Pomegranate peel extract shows potential SARS-CoV-2 virus inhibitor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which causes COVID-19 (coronavirus disease 2019) has infected over 58.5 million people worldwide and killed over 1.38 million is one of the health crises most significant global in recent memory. There are currently no effective and safe vaccines to prevent SARS CoV-2 infection and no effective drugs to treat COVID-19 disease. Researchers around the world are therefore trying to find effective molecules and compounds that could fight the virus.

Researchers led by first author Relja Suručić from the Department of Pharmacognosy, Faculty of Medicine, Banja Luka University, Banja Luka, Bosnia and Herzegovina, investigated the use of pomegranate peel extracts in the prevention of SARS-CoV-2 infections . Their study titled “Computational study of polyphenols from pomegranate peel extract as potential inhibitors of SARS-CoV-2 virus internalization”, was published in the latest issue of the journal Molecular and cellular biochemistry.

background

Coronaviruses, the researchers explain, are known to cause respiratory tract infections in humans. These include the Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), and the novel SARS-CoV-2 coronavirus. SARS-CoV-2 is known to cause severe symptoms in some individuals requiring hospitalization, ventilation, and intensive care care. The World Health Organization declared the COVID-19 pandemic on 11^th of March this year.

Viral structure, transmission and infection

The SARS-CoV-2 virus also has a rapid transmission rate among humans. The virus has four main structural proteins along with other accessory proteins:

• peak (S) glycoprotein
• small envelope glycoprotein (E)
• membrane glycoprotein (M)
• nucleocapsid protein (N)

SARS-CoV-2 enters the cells of the respiratory tract using S-glycoprotein. The virus interacts with the angiotensin-converting enzyme 2 (ACE2) receptor found abundantly in the respiratory system.

S glycoprotein has two functional subunits known as S1, which is an amino (N) -terminal subunit and S2, a (C) -terminal carboxyl subunit. The S1 on the surface binds to the ACE2 receptor and the S2 interacts with the host cell membrane to allow the cell and virus membranes to fuse so that the viral particles can finally enter the cell. The host cell contains specific proteases that can break or cleave the S1 / S2 to allow for the fusion and entry process. The notable protease is the transmembrane serine protease 2 (TMPRSS2). Both ACE2 and TMPRSS2 are required for viral entry into the cell.

Furin also leads to the cleavage of S glycoprotein and thus facilitates the entry of the SARS-CoV-2 virus by binding to the ACE2 receptor. It is hypothesized that TMPRSS2 inhibitors and furin inhibitors prevent the virus from entering the host cell.

Pomegranate peel extract

Several natural products are being studied to prevent SARS-CoV-2 infection or treat it effectively. Pomegranate (Punica granatum L., Punicaceae family) consumed all over the world is known to have beneficial and useful health properties in the treatment of type 2 diabetes, atherosclerosis, cardiovascular diseases, inflammatory diseases, tumors, etc.

Pomegranate peel extracts are known to contain “phytobiotics such as hydrolyzable tannins (ellagitannin, punicalagin, punicalin, gallic and ellagic acid), flavonoids, anthocyanins and other phenols,” the researchers explain. These polyphenols are known to have several properties, including:

• anti-inflammatory effects
• antioxidant effects
• hypoglycemic or hypoglycemic effects
• lipid-lowering or cholesterol-lowering effects
• antihypertensive or blood pressure lowering effects
• antimicrobial effects

Pomegranate extracts are known to be useful against viruses such as “influenza viruses, herpes viruses, poxviruses and human immunodeficiency viruses,” say the researchers. The molecules present in the extract called “punicalagin, punicalin and ellagic acid” also show effects against the hepatitis C virus (HCV). Pomegranate peel extracts (PoPEx) also showed effects against the flu virus by preventing virus entry and RNA transcription.

This study targeted four major ellagitannin members present in PoPEx, “punicalagin, punicalin, ellagic acid and gallic acid”, to see their efficacy against SARS-CoV-2 in laboratory models (in silico instruments).

Study design

The researchers tested the binding affinities of ellagic acid, gallic acid, punicalagin and punicalin on four protein targets that could allow the virus to enter the host cell. These molecules tested were;

• Umifenovir
• Lopinavir
• Camostat and
• Selected PoPEx components (punicalagin, punicalin, ellagic acid and gallic acid)

The four ptoeitn objectives were:

• SARS-CoV-2 spike glycoprotein,
• Angiotensin 2 converting enzyme,
• Furin,
• Serine transmembrane protease 2 (TMPRSS2).

The 3D structures of the tested molecules were downloaded and computational techniques were used to verify their binding affinity.

Results

The results of this study showed that components of pomegranate peel extracts such as punicalagin and punicalin show significant potential in interacting with selected protein targets and thus could prevent viral entry into the host cell. This is to be followed by in vitro and in vivo studies they write.

• Using the DoGSiteScorer tool, potential binding pockets on proteins were determined.
• The most dopable pockets for S-glycoprotein, ACE2, furin and TMPRSS2 were chosen.
• A high non-polar amino acid ratio was found for glycoprotein S, which means that a good drug target was found (the non-polar amino acid ratio was 0.63)
• The non-polar amino acid ratios of ACE2, furin and TMPRSS2 were 0.38, 0.26 and 0.40, respectively.
• The best drug score values ​​for the targets analyzed were between 0.73 and 0.84
• The volumes of the drug binding pockets determined the potential of the drug to bind to the target. The most significant volume, surface and depth of the selected pocket were detected for ACE2.
• Punicalagin and punicalin formed the most stable complexes with the protein targets. They also showed intense interactions with TMPRSS2 amino acid residues

Conclusions and implications

Preventing viral entry into the host cell could effectively prevent infection. This study demonstrated that PoPEx polyphenols could offer potential inhibitory activity against SARS-CoV-2, especially during its entry into the host cell. The study authors write: “Punicalagin and punicalin are promising candidates for further in vitro anti-SARS-CoV-2 studies.” The team concluded: “Being the ingredients of a natural product that is used as a food, these candidates also have a confirmed safety profile which is their additional and important advantage in treating the disease.”