Direct radical scavenging by the bisbenzylisoquinoline alkaloid cepharanthine.

Cepharanthine (Ceph) is known as a potent antiperoxidative agent. Recently, we characterized the antiperoxidative effects of Ceph [Biochim. Biophys. Acta 1426 (1999) 133]. However, it was not clear whether the antiperoxidative effect is really due to its direct radical scavenging activity. Therefore, we studied the interaction of Ceph with the hydroxyl radical (*OH) by the electron paramagnetic resonance (EPR) technique. Results showed that Ceph actually scavenged *OH derived by the Fenton reaction. We also found that Ceph radicals were generated on interaction of Ceph with *OH in neutral aqueous solution, but not in acidic solution, consistent with the pH-dependent anti-lipid peroxidation activity of Ceph. Hence, we concluded that anti-lipid peroxidation by Ceph is due to its direct radical scavenging activity.