Direct scavenging of nitric oxide and superoxide by green tea

In the present study, we investigated the free radical scavenging effects of green tea extract and green tea tannin mixture and its components using a nitric oxide (NO) and superoxide (O2−) generating system in vitro. Green tea extract showed direct scavenging activity against NO and O2− and green tea tannin mixture, at the same concentration, showed high scavenging activity. Comparison of the activities of seven pure compounds isolated from green tea tannin mixture showed that (−)-epigallocatechin 3-O-gallate (EGCg), (−)-gallocatechin 3-O-gallate (GCg) and (−)-epicatechin 3-O-gallate (ECg) had higher scavenging activities than (−)-epigallocatechin (EGC), (+)-gallocatechin (GC), (−)-epicatechin (EC) and (+)-catechin (C), showing the importance of the structure of flavan-3-ol linked to gallic acid for this activity. Among the gallate-free tannins, EGC and GC were more effective O2− scavengers than EC and C, indicating the O-trihydroxy structure in the B ring is an important determinant of such activity. However, this structure did not affect the NO scavenging activity. These findings confirm that green tea tannin has excellent antioxidant properties, which may be involved in the beneficial effect of this compound.