Effects of Acute Experimental Hyperglycemia on Oxidative Markers and AGE-RAGE Dynamics in Obese Humans

Chronic hyperglycemia promotes oxidative stress and advanced glycation end product (AGE) formation, leading to recognition by the AGE receptor (RAGE). AGE-RAGE binding and inflammation perpetuates diabetic complications, however the study of these phenomenon present inherent challenges in vivo. Therefore, our purpose was to evaluate the effects of acute experimental hyperglycemia on AGEs, oxidative markers, and RAGE expression in healthy, obese subjects (n=10; 31.2±1.2 kg/m²; 56±3 y) subjected to hyperglycemic clamps (+5.4 mM above basal). Plasma was assayed at baseline, 2, and 24 h post glucose-infusion for well-known AGE-free adducts (CML, CEL, G-H1, MG-H1, 3DG-H) and oxidative markers (MethSO, AAA) via LC-MS/MS as well as soluble RAGE (sRAGE) isoforms via ELISA. Urine was also assayed (basal and 24 h) for AGEs and oxidative markers (normalized to creatinine) and skeletal muscle biopsies were used to study RAGE expression via Western blot. Most circulating factors (MethSO, AAA, CEL, MG-H1, and G-H1) decreased (p<0.05) over time, while CML increased (p<0.05) and 3DG-H remained unchanged (p>0.05). In urine, only MethSO was seen to increase at 24 h (p<0.05). Plasma:Urine ratios were decreased (p<0.05) for MethSO, AAA, CML, MG-H1, while ratios were increased (p<0.05) for CML. All species of sRAGE isoforms (total, cleaved and esRAGE) were unchanged (p>0.05). In skeletal muscle tissue, there was a trend (p<0.1) for decreased RAGE protein expression at 2 h which returned to baseline at 24 h. This study demonstrates AGEs and oxidative markers are sensitive to the physiological dynamics of acute hyperglycemia in obese, but otherwise healthy humans. The differential findings presented here were surprising and may be explained by increased AGE-RAGE binding or AGE sequestration, osmotic diuresis and/or oxidative defense mechanisms. These findings are relevant for postprandial glucose excursions and highlights the importance of appropriate glucose management.