Simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatography/mass spectrometry and automated online extraction

Here we describe a liquid chromatography/mass spectrometry (LC/MS) method with automated online extraction (LC/LC/MS) to simultaneously determine the in vitro inhibitory potency of herbal extracts on six major human drug‐metabolising cytochrome P450 enzymes. Substrates were incubated with a commercially available mixture of CYP1A2/2C8/2C9/2C19/2D6 and 3A4 from baculovirus‐infected insect cells and the resulting metabolites were quantified with LC/LC/MS using electrospray ionisation in the selected ion monitoring mode. Consistent inhibitory activities were obtained for known inhibitors and plant extracts using the enzyme/substrate cocktail and the individual enzymes/substrates. Popular herbal remedies including devil's claw root ( Harpagophytum procumbens ), feverfew herb ( Tanacetum parthenium ), fo‐ti root ( Polygonum multiflorum ), kava‐kava root ( Piper methysticum ), peppermint oil ( Mentha piperita ), eucalyptus oil ( Eucalyptus globulus ), red clover blossom ( Trifolium pratense ) and grapefruit juice (GJ; Citrus paradisi ) could be identified as inhibitors of the applied CYP enzymes with IC 50 values between 20 and 1000 μg/mL. Copyright © 2004 John Wiley & Sons, Ltd.