Competitive Inhibitor Of CYP3A4 Research Articles

Clinical poisoning events involving yunaconitine may be highly correlated with metabolism-based interactions: A critical role of CYP3A4.

Clinical poisoning events involving yunaconitine (YAC), a toxic Aconitum alkaloid, occur more and more frequently, and whether the mechanism is correlated with metabolism-based interactions remains unknown. This study aimed to reveal the presumable mechanism by clarifying the metabolic profiles and kinetic-based mechanism of YAC. YAC could be oxidized into 20 metabolites by human liver microsomes, while CYP3A4 have a critical metabolic superiority. Sixteen of the metabolites were primary generated by CYP3A4, and 4 of them were generated only by CYP3A4. The presence of CYP3A inhibitor ketoconazole (KCZ) significantly suppressed the generation of all the 20 metabolites, with 9 of them being suppressed completely (P<0.05). The plasma exposure (Cmax and AUC0-t values), cardiotoxicity and neurotoxicity of YAC enhanced remarkably in mice when Cyp3a were inhibited (P<0.05). Moreover, the CYP3A4-based kinetics of YAC is an example of substrate inhibition, and the inhibitory manner of YAC on CYP3A4 was competitive, with Ki value being 1.76μmol/L. Overall, YAC was a sensitive substrate and moderately competitive inhibitor of CYP3A4. The inhibition on CYP3A4 could sharply increase the in vivo exposure and toxicity of YAC. Thus, clinical poisoning events involving YAC may be highly correlated with CYP3A4-mediated interactions.

Effect of Betanin, the Major Pigment of Red Beetroot (Beta vulgaris L.), on the Activity of Recombinant Human Cytochrome P450 Enzymes.

Most of the currently available drugs are derived from natural sources, but they are used only after extensive chemical modifications to improve their safety and efficacy. Natural products are used in health supplements and cosmetic preparations and have been used as auxiliary drugs or alternative medicines. When used in combination with conventional drugs, these herbal products are known to alter their pharmacokinetics and pharmacodynamics, reducing their therapeutic effects. Moreover, herb-drug interactions (HDIs) may have serious side effects, which is one of the major concerns in health practice. It is postulated that HDIs affect the pathways regulating cytochrome P450 enzymes (CYPs). Betanin, the chief pigment of red beetroot (Beta vulgaris L.), has various types of pharmacological activity, such as anti-inflammatory, antioxidant, and anticancer effects. However, the potential risk of HDIs for betanin has not yet been studied. Thus, we aimed to predict more specific HDIs by evaluating the effects of betanin on CYPs (CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4), the major phase I metabolic enzymes, using fluorescence-/luminescence-based assays. Our results showed that betanin inhibited CYP3A4 activity in a dose-dependent manner (IC50 = 20.97 µΜ). Moreover, betanin acted as a competitive inhibitor of CYP3A4, as confirmed by evaluating Lineweaver-Burk plots (Ki value = 19.48 µΜ). However, no significant inhibitory effects were observed on other CYPs. Furthermore, betanin had no significant effect on CYP1A2, CYP2B6, or CYP2C9 induction in HepG2 cells. In conclusion, betanin acted as a competitive inhibitor of CYP3A4, and thus it should be used cautiously with other drugs that require metabolic enzymes as substrates. Additional in vivo studies and clinical trials are needed to further elucidate the HDIs of betanin.

Investigation of cytochrome P450 inhibitory properties of deoxyshikonin, a bioactive compound from Lithospermum erythrorhizon Sieb. et Zucc.

Deoxyshikonin, a natural naphthoquinone compound extracted from Lithospermum erythrorhizon Sieb. et Zucc (Boraginaceae), has a wide range of pharmacological activities, including anti-tumor, anti-bacterial and wound healing effects. However, the inhibitory effect of deoxyshikonin on cytochrome P450 (CYP) remains unclear. This study investigated the potential inhibitory effects of deoxyshikonin on CYP1A2, 2B1/6, 2C9/11, 2D1/6, 2E1 and 3A2/4 enzymes in human and rat liver microsomes (HLMs and RLMs) by the cocktail approach in vitro. The single-point inactivation experiment showed that deoxyshikonin presented no time-dependent inhibition on CYP activities in HLMs and RLMs. Enzyme inhibition kinetics indicated that in HLMs, deoxyshikonin was not only a competitive inhibitor of CYP1A2 and 2E1, but also a mixed inhibitor of CYP2B6, 2C9, 2D6 and 3A4, with Ki of 2.21, 1.78, 1.68, 0.20, 4.08 and 0.44 μM, respectively. In RLMs, deoxyshikonin not only competitively inhibited CYP2B1 and 2E1, but also exhibited mixed inhibition on CYP1A2, 2C11, 2D1 and 3A2, with Ki values of no more than 18.66 μM. In conclusion, due to the low Ki values of deoxythiokonin on CYP enzymes in HLMs, this may lead to drug-drug interactions (DDI) and potential toxicity.

Assessment of the CYP1A2 Inhibition-Mediated Drug Interaction Potential for Pinocembrin Using In Silico, In Vitro, and In Vivo Approaches.

Pinocembrin, a bioflavonoid, is extensively used in complementary/alternative medicine. It turns out as a promising candidate against neurodegenerative diseases because of its multifaceted pharmacological action toward neuroprotection. However, literature evidence is still lacking for its inhibitory action on CYP1A2, which is responsible for xenobiotic metabolism leading to the generation of toxic metabolites and bioactivation of procarcinogens. In the present study, our aim was to evaluate the CYP1A2 inhibitory potential of pinocembrin via in silico, in vitro, and in vivo investigations. From the results of in vitro studies, pinocembrin is found to be a potent and competitive inhibitor of CYP1A2. In vitro–in vivo extrapolation results indicate the potential of pinocembrin to interact with CYP1A2 substrate drugs clinically. Molecular docking-based in silico studies demonstrate the strong interaction of pinocembrin with human CYP1A2. In in vivo investigations using a rat model, pinocembrin displayed a marked alteration in the plasma exposure of CYP1A2 substrate drugs, namely, caffeine and tacrine. In conclusion, pinocembrin has a potent CYP1A2 inhibitory action to cause drug interactions, and further confirmatory study is warranted at the clinical level.

Bulleyaconitine A is a sensitive substrate and competitive inhibitor of CYP3A4: One of the possible explanations for clinical adverse reactions

Bulleyaconitine A (BLA), a toxic Aconitum alkaloid, is a potent analgesic that is clinically applied to treat rheumatoid arthritis, osteoarthritis and lumbosacral pain. BLA-related adverse reactions occur frequently, but whether the underlying mechanism is related to its metabolic interplay with drug-metabolizing enzymes remains unclear. This study aimed to elucidate the metabolic characteristics of BLA and its affinity action and mechanism to drug-metabolizing enzymes to reveal whether BLA-related adverse reactions are modulated by enzymes. After incubation with human liver microsomes and recombinant human cytochrome P450 enzymes, we found that BLA was predominantly metabolized by CYP3A, in which CYP3A4 had an almost absolute advantage. In vitro, the CYP3A4 inhibitor ketoconazole noticeably suppressed the metabolism of BLA. In vivo, the AUC0-∞ values, cardiotoxicity and neurotoxicity of BLA in Cyp3a-inhibited mice were all obviously enhanced (P < 0.05) compared to those in normal mice. In the enzyme kinetics study, BLA was found to be a sensitive substrate of CYP3A4, and its characteristics were consistent with substrate inhibition (Km = 39.36 ± 10.47 μmol/L, Ks = 83.42 ± 19.65 μmol/L). BLA was further identified to be a competitive inhibitor of CYP3A4 with Ki = 53.64 μmol/L, since the intrinsic clearance (CLint) of midazolam, a selective CYP3A4 substrate, decreased significantly (P < 0.05) when incubated with BLA together in mouse liver microsomes. Overall, BLA is a sensitive substrate and competitive inhibitor of CYP3A4, and clinical adverse reactions of BLA may mechanistically related to the CYP3A4-mediated drug-drug interactions.

Agrimoniin inhibits the activity of CYP1A2, 2D6, and 3A4 in human liver microsomes

The effect of agrimoniin on the activity of cytochrome P450 (CYP450) enzymes would induce drug-drug interaction, which leads to adverse effects or even failure of therapy. Agrimoniin was incubated with the specific substrates of eight human liver CYP isoforms in pooled human liver microsomes. The enzyme kinetics and time-dependent study were performed to obtain kinetic parameters and characteristics in vitro. Agrimoniin significantly inhibited the activity of CYP1A2, 2D6, and 3A4 in a dose-dependent manner with IC50 values of 6.26, 9.35, and 8.30 μM, respectively. Agrimoniin served as a non-competitive inhibitor of CYP3A4 and a competitive inhibitor of CYP1A2 and 2D6. Moreover, the incubation time also significantly affected the inhibition of CYP3A4. In vitro inhibitory effect of agrimoniin on the activity of CYP1A2, 2A6, and 3A4 was reported in this study. The potential drug-drug interactions between agrimoniin and drugs metabolised by CYP1A2, 2D6, and 3A4 should be paid special attention.

Mechanism-Based Inactivation of Cytochrome P450 3A4 by Benzbromarone.

Benzbromarone (BBR), a potent uricosuric agent for the management of gout, is known to cause fatal fulminant hepatitis. Although the mechanism of BBR-induced idiosyncratic hepatotoxicity remains unelucidated, cytochrome P450 enzyme-mediated bioactivation of BBR to electrophilic reactive metabolites is commonly regarded as a key molecular initiating event. However, apart from causing aberrant toxicities, reactive metabolites may result in mechanism-based inactivation (MBI) of cytochrome P450. Here, we investigated and confirmed that BBR inactivated CYP3A4 in a time-, concentration-, and NADPH-dependent manner with K I, k inact, and partition ratio of 11.61 µM, 0.10 minutes-1, and 110, respectively. Coincubation with ketoconazole, a competitive inhibitor of CYP3A4, attenuated the MBI of CYP3A4 by BBR, whereas the presence of glutathione and catalase did not confer such protection. The lack of substantial recovery of enzyme activity postdialysis and after oxidation with potassium ferricyanide, combined with the absence of a Soret peak in spectral difference scans, implied that MBI of CYP3A4 by BBR did not occur through the formation of quasi-irreversible metabolite-intermediate complexes. Analysis of the reduced CO-difference spectrum revealed an ∼44% reduction in ferrous-CO binding and hinted that inactivation is mediated via irreversible covalent adduction to both the prosthetic heme moiety and the apoprotein. Finally, our in silico covalent docking analysis further suggested the modulation of substrate binding to CYP3A4 via the covalent adduction of epoxide-derived reactive intermediates of BBR to two key cysteine residues (Cys239 and Cys58) vicinal to the entrance of the orthosteric binding site. SIGNIFICANCE STATEMENT: Although the bioactivation of benzbromarone (BBR) to reactive metabolites has been well characterized, its potential to cause mechanism-based inactivation (MBI) of cytochrome P450 has not been fully investigated. This study reports the MBI of CYP3A4 by BBR via irreversible covalent adduction and develops a unique covalent docking methodology to predict the structural molecular determinants underpinning the inactivation for the first time. These findings lay the groundwork for future investigation of clinically relevant drug-drug interactions implicating BBR and mechanisms of BBR-induced idiosyncratic hepatotoxicity.

In vitro study on the effect of peucedanol on the activity of cytochrome P450 enzymes

Context Peucedanol is a major extract of Peucedanum japonicum Thunb. (Apiaceae) roots, which is a commonly used herb in paediatrics. Its interaction with cytochrome P450 enzymes (CYP450s) would lead to adverse effects or even failure of therapy. Objective The interaction between peucedanol and CYP450s was investigated. Materials and methods Peucedanol (0, 2.5, 5, 10, 25, 50, and 100 μM) was incubated with eight human liver CYP isoforms (CYP1A2, 2A6, 3A4, 2C8, 2C9, 2C19, 2D6, and 2E1), in pooled human liver microsomes (HLMs) for 30 min with specific inhibitors as positive controls and untreated HLMs as negative controls. The enzyme kinetics and time-dependent study (0, 5, 10, 15, and 30 min) were performed to obtain corresponding parameters in vitro. Results Peucedanol significantly inhibited the activity of CYP1A2, 2D6, and 3A4 in a dose-dependent manner with IC50 values of 6.03, 13.57, and 7.58 μM, respectively. Peucedanol served as a non-competitive inhibitor of CYP3A4 with a Ki value of 4.07 μM and a competitive inhibitor of CYP1A2 and 2D6 with a Ki values of 3.39 and 6.77 μM, respectively. Moreover, the inhibition of CYP3A4 was time-dependent with the Ki /Kinact value of 5.44/0.046 min/μM. Discussion and conclusions In vitro inhibitory effect of peucedanol on the activity of CYP1A2, 2A6, and 3A4 was reported in this study. As these CYPs are involved in the metabolism of various drugs, these results implied potential drug-drug interactions between peucedanol and drugs metabolized by CYP1A2, 2D6, and 3A4, which needs further in vivo validation.

Quantitative Assessment of Levonorgestrel Binding Partner Interplay and Drug-Drug Interactions Using Physiologically Based Pharmacokinetic Modeling.

Levonorgestrel (LNG) is the active moiety in many hormonal contraceptive formulations. It is typically coformulated with ethinyl estradiol (EE) to decrease intermenstrual bleeding. Due to its widespread use and CYP3A4‐mediated metabolism, there is concern regarding drug‐drug interactions (DDIs), particularly a suboptimal LNG exposure when co‐administered with CYP3A4 inducers, potentially leading to unintended pregnancies. The goal of this analysis was to determine the impact of DDIs on the systemic exposure of LNG. To this end, we developed and verified a physiologically‐based pharmacokinetic (PBPK) model for LNG in PK‐Sim (version 8.0) accounting for the impact of EE and body mass index (BMI) on LNG’s binding to sex‐hormone binding globulin. Model parameters were optimized following intravenous and oral administration of 0.09 mg LNG. The combined LNG‐EE PBPK model was verified regarding CYP3A4‐mediated interaction by comparing to published clinical DDI study data with carbamazepine, rifampicin, and efavirenz (CYP3A4 inducers). Once verified, the model was applied to predict systemic LNG exposure in normal BMI and obese women (BMI ≥ 30 kg/m2) with and without co‐administration of itraconazole (competitive CYP3A4 inhibitor) and clarithromycin (mechanism‐based CYP3A4 inhibitor). Total and free LNG exposures, when co‐administered with EE, decreased 2‐fold in the presence of rifampin, whereas they increased 1.5‐fold in the presence of itraconazole. Although changes in total and unbound exposure were decreased in obese women compared with normal BMI women, the relative impact of DDIs on LNG exposure was similar between both groups.

An unusually impressive atorvastatin-induced elevation of serum alkaline phosphatase

A 90-year-old woman is referred six months after a transient ischaemic attack (TIA) with asymptomatic cholestatic liver function test (LFT) derangement. Following the TIA, atorvastatin and clopidogrel therapy are initiated....

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.

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.

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.

Effect of single-walled carbon nanotubes on cytochrome P450 activity in human liver microsomes in vitro.

Single-walled carbon nanotubes (SWCNTs) are made from a rolled single sheet of graphene with a diameter in the nanometer range. SWCNTs are potential carriers for drug delivery systems because antibodies or drugs can be loaded on their surface; however, their effect on the activities of cytochrome P450 (CYP) remains unclear. The aim of this study was to investigate the effect of two kinds of SWCNTs with different lengths (FH-P- and SO-SWCNTs) on human CYP activity. In addition, other nano-sized carbon materials, such as carbon black, fullerene-C60 , and fullerene-C70 were also evaluated to compare their effects on CYP activities. Ten CYP substrates (phenacetin, coumarin, bupropion, paclitaxel, tolbutamide, S-mephenytoin, dextromethorphan, chlorzoxazone, midazolam, and testosterone) were used. Testosterone 6β-hydroxylation and midazolam 1'-hydroxylation, which are catalysed by both CYP3A4 and CYP3A5 in liver microsomes, were decreased by 25% and 45%, respectively, in the presence of 0.1mg/ml SO-SWCNT. Dextromethorphan O-demethylation, which is catalysed mainly by CYP2D6, was decreased by 40% in the presence of SO-SWCNT. Other CYP activities, however, were not attenuated by SO-SWCNT. FH-P-SWCNT, carbon black, fullerene-C60 , and fullerene-C70 at 0.1mg/ml had no effect on CYP activities. The Ki values for testosterone 6β-hydroxylation, midazolam 1'-hydroxylation, and dextromethorphan O-demethylation in liver microsomes were 136, 34, and 56μg/ml, respectively. SO-SWCNT was determined to be a competitive inhibitor of CYP3A4, CYP3A5, and CYP2D6. These results suggest that the effect of SO-SWCNT differs among CYP isoforms, and that the inhibition potency depends on the physicochemical properties of the nanocarbons.

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.

Prediction of drug-drug interactions using physiologically-based pharmacokinetic models of CYP450 modulators included in Simcyp software.

In recent years, physiologically based PharmacoKinetic (PBPK) modeling has received growing interest as a useful tool for the assessment of drug pharmacokinetics. It has been demonstrated to be informative and helpful to quantify the modification in drug exposure due to specific physio-pathological conditions, age, genetic polymorphisms, ethnicity and particularly drug-drug interactions (DDIs). In this paper, the prediction success of DDIs involving various cytochrome P450 isoenzyme (CYP) modulators namely ketoconazole (a competitive inhibitor of CYP3A), itraconazole (a competitive inhibitor of CYP3A), clarithromycin (a mechanism-based inhibitor of CYP3A), quinidine (a competitive inhibitor of CYP2D6), paroxetine (a mechanism-based inhibitor of CYP2D6), ciprofloxacin (a competitive inhibitor of CYP1A2), fluconazole (a competitive inhibitor of CYP2C9/2C19) and rifampicin (an inducer of CYP3A) were assessed using Simcyp® software. The aim of this report was to establish confidence in each CYP-specific modulator file so they can be used in the future for the prediction of DDIs involving new victim compounds. Our evaluation of these PBPK models suggested that they can be successfully used to evaluate DDIs in untested scenarios. The only noticeable exception concerned a quinidine inhibitor model that requires further improvement. Additionally, other important aspects such as model validation criteria were discussed.

Inhibitory Effects of Triptolide on Human Liver Cytochrome P450 Enzymes and P-Glycoprotein.

Triptolide is an active component derived from Tripterygium wilfordii and it possesses numerous pharmacological activities. However, it remains unclear how triptolide influences the activity of human liver cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp). In this study, the inhibitory effects of triptolide 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), and the effects of triptolide on the activity of P-gp were investigated using a rhodamine-123 uptake assay. The results showed that triptolide inhibited the activity of CYP1A2 and CYP3A4, with 50 % inhibitory concentration (IC50) values of 14.18 and 8.36μM, respectively, but that other CYP isoforms were not affected. Enzyme kinetic studies showed that triptolide was not only a non-competitive inhibitor of CYP1A2, but also a competitive inhibitor of CYP3A4, with inhibition constant (K i) values of 7.32 and 5.67μM, respectively. In addition, triptolide is a time-dependent inhibitor for CYP1A2, and the concentration at 50 % maximum inactivation (K I) and maximum inactivation (K inact) values were 286.5μM and 0.024min-1, respectively. The rhodamine-123 uptake assay showed that triptolide could not affect the activity of P-gp. The in vitro studies of triptolide with CYP isoforms and P-gp indicate that triptolide has the potential to cause pharmacokinetic drug interactions with other co-administered drugs metabolized by CYP1A2 and CYP3A4. Further clinical studies are needed to evaluate the significance of this interaction.

Investigation of cytochrome P450 inhibitory properties of maslinic acid, a bioactive compound from Olea europaea L., and its structure–activity relationship

Maslinic acid (MA), the main pentacyclic triterpene of Olea europaea L. fruit, possesses a variety of pharmacological actions, including hypoglycemic, antioxidant, cardioprotective and antitumoral activities. Despite its importance, little is known about its effects on the cytochrome P450 (CYP) activity in both humans and animals. Therefore, the aim of this study was to investigate the effects of MA on the CYP 1A2, 2C9/11, 2D1/6, 2E1 and 3A2/4 activities by human and rat liver microsomes and specific CYP isoforms. In humans, MA only weakly inhibited CYP3A4 activity in human liver microsomes and specific CYP3A4 isoform with IC50 value at 46.1 and 62.3µM, respectively. In rats, MA also exhibited weak inhibition on CYP2C11, CYP2E1 and CYP3A2 activities with IC50 values more than 100µM. Enzyme kinetic studies showed that the MA was not only a competitive inhibitor of CYP3A4 in humans, but also a competitive inhibitor of CYP2C11 and 3A2 in rats, with Ki of 18.4, 98.7 and 66.3µM, respectively. Moreover, the presence of hydroxyl group at C-2 position of triterpenic acid in MA compared with oleanolic acid could magnify its competitive inhibition on human CYP3A4 activity. The relatively high Ki values of MA would have a low potential to cause the possible toxicity and drug interactions involving CYP enzymes, thus suggesting a sufficient safety for its putative use as a nutraceutical taken together with drugs.

A Comparison of the In Vitro Inhibitory Effects of Thelephoric Acid and SKF-525A on Human Cytochrome P450 Activity.

Thelephoric acid is an antioxidant produced by the hydrolysis of polyozellin, which is isolated from Polyozellus multiplex. In the present study, the inhibitory effects of polyozellin and thelephoric acid on 9 cytochrome P450 (CYP) family members (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4) were examined in pooled human liver microsomes (HLMs) using a cocktail probe assay. Polyozellin exhibited weak inhibitory effects on the activities of all 9 CYPs examined, whereas thelephoric acid exhibited dose- and time-dependent inhibition of all 9 CYP isoforms (IC50 values, 3.2–33.7 μM). Dixon plots of CYP inhibition indicated that thelephoric acid was a competitive inhibitor of CYP1A2 and CYP3A4. In contrast, thelephoric acid was a noncompetitive inhibitor of CYP2D6. Our findings indicate that thelephoric acid may be a novel, non-specific CYP inhibitor, suggesting that it could replace SKF-525A in inhibitory studies designed to investigate the effects of CYP enzymes on the metabolism of given compounds.