The methylglyoxal-derived AGE tetrahydropyrimidine is increased in plasma of individuals with type 1 diabetes mellitus and in atherosclerotic lesions and is associated with sVCAM-1

AIMS/HYPOTHESIS

Methylglyoxal (MGO) is a major precursor for advanced glycation end-products (AGEs), which are thought to play a role in vascular complications in diabetes. Known MGO-arginine-derived AGEs are 5-hydro-5-methylimidazolone (MG-H1), argpyrimidine and tetrahydropyrimidine (THP). We studied THP in relation to type 1 diabetes, endothelial dysfunction, low-grade inflammation, vascular complications and atherosclerosis.

METHODS

We raised and characterised a monoclonal antibody against MGO-derived THP. We measured plasma THP with a competitive ELISA in two cohort studies: study A (198 individuals with type 1 diabetes and 197 controls); study B (individuals with type 1 diabetes, 175 with normoalbuminuria and 198 with macroalbuminuria [>300 mg/24 h]). We measured plasma markers of endothelial dysfunction and low-grade inflammation, and evaluated the presence of THP and N (ε)-(carboxymethyl)lysine (CML) in atherosclerotic arteries.

RESULTS

THP was higher in individuals with type 1 diabetes than in those without (median [interquartile range] 115.5 U/μl [102.4-133.2] and 109.8 U/μl [91.8-122.3], respectively; p = 0.03). THP was associated with plasma soluble vascular cell adhesion molecule 1 in both study A (standardised β = 0.48 [95% CI 0.38, 0.58]; p < 0.001) and study B (standardised β = 0.31 [95% CI 0.23, 0.40]; p < 0.001), and with secreted phospholipase A2 (standardised β = 0.26 [95% CI 0.17, 0.36]; p < 0.001) in study B. We found no association of THP with micro- or macro-vascular complications. Both THP and CML were detected in atherosclerotic arteries.

CONCLUSIONS/INTERPRETATION

Our results suggest that MGO-derived THP may reflect endothelial dysfunction among individuals with and without type 1 diabetes, and therefore may potentially play a role in the development of atherosclerosis and vascular disease.

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

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

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.

[The biological reaction of inflammation, methylglyoxal of blood plasma, functional and structural alterations in elastic type arteries at the early stage of hypertension disease]

The article deals with studying of the relationship between biologic reaction of inflammation with glycosylation reaction and content of methylglyoxal in blood serum. The positive correlation between pulse wave velocity and content of methylglyoxal, C-reactive protein in intercellular medium and malleolar brachial index value was established. This data matches the experimental results concerning involvement of biological reaction of inflammation into structural changes of elastic type arteries under hypertension disease, formation of arteries' rigidity and increase of pulse wave velocity. The arterial blood pressure is a biological reaction of hydrodynamic pressure which is used in vivo by several biological functions: biological function of homeostasis, function of endoecology, biological function of adaptation and function of locomotion. The biological reaction of hydrodynamic (hydraulic) pressure is a mode of compensation of derangement of several biological functions which results in the very high rate of hypertension disease in population. As a matter of fact, hypertension disease is a syndrome of lingering pathological compensation by higher arterial blood pressure of the biological functions derangements occurring in the distal section at the level of paracrine cenoses of cells. The arterial blood pressure is a kind of in vivo integral indicator of deranged metabolism. The essential hypertension disease pathogenically is a result of the derangement of three biological functions: biological function of homeostasis, biological function of trophology - nutrition (biological reaction of external feeding - exotrophia) and biological function of endoecology. In case of "littering" of intercellular medium in vivo with nonspecific endogenic flogogens a phylogenetically earlier activation of biological reactions of excretion, inflammation and hydrodynamic arterial blood pressure occur. In case of derangement of biological function of homeostasis, decreasing of perfusion even in single paracrine cenoses and derangement of biological function of endoecology ("purity" of intercellular medium) the only response always will be the increase of arterial blood pressure.

Reactive carbonyl compounds (RCCs) cause aggregation and dysfunction of fibrinogen

Fibrinogen is a key protein involved in coagulation and its deposition on blood vessel walls plays an important role in the pathology of atherosclerosis. Although the causes of fibrinogen (fibrin) deposition have been studied in depth, little is known about the relationship between fibrinogen deposition and reactive carbonyl compounds (RCCs), compounds which are produced and released into the blood and react with plasma protein especially under conditions of oxidative stress and inflammation. Here, we investigated the effect of glycolaldehyde on the activity and deposition of fibrinogen compared with the common RCCs acrolein, methylglyoxal, glyoxal and malondialdehyde. At the same concentration (1 mmol/L), glycolaldehyde and acrolein had a stronger suppressive effect on fibrinogen activation than the other three RCCs. Fibrinogen aggregated when it was respectively incubated with glycolaldehyde and the other RCCs, as demonstrated by SDS-PAGE, electron microscopy and intrinsic fluorescence intensity measurements. Staining with Congo Red showed that glycolaldehyde- and acrolein-fibrinogen distinctly formed amyloid-like aggregations. Furthermore, the five RCCs, particularly glycolaldehyde and acrolein, delayed human plasma coagulation. Only glycolaldehyde showed a markedly suppressive effect on fibrinogenesis, none did the other four RCCs when their physiological blood concentrations were employyed, respectively. Taken together, it is glycolaldehyde that suppresses fibrinogenesis and induces protein aggregation most effectively, suggesting a putative pathological process for fibrinogen (fibrin) deposition in the blood.

Study on the changes of carbonic anhydrase activity in insulin resistance and the effect of methylglyoxal

OBJECTIVES

To determine the serum levels of methylglyoxal (MG) and carbonic anhydrase (CA) activity in known cases of type-II diabetes mellitus with insulin resistance and to compare them with age-sex matched healthy controls.

METHODS

Eightysix participants were enrolled for the present case-controlled study with ages ranging from 25 to 44 years. The analytes measured were fasting blood glucose, serum insulin, methylglyoxal and carbonic anhydrase assay by standard procedures. Further carbonic anhydrase activities were measured in erythrocytes haemolysate and the effect of methylglyoxal on erythrocyte membrane was studied. The effects of methylglyoxal on erythrocyte carbonic anhydrase activity and insulin reactivity were also measured.

RESULTS

The mean serum levels of insulin, fasting blood glucose, carbonic anhydrase activity, methylglyoxal and body mass index (BMI) was significantly higher (p < 0.001) in patients compared to the controls. The carbonic anhydrase activity was directly proportional to increasing blood glucose concentration. The haemolysate prepared from the erythrocytes of patients and controls also showed significantly higher carbonic anhydrase activities in patients than the controls. Increased carbonic anhydrase activity in a dose-dependent manner with methylglyoxal was also observed.

CONCLUSION

Insulin resistance is accompanied by increased activity of carbonic anhydrase which is significantly related to increasing methylglyoxal levels.

Maternal plasma advanced glycation end products concentrations in response to oral 50-gram glucose load in mid-pregnancy: a pilot study

BACKGROUND

Accumulating evidence documents the initiation of diverse physiologic and biochemical responses subsequent to an oral glucose load.

OBJECTIVES

We sought to evaluate the extent to which acute hyperglycemia, resulting from a 50-gram glucose load, contributes to changes in maternal plasma concentrations of advanced glycation end products (AGEs), a heterogeneous group of molecules formed from the non-enzymatic reaction of reducing sugars with free amino groups of proteins, lipids, and nucleic acids.

METHODS

Blood specimens were collected from each participant in mid-pregnancy using standard procedures before and after a 50-gram oral glucose load. Maternal plasma methylglyoxal (MG), pentosidine and N(epsilon)-(carboxymethyl)lysine (CML) (free and bound) were measured by HPLC-MS/MS method. Non-parametric methods were employed for statistical analysis.

RESULTS AND CONCLUSIONS

Median plasma MG increased 1.27 fold as a result of acute hyperglycemia. Median bound CML concentrations were elevated 21% in post-load plasma samples as compared with pre-load samples, while median free pentosidine concentrations were 51% lower (both p-values < 0.05). Future studies of larger populations and longer periods of follow-up are warranted to investigate the consequences of acute and chronic hyperglycemia on placental function and fetal development.

Serum concentration of an inflammatory glycotoxin, methylglyoxal, is associated with increased cognitive decline in elderly individuals

BACKGROUND

Advanced glycations end products increase oxidant stress, inflammation, and neurotoxicity. Serum levels are increased in diabetes and aging. We examined the relationship between serum methylglyoxal derivatives (sMG), and cognitive decline, in 267 non-demented elderly.

METHODS

Tobit mixed regression models assessed the association of baseline sMG with cognitive decline in the Mini Mental State Exam (MMSE) over time, controlling for sociodemographic factors (age, sex, and years of education), cardiovascular risk factors (diabetes and presence of an ApoE4 allele), and kidney function. sMG was assessed by ELISA.

RESULTS

The fully adjusted model showed an annual decline of 0.26 MMSE points per unit increase in baseline sMG (p = 0.03). Significance was unchanged as additional risk factors were added to the model. The interactions of sMG with diabetes, sex, age, kidney function, and ApoE4 genotype were not significant.

CONCLUSIONS

Higher levels of baseline sMG were associated with a faster rate of cognitive decline, after adjusting for several sociodemographic and clinical characteristics. This relationship did not differ by sex, ApoE4 genotype, or diabetes status suggesting its generality. Since subjects were cognitively normal at the beginning of the study, elevated sMG may be indicative of brain cell injury initiated before clinically evident cognitive compromise.

γ-Tocopherol abolishes postprandial increases in plasma methylglyoxal following an oral dose of glucose in healthy, college-aged men

Postprandial hyperglycemia contributes to the risk of cardiovascular disease in part by increasing concentrations of the reactive dicarbonyl methylglyoxal (MGO), a byproduct of glucose metabolism. Oxidative stress increases MGO formation from glucose in vitro and decreases its glutathione-dependent detoxification to lactate. We hypothesized that the antioxidant γ-tocopherol, a form of vitamin E, would decrease hyperglycemia-mediated postprandial increases in plasma MGO in healthy, normoglycemic, college-aged men. Participants (n=12 men; 22.3±1.0 years; 29.3±2.4 kg/m(2)) received an oral dose of glucose (75 g) in the fasted state prior to and following 5-day ingestion of a vitamin E supplement enriched in γ-tocopherol (500 mg/day). γ-Tocopherol supplementation increased (P<.0001) plasma γ-tocopherol from 2.22±0.32 to 7.06±0.71 μmol/l. Baseline MGO concentrations and postprandial hyperglycemic responses were unaffected by γ-tocopherol supplementation (P>.05). Postprandial MGO concentrations increased in the absence of supplemental γ-tocopherol (P<.05), but not following γ-tocopherol supplementation (P>.05). Area under the curve for plasma MGO was significantly (P<.05) smaller with the supplementation of γ-tocopherol than without (area under the curve (0-180 min), -778±1010 vs. 2277±705). Plasma concentrations of γ-carboxyethyl-hydroxychroman, reduced glutathione and markers of total antioxidant capacity increased after supplementation, and these markers and plasma γ-tocopherol were inversely correlated with plasma MGO (r=-0.48 to -0.67, P<.05). These data suggest that short-term supplementation of γ-tocopherol abolishes the oral glucose-mediated increases in postprandial MGO through its direct and indirect antioxidant properties and may reduce hyperglycemia-mediated cardiovascular disease risk.

Enhanced methylglyoxal formation in the erythrocytes of hemodialyzed patients

Methylglyoxal (MG) contributes significantly to the carbonyl stress in uremia; however, the reason for its increased concentration is not clear. Thus, the present study was aimed to investigate the formation and degradation of MG in the erythrocytes of hemodialyzed (HD) patients with end-stage renal disease. In 22 nondiabetic patients on long-term HD, erythrocyte MG and d-lactate levels, glyoxalase activities, and whole blood reduced glutathione content were determined. The data were compared with those from 22 healthy controls. Erythrocyte MG and d-lactate production were also investigated in vitro under normoglycemic (5 mmol/L) and hyperglycemic (50 mmol/L) conditions. The erythrocyte MG levels were elevated (P < .001) in the HD patients. The blood reduced glutathione content and glyoxalase I activity were similar to the control levels, but the glyoxalase II activity was significantly (P < .005) increased. In the normoglycemic in vitro model, production of both MG (P < .001) and d-lactate (P < .002) was significantly enhanced in the HD erythrocytes relative to the controls. During hyperglycemia, the MG formation and degradation rates were further increased (P < .001). The present study demonstrated an increased formation of MG in the erythrocytes of HD patients. This seemed to be related to a glucose metabolism disturbance of the cells. The degradation system of MG was also activated; still, it was not able to counteract the high rate of MG formation. The alterations and imbalance of these metabolic processes may contribute to the carbonyl overload and stress in the HD patients.

Leptin decreases postprandially in people with type 2 diabetes, an effect reduced by the cooking method

Leptin modulates satiety and increases in obesity and type 2 diabetes mellitus in parallel with leptin resistance. Postprandial leptin regulation has been previously postulated to depend on meal composition, but data are controversial. The hypothesis of our study was that in people with type 2 diabetes mellitus, a postprandial leptin regulation exists that can be regulated not only by meal composition but also by the cooking method. In 20 inpatients with type 2 diabetes (mean age: 55.9 years), the acute effects of 2 meals, a high-heat-processed meal HHPM or a low-heat-processed meal LHPM, on leptin levels were studied on 2 different days in a randomized, crossover design. Both test meals had similar ingredients and differed only in the cooking method used. Parameters were measured after an overnight fast and at 2, 4, and 6 h postprandially. The HHPM induced a marked decrease in leptin levels, from 8 717+/-2 079 pg/ml at baseline to 6 788+/-1 598 pg/ml at 2 h postprandially (-1 929 pg/ml, -22%*), an effect significantly reduced by the LHPM, where values were 8 563+/-1 900 pg/ml at baseline and 7 425+/-1 591 pg/ml at 2 h postprandially (-1 138 pg/ml, -13%* (double dagger)) (*p<0.05 vs. baseline, (double dagger)p<0.05 vs. HHPM). Parameters of oxidative stress and blood AGEs increased only following the HHPM, while postprandial glucose, triglycerides, and insulin excursions were similar between meals. Postprandial leptin decreases following a HHPM meal in people with T2DM, an effect reduced by the cooking method.

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.

Methylglyoxal production in human blood

The research of Szent-Györgyi and others has suggested that the three-carbon ketoaldehyde methylglyoxal has a potential role in the control of cell growth. Its metabolism to D-lactate (not the L-lactate of glycolysis) is catalysed by the mammalian enzymes glyoxalase I (S-lactoyl-glutathione methylglyoxal-lyase, isomerizing; EC 4.4.1.5) and glyoxalase II (S-2-hydroxyacylglutathione hydrolase; 3.1.2.6), with glutathione as a coenzyme. Direct determination of methylglyoxal in biological tissues is difficult because of the active glyoxalase system. However, the product of the glyoxalase system, D-lactate, should indicate formed or added methylglyoxal. A stereospecific assay was used to measure D-lactate in human plasma; it involved the spectrophotometric analysis of NADH at 340 nm catalysed by D-lactate dehydrogenase (D-lactate:NAD+ oxidoreductase; EC 1.1.1.28) from Lactobacillus leichmannii. Blood collected by venepuncture was used for the determination of the plasma concentration of D-lactate. The mean concentration for seven normal subjects was 0.023 mM +/- 0.002 S.E.M. When the glycolytic pathway in whole blood was inhibited in vitro with fluoride, a significant increase in D-lactate was found (about 0.15 mM/hour at 37 degrees C). Added methylglyoxal also produced an increase in D-lactate formation. Some specific precursors of L-lactate (dihydroxyacetone phosphate, for example) added to whole blood produced an increased concentration of D-lactate, even when glycolysis was not inhibited. This finding indicates that catabolites of glucose lead to methylglyoxal synthesis and suggest a control function for the glyoxalase enzyme system in glycolysis that could be exploited for cancer therapy.

Different patterns of in vivo pro-oxidant states in a set of cancer- or aging-related genetic diseases

A comparative evaluation is reported of pro-oxidant states in 82 patients with ataxia telangectasia (AT), Bloom syndrome (BS), Down syndrome (DS), Fanconi anemia (FA), Werner syndrome (WS), and xeroderma pigmentosum (XP) vs 98 control donors. These disorders display cancer proneness, and/or early aging, and/or other clinical features. The measured analytes were: (a) leukocyte and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), (b) blood glutathione (GSSG and GSH), (c) plasma glyoxal (Glx) and methylglyoxal (MGlx), and (d) some plasma antioxidants [uric acid (UA) and ascorbic acid (AA)]. Leukocyte 8-OHdG levels ranked as follows: WS>BS approximately FA approximately XP>DS approximately AT approximately controls. Urinary 8-OHdG levels were significantly increased in a total of 22 patients with BS, FA, or XP vs 47 controls. The GSSG:GSH ratio was significantly increased in patients with WS and in young (< or =15 years) patients with DS or with FA and decreased in older patients with DS or FA and in AT, BS, and XP patients. The plasma levels of Glx and/or MGlx were significantly increased in patients with WS, FA, and DS. The UA and AA levels were significantly increased in WS and DS patients, but not in AT, FA, BS, nor XP patients. Rationale for chemoprevention trials is discussed.

Proinflammatory and proapoptotic effects of methylglyoxal on neutrophils from patients with type 2 diabetes mellitus

OBJECTIVE

To determine the effect of methylglyoxal (MG) on cytokine production by, and apoptosis of, neutrophils from type 2 diabetes mellitus (T2DM) patients.

DESIGN AND METHODS

The levels of plasma MG, cytokines released by isolated neutrophils and the apoptotic status of neutrophils were determined.

RESULTS

The higher level of plasma MG in T2DM patients was correlated positively with glycated hemoglobin levels, fasting plasma glucose levels and urine albumin/creatinine ratios. The basal levels of cytokines released from neutrophils were markedly higher in patients. MG treatment of the neutrophils isolated from diabetic patients either did not alter, or decreased, the production of cytokines. In contrast, MG induced the release of cytokines from neutrophils of non-diabetics. Moreover, the neutrophils from T2DM patients showed a greater proclivity for apoptosis, which was further increased by in vitro MG treatment.

CONCLUSION

MG stimulated neutrophils to release more cytokines, which might play a role in the development of infection in T2DM.

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.

Glutathione levels in blood from ataxia telangiectasia patients suggest in vivo adaptive mechanisms to oxidative stress

OBJECTIVE

To evaluate an in vivo pro-oxidant state in patients with ataxia telangiectasia (AT).

METHODS

A set of oxidative stress endpoints were measured in 9 AT homozygotes, 16 AT heterozygotes (parents) and 83 controls (grouped in age ranges as for patients and parents, respectively). The following analytes were measured: (a) leukocyte 8-hydroxy-2'-deoxyguanosine (8-OHdG); (b) blood glutathione (GSSG and GSH); and (c) plasma levels of glyoxal (Glx) and methylglyoxal (MGlx).

RESULTS

AT patients displayed a significant decrease in blood GSSG (p=0.012) and in MGlx plasma concentrations (p=0.012). A non-significant decrease in the GSSG:GSH ratio (p=0.1) and a non-significant increase in 8-OHdG and Glx levels were observed in AT patients vs. young controls (age range 4-35 years). AT heterozygotes failed to display any significant changes vs. adult controls (age range 36-68 years).

CONCLUSION

No significant increase in oxidative stress biomarkers was detected in blood from AT patients. The decrease in GSSG and MGlx levels in AT patients may suggest an adaptive response to a pro-oxidant state in AT-related target organs.

Stimulation of suicidal erythrocyte death by methylglyoxal

Diabetes increases the percentage of circulating erythrocytes exposing phosphatidylserine (PS) at the cell surface. PS-exposing erythrocytes are recognized, bound, engulfed and degraded by macrophages. Thus, PS exposure, a feature of suicidal erythrocyte death or eryptosis, accelerates clearance of affected erythrocytes from circulating blood. Moreover, PS-exposing erythrocytes bind to the vascular wall thus interfering with microcirculation. The present study explored mechanisms involved in the triggering of PS exposure by methylgloxal, an extra- and intracellular metabolite which is enhanced in diabetes. PS exposure, cell size and cytosolic Ca(2+)-activity after methylglyoxal treatment were measured by FACS analysis of annexin V binding, forward scatter and Fluo-3-fluorescence, respectively, and it was shown that the treatment significantly enhanced the percentage of PS-exposing erythrocytes at concentrations (0.3 microM) encountered in diabetic patients. Surprisingly, methylglyoxal did not significantly increase cytosolic Ca(2+) concentration, and at concentrations up to 3 microM, did not decrease the forward scatter. Instead, exposure to methylglyoxal inhibited glycolysis thus decreasing ATP and GSH concentrations. In conclusion, methylglyoxal impairs energy production and anti-oxidative defense, effects contributing to the enhanced PS exposure of circulating erythrocytes and eventually resulting in anemia and deranged microcirculation.

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.

Evaluation of Glyoxal and Methylglyoxal Levels in Uremic Patients under Peritoneal Dialysis

Advanced glycation end products (AGEs) accumulate in serum and tissues of patients with chronic renal failure, even in the absence of diabetes, and a different clearance of these species has been observed by hemodialysis and peritoneal dialysis (CAPD). Furthermore, it has been shown that not only AGE but also 1,2-dicarbonyl compounds are formed during heat sterilization of glucose-based peritoneal dialysis fluids. Therefore, we investigated the level of some AGEs (pentosidine and free pentosidine) and dicarbonyl compounds (glyoxal and methylglyoxal) in end-stage renal disease patients subjected to peritoneal dialysis. Samples (20 from healthy subjects, 16 from uremic patients before and after 12 h of peritoneal dialysis) were analyzed, and the plasma and dialysate levels of glyoxal, methylglyoxal, pentosidine, and free pentosidine were determined. In plasma of uremic patients, mean values of pentosidine showed a small decrease after dialysis and were always higher than those of healthy control subjects. An analogous trend was observed for free pentosidine. In the case of peritoneal dialysate, no pentosidine and free pentosidine were found at time zero, whereas both compounds were detected after 12 h of dialysis. Glyoxal and methylglyoxal mean levels showed a decrease in plasma after dialysis even if their values were always higher than those of healthy control subjects. Surprisingly, an analogous trend was observed also in dialysate. These results might indicate that glyoxal and methylglyoxal already present in the dialysis fluid react with the peritoneal matrix proteins, accounting for the gradual loss of peritoneal membrane function that is often observed in patients subjected to CAPD for a long time.

Methylglyoxal, glyoxal, and their detoxification in Alzheimer's disease

The accumulation of advanced glycation end products (AGEs) in brains with Alzheimer's disease (AD) has been implicated in the formation of insoluble deposits such as amyloid plaques and neurofibrillary tangles. AGEs are also known to activate glia, resulting in inflammation and neuronal dysfunction. As reactive intermediates of AGE formation, neurotoxic reactive dicarbonyl compounds such as glyoxal and methylglyoxal have been identified. One of the most effective detoxification systems for methylglyoxal and glyoxal is the glutathione-dependent glyoxalase system, consisting of glyoxalase I and glyoxalase II. In this study, we have determined the methylglyoxal and glyoxal levels in the cerebrospinal fluid of AD patients compared to healthy controls. Methylglyoxal levels in AD patients were twofold higher than in controls, but this difference was not significant due to the large intergroup variations and the small sample size. However, the concentrations of both compounds were five to seven times higher in CSF than in plasma. We also investigated the glyoxalase I level in AD and healthy control brains. The number of glyoxalase I- positive neurons were increased in AD brains compared to controls. Our findings suggest that glyoxalase I is upregulated in AD in a compensatory manner to maintain physiological methylglyoxal and glyoxal levels.

In vivo prooxidant state in Werner syndrome (WS): results from three WS patients and two WS heterozygotes

The hypothesis was tested that Werner syndrome (WS) phenotype might be associated with an in vivo prooxidant state. A set of redox-related endpoints were measured in three WS patients, two of their parents, and 99 controls within a study of some cancer-prone and/or ageing-related genetic disorders. The following analytes were measured: (a) leukocyte 8-hydroxy-2'-deoxyguanosine; (b) glutathione from whole blood, and (c) plasma levels of glyoxal, methylglyoxal, 8-isoprostane, and some plasma antioxidants (uric acid, ascorbic acid, alpha- and gamma-tocopherol). Leukocyte 8-hydroxy-2'-deoxyguanosine levels showed a significant increase in the 3 WS patients vs. 85 controls (p<10(-7)). The disulfide glutathione:glutahione ratio was significantly altered in WS patients (p=0.005). Glyoxal and methylglyoxal levels were significantly increased (p=0.018 and p=0.007, respectively). The plasma levels of uric acid (p=0.002) and ascorbic acid (p=0.003) were also increased significantly in WS patients and in their parents. No significant alterations were found in the plasma levels of alpha- and gamma-tocopherol, nor of 8-isoprostane. This is the first report of in vivo alterations of oxidative stress parameters in WS patients. Further investigations on more extensive study populations are warranted to verify the relevance of an in vivo prooxidant state in WS patients.

The effects of partial thiamin deficiency and oxidative stress (i.e., glyoxal and methylglyoxal) on the levels of α-oxoaldehyde plasma protein adducts in Fischer 344 rats

We hypothesized that in marginal thiamin deficiency intracellular alpha-oxoaldehydes form macromolecular adducts that could possibly be genotoxic in colon cells; and that in the presence of oxidative stress these effects are augmented because of decreased detoxification of these aldehydes. We have demonstrated that reduced dietary thiamin in F344 rats decreased transketolase activity and increased alpha-oxoaldehyde adduct levels. The methylglyoxal protein adduct level was not affected by oral glyoxal or methylglyoxal in the animals receiving thiamin at the control levels but was markedly increased in the animals on a thiamin-reduced diet. These observations are consistent with our suggestion that the induction of aberrant crypt foci with marginally thiamin-deficient diets may be a consequence of the formation of methylglyoxal adducts.