Nisin-Loaded Solid Lipid Nanoparticles (SLN-Nisin) Mitigate Treponema denticola Intracellular Infection and Restore...

Background/Objectives: Periodontal disease is a bacterially driven chronic inflammatory condition that compromises tooth-supporting tissues. Treponema denticola is strongly associates with periodontal tissue destruction and tooth loss. Given the contribution of antibiotic overuse, the rise of multi-drug resistance represents a major therapeutic challenge. Previous literature has shown that nisin, an antimicrobial peptide, exhibits activity against periodontal pathobionts, including T. denticola. Yet, nanoparticle-based delivery systems, such as solid lipid nanoparticles (SLNs), may enhance nisin's intracellular activity and therapeutic potential. Therefore, the objective of this work was to evaluate the therapeutic potential of SLN-Nisin in treating intracellular T. denticola infection in human periodontal ligament cells in periodontal disease in vitro settings. Methods: SLNs and SLN-Nisin were prepared by microemulsion extrusion. T. denticola intracellular trafficking in human-derived periodontal ligament (hPDL) cells was assessed by confocal microscopy using endocytosis fluorescent markers. RNA-seq characterized T. denticola-induced transcriptional alterations. SLN-Nisin intracellular antimicrobial activity was assessed by confocal microscopy and bacterial viability assays, while mitigation of host transcriptional alterations by RT-qPCR. Results: T. denticola invades hPDL cells and undergoes dynamic intracellular trafficking through the endocytic pathway, resulting in sustained late endosomal colonization, promoting significant host transcriptional alterations. Further, SLN-Nisin is efficiently internalized by hPDL cells through clathrin-mediated endocytosis and phagocytosis, and both nisin and SLN-Nisin significantly reduce bacterial burden. SLN-Nisin restores four of the most strongly dysregulated host genes to control levels, whereas nisin restores only two. Conclusions: These findings demonstrate that SLN-based delivery enhances the intracellular efficacy of nisin, limiting T. denticola burden and reversing infection-induced host transcriptional alterations. SLN-Nisin represents a promising therapeutic approach for targeting intracellular T. denticola infection in periodontal disease.