Abstract: In this study, the in vitro antioxidant activity of different geometric isomers of astaxanthin (all-trans, 9-cis, and 13-cis) was studied as well as the protective effect against oxidative stress in vivo. The results showed no significant difference among these geometric isomers of astaxathin (P > 0.05) in 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging capacity, but in terms of 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical scavenging capacity, 9-cis astaxanthin was significantly better than 13-cis and all-trans astaxanthin (P < 0.05); in terms of total antioxidant capacity, 9-cis astaxanthin was significantly better than 13-cis astaxanthin (P < 0.05) although there was no significant difference between 13-cis and all-trans astaxanthin (P > 0.05). Under the condition of oxidative stress induced by paraquat (PQ), all geometric isomers of astaxathin could significantly increase the survival rate of Caenorhabditis elegans (P < 0.05) and their effects were not significantly different (P > 0.05). Compared with the control group, 9-cis and all-trans astaxanthin could significantly reduce the accumulation of reactive oxygen species (ROS) in nematodes by 56.05% and 15.07%, respectively (P < 0.05), and there was a significant difference between the 9-cis group and other treatment groups (P < 0.05). Therefore, all three geometric isomers of astaxathin exhibit antioxidant activity and protection against oxidative stress, and 9-cis astaxathin has better antioxidant activity than all-trans and 13-cis astaxanthin.

Key words: astaxanthin, geometric isomer, antioxidant, oxidative stress, Caenorhabditis elegans