Anti-inflammatory Effects of Catechin on Rat Odontoblastic Cells (KN-3)

<p> Purpose: Odontoblasts, which are located in the outermost layer of dental pulp, first recognize caries-related pathogens, sense such external mechanical and chemical irritations, and play important roles in the innate immune system of dental pulp tissues. We recently reported that nucleotide-binding oligomerization domain (NOD) 1, one of the pattern recognition receptors in innate immunity, is expressed in rat odontoblastic cells (KN-3) and functions to up-regulate the chemokines expression, and suggested that NOD1 may play important roles in the initiation and progression of pulpitis. It has been reported that epigallocatechin gallate (EGCG), one of the major active components of green tea catechin, has anti-inflammatory effects. The aim of this study was to determine the anti-inflammatory effects of EGCG on odontoblasts stimulated with NOD1-specific ligand or pro-inflammatory cytokines.</p><p> Methods: The cytotoxicity of EGCG to KN-3, rat odontoblastic cell line, was analyzed by lactate dehydrogenase (LDH) cytotoxicity assay. γ-D-diaminopimelic acid (iE-DAP), NOD1-specific ligand, tumor necrosis factor (TNF) -α- or interleukin (IL) -1β-stimulated KN-3 was treated with EGCG and then the expression and production of pro-inflammatory mediators, such as chemokines and inducible nitric oxide synthase (iNOS), were determined by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively.</p><p> Results: EGCG (up to 10μg/ml) had no cytotoxic effect on KN-3. EGCG significantly inhibited the production of chemokines, such as cytokine-induced neutrophil chemoattractant (CINC) -2 and C-C motif chemokine ligand (CCL) 20, in a dose-dependent manner. The expression of iNOS mRNA was also significantly reduced by treatment with EGCG at 10μg/ml.</p><p> Conclusions: These findings demonstrated that EGCG treatment significantly reduced the expression and production of various pro-inflammatory mediators via NOD1-mediated innate immune response as well as inflammatory response elicited by TNF-α or IL-1β stimulation in rat odontoblastic cells (KN-3), suggesting that EGCG might be useful therapeutically as an anti-inflammatory modulator of dental pulpal inflammation.</p>