Ex vivo absorption of STW 5 and some of its components using a new HPLC method

STW 5 (Iberogast®) is a combination of nine herbal drugs. The fresh whole plant extract of STW 6, a characteristic component of STW 5, contains flavonoids, glucosinolates and low amounts of cucurbitacins. STW 5 and STW 6 as well as cucurbitacins E and I were able to affect protectively inflammatory processes in an in-vitro model. STW 6 (24.1µg/ml) as well as cucurbitacin E (10µM) increased the gene expression of the anti-inflammatory agent cytokine IL-10. As they therefore may contribute to the pharmacological properties, there it is of relevance to analyze the absorption of these cucurbitacins in the gastrointestinal tract. Therefore, an absorption chamber and a refined HPLC method for quantification of cucurbitacins were developed. For the HPLC an isocratic eluent was used to detect the two cucurbitacins into the same sample. The experiments were done with untreated and inflamed (0.01M TNBS, 30min) intestinal preparations from rats. The test substance was applied in the donor compartment. The concentrations of the cucurbitacins in the donor and acceptor compartments and in tissue preparations were analysed using solid phase extraction columns followed by HPLC. Fluorescein was used as negative control. Using untreated tissue preparations, no cucurbitacins were detected neither in the acceptor compartment nor in the intestinal preparation after application of commercially available cucurbitacin E and I (0.01–10µM). Low amount of cucurbitacin E and I penetrated into the acceptor compartment after application of STW 5 and STW 6. Comparable results were found when the experiments were conducted with preparations preincubated with TNBS. Our results indicate that cucurbitacins from STW 5 and STW 6 do not penetrate the gastrointestinal wall under normal or inflamed conditions in relevant concentrations. Analysis of the tissue preparations focuses on the assumption that cucurbitacins might be metabolised rapidly in the intestine. Therefore further studies are needed to characterize their potential pharmacological relevance.