Impact of E-Liquids on Phagocytosis, Escape and Invasion of Porphyromonas gingivalis

This study seeks to understand the effects of electronic cigarettes on the oral microenvironment. Macrophages are paramount in the oral innate immune response against pathogens. Porphyromonas gingivalis is a Gram-negative bacterium that invades oral epithelial cells, escapes phagocytosis and is associated with the progression of periodontitis. We hypothesize that e-liquid treatments enhance P. gingivalis’s escape from post-macrophage phagocytosis and subsequent invasion into oral epithelial cells. THP-1-derived macrophages were polarized to M1 ± 1% e-liquids (±menthol or cinnamon). The M1 cellular morphology and surface area were determined after e-liquid treatments. Escherichia coli or P. gingivalis were added to M1 macrophages ± e-liquids. Phagocytosis and escape were determined by multiple assays. After e-liquid treatments and phagocytosis, OKF6/TERT-2 cells (oral epithelial cells) were exposed to M1 macrophages with intracellular P. gingivalis to evaluate escape and invasion. The results show that cinnamon e-liquids alter M1 morphology by diminishing pseudopodia extensions and actin stress fibers, which persist after a second polarization attempt. Phagocytosis of P. gingivalis by e-liquid-treated macrophages also decreases. Furthermore, P. gingivalis absolute escape and OKF6/TERT-2 cell invasion increase after menthol and cinnamon e-liquid treatments, respectively. Thus, following e-liquid exposure, phagocytosis and retention of P. gingivalis deteriorate.