Astaxanthin and omega-3 fatty acids individually and in combination protect against oxidative stress via the Nrf2–ARE pathway

Oxidative stress is a major driver of many diseases, including cancer. The induction of Nrf2–ARE-mediated antioxidant enzymes provides a cellular defense against oxidative stress. Astaxanthin (AST), a red dietary carotenoid, possesses potent antioxidant activity, and inhibits oxidative damages. Polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are important nutritional essentials and potent antioxidants found in fish oil. In the present study, we investigated whether AST in combination with low concentrations of DHA or EPA has a synergistic antioxidant effect in a HepG2-C8-ARE-luciferase cell line system. Using free radical scavenging DPPH assay, AST was more potent DPPH radical scavenger than DHA and EPA. MTS assay revealed that AST was non-toxic up to 100 μM compared with more toxic DHA and EPA. The three compounds alone and in combination elevated cellular GSH levels, increased the total antioxidant activity, induced mRNA expression of Nrf2 and Nrf2 downstream target genes NQO1, HO-1, and GSTM2. Lower concentrations of AST show synergistic effects when combined with DHA or EPA. In summary, our study shows synergistic antioxidant effects of AST and PUFAs at low concentrations. The Nrf2/ARE pathway plays an important role in the antioxidative effects induced by AST, DHA, and EPA.