Minimally Processed Adipose-Derived Stem Cells Increase Union Rates, Vascularity, and Cellularity During Fracture Repair of the Irradiated Murine Mandible
Kevin M. Urlaub, BS, Kavitha Ranganathan, MD, Jeremy V. Lynn, BS, Alexandra O. Luby, BS, Noah S. Nelson, MPH, Alexis Donneys, MD, MS, Steven R. Buchman, MD.
University of Michigan, Ann Arbor, MI, USA.
PURPOSE: Vascular and cellular depletion secondary to radiotherapy represents a major clinical challenge in mandibular reconstruction. Adipose-derived stem cells (ASCs) represent a promising component of regenerative medicine due to their multipotent potential and relative ease of harvest, yet remain under-investigated in the setting of radiotherapy. Furthermore, clinical translation of ASCs is currently impeded by arduous processing techniques and FDA regulations surrounding cell culture. This investigation examines the ability of minimally-processed ASCs (MPASCs) to enhance irradiated bone healing during fracture repair in the murine mandible to further delineate translatable methods of efficient ASC administration that ultimately expand the use of cell-based therapeutics in craniofacial reconstruction.
METHODS: Isogenic male Lewis rats were divided into the following groups: fracture (Fx, n =12), irradiated fracture (XFx, n =12), and irradiated fracture with MPASCs (XFxMP, n =11). Two weeks before surgery, irradiated groups received a fractioned dose of 35Gy over 5 days, equivalent to 70Gy administered to head and neck cancer patients clinically. All rats underwent osteotomy of the left hemi-mandible and external fixation. MPASCs were harvested from the inguinal fat of isogenic donors, centrifuged, and immediately placed intraoperatively into the osteotomy site. On post-operative day 40, all mandibles were perfused and evaluated for bony union upon dissection. Vascularity was evaluated at the fracture site through microcomputed tomography prior to histologic analysis of osteocyte proliferation and mature bone volume using Gomori Trichrome stain.
RESULTS: Bony union rates were significantly improved by MPASC implantation in the XFxMP group (82%) compared to XFx (25%) and were not statistically different from Fx (100%) (p = 0.01, 0.12). MPASC therapy significantly improved vessel volume, vessel volume fraction, vessel number, vessel thickness, and reduced vessel separation compared to the XFx group (p = 0.01, 0.01, 0.01, 0.01, 0.09, respectively). No significant differences in vascular metrics were observed between the Fx and XFxMP group. Histologic analysis revealed a significant reduction in both osteocyte proliferation and mature bone volume in the XFx group compared to Fx (p = 0.00, 0.00). Bone cellularity and mature bone formation were significantly increased in the XFxMP group compared to XFx and were restored to non-irradiated levels (p = 0.00, 0.04).
CONCLUSION: Impairment of angiogenesis and the destruction of osteocompetent cells secondary to radiotherapy are principal obstacles to irradiated bone healing. This study demonstrates the efficacy of MPASCs in remediating these damaging effects and provides a promising foundation for future studies aimed at developing minimally-processed cell-based therapeutics for clinical implementation. Facilitation of normal bone healing in the setting of radiotherapy through MPASCs may offer an effective strategy to address the sequelae of pathologic fractures and osteoradionecrosis that currently present significant challenges in the management of head and neck cancer.
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