Saikosaponins and the deglycosylated metabolites exert liver meridian guiding effect through PXR/CYP3A4 inhibition.

ETHNOPHARMACOLOGICAL RELEVANCE: Radix Bupleuri (RB), traditionally used to treat inflammatory disorders and infectious diseases, represents one of the most successful and widely used herbal drugs in Asia over the past 2000 years. Being realized the role in regulating metabolism and controlling Yin/Yang, RB is not only chosen specifically for treating liver meridian and the corresponding organs, but also believed to have liver meridian guiding property and help potentiate the therapeutic effects of liver. However, the ingredients in RB with liver meridian guiding property and the underly mechanism have not been comprehensively investigated. AIM OF STUDY: Considering the important role of CYP3A4 in first-pass metabolism and the liver exposure of drugs, the present study aimed to determine whether saikosaponins (SSs) and the corresponding saikogenins (SGs) have a role in inhibiting the catalytic activity of CYP3A4 in human liver microsomes and HepG2 hepatoma cells and whether they could suppress CYP3A4 expression by PXR-mediated pathways in HepG2 hepatoma cells. MATERIALS AND METHODS: The effect of SSs and SGs on CYP3A4-mediated midazolam1'-hydroxylation activities in pooled human liver microsomes (HLMs) was first studied. Dose-dependent experiments were performed to obtain the half inhibit concentration (IC50) values. HepG2 cells were used to assay catalytic activity of CYP3A4, reporter function, mRNA levels, and protein expression. The inhibitory effects of SSa and SSd on CYP3A4 activity are negligible, while the corresponding SGs (SGF and SGG) have obvious inhibitory effects on CYP3A4 activity, with IC50 values of 0.45 and 1.30 µM. The similar results were obtained from testing CYP3A4 catalytic activity in HepG2 cells, which correlated well with the suppression of the mRNA and protein levels of CYP3A4. Time-dependent testing of CYP3A4 mRNA and protein levels, as well as co-transfection experiments using the CYP3A4 promoter luciferase plasmid, further confirmed that SSs and SGs could inhibit the expression of CYP3A4 at the transcription level. Furthermore, PXR protein expression decreased in a concentration- and time-dependent manner after cells were exposed to SSs and SGs. PXR overexpression and RNA interference experiments further showed that SSs and SGs down-regulate the catalytic activity and expression of CYP3A4 in HepG2 may be mainly through PXR-dependent manner. CONCLUSION: SSs and SGs inhibit the catalytic activity and expression of CYP3A4 in a PXR-dependent manner, which may be highly related to the liver meridian guiding property of RB.

Screening of Human CYP1A2 and CYP3A4 Inhibitors from Seaweed In Silico and In Vitro.

Phenolic compounds and carotenoids are potential inhibitors of cytochrome P450s. Sixteen known compounds, phenolic compounds and carotenoids from seaweed were examined for potential inhibitory capacity against CYP1A2 and CYP3A4 in silico and in vitro. Morin, quercetin, and fucoxanthin inhibited the enzyme activity of CYP1A2 and CYP3A4 in a dose-dependent manner. The IC50 values of morin, quercetin, and fucoxanthin were 41.8, 22.5, and 30.3 µM for CYP1A2 and 86.6, 16.1, and 24.4 µM for CYP3A4, respectively. Siphonaxanthin and hesperidin did not show any significant effect on CYP1A2, but they slightly inhibited CYP3A4 activity at high concentrations. In silico modeling of CYP's binding site revealed that the potential inhibitors bound in the cavity located above the distal surface of the heme prosthetic group through the 2a or 2f channel of CYPs. This study presents an approach for quickly predicting CYP inhibitory activity and shows the potential interactions of compounds and CYPs through in silico modeling.

Differential Impacts of Azole Antifungal Drugs on the Pharmacokinetic Profiles of Dasatinib in Rats by LC-MS-MS.

BACKGROUND: Dasatinib, as an oral multi-targeted inhibitor of BCR-ABL and SRC family kinases, has been widely used for the treatment of Philadelphia Chromosome Positive Leukemias in imatinib-acquired resistance and intolerance. The study aimed to develop and validate a simple and robust assay with a small volume of plasma based on liquid chromatography coupled with tandem mass spectrometry to determine the concentration of dasatinib and to investigate the impact of the cytochrome 3A4 inhibitors, including ketoconazole, voriconazole, itraconazole and posaconazole, on the pharmacokinetics of dasatinib in rats. METHODS: Thirty rats were divided randomly into five groups, control group (0.5% carboxymethylcellulose sodium), ketoconazole (30 mg/kg) group, voriconazole group (30 mg/kg), itraconazole group (30 mg/kg) and posaconazole group (30 mg/kg). After 150 µL blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, 24, and 48 h and precipitated with acetonitrile, the plasma concentration of dasatinib was determined through Fluoro- Phenyl column (150 mm×2.1 mm, 3 µm) in a positive ionization mode. RESULTS: The results suggested that ketoconazole, voriconazole, and posaconazole could increase the AUC0-t of dasatinib to varying degrees while significantly reducing its clearance. However, there was no significant impact on the pharmacokinetics of dasatinib, co-administered with itraconazole except for the CL and MRT0-t of dasatinib. Additionally, voriconazole could significantly increase Cmax of dasatinib by approximately 4.12 fold. CONCLUSION: These data indicated that ketoconazole, posaconazole and voriconazole should be cautiously co-administered with dasatinib or close therapeutic drug monitoring of dasatinib concentration, which might cause the drug-drug interaction.

Inhibitory Effect of Lygodium Root on the Cytochrome P450 3A Enzyme in vitro and in vivo.

PURPOSE: The aim of the present study was to investigate the interactions of the main components of Lygodium root (ie, p-coumaric acid, acacetin, apigenin, buddleoside and Diosmetin-7-O-ß-D-glucopyranoside) with cytochrome P450 3A enzyme activity both in vitro and in vivo. METHODS: In vitro inhibition of drugs was assessed by incubating rat liver microsomes (RLMs) with a typical P450 3A enzyme substrate, midazolam, to determine their 50% inhibitory concentration (IC50) values. For the in vivo study, healthy male Sprague Dawley rats were consecutively administered acacetin or apigenin for 7 days at the dosage of 5 mg/kg after being randomly divided into 3 groups: Group A (control group), Group B (acacetin group) and Group C (apigenin group). RESULTS: Among the five main components of Lygodium root, only acacetin and apigenin showed inhibitory effects on the cytochrome P450 3A enzyme in vitro. The IC50 values of acacetin and apigenin were 58.46 µM and 8.20 µM, respectively. Additionally, the in vivo analysis results revealed that acacetin and apigenin could systemically inhibit midazolam metabolism in rats. The Tmax, AUC(0-t) and Cmax of midazolam in group B and group C were significantly increased (P<0.05), accompanied by a significant decrease in Vz/F and CLz/F (P<0.05). CONCLUSION: Acacetin and apigenin could inhibit the activity of the cytochrome P450 3A enzyme in vitro and in vivo, indicating that herbal drug interactions might occur when taking Lygodium root and midazolam synchronously.

Effect of Cinnamomum cassia on the Pharmacokinetics and Pharmacodynamics of Pioglitazone.

BACKGROUND: Millions of people today use herbs either as food or in the form of medicine along with other medications. Many of the herbs can interact with these medications, causing either potentially dangerous side effects or improved or reduced benefits from the medication. OBJECTIVE: The present study was performed to determine the influence of cinnamon, on the pharmacokinetics and pharmacodynamics of pioglitazone. METHOD: Studies were conducted in normal and alloxan induced diabetic rats and rabbits with oral administration of selected doses of pioglitazone, cinnamon and their combination. Blood samples were collected at regular intervals of time and were analysed for glucose by GOD/POD method and for pioglitazone by HPLC method respectively. Body weights were also measured every week. RESULTS: Significant differences were seen in pharmacokinetic parameters of pioglitazone like AUC, t1/2, Ke, Cl/F, Vd/F when given in combination with cinnamon in normal and diabetic rabbits. The combination of pioglitazone and cinnamon was found to reduce the glucose levels and body weights significantly than pioglitazone. The results indicating increased AUC of pioglitazone on pretreatment with cinnamon suggest an interaction indicating decreased metabolism of pioglitazone as a result of CYP 3A4 inhibition and thereby producing a potentiating effect. CONCLUSION: Cinnamon enhanced the bioavailability of pioglitazone by inhibiting the CYP3A4 enzyme. Hence, cinnamon might be beneficial when used in combination with pioglitazone in diabetic patients and an adjustment of dose of pioglitazone may be necessary.

Iridoid Glycosides from Tabebuia avellanedae.

Five novel iridoid glycosides, avellanedaesides A-E (1 - 5) were isolated from the H2 O extract of Tabebuia avellanedae. Their structures were determined on the basis of NMR and MS analysis. Isolated compounds suppressed inflammatory cytokine, tumor-necrosis factor-α and interleukin-1ß production in cultured human myeloma THP-1 cells co-stimulated with lipopolysaccharide (LPS). In addition, the study revealed iridoid glycosides inhibited the activity of cytochrome CYP3A4 enzyme.

The significant inhibition on CYP3A caused by radix Aconiti single herb is not observed in the Wutou decoction: The necessity of combination therapy of radix Aconiti.

ETHNOPHARMACOLOGICAL RELEVANCE: Wutou (WT, Radix Aconiti), the mother root of Aconitum carmichaelii Debx., is a famous Chinese herb against rheumatoid arthritis. In Chinese clinics, PWT is often prepared as a decoction in combination with other herbs, such as Wutou decoction (WTD). The present study aimed to compare the effects of PWT single herb and WTD on CYP3A activity ex vivo and in vivo. MATERIALS AND METHODS: In the ex vivo study, CYP3A activity was determined by using testosterone (Tes) as a specific probe. Levels of Tes and its metabolite 6ß-hydroxytestosterone (6ß-OH-Tes) were measured using a validated ultra-performance liquid chromatography (UPLC) method. CYP3A protein and mRNA levels were measured by using Western blot and real-time PCR, respectively. In the in vivo study, CYP3A activity was determined by using buspirone (BP) as a specific probe. The plasma concentrations of BP and its primary metabolites, namely, 1-(2-pyrimidinyl) piperazine (1-PP) and 6'-hydroxybuspirone (6'-OH-BP), were determined using a validated UPLC-tandem mass spectrometry (UPLC/MS/MS) method. RESULTS: Compared with the control group, the formation rates of 6ß-OH-Tes from Tes ex vivo significantly decreased in groups treated with PWT at the tested doses, and this decrease was accompanied by a striking decrease in CYP3A protein and mRNA levels. However, a significant increase was observed in the ratios in the WTD groups compared with PWT single herb groups. In vivo, both formation ratios of 6'-OH-BP and 1-PP from BP showed no significant change in the WTD group. CONCLUSIONS: PWT can significantly inhibit CYP3A activity ex vivo at the tested doses because of the down-regulation of CYP3A protein and mRNA expression levels. WTD can significantly reverse the inhibition caused by PWT. WTD also had no significant effect on CYP3A activity in vivo. Results implied that the use of PWT as a part of the WTD prescription rather than PWT single herb is more appropriate in clinics.

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 (k(inact) and K(I)) 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.

In Vitro Evaluation of Reversible and Time-Dependent Inhibitory Effects of Kalanchoe crenata on CYP2C19 and CYP3A4 Activities.

Kalanchoe crenata popularly known as "dog's liver" is used in most African countries for the treatment of chronic diseases such as diabetes, asthma and HIV/AIDS related infections. The evaluation of K. crenata for herb-drug interactions has not been reported. This study therefore aims to evaluate the risk of K. crenata for herb-drug interaction in vitro. Crude methanol and fractions of K. crenata were incubated and preincubated with recombinant human CYP2C19 and CYP3A4. Comparative studies were conducted in both human liver microsomes and recombinant human CYP to ascertain the inhibition profile of the crude extract and the various fractions. The cocktail approach of recombinant human CYPs was conducted to confirm the inhibition potential of the fractions in the presence of other CYPs. The results showed significant time-dependent inhibition of tested samples on CYP3A4 with crude methanol (39KC), fractions 45A, 45B and 45D given IC50 fold decrease of 3.29, 2.26, 1.91 and 1.49, respective. Time dependent kinetic assessment of 39KC and 45D showed KI and kinact values for 39KC as 1.77 µg/mL and 0.091 min(-1) while that of 45D were 6.45 µg/mL and 0.024 min(-1), respectively. Determination of kinact based on IC50 calculations yielded 0.015 and 0.04 min(-1) for 39KC and 45D, respectively. Cocktail approach exhibited fold decreases in IC50 for all test fractions on CYP3A4 within the ranges of 2.10 - 4.10. At least one phytoconstituent in the crude methanol extract of Kalanchoe crenata is a reversible and time-dependent inhibitor of CYP3A4.

The effect of Cree traditional medicinal teas on the activity of human cytochrome P450-mediated metabolism.

ETHNOPHARMACOLOGICAL RELEVANCE: Rhododendron groenlandicum (Bog Labrador tea), Rhododendron tomentosum (Marsh Labrador tea) and Juniperus communis (Juniper) are used in medicinal teas by Canadian aboriginal cultures alone and in combination with conventional drug products. The safety of this combination had not been previously examined and this study was initiated to examine the potential of medicinal teas to inhibit the major human drug metabolizing enzyme, cytochrome P450 3A4 (CYP3A4). MATERIALS AND METHODS: The decoctions of Rhododendron groenlandicum and Rhododendron tomentosum leaves and Juniperus communis berries were examined in a microtiter fluorometric assay to examine their potential to inhibit CYP-mediated metabolism. RESULTS: The decoctions showed progressive inhibition towards CYP3A4 the longer the leaves or berries were brewed. R. Rhododendron groenlandicum and Juniperus communis may have the potential to inhibit CYP3A4-mediated metabolism. CONCLUSIONS: The findings of this study with these traditional medicines are significant in that they provide mechanistic support that these products have the potential to affect the safety and efficacy of other health and medicinal products. As this study only examined CYP3A4, it is possible that these medicinals contain substances that could also affect other metabolic enzymes.