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PubMed1997

[The role of methylglyoxal in the development of diabetic complications].

The formation of methylglyoxal is increased during hyperglycemia associated with diabetes mellitus. Enhanced methylglyoxal concentration in biological systems is associated with increased reversible and irreversible modification of protein. The chronic exposure to high methylglyoxal concentrations appears to be linked to the development of diabetic complications. Intervention with aldose reductase inhibitors or aminoguanidine, which is an efficient scavenger of methylglyoxal, in diabetes mellitus may prevent increased methylglyoxal concentration.

Diabetes Mellitus↗
PubMed1998

[Participation of glyoxalases and methylglyoxal in diabetic complication development].

The glyoxalase system catalyses the conversion of methylglyoxal to D-lactate via intermediate S-D-lactoylgutathione. This system consists of two enzymes, glyoxalase I and glyoxalase II. A link between the development of diabetic complications and the glyoxalase system has been suggested at the genetic and metabolic level. Insulin-dependent diabetic patients without complications (retinopathy, neuropathy) had a significantly higher frequency of the glyoxalase phenotype GLO 1-1 than patients with complications. Periodic hyperglycaemia may contribute to the development of diabetic complication through methylglyoxal-mediated changes in protein solubility and aggregation characteristics.

Diabetes Mellitus, Type 1↗
PubMed1998

Methylglyoxal-derived modifications in lens aging and cataract formation.

PURPOSE: To determine whether the Maillard reaction of methylglyoxal is associated with human lens aging and cataractogenesis and to investigate how glutathione depletion affects methylglyoxal-derived modifications in organ-cultured lenses. METHODS: Antibodies against methylglyoxal-derived modifications were developed in rabbits and purified by immunoaffinity chromatography. A competitive enzyme-linked immunosorbent assay (ELISA) measured methylglyoxal-derived products in human lens proteins. Lenses of galactosemic rats grown in organ culture were used to assess the role of glutathione-dependent pathways in methylglyoxal metabolism and Maillard reactions. RESULTS: Methylglyoxal-derived modifications in the human lens were age dependent, and brunescent lenses had the highest levels of these modifications. Immunofluorescence staining identified antigens distributed throughout the lens, with higher levels in old lenses than in younger ones. Experiments with normal or galactosemic rat lenses grown in organ culture showed that lens proteins do not have an increase in methylglyoxal-modified proteins when cultured in medium containing 500 microM methylglyoxal alone, but they accumulate modified proteins when cultured with DL-glyceraldehyde. Inclusion of 30 mM glucose in the medium marginally increased methylglyoxal-derived products, but there was no correlation between lens glutathione content and methylglyoxal-derived modifications. CONCLUSIONS: Methylglyoxal-mediated Maillard reactions that occur in the human lens may play a role in lens aging and cataract formation. Methylglyoxal is probably derived from metabolic pathways within the lens. Decreased glutathione in organ-cultured rat lenses does not significantly influence methylglyoxal-mediated Maillard reactions.

Adolescent↗
PubMed1998

Immunohistochemical detection of imidazolone and N(epsilon)-(carboxymethyl)lysine in aortas of hemodialysis patients.

The modification of long-lived proteins with advanced glycation endproducts (AGEs) has been hypothesised to contribute to the development of pathologies associated with uremia. Imidazolone and N(epsilon)-(carboxymethyl)lysine (CML) are common epitopes of AGE-modified proteins. Imidazolone is a reaction product of arginine with 3-deoxyglucosone (3-DG) which is markedly accumulated in uremic serum. CML is produced by glycoxidation, and represents a marker of oxidative stress. The specificity of anti-imidazolone antibody that we had developed was further examined using ELISA. The antibody reacted only with imidazolone derived from 3-DG and arginine, but did not react at all with the other imidazolone-like compounds such as reaction products of glyoxal, methylglyoxal, glucosone with arginine or a reaction product of 3-DG with creatine. Further, to determine if AGEs are involved in the development of atherosclerosis in hemodialysis (HD) patients, we studied the localisation of imidazolone and CML in the aortas obtained from HD patients by immunohistochemistry using the anti-imidazolone and anti-CML antibodies. Imidazolone and CML were localised in all atherosclerotic aortic walls of the HD patients. In conclusion, imidazolone and CML are localised in the characteristic lesions of atherosclerosis in HD patients. These results strongly suggest that imidazolone produced by 3-DG, and CML produced by glycoxidation may contribute to the development of atherosclerosis in uremic patients.

Aged↗
PubMed1998

Chemical modification of proteins by methylglyoxal.

Methylglyoxal is formed in vivo by spontaneous decomposition of triose phosphate intermediates in aerobic glycolysis. It may also be formed during oxidative degradation of both carbohydrates (pentoses and ascorbate) and lipids (arachidonate). In addition to reaction with arginine residues to form imidazolone adducts, methylglyoxal reacts with lysine residues in protein to form N(epsilon)-(carboxyethyl)lysine (CEL) and the imidazolium crosslink, methylglyoxal-lysine dimer (MOLD). Like the glycoxidation products, N(epsilon)-(carboxymethyl)lysine (CML) and glyoxal-lysine dimer (GOLD) which are formed on reaction of glyoxal with protein, CEL and MOLD increase in lens proteins and skin collagen with age. CML and CEL also increase in skin collagen in diabetes, while all four compounds increase in plasma proteins in uremia. Overall, CML, CEL, GOLD and MOLD are quantitatively the major biomarkers of the Maillard reaction in tissue proteins. GOLD and MOLD, in particular, are present at 10-50 fold higher concentrations than the fluorescent crosslink, pentosidine. Together, these dicarbonyl-derived advanced glycation endproducts (AGEs) represent the major chemical modifications that accumulate in tissue proteins with age and in chronic diseases such as diabetes and atherosclerosis.

Adolescent↗
PubMed1998

Molecular mechanisms of diabetic complications.

The main molecular process responsible for the development of diabetic complications is the activation of intracellular protein kinase C by long-term hyperglycemia. In ordinary somatic cells (e.g., endothelial or retinal cells) this activation disturbs the metabolism of these cells, whereas a transition into an "excited state" of effector cells such as monocytes or polymorphonuclear leukocytes causes an avalanche-like increase of various pathological processes damaging the body. In relatively compensated diabetes mellitus, when the duration of hyperglycemia is not long and levels of hyperglycemia are not too high, the intensity of the above-mentioned processes is low. However, due to the long time course of reparative processes, some damages which appear in short periods of decompensation can accumulate in the body, finally causing the clinical manifestation of vascular complications of diabetes mellitus.

Diabetes Complications↗