local-delivery-of-il-1ra-as-a-strategy-to-enhance-long-bone-healing

Background

Although 90% of fractures typically heal without complications, there remains a small proportion (≤ 10%) of fractures that experience delayed healing or non-union. In patients with such healing complications, there appears to be an important contribution of an inappropriately maintained pro-inflammatory environment to the defective fracture healing process. Thus, immunomodulation of the local fracture microenvironment, such as by enhancing anti-inflammatory cytokine production, could be an effective way to enhance fracture healing in troublesome healing environments. This project focuses on investigating the therapeutic efficacy of IL-1Ra, the receptor antagonist of the potent pro-inflammatory cytokine IL-1β.

Goal

The goals of this project include the identification and characterization of a suitable pro-inflammatory endochondral bone healing model, and to test the efficacy of IL-1Ra delivered locally to the site of injury to promote bone healing.

Results

A 2 mm femoral defect was created in skeletally mature female Fischer 344 rats, following internal plate fixation using a customized 1.25 mm-thick PEEK plate. This model of non-union has been characterized based on microCT and histological assessment, with robust bone formation but an ultimate failure to bridging up to after 14 weeks post-surgery. The creation of the defect led to elevated circulating levels of IL-1β, which were maintained up to 10 days after surgery. Characterization of the early and local inflammatory response to the defect demonstrated there was a time-dependent shift in the ratio between IL-1β and IL-1Ra. Our results show that IL-1β protein levels at the defect site persisted up to 7 days post-surgery, whilst IL-1Ra markedly increased from 10 days onwards (p<0.01). Additionally, we have shown that up to 16 different inflammatory cytokines and chemokines in the bone marrow of the femur undergo significant changes in expression within 14 days post-surgery. Taken together, our findings suggest that, despite the small size of the defect, this model can be characterized by non-union in the long-term (14 weeks), and a persistent inflammatory response in the short-term (<2 weeks). With these characteristics, this model represents an excellent platform to determine the therapeutic efficacy of immunomodulatory strategies, including local delivery of IL-1Ra. On-going studies are investigating the efficacy of different biomaterials for delivery of recombinant proteins, including IL-1Ra and BMP-2, as a means of enhancing bone formation.