Abstract: The aim of the present study was to investigate the in vitro antioxidant activity of three curcuminoids in terms of radical scavenging capacity and protective effect against oxidative stress-induced damage in chicken erythrocytes. The scavenging capacity of curcumin (CUR), demethoxycurcumin (DUR) and bisdemethoxycurcumin (BUR) against 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, hydroxyl radical (·OH), and superoxide anion O2-· radical were evaluated as well as their ferric-reducing antioxidant power (FRAP) and lipid peroxidation inhibitory potential. The synthetic antioxidants butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) were used as reference standards. The results showed that all three curcuminoids exhibited strong ABTS, DPPH, ·OH and O2-· scavenging capacity in a dose-dependent manner. Compared with BHT, the DPPH radical scavenging capacity of DUR was significantly increased, while that of CUR was significantly decreased (P < 0.05). The ·OH scavenging capacity of the three curcuminoids was significantly decreased when compared with both BHA and BHT (P < 0.05). BUR and CUR had stronger ·OH scavenging activity than did CUR. Compared with DUR, the O2-· scavenging activity of BUR and CUR was significantly increased (P < 0.05). When used at a concentration of 400 μmol/L, BHA had the highest FRAP value and BUR exhibited the strongest inhibition of lipid peroxidation. Compared with CUR, BUR and DUR were significantly more effective against lipid peroxidation (P < 0.05). Moreover, all the curcuminoids significantly suppressed 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced hemolysis of chicken erythrocytes, as well as decreased MDA level and increased superoxide dismutase (SOD) activity in a dose- and time-dependent manner. After 5 h incubation, DUR and BUR at 20 μmol/L showed lower hemolysis rate when compared with CUR. Compared with those treated with CUR and DUR, the MDA level and SOD activity in BUR-treated cells were significantly decreased (P < 0.05). In conclusion, DUR and BUR, similar to CUR, have good antioxidant activity. The three curcuminoids can sufficiently scavenge free radicals, have high FRAP values and potent inhibitory activity against lipid peroxidation, and can protect erythrocytes from AAPH-induced oxidative stress damage. Among these, BUR exhibits the highest antioxidant activity in free radical (including ABTS, ·OH and O2-·) scavenging and lipid peroxidation assays. DUR and BUR are more effective in protecting erythrocytes from oxidative stress damage than CUR.

Key words: curcumin, demethoxycurcumin, bisdemethoxycurcumin, free radical, erythrocytes, antioxidant