Abstract
Background: α-Linolenic acid (ALA) is a plant-derived omega-3 unsaturated fatty acid that is rich in flaxseed oil (FO). The effect of FO on bone health is controversial. This study aims to evaluate the effect of FO on bone damage induced by a high-fat diet (HFD) and to explore the possible mechanism.
Methods: Male Sprague-Dawley rats were fed a normal control diet (NC, 10% fat), FO diet (NY, 10% fat), HFD (60% fat), or HFD containing 10% FO (HY, 60% fat) for 22 weeks. Micro CT and three-point bending tests were conducted to evaluate bone microstructure and biomechanics. Serum was collected for the detection of ALP, P1NP, and CTX-1. Rat primary osteoblasts (OBs) were treated with different concentrations of ALA with or without palmitic acid (PA) treatment. The ALP activity, osteogenic-related gene and protein expression were measured. Results: Rats in the HFD group displayed decreased biomechanical properties, such as maximum load, maximum fracture load, ultimate tensile strength, stiffness, energy absorption, and elastic modulus, compared with the NC group (p < 0.05). However, HY attenuated the HFD-induced decreases in bone biomechanical properties, including maximum load, maximum fracture load, and ultimate tensile strength (p < 0.05). Trabecular bone markers such as trabecular volume bone mineral density (Tb. vBMD), trabecular bone volume/total volume (Tb. BV/TV), trabecular number (Tb. N), trabecular thickness (Tb. Th) were decreased, trabecular separation (Tb. Sp) and the structure model index (SMI) were increased in the HFD group compared with the NC group, and all parameters were remarkably improved in the HY group compared to the HFD group (p < 0.05). However, cortical bone markers such as cortical volume bone mineral density (Ct. vBMD), cortical bone volume/total volume (Ct. BV/TV) and cortical bone thickness (Ct. Th) were not significantly different among all groups. Moreover, the serum bone formation markers ALP and P1NP were higher and the bone resorption marker CTX-1 was lower in the HY group compared with levels in the HFD group. Compared with the NC group, the NY group had no difference in the above indicators. In rat primary OBs, PA treatment significantly decreased ALP activity and osteogenic gene and protein (β-catenin, RUNX2, and osterix) expression, and ALA dose-dependently restored the inhibition induced by PA.
Conclusions: FO might be a potential therapeutic agent for HFD-induced bone loss, most likely by promoting osteogenesis.
Link to Full Text
Key Points
Diet is one of the risk factors for osteoporosis in addition to heredity, age, oestrogen deficiency, and calcium and phosphorus metabolism. Whether FO has a protective effect on HFD-induced bone damage has not been clarified, and the specific mechanism of bone protection is unclear. Therefore, this study aimed to evaluate whether totally replacing soybean oil and partly replacing lard with FO in HFD can improve high-fat-induced bone damage in vivo. We treated rat primary OBs with ALA in vitro to observe the effect of ALA on osteoblastic function, osteogenic-related gene and protein expression and tried to explore the mechanism of ALA on bone protection.
The major finding of this study was that FO alleviated bone loss in HFD rats. Meanwhile, ALA can promote primary osteoblastic function through increasing β-catenin/RUNX2/osterix genes and proteins expression and restoring PA induced ALP activity decreases. The current study also focused on male rats, and trabecular bone loss was observed in HFD induced male SD rats. The bone loss induced by HFD was attenuated by treatment with FO, as shown by micro-CT, three-point bending test and bone histology analysis.
The results showed that ALA dramatically promoted β-catenin gene and protein expression in OBs, which suggested that ALA may promote osteogenic differentiation through the Wnt pathway. In the present study, the main finding was that FO alleviated bone loss in HFD rats, probably by promoting osteoblastic β-catenin/RUNX2/osterix gene and protein expression and restoring PA-induced ALP activity decreases. These findings indicated that FO might be a potential therapeutic agent for HFD-induced bone loss, most likely by promoting osteogenesis.