Discovery of cytochrome P450 enzymes-inhibiting components in traditional Chinese medicine / 中国中药杂志

With the widespread use of traditional Chinese medicine(TCM) and the integration of TCM and western medicine, drug-drug interaction(DDI) is considered as a major cause of therapeutic failures and side effects. Cytochrome P450 enzymes(CYPs) are responsible for large number of drug metabolism. CYP3 A4 and CYP2 D6, two important CYP isoforms, are responsible for about 80% drug metabolism of CYPs super family. The inhibition of CYPs is likely to be the most common factor leading to adverse DDI. Therefore, it is of great significance to predict potential CYP3 A4 and CYP2 D6 inhibitors to prevent the DDI. A fast and low-cost me-thod for calculating and predicting CYP inhibiting components was established in this paper, namely support vector machine(SVM) and molecular docking technology which are used to predict and screen drugs. Firstly, 12 qualitative models of two targets were established by using SVM, and the optimal model was selected to predict the compounds in traditional Chinese medicine database(TCMD). Then, molecular docking technology was used to establish docking model. By analyzing the key amino acids involved in drug-target interactions and combining with SVM model, potential inhibitors of CYP3 A4 and CYP2 D6 were found. From the computational results, astin D and epiberberine exhibited inhibition effect on CYP3 A4 and CYP2 D6, respectively. Astin D was only found in astins family from Aster tataricus, while epiberberine was considered to be the active constituent of Coptidis Rhizoma. Therefore, for the risk of DDI, extra attention should be paid to the source of these potential inhibitors, Asteris Radix et Rhizoma and Coptidis Rhizoma. This computational method provides technical support for discovering potential natural inhibitors of CYPs from Chinese herbs by using SVM and molecular docking model, and it is also helpful to recognize the CYPs-mediated DDI existing in TCM, providing research ideas for further pharmacovigilance of integrated therapy.

Inhibitory effect of flavonoids from Scutellariae Radix on human cytochrome P450 1A / 中国中药杂志

This study investigated the inhibitory effect of eight natural flavonoids in Chinese herb Scutellariae Radix on huamn cytochrome P450 1 A(CYP1 A), a key cancer chemo-preventive target. In this study, phenacetin was used as a probe substrate for CYP1 A, while human liver microsomes and recombinant human CYP1 A enzymes were used as enzyme sources. Liquid chromatography-tandem mass spectrometry was used to monitor the formation rates of acetaminophen, the O-deethylated metabolite of phenacetin. The dose-dependent inhibition curves were depicted based on the changes of the formation rates of acetaminophen, while the IC_(50) were determined. Inhibition kinetic analyses and docking simulations were used to investigate the inhibition modes and mechanism of wogonin(the most potent CYP1 A inhibitor in this herb), while the inhibition constants(K_i) of wogonin against both CYP1 A1 and CYP1 A2 were determined. Among all tested flavonoids, wogonin, 7-methoxyflavanone and oroxylin A displayed a strong inhibitory effect on CYP1 A(IC_(50)100 μmol·L~(-1)). Further investigations demonstrated that wogonin had a weak inhibitory effect on other human CYP enzymes, suggesting that it could be used as a lead compound for the development of specific inhibitors of CYP1 A. Furthermore, the inhibition kinetic analyses clearly demonstrated that wogonin could strongly inhibit phenacetin O-deethylation in both CYP1 A1 and CYP1 A2 in a competitive manner, with K_i values at 0.118 and 0.262 μmol·L~(-1), respectively. Molecular docking demonstrated that wogonin could strongly interact with CYP1 A1 and CYP1 A2 via hydrophobic and π-π interactions, as well as Ser120 and Ser116 in CYP1 A1 via hydrogen-bonding. In conclusion, this study found that some flavonoids in Scutellariae Radix displayed a strong inhibitory effect on CYP1 A, while wogonin is the most potent CYP1 A inhibitor with a relatively high selectivity towards CYP1 A over other human CYPs.

Isochlorogenic acid A affects P450 and UGT enzymes in vitro and in vivo / 中国天然药物

Isochlorogenic acid A (ICQA), which has anti-inflammatory, hepatoprotective, and antiviral properties, is commonly presented in fruits, vegetables, coffee, plant-based food products, and herbal medicines. These herbal medicines are usually used in combination with other medicines in the clinic. However, little is known about the regulatory effects of ICQA on drug-metabolizing enzymes and the herb-drug interactions. In the present study, we evaluated the inhibitory potentials of ICQA on CYP1A2, CYP2C9, CYP2C19, CYP3A4, CYP2D6, and CYP2E1 in vitro based on a cocktail approach. The P450 and UGT activities in mice treated with ICQA for a prolonged period were also determined. Our results demonstrated that ICQA exhibited a weak inhibitory effect on CYP2C9 in human liver microsomes with IC being 57.25 μmol·L and Ki being 26.77 μmol·L. In addition, ICQA inhibited UGT1A6 activity by 25%, in the mice treated with ICQA (i.p.) at 30 mg·kg for 14 d, compared with the control group. Moreover, ICQA showed no mechanism-based inhibition on CYP2C9 or UGT1A6. In conclusion, our results further confirm a safe use of ICQA in clinical practice.

Interaction between CYP450 enzymes and metabolism of traditional Chinese medicine as well as enzyme activity assay / 中国中药杂志

Drugs are exogenous compounds for human bodies, and will be metabolized by many enzymes after administration. CYP450 enzyme, as a major metabolic enzyme, is an important phase I drug metabolizing enzyme. In human bodies, about 75% of drug metabolism is conducted by CYP450 enzymes, and CYP450 enzymes is the key factor for drug interactions between traditional Chinese medicine( TCM) -TCM, TCM-medicine and other drug combination. In order to make clear the interaction between metabolic enzymes and TCM metabolism, we generally chose the enzymatic activity as an evaluation index. That is to say, the enhancement or reduction of CYP450 enzyme activity was used to infer the inducing or inhibitory effect of active ingredients and extracts of traditional Chinese medicine on enzymes. At present, the common method for measuring metabolic enzyme activity is Cocktail probe drugs, and it is the key to select the suitable probe substrates. This is of great significance for study drug's absorption, distribution, metabolism and excretion (ADME) process in organisms. The study focuses on the interaction between TCMs, active ingredients, herbal extracts, cocktail probe substrates as well as CYP450 enzymes, in order to guide future studies.

Tetramethoxystilbene, a selective CYP1B1 inhibitor, suppresses adipogenesis of C3H10T1/2 pluripotent stem cells / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the inhibitory effects of tetramethoxystilbene, a selective CYP1B1 inhibitor, on adipogenic differentiation of C3H10T1/2 multi-potent mesenchymal cells.</p><p><b>METHODS</b>In vitro cultured C3H10T1/2 cells at full confluence were induced by adipogenic agents (10 µg/ml insulin, 2 µmol/L dexamethasone and 0.5 mmol/L 3-isobutyl-1-methylxanthine) and exposed simultaneously to TMS at the final concentrations of 1.0, 2.0 or 4.0 µg/ml. Oil Red-O staining was used to observe the cell differentiation. The expression of peroxisome proliferator-activated receptor gamma (PPARγ) and its target genes cluster of differentiation 36 (CD36) and fatty acid binding protein 4 (FABP4) were quantified by real-time RT-PCR and Western blotting.</p><p><b>RESULTS</b>Oil Red-O staining and TG contents revealed that TMS suppressed induced differentiation of C3H10T1/2 cells. TMS exposure of the cells dose-dependently decreased both mRNA and protein expressions of PPARγ, a key nuclear transcription factor during adipogenesis, and also lowered the mRNA expressions of PPARγ target genes CD36 and FABP4.</p><p><b>CONCLUSION</b>TMS can suppress adipogenic differentiation of C3H10T1/2 cells by inhibiting PPARγ</p>

Study on inhibitory effect of water extract of Polygonum multiflorum on CYP1A2 and CYP2E1 enzymatic activities and mRNA expressions in rat liver / 中国中药杂志

Rats were continuously given different doses of water extract of Polygonum multiflorum (1, 10 g x kg(-1)) for 7 days to prepare liver microsomes. Cocktail in vitro incubation approach and Real-time quantitative PCR technology were used to observe the effect of water extract of P. multiflorum on CYP450 enzymatic activities and mRNA expressions in rat liver. Compared with the blank control group, both 1, 10 g x kg(-1) water extract of P. multiflorum treated groups showed significant inhibitions in CYP2E1 enzymatic activities and mRNA expressions (enzymatic activities of CYP2E1, P < 0.01; mRNA expression of CYP2E1, P < 0.05 in 1 g x kg(-1) group, P < 0.01 in 10 g x kg(-1) group). They revealed a significant increase in the enzymatic activity of CYP3A1 (P < 0.01), but without significant change in mRNA expressions. The 10 g x kg(-1) group showed a significant inhibition in CYP1A2 enzymatic activities and mRNA expressions in rat livers (P < 0.01).

Interaction of butylphthalide with rat and human liver CYP450 isoenzymes / 药学学报

The work aims to study the drug metabolizing enzymes involved in the metabolism of butylphthalide and evaluate the induction and inhibition activities of butylphthalide on CYP450 isoenzymes by using in vitro (liver microsome incubation system of rats and human) and in vivo (CYP induced model of rats) method. Butylphthalide was incubated with selective inhibitors of CYP450, and its metabolic rate was determined to identify the metabolizing isoenzymes of NBP in rat (normal and induced rats) and human liver microsomes. The in vitro inhibition effect of butylphthalide on 6 main liver microsomal CYP450 isoenzymes was evaluated by using probe drugs; the induction and inhibition activities in vivo of butylphthalide on CYP450 isoenzymes were evaluated by NBP ig dosing (160 mg x kg(-1)) and iv dosing (20 mg x kg(-1)) in rats. After adding the specific inhibitors of CYP2C11, 2E1 and 3A 1/2 for rat, CYP2C19, 2E1 and 3A4/5 for human, the metabolism of NBP in rat and human liver microsomes were reduced 38.8%, 86.2%, 78.4% and 51.0%, 92.0%, 58.9% of control, respectively. The metabolic rates of NBP in CYP2E1 and 3A 1/2 induced rat liver microsomes were increased 25.5% and 68.9%. High concentration of NBP (≥ 200 μmol x L(-1), in vitro) could inhibit the activities of CYP1A2, 2C6, 2C11 and 2D2 in rats, and high concentration of NBP ( ≥ 15 μmol x L(-1), in vitro) could inhibit the activity of CYP2C19 in human. All the results indicated that NBP should be mainly metabolized by CYP2E1, 2C11 and 3A 1/2 in rats and CYP2E1, 2C19 and 3A4/5 in human. High concentration of NBP could inhibit human CYP2C19 in vitro. No significant induction/inhibition effects of NBP were observed on rat liver CYP450 isoforms after ig 160 mg x kg(-1) NBP or iv 20 mg x kg(-1) NBP.

Advance in studies on natural antidepressant drugs and cytochrome P450 / 中国中药杂志

In the fast pace of modern life and under the heavy work pressure, the prevalence of depression has increased year by year. Meanwhile, the demands for antidepressant drugs have also grown, especially the high-efficiency and low-toxicity natural antidepressant drugs, mainly including polyphenols, flavonoids, organic acids, alkaloids and terpenoids. Cytochrome P450 (CYP450) is a type of enzymes involving oxidative metabolism of drugs in vivo, and can change the pharmacokinetics and efficacy of drugs. Therefore, it is of important significant to define the effect of natural antidepressant drugs on CYP450 in human bodies, in order to improve the rational clinical medication, avoid drug interactions and reduce adverse reactions.

Effect of Gegen Qinlian decoction on hepatic cytochrome CYP450 isozymes in rats by HPLC-MS/MS / 中国中药杂志

To study the effect of Gegen Qinlian decoction and its major effective components on five hepatic microsomal CYP450 isozymes in rats. The in vitro hepatic microsomal incubation technique was used to co-culture Gegen Qinlian decoction and its major effective components together with each probe substrate. HPLC-MS/MS was used to establish the analytical method for metabolites of the five isoform probe substrates of CYP450 isozymes, detect the linearity among micoromal protein concentration, incubation time and metabolite formation amount. And HPLC-MS/MS was applied to determine the formation rate (V) of corresponding metabolites (acetaminophen, 4-OH-chlorzoxazone, dextrophan, 6-OH-chlorzoxazone and 6β-hydroxytestosterone) specific probe substrates of the five isoform probe substrates of CYP450 isozymes (phenacetin, polbutamide, dextromethorphan, chlorzoxazone, testosterone), in order to determine the activity of each isozyme. The result showed good linearity among acetaminophen, 4-OH-tolbutamide, dextrophan, 6-OH-chlorzoxazone and 6β-hydroxytestosterone, satisfactory precision, stability and average recovery, suggesting the method was feasible. The optimized in vitro microsomal incubation conditions conformed to the requirements in the guideline of drug-drug interaction. Gegen Qinlian decoction showed different degrees of inhibitor effect on 5 CYP450 isoforms (CYP1A2, CYP2C11, CYP2D2, CYP2E1, CYP3A1/2). Its major effective component berberine could inhibit each CYP450 isoform at high concentrations (except for CYP1A2, CYP3A1/2).

Investigation of metabolic kinetics and reaction phenotyping of ligustrazin by using liver microsomes and recombinant human enzymes / 药学学报

The metabolic characteristics of ligustrazin (TMPz) in liver microsomes were investigated in the present study. The reaction phenotyping of TMPz metabolism was also identified by in vitro assessment using recombinant human cytochrome P450 enzymes (CYP) and UDP glucuronosyltransferases (UGT). TMPz was incubated at 37 degrees C with human (HLM) and rat liver microsomes (RLM) in the presence of different co-factors. The metabolic stability and enzyme kinetics of TMPz were studied by determining its remaining concentrations with a LC-MS/MS method. TMPz was only metabolically eliminated in the microsomes with NADPH or NADPH+UDPGA. In the HLM and RLM with NADPH+UDPGA, t1/2, K(m) and V(max) of TMPz were 94.24 +/- 4.53 and 105.07 +/- 9.44 min, 22.74 +/- 1.89 and 33.09 +/- 2.74 micromol x L(-1), 253.50 +/- 10.06 and 190.40 +/- 8.35 nmol x min(-1) x mg(-1) (protein), respectively. TMPz showed a slightly higher metabolic rate in HLM than that in RLM. Its primary oxidative metabolites, 2-hydroxymethyl-3, 5, 6-trimethylpyrazine (HTMP), could undergo glucuronide conjugation. The CYP reaction phenotyping of TMPz metabolism was identified using a panel of recombinant CYP isoforms (rCYP) and specific CYP inhibitors in HLM. CYP1A2, 2C9 and 3A4 were found to be the major CYP isoforms involved in TMPz metabolism. Their individual contributions were assessed b) using the method of the total normalized rate to be 19.32%, 27.79% and 52.90%, respectively. It was observed that these CYP isoforms mediated the formation of HTMP in rCYP incubation. The UGT reaction phenotyping of HTMP glucuronidation was also investigated preliminarily by using a panel of 6 UGT isoforms (rUGT). UGT1A1, 1A4 and 1A6 were the predominant isoforms mediated the HTMP glucuronidation. The results above indicate that the metabolism of TMPz involves multiple enzymes mediated phase I and phase II reactions.

Research progresses of Mycobacterium tuberculosis cytochrome P450s as a potential drug target / 药学学报

Identification and validation of a new target is one of the most important steps for new antituberculosis (TB) drug discovery. Researches have shown that Mycobacterium tuberculosis (Mtb) encodes 20 CYP450 enzymes which play important roles in the synthesis and metabolism of lipid, cholesterol utilization, and the electron transport of respiratory chain in Mtb. With the critical roles within the organism as well as the protein structures of six Mtb CYP450 enzymes being clarified, some of them have been highlighted as potential anti-tuberculosis targets. In this paper, the phylogenetic analysis, the structural features, and the enzymatic functions of Mtb CYPs, as well as the mechanism of interactions with selective inhibitors such as azole antifungal agents for the CYPs have been reviewed and summarized. The druggability of the CYPs has also been analyzed for their further utility as targets in high throughput screening and rational design of more selective inhibitors.

The metabolic fingerprint of the compatibility of Radix Aconite and Radix Paeoniae Alba and its effect on CYP450 enzymes / 药学学报

Using a UPLC-MS/MS (MRM) and cocktail probe substrates method, the metabolic fingerprint of the compatibility of Radix Aconite (RA) and Radix Paeoniae Alba (RPA) and its effect on CYP450 enzymes were investigated. These main CYP isoforms include CYP 1A2, CYP 2C, CYP 2E1, CYP 2D and CYP 3A. Compared with the inhibition effect of RA decoctions on CYP450 isoforms, their co-decoctions of RA and RPA with different proportions can decrease RA' inhibition on CYP3A, CYP2D, CYP2C and CYP1A2, but can not reduce RA' effect on CYP2E1. The metabolic fingerprints of RA decoction and co-decoctions with different proportions of RPA in CYP450 of rat liver were analyzed by UPLC-MS. Compared with the metabolic fingerprints of RA decoction, the intensity of diester-diterpenoid aconitum alkaloids decreased significantly, while the intensity of monoester-diterpenoid alkaloids significantly increased in the metabolic fingerprints of co-decoctions of RA and RPA. The results suggest that RA coadministration with RPA increased the degradation of toxic alkaloid and show the effect of toxicity reducing and efficacy enhancing.

Assessment of the effects of Radix bupleuri and vinegar-baked Radix bupleuri on cytochrome 450 activity by a six-drug cocktail approach / 中国天然药物

AIM@#To assess the effects of Radix Bupleuri and vinegar-baked Radix Bupleuri on cytochrome 450 activity of rats.@*METHODS@#Six probe drugs (caffeine, midazolam, dextromethorphan, tolbutamide, omeprazole, chlorzoxazone) were simultaneously given to rats after different dosing of Radix Bupleuri or vinegar-baked Radix Bupleuri for seven days. The plasma concentrations of the six probes were measured by high performance liquid chromatography-triple quadrupole mass spectrometry (HPLC-MS/MS) and their corresponding pharmacokinetic parameters were calculated.@*RESULTS@#The AUC and T1/2 of midazolam, dextromethorphan and chlorzoxazone decreased significantly (P 0.05) from that of controlled rats, however, treatment of Radix Bupleuri decreased tolbutamide T1/2. The pharmacokinetics of caffeine in all Radix Bupleuri or vinegar-baked Radix Bupleuri-treated rats showed no statistically significant difference (P > 0.05) from that of controlled rats.@*CONCLUSION@#The Radix Bupleuri and vinegar-baked Radix Bupleuri have different effects on the CYP2C9 and CYP2C19. Radix Bupleuri and vinegar-baked Radix Bupleuri have strong induction effects on the CYP2E1, CYP2D6 and CYP3A4, however, have no impact on CYP1A2. The reason of different therapeutic effects of Radix Bupleuri and vinegar-baked Radix Bupleuri extract may be the different effects of Radix Bupleuri and vinegar-baked Radix Bupleuri on the CYP2C9 and CYP2C19.

CYP450 enzyme inhibition of berberine in pooled human liver microsomes by cocktail probe drugs / 中国中药杂志

<p><b>OBJECTIVE</b>To investigate the effect of CYP450 enzyme inhibition of berberine in pooled human liver microsomes by cocktail probe drugs.</p><p><b>METHOD</b>Cocktail probe drugs method has been established, an LC-MS/MS analytical method has been established to determine the five probes of midazolam, phenacetin, dextromethorphan, tolbutamide, chlorzoxazone and the internal standard was benzhydramine to evaluate the effect of CYP450 activity following administration of berberine in pooled human liver microsomes.</p><p><b>RESULT</b>Compared with control group, the pharmacokinetics of midazolam, phenacetin and tolbutamide were no significant differences, but the pharmacokinetics of chlorzoxazone was significantly decreased. There were no significant differences for the pharmacokinetics of dextromethorphan when the concentration of berberine was 50 microg x L(-1). The pharmacokinetics of dextromethorphan was significantly decreased when the concentration of berberine was exceed 200 microg x L(-1).</p><p><b>CONCLUSION</b>Berberine has no influence on the activities of CYP3A4, CYP1A2 and CYP2C19 below 2 000 microg x L(-1), but can inhibit the activity of CYP2E1 and CYP2D6 in concentration-dependent.</p>

Inhibitory effect of imperatorin and isoimperatorin on activity of cytochrome P450 enzyme in human and rat liver microsomes / 中国中药杂志

Imperatorin (IM) and isoimperatorin (ISOIM) are major active components of common herbal medicines from Umbelliferae plants, and widely used in clinic. This article studies the inhibitory effect of IM and ISOIM on the activity of cytochrome P450 (CYP) enzyme, and assesses their potential drug-drug interaction. IM and ISOIM were incubated separately with human or rat liver microsomes for 30 min, with phenacetin, bupropion, tolbutamide, S-mephenytoin, dextromethorphan and midazolam as probe substrates. Metabolites of the CYP probe substrates were determined by LC-MS/MS, and IC50 values were calculated to assess the inhibitory effect of the two drugs on human CYP1A2, 2B6, 2C9, 2C19, 2D6 and 3A4 enzymes, as well as on rat CYP1A2, 2B6, 2D2 and 3A1/2, and grade their inhibitory intensity. In human liver microsomes, IM and ISOIM showed different inhibitory effects on all of the six CYP isoenzymes. They were strong inhibitors for 1A2 and 2B6. The IC50 values were 0.05 and 0.20 micromol x L(-1) for 1A2, and 0.18 and 1.07 micromol x L(-1) for 2B6, respectively. They also showed moderate inhibitory effect on 2C19, and weak effect on 2C9, 2D6 and 3A4. In rat liver microsomes, IM and ISOIM were identified as moderate inhibitors for 1A2, with IC50 values of 1.95 and 2.98 micromol x L(-1). They were moderate and weak inhibitors for 2B6, with IC50 values of 6.22 and 21.71 micromol x L(-1), respectively. They also had weaker inhibitory effect on 2D2 and 3A1/2. The results indicated that IM and ISOIM had extensive inhibitory effects on human CYP enzymes. They are strong inhibitors of CYP1 A2 and 2B6 enzymes. However, it is worth noting the interaction arising from the inhibitory effect of CYP enzymes in clinic.

Metabolites and metabolic pathways of mesaconitine in rat liver microsomal investigated by using UPLC-MS/MS method in vitro / 药学学报

Mesaconitine was incubated with rat liver microsomes in vitro. The metabolites of mesaconitine in rat liver microsomes were identified by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method with high resolution power. A typical reaction mixture of 100 mol L-1 Tris-HCI buffer (pH 7.4) containing 0.5 gL-1 microsomal protein and 50 micro molL-1 mesaconitine was prepared. The above reaction mixture was divided into six groups, and the volume of each group was 200 micro L. The incubation mixture was pre-incubated at 37 degrees C for 2 min and the reactions were initiated by adding NADPH generating system. After 90 min incubation at 37 degrees C, 200 micro L of acetonitrile was added to each group to stop the reaction. The metabolites of mesaconitine were investigated by UPLC-MS/MS method. Mesaconitine and 6 metabolites M1-M6 were found in the incubation system. The structures were characterized according to the data from MS/MS spectra and literatures. The metabolic reactions of mesaconitine in rat liver microsomes included the demethylation, deacetylation, dehydrogenation and hydroxylation. The major metabolic pathways of mesaconitine in rat liver microsomes were determined by UPLC-MS/MS on multiple reaction monitoring (MRM) mode combined with specific inhibitors of cytochrome P450 (CYP) isoforms, including alpha-naphthoflavone (CYP1A2), quinine (CYP2D), diethyldithiocarbamate (CYP2E1), ketoconazole (CYP3A) and sulfaphenazole (CYP2C), separately. Mesaconitine was mainly metabolized by CYP3A. CYP2C and CYP2D were also more important CYP isoforms for the metabolism reactions of mesaconitine, but CYP1A2 and CYP2E1 haven't any contribution to MA metabolism in rat liver microsomes.

Inhibitory effects of astragaloside IV on cytochrome P450 enzyme of rat liver microsomes / 中国中药杂志

<p><b>OBJECTIVE</b>To provide a scientific basis for the drug-combination and aim to examine whether astragaloside IV has the impact on the cytochrome P450 enzymes.</p><p><b>METHOD</b>Tolbutamide, chlorzoxazone, coumarin, nifedipine, and phenacetin were as probe substrates of rat CYP2C9, CYP2E1, CYP2A6, CYP3A4, and CYP1A2, and were incubated in rat liver microsomes with astragaloside IV. Triplicate samples were run to generate IC50 value by incubating P450 probe substrates in the presence of five concentrations of astragaloside IV in the incubation mixture. The K(i) values were determined by fitting the probe substrate at various inhibitor concentrations to the equations for competitive inhibition, noncompetitive inhibition, noncompetitive inhibition, and mixed-type inhibition.</p><p><b>RESULT</b>IC50 and K(i) values were estimated, and the types of inhibition were determined. Among the five probe substrates, astragaloside IV might not significantly affect CYP2E1, CYP2A6 and CYP1A2-mediated metabolism in rats, but was a competitive inhibitor of CYP2C9 (IC50 35.40 micromol x L(-1), K(i) 42.88 micromol x L(-1)), and was a uncompetitive inhibitor of CYP3A4 (IC50 88.24 micromol x L(-1), K(i) 33.31 micromol x L(-1)).</p><p><b>CONCLUSION</b>These results suggested that astragaloside IV inhibited CYP2C9 and CYP3A4, which provided useful information for safe and effective use of astragaloside IV.</p>

Mechanism related to docosahexaenoic acid induced large conductance calcium-activated potassium channel currents increase in coronary smooth muscle cells / 中华心血管病杂志

<p><b>OBJECTIVE</b>To investigate the mechanism of enhanced large conductance calcium-activated potassium channel currents (BK) in coronary smooth muscle cells (SMCs) by docosahexaenoic acid (DHA).</p><p><b>METHODS</b>Coronary SMCs were isolated by enzyme digestion. Potassium channels in coronary SMCs were identified by applications of different potassium blockers. Effects of DHA and its metabolite 16, 17-epoxydocosapentaenoic acid (16, 17-EDP) on BK channels in the absence and presence of cytochrome P450 epoxygenase inhibitor SKF525A were studied by patch clamp in whole-cell configuration.</p><p><b>RESULTS</b>BK channels were widely distributed in SMCs, and BK currents in normal SMCs accounted for (64.2 ± 2.7)% of total potassium currents (n = 20). DHA could activate BK channels, and its 50% effective concentration (EC(50)) was (0.23 ± 0.03) µmol/L, however, the effect of DHA on BK channels was abolished after SMCs were incubated with cytochrome P450 epoxygenase inhibitor SKF525A. 16, 17-EDP, a metabolite of DHA, could reproduce the effects of DHA on BK channels, and its EC(50) was (19.7 ± 2.8) nmol/L.</p><p><b>CONCLUSION</b>DHA and metabolites can activate BK channels and dilate coronary arteries through activating cytochrome P450 epoxygenase pathway.</p>

Research progress on drug metabolism of flavanoids / 中国中药杂志

Flavanoids are important phytochemistry compositions in foods and traditional Chinese medicines (TCM) and are mainly oxidized by CYP1A family in vivo. Some methoxyflavones could also be metabolized through demethylation. Usually, flavanoids own one or more phenolic hydroxyl group in their molecular structures, which facilitate conjugation with glucuronic acid and sulphuric acid, forming metabolites with good water-solubility to excrete. Natural flavanoids mainly exist in glycoside, and after oral ,they would be easily metabolized to aglycone by hydratase in gut microflora and then absorbed into blood. Besides, many flavanoids have strong inhibitory actions on Cytochrome P450 enzymes, which are significant mechanisms in cancer precaution and tumor inhibition. In this paper, we reviewed lots of articles and summarized metabolism characteristics of flavanoids and metabolism interaction with Cytochrome P450 enzymes.

Metabolism of osthol in isolated hepatocytes of rat / 药学学报

The paper is aimed to study the metabolic characteristics of osthol (Ost) in isolated hepatocytes of rat to identify which isoforms of CYP450 were responsible for Ost metabolism in vitro. The concentration of Ost in isolated hepatocytes incubation system was determined by HPLC-UV. The effects of incubation time, substrate concentration and hepatocytes amount on the metabolic characteristics of Ost were investigated. CYP2C8 inhibitor quercetin (Que), CYP2C9 inhibitor sulfaphenazole (Sul), CYP2D6 inhibitor yohimbine (Yoh), CYP3A4 inhibitor troleandomycin (Tro) and CYP450 inducer rifampicin (Rif) were used to investigate their effects on the metabolism of Ost. The metabolism of Ost in isolated rat hepatocytes showed an enzymatic kinetic characteristics. Rif induced Ost elimination in rat hepatocytes; Yoh, Sul, Que did not have effects on Ost metabolism in vitro. Between 0-200 micromol x L(-1), Tro inhibited Ost metabolism in a concentration-dependent manner. CYP3A4 is the enzyme metabolizing Ost in vitro; CYP2C8, CYP2C9 and CYP2D6 did not involve in Ost metabolism in rat hepatocytes.