Original Full Length ArticleEffects of ovariectomy on the changes in microarchitecture and material level properties in response to hind leg disuse in female rats
Highlights
► Neurectomy and ovariectomy have an additive effect on bone volume alteration. ► Neurectomy with or without ovariectomy markedly alter material level properties. ► The alteration of materiel level property remains intervention dependent. ► Nanoindentation technique may help to fully characterize the effects of various bone diseases or drugs.
Introduction
Mechanical loading plays a crucial role in the maintenance of normal bone remodeling and structure. In humans, this is particularly well demonstrated in conditions of reduced or suppressed mechanical constraints, including situations of weightlessness [1] and immobilization [2], but also in patients with spinal cord injuries [3]. The major clinical alteration observed is a reduction of bone mineral density (BMD) due to an imbalance between bone formation and bone resorption [2], [3]. Various experimental conditions, such as tail-suspension [4] or sciatic neurectomy (NX) [5], are most commonly used to study the mechanisms related to the reduction of mechanical constraints generated by decreased muscle contractions and/or weight-bearing activities. These two models are well known to cause a considerable loss of bone mass and a deterioration of bone microarchitecture [4], [5].
It is widely recognized that sex hormone deficiency as produced by ovariectomy (OVX) induces changes in bone tissue that include decreases in BMD and mechanical resistance [6], [7], [8]. Deterioration of bone strength associated with either immobilization or OVX is explained by different changes in bone remodeling. For instance, immobilization-induced bone loss results from higher bone resorption and/or reduced bone formation [9], [10], while the overall increased turnover occurring in OVX favors bone resorption as determined by histomorphometry [11] or bone biochemical markers [7], [8], [12].
In addition to BMD, bone strength is also determined by factors such as bone geometry, trabecular and cortical microarchitecture, and the accumulation of micro-damages [13], [14]. Bone material level properties, as assessed by nanoindentation, contribute to bone strength, hence to the resistance to fracture [15], [16]. The effect of OVX on material level properties has been reported [15], [17], but the response to disuse has not been described, as well as the role of sex hormone deprivation in this response. Moreover, the interaction between estrogen deficiency and immobilization may reflect a frequent clinical situation, particularly in elderly patients.
The purpose of this study was to evaluate the effect of unilateral NX on bone microarchitecture and material level properties by comparing the effect of NX in sham-operated and OVX animals and to investigate whether the changes observed were modified by sex hormone status.
Section snippets
Animals and experimental procedures
Sixteen six-month-old Sprague Dawley female rates (Ciba-Geigy Laboratories, Basel, Switzerland) were housed individually at a temperature of 25 °C with an alternating 12 h light/dark cycle. The rats were strictly pair-fed a laboratory diet (Provimi Kliba AG, Kaiseraugst, Switzerland) containing 15% casein, 0.8% phosphorus, 1% calcium, 70–80% carbohydrates, and 5% fat throughout the experimental period. Demineralized water was available ad libitum. After 2 weeks of adaptation to the experimental
Statistical analysis
All results are expressed as means ± SEM for all parameters measured. The distribution of continuous variables (BV/TV, Tb.Th, Tb.Sp, Tb.N, Ct.Th, elastic modulus, hardness, and dissipated energy) was tested with the Shapiro–Wilk statistical test and was found to be normal. When only one measure per animal was available (BV/TV, Tb.Th, Tb.Sp, Tb.N, Ct.Th at vertebral body), Student's t-test was used to compare the means between Sham and OVX. For the other parameters, the effect of OVX and/or NX and
Results
At the end of the study, the total body weight was higher in the OVX compared to the Sham group (282.2 ± 5.0 vs. 254.9 ± 3.8 g, p < 0.001).
Discussion
We investigated the effects of NX alone or in combination with OVX on proximal tibia bone microarchitecture and material level properties. Our results demonstrate that OVX induced a marked reduction in trabecula number at the proximal tibia with minor modifications to thickness. Estrogen deficiency causes an increase in bone resorption that leads to a perforation and an erosion of trabecular bone [7], [8], [12], [19]. Of note, OVX is associated also with increased formation [7], [8], [12], [20]
Acknowledgments
We thank I. Badoud for biomechanical testing, S. Clement for animal management, and S. Vouillamoz for technical assistance.
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Present address: Department of Hormonology, Lapeyronie Hospital, CHRU Montpellier and University Montpellier I, France.