Rats treated with AZD2858, a GSK3 inhibitor, heal fractures rapidly without endochondral bone formation.

Fracture healing is a complex interplay between endochondral and intramembranous bone formation processes. The canonical Wnt/β-catenin pathway enhances new bone formation and may play a role in fracture healing. Glycogen synthase kinase 3β (GSK3β) is a key regulator of β-catenin degradation. In this study, we investigate the effects of AZD2858, an orally bioactive GSK3 inhibitor, on fracture healing. Femoral fractures were produced in rats after the insertion of a femoral nail. The rats were treated with oral administration of AZD2858 at a dose of 30μmol/kg (20mg/kg) daily for up to 3weeks, while control animals were administered vehicle. At 4days, and at 1, 2 and 3weeks, histological analysis was performed, and at the 2 and 3week time points, we performed peripheral quantitative computed tomography (pQCT), X-rays, and four-point bending tests. Peripheral QCT showed an increase in both mineral density (of 28% at 2weeks and 38% at 3weeks) and mineral content (of 81% at 2weeks and 93% at 3weeks) in the calluses from AZD2858 treated animals as compared to vehicle treated animals. Histological analysis demonstrated that rats treated with GSK3 inhibitor healed their fractures rapidly, but without the pre-formation of cartilage tissue. Furthermore, four-point bending tests of fractured femora from animals treated for 2 and 3weeks showed an increase in strength in treated animals compared to their vehicle-treated controls. In conclusion, AZD2858, a potent GSK3 inhibitor, has a substantial impact on fracture healing. The fractures healed with a bony callus without an obvious endochondral component, suggesting that AZD2858 drives mesenchymal cells into the osteoblastic pathway. This leads to direct bone repair in an unstable fracture milieu.