Scientists endorse more herbal cures for COVID-19

•Green seaweed, licorice, gum laced with plant-grown protein found to reduce transmission by 95%
•Researchers establish therapeutic convergence in use of antimalarial plants against viral infections in Africa
•Say discovery could explain why Nigeria, other countries in malaria endemic regions are spared by pandemic

Scientists have recorded major breakthroughs in herbal remedies for COVID-19 with discovery of green seaweed, licorice, gum laced with plant-grown protein, and antimalarial plants.

In fact, scientists said the regular use of antimalarial plants against viral infections might be the reason most countries endemic to malaria are ‘spared’ by COVID-19 compared to Western countries.

Currently available antiviral drugs for the treatment of COVID-19 are neither broadly accepted nor highly effective. Therefore, there is a pressing need to find biomolecules and synthetic compounds exhibiting antiviral properties for effective COVID-19 treatment.

The study published in Frontiers in Pharmacology is itled, ‘Therapeutic Potentials of Antiviral Plants Used in Traditional African Medicine With COVID-19 in Focus: A Nigerian Perspective’.

The researchers are from the Department of Pharmacognosy and Drug Development, Faculty of Pharmaceutical Sciences, University of Ilorin, Ilorin, Kwara State; Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Ibadan, Ibadan, Oyo State; Department of Pharmaceutical Chemistry, Obafemi Awolowo University, Ile-Ife, Osun State; Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, Jülich, Germany; Department of Medical Microbiology and Parasitology, College of Medicine, University of Ibadan, Ibadan; Nestle Nigeria Plc, Ilupeju Avenue, Lagos; Department of Pharmacognosy, Faculty of Pharmacy, Obafemi Awolowo University, Ile-Ife; Centre for Drug Discovery, Development and Production, University of Ibadan, Ibadan; and College of Basic Medical Sciences, Chrisland University, Abeokuta, Ogun State.

According to the study, antimalarial drugs derived from medicinal plants used in Traditional African Medicine (TAM) have been found useful as repurposed drugs in managing other diseases including viral infections such as Human Immuno-deficiency Virus (HIV), Ebola, and other viral haemorrhagic diseases due to lack of effective therapeutic agents. The active constituents of these plants have various mechanisms of action, which are often not fully elucidated against malaria parasites. The complexity of these constituents sometimes lead to side effects that have been studied for repurposing them for the treatment of other conditions such as non-malaria infectious diseases.

The geographical distribution between malaria and viral diseases where malaria endemic regions of the world such as Africa and Asia appear to experience relatively low cases of COVID-19-related mortalities, led to the consideration of a possible therapeutic convergence between antimalarial plants (which have continued to be used against malaria in Africa) and viral pathogens including the dreaded Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS CoV-2) that causes COVID-19.

One possible explanation attributable to this unresolved therapeutic convergence is the mechanism of activity of these medicinal plants; several antimalarial phytomedicines, which tend to produce more bioactivity as antioxidants, anti-inflammatory and immuno-modulatory, may function both as antimalarials and antivirals, since the underlying mechanism of activity is not directly targeting the pathogen but rather boosting the immunity of the host, effective and efficient resolution of early inflammatory/anti-inflammatory cytokines and scavenging of generated lethal free radicals.

This school of thought has been put forward to explain why many widely used African phytomedicines have gained more anecdotal claims of efficacy, yet they do not easily kill the malaria parasite in vitro but produce good in vivo activity. For instance, Adebayo et al. (2017) demonstrated the poor in vitro but potent in vivo antimalarial activity of disulphide-rich peptide fraction of Morinda lucida. These antimicrobial peptides have been reported to possess immunostimulating and antioxidant activities as well as antiviral property.

Apparently, the lethal COVID-19 is reported to be induced by the invasion of SARS CoV-2 into a human host and has been associated with cytokine storm and neutrophil-induced oxidative stress which often result in mortality. So, it is reasonable to assume that antimalarial plants widely used in TAM with well documented in vivo antioxidant, anti-inflammatory and immunomodulatory potentials might offer some therapeutic benefits in COVID-19 management. A treatise of antimalarial plants used in TAM with documented antioxidant, anti-inflammatory and immunomodulatory activities as well as level of documented evidence has been presented. However, the authorisation of the repurposed use of these botanical antimalarials should be evidence-informed with impressive clinical data and supported by the best evidence.

Considering repurposing antimalarial African traditional phytomedicines for COVID-19 management, endemic and naturalised African plants, which have shown therapeutic promise as anti-malarials following clinical studies should be considered and these include: Vernonia amygdalina, Nuclea pobeguinii, Argemone mexicana, Artemisia annua, Citrus aurantiifolia and Morinda lucida.

Interestingly, available evidence indicates that these promising antimalarial plants additionally have the potential to tackle oxidative stress, regulate inflammatory response and stimulate the immune system to overcome complications observed in COVID-19.

Meanwhile, some of these reports lack quality and will require validation. Bioactive compounds identified in the plants… Overwhelming evidence supports the standardisation of the leaf and seed of Moringa oleifera for a possible clinical application, as it has demonstrated broad range of antiviral activity in various studies while the disulphide-stabilised miniproteins (Morintides), lectins, hevein-like peptides, protein hydrolysates and glucosinolates/isothiocynates isolated from the plant have shown impressive effects, including as anti-adhesives, anti-inflammatory, antioxidants and immuno-modulatory compounds. Aside immunomodulation and free radical scavenging, one mechanism of activity of these lectins and stable polypeptides involve the competitive inhibition of adhesion of pathogen proteins to host polysaccharide receptors. Further in vivo and clinical evaluations will be required to assess the specific significance of these reports and in particular the possible role of Moringa-derived products in COVID-19 management.

Neem (Azadirachta indica)

Furthermore, the aqueous root extract of N. latifolia otherwise known as NIPRD AM1®, has been clinically stu
died in uncomplicated malaria and found to be therapeutically helpful as an antimalarial and should therefore be given attention for investigative management of COVID-19 [Level I, for malaria]. Nevertheless, such investigation should follow after these chemically complex herbal mixtures have been taken through extensive acute, subacute and chronic toxicity studies as well as the metabolite profiling using modern analytical methods.

MAMA Powder and MAMA Decoction are authorised indigenous polyherbal antimalarials, which have been scientifically formulated by Prof Elujoba, the Head of the Village Chemist located within Obafemi Awolowo University, Ife, Nigeria. MAMA Powder contains stem bark of Alstonia boonei De Wild (Apocynaceae) and seed of Picralima nitida Stapf (Apocynaceae) while MAMA Decoction is made up of the leaves of Mangifera indica L. (Anacardiaceae), Alstonia boonei De Wild (Apocynaceae), M. lucida and Azadirachta indica A. Juss (Meliaceae).

In an in vivo experiment using rodents, MAMA Decoction showed antimalarial activity at 240 mg/kg without any observable toxic effect when administered up to 2 g/kg body weight. Human observational study has further reinforced the in vivo activity, while the efficacy claims by treated patients on MAMA herbal remedy has multiplied malarial patients’ demand for the herbal medicine. An elaborate preclinical study with superior scientific quality, documentation of chemical fingerprint as well as clinical trial and a possible repurposing for COVID-19 management is encouraged.

Also, macroalgae or seaweed, which are marine multicellular organisms encompassing several thousand species are previously known to exhibit antiviral properties. Several studies have suggested that seaweed sulfated polysaccharides (SSPS), located in the cell wall of seaweeds, play a vital role in their defense against pathogens and other opportunistic organisms.

The effectiveness of inhibitory effects of SSPS on viral replication under in vitro conditions has also been known for more than 60 years. Subsequently, they are used against several enveloped ribonucleic acid (RNA) viruses, including SARS-CoV-2 that causes COVID-19.

The antiviral properties exhibited by SSPS, a polysaccharide; against SARS-CoV-2 partially correlate with the presence of sulphonate groups and partly with its structural diversity and high charge density of its sulfated polymer. All these structural and functional aspects help SSPS efficiently bind to the proteins located on the surface of viruses like SARS-COV-2.

The authors of a recently published study on the Peerj preprint server investigated the antiviral activities of SSPS extracted from cultivated green seaweed Ulva sp. to demonstrate the anti-SARS-CoV-2 activity of ulvans.

The extraction was carried out with the help of an in vitro cytopathic effect (CPE) reduction assay using Vero E6 cells. These cells express the angiotensin-converting enzyme 2 (ACE2) receptor, to which the SARS-CoV-2 virus typically binds.

The researchers used two distinct extraction protocols including hydrochloric acid (HCl) and ammonium oxalate (AOx) extraction protocols. The extraction protocols changed the ulvan extracts qualitatively and quantitatively.

Subsequently, the extracted ulvans had different purity, molecular weight (MW) distribution, sulfate content, and bioactivity. The team analyzed the composition of extracts using infrared spectroscopy, carbon, hydrogen, nitrogen, and sulfur (CHNS) elemental analysis, as well as size exclusion (SE) and anion exchange (AE) chromatography.

The researchers used several advanced analytical methodologies such as Fourier-transform infrared (FT-IR) spectroscopy analyses, SE chromatography, and AE chromatography to analyze crude Ulva sp. extracts. They found that the AOx and HCl extraction protocols of Ulva sp. resulted in mixtures of compounds having a different distribution of MW, overall molecular charges, and nitrogen-containing contaminating molecules. Both the extracts exhibited slightly different antiviral activity, thereby indicating variability in the biological activity of SSPS compounds obtained through two different extraction protocols.

The AOx extracts showed positive in vitro antiviral activity, as demonstrated by their ability to protect VERO E6 cells against the cytopathic effect of the SARS-CoV-2 as a result of a higher charge density on SSPS biopolymers, higher average MWs compared to HCl-based extracts and the flexibility of the polysaccharide backbone.

Further, these results indicated that only a specific fraction of this AOx-based extract is active against SARS-CoV-2. To this end, this fraction exhibited a 11.3-fold difference in its maximum inhibition activity against SARS-CoV-2 as compared to the HCl-based extracts. Furthermore, these AOx-based extracts, compared to the HCl-based extracts, exhibited a higher level of alkaloids, peptides, proteins, and nucleic acids fragments.

These nitrogen-containing contaminating compounds could be responsible for the difference in the antiviral activity of the two extracts. Interestingly, lectins, co-extracted with the SSPS from the Ulva sp., could also be used to exhibit antiviral activities, including against SARS-CoV-2.

This current study is just a starting point, as it would be challenging to develop thorough bioassay-guided fractionation approaches for the isolation and precise identification of the active components in AOx-based SSPS extracts in the future. Also, future in vivo studies will have to address the challenge of delivering the active fractions of Ulva sp. crude extract.

Despite global vaccination campaigns, it is crucial to find new antiviral candidates against SARS-CoV-2 infection for two reasons. One, SARS-CoV-2 is continuously producing new mutant strains that exhibit resistance to both vaccine-based immunity and known antivirals. Second, the vast antiviral activity of certain SSPS presents an opportunity to develop broadly active and highly potent antivirals with high specific activity against certain viruses, including SARS-CoV-2.

The current study provides experimental evidence that Ulva sp. could be a promising antiviral as a source of SSPS, as its crude extract could direct the development of natural product-based therapeutic agents against SARS-CoV-2.

Also, a popular traditional Chinese medicine (TCM), Glycyrrhiza uralensis Fisch (licorice, Gan-Cao) has demonstrated antiviral activity against H1N1 influenza and other SARS-CoV viruses, but information on its use against SARS-CoV-2 is scarce.

In a study recently published in the Journal of Advanced Research, researchers from China conducted an experiment to determine the potency of licorice and related TCM products against SARS-CoV-2. The main aim of the work was to discover small-molecule inhibitors that can target the SARS-CoV-2 spike protein receptor-binding domain (RBD) from licorice.

The researchers performed virtual screening of 125 small molecules obtained after optimization of Glycyrrhiza uralensis Fisch against the ligand structure RBD of SARS-CoV-2 spike protein (S) and non-structural protein – 7 (nsp7). Surprisingly, glycyrrhetinic acid (GA), 3-O-β-D-glucuronosyl-glycyrrhetinic acid (GA-g), and licorice-saponin A3 (A3) displayed remarkably high affinity compared to glycyrrhizic acid (GA-gg), which was earlier reported as a SARS-CoV-2 inhibitor. Further evaluation of the potential hits identified from virtual screening was performed using studies in Vero E6 cells and a pharmacokinetic study.

The examination of the inhibitory activities of licorice triterpenoids against SARS-CoV-2 spike protein by enzyme-linked immunoassay (ELISA) demonstrated that at 10 μM concentration of GA, GA-g, and A3 they displayed inhibition rates of 51.9 per cent, 50.2 per cent, and 45.1 per cent, respectively, which were significantly higher than other licorice compounds such as GA-gg. Six non-licorice triterpenoids were also evaluated among which ursolic acid and betulinic acid exhibited observable inhibitory activities. The half-maximal inhibitory concentration (IC50) values for GA, GA-g, A3, betulinic acid, and ursolic acid were found to be 10.9, 14.1, 8.3, 15.1, and 9.0 μM, respectively.

Similar results were observed when GA, GA-g, and A3 were tested in Vero E6 cells infected with SARS-CoV-2 pseudovirus. Although the non-licorice compounds ursolic acid and betulinic acid exhibited noticeable inhibitory activity, they were not further evaluated due to significant cytotoxicity.

The inhibitory activities of GA and A3 against SARS-CoV-2 were assessed in Vero E6 cells using remdesivir as a positive control and it revealed that GA and A3 both possess significant inhibitory activity against SARS-CoV-2 at 3 μM. Viral RNA levels decreased in a dose-dependent manner with a half-maximal effective concentration (EC50) of 3.17 μM for GA and 75 nM for A3.

Since RNA-dependent RNA polymerase (RdRp) is one of the main targets for SARS-CoV-2 and the proteins nsp12, nsp7, and nsp8 are its essential components; the researchers assessed the binding affinities of A3 and GA with nsp12, nsp7, and nsp8 through surface plasmon resonance (SPR) analysis. The results revealed a higher binding affinity for A3 to nsp7 compared to the other two proteins, suggesting that nsp7 may be the desirable target for A3.

The pharmacokinetics (PK) study findings showed that both GA and GA-gg were easily absorbed into the circulation and were inter-convertible. Even the abundant GA-gg exhibits low anti-viral activity and may reduce ACE2 expression in the lungs; it could readily be metabolized into GA, which is an active inhibitor of SARS-CoV-2.

The elimination rate of GA was low and thus its plasma concentration between 8-24 hours was high. GA was also obtained from lung samples, as lungs are the key target organs for SARS-CoV-2. When A3 was administered intravenously in rats, it displayed first-order elimination with a slow elimination rate and plasma concentration of 48.9 μM at one hour, which decreased to 27.3 μM at 24 hours.

PK data demonstrating the highest plasma concentration of GA as 7.7 μM after the administration of 200 mg/kg licorice extract along with EC50 of GA (3.17 μM) supports the use of licorice as a potent drug for COVID-19 prevention and treatment after oral administration.

The researchers concluded that licorice triterpenoids could be promising candidates for anti-SARS-CoV-2 drug development as confirmed by Vero cell models and PK studies. The licorice compounds A3 and GA inhibit SARS-CoV-2 by targeting different proteins i.e., nsp7 and S-RBD protein, respectively.

The researchers recommended further evaluation of the effects of GA-gg against COVID-19 as a pro-drug of GA in both clinical and animal studies.

Also, new type of gum has been found to nearly eliminate transmission of the coronavirus by neutralising the virus in the person’s saliva.

A team of scientists led by Pennsylvannia State University, United States, infused gum with a plant-grown protein and found it ‘traps’ the SARS-CoV-2 virus.

The protein, known as ACE2, prevents the virus from attaching to a host cell in the human body by interacting with SARS-CoV-2’s receptor binding domain – this facilitates virus attachment to the receptor and fusion with cell membrane.

When saliva samples from coronavirus patients were exposed to the ACE2 gum, researchers observed 50 mg of the cinnamon-flavored gum reduced viral entry by 95 percent.

The research team is currently working toward obtaining permission to conduct a clinical trial to evaluate whether the approach is safe and effective when tested in people infected with SARS-CoV-2.

Henry Daniell at Penn State’s School of Dental Medicine, who led the research, said in a statement: : “SARS-CoV-2 replicates in the salivary glands, and we know that when someone who is infected sneezes, coughs, or speaks some of that virus can be expelled and reach others.

“This gum offers an opportunity to neutralize the virus in the saliva, giving us a simple way to possibly cut down on a source of disease transmission.”

Coronavirus gains access to bodily cells by attaching itself to a protein called ACE2 and the new chewing gum was developed with a copy of that protein, allowing it to mimic bodily cells.

This tricks the virus into attaching to chewing gum chemicals, instead of the saliva, where it is neutralized and unable to be transmitted to someone else.

To test the gum, the team grew ACE2 in plants, paired with another compound that enables the protein to cross mucosal barriers and facilitates binding and incorporated the resulting plant material into cinnamon-flavored gum tablets.

Incubating samples obtained from nasopharyngeal swabs from COVID-positive patients with the gum, they showed that the ACE2 present could neutralize SARS-CoV-2 viruses.

The scientists observed that the gum largely prevented viral particles from entering cells, which was done by blocking the ACE2 receptor on the cells or binding directly to the spike protein.

And the results showed that levels of the viral RNA in the person’s saliva were almost undetectable. Though the research is still in the early stages of development, if the clinical trials prove the gum is safe and effective, it could be given to patients whose infection status is unknown or even for dental check-ups when masks must be removed, to reduce the likelihood of passing the virus to caregivers, according to the researchers.

“We are already using masks and other physical barriers to reduce the chance of transmission,” said Daniell. “This gum could be used as an additional tool in that fight”‘