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Query: UMLS:C0019158 (hepatitis)
 30,205 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hepatitis C virus (HCV) is the major etiological agent of both parenterally transmitted and sporadic non-A, non-B hepatitis. The disease is a major health problem with an estimated 50 million people infected worldwide, a high percentage of whom become chronically infected and are at high risk for liver cirrhosis. The serine protease contained within the N-terminal region of the nonstructural protein 3 (NS3 protease) of HCV is considered a promising target for the development of an antiviral therapy. A prime requisite to study in detail the biochemistry of the protease as well as develop inhibitors is the availability of a fast and sensitive in vitro assay of enzyme activity. However, due to their low kcat/Km values, synthetic peptide substrates based on the natural cleavage sites appear unsuitable for this purpose. We show here that appropriate substrates can be obtained by substituting the scissile amide bond with an ester linkage. The resulting depsipeptides show >100-fold improvement in kcat/Km values, up to 13,000 M-1 s-1, enabling detection of activity with subnanomolar NS3 concentrations. The ester substrates are obtained in high yield entirely by solid-phase synthesis using commercially available materials, without the need for any preassembled building blocks.(c) 1996 Academic Press, Inc.
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PMID:Synthetic depsipeptide substrates for the assay of human hepatitis C virus protease. 866 May 72

The genomes of two novel members of the Flaviviridae associated with GB agent hepatitis (GB viruses A and B) were cloned and sequenced recently. The genome of a third novel virus (GB virus C), related to but distinct from GB viruses A and B, has also been identified and characterized. Overlapping clones encompassing the large open reading frames of these three viruses have been expressed in E. coli as CTP:CMP-3-deoxy-D-manno-octulosonate cytidylyltransferase (CKS) fusion proteins. Bacterial lysates were subjected to Western blot analyses using sera from GB agent-infected tamarins and human sera from various individuals with or "at risk" for non-A, non-B, non-C, non-D, non-E hepatitis. Antigenic regions were identified in the putative NS3, NS4, and NS5 proteins from all three viruses. An antigenic region was also identified in the putative core protein of GB virus B. Many of the clones identified originally as encoding antigenic proteins were quite large. To map these regions more narrowly, smaller overlapping clones were generated by polymerase chain reaction (PCR), expressed as recombinant CKS fusion proteins and tested by Western blot. Additionally, a lambda gt11 expression library was generated from infectious tamarin sera and immunoscreened. These studies have identified at least three epitopes in GB virus A, five epitopes in GB virus B and four epitopes in GB virus C.
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PMID:Identification of antigenic regions in the GB hepatitis viruses GBV-A, GBV-B, and GBV-C. 869 65

The recent cloning and genomic identification of hepatitis C virus (HCV) by sensitive and specific immune techniques has allowed a better definition of both histopathological and clinical features of the previously not well defined non-A, non-B hepatitis. In this regard, antibodies to different HCV antigens are usually found during infection, even if some of them such as anti-E1 and anti-E2/NS1 have been shown to be associated with significant viraemic levels. Acute hepatitis C is self-limiting in a minority of cases only. Over 60% of acute hepatitis becomes in fact chronic and may progress towards cirrhosis. In about 10% of cases, hepatocellular carcinoma may develop in cirrhotic livers. The occurrence of a strict relationship between immunoresponsiveness and disease activity is suggested by the observation that peripheral blood mononuclear cell (PBMC) proliferation induced by NS3 structure is associated with self-limiting acute hepatitis, while PBMC stimulation by core antigen characterizes chronic C hepatitis. The demonstration of lymphoid aggregates, bile duct lesions, intraportal lymphocyte infiltration, increased adhesion molecule expression and augmented cytokine release clearly emphasizes the involvement of immune-mediated reactions in the development of liver damage, even if a direct cytopathic effect cannot be excluded. Finally, it is likely that HCV may favour, through immune-mediated mechanisms, autoantibody generation and/or the appearance of some extrahepatic autoimmune manifestations during the course of HCV chronic infection.
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PMID:Hepatitis C virus infection. Biological and immunological features. 876 58

A new animal model for the causation of liver tumors via a bacterial infection presented itself fortuitously in the form of a new species, Helicobacter hepaticus. This species of Helicobacter colonizes the hepatic bile canaliculi in susceptible strains of mice, resulting in hepatitis and hepatocellular and hepatocholangiolar adenomas and carcinomas. The mechanism by which this infection leads to cancer is unknown. Tests with Helicobacter hepaticus have revealed thus far that the bacteria do not secrete a mutagen which is capable of detection by the Ames Assay. Measurement of oxidatively damaged bases in the liver DNA of hepaticus infected mice have shown accumulation of 8-oxodeoxyguanosine with disease progression. Other promutagenic DNA lesions, 7-methylguanine and O6-methylguanine, indicative of nitrosation of endogenous amines by nitric oxide, were not detected. Analysis of carcinomas and adenomas taken from H. hepaticus infected A/JCr mice revealed no mutations in ras oncogenes or in exons 5-8 of the p53 gene. These preliminary results indicate that a non-genotoxic tumor promotion mechanism, possibly implemented by reactive oxygen species from the immune response, is more likely than a genotoxic mechanism.
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PMID:Liver tumorigenesis by Helicobacter hepaticus: considerations of mechanism. 879 29

Hepatitis C virus (HCV) is the major causative agent of non-A non-B hepatitis, an important health problem with an estimated 50 million people infected worldwide. Among the possible targets for therapeutic intervention, the serine protease contained within the N-terminal region of nonstructural protein 3 (NS3 protease) is so far the best characterized. In vitro characterization of synthetic substrates based on all the natural cleavage sites (as well as a series of analogs) has consistently revealed poor kinetic parameters, making them unsuitable for sensitive high-throughput screening. To overcome these difficulties, we have recently developed depsipeptide substrates incorporating an ester bond between residues P1 and P&prime1. Due to ready transesterification of the scissile bond to the acyl-enzyme intermediate, these substrates showed very high kcat/Km values, enabling detection of activity with subnanomolar NS3 concentrations. We have used the same principle to synthesize internally quenched depsipeptide fluorogenic substrates based on resonance energy transfer between the donor/acceptor couple 5-[(2'-aminoethyl)amino]naphthalene sulfonic acid/4-[[4'-(dimethylamino)phenyl]azo]benzoic acid, and developed a continuous assay for NS3 activity. Substrate cleavage is linear with enzyme concentration: depending on the conditions chosen, we estimated a detection limit for NS3 between 1 nM and 250 pM. The suitability of the assay for evaluation of inhibitors was established using as competitor a tridecapeptide corresponding to the natural NS4A/4B cleavage site; this gave an IC50 of 30 microM, well in agreement with the previously found Km value (40 microM).
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PMID:A continuous assay of hepatitis C virus protease based on resonance energy transfer depsipeptide substrates. 881 80

Hepatitis C virus (HCV) is the major etiological agent of posttransfusion and community-acquired non-A, non-B hepatitis. It is an enveloped virus, grouped as a separate genus in the Flaviviridae family. The plus-stranded RNA genome encodes a polyprotein of about 3000 amino acids with the structural proteins core, E1 and E2 residing in the amino terminal quarter of the polyprotein and the nonstructural proteins NS2, NS3, NS4A, NS4B, NS5A and NS5B in the remainder. Maturation of the structural proteins is mediated by host cell signalases located in the lumen of the endoplasmic reticulum and cleaving behind stretches of hydrophobic amino acids. At least two virally encoded proteinases are responsible for processing of the NS proteins: a zinc-dependent metallo-proteinase encompassing the NS2 domain and the amino terminal portion of NS3, which is essential for cleavage at the NS2/3 junction; a serine-type proteinase located in the amino terminal domain of NS3 is required for cleavage at all sites downstream of the NS3 carboxy terminus. However, although the NS3 domain contains proteolytic activity, with the exception of the NS5A/5B junction cleavage only occurs in the presence of NS4A. This 54 amino acid long peptide can modulate the proteolytic activity of the enzyme in cis and in trans, probably by the formation of a stable NS3/NS4A complex. Modulation of the proteinase activity may be a way to regulate the expression and replication of the HCV genome.
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PMID:Processing pathways of the hepatitis C virus proteins. 883 84

The NS3 protein of hepatitis C virus contains a chymotrypsin-like serine proteinase domain. We built a homology model of this domain which predicts the presence of a tetradentate metal binding site formed by three cysteines and one histidine. These residues are strictly conserved in all known hepatitis C viral genotypes as well as in other recently discovered related hepatitis viruses. We show that the hepatitis C virus enzyme does indeed contain a Zn2+ ion with S3N ligation and that the metal is required for structural integrity and activity of the enzyme. Strikingly, the residues forming the metal binding site are also conserved in the chymotrypsin-like 2A cysteine proteinases of picornaviruses. Remarkably, in these highly variable viral genomes the metal binding site is more conserved than the catalytic residues and thus allows us to define a novel class of zinc binding chymotrypsin-like proteinases and to identify a new attractive target for antiviral therapy.
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PMID:A zinc binding site in viral serine proteinases. 887 93

Hepatitis C virus (HCV) is the major etiologic agent of non-A, non-B hepatitis. One of the difficulties in developing anti-HCV drugs is the lack of an efficient HCV cultivation system. We have generated an artificial surrogate virus suitable for testing the antiviral effects of drugs affecting HCV protease NS3, an enzyme believed to be essential for HCV proliferation. The surrogate virus genome is composed of most of the poliovirus genome and HCV protease NS3 and an NS3-specific cleavage site. The activity of HCV protease NS3 is required for proliferation of this chimeric virus. The antiviral efficacy of HCV protease inhibitors can, therefore, be evaluated by examining the effects of the drugs on the surrogate virus proliferation.
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PMID:Generation of a novel poliovirus with a requirement of hepatitis C virus protease NS3 activity. 895 51

Recently, GBV-C and HGV-two isolates of the same new flavivirus-were identified in serum samples of patients with indeterminate hepatitis and posttransfusion hepatitis, respectively. The pathogenic relevance of these viruses is still uncertain. As viral infections are presumed to trigger autoimmune processes, we investigated GBV-C in autoimmune hepatitis as well as in cryptogenic hepatitis, and compared the prevalences to patients with chronic viral hepatitis and those of blood donors. We found only a slightly higher prevalence of the virus in cryptogenic (12%) and autoimmune hepatitis type I-III (6.7%, 10%, and 12.5%) compared to blood donors (4.7%). In contrast, patients with viral hepatitis B, C, and D were more frequently infected with GBV-C (16%, 20%, 36%). These results suggest that GBV-C is not a major cause for inducing autoimmunity and leading to autoimmune hepatitis. We analyzed the nucleic acid sequences of a representative number of GBV-C positive patients (24/42) and found a broad range of nucleotide similarity in the NS3 helicase region (74-100%) among the isolates and the prototype sequences. However, we could not identify a specific sequence, which would point to a certain strain or subtype of the virus associated with autoimmune or cryptogenic liver disease.
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PMID:GBV-C/HGV is not the major cause of autoimmune hepatitis. 900 30

In 1995, a new human hepatitis virus belonging to the family Flaviviridae was described and designated hepatitis GBV-C. To investigate variations within the genome of GBV-C and to study the relationship of GBV-C to GBV-A/B or hepatitis C virus (HCV), we established a detection system using reverse transcriptase polymerase chain reaction (RT-PCR) of the putative helicase region (NS3). So far, isolates derived from 14 different GBV-C-positive sera were analyzed (GBV-C/S3-36), showing 80.1-89.4% (mean: 85%) identical nucleotides. The deduced amino acid sequences revealed 97.3% homology. Nucleotide sequences of GBV-C/S3-36 revealed about 60% identity to GBV-A as well as to HCV, but only 56% identity to GBV-B. Amino acid sequences revealed 73.4 and 68.6% similarity to GBV-A and GBV-B, respectively, but a slightly higher percentage of 78.5% to HCV sequences. Thus, according to the putative GBV-C helicase sequence, a subtyping of GBV-C into different genotypes may be necessary.
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PMID:Sequence analysis of hepatitis GB virus C (GBV-C) isolates from 14 patients. 902 80


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