Effect of irisin on the healing of tibial fracture in rats

Abstract:

Objective：To investigate the effect of irisin on fracture healing in rats and the regulating role on bone metabolism of whole body and bone fracture sites. Methods：SD rat tibial fracture models were established and were randomly divided into the control group（local injection of normal saline at the fracture gap） and the experimental group（local injection of 1 mL irisin protein solution，100 ng/mL）. X-ray，Micro-CT，biomechanical analysis and HE staining were used to observe the early fracture healing. Immunohisto－chemical staining and ELISA were used to detect the bone metabolism. SPSS 20.0 software was used to perform the statistical analysis. Results：Results of X-ray and Micro-CT showed new bone calluses in the experimental group were more than those in the control group at the 4th week after fracture. At the 8th week after frac－ture，fracture line in the experimental group was closely to dis－appear，while fracture line on images of bone fractured end in the control group were seen indistinctly. Total volume（TV），bone volume（BV），bone volume fraction（BVF，BV/TV），trabec－ular thickness（Tb.Th） and trabecular number（Tb.N） in the ex－perimental group at the 4th and 8th week after fracture were al－so significantly higher than those in the control group（P<0.05）. Results of biomechanical analysis indicated that maximum load，stiffness and energy absorption in the experimental group was significantly greater than those in the control group at the 4th and 8th week after fracture（P<0.05）. HE staining results showed that bone bridges in the experimental group were more than those the control group at the 4th week after fracture，and the lamellar bone in the experimental group was thicker than that in the control group at the 8th week after fracture. Immunohistochemical staining results showed that the expression of oxypolygelatin（OPG） in the experimental group was significantly enhanced and the expression of receptor activator of nuclear factor-κB ligand（RANKL） in the experimental group was significantly inhibited when compared with those in the control group. At the same time，a stronger uncoupling protein 1（UCP1） immunopositive staining was observed in the bone marrow tissue in the experimental group. ELISA results showed that serum levels of bone alkaline phosphatase（BALP） in the experimental group were significantly increased than that in the control group at the 4th and 8th week after fracture，and serum levels of tartrate-resistant acid phosphatase 5b（TRAP 5b） were significantly decreased（P<0.05）. Conclusion：Irisin can improve bone metabolism of the whole body and bone fracture sites，so as to promote osteogenesis and healing within a short time.