Dose-Dependent Production of Mammalian Lignans in Rats and In Vitro from the Purified Precursor Secoisolariciresinol Diglycoside in Flaxseed.
Dose-Dependent Production of Mammalian Lignans in Rats and In Vitro from the Purified Precursor Secoisolariciresinol Diglycoside in Flaxseed.
Year: 1996
Authors: S E Rickard, L J Orcheson, M M Seidl, L Luyengi, H H S Fong, L U Thompson.
Publication Name: J. Nutr.
Publication Details: Volume 126; 2012.
Abstract:
The mammalian lignans enterodiol (ED) and enterolactone (EL) produced from colonic bacterial action on dietary precursors have been shown to have anticarcinogenic effects in vitro. SDG, the major lignan precursor in flaxseed, is metabolized to ED which is then oxidized to EL. EL can also be formed directly from another flaxseed lignan, MS. The purpose of this study was to first isolate SDG and then to determine whether 1) SDG accounted for all the lignan produced from flaxseed; 2) this production was dose-related; and 3) a relationship between in vitro production and in vivo urinary excretion existed. The authors were interested in these objectives in order to develop a predictor of potential lignan production from a given food or diet. Extraction of flaxseed with dioxane:ethanol (1:1, v/v) followed by chromatographic separations yielded the purified SDG. After a 2 week basal diet, forty two rats were separated into 7 treatment groups. They were fed a high fat basal diet without (control) or with 2.5, 5 or 10 g/100 g ground flaxseed or 1.1, 2.2 or 4.4 ?mol SDG/day (equivalent to levels in the respective flaxseed diets) for 4 weeks. In vitro lignan production was assessed by fermenting flaxseed or SDG for 24 hours with human fecal inoculum. The results indicated that SDG, a lignan precursor, can be isolated from food and can be metabolized to produce mammalian lignans in vivo. Urinary lignan excretion increased linearly with doses from 0-5% flaxseed and from 0-2.2 ?mol SDG/d followed by a plateau, indicating a threshold response. When all doses were considered, a curvilinear relationship was observed. These results suggest that doses of flaxseed higher than 5% or 2.2 ?mol SDG/day may not be necessary for increased lignan production. Urinary lignan levels from doses of 2.5% flaxseed and 2.2 ?mol SDG/day were not significantly different which lead the authors to speculate that these levels may be comparable in their biological effects. A trend similar to urinary lignan excretion was seen in vitro for SDG, resulting in a significantly high correlation between in vitro production and in vivo excretion of lignans. The authors indicated that in vivo responses can be predicted with confidence based on in vitro results. Theoretical urinary ED + EL from the SDG present in flaxseed were significantly correlated with the actual excretion in flaxseed fed animals. However, the urinary ED + EL of SDG fed rats was only 20% of the levels observed in the flaxseed fed rats, indicating the presence of other precursors such as MS, an incomplete conversion of SDG to ED and EL or metabolism of ED and EL to other products. HPLC estimates of SDG accounted for 80% of the lignans produced by in vitro fermentation of flaxseed, confirming that SDG is the primary lignan precursor. It was concluded that in vitro methods may be a useful tool for screening foods for their lignan producing ability.
