Background: External irradiation (IRR) of advanced head and neck tumors often includes tissues of the larynx and trachea unaffected by cancer. In these normal tissues, both single-cell damage (necrosis, apoptosis, functional cell death) and interstitial damage (edema, fibrosis, vascular alterations, cellular infiltrations) resulting in tissue remodeling can occur, depending on various IRR parameters. However, reports on radiogenic intermediate filament protein alterations in laryngeal-tracheal tissues are very rare. In this study, we investigated the phenotypic characterization of the normal integrity-supporting cytokeratins (CK) and vimentin following a clinically relevant IRR protocol in laryngeal-tracheal tissues.
Materials and methods: In 61 laryngo-tracheal specimens from Wistar rats the expression profile and distribution pattern of CK (CK13, CK17/19, CK18) and vimentin were investigated according to IRR dose (fractionated IRR, 2 Gy per day, total dose of 20, 40 or 60 Gy), time from IRR (6 months vs. 12 months) and animal age (1 year vs. 1.5 years) using immunohistochemical methods, semiquantitative assessment and multivariate analysis.
Results: In irradiated specimens, expression of both CK and vimentin showed slight to moderate dose-dependent alterations. The expression differed in frequency and level among the various tissue structures and showed remarkable heterogeneity, with increases, decreases and fluctuations in staining. In the glottic mucosal layer (non-keratinizing squamous epithelium), CK13 expression decreased with increasing dose. The CK17/19 expression of supra- and subglottic respiratory epithelia following 20 and 60 Gy exposure was significantly lower than in controls. The respiratory epithelia and, in part, the cuboidal epithelia of the indifferent type at the inner side of the aryepiglottic fold revealed increasing CK17/19 immunoreactions up to 40 Gy IRR, but a distinct decrease in expression at 60 Gy. In subglottic gland structures, CK18 was detected at significantly higher levels than in controls. There was increasing expression with increasing dose. CK18 reactions of supra- and subglottic respiratory mucosal layer, supraglottic gland structures and thyrocytes tended towards increasing expression with increasing dose and in older animals. Tracheal mucosal epithelia, tracheal glands, and respiratory epithelia of the inner side of the aryepiglottic fold tended towards decreasing expression of CK18 with increasing dose and in older animals. In part, these tissues showed dose-dependent fluctuations. Furthermore, the vimentin reactions showed dose-dependent, heterogeneous patterns, with increases, decreases, and fluctuations in staining. Moreover, there were differences in frequency and intensity of expression among the various tissue structures. Age and time from IRR had no significant effect on immunoreaction.
Conclusion: The staining of CK and vimentin predominantly showed a notable dose-dependent heterogeneity, with increases, decreases and fluctuations in expression. The expression pattern persisted for up to 1 year after the completion of irradiation. Thus, these findings must reflect late radiation effects. The altered expression of CK and vimentin may play at least a partial role in structural (e.g. edema) and functional (e.g. voice disorders) changes associated with irradiation of the head and neck.