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 Cβ 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.

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.

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.

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.

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.

Mortality attributable to cigarette smoking in China

CONTEXT

The few published prospective studies of smoking and mortality in China have reported low relative risks, but the durations of follow-up were short.

OBJECTIVE

To assess the mortality of ever- and never-smokers in a cohort after 20 years of follow-up.

DESIGN, SETTING, AND SUBJECTS

A cohort analytic study in a machinery factory in Xi'an, China, involving 1696 people aged 35 years or older (1124 men and 572 women) examined in May 1976.

MAIN OUTCOME MEASURES

All-cause and tobacco-associated mortality.

RESULTS

A total of 56% of the men and 12% of the women were ever-smokers at baseline. Through August 31, 1996, 218 persons (173 men and 45 women) had died. The relative risks (95% confidence intervals [CIs]) for ever smoking (after adjusting for age, marital status, occupation, education, diastolic blood pressure, and triglyceride and cholesterol levels) for deaths resulting from all causes, all cancer, and coronary heart disease were, respectively, 2.42 (95% CI, 1.72-3.42), 2.50 (95% CI, 1.41-4.43), and 3.61 (95% CI, 1.35-9.67) in men and 2.32 (95% CI, 1.18-4.56), 1.98 (95% CI, 0.50-7.92), and 4.67 (95% CI, 0.78-27.8) in women.

CONCLUSIONS

Previous prospective studies of smoking-related mortality in China tended to underestimate the risks, probably because of short durations of follow-up. We have demonstrated that smoking is a major cause of death in China, and the risks are similar to those seen in the United States and the United Kingdom. Thus, about half of the 300 million smokers in China will eventually die of smoking-related diseases if urgent tobacco-control measures are not instituted to prevent this growing epidemic.