Modulation of Major Human Liver Microsomal Cytochromes P450 by Component Alkaloids of Goldenseal: Time-Dependent Inhibition and Allosteric Effects.

Botanical and other natural products (NPs) are often coconsumed with prescription medications, presenting a risk for cytochrome P450 (P450)-mediated NP-drug interactions. The NP goldenseal (Hydrastis canadensis) has exhibited antimicrobial activities in vitro attributed to isoquinoline alkaloids contained in the plant, primarily berberine, (-)-ß-hydrastine, and to a lesser extent, hydrastinine. These alkaloids contain methylenedioxyphenyl rings, structural alerts with potential to inactivate P450s through formation of metabolic intermediate complexes. Time-dependent inhibition experiments were conducted to evaluate their ability to inhibit major P450 activities in human liver microsomes by using a cocktail of isozyme-specific substrate probes. Berberine inhibited CYP2D6 (dextromethorphan O-demethylation; K I = 2.7 µM, kinact = 0.065 minute-1) and CYP3A4/5 (midazolam 1'-hydroxylation; K I = 14.8 µM, kinact = 0.019 minute-1); (-)-ß-hydrastine inhibited CYP2C9 (diclofenac 4'-hydroxylation; K I = 49 µM, kinact = 0.036 minute-1), CYP2D6 (K I > 250 µM, kinact > 0.06 minute-1), and CYP3A4/5 (K I = 28 µM, kinact = 0.056 minute-1); and hydrastinine inhibited CYP2D6 (K I = 37 µM, kinact = 0.049 minute-1) activity. Berberine additionally exhibited allosteric effects on midazolam hydroxylation, showing both positive and negative heterotropic cooperativity. Experiments with recombinant isozymes showed that berberine activated midazolam 1'-hydroxylation by CYP3A5, lowering K m(app), but showed mixed inhibition and negative cooperativity toward this reaction when catalyzed by CYP3A4. Berberine inactivated CYP3A4 at a much faster rate than CYP3A5 and was a noncompetitive inhibitor of midazolam 4-hydroxylation by CYP3A4 but a strong mixed inhibitor of the CYP3A5 catalyzed reaction. These complex kinetics should be considered when extrapolating the risk for NP-drug interactions involving goldenseal. SIGNIFICANCE STATEMENT: Robust kinetic parameters were determined for the reversible and time-dependent inhibition of CYP2C9, CYP2D6, and CYP3A4/5 activities in human liver microsomes by major component isoquinoline alkaloids contained in the botanical natural product goldenseal. The alkaloid berberine also exhibited opposing, isozyme-specific allosteric effects on midazolam hydroxylation mediated by recombinant CYP3A4 (inhibition) and CYP3A5 (activation). These data will inform the development of a physiologically based pharmacokinetic model that can be used to predict potential clinically relevant goldenseal-drug interactions.

A new LC-MS assay for the quantitative analysis of vitamin K metabolites in human urine.

Vitamin K (VK), in both its phylloquinone and menaquinone forms, has been hypothesized to undergo ω- and ß-oxidation on its hydrophobic side chain in order to generate the observed urinary metabolites, K acid I and K acid II, which are excreted primarily as glucuronide conjugates. Synthetic standards of K acid I, K acid II, and a putative intermediate metabolite, menaquinone (MK)1 ω-COOH, were used to develop and optimize a new atmospheric pressure negative chemical ionization LC-MS/MS assay for the quantitation of these compounds in urine from untreated individuals and subjects treated with a high dose VK supplement. VK catabolites were extracted from urine, deconjugated, and converted to their methyl ester derivatives using previously reported methodology. The assay showed a high degree of sensitivity, with limits of detection below 10-50 fmol of metabolite per milliliter of urine, as well as an inter-assay precision of 8-12%. Metabolite standards provided unambiguous evidence for MK1 ω-COOH as a new human urinary metabolite of VK. This assay provides a minimally invasive, highly sensitive, and specific alternative for monitoring VK status in humans.

A cellular system for quantitation of vitamin K cycle activity: structure-activity effects on vitamin K antagonism by warfarin metabolites.

Warfarin and other 4-hydroxycoumarins inhibit vitamin K epoxide reductase (VKOR) by depleting reduced vitamin K that is required for posttranslational modification of vitamin K-dependent clotting factors. In vitro prediction of the in vivo potency of vitamin K antagonists is complicated by the complex multicomponent nature of the vitamin K cycle. Here we describe a sensitive assay that enables quantitative analysis of γ-glutamyl carboxylation and its antagonism in live cells. We engineered a human embryonic kidney (HEK) 293-derived cell line (HEK 293-C3) to express a chimeric protein (F9CH) comprising the Gla domain of factor IX fused to the transmembrane and cytoplasmic regions of proline-rich Gla protein 2. Maximal γ-glutamyl carboxylation of F9CH required vitamin K supplementation, and was dose-dependently inhibited by racemic warfarin at a physiologically relevant concentration. Cellular γ-glutamyl carboxylation also exhibited differential VKOR inhibition by warfarin enantiomers (S > R) consistent with their in vivo potencies. We further analyzed the structure-activity relationship for inhibition of γ-glutamyl carboxylation by warfarin metabolites, observing tolerance to phenolic substitution at the C-5 and especially C-6, but not C-7 or C-8, positions on the 4-hydroxycoumarin nucleus. After correction for in vivo concentration and protein binding, 10-hydroxywarfarin and warfarin alcohols were predicted to be the most potent inhibitory metabolites in vivo.

CYP4F2 is a vitamin K1 oxidase: An explanation for altered warfarin dose in carriers of the V433M variant.

Genetic polymorphisms in VKORC1 and CYP2C9, genes controlling vitamin K(1) (VK1) epoxide reduction and (S)-warfarin metabolism, respectively, are major contributors to interindividual variability in warfarin dose. The V433M polymorphism (rs2108622) in CYP4F2 has also been associated with warfarin dose and speculatively linked to altered VK1 metabolism. Therefore, the purpose of the present study was to determine the role of CYP4F2 and the V433M polymorphism in the metabolism of VK1 by human liver. In vitro metabolic experiments with accompanying liquid chromatography-tandem mass spectrometry analysis demonstrated that recombinant CYP4F2 (Supersomes) and human liver microsomes supplemented with NADPH converted VK1 to a single product. A screen of all commercially available P450 Supersomes showed that only CYP4F2 was capable of metabolizing VK1 to this product. Steady-state kinetic analysis with recombinant CYP4F2 and with human liver microsomes revealed a substrate K(m) of 8 to 10 microM. Moreover, anti-CYP4F2 IgG, as well as several CYP4F2-selective chemical inhibitors, substantially attenuated the microsomal reaction. Finally, human liver microsomes genotyped for rs2108622 demonstrated reduced vitamin K(1) oxidation and lower CYP4F2 protein concentrations in carriers of the 433M minor allele. These data demonstrate that CYP4F2 is a vitamin K(1) oxidase and that carriers of the CYP4F2 V433M allele have a reduced capacity to metabolize VK1, secondary to an rs2108622-dependent decrease in steady-state hepatic concentrations of the enzyme. Therefore, patients with the rs2108622 polymorphism are likely to have elevated hepatic levels of VK1, necessitating a higher warfarin dose to elicit the same anticoagulant response.