Flaxseed and Lower-dose Estrogen: Studies on Their Protective Actions and Mechanisms in Bone Using the Ovariectomized Rat Model

Flaxseed (FS) is a rich source of lignans and n-3 polyunsaturated fatty acids (PUFA), compounds that may help preserve normal bone cell function during aging. Understanding the effect of FS alone or combined with lower doses of estrogen therapy on bone and other estrogen-responsive tissues (e.g. uterus) is of particular interest to postmenopausal women who combine dietary bioactives (e.g. FS) with pharmacological agents (e.g. estrogen monotherapy) to attenuate postmenopausal bone loss. The overall objective of my research was to determine the effects and mechanisms of FS, alone or combined with lower doses of estrogen therapy, on bone and uterus health by measuring a comprehensive set of outcomes in the ovariectomized rat model of postmenopausal osteoporosis. The results demonstrated that FS enhances the protective effect of low-dose estrogen therapy (LD) on vertebral bone mineral density (BMD), three-dimensional microarchitecture and strength in ovariectomized rats. Moreover, FS exerts a stronger effect on bone outcomes when combined with LD than when combined with ultra-low-dose estrogen therapy (ULD). These studies also showed that FS feeding results in higher lignans and n-3 PUFAs in vertebrae, tibias and femurs. Histological analyses at the lumbar vertebra (LV) showed that there were no differences in TRAP-5β, CTX, or OPG/RANKL ratio between the FS+LD and LD groups. FS+LD did however result in lower protein expression of osteocalcin, a marker of bone formation and overall bone turnover, and higher expression of OPG compared to the negative control (NEG), while LD did not. While these findings suggest that FS+LD results in greater attenuation of deterioration of bone tissue compared to LD due to a reduction in bone turnover, significant differences between FS+LD and LD were not observed. Elucidating these specific mechanisms of action require further investigation. In the uterus, FS+LD did not induce greater cell proliferation or differences in qualitative indices of uterine morphology compared to LD. These findings suggest that there may be no increase in the risk of endometrial hyperplasia and carcinoma with FS+LD compared to LD. These findings may lead to the development of strategies that combine food bioactives and current pharmacological agents to more effectively normalize bone turnover during aging.Ph