In a rabbit study, a short version of the natural protein LL‑37 could wipe out Pseudomonas biofilms in the sinuses, but the doses that worked also irritated the tissue and damaged the tiny hair‑like cilia that keep the nose clean. Lower doses didn’t clear the infection well, and a standard antibiotic (tobramycin) worked similarly without the tissue damage.

LL-37, an innate immunity protein expressed within sinonasal mucosa, has in vitro antibacterial and antifungal properties as well as efficacy against preformed Pseudomonas aeruginosa biofilms. We hypothesize that a 24 amino acid peptide derivative of LL-37 will show efficacy against biofilm-forming P. aeruginosa in an established animal model of sinusitis. Five groups of six New Zealand rabbits were each infected with P. aeruginosa (PAO-1) and fitted with irrigating catheters 7 days later. Each group was instilled with either one of three different concentrations of peptide, a positive control of topical tobramycin, or the carrier solution without the peptide once a day for 10 days. Nasal diluent was collected throughout the irrigation period to assess for persistence or resolution of infection by determining colony-forming units (CFU). At study end, sinus mucosa was harvested for histological assessment of inflammation and SEM evaluation for ciliary integrity and presence of biofilms. Topical tobramycin at 400x minimum inhibitory concentration and 2.5 mg/mL of peptide were effective in significantly lowering CFUs after 10 days of irrigation. Histological evaluation showed increased signs of inflammation in a dose-dependent manner within mucosa and bone of the groups receiving the peptide. SEM analysis showed ciliary loss in a dose-dependent manner. Biofilms were present in all groups except for the highest concentration of peptide and tobramycin. High concentrations of LL-37-derived peptide showed in vivo ability to eradicate Pseudomonas biofilms and decrease bacterial counts. However, increasing concentrations of peptide showed proinflammatory and ciliotoxic effects on sinus mucosa.