Antioxidant and free radical-scavenging activity of Choto-san and its related constituents.

The antioxidant properties of Choto-san and its related constituents such as Chotoko and Choto-san without Chotoko, and phenolic compounds contained in Chotoko such as epicatechin, caffeic, acid and quercetin were evaluated. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging assay, the scavenging activity of Chotoko (IC(50) 14.3 microg/ml) was found to be higher than that of Choto-san (IC(50) 206.2 microg/ml) and Choto-san without Chotoko (IC(50) 244.3 microg/ml). Epicatechin (IC(50) 10.4 microM), caffeic acid (IC(50) 13.8 microM), and quercetin (IC(50) 7.1 microM) also revealed scavenging activity against DPPH radicals. Choto-san (IC(50) 67.7 microg/ml) exhibited stronger inhibitory activity against superoxide anion formation than Choto-san without Chotoko (IC(50) 92.4 microg/ml) but weaker activity than Chotoko (IC(50) 18.3 microg/ml). The generation of superoxide anion was also inhibited by epicatechin (IC(50) 175.2 microM), caffeic acid (IC(50) 141.7 microM), and quercetin (IC(50) 18.7 microM). In a hydroxyl radical-scavenging experiment, Choto-san (IC(50) 2.4 mg/ml), Chotoko (IC(50) 2.2 mg/ml), Choto-san without Chotoko (IC(50) 2.8 mg/ml), epicatechin (IC(50) 3.9 mM), caffeic acid (IC(50) 3.6 mM), and quercetin (IC(50) 1.9 mM) exhibited activity. In NG108-15 cells, when added simultaneously with H(2)O(2) (500 microM), Choto-san (250 microg/ml), Chotoko (250 microg/ml), Choto-san without Chotoko (500 microg/ml), epicatechin (200 microM), caffeic acid (200 microM), and quercetin (200 microM) effectively protected cells from oxidative damage. In conclusion, the present results provide evidence that Choto-san acts as an antioxidant and cytoprotective agent against oxidative damage, which is due at least partly to the phenolic compounds contained in Chotoko.