Peroxyl radical scavenging activities of hamamelitannin in chemical and biological systems.

The antioxidative activities of hamamelitannin (2',5-di-O-galloyl-hamamelose), gallic acid and dl-alpha-tocopherol against lipid peroxyl radicals were evaluated in chemical and biological systems. The peroxyl radical scavenging activity was evaluated by electron spin resonance (ESR) method in which both spin-trapping and direct reaction methods were used. In the spin-trapping method, as evaluated by 50% inhibition concentration (IC50) of peroxyl radicals generated in a t-butylhydroperoxide-methemoglobin system, hamamelitannin (IC50 = 95.3 +/- 2.7 microM) showed the highest activity, followed by gallic acid (IC50 = 152.8 +/- 14.6 microM) and dl-alpha-tocopherol (IC50 = 221.5 +/- 4.6 microM) as a positive control. When estimating by the direct method, IC50 values of hamamelitannin, gallic acid and dl-alpha-tocopherol were 93.5 +/- 2.1 microM, 141.6 +/- 2.0 microM and 1590.0 +/- 330.0 microM, respectively. On peroxidation of lipid bilayers induced by 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH) in terms of inhibition period (tinh), hamamelitannin showed the longest tinh time (1107.0 +/- 38.18 sec), followed by those of dl-alpha-tocopherol (877.5 +/- 31.8 sec) and gallic acid (771.0 +/- 4.2 sec). The kinetic chain length, defined as the propagation numbers of a lipid peroxyl radical, and calculated from the ratio (Rp/Ri) of the rate of lipid peroxidation to that of inhibition by dl-alpha-tocopherol, hamamelitannin and gallic acid were 27.23, 7.86 and 7.09, respectively. The effects of hamamelitannin, gallic acid and dl-alpha-tocopherol were evaluated on murine fibroblasts exposed to t-butylhydroperoxide (BHP) in terms of the cell survivals. In the protection, hamamelitannin induced the highest survival of 27.6 +/- 0.6% at 50 microM, while both gallic acid and dl-alpha-tocopherol were less active at the same concentrations. On the basis of the results, hamamelitannin was concluded to have a high protective activity on cell damage induced by peroxides.