Quercetin ameliorates Aspergillus fumigatus keratitis by inhibiting fungal growth, toll-like receptors and inflammatory cytokines

Purpose: To investigate the antifungal and anti-inflammatory effects of quercetin on Aspergillus fumigatus (A. fumigatus) keratitis. Methods: Human corneal epithelial cells (HCECs) and C57BL/6 mice were stimulated by A. fumigatus and treated with quercetin or dimethyl sulfoxide (DMSO) after infection. In HCECs, minimum inhibitory concentration (MIC) and cytotoxicity tests (CCK-8) were used to detect the antifungal effect and cytotoxicity of quercetin. In mice with A. fumigatus keratitis, clinical score, plate counting and hematoxylin-eosin (HE) staining were performed to evaluate the effects of quercetin in vivo. Myeloperoxidase (MPO) assay and immunofluorescence staining were applied to assess neutrophil recruitment and infiltration. Real time PCR (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and western blot were used to detect the mRNA and protein expressions of inflammatory mediators. Results: Compared with DMSO control, quercetin (16-64 mu M) significantly inhibited the growth of A. fumigatus in a concentration-dependent manner without affecting cell viability in HCECs. In corneas of mice with A. fumigatus keratitis, quercetin decreased clinical score and fungal load, and reduced neutrophil recruitment and infiltration to the corneal stroma. Moreover, quercetin attenuated the expression of inflammatory mediators including toll-like receptor-4 (TLR-4), TLR-2, interleukin-113 (IL-113), tumor necrosis factor-alpha (TNF-alpha) and high mobility group box 1 (HMGB1) in vitro and in vivo. Conclusions: Our study demonstrated that quercetin treatment can ameliorate A. fumigatus keratitis by inhibiting the growth of A. fumigatus, decreasing neutrophil recruitment and infiltration, and downregulating the productions of TLR-4, TLR-2, TNF-alpha, IL-113 and HMGB1, indicating quercetin is likely to become a potential therapeutic agent in FK treatment.