An in vitro model of radiation-induced craniofacial bone growth inhibition

Localized deferoxamine injection augments vascularity and improves bony union in pathologic fracture healing after radiotherapy

BACKGROUND

Medically based efforts and alternative treatment strategies to prevent or remediate the corrosive effects of radiotherapy on pathologic fracture healing have failed to produce clear and convincing evidence of success. Establishing an effective pharmacologic option to prevent or treat the development of non-unions in this setting could have immense therapeutic potential. Experimental studies have shown that deferoxamine (DFO), an iron-chelating agent, bolsters vascularity and subsequently enhances normal fracture healing when injected locally into a fracture callus in long bone animal models. Since radiotherapy is known to impede angiogenesis, we hypothesized that the pharmacologic addition of DFO would serve to mitigate the effects of radiotherapy on new vessel formation in vitro and in vivo.

MATERIALS AND METHODS

In vitro investigation of angiogenesis was conducted utilizing HUVEC cells in Matrigel. Endothelial tubule formation assays were divided into four groups: Control, Radiated, Radiated+Low-Dose DFO and Radiated+High-Dose DFO. Tubule formation was quantified microscopically and video recorded for the four groups simultaneously during the experiment. In vivo, three groups of Sprague-Dawley rats underwent external fixator placement and fracture osteotomy of the left mandible. Two groups received pre-operative fractionated radiotherapy, and one of these groups was treated with DFO after fracture repair. After 40 days, the animals were perfused and imaged with micro-CT to calculate vascular radiomorphometrics.

RESULTS

In vitro, endothelial tubule formation assays demonstrated that DFO mitigated the deleterious effects of radiation on angiogenesis. Further, high-dose DFO cultures appeared to organize within 2h of incubation and achieved a robust network that was visibly superior to all other experimental groups in an accelerated fashion. In vivo, animals subjected to a human equivalent dose of radiotherapy (HEDR) and left mandibular fracture demonstrated quantifiably diminished μCT metrics of vascular density, as well as a 75% incidence of associated non-unions. The addition of DFO in this setting markedly improved vascularity as demonstrated with 3D angiographic modeling. In addition, we observed an increased incidence of bony unions in the DFO treated group when compared to radiated fractures without treatment (67% vs. 25% respectively).

CONCLUSION

Our data suggest that selectively targeting angiogenesis with localized DFO injections is sufficient to remediate the associated severe vascular diminution resulting from a HEDR. Perhaps the most consequential and clinically relevant finding was the ability to reduce the incidence of non-unions in a model where fracture healing was not routinely observed.

The effects of low dose X-irradiation on osteoblastic MC3T3-E1 cells in vitro

BACKGROUND

It has been indicated that moderate or high dose of X-irradiation could delay fracture union and cause osteoradionecrosis, in part, mediated by its effect on proliferation and differentiation of osteoblasts. However, whether low dose irradiation (LDI) has similar roles on osteoblasts is still unknown. In this study, we investigated whether and to what extent LDI could affect the proliferation, differentiation and mineralization of osteoblasts in vitro.

METHODS

The MC3T3-E1 cells were exposed to single dose of X-irradiation with 0, 0.1, 0.5, 1.0 Gy respectively. Cell proliferation, apoptosis, alkaline phosphatase (ALP) activity, and mineralization was evaluated by methylthiazoletetrazolium (MTT) and bromodeoxyuridine (BrdU) assay, flow cytometry, ALP viability kit and von Kossa staining, respectively. Osteocalcin (OCN) and core-binding factor α1 (Cbfα1) expressions were measured by real time-PCR and western blot, respectively.

RESULTS

The proliferation of the cells exposed to 2.0 Gy was significantly lower than those exposed to ≤1.0 Gy (p < 0.05) from Day 4 to Day 8, measured by MTT assay and BrdU incorporation. For cells exposed to ≤1.0 Gy, increasing dosages of X-irradiation had no significant effect on cell proliferation and apoptosis. Importantly, LDI of 0.5 and 1 Gy increased ALP activities and mineralized nodules of MC3T3-E1 cells. In addition, mRNA and protein expressions of OCN and Cbfα1 were also markedly increased after treatment with LDI at 0.5 and 1 Gy.

CONCLUSIONS

LDI have different effects on proliferation and differentiation of osteoblasts from those of high dose of X-irradiation, which might suggest that LDI could lead to promotion of fracture healing through enhancing the differentiation and mineralization of osteoblasts.

In vitro culture and characterization of alveolar bone osteoblasts isolated from type 2 diabetics

In order to understand the mechanisms of poor osseointegration following dental implants in type 2 diabetics, it is important to study the biological properties of alveolar bone osteoblasts isolated from these patients. We collected alveolar bone chips under aseptic conditions and cultured them in vitro using the tissue explants adherent method. The biological properties of these cells were characterized using the following methods: alkaline phosphatase (ALP) chemical staining for cell viability, Alizarin red staining for osteogenic characteristics, MTT test for cell proliferation, enzyme dynamics for ALP contents, radio-immunoassay for bone gla protein (BGP) concentration, and ELISA for the concentration of type I collagen (COL-I) in the supernatant. Furthermore, we detected the adhesion ability of two types of cells from titanium slices using non-specific immunofluorescence staining and cell count. The two cell forms showed no significant difference in morphology under the same culture conditions. However, the alveolar bone osteoblasts received from type 2 diabetic patients had slower growth, lower cell activity and calcium nodule formation than the normal ones. The concentration of ALP, BGP and COL-I was lower in the supernatant of alveolar bone osteoblasts received from type 2 diabetic patients than in that received from normal subjects (P < 0.05). The alveolar bone osteoblasts obtained from type 2 diabetic patients can be successfully cultured in vitro with the same morphology and biological characteristics as those from normal patients, but with slower growth and lower concentration of specific secretion and lower combining ability with titanium than normal ones.

Quantitative histomorphometric assessment of regenerate cellularity and bone quality in mandibular distraction osteogenesis after radiation therapy

BACKGROUND

The use of mandibular distraction osteogenesis (MDO) for tissue replacement after oncologic resection in head and neck cancer could have immense therapeutic ramifications. We have previously demonstrated significantly decreased mechanical and microdensitomeric metrics of our MDO regenerate after 36-Gy radiation. Quantitative histomorphometry, a third metric, would permit objective investigation of the effects of radiation on tissue and cellular composition. Our hypothesis is that radiation-induced cellular depletion and diminution in function impair optimal bone regeneration.

METHODS

Five rats received radiation to the left mandible; 5 received none. All animals underwent surgical placement of external fixators, creation of mandibular osteotomies, distraction to a 5.1-mm gap width, and consolidation. Point counting and color thresholding were performed.

RESULTS

There was a significant increase in empty lacunae and a corresponding diminution in osteocytes after radiation. Whereas the volume fraction of mineralized, mature bone was not different, that of nonmineralized, immature osteoid was significantly increased in the radiated group compared with that in the nonradiated group.

CONCLUSIONS

Our findings confirm our prior 2 metrics. Actually, all 3 diverse metrics--microdensitometry, biomechanical analysis, and histomorphometry--corroborate our hypothesis of cellular depletion and diminution of function as the potential mechanism of radiation-induced attenuation in the distracted regenerate. Furthermore, our findings of tissue and cellular changes in the irradiated regenerate elucidate the pathophysiology of decreased bone quality when amalgamated with our previous results. Therapeutic agents may now be introduced, and their effects on the irradiated regenerate critically measured, so that MDO may be used as a viable reconstructive option in patients with head and neck cancer.

Early increase in osteoclast number in mice after whole-body irradiation with 2 Gy X rays

Bone loss is a consequence of exposure to high-dose radiotherapy. While damage to bone vasculature and reduced proliferation of bone-forming osteoblasts has been implicated in this process, the effect of radiation on the number and activity of bone-resorbing osteoclasts has not been characterized. In this study, we exposed mice to a whole-body dose of 2 Gy of X rays to quantify the early effects of radiation on osteoclasts and bone structural properties. Female C57BL/6 mice (13 weeks old) were divided into two groups: irradiated and nonirradiated controls. Animals were killed humanely 3 days after radiation exposure. Analysis of serum chemistry revealed a 14% increase in the concentration of tartrate resistant acid phosphatase (TRAP)-5b, a marker of osteoclast activity, in irradiated mice (P < 0.05). Osteoclast number (+44%; P < 0.05) and osteoclast surface (+213%; P < 0.001) were elevated in TRAP-stained histological sections of tibial metaphyses. No significant change was observed in osteoblast surface or osteocalcin concentration or in trabecular microarchitecture (i.e. bone volume fraction) as measured through microcomputed tomography (P > 0.05). This study provides definitive, quantitative evidence of an early, radiation-induced increase in osteoclast activity and number. Osteoclastic bone resorption may represent a contributor to bone atrophy observed after therapeutic irradiation.