Drynaria fortunei J. Sm. improves the bone mass of ovariectomized rats through osteocalcin-involved endochondral ossification

Aim of this study Our previous study showed that Drynaria fortunei J. Sm. (Kunze), a traditional Chinese medical herb, can promote osteoblast differentiation and maturation. This study was further aimed to confirm the traditional effects of Kunze on the bone mass of ovariectomized rats.

Materials and methods Female Wistar rats were given an ovariectomy and then administered the water extract of Kunze (WEK). Systemic and tissue toxicities of WEK were assessed. A biomechanical test, bone mineral contents, and bone histomorphometry were analyzed to determine the effects of the WEK on the bone mass. Levels of osteocalcin (OCN) in bone tissues were determined by immunohistochemistry and immunoblotting. The effects of naringin, one of the bioactive compounds of the WEK, on the bone mass were evaluated.

Results A bilateral ovariectomy in rats caused a time-dependent decrease in levels of serum 17β-estradiol. Exposure of ovariectomized rats to the WEK at 0.5 and 1 g/kg body weight/day for 1, 2, 3, and 6 months did not induce systemic or tissue toxicities. Biomechanical testing and a bone mineral content analysis showed that the ovariectomy decreased the bone torsion force and bone ash in time-dependent manners. In comparison, after exposure to the WEK, the ovariectomy-induced reductions in the bone torsion force and bone ash were significantly alleviated. In parallel, results of a bone histomorphometric assay further revealed that the ovariectomy caused significant diminution in the production of prehypertrophic chondrocytes and trabecular bone but enhanced hypertrophic chondrocyte numbers in the growth plate. However, exposure to the WEK lowered ovariectomy-induced changes in these cellular events. As to the mechanism, the WEK increased OCN biosynthesis in bone tissues of ovariectomized rats. Administration of naringin to ovariectomized rats caused significant amelioration of the bone strength, bone mineral contents, and trabecular bone amounts.

Conclusions This study shows that the WEK can translationally promote the bone mass in ovariectomized rats through stimulating OCN-involved endochondral ossification.