The aim of this study was to evaluate the in vitro inductive potential of six commonly used trade herbal products on CYP1A2, CYP2D6 and CYP3A4 metabolic activities. Herbal components were extracted from the trade products in a way that ensured a composition equal to that present in the original product. Primary human hepatocytes and specific CYP substrates were used. Classic inducers were used as positive controls and herbal extracts were added in in vivo -relevant concentrations. Metabolites were determined by high performance liquid chromatography (HPLC). St. John's wort and common valerian were the strongest inducing herbs. In addition to induction of CYP3A4 by St. John's wort, common valerian and Ginkgo biloba increased the activity of CYP3A4 and 2D6 and CYP1A2 and 2D6, respectively. A general inhibitory potential was observed for horse chestnut, Echinacea purpurea and common sage. St. John's wort inhibited CYP3A4 metabolism at the highest applied concentration. Horse chestnut might be a herb with high inhibition potentials in vivo and should be explored further at lower concentrations. We show for the first time that G. biloba may exert opposite and biphasic effects on CYP1A2 and CYP2D6 metabolism. Induction of CYP1A2 and inhibition of CYP2D6 were found at low concentrations; the opposite was observed at high concentrations. CYP2D6 activity, regarded generally as noninducible, was increased by exposure to common valerian (linear to dose) and G. bilob a (highest concentration). An allosteric activation is suggested. From the data obtained, G. biloba , common valerian and St. John's wort are suggested as candidates for clinically significant CYP interactions in vivo .The use of herbs as alternative and/or complementary therapy in the Western world is on the rise and gaining increasing popularity. As people often take different herbs in combination with prescribed Western medication [1], there is a potential for both pharmacokinetic and pharmacodynamic herb-drug interactions. In addition to doctor's recommendations [2], patients are also self-medicating with several different herbs and herbal preparations, thinking it is safe [3,4], and often without informing their primary physician.It is important that possible interactions are discovered in order to avoid clinical implications, as shown for example between oral contraceptives and St. John's wort [5], cyclosporine and St. John's wort [6], and between Ginkgo and warfarin [7]. These are just a few of many [8], and we need to identify such harmful combinations in order to avoid serious and negative effects of concurrent use.Cytochrome P450 (CYP) is a superfamily of enzymes, predominantly expressed in the liver, but also in the respiratory tract, lungs, brain and the small intestine [9,10]. CYP isoenzymes are the most important phase 1 enzyme system in the metabolism of xenobiotics, including Western medicines, endogenous compounds and herbal components as effective substrates [11]. Herb-drug interactions can appear when herbs and chemical drugs are co...

Extracts of six commonly used commercially available herbal products, St. John's wort, common valerian, common sage, Ginkgo biloba , Echinacea purpurea and horse chestnut were investigated for their in vitro inhibitory potential of CYP3A4 mediated metabolism and P-glycoprotein efflux transport activity. C-DNA baculovirus expressed CYP3A4 and Caco-2 cells were used. Ketoconazole and verapamil were applied as positive control inhibitors, respectively. A validated high-performance liquid chromatography methodology was used to quantify the formation of 6-OH-testosterone and scintillation counting was used to quantify the transport of 3 H-digoxin. All the investigated herbs inhibited CYP3A4 activity. St. John's wort was the strongest inhibiting herb with an IC 50 value of 15.4 μ g/ml, followed by common sage, Ginkgo biloba , common valerian, horse chestnut and Echinacea purpurea . All herbs also inhibited P-glycoprotein activity. Ginkgo biloba was the strongest inhibiting herb, inhibiting the net digoxin flux with an IC 50 value of 23.6 μ g/ml, followed by St. John's wort, horse chestnut, common sage, common valerian and Echinacea purpurea . No correlation was found between the herbs inhibitory potentials towards CYP3A4 and P-glycoprotein activities. Ginkgo biloba , horse chestnut and common sage, besides St. John's wort, are suggested candidates for in vivo intestinal herb-drug pharmacokinetic interactions.

Abstract:The six commonly used trade herbal products, St. John's wort, common valerian, common sage, Ginkgo biloba , Echinacea purpurea and horse chestnut, and ethanol, were investigated for their in vitro inhibitory potential of cytochrome P450 2D6 (CYP2D6)-mediated metabolism. Herbal components were extracted from commercially available products in a way that ensured the same composition of constituents in the extract as in the original trade products. c-DNA baculovirus expressed CYP2D6 was used with dextromethorphan as substrate. Quinidine was included as a positive control inhibitor. A validated high performance liquid chromatography methodology was used to quantify the formation of dextrorphan (product of dextromethorphan O-demethylation). Ethanol showed a biphasic effect on CYP2D6 metabolism, increasing initially the CYP2D6 activity with 175% of control up to a concentration of 1.1%, where after ethanol linearly inhibited the CYP2D6 activity. All the investigated herbs inhibited CYP2D6 activity to some extent, but only St. John's wort, common sage and common valerian were considered possible candidates for in vivo clinically significant effects. They showed IC 50 values of 0.07 ± 7 × 10 -3 mg/ml, 0.8 ± 0.05 mg/ml and 1.6 ± 0.2 mg/ml, respectively. St. John's wort inhibited CYP2D6-mediated metabolism in an uncompetitive manner, while common valerian and common sage in a non-competitive manner demonstrated interherb differences in inhibition patterns and differences when compared to the more homogenous competitive inhibitor quinidine. Common valerian was the only herb that showed a mechanistic inhibition of CYP2D6 activity and attention should be paid to a possible toxicity of this herb.The use of herbs as alternative and/or complementary therapy in the Western world is on the rise and gaining increasing popularity. As people often take different herbs in combination with prescribed Western medication [1][2][3], there is a potential for both pharmacokinetic and pharmacodynamic herb-drug interactions that can disturb Western drug efficacy and safety. This is shown among others with St. John's wort and cyclosporine, Ginkgo biloba and warfarin, garlic and saquinavir, Allium sativum and chloropropamid, and milk thistle and indinavir [4 -6].As herbal preparations consist of multiple, often unidentified, biological active or inactive constituents, the chance that an interaction for a single drug might be higher towards a complex herbal product than towards another single drug. Furthermore, the combined effect of all constituents together in a herb may be different from the anticipated sum effect evaluated from single isolated constituents. This emphasizes the importance of performing interaction studies with crude herbal extracts as an important supplement to studies on isolated herbal fractions.The cytochrome P450 2D6 (CYP2D6) enzyme is anticipated to be involved in the metabolism of about 25% of all used drugs, including cardiovascular drugs, β -adrenergic blocking agents, tricyclic antidepressants, analgesics a...

The purpose of this study was to investigate the in vitro inhibition potential of the three purified herbal constituents tetrahydropalmatine (Tet), neferine (Nef) and berberine (Ber) towards recombinant human CYP1A2, CYP2D6 and CYP3A4 metabolic activities. In vitro incubations were performed with phenacetin, dextromethorphan and testosterone, respectively, as CYP substrates and their metabolites were determined by validated HPLC methods. Positive control inhibitors were run for each CYP in all incubation series. Inhibition was expressed by IC₅₀ values. All herbal constituents demonstrated some, but variable, inhibition potencies towards the investigated CYP enzymes. CYP2D6 was the most sensitive for inhibition and then mainly by Tet and Ber with IC₅₀ values of 3.04 ± 0.26 µM and 7.40 ± 0.36 µM, respectively. CYP3A4 and especially CYP1A2 were inhibited to a much smaller extent by all constituents. Neferine showed the lowest overall interaction potential towards the CYP enzymes investigated. The CYP inhibition potential for the purified constituents could be related to their chemical structures. No clinical significant metabolic interaction seems likely to occur between the CYP enzymes and herbal constituents tested, with a possible exception for the CYP2D6 inhibition by Tet and Ber.

Six clones of RHODIOLA ROSEA, obtained from plants originating from widely different areas in Norway, were investigated for their IN VITRO inhibitory potential on CYP3A4-mediated metabolism and P-gp efflux transport activity. Presumed active constituents in the ethanol extracts of the different clones were quantified. C-DNA baculovirus expressed CYP3A4 and Caco-2 cells were used for inhibitory assays, and as positive control inhibitors ketoconazole and verapamil were applied, respectively. A validated HPLC methodology was used to quantify the formation of 6-beta-OH-testosterone and scintillation counting was used to quantify the transport of (3)H-digoxin in Caco-2 cells. All clones showed potent inhibition of CYP3A4 and P-gp activities, with IC (50) values ranging from 1.7 to 3.1 microg/mL and from 16.7 to 51.7 microg/mL, respectively, being below that reported for other herbs and some known classic drug inhibitors, such as St. John's wort and fluoxetine. RHODIOLA ROSEA might thus be a candidate for clinically relevant drug interactions. The concentration of presumed biologically active constituents in the different clones varied considerably, but this variation was not related to the clones' inhibitory potential on CYP3A4 or P-gp activities. Other constituents might thus be responsible for the observed inhibitory properties. The place of origin seemed to be of minor importance for CYP3A4 or P-gp inhibition.