Aggregatibacter Actinomycetemcomitans-Induced AIM2 Inflammasome Activation Is Suppressed by Xylitol in Differentiated THP-1 Macrophages

Background: Aggressive periodontitis is characterized by rapid destruction of periodontal tissue caused by Aggregatibacter actinomycetemcomitans. Interleukin (IL)-1β is a proinflammatory cytokine, and its production is tightly regulated by inflammasome activation. Xylitol, an anticaries agent, is anti-inflammatory, but its effect on inflammasome activation has not been researched. This study investigates the effect of xylitol on inflammasome activation induced by A. actinomycetemcomitans.

Methods: The differentiated THP-1 macrophages were stimulated by A. actinomycetemcomitans with or without xylitol and the expressions of IL-1β and inflammasome components were detected by real time PCR, ELISA, confocal microscopy and Immunoblot analysis. The effects of xylitol on the adhesion and invasion of A. actinomycetemcomitans to cells were measured by viable cell count.

Results: A. actinomycetemcomitans increased pro IL-1β synthesis and IL-1β secretion in a multiplicity of infection- and time-dependent manner. A. actinomycetemcomitans also stimulated caspase-1 activation. Among inflammasome components, apoptosis-associated speck-like protein containing a CARD (ASC) and absent in melanoma 2 (AIM2) proteins were upregulated by A. actinomycetemcomitans infection. When cells were pretreated with xylitol, proIL-1β and IL-1β production by A. actinomycetemcomitans infection was significantly decreased. Xylitol also inhibited ASC and AIM2 proteins and formation of ASC puncta. Furthermore, xylitol suppressed internalization of A. actinomycetemcomitans into differentiated THP-1 macrophages without affecting viability of A. actinomycetemcomitans within cells.

Conclusions: A. actinomycetemcomitans induced IL-1β production and AIM2 inflammasome activation. Xylitol inhibited these effects, possibly by suppressing internalization of A. actinomycetemcomitans into cells. Thus, this study proposes a mechanism for IL-1β production via inflammasome activation and discusses a possible use for xylitol in periodontal inflammation caused by A. actinomycetemcomitans.