Ferrous sulfate-loaded hydrogel cures Staphylococcus aureus infection via facilitating a ferroptosis-like bacterial cell death in a mouse keratitis model

Hydrogels loaded with ampicillin, vancomycin or other antibiotics are one of the most widely used therapeutic agents for keratitis caused by Staphylococcus aureus. However, emergence of methicillin-resistant S. aureus (MRSA) makes infections harder to be treated by antibiotic-based hydrogels, urging the development of novel antibacterial materials. Inspired by mammalian ferroptosis, we determined the bactericidal effects of ferrous sulfate (FeSO4) on S. aureus, and evaluated the therapeutic potential of FeSO4-loaded hydrogel in a mouse keratitis model. The results showed that FeSO4 facilitated ferroptosis-like cell death in S. aureus with the key characteristics of reactive oxygen species (ROS) generation and lipid peroxidation. Notably, FeSO4 also efficiently killed persisters and MRSA, and eliminated biofilms of S. aureus. RNA profiles demonstrated that ferroptosis-related genes were significantly up-regulated, and the genes responsible for cell wall and cell membrane biosynthesis were down-regulated after exposure to Fe2+, supporting the occurrence of ferroptosis and cell lysis. We further prepared a FeSO4-loaded hydrogel by using hyaluronic acid (HA) and ascorbate. The FeSO4 hydrogel has the characteristics of injectability, self-healing, uniform distribution of Fe2+ in the three-dimensional gel structure, appropriate fluidity, high-water retention, high efficacy to kill MRSA, and excellent biocompatibility. In a mouse keratitis model, we showed that treatment of animals with FeSO4 hydrogel led to a rapid recovery of from keratitis, prevented the dissimilation of MRSA to the lung, and alleviated systemic inflammation, demonstrating the therapeutic potential of FeSO4 hydrogel. Taken together, our results indicated that FeSO4 hydrogel is a promising alternative to current antibiotics-dependent therapeutic materials for the treatment of infections by MRSA.