Calcium hydroxide attenuates inflammatory potential of lipoteichoic acid from Enterococcus faecalis (135.33)

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 E. faecalis LTA, RAW 264.7 cells substantially produced tumor necrosis factor-α (TNF-α) in concentration- and time-dependent manner. Notably, the LTA was able to stimulate Toll-like receptor 2 (TLR2), but not TLR4. Concomitantly, LTA enhanced the DNA-binding activity of a transcription factor, NF-κB, which plays an important role in the transcriptional activation of genes encoding inflammatory mediators. However, induction of TNF-α production was not observed in the cells exposed to LTA pre-treated with calcium hydroxide, which is widely used endodontic medicament for eliminating viable bacteria and inactivating virulence factors. Furthermore, calcium hydroxide-treated LTA was not able to stimulate TLR2. These results suggest that E. faecalis LTA could stimulate inflammatory responses through TLR2 and calcium hydroxide could detoxify LTA, resulting in attenuation of the inflammatory responses. Supported by the Korea Research Foundation Grant (KRF-2007-314-E00186).