Objective  To investigate the protective effect of the kidney-tonifying traditional Chinese medicine Shen Gu An on endplate degeneration in ovariectomized mice and its potential mechanisms.

Methods  Thirty female C57BL/6J mice were randomly divided into a Sham operation group (Sham group), an ovariectomy group (OVX group), and a herbal medicine group (HB group) , with 10 mice in each group. The Sham group underwent sham surgery, while the OVX and HB groups underwent bilateral ovariectomy. Five days after modeling, the HB group received intragastric administration of the herbal decoction, while the Sham and OVX groups received intragastric saline. Three months later, L4-5 spinal segments were harvested. Micro-CT was used to observe the microstructure of vertebral bodies and endplates; Safranin O-Fast Green staining was used to observe pathological changes of the endplates; TRAP staining was used to assess osteoclasts; and immunohistochemistry was used to detect the expression of Col2 and CD31 in the endplates.

Results  Micro-CT results showed that in the OVX group, vertebral trabeculae became sparse and reduced in number, bone mineral density of total volume (BMDtv), bone volume/total volume (BV/TV), and trabecular number (Tb.N) decreased, while trabecular separation (Tb.Sp) increased (all P ＜ 0.05); pathological remodeling of the endplates occurred, with increases in total volume (TV) and total porosity (Po.V(tot)) (both P ＜ 0.05). Compared with the OVX group, the HB group showed improved vertebral trabecular structure, with increased BMDtv, BV/TV, and Tb.N, and decreased Tb.Sp (all P ＜ 0.05); endplate remodeling was inhibited, and both TV and Po.V(tot) decreased (both P ＜ 0.05). Safranin O-Fast Green staining showed ossific remodeling of the endplates in the OVX group, while endplate structure was improved in the HB group. TRAP staining showed increased osteoclasts in subchondral bone in the OVX group and reduced osteoclasts in the HB group. Immunohistochemistry showed that, compared with the Sham group, Col2 expression in the intervertebral disc and endplate was decreased and CD31 expression was increased in the OVX group, most prominently in areas of ossific remodeling of the endplate. Compared with the OVX group, ossific remodeling and CD31 expression in the endplate were significantly inhibited and Col2 expression was increased in the HB group.

Conclusions  OVX induces vertebral osteoporosis and ossific remodeling of the endplates in mice. HB can inhibit endplate osteoclast activity and angiogenesis, promote Col2 expression, and improve vertebral trabecular structure and pathological remodeling of the endplates.