Calcium hydroxide attenuates the inflammatory potential of lipoteichoic acid (LTA) from Enterococcus faecalis by deacylating the LTA (89.22)

Abstract

Abstract Enterococcus faecalis is a pathogenic gram-positive bacterium closely related with refractory apical periodontitis. Since lipoteichoic acid (LTA) is a major virulence factor of gram-positive bacteria, we prepared highly pure LTA from E. faecalis and investigated its inflammatory responses in a murine macrophage-like cell line, RAW 264.7. Upon exposure to the E. faecalis LTA, the cells substantially produced tumor necrosis factor-α (TNF-α) and nitric oxide (NO) in a dose- and time-dependent manner. Notably, the action of the LTA was through Toll-like receptor 2 (TLR2), but not TLR4. The LTA enhanced the DNA-binding activity of a transcription factor, NF-κB, which plays an important role in the transcriptional activation of genes encoding various inflammatory mediators. However, induction of TNF-α and NO production was not observed in the cells exposed to LTA pre-treated with calcium hydroxide, which is a widely used as intracanal medicament for sterilizing root canals of teeth. Furthermore, calcium hydroxide-treated LTA was not able to stimulate TLR2. Structural analysis using MALDI-TOF mass spectrometry showed that calcium hydroxide deacylated the glycolipid moiety in the LTA structure. Conclusively, we suggest that calcium hydroxide attenuates the inflammatory activity of E. faecalis LTA through deacylation of the LTA structure.