Antibiotic resistance is a major global health threat, necessitating the development of new treatments and diverse molecules to combat severe infections and preserve the efficacy of existing drugs. Antimicrobial peptides (AMPs) offer a versatile arsenal against bacteria, and peptide structure branching can enhance their resistance to proteases and improve their overall efficacy. A small library of peptides derived from natural host defense peptides and synthesized in a tetrabranched form was selected against E. coli. Six selected branched peptides were further studied for antibacterial activity against a panel of strains, biofilm inhibition, protease resistance, and cytotoxicity. Their structure was predicted computationally and their mechanism of action was investigated by electron microscopy and by using fluorescent dyes. The peptide BAMP2 showed promise in a mouse skin infection model, indicating the potential for local infection treatment.

Endodontic and periodontal disease are conditions of infectious origin that can lead to tooth loss or develop into systemic hyperinflammation, which may be associated with a wide variety of diseases, including cardiovascular. Endodontic and periodontal treatment often relies on antibiotics. Since new antimicrobial resistances are a major threat, the use of standard antibiotics is not recommended when the infection is only local. Antimicrobial peptides were recently demonstrated to be valid alternatives for dental treatments. The antimicrobial peptide M33D is a tetrabranched peptide active against Gram-negative and Gram-positive bacteria. It has a long life, unusual for peptides, because its branched form provides resistance to proteases. Here the efficacy of M33D and of its analog M33i/l as antibiotics for local use in dentistry was evaluated. M33D and M33i/l were active against reference strains and multidrug-resistant clinical isolates of Gram-negative and Gram-positive species. Their minimum inhibitory concentration against different strains of dental interest was between 0.4 and 6.0 μM. Both peptides acted rapidly on bacteria, impairing membrane function. They also disrupted biofilm effectively. Disinfection of the root canal is crucial for endodontic treatments. M33D and M33i/l reduced E. faecalis colonies to one-twentieth in a dentin slices model reproducing root canal irrigation. They both captured and neutralized lipopolysaccharide (LPS), a bacterial toxin responsible for inflammation. The release of IL-1β and TNFα by LPS-stimulated murine macrophages was reduced by both peptides. Human cardiac fibroblasts respond to different insults with the release of proinflammatory cytokines, and consequently, they are considered directly involved in atherogenic cardiovascular processes, including those triggered by infections. The presence of M33D and M33i/l at MIC concentration reduced IL6 release from LPS- stimulated human cardiac fibroblasts, hence proving to be promising in preventing bacteria-induced atherogenesis. The two peptides showed low toxicity to mammalian cells, with an EC50 one order of magnitude higher than the average MIC and low hemolytic activity. The development of antimicrobial peptides for dental irrigations and medication is a very promising new field of research that will provide tools to fight dental infections and their severe consequences, while at the same time protecting standard antibiotics from new outbreaks of antimicrobial resistance.

Staphylococcus species are often the cause of implant-related infections, posing a significant clinical challenge in orthopedics. Antimicrobial peptides (AMPs) like LL-37-derived FK-16 and GF-17 offer promising alternatives to conventional antibiotics; however, they require suitable delivery systems to overcome rapid degradation. The aim of this study was to develop and evaluate silk fibroin (SF) and osteoinductive peptide-enriched silk fibroin (PSF) sponges that can be used locally for FK-16 and GF-17 delivery. Two concentrations of FK-16 or GF-17 were loaded into SF and PSF sponges. Swelling behavior and AMP release profiles were analyzed for 72 h. Time-kill assays were conducted on MRSE and MRSA clinical strains to assess antimicrobial activity. FK-16 released quickly (>90% within 24 h) and then maintained a stable plateau from both SF and PSF matrices, which was associated with bactericidal activity against MRSE strains. In contrast, the release efficiency of GF-17 was lower and did not achieve significant antimicrobial effects. Neither peptide exhibited effective activity against MRSA under the tested conditions. PSF sponges showed higher swelling and enhanced FK-16-mediated antibacterial performance compared to SF counterparts. FK-16-loaded PSF sponges are a promising biomaterial for treating local orthopedic infections related to MRSE. The findings underscore the significance of peptide–matrix interactions in determining therapeutic outcomes and suggest the need for more in vivo evaluation of AMP-functionalized PSF scaffolds.

Background: Orthopedic implant-associated infections are difficult to eradicate because of biofilm formation and impaired healing. FK-16 and GF-17 are short synthetic antimicrobial fragments of the human cathelicidin LL-37; FK-16 consists of 16 amino acids and differs from the 17-amino-acid GF-17 by the absence of its N-terminal glycine. This study aimed to assess their acute tolerability following single-dose intravenous administration in mice and to evaluate the local antibacterial efficacy of FK-16 delivered via peptide-enriched silk fibroin (PSF) scaffolds in a rat model of methicillin-resistant Staphylococcus epidermidis (MRSE)-associated femoral nonunion. Methods: Thirty-six BALB/c mice (18 males and 18 females) received vehicle, FK-16, or GF-17 (0.1 or 1 mg/kg for each peptide) and underwent clinical and functional assessments, hemolysis testing, biochemical analyses, organ-weight measurements, and histopathological examination. Thirty-two male Wistar rats were assigned to a noninfected control group or infected groups treated with unloaded PSF, vancomycin-loaded PSF, or FK-16-loaded PSF. On day 56, antibacterial activity and bone healing were evaluated using microbiological culture, micro-computed tomography, and histopathology. Results: No mortality, persistent neurobehavioral abnormalities, or treatment-related organ lesions occurred in mice. Transient hind-limb paralysis occurred in one mouse treated with FK-16 and one treated with GF-17 at 1 mg/kg. Biochemical and hemolysis-related changes were isolated and did not follow a consistent dose–response pattern; no corresponding treatment-related organ lesions were observed. In rats, viable MRSE was recovered from 3/4 untreated specimens and none from those treated with vancomycin or FK-16. FK-16 was associated with partial normalization of the circulating ratio of osteoprotegerin to receptor activator of nuclear factor-κB ligand without significantly reducing early systemic inflammation. Bone mineral density, tissue mineral density, and bone volume fraction increased numerically, but no quantitative micro-computed tomography healing parameter improved significantly; the radiographic osteomyelitis score decreased significantly. Untreated PSF showed absent bridging, abundant fibrovascular tissue, chronic inflammation, rare Gram-positive cocci, and higher histological scores than noninfected controls; both treated groups showed minimal inflammation but incomplete bridging. Conclusions: FK-16 and GF-17 showed generally acceptable acute tolerability despite transient high-dose neurological effects. Locally delivered FK-16 demonstrated antibacterial activity, reduced osteomyelitis severity, and was associated with minimal histological evidence of inflammation, but did not significantly improve quantitative bone healing or restore complete bridging by day 56.