Human Liver Cytochrome P450 Enzymes Research Articles

Elucidating the Mechanism of Metabolism of Cannabichromene by Human Cytochrome P450s.

Cannabichromene (CBC) is a nonpsychoactive phytocannabinoid well-known for its wide-ranging health advantages. However, there is limited knowledge regarding its human metabolism following CBC consumption. This research aimed to explore the metabolic pathways of CBC by various human liver cytochrome P450 (CYP) enzymes and support the outcomes using in vivo data from mice. The results unveiled two principal CBC metabolites generated by CYPs: 8'-hydroxy-CBC and 6',7'-epoxy-CBC, along with a minor quantity of 1″-hydroxy-CBC. Notably, among the examined CYPs, CYP2C9 demonstrated the highest efficiency in producing these metabolites. Moreover, through a molecular dynamics simulation spanning 1 μs, it was observed that CBC attains stability at the active site of CYP2J2 by forming hydrogen bonds with I487 and N379, facilitated by water molecules, which specifically promotes the hydroxy metabolite's formation. Additionally, the presence of cytochrome P450 reductase (CPR) amplified CBC's binding affinity to CYPs, particularly with CYP2C8 and CYP3A4. Furthermore, the metabolites derived from CBC reduced cytokine levels, such as IL6 and NO, by approximately 50% in microglia cells. This investigation offers valuable insights into the biotransformation of CBC, underscoring the physiological importance and the potential significance of these metabolites.

In vitro inhibition of six active sesquiterpenoids in zedoary turmeric oil on human liver cytochrome P450 enzymes

In vitro inhibition of six active sesquiterpenoids in zedoary turmeric oil on human liver cytochrome P450 enzymes

Roles of Human Liver Cytochrome P450 Enzymes in Tenatoprazole Metabolism.

Tenatoprazole, a newly developed proton pump inhibitor candidate, was developed as an acid inhibitor for gastric acid hypersecretion disorders such as gastric ulcer and reflux esophagitis. It is known that tenatoprazole is metabolized to three major metabolites of 5'-hydroxy tenatoprazole, tenatoprazole sulfide, and tenatoprazole sulfone in human liver, primarily catalyzed by CYPs 2C19 and 3A4. While CYP2C19 prefers the hydroxylation of tenatoprazole at C-5' position, CYP3A4 is mainly involved in sulfoxidation reaction to make tenatoprazole sulfone. Tenatoprazole sulfide is a major human metabolite of tenatoprazole and is formed spontaneously and non-enzymatically from tenatoprazole. However, its metabolic fate in the human liver is not fully known. Furthermore, no systematic metabolic study has been performed to study tenatoprazole or tenatoprazole sulfide. Here, we studied the functions of human cytochromes P450 in the metabolic pathway of tenatoprazole and tenatoprazole sulfide by using recombinant human P450s and human liver microsomes. Both CYP 2C19 and CYP3A4 showed distinct regioselective and stereospecific monooxygenation activities toward tenatoprazole and tenatoprazole sulfide. Furthermore, a new major metabolite of tenatoprazole sulfide was found, 1'-N-oxy-5'-hydroxytenatoprzole sulfide, which has never been reported. In conclusion, the metabolic fates of tenatoprazole and tenatoprazole sulfide should be considered in the clinical use of tenatoprazole.

Ilexsaponin A1: In vitro metabolites identification and evaluation of inhibitory drug-drug interactions

As a triterpene saponin, ilexsaponin A1 is one of the most abundant, representative and active components in plants of Ilex pubescens, used in the treatment of cardiovascular diseases. This study aimed to identify the metabolites of ilexsaponin A1 and evaluate its in vitro inhibitory drug-drug interaction (DDI) potential by using human liver microsomes (HLM) and cytochrome P450 enzymes (CYPs)-specific probes, with all the qualitative and quantitative analysis performed by LC-MS/MS. As a result, two metabolites generated through the metabolic pathways of glucuronic acid conjugation and glucose conjugation were first time detected in the HLM. An inhibitory DDI evaluating system consisting of 7 major CYP enzymes involving 8 CYP-catalyzed reactions was established, validated and then used for the DDI evaluation. Our data suggested ilexsaponin A1 and its metabolite, ilexgenin A, are not direct or mechanism-based inhibitors of CYP1A2, 2B6, 2C8, 2C9, 2D6, 2E1 or 3A4/5 at 0.05–10 μM. A significant decreased remaining activity of CYP2B6 (from 77.89 % to 23.19 %) was observed in a dose-dependent manner when increased the concentration of ilexsaponin A1 from 50 to 500 μM. Collectively, our data demonstrate ilexsaponin A1 is unlikely to cause DDIs by inhibiting co-administered drugs metabolized by these CYP enzymes.

In vitro inhibition and induction of human liver cytochrome P450 enzymes by a novel anti-fibrotic drug fluorofenidone

Fluorofenidone (AKF-PD) is an analog of pirfenidone and shows stronger antifibrotic effect and lower toxicity compared to pirfenidone in preclinical studies. However, the inhibitory and inducible effects of AKF-PD on human CYP450s are unclear. The aim of this study was to evaluate the ability of AKF-PD to inhibit and induce CYP450s in vitro. In inhibition study, the inhibitory effects of CYP1A2, CYP3A4, CYP2C9, CYP2E1, CYP2C19 and CYP2D6 by AKF-PD were evaluated with the metabolic rate of probe drug of each enzyme in pooled human liver microsomes. The enzyme inducible potential of AKF-PD was evaluated by the mRNA expression and enzyme activity of CYP1A2, CYP2B6 and CYP3A4 in human hepatocytes. The results suggested that AKF-PD produced weak inhibition on CYP1A2 and CYP2C19, while no inhibitory effects were found on the other enzymes. Since the plasma concentration of AKF-PD is much lower than the IC50 values of both CYP1A2 and CYP2C19, the inhibitory effects can be reasonably ignored. On the other hand, AKF-PD showed no inducible effects on CYP1A2 while showed potential inducible ability on CYP2B6 and CYP3A4 in some test groups. Further study of this novel anti-fibrotic drug should take into account in clinical therapies.

Co-expression of drug metabolizing cytochrome P450 enzymes and estrogen receptor alpha (ESR1) in human liver: racial differences and the regulatory role of ESR1.

The function and expression of cytochrome P450 (CYP) drug metabolizing enzymes is highly variable, greatly affecting drug exposure, and therapeutic outcomes. The expression of these enzymes is known to be controlled by many transcription factors (TFs), including ligand-free estrogen receptor alpha (ESR1, in the absence of estrogen). However, the relationship between the expression of ESR1, other TFs, and CYP enzymes in human liver is still unclear. Using real-time PCR, we quantified the mRNA levels of 12 CYP enzymes and nine TFs in 246 human liver samples from European American (EA, n = 133) and African American (AA, n = 113) donors. Our results showed higher expression levels of ESR1 and six CYP enzymes in EA than in AA. Partial least square regression analysis showed that ESR1 is the top-ranking TF associating with the expression of eight CYP enzymes, six of which showed racial difference in expression. Conversely, four CYP enzymes without racial difference in expression did not have ESR1 as a top-ranking TF. These results indicate that ESR1 may contribute to variation in CYP enzyme expression between these two ancestral backgrounds. These results are consistent with our previous study showing ESR1 as a master regulator for the expression of several CYP enzymes. Therefore, factors affecting ESR1 expression may have broad influence on drug metabolism through altered expression of CYP enzymes.

Assessment of in vitro inhibitory effects of novel anti MRSA benzoquinolizine fluoroquinolone WCK 771 (levonadifloxacin) and its metabolite on human liver cytochrome P450 enzymes

WCK 771 (INN: levonadifloxacin) is a novel antibacterial agent belonging to benzoquinolizine subclass of fluoroquinolones which is under clinical development as a parenteral formulation and its prodrug WCK 2349 (INN: alalevonadifloxacin) as an oral option. Both the drugs have been approved recently in India based on phase III trial completed for ABSSSI.In vitro CYP inhibition potential of levonadifloxacin and its sulfate metabolite (WCK 2146) were assessed in this study. The inhibitory effects of levonadifloxacin and its sulfate metabolite were assessed for seven key human liver CYP isoforms 1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4 using human liver microsome (HLM) employing validated LC-MS/MS method.The results showed that levonadifloxacin and its metabolite did not inhibit enzyme activity of any of the key CYP isoforms (1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4) even at supra therapeutic concentrations (12–24X, Clinical Cmax: 25–35µg/mL).These in vitro CYP inhibition studies of levonadifloxacin and its sulfate metabolite indicate lack of potential for pharmacokinetic drug interactions of levonadifloxacin when co-administered with drugs which are substrate of these isoforms. Therefore, further clinical studies evaluating CYP mediated drug–drug interactions are not warranted for levonadifloxacin and alalevonadifloxacin.

Metabolism of a New Antiaggregant, Indolinone Derivative.

Cytochrome p450-mediated metabolism of GRS (indolinone antiaggregant) and its effects on activities of cytochrome p450 isoenzymes were studied. Inhibition of 6 isomers of cytochrome p450 in human liver microsomes was studied with the use of specific substrates. It was found that human liver cytochrome p450 enzymes could not induce degradation of GRS and that GRS was not an inductor or inhibitor of cytochrome p450 family members 1A2, 2C9, 2C19, 2D6, 2C8, and 3A4. Hence, clinical use of the prospective antiaggregant would not involve the risk of uncontrolled fluctuations in GRS concentrations in the organism because of interactions between the drugs.

In vitro inhibitory effects of cepharanthine on human liver cytochrome P450 enzymes

Context Cepharanthine (CEP) extracted from the roots of Stephania cepharantha Hayata (Menispermaceae), has a range of therapeutic potential in clinical conditions. Whether it affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear. Materials and methods The effects of CEP (100 μM) on eight human liver CYP isoforms (i.e., 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19 and 2C8) were investigated in vitro using human liver microsomes (HLMs) with specific probe actions and probe substrates. In addition, the enzyme kinetic parameters were calculated. Results The results showed that the activity of CYP3A4, CYP2E1 and CYP2C9 was inhibited by CEP, with IC50 values of 16.29, 25.62 and 24.57 μM, respectively, but other CYP isoforms were not affected. Enzyme kinetic studies showed that CEP was not only a non-competitive inhibitor of CYP3A4 but also a competitive inhibitor of CYP2E1 and CYP2C9, with Ki values of 8.12, 11.78 and 13.06 μM, respectively. Additionally, CEP is a time-dependent inhibitor for CYP3A4 with KI /Kinact value of 10.84/0.058 min/μM. Discussion and conclusions The in vitro studies of CEP with CYP isoforms indicate that CEP has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP3A4, CYP2E1 and CYP2C9. Further clinical studies are needed to evaluate the significance of this interaction.

In vitro inhibitory effects of ganoderic acid A on human liver cytochrome P450 enzymes

Context Ganoderic acid A (GAA) is usually used to prevent cancers or other diseases, which make it likely to be used with other drugs metabolized by cytochromes P450. Objective This study investigates the effect of GAA on eight major cytochrome P450 isoforms in human liver microsomes. Material and method The effects of GAA (100 μM) on eight human liver CYP isoforms (i.e., 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19, and 2C8) were investigated in vitro using human liver microsomes (HLMs) with specific substrates for the CYPs, and the enzyme kinetic parameters were calculated. Results The results showed that GAA inhibited the activity of CYP3A4, 2D6, and 2E1, but did not affect other isoforms. The inhibition of CYP3A4, 2D6, and 2E1 was concentration-dependent with IC50 values of 15.05, 21.83, and 28.35 μM, respectively. Additionally, GAA was not only a non-competitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP2D6 and 2E1, with Ki values of 7.16, 10.07, and 13.45 μM. Meanwhile, the inhibition of CYP3A4 was time-dependent, with the KI/Kinact value of 7.91/0.048 μM/min. Discussion and conclusion The in vitro study indicated that GAA has the potential to result in drug-drug interactions with other drugs metabolized by CYP3A4, 2D6, and 2E1. Further clinical studies are needed for the identification of this interaction.

In vitro inhibitory effect of lysionotin on the activity of cytochrome P450 enzymes

Context Lysionotin, a major extraction of Lysionotus pauciflorus Maxim (Gesneriaceae), has a variety of pharmacological properties commonly used in the treatment of lung disease. A study of lysionotin on the activity of human liver cytochrome P450 (CYP) enzymes can provide guidance on the clinical application of lysionotin. Objective This study investigated the interaction between lysionotin and CYPs. Material and method The effects of 100 μM lysionotin on eight human liver CYP isoforms (i.e., 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19 and 2C8) were investigated in vitro using human liver microsomes (HLMs) with specific inhibitor as positive control and untreated HLMs as control. Meanwhile, the enzyme kinetic parameters were calculated. A time-dependent study was performed with a time interval of 5 min in 30 min. Results Lysionotin was found to inhibit the activity of CYP3A4, 2C19, and 2C8, with IC50 values of 13.85, 24.95, and 30.05 μM, respectively. The inhibition of CYP3A4 was performed in a non-competitive manner with the Ki value of 6.83 μM, while the inhibition of CYP2C19 and 2C8 was performed in a competitive manner with Ki values of 12.41 and 14.51 μM. Moreover, it was found that the inhibition of CYP3A4 was time-dependent with K I/K inact value of 6.618/0.048 min/μM. Discussion and conclusions: The in vitro inhibitory effect of lysionotin on the activity of CYP3A4, 2C19, and 2C8 indicated potential drug interactions between lysionotin and drugs metabolised by CYP3A4, 2C19, and 2C8. Further in vivo experiments are needed to assess the potential interactions.

In vitro Inhibitory Effects of Cynaroside on Human Liver Cytochrome P450 Enzymes

Introduction: Cynaroside is a biological component isolated from Lonicera japonica Thunb, and it possesses numerous pharmacological activities. However, whether cynaroside affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear. The purpose of this study was to investigate the effects of cynaroside on 8 major CYP isoforms in human liver microsomes (HLMs). Methods: In this study, the inhibitory effects of cynaroside on the 8 human liver CYP isoforms (i.e., 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19, and 2C8) were investigated in vitro using HLMs. Results: The results showed that cynaroside inhibited the activity of CYP1A2, 3A4, and 2C9, with IC50 values of 21.74, 15.88, and 16.58 μmol/L, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that cynaroside was not only a noncompetitive inhibitor of CYP3A4 but also a competitive inhibitor of CYP1A2 and 2C9, with Ki values of 7.33, 11.60, and 8.09 μmol/L, respectively. In addition, cynaroside is a time-dependent inhibitor for CYP3A4 with Kinact/KI value of 0.049/11.62 μmol/L–1min–1. Conclusion: The in vitro studies of cynaroside with CYP isoforms indicate that cynaroside has the potential to cause pharmacokinetic drug interactions with other coadministered drugs metabolized by CYP1A2, 3A4, and 2C9. Further clinical studies are needed to evaluate the significance of this interaction.

Effects of catalpol on the activity of human liver cytochrome P450 enzymes

1. Catalpol possesses numerous pharmacological activities, and however, little data available for the effects of catalpol on the activity of human liver cytochrome P450 (CYP) enzymes.2. This study investigates the inhibitory effects of catalpol on the main human liver CYP isoforms. In this study, the inhibitory effects of catalpol on the eight human liver CYP isoforms 1A2, 2A6, 2E1, 2D6, 2C9, 2C19, 2C8 and 3A4 were investigated in human liver microsomes.3. The results indicated that catalpol could inhibit the activity of CYP3A4, CYP2E1 and CYP2C9, with IC50 values of 14.27, 22.4 and 14.69 μM, respectively, but those other CYP isoforms were not affected. Enzyme kinetic studies showed that catalpol was not only a noncompetitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP2E1 and CYP2C9, with Ki values of 7.40, 10.75 and 7.37 μM, respectively. In addition, catalpol is a time-dependent inhibitor for CYP3A4, with maximum inactivation (kinact) and 50% maximum inactivation (KI) values of 0.02 min−1 and 1.86 μM, respectively.4. The in vitro studies of catalpol with CYP isoforms suggest that catalpol has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP3A4, CYP2E1 and CYP2C9. Further in vivo studies are needed in order to evaluate the significance of this interaction.

In vitro inhibitory effects of sophocarpine on human liver cytochrome P450 enzymes

1. Sophocarpine is a biologically active component isolated from the foxtail-like sophora herb and seed that is often orally administered for the treatment of cancer and chronic bronchial asthma. However, whether sophocarpine affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear.2. In this study, the inhibitory effects of sophocarpine on the eight human liver CYP isoforms (CYP1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19, and 2C8) were investigated in vitro using human liver microsomes (HLMs).3. The results indicate that sophocarpine could inhibit the activity of CYP3A4 and 2C9, with the IC50 values of 12.22 and 15.96 μM, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that sophocarpine is not only a noncompetitive inhibitor of CYP3A4 but also a competitive inhibitor of CYP2C9, with Ki values of 6.74 and 9.19 μM, respectively. Also, sophocarpine is a time-dependent inhibitor of CYP3A4 with Kinact/KI value of 0.082/21.54 μM−1 min−1.4. The in vitro studies of sophocarpine with CYP isoforms suggested that sophocarpine has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP3A4 and 2C9. Further clinical studies are needed to evaluate the significance of this interaction.

In vitro inhibitory effects of phellodendrine on human liver cytochrome P450 enzymes

1. Phellodendrine possesses numerous pharmacological activities. However, whether phellodendrine affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear.2. In this study, the inhibitory effects of phellodendrine on eight human liver CYP isoforms (i.e. 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19 and 2C8) were investigated in vitro using human liver microsomes (HLMs).3. The results showed that phellodendrine inhibited the activity of CYP1A2, 3A4 and 2C9, with IC50 values of 20.56, 14.98 and 16.30 μM, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that phellodendrine was not only a non-competitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP1A2 and 2C9, with Ki values of 7.15, 10.52 and 7.98 μM, respectively. In addition, phellodendrine is a time-dependent inhibitor for CYP3A4 with Kinact/KI value of 0.046/11.57 μM−1 min−1.4. The in vitro studies of phellodendrine with CYP isoforms indicate that phellodendrine could inhibit the activities of CYP1A2, 3A4 and 2C9. Further clinical studies are needed to evaluate the significance of this interaction.

Inhibitory Mechanisms of Myricetin on Human and Rat Liver Cytochrome P450 Enzymes.

Myricetin is a flavonoid compound that is abundant in teas, red wine, berries, herbs and vegetables with a variety of pharmacological properties such as antioxidant, anti-inflammatory and anti-cancer effects. Although there are in vitro studies showing that myricetin inhibits human cytochrome P450(CYP)2D6 and CYP3A, the inhibitory mechanisms of myricetin on CYP enzymes are still unclear. The aim of this study was to evaluate the inhibitory effects of myricetin on human and rat CYPs, including CYP3A2/3A4, CYP2B1/2B6, CYP2C9/2C11 and CYP2D1/2D6. This study was performed to investigate the inhibitory effects of myricetin on human CYP3A4, CYP2B6, CYP2C9, CYP2D6 and rat CYP3A2, CYP2B1, CYP2C11, CYP2D1 through the cocktail approach using ultra-performance liquid chromatography tandem mass spectrometry. Typical probe substrates were used as follows-midazolam for CYP3A2/3A4, dextromethorphan for CYP2D1/2D6, tolbutamide for CYP2C9/2C11, and bupropion for CYP2B1/2B6. The results of this study showed that myricetin might not be a time-dependent inhibitor. Moreover, myricetin inhibited CYP3A4 in an uncompetitive way with aninhibition constant (Ki)value of 143.1μM. It was also a noncompetitive inhibitor of CYP2C9 and CYP2D6 with Ki values of 31.12and 53.44μM and a competitive inhibitor of CYP2B1 with a Ki value of 69.70μM, as well as a mixed inhibitor of CYP3A2, CYP2C11 and CYP2D1with Ki values of 37.57, 14.88and 17.39μM, respectively. In conclusion, this study indicates that myricetin inhibited CYP3A4/3A2, CYP2C9/2C11, CYP2D6/2D1 and CYP2B1 by various mechanisms with different Kivalues. Given that our experiments are established in vitro, further in vivo work is needed to confirm the interaction between myricetin and CYP enzymes, thus providing better guidance for the safe clinical use of myricetin.

In vitro inhibitory effects of kaempferitrin on human liver cytochrome P450 enzymes

Context: Kaempferitrinis (KF) is a bioactive flavonoid and possesses numerous pharmacological activities. However, whether KF affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear.Objective: This study investigates the effects of KF on eight major CYP isoforms in human liver microsomes (HLMs).Materials and methods: In vitro, HLMs were used to investigate the inhibitory effects of KF (100 μM) on the eight human liver CYP isoforms (i.e., 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19, and 2C8), and corresponding probe substrates were used. Enzyme kinetic studies (0–50 μM of KF) were conducted to determine the inhibition mode of KF on CYP enzymes.Results: The results showed that KF inhibited the activity of CYP1A2, 3A4, and 2C9, with IC50 values of 20.56, 13.87, and 14.62 μM, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that KF was not only a noncompetitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP1A2 and 2C9, with Ki values of 7.11, 10.24, and 7.58 μM, respectively. In addition, KF is a time-dependent inhibitor for CYP3A4 with KI/Kinact value of 10.85/0.036 min/μM.Discussion: The in vitro studies of KF with CYP isoforms indicate that KF has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP1A2, 3A4, and 2C9.Conclusion: It is recommended that KF should not be used with other drugs metabolized by CYP1A2, 3A4, and 2C9. Further clinical studies are needed to evaluate the significance of this interaction.

In vitro Inhibitory Effects of Isofraxidin on Human Liver Cytochrome P450 Enzymes

Isofraxidin is a Coumarin compound widely distributed in plants, such as the Umbelliferae or Chloranthaceae, and it possesses numerous pharmacological activities. However, whether isofraxidin affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear. In this study, the inhibitory effects of isofraxidin on the 8 human liver CYP isoforms (i.e., 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19, and 2C8) were investigated in vitro using human liver microsomes. The results showed that isofraxidin inhibited the activity of CYP1A2, 3A4, and 2E1, with IC50 values of 23.01, 15.49, and 15.98 µmol/L, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that isofraxidin was not only a noncompetitive inhibitor of CYP3A4 but also a competitive inhibitor of CYP1A2 and 2E1, with Ki values of 7.91, 10.14, and 9.30 µmol/L, respectively. In addition, isofraxidin is a time-dependent inhibitor for CYP3A4 with Kinact/KI value of 0.047/12.33 µmol/L–1min–1. The in vitro studies of isofraxidin with CYP isoforms indicate that isofraxidin has the potential to cause pharmacokinetic drug interactions with other coadministered drugs metabolized by ­CYP1A2, 3A4, and 2E1. Further clinical studies are needed to evaluate the significance of this interaction.

In vitro inhibitory effects of pristimerin on human liver cytochrome P450 enzymes

1.Pristimerin (PTM) is a biological component isolated from Chinese herbal plant Celastrus and Maytenus spp. and it possesses numerous pharmacological activities. However, whether PTM affects the activity of human liver cytochrome P450 (CYP) enzymes remains unclear.2.In this study, the inhibitory effects of PTM on the eight human liver CYP isoforms (i.e. 1A2, 3A4, 2A6, 2E1, 2D6, 2C9, 2C19 and 2C8) were investigated in vitro using human liver microsomes (HLMs).3.The results showed that PTM inhibited the activity of CYP1A2, 3A4 and 2C9, with IC50 values of 21.74, 15.88 and 16.58 μM, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that PTM was not only a non-competitive inhibitor of CYP3A4, but also a competitive inhibitor of CYP1A2 and 2C9, with Ki values of 7.33, 11.60 and 8.09 μM, respectively. In addition, PTM is a time-dependent inhibitor for CYP3A4 with Kinact/KI value of 0.049/11.62 μM−1 min−1.4.The in vitro studies of PTM with CYP isoforms indicate that PTM has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP1A2, 3A4 and 2C9. Further clinical studies are needed to evaluate the significance of this interaction.

Effect of Endocannabinoid Oleamide on Rat and Human Liver Cytochrome P450 Enzymes in In Vitro and In Vivo Models.

The endocannabinoid system is important for many physiologic and pathologic processes, but its role in the regulation of liver cytochromes P450 (P450s) remains unknown. We studied the influence of the endocannabinoid oleamide on rat and human liver P450s. Oleamide was administered intraperitoneally to rats at doses of 0.1, 1, and 10 mg/kg per day for 7 days. The content and activity of key P450s were evaluated in rat liver microsomes. Moreover, interactions with nuclear receptors regulating P450 genes and serum levels of their ligands (prolactin, corticosterone, and free triiodothyronine) were tested in in vitro P450 inhibition assays. Decreased protein levels and metabolic activities of CYP1A2, CYP2B, and CYP2C11, along with a drop in metabolic activity of CYP2D2, were observed in animals treated with oleamide (10 mg/kg per day). The activities of CYP2C6, CYP2A, and CYP3A and the levels of hormones were not altered. In vitro, oleamide exhibited a weak inhibition of rat CYP1A2, CYP2D2, and CYP2C6. The activities of rat CYP2A, CYP2B, CYP2C11, and CYP3A and human CYP1A2, CYP2B6, CYP2C9, and CYP3A4 were not altered. Oleamide did not interact with human pregnane X, constitutive androstane, or aryl hydrocarbon receptors in reporter gene experiments and did not regulate their target P450 genes in primary human hepatocytes. Our results indicate that oleamide caused the downregulation of some rat liver P450s, and hormones are not mediators of this effect. In vitro oleamide inhibits mainly rat CYP2C6 and is neither an agonist nor antagonist of major human nuclear receptors involved in the regulation of xenobiotic metabolism.