The inhibitory effect of Sambucus nigra on CYP3A4 mediated metabolism in vitro
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Introduction: Herbal medicines are today becoming increasingly popular worldwide and most people consuming herbal medicine think of it as natural and thereby without side effects and risk for interactions with drugs. Herbs contain a number of constituents that can give a variety of effects. Sambucus nigra is one of many herbs that have become popular and well known in Norway. The aim of this thesis was to evaluate the inhibition potential of Sambucus nigra (using the product Sambucus Force) on CYP3A4 mediated metabolism in vitro. Method: A water extract of Sambucus Force was used in the experiments. A cDNAbaculovirus expressed CYP3A4 was used for metabolic studies with testosterone as substrate. The formation of 6-β-OH-testosterone was quantified by a validated HPLC method. The extract of Sambucus Force was investigated at 8 different concentrations and IC50 was estimated from the inhibition plots. Different concentrations of Sambucus Force extracts were also investigated to reveal whether Sambucus Force showed a mechanism-based inhibition of CYP3A4. Furthermore an inhibition profile was made by incubating IC25, IC50 and IC75 concentrations of Sambucus Force extracts with 5 different concentrations of testosterone. Ketoconazole was used aspositive inhibition control. Results: The IC50 value for Sambucus Force was estimated to be 1.2 mg/mL with an IC50/IC25 ratio of 2.4. The mechanism-based inhibition experiment showed that Sambucus Force was time- and concentration dependent but not NADPH dependent.The inhibition profile study showed a Km- and Vmax- value of 42.5 μM and 125.0pmol 6-β-OH-testosterone/ pmol CYP-1 x min-1, and Km(app) and Vmax(app)- values of41.4 μM and 59.2 pmol 6-β-OH-testosterone/ pmol CYP-1 x min-1 using IC50 concentration of Sambucus Force. Conclusions: Sambucus nigra did not fulfil the criteria as a mechanism-based inhibitor and the inhibition profile showed that Sambucus nigra is a non-competitive inhibitor of the CYP3A4 metabolism. The high IC50 value of Sambucus nigraindicates a minimal risk to inhibit liver CYP3A4 enzymes. However, the concentration estimated to occur in the gastrointestinal tracks shows that Sambucusnigra might inhibit CYP3A4 in the small intestines and thereby increasing the bioavailability of some CYP3A4 substrates. Echinacea purpurea, a constituent in Sambucus Force might be responsible for some of the inhibitory effect on CYP3A4.