Current and future therapies for hepatitis C virus infection: from viral proteins to host targets

Hepatitis C virus (HCV) infection is the most important problem across the world. It causes acute and chronic liver infection. Different approaches are in use to inhibit HCV infection, including small organic compounds, siRNA, shRNA and peptide inhibitors. This review article summarizes the current and future therapies for HCV infection. PubMed and Google Scholar were searched for articles published in English to give an insight into the current inhibitors against this life-threatening virus. HCV NS3/4A protease inhibitors and nucleoside/nucleotide inhibitors of NS5B polymerase are presently in the most progressive stage of clinical development, but they are linked with the development of resistance and viral breakthrough. Boceprevir and telaprevir are the two most important protease inhibitors that have been approved recently for the treatment of HCV infection. These two drugs are now the part of standard-of-care treatment (SOC). There are also many other drugs in phase III of clinical development. When exploring the various host-cell-targeting compounds, the most hopeful results have been demonstrated by cyclophilin inhibitors. The current SOC treatment of HCV infection is Peg-interferon, ribavirin and protease inhibitors (boceprevir or telaprevir). The future treatment of this life-threatening disease must involve combinations of therapies hitting multiple targets of HCV and host factors. It is strongly expected that the near future, treatment of HCV infection will be a combination of direct-acting agents (DAA) without the involvement of interferon to eliminate its side effects.     

The potential of RNA interference-based therapies for viral infections

RNA interference (RNAi) is a natural mechanism in cells that suppresses or silences the expression of aberrant or foreign genes. This activity is being developed as a potential antiviral therapeutic strategy. Studies in vitro, and some in vivo, appear to show the feasibility of using RNAi to treat virus infection. Therapeutic use of RNAi seems to be promising when directed against viruses that cause localized acute infections in accessible target cells. Therapeutic strategies using RNAi against viruses that cause chronic infections, such as HIV, hepatitis B virus, or hepatitis C virus, are more difficult to design, but studies have begun to address identifiable problems. Two clinical trials using RNAi have recently been initiated—one phase II trial against respiratory syncytial virus and a phase I trial against HIV. It will be of much interest to see whether nucleic acid therapies can offer another route to treating viral infection.     

Differential diagnosis of viral hepatitis based on hepatitis viral markers

192 patients of acute viral hepatitis (AVH) from three different hospitals of Madras metropolitan area during November 1985 to January 1986 were investigated for serologic markers of hepatitis A virus (anti HAVIgM) and hepatitis B virus (HBsAg, HBeAg, anti HBcIgM and anti HBs) by Enzyme linked immunosorbent assay (ELISA). While the overall pattern of AVH in Madras as revealed from the study showed Hepatitis A to be 36.4%, Hepatitis B 34.4% and Non-A Non-B 29.1%, the pattern differed significantly when areawise categorisation was done. The major AVH type in Government General Hospital was Hepatitis B (48.9%). While it was hepatitis A (46.9%) in Government Stanley Hospital and Non-A Non-B (40.0%) in Military Hospital. Using anti HBcIgM marker of Hepatitis B Virus and anti HAVIgM it was possible to make out that 13.5% of the cases, currently suffering from hepatitis A were either HBV carriers (8.3%) or cases convalescing from a previous Hepatitis B attack (5.3%). Various combinations of HBV markers positivity were observed and their diagnostic significance inferred.     

Immunopathogenesis of viral hepatitis

Conclusion It is clear from the aforementioned that hepatitis viruses causing persistent infection have developed different strategies to survive host’s immune pressure. Although very little is known on the pathogenetic mechanisms of HDV infection, a large amount of information is now available for its helper virus HBV. However, because of the difficulties in identifying acute cases evolving into chronic infection, it is impossible at this stage to identify specific immunological features associated with transition to chronic liver disease. Clinical recovery from acute hepatitis B would be the result of a complex interplay between host and viral factors. The former include efficient CD8 and CD4 responses specific for a variety of viral proteins; indeed, polyclonal and multispecific cell-mediated responses appear to be crucial for “viral clearance” as we use to define recovery from acute HBV infection.     

Treatment of viral hepatitis

The primary goals of treatment for viral hepatitis are to eradicate the infection early in the course of the disease, to prevent progression to end-stage liver disease, and to prevent the development of hepatocellular carcinoma. The secondary goal is to decrease the number of chronic carriers who serve as a reservoir for viral transmission. The major step in the management of hepatitis B was the introduction of successful vaccination. The treatment of hepatitis B includes nucleoside analogues (lamivudine and adefovir) and interferon. The major problem in lamivudine treatment is the development of resistant viral mutants. Hepatitis D can worsen hepatitis B and lead to progressive liver disease. The recommended treatment is interferon. Hepatitis C, due to the lack of vaccine and tendency to develop chronic liver disease, is the major health problem and the leading indication for liver transplantation today. The recommended treatment is the combination of pegylated interferon and ribavirin.     

Gene replacement therapies for duchenne muscular dystrophy using adeno-associated viral vectors

The muscular dystrophies collectively represent a major health challenge, as few significant treatment options currently exist for any of these disorders. Recent years have witnessed a proliferation of novel approaches to therapy, spanning increased testing of existing and new pharmaceuticals, DNA delivery (both anti-sense oligonucleotides and plasmid DNA), gene therapies and stem cell technologies. While none of these has reached the point of being used in clinical practice, all show promise for being able to impact different types of muscular dystrophies. Our group has focused on developing direct gene replacement strategies to treat recessively inherited forms of muscular dystrophy, particularly Duchenne and Becker muscular dystrophy (DMD/BMD). Both forms of dystrophy are caused by mutations in the dystrophin gene and all cases can in theory be treated by gene replacement using synthetic forms of the dystrophin gene. The major challenges for success of this approach are the development of a suitable gene delivery shuttle, generating a suitable gene expression cassette able to be carried by such a shuttle, and achieving safe and effective delivery without elicitation of a destructive immune response. This review summarizes the current state of the art in terms of using adeno-associated viral vectors to deliver synthetic dystrophin genes for the purpose of developing gene therapy for DMD.     

Microfluidic platform for hepatitis B viral replication study

Hepatocytes, the cells responsible for the metabolic and detoxification processes in the liver, are the predominant target of hepatitis B virus (HBV) infections, a major cause of liver cancer. The limited availability of normal human hepatocytes for cell-culture based studies is a significant challenge in HBV-associated liver cancer research. Therefore, there is a need for miniaturized cell-culture systems that can serve as a platform for studying the effect of HBV infections on hepatocyte physiology. Here, we present a microfluidic platform that can be used to study HBV replication in both rat and human hepatocytes. Polydimethylsiloxane (PDMS) microchannels fabricated using soft lithography techniques served as a culture vessel for both primary rat hepatocytes (PRH) and a human hepatoblastoma cell line, HepG2. The micro cell-culture chamber was then used as a model for HBV replication studies. Cells were grown in static culture conditions and either transfected with an HBV-genome cDNA or infected with the viral genome expressed from a recombinant adenovirus. Supernatants collected from the microchannels were assayed for secreted HBV using polymerase chain reaction (PCR). We achieved approximately 40 and 10% transfection efficiencies in HepG2 cells and PRH respectively, and 80–100% adenoviral infection efficiency in PRH comparable to standard tissue culture methods. Moreover, we successfully detected replicated HBV using our novel platform. This platform can be easily extended to studies involving DNA transfection or HBV infection of primary human hepatocytes since only a small number of cells are required for studies in microfluidic chambers.     

Changing indications for liver biopsy: viral hepatitis

Liver biopsy has been an integral part of the management of patients with chronic viral hepatitis. However, several developments have reduced the need for liver biopsy in these patients. Serum based and radiologic non-invasive methods of assessing fibrosis can distinguish between limited and advanced fibrosis and diagnose cirrhosis in these patients. In chronic active hepatitis B infection, antiviral therapy can often be initiated without a liver biopsy as the benefit of treatment extends across all stages of fibrosis. However, the difficulty of determining disease activity and fibrosis by serologic and biochemical data in chronic hepatitis B makes liver biopsy an important tool in the management of a subset of patients. The remarkable progress that has been made in the treatment of hepatitis C is poised to make liver biopsy unnecessary in a large number of patients who previously were treated based on the stage of disease as determined by biopsy. Together, these trends are altering the landscape of liver biopsy in chronic viral hepatitis.     

Developments in viral hepatitis.

Viral hepatitis is a major public health problem occurring endemically in all parts of the world. The general term viral hepatitis refers to infections caused by hepatitis virus type A, type B and a more recently identified infection referred to as "non-A: non-B" hepatitis. These clinically and pathologically similar forms of hepatitis have been studied intensively following the discovery of a specific antigen, Australia antigen, one of the markers of infection with hepatitis B virus.     

Autoimmune manifestations in viral hepatitis

Infections by the viruses responsible for hepatitis B, C and D are accompanied by a number of immunopathological manifestations. A link between infection and autoimmunity is particularly well documented for the hepatitis C virus. Immunopathological manifestations range from production of autoantibodies to overt autoimmune disease, including thyroiditis and autoimmune hepatitis, and to immune-complex-mediated disorders, including cryoglobulinaemia, glomerulonephritis and vasculitis. Several of these manifestations improve with successful antiviral treatment, directly incriminating the virus in their pathogenesis. Mechanisms considered responsible for hepatitis virus-related immunopathology, including molecular mimicry, impairment of regulatory T cells and activation of B lymphocytes, will be examined in this review.     

Recurrences of viral hepatitis A

The aim of the study was to examine the frequency, severity, persistence and etiology of relapses occurring during the hepatitis A viral infection. Therefore, a prospective study of 910 patients suffering from hepatitis A (HA) was carried out. The clinical examination and determination of glutamyl pyruvic transaminase (GPT) in the serum every 7-14 days till recovery (usually during 6--8 months) were performed. HAV infection was confirmed by detecting anti-HAV IgM in the blood of all the examined by radioimmunoassay. In 876 (93.3%) patients HA had typical clinical features and a monophasic course. All cases made a rapid clinical recovery and liver function tests improved strikingly between 1 and 4 months after the onset of illness. However, in 34 (3.7%) of 910 patients, after an asymptomatic interval of 4--8 weeks, relapsing hepatitis occurred. Mild clinical symptoms: fatigue, myalgia, nausea, epigastric discomfort accompanied by the elevated levels of GPT in the serum were noticed in 11 patients, while 3 of them redeveloped jaundice. In 23 remaining patients relapses of hepatitis were asymptomatic, except for the reappearance of icterus in six cases. The only way to establish the exacerbation of the disease was through the pathological findings of GPT in the serum, which increased 10--60 times above the upper limit of the normal value. While 25 patients had one relapse, in 9 there were two or more relapses, so that hepatitis had a biphasic or polyphasic course. The second relapse was registered 3--6 weeks after the first one disappeared. Through biochemical tests the average values of the GPT were established: 1566 U/L in the acute stage, 107 U/L during the early stage of convalescence and 1016 U/L during the first relapse of hepatitis. After the first relapse and during remission, in 9 patients the average values of GPT in the serum were 84 U/L, while during the second relapse 518 U/L. Clinical signs of relapsing hepatitis disappeared approximately in 4 days, but liver function tests decreased slowly and persisted elevated between 5 and 12 months. A possibility of establishing the etiology of relapsing hepatitis, which has yet remained unknown, is discussed. Anti-HAV IgM were present in all 34 patients during the initial and relapsing phase of hepatitis and in 26 cases in the latter phase of convalescence between 9 and 11 months after the beginning of the disease. Serological tests excluded infection with hepatitis B, cytomegalovirus and Epstein-Barr virus. With a great probability other infections and toxic agents damaging the liver could have been excluded.(ABSTRACT TRUNCATED AT 400 WORDS)