Concentration-dependent Effect of Rikko-san on the Prostaglandin E₂ Production by Mouse Macrophage-like Cells

Abstract

Rikko-san (RKS) and its ingredients were investigated for their activity to stimulate prostaglandin E₂ (PGE₂) production by unstimulated and lipopolysaccharide (LPS)-stimulated mouse macrophage-like Raw 264.7 cells. LPS significantly stimulated the production and extracellular secretion of PGE₂ by Raw 264.7 cells. RKS dose-dependently modified the LPS-stimulated PGE₂ production. A lower concentration (0.04-0.4 mg/ml) of RKS stimulated PGE₂ production without or with LPS, whereas a higher concentration (4 mg/ml) of RKS inhibited the LPS-stimulated PGE₂ production, suggesting the presence of both stimulator(s) and inhibitor(s) for PGE₂ production. The inhibitory effect of a higher concentration of RKS was slightly neutralized by supplementation of exogenous arachidonic acid. Among five RKS ingredients, Kanzo inhibited the LPS-stimulated PGE₂ production to the greatest extent, whereas other ingredients (Shoma, Ryutan, Saishin, Bofu) stimulated PGE₂ production. Western blot analysis demonstrated that RKS and all its ingredients enhanced the intracellular concentration of cyclooxygenase-2, whereas RKS did not significantly affect the phospholipase A₂ protein level. The present study demonstrates that the concentration-dependent effect of RKS on the PGE₂ production by macrophage cannot be explained only by the expression levels of cyclooxygenase-2 or phospholipase A₂.