Single Dose of X-ray Irradiation as a Model for Non-Tumorigenic Tissue: Effects on Morphology and MMP-2 Expression in Rat Incisor Periodontal Ligament

Background During radiation treatment for eliminating cancer cells, numerous progressive alterations occur in healthy oral tissues, including the salivary glands and periodontal tissues, although the onset of these changes is not well established. Therefore, the aim of this study was use the model of a single dose of X-ray irradiation applied to the heads of rats to evaluate the expression of MMP-2 and the morphology of the components of the periodontal ligament in the rat incisor. Methods Groups of five rats were divided into four experimental groups, each exposed to a single dose of 15 Gy of X-ray radiation to the head and neck on day zero. They were subsequently euthanized on days 4, 9, 14, or 25 post-irradiation. A control group that was not irradiated was euthanized on day 4. The lower left hemimandibles were extracted and immersed in 4% paraformaldehyde for 48 hours. Following demineralization in EDTA solution, the hemimandibles were sectioned into transverse fragments at the level of the third molar, dehydrated in an alcohol solution, cleared in xylene, and embedded in paraplast. Semi-serial cross-sections of 5 µm were prepared on slides for H&E, Masson’s trichrome, and Picro Sirius red staining, as well as for MMP-2 immunohistochemistry. All analyses were conducted on the lingual side of the periodontal ligament to evaluate its morphology, collagen maturation index, and MMP-2 expression. Results The results showed that X-ray radiation caused changes in the morphology of the lingual side of the periodontal ligament, observed through H&E and Masson's staining. The changes included the morphology of the fibroblast nucleolus and of the collagen fibers. Additionally, a reduction in the maturation index of collagen fibers was noted, measured by Picro Sirius staining (PSR). Furthermore, X-ray irradiation increased MMP-2 expression of MMP-2, suggesting a potential role in the degradation of collagen present in periodontal ligament. Conclusions We concluded that our model using a single dose of X-ray irradiation applied to the rat skull initially alters the structure of the rat incisor periodontal ligament, as evidenced by the loss of normal fibroblast and collagen fiber morphology, along with changes in the collagen maturation index suggesting a role for MMP-2 expression, which was increased by the irradiation.