Targeting the lateral but not the third ventricle induces bone loss in ewe: An experimental approach to generate an improved large animal model of osteoporosis

Why Animal Experiments Are Still Indispensable in Bone Research: A Statement by the European Calcified Tissue Society

Major achievements in bone research have always relied on animal models and in vitro systems derived from patient and animal material. However, the use of animals in research has drawn intense ethical debate and the complete abolition of animal experimentation is demanded by fractions of the population. This phenomenon is enhanced by the reproducibility crisis in science and the advance of in vitro and in silico techniques. 3D culture, organ-on-a-chip, and computer models have improved enormously over the last few years. Nevertheless, the overall complexity of bone tissue cross-talk and the systemic and local regulation of bone physiology can often only be addressed in entire vertebrates. Powerful genetic methods such as conditional mutagenesis, lineage tracing, and modeling of the diseases enhanced the understanding of the entire skeletal system. In this review endorsed by the European Calcified Tissue Society (ECTS), a working group of investigators from Europe and the US provides an overview of the strengths and limitations of experimental animal models, including rodents, fish, and large animals, as well the potential and shortcomings of in vitro and in silico technologies in skeletal research. We propose that the proper combination of the right animal model for a specific hypothesis and state-of-the-art in vitro and/or in silico technology is essential to solving remaining important questions in bone research. This is crucial for executing most efficiently the 3R principles to reduce, refine, and replace animal experimentation, for enhancing our knowledge of skeletal biology, and for the treatment of bone diseases that affect a large part of society. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Development and in vivo assessment of a novel MRI-compatible headframe system for the ovine animal model

BACKGROUND

The brain of sheep has primarily been used in neuroscience as an animal model because of its similarity to the human brain, in particular if compared to other models such as the lissencephalic rodent brain. Their brain size also makes sheep an ideal model for the development of neurosurgical techniques using conventional clinical CT/MRI scanners and stereotactic systems for neurosurgery.

METHODS

In this study, we present the design and validation of a new CT/MRI compatible head frame for the ovine model and software, with its assessment under two real clinical scenarios.

RESULTS

Ex-vivo and in vivo trial results report an average linear displacement of the ovine head frame during conventional surgical procedures of 0.81 mm for ex-vivo trials and 0.68 mm for in vivo tests, respectively.

CONCLUSIONS

These trial results demonstrate the robustness of the head frame system and its suitability to be employed within a real clinical setting.

The old sheep: a convenient and suitable model for senile osteopenia

INTRODUCTION

Existing osteoporosis models in sheep exhibit some disadvantages, e.g., challenging surgical procedures, serious ethical concerns, failure of reliable induction of substantial bone loss, or lack of comparability to the human condition. This study aimed to compare bone morphological and mechanical properties of old and young sheep, and to evaluate the suitability of the old sheep as a model for senile osteopenia.

MATERIALS AND METHODS

The lumbar vertebral body L3 of female merino sheep with two age ranges, i.e., old animals (6-10 years; n = 41) and young animals (2-4 years; n = 40), was analyzed concerning its morphological and mechanical properties by bone densitometry, quantitative histomorphometry, and biomechanical testing of the corticalis and/or central spongious region.

RESULTS

In comparison with young sheep, old animals showed only marginally diminished bone mineral density of the vertebral bodies, but significantly decreased structural (bone volume, - 15.1%; ventral cortical thickness, - 11.8%; lateral cortical thickness, - 12.2%) and bone formation parameters (osteoid volume, osteoid surface, osteoid thickness, osteoblast surface, all - 100.0%), as well as significantly increased bone erosion (eroded surface, osteoclast surface). This resulted in numerically decreased biomechanical properties (compressive strength; - 6.4%).

CONCLUSION

Old sheep may represent a suitable model of senile osteopenia with markedly diminished bone structure and formation, and substantially augmented bone erosion. The underlying physiological aging concept reduces challenging surgical procedures and ethical concerns and, due to complex alteration of different facets of bone turnover, may be well representative of the human condition.

Preclinical and Translational Studies in Small Ruminants (Sheep and Goat) as Models for Osteoporosis Research

PURPOSE OF THE REVIEW

This review summarizes research on the use of sheep and goats as large animal models of human osteoporosis for preclinical and translational studies.

RECENT FINDINGS

The most frequent osteoporotic sheep model used is the ovariectomized sheep with 12 months post-operatively or more and the combined treatment of ovariectomized sheep associated to calcium/vitamin D-deficient diet and glucocorticoid applications for 6 months, but other methods are also described, like pinealectomy or hypothalamic-pituitary disconnection in ovariectomized sheep. The goat model for osteoporosis research has been used in a very limited number of studies in osteoporosis research relative to sheep. These osteoporotic small ruminant models are applied for biomaterial research, bone augmentation, efficacy of implant fixation, fragility fracture-healing process improvement, or bone-defect repair studies in the osteopenic or osteoporotic bone. Sheep are a recognized large animal model for preclinical and translational studies in osteoporosis research and the goat to a lesser extent. Recently, the pathophysiological mechanism underlying induction of osteoporosis in glucocorticoid-treated ovariectomized aged sheep was clarified, being similar to what occurs in postmenopausal women with glucocorticoid-induced osteoporosis. It was also concluded that the receptor activator of NF-κB ligand was stimulated in the late progressive phase of the osteoporosis induced by steroids in sheep. The knowledge of the pathophysiological mechanisms at the cellular and molecular levels of the induction of osteoporosis in small ruminants, if identical to humans, will allow in the future, the use of these animal models with greater confidence in the preclinical and translational studies for osteoporosis research.

Leptin Influences Healing in the Sprague Dawley Rat Fracture Model

Background

Leptin plays a crucial role in bone metabolism, and its level is related to bone callus formation in the fracture repair process. The objective of this study was to evaluate the effect of recombinant leptin on the healing process of femoral fractures in rats.

Material/Methods

Forty-eight male Sprague Dawley (SD) rats with an average body weight of 389 g (range: 376–398 g) and an average age of 10 weeks were included in this animal research, and all rats were randomly divided into two major groups. Then standardized femur fracture models were implemented in all SD rats. Rats in the control group were treated with only 0.5 mL of physiological saline, and rats in the experimental group were treated with recombinant leptin 5 μg/kg/d along with the same 0.5 mL of physiological saline for 42 days intraperitoneally. At the same time, each major group was evenly divided into three parallel subgroups for each parallel bone evaluation separately at the second, fourth, and sixth weeks. Each subgroup included eight rats.

Results

The total radiological evaluation results showed that the healing progress of femoral fracture in the experimental group was superior to that in the control group from the fourth week. At the sixth week, experimental group rats began to present significantly better femoral fracture healing progress than that of the control group rats. Results of biomechanics show the ultimate load (N) and deflection ultimate load (mm) of the experimental group rats was significantly increased compared with that of the control group rats from the fourth week.

Conclusions

Our results suggest that leptin may have a positive effect on SD rat femur fracture healing.

Can we induce osteoporosis in animals comparable to the human situation?

Osteoporosis is a chronic systemic bone disease of growing relevance due to the on-going demographic change. Since the underlying regulatory mechanisms of this critical illness are still not fully understood and treatment options are not satisfactorily resolved, there is still a great need for osteoporosis research in general and animal models in particular. Ovariectomized rodents are standard animal models for postmenopausal osteoporosis and highly attractive due to the possibility to specifically modify their genetic background. However, some aspects can only be addressed in large animal models; such as metaphyseal fracture healing and advancement of orthopedic implants. Among other large animal models sheep in particular have been proven invaluable for osteoporosis research in this context. In conclusion, today we are able to influence the bone metabolism in animals causing a more or less pronounced systemic bone loss and structural deterioration comparable to the situation found in patients suffering from osteoporosis. However, there is no perfect model for osteoporosis, but a variety of models appropriate for answering specific questions. Though, the appropriateness of an animal model is not only defined in regard to the similarity to human physiology and the disease itself, but also in regard to acquisition, housing requirements, handling, costs, and particularly ethical concerns and animal welfare.