Accelerating Ridge Augmentation via a Xenograft and Wnt Therapeutic Combination

Objectives: The present study aimed to demonstrate the mechanisms of actions of a xenogeneic bone substitute in a murine vertical ridge augmentation model, and to test if utilizing a Wnt therapeutic would accelerate the bone forming process.
Methods: The edentulous ridge located anterior to the maxillary first molar was chosen as the grafting site and a minimally invasive tunneling procedure was adopted. Deproteinized bovine bone mineral was either grafted alone (n=9), or in combination with a liposomal formulation of WNT3A protein (L-WNT3A, n=9) or liposomal PBS (L-PBS, n=9). Mice were harvested at post-surgery-day (PSD) 6, 9, and 14, followed by micro-CT imaging, histological analyses and immunohistochemistry staining (IHC) for PCNA and Runx2.
Results: CT imaging of xenograft-transplanted mice on PSD6 illustrated that the pocket created by the tunneling procedure stabilized the graft on the thin edentulous ridge, and data from PSD9 and PSD14 showed the xenograft particles gradually became embedded in newly formed bone. Histology and IHC demonstrated the source of this new bone: the tunneling procedure instigated the proliferation of Runx2-positive osteoprogenitor cells from the maxillary bone periosteum; over time, these cells secreted a collagen-rich matrix as shown by picro-sirius red staining and ALP activity, that gradually encapsulated the xenograft particles. Compared to xenografts treated with L-PBS, WNT-treated xenografts were associated with significantly more Runx2-positive osteoprogenitor cells at PSD6. Furthermore, as shown by picro-sirius red staining, L-WNT3A accelerated the mineralization of newly formed collagen fibers around the xenograft. Histomorphometric quantification demonstrated that WNT-incorporated group gave rise to over two times as much new bone than the L-PBS treated group at PSD9 (28.82±6.39µm V.S. 11.96±4.18µm).
Conclusions: First, the xenograft functions as a scaffold for osteoprogenitor cells that are activated in response to the tunneling procedure. Second, this endogenous osteogenic repair response can be boosted by a Wnt therapeutic.