Histologic Improvements in Irradiated Bone Through Pharmaceutical Intervention in Mandibular Distraction Osteogenesis

A novel approach for the prevention of ionizing radiation-induced bone loss using a designer multifunctional cerium oxide nanozyme

The disability, mortality and costs due to ionizing radiation (IR)-induced osteoporotic bone fractures are substantial and no effective therapy exists. Ionizing radiation increases cellular oxidative damage, causing an imbalance in bone turnover that is primarily driven via heightened activity of the bone-resorbing osteoclast. We demonstrate that rats exposed to sublethal levels of IR develop fragile, osteoporotic bone. At reactive surface sites, cerium ions have the ability to easily undergo redox cycling: drastically adjusting their electronic configurations and versatile catalytic activities. These properties make cerium oxide nanomaterials fascinating. We show that an engineered artificial nanozyme composed of cerium oxide, and designed to possess a higher fraction of trivalent (Ce³⁺) surface sites, mitigates the IR-induced loss in bone area, bone architecture, and strength. These investigations also demonstrate that our nanozyme furnishes several mechanistic avenues of protection and selectively targets highly damaging reactive oxygen species, protecting the rats against IR-induced DNA damage, cellular senescence, and elevated osteoclastic activity in vitro and in vivo. Further, we reveal that our nanozyme is a previously unreported key regulator of osteoclast formation derived from macrophages while also directly targeting bone progenitor cells, favoring new bone formation despite its exposure to harmful levels of IR in vitro. These findings open a new approach for the specific prevention of IR-induced bone loss using synthesis-mediated designer multifunctional nanomaterials.

Intraoperative Stromal Vascular Fraction Therapy Improves Histomorphometric and Vascular Outcomes in Irradiated Mandibular Fracture Repair

BACKGROUND

Cell-based treatments have demonstrated the capacity to enhance reconstructive outcomes in recent decades but are hindered in clinical utility by regulatory hurdles surrounding cell culture. This investigation examines the ability of a noncultured stromal vascular fraction derived from lipoaspirate to enhance bone healing during fracture repair to further the development of translatable cell therapies that may improve outcomes in irradiated reconstruction.

METHODS

Isogenic male Lewis rats were divided into three groups: fracture, irradiated fracture, and irradiated fracture with stromal vascular fraction treatment. Irradiated groups received a fractioned dose of 35 Gy before mandibular osteotomy. Stromal vascular fraction was harvested from the inguinal fat of isogenic donors, centrifuged, and placed intraoperatively into the osteotomy site. All mandibles were evaluated for bony union and vascularity using micro-computed tomography before histologic analysis.

RESULTS

Union rates were significantly improved in the irradiated fracture with stromal vascular fraction treatment group (82 percent) compared to the irradiated fracture group (25 percent) and were not statistically different from the fracture group (100 percent). Stromal vascular fraction therapy significantly improved all metrics of bone vascularization compared to the irradiated fracture group and was not statistically different from fracture. Osteocyte proliferation and mature bone formation were significantly reduced in the irradiated fracture group. Bone cellularity and maturity were restored to nonirradiated levels in the irradiated fracture with stromal vascular fraction treatment group despite preoperative irradiation.

CONCLUSIONS

Vascular and cellular depletion represent principal obstacles in the reconstruction of irradiated bone. This study demonstrates the efficacy of stromal vascular fraction therapy in remediating these damaging effects and provides a promising foundation for future studies aimed at developing noncultured, cell-based therapies for clinical implementation.

Noncultured Minimally Processed Adipose-Derived Stem Cells Improve Radiated Fracture Healing

Adipose-derived stem cells mitigate deleterious effects of radiation on bone and enhance radiated fracture healing by replacing damaged cells and stimulating angiogenesis. However, adipose-derived stem cell harvest and delivery techniques must be refined to comply with the US Food and Drug Administration restrictions on implantation of cultured cells into human subjects prior to clinical translation. The purpose of this study is to demonstrate the preservation of efficacy of adipose-derived stem cells to remediate the injurious effects of radiation on fracture healing utilizing a novel harvest and delivery technique that avoids the need for cell culture. Forty-four Lewis rats were divided into 4 groups: fracture control (Fx), radiated fracture control (XFx), radiated fracture treated with cultured adipose-derived stem cells (ASC), and radiated fracture treated with noncultured minimally processed adipose-derived stem cells (MP-ASC). Excluding the Fx group, all rats received a fractionated human-equivalent dose of radiation. All groups underwent mandibular osteotomy with external fixation. Following sacrifice on postoperative day 40, union rate, mineralization, and biomechanical strength were compared between groups at P < 0.05 significance. Compared with Fx controls, the XFx group demonstrated decreased union rate (100% vs 20%), bone volume fraction (P = 0.003), and ultimate load (P < 0.001). Compared with XFx controls, the MP-ASC group tripled the union rate (20% vs 60%) and demonstrated statistically significant increases in both bone volume fraction (P = 0.005) and ultimate load (P = 0.025). Compared with the MP-ASC group, the ASC group showed increased union rate (60% vs 100%) and no significant difference in bone volume fraction (P = 0.936) and ultimate load (P = 0.202). Noncultured minimally processed adipose-derived stem cells demonstrate the capacity to improve irradiated fracture healing without the need for cell proliferation in culture. Further refinement of the cell harvest and delivery techniques demonstrated in this report will enhance the ability of noncultured minimally processed adipose-derived stem cells to improve union rate and bone quality, thereby optimizing clinical translation.