On March 23, 2023, Mary Zoepfl and colleagues from the University of Mississippi and Virginia Commonwealth University published an article in the journal Scientific Reports titled " Antiviral activity of marine sulfated glycans against pathogenic human coronaviruses." The research demonstrates that five specific marine sulfated glycans (MSGs) exhibit potent inhibitory effects against a range of human pathogens, including severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), SARS-CoV-2 (multiple variants), Middle East respiratory syndrome coronavirus (MERS-CoV), and influenza A. The findings reveal that these marine polysaccharides match the antiviral potency of heparin while maintaining a significantly more favorable safety profile by reducing the risk of unwanted anticoagulant activity.

Research Background

The field of Marine Glycobiology has long recognized that the oceans are a reservoir of structurally diverse Polysaccharides. Marine organisms, living in diverse and often harsh environments, have evolved unique extracellular matrices and protective cell walls composed of complex glycans. These molecules, such as Fucoidans, Carrageenans, and Sulfated Galactans, serve as the organism's first line of defense and structural support.

In the context of human health, the importance of these glycans has surged following the global health crises caused by coronaviruses. Most enveloped viruses utilize host-cell surface heparan sulfate proteoglycans (HSPGs) as initial attachment receptors. Because the viral spike proteins have evolved to "recognize" the negative charge density and specific spatial arrangement of sulfate groups on these host sugars, researchers have sought mimetic molecules that serve as decoys.

Historically, heparin was the primary candidate for this role. However, its origin (typically porcine or bovine) and its powerful effect on blood thinning limited its utility. This paper addresses the urgent need for "non-anticoagulant" heparin mimetics. Marine glycans are ideal candidates because they are abundant, biocompatible, and possess a level of structural regularity rarely found in the animal kingdom, allowing for a more targeted pharmacological approach.

Research Results

The study meticulously characterizes the biochemical interactions between complex marine glycans and viral entry mechanisms. The researchers divided their investigation into several phases, focusing on efficacy, Structural Specificity, and physiological safety.

• Broad-Spectrum Inhibition of Viral Entry via Spike-Glycan Interactions

The primary focus of the experimental design was to evaluate how MSGs interfere with the early stages of viral infection. Using pseudotyped lentivirus-based virus-like particles (VLPs) that express the spike glycoproteins of SARS-CoV-1, SARS-CoV-2, and MERS-CoV, the team monitored the ability of these glycans to prevent host cell entry. The results were striking: all five tested MSGs, derived from red algae (Botryocladia occidentalis), sea urchins (Lytechinus variegatus), and sea cucumbers (Isostichopus badionotus and Pentacta pygmaea), blocked viral transduction in ACE2-expressing HEK-293T cells.

Fig.1 Structural representations of heparan sulfate, heparin, and the five MSGs studied. (Zoepfl, et al., 2023)

The EC₅₀ values were consistently in the low microgram-per-milliliter range. Specifically, the sulfated galactan BoSG and the sulfated fucan IbSF showed exceptional performance across all tested coronavirus strains. This suggests that the mechanism of action involves the competitive binding of MSGs to the heparin-binding domains on the viral spike proteins, effectively "shielding" the virus from its primary attachment points on the host's cell surface.

Fig.2 Antiviral activity of MSGs against SARS-CoV-1 and SARS-CoV-2. (Zoepfl, et al., 2023)

• Structural Regularity and the Efficacy of Sulfation Patterns

One of the most innovative aspects of this research is the correlation between the precise chemical architecture of marine glycans and their Biological Activity. Unlike mammalian glycosaminoglycans (GAGs) like heparan sulfate, which exhibit high degrees of structural heterogeneity, marine glycans often possess highly regular repeating units.

The researchers analyzed five distinct structures:

• BoSG: A sulfated galactan with a regular [-3)-galactose-(β1-4)-galactose-(α1-] backbone.
• LvSF: A sulfated fucan with a tetrasaccharide repeating unit containing 2,4-disulfated and 2-sulfated fucose residues.
• IbSF: A similar fucan but with a different sulfation distribution.
• IbFucCS and PpFucCS: Fucosylated chondroitin sulfates with varying fucose branch patterns.

The study found that the specific placement of sulfate groups, particularly the 2,4-disulfation in fucose residues, plays a critical role in binding affinity. By utilizing these regular structures, the research demonstrates that glycobiology moves beyond the "one-size-fits-all" approach of heparin. The innovations here lie in identifying that marine-sourced molecules provide a cleaner, more predictable template for pharmaceutical design than their mammalian counterparts.

• Decoupling Antiviral Potency from Anticoagulant Risk

A major hurdle in using sulfated polysaccharides like heparin as antivirals is their inherent anticoagulant property, which leads to life-threatening bleeding complications. The researchers conducted rigorous coagulation assays, including activated partial thromboplastin time (aPTT) and factor Xa/IIa inhibition tests, to compare the MSGs against unfractionated heparin.

The data revealed that heparin is a potent anticoagulant even at low concentrations. Several MSGs, such as the sulfated galactan BoSG and the fucosylated chondroitin sulfate PpFucCS, showed negligible anticoagulant activity at concentrations where their antiviral effects were maximal. This breakthrough suggests that it is possible to engineer or select marine glycans that target viral proteins without interfering with the human coagulation cascade. This decoupling is a major innovation in marine glycobiology, paving the way for systemic antiviral treatments that do not require the intensive monitoring associated with heparin therapy.

Bioactivity Analysis of Marine Glycan&Glycoprotein at CD BioGlyco

Conclusion

The study by Zoepfl et al. represents a significant leap forward in our understanding of how marine glycobiology is harnessed for modern medicine. By demonstrating that sulfated glycans from sea cucumbers, sea urchins, and red algae potently inhibit a broad spectrum of coronaviruses and influenza viruses, the authors have provided a robust proof-of-concept for a new class of antiviral therapeutics.

The true innovation lies in the identification of molecules that maintain high-affinity binding to viral glycoproteins while exhibiting low-to-negligible affinity for coagulation factors. This suggests a future where marine-derived drugs could be used as prophylactic or therapeutic agents against emerging viral threats, providing a safer alternative to current Carbohydrate-based Drugs. As we continue to explore the molecular diversity of the marine environment, the precise mapping of glycan structure to biological function will undoubtedly lead to the development of highly specific, biocompatible, and effective broad-spectrum antivirals. These findings underscore the vital role that marine natural products continue to play in solving some of the most pressing challenges in global health.