Free Radicals Generated during the Glycation Reaction of Amino Acids by Methylglyoxal

Abstract

The formation of ␣-dicarbonyl compounds seems to be an important step for cross-linking proteins in the glycation or Maillard reaction. To elucidate the mechanism for the cross-linking reaction, we studied the reaction between a three-carbon ␣-dicarbonyl compound, methylglyoxal, and amino acids. Our results showed that this reaction generated yellow fluorescent products as formed in some glycated proteins. In addition, three types of free radical species were also produced, and their structures were determined by EPR spectroscopy. These free radicals are 1) the cross-linked radical cation, 2) the methylglyoxal radical anion as the counterion, and 3) the superoxide radical anion produced only in the presence of oxygen. The generation of the crosslinked radical cations and the methylglyoxal radical anions does not require metal ions or oxygens. These results indicate that dicarbonyl compounds cross-link free amino groups of protein by forming Schiff bases, which donate electrons directly to dicarbonyl compounds to form the cross-linked radical cations and the methylglyoxal radical anions. Oxygen can accept an electron from the radical anion to generate a superoxide radical anion, which can initiate damaging chain reactions. Time course studies suggest that the cross-linked radical cation is a precursor of yellow fluorescent glycation end products.

Glucitol-core containing gallotannins inhibit the formation of advanced glycation end-products mediated by their antioxidant potential

“…For modulation amplitude of 1 G, a multi-line spectrum was detectable within about three minutes (see Supplementary Information Figure S3) which closely matched the results obtained by Yim et al . 44 Signal intensity increased for about 10 minutes and then decreased. Blank solutions containing either MGO or GA alone did not produce a detectable signal confirming that the radical species are generated from the reaction solely between MGO and L-alanine.…”

Edaravone Protects against Methylglyoxal-Induced Barrier Damage in Human Brain Endothelial Cells

“…As methylglyoxal generates not just carbonyl [18] but also oxidative stress [23], [24], ROS production in cells treated with 600 µM methylglyoxal was investigated at different time points (Figure 2A). The fluorescence intensity in cultured human brain endothelial cells measured by DCFDA assay at 1 hour time point was considered as 100% (1285.6±105.2, fluorescence intensity in arbitrary units).…”

“…The end products of the reactions between methylgyoxal and free amino groups of molecules are insoluble protease-resistant polymers (advanced glycation end products AGE) [22]. Methylglyoxal triggers carbonyl [18] and oxidative stress [23], [24] and activates a series of inflammatory responses leading to accelerated vascular endothelial damage [25]–[27].…”

LR-90 prevents methylglyoxal-induced oxidative stress and apoptosis in human endothelial cells

“…There are several ways by which intracellular ROS levels could be increased by MGO. These include production of superoxide anion and hydrogen peroxide during the glycation reaction of amino acids or proteins, depletion of the glutathione content of cells during MGO metabolism by the glyoxalase system, and inactivation of enzymes which scavenge ROS such as superoxide dismutases, glutathione peroxidases, and glutathione transferases [33–35]. More importantly, MGO-stimulated increase in ROS levels can also contribute to the vicious cycle of ROS-AGE-RAGE-ROS formation in the vasculature [36].…”