Histochemical assessment of the anabolic effects of abaloparatide on the femoral metaphyses of ovariectomized mice

Abstract

Objective

To clarify the mechanism of bone anabolism induced by the parathyroid hormone-related peptide analog abaloparatide, we histochemically examined the femora of ovariectomized mice treated with abaloparatide.

Methods

Twelve-week-old female C57BL/6J mice underwent ovariectomies (OVX), and were then administered either abaloparatide (30 μg/kg/day: OVX + ABL group) or vehicle (OVX group) via daily intraperitoneal injection. Femora were harvested at 0, 2, 4, and 6 weeks post-administration and subjected to micro-CT imaging, TRAP, cathepsin K, ALP, and PHOSPHO1 staining, along with calcein labeling.

Results

In the OVX group, trabecular number and bone volume gradually decreased over time, whereas the OVX + ABL group maintained these values to 6 weeks after OVX. The numbers of TRAP-positive/cathepsin K-reactive osteoclasts per bone surface area were similar between the OVX and OVX + ABL group, except for a temporary increase at 4 weeks in the OVX group. In the OVX group, the areas of ALP-positive osteoblastic cells and PHOSPHO1-reactive mature osteoblasts decreased, whereas in the OVX + ABL group, ALP-positive osteoblastic cells surrounded the trabeculae, and long lines of PHOSPHO1-reactive mature osteoblasts expanded to the terminal region of the trabeculae. In addition, long continuous calcein labeling was seen on slightly convex new bone, indicating modeling-based bone formation in the OVX + ABL group. The bone formation rate/bone surface ratio and the total length of modeling-based bone formation sites were higher in the OVX + ABL group than in the OVX group.

Conclusion

Abaloparatide suppresses bone loss following ovariectomy by promoting both remodeling-based and modeling-based bone formation.