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Screening Herbal Medicinal Products for CYP P450 enzyme inhibition with the fast, robust Supersome assay
The Supersome assay has long been used for industrial purposes to identify possible in vitro drug-drug interactions. Many of these interactions occur via induction or inhibition of the cytochrome P450 (CYP P450) enzyme system. The CYP P450 are a superfamily of membrane-bound, haeme-thiolate proteins, which are principally responsible for phase 1 oxidative metabolism and detoxification of xenobiotics and endobiotics (e.g. steroids, fatty acids, retinoids, eicosanoids, vitamins, cholesterol and prostaglandins).
We have optimised and assessed the use of this assay for identifying possible herbal medicinal product (HMP)-drug interactions.
The high throughput, rapid and cost effectiveness are key features of this approach. The approach uses a modified fluorometric 96-well plate assay measuring enzyme activity by detecting the fluorescent metabolite produced from the reaction of the substrate with single CYP isoforms (so called Supersomes, ). The substrates used were 7-Benzyl-4-(trifluoromethyl)-coumarin (BFC) (CYP3A4), 3-Cyano-7-EthoxyCoumarin (CEC) (CYP1A2, CYP2C19) and 3-(2-N, N-diethyl-N-methylaminoethyl)-7-methoxy-4-methylcoumarin (AMMC) (CYP2D6).
It is well known that potentially intrinsic and quenching effects of extracts can interfere with fluorescence based assays. However we have controlled for these factors and we have also controlled for the solvent effects from extracts as it is well known that organic solvents can inhibit enzyme activity. With these controls in place extracts can be directly assessed in the assay.
The assay has been successfully used to assess a wide range of Echinacea extracts, and showed that inhibitory activity for Echinacea extracts is unlikely in a clinical setting . However, recent research on a well characterised Cannabis extract  has revealed potential inhibitory activity on the CYP3A4 isoform with median inhibitory concentration ranges (IC50 value – indication of concentration required to inhibit 50% enzyme activity) in the regions of 0.4µg/ml.
These findings indicate that little evidence points to interactions between Echinacea preparations with other medications, however further studies are warranted to assess the potential inhibitory CYP P450 risk of the Cannabis extract. We have shown that the Supersome assay is an ideal method for fast data acquisition of potential CYP mediated interactions with HMP. This is no doubt a valuable assay which can be used for routine screening of potential HMP-drug interactions.
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We are grateful to Bioforce UK, for the funding of this research.