Dr Ashish Kumar Jha, Dr Suseela Mathew and Dr Ravishankar C.N
Seaweeds are rich sources of food, nutrition and traditional medicine. The potential of the seaweeds are underutilized.
Seaweeds are marine photosynthetic algae abundantly grown in ocean. onthe basis of the photosynthetic pigments. They are classified in three different classes i.e red (Rhodophyta), green(Chlorophyta) and brown (Phaeophyta).Seaweeds are used in many maritime countries as a source of food, animal feeds, and fertilizers and as a source of traditional medicine.
It constitutes an important component of food in Asian countries but is still considered as an underutilized resource (Tseng 2004). Seaweeds are known as highly nutritive food containing carbohydrate, protein, vitamins, mineral, fibre, and essential fatty acids (Ortiz et al. 2006). The presence of low-fat content in seaweeds makes them low-calorie food (Ruperez 2002). On an average, they contain 80-90% water and nearly 50% carbohydrates and 1-3% lipids. Besides being a source of healthy food due to low calorie and significantly higher mineral and fiber content, it is an important resource of diverse kinds of bioactive principles (Jha et al 2020).
Apart from the nutritional significance, the therapeutic effects of the seaweed have been extensively studied.Bioactive principles of the seaweeds are known to exhibit anticoagulant, antioxidant, antibacterial, antiviral, anticancer properties etc (Jha et al 2020).
Immunity literally means protection of body from forign substance including bacteria, virus and any other substances (Zhao et al. 2016). There are several mechanism by which the immunological activities of the body is achieved and the key components are neutrophils, lymphocytes, monocytes and other related cells which either work independently or in tandem (Kim et al 2012).
Molecules like polysaccharides, protein, lipids, small peptides are of great importance in regulating the immune functions and maintan the homeostasis (Xiao, Muzashvili, &Georgiev, 2014).The sulphated polysaccharide is one of the important componet in the seaweed which is studied for its immunological and therapeutic potential.
Sulphated polysaccharides are complex poly-anionic macromolecules containing sulphate moieties and sugar backbone.Sulphated polysaccharide along with its oligosaccharide derivatives from seaweed are known for its biological activities (Jiao et al 2011).Sulphated polysaccharides from seaweed have a wide range of bioactive properties including antioxidant, anti-inflammatory, antibacterial, antiviral, antitumor, immunomodulatory and anticoagulant activities.The unique chemical structure of the sulphated polysaccharide allowsinteracting with a variety of molecules and cellular protein which manifest different immunological as well as therapeutic propertires (Arfors et al., 1993).
The sulphated polysaccharides from seaweeds have long been known for its immunomodulatory activities that can be of great application in inducing the immune response or in regulating the activities of immunological cells or to ameliorate the effects of inflamations or inflamatory response (Chen et al., 2008). There are number of studies revealing that the seaweed polysaccharides can regulate the innate immunity directly by binding to different immunogenic molecules such as pattern recognition receptors (PRRs) like mannose receptor, toll like receptors and macrophages (Chen et al., 2008).
Macrophages are an important immune cells with multipronged activities, they generally regulate the immune system by presenting the antigens and releasing active mediators to immune cells (Zirk et al.,1999). It is observed that higher the level of sulphate group in fucoidan a sulphated polysaccharide from brown seaweed higher the activities of macrophages (Qiao et al., 2010) and reduction of sulphate group reduces the activities significantly. Seema patel reported that the water soluble sulphated polysaccharide extract from enteromorpha prolifera has shown in vitro and in vivo immunomodulatory activities.The in vivo experiment has shownthe increase in IFN-α and IL-2 secretions, suggesting that sulphated polysaccharide has strong immunostimulator.
Since long sulphated polysaccharide from seaweed has been used for the pharmaceutical purpose. There are several studies on the antibacterial activities of seaweeds available. The probable mechanism of antibacterial activity is attributed to the glycoprotein receptors on the surface of polysaccharide which bind with the compound on the bacterial cell wall, in turn increases the permeability of cytoplasmic membrane causing protein leakage and binding to bacterial DNA. Fucoidan and laminarin from brown seaweed have been used as oral antibiotics to inhibit the growth of Staphylococcus aureus and E. Coli
The know how of the antiviral activities of sulphated polysaccharide goes back to more than 50 years when it was observed that the seaweed extracts protected chicken embryos against influenza B and mumps virus (Gerber et al 1958).
The efficacy of sulphated polysaccharides from seaweed in inhibiting the replication of enveloped viruses viz. herpes simplex virus (HSV), human immunodeficiency virus (HIV), dengue virus are well established (Jiao et al 2011). There are different pathways or mode of action of sulphated polysaccharide but the reduction, inhibition and down regulation of pro-inflamatory factors such as NO, myeloperoxidase, interleukin IL-1β, IL-6, and TNF-α is the key to the suppression of inflamation activities.
The immunomodulatory activities of seaweeds are maintained by regulating macrophages, T/B lymphocytes, natural killer cells (NK cells), complement systems etc. The in vitro study has revealed that the seaweed polysaccharide such as iota-carrageenan was effective against the H1N1/2009 pandemic (Leibbrandt et al., 2010). Kwon and his team have reported that sulphated polysaccharide effectively inhibit SARS-CoV-2 in vitro.
There are plethora of literature available on the different pharmaceutical and other health benefits of the biomolecule present in the marine seaweed but still the potential of the seaweed is underutilized. The era of COVID pandemic is the best time to tap the potential of seaweed both as food source and for the therapeutic uses.It is now established that seaweed polysaccharides are quite effectively inhibit even COVID-19.
(Dr Jha is the scientist in ICAR-CIFT and Dr Mathew is the Principal Scientist& HoD, Department of Biochemestry& Nutrition, ICAR-CIFTand Dr Ravishankar is the Director, ICAR-CIFT. Views expressed are their personal. References can be provided on request.)