Evaluation of changes in carbonyl stress markers with treatment in male patients with bipolar disorder manic episode: A controlled study

BACKGROUND

Carbonyl stress, a metabolic state characterized by elevated production of reactive carbonyl compounds (RCCs), is closely related to oxidative stress and has been implicated in various diseases. This study aims to investigate carbonyl stress parameters in drug-free bipolar disorder (BD) patients compared to healthy controls, explore their relationship with clinical features, and assess the effect of treatment on these parameters.

METHODS

Patients with a primary diagnosis of a manic episode of BD and healthy controls were recruited. Exclusion criteria included intellectual disability, presence of neurological diseases, chronic medical conditions such as diabetes mellitus and metabolic syndrome, and clinical signs of inflammation. Levels of serum carbonyl stress parameters were determined using high-performance liquid chromatography.

RESULTS

Levels of glyoxal (GO) and methylglyoxal (MGO) did not differ between pre- and post-treatment patients, but malondialdehyde (MDA) levels decreased significantly post-treatment. Pre-treatment MGO and MDA levels were higher in patients compared to controls, and these differences persisted post-treatment. After adjusting for BMI and waist circumference, only MDA levels remained significantly higher in patients compared to controls.

LIMITATIONS

The study's limitations include the exclusion of female patients, which precluded any assessment of potential gender differences, and the lack of analysis of the effect of specific mood stabilizers or antipsychotic drugs.

CONCLUSIONS

This study is the first to focus on carbonyl stress markers in BD, specifically GO, MGO, and MDA. MDA levels remained significantly higher in patients, suggesting a potential role in BD pathophysiology. MGO levels were influenced by metabolic parameters, indicating a potential link to neurotoxicity in BD. Further research with larger cohorts is needed to better understand the role of RCCs in BD and their potential as therapeutic targets.

GC-MS validation and analysis of targeted plasma metabolites related to carbonyl stress in type 2 diabetes mellitus patients with and without acute coronary syndrome

Methylglyoxal (MG) is responsible for advanced glycation end-product formation, the mechanisms leading to diabetes pathogenesis and complications like acute coronary syndrome (ACS). Sugar metabolites, amino acids and fatty acids are possible substrates for MG. The study aimed to measure plasma MG substrate levels using a validated gas chromatography-mass spectrometry (GC-MS) method and explore their association with ACS risk in type 2 diabetes mellitus (T2DM). The study included 150 T2DM patients with ACS as cases and 150 T2DM without ACS as controls for the analysis of glucose, fructose, ribulose, sorbitol, glycerol, pyruvate, lactate, glycine, serine, threonine, C16:0, C16:1, C18:0, C18:1, C18:2, C18:3, C20:0 and C22:6 by GC-MS. Validated GC-MS methods were accurate, precise and sensitive. Cases significantly differed in plasma MG and metabolite levels except for lactate, C16:0, C18:0, C18:2, and C18:3 levels compared with controls. On multivariable logistic regression, plasma C20:0, C18:1, glycine and glycerol levels had increased odds of ACS risk. On multivariate receiver operating characteristic analysis, a model containing plasma C20:0, C16:1, C18:1, C18:2, serine, glycerol, lactate and threonine levels had the highest area under the curve value (0.932) for ACS diagnosis. In conclusion, plasma C20:0, C16:1, C18:1, glycine, glycerol and sorbitol levels were associated with ACS risk in T2DM.

Placental Methylglyoxal in Preeclampsia: Vascular and Biomarker Implications

BACKGROUND

Preeclampsia is a multifaceted syndrome that includes maternal vascular dysfunction. We hypothesize that increased placental glycolysis and hypoxia in preeclampsia lead to increased levels of methylglyoxal (MGO), consequently causing vascular dysfunction.

METHODS

Plasma samples and placentas were collected from uncomplicated and preeclampsia pregnancies. Uncomplicated placentas and trophoblast cells (BeWo) were exposed to hypoxia. The reactive dicarbonyl MGO and advanced glycation end products (Nε-(carboxymethyl)lysine [CML], Nε-(carboxyethyl)lysine [CEL], and MGO-derived hydroimidazolone [MG-H]) were quantified using liquid chromatography-tandem mass spectrometry. The activity of GLO1 (glyoxalase-1), that is, the enzyme detoxifying MGO, was measured. The impact of MGO on vascular function was evaluated using wire/pressure myography. The therapeutic potential of the MGO-quencher quercetin and mitochondrial-specific antioxidant mitoquinone mesylate (MitoQ) was explored.

RESULTS

MGO, CML, CEL, and MG-H2 levels were elevated in preeclampsia-placentas (+36%, +36%, +25%, and +22%, respectively). Reduced GLO1 activity was observed in preeclampsia-placentas (-12%) and hypoxia-exposed placentas (-16%). Hypoxia-induced MGO accumulation in placentas was mitigated by the MGO-quencher quercetin. Trophoblast cells were identified as the primary source of MGO. Reduced GLO1 activity was also observed in hypoxia-exposed BeWo cells (-26%). Maternal plasma concentrations of CML and the MGO-derived MG-H1 increased as early as 12 weeks of gestation (+16% and +17%, respectively). MGO impaired endothelial barrier function, an effect mitigated by MitoQ, and heightened vascular responsiveness to thromboxane A2.

CONCLUSIONS

This study reveals the accumulation of placental MGO in preeclampsia and upon exposure to hypoxia, demonstrates how MGO can contribute to vascular impairment, and highlights plasma CML and MG-H1 levels as promising early biomarkers for preeclampsia.

Elevated serum levels of methylglyoxal are associated with impaired liver function in patients with liver cirrhosis

Methylglyoxal (MGO) is a highly reactive dicarbonyl species that forms advanced glycation end products (AGEs). The binding of these AGEs to their receptor (RAGE) causes and sustains severe inflammation. Systemic inflammation is postulated to be a major driver in the progression of liver cirrhosis. However, the role of circulating MGO levels in liver cirrhosis remains unknown. In this study, we investigated the serum levels of two dicarbonyl species, MGO and glyoxal (GO) using tandem mass spectrometry (HPLC-MS/MS) and evaluated their association with disease severity. A total of 51 inpatients and outpatients with liver cirrhosis of mixed etiology and different disease stages were included. Elevated MGO levels were seen in an advanced stage of liver cirrhosis (p < 0.001). High MGO levels remained independently associated with impaired liver function, as assessed by the model for end-stage liver disease (MELD) (β = 0.448, p = 0.002) and acute decompensation (AD) (β = 0.345, p = 0.005) scores. Furthermore, MGO was positively correlated with markers of systemic inflammation (IL-6, p = 0.004) and the development of ascites (p = 0.013). In contrast, no changes were seen in GO serum levels. Circulating levels of MGO are elevated in advanced stages of liver cirrhosis and are associated with impaired liver function and liver-related parameters.

Irbesartan treatment does not influence plasma levels of the dicarbonyls methylglyoxal, glyoxal and 3-deoxyglucosone in participants with type 2 diabetes and microalbuminuria: An IRMA2 sub-study

AIM

Angiotensin receptor blockers (ARBs) reduce vascular complications in diabetes independently of blood pressure. Experimental studies suggested that ARBs may restore the detoxifying enzyme glyoxalase 1, thereby lowering dicarbonyls such as methylglyoxal. Human data on the effects of ARBs on plasma dicarbonyl levels are lacking. We investigated, in individuals with type 2 diabetes, whether irbesartan lowered plasma levels of the dicarbonyls methylglyoxal, glyoxal, 3-deoxyglucosone and their derived advanced glycation end products (AGEs), and increased d-lactate, reflecting greater methylglyoxal flux.

METHODS

We analysed a subset of the Irbesartan in Patients with T2D and Microalbuminuria (IRMA2) study. We measured plasma dicarbonyls methylglyoxal, glyoxal and 3-deoxyglucosone, free AGEs and d-lactate using ultra-performance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS) in the treatment arm receiving 300 mg irbesartan (n = 121) and a placebo group (n = 101) at baseline and after 1 and 2 years. Effect of treatment was analysed with repeated measurements ANOVA.

RESULTS

There was a slight, but significant difference in baseline median methylglyoxal levels [placebo 1119 (907-1509) nmol/l vs. irbesartan 300 mg 1053 (820-1427) nmol/l], but no significant changes were observed in any of the plasma dicarbonyls over time in either group and there was no effect of irbesartan treatment on plasma free AGEs or d-lactate levels at either 1 or 2 years.

CONCLUSION

Irbesartan treatment does not change plasma levels of the dicarbonyls methylglyoxal, glyoxal and 3-deoxyglucosone, free AGEs or d-lactate in type 2 diabetes. This indicates that increased dicarbonyls in type 2 diabetes are not targetable by ARBs, and other approaches to lower systemic dicarbonyls are needed in type 2 diabetes. (Clinical Trial Registry No: #NCT00317915).

Reversal of Insulin Resistance in Overweight and Obese Subjects by trans-Resveratrol and Hesperetin Combination-Link to Dysglycemia, Blood Pressure, Dyslipidemia, and Low-Grade Inflammation

The dietary supplement, trans-resveratrol and hesperetin combination (tRES-HESP), induces expression of glyoxalase 1, countering the accumulation of reactive dicarbonyl glycating agent, methylglyoxal (MG), in overweight and obese subjects. tRES-HESP produced reversal of insulin resistance, improving dysglycemia and low-grade inflammation in a randomized, double-blind, placebo-controlled crossover study. Herein, we report further analysis of study variables. MG metabolism-related variables correlated with BMI, dysglycemia, vascular inflammation, blood pressure, and dyslipidemia. With tRES-HESP treatment, plasma MG correlated negatively with endothelial independent arterial dilatation (r = -0.48, p < 0.05) and negatively with peripheral blood mononuclear cell (PBMC) quinone reductase activity (r = -0.68, p < 0.05)-a marker of the activation status of transcription factor Nrf2. For change from baseline of PBMC gene expression with tRES-HESP treatment, Glo1 expression correlated negatively with change in the oral glucose tolerance test area-under-the-curve plasma glucose (ΔAUGg) (r = -0.56, p < 0.05) and thioredoxin interacting protein (TXNIP) correlated positively with ΔAUGg (r = 0.59, p < 0.05). Tumor necrosis factor-α (TNFα) correlated positively with change in fasting plasma glucose (r = 0.70, p < 0.001) and negatively with change in insulin sensitivity (r = -0.68, p < 0.01). These correlations were not present with placebo. tRES-HESP decreased low-grade inflammation, characterized by decreased expression of CCL2, COX-2, IL-8, and RAGE. Changes in CCL2, IL-8, and RAGE were intercorrelated and all correlated positively with changes in MLXIP, MAFF, MAFG, NCF1, and FTH1, and negatively with changes in HMOX1 and TKT; changes in IL-8 also correlated positively with change in COX-2. Total urinary excretion of tRES and HESP metabolites were strongly correlated. These findings suggest tRES-HESP counters MG accumulation and protein glycation, decreasing activation of the unfolded protein response and expression of TXNIP and TNFα, producing reversal of insulin resistance. tRES-HESP is suitable for further evaluation for treatment of insulin resistance and related disorders.

Evaluation of the nephrotoxicity and safety of low-dose aristolochic acid, extending to the use of Xixin (Asurum), by determination of methylglyoxal and d-lactate

ETHNOPHARMACOLOGICAL RELEVANCE

Most Aristolochiaceae plants are prohibited due to aristolochic acid nephropathy (AAN), except Xixin (Asarum spp.). Xixin contains trace amounts of aristolochic acid (AA) and is widely used in Traditional Chinese Medicine. Methylglyoxal and d-lactate are regarded as biomarkers for nephrotoxicity.

AIM OF THE STUDY

The use of Xixin (Asarum spp.) is essential and controversial. This study aimed to evaluate tubulointerstitial injury and interstitial renal fibrosis by determining urinary methylglyoxal and d-lactate after withdrawal of low-dose AA in a chronic mouse model.

MATERIALS AND METHODS

C3H/He mice in the AA group (n = 24/group) were given ad libitum access to distilled water containing 3 μg/mL AA (0.5 mg/kg/day) for 56 days and drinking water from days 57 to 84. The severity of tubulointerstitial injury and fibrosis were evaluated using the tubulointerstitial histological score (TIHS) and Masson's trichrome staining. Urinary and serum methylglyoxal were determined by high-performance liquid chromatography (HPLC); urinary d-lactate were determined by column-switching HPLC.

RESULTS

After AA withdrawal, serum methylglyoxal in the AA group increased from day 56 (429.4 ± 48.3 μg/L) to 84 (600.2 ± 99.9 μg/L), and peaked on day 70 (878.3 ± 171.8 μg/L; p < 0.05); TIHS and fibrosis exhibited similar patterns. Urinary methylglyoxal was high on day 56 (3.522 ± 1.061 μg), declined by day 70 (1.583 ± 0.437 μg) and increased by day 84 (2.390 ± 0.130 μg). Moreover, urinary d-lactate was elevated on day 56 (82.10 ± 18.80 μg) and higher from day 70 (201.10 ± 90.82 μg) to 84 (193.28 ± 61.32 μg).

CONCLUSIONS

Methylglyoxal is induced after AA-induced tubulointerstitial injury, so methylglyoxal excretion and metabolism may be a detoxification and repair strategy. A low cumulative AA dose is the key factor that limits tubulointerstitial injury and helps to repair. Thus, AA-containing herbs, especially Xixin, should be used at low doses for short durations (less than one month).

The Effects of Taurine Supplementation on Metabolic Profiles, Pentosidine, Soluble Receptor of Advanced Glycation End Products and Methylglyoxal in Adults With Type 2 Diabetes: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVES

Advanced glycation end products, along with methylglyoxal (MGO) as their precursor, play a major role in increased complications of type 2 diabetes mellitus (T2DM). Taurine (2-aminoethanesulphonic acid), a conditionally essential amino acid, is found in most mammalian tissues. Taurine is known as an antiglycation compound. This study was designed to investigate the effects of taurine supplementation on metabolic profiles, pentosidine, MGO and soluble receptors for advanced glycation end products in patients with T2DM.

METHODS

In this double-blind randomized controlled trial, 46 patients with T2DM were randomly allocated into taurine and placebo groups. Participants received either 3,000 mg/day taurine or placebo for 8 weeks. Metabolic profiles, pentosidine, MGO and soluble receptors for advanced glycation end products levels were assessed after 12 h of fasting at baseline and completion of the clinical trial. Independent t test, paired t test, Pearson correlation and analysis of covariance were used for analysis.

RESULTS

The mean serum levels of fasting blood sugar (p=0.01), glycated hemoglobin (p=0.04), insulin (p=0.03), homeostasis model assessment-insulin resistance (p=0.004), total cholesterol (p=0.01) and low-density lipoprotein cholesterol (p=0.03) significantly were reduced in the taurine group at completion compared with the placebo group. In addition, after completion of the study, pentosidine (p=0.004) and MGO (p=0.006) were significantly reduced in the taurine group compared with the placebo group.

CONCLUSIONS

The results of this trial show that taurine supplementation may decrease diabetes complications through improving glycemic control and advanced glycation end products.

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.

Dietary Genistein Inhibits Methylglyoxal-Induced Advanced Glycation End Product Formation in Mice Fed a High-Fat Diet

BACKGROUND

Methylglyoxal (MGO), an important precursor of advanced glycation end products (AGEs), circulates at high concentrations in diabetic patients' blood and plays an important role in the pathogenesis of diabetes and other chronic diseases.

OBJECTIVES

The aim of this study was to determine whether dietary genistein can prevent indicators of metabolic syndrome (MetS) induced by a very-high-fat (VHF) diet or a high-fat (HF) diet plus exogenous MGO, and the accumulation of MGO and AGEs in mice.

METHODS

Male, 6-wk-old C57BL/6J mice (n = 15) were fed a low-fat (LF) diet (10% fat energy) or a VHF diet (60% fat energy) alone or including 0.25% genistein (VHF-G) for 16 wk in study 1. In study 2, 75 similar mice were fed the LF diet (LF) or the HF diet alone (HF) or in combination with up to 0.2% MGO in water (HFM) and 0.067% (HFM-GL) or 0.2% (HFM-GH) dietary genistein for 18 wk. Anthropometric and metabolic data were obtained in both studies to determine the effects of MGO and genistein on variables indicative of MetS.

RESULTS

Body weight gain, fat deposits, dyslipidemia, hyperglycemia, and fatty liver were ameliorated by dietary genistein in both studies. The plasma MGO concentration in VHF-G mice was 52% lower than that in VHF mice. Moreover, the AGE concentrations in plasma, liver, and kidney of VHF-G mice were 73%, 52%, and 49%, respectively, lower than in the VHF group (study 1). Similarly, the concentrations of plasma MGO and AGE in plasma, liver, and kidney of HFM-GH mice were 33.5%, 49%, 69%, and 54% lower than in HFM mice (study 2). Genistein inhibited AGE formation by trapping MGO to form adducts and upregulating the expressions of glyoxalase I and II and aldose reductase in liver and kidney to detoxify MGO in both studies.

CONCLUSIONS

Our data demonstrate for the first time that genistein significantly lowers MGO and AGE concentrations in 2 mouse MetS models via multiple pathways.

Advanced Glycation End Products and esRAGE Are Associated With Bone Turnover and Incidence of Hip Fracture in Older Men

BACKGROUND

Diabetes mellitus is associated with increased fracture risk despite preservation of bone density and reduced bone turnover.

AIMS

We tested the hypothesis that circulating advanced glycation end products (AGEs) and endogenous secretory receptor for AGEs (esRAGE) differentially modulate bone turnover and predict fracture risk in older men.

PARTICIPANTS

A total of 3384 community-dwelling men aged 70 to 89 years.

METHODS

Collagen type I C-terminal cross-linked telopeptide, N-terminal propeptide of type I collagen (P1NP), and total osteocalcin (TOC) were assayed using immunoassay and undercarboxylated osteocalcin (ucOC) following hydroxyapatite binding. Plasma N-carboxymethyllysine (CML) and esRAGE were assayed using immunoassay. Methylglyoxal and glyoxal were assayed using mass spectrometry. Incident hip fractures were ascertained.

RESULTS

Median age was 76.3 years (interquartile range, 74.2 to 79.1 years). Plasma CML was measured in 3011 men, methylglyoxal and glyoxal in 766 men, and esRAGE in 748 men. Plasma CML, methylglyoxal, glyoxal, and esRAGE were similar in men without and with diabetes (all P > 0.05). CML was positively associated with fasting glucose (r = 0.06, P < 0.001), and esRAGE was inversely associated (r = -0.08, P = 0.045). esRAGE was positively associated with bone formation (P1NP, r = 0.17, P < 0.001; ucOC, r = 0.11, P = 0.008; TOC, r = 0.16, P < 0.001). Incident hip fractures occurred in 106 men during follow-up. Men with CML in the third quartile of values had reduced incidence of hip fracture compared with men in the lowest quartile (hazard ratio, 0.49; 95% CI, 0.24 to 0.99; P = 0.045).

CONCLUSIONS

Glycemia associates positively with CML and reciprocally with esRAGE in older men. Circulating esRAGE modulates bone turnover in older men, whereas CML predicts incidence of hip fracture.

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.

Advanced Glycation Endproducts Are Increased in the Animal Model of Multiple Sclerosis but Cannot Be Reduced by Pyridoxamine Treatment or Glyoxalase 1 Overexpression

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system (CNS). The immune response in MS patients leads to the infiltration of immune cells in the CNS and their subsequent activation. Immune cell activation induces a switch towards glycolysis. During glycolysis, the dicarbonyl product methylglyoxal (MGO) is produced. MGO is a glycating agent that can rapidly form advanced glycation endproducts (AGEs). In turn, AGEs are able to induce inflammatory responses. The glyoxalase system is the endogenous defense system of the body to reduce the burden of MGO thereby reducing AGE formation. This system consists of glyoxalase-1 and glyoxalase-2 which are able to detoxify MGO to D-lactate. We investigated whether AGE levels are induced in experimental autoimmune encephalitis (EAE), an inflammatory animal model of MS. Twenty seven days post EAE induction, MGO and AGE (N^&epsilon;-(carboxymethyl)lysine (CML), N^&epsilon;-(carboxyethyl)lysine (CEL), 5-hydro-5-methylimidazolone (MG-H1)) levels were significantly increased in the spinal cord of mice subjected to EAE. Yet, pyridoxamine treatment and glyoxalase-1 overexpression were unable to counteract AGE production during EAE and did not influence the clinical course of EAE. In conclusion, AGEs levels increase during EAE in the spinal cord, but AGE-modifying treatments do not inhibit EAE-induced AGE production and do not affect disease progression.

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

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

Higher Plasma Methylglyoxal Levels Are Associated With Incident Cardiovascular Disease in Individuals With Type 1 Diabetes: A 12-Year Follow-up Study

Methylglyoxal (MGO), a major precursor for advanced glycation end products, is increased in diabetes. In diabetic rodents, inhibition of MGO prevents cardiovascular disease (CVD). Whether plasma MGO levels are associated with incident CVD in people with type 1 diabetes is unknown. We included 159 individuals with persistent normoalbuminuria and 162 individuals with diabetic nephropathy (DN) from the outpatient clinic at Steno Diabetes Center. We measured MGO at baseline and recorded fatal and nonfatal CVD over a median follow-up of 12.3 years (interquartile range 7.6-12.5 years). Data were analyzed by Cox regression, with adjustment for sex, age, HbA_1c, DN, diabetes duration, smoking, systolic blood pressure, antihypertensive medication, and BMI. During follow-up, 73 individuals suffered at least one CVD event (36 fatal and 53 nonfatal). Higher MGO levels were associated with total, fatal, and nonfatal incident CVD (hazard ratios [HRs] 1.47 [95% CI 1.13-1.91], 1.42 [1.01-1.99], and 1.46 [1.08-1.98], respectively). We observed a similar trend for total mortality (HR 1.24 [0.99-1.56]). This study shows for the first time in our knowledge that plasma MGO levels are associated with cardiovascular events in individuals with type 1 diabetes. MGO may explain, at least in part, the increased risk for CVD in type 1 diabetes.

A Retrospective Study in Adults with Metabolic Syndrome: Diabetic Risk Factor Response to Daily Consumption of Agaricus bisporus (White Button Mushrooms)

Adults with metabolic syndrome from different race/ethnicities are often predisposed to developing type 2 diabetes (T2D); however, growing evidence suggests that healthy diets and lifestyle choices can significantly slow or prevent progression to T2D. This poorly understood relationship to healthy dietary patterns and prevention of T2D motivated us to conduct a retrospective analysis to determine the potential impact of a minor dietary lifestyle change (daily mushroom consumption) on known T2D risk factors in racially diverse adults with confirmed features of the metabolic syndrome. Retrospectively, we studied 37 subjects who had participated in a dietary intervention focused on vitamin D bioavailability from white button mushrooms (WBM). All 37 had previously completed a 16-week study where they consumed 100 g of WBM daily and were then followed-up for one month during which no mushrooms were consumed. We analyzed differences in serum risk factors from baseline to 16-week, and from baseline to one-month follow-up. Measurement of serum diabetic risk factors included inflammatory and oxidative stress markers and the antioxidant component naturally rich in mushrooms, ergothioneine. Significant beneficial health effects were observed at 16-week with the doubling of ergothioneine from baseline, increases in the antioxidant marker ORAC (oxygen radical absorption capacity) and anti-inflammatory hormone, adiponectin and significant decreases in serum oxidative stress inducing factors, carboxymethyllysine (CML) and methylglyoxal (MG), but no change in the lipid oxidative stress marker 8-isoprostane, leptin or measures of insulin resistance or glucose metabolism. We conclude that WBM contain a variety of compounds with potential anti-inflammatory and antioxidant health benefits that can occur with frequent consumption over time in adults predisposed to T2D. Well-controlled studies are needed to confirm these findings and identify the specific mushroom components beneficial to health.

Methylglyoxal mediates streptozotocin-induced diabetic neuropathic pain via activation of the peripheral TRPA1 and Nav1.8 channels

OBJECTIVE

Methylglyoxal is known to be associated with the development of nephropathy, retinopathy, and other complications in diabetes. The present study tested the hypothesis that endogenously increased levels of methylglyoxal in diabetes are causally associated with the induction of neuropathic pain.

MATERIALS AND METHODS

Streptozotocin- and methylglyoxal-induced pain models were established in rats, and the anti-nociceptive effects of the methylglyoxal scavenging agents, selective transient receptor potential channel ankyrin 1 (TRPA1) antagonist, and Nav1.8 antagonist were tested.

RESULTS

Systemic injection of streptozotocin in rats induced a prolonged increase in plasma methylglyoxal by approximately 60%, which was correlated with the progressive development of mechanical allodynia and thermal hyperalgesia. Local subcutaneous injection of methylglyoxal into the hindpaw produced dose-dependent and biphasic flinching nociceptive responses, which resembled formaldehyde (formalin)-induced nociception. The local methylglyoxal nociception was significantly blocked by co-injection into the hindpaw of the selective transient receptor potential channel ankyrin 1 (TRPA1) antagonist, A967079, and the Nav1.8 antagonist, A803467. Co-incubation with the methylglyoxal scavengers, aminoguanidine, d-arginine, and metformin, reduced the level of free methylglyoxal by more than 90%, and injection of their incubation solutions into the hindpaw produced negligible (3-17%) nociception. Like the clinically effective anti-diabetic neuropathic pain drug gabapentin, systemic injection of aminoguanidine, d-arginine, and metformin at doses that effectively inhibit paw-injected methylglyoxal-induced nociception significantly blocked streptozotocin-induced mechanical allodynia.

CONCLUSION

Endogenously increased methylglyoxal may mediate diabetic neuropathic pain via activation of both TRPA1 and Nav1.8 expressed on primary afferent sensory neurons, and injection of methylglyoxal into the hindpaw may serve as a simple and robust model for testing the anti-diabetic pain drugs.

Site specific modification of the human plasma proteome by methylglyoxal

Increasing evidence identifies dicarbonyl stress from reactive glucose metabolites, such as methylglyoxal (MG), as a major pathogenic link between hyperglycemia and complications of diabetes. MG covalently modifies arginine residues, yet the site specificity of this modification has not been thoroughly investigated. Sites of MG adduction in the plasma proteome were identified using LC-MS/MS analysis in vitro following incubation of plasma proteins with MG. Treatment of plasma proteins with MG yielded 14 putative MG hotspots from five plasma proteins (albumin [nine hotspots], serotransferrin, haptoglobin [2 hotspots], hemopexin, and Ig lambda-2 chain C regions). The search results revealed two versions of MG-arginine modification, dihydroxyimidazolidine (R+72) and hydroimidazolone (R+54) adducts. One of the sites identified was R257 in human serum albumin, which is a critical residue located in drug binding site I. This site was validated as a target for MG modification by a fluorescent probe displacement assay, which revealed significant drug dissociation at 300 μM MG from a prodan-HSA complex (75 μM). Moreover, twelve human plasma samples (six male, six female, with two type 2 diabetic subjects from both genders) were analyzed using multiple reaction monitoring (MRM) tandem mass spectrometry and revealed the presence of the MG-modified albumin R257 peptide. These data provide insights into the nature of the site-specificity of MG modification of arginine, which may be useful for therapeutic treatments that aim to prevent MG-mediated adverse responses in patients.

Impact of intensive treatment on serum methylglyoxal levels among individuals with screen-detected type 2 diabetes: the ADDITION-Denmark study

AIMS

Methylglyoxal (MG) has been implicated in the development of micro- and macrovascular diabetic complications, but it remains unclear how current treatments of type 2 diabetes affect its circulating levels.

METHODS

In the Danish arm of the ADDITION trial, we (a) described serum MG levels at baseline and at 6-year follow-up among individuals with screen-detected type 2 diabetes, (b) examined the effect of intensive multifactorial treatment compared with routine care on MG, (c) examined the associations between MG and risk factors at baseline and at follow-up and (d) examined the associations between changes in MG and changes in risk factors.

RESULTS

Patients in both treatment arms experienced a significant decline in MG from baseline to follow-up, with no effect of allocation to intensive treatment. In cohort analyses, MG was associated with smoking and fasting glucose at baseline and smoking and LDL cholesterol at follow-up. Compared with patients receiving no lipid-lowering treatment, patients receiving lipid-lowering treatment had higher MG at follow-up, and those initiating lipid-lowering treatment experienced a less pronounced decline in MG.

CONCLUSIONS

Further studies are required to explore any possible effects of the observed decrease in MG in type 2 diabetes patients as well as the potential interplay between MG, lipids, lipid-lowering treatment and smoking.

The role of serum methylglyoxal on diabetic peripheral and cardiovascular autonomic neuropathy: the ADDITION Denmark study

AIMS

Cardiovascular autonomic neuropathy and diabetic peripheral neuropathy are common diabetic complications and independent predictors of cardiovascular disease. The glucose metabolite methylglyoxal has been suggested to play a causal role in the pathogeneses of diabetic peripheral neuropathy and possibly diabetic cardiovascular autonomic neuropathy. The aim of this study was to investigate the cross-sectional association between serum methylglyoxal and diabetic peripheral neuropathy and cardiovascular autonomic neuropathy in a subset of patients in the ADDITION-Denmark study with short-term screen-detected Type 2 diabetes (duration ~ 5.8 years).

METHODS

The patients were well controlled with regard to HbA(1c), lipids and blood pressure. Cardiovascular autonomic neuropathy was assessed by measures of resting heart rate variability and cardiovascular autonomic reflex tests. Diabetic peripheral neuropathy was assessed by vibration detection threshold (n = 319), 10 g monofilament (n = 543) and the Michigan Neuropathy Screening Instrument questionnaire (n = 966). Painful diabetic neuropathy was assessed using the Brief Pain Inventory short form (n = 882).

RESULTS

No associations between methylglyoxal and cardiovascular autonomic reflex tests or any measures of diabetic peripheral neuropathy or painful diabetic neuropathy were observed. However, a positive association between methylglyoxal and several heart rate variability indices was observed, although these associations were not statistically significant when corrected for multiple testing.

CONCLUSION

Serum methylglyoxal is not associated with cardiovascular autonomic neuropathy, diabetic peripheral neuropathy or painful diabetic neuropathy in this cohort of well-treated patients with short-term diabetes.

High glucose, glucose fluctuation and carbonyl stress enhance brain microvascular endothelial barrier dysfunction: Implications for diabetic cerebral microvasculature

We previously demonstrated that in normal glucose (5 mM), methylglyoxal (MG, a model of carbonyl stress) induced brain microvascular endothelial cell (IHEC) dysfunction that was associated with occludin glycation and prevented by N-acetylcysteine (NAC). Herein, we investigated the impact of high glucose and low GSH, conditions that mimicked the diabetic state, on MG-induced IHEC dysfunction. MG-induced loss of transendothelial electrical resistance (TEER) was potentiated in IHECs cultured for 7 or 12 days in 25 mM glucose (hyperglycemia); moreover, barrier function remained disrupted 6 h after cell transfer to normal glucose media (acute glycemic fluctuation). Notably, basal occludin glycation was elevated under these glycemic states. TEER loss was exaggerated by inhibition of glutathione (GSH) synthesis and abrogated by NAC, which corresponded to GSH decreases and increases, respectively. Significantly, glyoxalase II activity was attenuated in hyperglycemic cells. Moreover, hyperglycemia and GSH inhibition increased MG accumulation, consistent with a compromised capacity for MG elimination. α-Oxoaldehydes (MG plus glyoxal) levels were elevated in streptozotocin-induced diabetic rat plasma. Immunohistochemistry revealed a prevalence of MG-positive, but fewer occludin-positive microvessels in the diabetic brain in vivo, and Western analysis confirmed an increase in MG–occludin adducts. These results provide the first evidence that hyperglycemia and acute glucose fluctuation promote MG–occludin formation and exacerbate brain microvascular endothelial dysfunction. Low occludin expression and high glycated-occludin contents in diabetic brain in vivo are factors that would contribute to the dysfunction of the cerebral microvasculature during diabetes.

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Methylglyoxal (MG) induced electrical resistance (TEER)loss in brain microvascular endothelial cells.

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TEER loss was potentiated by hyperglycemia, and low glutathione.

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TEER loss was correlated with occludin-glycation and was attenuated and exacerbated by NAC and BSO, respectively.

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Hyperglycemia decreased glyoxalase II activity and promoted free MG accumulation.

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Diabetic brain in vivo exhibiteda prevalence of MG-positive microvessels and increased occludin–MG adducts.

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.

Methylglyoxal (MG) and cerebro-renal interaction: does long-term orally administered MG cause cognitive impairment in normal Sprague-Dawley rats?

Methylglyoxal (MG), one of the uremic toxins, is a highly reactive alpha-dicarbonyl compound. Recent clinical studies have demonstrated the close associations of cognitive impairment (CI) with plasma MG levels and presence of kidney dysfunction. Therefore, the present study aims to examine whether MG is a direct causative substance for CI development. Eight-week-old male Sprague-Dawley (SD) rats were divided into two groups: control (n = 9) and MG group (n = 10; 0.5% MG in drinking water), and fed a normal diet for 12 months. Cognitive function was evaluated by two behavioral tests (object exploration test and radial-arm maze test) in early (4–6 months of age) and late phase (7–12 months of age). Serum MG was significantly elevated in the MG group (495.8 ± 38.1 vs. 244.8 ± 28.2 nM; p < 0.001) at the end of study. The groups did not differ in cognitive function during the course of study. No time-course differences were found in oxidative stress markers between the two groups, while, antioxidants such as glutathione peroxidase and superoxide dismutase activities were significantly increased in the MG group compared to the control. Long-term MG administration to rats with normal kidney function did not cause CI. A counter-balanced activation of the systemic anti-oxidant system may offset the toxicity of MG in this model. Pathogenetic significance of MG for CI requires further investigation.

Increased circulating advanced glycation endproducts (AGEs) in acute trauma patients

BACKGROUND

Circulating levels of pro-inflammatory advanced glycation end products (AGEs) are increased in diabetes and other conditions characterized by chronically elevated oxidant stress (OS). OS also increases after acute trauma and is implicated in the development of complications such as multiple organ failure. Herein, we assess the effect of acute OS on circulating levels of AGEs in a cohort of acute trauma victims.

METHODS

An observational study was performed at a large Level 1 Trauma Center. Blood samples for measurement of two AGEs, carboxymethyllysine (CML) and methylglyoxal (MG), were obtained at admission, and serially afterwards in patients admitted to the ICU. Demographics, dietary history, markers of injury severity and ICU morbidity and mortality data were collected.

RESULTS

One hundred and fifty-six trauma patients (TP) (age: 39±17 years, 83% males, injury severity score: 18±14) were included in the study. TP had significantly higher serum AGE levels than normal healthy controls (CML, TP 12.4±8.2 U/mL vs. controls 8.9±5.3 U/mL, p<0.001; MG, TP 2.1±1.4 nmol/mL vs. controls 0.79±0.3 nmol/mL, p<0.001). Admission serum AGE levels in 49 severe TP admitted to the ICU were lower than those who were not. However, among the ICU patients, serum AGEs increased further for about 7 days in patients with an uncomplicated course, and remained markedly elevated in those with a complicated course.

CONCLUSIONS

Circulating AGEs are transiently increased after acute trauma and persistently elevated AGE levels are associated with greater severity of injury.

Increased methylglyoxal formation with upregulation of renin angiotensin system in fructose fed Sprague Dawley rats

The current epidemic of obesity and type 2 diabetes is attributed to a high carbohydrate diet, containing mainly high fructose corn syrup and sucrose. More than two thirds of diabetic patients have hypertension. Methylglyoxal is a highly reactive dicarbonyl generated during glucose and fructose metabolism, and a major precursor of advanced glycation end products (AGEs). Plasma methylglyoxal levels are increased in hypertensive rats and diabetic patients. Our aim was to examine the levels of methylglyoxal, mediators of the renin angiotensin system and blood pressure in male Sprague-Dawley rats treated with a high fructose diet (60% of total calories) for 4 months. The thoracic aorta and kidney were used for molecular studies, along with cultured vascular smooth muscle cells (VSMCs). HPLC, Western blotting and Q-PCR were used to measure methylglyoxal and reduced glutathione (GSH), proteins and mRNA, respectively. Fructose treated rats developed a significant increase in blood pressure. Methylglyoxal level and protein and mRNA for angiotensin II, AT₁ receptor, adrenergic α_1D receptor and renin were significantly increased, whereas GSH levels were decreased, in the aorta and/or kidney of fructose fed rats. The protein expression of the receptor for AGEs (RAGE) and NF-κB were also significantly increased in the aorta of fructose fed rats. MG treated VSMCs showed increased protein for angiotensin II, AT₁ receptor, and α_1D receptor. The effects of methylglyoxal were attenuated by metformin, a methylglyoxal scavenger and AGEs inhibitor. In conclusion, we report a strong association between elevated levels of methylglyoxal, RAGE, NF-κB, mediators of the renin angiotensin system and blood pressure in high fructose diet fed rats.