Antibiotic loaded solid lipid nanoparticles target bacteria in a pyogenic spondylitis rat model

Pyogenic spondylitis is treated with high-dose antibiotics for at least six weeks. In this study, we aimed to develop a novel therapeutic agent that can enhance bacterial targeting. We used solid lipid nanoparticles (SLNs) containing the antibiotic ampicillin (AMP), which were functionalized with the positively charged peptide LL-37. AMP-loaded SLNs (AMP-SLNs) were prepared, and LL-37 was attached to the AMP-SLNs (LL-37@AMP-SLNs). The physicochemical properties of the nanoparticles were characterized by particle size, zeta potential, morphology, drug release behavior, and hemocompatibility analyses. Furthermore, antibacterial activity, bacterial-targeting capability, and therapeutic efficacy were evaluated using Enterococcus faecalis-infected mesenchymal stem cells and a rat model of pyogenic spondylitis. The antibacterial performance of LL-37@AMP-SLNs was compared with that of SLNs and AMP-SLNs. The average size of the SLNs was approximately 342.66 ± 48.04 nm, which increased to 528.58 ± 35.64 nm after AMP loading and 695.58 ± 75.58 nm following LL-37 modification. The LL-37@AMP-SLNs exhibited sustained AMP release over four days and demonstrated enhanced antibacterial activity and bacterial-targeting capability compared with unmodified SLNs and AMP-SLNs. LL-37@AMP-SLNs were shown to inhibit bacterial growth by targeting the cytoplasmic membrane and the cell walls of Gram-positive bacteria. Moreover, the LL-37@AMP-SLNs treatment led to significantly enhanced antibacterial effects. In vitro studies showed significantly greater inhibition of bacterial growth, while intravenous administration of LL-37@AMP-SLNs significantly reduced bacterial burden and improved therapeutic outcomes in the pyogenic spondylitis rat model compared with free AMP treatment. We suggest that LL-37@AMP-SLNs can be a useful therapeutic agent for targeting bacteria in pyogenic spondylitis.