Abstract
Terminalia arjuna (T. arjuna) is an Indian medicinal plant credited with cardiotonic and cardioprotective properties; and baicalein is the active ingredient. To determine the possible mechanisms of protective action of T. arjuna and baicalein, we studied the reactions of T. arjuna extracts and baicalein with the biologically important superoxide (O2·−) and singlet oxygen (1O2) by measuring O2·− or 1O2 induced damage of lipids, lipid preoxidation, in the reaction mixture containing rat liver mitochondria and cardiac homogenate. Absorption of T. arjuna and baicalein in rat small intestine was also assessed. In addition, inhibitory effect of T. arjuna and baicalein on radiation-induced ROS generation in NIH3T3 cells and a cell-free chemical system, as well as on whole plasma oxidation were studied. Significant absorption of T. arjuna and baicalein from the intestine was observed. Baicalein is highly effective in inhibiting lipid peroxidation, reactive oxygen species generation, and plasma oxidation, even at low concentrations of 10-25 μM. To determine the possible mechanisms in this phenomena, we studied the reaction of T. arjuna extracts and baicalein with O2·− and 1O2 using electron spin resonance and found that T. arjuna extracts and baicalein possess higher scavenging activities than that of standard antioxidants; 50% Inhibitory concentration (IC50) of the aqueous extract of T. arjuna is 0.6 × 10−3 and 22.5 × 10−3% (w/v) and IC50 of baicalein for O2·− is 18 μM, while IC50 for 1O2 is 129 μM. Pulse radiolysis study with baicalein shows that the bimolecular rate constant between baicalein and O2·− is 1 × 108 M−1s−1. In conclusion, our results show that T. arjuna and baicalein are very potent in membrane protection against O2·− and 1O2 in vitro, and their ability to react with these species may explain previously observed effects of this plant and its active ingredient.
