Urinary Composition and Postprandial Blood Changes in 3H-Secoisolariciresinol Diglycoside (SDG) Metabolites in Rats Do Not Differ between Acute and Chronic SDG Treatments

Abstract

Although chronic exposure to secoisolariciresinol diglycoside (SDG) was shown to alter (3)H-SDG metabolite disposition in rats, the proportion of measured radioactivity attributed to known or unknown SDG metabolites was not determined. Using HPLC and GC-MS, two experiments were conducted to determine the effect of acute (1 d) vs. chronic (10 d) SDG treatment on major urinary metabolites of (3)H-SDG in female, Sprague-Dawley rats (70-72-d-old) over a 48-h period and if new urinary metabolites were detectable in rats fed nonradioactive flaxseed or SDG. A third experiment was conducted to determine changes in postprandial blood levels of (3)H-SDG metabolites over a 24-h period with acute or chronic SDG treatment. Regardless of treatment, enterodiol, enterolactone and secoisolariciresinol accounted for 75-80% of urine radioactivity. Four potential new lignan metabolites, two of which were detected in the urine of rats fed nonradioactive flaxseed or SDG, were found. Type of treatment had no effect on levels of individual urinary metabolites of (3)H-SDG. As observed for plasma lignans in women fed flaxseed, blood radioactivity peaked at 9 h and remained high until 24 h in both treatment groups, suggesting that blood lignan kinetics might be similar with flaxseed or SDG consumption and that they were comparable between humans and rats. In conclusion, the main urinary lignan metabolites were enterodiol, enterolactone and secoisolariciresinol. Urinary composition or blood levels of radioactive lignans were not affected by the duration of SDG exposure. Thus, while chronic SDG exposure alters lignan disposition in rats, it does not change the metabolite profile.