Rhein-induced free fatty acid generation cooperates with silver ions for biofilm-infected diabetic wound healing

Diabetic foot infection (DFI) significantly increases the risks of hospitalization and amputation, with biofilm infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and carbapenem-resistant Escherichia coli (CREC) being key drivers of treatment failure. Here, we analyzed MRSA/CREC biofilm-infected ulcer tissues from patients using proteomics and metabolomics. Compared with nonhealing tissues, healed tissues exhibit activation of low-density lipoprotein receptor (LDLR)-mediated low-density lipoprotein cholesterol (LDL-C) endocytosis and increased free fatty acid production; thus, we hypothesize a potential countermeasure against biofilms. However, the oxidative instability of free fatty acids limits their therapeutic use. Building on our findings demonstrating the potent anti-MRSA/CREC activity of rhein and its synergy with Ag⁺, we developed an injectable hydrogel for sustained codelivery of both agents. This formulation outperforms Ag⁺ monotherapy, accelerating wound closure in biofilm-infected diabetic wounds. Mechanistically, rhein binds to LDLR, upregulates its expression, and enhances the LDL-C endocytosis pathway in vascular endothelial cells to generate more free fatty acids. Among these, eicosapentaenoic acid (EPA) is identified as the most critical free fatty acid that promotes healing, as it inhibits biofilm formation and synergizes with Ag⁺ to exert antibacterial and pro-healing effects. In summary, this study identifies endogenous host lipid metabolites as "metabolic antibiotics" and establishes a synergistic therapeutic strategy that concurrently suppresses biofilm formation, inhibits planktonic bacteria, alleviates inflammation, and promotes tissue repair in drug-resistant biofilm-infected diabetic wounds.