Prostaglandin-H-synthase (PGHS)-1 and -2 microtiter assays for the testing of herbal drugs and in vitro inhibition of PGHS-isoenzyms by polyunsaturated fatty acids from Platycodi radix

In order to test inhibition of prostaglandin-H-synthase-1 and -2 (PGHS-1 and -2) by plant extracts, we have established two enzyme based in vitro assays with enzyme immunoassay (EIA) evaluation. The assays have been evaluated with known synthetic inhibitors and with plant extracts.In a screening of traditionally used Chinese herbs for anti-inflammatory activity, a series of n-hexane and dichloromethane extracts showed significant inhibitory effect in comparison with the known specific PGHS-2 inhibitors NS-398 (IC50=2.6 μM) and nimesulide (IC50=36 μM).The lipophilic extracts of the Chinese drug Jiengeng, the dried roots of Platycodon grandiflorum (Jacq.) A. DC. (Campanulaceae), showed good inhibitory activity against both PGHS isoenzymes. The directly prepared DCM-extract exhibited better activity against PGHS-2 (IC50=4.0 μg/ml) than against PGHS-1 (IC50=17.6 μg/ml). We identified fatty acids as main active constituents and quantified them. Linoleic acid showed the highest content (ca. 20% of the dried extract) and a high and preferential PGHS-2 inhibitory activity (IC50 (PGHS-1)=20 μM; IC50 (PGHS-2)=2 μM). The comparison of the concentration of linoleic acid and the inhibitory activity of the direct DCM-extract showed, that linoleic acid is mainly responsible for the in vitro activity of the extract on PGHS-2.