A Synthetic Small Molecule, LGM2605: A Promising Modulator of Increased Pro-Inflammatory Cytokine and Osteoclast Differentiation by Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin

Abstract

Our research explores the interplay between Aggregatibacter actinomycetemcomitans (Aa) cytolethal distending toxin (Cdt) and the host’s inflammatory response in molar/incisor pattern periodontitis (MIPP). Cdt disrupts phosphatidylinositol-3,4,5-triphosphate (PIP3) signaling, influencing cytokine expression through canonical and non-canonical inflammasome activation as well as nuclear factor-κB (NF-κB) activation, leading to inflammation in MIPP. THP-1 differentiated macrophages (TDMs) exposed to Cdt exhibited an upregulation of pro-inflammatory genes and subsequent cytokine release. We analyzed the ability of a small molecule therapeutic, LGM2605, known for its anti-inflammatory properties, to reduce pro-inflammatory gene expression and cytokine release in Cdt-exposed and Aa-inoculated TDMs. LGM2605’s mechanism of action involves inhibiting NF-κB while activating the Nrf2–transcription factor and antioxidants. Herein, we show that this small molecule therapeutic mitigates Cdt-induced pro-inflammatory cytokine expression and secretion. Our study also further defines Cdt’s impact on osteoclast differentiation and maturation in MIPP. Cdt promotes increased TRAP+ cells, indicating heightened osteoclast differentiation, specific to Cdt’s phosphatase activity. Cathepsin K levels rise during this process, reflecting changes in TRAP distribution between control and Cdt-treated cells. Exploring LGM2605’s effect on Cdt-induced osteoclast differentiation and maturation, we found TRAP+ cells significantly reduced with LGM2605 treatment compared to Cdt alone. Upon LGM2605 treatment, immunocytochemistry revealed a decreased TRAP intensity and number of multinucleated cells. Moreover, immunoblotting showed reduced TRAP and cathepsin K levels, suggesting LGM2605’s potential to curb osteoclast differentiation and maturation by modulating inflammatory cytokines, possibly involving Nrf2 activation. In summary, our research reveals the intricate connections between Cdt, pro-inflammatory cytokines, and osteoclast differentiation, offering novel therapeutic possibilities for managing these conditions.