PLANTS AGAINST CORONAVIRUS

POST BY: Shilpa Shantharam

Humans have always relayed on plants for numerous reasons. Plants have excessive application in human life whether alive or dead. Killing plants gives us firewood, timber etc., whereas growing a plant provides us with food, medicine. The knowledge of the application of plants to acquire food and medicine is gained by trial and error process, thus gathered information is gradually transmitted from generations to generation with further improvisation by new experiments. Worldwide more than one-tenth of plant species are used in drugs and health products, with more than 50,000 species being used. Many pharmaceutical products are derived from plants, the branch dealing with studies on medicinal drugs obtained from plants or other natural sources is called Pharmacognosy. Till date, plants has been useful in providing many of the successful drugs which includes aspirin, caffeine, morphine etc.

Different reagents derived from different plants are tested for its antiviral properties against the novel coronavirus. This study involves various steps, first of all, it includes the selection of the compounds and its derivation from plants, then the chemicals obtained will be grouped into potential compounds by use of a method known as MOLECULAR DOCKING(it’s a kind of bioinformatic modelling which involves the interaction of two or more molecules to give a stable product, depending on the binding properties of Ligand and target).  A similar study was made on 67 compounds acquired from natural origin had shown signs of antiviral properties against novel coronavirus. Among them Corcin (a compound  from Crocus sativus L), Digitoxigenin (a compound from Nerium oleander) and β-Eudesmol (a compound from Lauris Nobilis L) have been suggested as the inhibitor of SARS-coV-2. Many Chinese herbal extracts were studied to find its antiviral properties against SARS-CoV-2. Four of the extracts Lycoris Radiata, Artemisia Annua, Pyrrosia Lingua and  Lindera aggregata showed effects on the virus, Among them, extract from Lycoris Radiata was essentially potent, further studies on the extract lead to the identification of lycorine as the material with virus inhibiting properties.

Some other extracts are:

•   The extracts from Canavalia ensiformis (jack beans) known as concanavalin A (con A) was able to bind to glycosylated membrane proteins (which aids the virus to recognize the host cell) of hemagglutinating encephalomyelitis. As the binding sites were not empty the virus lost its property to identify the host cell.
•  Bromelain an enzyme present in pineapple  could reduce the viability of coronavirus obtained from pigs.
•  A research published by Lau and team shows that the aqueous extract of Houttuynia cordata inhibits two key proteins of SARS-CoV i.e, chymotrypsin-like proteases and RdRp ( RNA dependent RNA polymerase).
• Another aqueous leaf extract from Toona sinensis inhibited SRAS-coV replication.
• According to research by Yu and team the flavonoids myricetin and scutellarein exert SARS-CoV 3CL^pro inhibitory effect.        
• Tannic acid, 3‐isotheaflavin‐3‐gallate, and theaflavin‐3,3′‐digallate, three phenolic compounds from black tea exerted inhibitory effects on SARS‐CoV 3CL ^pro
• broussochalcone B, broussochalcone A, 4‐hydroxyisolonchocarpin, papyriflavonol A, 3′‐(3‐methyl but‐2‐enyl)‐3′,4,7‐trihydroxyflavane, kazinol A, kazinol B, broussoflavan A, kazinol F, and kazinol J isolated from Broussonetia papyrifera inhibited both SARS‐CoV 3CL^pro
• Two alkaloids isolated from Tylophora indica inhibited N and S protein activity as well as viral replication of enteropathogenic coronavirus transmissible gastroenteritis virus
• lycorine, emetine and mycophenolate mofetil were seen to act against HCoV‐OC43, HCoV‐NL63, MERS‐CoV, and MHV‐A59
• The natural compounds, procyanidin A2, procyanidin B1, and cinnamtannin B1, isolated from Cinnamomi cortex inhibited SARS‐CoV infection
• Plant lectins are carbohydrate-binding proteins capable of specific recognition and reversible binding. The plant lectins possessed marked antiviral properties against coronaviruses.

Use of Biotechnology:

Plants derived products can be used as either a diagnostic reagent or as a source of vaccination. Diagnostic reagents help in detection of the virus, this process falls into two streams: 1. based on detection of virus genomic RNA;  2. based on detection of virus proteins. A group of researchers from John Innes Centre is trying to develop a diagnostic reagent for the detection of the virus with the help of virus-like particles(VLP’S) derived from cowpea mosaic virus(virus infecting cowpea leaf). Vlp’s are molecules that closely resemble the viruses but do not tend to be infectious as they lack viral genomic material. The researchers are successful in packaging artificial RNA containing all of the SARS-CoV-2 genome regions, these will be produced and assembled in plants.

Structural proteins of the virus

Detection of virus proteins includes identification of corresponding antibodies, The virus has four structural proteins known as envelope, membrane, nucleocapsid, spike. Among these, spike protein is very important in antibody identification as it provides an active site for the binding of the virus to the host cell. Thus identified antibody can be manufactured by MOLECULAR FARMING(technology using plants to produce quantities of pharmaceutical substances). A conventional method of vaccine production by making use of weak attenuated strains of the virus may not be successful all the times. Instead, production of subunit vaccines and then merging them is more productive i.e, producing vaccine separately against every infectious feature of the virus and then combining them into one. Blocking the entry of the viral particle is the most effective strategy to fight against the viruses, hence many types of research have been held on tackling the spike protein. The discovered subunits can be produced in large scale using plants. 

REFERENCE:

1. https://onlinelibrary.wiley.com

2. https://www.cell.com

3."Medicinal plants: Past history and future perspective" by Fatemeh Jamshidi-Kia1, Zahra Lorigooini1*, Hossein Amini-Khoei1