In vitro metabolism of plant lignans: New precursors of mammalian lignans enterolactone and enterodiol

The metabolism of the plant lignans matairesinol, secoisolariciresinol, pin oresinol, syringaresinol, arctigenin, 7-hydroxymatairesinol, isolariciresin ol, and lariciresinol by human fecal microflora was investigated to study t heir properties as mammalian lignan precursors. The quantitative analyses o f lignan precursors and the mammalian lignans enterolactone and enterodiol were performed by HPLC with coulometric electrode array detector. The metab olic products, including mammalian lignans, were characterized as trimethyl silyl derivatives by gas chromatography-mass spectrometry. Matairesinol, se coisolariciresinol, lariciresinol, and pinoresinol were converted to mammal ian lignans only. Several metabolites were isolated and tentatively identif ied as for syringaresinol and arctigenin in addition to the mammalian ligna ns. Metabolites of 7-hydroxymatairesinol were characterized as enterolacton e and 7-hydroxyenterolactone by comparison with authentic reference compoun ds. A metabolic scheme describing the conversion of the most abundant new m ammalian lignan precursors, pinoresinol and lariciresinol, is presented.