Succinate induces skeletal muscle fiber remodeling via SUNCR1 signaling.

The conversion of skeletal muscle fiber from fast twitch to slow-twitch is important for sustained and tonic contractile events, maintenance of energy homeostasis, and the alleviation of fatigue. Skeletal muscle remodeling is effectively induced by endurance or aerobic exercise, which also generates several tricarboxylic acid (TCA) cycle intermediates, including succinate. However, whether succinate regulates muscle fiber-type transitions remains unclear. Here, we found that dietary succinate supplementation increased endurance exercise ability, myosin heavy chain I expression, aerobic enzyme activity, oxygen consumption, and mitochondrial biogenesis in mouse skeletal muscle. By contrast, succinate decreased lactate dehydrogenase activity, lactate production, and myosin heavy chain IIb expression. Further, by using pharmacological or genetic loss-of-function models generated by phospholipase Cß antagonists, SUNCR1 global knockout, or SUNCR1 gastrocnemius-specific knockdown, we found that the effects of succinate on skeletal muscle fiber-type remodeling are mediated by SUNCR1 and its downstream calcium/NFAT signaling pathway. In summary, our results demonstrate succinate induces transition of skeletal muscle fiber via SUNCR1 signaling pathway. These findings suggest the potential beneficial use of succinate-based compounds in both athletic and sedentary populations.

Assessment of 25 CYP2D6 alleles found in the Chinese population on propafenone metabolism in vitro.

Cytochrome P450 enzyme 2D6 (CYP2D6) is an important member of the cytochrome P450 enzyme superfamily, with more than 100 CYP2D6 allelic variants being previously reported. The aim of this study was to assess the catalytic characteristics of 25 alleles (CYP2D6.1 and 24 CYP2D6 variants) and their effects on the metabolism of propafenone in vitro. Twenty-five CYP2D6 alleles were expressing in 21 Spodoptera frugiperda (Sf) insect cells, and each variant was evaluated using propafenone as the substrate. Reactions were performed at 37 °C with 1-100 µmol/L propafenone for 30 min. After termination, the product 5-OH-propafenone was extracted and used for signal collection by ultra-performance liquid chromatography (UPLC). Compared with wild type CYP2D6.1, the intrinsic clearance (Vmax and Km) values of all variants were significantly altered. Three variants (CYP2D6.87, CYP2D6.90, CYP2D6.F219S) exhibited markedly increased intrinsic clearance values (129% to 165%), whereas 21 variants exhibited significantly decreased values (16% to 85%) due to increased Km and (or) decreased Vmax values. These results indicated that the majority of tested alleles had significantly altered catalytic activity towards propafenone hydroxylation in this expression system. Attention should be paid to subjects carrying these rare alleles when treated with propafenone.

Effect of CYP2D6 variants on venlafaxine metabolism in vitro.

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.

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

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.

Effects of 22 CYP2D6 Genetic Variations Newly Identified in Chinese Population on Olanzapine Metabolism in vitro.

The objective of this study was to assess the catalytic activity of 22 novel CYP2D6 allelic variants (2D6*87-*98, R25Q, F164L, E215K, F219S, V327M, D336N, V342M, R344Q, R440C and R497C) to olanzapine in vitro. Their protein products expressed in Spodoptera frugiperda 21 (Sf21) insect cells were incubated with olanzapine 100-2,000 µmol/l for 30 min. The kinetic parameters of Km, Vmax and intrinsic clearance were determined by 2-hydroxymethylolanzapine, the metabolite of olanzapine mediated by CYP2D6, using ultra-performance liquid chromatography tandem mass spectrometry. Results showed that the kinetic parameters of 2 alleles, CYP2D6*92 and 2D6*96, could not be detected; 17 allelic variants, CYP2D6*87-*88, 2D6*90-*91, 2D6*93-*95, 2D6*97, R25Q, F164L, E215K, F219S, V327M, V342M, R344Q, R440C and R497C, significantly reduced the intrinsic clearance of olanzapine; 2 variants, CYP2D6*89 and 2D6*98, increased the intrinsic clearance of olanzapine; no difference was found in intrinsic clearance of D336N. Furthermore, 6 alleles, CYP2D6*87, 2D6*88, 2D6*91, 2D6*93, 2D6*97 and R497C, exhibited higher Km values in a range of 120.80-217.56% relative to wild-type CYP2D6*1. The research demonstrated the metabolic phenotype of the 22 novel CYP2D6 variants for olanzapine that were different from probe drugs we used previously and might provide beneficial information to the personalized medicine of olanzapine.

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 CYP2C9 genetic polymorphism on the metabolism of flurbiprofen in vitro.

CYP2C9 is an important member of the cytochrome P450 enzyme superfamily, and 57 cytochrome P450 2C9 alleles have been previously reported. To examine the enzymatic activity of the CYP2C9 alleles, kinetic parameters for 4'-hydroxyflurbiprofen were determined using recombinant human P450s CYP2C9 microsomes from insect cells Sf21 carrying wild-type CYP2C9*1 and other variants. The results showed that the enzyme activity of most of the variants decreased comparing with the wild type as the previous studies reported, while the enzyme activity of some of them increased, which were not in accordance with the previous researches. Of the 36 tested CYP2C9 allelic isoforms, two variants (CYP2C9*53 and CYP2C9*56) showed a higher intrinsic clearance value than the wild-type protein, especially for CYP2C9*56, exhibited much higher intrinsic clearance (197.3%) relative to wild-type CYP2C9*1, while the remaining 33 CYP2C9 allelic isoforms exhibited significantly decreased clearance values (from 0.6 to 83.8%) compared to CYP2C9*1. This study provided the most comprehensive data on the enzymatic activities of all reported CYP2C9 variants in the Chinese population with regard to the commonly used non-steroidal anti-inflammatory drug, flurbiprofen (FP). The results indicated that most of the tested rare alleles decreased the catalytic activity of CYP2C9 variants toward FP hydroxylation in vitro. This is the first report of all these rare alleles for FP metabolism providing fundamental data for further clinical studies on CYP2C9 alleles for FP metabolism in vivo.

The Effect of Myricetin on Pharmacokinetics of Atomoxetine and its Metabolite 4-Hydroxyatomoxetine In Vivo and In Vitro.

BACKGROUND AND OBJECTIVES: Atomoxetine is the first non-stimulant drug to be approved for the treatment of ADHD, while the effect of myricetin on the pharmacokinetic of atomoxetine in rats or human is still unknown. The present work was to study the impact of myricetin on the metabolism of atomoxetine both in vivo and in vitro. METHODS: Twenty healthy male Sprague-Dawley rats were randomly divided into four groups: A (control group), B (100 mg/kg myricetin), C (50 mg/kg myricetin), and D (25 mg/kg myricetin). A single dose of atomoxetine (10 mg/kg) was administrated half an hour later. In addition, human and rat liver microsomes were performed to determine the effect of myricetin on the metabolism of atomoxetine in vitro. RESULTS: Group B, C, D all increased the C max and AUC of atomoxetine, but decreased the C max and AUC of 4-hydroxyatomoxetine. Moreover, myricetin showed inhibitory effect on human and rat microsomes, the IC50 of myricetin was 8.651 and 35.45 µmol/L, respectively. CONCLUSIONS: Our study showed that myricetin could significantly inhibit the formation of atomoxetine metabolite both in vivo and in vitro. It is recommended that the effect of myricetin on the metabolism of atomoxetine should be noted and atomoxetine plasma concentration should be monitored.

Effect of 22 CYP2D6 variants found in the Chinese population on tolterodine metabolism in vitro.

Cytochrome P450 2D6 (CYP2D6) is an important member of the cytochrome P450 enzyme superfamily. We recently identified 22 novel variants in the Chinese population using PCR and bidirectional sequencing methods. The aim of this study is to characterize the enzymatic activity of these variants and their effects on the metabolism of the antimuscarinic drug tolterodine in vitro. A baculovirus-mediated expression system was used to express wild-type CYP2D6 and 24 variants (CYP2D6*2, CYP2D6*10, and 22 novel CYP2D6 variants) at high levels. The insect microsomes expressing CYP2D6 proteins were incubated with 0.1-50 µM tolterodine at 37 °C for 30 min and the metabolites were analyzed by high-performance liquid chromatography-tandem mass spectrometry system. Of the 24 CYP2D6 variants tested, 2 variants (CYP2D6*92 and CYP2D6*96) were found to be catalytically inactive, 4 variants (CYP2D6*94, F164L, F219S and D336N) exhibited markedly increased intrinsic clearance values (Vmax/Km) compared with the wild-type (from 66.34 to 99.79%), whereas 4 variants (CYP2D6*10, *93, *95 and E215K) exhibited significantly decreased values (from 49.02 to 98.50%). This is the first report of all these rare alleles for tolterodine metabolism and these findings suggest that more attention should be paid to subjects carrying these infrequent CYP2D6 alleles when administering tolterodine in the clinic.

Functional characterization of 22 novel CYP2D6 variants for the metabolism of Tamoxifen.

OBJECTIVES: This study aimed to assess the catalytic characteristics of 24 CYP2D6 allelic isoforms found in Chinese Han population on the metabolism of tamoxifen in vitro. METHODS: Recombinant CYP2D6 microsomes of distinguished genotypes were used to characterize the corresponding enzyme activity towards tamoxifen. About 5-2500 µm tamoxifen was incubated for 30 min at 37 °C. Using high-performance liquid chromatography to detect the products, the kinetic parameters Km , Vmax and intrinsic clearance (Vmax /Km ) of N-desmethyltamoxifen were determined. KEY FINDINGS: Of the 24 tested allelic variants, the differences of intrinsic clearance value were shown as follows: CYP2D6.89 was much higher than wild-type CYP2D6.1, 2 allelic isoforms (CYP2D6.88 and D336N) exhibited similar intrinsic clearance values as the wild-type enzyme, two variants displayed weak or no activity, while the rest 19 variants showed significantly reduced intrinsic clearance values ranging from 7.46 to 81.11%. CONCLUSION: The comprehensive assessment of CYP2D6 variants provides significant insights into allele-specific activity towards tamoxifen in vitro, suggesting that most of the carriers of these alleles might be paid more attention when using CYP2D6-mediated drugs clinically.