Antioxidant activity of the flaxseed lignan secoisolariciresinol diglycoside and its mammalian lignan metabolites enterodiol and enterolactone

The antioxidant activities of the flaxseed lignan secoisolariciresinol digl ycoside (SDG) and its mammalian lignan metabolites, enterodiol (ED) and ent erolactone (EL), were evaluated in both lipid and aqueous in vitro model sy stems. All three lignans significantly (p less than or equal to 0.05) inhib ited the linoleic acid peroxidation at both 10 and 100 mu M over a 24-48 h of incubation at 40 degrees C. In a deoxyribose assay, which evaluates the non site-specific and site-specific Fenton reactant-induced . OH scavenging activity, SDG demonstrated the weakest activity compared to ED and EL at b oth 10 and 100 mu M; the greatest . OH scavenging for ED and EL was observe d at 100 mu M in both assays. The incubation of pBR322 plasmid DNA with Fen ton reagents together with SDG, ED or EL showed that the inhibition of DNA scissions was concentration dependent. The greatest non site-specific activ ity of lignans was at 100 mu M, thus, confirming the results of the deoxyri bose test. In contrast, the protective effect of SDG and EL in the site-spe cific assay was lost and that of ED was minimal. Therefore, the results ind icate a structure-activity difference among the three lignans with respect to specific antioxidant efficacy. All three lignans did not exhibit reducin g activity compared to ascorbic acid, therefore, did not possess indirect p rooxidant activity related to potential changes in redox state of transitio n metals. The efficacy of SDG and particularly the mammalian lignans ED and EL to act as antioxidants in lipid and aqueous in vitro model systems, at relatively low concentrations (i.e. 100 mu M), potentially achievable in vi vo, is an evidence of a potential anticarcinogenic mechanism of flaxseed li gnan SDG and its mammalian metabolites ED and EL.