Resolvin E1 Regulation of Bone Remodeling After Injury

Objective: Resolution of inflammation is defined by return to homeostasis and restoration of the morphology and function of tissues after injury or infection.  Resolution of inflammation is an active process mediated by receptor agonists such as resolvin E1 (RvE1), a derivative of the ω-3 polyunsaturated eicosapentaenoic acid.  RvE1 promotes healing after inflammatory tissue damage, acting through the ChemR23 receptor.  The goal of the project was to determine the action of RvE1 on bone healing.

Methods: In a calvarial model of bone formation in FVB mice, a 1 mm craniotomy defect was created.  RvE1 100ng or vehicle was injected in the defect area daily for 2 weeks after creation of the defect.  Bone healing was measured in histological sections as percentage of the original defect.  In a second experiment in vitro, neonatal calvarial osteblasts were used to test the action of RvE1.  Expression of sRANKL and OPG in culture supernatants was measured by ELISA following co-stimulation with RvE1 and pro-inflammatory cytokines.

Results: RvE1 significantly enhanced bone formation: 27.21 ± 1.03% vs 20.12 ± 1.24% in the vehicle group (Mean ± SEM, n=16, p<0.05, T-test).  No differences were found in osteoclast numbers (cells/mm²): 6.5 ± 0.64 in the vehicle group vs. 5.14 ± 1.68 in the RvE1 group.  ChemR23 mRNA was expressed by calvarial osteoblasts.  RvE1 increased OPG secretion into the culture media 48 hours after stimulation.  RvE1 did not induce changes in sRANKL, nor the expression of osteoblast markers mRNA.  

Conclusions: In this study, we show that RvE1 has anabolic actions in a mouse model of bone injury mainly through action on osteoblasts.  In addition, RvE1 shifted the balance between OPG and RANKL in vitro to favor bone formation.