J Korean Assoc Oral Maxillofac Surg.  2020 Aug;46(4):240-249. 10.5125/jkaoms.2020.46.4.240.

Development of a standardized mucositis and osteoradionecrosis animal model using external radiation

• Seo MH
• Lee MY
• Eo MY
• Lee SK
• Woo KM
• Kim SM

• KMID: 2505440
• DOI: http://doi.org/10.5125/jkaoms.2020.46.4.240

Abstract

Objectives
Although the side effects of radiation therapy vary from mucositis to osteomyelitis depending on the dose of radiation therapy, to date, an experimental animal model has not yet been proposed. The aim of this study was to develop an animal model for assessing complications of irradiated bone, especially to quantify the dose of radiation needed to develop a rat model.
Materials and Methods
Sixteen Sprague-Dawley rats aged seven weeks with a mean weight of 267.59 g were used. Atraumatic extraction of a right mandibular first molar was performed. At one week after the extraction, the rats were randomized into four groups and received a single dose of external radiation administered to the right lower jaw at a level of 14, 16, 18, or 20 Gy, respectively. Clinical alopecia with body weight changes were compared and bony volumetric analysis with micro-computed tomography (CT), histologic analysis with H&E were performed.
Results
The progression of the skin alopecia was different depending on the irradiation dose. Micro-CT parameters including bone volume, bone volume/tissue volume, bone mineral density, and trabecular spaces, showed no significant differences. The progression of osteoradionecrosis (ORN) along with that of inflammation, fibrosis, and bone resorption, was found with increased osteoclast or fibrosis in the radiated group. As the radiation dose increases, osteoclast numbers begin to decrease and osteoclast tends to increase. Osteoclasts respond more sensitively to the radiation dose, and osteoblasts are degraded at doses above 18 Gy.
Conclusion
A standardized animal model clinically comparable to ORN of the jaw is a valuable tool that can be used to examine the pathophysiology of the disease and trial any potential treatment modalities. We present a methodology for the use of an experimental rat model that incorporates a guideline regarding radiation dose.

Keyword

Osteoradionecrosis of jaw; External radiation therapy; Experimental animal model; Mucositis; Osteoclast

Figure

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  Fig. 1 A. Animal receiving irradiation. B. Experimental radiological setting used in this study, 260 kV, 10 mA, 2 mL Al filter. C. Specimens for evaluation after harvesting of the lower jaw including soft tissue.

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  Fig. 2 Progression of hair loss in the clinical photo. A. Control group. B. Two weeks after irradiation. C. Two weeks after irradiation (contralateral side).

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  Fig. 3 Differences in bone volume/tissue volume (BV/TV) (A), bone mineral densities (BMD) (B), and trabecular spaces (Tb.Sp.) (C) between radiation doses and observation period.

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  Fig. 4 Histological findings of H&E staining of the jaw bone irradiated with 16 Gy showing resorption line (A1; arrows), microabscess (A2; arrows, A3), and dead bone (C1, C2, E1, E2; arrows), with empty osteocyte lacunae (B, D, E1; arrowheads) in the defect site. A1 arrows: resorption line; A2 arrow, A3: abscess border line and abscess area; B arrowheads: empty osteocyte lacunae; C1, C2 arrows: dead bone borderline; D, E1 arrowheads: empty osteocyte lacunae; E1, E2 arrows: dead bone borderline. (A1: ×100; A2: ×200; A3, B: ×400; C1, C2: ×200 and polarized view in C2; D, E1, E2: ×1,000 and polarized view in E2)

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  Fig. 5 Histological findings of H&E staining of the jaw bone irradiated with 18 Gy showing more dead bone than that seen with 16 Gy dose and the presence of resorption with osteoclast cells. Abscesses (A1, A2; arrows, A3), inflammatory infiltrate (B1; arrows), and empty osteocyte lacunae (B2, B3; arrowheads) were observed. The close-up of the box in C1 is C2. There are numerous osteoclast cells observed in the radionecrotic lesion borderlines. A1, A2 arrows, A3: abscess and abscess borderline; B1 arrows: inflammatory cell; B2, B3 arrowheads: empty osteocyte lacunae; C1, C2 arrows: osteoclast cells; C3 arrows: internal osteoclast cells. (A1: ×100; A2: ×400, A3: ×1,000, B1: ×200, B2, B3: ×400; C1: ×200; C2, C3: ×1,000)

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  Fig. 6 Histological findings of H&E staining of the jaw bone irradiated with 20 Gy. The histological features with 20 Gy irradiation showed the presence of resorption line (A1, A2) with osteoclast cells (C1, C2, C3; arrows), inflammatory infiltrate (A3) and empty osteocyte lacunae (B1, B2, B3; arrowheads). A1, A2: resorption line; A3 arrows: inflammatory cell; B1, B2, B3 arrowheads: empty osteocyte lacunae; C1, C2, C3 arrows: osteoclast cells; C3 arrowheads: dead bone border line. (A1: ×100; A2: ×200, A3, B1, B2, B3, C1: ×400; C2, C3: ×1,000)

Reference

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