Yunyun Zhan

Effects of 22 Novel CYP2D6 Variants Found in the Chinese Population on the Bufuralol and Dextromethorphan Metabolisms In Vitro

Cytochrome P450 2D6 (CYP2D6) is a highly polymorphic enzyme that metabolizes a large number of therapeutic drugs. To date, more than 100 CYP2D6 allelic variants have been reported. Among these variants, we recently identified 22 novel variants in the Chinese population. The aim of this study was to functionally characterize the enzymatic activity of these variants in vitro. A baculovirus‐mediated expression system was used to express wild‐type CYP2D6.1 and other variants (CYP2D6.2, CYP2D6.10 and 22 novel CYP2D6 variants) at high levels. Then, the insect microsomes containing expressed CYP2D6 proteins were incubated with bufuralol or dextromethorphan at 37°C for 20 or 25 min., respectively. After termination, the metabolites were extracted and used for the detection with high‐performance liquid chromatography. Among the 24 CYP2D6 variants tested, two variants (CYP2D6.92 and CYP2D6.96) were found to be catalytically inactive. The remaining 22 variants exhibited significantly decreased intrinsic clearance values for bufuralol 1′‐hydroxylation and 20 variants showed significantly lower intrinsic clearance values for dextromethorphan O‐demethylation than those of the wild‐type CYP2D6.1. Our in vitro results suggest that most of the variants exhibit significantly reduced catalytic activities compared with the wild‐type, and these data provide valuable information for personalized medicine in Chinese and other Asian populations.

Effects of Cytochrome P450 2C9 Polymorphism on Bosentan Metabolism

Cytochrome P450 (P450) 2C9 is an important member of the P450 enzyme superfamily, with 58 CYP2C9 allelic variants previously reported. Genetic polymorphisms of CYP2C9 significantly influence the efficacy and safety of some drugs, which might cause adverse effects and therapeutic failure. The aim of this study was to assess the catalytic activities of 38 human CYP2C9 alleles, including 24 novel alleles (*36–*60) found in the Han Chinese population, toward bosentan (BOS) in vitro. Insect microsomes expressing the 38 CYP2C9 alleles were incubated with 10–625 μM bosentan for 30 minutes at 37°C and terminated by cooling to −80°C immediately. BOS and hydroxyl bosentan, the major metabolite of BOS, were analyzed by ultra-performance liquid chromatography–tandem mass spectrometry system. Thirty-eight defective alleles can be classified into three categories according to the relative clearance value compared with wild type: nine alleles exhibited significantly increased intrinsic clearance values (Vmax/Km) compared with the wild type (1.5-fold–∼4.9-fold relative clearance); nine alleles exhibited significantly reduced intrinsic clearance values compared with the wild type (0.6–28.9% relative clearance). The remaining 20 alleles exhibited no significant difference (1-fold) in enzyme activity compared with the wild type. These findings suggest that more attention should be directed to subjects carrying these infrequent CYP2C9 alleles when administering BOS in the clinic. This is the first report of all these rare alleles for BOS metabolism, providing fundamental data for further clinical studies on CYP2C9 alleles.

Effect of CYP2D6 variants on venlafaxine metabolism in vitro.

Abstract 1. CYP2D6 is an important member of the cytochrome P450 (CYP450) enzyme superfamily, we recently identified 22 CYP2D6 alleles in the Han Chinese population. The aim of this study was to assess the catalytic activities of these allelic isoforms and their effects on the metabolism of venlafaxine in vitro. 2. The wild-type and 24 CYP2D6 variants were expressed in insect cells, and each variant was characterized using venlafaxine as the substrate. Reactions were performed at 37 °C with 5–500 μM substrate (three variants was adjusted to 1000 μM) for 50 min. By using high-performance liquid chromatography to detect the products, the kinetic parameters Km, Vmax, and intrinsic clearance (Vmax/Km) of O-desmethylvenlafaxine were determined. 3. Among the 22 CYP2D6 variants, the intrinsic clearance (Vmax/Km) values of all variants were significantly decreased (from 0.2% to 84.5%) compared with wild-type CYP2D6*1. In addition, the kinetic parameters of two CYP2D6 variants could not be detected because they have no detectable enzyme activity. 4. The comprehensive in vitro assessment of CYP2D6 variants provides significant insights into allele-specific activity towards venlafaxine in vivo.

In vitro assessment of 24 CYP2D6 allelic isoforms on the metabolism of methadone.

CYP2D6 is an important member of the cytochrome P450 (CYP450) enzyme super family, with at least 100 CYP2D6 alleles being previously identified. Genetic polymorphisms of CYP2D6 significantly influence the efficacy and safety of some drugs, which might cause adverse effects and therapeutic failure. The aim of this study was to clarify the catalytic activities of 24 CYP2D6 alleles on the oxidative in vitro metabolism of methadone. Reactions were incubated with 50-2000  µM methadone for 30 min at 37 °C and terminated by cooling to -80 °C immediately. Methadone and the major metabolite EDDP were analyzed by an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) system. Compared with wild-type CYP2D6*1, most variants showed significantly altered values in Vmax and intrinsic clearance (Vmax /Km ). Only three variants (CYP2D6*88, *91 and E215K) exhibited markedly increased intrinsic clearance values, and one variant CYP2D6*94 showed no significant difference. On the other hand, the kinetic parameters of two CYP2D6 variants (CYP2D6*92 and *96) could not be determined because they had no detectable enzyme activity, whereas 18 variants exhibited significantly decreased values. To sum up, this study demonstrated that more attention should be paid in clinical administration of methadone to individuals carrying these CYP2D6 alleles. Copyright

Inhibitory Effect of Apigenin on Pharmacokinetics of Venlafaxine in vivo and in vitro

Objective: This study was conducted to investigate the effects of orally administered apigenin on the pharmacokinetics of venlafaxine (VEN) in rats and on the metabolism of VEN in human and rat liver microsomes in vitro. Methods: Ten healthy male SD rats were randomly divided into 2 groups: A group (control group), B group (a single dose of 250 mg/kg apigenin). A single dose of 20 mg/kg VEN was administered orally 30 min after administration of apigenin (250 mg/kg). VEN plasma levels were measured by HPLC with fluorescence detection, and pharmacokinetic parameters were calculated by DAS 3.0 software. Results: The single dose of 250 mg/kg apigenin significantly increased the AUC0-t of VEN by 40.9% (p < 0.05) and obviously increased the peak plasma concentration (Cmax) of VEN (p < 0.05). Furthermore, apigenin showed inhibitory effect on human and rat microsomes and the IC50 of apigenin was 58.37 and 25.73 μmol/l, respectively. Conclusions: Our results indicated that an intake of apigenin could increase VEN plasma levels and some of its pharmacokinetic parameters (AUC, Tmax). Thus, more attention should be paid when VEN was administrated combined with apigenin.

Effect of 24 Cytochrome P450 2D6 Variants Found in the Chinese Population on Atomoxetine Metabolism in vitro

Objective: The aim of this article was to assess the catalytic activities of 24 cytochrome P450 2D6 (CYP2D6) variants found in the Chinese population toward atomoxetine in vitro as well as CYP2D6.1. Methods: In this study, the co-expression enzyme of human recombinant CYPOR, CYPb5, and CYP2D6.1 or other CYP2D6 variants with the baculovirus-mediated insect cells (Sf21) was used to study the catalytic activities of 24 CYP2D6 variants toward atomoxetine metabolism. The metabolite of atomoxetine (4-hydroxyatomoxetine) was detected by ultra-high performance liquid chromatography-mass spectrometry method. Results: The intrinsic clearance (Vmax/Km) values of most variants were significantly altered when compared with CYP2D6.1. CYP2D6.94, CYP2D6.D336N, CYP2D6.R440C exhibited marked increased values 172, 126, 121% respectively. CYP2D6.89 and CYP2D6.98 exhibited similar catalytic activity as the wild type, whereas 17 variants exhibited significantly decreased values (from 5 to 87%) due to increase Km and/or decrease Vmax values. However, CYP2D6.92 and CYP2D6.96 showed no or few activity because of producing nothing. Conclusions: Our results suggest that most of these newly found variants exhibit significantly changed catalytic activities compared with the wild type. And these findings provide valuable information for the growth and development of personalized medicine in China.

Effects of 24 CYP2D6 Variants Found in the Chinese Population on the Metabolism of Risperidone.

Aims: Cytochrome P450 (CYP450) 2D6 is an important member of the P450 enzyme superfamily and responsible for clearing 25% of clinically important drugs. The aim of this study was to assess the catalytic characteristics of 24 CYP2D6 allelic isoforms found in the Chinese population and their effects on the metabolism of risperidone in vitro. Methods: Insect microsomes expressing wild-type CYP2D6 and 24 CYP2D6 allelic variants were incubated with 20-1,000 μmol/l risperidone for 40 min at 37°C. After termination, risperidone and 9-OH risperidone, the metabolite of risperidone, were precipitated and used for signal collection by ultra-performance liquid-chromatography tandem mass spectrometry. Results: Among 24 CYP2D6 variants tested, 2 variants (CYP2D6*92 and CYP2D6*96) were found to be with no detectable activity. Two variants (E215K and R440C) exhibited higher intrinsic clearance values than the wild-type protein, while the remaining 20 CYP2D6 allelic variants exhibited significantly decreased clearance values (2.01-87.56%) compared to CYP2D6*1. Conclusion: These findings suggest that more attention should be directed to subjects carrying these infrequent CYP2D6 alleles when administering risperidone in the clinic. This is the first report of all these novel alleles for risperidone metabolism, providing fundamental data for further clinical studies on CYP2D6 alleles.

The effect of resveratrol on pharmacokinetics of aripiprazole in vivo and in vitro

Abstract 1. The objective of this study were to investigate the effect of orally administered resveratrol on the pharmacokinetics of aripiprazole (APZ) in rat, and the inhibitory effects of resveratrol on APZ dehydrogenation activity in liver microsomes and human cytochrome P450 3A4 and 2D6. 2. Twenty-five healthy male Sprague–Dawley rats were randomly divided into five groups: A (control group), B (multiple dose of 200 mg/kg resveratrol), C (multiple dose of 100 mg/kg resveratrol), D (a single dose of 200 mg/kg resveratrol) and E (a single dose of 100 mg/kg resveratrol). A single dose of 3 mg/kg APZ administered orally 30 min after administration of resveratrol. In addition, CYP2D6*1, CYP3A4*1, human and rat liver microsomes were performed to determine the effect of resveratrol on the metabolism of APZ in vitro. 3. The multiple dose of 200 or 100 mg/kg resveratrol significantly increased the AUC and Cmax of APZ. The resveratrol also obviously decreased the CL, but without any significant difference on t1/2 in vivo. On the other hand, resveratrol showed inhibitory effect on CYP3A4*1, CYP2D6*1, human and rat microsomes, the IC50 of resveratrol was 6.771, 87.87, 45.11 and 35.59 μmol l−1, respectively. 4. Those results indicated more attention should be paid when APZ was administrated combined with resveratrol.

Effect of CYP2D6 genetic polymorphism on the metabolism of citalopram in vitro

Genetic polymorphisms of CYP2D6 significantly influence the efficacy and safety of some drugs, which might cause adverse effects and therapeutic failure. We aimed at investigating the role of CYP2D6 in the metabolism of citalopram and identifying the effect of 24 CYP2D6 allelic variants we found in Chinese Han population on the metabolism of citalopram in vitro. These CYP2D6 variants expressed by insect cells system were incubated with 10-1000 μM citalopram for 30 min at 37 °C and the reaction was terminated by cooling to -80 °C immediately. Citalopram and its metabolites were analyzed by high-performance liquid chromatography (HPLC). The intrinsic clearance (Vmax/Km) values of the variants toward citalopram metabolites were significantly altered, 38-129% for demethylcitalopram and 13-138% for citalopram N-oxide when compared with CYP2D6*1. Most of the tested rare alleles exhibited significantly decreased values due to increased Km and/or decreased Vmax values. We conclude that recombinant system could be used to investigate the enzymes involved in drug metabolism and these findings suggest that more attention should be paid to subjects carrying these CYP2D6 alleles when administering citalopram in the clinic.

Role of cytochrome P450 2D6 genetic polymorphism in carvedilol hydroxylation in vitro

Cytochrome P450 2D6 (CYP2D6) is a highly polymorphic enzyme that catalyzes the metabolism of a great number of therapeutic drugs. Up to now, >100 allelic variants of CYP2D6 have been reported. Recently, we identified 22 novel variants in the Chinese population in these variants. The purpose of this study was to examine the enzymatic activity of the variants toward the CYP2D6 substrate carvedilol in vitro. The CYP2D6 proteins, including CYP2D6.1 (wild type), CYP2D6.2, CYP2D6.10, and 22 other novel CYP2D6 variants, were expressed from insect microsomes and incubated with carvedilol ranging from 1.0 μM to 50 μM at 37°C for 30 minutes. After termination, the carvedilol metabolites were extracted and detected using ultra-performance liquid chromatography tandem mass-spectrometry. Among the 24 CYP2D6 variants, CYP2D6.92 and CYP2D6.96 were catalytically inactive and the remaining 22 variants exhibited significantly decreased intrinsic clearance values (ranging from ~25% to 95%) compared with CYP2D6.1. The present data in vitro suggest that the newly found variants significantly reduced catalytic activities compared with CYP2D6.1. Given that CYP2D6 protein activities could affect carvedilol plasma levels, these findings are greatly relevant to personalized medicine.