[Intermittent low-dose administration of recombinant human parathyroid hormone (1-34) promotes the expression of Runx2 during early stage of fracture healing].

Objective: To study the correlation of intermittent low-dose administration of recombinant human parathyroid hormone (1-34) [rhPTH (1-34)] and the expression of Runx2 during early stage of fracture healing.

Method: Sixty 2-month old male Sprague-Dawley rats underwent close unilateral femoral fracture and intramedullary nail fixation, and then were randomly divided into 2 equal groups: treatment group undergoing subcutaneous injection of rhPTH (1-34) 10 microgxkg(-1)xd(-1) immediately after the operation, and control group undergoing subcutaneous injection of normal saline of the same dose. Six rats from each group were killed with their bilateral femurs taken out on days 2, 4, 7, 14, and 21 after the operation to undergo X-ray photography Tissue RNA and protein were extracted from the bone tissues and the levels of Runx2 mRNA and protein expression were evaluated through real time quantitative PCR and Western-blotting. Blood samples were collected from the abdominal aorta before the rats were killed to undergo detection of serum calcium, phosphorus, and alkaline phosphatase (AKP).

Results: The Runx2 mRNA levels in the fractured femurs of the rhPTH (1-34) group on days 14 and 21 after the operation were 2.6 and 3.8 times as those of the control group respectively (both P<0.05). The Runx2 protein levels in the fractured femurs of the rhPTH (1-34) group on days 14 and 21 after the operation were significantly higher than those of the control group respectively too. Since day 14 fracture healing was seen, and the status of fracture healing was better in the rhPTH (1-34) group than in the control group on days 14 and 21. The levels of serum calcium ion on days 14 and 21 of the rhPTH (1-34) group were both significantly higher than those of the control group (both P<0.05). There were not significant differences in the serum levels of AKP, osteocalcin and collagen type Iat any time point between the 2 groups.

Conclusion: Intermittent low-dose administration of rhPTH (1-34) up-regulates the levels of osteogenesis-specific Runx2 mRNA and protein expression to accelerate the early stage fracture healing during the early stage.