Fate of the glucose degradation products 3-deoxyglucosone and glyoxal during peritoneal dialysis

Conventional fluids for peritoneal dialysis (PD) contain reactive glucose degradation products (GDPs) as a result of glucose breakdown during heat-sterilization. GDPs in PD fluids (PDFs) have been associated with the progressive alteration of the peritoneal membrane during long-term PD by cytotoxic effects and formation of advanced glycation endproducts (AGEs). In this study, we investigated the possible fate of two characteristic GDPs, 3-deoxyglucosone (3-DG) and glyoxal, during PD. In vivo, 3-DG and glyoxal concentrations, which were analyzed by high-performance liquid chromatography (HPLC), decreased in PDFs by 78% and 88% during 4 h of dwell time. The PDFs were then incubated in vitro in the presence of the most important reaction partners of GDPs in the peritoneal cavity. Neither human peritoneal mesothelial cells, human peritoneal fibroblasts, soluble protein, an insoluble collagen surface, nor components of spent dialysate led to a significant reduction of 3-DG or glyoxal after 6 h. Only after long-term incubation, a noticeable decrease of 3-DG was observed (-37% after three weeks), more likely due to spontaneous degradation reaction than formation of advanced glycation endproducts. These results suggest that in the course of PD, 3-DG, and glyoxal are absorbed into the organism and thus might contribute to the systemic pool of reactive carbonyl compounds.     

Advanced glycation endproducts (AGEs) as uremic toxins

Products of non‐enzymatic glycation accumulate both in diabetic and non‐diabetic patients with renal failure. The increase in concentration is presumably due to increased generation, secondary to oxydative stress and due to decreased (renal) elimination; whether accumulation of AGEs of dietary origin plays a role is currently under investigation. AGE's have been related to progression of diabetic (and possibly also non‐diabetic) renal disease and to a number of complications of the uremic syndrome. These comprise beta‐2‐microglobulin‐derived dialysis‐related amyloidosis, dyslipidemia, vascular dysfunction and accelerated atherogenesis. A specific case is AGE related damage to the peritoneal membrane in CAPD patients. Removal of AGE by dialysis is negligible and even high flux dialysis eliminates only a quantitatively limited amount of AGE. In contrast, a rapid decrease of AGE concentrations in plasma is noted after renal transplantation. Dietary AGEs may contribute significantly to the total AGE load of the body, particularly in uremia.     

Advanced glycation endproducts (AGEs) as uremic toxins.

Products of non-enzymatic glycation accumulate both in diabetic and non-diabetic patients with renal failure. The increase in concentration is presumably due to increased generation, secondary to oxidative stress and due to decreased (renal) elimination; whether accumulation of AGEs of dietary origin plays a role is currently under investigation. AGE's have been related to progression of diabetic (and possibly also non-diabetic) renal disease and to a number of complications of the uremic syndrome. These comprise beta-2-microglobulin-derived dialysis-related amyloidosis, dyslipidemia, vascular dysfunction and accelerated atherogenesis. A specific case is AGE related damage to the peritoneal membrane in CAPD patients. Removal of AGE by dialysis is negligible and even high flux dialysis eliminates only a quantitatively limited amount of AGE. In contrast, a rapid decrease of AGE concentrations in plasma is noted after renal transplantation. Dietary AGEs may contribute significantly to the total AGE load of the body, particularly in uremia.     

Composition of amino acid in blood and dialysate by patients with in chronic renal insufficiency by peritoneal dialysis

Examination composition of amino acid in blood and dialysate by patients with in chronic renal insufficiency by peritoneal dialysis. As it turned out by these patients composition of amino acid in blood and dialysate near. Only variation composition and lowering concentration amino acid with branching chain.     

Preventive effects of guava (Psidium guajava L.) leaves and its active compounds against α-dicarbonyl compounds-induced blood coagulation

Diabetes is associated with a hypercoagulable state which may accelerate atherosclerosis, thrombosis and the diabetic microvascular complication. Endogenously produced α-dicarbonyl compounds are linked to the pathophysiology of diabetic complications. The effects of α-dicarbonyl compounds on coagulation parameters in vitro and the anticoagulant activities of aqueous extracts from guava leaves were examined. Incubation of plasma with glyoxal or methylglyoxal at 0.1 mM showed a significant decrease in thrombin clotting time (TT) (P < 0.05). However, they exhibited slight prolongation of the prothrombin time (PT) at 0.5 mM and no effect on the activated partial thromboplastin time (APTT). In order to define the action mechanism of the hypercoagulant activity, coagulation factors such as fibrinogen and antithrombin III activity were evaluated. The fibrinogen contents in plasma were decreased slightly with increasing concentrations of glyoxal and methylglyoxal. Moreover, methylglyoxal inhibited antithrombin III activity and over 80% of the activity was lost at 1.2 mM methylglyoxal. In contrast, guava leaf extracts exhibited significant inhibition of TT shortening induced by methylglyoxal. Guava leaf extracts and its active phenolic compounds including ferulic acid, gallic acid and quercetin also displayed a protective effect against methylglyoxal-induced loss of activity of antithrombin III. Thus, guava leaf extracts are a potent antiglycative agent and anticoagulant, which can be of great value in the preventive glycation-associated cardiovascular diseases in diabetes.     

Anti‐glycative and anti‐inflammatory effects of caffeic acid and ellagic acid in kidney of diabetic mice

Protective effects of caffeic acid (CA) and ellagic acid (EA) in kidney of diabetic mice were examined. CA or EA at 2.5 and 5% was mixed in diet and supplied to diabetic mice for 12 wk. Results showed that the intake of CA or EA increased renal content of these compounds, alleviated body weight loss, decreased urine output, increased plasma insulin and decreased blood glucose levels at weeks 6 and 12 (p<0.05). The intake of these compounds dose dependently reduced plasma blood urea nitrogen and elevated creatinine clearance (p<0.05). CA or EA at 5% significantly decreased the levels of plasma HbA1c, urinary glycated albumin, renal carboxymethyllysine, pentosidine, sorbitol and fructose (p<0.05), and significantly diminished renal activity of aldose reductase and sorbitol dehydrogenase, as well as suppressed renal aldose reductase mRNA expression (p<0.05). CA or EA dose dependently lowered renal levels of IL‐6, IL‐1β, tumor necrosis factor (TNF)‐α and monocyte chemoattractant protein 1 (MCP‐1) (p<0.05). Furthermore, CA or EA dose dependently down‐regulated tumor necrosis factor‐α and monocyte chemoattractant protein‐1 mRNA expression in kidney (p<0.05). Based on the observed anti‐glycative and anti‐inflammatory effects, the supplement of CA or EA might be helpful for the prevention or attenuation of diabetic kidney diseases.     

Phytochemicals from berries and grapes inhibited the formation of advanced glycation end‐products by scavenging reactive carbonyls

Phenolic phytochemicals were extracted from blueberries, blackberries, strawberries, raspberries, cranberries, and Noble muscadine grapes. These extracts were purified to remove free sugars. Blueberry extract was separated into five fractions using a Sephadex LH‐20 column. Berry extracts and fractions significantly inhibited AGEs generation in (bovine serum albumin) BSA‐fructose, BSA‐methylglyoxal, and arginine‐methylglyoxal models, respectively. Their capacity to scavenge methylglyoxal suggested carbonyl scavenging as a major mechanism of protein glycation inhibition. Procyanidins were detected in all berry extracts and blueberry subfractions and were deduced to be one class of active compounds. (+)‐Catechin, constituent unit of procyanidins, was used as a model compound to react with glyoxal and methylglyoxal. Five catechin‐carbonyl adducts were detected and their structures were tentatively identified using HPLC‐ESI‐MSⁿ. Results in this study suggested that sugar‐free phytochemicals extracted from berries were effective carbonyl scavengers and protein glycation inhibitors. These phytochemicals could be beneficial to prevent AGE‐related chronic diseases.     

Cranberry phytochemicals inhibit glycation of human hemoglobin and serum albumin by scavenging reactive carbonyls

Protein glycation caused by sugars and reactive carbonyls is a contributing factor to diabetic complications, aging, and other chronic diseases. The objective of this study was to investigate the inhibitory effects of cranberry phytochemicals on protein glycation. Cranberries, purified to yield sugar-free phytochemical powder, were fractionated into ethyl acetate and water fractions. Water fraction was further separated into water fraction I, II, and III on a Sephadex LH-20 column. Cranberry phytochemical powder and its fractions significantly inhibited the formation of glycated hemoglobin. The concentrations of cranberry phytochemicals required to inhibit 50% of albumin glycation (EC(50)) in albumin-glucose assay were lower than that of aminoguanidine except for water fraction I. Cranberry phytochemicals inhibited glycation of human serum albumin mediated by methylglyoxal, but the EC(50) were higher than that of aminoguanidine. Carbonyl scavenging assay showed that water fraction II scavenged 89.3% of methylglyoxal at 6 h of reaction. Fractions enriched with procyanidins showed higher antiglycation activities, suggesting procyanidins were the major active components. The hypothesis whether cranberry procyanidins scavenged reactive carbonyls by forming adducts was tested. Epicatechin was used as a model compound to react with methylglyoxal and glyoxal at pH 7.4. Five adducts were detected and their structures were tentatively identified using HPLC-ESI-MS/MS.     

A method for the detection of carbonyl compounds in wine: Glyoxal and methylglyoxal

Wine aldehydes were identified as O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine derivatives by GC-MS or with a GC-electron-capture detector. This method has been used to evaluate levels of glyoxal and methylglyoxal in wine. Reproducibility and linearity studies gave satisfying results. Glyoxal and methylglyoxal are formed during fermentation. Among the factors affecting their production, high musts pH increased the levels found in the corresponding wines. Various microorganisms of the wine such as Saccharomyces cerevisiae and Leuconostoc ænos can produce glyoxal and methylglyoxal. The concentrations in Sherry wines were particularly high. Because of the toxicological properties of these substances, their determination and the knowledge of their metabolism by wine microorganisms are very important.     

Reducing the formation of glucose degradation products in peritoneal dialysis solutions by ultrahigh temperature ohmic heating

Peritoneal dialysis (PD) is commonly performed by using preprepared dialysis solutions containing glucose, which are thermally treated to achieve commercial sterilization. A series of glucose degradation products (GDPs) are being formed, which react with the tissue during the dialysis procedure, thus baring a negative effect on the patient and the dialysis process. The present study tested the efficacy of ohmic heating as an alternative thermal treatment for continuous sterilization of PD solutions. The process was compared to conventional retort treatment, and GDPs accumulation was measured. Thermal treatments using the ohmic heating system were performed at three temperatures (105, 125, and 150 degrees C) with residence time at each temperature ranging from 0.84 to 12.0 s. The resulting concentrations of glyoxal (GO), methylglyoxal (MGO), and 3-deoxyglucosone (3-DG) in the PD solutions were measured. None of these GDPs were found in PD fluids treated by ohmic heating at 105 degrees C. The concentration of 3-DG, after a standard sterilization treatment (121 degrees C, 20 or 40 min) was one order of magnitude higher (approximately 140 and 242 microM) than after ohmic heating treatment at 125 degrees C. The results of the present study suggest that this technique can be used to produce solutions with much lower content of GDPs. It also demonstrates the advantage of using the ohmic heating technology as a tool for high temperature short time treatment of PD fluids.     

Effect of combined UV-thermosonication and Ecklonia cava extract on advanced glycation end-products in soymilk

Thermal treatment is used to inactivate microbes in soymilk, but it increases the amount of advanced glycation end products (AGEs). Therefore, this study examined if ultraviolet light with thermo-sonication (UVTS) and Ecklonia cava extract (EX) could provide an alternative process to prevent AGEs formation in processed soymilk. A coiled tube UV reactor was used simultaneously with an ultrasonic generator for UVTS treatment, while an autoclave was employed for thermal treatment. UVTS treatment was examined at different temperatures and flow rates to achieve a 5-log reduction of pre-inoculated Escherichia coli and Salmonella typhimurium in soymilk. After confirming EX's anti-glycation effects against fructosamine, ɑ-dicarbonyl compounds, protein carbonyl content, and AGEs formation, it was added to soymilk before the UVTS. The ɑ-dicarbonyl compounds (glyoxal and methylglyoxal) and AGEs (N^ε-(1-carboxymethyl)-l -lysine [CML] and N^ε-(1-carboxyethyl)-l -lysine [CEL]) in soymilk increased after autoclaving (AC). Compared with AC, the UVTS with .05% EX decreased glyoxal, methylglyoxal, CML, and CEL by 78%, 82%, 32%, and 59%, respectively. These results indicated that UVTS with EX could be an alternative pasteurization process for soymilk that minimizes AGEs formation.     

Antiglycative and anti-VEGF effects of s-ethyl cysteine and s-propyl cysteine in kidney of diabetic mice

Antiglycative and antivascular endothelial growth factor (VEGF) effects of s-ethyl cysteine (SEC), and s-propyl cysteine (SPC) in kidney of diabetic mice were examined. SEC and SPC at 1 and 2 g/L were added to the drinking water for 12 wk. Results showed that diabetic mice with SEC or SPC intake had significantly higher final body weight, lower kidney weight, lower levels of plasma glucose, urinary albumin (UA), and urinary creatinine (UC) (p < 0.05), in which dose-dependent effects were observed in reducing plasma glucose, UA, and UC (p < 0.05). The intake of these compounds significantly and dose-dependently decreased the levels of plasma glycated hemoglobin (HbA1c), renal carboxymethyllysine and urinary glycated albumin (p < 0.05). SEC or SPC intake significantly and dose-dependently diminished renal aldose reductase (AR) activity and enhanced glyoxalase I (GLI) activity (p < 0.05); also significantly decreased renal sorbitol and fructose concentrations (p < 0.05). The intake of SEC or SPC significantly lowered renal VEGF level (p < 0.05), and caused dose-dependent downregulation in AR mRNA expression, and upregulation in GLI mRNA expression (p < 0.05). Our present study suggests the supplement of SEC or SPC might be helpful for the prevention or treatment of diabetic kidney diseases via alleviating renal glycative injury.     

Antiinflammatory and antifibrogenic effects of s-ethyl cysteine and s-methyl cysteine in the kidney of diabetic mice

Protective effects of s-ethyl cysteine (SEC) and s-methyl cysteine (SMC) in kidney of diabetic mice were examined. SEC and SMC at 0.5, 1, 1.5, 2 g/L were added to the drinking water for 6 wk. Results showed that the intake of SEC or SMC alleviated body weight loss and urine output, as well as markedly decreased plasma blood urea nitrogen (BUN) and creatinine clearance (CCr) in diabetic mice (P < 0.05). The intake of SEC caused significantly dose-dependent increase in insulin and decrease in blood glucose, urinary albumin and type IV collagen (P < 0.05). SEC and SMC intake significantly and dose-dependently decreased malondialdehyde level and increased glutathione content in kidney (P < 0.05). The intake of these agents also increased renal GPx activity (P < 0.05), but there was no dose-dependent effect. SEC treatments dose-dependently decreased IL-6 and TNF-alpha levels, increased IL-4 and IL-10 levels, as well as upregulated IL-10 mRNA expression (P < 0.05). SMC treatments significantly suppressed renal IL-6 and TNF-alpha levels (P < 0.05), but did not affect IL-4 and IL-10 levels (P < 0.05). SEC or SMC intake significantly suppressed renal TGF-beta1 level and renal PKC activity (P < 0.05); however, only SEC treatments showed dose-dependent effect. SEC and SMC treatments significantly down-regulated mRNA expression of renal TGF-beta1 (P < 0.05), only SEC treatments had dose-dependent effects. Based on the observed antioxidative, antiinflammatory, and antifibrogenic effects, the supplement of SEC or SMC might be helpful for the prevention or treatment of diabetic kidney diseases.     

Cytotoxicity of α-dicarbonyl compounds submitted to in vitro simulated digestion process

α-Dicarbonyl compounds (α-DCs), such as glyoxal, methylglyoxal and 2,3-butanedione, are highly reactive substances occurring in thermally treated and fermented foods, that may react with amino and sulphydryl groups of side chains of proteins to form Maillard reaction end products, inducing a negative impact on the digestibility and on nutritional value of protein. In recent years the role of food derived α-DCs in gastroduodenal tract is under investigation to understand whether excess consumption of such dietary compounds might be a risk for human health. In this study the interactions between a mixture of glyoxal, methylglyoxal and 2,3-butanedione and the digestive enzymes (pepsin and pancreatin) were studied. The results showed that during gastroduodenal digestion α-DCs react with digestive enzymes to produce carbonylated proteins. Moreover, undigested and digested α-DC cytotoxicity against human cells, as well as their ability to inhibit the function of human enzymes responsible for DNA repair were shown.     

Anti‐Diabetic Effects of Gynura Bicolor Aqueous Extract in Mice

The effects of Gynura bicolor aqueous extract (GAE) upon glycemic control, coagulation disorder, lipid accumulation, and glycative, oxidative, and inflammatory stresses in diabetic mice were investigated. Mice were treated with streptozotocin to induce type 1 diabetes. Diabetic mice were divided into four groups, consumed GAE at 0%, 0.25%, 0.5%, or 1%. Normal group consumed standard mouse basal diet. After 8‐week treatments, mice were sacrificed after overnight fasting. Results showed that GAE supplement at 0.5% and 1% decreased plasma glucose level and increased plasma insulin level. Diabetes lowered plasma level of protein C and anti‐thrombin III; and raised plasminogen activator inhibitor‐1 activity and fibrinogen level in plasma. GAE supplement at 0.5% and 1% reversed these alterations. Histological data, assayed by Oil Red O stain, indicated that GAE supplement decreased lipid accumulation in liver. GAE supplement at 0.5% and 1% reduced aldose reductase activity in heart and kidney; and lowered the levels of carboxymethyllysine and pentosidine in plasma and two organs. Diabetes decreased glutathione content, and increased reactive oxygen species, interleukin (IL)‐1β, IL‐6, and tumor necrosis factor‐α production in heart and kidney. GAE supplement at three test doses reversed these changes. Diabetes upregulated the mRNA expression of p38 and nuclear factor kappa (NF‐κ)B in heart and kidney. GAE supplement suppressed the mRNA expression of both p38 and NF‐κB. These novel findings suggest that Gynura bicolor is a potent functional food for diabetic prevention or alleviation.     

Cytoprotective effects of phenolic acids on methylglyoxal-induced apoptosis in Neuro-2A cells

In the process of glycation, methylglyoxal is a reactive dicarbonyl compound physiologically generated as an intermediate of glycolysis, and is found in high levels in blood or tissue of diabetic models. Biological glycation has been commonly implicated in the development of diabetic microvascular complications of neuropathy. Increasing evidence suggests that neuronal cell cycle regulatory failure followed by apoptosis is an important mechanism in the development of diabetic neuropathy complication. Naturally occurring antioxidants, especially phenolic acids have been recommended as the major bioactive compounds to prevent chronic diseases and promote health benefits. The objective of this study was to investigate the inhibitory abilities of phenolic acids (chlorogenic acid, syringic acid and vanillic acid) on methylglyoxal-induced mouse Neuro-2A neuroblastoma (Neuro-2A) cell apoptosis in the progression of diabetic neuropathy. The data indicated that methylglyoxal induced mouse Neuro-2A neuroblastoma (Neuro-2A) cell apoptosis via alternation of mitochondria membrane potential and Bax/Bcl-2 ratio, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase. Furthermore, the results demonstrated that activation of mitogen-activated protein kinase signal pathways (JNK and p38) participated in the methylglyoxal-induced Neuro-2A cell apoptosis process. Treatment of Neuro-2A cells with phenolic acids markedly suppresses cell apoptosis induced by methylglyoxal, suggesting that phenolic acids possess cytoprotective ability in the prevention of diabetic neuropathy complication.     

Copper-catalyzed ascorbate oxidation results in glyoxal/AGE formation and cytotoxicity

Previously we showed that 10 muM glyoxal compromised hepatocyte resistance to hydrogen peroxide (H(2)O(2)) by increasing glutathione (GSH) and NADPH oxidation and decreasing mitochondrial membrane potential (MMP) before cytotoxicity ensued. Since transition metal-catalyzed oxidation of ascorbate (Asc) has been shown to result in the generation of both glyoxal and H(2)O(2), we hypothesized that glyoxal formation during this process compromises hepatocyte resistance to H(2)O(2). We used isolated rat hepatocytes and incubated them with Asc/copper and measured cytotoxicity, glyoxal levels, H(2)O(2), GSH levels, and MMP. To investigate the role of Asc/copper on glyoxal-BSA adducts, we measured the appearance of advanced glycation end-products (AGE) in the presence and absence of catalase or aminoguanidine (AG). Asc/copper increased glyoxal and H(2)O(2) formation. Hepatocyte GSH levels were decreased and cytotoxicity ensued after a collapse of the hepatocyte MMP. Glyoxal traps protected hepatocytes against Asc/copper-induced cytotoxicity. In cell-free studies with BSA, incubation with Asc and copper resulted in glyoxal-hydroimidazolone formation, which was decreased by both AG and catalase. To the best of our knowledge, this is the first study that illustrates the importance of glyoxal production by transition metal-catalyzed Asc autoxidation. Understanding this mechanism of toxicity could lead to the development of novel copper chelating drug therapies to treat diabetic complications.     

New Imidazoles Formed in Nonenzymatic Browning Reactions

1,3-Bis(carboxymethyl)imidazole was identified in a model reaction mixture derived from glycine, glyoxal, and formaldehyde. The same compound was also found in the reaction of glycine with glyoxal. The structure of this compound was elucidated from the measured molecular, mass and ¹H-NMR and ¹³C-NMR spectral data and confirmed by X-ray crystallographic measurements. Similarly, a 2-methyl-, 4-methyl-, and 2,4-dimethyl-1,3-bis(carboxymethyl)-imidazole were formed in reactions of glycine with glyoxal or methylglyoxal and formaldehyde or acetaldehyde. These 1,3-symmetrically substituted imidazoles represent quite a new group of N-containing heterocyclic compounds originating in model systems containing amino acids and α-dicarbonyl compounds and probably also in natural systems.     

The existence of the 1,2-dicarbonyl compounds glyoxal,methyl glyoxal and diacetyl in autoxidised edible oils

The 1,2-dicarbonyl compounds glyoxal, methyl glyoxal and diacetyl which are known to be mutagens without metabolic activation in the Salmonella typhimurium TA100 system, were detected in autoxidised edible oils (sesame, safflower and sardine oil). The method is based on the fact that the 1,2-dicarbonyl compounds react with 4-chloro-1,2-phenylenediamine to give 6-chloroquinoxaline derivatives, which can be detected by ⁶³Ni ECD-gas chromatography. Glyoxal, methyl glyoxal and diacetyl were detected at 4.7, 7.0 and 1.6 μg g^?1, respectively, in 20 h autoxidised methyl linolenate. Glyoxal, methyl glyoxal and diacetyl were also detected at 6.5, 7.0 and 3.1 μg g^?1, respectively, in 30 h autoxidised sardine oil.     

The detection of α‐dicarbonyl compounds in wine by formation of quinoxaline derivatives

A method to determine the most abundant α‐dicarbonyl compounds in wine was developed by reaction with 2,3‐diaminobenzene. Products such as quinoxaline derivatives were detected by high‐performance liquid chromatography (HPLC) or by gas chromatography with a mass‐selective detector (GC–MS) or a thermoionic detector (GC–NPD). HPLC and detection with a spectrophotometer (313 nm) were used for routine quantitative analysis of wines. The method is sensitive, linear and has good repeatability. Diacetyl, pentane‐2,3‐dione, glyoxal and methylglyoxal were quantified in a single run; these compounds are always encountered in wines, but levels vary with different types of wine and also during fermentation and maturation processes. A new dicarbonyl compound, phenylglyoxal, was found in wine. The evolution of dicarbonyl compounds during fermentation is reported in this paper. © 2000 Society of Chemical Industry