Anti-inflammatory potential of Rikkosan based on IL-1β network through macrophages to oral tissue cells

Abstract

Rikkosan is a traditional Kampo medicine using the control of oral pain caused by dental caries, pulpitis, periodontitis and stomatitis. In order to provide evidence for its clinical effects, we herein investigated whether Rikkosan inhibits the production of pro-inflammatory substances in human and mouse models of inflammation. Rikkosan alone did not induce prostaglandin E2 (PGE2) production, but inhibited interleukin-1β (IL-1β) (5 ng/ml)-stimulated PGE2 production in human gingival fibroblasts and human periodontal ligament fibroblasts, with a selectivity index higher than 4.0 and 4.3, respectively. Rikkosan alone dose-dependently stimulated tumor necrosis factor-α (TNF-α) production, reaching a peak level slightly lower than that attained by lipopolysaccharide (LPS) at 0.4 mg/ml in mouse macrophage-like RAW264.7 cells. At a higher concentration of Rikkosan (4 mg/ml), TNF-α production, however, declined significantly regardless of the presence or absence of LPS. Rikkosan dose-dependently inhibited IL-1β production by LPS-stimulated RAW264.7 cells, with a selective index of 7.6. Five constituent extracts of Rikkosan, either alone or in combination, showed similar effects on TNF-α and IL-1β productions in activated RAW264.7 cells, but to lower extents than that of Rikkosan. These results demonstrated that Rikkosan inhibited both IL-1β production by LPS-activated macrophages and PGE2 production by IL-1β-stimulated human gingival fibroblasts and human periodontal ligament fibroblasts, suggesting that anti-inflammatory effects of Rikkosan may partially be generated by the inhibition of these pro-inflammatory substances via the IL-1β network through macrophages to oral tissue cells.

Keywords: Rikkosan; human gingival fibroblast; interleukin-1β; mouse macrophage-like RAW264.7 cells; periodontal ligament fibroblast; prostaglandin E2.