Cautions in the use of biomarkers of oxidative damage; the vascular and antioxidant effects of dark soy sauce in humans

Dark soy sauce (DSS) is a powerful antioxidant in vitro. We investigated whether this effect could occur in vivo and improve vascular function. Healthy human subjects were given DSS or placebo meals in a randomized, crossover study. Blood and urine were sampled before and 1, 2, 3, and 4 h after the meal for F2-isoprostanes (total, free, and esterified) and 8OHdG measurements. Blood pressure, vascular augmentation index (AIx), and heart rate (HR) were also measured. Plasma total F2-isoprostanes significantly decreased 3 h after placebo and the decrease was greater for DSS. Plasma free and esterified F2-isoprostanes were also significantly decreased after DSS. Both placebo and DSS meals increased urinary F2-isoprostanes at 1 h but not thereafter, and lowered urinary 8OHdG levels, DBP and AIx, and increased HR. We conclude that DSS decreases lipid peroxidation in vivo. However, oxidative damage biomarkers changed after the placebo meal, a phenomenon to consider when designing interventional studies.