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Evaluation of biological activity of lignans extracted from tree knots
Knots in trees, i.e. the branch bases situated inside the tree stem, contain high amounts of polyphenols, with lignans as the dominating group. Hydroxymatairesinol isomer 1 and isomer 2, pinoresinol, lariciresinol and secoisolariciresinol which are common lignans in tree knots, have recently been identified in human urine and plasma. Oil seeds, wheat bread and fruits are important sources of these four lignans.
In the present study we investigated the biological activity of hydroxymatairesinol isomer 2, pinoresinol, lariciresinol and secoisolariciresinol isolated from forest tree knots from Finland. We determined the potential of the above compounds to influence i) the activity of the estrogen receptor (ER) in MCF-7 cells transfected with an estrogen response element (ERE)-driven luciferace (Luc) reporter gene, and ii) the cell proliferation of MCF-7 cells using the MTT assay. Our results demonstrate that hydroxymatairesinol isomer 2 (10-9-10-7M) inhibited significantly the 17β-estradiol (E2) induced ERE-driven gene activity in MCF-7 cells; pinoresinol (10-9-10-7M) enhanced significantly the E2-induced ERE-driven gene activity, whereas secoisolariciresinol (10-9-10-7M) did not exhibit such an effect in this cell system. Hydroxymatairesinol isomer 2 and pinoresinol (0.01–100µM) inhibited significantly the E2-induced proliferation in MCF-7 cells. Secoisolariciresinol when alone increased significantly the proliferation of MCF-7 cells and did not affect the E2-induced MCF-7 cell proliferation. Lariciresinol (0.01–100µM) did not cause any changes in the proliferation of MCF-7 cells when alone or in present of E2. Our results demonstrate that the identified lignans hydroxymatairesinol isomer2, pinoresinol, lariciresinol and secoisolariciresinol, present in abundance in tree knots, and also in human urine and plasma, are modulators of estrogen signaling and cell proliferation. These data expand our knowledge about the role of dietary lignans in human health and corroborate that tree knots are a significant source of biologically active compounds.