Sequence analysis of hepatitis GB virus C (GBV-C) isolates from 14 patients

Bayesian coalescent analysis reveals a high rate of molecular evolution in GB virus C

GB virus C/hepatitis G (GBV-C) is an RNA virus of the family Flaviviridae. Despite replicating with an RNA-dependent RNA polymerase, some previous estimates of rates of evolutionary change in GBV-C suggest that it fixes mutations at the anomalously low rate of approximately 10(-7) nucleotide substitution per site, per year. However, these estimates were largely based on the assumption that GBV-C and its close relative GBV-A (New World monkey GB viruses) codiverged with their primate hosts over millions of years. Herein, we estimated the substitution rate of GBV-C using the largest set of dated GBV-C isolates compiled to date and a Bayesian coalescent approach that utilizes the year of sampling and so is independent of the assumption of codivergence. This revealed a rate of evolutionary change approximately four orders of magnitude higher than that estimated previously, in the range of 10(-2) to 10(-3) sub/site/year, and hence in line with those previously determined for RNA viruses in general and the Flaviviridae in particular. In addition, we tested the assumption of host-virus codivergence in GBV-A by performing a reconciliation analysis of host and virus phylogenies. Strikingly, we found no statistical evidence for host-virus codivergence in GBV-A, indicating that substitution rates in the GB viruses should not be estimated from host divergence times.

GB virus C/hepatitis G virus replicates in human haematopoietic cells and vascular endothelial cells

A novel flavivirus, GB virus C (GBV-C)/hepatitis G virus (HGV), has been detected in chronic liver disease patients. It is known that the viral RNA can be detected in ∼5% of American blood donors. However, the implications for liver disease and the sites of virus replication remain unknown. Possible sites of virus replication were studied by using cell lines and/or primary cells derived from human lymphoid cells, myeloid cells, hepatocytes and endothelial cells. RNA was detected by virus strand-specific RT–PCR and GBV-C/HGV antigen was detected with a rabbit polyclonal anti-E2 (envelope 2) antibody by Western blot analysis. Negative-strand RNA, representative of replicating virus, was detected in lymphoid and megakaryocytoid cell lines and primary vascular endothelial cells. In addition, an increase in virus titre over time was demonstrated and viral antigen was detected, and virus could be passaged to infect fresh cells. However, viral RNA or antigen could not be detected in any of the hepatocyte lines tested. These results indicate that the replication site of GBV-C/HGV is not primarily in hepatocytes and that detection of replicating virus in hepatic tissue may reflect virus replication in haematopoietic cells and/or vascular endothelial cells present in the liver.

Hepatotropism of GB virus C (GBV-C): GBV-C replication in human hepatocytes and cells of human hepatoma cell lines

BACKGROUND/AIMS

Recently, GB virus C (GBV-C) has been identified as another virus potentially causing viral hepatitis. However, its hepatotropism and pattern of infection in humans is still unknown. To elucidate the presence and replication of GBV-C in the human liver, we investigated tissue samples of six explanted livers from five GBV-C mono- or GBV-C/HCV co-infected patients for GBV-C RNA plus- and minus-strand RNA.

METHODS

These tissues were examined using nested RT-PCR followed by Southern blot hybridization as well as fluorescence in situ hybridization on liver cryosections. To further substantiate susceptibility of liver cells for GBV-C, in vitro infection of human hepatoma cells (HuH7, HepG2) with GBV-C mono-infected serum was performed.

RESULTS

By reverse transcription followed by nested PCR (RT-PCR), 5 of 6 liver specimens (4/5 patients) were positive for GBV-C plus-strand RNA, and viral minus-strand RNA could be detected in 4 of 6 liver specimens (4/5 patients). One liver sample was negative for GBV-C RNA. In two specimens we could identify GBV-C infection by in situ hybridization. Virus infection appeared to be restricted to hepatocytes and detection of minus-strand RNA showed viral replication in a few highly infected liver cells. In vitro infection of HepG2 or HuH7 cells confirmed these findings by a release of virions into supernatant.

CONCLUSION

In conclusion, our results establish GBV-C as a hepatotropic virus infecting human cells of hepatic origin in vivo and in vitro.

Clinical relevance of hepatitis G virus (HGV) infection in heart transplant patients

To investigate whether the recently discovered hepatitis G virus (HGV) influences the clinical outcome of heart transplant recipients under immunosuppression, we determined the prevalence of HGV infections correlated with liver function and survival in 51 patients. Presence of HGV RNA and anti-E2, a marker for resolved HGV infection, were serially tested in sera from patients before and after heart transplantation (HTX) by nested RT-PCR and ELISA. Four of 51 (7.8%) patients before transplantation, and 22 of 50 patients (44%) after transplantation showed signs of persistent or resolved HGV infection. HGV infection was not associated with impairment of liver function or with patient survival. In summary, presence of HGV infection does not influence the clinical outcome in heart transplant patients.

The distribution of HBV, HCV and HGV among livers with fulminant hepatic failure of different aetiology

BACKGROUND/AIMS

The aim of the study was to assess the impact factor of HCV and HGV in fulminant hepatic failure.

METHODS

The 5'-untranslated regions of HCV RNA and HGV RNA and a segment of the core antigen sequence of HBV were amplified after extracting the nucleic acids from snap-frozen tissue aliquots from explanted livers of 26 consecutive patients undergoing orthotopic liver transplantation for fulminant hepatic failure preoperatively diagnosed as either autoimmune (n=2), HAV/HBV (n=8), toxic (n=4) or aetiologically unknown (n=12).

RESULTS

HCV RNA was detected in five of 26 (19.2%) livers with fulminant hepatic failure. All five HCV RNA-positive livers belonged to the group of non-toxic, non-autoimmune liver failure (n=20), three of them were found in the group of liver failure with unknown aetiology (n=12) and two in the group of HBV-associated liver failure (n=7), making an HCV incidence of 25%, 25% and 28.6%, in the different groups, respectively. HGV RNA was detected in 10 of 17 (58.8%) explants and in all four groups of fulminant hepatic failure as defined preoperatively. HBV DNA was identified in six livers of 26 patients (23.1%) with fulminant hepatic failure. Neither HCV RNA nor HBV DNA was detected in the livers of patients with toxic or autoimmune fulminant hepatic failure.

CONCLUSIONS

These results indicate that HBV and HCV, but not HGV, play an aetiologic role in fulminant hepatic failure. HCV-positive cases were concentrated either in the group of otherwise unexplained fulminant hepatic failure or in the group of HBV fulminant hepatic failure. HGV-positive cases, on the other hand, were found within all four preoperatively defined groups, indicating a role as cofactor rather than as single aetiologic agent.

Hepatitis G virus in multitransfused thalassaemics from India

Hepatitis G virus (HGV)/GB virus-C (GBV-C) has been identified as a blood-borne agent with disputed pathogenicity. This virus belongs to the flaviviridae with a distant relationship to hepatitis C virus (HCV). Genetically divergent HGV isolates have been reported from different parts of the world. This study describes the prevalence of HGV in multitransfused thalassaemic children in India and genomic sequence variations in 11 HGV isolates from the same geographical location. Hepatitis G virus RNA was detected in 39.7% multitransfused thalassaemic children. The seroprevalence of hepatitis B virus (HBV) and HCV was 23.8% and 17.1%, respectively, and 11.4% had dual infection. The nucleotide sequence of a 166 bp HGV genomic segment from the putative capsid-envelope region (nucleotide; nt 578-743) from 11 Indian isolates was compared to the sequences available in the nucleotide databases. The isolates from India were 81.3-94.5% homologous to the isolates from other parts of the world. On phylogenetic analysis, it was observed that HGV isolates from India may belong to two genetically divergent types.

Establishment of a highly specific detection system for GB virus C (GBV-C) minus-strand RNA

Although the clinical relevance of GB virus C (GBV-C) is still elusive, this virus has been found with high prevalence in several groups of patients with liver disease. As was shown for hepatitis C virus (HCV), minus-strand RNA is supposed to function as a replicative intermediate. We have established a reliable and sensitive detection system for GBV-C minus-strand RNA based on nested RT-PCR (reverse transcription-polymerase chain reaction) with a tagged primer system. Sensitivity and specificity was extensively tested using in-vitro transcribed GBV-C sequences and genomic viral RNA. Specificity of the amplified fragments was proven by Southern blot hybridization. Using this detection system, we found the presence of GBV-C minus-strand RNA in 6/41 (14.6%) sera of GBV-C infected or GBV-C/HCV coinfected patients. No correlation with virological parameters such as amount of GBV-C plus-strand RNA, genotype or titer of HCV could be detected.

Incidence, prevalence, and clinical outcome of hepatitis GB-C virus infection in liver transplant patients

A novel RNA virus of the Flaviviridae family has been discovered recently and designated hepatitis GB-C virus (GBV-C). Previous studies have reported that GBV-C is associated with posttransfusion hepatitis, chronic viral hepatitis, and cryptogenic hepatitis. However, the clinical significance of GBV-C infection has been questioned increasingly in patients not undergoing transplantation. To investigate whether GBV-C infection under immunosuppression affects the clinical or the histological outcome in liver transplant recipients, we determined the prevalence and incidence of GBV-C infections and the clinical and histological signs in patients after orthotopic liver transplantation (OLT). The presence of GBV-C was tested in sera from patients before and in regular intervals up to 6 years after OLT by nested reverse transcription-polymerase chain reaction using primers derived from the NS3 region. A total of 72 patients were studied. Before OLT, 8 of 72 (11.1%) patients were positive for GBV-C. After OLT, 7 of 8 (87.5%) remained positive. Of 64 patients who were negative for GBV-C before OLT, 23 became positive after OLT, resulting in a de novo rate of GBV-C infection of 35.9%. We could not detect a higher rate of histologically proven hepatitis in GBV-C-positive patients (29.1%) than in GBV-C-negative patients (14.6%, P > 0.057). Comparing GBV-C-positive with GBV-C-negative liver transplant patients, we could not find any differences in age, gender, liver function tests, number of blood transfusions, histological degree of hepatitis, or number of rejection episodes. Survival was not negatively influenced by GBV-C positivity. In conclusion, the presence of GBV-C did not influence the clinical or histological outcome in liver transplant patients.

Expression and characterization of the hepatitis G virus helicase

The hepatitis G virus (HGV) is a new member of the Flaviviridae family and has a genomic organization similar to that of hepatitis C virus (HCV). Protein sequence motifs are present suggesting that HGV encodes a serine proteinase, an RNA-dependent RNA polymerase and a helicase. We have cloned and expressed the putative helicase of HGV and have shown that it contains a poly (U)-stimulated NTPase activity and is able to function as a DNA helicase. Preliminary characterization of the HGV helicase activity reveals similarities with other members of the Flaviviridae, but especially with HCV, raising the possibility that HGV could be used as a surrogate virus for the development of therapies against HCV.