Inhibitory effects of atropine, protamine, and their combination on hepatitis A virus replication in PLC/PRF/5 cells

Identification of Mulberrofuran as a potent inhibitor of hepatitis A virus 3Cpro and RdRP enzymes through structure-based virtual screening, dynamics simulation, and DFT studies

Hepatitis is a medical condition characterized by inflammation of the liver. It is commonly caused by the hepatitis viruses A, B, C, D, and E. Hepatitis A virus (HAV) is highly contagious and can spread from infected individuals, through contaminated food, blood, or can also be water-borne. As per the statistics of World Health Organization (WHO), HAV infects about 1.4 million individuals each year globally. In this research work, we have focused on identifying natural product-based potential inhibitors for the two major enzymes of HAV namely 3C proteinase (3Cpro) and RNA-directed RNA polymerase (RdRP). The enzyme 3Cpro plays an important role in proteolytic activity that promotes viral maturation and infectivity. RNA-directed RNA polymerase facilitate viral replication and transcription. Structure-based virtual screening was carried out using NPACT database that contains a collection of 1574 curated plant-derived natural compounds that are validated by experiments. The screening procedure identified the phytochemical Mulberrofuran W, which could bind to both the targets 3Cpro and RdRP. The phytochemical Mulberrofuran W also had better binding affinity compared to the control compounds atropine and pyridinyl ester, which are previously identified inhibitors of HAV 3Cpro and RdRP, respectively. The Mulberrofuran W bound 3Cpro and RdRP complexes were subjected to 200 ns molecular dynamics simulations and were found to be stable and interacting with the active site of the enzymes throughout the course of complex MD simulations. In addition to DFT, MMGBSA studies were also performed to validate the identified potential inhibitor further. The identified phytochemical Mulberrofuran W can be considered as a new potential drug candidate and could be taken up for experimental evaluation against HAV infection.

Cell Culture Systems and Drug Targets for Hepatitis A Virus Infection

Hepatitis A virus (HAV) infection is one of the major causes of acute hepatitis, and this infection occasionally causes acute liver failure. HAV infection is associated with HAV-contaminated food and water as well as sexual transmission among men who have sex with men. Although an HAV vaccine has been developed, outbreaks of hepatitis A and life-threatening severe HAV infections are still observed worldwide. Therefore, an improved HAV vaccine and anti-HAV drugs for severe hepatitis A should be developed. Here, we reviewed cell culture systems for HAV infection, and other issues. This review may help with improving the HAV vaccine and developing anti-HAV drugs.

Molecular biology and inhibitors of hepatitis A virus

Hepatitis A virus (HAV) is a faeco-orally transmitted picornavirus and is one of the main causes of acute hepatitis worldwide. An overview of the molecular biology of HAV is presented with an emphasis on recent findings. Immune evasion strategies and a possible correlation between HAV and atopy are discussed as well. Despite the availability of efficient vaccines, antiviral drugs targeting HAV are required to treat severe cases of fulminant hepatitis, contain outbreaks, and halt the potential spread of vaccine-escape variants. Additionally, such drugs could be used to shorten the period of illness and decrease associated economical costs. Several known inhibitors of HAV with various mechanisms of action will be discussed. Since none of these molecules is readily useable in the clinic and since the availability of an anti-HAV drug would be of clinical importance, increased efforts should be targeted toward discovery and development of such antivirals.

Rapid and convenient assays to assess potential inhibitory activity on in vitro hepatitis A replication

Three different antiviral assays were developed for the in vitro screening of inhibitors of the hepatitis A virus (HAV) of which (i) a cytopathic effect reduction assay suitable for medium-to-high-throughput screening and (ii) two virus yield reduction assays (based on quantification of viral RNA) for genotypes IB and IIIA. The assays were validated for antiviral studies with interferon-alpha (IFNα) and amantadine HCl, two known inhibitors of HAV replication. IFNα effectively inhibited HAV replication, whereas the activity of amantadine HCl appeared to be strain-dependent. Employing these assays, we assessed the effect of the known enterovirus inhibitors pleconaril, rupintrivir and enviroxime on HAV replication. Pleconaril exhibited some very moderate activity, the effect of rupintrivir proved to be strain-dependent. Enviroxime did not inhibit HAV replication, suggesting that phosphatidylinositol-4-kinase IIIβ is not crucial in the HAV life cycle.

Antiviral activity of recombinant interferon-alpha on hepatitis A virus replication in human liver cells

Human recombinant interferon-alpha (IFN-alpha) was assayed for its antiviral effect on hepatitis A virus (HAV) replication in the human hepatoma cell line PLC/PRF/5. IFN-alpha resulted in concentration-dependent reduction of HAV antigen expression and HAV replication. IFN-alpha had a prophylactic effect, but was still effective when it was added after the infection, even at the end of the first replication cycle. An important increase in 2',5'-oligoadenylate synthetase activity in the IFN-treated human liver cells was observed. The antiviral effect of IFN-alpha could be attributed to the induction of this enzyme. Moreover we have shown that IFN-alpha and glycyrrhizin were synergistic in their antiviral actions against HAV. IFN-alpha emerged, from the present study, as a promising candidate for chemotherapy of severe forms of hepatitis A.

Studies on mechanism of action of glycyrrhizin against hepatitis A virus replication in vitro

Glycyrrhizin (GL) achieved a concentration-dependent inhibition of the replication of hepatitis A virus (HAV) in PLC/PRF/5 cells. GL has been shown to inhibit an early stage of the HAV replication. GL was not virucidal and had no measurable effect on the adsorption of [3H]uridine-labelled virions to cells. GL inhibited HAV penetration of the plasma membrane as measured by the amount of infective virus no longer neutralizable by specific antibody over time.

Antiviral activity of carrageenan on hepatitis A virus replication in cell culture

Sulphated polysaccharides such as iota-, lambda- and kappa-carrageenans showed a potent inhibitory effect on the replication of hepatitis A virus (HAV) in the human hepatoma cell line PLC/PRF/5. No cytotoxic effects were detected with concentrations of carrageenans up to 200 micrograms/ml. The selectivity indices of these substances, calculated as the ratio of the dose that reduced the number of viable cells to 50% (CD50) to the effective dose that inhibited 50% of viral antigen expression (ED50), were greater than 400 with iota-carrageenan, greater than 222 with lambda-carrageenan and greater than 10 with kappa-carrageenan. The selectivity index of ribavirin (reference substance) was only 5. The 3 types of carrageenans resulted in concentration-dependent reduction of HAV-antigen expression and HAV infectivity. lota-and lambda-carrageenan emerged, from the present study, as promising candidates for chemotherapy of acute hepatitis A.