In-vitro Antiviral Activity of Natural Products against Coronavirus Strains: A Systemic Review

Coronavirus is a non-segmented, positive-sense RNA genome belonging to the family coronaviridae in the order Nidovirales Corona viral infections have created serious threats in the last couple of decades and recently claiming the death of thousands of human beings. Natural products provide a valuable and powerful resource of chemical compounds alkaloids, tannins, caffeine, biopterin, actinophnine, etc. displaying antiviral properties. The data was reviewed from various databases or search engines: PubMed, Science Direct, MedLine, Google Scholar, and Biomed central for published articles. The data inclusion criteria was natural products and their isolated and different synthetic compounds. Data duplication and titles or contents that do not meet the inclusion criteria and Reports on antiviral activities of natural products or their derivatives against other than CoV strains were excluded. We encountered 49 plants and 19 compound chemically dened natural molecules reported in the literature, which have evaluated for potent antiviral activity against different coronavirus strains. The listed plants and their compounds in this review are highly potent with promising results against coronavirus. These can be further screened for invasive tests and used for making different formulations or may be polyherbal formulations considering its safety prole and toxicity. most potent IC50 value activity against plaque formation (IC50=1.75) and for virus attachment (4.67µg/ml) in host cells infected with HCoV-NL63 strain of the virus. Torilis fructus, Acanthopancis cortex showed the highest value for reducing intracellular viral mRNA by 93% and 90%, respectively. Euphoria nerifolia was showed >100% cell survival through inhibition of virus activity against coronavirus when compared with standard. and Isobavachalcole against 3CL pro-MERS CoV with IC50 (35.8µm) gallate 3CL CoV with IC50


Introduction
Coronavirus (diameters of approximately 125 nm) is a non-segmented, positive-sense RNA genome belonging to the family coronaviridae in the order Nidovirales [1,2]. The genome packed inside a helical capsid formed by the nucleocapsid protein (N) and further surrounded by an envelope.
The viral envelope consists of four main structural proteins, i.e., spike protein (S) responsible for the formation of structure and attachment to the host receptor. The membrane protein (M) responsible for giving the virion its shape helping to bind to the nucleocapsid, envelope protein (E) responsible for assembly, and release of the virus, which are required for pathogenesis and nucleocapsid protein (N) responsible for replication [3][4][5].These four proteins are encoded within the 3' end of the viral genome. Some coronavirus also encodes an envelope-associated Hemagglutinin esterase protein that enhances spike protein to mediate cell entry and virus spread through the mucosa. Coronavirus can be classi ed into four genera, which are alpha, beta, gamma, and delta. Among them, alpha and beta infect mammals, whereas gamma infects avian species, and delta infects mammalian and avians both. The S-protein-receptor collaboration is the essential determinant for a coronavirus to contaminate a host animal category and oversees the infection's tissue tropism. Diverse coronaviruses use peptidases as their cell receptor. It is indistinct why peptidases are utilized, as passage happens even without the enzymatic area of these proteins. Numerous α-coronaviruses use aminopeptidase (APN) as their receptor, SARS-CoV and HCoV-NL63 use angiotensin-changing over enzyme 2 (ACE2) as their receptor, MHV enters through CEACAM1, and as of late recognized MERS-CoV ties to dipeptidyl-peptidase 4 (DPP4) to pick up section into the human cell [6][7][8][9][10].
The rst coronavirus was discovered in 1930 when the infectious bronchitis virus caused an acute respiratory tract infection of domesticated chicken. In 1940, two more animal coronavirus, mouse hepatitis virus (MHV) [11,12], and transmissible gastroenteritis virus isolated. Similarly, the rst human coronavirus was identi ed in 1960 in the form of common cold among human beings. A study carried out in Canada in 2001 showed that more than 500 patients present with u-like symptoms, on virological analyses, 3.6% of those cases were positive for the HCoV-NL63 strain by polymerase chain reaction [13]. Until 2002, coronavirus was considered a relatively simple, nonfatal virus; however, an outbreak in 2002-2003 in Guangdong province in China, which result in spread to many other countries, caused severe acute respiratory syndrome (SARS-CoV) and high mortality rate in over 1000 patient [14]. Since 2012 middle-east respiratory syndrome coronavirus (MERS-CoV) has infected more than 1700 people with a fatality rate of nearly 36% [15]. Since 2013, the porcine epidemic diarrhoea coronavirus (PEDV) has swept throughout the united states, causing an almost 100% fatality rate in piglets in less than a year [16]. At the end of 2019, in Wuhan province of China, a novel coronavirus, i.e., COVID-19 outbreak, killed more than eighteen hundred and infected over seventy thousand individuals within the rst fty days of the epidemic [17,18]. In the past, SARS-CoV (2003) infected 8098 individuals with a mortality rate of 9%, across 26 countries in the world whereas novel coronavirus (COVID-19 affected 4218212 individuals with a mortality rate of 3.4% across 116 countries, till the date of this writing which shows transmission rate of SARS-CoV-2 is higher than SARS-CoV. The reason behind it could be genetic recombination event at S protein in the RBD region of SARS-CoV-2, which may have enhanced its transmission ability [19].
The evolution of this virus demonstrates that coronavirus is not a stable virus and can adapt to the new environment through mutation and recombination with relative ease. Hence coronavirus are programmed to alter host range and tissue tropism e ciently to become more virulent, even lethal to human and animal by causing widespread respiratory, GI and CNS diseases in human and another animal. So, mutating this virus's mutating behaviour is becoming a great topic of research among drug developers, researchers, and scientists [20]. After the outbreak of MERS-CoV, SARS-CoV, and other respiratory like diseases bring high mortality and incidence of occurrence, which make it essential public health and economic issue due to which effective prevention is required. There are no speci c vaccines or drugs or any formulations that can treat or cure novel coronavirus, and the researcher starts studying the alternative method by comparing the e cacy of the natural product. Resources against the various strains of these viruses with the standard one and emerging viral replication lead to the development and search of a distinct form of solutions from the natural product for drug discovery.
Plants have been the major source of many powerful drugs worldwide, and humans have been using it to heal different illnesses since prehistoric times. Thus, plants are considered the most important source of modern medicines that possess various therapeutic effects [21]. About 25 % of the medicines used worldwide are derived from plant sources [22]. The phytochemicals or metabolites (primary or secondary) are responsible for various pharmacological activities [23,24]. Its variation within the plant species confers the speci city in its therapeutic effects [25]. It has always been the challenge and opportunity for researchers to identify the phytochemicals responsible for the particular effects. The emergence of antiviral agents' importance from natural sources requires more research to develop more drugs to treat viral infection. Thus, we need to apply antiviral phyto-constitutes within medication therapy to achieve an increased pharmacological response. Herbal medicine is a promoting subject in medicine, and of course, we have to increase our knowledge about them. Therefore, in this review, an effort has been made to provide information about the medicinal plant that possesses antiviral activity against different coronavirus strains.

Results And Discussion
In common use today, many phytochemicals are associated with health bene ts. Natural products have been the primary source of commercial medicines and drug leads until now. A recent survey revealed that 61% of the 877 drugs introduced worldwide could be traced to or inspired by natural products, out of roughly 350000 species of plants believed to exist, one-third of those yet to be discovered [26]. The search for antiviral materials from plants is inadequate compared to the investigation of the antimicrobial properties. Preliminary studies have shown that plants have an optimistic antiviral activity in vitro and in vivo [27]. However, the same plants can have different antiviral activities against RNA or DNA viruses, regardless of whether they are coated or not, and even against different types or strains of viruses [28,29]. Many viral infectious diseases still cause high mortality. Although antiviral chemotherapy has made great strides, antivirals are still mandatory. The appearance of drug-resistant viruses during treatment poses a potential di culty for effective therapy. New viral pathogens can also be discovered. Biologically active substances of plant origin have long been recognized as viral inhibitors. These antiviral compounds can be extracted from sources such as higher plants, which, for many reasons, have been discovered much less than the traditional ones [30].
There is a great need for readily available antiviral drugs at a reasonable cost with the least side effects. From now on, traditional drugs need to be investigated as new antivirals because many of these old drugs, which contain various plant metabolites, have strong antiviral activities [31].
Research into the antiviral potential of plants began in 1952, and 12 of the 288 plants are effective against in uenza. Various screening studies have been conducted in recent years to determine the antiviral e cacy of natural products using in vitro and in vivo tests [32]. The fall of the SARS CoV and MERS CoV highlight the inadequacy of available treatment for life-threatening zoonotic CoV infection in humans. Still, there is no speci c drug or vaccine that has been available for its treatment. The FDA (Food Drug Administration) has approved various drugs that inhibit entry and replication of MERS-CoV, SARS-CoV, or another human coronavirus in multiple cell lines; still, various plants and their compounds are on investigation for the search of the antiviral agent against coronavirus strain in this pandemic condition [33]. IC 50: concentration required to inhibit 50% of virus growth, TC 50 : drug concentration that reduces the cell growth by 50% (cellular toxicity), CC 50 : concentration required for the reduction of cell viability by 50%, SI: Selectivity Index, ND: Not Defined  [68] In this review, as per the data available on the various parts of the plants and compounds from different articles published, they showed that they possess antiviral activity against coronavirus strains (human coronavirus and non-human coronavirus)in the mild, moderate and strong condition. Through in-vitro tests on various parts of the plant (leaves, ower, aerial parts, rhizomes, and fruit) and different compound bought from the market/pharmaceutical/chemical company. Among various techniques used for the detection of viral inhibition, cytopathic reduction assay was the most common technique for in-vitro analyzation in the antiviral study. We know that medicinal plants are the good sources of various phytochemical compounds that provide the basis for the development of new antiviral agents against different virus strains. The WHO (world health organization) has an estimated 80% of the world population ful l their healthcare needs from phytomedicinal sources. The mechanism of the antiviral potential of plant extract or various compounds varies among the different strains of the virus. Some phytochemical compounds target viral envelope, some membrane protein, some of them focus ion channel, some inhibit the virus's attachment to the host cell, and some inhibit CPE (cytopathogenic effect) on host cells/plagues formation or ion concentration intracellularly.
The present review showed that the above mention plant and compound (Table 1 and Table 2) containing bioactive substances have some amount of promising antiviral activity. Among the listed plants, the most prominent and potent effect shown by Allium porum, Urtica dioica, Lycoris radiata, Juniperus formosa and Cryptomerica japonica against SARS-CoV with SI value 222, >77, >900,>180 and >111 respectively as compared with standard mentioned by [69]. Similarly, Sophorae radix was found to have the highest inhibition activity against MHV -A59 coronavirus with SI value 696 compared with other compounds. Plant and for SARS-CoV 3 CL proenzyme Dioscorea batatas showed the most effective reasultCibotium barometz, Cassia tora with SI value >62,> 59.4, >59.3 respectively.
We encountered 49 plants and 19 compound chemically de ned natural molecules reported in the literature, which have evaluated for potent antiviral activity against different coronavirus strains. The active compounds, which have been isolated and identi ed, belong to the classes of alkaloids, terpenoids, xanthones,), avonoids, steroid, lipids, oxygen benzenoids, carbohydrates, lignans, proteins, coumarins, phenylpropanoids, polyphenols,resins, glycosides, etc. These natural metabolites act as a key for antiviral activity.