Engineered lipid nanoparticles loaded with LL-37 peptide as inhalable drug delivery carriers for the treatment of bacterial infections

Human cathelicidin LL-37 is a promising antibacterial agent; however, conventional administration routes limit its efficacy. This study aimed to develop cetyl palmitate (CP)-based lipid nanoparticles loaded with LL-37 peptide (LL) for pulmonary delivery. The nanoparticles manufactured using emulsification method with different CP:LL ratios were spherical with median diameters of 35-42 nm. Encapsulation efficacy was approximately 30%, resulting in a maximum peptide loading of 6.1%. The unloaded CP nanoparticles were negatively charged, while those loaded with LL-37 were neutral (CP + LL20:1) or positively charged (CP + LL10:1, CP + LL5:1). Increased zeta potential and the presence of mucopenetrative poly(vinyl alcohol) molecules at the nanoparticles surface (as evidenced by XPS studies) allowed effective adsorption of mucins on the surface of nanoparticles and enhanced penetration through mucus. The nanoparticles were cytocompatible with BEAS-2B lung epithelial cells. Encapsulation of LL-37 in CP protected cells from the negative impact of the peptide. In the presence of nanoparticles, Calu-3 lung epithelial cells were able to maintain their barrier properties in the advanced air-liquid interface model. The nanoparticles prevented the formation of the Pseudomonas aeruginosa biofilm and were also able to disrupt the existing early biofilm. The dose of LL-37 required to reduce biofilm viability was lower in the case of CP + LL5:1 nanoparticles, than for LL-37 alone (LD₅₀: 103 μg/ml and 310 μg/ml, respectively). The developed nanoparticles exhibited suitable properties for inhalation, the ability to migrate through mucus, cytocompatibility, and antibiofilm properties against P. aeruginosa. This paves the way for their use for pulmonary administration by nebulization.