Anti-osteoporosis effects of mammalian lignans and their precursors from flaxseed and safflower seed using zebrafish model

Secoisolariciresinol diglucoside (SDG) and tracheloside (TCL) are the main lignan components of flaxseed
cake and safflower seed cake, which are by-products of oil extraction. Both SDG and TCL are
metabolized into mammalian lignan enterolactone (EL) with the involvement of intestinal bacteria. In
this research, we evaluated the anti-osteoporosis effects of SDG and the in vivo metabolites EL and
enterodiol (ED) prepared in our previous work, as well as the newly isolated chemical constituents from
safflower seed, including TCL, the lactone ring opening product of TCL (OTCL) and two alkaloids on the
alloxan-induced zebrafish model. All the compounds showed significant anti-osteoporosis effects at 80
µM, with p < 0.05 for EL and p < 0.001 for other compounds compared with the model. SDG and TCL
showed the most significant and concentration-dependent effects, with p < 0.001 compared with model
at 20 µM. The alkaloids, N-coumaroylserotonin glucoside and N-feruloylserotonin glucoside, also
showed anti-osteoporosis at 20 µM with p < 0.01, whereas EL, ED, and OTCL showed no significant effects. Quantitative real-time polymerase chain reaction revealed that SDG and TCL upregulated the
expression of osteogenic genes Runx2, SP7, OPG, Col1a1a, Alp, ON, OPN, and OCN in alloxan-treated
zebrafish. The in vivo metabolite of lignans, EL, showed significant anti-inflammatory effect (p < 0.01) at
20 µM, which might also help to combat osteoporosis and other complications caused by excessive
immune response in the body. The results provided scientific data for using the oil extraction by-
products as sources of anti-osteoporosis compounds. PRACTICAL APPLICATION: This study found that
lignans in flaxseed cake and safflower seed cake exhibited anti-osteoporosis effects by upregulating the
expression of osteogenic genes, making the oil extraction by-products sources of anti-osteoporosis
compounds.