Protection against peroxynitrite reactions by flavonoids.

Peroxynitrite is believed to contribute to pathogenesis of various diseases. Search for drugs and nutraceuticals able to limit peroxynitrite reactions is thus of interest. This study aimed to compare the capacity of 16 flavonoids and several other compounds present in food to prevent peroxynitrite reactions in three different test systems, based on fluorescein bleaching, tyrosine nitration and serum albumin thiol oxidation. The sequence of protective capacity of the antioxidants was different in various systems. Correlation analysis revealed that the hydroxyl group at the R'4 position of the flavonoids contributes significantly to prevention of fluorescein bleaching, R3-OH is important for prevention of thiol oxidation while R5-OH and R'3-OH are significant in prevention of tyrosine nitration. The total number of hydroxyl groups correlated with the ability of flavonoids to prevent oxidation reactions and the presence of vicinal hydroxyl groups correlated with flavonoid reactivity in all systems used.