Prolonged Impact of Bisphosphonates and Glucocorticoids on Bone Mechanical Properties

Background: This study aimed at investigating the prolonged effects of glucocorticoids and bisphosphonates on bone. Methods: Six-to-eight-month-old skeletally mature male Sprague Dawley rats were randomized to receive a cancer therapy combination of zoledronic acid (ZA = 0.13 mg/kg) and dexamethasone (DX = 3.8 mg/kg) (treatment group, n = 10) or sterile phosphate buffer saline solution (control group, n = 10). The rats received weekly intraperitoneal injections for 8 weeks, which were stopped 6 weeks before euthanasia. Mineralized bone samples were characterized by three-point bending tests, micro-CT imaging, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Bone collagen was assessed using tensile tests on the demineralized bones and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy on mineralized and demineralized bones. Results: The samples in the treatment group showed increased tibial cortical thickness, mineral crystal size, and toughness. Analyses of demineralized tibiae revealed decreased collagen tensile strength in the experimental group. The spectroscopic and TGA/DSC analyses showed that the ZA + DX treatment increased the collagen amide I 1660/1690 cm^-1 area ratio and collagen denaturalization temperature, indicating a higher level of collagen cross-linking. Conclusions: Bisphosphonates and glucocorticoids led to prolonged changes in the mechanical properties of bone as a result of increased cortical thickness, increased crystal size, and the deterioration of collagen quality.