Early Alterations of Cytoskeletal Proteins Induced by Radiation Therapy in the Parenchymal Cells of Rat Major Salivary Glands: A Comparative Immunohistochemical Analysis

Objectives: Head and neck malignancies (HNMs) encompass a variety of cancers that affect the oral and para-oral tissues, the most common of which are squamous cell carcinomas. Radiotherapy is commonly used to treat these cancers, often involving radiation exposure to the salivary glands. This study aims to investigate the early impacts of radiotherapy on the internal microstructure of the salivary gland cells and identify which gland exhibits the highest level of radiosensitivity.

Methods: Twelve male albino rats were divided into two groups (control group and experimental group subjected to radiotherapy). The experimental group underwent a daily dose of 5 Grays of radiotherapy for six days with a total dose of 30 Grays, targeting the salivary glands. One month later, the salivary gland complex was dissected and processed for histological analysis and cytokeratin 17 (CK17) immunostaining.

Results: Histological examination of the irradiated salivary glands revealed atrophic changes in the gland parenchyma, accompanied by the proliferation of dense fibrous stroma. The parenchymal components consisted of small serous acini with poorly defined lumens, many of which had been replaced by fatty tissue with the formation of duct-like structures. Immunohistochemical findings of control glands exhibited weak to mild CK17 expression in duct cells, with the staining pattern typically diffuse or localized to the basal region of the cell. Some serous acini and serous demilunes within mixed acini exhibited diffuse, weak to mild CK17 expression, whereas the mucous acinar cells showed no expression. Radiated major glands revealed moderate to strong CK17 expression in the duct and serous acinar cells (p<0.05). Two distinct expression patterns were identified: the first exhibited diffuse expression across the cells, while the second showed intense expression at the apical region with mild expression at the basal part.

Conclusions: The positive immunostaining in control salivary glands suggests that small amounts of intermediate filaments are essential for saliva secretion. Radiotherapy significantly disrupts the cytokeratin arrangement and density in major salivary glands, impairing saliva production. The most prominent changes occurred in the submandibular gland, followed by the parotid gland, with the sublingual gland showing the least impact. However, CK17 intensity in acinar cells was highest in the parotid, then submandibular, and lowest in the sublingual gland. Further research is needed to assess the short- and long-term effects and potential for recovery over time.