In the blog, I would like to present the study, “A state-of-the-art review on fucoidan as an antiviral agent to combat viral infections,” by Biswajita Pradhan et al. The study proposes to address fucoidan as a potential protective therapy against COVID-19 and the antiviral activity of sulfated polysaccharides. Even though COVID-19 has declined, it still goes into society. Thus, the seaweed-derived fucoidan may also be used as an anti-COVID-19 drug.
The spike of coronavirus glycoproteins is essential for virus attachment and entry into host cells. Coronavirus entry is mediated by protein-dependent and supports the splitting of spike proteins, leading to further penetration. The coronavirus requires ACE2 (angiotensin-converting enzyme 2) as its primary receptor on human cells, and the spike protein binds to the ACE2 receptor and starts replicating CoV. Coronaviruses use the high expression of ACE2 receptors in endothelial and airway epithelial cells to enter the cells. As a result, acute illness is caused by a viral infection and an active immune response.
First, Sulfated polysaccharides can impede viral entry into host cells by directly limiting viral binding to the cell surface. When viruses bind to host cells, irreversible adsorption occurs through electrostatic interactions between host cells and viral receptors. Some sulfated algal polysaccharides interact with viral receptors, blocking contact with the host cell surface or interacting directly with viral particles, thus preventing viral infection. The study also revealed that the negative charge of the sulfate group of fucoidan interacts with the virus by masking the positive control of the virus receptor.
Several algal-derived polysaccharides can hinder virus transcription and replication once they reach the host cell by interfering with replicating enzymes like reverse transcriptase or blocking the synthesis of proteins from mRNA.
In vitro experience, fucoidan (15.6 μg/mL) inhibited SARS-CoV-2 in vitro via binding of the virus to her S glycoprotein. Likewise, sulfated polysaccharide (9.10 μg/mL) inhibited SARS-CoV-2 in an in vitro model via S-glycoprotein binding. Also, Sulfated fucoidan and crude polysaccharides isolated from six seaweed species, including Laminaria japonica, Undaria pinnatifida sporophyll, Sargassum horneri, Hizikia fusiforme, Porphyra tenera, and Codium fragile, exhibited IC50 values (12–289 μg) against SARS-CoV. /mL) suppressed viral infection.
On the other hand, a healthy gut microbiome is essential for modulating antiviral immunity by improving gut flora. In such circumstances, algae-based sulfated polysaccharides can be used as food supplements to enhance gut microbiota and reduce the infection of novel SARS-CoV-2. Gut microbiota symbiosis associated with ACE2 is pivotal in improving antiviral immunity by stimulating interferon production, decreasing immunopathology, and increasing natural killer (NK) and cytotoxicity in COVID-19-suffering patients. As seaweed is rich in vitamins, minerals, and sulfated polysaccharides, it can be used as a dietary supplement for COVID-19 patients.
Additionally, immunocompromised people have a reduced ability to fight infections and other disorders. Fucoidan (9 kDa) from Undaria pinnatifida tested with H1N1 (A/NWS/33) virus was decreased in the mucosa of immunocompetent and immunocompromised mice with an IC50 value of 15 μg/mL at 5 mg/day post-infection and stimulated mucosal immune responses. On a positive note, fucoidan from Undaria pinnatifida has been shown to inhibit influenza A virus replication in vivo in infected mice and to improve innate immunity (natural killer and macrophage activity) through immune pathways. Fucoidan may also be a promising supplement for immunocompromised patients.
Algal sulfated polysaccharides can be used individually as antiviral agents or in combination with clinically approved antiviral drugs that can combat COVID-19. Vaccination programs have been initiated, but sulfated polysaccharides like fucoidan may exert potential immunomodulatory effects against COVID-19 infection. In addition, it can also modulate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and reduce the risk of viral contamination in the post-COVID era. Therefore, fucoidan makes a great dietary supplement that can limit respiratory damage after viral infection by restoring innate immune function and preventing inflammation.
In conclusion, as it functions as a food supplement, there is crucial to establish it as an antiviral and immunomodulatory agent in the pharmaceutical field.
Source: Carbohydrate Polymers Volume 291 (2022), 119551