Trans-cinnamic aldehyde inhibits Aggregatibacter actinomycetemcomitans-induced inflammation in THP-1-derived macrophages via autophagy activation.

BACKGROUND: Inflammation is an essential response against bacterial infection as a host defense mechanism, which can lead to tissue damage. Aggregatibacter actinomycetemcomitans (Aa) is major pathogen for aggressive periodontitis characterized by rapid destruction of periodontal tissue surrounding teeth. Trans-cinnamic aldehyde is a key bioactive compound of the cinnamon extracts, which has anti-inflammatory, antioxidant, antipyretic, antimicrobial, and anti-cancer properties. The objective of the present study was to investigate the anti-inflammatory effect of trans-cinnamic aldehyde against Aa infection in human THP-1 derived macrophages and on Aa-induced periodontitis in mice.

METHODS: THP-1 cells were differentiated with phorbol 12-mystristate 13-acetate and were infected with live Aa. Trans-cinnamic aldehyde was pretreated 30 minutes before the bacterial infection. Cytokine production was determined by enzyme-linked immunosorbent assay (ELISA) and protein expressions were detected by Western blot analysis. Autophagosome formation was detected by Cyto-ID. Viable cell count was carried out to determine bacterial adhesion, internalization, and intracellular survival. Experimental periodontitis was induced by inoculating Aa orally to mice, and microcomputed tomography was used to evaluate bone loss.

RESULTS: Pretreatment of trans-cinnamic aldehyde significantly inhibited Aa-stimulated release of tumor necrosis factor-α and interleukin (IL)-1β. Pretreatment of trans-cinnamic aldehyde inhibited Aa-induced expression of TLR signaling pathway as well as the phosphorylation of JNK, p38, and nuclear factor (NF)-κB. Also, trans-cinnamic aldehyde treatment downregulated the expression of pro-IL-1β, caspase-1, and inflammasome components. Trans-cinnamic aldehyde treatment significantly decreased intracellular survival of Aa. Moreover, the autophagosome formation and the expressions of autophagy markers including Beclin-1, ATG5, and LC3 were increased. Finally, trans-cinnamic aldehyde significantly inhibited bone loss in Aa-induced mouse periodontitis.

CONCLUSIONS: Trans-cinnamic aldehyde inhibited Aa-stimulated expression of inflammatory responses and inhibited intracellular bacterial survival via autophagy activation. These results suggest that trans-cinnamic aldehyde may serve as an anti-inflammatory agent for aggressive periodontitis.