Bone Abstracts

Introduction: In accidental irradiations, skin, muscle and bone are altered. Mesenchymal Stem Cell (MSC) treatment has already been used for skin healing in accidental irradiations, but its effects on irradiated bone are still unknown.

In this study, we characterised a mouse model of high dose local irradiation of bone and the effects of MSCs injections on osteoradionecrosis.

Methods: Nude mice were locally irradiated in the left tibia, at a high dose (120 Gy). One week after irradiation, the mice were injected with 1.10⁶ MSCs from bone marrow, systemically, or inside the medullary of the irradiated tibia. PBS was injected in control mice.

Bone microarchitecture was analysed by μCT scanning and bone strength by nanoindentation. The vascular network was observed using barium sulfate perfusion. Bone fibrosis and osteocyte number were quantified on sirius red and toluidine blue stained histological images.

Results: We observed an increase of BV/TV, Tb.Th and Ct.Th in the irradiated leg compared to control leg as early as 15 days after irradiation. Collagen fibrotic content was decreased in the bone matrix, and increased in the bone marrow. The percentage of full lacunae in bone matrix was also decreased. Bone hardness was reduced in the irradiated bones after 1 month. Finally, we observed a reduction in blood vessel perfusion in the irradiated bone.

Interestingly, in the MSC treated mice, the percentage of full lacunae was higher than in PBS controls but remained lower in the irradiated leg than in contralateral one.

Conclusion: We demonstrate here that a high dose local irradiation strongly alters bone: we observed an early increase of matrix thickness associated with a decrease in collagen density and osteocyte number, leading to a weakening of bone. MSC injection has positive effects on the number of full lacunae demonstrating a promising potential of this treatment.