Cytochrome P450 enzymes

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Warum reagiert mein Patient anders auf dieses Medikament? : Pharmakogenomik und personalisierte Medizin in der Praxis

Inter- und intraindividuelle Variabilität in der Arzneimittelwirkung ist häufig. Die Ursachen dieser Unterschiede sind vielseitig und bei jedem Patienten in verschiedener Kombination vorhanden. Hauptursachen sind genetische Diversität und wechselnde Umweltfaktoren wie Ernährung,andere Arzneimittel und "Lifestyle". Variabilität kann die Pharmakokinetik, z.B. den Arzneimittelabbau, oder die Pharmakodynamik, d.h. den Wirkungsmechanismus eines Medikamentes betreffen. Diese individuellen Unterschiede im Ansprechen auf ein Medikament sind ein wichtiger Teil des Konzeptes der "Personalisierten Medizin" mit dem Anspruch, für jeden Patienten eine massgeschneiderte Therapie anzuwenden, d.h. das für seine persönliche Problematik richtige Medikament in der richtigen Dosierung. Durchbrüche in den Technologien der Genomik haben dazu geführt, dass vor allem die genetische Variation der Arzneimittelwirkung besser untersucht werden kann. Diese Studien haben zu molekulargenetischen Tests geführt, die die Wirksamkeit oder das Risiko unerwünschter Nebenwirkungen besser voraussagen können. Am häufigsten wird die "Personalisierte Medizin" heute in der Krebstherapie oder bei HIV Infektionen angewandt, zunehmend aber auch in anderen therapeutischen Gebieten. Die heute bekannten Situationen, die auch für die Praxis von Bedeutung sein können, werden hier zusammengefasst. Patienten der Internet-Generation sind besser informiert über ihre Krankheit und über die Therapie, die sie erhalten. Zunehmend werden auch Patienten in der Praxis mit bereits vorhandenen Informationen zu ihrer Gensequenz oder gewissen Gentests erscheinen

Cytosolic persistence of mouse brain CYP1A1 in chronic heme deficiency

Previous work has demonstrated that the function of extrahepatic cytochrome P450 CYP1A1 is dependent on the availability of heme. CYP1A1 is involved in the activation of polyaromatic hydrocarbons. In the present study we used a transgenic mouse model with chronic impairment of heme synthesis - female porphobilinogen deaminase-deficient (PBGD-/-) mice - to investigate the effects of limited heme in untreated and β-naphthoflavone (β-NF)-treated animals on the function of CYP1A1 in brain. The heme content of PBGD-/- mice was diminished in the liver and brain compared to wild types. In the liver, partial heme deficiency led to less potent induction of CYP1A1 mRNA after β-NF treatment. In the brain, CYP1A1 protein was detected not only at the endoplasmic reticulum (ER), but also in the cytosol of PBGD-/- mice. Furthermore, 7-deethylation of ethoxyresorufin, an indicator of CYP1A1 metabolic activity, could be restored by heme in cytosol of PBGD-/- mouse brain. Independent of the genotype, we found only one cyp1a1 gene product, indicating that the cytosolic appearance of CYP1A1 most likely did not originate from mutant alleles. We conclude that heme deficiency in the brain leads to incomplete heme saturation of CYP1A1, which causes its improper incorporation into the ER membrane and persistence in the cytosol. It is suggested that diseases caused by relative heme deficiency, such as hepatic porphyrias, may lead to impaired hemoprotein function in brai

PARENCHYMAL CELLS FROM ADULT RAT LIVER IN NONPROLIFERATING MONOLAYER CULTURE : I. Functional Studies

Parenchymal cells from adult rat liver have been established in primary monolayer culture. Donor animals are subjected to a partial hepatectomy and, 4 days later, cells are prepared by collagenase perfusion of the regenerated liver. The hepatic parenchymal cells, separated from nonparenchymal material and suspended in serum-free medium, are placed in plastic tissue culture dishes, where they form a monolayer within 24 h. The monolayer cells exhibit minimal mitotic activity and demonstrate several major metabolic functions characteristic of liver in vivo; these include albumin synthesis and secretion, gluconeogenesis from 3-carbon precursors, responsiveness to insulin and glucagon, glycogen synthesis, and activity of two microsomal enzymes. These functions are present in the monolayer cells for several days at activities similar to those observed in the liver in vivo. The findings indicate that hepatic parenchymal cells in this monolayer system are viable and behave in many respects like normal adult rat liver

Dynamics of the 2d Potts model phase transition

The dynamics of 2d Potts models, which are temperature driven through the phase transition using updating procedures in the Glauber universality class, is investigated. We present calculations of the hysteresis for the (internal) energy and for Fortuin-Kasteleyn clusters. The shape of the hysteresis is used to define finite volume estimators of physical observables, which can be used to study the approach to the infinite volume limit. We compare with equilibrium configurations and the preliminary indications are that the dynamics leads to considerable alterations of the statistical properties of the configurations studied.Comment: Lattice2002(spin

The role of the human acetylation polymorphism in the metabolic activation of the food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)

The metabolic activation of the heterocyclic food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) by two human cytochrome P450 monooxygenases (P4501A1 and P4501A2) and two human N-acetyltransferases (NAT1 and NAT2) was investigated. Various combinations of these enzymes were functionally expressed in COS-1 cells. DNA adducts resulting from the activation of IQ were assayed quantitatively by the 32P-postlabeling procedure. The highest adduct frequency was observed in cells expressing both CYP1A2 and NAT2. CYP1A2 in combination with NAT1 was 3-6 times less active. When expressed alone these enzymes gave rise to low adduct frequencies. Experiments with N-acetyl-IQ as substrate suggest that NAT1 and NAT2 in addition to their known role in N-acetylation display arylhydroxamic acid N,O-acetyttransferase (AHAT) activity. Quantitative differences in adduct formation between IQ and N-acetyl-IQ indicated that metabolic activation of these arylamines preferentially occurs by P4501A2-catalyzed N-hydroxylation followed by O-acetylation mediated through NAT1 and/or NAT2. These data, in combination with the known genetic polymorphism of NAT2, may explain the clinical observation that the acetylation polymorphism constitutes a risk factor in the carcinogenic activation of environmental mutagen

Effect of CAR activation on selected metabolic pathways in normal and hyperlipidemic mouse livers

<p>Abstract</p> <p>Background</p> <p>Detoxification in the liver involves activation of nuclear receptors, such as the constitutive androstane receptor (CAR), which regulate downstream genes of xenobiotic metabolism. Frequently, the metabolism of endobiotics is also modulated, resulting in potentially harmful effects. We therefore used 1,4-Bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP) to study the effect of CAR activation on mouse hepatic transcriptome and lipid metabolome under conditions of diet-induced hyperlipidemia.</p> <p>Results</p> <p>Using gene expression profiling with a dedicated microarray, we show that xenobiotic metabolism, PPARα and adipocytokine signaling, and steroid synthesis are the pathways most affected by TCPOBOP in normal and hyperlipidemic mice. TCPOBOP-induced CAR activation prevented the increased hepatic and serum cholesterol caused by feeding mice a diet containing 1% cholesterol. We show that this is due to increased bile acid metabolism and up-regulated removal of LDL, even though TCPOBOP increased cholesterol synthesis under conditions of hyperlipidemia. Up-regulation of cholesterol synthesis was not accompanied by an increase in mature SREBP2 protein. As determined by studies in CAR -/- mice, up-regulation of cholesterol synthesis is however CAR-dependent; and no obvious CAR binding sites were detected in promoters of cholesterogenic genes. TCPOBOP also affected serum glucose and triglyceride levels and other metabolic processes in the liver, irrespective of the diet.</p> <p>Conclusion</p> <p>Our data show that CAR activation modulates hepatic metabolism by lowering cholesterol and glucose levels, through effects on PPARα and adiponectin signaling pathways, and by compromising liver adaptations to hyperlipidemia.</p

The evolution of drug-activated nuclear receptors: one ancestral gene diverged into two xenosensor genes in mammals

BACKGROUND: Drugs and other xenobiotics alter gene expression of cytochromes P450 (CYP) by activating the pregnane X receptor (PXR) and constitutive androstane receptor (CAR) in mammals. In non-mammalian species, only one xenosensor gene has been found. Using chicken as a model organism, the aim of our study was to elucidate whether non-mammalian species only have one or two xenosensors like mammals. RESULTS: To explore the evolutionary aspect of this divergence, we tried to identify additional xenobiotic sensing nuclear receptors in chicken using various experimental approaches. However, none of those revealed novel candidates. Ablation of chicken xenobiotic receptor (CXR) function by RNAi or dominant-negative alleles drastically reduced drug-induction in a chicken hepatoma cell line. Subsequently, we functionally and structurally characterized CXR and compared our results to PXR and CAR. Despite the high similarity in their amino acid sequence, PXR and CAR have very distinct modes of activation. Some aspects of CXR function, e.g. direct ligand activation and high promiscuity are very reminiscent of PXR. On the other hand, cellular localization studies revealed common characteristics of CXR and CAR in terms of cytoplasmic-nuclear distribution. Finally, CXR has unique properties regarding its regulation in comparison to PXR and CAR. CONCLUSION: Our finding thus strongly suggest that CXR constitutes an ancestral gene which has evolved into PXR and CAR in mammals. Future studies should elucidate the reason for this divergence in mammalian versus non-mammalian species