IDENTIFICATION AND CHARACTERIZATION OF POTENT CYP3A4 INHIBITORS IN SCHISANDRA FRUIT EXTRACT

Co-administration of Wuzhi capsules and tacrolimus in patients with idiopathic membranous nephropathy: clinical efficacy and pharmacoeconomics

PURPOSE

Tacrolimus is an effective (but relatively expensive) immunosuppressant that is used widely in patients with membranous nephropathy. To reduce the tacrolimus dose while maintaining an equivalent therapeutic effect, we studied the clinical efficacy and pharmacoeconomic impact of co-administration of Wuzhi capsules (WZC that protects against damage to liver cells) and tacrolimus.

METHODS

Sixty patients with membranous nephropathy were divided randomly into two groups: experimental (tacrolimus + WZC + corticosteroids) and control (tacrolimus + corticosteroids). Each group received treatments continuously for >6 months. Liver function; renal function; and whole-blood concentrations of tacrolimus, sugars, lipids, as well as 24-h urinary protein levels were used in the clinical evaluation. The cost of drugs was calculated, and the pharmacoeconomic cost-effectiveness analyses were carried out to compare indices between the two groups.

RESULTS

Doses and costs of tacrolimus differed significantly between experimental and control groups (p < 0.01 or p < 0.05). Costs in the experimental group were 13,702.62 ± 1,458.6 CNY (2,194.10 ± 233.56 USD) and those in the control group were 17,796.87 ± 2,469.27 CNY (2,849.69 ± 395.39 USD), with clinical efficacy of 93.3 and 90.0 %, respectively. The cost-effectiveness ratios were 146.86 ± 15.63 and 197.73 ± 27.44, respectively. Compared with the experimental group, the control group showed an incremental cost-effectiveness ratio of 1,240.68 ± 306.25 CNY (198.66 ± 49.04 USD), whereas remission between the two groups was similar.

CONCLUSION

Co-administration of WZCs and tacrolimus can reduce the dose of tacrolimus and decrease the costs incurred by patients within the same therapeutic window to that seen for treatment with tacrolimus alone.

Reversing effects of lignans on CCl4-induced hepatic CYP450 down regulation by attenuating oxidative stress

Oxidative stress has been proved to be a critical reason of regulating CYP450s under hepatic injury status. The study was aimed to investigate the effect of pretreatment of schisandra lignan extracts (SLE) and dimethyl diphenyl bicarboxylate (DDB) on expressions and activities of the main liver P450 isoenzymes in CCl4 induced liver injury rats and their anti-oxidative effects on both CCl4 induced liver injury rats and a CCl4 induced HepG2 cell injury model. Acute experimental liver injury induced by CCl4 caused drastically decreasing activities of the main liver P450 isoenzymes such as CYP1A2, CYP2C6, CYP2E1 and CYP3A2, as well as their protein expressions. Pretreatment of SLE (500 mg/kg) and DDB (200 mg/kg) twice a day for three days significantly decreased the losses of activities of CYP1A2, CYP2C6, CYP2E1 and CYP3A2. Similar results were observed in protein expressions. In addition, in the CCl4 induced HepG2 cells injury model and the CYP3A activity level correlated well with ROS level in several ingredients of SLE treated groups, especially in γ-schisandrin group. These results indicated that the reversion of P450 after SLE/DDB treatment were, on one hand, due to hepatoprotective effects of these lignans on livers; on the other hand, due to their regulation of P450 through anti-oxidative effect and γ-schisandrin might be the most powerful ingredient of SLE. Also, there might be potential interactions between SLE or DDB and co-administered medicines and it is necessary to adjust the dosage of co-administrated medicines in clinical medication of liver disease.

Development of a sensitive LC-MS/MS method for simultaneous quantification of eleven constituents in rat serum and its application to a pharmacokinetic study of a Chinese medicine Shengmai injection

A sensitive LC-MS/MS method was developed and validated for simultaneous quantification of 11 constituents, ginsenoside Rg1, Re, Rf, Rg2, Rb1, Rd, Rc, ophiopogonin D, schisandrin, schisandrol B and schizandrin B, in rat serum using digoxin as the internal standard (IS). The serum samples were pretreated and extracted with a two-step liquid-liquid extraction. Chromatographic separation was achieved on a C18 analytical column with a proper gradient elution using 0.02% acetic acid aqueous solution and 0.02% acetic acid-acetonitrile as mobile phase at a flow rate of 0.5 mL/min. MS detection was performed using multiple reaction monitoring via an electrospray ionization source. Good linearity was observed in the validated concentration range for every analyte (r(2) ≥0.9929), and the lower limits of quantitation of the analytes were in the range of 0.044-1.190 ng/mL in rat serum. Intra- and inter-day precisions were <14.2%. The accuracy expressed as recovery was within the range of 85.1-112.8%. The extraction recoveries were >75.8%.The validated method was successfully applied to a pharmacokinetic study of all analytes in rats after single intravenous administration of Shengmai injection.

Inhibitory effects of phytochemicals on metabolic capabilities of CYP2D6(*)1 and CYP2D6(*)10 using cell-based models in vitro

AIM

Herbal products have been widely used, and the safety of herb-drug interactions has aroused intensive concerns. This study aimed to investigate the effects of phytochemicals on the catalytic activities of human CYP2D6(*)1 and CYP2D6(*)10 in vitro.

METHODS

HepG2 cells were stably transfected with CYP2D6(*)1 and CYP2D6(*)10 expression vectors. The metabolic kinetics of the enzymes was studied using HPLC and fluorimetry.

RESULTS

HepG2-CYP2D6(*)1 and HepG2-CYP2D6(*)10 cell lines were successfully constructed. Among the 63 phytochemicals screened, 6 compounds, including coptisine sulfate, bilobalide, schizandrin B, luteolin, schizandrin A and puerarin, at 100 μmol/L inhibited CYP2D6(*)1- and CYP2D6(*)10-mediated O-demethylation of a coumarin compound AMMC by more than 50%. Furthermore, the inhibition by these compounds was dose-dependent. Eadie-Hofstee plots demonstrated that these compounds competitively inhibited CYP2D6(*)1 and CYP2D6(*)10. However, their Ki values for CYP2D6(*)1 and CYP2D6(*)10 were very close, suggesting that genotype-dependent herb-drug inhibition was similar between the two variants.

CONCLUSION

Six phytochemicals inhibit CYP2D6(*)1 and CYP2D6(*)10-mediated catalytic activities in a dose-dependent manner in vitro. Thus herbal products containing these phytochemicals may inhibit the in vivo metabolism of co-administered drugs whose primary route of elimination is CYP2D6.

Effect of Tacrolimus on the pharmacokinetics of bioactive lignans of Wuzhi tablet (Schisandra sphenanthera extract) and the potential roles of CYP3A and P-gp

We recently reported that Wuzhi tablet (WZ), a preparation of the ethanol extract of Wuweizi (Schisandra sphenanthera), had significant effects on blood concentrations of Tacrolimus (FK506) in renal transplant recipients and rats. The active lignans in WZ are schisandrin A, schisandrin B, schisandrin C, schisandrol A, schisandrol B, schisantherin A, and schisantherin B. Until now, whether the pharmacokinetics of these lignans in WZ would be affected by FK506 remained unknown. Therefore, this study aimed to investigate whether and how FK506 affected pharmacokinetics of lignans in WZ in rats and the potential roles of CYP3A and P-gp. After a single oral co-administration of FK506 and WZ, the blood concentration of lignans in WZ was decreased by FK506; furthermore, the AUC of schisantherin A, schisandrin A, schisandrol A and schisandrol B was only 64.5%, 47.2%, 55.1% and 57.4% of that of WZ alone group, respectively. Transport study in Caco-2 cells showed that these lignans were not substrates of P-gp, suggesting decreased blood concentration of lignans by FK506 was not via P-gp pathway. Metabolism study in the human recombinant CYP 3A showed that these lignans had higher affinity to CYP3A than that of FK506, and thus had a stronger CYP3A-mediated metabolism. It was concluded that the blood concentrations of these lignans were decreased and their CYP3A-mediated metabolisms were increased in the presence of FK506 since these lignans had higher affinity to CYP3A.

Updates on the clinical evidenced herb-warfarin interactions

Increasing and inadvertent use of herbs makes herb-drug interactions a focus of research. Concomitant use of warfarin, a highly efficacious oral anticoagulant, and herbs causes major safety concerns due to the narrow therapeutic window of warfarin. This paper presents an update overview of clinical findings regarding herb-warfarin interaction, highlighting clinical outcomes, severity of documented interactions, and quality of clinical evidence. Among thirty-eight herbs, Cannabis, Chamomile, Cranberry, Garlic, Ginkgo, Grapefruit, Lycium, Red clover, and St. John's wort were evaluated to have major severity interaction with warfarin. Herbs were also classified on account of the likelihood of their supporting evidences for interaction. Four herbs were considered as highly probable to interact with warfarin (level I), three were estimated as probable (level II), and ten and twenty-one were possible (level III) and doubtful (level IV), respectively. The general mechanism of herb-warfarin interaction almost remains unknown, yet several pharmacokinetic and pharmacodynamic factors were estimated to influence the effectiveness of warfarin. Based on limited literature and information reported, we identified corresponding mechanisms of interactions for a small amount of “interacting herbs.” In summary, herb-warfarin interaction, especially the clinical effects of herbs on warfarin therapy should be further investigated through multicenter studies with larger sample sizes.

A pharmacokinetic and pharmacodynamic study of drug-drug interaction between ginsenoside Rg1, ginsenoside Rb1 and schizandrin after intravenous administration to rats

ETHNOPHARMACOLOGICAL RELEVANCE

Ginsenoside Rg1, ginsenoside Rb1 and schizandrin are main bioactive components from Panax ginseng and Schisandra chinensis. They have been found in many prescriptions of Traditional Chinese Medicines (TCM) and proven to be effective for prevention and treatment of cardiovascular disease. It is valuable to investigate their pharmacokinetic and pharmacodynamic behavior and potential synergistic effect for better drug development and clinical application.

MATERIALS AND METHODS

Pharmacokinetic and nitric oxide (NO) release pharmacodynamic drug-drug interactions of ginsenoside Rg1, ginsenoside Rb1 and schisandrin were studied after intravenous administration of each compound with the dose of 10 mg/kg and their mixture with the total dose of 10 mg/kg to isoproterenol (ISO)-induced myocardial ischemia rats. Drug concentrations in serum were determined using LC-MS method. Nitrite and nitrate (NOx(-)), the predominant oxidation product of NO in serum was used as an effective marker and quantitated by the method of high-performance liquid chromatography coupled with fluorescence detection (HPLC-FL). The main pharmacokinetic parameters of T(1/2β), MRT(0-∞), Vd, Cl, and AUC, and the main pharmacodynamic parameters of Cmax, Tmax and AUEC were calculated by non-compartment model.

RESULTS

The results indicated ginsenoside Rb1 and (or) schisandrin in mixture could significantly postpone the elimination of ginsenoside Rg1 in rat serum. Co-administration of three compounds markedly increased the systemic exposure level of each compound in vivo. Ginsenoside Rg1 and ginsenoside Rb1 had the effect of inducing real-time NO release in rats concentration dependently. Schisandrin had no effect of inducing real-time NO release in this study. The mixture of ginsenoside Rg1, Rb1 and schisandrin administration exhibited synergistic effect of inducing NO release in ISO treated rats.

CONCLUSIONS

The result obtained from this study suggested pharmacokinetic and pharmacodynamic drug-drug interactions between ginsenoside Rg1, Rb1 and schisandrin. The study provided valuable information for drug development and clinical application of TCM.

Schisandra chinensis peptidoglycan-assisted transmembrane transport of lignans uniquely altered the pharmacokinetic and pharmacodynamic mechanisms in human HepG2 cell model

Schisandra chinensis (Turz Baill) (S. chinensis) (SC) fruit is a hepatoprotective herb containing many lignans and a large amount of polysaccharides. A novel polysaccharide (called SC-2) was isolated from SC of MW 841 kDa, which exhibited a protein-to-polysaccharide ratio of 0.4089, and showed a characteristic FTIR spectrum of a peptidoglycan. Powder X-ray diffraction revealed microcrystalline structures within SC-2. SC-2 contained 10 monosaccharides and 15 amino acids (essential amino acids of 78.12%w/w). In a HepG2 cell model, SC-2 was shown by MTT and TUNEL assay to be completely non-cytotoxic. A kinetic analysis and fluorescence-labeling technique revealed no intracellular disposition of SC-2. Combined treatment of lignans with SC-2 enhanced the intracellular transport of schisandrin B and deoxyschisandrin but decreased that of gomisin C, resulting in alteration of cell-killing bioactivity. The Second Law of Thermodynamics allows this type of unidirectional transport. Conclusively, SC-2 alters the transport and cell killing capability by a "Catcher-Pitcher Unidirectional Transport Mechanism".

Irreversible enzyme inhibition kinetics and drug-drug interactions

This chapter describes the types of irreversible inhibition of drug-metabolizing enzymes and the methods commonly employed to quantify the irreversible inhibition and subsequently predict the extent and time course of clinically important drug-drug interactions.

Deoxyschizandrin, a naturally occurring lignan, is a specific probe substrate of human cytochrome P450 3A

To accurately predict the modifications done during metabolic processes by cytochrome P450 (P450) 3A enzyme, selecting substrates that best represent a broad range of substrate substitutions and that follow the Michaelis-Menten kinetic properties is highly necessary. In the present study, the oxidative pathways of deoxyschizandrin (DS), the most abundant lignan in Fructus Schisandrae fruit extract, were characterized with liver microsomes from human (HLM) and rat (RLM). Only one monohydroxylated metabolite 7(S)-hydroxylated metabolite (isoschizandrin, ISZ), was identified using liquid chromatography-mass spectrometry and nuclear magnetic resonance techniques. CYP3A4 and CYP3A5 were found to be the major isoforms involved in the monohydroxylation of DS. Also, the kinetic studies showed that DS hydroxylation obeyed Michaelis-Menten kinetics both in HLM and in RLM. However, the subsequent metabolism of ISZ was nearly nonexistent when DS was present. More importantly, the interactions between DS and three well characterized CYP3A probe substrates, testosterone (TST), midazolam (MDZ), and nifedipine (NIF), were studied. TST and MDZ were shown to compete with DS for the mutual binding site, causing Km to be increased. The presence of DS also lowered the binding affinities for MDZ and TST. However, DS showed only slight inhibitory effects on nifedipine (NIF) oxidation even though NIF was able to inhibit DS hydroxylation in a noncompetitive fashion. These results show that DS is a good representative substrate of MDZ and TST primarily due to their shared, large binding regions on CYP3A. Therefore, DS is an attractive candidate as a novel CYP3A probe substrate for predicting the metabolic modifications in CYP3A activity.

Effects of herbal supplements on the bioactivation of chemotherapeutic agents

OBJECTIVES

The aim of this study was to investigate the impact of commercially available, over-the-counter herbal supplements (St John's wort, black cohosh and ginger root extract) on the metabolic activation of tamoxifen and irinotecan.

METHODS

Co-incubation of each drug and supplement combination over a range of concentrations was conducted in human liver microsomes and the decrease in the rate of active metabolite formation was monitored using high-performance liquid chromatography tandem mass spectrometry. Data was analysed using non-linear regression analysis and Dixon plots to determine the dominant mechanism of inhibition and to estimate the Ki and IC50 values of the commercial supplements.

KEY FINDINGS

The data suggest that black cohosh was the strongest inhibitor tested in this study for both CYP450 and carboxyesterase mediated biotransformation of tamoxifen and irinotecan, respectively, to their active metabolites. St John's wort was a stronger inhibitor compared with ginger root extract for tamoxifen (CYP mediated pathway), while ginger root extract was a stronger inhibitor compared with St John's wort for the carboxyesterase mediated pathway.

CONCLUSIONS

Commercially available supplements are widely used by patients and their potential impact on the efficacy of the chemotherapy is often unknown. The clinical significance of these results needs to be evaluated in a comprehensive clinical trial.

In vivo effect of Schisandrin B on cytochrome P450 enzyme activity

To investigate the possible drug interaction, this study is designed to evaluate the ability of Schisandrin B (Sch B) to modulate cytochrome P450 3A activity (CYP3A) in vivo and to alter the pharmacokinetic profiles of CYP3A substrate (midazolam) in treated rats. Rats were repeated administered with physiological saline (negative control group), ketoconazole (75 mg/kg, positive control group) or varied doses of Sch B (experimental groups) for three consecutive days. Subsequently, changes in hepatic microsomal CYP3A activity and the pharmacokinetic profiles of midazolam and 1'-hydroxy midazolam in plasma were studied to evaluate CYP3A activity. The results indicated that Sch B significantly dose-dependently inhibited rat hepatic microsomal CYP3A activity with Ki value of 16.64 mg/kg and showed the characteristic of a noncompetitive inhibitor. Oral administration of Sch B for 3 days in rats produced significant effect on the pharmacokinetics of oral midazolam. Sch B resulted in a significant, dose-dependent increase in midazolam AUC0-∞ except at the dose of 2 mg/kg, while AUC0-∞ increased by 26.1% (8 mg/kg) and 60.6% (16 mg/kg), respectively. In the pharmacokinetic profiles of 1'-hydroxy midazolam, the significant, dose-dependent decrease in AUC0-∞ was observed except at the dose of 2 mg/kg, while AUC0-∞ reduced by 44.5% (8 mg/kg) and 49.2% (16 mg/kg), respectively. These results suggested that 3-day treatment of Sch B could increase concentration and oral bioavailability of drug metabolized by CYP3A. When the drug, consisting of Sch B, is used in the clinic for more than 3 days, the possible drug-drug interactions should be taken into consideration.

Profiling and identification of the absorbed constituents and metabolites of schisandra lignans by ultra-performance liquid chromatography coupled to mass spectrometry

Schisandra chinensis Baill grows wild in Russia, China, Korea and Japan, and its fruit has been found to be effective in amnesia and insomnia. It is enriched in schisandra lignans (SL) that are major components responsible for therapeutic action. However, there are no reports on the biotransformation analysis of SL. An ultra-performance liquid chromatography/electrospray-ionization high-definition mass spectrometry (UPLC-Q-TOF-HDMS) method was developed to investigate the metabolism of SL in vivo. MS was performed on a Waters Micromass high-definition system with an electrospray ionization source in positive ion mode and automated MetaboLynx software analysis with excellent MS accuracy and enhanced MS data acquisition. An improved mass defect filter (MDF) method employing both drug and core structure filter templates was applied to the processing of UPLC-Q-TOF-HDMS data for the detection and structural characterization of metabolites. In this study, 30 metabolites were detected and identified in vivo, and demethylation and hydroxylation were confirmed as the primacy metabolic pathway for SL in rat plasma. In conclusion, the presently developed methodology was suitable for biotransformation research of SL and will find wide use in metabolic studies for other herbal medicines.

Effects of unprocessed versus vinegar-processed Schisandra chinensis on the activity and mRNA expression of CYP1A2, CYP2E1 and CYP3A4 enzymes in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis (SC) is a well-known traditional Chinese herbal medicine that has been used in clinical practices for thousands of years. However, the differences between the effects of unprocessed and vinegar-processed Schisandra chinensis (VSC) on cytochrome P450 (CYP450) activities are poorly understood.

AIM OF THE STUDY

To evaluate the differences between processed and unprocessed SC on the metabolism of CYP1A2, CYP2E1 and CYP3A4 substrates in rats using a cocktail method based on a developed and validated HPLC method. We also investigate the influence of processing on the levels of CYP mRNA.

MATERIALS AND METHODS

Three probe substrates (theophylline, dapsone and chlorzoxazone) were delivered simultaneously into rats treated with single or multiple doses of processed or unprocessed SC extract. The plasma concentrations of the three probes were profiled by HPLC, and their corresponding pharmacokinetic parameters were calculated. Real-time RT-PCR was performed to determine the effects of processed and unprocessed SC on the mRNA expression of CYP1A2, CYP2E1 and CYP3A4 in the liver.

RESULTS

Treatment with single or multiple doses of either extract of SC induced CYP3A4 enzyme activity and inhibited CYP1A2 enzyme activity in rats. Furthermore, the inhibitory effect of SC was more potent after vinegar processing than without vinegar processing. CYP2E1 enzyme activity was induced after treatment with a single dose but was inhibited after multiple doses. The mRNA expression results were in accordance with the pharmacokinetic results.

CONCLUSIONS

These results provide useful scientific data for the safe clinical application of either extract of SC in combination with other drugs, which should lack the side effects induced by other herb-drug interactions.

Effect of long-term co-administration of Wuzhi tablet (Schisandra sphenanthera extract) and prednisone on the pharmacokinetics of tacrolimus

Tacrolimus (TAC) is an immunosuppressant that has been widely used alone or in combination with prednisone (PRED) to prevent acute rejection after organ transplantation. Wuzhi tablet (WZ, Schisandra sphenanthera extract) is often prescribed with TAC to prevent drug-induced hepatitis. We recently reported that WZ could significantly increase TAC blood exposure by inhibiting P-gp-mediated efflux and CYP3A-mediated metabolism of TAC. PRED is also a substrate of P-gp and is a weak inducer of CYP3A, and drug-drug interactions within this combination therapy might occur. Therefore, the purpose of this study was to investigate the effect of long-term treatment of WZ and PRED on the pharmacokinetics of TAC in rats. After 14 days of co-administration of WZ and PRED, the AUC(0-24h) of oral TAC was increased (from 59.6±37.3 to 95.3±39.4 ng h/ml, p=0.18) and the clearance was decreased (from 38.4±28.4 to 17.7±6.4 l/h/kg, p=0.15). When only co-administered with WZ, AUC(0-24h) of TAC was demonstrated a significantly increase (from 59.6±37.3 to 135.9±34.8 ng h/ml, p<0.05). The concomitant administration of PRED resulted in a reduction in the systemic exposure of TAC and an increase in its clearance, though neither was statistically significant. Thus, our study suggested that the presence of WZ and PRED still could increase the systemic exposure of TAC in rats. The drug-drug interactions among this combination therapy should still be taken into consideration in clinical practice.

Effect of Wuzhi tablet (Schisandra sphenanthera extract) on the pharmacokinetics of cyclosporin A in rats

In our previous reports, Wuzhi tablet (an herbal preparation of ethanol extract of Wuweizi (Schisandra sphenanthera)) can significantly increase the blood concentration of tacrolimus and paclitaxel in rats by inhibiting the CYP3A-mediated metabolism and the P-gp-mediated efflux. Cyclosporin A (CsA), a well-known immunosuppressant agent, is also a substrate of CYP3A and P-gp. Therefore, this study aimed to investigate whether and how WZ affects pharmacokinetics of CsA in rats. The AUC0-48 h and Cmax of CsA were increased by 40.1% and 13.1%, respectively, with a single oral co-administration of WZ and high dose of CsA (37.8 mg/kg). Interestingly, after a single oral co-administration of WZ and low dose of CsA (1.89 mg/kg), the AUC0-36 h and Cmax of CsA were dramatically increased by 293.1% (from 1103.2 ± 293.0 to 4336.5 ± 1728.3 ng.h/mL; p < 0.05) and 84.1% (from 208.5 ± 67.9 to 383.1 ± 92.5 ng/mL; p < 0.05), respectively. The CL/F was decreased from 1.7 L/h/kg to 0.5 L/h/kg. Thus, the effect of WZ on high dose of CsA was not significant, but pharmacokinetic parameters of CsA at low dose were significantly influenced by co-administration of WZ. The herb-drug interaction should be taken into consideration at this situation.

A study about drug combination therapy of Schisandra sphenanthera extract and Rapamycin in healthy subjects

To assess the effect of the drug combination of Schisandra sphenanthera extract (SchE) and Rapamycin (RAPA), 18 healthy subjects were given oral treatments of RAPA alone and with SchE. Pharmacokinetic investigations and indexes of hepatic and renal functions, as well as other indices of oral RAPA administration (2 mg), were performed both before and after the SchE treatment period. Whole-blood RAPA concentrations were determined by enzyme-linked immunosorbent assay. The research found that the mean whole-blood RAPA AUC0–∞, Cmax, and tmax increased almost 2-, 2.1-, and 1.3-fold, respectively, and CL/F (–38.0%) decreased almost 1.6-fold in these subjects when RAPA was administered with SchE compared with oral RAPA administered alone. The results of this study proved that SchE can increase the oral bioavailability of RAPA and will add important information to the interaction area between drugs and herbal products.

Toxicological actions of plant-derived and anthropogenic methylenedioxyphenyl-substituted chemicals in mammals and insects

The methylenedioxyphenyl (MDP) substituent is a structural feature present in many plant chemicals that deter foraging by predatory insects and herbivores. With increasing use of herbal extracts in alternative medicine, human exposure to MDP-derived plant chemicals may also be significant. Early studies found that most MDP agents themselves possess relatively low intrinsic toxicity, but strongly influence the actions of other xenobiotics in mammals and insects by modulating cytochrome P-450 (CYP)-dependent biotransformation. Thus, after exposure to MDP chemicals an initial phase of CYP inhibition is followed by a sustained phase of CYP induction. In insects CYP inhibition by MDP agents underlies their use as pesticide synergists, but analogous inhibition of mammalian CYP impairs the clearance of drugs and foreign compounds. Conversely, induction of mammalian CYP by MDP agents increases xenobiotic oxidation capacity. Exposure of insects to MDP-containing synergists in the environment, in the absence of coadministered pesticides, may also enhance xenobiotic detoxication. Finally, although most MDP agents are well tolerated, several, typified by safrole, aristolochic acid, and MDP-kavalactones, are associated with significant toxicities, including the risk of hepatotoxicity or tumorigenesis. Thus, the presence of MDP-substituted chemicals in the environment may produce a range of direct and indirect toxicities in target and nontarget species.

Experimental Adjustment on Drug Interactions through Intestinal CYP3A Activity in Rat: Impacts of Kampo Medicines Repeat Administered

TO PROVIDE THE INFORMATION THAT IS NECESSARY FOR MAKING THE PROPER USE OF KAMPO MEDICINES, WE HAVE PROPOSED THE ADEQUATE METHODOLOGY FOCUSED ON THE FOLLOWING ISSUES: (i) kampo medicines emphasize the effects produced by the combination of herbal drugs rather than the individual effect of any single herb and (ii) Intestinal CYP3A has become a key factor for the bioavailability of orally administrated drugs. In the present study, we investigated both the in vivo and in vitro effects of Saireito and Hochuekkito (kampo formulas) on CYP3A activities. From our study, oral pre-treatment with Saireito or Hochuekkito did not affect the pharmacokinetics of nifedipine after intravenous administration to rats. When nifedipine was administered to rat intrajejunum, a significant decrease of AUC was showed by pre-treatment with both kampo formulas. Saireito pre-treatment led to 80% decrease in C(max) of nifedipine. Saireito caused significant increases in both protein expression and metabolic activity of CYP3A in intestinal microsome, whereas it had no effect on CYP3A in hepatic microsome. Our result also showed that this affect of Saireito can be gone by wash-out with 1 week. These findings demonstrated that Saireito may induce CYP3A activity of intestine but not of liver in rats. When resources for research are limited, well-designed scientific studies except clinical trials also have many advantages.

The protective effect of Schisandra lignans on stress-evoked hepatic metastases of P815 tumor cells in restraint mice

AIM OF THE STUDY

The present study was conducted to investigate the effects of schisandra lignans extract (SLE) on stress-evoked hepatic metastases of mastocytoma P815 tumor cells, which was closely related with immune function.

MATERIALS AND METHODS

The high-performance liquid chromatography (HPLC) fingerprint of SLE was recorded and the percentage composition of schisandra lignans was determined as 82.63%. The contributions of the immunomodulatory properties of SLE to the protective effects on stress-induced hepatic metastases were studied.

RESULTS

Our results found that restraint stress significantly promoted hepatic metastases of P815 tumor cells. However, oral administration of SLE (100 and 200mg/kg/d, 14d) significantly reduced the number of metastatic colonies in liver of restrained mice. SLE was further found to be significantly improving T lymphocyte proportions and increasing cytotoxic T lymphocyte (CTL) activity of immunized spleen cells in stressed mice.

CONCLUSION

These results indicated that the protective effects of SLE on hepatic metastases were related to its alleviation of the adverse effects of stressors for bio-homeostasis and immunoprotection. The obtained data provided evidences to elucidate the traditional use of Fructus schisandrae as a tonic or sedative.

Effect of Wuzhi tablet (Schisandra sphenanthera extract) on the pharmacokinetics of paclitaxel in rats

Wuzhi tablet (WZ, registration no. in China: Z20025766) is a preparation of an ethanol herb extract of Wuweizi (Schisandra sphenanthera) containing 7.5 mg Schisantherin A per tablet. It was reported recently that WZ could significantly increase the blood concentrations of tacrolimus, which might be due to the inhibitory effect of WZ and its ingredients on P-gp and/or CYP450 activity. Paclitaxel is a substrate of the efflux transporter P-gp, and is mainly metabolized by CYP450 enzymes in the liver. Therefore, the purpose of this study was to investigate whether and how WZ affects the pharmacokinetics of paclitaxel in rats. After pretreatment with WZ, there were significant increases in the AUC(0-24h) of oral paclitaxel (from 280.8 ± 97.3 to 543.5 ± 115.2 h ng/mL; p < 0.05) and C(max) (from 44.6 ± 16.4 to 86.8 ± 16.1 ng/mL; p < 0.05). The pharmacokinetic data for i.v. paclitaxel with WZ showed a relatively small (when compared against oral paclitaxel) but still significant increase in AUC(0-24h) (from 163.6 ± 22.1 to 212.7 ± 17.7 h ng/mL; p < 0.05) and a decrease in clearance (from 3.2 ± 0.6 to 2.2 ± 0.3 L/h/kg; p < 0.05). Thus, the presence of WZ improved the systemic exposure of paclitaxel in rats. The herb-drug interaction between WZ and paclitaxel should be taken into consideration in clinical use.

Cytochrome P450 3A4 inhibitory constituents of the wood of Taxus yunnanensis

From the aqueous extract of the wood of Taxus yunnanensis, which showed cytochrome P450 3A4 (CYP3A4) inhibition, a new isoflavan [(3S,4R)-4'-hydroxy-6,3'-dimethoxyisoflavan-4-ol (1)], a new degraded lignan [2,3-bis(hydroxymethyl)-7-hydroxy-6-methoxy-1-tetralone (2)], and a new lignan [(7R)-7-hydroxytaxiresinol (3)] were isolated, together with nine known lignans. Among the isolates obtained, α-conidendrin (12) showed strong CYP3A4 inhibition with an IC(50) value of 0.2 μM.

Schisandrin B-induced glutathione antioxidant response and cardioprotection are mediated by reactive oxidant species production in rat hearts

To investigate the involvement of reactive oxidant species (ROS), presumably arising from cytochrome P-450 (CYP)-catalyzed metabolism of schisandrin B (Sch B), in triggering glutathione antioxidant response, Sch B induced reduced nicotinamide adenine dinucleotide phosphate (NADPH)-dependent and CYP-catalyzed reaction and associated ROS production were examined in rat heart microsomes. Sch B analogs were also studied for comparison. Using rat heart microsomes as a source of CYP, Sch B and schisandrin C (Sch C), but not schisandrin A and dimethyl diphenyl bicarboxylate (an intermediate compound derived from the synthesis of Sch C), were found to serve as co-substrate for the CYP-catalyzed NADPH oxidation reaction, with concomitant production of ROS. The stimulation of CYP-catalyzed NADPH oxidation reaction and/or ROS production by Sch B or Sch C correlated with the increase in mitochondrial reduced glutathione level and protection against ischemia/reperfusion (I/R) injury in rat hearts. The involvement of ROS in Sch B-induced cardioprotection was further confirmed by the suppressive effect produced by N-acetylcysteine or alpha-tocopherol pretreatment. Taken together, these results suggest that Sch B-induced glutathione antioxidant response and cardioprotection may be mediated by ROS arising from CYP-catalyzed reaction.

Inhibition of cytochrome P450 3A4 activity by schisandrol A and gomisin A isolated from Fructus Schisandrae chinensis

We studied the effects of schisandrol A (SCH) and gomisin A (GOM), two of the main bioactive components of Fructus Schisandrae chinensis, on cytochrome P450-3A4 (CYP3A4) activity and cellular glutathione (GSH) level. In a cell-free system both SCH and GOM inhibited CYP3A4 activity with IC(50) values of 32.02 microM and 1.39 microM, respectively. SCH or GOM at concentrations up to 100 microM did not alter cellular GSH level in regular HepG2 cells and P-glycoprotein overexpressing HepG2-DR cells. Since SCH and GOM may reverse multidrug resistance (MDR) by impeding the activity of P-glycoprotein, a membrane xenobiotic exporter, SCH or GOM could affect cellular drug metabolism in addition to drug uptake.

Inhibitory effects of polyphenols on human cytochrome P450 3A4 and 2C9 activity

Polyphenols present in foods and supplements may contribute to human health by preventing cardiovascular diseases and cancer. Drug-food or drug-herb interactions have recently come into focus but, except for some phytochemicals, few components of food or herbs participate in such interactions. In this study, we systematically evaluated the inhibitory effects of 60 polyphenols and related compounds on human cytochrome P450 (CYP) 3A4 and CYP2C9 activity by in vitro assay to investigate whether some polyphenols induce drug interactions. In addition, the kinetics of potent CYP inhibitors was investigated by Lineweaver-Burk plot analysis. Three coumarins and 12 flavonoids significantly suppressed CYP3A4 or CYP2C9 activities. Lineweaver-Burk plot analysis indicated that apigenin and its dimer amentoflavone and imperatorin displayed a mixed type of inhibition on CYP3A4 or CYP2C9. Among the inhibitors, amentoflavone was the most potent inhibitor of CYP3A4 and CYP2C9 activities with IC(50) values of 0.07 and 0.03 microM, respectively. The K(i) value of amentoflavone was significantly lower than that of the CYP2C9 inhibition positive control sulfaphenazole. These findings suggest that some dietary polyphenols may have the potential to inhibit the metabolism of clinical drugs.

Technology for improving the bioavailability of small molecules extracted from traditional Chinese medicines

Evidence that small molecules extracted from traditional Chinese medicines (TCMs) have beneficial effects on health is increasingly being reported in the scientific literature and these compounds are now widely recognized as potential therapeutic drugs. There have been several detailed studies of the absorption, distribution, metabolism and excretion of these compounds in rats and humans. However, some active components have low bioavailability owing to their unsuitable physicochemical and biopharmaceutical characteristics, resulting in differences in vivo. The main problem in using natural products as a source of pharmaceutical lead compounds is the need to improve the bioavailability of these compounds. This review presents and discusses the current methods used for improvement and their impact on the bioavailability of some new pharmaceutical lead compounds from TCMs.

In vitro inhibition of CYP3A4 by herbal remedies frequently used by cancer patients

The herbal remedies Natto K2, Agaricus, mistletoe, noni juice, green tea and garlic, frequently used by cancer patients, were investigated for their in vitro inhibition potential of cytochrome P-450 3A4 (CYP3A4) metabolism. To our knowledge, only garlic and green tea had available data on the possible inhibition of CYP3A4 metabolism. Metabolic studies were performed with human c-DNA baculovirus expressed CYP3A4. Testosterone was used as a substrate and ketoconazole as a positive quantitative inhibition control. The formation of 6-beta-OH-testosterone was quantified by a validated HPLC methodology. Green tea was the most potent inhibitor of CYP3A4 metabolism (IC(50): 73 microg/mL), followed by Agaricus, mistletoe and noni juice (1324, 3594, >10 000 microg/mL, respectively). All IC(50) values were high compared with those determined for crude extracts of other herbal remedies. The IC(50)/IC(25) ratios for the inhibiting herbal remedies ranged from 2.15 to 2.67, indicating similar inhibition profiles of the herbal inhibitors of CYP3A4. Garlic and Natto K2 were classified as non-inhibitors. Although Agaricus, noni juice, mistletoe and green tea inhibited CYP3A4 metabolism in vitro, clinically relevant systemic or intestinal interactions with CYP3A4 were considered unlikely, except for a probable inhibition of intestinal CYP3A4 by the green tea product.

Pharmacokinetic and pharmacodynamic study of interaction of Rhodiola rosea SHR-5 extract with warfarin and theophylline in rats

Significant pharmacokinetic/pharmacodynamic interactions between various herbal products and drugs being substrates of cytochrome P450 have recently been reported. The aim of this study was to determine whether Rhodiola rosea SHR-5 extract interacts with warfarin and theophylline when administered concomitantly. Thus, concomitant treatment of rats with theophylline and SHR-5 did not give rise to significant effects on the pharmacokinetics of theophylline. Simultaneous administration of SHR-5 and warfarin did not alter significantly the pharmacokinetics or the anticoagulant activity of warfarin. It is concluded that SHR-5 might be of value in the treatment of patients with mild or moderate depression, and that its interaction with co-administered drugs is likely to be negligible.