Key Findings
In previous work, synergistic effects on BMD and bone strength at the lumbar vertebrae was observed when flaxseed was combined with low-dose estrogen therapy. The objective of this study was to determine, using the ovariectomized rat model of postmenopausal osteoporosis and radiolabeled SDG, whether SDG metabolites are accessible to the skeleton. Because the distribution of SDG metabolites varies among tissues. A secondary objective of this study was to compare the radioactive levels of SDG metabolites in skeletal tissue with those in other tissues (i.e., liver, uterus, vagina, mammary gland, thymus, spleen, kidney, lungs, bladder, heart, and gastrointestinal tissue). The study showed that SDG metabolites are accessible to the lumbar vertebrae, femurs, and tibias of ovariectomized rats fed a 10% flaxseed diet while being gavaged daily with 3H-SDG. However, whether SDG metabolites can exert direct or indirect action on bone cells and thus may play a role in the mechanism whereby flaxseed and low-dose estrogen therapy exerts a synergistic action on bone mass and strength in the ovariectomized rat model of postmenopausal osteoporosis requires further study.
ABSTRACT
Flaxseed, rich in the phytoestrogen lignan secoisolariciresinol diglycoside (SDG), provides protection against bone loss at the lumbar vertebrae primarily when combined with low-dose estrogen therapy in the ovariectomized rat model of postmenopausal osteoporosis. Whether SDG metabolites are accessible to skeletal tissue, and thus have the potential to interact with low-dose estrogen therapy to exert direct local action on bone metabolism, is unknown. The objective of this study was to determine whether metabolites of SDG are accessible to the skeleton of ovariectomized rats and to compare the distribution of SDG metabolites in skeletal tissue with that in other tissues. Rats were fed a 10% flaxseed diet and gavaged daily with tritium-labeled SDG (7.4 kBq/g of body weight) in deionized water (500 μL) (n=3) or deionized water alone (n=3) for 7 days, after which tissues were collected for liquid scintillation counting. Radioactivity was detected in similar concentrations in the lumbar vertebrae, femurs, and tibias. Compared with non-skeletal tissues, total radioactivity in the skeleton was significantly lower than in the liver, heart, kidney, thymus, and brain (P < .001). There were no significant differences in levels of radioactivity between skeletal tissue versus the spleen, lung, bladder, uterus, vagina, and mammary gland. In conclusion, SDG metabolites are accessible to skeletal tissue of ovariectomized rats. Thus, it is biologically plausible that SDG metabolites may play a direct role in the protective effects of flaxseed combined with low-dose estrogen therapy against the loss of bone mass and bone strength in the ovariectomized rat model of postmenopausal osteoporosis.
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