Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pathological disorders of the liver were shown to be associated with an impairment of hepatic drug metabolism mediated in part by growth factors. Augmenter of liver regeneration (ALR) is a novel liver-specific hepatotrophic growth factor, whereas its action on cytochrome P450 (P450) metabolism is completely unknown. Application of ALR to primary human hepatocytes in vitro reduced P450 isoenzyme activities (1A2 and 2A6) in a dose-dependent manner. Time-course analysis revealed that the maximal inhibitory effect was reached after 24 to 72 h of exposure with 50 nM ALR. The reduction of basal activities upon ALR treatment was 35% for CYP1A2, 56% for CYP2A6, 18% for CYP2B6, and 45% for CYP2E1. Additionally, after induction of P450 with specific inducers, ALR revealed an inhibitory effect on the isoenzyme activities (CYP1A2, 41%; CYP2B6, 35%). Investigations of protein and mRNA expression of basal and induced CYP1A2 and CYP3A4 after ALR treatment by Western blotting and real-time reverse transcriptase-polymerase chain reaction, respectively, suggest a regulation on the transcriptional level. Furthermore, ALR treatment increased nuclear factor kB activity and reduced constitutive androstane receptor but not pregnane X receptor or aryl hydrocarbon receptor expression. In contrast, ALR revealed no effects on phase II reactions (glutathione/oxidized glutathione, UDP-glucuronyltransferase conjugation). Our results indicate that ALR, as a member of hepatotrophic factors, down-regulates basal and induced P450 in human liver and therefore cross-links growth signals to regulation of hepatic metabolism. These findings further imply a possible role of ALR in drug interactions during impaired hepatic function, whereas liver regeneration is triggered.
...
PMID:Repression of cytochrome P450 activity in human hepatocytes in vitro by a novel hepatotrophic factor, augmenter of liver regeneration. 1621 78

There is significant human exposure to polycyclic aromatic hydrocarbons (PAHs), many of which are bioactivated by the cytochrome P450 (P450) 1A family of enzymes to metabolites that are capable of covalently binding to DNA, a critical step in the initiation of carcinogenesis. We reported earlier that exposure of rats to 3-methylcholanthrene (MC) causes sustained induction of hepatic cytochrome P4501A expression for up to 45 days. Here, we tested the hypothesis that MC elicits persistent induction of other genes that are regulated by the Ah receptor (AHR). Female Sprague-Dawley rats were treated with MC (100 micromol/kg) ip once daily for 4 days, and gene expression patterns were investigated using total liver RNA isolated from animals at 1, 15, and 28 days after MC withdrawal. Gene expression was studied by cDNA microarray analyses using 4608 unique clones from liver-derived expressed sequence tag (EST) libraries fortified with clones of known liver genes representing approximately 4000 genes. Several phase I (P4501A1, -1A2) and phase II [e.g., glutathione-S-transferase (GST)-M1, UDP-glucuronosyl transferases (UGT)] genes were persistently induced (3-10-fold) by MC for 15-28 days. The persistent induction of P4501A1 gene expression was confirmed by real time reverse transcriptase polymerase chain reaction (RT-PCR) experiments. MC also elicited a 5-fold persistent augmentation of acute phase genes such as orosomucoid 1 and alpha-1-acid glycoprotein (AGP), and this was accompanied by sustained liver damage and inflammation in the MC-exposed rats. In conclusion, our results strongly suggest that sustained induction of P4501A1 by MC is accompanied by persistent expression of other genes belonging to the Ah gene battery, as well as certain other genes involved in toxic responses. Elucidating the mechanisms of persistent induction of P4501A1 and other genes by MC might lead to a better understanding of the mechanisms of toxicity mediated by PAHs.
...
PMID:Effects of 3-methylcholanthrene on gene expression profiling in the rat using cDNA microarray analyses. 1630 Mar 71

The administration of xenobiotics may significantly alter the expression of cytochromes P450 (CYPs), thereby leading to potentially toxic cellular, physiologic, and pharmacologic responses. Indeed, an important task in the development of new therapeutic entities is to evaluate efficiently and quantitatively their potential effects on the expression level of different CYPs. In this report, reverse transcriptase polymerase chain reaction (RT-PCR) was used to measure basal and induced mRNA of a wide range of rat CYP isoforms. Rats (n=3 per treatment) were treated with five prototype inducers of CYP isoforms or with vehicle only. RT and PCR efficiencies were determined using appropriate RNA and DNA standards. Messenger RNA was quantified by PicoGreen standard curves and normalized to cyclophilin. Quantitative RT-PCR was used successfully to demonstrate that CYP isoforms were induced at the mRNA level following drug administration. Notably, phenobarbital resulted in significant induction of CYP2B1, CYP2B2, CYP2C6, CYP2C13, CYP2E1, CYP3A1, and CYP3A2. 3-Methylcholanthrene induced CYP1A1, CYP1A2, and CYP1B1. CYP2C11 expression was highly variable and suppressed by pyridine, whereas the expression of CYP2E1 was suppressed by dexamethasone. We demonstrated that quantitative RT-PCR can be used to evaluate efficiently the effect of compounds on the expression of a wide range of CYP isoforms. The technique is advantageous over others in that it is very sensitive, efficient and applicable to highly homologous CYP isoforms.
...
PMID:Quantification of the expression and inducibility of 12 rat cytochrome P450 isoforms by quantitative RT-PCR. 1642 97

When larvae of the salamander Hynobius retardatus were reared at a high temperature (28 degrees C) during their thermosensitive period (TSP=15-30 days after hatching), all larvae developed to phenotypic females irrespective of their genetic sexes. Hynobius P450 aromatase (P450arom) and Dmrt-1 complementary DNAs were isolated and their expression patterns were analyzed by competitive and conventional reverse transcriptase-polymerase chain reaction. While the P450arom gene was expressed predominantly in the ovary, Dmrt-1 was expressed exclusively in the testis. When larvae were reared at the female-producing temperature (28 degrees C) during the TSP, a strong expression of the P450arom gene and a complete suppression of the Dmrt-1 gene were induced in all experimental larvae. Up-regulation of the P450arom gene and down-regulation of the Dmrt-1 gene even in genetic males constitute a part of the molecular biological cascade for the temperature-dependent sex reversal from genetic males to phenotypic females in this salamander.
...
PMID:Up-regulation of P450arom and down-regulation of Dmrt-1 genes in the temperature-dependent sex reversal from genetic males to phenotypic females in a salamander. 1650 70

Efavirenz is a non-nucleoside human immunodeficiency virus (HIV)-1 reverse transcriptase inhibitor used in combination therapy to treat HIV-1. Efavirenz metabolism is catalyzed primarily by the polymorphic enzyme P450 2B6. Metabolism of efavirenz by P450 2B6 and the naturally occurring P450 2B6.4 mutant led to the formation of 8-hydroxyefavirenz. Efavirenz inactivated the 7-ethoxy-4-(trifluoromethyl)coumarin activity of the wild-type P450 2B6 enzyme in a time-, concentration-, and NADPH-dependent manner. However, the P450 2B6.4 variant was not inactivated by efavirenz. The ability of efavirenz to inactivate both enzymes was investigated using cyclophosphamide and bupropion, two structurally unrelated substrates of P450 2B6, as probes. Preincubations with efavirenz decreased the ability of the wild-type enzyme to hydroxylate both substrates to similar extents but had no effect on the activities of the mutant enzyme. Interestingly, the inactivation of the wild-type enzyme was completely reversible after 24 h of dialysis as determined by heme, reduced CO spectra, and activity loss. In contrast, 8-hydroxyefavirenz, a metabolite of efavirenz, was able to inactivate both enzymes irreversibly. These data suggest that incubations of P450 2B6 and P450 2B6.4 with either the parent compound efavirenz or the metabolite 8-hydroxyefavirenz in the reconstituted system result in the formation of two different reactive intermediates that lead to losses in enzymatic activity by two different mechanisms, one reversible and one irreversible.
...
PMID:Metabolism of efavirenz and 8-hydroxyefavirenz by P450 2B6 leads to inactivation by two distinct mechanisms. 1661 50

Cytochrome P450 (P450) induction may have considerable implications for drug therapy. Therefore, understanding the induction potential of a new chemical entity at an early stage in discovery is crucial to reduce the risk of failure in the clinic and help the identification of noninducing chemical structures. Availability of human viable tissue often limits evaluation of induction potential in human hepatocytes. A solution is to increase the time period during which the hepatocytes remain viable. In this study we have investigated the induction of several P450 isozymes in long-term cultured hepatocytes compared with short-term cultured hepatocytes from the same individuals. Short- and long-term cultured primary hepatocytes isolated from each individual were cultured in a 96-well format and treated for 24 h with a range of prototypical P450 inducers and Merck Research Laboratories compounds. CYP3A4, 1A1, 1A2, 2B6, and 2C9 mRNA levels were measured using quantitative real-time reverse transcriptase-polymerase chain reaction (TaqMan) from the same cultured hepatocyte wells. CYP3A4, 1A1, 1A2, 2B6, and 2C9 were shown to be inducible in long-term cultured hepatocytes. The -fold induction varied between donors, and between short- and long-term cultured hepatocytes from the same donor. However, this variability can be controlled by normalizing data from each hepatocyte preparation to a positive control. The use of long-term cultured hepatocytes on 96-well plates has proven to be sensitive, robust, and convenient for assessing P450 induction potential of new compound entities during the drug discovery process.
...
PMID:Utility of long-term cultured human hepatocytes as an in vitro model for cytochrome p450 induction. 1709 7

Our objective was to investigate the expression of different cytochromes P450 3A (CYP3A4, CYP3A5, and CYP3A7) and P-glycoprotein (ABCB1) genes along the human large intestine in paired tumour and normal samples. Real-time reverse transcriptase-polymerase chain reaction was used to measure CYP3A4-, CYP3A5-, CYP3A7- and ABCB1-specific mRNA expression, and Western blot analysis was used to measure membrane protein levels of CYP3A4/7, CYP3A5 and P-glycoprotein. Levels of mRNA and membrane protein fractions in the large intestine were compared with those of normal human liver. The mRNA expressions of CYP3A4, CYP3A5, CYP3A7 and ABCB1 in the large intestine were found to be highly variable, but overall the levels were significantly lower than those measured in liver (P < 0.0001, P < 0.001, P < 0.0001 and P < 0.01, respectively). At the membrane protein level, CYP3A4/7 was detected in all large intestine samples examined and the levels were substantially higher than those of the liver (P < 0.01). Although expression of CYP3A5 was detected in all large intestine samples, in most the levels were too low to allow quantification. P-glycoprotein was readily detected at levels slightly higher than those of liver (P < 0.05). Comparison between paired samples of normal and tumour in large intestine showed no significant differences in either the mRNA or membrane protein levels of these genes. In conclusion, this work suggests a potential role of the large intestine in the absorption and metabolism of xenobiotics and nutrients and no difference in the CYP3A and P-glycoprotein membrane protein fractions and mRNA expression between normal and tumour tissues.
...
PMID:Expression of cytochromes P450 3A and P-glycoprotein in human large intestine in paired tumour and normal samples. 1737 28

Traditionally, the liver has been considered a homogeneous organ, but literature suggests that the cytochromes P450 are differentially distributed among the hepatocytes and that the pattern of this distribution is altered by various xenobiotics. In this study, the CYP2B1/2 messenger RNA (mRNA) in the hepatocytes was compared following treatment of rats with either of two inducers, phenobarbital (PB), or dieldrin. Adult male Sprague-Dawley-derived rats were treated with either ip PB in saline at 80 mg/kg/day for 5 days or dieldrin in corn oil by oral gavage at 2.5 mg/kg/day for 13 days. Control rats received ip saline or po corn oil for the same time. Laser capture microdissection (LCM) followed by duplex quantitative real-time reverse transcriptase PCR was used to measure the CYP2B1/2 mRNA produced in bands of hepatocytes isolated from three locations along the sinusoidal path. The amounts of mRNA present in whole liver subsamples were also analyzed. CYP2B1/2 enzyme activity was determined by assaying 16beta-hydroxytestosterone formation. Whole liver mRNA samples exhibited significant induction in CYP2B1/2 transcript levels: sixfold for PB and 2200-fold for dieldrin. All the LCM band samples also showed significant fold induction in CYP2B1/2 mRNA compared to controls. Dieldrin caused marked increases in CYP2B1/2 mRNA levels in the direction of blood flow through the acinus: periportal, 300-fold; midzonal, 600-fold; and centrilobular, 1700-fold. A different pattern of induction was observed in the PB-treated rats: periportal, 1800-fold; midzonal, 8800-fold; and centrilobular, 1600-fold. The present study indicates the differences in spatial responses that can be exhibited within the liver following exposure to various xenobiotics. It also indicates the importance of examining xenobiotic metabolism in the liver in light of its nonhomogeneous, zoned microenvironment.
...
PMID:Spatial distribution of CYP2B1/2 messenger RNA within the rat liver acinus following exposure to the inducers phenobarbital and dieldrin. 1751 22

The success of antiretroviral therapy leads to a chronification of HIV-infection resulting in a decline of lethality. The lifelong intake of antiinfectives, though, may result in drug side effects with clinical dental implications. Despite fundamental cellular alterations, including prolonged hemorrhage following surgical interventions, antiretrovirals of all classes, of protease inhibitors, (non-nucleoside) reverse transcriptase inhibitors and of fusion inhibitors may promote oral manifestions like oral ulcera, dysgeusia, salivary gland disorders, papilloma, (peri)oral paresthesia or aphtous stomatitis. Due to inhibitory effects especially of protease inhibitors of cy tochrome P450-isoenzyme CYP3A4 therapeutical interactions with psychotropics/sedatives, antifungal agents, corticoids and intiinfectives, particularly metronidazole, may raise. The application and prescription of systemically metabolized adjuvant drugs as well as the monitoring of the possible progression of HIV infection is a key task in the oral health care of HIV-seropositive patients calling for a close medical coordination of therapeutical interventions.
...
PMID:[Implications of antiretroviral therapy in oral medicine--a review of literature]. 1822 98

To elevate the production level of heterologous polyketide in Streptomyces venezuelae, an additional copy of the positive regulatory gene pikD was introduced into the pikromycin (Pik) polyketide synthase (PKS) deletion mutant of S. venezuelae ATCC 15439 expressing tylosin PKS genes. The resulting mutant strain showed enhanced production of both tylactone (TL) and desosaminyl tylactone (DesTL) of 2.7- and 17.1-fold, respectively. The notable increase in DesTL production strongly suggested that PikD upregulates the expression of the desosamine (des) biosynthetic gene cluster. In addition, two hydroxylated forms of DesTL were newly detected from the extract of this mutant. These hydroxylated forms presumably resulted from a PikD-dependent increase in expression of the pikC gene that encodes P450 hydroxylase. Gene expression analysis by reverse transcriptase PCR and bioconversion experiments of 10-deoxymethynolide, narbonolide, and TL into the corresponding desosaminyl macrolides indicated that PikD is a positive regulator of the des and pikC genes, as well as the Pik PKS genes. These results demonstrate the role of PikD as a pathway-specific positive regulator of the entire Pik biosynthetic pathway and its usefulness in the development of a host-vector system for efficient heterologous production of desosaminyl macrolides and novel hydroxylated compounds.
...
PMID:Enhanced heterologous production of desosaminyl macrolides and their hydroxylated derivatives by overexpression of the pikD regulatory gene in Streptomyces venezuelae. 1824 60


<< Previous 1 2 3 4 5 6 7 8 Next >>

---