Degradation products of proteins damaged by glycation, oxidation and nitration in clinical type 1 diabetes

Abstract

Aims/hypothesis: Hyperglycaemia in diabetes is associated with increased glycation, oxidative stress and nitrosative stress. Proteins modified consequently contain glycation, oxidation and nitration adduct residues, and undergo cellular proteolysis with release of corresponding free adducts. These free adducts leak into blood plasma for eventual renal excretion. The aim of this study was to perform a comprehensive quantitative analysis of protein glycation, oxidation and nitration adduct residues in plasma protein and haemoglobin as well as of free adducts in plasma and urine to quantify increased protein damage and flux of proteolytic degradation products in diabetes. Methods: Type 1 diabetic patients (n=21) and normal healthy control subjects (n=12) were studied. Venous blood samples, with heparin anticoagulant, and 24-h urine samples were taken. Samples were analysed for protein glycation, oxidation and nitration adducts by a quantitative comprehensive screening method using liquid chromatography with triple quadrupole mass spectrometric detection. Results: In type 1 diabetic patients, the concentrations of protein glycation, oxidation and nitration adduct residues increased up to three-fold in plasma protein and up to one-fold in haemoglobin, except for decreases in pentosidine and 3-nitrotyrosine residues in haemoglobin when compared with normal control subjects. In contrast, the concentrations of protein glycation and oxidation free adducts increased up to ten-fold in blood plasma, and urinary excretion increased up to 15-fold in diabetic patients. Conclusions/interpretation: We conclude that there are profound increases in proteolytic products of glycated and oxidised proteins in diabetic patients, concurrent with much lower increases in protein glycation and oxidation adduct residues.

Relationship between free iron and glycated hemoglobin in uncontrolled type 2 diabetes patients associated with complications

“…However we did not observe increase in free iron in group II cases who were in good glycemic control (The means of the parameters in all the groups are presented in Table I). According to previous studies, poor glycemic control leads to increase in the levels of lipid hydroperoxides and decrease in total thiols (15). In line with previous studies we found significant decrease in protein bound thiols (p<0.01), which may be due to increased oxidative degradation of proteins especially albumin or increased consumption of this antioxidant in stress environment.…”

“…Existence of oxidative stress in diabetes is well proved by numerous studies (14). Previous studies have proved that poor glycemic control causes glycation of proteins and increased oxidative damage of proteins which are responsible for the diabetes related complications (15). In this context, the presence of oxidative stress, hyperglycemia, hyperinsulinaemia, iron overload, and protein glycation will all lead to insulin resistance and poor glycemic control that causes early appearance of complications associated with diabetes (3).…”

Glycated and Oxidized Protein Degradation Products Are Indicators of Fasting and Postprandial Hyperglycemia in Diabetes

“…The hydroimidazolones MG-H1 and 3DG-H emerged as sensitive indicators of this because the concentrations of their precursors increase rapidly (21) in response to increased glucose concentration. Hydroimidazolones are also the major quantitative glycation adducts formed from these precursors, with diabetes-associated MG-H1-free adduct concentrations achieving levels 3-to 10-fold higher than other free AGE adducts, as shown in the present and prior studies (26,39). CML probably emerged as an indicator sensitive to PPG because oxidative stress enhanced in the postprandial period increased the rate of degradation of fructosyl-lysine to CML.…”

Autoimmunity and oxidatively modified autoantigens

“…Sera from patients with type 1 diabetes mellitus bind these complexes much more strongly than they bind the glutamic acid decarboxylase monomer. Thus, oxidative modification of glutamic acid decarboxylase may be important in type 1 diabetes mellitus patients pathogenesis [6,39].…”