ascorbic-acid and pyrogallol-sulfonphthalein

The oxygen radical absorbance capacity (ORAC) methodology has been employed to estimate the antioxidant capacity of human blood plasma and human urine using pyrogallol red (ORAC-PGR) as target molecule. Uric acid, reduced glutathione, human serum albumin, and ascorbic acid (ASC) inhibited the consumption of pyrogallol red, but only ASC generated an induction time. Human blood plasma and human urine protected efficiently pyrogallol red. In these assays, both biological fluids generated neat induction times that were removed by ascorbate oxidase. From these results, ORAC-PGR method could be proposed as a simple alternative to evaluate an ORAC index and, simultaneously, to estimate the concentration of ascorbic acid in human blood plasma or human urine.

Topics: Antioxidants; Ascorbic Acid; Glutathione; Humans; Kinetics; Pyrogallol; Reactive Oxygen Species

Peroxynitrite is implicated in numerous human diseases. Hence, there is considerable interest in potential therapeutic peroxynitrite scavengers. It has been claimed that uric acid is a powerful peroxynitrite scavenger. We previously observed that uric acid is a powerful inhibitor of tyrosine nitration induced by peroxynitrite, but fails to prevent alpha(1)-antiproteinase (alpha(1)-AP) inactivation induced by peroxynitrite. However, the reactivity of peroxynitrite is significantly modified by bicarbonate and this has not been considered in evaluating the scavenging activity of uric acid and other endogenous antioxidant compounds. In the presence of bicarbonate (25 mM), the ability of uric acid, ascorbate, Trolox, and GSH to inhibit peroxynitrite-mediated tyrosine and guanine nitration is decreased. Protection against peroxynitrite-mediated alpha(1)-AP inactivation is also decreased by ascorbate, Trolox, and GSH, but it is enhanced by uric acid. Bicarbonate also inhibits the ability of these compounds to prevent peroxynitrite-mediated ABTS radical cation formation. However, the abilities of these antioxidants to prevent peroxynitrite-mediated bleaching of pyrogallol red are enhanced by bicarbonate. These results show that physiologic concentrations of bicarbonate substantially modify the ability of uric acid to prevent peroxynitrite-mediated reactions. This study highlights the need to use several different assays in the presence of physiologically relevant concentrations of bicarbonate when assessing compounds for peroxynitrite scavenging, in order to avoid misleading results.

Topics: alpha 1-Antitrypsin; Antioxidants; Ascorbic Acid; Benzothiazoles; Bicarbonates; Chromans; Coloring Agents; Glutathione; Guanine; Humans; Indicators and Reagents; Peroxynitrous Acid; Pyrogallol; Reactive Nitrogen Species; Serine Proteinase Inhibitors; Sulfonic Acids; Tyrosine; Uric Acid