Defining Pathways of Tissue Damage in Chemotherapy-Induced Oral Mucositis

Objectives: Mucositis is a frequent complication of chemotherapy. The hallmarks of oral mucositis are believed to be cell death and inflammation. However, there is a paucity of in vivo data demonstrating which specific cellular processes and pathways are involved in lesion development. This study aimed to evaluate gene expression and histopathological features of oral mucositis utilizing a mouse model.
Methods: The chemotherapeutic 5-fluorouracil (5-FU) was administered intraperitoneally to C57BL/6 mice ages 8-12 weeks. 100mg/kg 5-FU was administered on day 0 and 1 and 50 mg/kg 5-FU was administered on days 2-6. Mice were sacrificed on days 1, 2, 4, 6, 8, and 10. Gene expression was evaluated via RNASeq of tongue tissues followed by DESeq2 analysis. Lesions were evaluated after toluidine blue staining. Histological features were evaluated after hematoxylin and eosin staining, TUNEL assay, and immunohistochemistry for Ki67, cleaved Caspase-3, and CD45.
Results: Tongues of mice treated with 5-FU showed macroscopic lesions and microscopic evidence of atrophy, keratin desquamation, epithelial clefts and decreased basal layer cell density. Transcriptomic changes were characterized by a rapid and sustained upregulation of p53 signaling, response to DNA damage, apoptotic process and cell death. Day 2 showed upregulation of cell cycle arrest while at later stages there was upregulation of GO terms related to positive regulation of the cell cycle. Late gene expression responses also included downregulation of cell adhesion mediators and upregulation of genes involved in necroptosis. Immunohistochemistry showed a dramatic decrease in Ki67-positive cells, but no evidence of apoptosis or of an inflammatory infiltrate.
Conclusions: Decreased cell proliferation is the dominant feature of the in vivo response to 5-FU. The data suggest that p53 controls this response but rather than leading to apoptosis, cell cycle arrest seems to be the main effect of p53 activation. Other cell death pathways such as necroptosis could also be implicated at later stages in the response.