Determination of plant and enterolignans in human serum by high-performance liquid chromatography with tandem mass spectrometric detection

An HPLC-MS/MS method was validated for the determination of the plant lignans 7-hydroxymatairesinol (HMR), matairesinol (Mat), secoisolariciresinol (Seco), lariciresinol (Lar), and cyclolariciresinol (CLar) and for the enterolignans 7-hydroxyenterolactone (HEL), enterodiol (ED), and enterolactone (EL) in human serum. The method included sample enzymatic hydrolysis, solid-phase extraction, and lignan analysis using a triple quadrupole mass spectrometer with electrospray ionisation in the multiple-reaction monitoring mode. The serum lignans were quantified using deuterated Mat or EL as internal standards. The method met the validation criteria for selectivity, intra- and inter-assay precision, and accuracy. The method was applied to ten serum samples collected from healthy individuals (five men and five women) consuming their habitual Finnish diet. All lignans except HMR and Seco were found in quantifiable amounts in the samples. All serums contained EL; the average concentration was 34nM. In three individuals, the serum concentration of plant lignans was higher than that of enterolignans. Using the method, common dietary plant lignans and their major metabolites can be reliably quantified in human serum at low-nanomolar concentrations in a simple and rapid way.