Beetroot betalain inhibits peroxynitrite-mediated tyrosine nitration and DNA strand cleavage

Abstract

Two major betalains, red-purple betacyanins and yellow betaxanthins, were isolated from red beetroots (Beta vulgaris L.), and their peroxynitrite (ONOO − ) scavenging capacity was investigated. Apparent colours of the betalains were bleached by the addition of ONOO − , and the absorbance decreases were suppressed in the presence of glutathione, a ONOO − scavenger. After bleaching, a new absorption maximum was observed at 350 nm in the spectrum of the resulting reaction mixture. New peaks were detected from HPLC analysis of the reaction products of betanin, a representative constituent of red beetroot betacyanins, treated with ONOO − monitoring at 350 nm, and the intensity of the major peak was positively correlated with ONOO − concentration. Betanin inhibited the ONOO − (0.5 mM)-dependent nitration of tyrosine (0.1 mM). Additionally, the IC50 value of betanin (19.2 μM) was lower than that of ascorbate (79.6 μM). The presence of betanin (0.05–1.0 mM) also inhibited ONOO − (0.5 mM)-dependent DNA strand cleavage in a concentration-dependent manner. These results suggest that betalains can protect cells from nitrosative stress in addition to protecting them from oxidative stresses.