Parameters of oxidative stress status in healthy subjects: Their correlations and stability after sample collection

It has been proposed that sample storage may have some influence on the parameters of oxidative stress status (OSS) in biological fluids. We measured four important OSS parameters in plasma of 23 healthy subjects and repeated the measurements in the same samples kept at -70 degrees C after different time intervals. Hydroperoxides and total antioxidant capacity (TAC) were determined by ferrous ion oxidation in presence of xylenol orange (FOX) and ferric reducing antioxidant power (FRAP) assays, respectively. Sulfhydryls and carbonyls were measured spectrophotometrically. In fresh samples, OSS seemed to increase with age and relatively good correlations were found among different parameters. The mean values of hydroperoxides (6.08 mu M), TAC (0.334 mM Trolox equivalent), and sulfhydryls (0.562 mM) in fresh samples did not show any significant change after 1, 7, and 30 days of storage. Mean carbonyl concentration determined after 1 day storage (2.0 nmol/mg protein) did not change after 30 days. However, extents of changes in hydroperoxide concentrations varied considerably from one individual to another, even after 1 day. A similar phenomenon was observed in TAC, but after 7 days. We suggest measuring hydroperoxides in fresh samples and TAC maximally after 1 week. Sulfhydryls and carbonyls showed more stability and can be measured at least 1 month after sample collection.