Competitive Inhibitor Of CYP2D6 Research Articles

Mechanism-Based Inactivation of CYP2D6 by Phellopterin and Related Drug-Drug Interaction with Metoprolol.

Phellopterin (PLP) is a linear furanocoumarin widely found in citrus fruits and herbal medicines. The study aims to comprehensively investigate the mechanism of inhibition of CYP2D6 enzyme activity by PLP and its alteration of metoprolol pharmacokinetics. PLP was found to irreversibly inhibit CYP2D6 in time-, concentration-, and nicotinamide adenine dinucleotide phosphate-dependent manners. Coincubation with quinidine, which is a competitive inhibitor of CYP2D6, attenuated this time-dependent inhibition. Glutathione (GSH) and catalase/superoxide dismutase failed to reverse the PLP-induced CYP2D6 inactivation. GSH trapping experiments provided strong evidence that PLP metabolic activation produces epoxide or γ-ketoaldehyde intermediates. In addition, pretreatment with PLP resulted in significant increases in Cmax and area under curve of plasma metoprolol in rats.

Effect of tubeimoside I on the activity of cytochrome P450 enzymes in human liver microsomes

This study assessed the effect of tubeimoside I on CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 to reveal the potential of tubeimoside I to induce drug-drug interaction. The evaluation of cytochromes P450 enzyme (CYP) activity was performed in pooled human liver microsomes with probing substrates of CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4. Typical inhibitors were employed as positive controls and the effect of 0, 2.5, 5, 10, 25, 50, and 100 μM tubeimoside I was investigated. The activity of CYP2D6, 2E1, and 3A4 was significantly inhibited by tubeimoside I with the IC50 values of 10.34, 11.58, and 9.74 μM, respectively. The inhibition of CYP2D6 and 2E1 was competitive with the Ki value of 5.66 and 5.29 μM, respectively. While the inhibition of CYP3A4 was non-competitive with the Ki value of 4.87 μM. Moreover, the inhibition of CYP3A4 was time-dependent with the KI and K inact values of 0.635 μM−1 and 0.0373 min−1, respectively. Tubeimoside I served as a competitive inhibitor of CYP2D6 and 2E1 exerting weak inhibition and a non-competitive inhibitor of CYP3A4 exerting moderate inhibition.

In vitro enantioselective inhibition of the main human CYP450 enzymes involved in drug metabolism by the chiral pesticide tebuconazole

Tebuconazole (TEB) is a chiral triazole fungicide worldwide employed to control plant pathogens and preserve wood. People can be exposed to TEB either through diet and occupational contamination. This work investigates the in vitro inhibitory potential of rac-TEB, S-(+)-TEB, and R-(−)-TEB over the main cytochrome P450 enzymes (CYP450) using human liver microsomes to predict TEB in vivo inhibition potential. The IC50 values showed that in vitro inhibition was enantioselective for CYP2C9, CYP2C19, and CYP2D6, but not for CYP3A4/5. Despite enantioselectivity, rac-TEB and its single enantiomers were always classified in the same category. The inhibition mechanisms and constants were determined for rac-TEB and it has shown to be a mixed inhibitor of CYP3A4/5 (Ki = 1.3 ± 0.3 μM, αKi = 3.2 ± 0.5 μM; Ki = 0.6 ± 0.3 μM, αKi = 1.3 ± 0.3 μM) and CYP2C9 (Ki = 0.7 ± 0.1 μM, αKi = 2.7 ± 0.5 μM), and a competitive inhibitor of CYP2D6 (Ki = 11.9 ± 0.7 μM) and CYP2C19 (Ki = 0.23 ± 0.02 μM), respectively, suggesting that in some cases, rac-TEB has a higher or comparable inhibitory potential than well-known strong inhibitors of CYP450 enzymes, especially for CYP2C9 and CYP2C19. In vitro-in vivo extrapolations (IVIVE) were conducted based on the results and data available in the literature about TEB absorption and metabolism. R1 values were estimated based on the Food and Drug Administration guideline and suggested that in a chronic oral exposure scenario considering the acceptable daily intake dose proposed by the European Food and Safety Authority, the hypothesis of rac-TEB to inhibit the activities of CYP3A4/5, CYP2C9, and CYP2C19 in vivo and cause pesticide-drug interactions cannot be disregarded.

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.

Mechanism-based inactivation of cytochrome P450 2D6 by chelidonine.

Chelidonine (CHE) is a major bioactive constituent of greater celandine, a plant used in traditional herbal medicines. CHE has widely been used as an analgesic in clinical settings. We evaluated the inhibitory effects of CHE on human cytochrome P450 enzymes. CHE produced time-, concentration-, and NADPH-dependent inhibition of CYP2D6, with K I and k inact values of 20.49 μM and 11.05 min -1 , respectively. Approximately 76% of CYP2D6 activity was suppressed after 9 minute incubation with CHE (50 μM). The loss of enzyme activity was not restored following dialysis. The estimated partition ratio of the inactivation was about 156. Quinidine, a competitive inhibitor of CYP2D6, attenuated the CHE-mediated enzyme inactivation, while glutathione and catalase/superoxide dismutase did not markedly ameliorate the inhibitory effect. Upon oxidation using potassium ferricyanide, the 15.1% activity of CYP2D6 was restored. These findings indicate that CHE acted as a mechanism-based inactivator of CYP2D6 and the observed effects may induce potential drug-drug interactions.

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.

MDMA, methamphetamine, and CYP2D6 pharmacogenetics: what is clinically relevant?

In vitro human studies show that the metabolism of most amphetamine-like psychostimulants is regulated by the polymorphic cytochrome P450 isozyme CYP2D6. Two compounds, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA), were selected as archetypes to discuss the translation and clinical significance of in vitro to in vivo findings. Both compounds were chosen based on their differential interaction with CYP2D6 and their high abuse prevalence in society. Methamphetamine behaves as both a weak substrate and competitive inhibitor of CYP2D6, while MDMA acts as a high affinity substrate and potent mechanism-based inhibitor (MBI) of the enzyme. The MBI behavior of MDMA on CYP2D6 implies that subjects, irrespective of their genotype/phenotype, are phenocopied to the poor metabolizer (PM) phenotype. The fraction of metabolic clearance regulated by CYP2D6 for both drugs is substantially lower than expected from in vitro studies. Other isoenzymes of cytochrome P450 and a relevant contribution of renal excretion play a part in their clearance. These facts tune down the potential contribution of CYP2D6 polymorphism in the clinical outcomes of both substances. Globally, the clinical relevance of CYP2D6 polymorphism is lower than that predicted by in vitro studies.

Prolonged Pharmacokinetic Drug Interaction Between Terbinafine and Amitriptyline

Drugs with long terminal half-lives, such as terbinafine, have a potential for involvement in both long-lasting drug-drug interactions and interactions appearing weeks after discontinuation. We present a case report on a 37-year-old white woman with normal CYP2D6 metabolic capacity who was treated with amitriptyline, valproate, and olanzapine when terbinafine was introduced. Shortly thereafter she experienced extreme dryness of the mouth, nausea, and dizziness accompanied by a large increase in the serum concentrations of amitriptyline and nortriptyline. Terbinafine therapy was discontinued, and the amitriptyline dose was reduced. Surprisingly, the serum concentrations of amitriptyline and nortriptyline did not return to baseline until approximately 6 months later. Studies have shown that terbinafine is a highly potent competitive inhibitor of CYP2D6. CYP2D6 is an important intermediate enzyme in metabolism of amitriptyline to nortriptyline. Nortriptyline is further metabolized to 10-hydroxy metabolites, mainly by CYP2D6. It is, therefore, likely that the concomitant use of terbinafine was the major cause of the increased serum concentrations of amitriptyline and nortriptyline. Very different terbinafine elimination half-lives (17-400 hours) are stated in the physicians' reference guides. If the shortest estimates are used when adjusting the dose of interacting drugs, the risk of underestimating the duration of the interaction is large. Based on our data there is a risk of clinically significant drug-drug interactions for at least 3 months after stopping terbinafine intake.

Inhibition of cytochrome P450 (CYP450) isoforms by isoniazid: potent inhibition of CYP2C19 and CYP3A.

Isoniazid (INH) remains the most safe and cost-effective drug for the treatment and prophylaxis of tuberculosis. The use of INH has increased over the past years, largely as a result of the coepidemic of human immunodeficiency virus infection. It is frequently given chronically to critically ill patients who are coprescribed multiple medications. The ability of INH to elevate the concentrations in plasma and/or toxicity of coadministered drugs, including those of narrow therapeutic range (e.g., phenytoin), has been documented in humans, but the mechanisms involved are not well understood. Using human liver microsomes (HLMs), we tested the inhibitory effect of INH on the activity of common drug-metabolizing human cytochrome P450 (CYP450) isoforms using isoform-specific substrate probe reactions. Incubation experiments were performed at a single concentration of each substrate probe at its K(m) value with a range of INH concentrations. CYP2C19 and CYP3A were inhibited potently by INH in a concentration-dependent manner. At 50 microM INH (approximately 6.86 microg/ml), the activities of these isoforms decreased by approximately 40%. INH did not show significant inhibition (<10% at 50 microM) of other isoforms (CYP2C9, CYP1A2, and CYP2D6). To accurately estimate the inhibition constants (K(i) values) for each isoform, four concentrations of INH were incubated across a range of five concentrations of specific substrate probes. The mean K(i) values (+/- standard deviation) for the inhibition of CYP2C19 by INH in HLMs and recombinant human CYP2C19 were 25.4 +/- 6.2 and 13 +/- 2.4 microM, respectively. INH showed potent noncompetitive inhibition of CYP3A (K(i) = 51.8 +/- 2.5 to 75.9 +/- 7.8 microM, depending on the substrate used). INH was a weak noncompetitive inhibitor of CYP2E1 (K(i) = 110 +/- 33 microM) and a competitive inhibitor of CYP2D6 (K(i) = 126 +/- 23 microM), but the mean K(i) values for the inhibition of CYP2C9 and CYP1A2 were above 500 microM. Inhibition of one or both CYP2C19 and CYP3A isoforms is the likely mechanism by which INH slows the elimination of coadministered drugs, including phenytoin, carbamazepine, diazepam, triazolam, and primidone. Slow acetylators of INH may be at greater risk for adverse drug interactions, as the degree of inhibition was concentration dependent. These data provide a rational basis for understanding drug interaction with INH and predict that other drugs metabolized by these two enzymes may also interact.