Methylglyoxal

About: Methylglyoxal is a research topic. Over the lifetime, 2844 publications have been published within this topic receiving 102037 citations. The topic is also known as: acetylformaldehyde & pyruvaldehyde.

Insulin glycation by methylglyoxal results in native-like aggregation and inhibition of fibril formation

Abstract: Insulin is a hormone that regulates blood glucose homeostasis and is a central protein in a medical condition termed insulin injection amyloidosis. It is intimately associated with glycaemia and is vulnerable to glycation by glucose and other highly reactive carbonyls like methylglyoxal, especially in diabetic conditions. Protein glycation is involved in structure and stability changes that impair protein functionality, and is associated with several human diseases, such as diabetes and neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Familiar Amyloidotic Polyneuropathy. In the present work, methylglyoxal was investigated for their effects on the structure, stability and fibril formation of insulin. Methylglyoxal was found to induce the formation of insulin native-like aggregates and reduce protein fibrillation by blocking the formation of the seeding nuclei. Equilibrium-unfolding experiments using chaotropic agents showed that glycated insulin has a small conformational stability and a weaker dependence on denaturant concentration (smaller m-value). Our observations suggest that methylglyoxal modification of insulin leads to a less compact and less stable structure that may be associated to an increased protein dynamics. We propose that higher dynamics in glycated insulin could prevent the formation of the rigid cross-β core structure found in amyloid fibrils, thereby contributing to the reduction in the ability to form fibrils and to the population of different aggregation pathways like the formation of native-like aggregates.

Immunological Detection of a Novel Advanced Glycation End-Product

Abstract: The advanced stage of the Maillard reaction that leads to the formation of advanced glycation end-products (AGEs) plays an important role in the pathogenesis of angiopathy in diabetic patients and in the aging process. Recently, it has been proposed that the intermediates contributing to AGE formation include dicarbonyl intermediates such as glyoxal, methylglyoxal, and 3-deoxyglucosone (3-DG). In the present study, we developed a novel, non-carboxymethyllysine (CML) anti-AGE antibody that recognizes serum proteins and peptides modified by 3-DG in vivo. AGE-modified serum albumins were prepared by incubation of rabbit serum albumin with 3-DG or D-glucose. After immunization of rabbits, anti-AGE antisera were subjected to affinity chromatography on a Sepharose 4B column coupled with CML-BSA, or AGE-BSA created by incubation with 3-DG (AGE-6) or D-glucose (AGE-1). The AGE-Ab-6 and AGE-Ab-1 thus obtained was used to investigate AGEs in serum from diabetic patients on hemodialysis. Characterization of the novel AGE-Ab-6 obtained by immunoaffinity chromatography was performed with a competitive ELISA and immunoblot analysis. This antibody specifically cross-reacted with proteins modified by 3-DG. AGE-6 was detected in diabetic serum as three peaks with apparent molecular weights of 200, 1.15, and 0.85 kD, while AGE-1 was detected as four peaks with apparent molecular weights of 200, 65, 1.15, and 0.85 kD. This study provides new data on the pathways of AGE formation from 3-DG and methods for the immunochemical detection of AGEs. We also provide immunochemical evidence for the existence of six distinct AGEs in vivo among the AGE-modified proteins and peptides in the serum of diabetic patients on hemodialysis.

The Saccharomyces cerevisiae aldose reductase is implied in the metabolism of methylglyoxal in response to stress conditions.

Abstract: The enzyme aldose reductase plays an important role in the osmo-protection mechanism of diverse organisms. Here, we show that yeast aldose reductase is encoded by the GRE3 gene. Expression of GRE3 is carbon-source independent and up-regulated by different stress conditions, such as NaCl, H2O2, 39 °C and carbon starvation. Measurements of enzyme activity and intracellular sorbitol in wild-type cells also indicate that yeast aldose reductase is stress-regulated. Overexpression of GRE3 increases methylglyoxal tolerance in Saccharomyces cerevisiae. Furthermore, high expression of GRE3 complements the deficiency of the glyoxalase system of a glo1Δ mutant strain. Consistent with this, in vitro and in vivo assays of yeast aldose reductase activity indicate that methylglyoxal is an endogenous substrate of aldose reductase. Furthermore, addition of NaCl or H2O2 to exponential-phase cells triggers an initial transient increase in the intracellular level of methylglyoxal, which is dependent on the Gre3p and Glo1p function. These observations indicate that the metabolism of methylglyoxal is stimulated under stress conditions; and they support a methylglyoxal degradative pathway, in which this compound is metabolised by the action of aldose reductase.

Formation of Pyrazines in Maillard Model Systems of Lysine-Containing Dipeptides

Abstract: Whereas most studies concerning the Maillard reaction have focused on free amino acids, little information is available on the impact of peptides and proteins on this important reaction in food chemistry. Therefore, the formation of flavor compounds from the model reactions of glucose, methylglyoxal, or glyoxal with eight dipeptides with lysine at the N-terminus was studied in comparison with the corresponding free amino acids by means of stir bar sorptive extraction (SBSE) followed by GC-MS analysis. The reaction mixtures of the dipeptides containing glucose, methylglyoxal, and glyoxal produced 27, 18, and 2 different pyrazines, respectively. Generally, the pyrazines were produced more in the case of dipeptides as compared to free amino acids. For reactions with glucose and methylglyoxal, this difference was mainly caused by the large amounts of 2,5(6)-dimethylpyrazine and trimethylpyrazine produced from the reactions with dipeptides. For reactions with glyoxal, the difference in pyrazine production was rather small and mostly unsubstituted pyrazine was formed. A reaction mechanism for pyrazine formation from dipeptides was proposed and evaluated. This study clearly illustrates the capability of peptides to produce flavor compounds that can differ from those obtained from the corresponding reactions with free amino acids.