Seaweed metabolites as new drugs against viruses

Bioactive metabolites extracted from natural resources serve as drugs for the treatment of various diseases. A new review article published in the Journal of Biotechnology provided information on various nutraceutical metabolites extracted from seaweed. The authors also discussed the efficacy of these bioactive metabolites to treat several diseases, including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of the coronavirus pandemic 2019 (COVID-19 ) In progress.

Study: Microalgal drugs: A promising therapeutic reserve for the future. Image Credit: Bigone/Shutterstock

Algae, a promising source of bioactive metabolites

Algae, eukaryotic plants belonging to the kingdom Protista, were born about a billion years ago. Based on their size, these photosynthetic organisms are classified into macroalgae (multicellular) and microalgae (unicellular). In addition to maintaining carbon dioxide levels on earth and preventing climate change, seaweed contains various proteins and dietary fibers that can serve as anti-inflammatories, anti-microbials and disease prevention agents. One of the main advantages of drugs derived from microalgae is their metabolic plasticity. Pharmacologically significant algae can be grown on a large scale using photo-bioreactors.

In 1950, marine organisms were explored for the first time to obtain new drugs. Among red, green and brown algae, red algae contains the highest number of bioactive compounds, for example, polysaccharides, lipids, polyphenols, steroids, glycosides, flavonoids, tannins, saponins, alkaloids, triterpenoids, anthraquinones and cardiac glycosides. Many of these metabolites have antimicrobial, anti-inflammatory and antioxidant properties. Moreover, in microalgae, many chemicals are deposited in their cell walls, making them thick and resistant to environmental changes. This is the reason why algae can withstand harsh conditions.

The edible form of seaweed contains valuable compounds, such as carotenoids and astaxanthin, which exhibit exceptional antioxidant properties. This is why seaweed has been widely used as a health supplement for humans, its market value reaching $3.4 billion. Marine microalgae (algae) naturally produce carrageenans, sulfated polysaccharides composed of fucoidan, fucosterol, sodium alginate and protein. Additionally, Spirulina, known as a super food, is extracted from the seaweed named, Spirulina platensis. Moreover, several metabolites, such as cyanovirin, scytovirin and microvirin, isolated from cyanobacteria, are effective against various viral, bacterial and fungal diseases.

Many algae contain lipids, low value compounds present in various forms such as fatty acids, sterols, glycerides, fat soluble vitamins and phospholipids. Several studies have revealed that microalgae and macroalgae can synthesize a therapeutically relevant class of fatty acids, for example, polyunsaturated fatty acids (PUFAs). Seaweed-based sterols, such as fucosterol, ergosterol, and chondrillasterol, exhibit anti-inflammatory reactions. Various medically important lipids and fatty acids are obtained from Chlorella vulgaris, Undaria pinnatifida, Haematococcus pluvialisand Cladophora rupestris. Several types of vitamins, for example, vitamin C, vitamin E, vitamin B2, B3, B9, B12, vitamin K, etc., are synthesized by algae, for example, Skeletonema marinoi, Tetraselmis suicide, and Chaetoceros sp.

Study: Algae Chlorella vulgaris under microscopic view Image credit: Elif Bayraktar / ShutterstockStudy: Algae Chlorella vulgaris under microscopic view Image credit: Elif Bayraktar / Shutterstock

Microalgae and macroalgae contain all essential amino acids that are not synthesized by the human body. These essential amino acids protect cells against damage and attack by free radicals. Palmaria palmata includes amino acids, such as leucine, valine, methionine, isoleucine, and threonine, which resemble the protein content found in egg white protein and ovalbumin.

Seaweed metabolites for the treatment of diseases

The majority of microalgae contain PUFAs, including eicosapentaenoic acid and docosahexaenoic acid, i.e. the two most important omega-3 fatty acids. These compounds significantly reduce the risk of heart disease. Griffithsin (GRFT), a protein extracted from macroalgae Griffithsia sp, exhibits anti-human immunodeficiency virus (HIV)-1 property. This antiviral agent has also shown efficacy against hantaviruses and coronaviruses (eg, SARS-CoV-2 and MERS). Scientists revealed that GRFT binds to glycosylation sites of the S1 subunit of the coronavirus Spike protein, possibly a receptor binding domain (RBD), and inhibits viral infection. Carrageenans obtained from red algae exhibit antiviral activity. Several studies have shown that they can inhibit the replication of viruses, such as HIV, hepatitis A, human papillomaviruses, dengue virus, Japanese encephalitis virus and murine cytomegalovirus.

Fucoidans are extracted from the cell walls of brown algae, which contain groups of L-fucose and sulfate residues. This compound exhibited various therapeutic activities including efficacy against coronavirus, HIV, human cytomegalovirus, coronavirus, influenza virus, and murine norovirus. The main mechanism of action has been associated with the sulfate group blocking virus entry into the host via competition for attachment of the positively charged viral glycoprotein envelope to the host cell. Recently, fucoidan isolated from brown algae Saccharina japonica has shown efficacy against SARS-CoV-2. Ulvans, which are sulfur polysaccharides (SPS) obtained from green algae, for example, Ulva sp. revealed antiviral, immunomodulatory, antioxidant, antihyperlipidemic and anticancer properties. Additionally, this metabolite helps reduce chronic illnesses related to gastrointestinal health.

Seaweed metabolites extracted from Hydroclathrus clathratus, Ulva prolifera, Gracilaria lemaneiformis, Laurencia papillosa, Sargassum fusiforme, etc., also exhibit antibacterial and antifungal properties.

Thanks to the continuous research and development of marine resources, algae and their metabolites play an increasingly important role in functional foods and nutrition. Clinical and experimental trials are currently being conducted on many drugs derived from algae metabolites. Macro and microalgae contain carotenoids, sulfur polysaccharides, lipids, proteins and vitamins essential for health and can also be used to treat and prevent many life-threatening infections and diseases, such as SARS-CoV-2. Algae represent a vast reservoir and treasure trove for high value-added biocompounds widely used in food, nutraceutical, pharmaceutical, cosmetic and other industries.

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