Bone degeneration and recovery after early and late bisphosphonate treatment of ovariectomized wistar rats assessed by in vivo micro-computed tomography

Abstract

Bisphosphonates are antiresorptive drugs commonly used to treat osteoporosis. It is not clear, however, what the influence of the time point of treatment is. Recently developed in vivo micro-computed tomographic (CT) scanners offer the possibility to study such effects on bone microstructure in rats. The aim of this study was to determine the influence of early and late zoledronic acid treatment on bone in ovariectomized rats, using in vivo micro-CT. Twenty-nine female Wistar rats were divided into the following groups: ovariectomy (OVX, n = 5), OVX and zoledronic acid (ZOL) at week 0 (n = 8), OVX and ZOL at week 8 (n = 7), and sham (n = 9). CT scans were made of the proximal tibia at weeks 0, 2, 4, 8, 12, and 16; and bone structural parameters were determined in the metaphysis. Two fluorescent labels were administered to calculate dynamic histomorphometric parameters. At week 16, all groups were significantly different from each other in bone volume fraction (BV/TV), connectivity density, and trabecular number (Tb.N), except for the early ZOL and control groups which were not significantly different for any structural parameter. After ZOL treatment at week 8, BV/TV, structure model index, Tb.N, and trabecular thickness significantly improved in the late ZOL group. The OVX and ZOL groups showed, respectively, higher and lower bone formation rates than the control group. Early ZOL treatment inhibited all bone microstructural changes seen after OVX. Late ZOL treatment significantly improved bone microstructure, although the structure did not recover to original levels. Early ZOL treatment resulted in a significantly better microstructure than late treatment. However, late treatment was still significantly better than no treatment.

Fig. 1

Average percentage change in structural parameters in the metaphyseal proximal tibia and upper standard deviation for all groups at all time points. Brackets indicate P < 0.05 at week 16

Fig. 2

Same slice of an unprocessed CT scan of the same rat in the OVX group taken at weeks 0 (a), 2 (b), 4 (c), 8 (d), 12 (e), and 16 (f). Images show typical trabecular bone loss due to OVX in the metaphysis. Green line shows the analyzed metaphyseal bone

Fig. 3

Average percentage change in cortical thickness in the metaphyseal proximal tibia and upper standard deviation for all groups at all time points. At week 4 the OVX and the late ZOL groups were significantly lower than the early ZOL group, and at week 16 the OVX group was significantly higher than the control group

Fig. 4

Stiffness, ultimate force, and ultimate displacement determined from three-point bending tests on diaphyseal tibia (a) and axial compression tests (b) on metaphyseal bone. Groups: 1, control; 2, OVX; 3, late ZOL; 4, early ZOL. *Significant difference between groups based on ANOVA and Bonferroni post-hoc test (P < 0.05)

Fig. 5

Dynamic bone histomorphometric parameters for all groups in the metaphyseal proximal tibia. Groups: 1, control; 2, OVX; 3, late ZOL; 4, early ZOL. Based on ANOVA and a Bonferroni test, ^asignificantly different from group 1, ^bsignificantly different from group 2, ^csignificantly different from group 3, and ^dsignificantly different from group 4 (P < 0.05)