The therapeutic effect and mechanism of carnosic acid in Aspergillus fumigatus keratitis.

Fungal keratitis is a vision-threatening corneal infectious disease. However, clinically therapeutic medicines cannot attain ideal efficacy due to limited control of fungal virulence and excessive inflammatory response. Carnosic acid (CA) is a phenolic diterpene, which has been reported to have multiple abilities including antibacterial, anti-inflammatory and antioxidant. The therapeutic efficacy and potential mechanism of CA in fungal keratitis remain unknown. This study aimed to confirm the therapeutic role and potential mechanism of CA in Aspergillus fumigatus (A. fumigatus)-caused keratitis. In this study, we demonstrated that CA markedly suppressed the growth of A. fumigatus hyphae, the generation of biofilms and the integrity of the hyphal membrane. A. fumigatus-related genes (RodA, RodB, FKs, Rho1, CshA-C and Cyp51A-B) levels were suppressed under CA treatment. CA at 5 μg/mL and 10 μg/mL obviously promoted cell proliferation. In A. fumigatus-infected mice cornea, CA relieved the severity of corneal impairment, inhibited neutrophil recruitment and fungal load. Compared with inactivated hyphae, CA down-regulated the mRNA and protein levels of inflammatory cytokines, Dectin-1, NLRP3, cleaved caspase-1, IL-18 and IL-1β. Moreover, Curdlan (a specific agonist of Dectin-1) stimulation could promote the expression of NLRP3, cleaved caspase-1, IL-18 and IL-1β, which could be down-regulated by CA treatment. In conclusion, CA displays antifungal function on A. fumigatus. CA ameliorates the prognosis of keratomycosis by suppressing inflammatory cytokines production, which is regulated by Dectin-1 and pyroptosis.