Phytochemicals Effective against COVID-19 and Future Perspective

Afshan Shafi¹, Kashif Akram², Ismail Shah³, Fazlullah Khan^{4, *}

¹ Department of Food Science and Technology, MNS University of Agriculture, Multan, Pakistan

² Department of Food Sciences, Faculty of Bio-Sciences, Cholistan University of Veterinary and Animal Sciences-Bahawalpur, Pakistan

³ Department of Pharmacy, Garden Campus, Abdul Wali Khan University, Mardan, Pakistan

⁴ Department of Allied Health Sciences, Bashir Institute of Health Sciences, Bharakahu, Islamabad, Pakistan

Abstract

Novel coronavirus disease-19 (COVID-19) is the deadliest form of coronavirus, which has caused pandemics across the world. According to a recent survey of the World Health Organization (WHO), by August 8, 2020, shows around 19187943 cases and 716075 deaths from this virus globally. In addition to the shortage of effective drugs and vaccines, the outbreak of COVID-19 triggered by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) prompted the medical community to scramble for new antiviral formulations. Mankind utilizes the plants' origin medicines from ancient to treat and cure various diseases. They are the best possible tools to tackle the disease as they have the lowest possible side effects compared to other forms of drugs available and in use to treat the diseases. Several phytochemicals extracted from plants could provide a baseline for research into plant extracts in treating and preventing coronavirus. The present chapter aims to summarize phytochemicals' effectiveness against COVID-19.

Keywords: Antiviral, COVID-19, Inhibition mechanism, Phytochemicals, Phytoextracts activity.

^* Corresponding author Fazlullah Khan: Department of Allied Health Sciences, Bashir Institute of Health Sciences, Bharakahu, Islamabad, Pakistan; Tel: +92-3469433155; E-mail: fazlullahdr@gmail.com

INTRODUCTION

Novel coronavirus disease-19 (COVID-19) belongs to the family Coronaviridae and genus beta-coronavirus. An enveloped RNA virus has an average size from 60 nm to 140 nm in diameter and 79% identical to severe acute respiratory syndrome-coronavirus (SARS-CoV). Laboratory analysis of this virus showed that it is 88% identical to two SARS-like coronaviruses which are derived from

the bat; (a) bat-SLCoVZXC21 and (b) bat-SL-CoVZC45, 50% identical to MERS-CoV (Middle East respiratory syndrome coronavirus) and 'its' similarity index to bat-CoV RaTG13 is 96.2% [1]. The novel coronavirus (nCoV-2019) or severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was first reported in Wuhan (China), followed by a spread to other countries [2]. In December 2019, the first case was reported, then five patients were hospitalized with acute respiratory signs followed by the death of one of these patients [3]. The complete genome of a strain of SARS-CoV-2 (Wuhan-Hu-1-coronavirus WHCV) was first isolated and identified from a pneumonia patient in Wuhan. The size of the genome was 29.9 kb [4]. World Health Organization declared a public health emergency on January 30, 2020, of international concern for COVID-19 [5].

Novel COVID-19 has proved to be a highly deadly form of coronavirus that has special glycoprotein components on its surface that attach to the host body's immune complexes and leads to the arrest of the respiratory system of the host body. So far, there is no approved therapeutic drug or vaccine to combat coronavirus infection. As SARS-CoV-2 has created a global pandemic situation, the urgent discovery of novel antivirals is of utmost importance. Frequent mutations of the virus have made the discovery of vaccines a more challenging job for researchers [6]. Moreover, many vaccines are under trial, and researchers try their best to develop effective vaccines as soon as possible [7].

Globally, medicinal plants are used as alternative sources for the preparation of drugs. Several viral infections have long been treated using traditional medicinal plants that possess strong antiviral properties [8]. Secondary metabolites of medicinal plants (phytochemicals) pose beneficial health effects against viral infections. In many studies, the antiviral properties of phytochemicals such as glycosides, aliphatics, lactones, steroids, and alkaloids have been proved to cause beneficial health effects [9]. Plants have potential antiviral components, as found in flavonoids, coumarins, steroids, lignans, alkaloids, terpenes, and polyketides, etc[10]. Researchers have investigated luteolin-7-glucoside, kaempferol, catechin, quercetin, demethoxycurcumin, gingerol, apigenin-7-glucoside, naringenin, oleuropein, epicatechin gallate, zingerol, curcumin and allicin have inhibition activity against COVID-19 Table 1. These phytochemicals ultimately lead to damage the cell membrane of this COVID-19, thus damaging its DNA components and composition and killing the virus. Another possibility is to develop phytocompounds which can damage the glycoprotein present on this COVID-19 coronavirus. Recent research on phytochemicals revealed that glycosides and flavonoids derived from garlic and Sena or Salvia officinalis could help develop specific phytochemicals that can damage the DNA gyrase SARS-CoV-2 [11]. From these all compounds such as catechin, kaempferol, epigallocatechin, quercetin, luteolin-7-glucoside, apigenin-7-glucoside, naringenin, demethoxycurcumin, curcumin, and oleuropein are the most suggested biological compounds extracted from medicinal plants that have inhibitory potential against COVID-19 Major protease (Mpro) [12], and their structure has been shown in Fig. (1). In the present chapter, the effectiveness of plant phytochemicals and possible antiviral therapies are highlighted, proving to be fruitful and effective to prevent and control this deadly disease.

Fig. (1))

Structures of various compounds active in COVID-19.

Table 1 Active constituents, molecular formula, and mechanism of action in COVID-19.

Various Phytochemicals Activities against COVID-19

Allicin (garlic compounds)

Most recent research on the antiviral potential of essential garlic oil against coronavirus demonstrated remarkable findings. The research also reported the inhibitory effect of garlic compounds against angiotensin-converting enzyme 2 (ACE2) proteins in the human body, leading to a crucial foundation for coronavirus resistance of individual compounds on the main protease (PDB6LU7) protein of SARS-CoV-2. The research outcomes demonstrated strong interaction with the amino acids of the ACE2 protein and the main protease PDB6LU7 of SARS-CoV-2. Study results concluded that garlic compounds' anti-coronavirus potential (allyl disulfide and allyl trisulfide) suggests that the essential garlic oil contributes to preventing the coronavirus's invasion into the human body [21]. The Anti-corona viral effect of garlic extract has been reported in research. The authors performed experimental trials on the chicken's embryonic stage. The study results expressed that garlic has a strong potential to inhibit the multiplication of coronavirus either through strengthening the immune responses or blocking the virus protein synthesis and genetic material [23].

Glycyrrhizin

The outbreak of SARS warrants the search for antiviral compounds to treat the disease. At present, no specific treatment has been identified for SARS-associated coronavirus infection. The antiviral potential of ribavirin, 6-azauridine, pyrazofurin, mycophenolic acid, and glycyrrhizin has been assessed against two clinical isolates of coronavirus (FFM-1 and FFM-2) from patients with SARS admitted to the clinical center of Frankfurt University, Germany. Of all the compounds, glycyrrhizin was the most active in inhibiting replication of the SARS-associated virus. The research findings suggest that glycyrrhizin should be assessed for the treatment of SARS [24].

Quercetin

The quercetin interferes with the dimer HA2 as well. The viral dimer HA2 is recognized as an antiviral vaccine base. In this way, quercetin interaction with HA2 could present an antiviral effect. In addition, quercetin may inhibit virus entry [19]. Quercetin interferes with the S-protein S2 region with bonding energies of -8.5 kcal/mol. Quercetin creates hydrogen bonding with residues LEU 861, LYS 733, MET 731, PRO 1057, ALA 1056, SER 730, HIS 1058, and GLY 1059 and have hydrophobic interactions with ASP 867, ILE 870, PRO 863, MET 730, and VAL 860. Quercetin prevents the growth of tumor necrosis factor (TNF-) and IL-8 in cells [25].

Flavonoids

Catechin

Gallocatechin gallate and Catechin gallate are known as a type of catechin. Gallocatechin gallate and catechin gallates are the most abundant catechins, particularly in tea (especially green tea) and other plants, and they have antioxidant activity. This study revealed that the use of catechin and curcumin having significant antiviral properties (Table 2). Infection of the virus may be treated with the use of catechin and curcumin. They are also known as inhibitory machinery because of blocking the entry of viral protein and receptors of the host cell to the virus [26].

Curcumin

Curcumin is a major constituent of turmeric, was already characterized to present increased anti-viral properties against a wide range of viruses, including Zika and chikungunya virus, dengue virus (serotype 2), HIV, herpes simplex virus. Curcumin attaches to the S1 region of the C-terminal of the S-protein through binding energy of -7.1 Kcal/mol in the prevention of coronavirus. This attachment quite likely inhibits the virus from bonding to ACE or internalizing throughout fusion. Reduced binding energy indicates a strong affinity of the ligand to the receptor. Curcumin forms H-bonding with amino acid residues like ASN 544, GLN 564, and ALA 520, and hydrophobic interactions exist with LEU 517, LEU 390, PHE 565, VAL 382, and THR 430 on the S1 domain [25]. Curcumin was shown to impede NF-B stimulation enhanced by numerous inflammatory impulses, including certain markers of inflammation (oxidized CD40 ligand, sCD40L), interleukin 6, solubilized vascular cell adhesion molecule 1 (sVCAM-1), and interleukin 1 beta [19].

Table 2 Phytochemicals with their antiviral effects.

Miscellaneous Phytochemicals against COVID-19

Carvacrol, Oleanolic Acid and Ursolic Acid

The effect of natural polyphenols against COVID-19 while working on Potent COVID-19 Mpro Inhibitors from Natural Polyphenols: An in-silicof Strategy Unveils a Hope against CORONA has been studied. It has been found that phytochemicals hesperidin, rutin, diosmin, apiin, diacetyl curcumin, (E)-1-(2-Hydroxy-4-methoxyphenyl)-3-[3-[(E)-3-(2-hydroxy-4- methoxyphenyl)-3-oxoprop-1-enyl]phenyl]prop-2 -en-1-one, and beta,beta'-(4-Methoxy-1,3- phenylene)bis( 2'- hydroxy- 4',6'-dimethoxyac rylophenone have strong potential against COVID-19. The Mpro protein is seen to be an essential and fast-acting substrate for innovative COVID-19 inhibitors. The residues of amino acids have been involved in hydrophobic interactions between proteolytic enzymes and ligand molecules. Intermolecular interaction (hydrogen bonds and hydrophobic interactions) plays a crucial role in forming and sustaining the complexes at docking [22].

Gly143 amino acid was accused of developing a hydrogen bond with carvacrol (the major constituent of oregano and thyme) through Auto-Dock bonding energy 4.0 kcal/mol. Additionally, 6 more residues (Leu27, Met49, Met165, Asn142, His41, and Cys145) participated in hydrophobic interactions (d).

Oleanolic acid participated in docking with bonding energy of 6.0 kcal/mol. 2 amino acid residues exhibit (Cys145, His163) hydrophobic bonding whereas Gln189 forms hydrogen bonding (c) Bonding energy for ursolic acid was found to be 5.9 kcal/mol. The Ser46 makes hydrogen bonding at the active site of the protease. 9 amino acids (Thr24, Thr26, Asn142, Cys44, Thr25, Gly143, Glu166, Cys145, and Thr45) are involved in the van der Waals interactions (e) [28].

· Catechin Quercetin

· Gallate Allicin

· Curcumin Aloe emodin

· Hesperidin Pectolinarin

· Rutin

Mechanism of Phytochemicals in Altering SARS-CoV-2 Infection

The treatment therapies against infection caused by SARS-CoV-2 can target and alter different pathways, including (a) Inhibition of structural proteins to bind with ACE2, which blocks its' entry into the host cell, and (b) Altering enzymes that are involved in RNA synthesis and viral replication. Advanced approaches in biology and bioinformatics help to estimate the treatment potential of phytochemicals against viral infections. These approaches also make drug development speedy, economical, safer, and reliable. Drug targets against viral infections are enzymes and receptors involved in the entry and development of SARS-CoV-2 in the host cells [29].

a. Inhibition of Spike Proteins to Bind with Angiotensin-converting Enzyme 2 (ACE2)

Four structural proteins of the coronavirus are; nucleocapsid protein (N), membrane protein (M), envelop protein (E), and spike protein (S) [30]. Spike proteins of SARS-CoV-2 play a crucial role in the entry of virus in host cells because these proteins attach with cell receptor ACE2 [31], diagrammatically showed in Fig. (2). In designing drugs against viral infections, both non-structural proteins and structural proteins play a crucial role. Recent studies have shown that ACE2 assists the entry of viruses into the host cells by viral binding spike (S) protein [32]. At the early stages of infection, the perfect drug target is spike protein involved in the entry of the virus into host cells. In RBD (Receptor binding domain), ACE2 binds with receptor binding motif (RBM) of spike protein and acts as a receptor of SARS-CoV-2 [33]. In host cells, the binding of ACE2 receptor with spike (S) protein of virus can be inhibited by different inhibitors. The drug nafamostat mesylate (Fusan) used against pancreatitis, has also shown inhibition properties that inhibit entry of MERS-SARS viruses in the host cells [34].

b. Inhibition of Viral Replication

In different viral infections such as Hepatitis C virus (HCV) and Human immunodeficiency virus (HIV), viral proteases have shown to be actual targets of antiviral therapies. Viral replication can be inhibited by targeting proteases that are involved in the replication. The main protease (M^pro, also called 3CL^pro) is the best drug target to inhibit replication among coronaviruses [35]. There is a 96% similarity in the protein sequence of SARS-CoV-M^pro and SARS-CoV-2-M^pro [36]. In the life cycle of the virus, the functional significance of M^pro and the lack of similar homologs in humans make it an effective target in designing a drug against viral infection. Examples of protease inhibitors that are being used to treat COVID-19 infection are lopinavir-ritonavir combinations [37]. RNA replication is carried out by RdRp (RNA-dependent RNA-polymerase), which is another effective target in developing antiviral therapeutics.

Fig. (2))

Binding of Spike protein with ACE2 receptor. The figure illustrates that SARS-CoV-2 comprises four structural proteins, among which spike protein can bind with the ACE2 receptor on the host cell's surface. After binding with receptor hijacking of host cell machinery is carried out by the virus.

Plant Extracts and their Possible Anti-Viral Activities in COVID-19

Due to the lack of conventional therapeutic agents (vaccines, antibiotics) for COVID-19, broad-spectrum antibiotics along with antivirals and corticosteroids are in general use [13]. The WHO, US Food and Drug Administration (FDA), European Medicines Agency, and the Chinese Government and drug manufacturers are coordinating with scientists and industrials to speed up the development of new drugs for COVID-19 [38]. Natural products have high potentials in the treatment of viral infections [39]. Medicinal plants are used to be effective against SARS-CoV-2 with assorted secondary metabolites. Many can interrupt viral protein and enzymatic activities and stop viral penetration into host cells and (or) its replication [40]. Phytochemicals such as quercetin, catechin, and curcumin act to inhibit ACE2, demethylation of the gene, and histone modification (Fig. 3).

Fig. (3))

Mechanism of action of phytochemicals against SARS-CoV-2.

Many medicinal plants have been testified to possess anti-coronaviral activity. Platycodon grandiflorum, a medicinal plant, has been tested scientifically on the PRRSV virus, and the result has been shown to inhibit viral replication and expression of pro-inflammatory cytokine [41]. Reseda luteola, another plant that has inhibited the entry of SARS-CoV, has a great attraction for S2 protein, thus interfering with the process of virus-cell fusion [42]. Medicinal plants can prevent replication of viruses are often preferred as favorable options against viral outbreaks. Thus, Glycyrrhiza glabra induces nitrous oxide synthase, which blocks viral replication in SARS-CoV [43]. Clerodendrum inerme Gaertn inactivates viral ribosome and protein translation of SARS-CoV 2 [44]. Strobilanthes cusia targets the HCoVs and inhibits RNA genome formation [45]. Similarly, Anthemis hyaline decreases gene expression of transient receptor potential proteins (TRP's) in coronavirus [46]. Camellia japonica, affects key structural protein synthesis in PEDV coronavirus, thus blocking viral replication [47]. Isatis indigotica, inhibits viral cleavage activity in SARS-CoV [48]. Vitis vinifera reduces nucleocapsid (N) protein expression, also reduces MERS-CoV virus-induced apoptosis [49]. Rosmarinus officinalis blocks replication of the human respiratory syncytial (hRSV) virus [50]. Similarly, Cedrela sinensis inhibits SARS-CoV replication [51]. Clerodendrum inerme inactivates SARS-CoV-2 virus [52], and Clitoria ternatea inhibits metalloproteinase of SARS-CoV-2 [53]. Coriandrum sativum and Embelia ribes both inhibit ACE2 in SARS-CoV-2 [54]. Similarly, Hyoscyamus niger inhibits Ca2+ channels and acts as a bronchodilator in SARS-CoV-2 [55], and Vitex trifolia inhibits virus in SARS-CoV-2 [56]. Similarly, herbal extracts from Dioscoreae rhizoma, Gentianae radix, Cassiae semen, Rhizoma cibotii, and Loranthi ramus have a potential inhibitory effect SARS-CoV. Plant extracts (Artemisia annua, Lycoris radiata, Lindera aggregate, and Pyrrosia lingua) have resulted in the antiviral activity of SARS-CoV. Similarly, Sanguisorbae radix, Sophorae radix, and Torilis fructus extracts have antiviral effect and Coptidis rhizome, Meliae bark, Phellodendron bark extracts and Cimicifuga rhizomes have an effect on replication of coronavirus [57].

Many other plant extracts have an inhibitory role against HIV infections. They can also serve as favorable candidates in the development of the COVID-19 drug. Eugenia jambolana [58], Acacia nilotica, and Euphorbia granulate [59] are among these plants. Other plants like Vitex negundo [60] Ocimum sanctum [61], and Solanum nigrum [62] can target reverse transcriptase activity of HIV can also serve as favorable candidates in the development of COVID-19 drug. During pandemics, appropriateness is the basic requirement for developing any drug. Thus natural products can serve as proper and potential options as their safety is well-known. So it can be promptly assessed for combating patients.

FUTURE PERSPECTIVE OF PHYTOCHEMICALS IN COVID-19

Phytochemicals derived from plants such as Allium sativum, Salvia officinalis, and Ficus racemose, can help develop specific composition compounds that can ultimately damage DNA gyrase of SARS-CoV-2. Antiviral drug available which can kill the virus specifically are also the possible remedies for treating this deadly coronavirus. Plant medicines as antiviral therapy are also the best possible resources to arrest coronavirus spread from humans to humans. To stop the spread of this deadly coronavirus, using an alcoholic-based disinfectant would be beneficial to wipe out the risk of any possible infection chances.

Inside the body, the best way to stop the infection is to develop a medicine that will ultimately protect the host body's immune system from forming complexes

with the SARS-CoV-2 glycoprotein, which further leads to the arrest of the respiratory system.

We need to develop a phytochemical component that makes the immune system flexible and strong to stop developing its complexes with viral glycoprotein. Using quantum computing technology, we can help develop unique components and compounds that make our immune system strong and have deadly environment development for the virus to survive inside the host body [63].

Phytochemicals can act as antioxidants, specific enzyme inhibitors, and protein receptors all over the virus's surface that blocks interactions. Specific medicinal plants with a broad range of biological activity can be used to source phytochemicals (polyphenols, sterols, and lipids). These substances offer hope that extracts from various plants described in this chapter may have antiviral effects, even against the family of coronaviruses. Awareness of their healing uses and application has been passed on from one generation to another. The new advances in biotechnology and medicine have made it possible to use substances of natural origin to a greater degree than in the preceding decades, often as nutritional supplements and nutraceuticals. A multidisciplinary approach (omics science-genomics, proteomics, metabolomics) has yet to examine their toxicity along with the processing period. New processing and formulating technologies may also help improve the solubility of bioactive antiviral compounds, their delivery strategies, and therapeutic activities, adapting these as useful antiviral foods and drugs. This way, the chances of developing better and speedy remedies to treat this deadly coronavirus will be possible, and we could stop this pandemic here itself.

CONCLUSION

COVID-19 is a severe respiratory infectious disease caused by a novel virus strain. The Coronavirus Study Group; taxonomists, working under the aegis of International Committee on Taxonomy of Viruses (ICTV), coined the nomenclature of SARS-COV-2 based on 82% identity to the SARS-CoV genome. This infectious disease has directed over 4,098,018 confirmed cases and 283,271 fatalities untill May 12, 2020. The number of cases across the globe is growing tersely. So far, no usual drug has proved to be effective for COVID-19 disease that has a high mortality rate, especially in immune-compromised patients. Nowadays, research and development programs are incessantly adopting methods focusing on plant-based products to develop drugs. There are several classes of phytochemicals, which are used as antiviral agents. These include phenolics, carotenoids, terpenoids, and alkaloids. The family of phenolics contains various subclasses, such as phenolic acids, flavonoids, stilbenes, coumarins, and tannins. These viruses have either DNA or RNA as genetic material. Thus, phytochemicals exhibit a different mode of action against any infection or disease. Viral attachment can be inhibited by either blocking the viral binding sites or host receptors. The virus can be inhibited at various stages of its infection. Some of the strategies directly inhibit viral replication by targeting DNA/RNA polymerase, post-translation modification of viral proteins, or viral assembly. Phytochemicals have adopted several mechanisms to inhibit viral replication. For instance, epigallocatechin gallate (EGCG) inactivates the host enzyme or viral enzyme that promotes the virus's growth, such as RNA polymerase, protease, and reverse transcriptase. Another mechanism adopted by flavonoids is to inhibit phosphorylation of the protein, which restricts the replication of viruses.

CONSENT FOR PUBLICATION

Not Applicable.

CONFLICT OF INTEREST

The authors confirm that this chapter contents have no conflict of interest.

ACKNOWLEDGEMENT

Declared none.

REFERENCES