Natural fucoidans inhibit coronaviruses by targeting viral spike protein and host cell furin

Harnessing traditional Chinese medicine polysaccharides for combatting COVID-19

With the global spread of COVID-19 posing ongoing challenges to public health systems, there is an ever-increasing demand for effective therapeutics that can mitigate both viral transmission and disease severity. This review surveys the landscape of polysaccharides derived from traditional Chinese medicine, acclaimed for their medicinal properties and potential to contribute to the COVID-19 response. We specifically focus on the capability of these polysaccharides to thwart SARS-CoV-2 entry into host cells, a pivotal step in the viral life cycle that informs transmission and pathogenicity. Moreover, we delve into the concept of trained immunity, an innate immune system feature that polysaccharides may potentiate, offering an avenue for a more moderated yet efficacious immune response against various pathogens, including SARS-CoV-2. Our comprehensive overview aims to bolster understanding of the possible integration of these substances within anti-COVID-19 measures, emphasizing the need for rigorous investigation into their potential applications and underlying mechanisms. The insights provided here strongly support ongoing investigations into the adjunctive use of polysaccharides in the management of COVID-19, with the anticipation that such findings could lead to a deeper appreciation and clearer elucidation of the antiviral potentials inherent in complex Chinese herbal remedies.

Systematic Characteristics of Fucoidan: Intriguing Features for New Pharmacological Interventions

Fucoidan, a sulfated polysaccharide found primarily in brown algae, is known for exhibiting various biological activities, many of which have been attributed to its sulfate content. However, recent advancements in techniques for analyzing polysaccharide structures have highlighted that not only the sulfate groups but also the composition, molecular weight, and structures of the polysaccharides and their monomers play a crucial role in modulating biological effects. This review comprehensively provides the monosaccharide composition, degree of sulfation, molecular weight distribution, and linkage of glycosidic bonds of fucoidan, focusing on the diversity of its biological activities based on various characteristics. The implications of these findings for future applications and potential therapeutic uses of fucoidan are also discussed.

Incorporation of Silver into Sulfate Groups Enhances Antimicrobial and Antiviral Effects of Fucoidan

The COVID-19 pandemic has significantly impacted our daily lives. Routine infection-control measures present an effective preventive strategy for a new infectious disease outbreak. Fucoidan, a fucose-rich sulfated polysaccharide found in brown algae, exhibits antiviral activity. Moreover, fucoidan exerts an antimicrobial effect; however, it requires considerably higher concentrations than those needed for its antiviral effect. In this study, we aimed to enhance the antimicrobial activity of fucoidan and prepared a fucoidan silver salt (Ag-Fuc) by incorporating silver ions into the sulfate groups of Yakult Fucoidan derived from Cladosiphon okamuranus Tokida. The fucoidan exhibited a weak inhibitory effect on Escherichia coli growth at significantly higher concentrations, whereas Ag-Fuc inhibited the growth of E. coli and Staphylococcus epidermidis at concentrations comparable to those required for its antiviral effects. Moreover, Ag-Fuc inhibited the growth of Cladosporium cladosporioides. Infections of human cells with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus were more effectively inhibited by lower concentrations of Ag-Fuc compared with fucoidan. Overall, silver ions added to the sulfate groups induced strong antimicrobial activity and enhanced the antiviral effect of fucoidan. We suggest a wide application of Ag-Fuc as a routine preventive material to avoid new infectious disease pandemics.

Targeting furin, a cellular proprotein convertase, for COVID-19 prevention and therapeutics

SARS-CoV-2 has triggered an international outbreak of the highly contagious acute respiratory disease known as COVID-19. Identifying key targets in the virus infection lifecycle is crucial for developing effective prevention and therapeutic strategies against it. Furin is a serine endoprotease that belongs to the family of proprotein convertases and plays a critical role in the entry of host cells by SARS-CoV-2. Furin can cleave a specific S1/S2 site, PRRAR, on the spike protein of SARS-CoV-2, which promotes viral transmission by facilitating membrane fusion. Hence, targeting furin could hold clinical implications for the prevention and treatment of COVID-19. This review offers an overview of furin's structure, substrates, function, and inhibitors, with a focus on its potential role in SARS-CoV-2 infection.

Inhibition of multiple SARS-CoV-2 variants entry by Lycium barbarum L. polysaccharides through disruption of spike protein-ACE2 interaction

Viral respiratory infections are major human health concerns. The most striking epidemic disease, COVID-19 is still on going with the emergence of fast mutations and drug resistance of pathogens. A few polysaccharide macromolecules from traditional Chinese medicine (TCM) have been found to have direct anti-SARS-CoV-2 activity but the mechanism remains unclear. In this study, we evaluated the entry inhibition effect of Lycium barbarum polysaccharides (LBP) in vitro and in vivo. We found LBP effectively suppressed multiple SARS-CoV-2 variants entry and protected K18-hACE2 mice from invasion with Omicron pseudovirus (PsV). Moreover, we found LBP interfered with early entry events during infection in time-of-addition (TOA) assay and SEM observation. Further surface plasmon resonance (SPR) study revealed the dual binding of LBP with Spike protein and ACE2, which resulted in the disruption of Spike-ACE2 interaction and subsequently triggered membrane fusion. Therefore, LBP may act as broad-spectrum inhibitors of virus entry and nasal mucosal protective agent against newly emerging respiratory viruses, especially SARS-CoV-2.

Fucoidan-based antibody-free magnetic nanoparticle for on-site detection of waterborne SARS-CoV-2

The portable and sensitive point-of-care-test (POCT) method is in urgent need to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for ensuring public health and safety. However, detection of trace number of pathogens in real water sample from the environment still faces challenges, because complex environment disruptors can rapidly degrade targets. Herein, magnetic beads coated with fucoidan and polydopamine (Fuc-PDA-MBs) were introduced as the capture carrier for pretreatment of samples. Fucoidan, a sulfated polysaccharide, can recognize the SARS-CoV-2 spike (S1) protein receptor-binding domain (S1 RBD) and was chosen for replacement of antibody in enrichment. Environmental water seeded with SARS-CoV-2 spike pseudovirus was applied to test performance of Fuc-PDA-MBs method. Under optimal conditions, the use of Fuc-PDA-MBs showed average 76 % capture efficiency at SARS-CoV-2 spike pseudovirus concentration ranging from 107.62 to 104.34 gene copies (gc)/L. Compared with Electronegative filtration (ENF), Fuc-PDA-MBs showed better virion sorption effectiveness. Fuc-PDA-MBs also validated by raw contaminated urban wastewater and showed high recovery results for SARS-CoV-2 variants. To rapidly detect virus in POCT, nucleic acid extraction-free Loop-Mediated Isothermal Amplification (LAMP) was used for simplifying experimental process. The Fuc-PDA-MBs-LAMP assay showed the quantitation limit of sample (LOQ) was 105.49 gc/L. The whole procedure could be completed within 90 min, including 30 min for virus pre-enrichment, 10 min nucleic acid release and 45 min LAMP analysis. Compared with regular antibody-based immunodetection, this integrated system provides broad-spectrum, economic way to detect SARS-CoV-2 mutants in complex environments and also adaptable for high throughput test, which might be used for on-site early warning of SARS-CoV-2 outbreaks in developing area.