Dietary n-3 Fatty Acids Decrease Osteoclastogenesis and Loss of Bone Mass in Ovariectomized Mice

Abstract

The mechanisms of action of dietary fish oil (FO) on osteoporosis are not fully understood. This study showed FO decreased bone loss in ovariectomized mice because of inhibition of osteoclastogenesis. This finding supports a beneficial effect of FO on the attenuation of osteoporosis.Introduction: Consumption of fish or n-3 fatty acids protects against cardiovascular and autoimmune disorders. Beneficial effects on bone mineral density have also been reported in rats and humans, but the precise mechanisms involved have not been described. Methods: Sham and ovariectomized (OVX) mice were fed diets containing either 5% corn oil (CO) or 5% fish oil (FO). Bone mineral density was analyzed by DXA. The serum lipid profile was analyzed by gas chromatography. Receptor activator of NF-B ligand (RANKL) expression and cytokine production in activated T-cells were analyzed by flow cytometry and ELISA, respectively. Osteoclasts were generated by culturing bone marrow (BM) cells with 1,25(OH) 2 D 3 . NF-B activation in BM macrophages was measured by an electrophoretic mobility shift assay. Results and Conclusion: Plasma lipid C16:1n6, C20:5n3, and C22:6n3 were significantly increased and C20:4n6 and C18:2n6 decreased in FO-fed mice. Significantly increased bone mineral density loss (20% in distal left femur and 22.6% in lumbar vertebrae) was observed in OVX mice fed CO, whereas FO-fed mice showed only 10% and no change, respectively. Bone mineral density loss was correlated with increased RANKL expression in activated CD4 ϩ T-cells from CO-fed OVX mice, but there was no change in FO-fed mice. Selected n-3 fatty acids (docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]) added in vitro caused a significant decrease in TRACP activity and TRACP ϩ multinuclear cell formation from BM cells compared with selected n-6 fatty acids (linoleic acid [LA] and arachidonic acid [AA]). DHA and EPA also inhibited BM macrophage NF-B activation induced by RANKL in vitro. TNF-␣, interleukin (IL)-2, and interferon (IFN)-␥ concentrations from both sham and OVX FO-fed mice were decreased in the culture medium of splenocytes, and interleukin-6 was decreased in sham-operated FO-fed mice. In conclusion, inhibition of osteoclast generation and activation may be one of the mechanisms by which dietary n-3 fatty acids reduce bone loss in OVX mice.

Long-chain polyunsaturated fatty acids: Selected mechanisms of action on bone

“…In an elegant study Cohen et al [114] reported data that IL-10(anti-inflammatory) knock-out mice fed flax seed oil, providing ALA, had significantly lower serum levels of TNF-α and higher bone density compared to IL-10 knock-out mice fed corn oil that is rich in omega-6 fatty acids. The difference in bone density was possibly partly due to the reduction in TNF-α by feeding of ALA. Downregulation of resorptive cytokines such as TNF-α and IL-6 by n-3 PUFA in OVX mice was also reported by other research groups [115,116]. Thus dietary modulation by increasing n-3 PUFA intake could affect the generation of IL-1, IL-6 and TNF-α which in turn could modulate bone health.…”

“…LCPUFAs have been shown to affect cellular proteins and receptor activator of nuclear factor κβ (RANK), a receptor found on the osteoclast which controls osteoclastogenesis. This will be discussed in detail below [25][26][27].…”

“…Exposure of cell cultures from primary murine bone marrow cells and RAW 264.7 cells to EPA or DHA or both, and examining TRAP (tartrate-resistant acid phosphatase) activity which is considered to be a marker of osteoclast maturation, showed a significant decrease in osteoclast maturation compared with the n-6 PUFAs LA and AA [27,102]. The observed inhibition correlated with inhibition of several osteoclast-specific genes such as TRAP, cathepsin K, c-FOS as well as TNF-α.…”

Effects of arachidonic acid and docosahexaenoic acid on differentiation and mineralization of MC3T3‐E1 osteoblast‐like cells

“…Polyunsaturated fatty acids (PUFAs) have been implicated in bone homeostasis both in vitro [1][2][3] and in vivo. [4][5][6][7][8] There is increasing evidence that lack of certain PUFAs in the diet can induce bone loss, [9][10][11] while dietary supplementation of some PUFAs has been shown to be beneficial for bone.…”

“…12,13 A recent study by Högstrom et al 14 demonstrated that n-3 fatty acids, particularly docosahexaenoic acid (DHA), are positively associated with bone mineral accrual, and thus, with peak bone mineral density in healthy young men. Some in vivo studies have shown that supplementation with PUFAs such as GLA, EPA, and DHA, could decrease bone turnover in ovariectomized animals by decreasing bone resorption 3,5 while others have shown that n-3 PUFA treatment in rats could result in greater bone formation rates. 2 Some suggested mechanisms of action for the PUFAs in these models include the following: modulation of calcium absorption from the intestine, increased bone mineralization, enhancement of bone collagen synthesis, and reduction of urinary calcium excretion, thereby increasing the pool of available calcium for bone mineralization in the body.…”