The Effects of Tocotrienol on Bone Peptides in a Rat Model of Osteoporosis Induced by Metabolic Syndrome: The Possible Communication between Bone Cells

A positive association between metabolic syndrome (MetS) and osteoporosis has been demonstrated in previous animal studies. The mechanisms of MetS in orchestrating the bone remodelling process have traditionally focused on the interactions between mature osteoblasts and osteoclasts, while the role of osteocytes is unexplored. Our earlier studies demonstrated the bone-promoting effects of tocotrienol using a rat model of osteoporosis induced by MetS. This study aimed to investigate the expression of osteocyte-derived peptides in the bone of rats with MetS-induced osteoporosis treated with tocotrienol. Age-matched male Wistar rats (12-week-old; n = 42) were divided into seven experimental groups. Two groups served as the baseline and normal group, respectively. The other five groups were fed with a high-carbohydrate high-fat (HCHF) diet to induce MetS. The five groups of HCHF animals were treated with tocopherol-stripped corn oil (vehicle), annatto tocotrienol (60 and 100 mg/kg), and palm tocotrienol (60 and 100 mg/kg) starting from week 8. At the end of the study, the rats were sacrificed and their right tibias were harvested. Protein was extracted from the metaphyseal region of the proximal right tibia and levels of bone peptides, including osteoprotegerin (OPG), soluble receptor activator of nuclear factor-kappa B ligand (sRANKL), sclerostin (SOST), Dickkopf-related protein 1 (DKK-1), fibroblast growth factor-23 (FGF-23), and parathyroid hormone (PTH), were measured. The vehicle-treated animals displayed higher levels of sRANKL, SOST, DKK-1, FGF-23, and PTH as compared to the normal animals. Oral supplementation of annatto and palm tocotrienol (60 and 100 mg/kg) reduced the levels of sRANKL and FGF-23 in the HCHF animals. Only 100 mg/kg annatto and palm tocotrienol lowered SOST and DKK-1 levels in the HCHF animals. In conclusion, tocotrienol exerts potential skeletal-promoting benefit by modulating the levels of osteocytes-derived bone-related peptides.