Carbonized nanogels for simultaneous antibacterial and antioxidant treatment of bacterial keratitis

[Display omitted] •Bifunctional carbon nanogels (CNGs) are prepared from biogenic quercetin and lysine.•CNGs exhibit antioxidant effect of quercetin and antimicrobial activity of lysine.•Bacterial keratitis is a corneal infection that leads to severe visual disability.•CNGs can temporarily open the tight junctions of corneal epithelial cells.•Topical CNGs-based eye drop effectively alleviates S. aureus-induced keratitis. To prevent visual loss, clinical therapy of severe bacterial keratitis (BK) demands simultaneous remedying of the damage caused by bacterial infection and its induced oxidative stress/inflammation of the cornea. Here, we have developed a one-step method to synthesize carbonized nanogels (CNGs) from biogenic quercetin (Qu) and lysine (Lys) as a bifunctional agent with antibacterial and antioxidant properties for topical BK therapy. These Qu/Lys-CNGs synthesized by dry heating inherit and amplify the advantages of two natural products, including excellent antioxidant capacity and high positive charge. The Qu/Lys-CNGs display broad-spectrum bacteriostatic effects against non-multidrug-resistant bacteria, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella enteritidis, and also against multidrug-resistant bacteria, methicillin-resistant Staphylococcus aureus. Disintegration of peripheral structures of the bacteria caused by Qu/Lys-CNGs is due to their strong and specific interaction with bacterial membranes. In vitro cytotoxicity and hemolysis assays and in vivo corneal biocompatibility evaluations revealed good biocompatibility of Qu/Lys-CNGs as a safe nanomedicine in ophthalmic drop formulation. Furthermore, the Qu/Lys-CNGs can penetrate into the cornea via epithelial tight junction opening, thereby exerting superior antibacterial and antioxidant therapeutic effects against S. aureus-induced keratitis in rabbits. Our results indicate Qu/Lys-CNGs could be an effective bifunctional agent for clinical applications to treat bacterial ocular diseases.