Elsevier

Bone

Volume 51, Issue 3, September 2012, Pages 586-591
Bone

Original Full Length Article
Effects of ovariectomy on the changes in microarchitecture and material level properties in response to hind leg disuse in female rats

https://doi.org/10.1016/j.bone.2012.05.001Get rights and content

Abstract

Background

Ovariectomy (OVX) and immobilization are known to decrease bone mineral density and alter its microarchitecture. Their effects on the material level properties of bone, a determinant of bone strength, are still largely unknown. We investigated the effect of OVX and/or disuse achieved by sciatic neurectomy (NX) in 6-month-old Sprague Dawley female rats.

Methods

At baseline, animals underwent OVX or sham operation. At week 16, NX was performed on the left hindlimb while the right hindlimb was sham-operated. All animals were sacrificed at week 40. Proximal tibiae and vertebral bodies (L4) were evaluated by micro-computed tomographic morphometry (μCT). Material level properties (elastic modulus, hardness, and dissipated energy) were evaluated by a nanoindentation test.

Results

At the proximal tibia, OVX and NX decreased relative bone volume, the former mainly through a reduction in trabecular number, and the latter through a decrease in trabecular thickness. NX decreased modulus (− 10%; p < 0.001) and dissipated energy (− 13.3%, p < 0.001) in cortical bone, and modulus (− 16.8%, p = 0.004), hardness (− 29.3%, p = 0.004), and dissipated energy (− 17.7%, p = 0.01) in trabecular bone, while OVX decreased cortical bone dissipated energy (− 14.6%, p < 0.001) and trabecular bone hardness (− 19.4%, p = 0.05). In the vertebral body, OVX altered mainly the trabecular microarchitecture and nanoindentation variables.

Conclusion

These results show that NX with and without OVX markedly alter material level properties in addition to an alteration of bone microarchitecture, although not in the same manner.

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.

References (31)

  • Z.Q. Peng et al.

    Long-term effects of ovariectomy on the mechanical properties and chemical composition of rat bone

    Bone

    (1997)
  • M. Michalsky et al.

    Rat cortical and trabecular bone collagen glycosylation are differently influenced by ovariectomy

    Biochem Biophys Res Commun

    (1993)
  • L.J. Dominguez et al.

    Collagen overglycosylation: a biochemical feature that may contribute to bone quality

    Biochem Biophys Res Commun

    (2005)
  • J.E. Zerwekh et al.

    The effects of twelve weeks of bed rest on bone histology, biochemical markers of bone turnover, and calcium homeostasis in eleven normal subjects

    J Bone Miner Res

    (1998)
  • L. Maimoun et al.

    Changes in osteoprotegerin/RANKL system, bone mineral density, and bone biochemicals markers in patients with recent spinal cord injury

    Calcif Tissue Int

    (2005)
  • Cited by (0)

    1

    Present address: Department of Hormonology, Lapeyronie Hospital, CHRU Montpellier and University Montpellier I, France.

    View full text