Study shows polysaccharides from seaweed and abalone inhibit SARS-CoV-2 in vitro.

During the early stages of the COVID-19 pandemic, in the absence of a cure or vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), several studies around the world searched for substances that could to inhibit the infection, replication and spread of SARS-CoV-2 from marine bioactive compounds including polyphenols, polysaccharides and carotenoids.

Polyphenols obtained from brown algae, also known as phlorotannins, have been predicted to be an inhibitor of SARS-CoV-2 infection. in silico. Siphonaxanthin, which is a marine carotenoid obtained from seawater. Codium fragile, could inhibit the entry of SARS-CoV-2 pseudovirus into the cell in vitro.

Recent studies have indicated that iota-carrageenan can inhibit SARS-CoV-2 replication in several cell lines. It has also been reported to inhibit the replication of alpha, beta, gamma, and delta variants of SARS-CoV-2. In addition, an iota-carrageenan nasal spray was also identified as reducing the risk of SARS-CoV-2 infection by 79.8% in healthcare workers who cared for patients with COVID-19.

Furthermore, several marine sulfated polysaccharides have been observed to inhibit SARS-CoV-2 entry by interfering with the interaction between the host cell ACE2 receptor and SARS-CoV-2 spike protein in vitro. A previous study showed that crude polysaccharides (PC) from seaweed and abalone viscera could effectively inhibit the entry of SARS-CoV-2 pseudovirus.

A new study published in marine drugs evaluated the inhibitory effect of three polysaccharides, the raw polysaccharide of Hizikia fusiforme (CPHF), crude polysaccharide from Sargassum horneri (CPSH) and crude abalone viscera polysaccharide (CPAV) on the spread of SARS-CoV-2. in vitro.

Study: Evaluation of the antiviral effect against the spread of SARS-CoV-2 by crude polysaccharides from algae and abalone viscera in vitro. Image credit: mnimage / Shutterstock

About the study

The study consisted of an evaluation of the cytotoxicity of CPHF, CPSH and CPAV, followed by a plaque reduction assay using different concentrations of CPHF, CPSH and CPAV. The tissue culture infective dose of 50% (TCID50) was determined based on whether or not a cytopathic effect occurred.

An immunofluorescence test was performed to assess the spread of SARS-CoV-2. Western blot was performed to examine viral spike (S) and nucleocapsid (N) protein expression, followed by RNA isolation and quantitative RT-PCR (qRT-PCR) using RNA-dependent RNA polymerase (RdRp) and nucleocapsid (N) primers. Finally, a reporter assay was performed using the SARS-CoV-2 pseudovirus.

Evaluation of the antiviral effect against the spread of SARS-CoV-2 by crude polysaccharides from algae and abalone viscera in vitro.

Study results

The results indicated that the crude polysaccharide from abalone viscera was somewhat more toxic compared to the other two PCs. Plaque formation was observed to be reduced in a dose-dependent manner by PCs, with 500μg/mL PC reducing plaque formation by 98%. Plaque formation was reported to be reduced by more than 60% by CPHF and CPSH and by 40% by CPAV for cells treated with CP concentrations of 0.8 μg/mL before infection with the SARS-CoV-2. In addition, the 50% inhibitory concentrations (IC50) of CPHF, CPSH and CPAV were 0.35, 0.56 and 4.37 μg/mL, respectively.

Crude polysaccharides were shown to inhibit SARS-CoV-2 infection at 3 days and 4 days post-infection. The infectivity of SARS-CoV-2 in the presence of 500 μg/mL of CPAV, CPSH and CPHF before the cells were processed by the virus was 16.5 ± 2.5%, 9.5 ± 3.2 % and 8.7 ± 2.7%. At the same time, it increased to 47.8 ± 6.6%, 48.7 ± 3.3% and 45.7 ± 1.4% when cells were treated with PCs after viral infection.

The results also indicated that cells treated with PCs before viral infection did not express viral proteins S and N. However, their expression was observed in cells treated with PCs after viral infection. However, their expression was observed in PC-treated cells after viral infection. Moreover, RdRp and N RNA copies were not detected in CP-pretreated cells, while RdRp and N RNA copies were slightly increased in CP-treated cells after infection. In addition, entry into cells of the SARS-CoV-2 pseudovirus was strongly inhibited by pretreatment with PCs. However, the inhibitory effect was weak when post-treated with PCs.

Therefore, the current study demonstrated that the spread of SARS-CoV-2 before and after viral infection could be inhibited by crude polysaccharides from algae and abalone viscera. These crude polysaccharides must be further purified and characterized in order to be used to develop therapeutics and prophylactics against the spread of the virus. Further studies are needed to examine pharmacokinetics, perform non-clinical trials, and clarify antiviral mechanisms when the structures of marine polysaccharides are analyzed.

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