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 have been looking for substances that increase the infection, replication could inhibit and spread SARS-CoV-2 from marine bioactive compounds, including polyphenols, polysaccharides and carotenoids.
Polyphenols obtained from brown algae, also known as florotannins, have been predicted to be an inhibitor of SARS-CoV-2 infection. in silico† Siphonaxanthin, a marine carotenoid obtained from seawater. brittle sodium, could inhibit the entry of SARS-CoV-2 pseudovirus into the cell in vitro†
Recent studies have shown 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 found to reduce the risk of SARS-CoV-2 infection by 79.8% in healthcare professionals caring for patients with COVID-19.
In addition, several marine sulfated polysaccharides have been observed to inhibit SARS-CoV-2 entry by interfering with the interaction between the host cell’s ACE2 receptor and the SARS-CoV-2 spike protein in vitro. A previous study showed that crude polysaccharides (PC) from seaweed and abalone viscera can effectively inhibit the entry of SARS-CoV-2 pseudovirus.
A new study published in marine drugs evaluated the inhibitory effect of three polysaccharides, the crude polysaccharide of Fusiform Hizikia (CPHF), crude polysaccharide of Sargassum horneric (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 gut 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 test with different concentrations of CPHF, CPSH and CPAV. The tissue culture infection dose of 50% (TCID50) was determined based on whether or not a cytopathic effect occurred.
An immunofluorescence assay 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.
The results indicated that the crude polysaccharide from abalone viscera was slightly more toxic compared to the other two PCs. Plaque formation was observed to be reduced by PCs in a dose-dependent manner, with 500 g/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 SARS-CoV-2. In addition, the 50% inhibitory concentrations (IC50 ) of CPHF, CPSH and CPAV were 0.35, 0.56 and 4.37 g/ml, respectively.
Crude polysaccharides were found to inhibit SARS-CoV-2 infection 3 days and 4 days after infection. The infectivity of SARS-CoV-2 in the presence of 500 µg/ml 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. In addition, 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, access to cells of the SARS-CoV-2 pseudovirus was strongly inhibited by pretreatment with PCs. However, the inhibitory effect was weak in PC post-treatment.
Therefore, the present study showed that the spread of SARS-CoV-2 before and after viral infection can be inhibited by crude polysaccharides from algae and abalone viscera. These crude polysaccharides must be further purified and characterized in order to be used for the development of therapies and prophylactics against the spread of the virus. Further studies are needed to investigate pharmacokinetics, conduct non-clinical studies, and clarify antiviral mechanisms when analyzing marine polysaccharide structures.