Sodium Butyrate Alleviates Fungal Keratitis by Exerting Antifungal Activity and Dampening Inflammation Through the Nrf2/HO-1 Axis

Purpose: The purpose of this study was to determine whether sodium butyrate (NaB) alleviates fungal keratitis (FK) through combined antifungal and Nrf2/HO-1-associated anti-inflammatory effects. Methods: NaB safety was assessed by Cell Counting Kit-8 assays, scratch-wound assays, and fluorescein sodium staining. Antifungal activity against Aspergillus fumigatus (A. fumigatus) was evaluated by minimum inhibitory concentration assays, crystal violet staining, propidium iodide uptake, calcofluor white staining, conidial adhesion assays, and scanning and transmission electron microscopy. HSP90 and RpdA mRNA levels in A. fumigatus were measured by qRT-PCR. In a mouse FK model, therapeutic efficacy was examined by clinical corneal scoring, hematoxylin and eosin (H&E) staining, and fungal plate counts. The qRT-PCR, ELISA, and Western blotting were used to analyze inflammatory responses. Results: NaB showed no overt toxicity in RAW 264.7 cells, human corneal epithelial cells, or mouse ocular surface epithelium at concentrations up to 4 mM. In vitro, NaB inhibited A. fumigatus conidial germination and biofilm formation, disrupted the fungal cell wall and membrane, reduced conidial adhesion to epithelial cells, and downregulated HSP90 and RpdA. Electron microscopy confirmed hyphal ultrastructural damage. In vivo, NaB decreased corneal fungal burden, improved clinical manifestations, and reduced inflammatory cell infiltration. Mechanistically, NaB activated the Nrf2/HO-1 pathway and decreased IL-6, IL-1β, and TNF-α expression. Conclusions: NaB exerts antifungal and anti-inflammatory effects in A. fumigatus keratitis, supporting its therapeutic potential for FK.