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.Keywords Osteoporosis Á Bisphosphonate Á In vivo micro-computed tomography Á Rat Postmenopausal osteoporosis affects millions of women worldwide and results in loss of bone mass and bone microstructural changes, which lead to reduced bone strength. It remains unknown how exactly the microstructure is affected over the time course of osteoporosis development and to what extent this structure can be recovered by drug treatment. Since the assessment of bone structure in humans is still limited to a few peripheral sites, the ovariectomized rat is used in many studies as an animal model for osteoporosis in cross-sectional evaluations. Numerous cross-sectional studies have determined the loss of trabecular bone in the proximal tibia in rats following ovariectomy (OVX) at different time points by measuring bone structural parameters [1][2][3]. OVX has been shown to decrease bone volume fraction, connectivity, and trabecular number and to increase trabecular separation and structure model index, which indicates that trabecular bone changes from plate-like to more rod-like in the proximal tibial metaphysis of the female rat. However, conflicting results were found for the effects of OVX on trabecular thickness, showing increases, decreases, or no response at

Influence of Early and Late Zoledronic Acid Administration on Vertebral Structure and Strength in Ovariectomized Rats

“…As such, our study includes novel and relevant information on the effects of a single ZOL injection on trabecular bone microarchitecture and cortical thickness in lumbar as well as in caudal vertebrae. The pattern in bone volume fraction between the four groups in the lumbar vertebrae was exactly the same as that seen in the proximal tibiae [10]. Also, a significant correlation was found between all individual values for bone volume fraction of the lumbar vertebrae and those of the tibiae (r 2 = 0.4, P \ 0.001; data not shown).…”

“…Previously, it was shown that 1 year of weekly injections of ZOL inhibited OVX-induced changes in bone microstructure and bone strength of femora and lumbar vertebrae of rats [7][8][9]. Also, in the same rats as used in this study, a single injection of ZOL prevented deterioration of bone microstructure and strength in tibiae of OVX rats for 16 weeks and a single injection at 8 weeks after OVX prevented further deterioration of structure and strength [10]. Additionally, in a dose-response study, it was shown that a single injection can inhibit structural changes seen after OVX in the tibia and retain mechanical properties in the vertebra [12].…”

“…It is known that 8 weeks after OVX bone microarchitecture has significantly deteriorated in the rat vertebra [18]. As bone volume fraction was similar in the early and late ZOL groups, we postulate that after ZOL treatment bone volume fraction somewhat increased, as seen in the tibiae as well [10], probably due to the filling of resorption cavities [19].…”

“…Twenty-nine female 35-week-old Wistar rats were used from a previous study [10]. In brief, rats were divided into four groups based on weight: SHAM-OVX (n = 9), OVX (n = 5), OVX and early ZOL (n = 8), and OVX and late ZOL (n = 7).…”

“…As the number and depth of in vivo analyses in patients are limited, animal research is ongoing to further elucidate the effects of ZOL on skeletal fragility [6][7][8][9]. Previously, we showed in a longitudinal study of adult rats that a single injection of ZOL at the time of ovariectomy (OVX) inhibited OVX-induced deterioration of bone microstructure and strength in the proximal tibiae for up to 16 weeks [10]. Furthermore, a single injection of ZOL 8 weeks after OVX inhibited further deterioration of the bone microstructure and strength in rat tibiae compared to untreated OVX rats.…”