A mechanistic approach to the in vivo anti-inflammatory activity of sesquiterpenoid compounds isolated from Inula viscosa

The present study was designed to examine the anti-inflammatory activity of the sesquiterpenoids ilicic acid and inuviscolide, isolated from Inula viscosa, on cell degranulation, leukotriene biosynthesis, neurogenic drive and glucocorticoid-like interactions. Swiss female mice were used to measure the ear oedema induced by phorbol esters or ethyl phenylpropiolate (EPP), and the paw oedema induced by Phospholipase A(2) (PLA(2)) or serotonin. Drug treatment consisted of one topically-applied dose in the ear models and a subcutaneous or intraperitoneal injection in the paw models. Quantitative analysis of leukotriene B(4) (LTB(4)) formation was performed on rat peritoneal neutrophils by high performance liquid chromatography (HPLC). The lactone inuviscolide reduced the PLA(2)-induced oedema (ID(50): 98 micromol/kg). The effect on serotonin-induced oedema was not changed by modifiers of the glucocorticoid response. Ilicic acid showed minor in vivo effects, but was slightly more potent than inuviscolide on the 12-O-tetradecanoylphorbol 13-acetate (TPA) acute oedema test (ID(50): 0.650 micromol per ear). Inuviscolide reduced LTB(4) generation in intact cells, with an IC(50) value of 94 microM. On the basis of the reported results, inuviscolide is the main anti-inflammatory sesquiterpenoid from Inula viscosa, and may act by interfering with leukotriene synthesis and PLA(2)-induced mastocyte release of inflammatory mediators.