Boldine and Laurolitsine Protect against Periodontitis-Associated Bone Loss via RANKL Downregulation

Periodontitis is a chronic inflammatory disease driven by dysbiosis of the subgingival microbiota, leading to immune dysregulation and progressive alveolar bone loss. In recent years, immunotherapeutic approaches, particularly those involving natural products, have gained attention as potential adjuvants to conventional therapy. This study evaluated the effects of four alkaloids, boldine, laurolitsine, laurotetanine, and <i>N</i>-methyl-laurotetanine, on alveolar bone loss and local immune regulation in experimental periodontitis.Male and female C57BL/6 mice with ligature-induced periodontitis received daily oral administration of each alkaloid (20 mg/kg) for 10 days. Alveolar bone loss was quantified by micro-computed tomography (micro-CT). Periodontal immune responses were assessed by RT-qPCR analysis of pro-inflammatory cytokines, T-cell-related transcription factors, and bone metabolism mediators (RANKL and OPG). In addition, regulatory T (Treg) cells in cervical lymph nodes were analyzed by flow cytometry.Boldine and laurolitsine significantly reduced alveolar bone loss compared with untreated periodontitis, in parallel with decreased RANKL expression. All four alkaloids significantly reduced IL-6 expression, with laurolitsine additionally suppressing IL-17A expression in periodontal tissues, whereas <i>N</i>-methyl-laurotetanine reduced IL-10 expression. No significant changes were observed in CD4⁺, CD4⁺FoxP3⁺, and CD4⁺FoxP3⁺CD25⁺ T-cell frequencies between treated and untreated groups.Oral administration of boldine and laurolitsine attenuates periodontitis-associated alveolar bone loss, likely through differential modulation of cytokine networks and osteoclastogenic signaling. These findings support their potential as host-modulating agents in the management of periodontitis.