Abstract: Lipoic acid(LA) widely exists in all kinds of cells. It can be converted to dihydrolipoic acid (DHLA) in mammalian cell. The ability of alpha-LA and DHLA to scavenge reactive oxygen species and prevent DNA from oxidative damage by •OH was evaluated using chemiluminescence systems and colorimetric systems. The experiments show that LA and DHLA can directly scavenge •OH、H₂O₂、ONOO^-and DPPH• ，effectively inhibit lipid peroxidation and DNA oxidative damage by •OH； DHLA can also effectively scavenge O•₂^-. These results indicate that both LA and DHLA are effective antioxidants and the anti-oxidative ability of DHLA is obviously stronger than that of LA. The present investigation can provide new free radical biological data for the further study on the medical and health-care applications of LA and DHLA.

Key words: dihydrolipoic acid, antioxidant, active oxygen species, DNA oxidative damage, chemiluminescence, lipoic acid, dihydrolipoic acid, antioxidant, active oxygen species, DNA oxidative damage, chemiluminescence