PTH(1-34) and zoledronic acid have differing longitudinal effects on juvenile mouse femur strength and morphology

Zoledronate treatment exerts sex-independent effects on bone and dental physicochemical properties in mice jaw necrosis

INTRODUCTION

Bisphosphonate (BF) therapy is strongly related to the occurrence of medication-related osteonecrosis of the jaw (ONJ). However, no previous study has evaluated if there are sex-related differences on the ONJ establishment together with bone biomechanical alterations, and if they could have a synergy with the ZA treatment.

MATERIALS AND METHODS

This study aimed to analyze the physicochemical properties of mineralized tissues in a zoledronate (ZA)-related osteonecrosis mouse model, by a 2 × 2-factorial design, considering sex (female/male) and treatment (ZA/Saline) factors (n = 8/group). After three ZA (1.0 mg/kg) or saline administrations (days 0, 7, 14), the lower left second molar was extracted (day 42). Further ZA administration (day 49) and euthanasia (day 70) were conducted. After confirmation of ZA-induced jaw necrosis (histologic and microtomographic analysis), spectroscopic and mechanical parameters were assessed.

RESULTS

ZA-treated groups presented lower bone density due to impaired healing of tooth extraction socket. Sex-related alterations were also observed, with lower bone density in females. Regarding biomechanical parameters, sex and treatment exerted independent influences. ZA, although decreasing flexural modulus and yield stress, increases stiffness mainly due to a higher bone volume. Females show less resistance to higher loads compared to males (considering dimension-independent parameters). Additionally, ZA increases crystallinity in bone and dental structure (p < 0.05). In summary, although strongly related to osteonecrosis occurrence, ZA modifies bone and dental mineral matrix, improving bone mechanical properties.

CONCLUSION

Despite sex-dependent differences in bone biomechanics and density, osteonecrosis was established with no sex influence. No synergistic association between sex and treatment factors was observed in this study.

Orchestrated delivery of PTH [1-34] followed by zoledronic acid prevents radiotherapy-induced bone loss but does not abrogate marrow damage

Postradiotherapy bone fragility fractures are a frequent late-onset complication in cancer survivors. There is a critical need to develop preventative interventions, and the use of Food and Drug Administration-approved drugs remains an attractive option. Prior data from our lab and others have shown that parathyroid hormone [1-34] mitigates radiotherapy-induced bone loss, but only for the duration of drug delivery. Utilizing a murine hindlimb radiotherapy model, we investigated whether orchestrated delivery of single-dose zoledronic acid could extend these anabolic benefits after cessation of parathyroid hormone delivery. We then explored the potential use of parathyroid hormone as a bone marrow radioprotectant. While the addition of zoledronic acid to parathyroid hormone increased irradiated bone mass, there was no increase in femur bending strength. In this model, the parathyroid hormone was not effective as a marrow radioprotectant, although this could be due to the short course of parathyroid hormone treatment. Marrow repopulation kinetics differed from those in total body irradiation, with hematopoietic stem cell repopulation occurring relatively early at four weeks postirradiation. Furthermore, we found radiation induced a loss of marrow stromal cells and an increase in inflammatory monocytes. Statement of Clinical Significance: Staged delivery of parathyroid hormone and zoledronic acid shows promise as an off-the-shelf intervention to mitigate post-radiotherapy bone damage in cancer patients, but parathyroid hormone is unlikely to function as a broad-spectrum marrow radioprotectant.