Influence of ovariectomy on bone turnover and trabecular bone mass in mature cynomolgus monkeys

The Gradual Release of Alendronate for the Treatment of Critical Bone Defects in Osteoporotic and Control Rats

Purpose

Osteoporosis is a severe health problem with social and economic impacts on society. The standard treatment consists of the systemic administration of drugs such as bisphosphonates, with alendronate (ALN) being one of the most common. Nevertheless, complications of systemic administration occur with this drug. Therefore, it is necessary to develop new strategies, such as local administration.

Methods

In this study, emulsion/dispersion scaffolds based on W/O emulsion of PCL and PF68 with ALN, containing hydroxyapatite (HA) nanoparticles as the dispersion phase were prepared using electrospinning. Scaffolds with different release kinetics were tested in vitro on the co-cultures of osteoblasts and osteoclast-like cells, isolated from adult osteoporotic and control rats. Cell viability, proliferation, ALP, TRAP and CA II activity were examined. A scaffold with a gradual release of ALN was tested in vivo in the bone defects of osteoporotic and control rats.

Results

The release kinetics were dependent on the scaffold composition and the used system of the poloxamers. The ALN was released from the scaffolds for more than 22 days. The behavior of cells cultured in vitro on scaffolds with different release kinetics was comparable. The difference was evident between cell co-cultures isolated from osteoporotic and control animals. The PCL/HA scaffold show slow degradation in vivo and residual scaffold limited new bone formation inside the defects. Nevertheless, the released ALN supported bone formation in the areas surrounding the residual scaffold. Interestingly, a positive effect of systemic administration of ALN was not proved.

Conclusion

The prepared scaffolds enabled tunable control release of ALN. The effect of ALN was proved in vitro and in in vivo study supported peri-implant bone formation.

Ovariectomy and timing of impaired maxillary alveolar bone regeneration: An experimental study in rats

BACKGROUND

The aim of this study was to seek the critical time for impairment of alveolar bone regeneration after ovariectomy (OVX) in rats.

METHODS

A total of 32 female rats were used. Test group rats were divided into a 2M group (n = 8), a 3M group (n = 8) and a 4M group (n = 8) according to the duration from OVX to defect creation. Bilateral OVX was performed in all test groups, and a sham operation was performed in the control group (n = 8). Drill-hole defects (1.5 mm diameter, 2 mm length) were created on both sides of the maxilla. All rats were euthanized 2 and 4 weeks after the surgery. Microcomputed tomographic (micro-CT), histological, and histomorphometric analyses and in vitro experiments were performed.

RESULTS

The 4M group showed significantly less new bone formation and a lower bone mineral density than the other groups in the micro-CT analysis. The histomorphometric analysis also revealed that the 4M group showed significantly less new bone formation than the control and 2M groups. The rats in the 4M group showed significantly higher alkaline phosphatase expression levels and a larger number of calcified nodules than rats in the other groups, whereas osteoclastic activity was significantly lower in the 4M group than in the other groups.

CONCLUSIONS

The critical time for impairment of alveolar bone regeneration was 4 months after OVX in rats.

Maintenance of bone mass despite estrogen depletion in female common marmoset monkeys (Callithrix jacchus)

Estrogen depletion leads to bone loss in almost all mammals with frequent regular ovarian cycles. However, subordinate adult female common marmosets (Callithrix jacchus) undergo socially induced anovulation and hypoestrogenism without clinically apparent adverse skeletal consequences. Thus, we speculated that this non human primate might have evolved a mechanism to avoid estrogen-depletion bone loss. To test this possibility, we performed three experiments in which lumbar-spine (L5-L6) bone mineral content (BMC) and density (BMD) were assessed using dual-energy X-ray absorptiometry: (i) cross-sectionally in 13 long-term ovariectomized animals and 12 age- and weight-matched controls undergoing ovulatory cycles; (ii) longitudinally in 12 animals prior to, 3-4 and 6-7 months following ovariectomy (ovx), and six controls; and (iii) cross-sectionally in nine anovulatory subordinate and nine dominant females. In Experiments 1 and 3, plasma estradiol and estrone concentrations were measured and uterine dimensions were obtained by ultrasound in a subset of animals as a marker of functional estrogen depletion. Estrogen levels, uterine trans-fundus width, and uterine dorso-ventral diameter were lower in ovariectomized and subordinate females than in those undergoing ovulatory cycles. However, no differences were found in L5-L6 BMC or BMD. These results indicate that estrogen depletion, whether surgically or socially induced, is not associated with lower bone mass in female common marmosets. Thus, this species may possess unique adaptations to avoid bone loss associated with estrogen depletion.

Persistence of vertebral growth plate cartilage in aged cynomolgus monkeys

Growth plates at each end of vertebral bodies play a pivotal role in longitudinal spinal growth. Epiphyseal closures are formed in adult humans. Although monkeys are frequently employed in bone and disc research, the age of epiphyseal closure has not been well documented. In this study, histological analyses of lumbar vertebral end plates and the surrounding tissue were performed in 11 normal cynomolgus monkeys aged approximately 9 to 15 years, and unclosed growth plate cartilage was detected in all the end plates. The data from this study constitute the first documentation of persistent vertebral growth plate cartilage in cynomolgus monkeys. The persistence of growth plate cartilage in cynomolgus monkeys approximately 15 years of age or younger, which differs from the complete epiphyseal closure exhibited in adult humans, may affect the biomechanical behavior of the spine. This is an important factor to consider in extrapolating the results of spine and intervertebral disc research using cynomolgus monkeys to adult humans.