Presence of dopa and amino acid hydroperoxides in proteins modified with advanced glycation end products (AGEs): amino acid oxidation products as a possible source of oxidative stress induced by AGE proteins

Abstract

Glycation and subsequent Maillard or browning reactions of glycated proteins, leading to the formation of advanced glycation end products (AGEs), are involved in the chemical modification of proteins during normal aging and have been implicated in the pathogenesis of diabetic complications. Oxidative conditions accelerate the browning of proteins by glucose, and AGE proteins also induce oxidative stress responses in cells bearing AGE receptors. These observations have led to the hypothesis that glycation-induced pathology results from a cycle of oxidative stress, increased chemical modification of proteins via the Maillard reaction, and further AGE-dependent oxidative stress. Here we show that the preparation of AGE-collagen by incubation with glucose under oxidative conditions in vitro leads not only to glycation and formation of the glycoxidation product Nepsilon-(carboxymethyl)lysine (CML), but also to the formation of amino acid oxidation products on protein, including m-tyrosine, dityrosine, dopa, and valine and leucine hydroperoxides. The formation of both CML and amino acid oxidation products was prevented by anaerobic, anti-oxidative conditions. Amino acid oxidation products were also formed when glycated collagen, prepared under anti-oxidative conditions, was allowed to incubate under aerobic conditions that led to the formation of CML. These experiments demonstrate that amino acid oxidation products are formed in proteins during glycoxidation reactions and suggest that reactive oxygen species formed by redox cycling of dopa or by the metal-catalysed decomposition of amino acid hydroperoxides, rather than by redox activity or reactive oxygen production by AGEs on protein, might contribute to the induction of oxidative stress by AGE proteins.

Assessment of in vivo Oxidative Stress in Hypertensive Rats and Hypertensive Subjects in Tanzania, Africa.

“…Our findings in a previous report suggested that the accumulation of advanced glycation end products (AGEs) in the thoracic aorta from 12-week-old SHRSP was significantly higher than that in age-matched normotensive WKY (20). Several studies have suggested that AGE proteins induce oxidative stress (21,22), and that hydrogen peroxide may be a candidate for reactive oxygen species that contribute to the oxidative damage of smooth muscle cells (23). In addition, findings in a cell culture study we conducted suggested that AGEs dose-dependently increased the 8-OHdG in a bathing solution of cultured smooth muscle cells from SHRSP (submitted).…”

Histone carbonylation in vivo and in vitro

“…It is known that oxidation and glycation lead to the formation of carbonyl groups on target proteins [3,8,9]. Proteins modified by carbonyl groups due to oxidative modifications can be detected by immunoassay following derivatization with the carbonylspecific reagent DNPH [20].…”

“…Protein-bound carbonyl groups are generated by direct oxidation of amino acid residues, such as lysine and arginine, by reaction with aldehydes, such as 4-hydroxy-2-nonenal and malondialdehyde, produced by lipid peroxidation, and as a result of reaction with reducing sugars or their oxidation products [3,6,7]. The reaction with reducing sugars can generate protein carbonyls as ketoamines derived from early glycation reactions and by more complex glycoxidation reactions that lead to the generation of fluorescent advanced glycation end products (AGEs) and protein cross-links [3,8,9]. The presence of nuclear protein carbonyls has been detected in i o [10], but specific protein targets have not yet been identified.…”

The Oxidation of Lipoproteins by Monocytes-Macrophages

“…However, such a suggestion is tempered because of known pathways, mentioned above, for ⅐ OH-independent, metal ion-mediated lipid peroxidation (94,96). Significant amounts of ⅐ OH-dependent protein oxidation products were observed in advanced lesions (111).…”