Bioguided determination of the anti-inflammatory action of STW 5 and STW 6

STW 5 (Iberogast®) is a fixed combination of nine hydroethanolic herbal extracts, each of which is reported to have multiple pharmacological properties relevant for gastrointestinal pathophysiology. Iberis amara fresh plant extract (STW 6), the main ingredient of STW 5 stimulates motor processes of the gut, acts anti-inflammatorily and protects the mucosa and smooth muscle layers of the gut. In order to further characterize the mode of action STW 5 and its main constituent herbal component STW 6 were tested in an in vitro inflammation model on rat small intestine. The inflammation was induced by intraluminal instillation of 2,4,6 trinitrobenzolsulfonic acid (TNBS, 0.01M). STW 6 dissolved in water was stepwise macerated by hexane (HEX), chloroform (CHCl₃) and ethylacetate (EA). These extracts were analysed qualitatively by thin layer chromatography und quantitatively by HPLC. Constituents of the CHCl₃ and EA extract were e.g. cucurbitacins E and I, of the residual aqueous fraction (rAF) e.g. glucosinolates. Flavonoids were identified in CHCl₃, EA and rAF. The HEX extract was almost free of constituents. Preincubation of the preparations with TNBS resulted in an inhibition of the ACh (1 mM)-induced contraction. After preincubation with STW 5 (64–512µg/ml) or STW 6 (3–24µg/ml) together with TNBS the inhibition was concentration-dependently reduced, indicating a protective effect of STW 5 and STW 6. The CHCl₃ and EA extracts were also protective against the TNBS-induced inhibition of the ACh-induced contractions. The rAF was without effect. Commercial available cucurbitacines E and I showed a comparable action as seen with the CHCl₃- and EA-fraction. Our experiments confirmed the anti-inflammatory effect of STW 5 and STW 6 and showed that constituents within the extracts macerated with CHCl₃ and EA may be part of the the anti-inflammatory acting agents within STW 6.