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)

Hepatitis C virus (HCV) is known to infect peripheral blood mononuclear cells (PBMC) of patients with chronic hepatitis C, but the proportion of HCV-infected circulating cells is not detectable by conventional reverse transcriptase-polymerase chain reaction (RT-PCR) and the pathogenic significance of HCV lymphotropism is still unclear. Therefore, we have devised an in situ RT-PCR technique using fluorescein-labeled HCV-specific primers revealed by flow cytometry. PBMC were isolated from 28 patients with chronic HCV-related liver disease; of these, 6 had previously received an orthotopic liver transplantation (OLT) and were on immuno-suppressive treatment. Fourteen patients (50%) were found positive for HCV genome within PBMC by in situ RT-PCR, the proportion of HCV-infected cells ranging from 0.2% to 8.1%. All 6 OLT patients tested positive. The fluorescent signal, corresponding to the HCV-specific 340-bp amplicon, was confined to part of the cytoplasmic compartment of scattered PBMC. Of these 14 patients, 12 had also negativestrand HCV RNA within PBMC detected by "tagged" RT-PCR. We conclude that HCV may infect a significant proportion of PBMC in chronic hepatitis C patients, especially immunosuppressed OLT cases, and that viral replication within PBMC is a common occurrence. Over time, the persistence of HCV-infected immune system cells might interfere with normal immunologic mechanisms and play a role in the pathogenic processes leading to extrahepatic disorders such as mixed cryoglobulinemia and B-cell malignant lymphoma.
...
PMID:Quantification of hepatitis C virus-infected peripheral blood mononuclear cells by in situ reverse transcriptase-polymerase chain reaction. 883 74

The deoxyguanosine analog penciclovir (PCV; 9-[4-hydroxy-3-hydroxymethyl-but-1-yl]guanine), has shown potent antiviral activity against herpes viruses and hepadnaviruses. Efficacy against chronic hepatitis B virus (HBV) infection has been demonstrated in an animal model and in recent clinical trials of famciclovir, the oral form of PCV. The antiviral activity of PCV is believed to be dependent on the intracellular formation of PCV-triphosphate (PCV-TP) which is presumed to inhibit HBV replication by interfering with viral DNA polymerase activity. The (S)-enantiomer is preferentially formed in herpes virus-infected cells, and is the more active against the herpes simplex virus; however, little is known about the biochemical mechanisms of PCV phosphorylation or of interference with viral replication in HBV-infected cells. Here, we report that in contrast with herpes simplex virus, the (R)-enantiomer of PCV-TP is a more potent inhibitor of HBV DNA polymerase-reverse transcriptase (pol-RT) in vitro than the (S)-enantiomer. In assays for HBV DNA pol-RT activity, in which purified viral core particles were the enzyme source, the IC50s for (R)- and (S)-enantiomers of PCV-TP were 2.5 micromol/L and 11 micromol/L, respectively. The estimated Kis for (R)- and (S)- PCV-TP were approximately 0.03 micromol/L and approximately .04 micromol/L, respectively, about 3-fold lower than the Km for deoxyguanosine triphosphate (dGTP) in the same system. In addition, we report that PCV metabolism is similar in both control (HepG2) and in HBV-transfected (2.2.15) hepatoblastoma cells in vitro, indicating that cellular enzyme(s) catalyze PCV phosphorylation. Peak PCV-TP concentrations of about .4 micromol/L were reached in both cell types in less than 12 hours, and intracellular PCV-TP was exceptionally stable with a half-life of about 18 hours. These observations provide a mechanistic basis for the potent activity of PCV against HBV.
...
PMID:Inhibition of hepatitis B virus DNA polymerase by enantiomers of penciclovir triphosphate and metabolic basis for selective inhibition of HBV replication by penciclovir. 890 66

We examined changes in the hypervariable region 1 of the hepatitis C virus (HCV) RNA that occurred with interferon therapy in 33 patients with chronic hepatitis C to assess the clinical significance of this region. The 33 patients had HCV genotype 1b and were classified into three groups based on serum aminotransferase levels during and after therapy with alpha interferon; long-term responders (n = 9), short-term responders (n = 11), and nonresponders (n = 13). Changes in the genetic heterogeneity of the hypervariable region 1 were determined by using nonisotopic polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). HCV RNA levels were evaluated by reverse transcriptase PCR and branched DNA probe assays. Changes in sequences were determined by cloning and sequencing analysis. Before therapy, the long-term responders had significantly lower degrees of heterogeneity and lower viral levels than nonresponders. There were no significant differences between short-term and nonresponders. With interferon therapy, viral levels and degree of heterogeneity decreased to a greater extent among long-term and short-term responders than among nonresponders. Sequencing analysis showed that the three groups had similar clone numbers initially, but long-term responders had rather homogeneous viral populations, whereas short-term and nonresponders had heterogeneous populations, but that there were no nucleotide sequences or amino acid alignments that were specific for any group before, during, and 6 months after therapy. Approximately half of short-term and nonresponders received a second course of interferon 7 to 10 months after the initial therapy; all showed an identical response to the second course of therapy regardless of interim changes in the heterogeneity of hypervariable region 1. These findings suggest that (1) patients who were nonresponders or short-term responders had mixed viral populations that had differing sensitivities to interferon, (2) the changes in the hypervariable region 1 (HVR 1) did not affect responsiveness to interferon, and (3) the lower heterogeneity in the HVR 1 was associated with a long-term response to interferon only when the viral levels were low.
...
PMID:The clinical significance of changes in genetic heterogeneity of the hypervariable region 1 in chronic hepatitis C with interferon therapy. 890 69

We tested the sera of 67 consecutive patients for hepatitis G virus (HGV) RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). These patients (42 males and 25 females, median age 35 years, range 13-64 years) had liver disease of unknown aetiology and were without markers of hepatitis (A-E) viruses or signs of genetically determined, autoimmune, alcoholic or drug-induced liver disease. The controls in this study were 110 patients (50 females and 60 males, median age 45 years, range 9-65 years) with chronic hepatitis B virus (HBV) infection (19 patients) or hepatitis C virus (HCV) infection (91 patients). Ten of 67 (14.9%) patients with cryptogenic disease were positive for HGV RNA by at least three separate tests; HGV RNA was also detected in one of 19 (5.3%) hepatitis B surface antigen (HBsAg) carriers and in nine of 91 (16.6%) patients with antibody to HCV. These data suggest that HGV occurs as frequently in HCV-infected patients as in those with cryptogenic disease. Elevated serum gamma glutamyl transpeptidase (gamma-GT) (higher than twice the normal value) and alkaline phosphatase levels were found in eight of 10 (80%) HGV RNA positive patients and in six of 57 (10.5%) HGV RNA negative patients (P < 0.0001). Five (50%) HGV RNA positive patients had non-specific inflammatory bile duct lesions. A statistically significant difference was observed between HGV RNA positive and negative patients with chronic HBV or HCV infections (P < 0.029). Therefore, the spectrum of liver disease associated with HGV is wide, but a characteristic lesion of the bile duct leading to elevation of cholestatic enzymes might be specific for this virus.
...
PMID:Hepatitis G virus RNA in the serum of patients with elevated gamma glutamyl transpeptidase and alkaline phosphatase: a specific liver disease? [corrected]. 894 81

Infection with hepatitis B virus can result in asymptomatic seroconversion with viral clearance, fulminant hepatic failure and death, or chronic, typically lifelong, transmissible infection. The mechanism(s) of viral persistence are poorly understood but viral clearance and fulminant hepatic failure are generally thought to result from co-ordinated and effective and abnormally vigorous immune responses, respectively, whereas viral persistence results from immunological failure in addition to poorly characterized viral factors promoting persistence. This paper proposes (1) that the predominant viral factor(s) promoting persistence of hepatitis B virus are homeostatic mechanism(s) responsible for modulating its replication and mutation and (2) that chronic hepatitis B results when these mechanisms are successful and other outcomes occur when these homeostatic mechanism(s) fail. Furthermore, it is proposed that seroconversion (e.g. from HBsAg to anti HBsAg positivity), when it occurs, is a consequence facilitated by restricted viral antigenic diversity and reduced viral replication rather than a proximate cause of it. The specific homeostatic mechanisms proposed--negative feedback inhibition of hepatitis B virus DNA polymerase/reverse transcriptase mediated by HBs antigen and a hepatitis B virus DNA polymerase fidelity modulating function of HBeAg--are consistent with the available data and resolve many paradoxical clinical observations. But, more importantly, this model has clear implications for therapy, including the rational design of drugs and therapeutic vaccines.
...
PMID:Hepatitis B virus replication and mutation are autoregulated by interactions between surface antigen and HBeAg and the HBV DNA polymerase: a functional model with therapeutic implications. 904 82

We compared the relative sensitivities of first-and-second generation branched nucleotide assays (Quantiplex HCV RNA 1.0 and 2.0, respectively, Chiron, Emeryville, Calif) for the detection of hepatitis C virus (HCV) RNA to that of a commercially available quantitative reverse transcriptase polymerase chain reaction (RT-PCR) method (Monitor, Roche Molecular Systems, Nutley, NJ) in 53 patients with chronic hepatitis C. The sensitivities of the second-generation branched DNA (bDNA) and RT-PCR assays were similar (91% and 92%, respectively), and both were significantly more sensitive (P < .001) than the first-generation method. Moreover, both assays detected HCV RNA in all 11 patients with type 2a, 2b, or 3a genotypes vs 45% with the HCV RNA 1.0 bDNA assay. We examined 174 serum samples by the bDNA 2.0 and RT-PCR assays. Major quantification differences were noted on a given specimen with the RT-PCR method reporting values an average 41-fold lower (range, 0-703-fold) than those obtained with the bDNA assay. We conclude that both methods can be used to detect HCV RNA in patients who are infected with the genotypes that are most commonly encountered in the United States. The HCV RNA 2.0 bDNA assay may offer advantages when attempting to quantify high-level viremia.
...
PMID:Comparison of quantitative HCV RNA assays in chronic hepatitis C. 905 89

For many years, acyclovir has been used to treat herpes simplex and varicella zoster infections in adults and children, although new drugs with improved bioavailability and dosage regimens (ie, famciclovir, valaciclovir) are replacing it for the outpatient management of these conditions in adults. Acyclovir remains the treatment of choice for severe herpes infections in both immunocompetent and immunosuppressed patients. Data on the newer antiherpes drugs in children are not available. Treatment of severe cytomegalovirus infections with ganciclovir and foscarnet is difficult because of toxicity; whether improved formulations of these drugs or newer agents prove clinically useful remains to be seen. For the most part, treatment of other herpesviruses is not indicated. The major advance in pediatric HIV treatment is the reduction in vertical transmission with peripartum zidovudine, although the optimal use of antiretrovirals in this situation remains to be determined. The nucleoside analogues zidovudine, zalcitabine, didanosine, and stavudine have been assessed in HIV-infected children; pediatric data about appropriate combinations (eg, with the protease inhibitors and the nonnucleoside reverse transcriptase inhibitors) and dosage regimens lag well behind the adult literature. The effectiveness of ribavirin in respiratory syncytial virus disease is uncertain. Preliminary data suggest that interferons may have a role in the management of chronic hepatitis B and C.
...
PMID:Advances in antiviral therapy. 908 51

Response to interferon-alpha (IFN-alpha) treatment in hepatitis C is poorer when cirrhosis is present. In the third Australian multicentre hepatitis C trial, Aushep-3, we examined the efficacy and tolerability of an intensive 24-week course of interferon-alpha 2a in Child-Pugh grade A patients with chronic hepatitis C and cirrhosis. This was an open uncontrolled trial of 4.5 million units (MU) of IFN-alpha 2a daily for 24 weeks; follow-up was 48 weeks. Chronic hepatitis C and cirrhosis were confirmed histologically. HCV RNA was determined in serum by reverse transcriptase polymerase chain reaction (PCR), and viral genotyping was by line-probe assay. Treatment response was defined as a reduction of alanine aminotransferase (ALT) to less than 1.5 times the upper limit of normal (and by at least 50% of pretreatment values) at weeks 20 and 24. Sustained response was defined as normal serum ALT after treatment from trial week 28 until week 48. Among the 56 patients, a treatment response occurred in 18 (32% by intention-to-treat; 42% of those who completed treatment) and eight (14%) had a sustained response. At 24 weeks, HCV RNA was not detectable in 12 of 17 treatment responders, and remained negative at 48 weeks in six of eight sustained responders. Treatment response by genotype occurred in 75% of patients with HCV type 2, in 38% with HCV type 3a and in 12% with HCV genotype 1. Sustained response occurred in only one (4%) patient with HCV genotype 1 but in five (20%) with genotypes 2 or 3a. Among 13 patients withdrawn, nine were for adverse effects, most often haematological; 10 others underwent dose reduction for adverse effects. It is concluded that a sustained biochemical and viral response to treatment with IFN-alpha 2a can be obtained in some patients with hepatitis C and cirrhosis, particularly those with genotypes 2 or 3a. Therefore, patients with cirrhosis should be considered for interferon treatment on an individual basis. Genotyping may improve case selection, but vigilance is required for haematological complications.
...
PMID:Efficacy and tolerance of a 6-month treatment course of daily interferon-alpha 2a for chronic hepatitis C with cirrhosis. The Australian Hepatitis C Study Group. 931 Sep 30

Hepatitis C virus (HCV) has been recognized as the cause of thrombocytopenia occurring in patients with chronic hepatitis C, possibly through autoimmune mechanisms. A patient is described with B cell chronic lymphocytic leukaemia, presenting with a marked leuko-thrombocytopenia and an associated mild haemolysis secondary to HCV infection, in the absence of clinical and biochemical signs of hepatitis. Anti-HCV antibodies were detected in the serum both by ELISA and RIBA but not 2 months before the onset of cytopenia. The presence of HCV RNA was documented both in the peripheral blood mononuclear cells and in the bone marrow by reverse transcriptase polymerase chain reaction of the 5' untranslated region of the viral genome. Of interest, HCV RNA was also found in the serum, showing that viraemia was associated with the presence of circulating anti-HCV antibodies. HCV genotyping, performed by PCR amplification of the core region, revealed the presence of an unclassifiable genotype. The hypothetical mechanisms leading to HCV-induced cytopenia in this patient are briefly discussed. Treatment with corticosteroids was effective in controlling blood cell counts, without increasing viraemia and deterioration of liver disease. HCV infection should be considered in the differential diagnosis of possible causes of cytopenia, mainly in immunosuppressed patients, even in absence of clinical and biochemical signs of hepatitis.
...
PMID:Hepatitis C virus-induced leuko-thrombocytopenia and haemolysis. 933 31

Chronic hepatitis C infection (CH-C) accounts for a significant number of patients undergoing orthotopic liver transplantation (OLT). Recently, hepatitis C virus (HCV) genotype-dependent differences in disease outcome and therapeutic responses have been suggested. The objectives of our study were to determine (1) the recurrence of HCV infection after OLT; (2) distribution of HCV genotypes in patients with CH-C who required liver transplantation compared with those who did not; and (3) the 1-year transplantation outcome in patients infected with different hepatitis C genotypes. RNA was extracted from sera of 20 patients who underwent OLT for end-stage liver disease secondary to CH-C (group I) and 52 patients with CH-C who did not require OLT (group II). For viral RNA detection, reverse transcriptase and polymerase chain reaction (RT/PCR) of 5'UT region was performed on all OLT patients both before and after OLT. For genotyping, RT-PCR of the NS 5 region was performed, followed by automated sequencing of the amplification products. Nineteen OLT patients had viral RNA detected by PCR both before and after OLT. One patient had no RNA detected before OLT but became viremic after OLT. The prevalence of HCV genotype 1b was significantly higher in group I patients compared with group II (53% v 23% respectively, P = .01). Examination of outcome at 1 year after OLT showed that 9 of 10 patients with HCV genotype 1b had histological evidence of hepatitis compared with 4 of 9 patients with other genotypes (non-1b) (P = .06). However, the number of patients who had one or more episodes of rejection, underwent retransplantation, or died at 1 year after OLT were similar. Recurrence of HCV infection after OLT was shown in all studied patients. Hepatitis C genotype 1b is more prevalent in our patients who underwent transplantation compared with a group with chronic hepatitis C who did not require transplantation (P = .01). Patients infected with HCV genotype 1b may have a higher risk of histological hepatitis after transplantation.
...
PMID:Hepatitis C genotypes in liver transplant recipients: distribution and 1-year follow-up. 934 11


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---