)-to-glutathione (GSH) status. Cerebral injury was reversed by N-acetylcysteine (NAC). Here we tested if the pro-thrombotic phenotype seen in the systemic circulation and brain during diabetes was associated with increased MG-glycation of proteins, and if NAC could reverse this.

Methods

The streptozotocin (STZ)-induced mouse model of type 1 diabetes was used. Thrombus formation in venules and arterioles (pial circulation) was determined by intravital videomicroscopy using the light-dye method. Circulating blood platelet-leukocyte aggregates (PLAs) were analyzed by flow cytometry 1 wk before other measurements. GSH and MG levels in platelets were measured by HPLC. MG-modified proteins, glutathione peroxidase-1 (GPx-1), and superoxide dismutase-1 (SOD1) levels were detected in platelets by western blot at 20 weeks. Proteins involved in coagulation were quantified by ELISA. NAC (2 mM) was given in drinking water for 3 weeks before the terminal experiment.

Results

Thrombus development was accelerated by diabetes in a time-dependent manner. % PLAs were significantly elevated by diabetes. Plasma activated plasminogen activator inhibitor type 1 levels were progressively increased with diabetes duration, with tail bleeding time reduced by 20 wks diabetes. Diabetes lowered platelet GSH levels, GPx-1 and SOD-1 expression. This was associated with higher MG levels, and increased MG-adduct formation in platelets. NAC treatment partly or completely reversed the effects of diabetes.

Conclusion

Collectively, these results show that the diabetic blood and brain become progressively more susceptible to platelet activation and thrombosis. NAC, given after the establishment of diabetes, may offer protection against the risk for stroke by altering both systemic and vascular prothrombotic responses via enhancing platelet GSH, and GSH-dependent MG elimination, as well as correcting levels of antioxidants such as SOD1 and GPx-1.

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Diabetes elevates dicarbonyl stress leading to enhanced thrombosis in the brain.

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Glutathione levels decrease leading to impaired elimination of methylglyoxal in platelets during diabetes.

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Platelet proteins are glycated and platelets form aggregates with leukocytes in diabetes.

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Diabetes increases circulating levels of plasminogen activator inhibitor-1.

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NAC, via GSH synthesis, reverses the platelet activation, protein glycation and pro-coagulation responses & protects against thrombosis in the diabetic brain.

Polydatin Prevents Methylglyoxal-Induced Apoptosis through Reducing Oxidative Stress and Improving Mitochondrial Function in Human Umbilical Vein Endothelial Cells

Methylglyoxal (MGO), an active metabolite of glucose, has been reported to induce vascular cell apoptosis in diabetic complication. Polydatin (PD), a small natural compound from Polygonum cuspidatum, has a number of biological functions, such as antioxidative, anti-inflammatory, and nephroprotective properties. However, the protective effects of PD on MGO-induced apoptosis in endothelial cells remain to be elucidated. In this study, human umbilical vein endothelial cells (HUVECs) were used to explore the effects of PD on MGO-induced cell apoptosis and the possible mechanism involved. HUVECs were pretreated with PD for 2 h, followed by stimulation with MGO. Then cell apoptosis, reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP) impairment, mitochondrial morphology alterations, and Akt phosphorylation were assessed. The results demonstrated that PD significantly prevented MGO-induced HUVEC apoptosis. PD pretreatment also significantly inhibited MGO-induced ROS production, MMP impairment, mitochondrial morphology changes, and Akt dephosphorylation. These results and the experiments involving N-acetyl cysteine (antioxidant), Cyclosporin A (mitochondrial protector), and LY294002 (Akt inhibitor) suggest that PD prevents MGO-induced HUVEC apoptosis, at least in part, through inhibiting oxidative stress, maintaining mitochondrial function, and activating Akt pathway. All of these data indicate the potential application of PD for the treatment of diabetic vascular complication.

AGEs induce ectopic endochondral ossification in intervertebral discs

Ectopic calcifications in intervertebral discs (IVDs) are known characteristics of IVD degeneration that are not commonly reported but may be implicated in structural failure and dysfunctional IVD cell metabolic responses. This study investigated the novel hypothesis that ectopic calcifications in the IVD are associated with advanced glycation end products (AGEs) via hypertrophy and osteogenic differentiation. Histological analyses of human IVDs from several degeneration stages revealed areas of ectopic calcification within the nucleus pulposus and at the cartilage endplate. These ectopic calcifications were associated with cells positive for the AGE methylglyoxal-hydroimidazolone-1 (MG-H1). MG-H1 was also co-localised with Collagen 10 (COL10) and Osteopontin (OPN) suggesting osteogenic differentiation. Bovine nucleus pulposus and cartilaginous endplate cells in cell culture demonstrated that 200 mg/mL AGEs in low-glucose media increased ectopic calcifications after 4 d in culture and significantly increased COL10 and OPN expression. The receptor for AGE (RAGE) was involved in this differentiation process since its inhibition reduced COL10 and OPN expression. We conclude that AGE accumulation is associated with endochondral ossification in IVDs and likely acts via the AGE/RAGE axis to induce hypertrophy and osteogenic differentiation in IVD cells. We postulate that this ectopic calcification may play an important role in accelerated IVD degeneration including the initiation of structural defects. Since orally administered AGE and RAGE inhibitors are available, future investigations on AGE/RAGE and endochondral ossification may be a promising direction for developing non-invasive treatment against progression of IVD degeneration.

The protection conferred against ischemia-reperfusion injury in the diabetic brain by N-acetylcysteine is associated with decreased dicarbonyl stress

Diabetes, a risk factor for stroke, leads to elevated blood methylglyoxal (MG) levels. This is due to increased MG generation from the high glucose levels, and because diabetes impairs the glutathione (GSH)-glyoxalase system for MG elimination. MG glycates proteins and causes dicarbonyl stress. We investigated the contribution of MG and GSH to stroke outcome. Cerebral ischemia/reperfusion was performed in chemical-induced (streptozotocin) and genetic Akita mouse models of Type 1 diabetes. Brain infarction and functions of the GSH-dependent MG elimination pathway were determined. Diabetes increased post-ischemia-reperfusion cerebral infarct area in association with elevated MG and diminished GSH levels. Infarct size correlated with brain MG-to-GSH ratio. Expression of glutamate-cysteine ligase catalytic subunit (GCLc) was increased in diabetic brain. GCL activity was unchanged. MG-adducts were elevated in the diabetic brain and, using immunoprecipitation, we identified one of the bands as glycated occludin. This was accompanied by increased blood-brain barrier permeability. Total protein carbonyls were elevated, indicative of oxidative/carbonyl stress. N-acetylcysteine (NAC) corrected MG-to-GSH ratio, and reduced diabetic brain infarct area, occludin glycation and permeability. In addition, protein carbonyls were decreased by NAC. We showed that the diabetic brain exhibited a lower GSH-dependent potential for MG elimination, which contributed to increased protein glycation, and oxidative/carbonyl stress. The consequence of these changes was aggravated post-stroke brain injury. NAC administration protected against the exacerbated brain damage via restored GSH generation and normalization of the MG-to-GSH ratio and possibly by attenuating oxidative/carbonyl stress. This treatment could contribute to the successful management of stroke risk/outcome in diabetes.

Aldehyde inhibition of antioxidant enzymes in the blood of diabetic patients

BACKGROUND

The aim of the present study was to examine the effect of aldehyde modification on antioxidant enzyme activity in diabetic patients.

METHODS

The activity of commercially available antioxidant enzymes (catalase, glutathione peroxidase [GPx], and Cu,Zn-superoxide dismutase [SOD]) was determined in vitro prior to and after aldehyde modification. The activity of erythrocyte Cu,Zn-SOD was assayed in blood drawn from healthy donors, diabetic patients with decompensated carbohydrate metabolism, and diabetic patients after glucose-lowering therapy.

RESULTS

In vitro aldehyde modification had no effect on catalase activity, but diminished GPx and Cu,Zn-SOD activity. In diabetic patients with decompensated carbohydrate metabolism, glucose-lowering therapy significantly increased Cu,Zn-SOD activity, the effect being especially pronounced after administration of metformin.

CONCLUSIONS

It is likely that metformin antagonizes the aldehyde-induced inhibition of erythrocyte Cu,Zn-SOD in diabetic patients more effectively than sulfonylurea drugs.

Chronic ingestion of advanced glycation end products induces degenerative spinal changes and hypertrophy in aging pre-diabetic mice

Intervertebral disc (IVD) degeneration and pathological spinal changes are major causes of back pain, which is the top cause of global disability. Obese and diabetic individuals are at increased risk for back pain and musculoskeletal complications. Modern diets contain high levels of advanced glycation end products (AGEs), cyto-toxic components which are known contributors to obesity, diabetes and accelerated aging pathologies. There is little information about potential effects of AGE rich diet on spinal pathology, which may be a contributing cause for back pain which is common in obese and diabetic individuals. This study investigated the role of specific AGE precursors (e.g. methylglyoxal-derivatives (MG)) on IVD and vertebral pathologies in aging C57BL6 mice that were fed isocaloric diets with standard (dMG+) or reduced amounts of MG derivatives (dMG-; containing 60-70% less dMG). dMG+ mice exhibited a pre-diabetic phenotype, as they were insulin resistant but not hyperglycemic. Vertebrae of dMG+ mice displayed increased cortical-thickness and cortical-area, greater MG-AGE accumulation and ectopic calcification in vertebral endplates. IVD morphology of dMG+ mice exhibited ectopic calcification, hypertrophic differentiation and glycosaminoglycan loss relative to dMG- mice. Overall, chronic exposure to dietary AGEs promoted age-accelerated IVD degeneration and vertebral alterations involving ectopic calcification which occurred in parallel with insulin resistance, and which were prevented with dMG- diet. This study described a new mouse model for diet-induced spinal degeneration, and results were in support of the hypothesis that chronic AGE ingestion could be a factor contributing to a pre-diabetic state, ectopic calcifications in spinal tissues, and musculoskeletal complications that are more generally known to occur with chronic diabetic conditions.

Increased plasma levels of the methylglyoxal in patients with newly diagnosed type 2 diabetes 2

BACKGROUND

Methylglyoxal (MG) is a reactive-dicarbonyl that is thought to contribute to the development of diabetes either as a precursor for advanced glycation end products or as a direct toxin. The present study was designed to determine plasma MG level in patients with newly diagnosed type 2 diabetes mellitus (T2DM) and to evaluate the relationship between MG and other parameters, such as oxidative stress and metabolic indices.

METHODS

Methylglyoxal was measured by high-performance liquid chromatographic/tandem mass spectrometry in plasma from 48 subjects with newly diagnosed T2DM. The relationship between two variables was analyzed using Spearman's correlation analysis. Multiple stepwise linear regression analysis was used to assess the association of plasma MG and other parameters.

RESULTS

Plasma MG level in patients with newly diagnosed T2DM (65.2 ± 19.2 ng/mL) were significantly higher than that in control individuals (40.1 ± 11.1 ng/mL, P < 0.05). The plasma level of MG was positively correlated with the glycosylated hemoglobin A1c (HbA1c, r = 0.670, P < 0.01) and malondialdehyde (MDA, r = 0.694, P < 0.01). Multiple linear regression analysis revealed that both HbA1c and MDA are significant independent determinants of plasma MG level.

CONCLUSIONS

These findings suggest that increased plasma MG level is associated with the elevation of HbA1c and MDA in newly diagnosed T2DM patients.

Measurement of methylglyoxal by stable isotopic dilution analysis LC-MS/MS with corroborative prediction in physiological samples

This protocol describes a method for the detection and quantification of methylglyoxal (MG), the major physiological substrate of the cytosolic glyoxalase system. Accumulation of MG, also called dicarbonyl stress, is implicated in tissue damage in aging and disease. Measurement of MG is important in physiological studies, in the development of glyoxalase 1 (Glo1) inducer and inhibitor therapeutics, and in the characterization of medical products, especially dialysis fluids, and of thermally processed foods and beverages. MG can be derivatized with 1,2-diaminobenzene (DB), resulting in an adduct that can be detected using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Quantification is achieved by stable isotopic dilution analysis with [(13)C3]MG. Pre-analytic processing at ambient temperature, under acidic conditions with peroxidase inhibition, avoids artifactual overestimation of MG. Estimates obtained from physiological samples can be validated by kinetic modeling of in situ rates of protein glycation by MG for confirmation of the results. This procedure was developed for the analysis of cultured cells, plasma and animal tissue samples, and it can also be used to analyze plant material. Experimental measurement requires 4.5 h for sample batch pre-analytic processing and 30 min per sample for LC-MS/MS analysis.

Two α-dicarbonyls downregulate migration, invasion, and adhesion of liver cancer cells in a p53-dependent manner

BACKGROUND

Hepatocellular carcinoma accounts for more than 600,000 deaths per year due to it being a highly invasive tumor. The α-dicarbonyl, methylglyoxal demonstrates efficacy at reducing tumor burden, however the anti-cancerous activities of 3-deoxyglucosone, have never been studied.

AIMS

To determine the anti-cancerous potential of methylglyoxal and 3-deoxyglucosone on liver tumor cells.

METHODS

The in vitro effects of methylglyoxal and 3-deoxyglucosone were studied by investigating migration, invasion, and adhesion of Huh-7, HepG2, and Hep3B cells.

RESULTS

3-Deoxyglucosone inhibited migration of Huh-7 and HepG2 cells. Methylglyoxal decreased migration of HepG2 cells. Additionally, 3-deoxyglucosone and methylglyoxal impaired invasion, and adhesion of Huh-7 and HepG2 cells. In Hep3B cells, a p53 null cell line, 3-deoxyglucosone and methylglyoxal had no effect on migration, invasion, or adhesion. However, both compounds inhibited invasion of wild-type p53 transfected Hep3B cells. Silencing of p53 in Huh-7 and HepG2 cells abrogated the effects of the α-dicarbonyls on cell invasion. 3DG and MG did not alter p53 total protein but promoted nuclear translocation of p53.

CONCLUSIONS

These studies suggest that 3-deoxyglucosone and methylglyoxal impair invasion, migration, and adhesion of hepatocellular carcinoma. The effects of both compounds on cell invasion are dependent on p53 and imply that α-dicarbonyls could be efficacious in the treatment of p53-expressing invasive liver tumors.

Methylglyoxal induces platelet hyperaggregation and reduces thrombus stability by activating PKC and inhibiting PI3K/Akt pathway

Diabetes is characterized by a dysregulation of glucose homeostasis and platelets from patients with diabetes are known to be hyper-reactive and contribute to the accelerated development of vascular diseases. Since many of the deleterious effects of glucose have been attributed to its metabolite methylgyloxal (MG) rather than to hyperglycemia itself, the aim of the present study was to characterize the effects of MG on platelet function. Washed human platelets were pre-incubated for 15 min with MG and platelet aggregation, adhesion on matrix-coated slides and signaling (Western blot) were assessed ex vivo. In vivo, the effect of MG on thrombus formation was determined using the FeCl₃-induced carotid artery injury model. MG potentiated thrombin-induced platelet aggregation and dense granule release, but inhibited platelet spreading on fibronectin and collagen. In vivo, MG accelerated thrombus formation but decreased thrombus stability. At the molecular level, MG increased intracellular Ca²⁺ and activated classical PKCs at the same time as inhibiting PI3K/Akt and the β3-integrin outside-in signaling. In conclusion, these findings indicate that the enhanced MG concentration measured in diabetic patients can directly contribute to the platelet dysfunction associated with diabetes characterized by hyperaggregability and reduced thrombus stability.

Kinetic and isotopic characterization of L-proline dehydrogenase from Mycobacterium tuberculosis

The monofunctional proline dehydrogenase (ProDH) from Mycobacterium tuberculosis performs the flavin-dependent oxidation of l-proline to Δ(1)-pyrroline-5-carboxylate in the proline catabolic pathway. The ProDH gene, prub, was cloned into the pYUB1062 vector, and the C-terminal His-tagged 37 kDa protein was expressed and purified by nickel affinity chromatography. A steady-state kinetic analysis revealed a ping-pong mechanism with an overall kcat of 33 ± 2 s(-1) and Km values of 5.7 ± 0.8 mM and 3.4 ± 0.3 μM for l-proline and 2,6-dichlorophenolindophenol (DCPIP), respectively. The pH dependence of kcat revealed that one enzyme group exhibiting a pK value of 6.8 must be deprotonated for optimal catalytic activity. Site-directed mutagenesis suggests that this group is Lys110. The primary kinetic isotope effects on V/KPro and V of 5.5 and 1.1, respectively, suggest that the transfer of hydride from l-proline to FAD is rate-limiting for the reductive half-reaction, but that FAD reoxidation is the rate-limiting step in the overall reaction. Solvent and multiple kinetic isotope effects suggest that l-proline oxidation occurs in a stepwise rather than concerted mechanism. Pre-steady-state kinetics reveal an overall kred of 88.5 ± 0.7 s(-1), and this rate is subject to a primary kinetic isotope effect of 5.2. These data confirm that the overall reaction is limited by reduced flavin reoxidation in the second half-reaction.

Combined anti-inflammatory and anti-AGE drug treatments have a protective effect on intervertebral discs in mice with diabetes

Objective

Diabetes and low back pain are debilitating diseases and modern epidemics. Diabetes and obesity are also highly correlated with intervertebral disc (IVD) degeneration and back pain. Advanced-glycation-end-products (AGEs) increase reactive-oxygen-species (ROS) and inflammation, and are one cause for early development of diabetes mellitus. We hypothesize that diabetes results in accumulation of AGEs in spines and associated spinal pathology via increased catabolism. We present a mouse model showing that: 1) diabetes induces pathological changes to structure and composition of IVDs and vertebrae; 2) diabetes is associated with accumulation of AGEs, TNFα, and increased catabolism spinal structures; and 3) oral-treatments with a combination of anti-inflammatory and anti-AGE drugs mitigate these diabetes-induced degenerative changes to the spine.

Methods

Three age-matched groups of ROP-Os mice were compared: non-diabetic, diabetic (streptozotocin (STZ)-induced), or diabetic mice treated with pentosan-polysulfate (anti-inflammatory) and pyridoxamine (AGE-inhibitor). Mice were euthanized and vertebra-IVD segments were analyzed by μCT, histology and Immunohistochemistry.

Results

Diabetic mice exhibited several pathological changes including loss in IVD height, decreased vertebral bone mass, decreased glycosaminoglycan content and morphologically altered IVDs with focal deposition of tissues highly expressing TNFα, MMP-13 and ADAMTS-5. Accumulation of larger amounts of methylglyoxal suggested that AGE accumulation was associated with these diabetic degenerative changes. However, treatment prevented or reduced these pathological effects on vertebrae and IVD.

Conclusion

This is the first study to demonstrate specific degenerative changes to nucleus pulposus (NP) morphology and their association with AGE accumulation in a diabetic mouse model. Furthermore, this is the first study to demonstrate that oral-treatments can inhibit AGE-induced ROS and inflammation in spinal structures and provide a potential treatment to slow progression of degenerative spine changes in diabetes. Since diabetes, IVD degeneration, and accumulation of AGEs are frequent consequences of aging, early treatments to reduce AGE-induced ROS and Inflammation may have broad public-health implications.

[The influence of natural dicarbonils on the antioxidant enzymes activity in vitro and in vivo]

Natural dicarbonyls, which may be accumulated during oxidative stress in atherosclerosis (e.g. malondialdehyde) or carbonyl stress in diabetes mellitus (glyoxal and methylglyoxal) effectively inhibited the activities of commercial preparations of antioxidant enzymes: catalase, Cu, Zn-superoxide dismutase (Cu, Zn-SOD) and Se-contained glutathione peroxidase from human and bovine erythrocytes and also rat liver glutathione-S-transferase. After incubation of human erythrocytes with 10 mM of each investigated dicarbonyls the decrease of intracellular Cu, Zn-SOD was observed. The decreased activity of erythrocyte Cu, Zn-SOD was also detected in diabetic patients with carbohydrate metabolism disturbance but effective sugar-lowered therapy was accompanied by the increase of this enzyme activity. The increase of erythrocytes activity of Cu, Zn-SOD of diabetic patients theated with metformin (which may utilize methylglyoxal) was higher than in erythrocytase of diabetic patients subjected to traditional therapy.

Where does plasma methylglyoxal originate from?

The elevation of plasma methylglyoxal levels in diabetic humans is widely observed, but it is unknown to what extent different sources of methylglyoxal contribute to its plasma concentration. A retrospective analysis of clinical findings has been undertaken. There is controversy about the correlation of plasma methylglyoxal concentrations with fasting or postprandial glucose levels, and the relationship with HbA1c. There is only one study in which plasma ketone body levels have been monitored in parallel with methylglyoxal and a positive correlation between plasma methylglyoxal and β-hydroxybutyrate was observed. There are no reports on plasma aminoacetone levels and methylglyoxal in diabetic humans. This paper suggests that although there is a close association between methylglyoxal and carbohydrate metabolism, the presence of this 1,2-dicarbonyl in the plasma is mainly due to other mechanisms. Protein glycation and aminoacetone degradation are proposed to be the major and the minor sources of plasma methylglyoxal under normal conditions.

Chromatographic determination of methyl glyoxal in blood plasma as the test for glycotoxicity and accumulation of glycation end-products

We developed a method of measuring methyl glyoxal concentration in blood serum using HPLC with UV detection. Methyl glyoxal concentration was determined in healthy subjects. The method was developed for indirect but reliable measurement of the levels of glycation end-products in patients with diabetes, hyperlipidemia, and cardiovascular pathologies.

Non-diabetic hyperglycemia exacerbates disease severity in Mycobacterium tuberculosis infected guinea pigs

Hyperglycemia, the diagnostic feature of diabetes also occurs in non-diabetics associated with chronic inflammation and systemic insulin resistance. Since the increased risk of active TB in diabetics has been linked to the severity and duration of hyperglycemia, we investigated what effect diet-induced hyperglycemia had on the severity of Mycobacterium tuberculosis (Mtb) infection in non-diabetic guinea pigs. Post-prandial hyperglycemia was induced in guinea pigs on normal chow by feeding a 40% sucrose solution daily or water as a carrier control. Sucrose feeding was initiated on the day of aerosol exposure to the H37Rv strain of Mtb and continued for 30 or 60 days of infection. Despite more severe hyperglycemia in sucrose-fed animals on day 30, there was no significant difference in lung bacterial or lesion burden until day 60. However the higher spleen and lymph node bacterial and lesion burden at day 30 indicated earlier and more severe extrapulmonary TB in sucrose-fed animals. In both sucrose- and water-fed animals, serum free fatty acids, important mediators of insulin resistance, were increased by day 30 and remained elevated until day 60 of infection. Hyperglycemia mediated by Mtb infection resulted in accumulation of advanced glycation end products (AGEs) in lung granulomas, which was exacerbated by sucrose feeding. However, tissue and serum AGEs were elevated in both sucrose and water-fed guinea pigs by day 60. These data indicate that Mtb infection alone induces insulin resistance and chronic hyperglycemia, which is exacerbated by sucrose feeding. Moreover, Mtb infection alone resulted in the accumulation tissue and serum AGEs, which are also central to the pathogenesis of diabetes and diabetic complications. The exacerbation of insulin resistance and hyperglycemia by Mtb infection alone may explain why TB is more severe in diabetics with poorly controlled hyperglycemia compared to non-diabetics and patients with properly controlled blood glucose levels.

Methylglyoxal activates nociceptors through transient receptor potential channel A1 (TRPA1): a possible mechanism of metabolic neuropathies

Neuropathic pain can develop as an agonizing sequela of diabetes mellitus and chronic uremia. A chemical link between both conditions of altered metabolism is the highly reactive compound methylglyoxal (MG), which accumulates in all cells, in particular neurons, and leaks into plasma as an index of the severity of the disorder. The electrophilic structure of this cytotoxic ketoaldehyde suggests TRPA1, a receptor channel deeply involved in inflammatory and neuropathic pain, as a molecular target. We demonstrate that extracellularly applied MG accesses specific intracellular binding sites of TRPA1, activating inward currents and calcium influx in transfected cells and sensory neurons, slowing conduction velocity in unmyelinated peripheral nerve fibers, and stimulating release of proinflammatory neuropeptides from and action potential firing in cutaneous nociceptors. Using a model peptide of the N terminus of human TRPA1, we demonstrate the formation of disulfide bonds based on MG-induced modification of cysteines as a novel mechanism. In conclusion, MG is proposed to be a candidate metabolite that causes neuropathic pain in metabolic disorders and thus is a promising target for medicinal chemistry.

Postprandial impairment of flow-mediated dilation and elevated methylglyoxal after simple but not complex carbohydrate consumption in dogs

Hyperglycemia produces oxidative stress, which may impair endothelial function. Methylglyoxal, a reactive intermediate metabolite of glucose, is known to cause oxidative stress and is produced when excess carbohydrate is consumed in diabetic patients, but postprandial responses in healthy patients are unknown. We hypothesize that methylglyoxal levels will cause impaired endothelial function via increased oxidative stress after consuming a high glycemic index meal in healthy animals. Normal-weight laboratory beagles (n = 6) were used in a crossover study that tested postprandial responses of 4 complex carbohydrate sources (barley, corn, peas, rice) vs a simple carbohydrate (glucose). Blood samples were taken prefeeding and at timed intervals after feeding to measure serum glucose, insulin, nitrotyrosine, and methylglyoxal. Flow-mediated dilation (FMD), cardiac function (echocardiography), and blood pressure measurements were determined before and 60 minutes after feeding. The mean (±SEM) glycemic indices of the complex carbohydrate sources were 29 ± 5 for peas, 47 ± 10 for corn, 51 ± 7 for barley, and 55 ± 6 for rice. Postprandial FMD was lowest in the glucose group and significantly different from both the corn group and the FMD value for all complex carbohydrates combined. Methylglyoxal was significantly elevated at 60 minutes postprandial after glucose compared with the other carbohydrate sources. No significant effects of carbohydrate source were observed for blood pressure, nitrotyrosine, or echocardiographic variables. The novel finding of this study was that methylglyoxal levels increased after a single feeding of simple carbohydrate and may be linked to the observed postprandial decrease in endothelial function. Thus, consuming low-glycemic-index foods may protect the cardiovascular system by reducing oxidative stress.

V, Patócs A, Lichthammer A, Veresné Bálint M, Rácz K, Reismann P. The role of methylglyoxal metabolism in type-2 diabetes and its complications

Transient or chronic hyperglycaemia increases the formation of intracellular reactive oxygen species and aldehydes. The accumulation of reactive aldehydes is implicated in the development of diabetic complications. Methylglyoxal, a glucose dependent α-dicarbonyl might be the most important reactive aldehyde in diabetes and its complications. Diabetes was the first disease in which evidence emerged for the increased formation of methylglyoxal in the cells and in the serum. Methylglyoxal has a toxic effect on insulin secretion from pancreatic beta-cells, and on modifications of proteins and nucleic acids. Moreover, methylglyoxal is one of the major precursors of advanced glycation end-products. The glyoxalase enzyme system that exists in all mammalian cells is catalyzing the detoxification of methylglyoxal. This review summarizes the methylglyoxal metabolism in normoglycaemic and hyperglycamic conditions and the role of methylglyoxal in the development of late diabetic microvascular complications. Orv. Hetil., 2012, 153, 574–585.

Relationship of methylglyoxal-adduct biogenesis to LDL and triglyceride levels in diabetics

AIMS

Protein glycation leading to advanced glycation-endproducts (AGE) is enhanced in diabetes by increased blood glucose and collateral endogenous production of reactive α-dicarbonyls. Among AGE precursors, methylglyoxal (MG) is considered as one of the key intermediates. We hypothesized it to be a common product of both carbonyl and oxidative stress, and investigated its biogenesis in relation to glycemic and lipid status in diabetic patients.

METHODS

Serum and urine MG-adducts were measured by competitive immunofluorometric assay in 83 diabetic and 20 healthy subjects.

KEY FINDINGS

A significant association of MG-adducts serum level with LDL (r=0.31;p=0.003) was observed. A correlation between LDL-c, HDL-C and PPG as independent variables and serum MG-adducts as a dependent variable was found (p<0.014) using multiple stepwise regression, whereas urine albumin/creatinine ratio was independently associated with urine MG-adducts. LDL cut-off >3.0mmol/l discriminated patients with higher serum MG-adducts (p=0.0052), although there was no between-subgroup difference in glycemic control. Patients on statin therapy had a lower MG-adduct level. The positive relationship between LDL-c and MG-adducts (r=0.38;p=0.042) was noted in patients free of statin treatment, whereas an inverse tendency was found in the statin-treated subgroup.

SIGNIFICANCE

Significant relationship between LDL and MG-adduct production, as well as tight correlation between triglycerides and urinary MG-adduct excretion suggest that the lipoxidation and glyceraldehyde-3-phosphate route, along with the glycolytic pathway, might be an important source of MG generation. The glycotoxin methylglyoxal seems to be a common factor linking hyperglycemia and intensive lipolysis, two dominant metabolic changes in diabetes.

Characterisation of glyoxalase I in a streptozocin-induced mouse model of diabetes with painful and insensate neuropathy

AIMS/HYPOTHESIS

Diabetic peripheral neuropathy (DN) is a common complication of diabetes; however, the mechanisms producing positive or negative symptoms are not well understood. The enzyme glyoxalase I (GLO1) detoxifies reactive dicarbonyls that form AGEs and may affect the way sensory neurons respond to heightened AGE levels in DN. We hypothesised that differential GLO1 levels in sensory neurons may lead to differences in AGE formation and modulate the phenotype of DN.

METHODS

Inbred strains of mice were used to assess the variability of Glo1 expression by quantitative RT-PCR. Non-diabetic C57BL/6 mice were used to characterise the distribution of GLO1 in neural tissues by immunofluorescence. Behavioural assessments were conducted in diabetic A/J and C57BL/6 mice to determine mechanical sensitivity, and GLO1 abundance was determined by western blot.

RESULTS

GLO1 immunoreactivity was found throughout the nervous system, but selectively in small, unmyelinated peptidergic dorsal root ganglia (DRG) neurons that are involved in pain transmission. GLO1 protein was present at various levels in DRG from different inbred mice strains. Diabetic A/J and C57BL/6 mice, two mouse strains with different levels of GLO1, displayed dramatically different behavioural responses to mechanical stimuli. Diabetic C57BL/6 mice also had a reduced abundance of GLO1 following diabetes induction.

CONCLUSIONS/INTERPRETATION

These findings reveal that the abundance of GLO1 varies between different murine strains and within different sensory neuron populations. These differences could lead to different responses of sensory neurons to the toxic effects of hyperglycaemia and reactive dicarbonyls associated with diabetes.

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.

Critical evaluation of toxic versus beneficial effects of methylglyoxal

In various organisms, an array of enzymes is involved in the synthesis and breakdown of methylglyoxal. Through these enzymes, it is intimately linked to several other physiologically important metabolites, suggesting that methylglyoxal has some important role to play in the host organism. Several in vitro and in vivo studies showed that methylglyoxal acts specifically against different types of malignant cells. These studies culminated in a recent investigation to evaluate a methylglyoxal-based formulation in treating a small group of cancer patients, and the results were promising. Methylglyoxal acts against a number of pathogenic microorganisms. However, recent literature abounds with the toxic effects of methylglyoxal, which are supposed to be mediated through methylglyoxal-derived advanced glycation end products (AGE). Many diseases such as diabetes, cataract formation, hypertension, and uremia are proposed to be intimately linked with methylglyoxal-derived AGE. However methylglyoxal-derived AGE formation and subsequent pathogenesis might be a very minor event because AGE are nonspecific reaction products that are derived through the reactions of carbonyl groups of reducing sugars with amino groups present in the side chains of lysine and arginine and in terminal amino groups of proteins. Moreover, the results of some in vitro experiments with methylglyoxal under non-physiological conditions were extrapolated to the in vivo situation. Some experiments even showed contradictory results and were differently interpreted. For this reason conclusions about the potential beneficial effects of methylglyoxal have often been neglected, thus hindering the advancement of medical science and causing some confusion in fundamental understanding. Overall, the potential beneficial effects of methylglyoxal far outweigh its possible toxic role in vivo, and it should be utilized for the benefit of suffering humanity.

Advanced glycation end-products activate extracellular signal-regulated kinase via the oxidative stress-EGF receptor pathway in renal fibroblasts

Advanced glycation end-products (AGEs), epidermal growth factor receptor (EGFR), reactive oxygen species (ROS), and extracellular signal-regulated kinases (ERK) are implicated in diabetic nephropathy (DN). Therefore, we asked if AGEs-induced ERK protein phosphorylation and mitogenesis are dependent on the receptor for AGEs (RAGE)-ROS-EGFR pathway in normal rat kidney interstitial fibroblast (NRK-49F) cells. We found that AGEs (100 microg/ml) activated EGFR and ERK1/2, which was attenuated by RAGE short-hairpin RNA (shRNA). AGEs also increased RAGE protein and intracellular ROS levels while RAGE shRNA and N-acetylcysteine (NAC) attenuated AGEs-induced intracellular ROS. Hydrogen peroxide (5-25 microM) increased RAGE protein level while activating both EGFR and ERK1/2. Low-dose hydrogen peroxide (5 microM) increased whereas high-dose hydrogen peroxide (100 microM) decreased mitogenesis at 3 days. AGEs-activated EGFR and ERK1/2 were attenuated by an anti-oxidant (NAC) and an EGFR inhibitor (Iressa). Moreover, AGEs-induced mitogenesis was attenuated by RAGE shRNA, NAC, Iressa, and an ERK1/2 inhibitor (PD98059). In conclusion, it was found that AGEs-induced mitogenesis is dependent on the RAGE-ROS-EGFR-ERK1/2 pathway whereas AGEs-activated ERK1/2 is dependent on the RAGE-ROS-EGFR pathway in NRK-49F cells.

Dietary soy isoflavones increase insulin secretion and prevent the development of diabetic cataracts in streptozotocin-induced diabetic rats

Soy isoflavone-containing diets have been reported to be beneficial in diabetes. This present study investigated the hypoglycemic effects of isoflavones in streptozotocin (STZ)-induced diabetes. Diabetes was induced in male Sprague-Dawley rats by intraperitoneal injection of 100 mg/kg STZ. Diabetic rats were then randomly divided into 3 groups and received a special diet supplemented with casein (control), low-isoflavone soy (LIS) protein, and high-isoflavone soy protein (HIS) for 8 weeks. Compared with the control or LIS groups, those rats on the HIS diet had significantly increased body weight and serum insulin levels and reduced serum glucose and methylglyoxal levels. Serum glutathione levels were also increased in rats given the HIS diet compared with those in the control or LIS (P < .01). Serum high-density lipoprotein cholesterol level was significantly higher in HIS-fed rats than that of the control or LIS rats (P < .05). More importantly, the death rate and incidence of cataracts in the diabetic rats were markedly decreased in the HIS group. In conclusion, ingestion of high-isoflavone soy protein not only lowers glucose levels but also reduces the incidence of cataracts in diabetic rats. The beneficial effects of soy isoflavones are attributed to increased insulin secretion, a better glycemic control, and antioxidant protection.

Modulation of methylglyoxal and glutathione by soybean isoflavones in mild streptozotocin-induced diabetic rats

BACKGROUND AND AIMS

Evidence shows that methylglyoxal (MG), a very reactive metabolite of glucose, plays a critical role in the pathogenesis of diabetes and diabetic complications. Although soy isoflavones have beneficial effects in diabetes, the role of soy isoflavones in regulating MG levels is unknown. The present study investigates the effects of soy protein isoflavones on MG and reduced glutathione (GSH).

METHODS AND RESULTS

Mild diabetes was induced in male Sprague-Dawley rats by intraperitoneal injection of 35 mg/kg streptozotocin (STZ). The diabetic rats were then randomly divided into three groups and received a special diet supplemented with casein (control), low-isoflavone soy protein (LIS), or high-isoflavone soy protein (HIS) for eight weeks, respectively. Compared to the control or LIS group, HIS diet significantly increased serum insulin levels (p<0.01 or 0.05) and reduced serum glucose and MG levels (p<0.05). Serum GSH levels were increased in HIS-fed rats compared with the control or LIS group (p<0.01). Serum total cholesterol and homocysteine levels were significantly lower in HIS and LIS rats than those of the control rats.

CONCLUSIONS

Both LIS and HIS diets can lower serum lipid and homocysteine levels in this mild diabetic model. HIS diet enhances insulin secretion and reduces glucose level. Moreover, the HIS diet has potential in reducing MG and increasing GSH levels. In addition to its hypoglycemic effect, the antioxidant protection may provide beneficial effects in preventing the development of diabetic complications.

A brief critical overview of the biological effects of methylglyoxal and further evaluation of a methylglyoxal-based anticancer formulation in treating cancer patients

A historical perspective on methylglyoxal research is briefly presented, mentioning the documented anticancer and antiviral effects of methylglyoxal. The idea and the supporting experimental evidence of Albert Szent-Györgyi et al. that methylglyoxal is a natural growth regulator and can act as an anticancer agent are mentioned. Previously a few in vivo studies suggested safe administration of methylglyoxal. However, recent literature abounds with the toxic effects of methylglyoxal. The authors present a brief critical overview of studies indicating both toxic and beneficial effects of methylglyoxal and suggest that the beneficial effects of methylglyoxal outweigh its toxic effects. Encouraged by the studies of Szent-Györgyi et al., the present authors undertook systematic investigations to understand the mechanism of the anticancer effect of methylglyoxal. The results of these investigations led to the proposal that the fundamental changes in malignant cells are critical alterations of glyceraldehyde-3-phosphate dehydrogenase and mitochondrial complex I, and methylglyoxal's anticancer effect might be mediated by acting on these altered sites. Moreover, a new hypothesis on cancer has been proposed, suggesting that excessive ATP formation in cells may lead to malignancy. Toxicity and pharmacokinetic studies were performed on animals and it was observed that methylglyoxal is potentially safe for humans. A methylglyoxal-based anticancer formulation was developed and a three-phase study of treating a total number of 86 cancer patients was carried out. The results appear to be promising. Most of the cancer patients benefited greatly and a significant number of patients became free of the disease. Contrary to the effect of existing anticancer drugs, this methylglyoxal-based formulation is devoid of any toxic effect and reasonably effective against a wide variety of cancers. The symptomatic improvements of the many patients who died of progressive disease suggest that the formulation could also be used for palliation. The authors urge the scientific community to test the formulation and if found effective then to improve it further.

Aging skin is functionally anaerobic: importance of coenzyme Q10 for anti aging skin care

The functional loss of mitochondria represents an inherent part in modern theories trying to explain the cutaneous aging process. The present study shows significant age-dependent differences in mitochondrial function of keratinocytes isolated from skin biopsies of young and old donors. Our data let us postulate that energy metabolism shifts to a predominantly non-mitochondrial pathway and is therefore functionally anaerobic with advancing age. CoQ10 positively influences the age-affected cellular metabolism and enables to combat signs of aging starting at the cellular level. As a consequence topical application of CoQ10 is beneficial for human skin as it rapidly improves mitochondrial function in skin in vivo.

Effect of biphasic insulin aspart on glucose and lipid control in patients with Type 2 diabetes mellitus

OBJECTIVE

This study examined the efficacy and safety of biphasic insulin aspart 30 (BIAsp 30) monotherapy in insulin-naive patients with Type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

In this 12-week, open-labelled, uncontrolled, clinical-experience study involving 71 patients with secondary oral antidiabetic agent failure, patients received BIAsp 30 after discontinuing oral antidiabetic drugs (OADs). Glucose and lipid concentrations, hypoglycaemic episodes and adverse events were assessed before and after treatment. Patient data were categorised according to previous OADs into the biguanides (BI) plus sulfonylureas/meglitinides (SU/MEG) and SU-only groups.

RESULTS

After treatment, glucose and lipid control was significantly improved in both groups, with a greater improvement in the SU-only group. Mean glycated haemoglobin, fasting blood glucose and postprandial blood glucose excursion improved by 2.15 +/- 1.24%, 3.70 +/- 3.18 mmol/l and 1.26 +/- 2.65 mmol/l in the BI plus SU/MEG group, and by 3.09 +/- 1.62%, 6.11 +/- 5.02 mmol/l and 2.06 +/- 2.33 mmol/l in the SU-only group, respectively. Mean high-density lipoprotein cholesterol and triglycerides improved by 0.09 +/- 0.18 mmol/l and 0.94 +/- 1.17 mmol/l in the BI plus SU/MEG group and by 0.09 +/- 0.18 mmol/l and 1.04 +/- 2.72 mmol/l in the SU-only group, respectively. No major hypoglycaemic episodes or serious treatment-related adverse events were reported.

CONCLUSIONS

Our study showed that BIAsp 30 treatment safely improved glucose and lipid control in insulin-naive patients with Type 2 diabetes poorly controlled on BI plus SU/MEG and SU-only. Key limitations were the lack of a comparator group and the short study duration.

Plasma methylglyoxal and glyoxal are elevated and related to early membrane alteration in young, complication-free patients with Type 1 diabetes

The reactive aldehydes methylglyoxal and glyoxal, arise from enzymatic and non-enzymatic degradation of glucose, lipid and protein catabolism, and lipid peroxidation. In Type 1 diabetes mellitus (T1DM) where hyperglycemia, oxidative stress, and lipid peroxidation are common, these aldehydes may be elevated. These aldehydes form advanced glycation end products (AGEs) with proteins that are implicated in diabetic complications. We measured plasma methylglyoxal and glyoxal in young, complication-free T1DM patients and assessed activity of the ubiquitous membrane enzyme, Na+/K+ ATPase. A total of 56 patients with TIDM (DM group), 6-22 years, and 18 non-diabetics (ND group), 6-21 years, were enrolled. Mean plasma A1C (%) was higher in the DM group (8.5+/-1.3) as compared to the ND group (5.0+/-0.3). Using a novel liquid chromatography-mass spectrophotometry method, we found that mean plasma methylglyoxal (nmol/l) and glyoxal levels (nmol/l), respectively, were higher in the DM group (841.7+/-237.7, 1051.8+/-515.2) versus the ND group (439.2+/-90.1, 328.2+/-207.5). Erythrocyte membrane Na+/K+ ATPase activity (nmol NADH oxidized/min/mg protein) was elevated in the DM group (4.47+/-0.98) compared to the ND group (2.16+/-0.59). A1C correlated with plasma methylglyoxal and glyoxal, and both aldehydes correlated with each other. A high correlation of A1C with Na+/K+ ATPase activity, and a regression analysis showing A1C as a good predictor of activity of this enzyme, point to a role for glucose in membrane alteration. In complication-free patients, increased plasma methylglyoxal, plasma glyoxal, and erythrocyte Na+/K+ ATPase activity may foretell future diabetic complications, and emphasize a need for aggressive management.

Methylglyoxal in food and living organisms

Methylglyoxal (MG) is a highly reactive alpha-oxoaldehyde formed endogenously in numerous enzymatic and nonenzymatic reactions. It modifies arginine and lysine residues in proteins forming advanced glycation end-products such as N(delta)-(5-methyl-4-imidazolon-2-yl)-L-ornithine (MG-H1), 2-amino-5-(2-amino-5-hydro-5-methyl-4-imidazolon-1-yl)pentanoic acid (MG-H2), 2-amino-5-(2-amino-4-hydro-4-methyl-5-imidazolon-1-yl)pentanoic acid (MG-H3), argpyrimidine, N(delta)-(4-carboxy-4,6-dimethyl-5,6-dihydroxy-1,4,5,6-tetrahydropyrimidine-2-yl)-L-ornithine (THP), N(epsilon)-(1-carboxyethyl)lysine (CEL), MG-derived lysine dimer (MOLD), and 2-ammonio-6-({2-[4-ammonio-5-oxido-5-oxopently)amino]-4-methyl-4,5-dihydro-1H-imidazol-5-ylidene}amino)hexanoate (MODIC), which have been identified in vivo and are associated with complications of diabetes and some neurodegenerative diseases. In foodstuffs and beverages, MG is formed during processing, cooking, and prolonged storage. Fasting and metabolic disorders and/or defects in MG detoxification processes cause accumulation of this reactive dicarbonyl in vivo. In addition, the intake of low doses of MG over a prolonged period of time can cause degenerative changes in different tissues, and can also exert anticancer activity. MG in biological samples can be quantified by HPLC or GC methods with preliminary derivatization into more stable chromophores and/or fluorophores, or derivatives suitable for determination by MS by use of diamino derivatives of benzene and naphthalene, 6-hydroxy-2,4,5-triaminopyrimidine, cysteamine, and o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine. The methods include three basic steps: deproteinization, incubation with derivatization agent, and chromatographic analysis with or without preliminary extraction of the formed products.

Glyoxalase II, a Detoxifying Enzyme of Glycolysis Byproduct Methylglyoxal and a Target of p63 and p73, Is a Pro-survival Factor of the p53 Family

The p53 family proteins are transcription factors and have both common and distinct functions. p53 is a classic tumor suppressor, whereas p63 and p73 have fundamental functions in development. To gain an insight into the functional diversities among the p53 family, target genes specifically regulated by p63 and p73 were examined. Here, we found that the GLX2 gene, which encodes glyoxalase II enzyme, is up-regulated by p63 and p73. Accordingly, a specific responsive element was found in intron 1 of the GLX2 gene, which can be activated and bound by p63 and p73. We also found that, upon overexpression, the cytosolic, but not the mitochondrial, GLX2 inhibits the apoptotic response of a cell to methylglyoxal, a by-product of glycolysis. Likewise, we showed that cells deficient in GLX2 are hypersensitive to methylglyoxal-induced apoptosis. Interestingly, a deficiency in GLX2 also enhances the susceptibility of a cell to DNA damage-induced apoptosis in a p53-dependent manner. These observations reveal a novel link between the p53 family and the glyoxalase system. Given that methylglyoxal is frequently generated under both physiological and pathological conditions, we postulate that GLX2 serves as a pro-survival factor of the p53 family and plays a critical role in the normal development and in the pathogenesis of various human diseases, including cancer, diabetes, and neurodegenerative diseases.

Elevated level of methylglyoxal during diabetic ketoacidosis and its recovery phase

Carbonyl stress is hypothesized to be an associated complication of diabetic ketoacidosis. The production of the glycolytic intermediate methylglyoxal (MG) was followed up in 7 diabetic patients treated for ketoacidosis during pretreatment and recovery phase. Blood samples for methylglyoxal analysis were collected upon patient arrival in emergency department (0 h), and during ketoacidosis treatment between 12-24 h and at 168 h. The study also included 10 normoglycaemic healthy volunteers and 31 type 1 diabetic patients (control diabetes group). The methylglyoxal assay, based on methylglyoxal derivation with 1,2-diamino-4,5-dimethoxybenzene (DDB), was performed by HPLC, only assessing the level of free methylglyoxal. The baseline level of methylglyoxal recorded in normoglycemic healthy controls was 338 +/- 62 nmol/l versus 374 +/- 89 nmol/l in control diabetes group (P = 0.0407). A consistent feature of diabetic ketoacidosis before and during treatment was striking elevation of methylglyoxal as compared with control diabetes group (median test chi(2) = 14.6, df = 3, P = 0.0021). Friedman's ANOVA indicated differences (P = 0.04) among the three sampling times with a peak value (601 +/- 95 nmol/l) at 12-24 h following therapy initiation. However, fasting treatment values at 168 h were still significantly higher than the mean fasting methylglyoxal level in control diabetes group (P = 0.008). The study indicated that diabetic ketoacidosis results in an increase in methylglyoxal level. Excessive production of toxic intermediates such are alpha-dicarbonyls may be a link connecting an acute metabolic event with accelerated tissue damage, a feature characteristic of long-term complications of diabetes.

Does chronic glycolysis accelerate aging? Could this explain how dietary restriction works?

The mechanisms by which dietary restriction (DR) suppresses aging are not understood. Suppression of glycolysis by DR could contribute to controlling senescence. Many glycolytic intermediates can glycate proteins and other macromolecules. Methyglyoxal (MG), formed from dihydroxyacetone- and glyceraldehyde-3-phosphates, rapidly glycates proteins, damages mitochondria, and induces a prooxidant state to create a senescent-like condition. Ad libitum-fed and DR animals differ in mitochondrial activity and glycolytic flux rates. Persistent glycolysis in the unrestricted condition would increase the intracellular load of glycating agents (e.g., MG) and increase ROS generation by inactive mitochondria. Occasional glycolysis during DR would decrease MG and reactive oxygen species (ROS) production and could be hormetic, inducing synthesis of glyoxalase-1 and anti-glycating agents (carnosine and polyamines).

Methylglyoxal-derived β-carbolines formed from tryptophan and its derivates in the Maillard reaction

Reaction of tryptophan, tryptophan methyl ester and tryptamine with methylglyoxal (a physiological alpha-oxoaldehyde), which resulted in beta-carboline formation, showed that this type of nonenzymatic (Maillard) reaction could spontaneously occur in living organisms or during commercial or domestic food processing and storage.

On the mechanisms of ageing suppression by dietary restriction-is persistent glycolysis the problem?

The mechanism(s) by which dietary restriction (DR) suppresses ageing and onset of age-related pathologies are discussed in relation to frequency of glycolysis, and the reactivity of glycolytic intermediates. Most glycolytic intermediates are potentially toxic and readily modify (i.e. glycate) proteins and other macromolecules non-enzymically. Attention is drawn to the reactivity of methyglyoxal (MG) which is formed predominantly from the glycolytic intermediates dihydroxyacetone- and glyceraldehyde-3-phosphates. MG rapidly glycates proteins, damages mitochondria and induces a pro-oxidant state, similar to that observed in aged cells. It is suggested that because DR animals' energy metabolism is less glycolytic than in those fed ad libitum, intracellular MG levels are lowered by DR The decreased glycolysis during DR may delay senescence by lowering intracellular MG concentration compared to ad libitum-fed animals. Because of the reactivity MG and glycolytic intermediates, occasional glycolysis could be hormetic where glyoxalase, carnosine synthetase and ornithine decarboxylase are upregulated to control cellular MG concentration. It is suggested that in ad libitum-fed animals persistent glycolysis permanently raises MG levels which progressively overwhelm protective processes, particularly in non-mitotic tissues, to create the senescent state earlier than in DR animals. The possible impact of diet and intracellular glycating agents on age-related mitochondrial dysfunction is also discussed.