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

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

4(S)-(6-Amino-9H-purin-9-yl)tetrahydro-2(S)-furanmethanol (IsoddA) is the most antivirally active member of a novel class of optically active isomeric dideoxynucleosides in which the base has been transposed from the natural 1' position to the 2' position and the absolute configuration is (S,S). IsoddA was active against human immunodeficiency virus type 1 (HIV-1) (strain IIIB), HIV-2 (strain ZY), and HIV-1 clinical isolates. Combinations of the compound with zidovudine (3'-azido-3'-deoxythymidine), 2',3'-dideoxyinosine, or 5-fluoro-2'-deoxy-3'-thiacytidine showed synergistic inhibition of HIV. A moderate reduction of activity was observed with clinical isolates resistant to zidovudine. An IsoddA-resistant virus (eightfold-increased 50% inhibitory concentration) was selected in vitro by repeated passage of HIV-1 (HXB2) in the presence of increasing concentrations of IsoddA. The reverse transcriptase-coding region of the mutant virus contained a single base change resulting in a change at codon 184 from Met to Val. IsoddA was also active against hepatitis B virus (HBV) in vitro; however, it lacked substantial selective activity in an in vivo HBV model. IsoddA was inefficiently phosphorylated in CEM cells; however, the half-life of the triphosphate was 9.4 h, and IsoddATP was a potent inhibitor of HIV-1 reverse transcriptase, with a Ki of 16 nM. The cytotoxicity 50% inhibitory concentrations of IsoddA were greater than 100 microM for CEM, MOLT-4, IM9, and the HepG2-derived HBV-infected 2.2.15 (subclone P5A) cell lines but were 12 and 11 microM for human granulocyte-macrophage (CFU-GM) and erythroid (BFU-E) progenitor cells, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Antiviral, metabolic, and pharmacokinetic properties of the isomeric dideoxynucleoside 4(S)-(6-amino-9H-purin-9-yl)tetrahydro-2(S)-furanmethanol. 854 Jul 5

Hepatitis B virus (HBV) replication is mediated by the viral polymerase that possesses three functional domains: primer, DNA polymerase/reverse transcriptase, and RNase H. Using the Pekin duck as an animal model, we demonstrate a novel mechanism of inhibition of duck hepatitis B virus (DHBV) by 2,6-diaminopurine 2',3'-dideoxyriboside (ddDAPR), a prodrug of 2',3'-dideoxyguanosine (ddG). A selective and irreversible inhibition of DHBV DNA replication is found in ducklings treated with high doses of ddDAPR (20 to 50 mg/kg), but not with similar doses of 2',3'-dideoxycytidine (ddC). The inhibition mediated by ddDAPR occurs at a very early stage of the reverse transcription. Despite the inhibition of DHBV DNA replication by ddDAPR, the DNA polymerase and reverse transcriptase activities of the polymerase are found to remain active when tested on exogenous templates in activity gels. We have demonstrated direct binding of [alpha-32P]ddGTP to the DHBV polymerase expressed in an in vitro transcription and translation system. These results suggest that the binding of ddGTP to the polymerase blocks the initial DNA replication.
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PMID:Selective inhibition of the reverse transcription of duck hepatitis B virus by binding of 2',3'-dideoxyguanosine 5'-triphosphate to the viral polymerase. 855 54

The heat shock protein Hsp90 is known as an essential component of several signal transduction pathways and has now been identified as an essential host factor for hepatitis B virus replication. Hsp90 interacts with the viral reverse transcriptase to facilitate the formation of a ribonucleoprotein (RNP) complex between the polymerase and an RNA ligand. This RNP complex is required early in replication for viral assembly and initiation of DNA synthesis through a protein-priming mechanism. These results thus invoke a role for the Hsp90 pathway in the formation of an RNP.
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PMID:Hsp90 is required for the activity of a hepatitis B virus reverse transcriptase. 857 14

Treatment of chronic hepatitis B virus (HBV) infections with the reverse transcriptase inhibitor lamivudine leads to a rapid decline in plasma viremia and provides estimates for crucial kinetic constants of HBV replication. We find that in persistently infected patients, HBV particles are cleared from the plasma with a half-life of approximately 1.0 day, which implies a 50% daily turnover of the free virus population. Total viral release into the periphery is approximately 10(11) virus particles per day. Although we have no direct measurement of the infected cell mass, we can estimate the turnover rate of these cells in two ways: (i) by comparing the rate of viral production before and after therapy or (ii) from the decline of hepatitis B antigen during treatment. These two independent methods give equivalent results: we find a wide distribution of half-lives for virus-producing cells, ranging from 10 to 100 days in different patients, which may reflect differences in rates of lysis of infected cells by immune responses. Our analysis provides a quantitative understanding of HBV replication dynamics in vivo and has implications for the optimal timing of drug treatment and immunotherapy in chronic HBV infection. This study also represents a comparison for recent findings on the dynamics of human immunodeficiency virus (HIV) infection. The total daily production of plasma virus is, on average, higher in chronic HBV carriers than in HIV-infected patients, but the half-life of virus-producing cells is much shorter in HIV. Most strikingly, there is no indication of drug resistance in HBV-infected patients treated for up to 24 weeks.
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PMID:Viral dynamics in hepatitis B virus infection. 863 78

The DNA-dependent DNA polymerase (DDDP) and RNA-dependent DNA polymerase (RDDP) activities of hepadnavirus polymerases are both essential for viral replication. Human hepatitis B virus (HBV) polymerase has been successfully expressed in Escherichia coli as a fusion protein in frame with maltose-binding protein. The present study was undertaken to characterize these two activities and introduce an in vitro assay system. In situ activity gel assays show that the polymerase has both types of activities. One hundred thirty-four kilodaltons of active full-length product was proteolytically cleaved into approximately 73 kDa of active fragment by proteinase K preincubation. Mutation of conserved YMDD motif also confirms that the activities were due to the recombinant polymerase and that this motif is essential to polymerase activity. Two activities of the polymerase show their optima under conditions of 1 mM (DDDP) or 0.25 mM (RDDP) of MnCl2, 400 mM KCl, 37 degrees C (DDDP) or 24 degrees C (RDDP), and pH 7.0-7.7. Substitution of Mg2+ for Mn2+ results in reduction of processivity, which may explain why Mn2+ supports nucleotide incorporation to a higher level than Mg2+. The polymerase is resistant to aphidicolin. Actinomycin D acts selectively on DDDP activity, whereas phosphonoformic acid inhibits both activities. The in vitro HBV polymerase assay system demonstrated herein will be useful for screening potential HBV polymerase inhibitor for the development of anti-HBV drugs.
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PMID:The catalytic properties of human hepatitis B virus polymerase. 867 Feb 70

Assembly of the enveloped hepatitis B virus (HBV) is initiated by packaging of the RNA pregenome and the viral reverse transcriptase-DNA polymerase into a nucleocapsid. The pregenome is then reverse transcribed into single-stranded minus-polarity DNA, which is subsequently replicated to double-stranded DNA. All replicative intermediates are observable in capsids within infected liver, but only relatively mature nucleocapsids containing partially double stranded DNA are found in secreted virions. This observation suggests that maturation of the genome within the capsid is required for envelopment and secretion. We show that the differential distribution of replicative intermediates between intracellular nucleocapsids and secreted virions is also observable in human hepatoma cells transfected with wild-type HBV genomes. However, nucleocapsids were not enveloped or secreted when they were produced by an HBV genome carrying a missense mutation in the DNA polymerase that eliminates all DNA synthesis. An HBV missense mutant defective in the RNase H activity of the polymerase which allowed minus-strand DNA synthesis but not formation of double-stranded DNA was able to form virion-like particles. These experiments demonstrate that immature nucleocapsids containing pregenomic RNA are incompetent for envelopment and that minus-strand DNA synthesis in the interior lumen of the capsid is coupled to the appearance of a signal on the exterior of the nucleocapsid that is essential for its envelopment.
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PMID:Hepatitis B virus nucleocapsid envelopment does not occur without genomic DNA synthesis. 867 48

Anti-viral drug treatment of human immunodeficiency virus type I (HIV-1) and hepatitis B virus (HBV) infections causes rapid reduction in plasma virus load. Viral decline occurs in several phases and provides information on important kinetic constants of virus replication in vivo and pharmacodynamical properties. We develop a mathematical model that takes into account the intracellular phase of the viral life-cycle, defined as the time between infection of a cell and production of new virus particles. We derive analytic solutions for the dynamics following treatment with reverse transcriptase inhibitors, protease inhibitors, or a combination of both. For HIV-1, our results show that the phase of rapid decay in plasma virus (days 2-7) allows precise estimates for the turnover rate of productively infected cells. The initial quasi-stationary phase (days 0-1) and the transition phase (days 1-2) are explained by the combined effects of pharmacological and intracellular delays, the clearance of free virus particles, and the decay of infected cells. Reliable estimates of the first three quantities are not possible from data on virus load only; such estimates require additional measurements. In contrast with HIV-1, for HBV our model predicts that frequent early sampling of plasma virus will lead to reliable estimates of the free virus half-life and the pharmacological properties of the administered drug. On the other hand, for HBV the half-life of infected cells cannot be estimated from plasma virus decay.
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PMID:Viral dynamics in vivo: limitations on estimates of intracellular delay and virus decay. 869 77

The expression of cytokine mRNA species was determined in liver biopsies from six normal subjects, 18 patients with PBC and 14 patients with hepatitis B e antigen (HBeAg)-positive CHB using a reverse transcriptase-polymerase chain reaction (RT-PCR) technique. cDNA, obtained by reverse transcription using oligo d(T) primers, was amplified by PCR using primers specific for the coding region of seven different cytokines (IL-1, IL-2, IL-4, IL-5, IL-6, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha)). The abundance of some cytokines (IL-2, IL-4, IL-5 and IFN-gamma) was also estimated by semiquantitative RT-PCR, using as standards dilutions of synthetic cytokine mRNA transcripts, that could be distinguished electrophoretically from respective native cytokine mRNAs. Hepatic inflammation was assessed by a semiquantitative histologic score and by amplification of mRNA for T cell receptor (TCR)-alpha. mRNAs for IL-1 and IL-6 were detected in only one control liver. In CHB, mRNAs for IL-1, IL-2, IL-4, IL-5 and IFN-gamma were detected in 43%, 60%, 80%, 20%, and 54% of biopsies, respectively. mRNA for IFN-gamma and IL-4, but not IL-1, tended to be associated with severe inflammation. In five biopsies semiquantitative analyses revealed increased levels of mRNA for TCR-alpha and, when transcripts were detectable, high levels of mRNA for IFN-gamma and IL-4. In PBC, mRNA for IFN-gamma was detected in 60% of biopsies, but no mRNAs for IL-1, IL-2, IL-4, IL-5, or IL-6, or for TNF-alpha, were detected. Semiquantitative analyses revealed that absolute levels of mRNA for IFN-gamma tended to correlate with the severity of hepatic inflammation. The results suggest that: (i) there may be fundamental differences in the roles that cytokines play in the hepatic inflammatory processes of PBC and CHB; and (ii) while hepatic IFN-gamma mRNA expression is not specific for PBC, IFN-gamma may play a prominent role in the immunopathogenesis of PBC.
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PMID:Cytokine mRNA expression in the liver of patients with primary biliary cirrhosis (PBC) and chronic hepatitis B (CHB). 870 30

Although recurrence of hepatitis C virus (HCV) in orthotopic liver transplant (OLT) patients is frequent, the relationship between HCV recurrence and graft pathology, particularly in patients who also have a history of hepatitis B virus (HBV), is unclear. The recurrence of HCV after OLT was determined by reverse transcriptase-nested polymerase chain reaction (RT-PCR) in the sera and livers of 41 patients with OLT, 32 of whom underwent transplants for HCV or HBV-related disease. Results were compared with liver function tests, liver histology (including HBV immunohistochemistry), and antibody status. HCV PCR was more frequently positive in OLT patients with a history of HCV only (59%) than in those with a history of both HCV and HBV (41%) or no history of viral infection (2%). Recurrent HCV (60% overall) was associated with mild elevation of liver function tests and mild to moderate hepatitis. In patients who underwent transplants for both HCV and HBV disease, hepatitis on biopsy was more frequently associated with recurrent HBV than with recurrent HCV. We conclude that graft reinfection with HCV, which is frequent in OLT patients with or without HBV recurrence, is usually associated with only mild to moderate hepatitic changes compatible with graft survival.
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PMID:Hepatitis C virus reinfection in orthotopic liver transplant patients with or without concomitant hepatitis B infection. 872 94

Lamivudine is a novel cytosine nucleoside analog, reverse transcriptase inhibitor that has shown activity against human immunodeficiency virus (HIV) types 1 and 2 and hepatitis B virus in vitro. This study was conducted to compare the absolute bioavailability, pharmacokinetics, and absorption characteristics of oral solution, 100-mg capsule, and 100-mg tablet formulations of lamivudine with those of intravenous lamivudine. Twelve patients with HIV were enrolled in a single-center, randomized, open-label, four-way cross-over study. Treatment arms consisted of 100 mg intravenous lamivudine (administered over 1 hour), 100 mg oral lamivudine (1 mg/mL), a 100-mg capsule, and a 100-mg tablet, each followed by a 3- to 14-day washout period. Serial blood samples over 24 hours were obtained after each dose administration. Serum concentration data were analyzed to determine pharmacokinetic parameter estimates including area under the curve (AUC), terminal half-life (t1/2), mean residence time (MRT) for each formulation, systemic clearance, oral clearance, and apparent volume of distribution (Vd). Absolute bioavailability and in vivo mean absorption time (MAT) and mean dissolution time (MDT) were calculated for the oral formulations. Deconvolution techniques were used to calculate the input rate for the oral solution, capsule, and tablet. The two one-sided t test was used to determine bioequivalency among oral formulations with respect to logarithmic transformed estimates of AUC and maximum peak concentration (Cmax). Mean (CV) systemic clearance and Vdss after intravenous administration of lamivudine were 22.6 L/h (15%) and 99 L (28%), respectively; mean t1/2 ranged from 8.41 to 9.11 hours for all formulations; and MRT ranged from 4.42 to 5.77 hours for all formulations. Mean absolute bioavailability ranged from 86% to 88% for the oral solution, capsule, and tablet. All oral formulations were considered bioequivalent for AUC and Cmax. The MAT was 1.32 hour for the oral solution, and MDT was 0.03 and -0.11 hours for the capsule and the oral solution, respectively. The oral formulations of lamivudine examined in this study demonstrated acceptable bioavailability for oral administration. The solid oral formulations (capsule and tablet) show rapid dissolution properties with an absorption rate similar to or exceeding those observed with the oral solution. This suggests that dissolution is not an important factor for the rate of absorption of lamivudine. The use of deconvolution techniques using PCDCON provides valuable insight into the absorption characteristics of lamivudine.
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PMID:Pharmacokinetics, absolute bioavailability, and absorption characteristics of lamivudine. 875 Mar 68


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