Growth hormone-regulated periportal expression of CYP2C7 in rat liver

Evaluation of Zuo-Gui Yin Decoction Effects on Six CYP450 Enzymes in Rats Using a Cocktail Method by UPLC-MS/MS

Background. Zuo-Gui Yin Decoction (ZGYD), a traditional Chinese prescription, is mainly used in various kinds of andrology and gynecology diseases. However, the study on the interaction of ZGYD and drugs has not been reported. Therefore, evaluating the interaction between ZGYD and metabolic enzymes is helpful to guide rational drug use. Objective. This study was conducted to explore the effects of ZGYD on the activity and mRNA expressions of six Cytochrome P450 (CYP450) enzymes in rats and to provide a basis for its rational clinical use. Methods. Sprague-Dawley rats were randomly divided into control, ZGYD high, medium, and low-dose group ( $n=6$ ). The concentrations of six probe substrates in plasma of rats in each group were determined by UPLC-MS/MS. In addition, RT-PCR and Western blot were used to determine the effects of ZGYD on the expression of CYP450 isoforms in the liver. Results. Compared with the control group, the main pharmacokinetic parameters AUC(0-t), AUC (0~∞), of omeprazole, dextromethorphan, and midazolam in the high-dose group were significantly decreased, while the CL of these were significantly increased. The gene expressions of CYP2C11 and CYP3A1 were upregulated in the ZGYD medium, high-dose group. The protein expression of CYP2C11 was upregulated in the high-dose group, and the protein expression of CYP3A1 was upregulated in the medium, high-dose group. Conclusion. The results showed that ZGYD exhibited the induction effects on CYP2C11 and CYP3A1 (CYP2C19 and CYP3A4 in humans) in rats. However, no significant change in CYP1A2, CYP2B1, CYP2C7, and CYP2D2 activities was observed. It would be useful for the safe and effective usage of ZGYD in clinic.

Feminization of Male Mouse Liver by Persistent Growth Hormone Stimulation: Activation of Sex-Biased Transcriptional Networks and Dynamic Changes in Chromatin States

Sex-dependent pituitary growth hormone (GH) secretory profiles-pulsatile in males and persistent in females-regulate the sex-biased, STAT5-dependent expression of hundreds of genes in mouse liver, imparting sex differences in hepatic drug/lipid metabolism and disease risk. Here, we examine transcriptional and epigenetic changes induced by continuous GH infusion (cGH) in male mice, which rapidly feminizes the temporal profile of liver STAT5 activity. cGH repressed 86% of male-biased genes and induced 68% of female-biased genes within 4 days; however, several highly female-specific genes showed weak or no feminization, even after 14 days of cGH treatment. Female-biased genes already in an active chromatin state in male liver generally showed early cGH responses; genes in an inactive chromatin state often responded late. Early cGH-responsive genes included those encoding two GH/STAT5-regulated transcriptional repressors: male-biased BCL6, which was repressed, and female-specific CUX2, which was induced. Male-biased genes activated by STAT5 and/or repressed by CUX2 were enriched for early cGH repression. Female-biased BCL6 targets were enriched for early cGH derepression. Changes in sex-specific chromatin accessibility and histone modifications accompanied these cGH-induced sex-biased gene expression changes. Thus, the temporal, sex-biased gene responses to persistent GH stimulation are dictated by GH/STAT5-regulated transcription factors arranged in a hierarchical network and by the dynamics of changes in sex-biased epigenetic states.

A novel vascular EET synthase: role of CYP2C7

We demonstrated previously that cytochrome P-450 (CYP) 2C29 is the epoxyeicosatrienoic acid (EET) synthase responsible for the EET-mediated flow/shear stress-induced dilation of vessels of female nitric oxide (NO)-deficient mice (Sun D, Yang YM, Jiang H, Wu H, Ojami C, Kaley G, Huang A. Am J Physiol Regul Integr Comp Physiol 298: R862-R869, 2010). In the present study, we aimed to identify which specific CYP isoform(s) is the source of the synthesis and release of EETs in response to stimulation by shear stress in vessels of rats. Cannulated mesenteric arteries isolated from both sexes of N(G)-nitro-L-arginine methyl ester (L-NAME)-treated rats were perfused with 2 and 10 dyn/cm(2) shear stress, followed by collection of the perfusate to determine EET concentrations and isoforms. Shear stress stimulated release of EETs in the perfusate of female (but not male) NO-deficient vessels, associated with an EET-mediated vasodilation, in which 11,12- and 14,15-EET contributed predominantly to the responses. Rat CYP cDNA array screened a total of 32 CYP genes of mesenteric arteries, indicating a significant upregulation of CYP2C7 in female L-NAME-treated rats. Endothelial RNA and protein were extracted from intact single vessels. Expression of CYP2C7 mRNA and protein in pooled extractions of endothelial lysate was identified by PCR and Western blot analyses. Transfection of the vessels with CYP2C7 short interfering RNA eliminated the release of EETs, consequently abolishing the EET-mediated flow-induced dilation; these responses, however, were maintained in vessels transfected with nonsilencing short interfering RNA. Knockdown of endothelial CYP2C7 was confirmed by PCR and Western blot analyses. In conclusion, CYP2C7 is an endothelial EET synthase in the female rat vasculature, by which, in NO deficiency, shear stress stimulates the release of EETs to initiate vasodilation.

beta-Catenin as a multilayer modulator of zonal cytochrome P450 expression in mouse liver

The liver is the major organ for metabolism of drugs and other xenobiotics. Expression of many drug-metabolizing enzymes is not equally distributed throughout the liver: under normal conditions, many of them, including the most relevant members of the cytochrome P450 superfamily, are exclusively expressed in a hepatocyte subpopulation located near branches of the efferent central vein. Activation of different ligand-dependent transcription factors by exogenous compounds stimulates high expression of certain cytochrome P450 isoforms. This process also occurs preferentially in perivenous hepatocytes. The mechanisms, however, which determine the zone-specificity of basal and xenobiotic-induced expression of cytochrome P450 enzymes, have remained largely unknown for decades. Very recently, signaling through the Wnt/beta-catenin pathway has been implicated in the regulation of zonal gene expression in mouse liver. In this review, current knowledge of cytochrome P450 regulation by beta-catenin-dependent transcription is summarized and underlying molecular mechanisms are discussed.

Serum components and activated Ha-ras antagonize expression of perivenous marker genes stimulated by beta-catenin signaling in mouse hepatocytes

Hepatocytes of the periportal and perivenous zones of the liver lobule show marked differences in the contents and activities of many enzymes and other proteins. Previous studies from our and other groups have pointed towards an important role of beta-catenin-dependent signaling in the regulation of expression of genes encoding proteins with preferential perivenous localization, whereas, in contrast, signaling through Ras-dependent pathway(s) may induce a 'periportal' phenotype. We have now conducted a series of experiments to further investigate this hypothesis. In transgenic mice with scattered expression of an activated Ha-ras (Ha-ras(G12V)) mutant in liver, expression of the perivenous markers glutamine synthetase and two cytochrome P450 isoforms was completely abolished in those hepatocytes demonstrating constitutively activated extracellular signal-regulated kinase activity, even though they were located directly adjacent to central veins. Similarly, incubation of primary hepatocytes or hepatoma cells with increasing amounts of serum caused a concentration-dependent attenuation of expression of perivenous marker mRNAs, whereas the expression of periportal markers was increased. The inhibitory effect of high amounts of serum on the expression of perivenous markers was also observed if their expression was stimulated by activation of beta-catenin signaling, and comparable inhibitory effects were seen in cells stably transfected with a T-cell factor/lymphoid-enhancing factor-driven luciferase reporter. Epidermal growth factor could partly mimic serum effects in hepatoma cells, and its effect could be blocked by an inhibitor of extracellular signal-regulated kinase activity. These data suggest that activation of the Ras/mitogen-activated protein kinase (extracellular signal-regulated kinase) pathway favors periportal gene expression while simultaneously antagonizing a perivenous phenotype of hepatocytes.

Zonal gene expression in mouse liver resembles expression patterns of Ha-ras and beta-catenin mutated hepatomas

Hepatocytes of the periportal and perivenous zones of the liver lobule differ in their levels and activities of various enzymes and other proteins. We have recently suggested that beta-catenin- and Ras-dependent signaling pathways play an important role in the regulation of perivenous and periportal gene expression profiles. This hypothesis was primarily based on similarities in zonal differences in gene expression of hepatocytes from normal liver with gene expression patterns of liver tumors: several proteins and mRNAs preferentially expressed in periportal hepatocytes were often overexpressed in Ha-ras mutated mouse liver tumors, whereas perivenous markers were overexpressed in Ctnnb1 (encoding beta-catenin) mutated tumors. We have now extended this work by use of data from two previously conducted microarray analyses aimed to analyze 1) global gene expression patterns of Ha-ras and Ctnnb1 mutated mouse liver tumors and 2) transcriptome differences between periportal and perivenous mouse hepatocytes. By comparison of the datasets, 134 genes or expressed sequences were identified that were present in both datasets. Gene expression patterns in perivenous hepatocytes and Ctnnb1 mutated hepatoma cells were strongly correlated: 96.5% of the genes present in both datasets were regulated in the same direction. In analogy, expression of 74.1% of the genes deregulated in Ha-ras mutated tumors was correlated with the respective expression patterns in periportal hepatocytes. These findings favor the hypothesis that gene expression patterns in periportal and perivenous hepatocytes are regulated, at least in part, by Ras- and beta-catenin-dependent signaling pathways.

Systems Toxicology: Integrated Genomic, Proteomic and Metabonomic Analysis of Methapyrilene Induced Hepatotoxicity in the Rat

Administration of high doses of the histamine antagonist methapyrilene to rats causes periportal liver necrosis. The mechanism of toxicity is ill-defined and here we have utilized an integrated systems approach to understanding the toxic mechanisms by combining proteomics, metabonomics by 1H NMR spectroscopy and genomics by microarray gene expression profiling. Male rats were dosed with methapyrilene for 3 days at 150 mg/kg/day, which was sufficient to induce liver necrosis, or a subtoxic dose of 50 mg/kg/day. Urine was collected over 24 h each day, while blood and liver tissues were obtained at 2 h after the final dose. The resulting data further define the changes that occur in signal transduction and metabolic pathways during methapyrilene hepatotoxicity, revealing modification of expression levels of genes and proteins associated with oxidative stress and a change in energy usage that is reflected in both gene/protein expression patterns and metabolites. The difficulties of combining and interpreting multiomic data are considered.

Enterohepatic circulation: physiological, pharmacokinetic and clinical implications

Enterohepatic recycling occurs by biliary excretion and intestinal reabsorption of a solute, sometimes with hepatic conjugation and intestinal deconjugation. Cycling is often associated with multiple peaks and a longer apparent half-life in a plasma concentration-time profile. Factors affecting biliary excretion include drug characteristics (chemical structure, polarity and molecular size), transport across sinusoidal plasma membrane and canniculae membranes, biotransformation and possible reabsorption from intrahepatic bile ductules. Intestinal reabsorption to complete the enterohepatic cycle may depend on hydrolysis of a drug conjugate by gut bacteria. Bioavailability is also affected by the extent of intestinal absorption, gut-wall P-glycoprotein efflux and gut-wall metabolism. Recently, there has been a considerable increase in our understanding of the role of transporters, of gene expression of intestinal and hepatic enzymes, and of hepatic zonation. Drugs, disease and genetics may result in induced or inhibited activity of transporters and metabolising enzymes. Reduced expression of one transporter, for example hepatic canalicular multidrug resistance-associated protein (MRP) 2, is often associated with enhanced expression of others, for example the usually quiescent basolateral efflux MRP3, to limit hepatic toxicity. In addition, physiologically relevant pharmacokinetic models, which describe enterohepatic recirculation in terms of its determinants (such as sporadic gall bladder emptying), have been developed. In general, enterohepatic recirculation may prolong the pharmacological effect of certain drugs and drug metabolites. Of particular importance is the potential amplifying effect of enterohepatic variability in defining differences in the bioavailability, apparent volume of distribution and clearance of a given compound. Genetic abnormalities, disease states, orally administered adsorbents and certain coadministered drugs all affect enterohepatic recycling.