DOPC Liposomal Formulation of Antimicrobial Peptide LL17-32 with Reduced Cytotoxicity: A Promising Carrier Against Porphyromonas gingivalis

Background/Objectives: The rapid emergence of antibiotic-resistant oral pathogens has rendered many conventional therapies increasingly ineffective. Antimicrobial peptides (AMPs) have emerged as a promising therapeutic alternative due to their unique mechanisms of action and low propensity for inducing resistance. The delivery of novel therapeutic AMPs against oral cavity bacterial infections requires effective pharmaceutical dosage formulations. This study investigated the potential of two liposomal formulations for the association and delivery of the antimicrobial peptide (AMP) LL17-32 against the dental bacterial pathogen Porphyromonas gingivalis. Methods: Liposomes composed of either negatively charged soya lecithin (SL) or neutrally charged dioleoyl-phosphatidylcholine (DOPC) phospholipids were formulated and characterized based on their hydrodynamic size distribution, ζ-potential, morphology, membrane fluidity, peptide association efficiency, stability and release of peptide in vitro under physiological conditions. The characterization of their biological activity included efficiency of bacterial killing, bacterial adherence, and mammalian cell cytotoxicity using human gingival keratinocyte (TIGK) cells. Results: Both liposomal formulations exhibited spherical morphology with hydrodynamic diameters smaller than ~170 nm and demonstrated good colloidal stability. LL17-32 showed high association efficiency with both liposomal membranes, with no detectable LL17-32 in vitro release. In biological assays, peptide-loaded DOPC liposomes exhibited dose-dependent bactericidal activity against P. gingivalis, whereas SL liposomes significantly attenuated the bactericidal effect of LL17-32. Both formulations displayed reduced cytotoxicity toward human gingival keratinocyte (TIGK) cells versus free peptide. Conclusions: These findings suggest that DOPC liposomes represent a promising delivery system for LL17-32 by adhering to P. gingivalis and exhibiting minimal cytotoxicity to mammalian cells. This study emphasises the critical role of lipid charge in designing AMP delivery systems for antibacterial applications, while it additionally demonstrates the utility of flow cytometry as a quantitative tool to assess liposome–bacteria association.