Cytochrome P450 enzymes are composed of many isozymes and involved in the biotransformation of both exogenous and endogenous substances. A growing number of studies have found that the P450 enzymes do not always follow the classical Michaelis-Menten kinetics, but show atypical kinetic behavior, which is also the current research hotspot. In this paper, the category and mechanisms of atypical kinetics of the P450 enzyme were reviewed, providing theoretical basis for the research of enzyme kinetics.
Animals ; Benzoflavones ; pharmacology ; Binding Sites ; Cytochrome P-450 CYP3A ; chemistry ; metabolism ; Cytochrome P-450 Enzyme System ; chemistry ; metabolism ; Enzyme Activation ; Humans ; Kinetics ; Protein Binding ; Substrate Specificity

<p>OBJECTIVETo study the inhibitory effect of total saponins of the root and rhizome of Panax notoginseng (PNS) on drug metabolism enzyme CYP3A in rat livers and its kinetic analysis.p><p>METHODMicrosome enzyme was prepared by differential velocity centrifugation. Michaelis constant (Km) and maximum velocity (Vmax) of CYP3A, 50% inhibitory concentration of PNS on CYP3A, and the inhibition type and the inhibition constant of CYP3A (Ki, Kis) of PNS on CYP3A were calculated by Lineweaver-Burk and the low of semi-effect-probit.p><p>RESULTTotal saponins of the root and rhizome of panax notoginseng inhibited CYP3A activity, with IC50 of 689.54 mg x L(-1). Compared with the substrate aminopyrine, CYP3A showed Km of 0.036 mmol x L(-1) and Vmax of 21.01 micromol min(-1) x g(-1). Total saponins of the root and rhizome of panax notoginseng showed a mixed inhibition on CYP3A, with the inhibition constants of 247.79 mg x L(-1) (Ki) and 321.79 mg x L(-1) (Kis).p><p>CONCLUSIONTotal saponins of the root and rhizome of panax notoginseng have a significant effect on CYP3A activity in rat livers.p>
Animals ; Cytochrome P-450 CYP3A ; chemistry ; genetics ; metabolism ; Cytochrome P-450 CYP3A Inhibitors ; Enzyme Inhibitors ; chemistry ; pharmacology ; Kinetics ; Liver ; chemistry ; drug effects ; enzymology ; Male ; Panax notoginseng ; chemistry ; Rats ; Rats, Sprague-Dawley ; Rhizome ; chemistry ; Saponins ; chemistry ; pharmacology

Licorice root has been frequently used as antitode in traditional Chinese medicine. As the main active component of Licorice root, glycyrrhetic acid (GA) is mainly metabolized in liver. This study was designed to investigate the in vitro metabolism of GA by human liver microsomes (HLM) and human recombinant cytochrome P450 (CYP) isoforms. The results indicated that GA was metabolized mainly by CYP3A4. The K(m), V(max) and CL(int) of GA in HLM were 18.6 micromol x L(-1), 4.4 nmol x mg(-1) (protein) x min(-1) and 0.237 mL x mg(-1) (protein) x min(-1), respectively. At concentration up to 50 micromol x L(-1), GA inhibited CYP2C19, CYP2C9 and CYP3A4 enzyme activities with the inhibitory potencies up to 50%.
Aryl Hydrocarbon Hydroxylases ; antagonists & inhibitors ; metabolism ; Cytochrome P-450 CYP2C19 ; Cytochrome P-450 CYP2C9 ; Cytochrome P-450 CYP3A ; metabolism ; Cytochrome P-450 CYP3A Inhibitors ; Enzyme Inhibitors ; pharmacology ; Glycyrrhetinic Acid ; isolation & purification ; pharmacokinetics ; pharmacology ; Glycyrrhiza ; chemistry ; Humans ; Isoenzymes ; metabolism ; Microsomes, Liver ; enzymology ; metabolism ; Plant Roots ; chemistry ; Plants, Medicinal ; chemistry

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.
Animals ; Cytochrome P-450 CYP1A2 ; metabolism ; Cytochrome P-450 CYP2C9 ; metabolism ; Cytochrome P-450 CYP3A ; metabolism ; Cytochrome P-450 Enzyme Inhibitors ; Cytochrome P-450 Enzyme System ; metabolism ; Drug Interactions ; Glucuronosyltransferase ; metabolism ; Humans ; Ligusticum ; chemistry ; Microsomes, Liver ; enzymology ; NADP ; metabolism ; pharmacology ; Pyrazines ; metabolism ; pharmacokinetics ; Rats ; Uridine Diphosphate Glucuronic Acid ; metabolism ; pharmacology

Cytochrome P450 3A4 (CYP3A4), is the dominant human liver hemoprotein enzyme localized in the endoplasmic reticulum (ER), and is responsible for the metabolism of more than 50% of clinically relevant drugs. While we were studying CYP3A4 expression and activity in human liver, we found that anti-CYP3A4 antibody cross-reacted with a lower band in liver cytoplasmic fraction. We assessed the activities of CYP3A4 and its truncated form in the microsomal and cytoplasmic fraction, respectively. In the cytoplasmic fraction, truncated CYP3A4 showed catalytic activity when reconstituted with NADPH-cytochrome P-450 reductase and cytochrome b5. In order to determine which site was deleted in the truncated form in vitro, we transfected cells with N-terminal tagged or C-terminal tagged human CYP3A4 cDNA. The truncated CYP3A4 is the N-terminal deleted form and was present in the soluble cytoplasmic fraction. Our result shows, for the first time, that N-terminal truncated, catalytically active CYP3A4 is present principally in the cytoplasm of human liver cells.
Blotting, Western ; Catalysis ; Cell Line ; Cytochrome P-450 CYP3A/chemistry/*metabolism ; Cytoplasm/*enzymology ; Humans ; Microsomes, Liver/*enzymology

Effects of six kinds of Chinese herb extracts, including Folium Crataegi extract, Herba Epimedii extract, Folium Acanthopanacis Senticosi extract, Trifolium pratense L. extract, Folium Ginkgo extract and Radix Puerariae extract, on the activities of CYP450 isozymes (CYP1A2, CYP2C, CYP2E1, CYP2D, CYP3A) in rat hepatic microsomals were studied by using a UPLC-MS/MS (MRM) and cocktail probe substrates method. The results showed that effects of six kinds of Chinese herb extracts on each CYP450 isozyme activity were inhibitory. The IC50 of Folium Crataegi extract for the inhibition of rat microsomal CYP2D activity was only for 4.04 microg x mL(-1), which showed the highest inhibition; Trifolium pratense L. extract had strong inhibitory action to CYP2D, the IC50 value was 5.73 microg x mL(-1); Folium Crataegi extract also had strong inhibitory action on CYP2E1, the IC50 value was 10.91 microg x mL(-1). Furthermore, the IC50 of Folium Ginkgo extract for the inhibition of rat microsomal CYP3A, 2D, 2E1 activities were 45.12, 35.45 and 22.41 microg x mL(-1), respectively, and the IC50 of Folium Acanthopanacis Senticosi extract on the inhibition of rat microsomal CYP2E1 activity was 32.89 microg x mL(-1). In addition, mechanism of inhibition experimental results showed that the inhibiting abilities of Folium Crataegi extract and Radix Puerariae extract on each CYP450 isozyme increased with the increasing of the preincubation time, therefore, the inhibitory effects were a mechanism-based inhibition.
Animals ; Chromatography, High Pressure Liquid ; Crataegus ; chemistry ; Cytochrome P-450 CYP1A2 ; metabolism ; Cytochrome P-450 CYP2E1 ; metabolism ; Cytochrome P-450 CYP3A ; metabolism ; Cytochrome P-450 Enzyme System ; metabolism ; Drugs, Chinese Herbal ; isolation & purification ; pharmacology ; Eleutherococcus ; chemistry ; Epimedium ; chemistry ; Ginkgo biloba ; chemistry ; Inhibitory Concentration 50 ; Male ; Microsomes, Liver ; enzymology ; Plants, Medicinal ; chemistry ; Pueraria ; chemistry ; Rats ; Rats, Sprague-Dawley ; Tandem Mass Spectrometry ; Trifolium ; chemistry

<p>OBJECTIVETo study the effects of the water extract of Rehmannia glutionsa, Scrophularia ningpoensis, Asparagus cochinchinensis and Ophiopogon japonicas, which are the drug from Tianwang Buxin Wan from nourishing vin, on the content of cytohrome P450 (CYP450) in rat and the activities of CYP3A, CYP2E1 and CYP1A2 to investigate the role of CYP450 in the biotransformation of Tianwang Buxin Wan.p><p>METHODThe rats were killed after administrated with extracts once daily for consecutive 7 days, the livers were removed rapidly and weighed, liver microsomes were prepared with ultra-centrifuge method, the contents of liver microsomal CYP450, cytochrome b5 (Cytb5) and the activities of CYP3A were examined by ultraviolet spectrophotometry, the activities of CYP2E1 and CYP1A2 were determined by high performance liquid chromatography (HPLC).p><p>RESULTAll groups had no difference in the levels of liver indexe compared with normal sodium group. The water extract of R. glutionsa obviously decreased the contents of P450 (P < 0.01) and increased the activity of CYP3A (P < 0.01) and CYP1A2 (P <0.05). The water extract of S. ningpoensis decreased the contents of P450 (P < 0.05) and significantly increased CYP3A and CYP1A2 activities (P < 0.01). A. cochinchinensis increased content of Cytb5 (P < 0.05) in rat and increased the activity of CYP2E1 (P < 0.05) and CYP1A2 (P < 0.01). O. japonicas had no significant difference on the contents of CYP450 and Cytb5 while increased the activities of CYP3A (P < 0.05), CYP2E1 (P < 0.05) and CYP1A2 (P < 0.01).p><p>CONCLUSIONR. glutionsa and S. ningpoensis could decrease the content of CYP450 enzyme in rat liver and induct the activities of CYP3A and CYP1A2. A. cochinchinensis could induct the activities of CYP2E1 and CYP1A2. O. japonicus could induction the activities of CYP3A, CYP2E1 and CYP1A2 in Tianwang Buxin Wan. By inhibiting CYP450 activity to decrease the metabolism of other drugs, the effect of other functional groups in the compatibility of Tianwang Buxin Wan can be enhanced, and a theoretical basis on studying the compatible mechanism can be provided.p>
Animals ; Asparagus Plant ; chemistry ; Cytochrome P-450 CYP1A2 ; metabolism ; Cytochrome P-450 CYP2E1 ; metabolism ; Cytochrome P-450 CYP3A ; metabolism ; Cytochrome P-450 Enzyme System ; metabolism ; Drugs, Chinese Herbal ; Enzyme Activation ; drug effects ; Humans ; Liver ; drug effects ; enzymology ; Male ; Microsomes, Liver ; drug effects ; enzymology ; Ophiopogon ; chemistry ; Rats ; Rats, Sprague-Dawley ; Rehmannia ; chemistry ; Scrophularia ; chemistry

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.
Animals ; Cells, Cultured ; Cnidium ; chemistry ; Coumarins ; isolation & purification ; metabolism ; Cytochrome P-450 CYP2D6 Inhibitors ; Cytochrome P-450 CYP3A ; Cytochrome P-450 Enzyme Inhibitors ; Cytochrome P-450 Enzyme System ; Hepatocytes ; metabolism ; Male ; Plants, Medicinal ; chemistry ; Quercetin ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Rifampin ; pharmacology ; Sulfaphenazole ; pharmacology ; Troleandomycin ; administration & dosage ; pharmacology ; Yohimbine ; pharmacology

The primary objective was to develope a UPLC method for determine the concentration of buspirone hydroxychloride in plasma and to evaluate the effects of Aconiti Laterlis Radix and Aconiti Laterlis Radix compatibility of Glycyrrhizae Radix on CYP3A4 in vivo. ACQUITY UPLC BEH C18 column (2.1 mm x 10 mm, 1.7 microm) was used for the gradient elution with a 2.0 mmol x L(-1) ammonium acetate (pH 7.4, A)-acetonitrile (B) solution, 0-2.2 min, 10% - 60% B, 2.2-2.5 min, 60% B, 2.5-3.0 min, 60%-75% B, 3.0-3.5 min, 75% B, 3.5-4.0 min, 75%-10% B, at the flow rate of 0.3 mL x min(-1) at room temperature. The UV wavelenght was detected at 243 nm. The linear calibration curve ranged between 0.078 125-20.0 microg (r = 0.9975). The average recovery (n = 6) of buspirone hydroxychloride was 85.62% (RSD 6.8%). The results showed that this method has good specificity and repeatability, and which can be used for the determination of buspirone hydrochlorid in serum. In animial studies, single dose Aconiti Laterlis Radix extract treatment (0.5 g x kg(-1)) decreased buspirone hydroxychloride AUC(0-2 h) (52.8%, P = 0.020), increased CL/F (122%, P = 0.045). Compared to the saline treatment group, Aconiti Laterlis Radix compatibility of Glycyrrhizae Radix extract treatment has no effect on CYP3A4 in rat. The results indicated that Aconiti Laterlis Radix extract induced CYP3A4 while Aconiti Laterlis Radix compatibility of Glycyrrhizae Radix extract had no effect on CYP3A4 in vivo. Aconiti Laterlis Radix had been detoxified when be used as compatibility of Glycyrrhizae Radix.
Aconitum ; chemistry ; Animals ; Chromatography, High Pressure Liquid ; methods ; Cytochrome P-450 CYP3A ; Cytochrome P-450 Enzyme System ; genetics ; metabolism ; Drugs, Chinese Herbal ; administration & dosage ; Gene Expression ; drug effects ; Glycyrrhiza ; chemistry ; Herb-Drug Interactions ; Male ; Rats ; Rats, Sprague-Dawley

This paper aimed to study the six chemical components of Polygoni Multiflori Radix (gallic acid, quercetin, luteolin, kaempferol, resveratrol, apigenin). By the established pregnane X receptor (human pregnant X receptor, PXR) CYP3A4 mediated drug induced rapid screening technique, the effect of chemical components on the cell activity was detected by MTS cell method, and the value of IC₅₀ was calculated. The dual luciferase reporter system was used to co-transfect PXR reporter gene expression vector containing transcriptional regulation and CYP3A4 with HepG2 cells, with 10 μmol·L⁻¹ rifampicin (RIF) as a positive control, and 10 μmol·L⁻¹ of ketoconazole (TKZ) as negative control. Gallic acid, quercetin, luteolin, kaempferol, apigenin, resveratrol(5, 10, 20 μmol·L⁻¹) were used to incubate for 24 h, and the luciferase activity was detected. The results showed that when plasmid pcDNA3.1 was co-transfected with pGL4.17-CYP3A4, gallic acid and resveratrol had an inhibitory effect on the regulation of CYP3A4, and quercetin, luteolin, kaempferol had an inductive effect on CYP3A4; when pcDNA3.14-PXR was co-transfected with pGL4.17-CYP3A4, quercetin, luteolin, kaempferol, apigenin, resveratrol had an inductive effect. To sum up, the 6 reported liver injury components had inhibitory or activating effects on CYP3A4. After PXR plasmid was involved, 5 components had an inductive effect on CYP3A4, and the inductive effects of 2 components were significantly different. In this experiment, we found that 2 kinds of potential liver injury components in Polygoni Multiflori Radix had been induced by CYP3A4, which was achieved through PXR regulation. It suggested that attention shall be paid to potential drug interactions when combined with Polygoni Multiflori Radix, so as to improve the safety and efficacy.
Cytochrome P-450 CYP3A ; metabolism ; Drugs, Chinese Herbal ; pharmacology ; Hep G2 Cells ; Humans ; Liver ; Phytochemicals ; pharmacology ; Plant Roots ; chemistry ; Polygonum ; chemistry ; Pregnane X Receptor ; metabolism