Rapid screening of commercially available herbal products for the inhibition of major human hepatic cytochrome P450 enzymes using the N-in-one cocktail.

Self-administration of complementary products concurrently with conventional medication is increasingly common. The potential for cytochrome P450 (CYP) inhibition requires investigation. The N-in-one assay with ten probe substrates for nine CYPs was used with human liver microsomes to investigate ten products. CYP inhibition was measured in a single liquid chromatography-tandem mass spectrometry (LC/MS-MS) analysis. Estimated IC(50)-values were determined for the extracts that produced significant inhibition (less than 100 microg ml(-1)). Inhibition of CYP2C19 by dong quai (IC(50) = 13.7-14.3 microg ml(-1) for the methanolic extract) and CYP2D6 by goldenseal (IC(50) = 6.7 and 6.3 microg ml(-1) for the aqueous and methanolic extracts, respectively), are of particular concern as the potential for adverse interactions is high. The inhibition of CYP2C8 by horsetail (IC(50) = 93 microg ml(-1) for the aqueous extract) requires further investigation, as the potential for concurrent use with products that require CYP2C8 for metabolism is significant. CYP3A4 inhibition varied depending on the probe reaction being monitored. The earlier reported findings of inhibition by black cohosh, goldenseal and gotu kola were confirmed. The present work has shown that the N-in-one cocktail is a rapid and reliable method that can be used as an initial screen to help prioritize products that require more detailed investigations and it can also be applied to monitor product variability.

Predictive value of animal models for human cytochrome P450 (CYP)-mediated metabolism: a comparative study in vitro.

One major challenge in drug development is defining of the optimal animal species to serve as a model of metabolism in man. The study compared the hepatic drug metabolism characteristics of humans and six widely used experimental animal species. Classical in vitro model enzyme assays with known human cytochrome P450 (CYP) enzyme selectivity were employed and optimized to target human hepatic CYP forms. The profile of CYP activities best resembling the human was seen in mouse followed by monkey, minipig, and dog liver microsomes, with rats displaying the most divergent. The widest interindividual variability was found in CYP3A-mediated midazolam -hydroxylase, and omeprazole sulphoxidase activities in human and monkey liver microsomes. These data demonstrate that if hepatic xenobiotic-metabolizing characteristics were to be the sole reason for the selection of animal species for toxicity studies, then the rat might not be the most appropriate model to mimic human CYP activity patterns.