Eugenol protects against Aspergillus fumigatus keratitis by inhibiting inflammatory response and reducing fungal load

Fungal keratitis is a corneal infection, which severely impairs vision. The fungal pathogen provokes host immune response, but the excessive inflammatory response causes significant collateral damage to the cornea. Eugenol, the main component of clove oil, has been found to have a broad range of pharmacological activities including anti-microbial, antioxidation and anti-inflammation. However, the role of eugenol in Aspergillus fumigatus (A. fumigatus) keratitis is unknown. In this study, we demonstrated that eugenol reduced mice keratitis severity, inflammatory cells infiltration, pro-inflammatory cytokine expression, and the fungal load. Eugenol also decreased the expressions of pro-inflammatory cytokines in human corneal epithelial cells (HCECs). We confirmed that the anti-inflammatory effects of eugenol were related to activating nuclear factor erythroid 2-related factor 2/Heme Oxygenase-1 (Nrf2/HO-1) signaling pathway. Moreover, we demonstrated that eugenol could inhibit the A. fumigatus growth and adhesion to host cells, as well as damage the fungal biofilm. The antifungal mechanism seemed to be disrupting the integrity of the fungal membrane and reducing the biosynthesis of ergosterol. Taken together, our research suggested that eugenol exerted protective effects on mouse A. fumigatus keratitis, due to its anti-inflammatory and antifungal activity.