Topical nano-chitosan mitigates alendronate-induced lingual mucosal injury in rats: histological, immunohistochemical, molecular, and ultrastructural study

BACKGROUND: Bisphosphonates (BPs) are widely used antiresorptive agents for skeletal disorders; however, their adverse effects on oral soft tissues, particularly the lingual mucosa and gustatory apparatus, remain incompletely understood. Nano-chitosan has emerged as a promising biomaterial with cytoprotective and regenerative properties in orofacial tissues, indicating potential utility in mitigating BP-associated mucosal injury. OBJECTIVES: To evaluate the protective effects of topical nano-chitosan on alendronate-induced lingual injury in a rat model. METHODS: Thirty adult male Wistar rats were randomized into three groups (n = 10 each): control (Group I), alendronate-treated (1 mg/kg, subcutaneously, three times weekly for 4 weeks), and alendronate plus daily topical nano-chitosan (0.5 mL/day). Lingual tissues were examined using histology (H&E and Masson's trichrome), immunohistochemistry (PCNA), histomorphometry, scanning electron microscopy, and RT-qPCR for α-gustducin (GNAT3). RESULTS: Alendronate induced significant lingual alterations, including reduced papillary height (48%), decreased epithelial proliferation (80% PCNA expression), increased disorganized collagen deposition (approximately 2.5-fold), ultrastructural disruption, and downregulation of GNAT3 (all p < 0.001 vs. control). Nano-chitosan treatment attenuated these changes, restoring papillary morphometry, PCNA expression (27.66% vs. 29.60%, p = 0.127), and collagen content (9.45% vs. 8.49%, p = 0.538) to levels comparable with controls. GNAT3 expression was partially restored but remained significantly reduced compared with controls. CONCLUSION: Topical nano-chitosan mitigates alendronate-induced lingual injury in rats by improving epithelial architecture and proliferation and partially restoring GNAT3 transcript levels. No functional gustatory assessment was performed; therefore, conclusions regarding taste function recovery are not drawn from the present data. These findings indicate a modulatory rather than fully restorative effect on BP-associated oral mucosal alterations and support further preclinical and translational investigation.