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.