Overexpression of Glyoxalase-I Reduces Hyperglycemia-induced Levels of Advanced Glycation End Products and Oxidative Stress in Diabetic Rats

Abstract

The reactive advanced glycation end product (AGE) precursor methylglyoxal (MGO) and MGO-derived AGEs are associated with diabetic vascular complications and also with an increase in oxidative stress. Glyoxalase-I (GLO-I) transgenic rats were used to explore whether overexpression of this MGO detoxifying enzyme reduces levels of AGEs and oxidative stress in a rat model of diabetes. Rats were made diabetic with streptozotocin, and after 12 weeks, plasma and multiple tissues were isolated for analysis of AGEs, carbonyl stress, and oxidative stress. GLO-I activity was significantly elevated in multiple tissues of all transgenic rats compared with wild-type (WT) littermates. Streptozotocin treatment resulted in a 5-fold increase in blood glucose concentrations irrespective of GLO-I overexpression. Levels of MGO, glyoxal, 3-deoxyglucosone, AGEs, and oxidative stress markers nitrotyrosine, malondialdehyde, and F2-isoprostane were elevated in the diabetic WT rats. In diabetic GLO-I rats, glyoxal and MGO composite scores were significantly decreased by 81%, and plasma AGEs and oxidative stress markers scores were significantly decreased by ϳ50%. Hyperglycemia induced a decrease in protein levels of the mitochondrial oxidative phosphorylation complex in the gastrocnemius muscle, which was accompanied by an increase in the lipid peroxidation product 4-hydroxy-2-nonenal, and this was counteracted by GLO-I overexpression. This study shows for the first time in an in vivo model of diabetes that GLO-I overexpression reduces hyperglycemia-induced levels of carbonyl stress, AGEs, and oxidative stress. The reduction of oxidative stress by GLO-I overexpression directly demonstrates the link between glycation and oxidative stress.Prolonged exposure to hyperglycemia has detrimental effects on various cellular functions and is believed to be the most important factor in the development of vascular complications in diabetes. One of the hypotheses about how hyperglycemia leads to complications is the formation of advanced glycation end products (AGEs) 3 (1). In addition to the formation of AGEs by the classical Maillard reaction (2, 3), dicarbonyls such as methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucocone (3-DG) are also known to form AGEs. MGO is probably the most important precursor in this formation of AGEs (4). This highly reactive oxo-aldehyde is formed mainly by the non-enzymatic and enzymatic fragmentation of the triose phosphates glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. MGO reacts primarily with arginine residues to form the major AGEs, hydroimidazolone (MG-H1), argpyrimidine (AP) and tetrahydropyrimidine (THP), and with lysine residues to minor AGEs such as N⑀-(1-carboxyethyl)lysine (CEL). MGO is efficiently detoxified by the glyoxalase system. In this pathway MGO reacts with reduced glutathione (GSH) to a hemithioacetal adduct and then to S-Dlactoyl-glutathione, which is catalyzed by glyoxalase-I (GLO-I). This product is converted into D-lactate by glyoxalase-II, thereby reforming the consumed GSH. A s...

Glyoxalase-1 overexpression reduces endothelial dysfunction and attenuates early renal impairment in a rat model of diabetes

“…This decrease in vascular tissue levels of MGO and GO-derived AGEs demonstrates the efficiency of Glo1 overexpression in the detoxification of both GO and MGO. This is in accordance with our previous study in which we demonstrated that Glo1 overexpression prevents elevated blood levels of GO and MGO, and thereby decreases plasma AGE levels after 12 weeks of diabetes [13]. In contrast, the CML levels in the plasma could not be significantly decreased by Glo1 overexpression after 24 weeks of diabetes, suggesting that an excessive formation of CML via additional pathways, like lipid peroxidation, possibly exceeds the detoxification rate in this prolonged state of diabetes.…”

“…Animal model Heterozygous transgenic Glo1-overexpressing rats were crossed with wild-type Wistar rats (Nippon Seibutsu Zairyo Center, Saitama, Japan) to obtain enough Glo1 -overexpressing progeny for the experiment [13]. Young adult wild-type and Glo1 transgenic male rats (10 weeks of age) were rendered diabetic for a period of 24 weeks by a single intravenous injection of STZ (Sigma-Aldrich, Zwijndrecht, the Netherlands; 45 mg/kg body weight).…”

“…We previously showed in a rat model of diabetes that Glo1 overexpression detoxifies MGO and GO, and thereby decreases AGEs and markers of oxidative stress [13]. Furthermore, we recently demonstrated in an ex vivo model that high glucose levels and short-term diabetes-induced impairment of endothelium-dependent vasorelaxation in rat mesenteric arteries are mediated by intracellular MGO levels [14].…”

Protection against methylglyoxal-derived AGEs by regulation of glyoxalase 1 prevents retinal neuroglial and vasodegenerative pathology

“…GLO1-overexpressing rats were crossed with wild-type (WT) Wistar rats to obtain enough GLO1 progeny for the experiment. The rats were obtained from the Nippon Seibutsu Zairyo Center (Saitama, Japan) and studies using these animals have been recently published [19,20]. All animal studies were carried out in accordance with the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health.…”

“…This was accompanied by protection against high glucose-mediated dysfunction [17,18]. Overexpression of GLO1 in diabetic rats has been shown to be protective against AGE formation and oxidative stress in muscle [19], and also prevent abnormalities in endothelium-dependent vasorelaxation [20]. Likewise, regulation of GLO1 activity in cells can prevent diabetes-related cell dysfunction [21,22].…”