Effects of flavonoids isolated from Scutellariae radix on cytochrome P-450 activities in human liver microsomes

Potential herb‒drug interactions between anti-COVID-19 drugs and traditional Chinese medicine

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread worldwide. Effective treatments against COVID-19 remain urgently in need although vaccination significantly reduces the incidence, hospitalization, and mortality. At present, antiviral drugs including Nirmatrelvir/Ritonavir (Paxlovid^TM), Remdesivir, and Molnupiravir have been authorized to treat COVID-19 and become more globally available. On the other hand, traditional Chinese medicine (TCM) has been used for the treatment of epidemic diseases for a long history. Currently, various TCM formulae against COVID-19 such as Qingfei Paidu decoction, Xuanfei Baidu granule, Huashi Baidu granule, Jinhua Qinggan granule, Lianhua Qingwen capsule, and Xuebijing injection have been widely used in clinical practice in China, which may cause potential herb-drug interactions (HDIs) in patients under treatment with antiviral drugs and affect the efficacy and safety of medicines. However, information on potential HDIs between the above anti-COVID-19 drugs and TCM formulae is lacking, and thus this work seeks to summarize and highlight potential HDIs between antiviral drugs and TCM formulae against COVID-19, and especially pharmacokinetic HDIs mediated by metabolizing enzymes and/or transporters. These well-characterized HDIs could provide useful information on clinical concomitant medicine use to maximize clinical outcomes and minimize adverse and toxic effects.

Drug-herb interactions between Scutellaria baicalensis and pharmaceutical drugs: Insights from experimental studies, mechanistic actions to clinical applications

Whilst the popular use of herbal medicine globally, it poses challenges in managing potential drug-herb interaction. There are two folds of the drug-herb interaction, a beneficial interaction that may improve therapeutic outcome and minimise the toxicity of drug desirably; by contrast, negative interaction may evoke unwanted clinical consequences, especially with drugs of narrow therapeutic index. Scutellaria baicalensis Georgi is one of the most popular medicinal plants used in Asian countries. It has been widely used for treating various diseases and conditions such as cancer, diabetes, inflammation, and oxidative stress. Studies on its extract and bioactive compounds have shown pharmacodynamic and pharmacokinetic interactions with a wide range of pharmaceutical drugs as evidenced by plenty of in vitro, in vivo and clinical studies. Notably, S. baicalensis and its bioactives including baicalein, baicalin and wogonin exhibited synergistic interactions with many pharmaceutical drugs to enhance their efficacy, reduce toxicity or overcome drug resistance to combat complex diseases such as cancer, diabetes and infectious diseases. On the other hand, S. baicalensis and its bioactives also affected the pharmacokinetic profile of many drugs in absorption, distribution, metabolism and elimination via the regulatory actions of the efflux pumps and cytochrome P450 enzymes. This review provides comprehensive references of the observed pharmacodynamic and pharmacokinetic drug interactions of Scutellaria baicalensis and its bioactives. We have elucidated the interaction with detailed mechanistic actions, identified the knowledge gaps for future research and potential clinical implications. Such knowledge is important for the practice of both conventional and complementary medicines, and it is essential to ensure the safe use of related herbal medicines. The review may be of great interest to practitioners, consumers, clinicians who require comprehensive information on the possible drug interactions with S. baicalensis and its bioactives.

Effects of Baoyuan decoction, a traditional Chinese medicine formula, on the activities and mRNA expression of seven CYP isozymes in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Baoyuan decoction (BYD), a traditional Chinese medicine (TCM) formula, is composed of four herbs and widely used with western drugs to treat coronary heart disease, aplastic anemia and chronic renal failure in clinic. However, no study of the effect of BYD on the cytochrome P450 (CYP) activities has been reported.

AIM OF THE STUDY

The purpose of the present study was to evaluate the potential influences of BYD on the activities of seven CYP isozymes (CYP1A2, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4) in rats.

MATERIALS AND METHODS

A sensitive and selective UPLC-MS/MS method for simultaneous determination of seven probe drugs and internal standard (IS) in rat plasma was developed and validated. The influence of BYD on the activities of CYP isozymes and mRNA expression levels were carried out by comparing plasma pharmacokinetics and real-time reverse transcription-polymerase chain reaction (RT-PCR) of probe drugs between control and BYD treatment groups respectively.

RESULTS

The calibration curve were linear, with correlation coefficient (r) > 0.99 for seven probe drugs. The intra and inter-assay accuracy and precision of the method were within ± 14.9% and the recoveries ranged from 83.2% to 106.1%. Compared with control group, BYD at low (1.46 g/kg) and high (7.30 g/kg) dosages could significantly increase C_max and AUC_0-t of chlorzoxazone and testosterone, while decrease AUC_0-t of phenacetin at high dosage and increase AUC_0-t of tolbu_tamide and metoprolol. Additionally, BYD had increased AUC_0-t of bupropion at low dosage and decreased it at high dosage. The mRNA expression results were in accordance with those of pharmacokinetic.

CONCLUSION

BYD exhibited inhibitory effects on CYP2C9, CYP2E1, and CYP3A4. Moreover, BYD had induction effects on CYP1A2, and CYP2D6 activities. However, no significant change in CYP2C19 activity was observed. It would be useful for the safe and effective usage of BYD in clinic.

The Effect of Yokukansan, a Traditional Herbal Preparation Used for the Behavioral and Psychological Symptoms of Dementia, on the Drug-Metabolizing Enzyme Activities in Healthy Male Volunteers

The concomitant use of herb and prescription medications is increasing globally. Herb-drug interactions are therefore a clinically important problem. Yokukansan (YKS), a Japanese traditional herbal medicine, is one of the most frequently used herbal medicines. It is effective for treating the behavioral and psychological symptoms of dementia. We investigated the potential effects of YKS on drug-metabolizing enzyme activities in humans. An open-label repeat-dose study was conducted in 26 healthy Japanese male volunteers (age: 22.7±2.3 years) with no history of smoking. An 8-h urine sample was collected after a 150-mg dose of caffeine and a 30-mg dose of dextromethorphan before and after the administration of YKS (2.5 g, twice a day for 1 week). The activities of cytochrome P450 (CYP) 1A2, CYP2D6, CYP3A, xanthine oxidase (XO) and N-acetyltransferase 2 (NAT2) were assessed based on the urinary metabolic indices of caffeine and dextromethorphan, and the urinary excretion ratio of 6β-hydroxycortisol to cortisol. There were no statistically significant differences in the activities of the examined enzymes before or after the 7-d administration of YKS. Although further studies assessing the influence of YKS on the pharmacokinetics and pharmacodynamics of the substrates of the drug-metabolizing enzymes are needed to verify the present results, YKS is unlikely that a pharmacokinetic interaction will occur with concomitantly administered medications that are predominantly metabolized by the CYP1A2, CYP2D6, CYP3A, XO and NAT2.

Chemical and pharmacological evaluations on the extract of Scutellaria baicalensis Georgi (Huang-Qin) prepared by various extraction methods

Background

This study reported a comprehensive approach (comparing the extraction yields, chemical profiles, antioxidant properties and CYP450-inhibitory effects) to evaluated the effectiveness of various extraction methods [microwave-assisted extraction using water (MAE-W), heat reflux extraction using water (HRE-W), ultrasonic extraction using 70 % ethanol and ultrasonic extraction using ethanol (UE-E)] for Huang-Qin (HQ), the dried root of Scutellaria baicalensis Georgi.

Results

The HQ extraction efficiency by MAE-W was the best. The chemical profiles of extracts obtained using HRE-W and MAE-W were similar; whereas more flavones but less flavone glycosides were detected in the UE-E extract. There was no difference in the antioxidant properties among different extracts. In vitro human liver microsome assays illustrated that all extracts possessed herb–drug interaction potentials but the UE-E extract are shown with a potent interaction with CYP3A4-metabolized drugs.

Conclusion

MAE-W is a favorable method for the preparation of HQ extracts based on extraction yield, pharmacological properties and safety.

Modulation of the pharmacokinetics, therapeutic and adverse effects of NSAIDs by Chinese herbal medicines

INTRODUCTION

Concomitant use of NSAIDs and Chinese herbal medicines (CHMs) is frequent, yet summarized information on their interactions is lacking.

AREAS COVERED

A systematic review of literature in four evidence-based English databases was performed. Articles which reported CHMs altering the pharmacokinetics, therapeutic and adverse effects of NSAIDs were identified and summarized. Such interactions may lead to beneficial, detrimental or no change in outcomes. The current review covers four therapeutic effects of NSAIDs, including: i) anti-inflammatory; ii) analgesic; iii) antiplatelet, cardiovascular and cerebrovascular; and iv) anticancer effects and four adverse effects of NSAIDs, including: i) gastrointestinal ulcer; ii) nephrotoxicity; iii) hepatotoxicity; and iv) antiplatelet effects and bleeding.

EXPERT OPINION

While majority of CHMs demonstrated effectiveness in alleviating NSAIDs-induced adverse effects and potentiating the therapeutic effects, this review provides insights for development of CHMs as add-on medications to NSAIDs therapies. However, since limited information was from well-designed clinical trials, the findings are not yet conclusive and more clinical studies are warranted to provide guidance for healthcare professionals. In future, researches on interactions between NSAIDs and CHMs are expected to grow and modern approaches such as pharmacogenomics might enhance the throughput and accuracy of identifying clinically relevant interactions.

Da-Chaihu-Tang alters the pharmacokinetics of nifedipine in rats and a treatment regimen to avoid this

Objectives

To investigate the influence of co-administrated Da-Chaihu-Tang (DCT; a traditional Chinese formulation) on the pharmacokinetics of nifedipine, as well as the safe optimal dosing interval to avoid the adverse interactions.

Methods

A single dose of DCT was administered with nifedipine simultaneously, 2 h before, 30 min before or 30 min after nifedipine administration. Pharmacokinetics of nifedipine with or without DCT were compared. The influences of DCT on nifedipine intestinal mucosal and hepatic metabolism were studied by using rat in-vitro everted jejunal sac model and hepatic microsomes.

Key findings

A simultaneous co-administration of DCT significantly increased the area under concentration-time curve from time zero to infinity (AUC0-inf) of nifedipine. In-vitro mechanism investigations revealed that DCT inhibited both the intestinal and the hepatic metabolism of nifedipine. Further study on the optimal dosing interval for nifedipine and DCT revealed that administration of DCT 30 min before or after nifedipine did not significantly change the AUC of nifedipine.

Conclusions

The bioavailability of nifedipine is significantly increased by a simultaneous oral co-administration of DCT. This increase is caused by the inhibitory effect of DCT on both the intestinal mucosal and the hepatic metabolism of nifedipine. The dose interval between DCT and nifedipine needs to be set for over 30 min to avoid such drug–drug interactions.

Scutellaria baicalensis in stroke management: nature's blessing in traditional Eastern medicine

Scutellaria baicalensis Georgi is the most widely used medicinal plant in traditional Eastern medicine, especially in Chinese medicine. The major phytochemicals isolated from S. baicalensis are flavonoids, glycosides and their glucoronides such as baicalin, baicalein, wogonin etc. More than 30 different kinds of flavonoids are isolated from this plant. S. baicalensis and its flavonoids are reported to have several pharmacological activities, which includes anti-allergic, antioxidant, anti apoptic, anti-inflammatory effects and many more. Recently, S. baicalensis and its isolated flavonoids have been studied for their neuroprotective effects, through a variety of in vitro and in vivo models of neurodegenerative diseases, plausibly suggesting that S. baicalensis has salutary effect as a nature's blessing for neuroprotection. In this review, we are focousing on the neuroprotective effects of S. baicalensis and its flavonoids in ischemia or stroke-induced neuronal cell death. We aimed at compiling all the information regarding the neuroprotective effect of S. baicalensis in various experimental models of cerebral ischemia or stroke.

Dietary flavonoids modulate CYP2C to improve drug oral bioavailability and their qualitative/quantitative structure-activity relationship

This study aims to improve the drug oral bioavailability by co-administration with flavonoid inhibitors of the CYP2C isozyme and to establish qualitative and quantitative (QSAR) structure-activity relationships (SAR) between flavonoids and CYP2C. A total of 40 naturally occurring flavonoids were screened in vitro for CYP2C inhibition. Enzyme activity was determined by measuring conversion of tolbutamide to 4-hydroxytolbutamide by rat liver microsomes. The percent inhibition and IC50 of each flavonoid were calculated and used to develop SAR and QSAR. The most effective flavonoid was orally co-administered in vivo with a cholesterol-reducing drug, fluvastatin, which is normally metabolized by CYP2C. The most potent CYP2C inhibitor identified in vitro was tamarixetin (IC50 = 1.4 μM). This flavonoid enhanced the oral bioavailability of fluvastatin in vivo, producing a >2-fold increase in the area under the concentration-time curve and in the peak plasma concentration. SAR analysis indicated that the presence of a 2,3-double bond in the C ring, hydroxylation at positions 5, 6, and 7, and glycosylation had important effects on flavonoid-CYP2C interactions. These findings should prove useful for predicting the inhibition of CYP2C activity by other untested flavonoid-like compounds. In the present study, tamarixetin significantly inhibited CYP2C activity in vitro and in vivo. Thus, the use of tamarixetin could improve the therapeutic efficacy of drugs with low bioavailability.

Scutellariae radix suppresses LPS-induced liver endothelial cell activation and inhibits hepatic stellate cell migration

ETHNOPHARMACOLOGICAL RELEVANCE

Liver fibrosis is the result of long-term liver damage and the wound-healing process, in which the hepatic stellate cell (HSC) plays a crucial role during fibrogenesis. The liver sinusoidal endothelial cell (LSEC) is a liver-resident scavenger, contributing to sinusoidal remodeling, HSC activation and liver fibrosis. Lipopolysaccharide (LPS) causes an inflammatory reaction associated with portal circulation and LSECs signaling. Scutellariae radix, the root of Scutellaria baicalensis Georgi, is a Chinese herb widely used for liver diseases. However, its effect on LSEC activation and HSC migration in liver fibrosis has not been investigated yet.

AIM OF THIS STUDY

LPS-induced rat LSEC (rLSEC) activation was used as a model to screen and explore the active components of Scutellariae radix. The anti-fibrotic effect of Scutellariae radix on rLSEC activation and rHSC migration was further investigated.

MATERIALS AND METHODS

LPS-induced rLSEC mRNA expression, including VEGF, VEGFR, MCP-1, and TGF-β1, were examined by real-time PCR analyses. MCP-1 protein levels were measured by an ELISA kit. rLSEC conditioned medium on rHSC migration was measured by wound-healing assay and transwell chemoattraction assay.

RESULTS

Results showed LPS-induced rLSEC activation with upregulated MCP-1 mRNA and protein expressions, and that rLSEC-condition medium enhanced rHSC migration. Both baicalein and wogonin from the active subfraction significantly reduced MCP-1 expression, but only baicalein markedly inhibited rHSC migration in rLSEC conditioned medium.

CONCLUSION

This study demonstrated that Scutellariae radix attenuates LPS-induced rLSEC activation and HSC migration with downregulation of MCP-1 expression. The results provide supporting evidence that Scutellariae radix may be beneficial for the amelioration of liver fibrosis.

Inhibitory effects of daiokanzoto (da-huang-gan-cao-tang) on p-glycoprotein

We have studied the effects of various Kampo medicines on P-glycoprotein (P-gp), a drug transporter, in vitro. The present study focused on Daiokanzoto (Da-Huang-Gan-Cao-Tang), which shows the most potent inhibitory effects on P-gp among the 50 Kampo medicines studied, and investigated the P-gp inhibitory effects of Daiokanzoto herbal ingredients (rhubarb and licorice root) and their components by an ATPase assay using human P-gp membrane. Both rhubarb and licorice root significantly inhibited ATPase activity, and the effects of rhubarb were more potent than those of licorice root. The content of rhubarb in Daiokanzoto is double that in licorice root, and the inhibition patterns of Daiokanzoto and rhubarb involve both competitive and noncompetitive inhibition, suggesting that the inhibitory effects of Daiokanzoto are mainly due to rhubarb. Concerning the components of rhubarb, concentration-dependent inhibitory effects were observed for (−)-catechin gallate, (−)-epicatechin gallate, and (−)-epigallocatechin gallate. In conclusion, rhubarb may cause changes in the drug dispositions of P-gp substrates through the inhibition of P-gp. It appears that attention should be given to the interactions between these drugs and Kampo medicines containing rhubarb as an herbal ingredient.

Inhibition against mosquito cytochrome P450 enzymes by rhinacanthin-A, -B, and -C elicits synergism on cypermethrin cytotoxicity in Spodoptera frugiperda cells

Rhinacanthus nasutus (Acanthaceae) is a shrub reported to contain insecticidal activities. The current study was conducted to determine whether R. nasutus constituents could inhibit benzyloxyresorufin O-debenzylation (BROD) mediated by CYP6AA3 and CYP6P7. Both enzymes have shown pyrethroid degradation activity and been implicated to play role in pyrethroid resistance in Anopheles minumus (Theobald) mosquito, a malaria vector. Three compounds, rhinacanthin-A, -B, and -C that exhibited potent inhibitory activity were isolated and purified from aerial part of R. nasutus. Their kinetic parameters and modes of inhibition were determined. Rhinacanthin-B was the most potent inhibitor in in vitro inhibition assay and exhibited mechanism-based inhibition against both CYP6AA3 and CYP6P7. Rhinacanthin-C which is a major compound of R. nasutus reversibly inhibited both enzymes in vitro with 2-4 folds less inhibitory potency than rhinacanthin-B. In contrast, rhinacanthin-A reversibly inhibited CYP6AA3, but inhibition against CYP6P7 was a mechanism-based inhibition type. Where mechanism-based inhibition was found, the inhibition showed characteristic of time-, concentration-dependence, and requirement of NADPH. Using 3-(4, 5-dimethylthiazol-2-y-l)-2, 5-diphenyltetrazolium bromide (MTT) cytotoxicity assay in intact Spodoptera frugiperda (Sf9) cells, the three compounds increased susceptibility of CYP6AA3- and CYP6P7-expressing cells to cypermethrin cytotoxicity because of inhibition effect on mosquito enzymes. The combined inhibition effect on mosquito cytochrome P450 enzyme and synergistic effect on cypermethrin cytotoxicity of the three R. nasutus compounds could be beneficial for resistance management strategies in mosquito vector control.

Astragaloside IV inhibited the activity of CYP1A2 in liver microsomes and influenced theophylline pharmacokinetics in rats

Objectives

With the growing popularity of herbal and natural medicinal products, attention has turned to possible interactions between these products and pharmaceutical drugs. In this study, we examined whether astragaloside IV (AGS-IV) could inhibit the activity of CYP1A2 in rat liver microsomes in vitro and in vivo.

Methods

The effect of AGS-IV on CYP1A2 activity was investigated using probe substrates: phenacetin in vitro and theophylline in vivo. Phenacetin was incubated in rat liver microsomes with or without AGS-IV, and the mechanism, kinetics and type of inhibition were determined. The inhibitory effect of AGS-IV on CYP1A2 activity in rats was also determined using theophylline in vivo. The pharmacokinetics of theophylline were observed after a single or week-long treatment with AGS-IV.

Key findings

AGS-IV was found to be a competitive inhibitor with a Ki value of 6.29 μm  in vitro. In the multiple-pretreatment rat group, it was found to have a significantly higher area under the concentration–time curve (AUC) for theophylline, as well as a lower apparent oral total body clearance value (CL/F). In contrast, no significant difference in metabolism of theophylline was found for the single pretreatment group.

Conclusions

These findings suggest that AGS-IV is a potent inhibitor of CYP1A2. This work offers a useful reference for the reasonable and safe use of clinically prescribed herbal or natural products to avoid unnecessary herb–drug interactions.

Induction of CYP3A4 and MDR1 gene expression by baicalin, baicalein, chlorogenic acid, and ginsenoside Rf through constitutive androstane receptor- and pregnane X receptor-mediated pathways

The herbal products baicalin, baicalein, chlorogenic acid, and ginsenoside Rf have multiple pharmacological effects and are extensively used in alternative and/or complementary therapies. The present study investigated whether baicalin, baicalein, chlorogenic acid, and ginsenoside Rf induced the expression of the cytochrome P450 3A4 (CYP3A4) and multi-drug resistance 1 (MDR1) genes through the pregnane X receptor and constitutive androstane receptor pathways. Real time PCR, western blotting, and a luminescent assay were used to assess the induction of gene expression and activity of CYP3A4 and MDR1 by the test compounds. The interactions of baicalein/chlorogenic acid/ginsenoside Rf with constitutive androstane receptor and pregnane X receptor were evaluated using luciferase reporter and gel shift assays. Baicalein induced the expression of CYP3A4 and MDR1 mRNA by activating pregnane X receptor and constitutive androstane receptor. Chlorogenic acid and ginsenoside Rf showed a relatively weak effect on CYP3A4 promoter activation only in HepG2 cells cotransfected with constitutive androstane receptor and demonstrated no effects on MDR1 via either the constitutive androstane receptor or pregnane X receptor pathway. Baicalin had no effect on either CYP3A4 or MDR1 gene expression. In conclusion, baicalein has the potential to up-regulate CYP3A4 and MDR1 through the direct activation of the constitutive androstane receptor and pregnane X receptor pathways. Chlorogenic acid and ginsenoside Rf only induced constitutive androstane receptor-mediated CYP3A4 expression.

Cytochrome P450 2C19 inhibitory activity of common berry constituents

The cytochrome P450 enzyme CYP2C19 is involved in the metabolism of many commonly prescribed drugs, including proton pump inhibitors, antiepileptics and antidepressants. CYP2C19 inhibitors from food and food supplements may augment the toxicity of these agents and lead to noncompliance with treatment. The present investigation addresses CYP2C19 inhibition by 18 berry constituents using a chemiluminescent assay. Test compounds displayed inhibitory properties in a concentration-dependent fashion, with IC(50) values ranging from 20.2 microM up to >316 microM. In the order of decreasing effect size, anthocyanidins were followed by anthocyanidin-monoglycosides and procyanidins. Anthocyanidin-diglucosides exhibited weak and biphasic effects. When compared with the CYP2C19 inhibitor fluvoxamine, the flavonoids under study were 50- to 750-fold less potent. It is concluded that the above natural substances are moderate to poor inhibitors of CYP2C19 in vitro.

The in-vivo effects of sho-saiko-to, a traditional Chinese herbal medicine, on two cytochrome P450 enzymes (1A2 and 3A) and xanthine oxidase in man

The Chinese herbal medicine sho-saiko-to is a mixture of seven herbal components (Bupleurum root, Pinellia tuber, Scutellaria root, Jujube fruit, Ginseng root, Glycyrrhiza root and Ginger rhizome) that is widely administered to patients with chronic hepatitis in Japan. We assessed the effects of sho-saiko-to on the activity of cytochrome P450 (CYP) 1A2, CYP3A and xanthine oxidase (XO) in man. Twenty-six healthy subjects were studied to evaluate their baseline activity of CYP1A2 and XO by the respective urinary metabolic ratios of an 8-h urine sample after an oral 150-mg dose of caffeine and of CYP3A by a urinary excretion ratio of 6β-hydroxycortisol (6β-HC) to free cortisol (FC). Thereafter, the subjects received a twice-daily 2.5-g dose of sho-saiko-to for five days, and underwent the caffeine test on day 1 and day 5. The mean activity of CYP1A2 decreased by 16% on both day 1 and day 5 compared with the baseline (P = 0.001). The mean activity of XO also significantly decreased by 25% on day 1 and 20% on day 5 (P < 0.0001) compared with the baseline value. The activity of CYP3A tended to be lower on day 5 than the baseline (P = 0.146). It is concluded that sho-saiko-to reduces CYP1A2 and XO activity in man.

The in-vivo effect of bakumondo-to (TJ-29), a traditional Japanese medicine used for treatment of chronic airway disease, on cytochrome P450 1A2, xanthine oxidase and N-acetyltransferase 2 activity in man

In Japan, patients with chronic airway disease are administered bakumondo-to (TJ-29), a mixture of six herbal components. We have assessed the effects of TJ-29 on the activities of cytochrome P450 (CYP) 1A2, xanthine oxidase and N-acetyltransferase 2 in 26 healthy subjects under a double-blind, randomized, placebo-controlled cross-over study design. The baseline activities of the three enzymes were assessed by the respective urinary metabolic ratios of an 8-h urine sample after an oral 150-mg dose of caffeine. Thereafter, the subjects received a thrice-daily 3.0-g dose of TJ-29 or placebo for seven days, and underwent the same caffeine test on the post-dose days 1 and 7. No statistically significant difference was observed in the activity of the three enzymes between those at baseline, and on day 1 after dosing with TJ-29 or placebo. The mean activity of CYP1A2, xanthine oxidase and N-acetyltransferase 2 tended to be lower on day 7 after dosing with TJ-29 compared with those at baseline and on day 7 after dosing with placebo. However, these changes were not statistically significant in CYP1A2 (P=0.120), xanthine oxidase (P=0.123) or N-acetyltransferase 2 (P=0.056). In conclusion, TJ-29 did not appear to substantially affect the activity of CYP1A2, xanthine oxidase or N-acetyltransferase 2 in man.

In vitro study of the tocolytic effect of oroxylin A from Scutellaria baicalensis root

Scutellariae Radix is one of the well-known tocolytic Chinese herbs. Oroxylin A is isolated from the root of Scutellaria baicalensis. The main syndrome of preterm birth is caused by uterus contractions from excitatory factors. Administration of tocolytic agents is a strategy to prevent the occurrence of preterm births. The aim of this study was to investigate the effects of oroxylin A on contractions of uterine strips isolated from non-pregnant female Wistar rats (250~350 g). Contractions of the uterus were induced with acetylcholine (Ach) (1 μM), PGF_2α (0.1 μM), oxytocin (10^-3 U/ml), KCl (56.3 mM), tetraethylammonium (TEA; 1 and 10 mM), 4-aminopyridine (4-AP; 5 mM), glipizide (30 μM), a nitric oxide synthase (NOS) inhibitor (LNNA; 10^-3M), a β-receptor blocker (propranolol; 10 μM), and a cyclooxygenase inhibitor (indomethacin; 60 μM). The inhibitory effects of the amplitude and frequency of spontaneous contractions by oroxylin A were antagonized with Ach (IC₅₀ 22.85 μM), PGF_2α (IC₅₀27.28 μM), oxytocin (IC₅₀ 12.34 μM), TEA; 1 and 10 mM (IC₅₀ 52.73 and 76.43 μM), 4-AP (IC₅₀ 67.16 μM), and glipizide (IC₅₀27.53 μM), but oroxylin A was not influenced by Ca²⁺-free medium, LNNA, propranolol, or indomethacin. Otherwise, oroxylin A-mediated relaxation of the rat uterus might occur through opening of uterine calcium-dependent potassium channels or adenosine triphosphate potassium channel activation. This suggests that oroxylin A is the tocolytic principle constituent of Scutellariae Radix, and oroxylin A may provide a lead compound for new tocolytic drug development in the future.

Mechanism of CYP2C9 inhibition by flavones and flavonols

This article describes an in vitro investigation of the inhibition of cytochrome P450 (P450) 2C9 by a series of flavonoids made up of flavones (flavone, 6-hydroxyflavone, 7-hydroxyflavone, chrysin, baicalein, apigenin, luteolin, scutellarein, and wogonin) and flavonols (galangin, fisetin, kaempferol, morin, and quercetin). With the exception of flavone, all flavonoids were shown to inhibit CYP2C9-mediated diclofenac 4'-hydroxylation in the CYP2C9 RECO system, with K(i) value <or= 2.2 microM. In terms of the mechanism of inhibition, 6-hydroxyflavone was found to be a noncompetitive inhibitor of CYP2C9, whereas the other flavonoids were competitive inhibitors. Computer docking simulation and constructed mutants substituted at residue 100 of CYP2C9.1 indicate that the noncompetitive binding site of 6-hydroxyflavone lies beside Phe100, similar to the reported allosteric binding site of warfarin. The other flavonoids exert competitive inhibition through interaction with the substrate binding site of CYP2C9 accessed by flurbiprofen. These results suggest flavonoids can participate in interactions with drugs that act as substrates for CYP2C9 and provide a possible molecular basis for understanding cooperativity in human P450-mediated drug-drug interactions.

Negundoside, an iridiod glycoside from leaves of Vitex negundo, protects human liver cells against calcium-mediated toxicity induced by carbon tetrachloride

AIM: To evaluate the protective effect of 2'-p-hydroxybenzoylmussaenosidic acid [negundoside (NG), against carbon tetrachloride (CCl₄)-induced toxicity in HuH-7 cells.

METHODS: CCl₄ is a well characterized hepatotoxin, and inducer of cytochrome P450 2E1 (CYP2E1)-mediated oxidative stress. In addition, lipid peroxidation and accumulation of intracellular calcium are important steps in the pathway involved in CCl₄ toxicity. Liver cells (HuH-7) were treated with CCl₄, and the mechanism of the cytoprotective effect of NG was assessed. Silymarin, a known hepatoprotective drug, was used as control.

RESULTS: NG protected HuH-7 cells against CCl₄ toxicity and loss of viability without modulating CYP2E1 activity. Prevention of CCl₄ toxicity was associated with a reduction in oxidative damage as reflected by decreased generation of reactive oxygen species (ROS), a decrease in lipid peroxidation and accumulation of intracellular Ca²⁺ levels and maintenance of intracellular glutathione homeostasis. Decreased mitochondrial membrane potential (MMP), induction of caspases mediated DNA fragmentation and cell cycle arrest, as a result of CCl₄ treatment, were also blocked by NG. The protection afforded by NG seemed to be mediated by activation of cyclic adenosine monophosphate (cAMP) synthesis and inhibition of phospholipases (cPLA2).

CONCLUSION: NG exerts a protective effect on CYP2E1-dependent CCl₄ toxicity via inhibition of lipid peroxidation, followed by an improved intracellular calcium homeostasis and inhibition of Ca²⁺-dependent proteases.

The ameliorating effect of oroxylin A on scopolamine-induced memory impairment in mice

Oroxylin A is a flavonoid and was originally isolated from the root of Scutellaria baicalensis Georgi., one of the most important medicinal herbs in traditional Chinese medicine. The aim of this study was to investigate the ameliorating effects of oroxylin A on memory impairment using the passive avoidance test, the Y-maze test, and the Morris water maze test in mice. Drug-induced amnesia was induced by administering scopolamine (1 mg/kg, i.p.) or diazepam (1 mg/kg, i.p.). Oroxylin A (5 mg/kg) significantly reversed cognitive impairments in mice by passive avoidance and the Y-maze testing (P<.05). Oroxylin A also improved escape latencies in training trials and increased swimming times and distances within the target zone of the Morris water maze (P<.05). Moreover, the ameliorating effects of oroxylin A were antagonized by both muscimol and diazepam (0.25 mg/kg, i.p., respectively), which are GABA(A) receptor agonists. Furthermore, oroxylin A (100 microM) was found to inhibit GABA-induced inward Cl(-) current in a single cortical neuron. These results suggest that oroxylin A may be useful for the treatment of cognitive impairments induced by cholinergic dysfunction via the GABAergic nervous system.

Effects of hydroxyl group numbers on the B-ring of 5,7-dihydroxyflavones on the differential inhibition of human CYP 1A and CYP1B1 enzymes

Flavonoids are polyphenols composed of two aromatic rings (A, B) and a heterocyclic ring (C). In order to determine the effects of the number of hydroxyl groups in the B-ring of the flavonoids on human cytochrome P450 (CYP) 1 family enzymes, we evaluated the inhibition of CYP1A-dependent 7-ethoxyresorufin omicron-deethylation activity by chrysin, apigenin and luteolin, using bacterial membranes that co-express human CYP1A1, CYP1A2, or CYP1B1 with human NADPH-cytochrome P450 reductase. Chrysin, which possesses no hydroxyl groups in its B-ring, exhibited the most pronounced inhibitory effects on CYP1A2-dependent EROD activity, followed by apigenin and luteolin. On the contrary, CYP1A1-mediated EROD activity was most potently inhibited by luteolin, which is characterized by two hydroxyl groups in its B-ring, followed by apigenin and chrysin. However, all of the 5,7-dihydroxyflavones were determined to similarly inhibit CYP1B1 activity. Chrysin, apigenin, and luteolin exhibited a mixed-type mode of inhibition with regard to CYP1A2, CYP1B1, and CYP1A1, with apparent Ki values of 2.4, 0.5, and 2.0 microM, respectively. These findings suggested that the number of hydroxyl groups in the B-ring of 5,7-dihydroxyflavone might have some influence on the degree to which CYP1A enzymes were inhibited, but not on the degree to which CYP1B1 enzymes were inhibited.

Retention behavior of silica-bonded and novel polymeric reversed-phase sorbents in studies on flavones as chemotaxonomic markers of Scutellaria L. genus

In this study, the effectiveness of both classical and novel polymeric sorbents used in solid-phase extraction (SPE) for isolation of pharmacologically active flavones (baicalin, luteolin, apigenin, wogonin and chrysin) from aerial parts of 13 species of Scutellaria L. (Skullcap) genus was assessed. The highest recoveries of hydrophilic (baicalin, luteolin) flavones for Oasis HLB were obtained, whereas for medium hydrophobic (apigenin) and hydrophobic (wogonin, chrysin) flavones better quantitative results for BakerBond phenyl cartridges were stated. Eluates were analysed using reversed-phase high-performance liquid chromatography with diode array detection (RP-HPLC-DAD). For the five target compounds the determined concentrations ranged from approximately 4 to approximately 15,500 microg/g dry wt. Very good linearities (r(2)>0.9995) of calibration curves were achieved for each flavone. The accuracy was below 5% for most compounds examined. This is the first method reported that enabled simultaneous qualification and quantitation of five flavones (being chemotaxonomic markers) in 13 species of Scutellaria L. genus.

Hepatoprotective effect of baicalin, a major flavone from Scutellaria radix, on acetaminophen-induced liver injury in mice

The protective effects of baicalin (BA), a major flavone from Scutellaria radix, on acetaminophen (AP)-induced hepatotoxicity and the possible mechanism(s) of its protective action were investigated in mice. Treatment with BA (300 mg/kg, p.o.) 0.5 h after AP administration significantly prevented an increase in plasma alanine aminotransferase and aspartate aminotransferase activities and AP-induced hepatic necrosis, and also reduced AP-induced mortality from 43% to 0%. In addition, oral treatment with BA significantly prevented AP-induced depletion of glutathione (GSH) contents. However, BA treatment, by itself, did not affect hepatic GSH contents. The effect of BA on the cytochrome P450 2E1 (CYP2E1), the major isozyme involved in AP bioactivation, was investigated. Oral treatment of mice with BA resulted in a significant decrease in AP-induced CYP2E1 activity together with its inhibition of AP-induced CYP2EI expression. These results show that the hepatoprotective effects of BA against AP overdose may be due to its ability to block the bioactivation of AP by inhibiting CYP2E1 expression.

Green tea polyphenol epigallocatechin-3-gallate protects HepG2 cells against CYP2E1-dependent toxicity

Chronic ethanol consumption causes oxidative damage in the liver, and induction of cytochrome P450 2E1 (CYP2E1) is one pathway involved in oxidative stress produced by ethanol. The hepatic accumulation of iron and polyunsaturated fatty acids significantly contributes to ethanol hepatotoxicity in the intragastric infusion model of ethanol treatment. The objective of this study was to analyze the effect of the green tea flavanol epigallocatechin-3-gallate (EGCG), which has been shown to prevent alcohol-induced liver damage, on CYP2E1-mediated toxicity in HepG2 cells overexpressing CYP2E1 (E47 cells). Treatment of E47 cells with arachidonic acid plus iron (AA + Fe) was previously reported to produce synergistic toxicity in E47 cells by a mechanism dependent on CYP2E1 activity and involving oxidative stress and lipid peroxidation. EGCG protected E47 cells against toxicity and loss of viability induced by AA+Fe; EGCG had no effect on CYP2E1 activity. Prevention of this toxicity was associated with a reduction in oxidative damage as reflected by decreased generation of reactive oxygen species, a decrease in lipid peroxidation, and maintenance of intracellular glutathione in cells challenged by AA+Fe in the presence of EGCG. AA+Fe treatment caused a decline in the mitochondrial membrane potential, which was also blocked by EGCG. In conclusion, EGCG exerts a protective action on CYP2E1-dependent oxidative stress and toxicity that may contribute to preventing alcohol-induced liver injury, and may be useful in preventing toxicity by various hepatotoxins activated by CYP2E1 to reactive intermediates.