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

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 F(2)-isoprostanes have shown great promise.

We evaluated the utility of both a direct measure of oxidative stress (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.

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 for 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 macrovascular complications compared with controls (P <0.001). Supplementation 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 were no significant differences in LDL oxidation in both diabetic groups compared with controls. alpha-Tocopherol supplementation led to significant increases in the lag phase of oxidation as measured by 3 indices in all groups.

The measurement of urinary F(2)-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.