PGE2, a major end product of cyclooxygenase (COX-2), has an important role in both acute and chronic inflammatory responses . First, we investigated whether DPB could stimulate PGE2 expression in various cell lines. As shown in Fig. 2a, PGE2 levels were significantly increased in DPB-stimulated RAW264.7 macrophages, and IHOK, IGF, and YD38. However, the pH changes occurred slowly in co-culture media with DPB during 24 h of incubation. Therefore, we extracted LPS from DPB, and used 1 μg/ml each of DPB#1-LPS, DPB#2-LPS, and DPB#3-LPS for the next experiments. In RAW264.7, IHOK, IGF, and YD38 cells, PGE2 levels were also increased after DPB-LPS treatment, although the different effects were cell line-specific (Fig. 2b). COX-2 mRNA was also increased by stimulation with DPB#1-LPS, DPB#2-LPS, or DPB#3-LPS (Fig. 2c). Treatment with EETC significantly suppressed the levels of PGE2 and COX-2 that had been increased by DPB-LPS (10 μg/ml) (Fig. 2d and e). YD38 cell viability remained unchanged after treatment with 5 and 30 μg/ml EETC (Fig. 2f). Thus, the EETC inhibited not only the growth of DPB through its anti-bacterial effect but also inflammation by abolishing PGE2 and COX-2 expression, thereby enhancing its preventive effect on gingival and periodontal diseases.Fig. 2Effect of the EETC on DPB-induced PGE2 and COX-2. a The effect of DPB on PGE2 levels in various cell types. Data are expressed as mean ± SE of three independent experiments. *P < 0.01 vs. bacteria-free control medium from each cell line. b The effect of LPS extracted from DPBs (DPB#1-LPS, DPB#2-LPS, and DPB#3-LPS) on PGE2 levels. PBS was used for control. *P < 0.01, # P < 0.001 vs. PBS control medium from each cell line. c The effect of DPBs-LPS on COX-2 expression. mRNA expression were detected by RT-PCR. The inhibitory effects of EETC on PGE2 (d) and COX-2 (e) levels in DPB-LPS-treated cells. DMSO was used for control. Data represent the mean ± SE of three independent experiments performed by triplicate. # P < 0.001 vs. DMSO control (Ctl) medium, *P < 0.01 vs. DPB#1 or DPB#1-LPS medium. f The effect of EETC on the cell viability