Functional phenotyping of the CYP2D6 probe drug codeine in the horse

Background In humans, the drug metabolizing enzyme CYP2D6 is highly polymorphic resulting in substantial differences in the metabolism of drugs including anti-arrhythmics, neuroleptics, and opioids. The objective of this study was to phenotype a population of 100 horses from five different breeds and assess differences in the metabolic activity of the equine CYP2D6 homolog using codeine as a probe drug. Administration of a probe drug is a common method used for patient phenotyping in human medicine, whereby the ratio of parent drug to metabolite (metabolic ratio, MR) can be used to compare relative enzyme function between individuals. A single oral dose of codeine (0.6 mg/kg) was administered and plasma concentrations of codeine and its metabolites were determined using liquid chromatography mass spectrometry. The MR of codeine O-demethylation [(codeine)/(morphine + morphine-3-glucuronide + morphine-6-glucuronide)] was determined using the area under the plasma concentration-time curve extrapolated from time zero to infinity (AUC0-∞) for each analyte and used to group horses into predicted phenotypes (high-, moderate-, and low-MR). Results The MR of codeine O-demethylation ranged from 0.002 to 0.147 (median 0.018) among all horses. No significant difference in MR was observed between breeds, age, or sex. Of the 100 horses, 11 were classified as high-MR, 72 moderate-MR, and 17 low-MR. Codeine AUC0-∞ and O-demethylation MR were significantly different (p < 0.05) between all three groups. The mean ± SD MR was 0.089 ± 0.027, 0.022 ± 0.011, and 0.0095 ± 0.001 for high-, moderate-, and low-MR groups, respectively. The AUC for the morphine metabolites morphine-3-glucuronide and morphine-6-glucuronide were significantly different between high-and low-MR groups (p < 0.004 and p < 0.006). Conclusions The MR calculated from plasma following codeine administration allowed for classification of horses into metabolic phenotypes within a large population. The range of codeine metabolism observed among horses suggests the presence of genetic polymorphisms in CYP2D82 of which codeine is a known substrate. Additional studies including CYP2D82 genotyping of high- and low-MR individuals are necessary to determine the presence of CYP2D polymorphisms and their functional implications with respect to the metabolism of therapeutics.

METABOLOMICS REVEALS FIVE ENDOGENOUS BIOMARKERS IN HUMAN URINE AND PLASMA TO PREDICT CYP2D6 ACTIVITY

Background and Purpose: Individualized assessment of the activity of cytochrome P450 2D6 (CYP2D6), a highly variable drug-metabolizing enzyme, is performed through phenotyping during which a probe drug is administered to measure the enzyme’s activity. In order to avoid any iatrogenic harm (allergic drug reaction, dosing error) related to the probe drug, the development of non-invasive tools for real-time phenotyping of CYP2D6 could significantly contribute to the expansion of precision medicine in clinical practice. This study focuses on the identification of endogenous markers of the CYP2D6 enzyme in human biofluids using a liquid chromatography (LC)-high-resolution mass spectrometry (HRMS)-based metabolomics approach. Experimental Approach: Data from a control session were compared to data from an inhibition session. Before the latter, healthy volunteers (extensive and ultrarapid metabolizers) received a daily dose of paroxetine 20 mg over seven days. CYP2D6 genotyping and phenotyping, using single oral dose of dextromethorphan 5 mg, were also performed in all participants. Key Results: In CYP2D6 extensive and ultrarapid metabolizers (n = 37), mean relative intensities of five features were significantly reduced during the inhibition session compared to the control session (fold changes ≤ 0.67, FDR-adjusted P < 0.0001). Furthermore, mean relative intensities of these candidates were significantly higher in the CYP2D6 extensive-ultrarapid metabolizer group (n = 37) compared to the poor metabolizer group (n = 6) (fold changes ≤ 0.67, P < 0.0001). Conclusion and Implications: The applied untargeted metabolomics strategy was able to identify five CYP2D6 endogenous metabolites, a promising discovery for non-invasive phenotyping and personalised medicine.

The interaction of supramolecular anticancer drug amphiphiles with phospholipid membranes

Molecular dynamics simulations probe drug delivery vehicle-membrane interaction.

Assessment of Herb-Drug Interactions Based on the Pharmacokinetic Changes of Probe Drug, Midazolam

Background: In healthy volunteers, the probe drug method is widely practised to assess the pharmacokinetic mediated herb-drug interactions (HDI). We analyzed the clinical evidence of CYP3A4 probe drug, Midazolam. Methods: Literatures where Midazolam was used as a probe drug for prediction of herb-drug interaction was survey through an online database such as google scholar, Scopus, Cochrane, PubMed and clinicaltrials.gov. Results: Midazolam was considered as a sensitive probe for CYP3A4 substrates due to its bioavailability. We observed that not all the herbs are causing drug interaction. However, significant changes of the Midazolam pharmacokinetics were found after high-dose and long-term intake of some herbs and food supplements, Suggesting the induction and/or inhibition of CYP activities. Conclusion: Probe drug technique is one of the easiest ways for predicting CYP enzyme-mediated herb-drug interactions. Midazolam shows a good response in clinical studies because of short half-life and low harmfulness compared with other probe drugs.

A short exploration of selected sensitive CYP3A4 substrates (Probe Drug)

Background: CYP450 enzymes in the liver have a significant role in the metabolism of xenobiotics. Probe drug strategy is broadly used to evaluate the pharmacodynamic & pharmacokinetic Drug/ herb-drug interactions/ Fooddrug interactions. Probe drugs guarantee the exact pathway of drug metabolism in the liver by its targeted tractability property. The CYP3A4 isoenzyme metabolizes majority of the drugs (65%). Methods: The characters of targeted probe drugs were observed from admetSAR (version2) online database. Results: Midazolam is widely used as a probe drug because of its peculiar character. Midazolam, affirms the accurate and consistent prediction of pharmacokinetic mediated drug interactions even within nanogram concentrations either within sight of and without a potent CYP3A inhibitor. Remarkably midazolam is used as CYP3A4 substrate in the majority of in vivo studies. Conclusion: However, midazolam shows a good response in all clinical studies because of its lesser half-life and bioavailability when compared with other probe drugs.

Effects of Naringin on the Activity and mRNA Expression of CYP Isozymes in Rats

Naringin (NRG) is a common dietary flavonoid in citrus fruits and has been documented to possess multiple pharmacological activities, including anti-oxidant, anti-inflammatory, and neuroprotective effects. Naringin is frequently consumed in combination with common clinical drugs. To date, the effects of NRG on cytochrome P450 enzymes have not been fully investigated yet. In this study, the activities of hepatic CYP1A2, CYP2D2, CYP2C9, CYP2C19, and CYP2E1 in rats after the continuous oral administration of NRG (50 and 500 mg/kg) were evaluated using cocktail probe-drug method. The concentrations of 5 probe drugs (phenacetin, dextromethorphan, diclofenac sodium, omeprazole, and chlorzoxazone) in rat plasma were simultaneously determined with a validated HPLC-MS/MS (high performance liquid chromatography-tandem mass spectrometry) method and then used to calculate corresponding pharmacokinetic parameters. Compared with the control group, the AUC(0- t), AUC(0-∞), t 1/2, and C max of each probe drug in treatment groups showed no significant differences. Meanwhile, fluorescence quantitative polymerase chain reaction (FQ-PCR) analysis revealed that NRG did not significantly affect the mRNA expressions of genes CYP1a2, CYP2d2, CYP2c6, CYP2c11, and CYP2e1 in rat liver. Based on these results, it could be concluded that NRG showed no significant effects on the activities and mRNA expressions of tested CYP450 in rats.