Divergence between LDL Oxidative Susceptibility and Urinary F2-Isoprostanes as Measures of Oxidative Stress in Type 2 Diabetes

Abstract

Abstract Background: Oxidative stress is pivotal in atherogenesis. Although the most widely used indirect assay to quantify oxidative stress is LDL oxidative susceptibility, direct assays such as urinary F2-isoprostanes have shown great promise. Methods: We evaluated the utility of both a direct measure of oxidative stress (urinary F2-isoprostanes) and an indirect measure of copper-catalyzed, LDL oxidation in a model of increased oxidative stress (diabetes). We also evaluated an enzyme immunoassay (EIA) method for urinary F2-isoprostanes with a gas chromatography–mass spectrometry method. Results: Excellent intraassay and interassay CVs of <4% were obtained with our EIA method. A good correlation was obtained between the two methods (r = 0.80; n = 68) of F2-isoprostane measurement. An excellent correlation for F2-isoprostane concentrations was obtained between a timed collection vs 24-h urine (r = 0.96; n = 46). Baseline F2-isoprostane concentrations by EIA were significantly higher in both type 2 diabetics with and without macrovascular complications compared with controls (P <0.001). Supplementation with α-tocopherol led to a significant reduction in F2-isoprostane concentrations in all diabetic patients compared with baseline values (2.51 ± 1.76 compared with 1.69 ± 1.32 ng/mg creatinine; P <0.001). There were no significant differences in LDL oxidation in both diabetic groups compared with controls. α-Tocopherol supplementation led to significant increases in the lag phase of oxidation as measured by 3 indices in all groups. Conclusions: The measurement of urinary F2-isoprostanes provides a direct measure of in vivo lipid peroxidation and oxidative stress and appears to be superior to an indirect measure, e.g., LDL oxidative susceptibility, in type 2 diabetes.