Self-Assembled Fmoc-Arg-Phe-Phe Peptide Gels with Highly Potent Bactericidal Activities

The emergence of antibiotic resistance and the increasing rate of bacterial infections have motivated scientists to explore novel antibacterial materials and strategies to circumvent this challenge. Gels fabricated from ultrashort self-assembled peptides have turned out to be the most promising bactericidal materials. Self-assembled Fmoc-Phe-Phe gels have been extensively investigated earlier, and it has been shown that these gels possess potent bactericidal properties but suffer from disadvantages, such as poor proteolytic stabilities. In the present work, we report the highly potent bactericidal activities and proteolytic stability of gels fabricated from Fmoc-l-Arg-d-Phe-d-Phe-CONH₂ (RFF) peptide, which are best in class. We fabricated and characterized self-assembled gels (1-2% w/v) from Fmoc-d-Phe-d-Phe-CONH₂ (FF), Fmoc-l-His-d-Phe-d-Phe-CONH₂ (HFF), and Fmoc-l-Arg-d-Phe-d-Phe-CONH₂ (RFF) in aq dimethyl sulfoxide (35% v/v). The gels were characterized for their surface morphology, viscoelastic, self-healing, and stability characteristics. On incubation with proteolytic enzymes, FF gels did not show statistically significant degradation, and HFF and RFF gels showed only 43 and 32% degradation within 72 h at 37 °C, which is much better than gels reported earlier. The RFF gels (2%) exhibited more than 90% inhibition against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) within 6 h, and the activities were sustained for up to 72 h. The high-resolution transmission electron microscopy studies indicated electrostatic interactions between the gel and bacterial membrane components, leading to cell lysis and death, which was further confirmed by the bacterial cell Live/Dead assay. MTT assay showed that the gels were not toxic to mammalian cells (L929). The bactericidal characteristics of RFF gels have not been reported so far. The RFF gels show strong potential for treating device-related infections caused by antimicrobial-resistant bacteria.