Divergence between LDL oxidative susceptibility and urinary F-2-isoprostanes as measures of oxidative stress in type 2 diabetes

Background: Oxidative stress is pivotal in atherogenesis. Although the most widely used indirect assay to quantify oxidative stress is LDL oxidative s usceptibility, direct assays such as urinary F-2-isoprostanes have shown gr eat promise. Methods: We evaluated the utility of both a direct measure of oxidative str ess (urinary F-2-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 F-2-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 F-2-isoprostane measurement. An excellent correlation fo r F-2-isoprostane concentrations was obtained between a timed collection vs 24-h urine (r = 0.96; n = 46). Baseline F-2-isoprostane concentrations by EIA were significantly higher in both type 2 diabetics with and without mac rovascular complications compared with controls (P < 0.001). Supplementatio n with alpha -tocopherol led to a significant reduction in F-2-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 w ere no significant differences in LDL oxidation in both diabetic groups com pared with controls. alpha -Tocopherol supplementation led to significant i ncreases in the lag phase of oxidation as measured by 3 indices in all grou ps. Conclusions: The measurement of urinary F-2-isoprostanes provides a direct measure of in vivo lipid peroxidation and oxidative stress and appears to b e superior to an indirect measure, e.g., LDL oxidative susceptibility, in t ype 2 diabetes. (C) 2001 American Association for Clinical Chemistry.