The oyster digs as a weapon against SARS-CoV-2

According to an article published in the journal Opinion in Medical Virology, the efficacy of antiviral agents derived from molluscs has been proven in numerous laboratory and animal studies, while its efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has also been proposed by recent in silico studies.

Since the onset of the 2019 coronavirus disease (COVID-19) pandemic, several different variants of SARS-CoV-2 of concern (including the most recent and widespread delta strain) have emerged with notable changes in the viral epidemiology and transmissibility.

Of course, this threatens the effectiveness of the vaccines we have, but also antiviral drugs that are currently in clinical trials or about to be approved. Therefore, as the scientific community continues to grapple with this moving target, the ongoing work on identifying new antiviral compounds against SARS-CoV-2 is critical and should not stop.

Unexplored potential of marine invertebrates

One realistic possibility concerns marine invertebrates, which represent an untapped source of medicinal compounds. Specifically, marine organisms of the phylum Mollusca have a miraculous innate immunity, which also involves the production of potent antiviral compounds.

The only antiviral drug derived from marine invertebrates currently available on the market is known as vidarabine; however, this compound subsequently inspired the design of acyclovir (the drug we used against herpes viruses) and zidovudine (one of the first drugs used in the treatment of herpes infection. HIV).

The success of these drugs thus illustrates how marine invertebrates are not only a direct source of antiviral compounds, but can also inspire the synthesis of entirely new compounds. And given the fact that there are around 100,000 species in the aforementioned phylum, we’ve barely scratched the surface of the opportunity here.

Molluscs that can inhibit viruses

Yet despite the proven activity of many mollusc-derived antivirals in vitro (which includes human viruses), as well as their various mechanisms of action, they were not yet used clinically. One reason is that their modes of action are not fully understood.

However, we do know that lipophilic digestive gland extract and circulatory fluid from green-lipped abalone (Haliotis laevigata) may inhibit entry or hinder the early intracellular stage of herpes simplex virus type 1 infection in Vero cells (i.e., renal epithelial cells taken from a green monkey d ‘Africa).

Inhibition of herpes simplex virus type 1 has also been observed in vitro with European flat oyster extracts (Ostrea edulis), common shell (Cerastoderma edule), whelk (Buccinum undatum), Japanese carpet shell (Ruditapes philippinarum), black-lipped abalone (Haliotis rubra), Mediterranean mussel (Mytilus galloprovincialis) and the veined rapa (Venous rapanosa).

Rapanosa venosa.  Image Credit: Tana Dan84

Rapanosa venosa. Image Credit: Tana Dan84

The antiviral activity of some mollusks also extends to other herpes viruses (such as the Epstein-Barr virus), while the oyster hemolymph also harbors compounds that are active against the herpes virus. infectious pancreatic necrosis and human adenovirus type 5.

cupped oyster

We know that intracellular zinc exhibits high inhibitory activity against various coronaviral enzymes, including 3C-type and papain-like proteases and RNA-dependent RNA polymerase, essential for viral replication. Therefore, zinc has the propensity to act as a therapeutic agent for SARS-CoV-2, which can be enhanced by coupling it with a metal chaperone.

Like the cupped oyster (Crassostrea gigas) is high in zinc and also contains cavortin (its major hemolymph protein) as a metal chaperone, it is indeed possible that there is potential antiviral activity against SARS-CoV-2. In addition, it can also act as a metal chaperone which allows the movement of zinc into host cells.

Nevertheless, the specific mechanism behind the antiviral activity of cavortin is still unknown, and its bioavailability in cell culture and in animal models also arises. However, the unexplored potential of a new antiviral compound against SARS-CoV-2 is definitely tempting.

Finally, there is a problem of strict biosafety level for laboratories working with SARS-CoV-2. However, in initial screening efforts, cold coronaviruses can be used to screen for compounds with potential universal action. In any case, the remarkable diversity of molluscs can still work in our favor.


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