Mechanism-Based Inactivation of Human Liver Microsomal CYP3A4 by Rutaecarpine and Limonin from Evodia Fruit Extract

Comparative metabolism of aschantin in human and animal hepatocytes

Aschantin, a tetrahydrofurofuran lignan with a 1,3-benzodioxole group derived from Flos Magnoliae, exhibits antioxidant, anti-inflammatory, cytotoxic, and antimicrobial activities. This study compared the metabolic profiles of aschantin in human, dog, mouse, and rat hepatocytes using liquid chromatography-high-resolution mass spectrometry. The hepatic extraction ratio of aschantin among the four species was 0.46-0.77, suggesting that it undergoes a moderate-to-extensive degree of hepatic metabolism. Hepatocyte incubation of aschantin produced 4 phase 1 metabolites, including aschantin catechol (M1), O-desmethylaschantin (M2 and M3), and hydroxyaschantin (M4), and 14 phase 2 metabolites, including O-methyl-M1 (M5 and M6) via catechol O-methyltransferase (COMT), six glucuronides of M1, M2, M3, M5, and M6, and six sulfates of M1, M2, M3, M5, and M6. Enzyme kinetic studies using aschantin revealed that the production of M1, a major metabolite, via O-demethylenation is catalyzed by cytochrome 2C8 (CYP2C8), CYP2C9, CYP2C19, CYP3A4, and CYP3A5 enzymes; the formation of M2 (O-desmethylaschantin) is catalyzed by CYP2C9 and CYP2C19; and the formation of M4 is catalyzed by CYP3A4 enzyme. Two glutathione (GSH) conjugates of M1 were identified after incubation of aschantin with human and animal liver microsomes in the presence of nicotinamide adenine dinucleotide phosphate and GSH, but they were not detected in the hepatocytes of all species. In conclusion, aschantin is extensively metabolized, producing 18 metabolites in human and animal hepatocytes catalyzed by CYP, COMT, UDP-glucuronosyltransferase, and sulfotransferase. These results can help in clarifying the involvement of metabolizing enzymes in the pharmacokinetics and drug interactions of aschantin and in elucidating GSH conjugation associated with the reactive intermediate formed from M1 (aschantin catechol).

Mechanism-Based Inactivation of Cytochrome P450 3A by Evodol

1. Evodol is one of the furanoids isolated from the fruits of Evodia rutaecarpa that has been widely prescribed for the treatment of gastrointestinal diseases in China. The aim of this study was to investigate the inhibitory effect of evodol on CYP3A.2. A 30-min preincubation of evodol with human liver microsomes raised an obvious left IC₅₀ shift, 3.9-fold for midazolam 1'-hydroxylation and 3.2-fold for testosterone 6β-hydroxylation. Evodol inactivated CYP3A in a time-, concentration- and NADPH-dependent manner, with K_I and k_inact of 5.1 μM and 0.028 min^-1 for midazolam 1'-hydroxylation and 3.0 μM and 0.022 min^-1 for testosterone 6β-hydroxylation.3. Co-incubation of ketoconazole attenuated the inactivation while inclusion of glutathione (GSH) and catalase/superoxide dismutase displayed no such protection.4. cis-Butene-1, 4-dial (BDA) intermediate derived from evodol were trapped by glutathione and N-acetyl-lysine in microsomes and characterized by HR-MS spectra. The BDA intermediate was believed to play a key role in CYP3A inactivation. CYP3A4 and 2C9 were the primary enzymes contributing to the bioactivation of evodol.5. To sum up, for the first time evodol was characterized as a mechanism-based inactivator of CYP3A.

Molecular mechanisms of hepatotoxicity induced by compounds occurring in Evodiae Fructus

Evodiae Fructus (EF) is a common herbal medicine with thousands of years of medicinal history in China, which has been demonstrated with many promising pharmacological effects on cancer, cardiovascular diseases and Alzheimer's disease. However, there have been increasing reports of hepatotoxicity associated with EF consumption. Unfortunately, in a long term, many implicit constituents of EF as well as their toxic mechanisms remain poorly understood. Recently, metabolic activation of hepatotoxic compounds of EF to generate reactive metabolites (RMs) has been implicated. Herein, we capture metabolic reactions relevant to hepatotoxicity of these compounds. Initially, catalyzed by the hepatic cytochrome P450 enzymes (CYP450s), the hepatotoxic compounds of EF are oxidized to generate RMs. Subsequently, the highly electrophilic RMs could react with nucleophilic groups contained in biomolecules, such as hepatic proteins, enzymes, and nucleic acids to form conjugates and/or adducts, leading to a sequence of toxicological consequences. In addition, currently proposed biological pathogenesis, including oxidative stress, mitochondrial damage and dysfunction, endoplasmic reticulum (ER) stress, hepatic metabolism disorder, and cell apoptosis are represented. In short, this review updates the knowledge on the pathways of metabolic activation of seven hepatotoxic compounds of EF and provides considerable insights into the relevance of proposed molecular hepatotoxicity mechanisms from a biochemical standpoint, for the purpose of providing a theoretical guideline for the rational application of EF in clinics.

A Green Extraction Method to Achieve the Highest Yield of Limonin and Hesperidin from Lime Peel Powder (Citrus aurantifolia)

Green extraction is aimed at reducing energy consumption by using renewable plant sources and environmentally friendly bio-solvents. Lime (Citrus aurantifolia) is a rich source of flavonoids (e.g., hesperidin) and limonoids (e.g., limonin). Manufacturing of lime products (e.g., lime juice) yields a considerable amount of lime peel as food waste that should be comprehensively exploited. The aim of this study was to develop a green and simple extraction method to acquire the highest yield of both limonin and hesperidin from the lime peel. The study method included ethanolic-aqueous extraction and variable factors, i.e., ethanol concentrations, pH values of solvent, and extraction temperature. The response surface methodology was used to optimize extraction conditions. The concentrations of limonin and hesperidin were determined by using UHPLC-MS/MS. Results showed that the yields of limonin and hesperidin significantly depended on ethanol concentrations and extraction temperature, while pH value had the least effect. The optimal extraction condition with the highest amounts of limonin and hesperidin was 80% ethanol at pH 7, 50 °C, which yields 2.072 and 3.353 mg/g of limonin and hesperidin, respectively. This study illustrates a green extraction process using food waste, e.g., lime peel, as an energy-saving source and ethanol as a bio-solvent to achieve the highest amount of double bioactive compounds.

In Vitro and In Vivo Studies of Metabolic Activation of Marrubiin, a Bioactive Constituent from Marrubium Vulgare

Marrubiin, a furanoid compound, is a well-known diterpenoid lactone isolated from Marrubium vulgare, which displays a wide spectrum of pharmacological effects and potential hepatotoxicity. Considering that marrubiin contains a structural alert, furan ring, metabolic activation may be one of the major metabolic pathways, and the reactive metabolite may be involved in the hepatotoxicity. The present study was carried out to investigate the bioactivation mechanism of marrubiin in rats and humans. Marrubiin was initially metabolized into cis-butene-1,4-dial intermediate, which was readily trapped by glutathione (GSH) and N-acetyl-lysine (NAL) in the microsomal incubations supplemented with NADPH. A total of nine conjugates were detected and identified by high-resolution mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. M1-M3 and M6 and M7 were characterized as mono-GSH conjugates, and M4 and M5 were identified as bis-GSH conjugates. M8 and M9 were identified as NAL conjugates. In rat bile, five GSH conjugates (M1-M3; M6 and M7) were detected. M1, M8, and M9 were chemically synthesized, and their structures were characterized by 13C NMR. Sulfaphenazole, ticlopidine, and ketoconazole displayed significant inhibitory effect on the bioactivation of marrubiin. Further phenotyping revealed that CYP2C9, CYP2C19, and CYP3A4 were the primary enzymes catalyzing the bioactivation of marrubiin. The current study provides evidence for the CYP-dominated bioactivation of marrubiin to the corresponding cis-butene-1,4-dial intermediate, which enables us to better understand the potential side effects caused by marrubiin.

Change in the active component of processed Tetradium ruticarpum extracts leads to improvement in efficacy and toxicity attenuation

ETHNOPHARMACOLOGICAL RELEVANCE

The dried and nearly ripe fruits of Tetradium ruticarpum (A. Juss.) T.G. Hartley (TR) have long been used in treating headache and gastrointestinal disorders in oriental medicine. TR is usually processed by stir-frying with licorice extract before use. Although processing procedure is considered as the way to relieve pungent smell, reduce toxicity, and improve efficacy, its effects on TR's toxicity and efficacy and bioactive compound profiles are largely unknown.

AIM OF THE STUDY

The purposes of the study are to evaluate the acute toxicity, efficacy and variation of toxic and effective components of TR before and after processing, and to explore the possible mechanism of how the processing procedure affect the quality of TR as a herbal medicine.

MATERIALS AND METHODS

Volatile oil, aqueous extract and ethanol extract of raw and processed TR were tested for their acute toxicity, analgesic, and anti-inflammatory effects in mouse models, respectively. To identify potential toxic and effective components, the extracts were analyzed with gas chromatography-mass spectrometry and ultra-performance liquid chromatography - quadrupole time-of-flight mass spectrometry, followed by fold-change-filtering analysis.

RESULTS

LD₅₀ and LD₅ tests indicated that although the aqueous extract has higher toxicity than volatile oil and ethanol extract, the use of TR is safe under the recommended does. The processing procedure could effectively decrease the toxicity of all three extracts with the largest decrease in volatile oil, which is likely due to the loss of volatile compounds during processing. Analgesic and anti-inflammatory studies suggested that volatile oil and ethanol extract of TR have better efficacy than the aqueous extract and the processing procedure significantly enhanced the efficacy of these two former extracts, whereas processing showed no substantially effects on the bioactivities of aqueous extract. Integrated analysis of animal trial and chromatographic analyses indicated that indole and quinolone type alkaloids, limonoids, amides and 18β-glycyrrhetinic acid were identified as the potential main contributors of TR's efficacy, whereas hydroxy or acetoxy limonoid derivates and coumarins could be the major causes of toxicity. Moreover, the reduced toxicity and improved efficacy of the processed TR are liked due to the licorice ingredients and altered alkaloids with better solubility.

CONCLUSIONS

In summary, the integrated toxicity and efficacy analyses of volatile, aqueous and ethanol extracts of TR indicated that the processing procedure could effectively reduce its acute toxicity in all three extracts and enhance its analgesic and anti-inflammatory effects in volatile and ethanol extracts. The promising candidate compounds related to the toxicity and efficacy of TR were also identified. The results could expand our understanding of the value of the standard processing procedure of TR, be valuable to the quality control of TR manufacturing and administration, as well as support clinical rational and safety applications of this medicinal plant.

Clinical Pharmacokinetic Drug Interaction Potential of MenoAct851 in Adult, Female Healthy Volunteers

BACKGROUND

MenoAct851 (Varanasi BioResearch Pvt. Ltd., Varanasi, India) is a patented polyherbal formulation developed to manage menopause symptoms that can be taken along with other allopathic medicines.

OBJECTIVE

The present study aims to evaluate the drug interaction potential of MenoAct851 to inhibit cytochrome (CY) P450 in vitro in rats, and to measure its effects on simvastatin pharmacokinetic parameters in healthy human volunteers.

METHODS

CYP450-carbon monoxide assay of MenoAct851 was performed in rat liver microsomes to calculate the percentage inhibition. Fluorometric assays of CYP3A4 and CYP2D6 determined half maximal inhibitory concentration value. A double-blind, randomized, placebo-controlled drug interaction study of MenoAct851 was conducted in 24 healthy adult female volunteers aged 25 to 50 years. The selected volunteers were randomized to receive placebo or MenoAct851 500 mg BID PO for 14 days. On the 15th day, each group received 40 mg single-dose simvastatin. Blood samples were drawn at different intervals to measure simvastatin pharmacokinetic parameters.

RESULTS

The mean (SD) CYP450 concentration of the diluted microsome sample was calculated and found to be 0.405 (0.12) nmol/mg. The inhibitory potential of MenoAct851 (41.16% [1.24%]) was found to be less than ketoconazole. Half maximal inhibitory concentration values of MenoAct851 on CYP3A4 and CYP2D6 were 11.96 (1.04) µg/mL and 15.24 (0.58) µg/mL, respectively, but they were higher than respective positive controls. There was no statistically significant difference between MenoAct851 and placebo groups concerning the pharmacokinetic parameters such as Cmax, Tmax, t½, and mean residence time of simvastatin; however, AUC showed a significant difference (P < 0.05) between the groups.

CONCLUSIONS

MenoAct851 produced weaker interaction potential with CYP3A4 and CYP2D6 substrates based on in vitro assays, but the findings of clinical pharmacokinetic analysis indicate that MenoAct851 increased the AUC of simvastatin and simvastatin hydroxy acid. Therefore, coadministration of MenoAct851 might lead to drug-herb interaction, thereby affecting the therapeutic effect of CYP3A4 substrates. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX).

Traditional uses, phytochemistry, pharmacology, pharmacokinetics and toxicology of the fruit of Tetradium ruticarpum: A review

ETHNOPHARMACOLOGICAL RELEVANCE

The fruit of Tetradium ruticarpum (FTR) known as Tetradii fructus or Evodiae fructus (Wu-Zhu-Yu in Chinese) is a versatile herbal medicine which has been prescribed in Chinese herbal formulas and recognized in Japanese Kampo. FTR has been clinically used to treat various diseases such as headache, vomit, diarrhea, abdominal pain, dysmenorrhea and pelvic inflammation for thousands of years.

AIM OF THE REVIEW

The present paper aimed to provide comprehensive information on the ethnopharmacology, phytochemistry, pharmacology, pharmacokinetics, drug interaction and toxicology of FTR in order to build up a foundation on the mechanism of ethnopharmacological uses as well as to explore the trends and perspectives for further studies.

MATERIALS AND METHODS

This review collected the literatures published prior to July 2020 on the phytochemistry, pharmacology, pharmacokinetics and toxicity of FTR. All relevant information on FTR was gathered from worldwide accepted scientific search engines and databases, including Web of Science, PubMed, Elsevier, ACS, ResearchGate, Google Scholar, and Chinese National Knowledge Infrastructure (CNKI). Information was also obtained from local books, PhD. and MSc. Dissertations as well as from Pharmacopeias.

RESULTS

FTR has been used as an herbal medicine for centuries in East Asia. A total of 165 chemical compounds have been isolated so far and the main chemical compounds of FTR include alkaloids, terpenoids, flavonoids, phenolic acids, steroids, and phenylpropanoids. Crude extracts, processed products (medicinal slices) and pure components of FTR exhibit a wide range of pharmacological activities such as antitumor, anti-inflammatory, antibacterial, anti-obesity, antioxidant, insecticide, regulating central nervous system (CNS) homeostasis, cardiovascular protection. Furthermore, bioactive components isolated from FTR can induce drug interaction and hepatic injury.

CONCLUSIONS

Therapeutic potential of FTR has been demonstrated with the pharmacological effects on cancer, inflammation, cardiovascular diseases, CNS, bacterial infection and obesity. Pharmacological and pharmacokinetic studies of FTR mostly focus on its main active alkaloids. Further in-depth studies on combined medication and processing approaches mechanisms, pharmacological and toxic effects not limited to the alkaloids, and toxic components of FTR should be designed.

Mechanism-based inactivation of cytochrome P450 enzymes by natural products based on metabolic activation

Cytochrome P450 enzymes (P450 enzymes) are the most common and important phase I metabolic enzymes and are responsible for the majority of the metabolism of clinical drugs and other xenobiotics. Drug-drug interactions (DDIs) can occur when the activities of P450 enzymes are inhibited. In particular, irreversible inhibition of P450 enzymes may lead to severe adverse interactions, compared to reversible inhibition. Many natural products have been shown to be irreversible inhibitors of P450 enzymes. The risks for intake of naturally occurring irreversible P450 enzyme inhibitors have been rising due to the rapid growth of the global consumption of natural products. Irreversible inhibition is usually called mechanism-based inactivation, which is time-, concentration- and NADPH- dependent. Generally, the formation of electrophilic intermediates is fundamental for the inactivation of P450 enzymes. This review comprehensively classifies natural P450 enzyme inactivators, including terpenoids, phenylpropanoids, flavonoids, alkaloids, and quinones obtained from herbs or foods. Moreover, the structure - activity correlations according to the IC₅₀ (or K_i) values reported in the literature as well as the underlying mechanisms based on metabolic activation are highlighted in depth.

Processing and Polyherbal Formulation of Tetradium ruticarpum (A. Juss.) Hartley: Phytochemistry, Pharmacokinetics, and Toxicity

Herbal medicine is a major part of traditional Chinese medicine (TCM), which is evolved as a system of medical practice from ancient China. The use of herbal medicine is mainly based on practice and theories and concepts rooted in ancient philosophy. In the era of evidence-based medicine, it is essential to accurately evaluate herbal remedy with standard/modern medical practice approaches. Tetradium ruticarpum (A. Juss.) Hartley (TR), a medicinal plant with diversify bioactive components, has been broadly used to treat pain and gastrointestinal disorders in TCM. However, TR has also been reported to have potential toxicity by long-term use or excessive doses, though the associated compounds are yet to be identified. TR is usually processed, and/or combined with other herbs in TCM formulas in order to achieve a synergistic effect or reduce its toxicity. Since processing or polyherbal formulation of TR may lead to changes in its chemical composition and contents, quality, efficacy and toxicity, comparison of TR samples before and after processing, as well as its combination with other medicines, would provide useful knowledge of bioactive compounds, efficacy and toxicity of this valuable medicinal plant. Here we reviewed the recent studies about the phytochemistry, pharmacokinetic behaviors and toxicity of TR under various processing or polyherbal formulation conditions, which would expand our understanding of mechanisms of TR's efficacy and toxicity and be valuable for quality control in industrial manufacturing, future medicinal research, and safety and rational use of TR in TCM.

Structural Perspectives of the CYP3A Family and Their Small Molecule Modulators in Drug Metabolism

Cytochrome P450 enzymes function to catalyze a wide range of reactions, many of which are critically important for drug response. Members of the human cytochrome P450 3A (CYP3A) family are particularly important in drug clearance, and they collectively metabolize more than half of all currently prescribed medications. The ability of these enzymes to bind a large and structurally diverse set of compounds increases the chances of their modulating or facilitating drug metabolism in unfavorable ways. Emerging evidence suggests that individual enzymes in the CYP3A family play discrete and important roles in catalysis and disease progression. Here we review the similarities and differences among CYP3A enzymes with regard to substrate recognition, metabolism, modulation by small molecules, and biological consequence, highlighting some of those with clinical significance. We also present structural perspectives to further characterize the basis of these comparisons.

Limonin: A Review of Its Pharmacology, Toxicity, and Pharmacokinetics

Limonin is a natural tetracyclic triterpenoid compound, which widely exists in Euodia rutaecarpa (Juss.) Benth., Phellodendron chinense Schneid., and Coptis chinensis Franch. Its extensive pharmacological effects have attracted considerable attention in recent years. However, there is no systematic review focusing on the pharmacology, toxicity, and pharmacokinetics of limonin. Therefore, this review aimed to provide the latest information on the pharmacology, toxicity, and pharmacokinetics of limonin, exploring the therapeutic potential of this compound and looking for ways to improve efficacy and bioavailability. Limonin has a wide spectrum of pharmacological effects, including anti-cancer, anti-inflammatory and analgesic, anti-bacterial and anti-virus, anti-oxidation, liver protection properties. However, limonin has also been shown to lead to hepatotoxicity, renal toxicity, and genetic damage. Moreover, limonin also has complex impacts on hepatic metabolic enzyme. Pharmacokinetic studies have demonstrated that limonin has poor bioavailability, and the reduction, hydrolysis, and methylation are the main metabolic pathways of limonin. We also found that the position and group of the substituents of limonin are key in affecting pharmacological activity and bioavailability. However, some issues still exist, such as the mechanism of antioxidant activity of limonin not being clear. In addition, there are few studies on the toxicity mechanism of limonin, and the effects of limonin concentration on pharmacological effects and toxicity are not clear, and no researchers have reported any ways in which to reduce the toxicity of limonin. Therefore, future research directions include the mechanism of antioxidant activity of limonin, how the concentration of limonin affects pharmacological effects and toxicity, finding ways to reduce the toxicity of limonin, and structural modification of limonin—one of the key methods necessary to enhance pharmacological activity and bioavailability.

Effect of Naltrexone Hydrochloride on Cytochrome P450 1A2, 2C9, 2D6, and 3A4 Activity in Human Liver Microsomes

BACKGROUND AND OBJECTIVE

Cytochrome P450 (CYP) 1A2, 2C9, 2D6, and 3A4 are the most important phase I drug-metabolizing enzymes in the liver, but there is a dearth of literature available on the effects of naltrexone hydrochloride on these major enzymes present in the human liver. Thus, in the present study, the effect of naltrexone hydrochloride on the activity of CYP1A2, 2C9, 2D6, and 3A4 using human liver microsomes (HLM) was investigated.

METHODS

A selective probe for CYP1A2, 2C9, 2D6, and 3A4 was incubated with HLM with or without naltrexone hydrochloride. Phenacetin O-deethylation, tolbutamide 4-hydroxylation, dextromethorphan O-demethylation, and testosterone 6β-hydroxylation reactions were monitored for enzyme activity.

RESULTS

The activity of all the studied CYP enzymes except 1A2 was significantly inhibited by naltrexone hydrochloride 1 µM. Furthermore, 1 µM naltrexone hydrochloride inhibited CYP3A4 enzyme activity, the most by 37.9% followed by CYP2C9 (36.5%) and CYP2D6 (31.8%). The CYP2C9 and CYP2D6 metabolic activities were greatly affected by naltrexone hydrochloride, which even at the lowest concentration of naltrexone hydrochloride (0.01 µM) significantly decreased the metabolic activity by 34.9 and 16.0%, respectively. The half maximal inhibition concentration (IC₅₀) values for CYP2C9 and CYP2D6 inhibition were 3.40 ± 1.78 and 5.92 ± 1.58 µM, respectively.

CONCLUSION

These outcomes advocate that there is a great possibility of drug interactions resulting from the concurrent administration of naltrexone hydrochloride with actives that are metabolized by these CYP enzymes, particularly CYP2C9 and CYP2D6. Nevertheless, further clarification is needed through detailed in vivo pharmacokinetic studies.

Detection and Structural Characterization of Nucleophiles Trapped Reactive Metabolites of Limonin Using Liquid Chromatography-Mass Spectrometry

Limonin (LIM), a furan-containing limonoid, is one of the most abundant components of Dictamnus dasycarpus Turcz. Recent studies demonstrated that LIM has great potential for inhibiting the activity of drug-metabolizing enzymes. However, the mechanisms of LIM-induced enzyme inactivation processes remain unexplored. The main objective of this study was to identify the reactive metabolites of LIM using liquid chromatography-mass spectrometry. Three nucleophiles, glutathione (GSH), N-acetyl cysteine (NAC), and N-acetyl lysine (NAL), were used to trap the reactive metabolites of LIM in in vitro and in vivo models. Two different types of mass spectrometry, a hybrid quadrupole time-of-flight (Q-TOF) mass spectrometry and a LTQ velos Pro ion trap mass spectrometry, were employed to acquire structural information of nucleophile adducts of LIM. In total, six nucleophile adducts of LIM (M1-M6) with their isomers were identified; among them, M1 was a GSH and NAL conjugate of LIM, M2-M4 were glutathione adducts of LIM, M5 was a NAC and NAL conjugate of LIM, and M6 was a NAC adduct of LIM. Additionally, CYP3A4 was found to be the key enzyme responsible for the bioactivation of limonin. This metabolism study largely facilitates the understanding of mechanisms of limonin-induced enzyme inactivation processes.

Metabolism-mediated interaction potential of standardized extract of Tinospora cordifolia through rat and human liver microsomes

Objective:

Tinospora cordifolia is used for treatment of several diseases in Indian system of medicine. In the present study, the inhibition potential of T. cordifolia extracts and its constituent tinosporaside to cause herb-drug interactions through rat and human liver cytochrome enzymes was evaluated.

Materials and Methods:

Bioactive compound was quantified through reverse phase high-performance liquid chromatography, to standardize the plant extracts and interaction potential of standardized extract. Interaction potential of the test sample was evaluated through cytochrome P450-carbon monoxide complex (CYP450-CO) assay with pooled rat liver microsome. Influence on individual recombinant human liver microsomes such as CYP3A4, CYP2D6, CYP2C9, and CYP1A2 isozymes was analyzed through fluorescence microplate assay, and respective IC₅₀ values were determined.

Results:

The content of tinosporaside was found to be 1.64% (w/w) in T. cordifolia extract. Concentration-dependent inhibition was observed through T. cordifolia extract. Observed IC₅₀ (μg/ml) value was 136.45 (CYP3A4), 144.37 (CYP2D6), 127.55 (CYP2C9), and 141.82 (CYP1A2). Tinosporaside and extract showed higher IC₅₀ (μg/ml) value than the known inhibitors. T. cordifolia extract showed significantly less interaction potential and indicates that the selected plant has not significant herb-drug interactions relating to the inhibition of major CYP450 isozymes.

Conclusions:

Plant extract showed significantly higher IC₅₀ value than respective positive inhibitors against CYP3A4, 2D6, 2C9, and 1A2 isozymes. Consumption of T. cordifolia may not cause any adverse effects when consumed along with other xenobiotics.

Inhibitory Effects of Dimethyllirioresinol, Epimagnolin A, Eudesmin, Fargesin, and Magnolin on Cytochrome P450 Enzyme Activities in Human Liver Microsomes

Magnolin, epimagnolin A, dimethyllirioresinol, eudesmin, and fargesin are pharmacologically active tetrahydrofurofuranoid lignans found in Flos Magnoliae. The inhibitory potentials of dimethyllirioresinol, epimagnolin A, eudesmin, fargesin, and magnolin on eight major human cytochrome P450 (CYP) enzyme activities in human liver microsomes were evaluated using liquid chromatography-tandem mass spectrometry to determine the inhibition mechanisms and inhibition potency. Fargesin inhibited CYP2C9-catalyzed diclofenac 4′-hydroxylation with a K_i value of 16.3 μM, and it exhibited mechanism-based inhibition of CYP2C19-catalyzed [S]-mephenytoin 4′-hydroxylation (K_i, 3.7 μM; k_inact, 0.102 min⁻¹), CYP2C8-catalyzed amodiaquine N-deethylation (K_i, 10.7 μM; k_inact, 0.082 min⁻¹), and CYP3A4-catalyzed midazolam 1′-hydroxylation (K_i, 23.0 μM; k_inact, 0.050 min⁻¹) in human liver microsomes. Fargesin negligibly inhibited CYP1A2-catalyzed phenacetin O-deethylation, CYP2A6-catalyzed coumarin 7-hydroxylation, CYP2B6-catalyzed bupropion hydroxylation, and CYP2D6-catalyzed bufuralol 1′-hydroxylation at 100 μM in human liver microsomes. Dimethyllirioresinol weakly inhibited CYP2C19 and CYP2C8 with IC₅₀ values of 55.1 and 85.0 μM, respectively, without inhibition of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, and CYP3A4 activities at 100 μM. Epimagnolin A, eudesmin, and magnolin showed no the reversible and time-dependent inhibition of eight major CYP activities at 100 μM in human liver microsomes. These in vitro results suggest that it is necessary to investigate the potentials of in vivo fargesin-drug interaction with CYP2C8, CYP2C9, CYP2C19, and CYP3A4 substrates.

Rapid screening the potential mechanism-based inhibitors of CYP3A4 from Tripterygium wilfordi based on computer approaches combined with in vitro bioassay

CYP3A4 is the main human metabolizing enzyme, and many clinically relevant drug/herb-drug interactions (DDIs/HDIs) involving CYP3A4 are due to mechanism-based inhibition. In this study, pharmacophore model together with molecular docking (MD) are used to rapidly screen the potential CYP3A4 mechanism-based inhibitors from Tripterygium wilfordii, and in vitro experiments are conducted to validate the computational data. The results showed that the rate of computational prediction could be improved based on a combination of pharmacophore model and MD, and a combination of computational approaches might be a useful tool to identify potential mechanism-based inhibitor of CYP3A4 from herbal medicines.

Interaction potential of Trigonella foenum graceum through cytochrome P450 mediated inhibition

Objective:

The seeds of Trigonella foenum-graecum (TFG) (family: Leguminosae) are widely consumed both as a spice in food and Traditional Medicine in India. The present study was undertaken to evaluate the inhibitory effect of standardized extract of TFG and its major constituent trigonelline (TG) on rat liver microsome (RLM) and cytochrome P450 (CYP450) drug metabolizing isozymes (CYP3A4 and CYP2D6), which may indicate the possibility of a probable unwanted interaction.

Materials and Methods:

Reverse phase-high performance liquid chromatography method was developed to standardize the hydroalcoholic seed extract with standard TG. The inhibitory potential of the extract and TG was evaluated on RLM and CYP isozymes using CYP450-carbon monoxide (CYP450-CO) complex assay and fluorescence assay, respectively.

Results:

The content of TG in TFG was found to be 3.38% (w/w). The CYP-CO complex assay showed 23.32% inhibition on RLM. Fluorescence study revealed that the extract and the biomarker had some inhibition on CYP450 isozymes e.g. CYP3A4 and CYP2D6 (IC₅₀ values of the extract: 102.65 ± 2.63–142.23 ± 2.61 µg/ml and TG: 168.73 ± 4.03–180.90 ± 2.49 µg/ml) which was very less compared to positive controls ketoconazole and quinidine. Inhibition potential of TFG was little higher than TG but very less compared to positive controls.

Conclusions:

From the present study, we may conclude that the TFG or TG has very less potential to inhibit the CYP isozymes (CYP3A4, CYP2D6), so administration of this plant extract or its biomarker TG may be safe.

Pharmacokinetic study of isocorynoxeine metabolites mediated by cytochrome P450 enzymes in rat and human liver microsomes

Isocorynoxeine (ICN) is one of the major bioactive tetracyclic oxindole alkaloids found in Uncaria rhynchophylla (Miq.) Jacks. that is widely used for the treatment of hypertension, vascular dementia, and stroke. The present study was undertaken to assess the plasma pharmacokinetic characteristics of major ICN metabolites, and the role of simulated gastric and intestinal fluid (SGF and SIF), human and rat liver microsomes (HLMs and RLMs), and seven recombinant human CYP enzymes in the major metabolic pathway of ICN. A rapid, sensitive and accurate UHPLC/Q-TOF MS method was validated for the simultaneous determination of ICN and its seven metabolites in rat plasma after oral administration of ICN at 40mg/kg. It was found that 18.19-dehydrocorynoxinic acid (DCA) and 5-oxoisocorynoxeinic acid (5-O-ICA) were both key and predominant metabolites, rather than ICN itself, due to the rapid and extensive metabolism of ICN in vivo. The further study indicated that ICN was mainly metabolized in human or rat liver, and CYPs 2C19, 3A4 and 2D6 were the major enzymes responsible for the biotransformation of ICN to DCA and 5-O-ICA in human. These findings are of significance in understanding of the pharmacokinetic nature of tetracyclic oxindole alkaloids, and provide helpful information for the clinical co-administration of the herbal preparations containing U. rhynchophylla with antihypertensive drugs that are mainly metabolized by CYP3A4 and CYP2C19.

Constituents of Indonesian Medicinal Plant Averrhoa bilimbi and Their Cytochrome P450 3A4 and 2D6 Inhibitory Activities

As constituents of Averrhoa bilimbi leaves we identified three new compounds (1-3) together with 12 known ones (4-15); their inhibitory activities on cytochrome P450 3A4 (CYP3A4) and 2D6 (CYP2D6) were examined. Among the isolated compounds, the mixture of 1 and 2, and compounds 4 and 9 showed strong inhibition on CYP3A4, but mild or no inhibition on CYP2D6. These compounds revealed the characteristics of 1) time- and concentration-dependent inhibition, 2) requirement of NADPH for the inhibition, 3) no protection by nucleophiles, and 4) suppression of the inhibition by competitive inhibitor. Thus, they are suggested to be mechanism-based inactivators of CYP3A4 and CYP2D6. The kinetic parameters for the inactivation (kinact and KI) were 0.19 min–1 and 36.7 μM for the mixture of 1 and 2, 0.126 min–1 and 10.5 μM for 4, and 0.29 min–1 and 23.4 μM for 9.

Hepatoprotective effect of limonin, a natural limonoid from the seed of Citrus aurantium var. bigaradia, on D-galactosamine-induced liver injury in rats

Toll-like receptors have been implicated in inflammation and injury in various tissues and organs including the liver. We have investigated the effects of limonin isolated from the dichloromethane fraction of the seeds of bittersweet orange (Citrus aurantium var. bigaradia) in two dose levels (50 and 100 mg/kg) against D-galactosamine (D-GalN)-induced liver toxicity in comparison with standard silymarin treatment on Toll-like receptors expression and hepatic injury, using a well-established rat model of acute hepatic inflammation. The limonoids in the seeds of bittersweet orange were identified. Oral administration of limonin before D-GalN injection, significantly attenuated markers of hepatic damage (elevated liver enzyme activities and total bilirubin) and hepatic inflammation (TNF-α, infiltration of neutrophils), oxidative stress and expression of TLR-4 but not TLR-2 in D-GalN-treated rats. Limonin effects were similar in most aspects to that of the lignan silymarin. The higher dose of limonin (100 mg/kg) performed numerically better for AST and bilirubin, and both doses yielded similar results for ALT and GGT. While the lower dose of limonin (50 mg/kg) performed better against oxidative stress and liver structural damage as compared to the higher dose. Limonin exerts protective effects on liver toxicity associated with inflammation and tissue injury via attenuation of inflammation and reduction of oxidative stress.

Subchronic oral toxicity of evodia fruit powder in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Evodia, a fruit from Evodia rutaecarpa, has been used in oriental medicine, and since its various pharmaceutical actions, including anti-cancer activity, have become known, evodia has been widely used as a dietary supplement. However, information regarding its toxicity is limited.

MATERIALS AND METHODS

Evodia fruit from Evodia rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang (0, 25, 74, 222, 667, and 2000 mg/kg) was administered orally five times per week for 13 weeks. Clinical signs, body weight, food consumption, hematology, serum chemistry, urinalysis, vaginal cytology, sperm morphology, organ weight, and gross and histopathological findings were evaluated.

RESULTS

Urinary ketone body excretion was detected in males at 667 and 2000 mg/kg and in females at 2000 mg/kg. An increase in absolute/relative liver weight was observed in both sexes at 2000 mg/kg. Although levels of serum alanine aminotransferase, glucose, total cholesterol, and triglycerides were significantly reduced in males and/or females at 200 and/or 667 and 2000 mg/kg, all values were within normal ranges and were considered non-adverse. In addition, no treatment-related differences in body weight, food consumption, hematology, vaginal cytology, sperm morphology, or gross and histopathological examination were detected.

CONCLUSIONS

The subchronic no-observable-adverse-effect level for evodia fruit powder following oral administration in rats is greater than 2000 mg/kg.

Inhibitory effects of astaxanthin, β-cryptoxanthin, canthaxanthin, lutein, and zeaxanthin on cytochrome P450 enzyme activities

Astaxanthin, β-cryptoxanthin, canthaxanthin, lutein and zeaxanthin, the major xanthophylls, are widely used in food, medicine, and health care products. To date, no studies regarding the inhibitory effects of these xanthophylls on the nine CYPs isozymes have been reported. This study investigated the reversible and time-dependent inhibitory potentials of five xanthophylls on CYPs activities in vitro. The reversible inhibition results showed that the five compounds had only a weak inhibitory effect on the nine CYPs. Lutein did not inhibit the nine CYPs activities. Astaxanthin weakly inhibited CYP2C19, with an IC₅₀ of 16.2 μM; and β-cryptoxanthin weakly inhibited CYP2C8, with an IC₅₀ of 13.8 μM. In addition, canthaxanthin weakly inhibited CYP2C19 and CYP3A4/5, with IC₅₀ values of 10.9 and 13.9 μM, respectively. Zeaxanthin weakly inhibited CYP3A4/5, with an IC₅₀ of 15.5 μM. However, these IC₅₀ values were markedly greater than the Cmax values reported in humans. No significant IC₅₀ shift was observed in the time-dependent inhibition screening. Based on these observations, it is unlikely that these five xanthophylls from the diet or nutritional supplements alter the pharmacokinetics of drugs metabolized by CYPs. These findings provide some useful information for the safe use of these five xanthophylls in clinical practice.

Mechanism-based inhibition of recombinant human cytochrome P450 3A4 by tomato juice extract

This study investigates whether tomato juice can inhibit cytochrome P450 (CYP) 3A4-mediated drug metabolism. Three commercially available, additive-free tomato juices, along with homogenized fresh tomato, were analyzed for their ability to inhibit testosterone 6β-hydroxylation activity using human recombinant CYP3A4. Results were compared to that of grapefruit juice. Ethyl acetate extracts of the tomato juices moderately reduced residual activity of CYP3A4 testosterone 6β-hydroxylation activity by 19.3-26.2% with 0-min preincubation. Residual activity was strongly reduced by 69.9-83.5% at 20-min preincubation, a reduction similar to that of grapefruit juice extract, known to contain constituents of mechanism-based inhibitors. One juice extract (tomato juice C) showed irreversible dose- and preincubation time-dependent and partial nicotinamide adenine dinucleotide phosphate (NADPH)-dependent inhibition of CYP3A4 activity. Furthermore, we examined whether the CYP3A4 inhibitory effect of tomato juice was substrate dependent by examining midazolam 1'-hydroxylation activity and nifedipine oxidation activity, in addition to testosterone 6β-hydroxylation activity. Tomato juice showed a potent inhibitory effect on nifedipine oxidation activity, which was comparable to that on testosterone 6β-hydroxylation activity; however, it showed a weak inhibitory effect on midazolam 1'-hydroxylation activity. We conclude that tomato juice contains one or more mechanism-based and competitive inhibitor(s) of CYP3A4. Additionally, significant CYP3A4 inhibitory activity did not result from lycopene, a major compound in tomato. Although the active compound was uncertain, a strong CYP3A4 inhibitory activity was observed in other solanaceous plants, i.e., potato, eggplant, sweet pepper, and capsicum. Therefore, responsible compounds in tomato are likely commonly shared among solanaceous vegetables.

Influences of Fructus evodiae pretreatment on the pharmacokinetics of Rhizoma coptidis alkaloids

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma coptidis is a traditional Chinese medicine with pharmacological properties. It is usually prescribed with Fructus evodiae as traditional Chinese medicine (TCM) formulas. Here we report the influences of Fructus evodiae on the pharmacokinetics of the Rhizoma coptidis alkaloids and propose possible mechanisms.

MATERIALS AND METHODS

Pharmacokinetic experiments were performed in rats. In vitro absorption experiments were performed in everted rat gut sacs, while in vitro metabolism experiments and determination of hepatic UDP-glucuronosyltransferase (UGT) 1A1 mRNA expression were performed in rat liver microsomes.

RESULTS

Pretreatment with Fructus evodiae extract for two weeks decreased the systemic exposure of the Rhizoma coptidis alkaloids. This effect was not due to inhibition of absorption or enhanced hepatic phase I metabolism of the Rhizoma coptidis alkaloids. However, Fructus evodiae pretreatment enhanced both the activity and expression of hepatic UGT1A1.

CONCLUSIONS

The results showed that Fructus evodiae pretreatment decreased the systemic exposure of the Rhizoma coptidis alkaloids by inducing hepatic UGT1A1.

Inhibitory effects of limonin on six human cytochrome P450 enzymes and P-glycoprotein in vitro

Among the various possible causes for drug interactions, pharmacokinetic factors such as inhibition of drug-metabolizing enzymes and transporters, especially cytochrome P450 (CYP) isoenzymes and P-glycoprotein (P-gp), are regarded as the most frequent and clinically important. Limonin is a widely used dietary supplement and one of the most prevalent citrus limonoids, which are known to have inhibitory effects on CYPs and P-gp. In this study, the in vitro inhibitory effects of limonin on the major human CYP isoenzymes (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) activities in human liver microsomes were examined using liquid chromatography-tandem mass spectrometry. The inhibitory effects of limonin on P-gp activity in a human metastatic malignant melanoma cell line WM-266-4 were examined using a calcein-AM fluorometry screening assay. It demonstrates that limonin has negligible inhibitory effects on human CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and P-gp. However, potent inhibition of CYP3A4 by limonin is observed with IC50 values of 6.20 μM (CYP3A4/testosterone) and 19.10 μM (CYP3A4/midazolam). This finding has important implications with regard to food-drug interactions between limonin and several narrow therapeutic index drugs that are metabolized by CYP3A4.

Antinociceptive action of limonexic acid obtained from Raulinoa echinata

The antinociceptive effect of the limonexic acid isolate of Raulinoa echinata Cowan in four models of pain in mice is described. When evaluated against acetic acid-induced abdominal constrictions, limonexic acid (10, 30 and 60 mg kg−1, i.p.) produced dose-related inhibition of the number of constrictions, with a mean ID50 value of 43 (2.3–79) μmol kg−1, and was more potent than some standard drugs. In the formalin test, limonexic acid inhibited both the first and second phases of formalin-induced pain. Furthermore, the effect was more pronounced in the second phase, with a mean ID50 value of 13.66 (9.35–19.61) μmol kg−1, and had a pharmacological profile that was similar to standard drugs such as acetaminophen and acetyl salicylic acid. Limonexic acid also produced dose-related inhibition of glutamate- and capsaicin-induced pain, with mean ID50 values of 11.67 (8.51–16.0) μmol kg−1 and 47.17 (36.51–60.93) μmol kg−1, respectively. The mechanism of action is not completely understood, but seems to involve direct interaction with the GABAergic and nitroxidergic pathways.

Up-regulation of CYP1A1 by rutaecarpine is dependent on aryl hydrocarbon receptor and calcium

Rutaecarpine is a quinazolinocarboline alkaloid isolated from a traditional Chinese medicinal fruit, Evodia rutaecarpa. In the present study, we investigated the effect of rutaecarpine on CYP1A1 expression mediated by [Ca(2+)] and the AhR pathway in mouse hepatoma Hepa-1c1c7 cells. Rutaecarpine also significantly increased CYP1A1 enzyme activity and mRNA and protein levels. Rutaecarpine markedly induced XRE and AhR binding activity. CH-223191, an AhR antagonist, blocked the rutaecarpine-induced CYP1A1 enzyme activity and mRNA and protein expression. In addition, rutaecarpine remarkably induced the phosphorylation of Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaMK). W7 and BAPTA/AM, a CaM antagonist and an intracellular Ca(2+) chelator, respectively, blocked the rutaecarpine-induced CYP1A1 enzyme activity and mRNA and protein expression. These results indicate that rutaecarpine induces CYP1A1 expression through AhR- and calcium-dependent mechanisms.

Evodiamine and rutaecarpine inhibit migration by LIGHT via suppression of NADPH oxidase activation

LIGHT acted as a new player in the atherogenesis. The dried, unripe fruit of Evodia Fructus (EF) has long been used as a traditional Chinese herbal medicine, and is currently widely used for the treatment of headache, abdominal pain, vomiting, colds and reduced blood circulation. Evodiamine and rutaecarpine are active components of EF. In this study, we investigated the inhibitory effect of evodiamine and rutaecarpine on LIGHT-induced migration in human monocytes. Evodiamine and rutaecarpine decreased the LIGHT-induced production of ROS, IL-8, monocyte chemoattractant protein-1 (MCP-1), TNF-alpha, and IL-6, as well as the expression of chemokine receptor (CCR) 1, CCR2 and ICAM-1 and the phosphorylation of the ERK 1/2 and p38 MAPK. Furthermore, NADPH oxidase assembly inhibitor, AEBSF, blocked LIGHT-induced migration and activation of CCR1, CCR2, ICAM-1, and MAPK such as ERK and p38 in a manner similar to evodiamine and rutaecarpine. These findings indicate that the inhibitory effects of evodiamine and rutaecarpine on LIGHT-induced migration and the activation of CCR1, CCR2, ICAM-1, ERK, and p38 MAPK occurs via decreased ROS production and NADPH oxidase activation. Taken together, these results indicate that evodiamine and rutaecarpine have the potential for use as an anti-atherosclerosis agent.

Mechanism-based inhibition of CYP1A2 by antofloxacin, an 8-NH2 derivative of levofloxacin in rats

A recent focus was to investigate whether antofloxacin, an 8-NH(2) derivative of levofloxacin, inhibited cytochrome P450 (CYP) 1A2 activity in rats. Phenacetin, the representative substrate of CYP1A2, was used as the model drug to evaluate the activity of CYP1A2. In an in vivo study, an oral single dose of antofloxacin (20 mg kg(-1)) did not affect the pharmacokinetic behaviour of phenacetin, but a multidose (20 mg kg(-1) twice daily for 7.5 days) significantly increased phenacetin's area under the curve (AUC). In an in vitro study, only when pre-incubated with beta-nicotinamide adenine dinucleotide phosphate, a reduced form (NADPH) system in rat liver microsomes, did antofloxacin inhibit phenacetin O-deethylation. The inhibition was NADPH-, pre-incubation time-, and antofloxacin concentration-dependent. A physiologically based pharmacokinetic model with mechanism-based inhibition was successfully developed for predicting the interaction between antofloxacin and phenacetin in vivo from the in vitro data. The simulated AUC was 1.4-fold of the control, which was near the observed value of 1.6-fold. From the results, it can be concluded that the inhibition of CYP1A2 by antofloxacin is mechanism-based.

Quality evaluation of Evodia rutaecarpa (Juss.) Benth by high performance liquid chromatography with photodiode-array detection

A simple, sensitive and accurate HPLC-DAD method was developed for simultaneous determination of wuchuyuamide-I, quercetin, limonin, evodiamine and rutaecarpine in Evodia rutaecarpa that has been widely used as one of the traditional Chinese medicines (TCMs). Chromatographic separations were performed on a reverse-phase C(18) column with the gradient elution of acetonitrile-water and the simultaneous detection at five wavelengths. Good linear behaviors over the investigated concentration ranges were observed with the values of r higher than 0.999 for all the analytes. The recoveries measured at three levels varied from 98.77 to 102.36%. The validated method was successfully applied for the simultaneous determination of the five chemical constituents in 36 batches of samples collected from different regions or time that were investigated and authenticated as E. rutaecarpa (Juss.) Benth. Hierarchical clustering analysis (HCA) and principal components analysis (PCA) were performed to differentiate and classify the samples based on the contents of the five characteristic constituents. The total contents of evodiamine and rutaecarpine in different samples were calculated and the blending method proposed was demonstrated to be very useful in saving resources and in guiding rational herb use.

Clinically important drug interactions potentially involving mechanism-based inhibition of cytochrome P450 3A4 and the role of therapeutic drug monitoring

Cytochrome P450 (CYP) 3A4 is the most abundant enzyme of CYPs in the liver and gut that metabolizes approximately 50% currently available drugs. A number of important drugs have been identified as substrates, inducers, and/or inhibitors of CYP3A4. The substrates of CYP3A4 considerably overlap with those of P-glycoprotein. Both CYP3A4 and P-glycoprotein are subject to inhibition and induction by a number of factors. Mechanism-based inhibition of CYP3A4 is characterized by NADPH-, time-, and concentration-dependent enzyme inactivation occurring when some xenobiotics or drugs are converted by CYPs to reactive metabolites. Such an inhibition of CYP3A4 is caused by chemical modification of the heme, the protein, or both as a result of covalent binding of modified heme to the protein. To date, the identified clinically important mechanism-based CYP3A4 inhibitors mainly include macrolide antibiotics (eg, clarithromycin and erythromycin), anti-HIV agents (eg, ritonavir and delavirdine), antidepressants (eg, fluoxetine and fluvoxamine), calcium channel blockers (eg, verapamil and diltiazem), steroids and their modulators (eg, gestodene and mifepristone), and several herbal and dietary components. The inactivation of CYP3A4 by drugs often causes unfavorable and long-lasting drug-drug interactions and probably fatal toxicity, depending on many factors associated with the enzyme, drugs, and the patients. Clinicians are encouraged to have a sound knowledge of drug-induced, mechanism-based CYP3A4 inhibition; take proper cautions, and perform close monitoring for possible drug interactions when using drugs that are mechanism-based CYP3A4 inhibitors. To minimize drug-drug interactions involving mechanism-based CYP3A4 inhibition, it is necessary to choose safe drug combination regimens, adjust drug dosages appropriately, and conduct therapeutic drug monitoring for drugs with narrow therapeutic indices.

Rutaecarpine induces chloride secretion across rat isolated distal colon

The present study evaluated the effect of rutaecarpine (Rut) on Cl(-) secretion across rat distal colonic mucosa. Basolateral application of Rut elicited an increase in short-circuit current (I(SC)) response in a concentration-dependent manner. Evidence that Rut-stimulated I(SC) was due to Cl(-) secretion is based on 1) inhibition of current by bumetanide; 2) Cl(-) channel blockers diphenylamine-2-carboxylate, 5-nitro-2-(3-phenylpropylamino)-benzoic acid, and glibenclamide; and 3) removal of Cl(-) ions in bath solution. Determination of neurogenic blockers on Rut-induced I(SC) indicated that pretreatment of tissues with tetrodotoxin or indomethacin, but not atropine or hexamethonium, inhibited Rut-induced response. Treatment with Rut led to release and synthesis of prostaglandin E(2) in rat colonic mucosa. Rut-stimulated I(SC) was markedly reduced by pretreatment with MDL-12,330A [cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine] and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, bisindolylmaleimide, and thapsigargin. Elimination of the extracellular Ca(2+) also did not alter Rut response. Rut treatment resulted in the increase in intracellular cAMP levels and the activation of protein kinase A. Depolarizing the basolateral membrane with high K(+) showed that Rut-stimulated apical Cl(-) current was largely prevented by cystic fibrosis transmembrane conductance regulator (CFTR) inhibitors. Permeabilizing apical membrane with nystatin revealed that Rut-stimulated basolateral K(+) current was specifically inhibited by Ba(2+) ions and chromanol 293B. The evidence derived from present study suggests that Rut-stimulated Cl(-) secretion is mediated by generation of endogenous prostaglandin E(2) and that it also involves the stimulation of cAMP and protein kinase A pathways, which subsequently lead to the activation of apical Cl(-) channels, mostly the CFTR and basolateral cAMP-dependent K(+) channels.

Mechanism-based inhibition of CYP3A4 and CYP2D6 by Indonesian medicinal plants

Thirty samples of Indonesian medicinal plants were tested for their mechanism-based inhibition on cytochrome P450 3A4 (CYP3A4) and CYP2D6 via erythromycin N-demethylation and dextromethorphan O-demethylation activities in human liver microsomes. From screening with 0 and 20min preincubation at 0.5mg/ml of methanol extracts, five plants (Cinnamomum burmani bark, Foeniculum vulgare seed, Strychnos ligustrina wood, Tinospora crispa stem, and Zingiber cassumunar rhizome) showed more than 30% increase of CYP3A4 inhibition, while three (Alpinia galanga rhizome, Melaleuca leucadendron leaf, and Piper nigrum fruit) showed more than 30% increase of CYP2D6 inhibition. In these eight plants, Foeniculum vulgare seed, Cinnamomum burmani bark, and Strychnos ligustrina wood showed time-dependent inhibition on CYP3A4 and Piper nigrum fruit and Melaleuca leucadendron leaf on CYP2D6. Among these, four plants other than Melaleuca leucadendron revealed NADPH-dependent inhibition. Thus, Foeniculum vulgare, Cinnamomum burmani, and Strychnos ligustrina should contain mechanism-based inhibitors on CYP3A4 and Piper nigrum contain that on CYP2D6.

Characterization of human liver cytochrome P450 enzymes involved in the metabolism of rutaecarpine

Rutaecarpine has recently been characterized to have an anti-inflammatory activity through cyclooxygenase-2 inhibition. The incubation of rutaecarpine with human liver microsomes in the presence of NADPH generated six isobaric mono-hydroxylated metabolites. The specific cytochrome P450 (CYP) isozymes responsible for rutaecarpine metabolites were identified using the combination of chemical inhibition, immuno-inhibition and metabolism by cDNA expressed CYP enzymes. The results suggested that CYP3A4 might play major roles in the metabolism of rutaecarpine in human liver microsomes. The production of M1, M2, M3, M4 and M6 formed in human liver microsomes was inhibited by ketoconazole, a selective CYP3A4 inhibitor, and anti-CYP3A4 antibody. CYP1A2 and CYP2C9 played minor roles in the metabolism of rutaecarpine. These results were confirmed in microsomes derived from cDNA expressed lymphoblastoid cells. CYP3A4 microsome clearly formed M1, M2, M3 and M6. CYP1A2 and CYP2C9 microsomes comparably formed M5.