Continuous infusion of PTH 1–34 delayed fracture healing in mice

Hyperparathyroidism, which is increased parathyroid hormone (PTH) levels in the blood, could cause delayed or non-union of bone fractures. But, no study has yet demonstrated the effects of excess continuous PTH exposure, such as that seen in hyperparathyroidism, for fracture healing. Continuous human PTH1–34 (teriparatide) infusion using an osmotic pump was performed for stabilized tibial fractures in eight-week-old male mice to determine the relative bone healing process compared with saline treatment. Radiographs and micro-computed tomography showed delayed but increased calcified callus formation in the continuous PTH1–34 infusion group compared with the controls. Histology and quantitative histomorphometry confirmed that continuous PTH1–34 treatment significantly increased the bone callus area at a later time point after fracture, since delayed endochondral ossification occurred. Gene expression analyses showed that PTH1–34 resulted in sustained Col2a1 and reduced Col10a1 expression, consistent with delayed maturation of the cartilage tissue during fracture healing. In contrast, continuous PTH1–34 infusion stimulated the expression of both Bglap and Acp5 through the healing process, in accordance with bone callus formation and remodeling. Mechanical testing showed that continuously administered PTH1–34 increased the maximum load on Day 21 compared with control mice. We concluded that continuous PTH1–34 infusion resulted in a delayed fracture healing process due to delayed callus cell maturation but ultimately increased biomechanical properties.