Hamamelitannin as a new potent active oxygen scavenger

Abstract

The active oxygen scavenging activities of hamamelitannin (2′, 5-di- O-galloylhamamelose), which is a major constituent of Hamamelis virginiana, gallic acid, which is thought to be the active moiety of hamamelitannin, and propyl gallate which is a well-known antioxidant, were evaluated. In superoxide anion scavenging, the IC 50 values, which represent the concentration giving 50% inhibition of active oxygens generated, of hamamelitannin (1.31±0.06 μM), gallic acid (1.01±0.03 μM) and propyl gallate (1.41±0.01 μM) were higher than that of ascorbic acid (23.31±2.23 μM). In hydroxyl radical scavenging, hamamelitannin gave the lowest IC 50 value (5.46±0.04 μM) among the compounds tested; the values of gallic acid and propyl gallate were 78.04±11.23 and 86.46±2.31 μM, respectively. In singlet oxygen scavenging, the IC 50 values of hamamelitannin, gallic acid and propyl gallate were 45.51±2.00, 69.81±4.66 and 66.66±2.46 μM, respectively. Hamamelitannin was also found to have antioxidative and scavenging activities against organic radicals like DPPH (1, 1-diphenyl-2-picrylhydrazyl). In a cell culture system, the protective activities of hamamelitannin on cell damage induced by active oxygens, such as superoxide anion radicals, hamamelitannin on cell damage induced by active oxygens, such as superoxide anion radicals, hydroxyl radicals and singlet oxygens, were also evaluated. Against superoxide anion radicals hamamelitannin and propyl gallate protected the cells at over 50 μM, while the protective activity of gallic acid was observed at 500 μM. In contrast, against hydroxyl radicals, hamamelitannin showed protective activity at over 500 μM, while gallic acid and propyl gallate protected at 50 μM. Against singlet oxygens, hamamelitannin indicated survival of 80.6±1.5% at 100 μM, in which the survival of the control was 60.4±6.2%. Gallic acid and propyl gallate showed survivals of 98.6±7.3 and 85.2±4.9% at 500 μM, respectively. DMPO (5,5-dimethyl-1-pyrroline- N-oxide) and PBN (α-phenyl- N-t-butylnitrone) typical ESR spin-trap reagents, were found to protect against cell damage induced by superoxide anion and hydroxyl radicals.