1. INTRODUCTION:
Nidovirales is the order from which the family of coronaviridae are classified they are further subdivided into four genera namely, α, β, γ and δ. The virus SARS-CoV-2 which has caused global pandemic and havoc is of the β genera of the coronaviridae family, which has four protein constructs where its frame is made of Nucleocapsid protein (N) which encompasses the single stranded viral RNA (ssRNA), Membrane protein (M), Envelope protein (E) and spike protein (S) 1. These proteins are replicated and multiple copies of the virus are produced within the human cell as per the well-known mechanism as described: The spike protein of the SARS-CoV-2 virus attaches to the Angiotensin Converting Enzyme-2 (ACE-2) and with host factors as Cell Surface Serine Protease (TMPRSS-2) and enters the cell resulting in the release of the viral contents to the cell cytoplasm in which the viral ssRNA is spontaneously translated as individual non- structural proteins which act as regulatory proteins along with protective vesicles which contain genomic RNA and subgenomic mRNA for viral replication and transcription. And the resultant structural proteins move towards the endoplasmic reticulum which in-turn produces newly replicated viral genomic RNA and the viral structural construct when transporting through the Endoplasmic Reticulum to Golgi Intermediate Compartment (ERGIC) and the newly made viral constructs are released out of the cell via exocytosis2. SARS-CoV-2 infection causes COVID-19 which is an upper respiratory infection emerged from Wuhan, China also it spread as a pandemic leading to more than 208 million cases, 4.3 million deaths and 186 million recoveries worldwide 3.
The production of more number of viral particles then results in the increased infection and lysis of the alveolar epithelial cells, Type I and II pneumocytes following cytokine storm and inflammatory reaction in the lungs thereby leading to Acute Respiratory Distress Syndrome (ARDS). The recoveries from COVID- 19 were made possible through treatment of symptoms, repurposing drugs, convalescent plasma therapy, and artificial oxygen supply to the patients. SARS-CoV-2 mainly causes damage in the lungs due to high concentration of ACE-2 receptors and presents drastic effects in the advanced stages of the disease progression as shock, ARDS, hypoxemia, coagulation defects, encephalopathy, acute kidney injury and heart failure resulting to the death of the affected person. The patients with symptoms are diagnosed with Reverse Transcriptase Polymerase Chain Reaction (RT-PCR), Basic blood work, Chest X ray, High Resolution Computer Tomography Chest, Serology and classified into five groups based on their severity of infection which are: Asymptomatic or Pre-symptomatic infection, Mild infection, Moderate infection, severe infection and Critical infection 4.
Treatments proposed according to the infection rate are: Mild infection the treatment for the symptoms is given and for Moderate infection treatment of symptoms is given individually or along with antibacterial medication only if a bacterial infection can be seen. For treatment with severe infection and critical infection the supplemental oxygen or non-invasive ventilation along with treatment of symptoms and interleukin 6 blockers (IL-6 Blockers), Ivermetcin, Hydroxychloroquine, Lopinavir or Ritonavir, Remdesivir and systemic corticosteroids are given according to the systemic evaluation or national health guidelines. However, these drugs are advised to be used with extreme caution as it may cause severe side effects and permanent damage the major organs such as kidney, liver and heart 5.
Due to these reasons natural product scientists have turned to nature for assistance to eradicate this dreadful disease. Natural products can have potential therapeutic use for the emerging diseases and also enable to eliminate them, it has been reported that 234 drugs for various diseases have been isolated and were approved from natural products for treating various diseases during the timeline of 1981 to 2014. About antiviral 64 small molecules and 138 antiviral drugs have been approved from the same time period 6. Mushrooms belong to the separate Kingdom of Fungi and Phylum Basidiomycota. They are also an excellent source of natural products and antivirals which expresses antiviral activity in both enveloped and non-enveloped RNA viruses by mechanisms which can prohibit the attachment and entry, replication, assembly and release of the same. Such antiviral activity is possible through compounds which are in different forms of like analogues, derivatives, fraction or direct polysaccharides, triterpenoids, proteoglycan, proteins, lectins, polyphenols and enzymes7. A recent study involving in silico approach for Main Protease (MPro) inhibition through 36 compounds with edible and medicinal mushrooms with anti-HIV activity 8 but they fail to investigate and recognize compounds with wide antiviral activity especially in the light of compounds which prohibit or totally eradicate the upper respiratory viruses, they are only single targeted and they are not validated by molecular dynamics which predicts the stability of the docked molecule.
In this study our focus is on edible mushrooms which accessible in super markets such as Lentinula edodes , Agaricus bisporus ,Pleutorus ostreatus and Hericium erinaceus . And we target their main compounds such as Eritadenine, Gallic acid, Pleuran and Ergosterol peroxide, these main compounds were chosen especially due to their ability to inhibit upper respiratory infections which are specifically caused by viruses from known existing literature. According to the literature, Eritadenine is a main compound of L. edodesand has been synthesized synthetically and was found to have antiviral activity against Poxviruses, Paramyxovirus, Rhabdovirus and Reovirus9, 10. A. bisporus has Gallic acid as its main component was reported to have activity against early viral entry of hepatitis C, Herpes Simplex Virus-1 (HSV-1), Human Immunodeficiency Virus-1 (HIV-1) and Influenza-A virus 11. Pleuran a main compound of P. ostreatus was studied to have activity against Influenza –A virus, provided cellular immune response and respiratory tract infections in athletes 12, 13, 14. Ergosterol Peroxide a main component from H. erinaceus was examined to have antiviral activity against porcine delta coronavirus and other upper respiratory infections 15, 16, 17.
Due to these molecules has such antiviral activities, we target them against the Main Protease (Mpro) and the spike protein (S) of the SARS-CoV-2 virus in order to inhibit these targets and prohibit the entry and replication of the virus within the cell by using molecular docking tools and molecular dynamics simulation studies. We have also undertaken studies to assess the target accuracy and pharmacokinetic parameters by in silico analysis and compare them to the existing antivirals proposed against the SARS-CoV-2 with the targets mentioned in the literature.