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Cytochrome P450 (cytochrome + p450)
Kinds of Cytochrome P450 Terms modified by Cytochrome P450 Selected AbstractsDose-dependent Induction of Cytochrome P450 (CYP) 3A4 and Activation of Pregnane X Receptor by TopiramateEPILEPSIA, Issue 12 2003Srikanth C. Nallani Summary:,Purpose: In clinical studies, topiramate (TPM) was shown to cause a dose-dependent increase in the clearance of ethinyl estradiol. We hypothesized that this interaction results from induction of hepatic cytochrome P450 (CYP) 3A4 by TPM. Accordingly, we investigated whether TPM induces CYP3A4 in primary human hepatocytes and activates the human pregnane X receptor (hPXR), a nuclear receptor that serves as a regulator of CYP3A4 transcription. Methods: Human hepatocytes were treated for 72 h with TPM (10, 25, 50, 100, 250, and 500 ,M) and known inducers, phenobarbital (PB; 2 mM), and rifampicin (10 ,M). The rate of testosterone 6,-hydroxylation by hepatocytes served as a marker for CYP3A4 activity. The CYP3A4-specific protein and mRNA levels were determined by using Western and Northern blot analyses, respectively. The hPXR activation was assessed with cell-based reporter gene assay. Results: Compared with controls, TPM (50,500 ,M),treated hepatocytes exhibited a considerable increase in the CYP3A4 activity (1. 6- to 8.2-fold), protein levels (4.6- to 17.3-fold), and mRNA levels (1.9- to 13.3-fold). Comparatively, rifampicin (10 ,M) effected 14.5-, 25.3-, and a 20.3-fold increase in CYP3A4 activity, immunoreactive protein levels, and mRNA levels, respectively. TPM (50,500 ,M) caused 1.3- to 3-fold activation of the hPXR, whereas rifampicin (10 ,M) caused a 6-fold activation. Conclusions: The observed induction of CYP3A4 by TPM, especially at the higher concentrations, provides a potential mechanistic explanation of the reported increase in the ethinyl estradiol clearance by TPM. It also is suggestive of other potential interactions when high-dose TPM therapy is used. [source] Protein engineering of Bacillus megaterium CYP102FEBS JOURNAL, Issue 10 2001The oxidation of polycyclic aromatic hydrocarbons Cytochrome P450 (CYP) enzymes are involved in activating the carcinogenicity of polycyclic aromatic hydrocarbons (PAHs) in mammals, but they are also utilized by microorganisms for the degradation of these hazardous environmental contaminants. Wild-type CYP102 (P450BM-3) from Bacillus megaterium has low activity for the oxidation of the PAHs phenanthrene, fluoranthene and pyrene. The double hydrophobic substitution R47L/Y51F at the entrance of the substrate access channel increased the PAH oxidation activity by up to 40-fold. Combining these mutations with the active site mutations F87A and A264G lead to order of magnitude increases in activity. Both these mutations increased the NADPH turnover rate, but the A264G mutation increased the coupling efficiency while the F87A mutation had dominant effects in product selectivity. Fast NADPH oxidation rates were observed (2250 min,1 for the R47L/Y51F/F87A mutant with phenanthrene) but the coupling efficiencies were relatively low (< 13%), resulting in a highest substrate oxidation rate of 110 min,1 for fluoranthene oxidation by the R47L/Y51F/A264G mutant. Mutation of M354 and L437 inside the substrate access channel reduced PAH oxidation activity. The PAHs were oxidized to a mixture of phenols and quinones. Notably mutants containing the A264G mutation showed some similarity to mammalian CYP enzymes in that some 9,10-phenanthrenequinone, the K -region oxidation product from phenanthrene, was formed. The results suggest that CYP102 mutants could be useful models for PAH oxidation by mammalian CYP enzymes, and also potentially for the preparation of novel PAH bioremediation systems. [source] Over expression of a Cytochrome P450 (CYP6P9) in a Major African Malaria Vector, Anopheles Funestus, Resistant to PyrethroidsINSECT MOLECULAR BIOLOGY, Issue 1 2008D. A. Amenya Abstract Anopheles funestus Giles is one of the major African malaria vectors. It has previously been implicated in a major outbreak of malaria in KwaZulu/Natal, South Africa, during the period 1996 to 2000. The re-emergence of this vector was associated with monooxygenase-based resistance to pyrethroid insecticides. We have identified a gene from the monooxygenase CYP6 family, CYP6P9, which is over expressed in a pyrethroid resistant strain originating from Mozambique. Quantitative Real-Time PCR shows that this gene is highly over expressed in the egg and adult stages of the resistant strain relative to the susceptible strain but the larval stages showed almost no difference in expression between strains. This gene is genetically linked to a major locus associated with pyrethroid resistance in this A. funestus population. [source] Mechanisms underlying the inhibition of the cytochrome P450 system by copper ionsJOURNAL OF APPLIED TOXICOLOGY, Issue 8 2009M. E. Letelier Abstract Copper toxicity has been associated to the capacity of free copper ions to catalyze the production of superoxide anion and hydroxyl radical, reactive species that modify the structure and/or function of biomolecules. In addition, nonspecific Cu2+ -binding to thiol enzymes, which modifies their catalytic activities, has been reported. Cytochrome P450 (CYP450) monooxygenase is a thiol protein that binds substrates in the first and limiting step of CYP450 system catalytic cycle, necessary for the metabolism of lipophilic xenobiotics. Therefore, copper ions have the potential to oxidize and bind to cysteinyl residues of this monooxygenase, altering the CYP450 system activity. To test this postulate, we studied the effect of Cu2+ alone and Cu2+/ascorbate in rat liver microsomes, to independently evaluate its nonspecific binding and its pro-oxidant effects, respectively. We assessed these effects on the absorbance spectrum of the monooxygenase, as a measure of structural damage, and p -nitroanisole O -demethylating activity of CYP450 system, as a marker of functional impairment. Data obtained indicate that Cu2+ could both oxidize and bind to some amino acid residues of the CYP450 monooxygenase but not to its heme group. The differences observed between the effects of Cu2+ and Cu2+/ascorbate show that both mechanisms are involved in the catalytic activity inhibition of CYP450 system by copper ions. The significance of these findings on the pharmacokinetics and pharmacodynamics of drugs is discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Mechanisms of cytochrome P450 substrate oxidation: MiniReviewJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2007F. Peter Guengerich Abstract Cytochrome P450 (P450) enzymes catalyze a variety of oxidation and some reduction reactions, collectively involving thousands of substrates. A general chemical mechanism can be used to rationalize most of the oxidations and involves a perfenyl intermediate (FeO3+) and odd-electron chemistry, i.e. abstraction of a hydrogen atom or electron followed by oxygen rebound and sometimes rearrangement. This general mechanism can explain carbon hydroxylation, heteroatom oxygenation and dealkylation, epoxidation, desaturation, heme destruction, and other reactions. Another approach to understanding catalysis involves analysis of the more general catalytic cycle, including substrate specificity, because complex patterns of cooperativity are observed with several P450s. Some of the complexity is due to slow conformational changes in the proteins that occur on the same timescale as other steps. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:163,168, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20174 [source] Metabolism of chlorpyrifos and chlorpyrifos oxon by human hepatocytes,JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 6 2006Kyoungju Choi Abstract The metabolism of chlorpyrifos (CPS) and chlorpyrifos oxon (CPO) by human hepatocytes and human liver S9 fractions was investigated using LC-MS/MS. Cytochrome P450 (CYP)-dependent and phase II-related products were determined following incubation with CPS and CPO. CYP-related products, 3,5,6-trichloro-2-pyridinol (TCP), diethyl thiophosphate, and dealkylated CPS, were found following CPS treatment and dealkylated CPO following CPO treatment. Diethyl phosphate was not identified because of its high polarity and lack of retention with the chromatographic conditions employed. Phase II-related conjugates, including O- and S-glucuronides as well as 11 GSH-derived metabolites, were identified in CPS-treated human hepatocytes, although the O -sulfate of TCP conjugate was found only when human liver S9 fractions were used as the enzyme source. O -Glucuronide of TCP was also identified in CPO-treated hepatocytes. CPS and CPO were identified using HPLC,UV after CPS metabolism by the human liver S9 fraction. However, CPO was not found following treatment of human hepatocytes with either CPS or CPO. These results suggest that human liver plays an important role in detoxification, rather than activation, of CPS. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:279,291, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20145 [source] Genetic polymorphisms in the metabolic pathway and non-Hodgkin lymphoma survival,AMERICAN JOURNAL OF HEMATOLOGY, Issue 1 2010Xuesong Han Metabolic pathway enzymes, such as Cytochrome P450 (CYP), glutathione S-transferase (GST), and N -acetyltransferases (NAT) are involved in activation and detoxification of environmental carcinogens as well as drug metabolism. We hypothesized that the genetic variations in such metabolic pathways may affect NHL prognosis and survival. Follow-up information of 496 female NHL incident cases diagnosed during 1996,2000 in Connecticut were abstracted from the Connecticut Tumor Registry in 2008; survival analyses were conducted by comparing the Kaplan-Meier curves, and hazard ratios (HR) were computed from the Cox Proportional Hazard models adjusting for demographic and tumor characteristics which were suggested by previous studies to be determinants of NHL survival. We identified six SNPs from four metabolism genes (CYP2E1, GSTP1, GSTT1, and NAT1) that were associated with NHL survival. Specifically, polymorphisms in GSTT1 were associated with follicular lymphoma survival; and polymorphisms in CYP2E1, GSTP1, and NAT1 were associated with survival of chronic lymphocytic leukemia/small lymphocytic lymphoma. Our study suggests that genetic polymorphisms in metabolic pathways may help improve the prediction of NHL survival and prognosis. Am. J. Hematol., 2010. © 2009 Wiley-Liss, Inc. [source] Calculated and Experimental Spin State of Seleno Cytochrome P450,ANGEWANDTE CHEMIE, Issue 39 2009Yongying Jiang Dr. Ein Wechsel zum Besseren: Das proximale Cysteinthiolat in einem Cytochrom-P450-Enzym wird durch ein Selenocystein ersetzt. Die UV/Vis- (siehe Spektrum, ,,,,), EPR- und Resonanz-Raman-Spektren des so erhaltenen selenolatverbrückten CYP119-Proteins ähneln denen des nativen Proteins (,). Damit wurde erstmals ein Hämprotein mit einem proximalen Selenolatliganden vollständig beschrieben. [source] Rapid determination of enzyme activities of recombinant human cytochromes P450, human liver microsomes and hepatocytesBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2003Anima Ghosal Abstract Cytochrome P450 (CYP) substrates that yield fluorescent metabolites were used for rapid screening of drug metabolism activities of 13 recombinant human cytochromes P450, human liver microsomes and human hepatocytes. Reproducible results were obtained using a fluorescent plate reader (CytoFluor) more expediently than those generated using conventional HPLC methods. Typically, results for 96 samples were obtained with the plate reader in less than 10 min as opposed to 15,35 min/sample required by conventional HPLC. The fluorescent substrates used to measure CYP activities were as follows: 3-cyano-7-ethoxycoumarin (CEC) for CYP1A1, CYP1A2, CYP2C9 and CYP2C19; 7-ethoxyresorufin (7-ER) for CYP1A1, CYP1A2 and CYP1B1; 3-[2-(N,N -diethyl- N -methylammonium)ethyl]-7-methoxy-4-methylcoumarin (AMMC) for CYP2D6; dibenzylfluorescein (DBF) for CYP3A4, CYP3A5 and CYP2C8; 7-methoxy-4-trifluoromethylcoumarin (7-MFC) for CYP2E1, CYP2B6 and CYP2C18; and coumarin for CYP2A6. The chemical inhibition and correlation data indicated that the following substrates can be used as specific functional probes for individual cytochrome P450 present in human liver microsomes: coumarin for CYP2A6 (r=0.82), AMMC for CYP2D6 (r=0.83) and DBF for CYP3A4 (r=0.92). The fluorescent plate reader was found to be useful for the rapid assessment of CYP activities (positive control) in both intact cells and subcellular fractions. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effect of zolpidem on human Cytochrome P450 activity, and on transport mediated by P-glycoproteinBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2002Lisa L. von Moltke Abstract The influence of high concentrations of zolpidem (100 ,M, corresponding to approximately 200 times maximum therapeutic concentrations) on the activity of six human Cytochrome P450 (CYP) enzymes was evaluated in a model system using human liver microsomes. Zolpidem produced negligible or weak inhibition of human CYP1A2, 2B6, 2C9, 2C19, 2D6, and 3A. Transport of rhodamine 123, presumed to be mediated mainly by the energy-dependent efflux transport protein P-glycoprotein, was studied in a cell culture system using a human intestinal cell line. High concentrations of zolpidem (100 ,M), exceeding the usual therapeutic range by more than 100-fold, produced only modest impairment of rhodamine 123 transport. The findings indicate that zolpidem is very unlikely to cause clinical drug interactions attributable to impairment of CYP activity or P-gp mediated transport. Copyright © 2002 John Wiley & Sons, Ltd. [source] Metabolic activation of polycyclic aromatic hydrocarbons to carcinogens by cytochromes P450 1A1 and1B1CANCER SCIENCE, Issue 1 2004Tsutomu Shimada Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously distributed environmental chemicals. PAHs acquire carcinogenicity only after they have been activated by xenobiotic-metabolizing enzymes to highly reactive metabolites capable of attacking cellular DNA. Cytochrome P450 (CYP) enzymes are central to the metabolic activation of these PAHs to epoxide intermediates, which are converted with the aid of epoxide hydrolase to the ultimate carcinogens, diol-epoxides. Historically, CYP1A1 was believed to be the only enzyme that catalyzes activation of these procarcinogenic PAHs. However, recent studies have established that CYP1B1, a newly identified member of the CYP1 family, plays a very important role in the metabolic activation of PAHs. In CYP1B1 gene-knockout mice treated with 7,12-dimethyl-benz[a]anthracene and dibenzo[a, l]pyrene, decreased rates of tumor formation were observed, when compared to wild-type mice. Significantly, gene expression of CYP1A1 and 1B1 is induced by PAHs and polyhalogenated hydrocarbons such as 2,3,7,8-tetrachlorodibenzo- p -dioxin through the arylhydrocarbon receptor. Differences in the susceptibility of individuals to the adverse action of PAHs may, in part, be due to differences in the levels of expression of CYP1A1 and 1B1 and to genetic variations in the CYP1A1 and 1B1 genes. [source] Influence of CYP3A5 and MDR1 polymorphisms on tacrolimus concentration in the early stage after renal transplantationCLINICAL TRANSPLANTATION, Issue 5 2005Xin Zhang Abstract:, Objective:, Tacrolimus is an immunosuppressive drug with a narrow therapeutic range and wide interindividual variation in its pharmacokinetics. Cytochrome P450 (CYP) 3A and P-glycoprotein (P-gp, encoded by MDR1) play an important role in the absorption and metabolism of tacrolimus. The objective of this study was to evaluate whether or not CYP3A5*1/*3 or MDR1 C3435T polymorphisms are associated with the tacrolimus concentration per dose. Methods:, CYP3A5 and MDR1 genotypes were determined by polymerase chain reaction followed by restriction fragment length polymorphism analysis in 118 Chinese renal transplant patients receiving tacrolimus. Whole blood trough tacrolimus concentration was measured by enzyme-linked immunosorbent assay and dose-adjusted concentration (ng/mL per mg/kg/d) was calculated at 1 wk, 1 month, and 3 months after transplantation. Results:, The dose-adjusted concentration of CYP3A5*1/*1 and *1/*3 patients was significantly lower than *3/*3 patients (32.8 ± 17.7 and 41.6 ± 15.8 vs. 102.3 ± 51.2 at 1 wk; 33.1 ± 7.5 and 46.4 ± 12.9 vs. 103 ± 47.5 at 1 month; 35.3 ± 20.9 and 59.0 ± 20.6 vs. 150 ± 85.3 at 3 months after transplantation respectively). At 1 wk, 46% of the CYP3A5*1 allele carriers had a tacrolimus concentration lower than 5 ng/mL and 77% lower than 8 ng/mL, whereas 20% of the *3/*3 patients had a concentration higher than 20 ng/mL. There was a mild difference between *1/*1 homozygotes and *1/*3 heterozygotes at 1 and 3 months after transplantation. No difference was found among the MDR1 genotypes. Conclusion:, CYP3A5*1/*3 polymorphisms are associated with tacrolimus pharmacokinetics and dose requirements in renal transplant recipients. Pharmacogenetic methods could be employed prospectively to help initial dose selection and to individualize immunosuppressive therapy. [source] Activation of PLA2 isoforms by cell swelling and ischaemia/hypoxiaACTA PHYSIOLOGICA, Issue 1-2 2006I. H. Lambert Abstract Phospholipase A2 (PLA2) activity is increased in mammalian cells in response to numerous stimuli such as osmotic challenge, oxidative stress and exposure to allergens. The increased PLA2 activity is seen as an increased release of free, polyunsaturated fatty acids, e.g. arachidonic acid and membrane-bound lysophospholipids. Even though arachidonic acid acts as a second messenger in its own most mammalian cells seem to rely on oxidation of the fatty acid into highly potent second messengers via, e.g. cytochrome P450, the cyclo-oxygenase, or the lipoxygenase systems for downstream signalling. Here, we review data that illustrates that stress-induced PLA2 activity involves various PLA2 subtypes and that the PLA2 in question is determined by the cell type and the physiological stress condition. [source] Neonatal estrogen exposure inhibits steroidogenesis in the developing rat ovaryDEVELOPMENTAL DYNAMICS, Issue 4 2001Yayoi Ikeda Abstract Treatment of newborn female rats with estrogens significantly inhibits the growth and differentiation of the ovary. To understand the molecular mechanism of estrogen action in the induction of abnormal ovary, we examined the expression profiles of steroidogenic factor 1 (SF-1) and several of its target genes in the developing ovaries after neonatal exposure to synthetic estrogen, estradiol benzoate (EB) by using reverse transcriptase polymerase chain reaction, in situ hybridization, and immunohistochemistry. Morphologic examination indicated inhibitory effects of estrogen on the stratification of follicles and development of theca and interstitial gland during postnatal ovarian differentiation. The expression of the steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage cytochrome P450 (P450SCC), which are both essential for steroid biosynthesis, markedly decreased in theca and interstitial cells throughout the postnatal development of the EB-treated ovary. However, expression of the transcriptional activator of the two genes, SF-1 was unaffected in theca and interstitial cells, although the number of these cells was lower in the EB-treated ovary than in the control ovary. The expression of the estrogen mediator, estrogen receptor-, (ER-,), diminished specifically in theca cells at P6 and recovered by P14 in the EB-treated ovary. These results indicate that the effect of estrogens is mediated by means of ER-, resulting in the down-regulation of StAR and P450SCC genes during early postnatal development of the ovary. These results suggest that the abnormal ovarian development by neonatal estrogen treatment is closely correlated with the reduced steroidogenic activity, and the data obtained by using this animal model may account in part the mechanism for aberrant development and function of the ovary in prenatally estrogen-exposed humans. © 2001 Wiley-Liss, Inc. [source] Pharmacokinetics of dipeptidylpeptidase-4 inhibitorsDIABETES OBESITY & METABOLISM, Issue 8 2010A. J. Scheen Type 2 diabetes (T2DM) is a complex disease combining defects in insulin secretion and insulin action. New compounds have been developed for improving glucose-induced insulin secretion and glucose control, without inducing hypoglycaemia or weight gain. Dipeptidylpeptidase-4 (DPP-4) inhibitors are new oral glucose-lowering agents, so-called incretin enhancers, which may be used as monotherapy or in combination with other antidiabetic compounds. Sitagliptin, vildaglipin and saxagliptin are already on the market in many countries, either as single agents or in fixed-dose combined formulations with metformin. Other DPP-4 inhibitors, such as alogliptin and linagliptin, are currently in late phase of development. The present paper summarizes and compares the main pharmacokinetics (PK) properties, that is, absorption, distribution, metabolism and elimination, of these five DPP-4 inhibitors. Available data were obtained in clinical trials performed in healthy young male subjects, patients with T2DM, and patients with either renal insufficiency or hepatic impairment. PK characteristics were generally similar in young healthy subjects and in middle-aged overweight patients with diabetes. All together gliptins have a good oral bioavailability which is not significantly influenced by food intake. PK/pharmacodynamics characteristics, that is, sufficiently prolonged half-life and sustained DPP-4 enzyme inactivation, generally allow one single oral administration per day for the management of T2DM; the only exception is vildagliptin for which a twice-daily administration is recommended because of a shorter half-life. DPP-4 inhibitors are in general not substrates for cytochrome P450 (except saxagliptin that is metabolized via CYP 3A4/A5) and do not act as inducers or inhibitors of this system. Several metabolites have been documented but most of them are inactive; however, the main metabolite of saxagliptin also exerts a significant DPP-4 inhibition and is half as potent as the parent compound. Renal excretion is the most important elimination pathway, except for linagliptin whose metabolism in the liver appears to be predominant. PK properties of gliptins, combined with their good safety profile, explain why no dose adjustment is necessary in elderly patients or in patients with mild to moderate hepatic impairment. As far as patients with renal impairment are concerned, significant increases in drug exposure for sitagliptin and saxagliptin have been reported so that appropriate reductions in daily dosages are recommended according to estimated glomerular filtration rate. The PK characteristics of DPP-4 inhibitors suggest that these compounds are not exposed to a high risk of drug,drug interactions. However, the daily dose of saxagliptin should be reduced when coadministered with potent CYP 3A4 inhibitors. In conclusion, besides their pharmacodynamic properties leading to effective glucose-lowering effect without inducing hypoglycaemia or weight gain, DPP-4 inhibitors show favourable PK properties, which contribute to a good efficacy/safety ratio for the management of T2DM in clinical practice. [source] Effect of artificial mixtures of environmental polycyclic aromatic hydrocarbons present in coal tar, urban dust, and diesel exhaust particulates on MCF-7 cells in cultureENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2 2004Brinda Mahadevan Abstract Human exposure to polycyclic aromatic hydrocarbons (PAHs) occurs through complex mixtures. The National Institute of Standards and Technology has established standard reference materials (SRMs) for selected PAH mixtures that are composed of carcinogenic, noncarcinogenic, and weakly carcinogenic compounds, such as those derived from coal tar (SRM 1597), atmospheric particulate matter (SRM 1649), and diesel particulate matter (SRM 1650). To study the effects of PAHs with different carcinogenic potential in complex mixtures, and to investigate the metabolic activation of noncarcinogenic and weakly carcinogenic PAHs to DNA-binding derivatives, artificial mixtures (1597H, 1649H, and 1650H) were prepared in the laboratory. These artificial mixtures contained the same relative ratios of noncarcinogenic and weakly carcinogenic PAHs present in SRM 1597, SRM 1649, and SRM 1650. The human mammary carcinoma-derived cell line MCF-7 was treated with these artificial mixtures and analyzed for PAH-DNA adduct formation and the induction of cytochrome P450 (CYP) enzymes. We found that the artificial mixtures formed lower but detectable levels of DNA adducts 24 and 48 hr after treatment than benzo[a]pyrene. Induction of CYP enzyme activity was measured by the ethoxyresorufin- O -deethylase assay, and the expression of CYP1A1 and CYP1B1 was confirmed by immunoblots. Both noncarcinogenic and weakly carcinogenic PAHs present in the artificial mixtures have the ability to induce CYP1A1 and CYP1B1 in MCF-7 cells and contribute to DNA binding. Therefore, it is necessary to take into account the noncarcinogenic and weakly carcinogenic PAHs present in environmental mixtures in assessing the potential risk associated with human exposure. Environ. Mol. Mutagen. 44:99,107, 2004. © 2004 Wiley-Liss, Inc. [source] Perinatal exposure to bisphenol-A changes N -methyl- D -aspartate receptor expression in the hippocampus of male rat offspringENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2010Xiao-Hong Xu Abstract Bisphenol-A (BPA) is one of the most common environmental endocrine disrupters with mixed estrogen agonist/antagonist properties. The toxicity of BPA has been extensively evaluated in a variety of tests in rodents, including developmental and reproductive toxicity, and carcinogenicity. The objective of the present study is to evaluate whether or not perinatal maternal exposure to BPA at 0.05, 0.5, 5, 50, and 200 mg/kg/d affects N -methyl- D -aspartate (NMDA) receptor (NMDAR) subunits NR1, NR2A, 2B, estrogen receptor beta (ER,), and aromatase cytochrome P450 (P450arom) protein expressions of hippocampus in male rat offspring during postnatal development. Western-blotting analyses showed that perinatal exposure to BPA significantly affected the expression of NMDAR subunits. At the lower doses of 0.05 to 50 mg/kg/d, BPA concentration dependently inhibited the expression of NMDAR subunits. However, at the higher dose (200 mg/kg/d), the effects of BPA on these subunits were different, with a stronger inhibition of NR1 expression and a slighter inhibition of NR2A, 2B expression when compared with those at the lower dosage of BPA. In addition, perinatal exposure to BPA inhibited the expression of ER, protein, but increased P450arom protein expression in a concentration-dependent manner, especially during the early postnatal period (the first 1,3 postnatal weeks). No significant influence of BPA on P450arom was observed at postnatal week 8. These data suggest that environmental BPA exposure may affect the development of the brain, enhancing the local biosynthesis of estrogen in the brain, inhibiting ER, and NMDAR expressions. Environ. Toxicol. Chem. 2010;29:176,181. © 2009 SETAC [source] Effects of brominated flame retardants and brominated dioxins on steroidogenesis in H295R human adrenocortical carcinoma cell lineENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2007Ling Ding Abstract Brominated flame retardants (BFRs) and brominated dioxins are emerging persistent organic pollutants that are ubiquitous in the environment and can be accumulated by wildlife and humans. These chemicals can disturb endocrine function. Recent studies have demonstrated that one of the mechanisms of endocrine disruption by chemicals is modulation of steroidogenic gene expression or enzyme activities. In this study, an in vitro assay based on the H295R human adrenocortical carcinoma cell line, which possesses most key genes or enzymes involved in steroidogenesis, was used to examine the effects of five bromophenols, two polybrominated biphenyls (PBBs 77 and 169), 2,3,7,8-tetrabromodibenzo- p -dioxin, and 2,3,7,8-tetrabromodibenzofuran on the expression of 10 key steroidogenic genes. The H295R cells were exposed to various BFR concentrations for 48 h, and the expression of specific genes,cytochrome P450 (CYP11A, CYP11B2, CYP17, CYP19, and CYP21), 3,-hydroxysteroid dehydrogenase (3,HSD2), 17,-hydroxysteroid dehydrogenase (17,HSD1 and 17,HSD4), steroidogenic acute regulatory protein (StAR), and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR),was quantitatively measured using real-time polymerase chain reaction. Cell viability was not affected at the doses tested. Most of the genes were either up- or down-regulated, to some extent, by BFR exposure. Among the genes tested, 3,HSD2 was the most markedly up-regulated, with a range of magnitude from 1.6- to 20-fold. The results demonstrate that bromophenol, bromobiphenyls, and bromodibenzo- p -dioxin/furan are able to modulate steroidogenic gene expression, which may lead to endocrine disruption. [source] Alteration of normal cellular profiles in the scleractinian coral (Pocillopora damicornis) following laboratory exposure to fuel oilENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2006Luc Rougée Abstract Petroleum contamination from oil spills is a continuing threat to our ocean's fragile ecosystems. Herein, we explored the effects of the water-soluble fraction of crude oil on a stony coral, Pocillopora damicornis (Linneaeus 1758). We developed methods for exposing corals to various concentrations of crude oil and for assessing the potential molecular responses of the corals. Corals were exposed to water-accommodated fraction solutions, and appropriate cellular biomarkers were quantified. When compared to the "healthy" control specimens, exposed corals exhibited shifts in biomarker concentrations that were indicative of a shift from homeostasis. Significant changes were seen in cytochrome P450 1-class, cytochrome P450 2-class, glutathione- S -transferase-pi, and cnidarian multixenobiotic resistance protein-1 biomarkers, which are involved the cellular response to, and manipulation and excretion of, toxic compounds, including polycyclic aromatic hydrocarbons. A shift in biomarkers necessary for porphyrin production (e.g., protoporphyrinogen oxidase IX and ferrochelatase) and porphyrin destruction (e.g., heme oxygenase-1 and invertebrate neuroglobin homologue) illustrates only one of the cellular protective mechanisms. The response to oxidative stress was evaluated through measurements of copper/zinc superoxide dismutase-1 and DNA glycosylase MutY homologue-1 concentrations. Likewise, changes in heat shock protein 70 and small heat shock proteins indicated an adjustment in the cellular production of proteins. Finally, the results of this laboratory study were nearly identical to what we observed previously among corals of a different species, Porites lobata, exposed to an oil spill in the field after the grounding of the Merchant Vessel Kyowa Violet. [source] Interaction of tributyltin with hepatic cytochrome P450 and uridine diphosphate-glucuronosyl transferase systems of fish: In vitro studiesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2004Yolanda Morcillo Abstract Hepatic microsomes of red mullet (Mullus barbatus) and flounder (Platichthys flesus) were preincubated in the presence of a concentration range of the antifouling agent tributyltin (TBT) chloride, and the interactions of TBT with cytochrome P450 and uridine diphosphate,glucuronyl transferase systems were investigated. The enzyme systems were examined in terms of cytochrome P4501A (CYP1A)-catalyzed 7-ethoxyresorufin O -deethylase (EROD) activity and benzo[a]pyrene (BaP) metabolism and in terms of glucuronidation of testosterone and 17,-estradiol, respectively. Ethoxyresorufin O -deethylase and BaP hydroxylase (BPH) activities of both fish species were progressively inhibited by increasing concentrations of TBT, and the effects were more pronounced for EROD than for BPH (maximal inhibition at 100 ,M TBT for EROD and 250,500 ,M TBT for BPH). Hydroxylated metabolites of BaP (3-hydroxy-, 7,8-dihydrodiol, and 9,10-dihydrodiol), representing 95% of the total metabolites formed, were reduced up to 75 % in the presence of 100 to 500 ,M TBT, whereas the formation of other metabolites was less affected. This may alter BaP toxicity and carcinogenicity. Overall, the results were consistent with a specific inhibitory effect of TBT on CYP1A in the two fish species. Additionally, the conjugation of testosterone was significantly inhibited (20%) at low TBT doses (5 ,M), with no effect on the glucuronidation of estradiol. [source] Hepatic microsomal cytochrome P450 enzyme activity in relation to in vitro metabolism/inhibition of polychlorinated biphenyls and testosterone in Baltic grey seal (Halichoerus grypus)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2003Hongxia Li Abstract Among other factors, cytochrome P450 (CYP) enzyme activity determines polychlorinated biphenyl (PCB) bioaccu-mulation, biotransformation, and toxicity in exposed species. We measured the oxidative metabolism in vitro of 12 PCB congeners, representing structural groups based on the number and position of the chlorine atoms, by the hepatic microsomes of one Baltic grey seal (Halichoerus grypus). Microsomal metabolism was observed for several PCBs with vicinal H atoms exclusively in the ortho and meta positions and without any ortho -Cl substituents (CB-15 [4,4,-Cl2] and CB-77 [3,3,,4,4,-Cl4]), vicinal meta and para -H atoms (CB-52 [2,2,,5,5,-Cl4], and ,101 [2,2,,4,5,5,-Cl5]) or with both characteristics in combination with either only one ortho -Cl (CB-26 [2,3,,5-Cl3], CB-31 [2,4,,5-Cl3]) or two ortho -Cl substituents (CB-44 [2,2,,3,5,-Cl4]). To allocate PCB biotransformation to specific CYPs, the inhibitive effect of compounds with known CYP-specific inhibition properties was assessed on in vitro PCB metabolism and on regio- and stereospecific testosterone hydroxylase activities. Metabolic inhibition was considered relevant at concentrations ,1.0 ,M because these inhibitors became decreasingly selective at higher concentrations. At <1.0 ,M, ellipticine (CYP1A1/2 inhibitor) selectively inhibited CB-15, ,26, ,31, and ,77 metabolism, with no significant inhibition of CB-44, ,52, and ,101 metabolism. Inhibition of CB-52 and ,101 metabolism by chloramphenicol (CYP2B inhibitor) started at 1.0 ,M and maximized at about 100% at 10 ,M. Ketoconazole (CYP3A inhibitor) appeared to selectively inhibit CB-26, ,31, and ,44 metabolism relative to CB-15, ,77, and ,52 at concentrations ,1.0 ,M. Major testosterone metabolites formed in vitro were 2,-(CYP3A), 6,- (CYP3A, CYP1A), and 16,- (CYP2B) hydroxytestosterone and androstenedione (CYP2B, CYP2C11). The CYP forms indicated are associated with the specific metabolism of testosterone in laboratory animals. Inhibition of 2,- and 6,-hydroxytestosterone formation at ellipticine and ketoconazole concentrations ,1.0,M suggested that both inhibitors were good substrates of CYP3A-like enzymes in grey seal. Chloramphenicol (model for CYP2B) is apparently not a good inhibitor of CYP1A and CYP3A activities in grey seal because the chemical did not inhibit any metabolic route of testosterone at concentrations from 0.1 to 10 ,M. Our findings demonstrated that at least CYP1A- and CYP3A-like enzymes in the liver of grey seals are capable of metabolizing PCBs with ortho - meta and/or meta - para vicinal hydrogens. A CYP2B form might also be involved, but this could not be proven by the results of our experiments. Defining the profiles of CYP enzymes that are responsible for PCB biotransformation is necessary to fully understand the bioaccumulation, toxicokinetics, and risk of PCB exposure in seals and other free-ranging marine mammals. [source] Environmental polychlorinated biphenyl exposure and cytochromes P450 in raccoons (Procyon lotor),ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2003Philip N. Smith Abstract An investigation involving raccoons as a sentinel species at the Paducah Gaseous Diffusion Plant (PGDP) and Ballard Wildlife Management Area in western Kentucky (USA) delineated the extent of exposure to polychlorinated biphenyls (PCBs). Three separate measures of hepatic cytochrome P450 (CYP) induction were used to evaluate raccoon physiological responses to PCB exposure. Hepatic CYP induction was estimated via determination of total CYP, dealkylase activities, and immunoreactive proteins. There were no differences in raccoon biomarker responses between study sites. Significant relationships between and among PCB residues and biomarkers indicated that hepatic CYP induction had occurred in response to PCB exposure. Pentoxy-resorufin O -deethylase (PROD) activity, CYP1A1, and CYP1A2 were biomarkers most closely associated with PCB exposure. The rank order of responses was CYP1A1 > CYP1A2 > PROD > ethoxyresorufin O -deethylase (EROD) as related to raccoon liver PCB concentrations, whereas the order was CYP1A1 > PROD > EROD > CYP1A2 when regressed with total PCB concentrations in abdominal fat. [source] Distribution of cytochrome P4501A1,inducing chemicals in sediments of the Delaware River-Bay system, USAENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2002Daniel L. McCoy Abstract The Delaware River-Bays system, USA, was the subject of a study by the National Oceanic and Atmospheric Administration that involved chemical and biological analyses, including the use of the biomarker P450 human reporter gene system (HRGS) to document the occurrence and distribution of cytochrome P450 (CYP) 1A1-inducing compounds. Sediment extracts from 81 locations along the Delaware River, Delaware Bay and immediate coastline were tested by utilizing HRGS as an inexpensive screening test, and were also analyzed for polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls, with selected stations analyzed for dioxins and furans. Benthic community degradation has been observed when benzo[a]pyrene equivalents (BaPEq) exceeded 60 ,g/g. The average levels of BaPEq for the largely industrialized upper, middle, and lower regions of the Delaware River were 107, 62, and 5 ,g/g, respectively, excluding outliers. Tributaries leading into river averaged 21 ,g/g BaPEq, whereas the central Bay and open coast had relatively low values (2.0 and 0.5 ,g/g BaPEq, respectively). The HRGS values were highly correlated with total PAHs measured in the same sediment samples (r2 = 0.81). Overall, contamination levels consistently decreased from the upper and middle river sites as collection locations progressed down through the lower river and bay to the coast. Thus, despite the relatively high contaminant load in the river system, Delaware Bay and the immediate coastline seem to have relatively low levels of contaminants, and, therefore, impacts on the benthic organisms in the bay and coast would not be expected from these findings. [source] Biotransformation of n -hexadecane by cell suspension cultures of Cinchona robusta and Dioscorea compositaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2001Carolina Vega-Jarquin Abstract This manuscript evaluates the phytotoxicity and biotransformation of n -hexadecane as well as peroxidase activity and cytochrome P450 concentration in microsomes for cell suspension cultures of Cinchona robusta and Dioscorea composita. Phytotoxicity was evaluated based on viability and growth. Cell cultures were exposed to a 2 and 4% (v/v) dose of n -hexadecane. The biotransformation of n -hexadecane was determined based on labeled recovery in polar, nonpolar, and cell residue fractions after cell culture extraction during exponential cell growth phase and stationary phase. Differences were observed in accumulation of label during cell growth phase and stationary phase for the cells of the two plants. Differences also were observed between phases for label in polar and nonpolar fractions. Thin-layer chromatography determined labeled intermediates and some were identified. The activity of peroxidase and concentration of cytochrome P450 was lower in C. robusta than in controls and greater in D. composita than in controls. In vitro biotransformation was not successful. [source] Rufinamide: Clinical pharmacokinetics and concentration,response relationships in patients with epilepsyEPILEPSIA, Issue 7 2008Emilio Perucca Summary Rufinamide is a new, orally active antiepileptic drug (AED), which has been found to be effective in the treatment of partial seizures and drop attacks associated with the Lennox-Gastaut syndrome. When taken with food, rufinamide is relatively well absorbed in the lower dose range, with approximately dose-proportional plasma concentrations up to 1,600 mg/day, but less than dose-proportional plasma concentrations at higher doses due to reduced oral bioavailability. Rufinamide is not extensively bound to plasma proteins. During repeated dosing, steady state is reached within 2 days, consistent with its elimination half-life of 6,10 h. The apparent volume of distribution (Vd/F) and apparent oral clearance (CL/F) are related to body size, the best predictor being body surface area. Rufinamide is not a substrate of cytochrome P450 (CYP450) enzymes and is extensively metabolized via hydrolysis by carboxylesterases to a pharmacologically inactive carboxylic acid derivative, which is excreted in the urine. Rufinamide pharmacokinetics are not affected by impaired renal function. Potential differences in rufinamide pharmacokinetics between children and adults have not been investigated systematically in formal studies. Although population pharmacokinetic modeling suggests that in the absence of interacting comedication rufinamide CL/F may be higher in children than in adults, a meaningful comparison of data across age groups is complicated by age-related differences in doses and in proportion of patients receiving drugs known to increase or to decrease rufinamide CL/F. A study investigating the effect of rufinamide on the pharmacokinetics of the CYP3A4 substrate triazolam and an oral contraceptive interaction study showed that rufinamide has some enzyme-inducing potential in man. Findings from population pharmacokinetic modeling indicate that rufinamide does not modify the CL/F of topiramate or valproic acid, but may slightly increase the CL/F of carbamazepine and lamotrigine and slightly decrease the CL/F of phenobarbital and phenytoin (all predicted changes were <20%). These changes in the pharmacokinetics of associated AEDs are unlikely to make it necessary to change the dosages of these AEDs given concomitantly with rufinamide, with the exception that consideration should be given to reducing the dose of phenytoin. Based on population pharmacokinetic modeling, lamotrigine, topiramate, or benzodiazepines do not affect the pharmacokinetics of rufinamide, but valproic acid may increase plasma rufinamide concentrations, especially in children in whom plasma rufinamide concentrations could be increased substantially. Conversely, comedication with carbamazepine, vigabatrin, phenytoin, phenobarbital, and primidone was associated with a slight-to-moderate decrease in plasma rufinamide concentrations, ranging from a minimum of ,13.7% in female children comedicated with vigabatrin to a maximum of ,46.3% in female adults comedicated with phenytoin, phenobarbital, or primidone. In population modeling using data from placebo-controlled trials, a positive correlation has been identified between reduction in seizure frequency and steady-state plasma rufinamide concentrations. The probability of adverse effects also appears to be concentration-related. [source] Dose-dependent Induction of Cytochrome P450 (CYP) 3A4 and Activation of Pregnane X Receptor by TopiramateEPILEPSIA, Issue 12 2003Srikanth C. Nallani Summary:,Purpose: In clinical studies, topiramate (TPM) was shown to cause a dose-dependent increase in the clearance of ethinyl estradiol. We hypothesized that this interaction results from induction of hepatic cytochrome P450 (CYP) 3A4 by TPM. Accordingly, we investigated whether TPM induces CYP3A4 in primary human hepatocytes and activates the human pregnane X receptor (hPXR), a nuclear receptor that serves as a regulator of CYP3A4 transcription. Methods: Human hepatocytes were treated for 72 h with TPM (10, 25, 50, 100, 250, and 500 ,M) and known inducers, phenobarbital (PB; 2 mM), and rifampicin (10 ,M). The rate of testosterone 6,-hydroxylation by hepatocytes served as a marker for CYP3A4 activity. The CYP3A4-specific protein and mRNA levels were determined by using Western and Northern blot analyses, respectively. The hPXR activation was assessed with cell-based reporter gene assay. Results: Compared with controls, TPM (50,500 ,M),treated hepatocytes exhibited a considerable increase in the CYP3A4 activity (1. 6- to 8.2-fold), protein levels (4.6- to 17.3-fold), and mRNA levels (1.9- to 13.3-fold). Comparatively, rifampicin (10 ,M) effected 14.5-, 25.3-, and a 20.3-fold increase in CYP3A4 activity, immunoreactive protein levels, and mRNA levels, respectively. TPM (50,500 ,M) caused 1.3- to 3-fold activation of the hPXR, whereas rifampicin (10 ,M) caused a 6-fold activation. Conclusions: The observed induction of CYP3A4 by TPM, especially at the higher concentrations, provides a potential mechanistic explanation of the reported increase in the ethinyl estradiol clearance by TPM. It also is suggestive of other potential interactions when high-dose TPM therapy is used. [source] Variable expression of CYP and Pgp genes in the human small intestineEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 6 2003M. Lindell Abstract Background ,The small intestine is receiving increased attention for its importance in drug metabolism. However, knowledge of the intervariability and regulation of the enzymes involved, cytochrome P450 and P-Glycoproteins (CYP and Pgp), is poor when compared with the corresponding hepatic enzymes. Methods ,The expression of eight different CYP genes and the Pgp were determined by reverse transcription polymerase chain reaction (RT-PCR) in 51 human duodenum biopsies. And the variability and correlation of expression was analyzed. Results ,Extensive interindividual variability was found in the expression of most of the genes. Only CYP2C9, CYP3A4 and Pgp were found in all samples. CYP1A2, CYP2A6 and CYP2E1 exhibited the highest interindividual variability. No strong correlation of expression existed between the genes. But a highly significant correlation was found between CYP2D6/1A2, 2D6/2E1, 1A2/2E1 and 2B6/2C9. Acetylsalicylic acid and omeprazole significantly increased the expression of CYPs 2A6, 2E1 and 3A4, respectively. Conclusions ,Extensive interindividual variability is characteristic for the expression of drug-metabolizing CYP and Pgp genes in human duodenum, and external factors such as drugs may further increase the variability. It is possible that the large interindividual variability may lead to variable bioavailability of orally used drugs and hence complicate optimal drug therapy, especially for drugs with a small therapeutic window. Elucidation of factors contributing to clinically important variances warrants further investigation. [source] Relationships between the ethanol utilization (alc) pathway and unrelated catabolic pathways in Aspergillus nidulansFEBS JOURNAL, Issue 17 2003Michel Flipphi The ethanol utilization pathway in Aspergillus nidulans is a model system, which has been thoroughly elucidated at the biochemical, genetic and molecular levels. Three main elements are involved: (a) high level expression of the positively autoregulated activator AlcR; (b) the strong promoters of the structural genes for alcohol dehydrogenase (alcA) and aldehyde dehydrogenase (aldA); and (c) powerful activation of AlcR by the physiological inducer, acetaldehyde, produced from growth substrates such as ethanol and l -threonine. We have previously characterized the chemical features of direct inducers of the alc regulon. These studies allowed us to predict which type of carbonyl compounds might induce the system. In this study we have determined that catabolism of different amino acids, such as l -valine, l -isoleucine, l -arginine and l -proline, produces aldehydes that are either not accumulated or fail to induce the alc system. On the other hand, catabolism of d -galacturonic acid and putrescine, during which aldehydes are transiently accumulated, gives rise to induction of the alc genes. We show that the formation of a direct inducer from carboxylic esters does not depend on alcA -encoded alcohol dehydrogenase I or on AlcR, and suggest that a cytochrome P450 might be responsible for the initial formation of a physiological aldehyde inducer. [source] Covalently crosslinked complexes of bovine adrenodoxin with adrenodoxin reductase and cytochrome P450sccFEBS JOURNAL, Issue 6 2001Edman degradation of complexes of the steroidogenic hydroxylase system, Mass spectrometry NADPH-dependent adrenodoxin reductase, adrenodoxin and several diverse cytochromes P450 constitute the mitochondrial steroid hydroxylase system of vertebrates. During the reaction cycle, adrenodoxin transfers electrons from the FAD of adrenodoxin reductase to the heme iron of the catalytically active cytochrome P450 (P450scc). A shuttle model for adrenodoxin or an organized cluster model of all three components has been discussed to explain electron transfer from adrenodoxin reductase to P450. Here, we characterize new covalent, zero-length crosslinks mediated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide between bovine adrenodoxin and adrenodoxin reductase, and between adrenodoxin and P450scc, respectively, which allow to discriminate between the electron transfer models. Using Edman degradation, mass spectrometry and X-ray crystallography a crosslink between adrenodoxin reductase Lys27 and adrenodoxin Asp39 was detected, establishing a secondary polar interaction site between both molecules. No crosslink exists in the primary polar interaction site around the acidic residues Asp76 to Asp79 of adrenodoxin. However, in a covalent complex of adrenodoxin and P450scc, adrenodoxin Asp79 is involved in a crosslink to Lys403 of P450scc. No steroidogenic hydroxylase activity could be detected in an adrenodoxin ,P450scc complex/adrenodoxin reductase test system. Because the acidic residues Asp76 and Asp79 belong to the binding site of adrenodoxin to adrenodoxin reductase, as well as to the P450scc, the covalent bond within the adrenodoxin,P450scc complex prevents electron transfer by a putative shuttle mechanism. Thus, chemical crosslinking provides evidence favoring the shuttle model over the cluster model for the steroid hydroxylase system. [source] Chromatin structure of the bovine Cyp19 promoter 1.1FEBS JOURNAL, Issue 5 2001DNA hypomethylation correlate with placental expression, DNaseI hypersensitive sites Expression of the Cyp19 gene, encoding aromatase cytochrome P450, is driven by several tissue-specific promoters. The underlying mechanisms of this complex regulation have not yet been elucidated in detail. In the present report we investigate a possible link between chromatin structure and tissue-specific regulation of the bovine Cyp19 gene. We analysed the DNA methylation status and mapped DNaseI hypersensitive sites in the region encompassing the Cyp19 promoter 1.1 (P1.1) which controls Cyp19 expression in the bovine placenta. We show that P1.1 is hypomethylated in placental cotyledons (foetal layer) whereas it is methylated in placental caruncles (maternal layer), testis and corpus luteum. Furthermore, two placenta-specific DNaseI hypersensitive sites, HS1 and HS2, were observed within P1.1. Both DNA hypomethylation and the presence of DNaseI hypersensitive sites correlate with transcriptional activity of P1.1. Sequence analysis of hypersensitive sites revealed potential cis -regulatory elements, an E-box in HS1 and a trophoblast-specific element-like sequence in HS2. It could be demonstrated by electrophoretic mobility shift assays that both sequence motifs are specific targets for placenta-derived nuclear factors. In conclusion, observed tissue-specific differences of the chromatin structure which correlate with tissue-specific promoter activity suggest that chromatin might be an important regulator of aromatase expression in cattle. [source] | |||||||||||||||||||||||||||||||