Bioactive compounds from different seaweeds.
Edible seaweeds are rich in bioactive compounds such as soluble dietary fibers, proteins, peptides, minerals, vitamins, polyunsaturated fatty acids and antioxidants. Previously, seaweeds were only used as gelling and thickening agents in the food or pharmaceutical industries, recent researches have revealed their potential as complementary medicine. The red, brown and green seaweeds have been shown to have therapeutic properties for health and disease management, such as anticancer, antiobesity, antidiabetic, antihypertensive, antihyperlipidemic, antioxidant, anticoagulant, anti-inflammatory, immunomodulatory, antiestrogenic, thyroid stimulating, neuroprotective, antiviral, antifungal, antibacterial and tissue healing properties. In proposed chapter, we discussed various active compounds include sulphated polysaccharides, phlorotannins, carotenoids (e.g. fucoxanthin), minerals, peptides and sulfolipids, with proven benefits against degenerative metabolic diseases. Moreover, therapeutic modes of action of these bioactive components and their reports are summarized in this chapter.
Consumer interest has been increased from previous decades towards the health food and nutrition is the prime focus in formulating the food products. Algae are the organisms capable of providing bioactive compounds for producing novel medicinal and pharmaceutical substances. Algae are widely studied for human nutritional purpose and correspondingly utilized as functional foods . Natural abundance, diverse origin and universal availability of algae makes it an essential source of biologically functional ingredients . The term marine algae are generally referred as marine macroalgae or seaweeds . Seaweeds are living resources found notably in littoral habitats or attached to rocks. They grow in shallow coastal waters as well as in deep sea areas up to a depth of 180 m. These macroscopic algae relatively occur in river mouth and saline waters. Seaweeds constitute the basis of the marine food chain and are subdivided in to three divisions, namely, brown algae, red algae and green algae .
Seaweeds, sometimes referred as edible marine algae, are regarded as good reservoir of compounds with numerous biological and biomedical activities and are most remarkably abundant in sulfated polysaccharides . These have been studied in recent years to develop novel pharmaceuticals and potent bioactive substances [6, 7]. Edible macro algae have become a good source of food and alternative medicine in Asian countries  and in the western countries they are extraction specific and used for many industrial applications in food , cosmetics and pharmaceuticals . The algal biotechnology industry is growing with an aquaculture division that produces large quantities of seaweeds, such as Laminaria, Gracilaria, and Spirulina. Additionally, the utilization phycocolloids derived from algae such as algin, agar, and carrageenan has developed into a well-established industry . Cultivation of macroalgae now contributes to over 90% of the global seaweed demand, with the remainder being naturally harvested. Despite the growing worth of algae as a source of food ingredients, the industry has developed with only varying amounts of success and its biotechnological application are still under-exploited .
1.1. Types of seaweeds
At present, algae are divided in to four domains: Bacteria, Plantae, Chromista and Protozoa. All these vary greatly in morphology and sizes, which ranges from unicellular to multicellular microalgae or colony forming marine organisms such as macrophytes and seaweeds. Macroalgae are traditionally classified based on their characteristic forms and sizes, however the most commonly use feature in algal classification is the presence of specific pigments.
Marine algae due to their richness in bioactive compounds may exhibit antioxidant, anti-inflammatory, anticoagulant, antimicrobial, antiviral, antitumour and hypocholesterolemic activity . Since seventeenth century marine macroalgae have long been used for biomedical purposes because of their potential phytochemical constituents and highly diverse nature. Algae can be classified into two groups based on their size: phytoplankton (microalgae) having 5000 different species and seaweed (macroalgae) with 6000 species .
Natural pigments determine the inherence of marine algae to one of the three algal divisions referred to as brown algae (
1.2. Nutritional profile
Seaweeds have been recently emerged as a potential source of bioactive compounds with unique nutritional value and therapeutic activities, and it has become an important field of research in food science and technology [15, 16]. One of the main dietary differences between Eastern and Western hemispheres is the higher seafood consumption such as fish and marine algae . Seaweeds are characterized as distinguished sources of various bioactive compounds with abundance in many minerals and could be utilized as novel functional foods which provide health benefit activities. Seaweed tissues are abundant in mineral elements such as iron, potassium, sulfur and iodine . Depending upon seasonal conditions and the geographic area, macroalgae differs in the content of biochemical elements such as proteins, lipids, carbohydrates, vitamins and minerals . Cell surface polysaccharides are responsible for high level of minerals and trace elements due to the retention of inorganic marine substances in marine algae . Marine microalgae are considered as potential source of high quality proteins.
Peptides with therapeutic potentials are referred as bioactive peptides and these peptides have potential applications in functional foods and nutraceuticals  for health improvement and better disease control.
1.3. Bioactive compounds
Numerous metabolites extracted from marine algae possess biological activities. These bioactive compounds have been widely acknowledged because of their potential health benefits [3, 29]. Commercial bioactive compounds of algal origin include natural pigments (NPs), polyunsaturated fatty acids (PUFAs), lipids, proteins and polysaccharides [15, 16]. Some of these bioactive compounds with their sources are mentioned in Table 1. Natural variability in the content of bioactive molecules may be attributed to evolutionary relationships, ecological and chemical diversification but these should not be considered as limitations to commercialization . Variation in the concentration of bioactive marine compounds of natural algal populations are influenced by environmental changes such as light, nutrients, contaminants, salinity, CO2 availability, pH, temperature and biotic interactions .
|Catechol, rutin and hesperidin|||
Functional materials of marine organisms occur in a wide variety and are enriched with polyunsaturated fatty acids, polysaccharides, pigments, minerals, vitamins, enzymes, phenolics and bioactive peptides . Recently, the importance of algae as a source of structurally diverse bioactive compounds has been immensely emerged and research showed various biological activities of these compounds which are antioxidant, immunomodulation, anticoagulation and antiulcerogenic activities .
Seaweeds are the sole source of certain valuable phytochemicals, namely agar and carrageenan . The richness of edible marine algae in sulfated polysaccharides (SPs)  as good sources of nutrients, span their uses from the food and pharmaceutical industries to biotechnology . These anionic polysaccharide polymers are not only widespread in marine algae but also in mammals and invertebrates. Seaweeds are also the most significant sources of non-animal SPs and the chemical structure of these polymers vary according to the type of algae . Major polysaccharides found in marine algae include fucoidan and laminarans found in brown algae, carrageenan in present red algae and ulvan in green algae .
Sulphated polysaccharides present in Rhodophyta are known as galactans which are composed of galactose or modified galactose units . The class of Phaeophyta comprises of sulfated l-fucose units which are named as fucans. The polysaccharides found in Chlorophyta exhibit polydispersity among heteropolysaccharides together with traces of homopolysaccharides . Carrageenan may also show anticoagulant activity , antiviral activity , and antitumor activity . Marine red algae primarily contain an agaran type polysaccharide, which was separated from
Fucoidan is a highly complex sulfated polysaccharide found in marine brown algae is also present in microorganisms, plants and animals . Fucoidan have been shown to exhibit antiviral and anti-inflammatory affect. Anti-metastatic effects of fucoidan obtained from
Seaweeds have been majorly studied for their biologically active polyphenolic derivatives called phlorotannins . Marine brown algae (
2. Remedial activities
2.1. Antioxidant activity
Antioxidants may affect the human health in a positive way as they can protect the human body against damage by Reactive oxygen species, which attack and impair macromolecules such as DNA, proteins and lipids lead to many health disorders such as diabetes, aging, cancer and other neurodegenerative diseases . Recently, marine flora and fauna gain considerable interest as natural sources for the development of antioxidants in the food and pharmaceutical industry. Marine algae represent one of the richest sources of natural antioxidants among marine resources . Antioxidant activity of marine derived bioactive peptides has been determined through radical scavenging activities which have been detected by electron spin resonance spectroscopy method as well as intra cellular free radical scavenging assays. The peptide chain contains hydrophobic amino acids which contribute towards their potential antioxidant activity [60, 61].
Marine algae have various classes of natural polysaccharides including fucoxanthin, phycoerythrobilin, chlorophyll-a and their derivatives show potent antioxidant activity. Cho et al.  suggested that strong antioxidant activity of the
NPs are useful effective bioactive substances in search for effective, non-toxic substances with potential antioxidant activity. NPs are distributed in large quantities in marine algae and could be used as a rich source of natural antioxidants with potential application in the food industry as well as cosmetic and pharmaceutical areas .
2.2. Anti-coagulant activity
Whenever an abnormal vascular condition occurs, blood coagulation begins to stop the flow of blood though the injured vessel wall and exposure to non-endothelial surfaces at sites of vascular injury occur. Blood coagulation is processed by coagulation factors. The blood coagulation can be prolonged or stopped when endogenous or exogenous anticoagulants interfere with these coagulation factors . The anticoagulants derived from marine bioactive peptides have been extensively reported, but they have also been isolated from marine organisms such as marine echiuroid worm . The anticoagulant activity of the bioactive peptides has been determined by prolongation of prothrombin time, thrombin time and activated partial thromboplastin time assays and the activity was compared with the standard commercial anticoagulant heparin. The normal clotting time of anticoagulant peptide isolated from marine echiuroid worm have been significantly prolonged .
Sulphated polysaccharides derived from marine brown algae are alternate sources for manufacturing of novel anticoagulants . Anticoagulant activity is the most extensively studied property of sulphated polysaccharides and have been reviewed previously . Two types of SPs have been recognized with high anticoagulant activity. Marine red algae produce sulfated galactans also known as carrageenan,  and marine brown algae produce sulfated fucoidans . There are very few reports of anticoagulant SPs reported from marine green algae. Jurd et al.  found that the anticoagulant active SPs from
Low molecular weight and unfractionated heparins are the only sulfated polysaccharides currently used as anticoagulant drugs. Seaweed derived SPs possess anticoagulant activity similar to or higher than the heparin . In the pharmaceutical industry, SPs derived from seaweeds are the promising bioactive agents to be used as anticoagulant agents. Phlorotannins derived from
2.3. Anti-cancer activity
Marine algae produce a range of diverse anti-cancer phytochemicals. Based on epidemiological data, the protective effect of edible seaweeds has been established against mammary, skin and intestinal carcinogenesis . The bioactive substances can kill cancerous cells by inducing apoptosis or they may affect cell signaling by the activation of cell signaling enzymes of protein kinase-c family of brown algae seaweeds .
Most remarkable compounds found naturally in the brown seaweeds are the fucoidans, glucans and some other secondary  metabolites. Most of these compounds are listed in (Table 2). These compounds are capable of producing anticancer activity. Fucoidans from
|Health claims||Bioactive compounds||References|
Phloroglucinol and its essential polymers which are eckol, dieckol, phlorofucofuroeckol A, and 8,8′-bieckol isolated from the brown alga
Various anticancer pathways are involved to accomplish the process of tumour cell death. Major pathways are anti-oxidation and immune stimulation, and apoptosis of cancerous cells. Tumors are in a ‘pro-oxidant’ state generating more free radicals. These free radicals usually accompanied by lack of DNA repair mechanisms. Reactive oxygen species are main sources of oxidative stress in cells, damaging DNA, proteins and lipids. Anti-oxidants cause inhibition of the growth of cancer cells through varied mechanisms. The most common is activation of apoptosis by antioxidant species and inhibition the process of tumour progression .
Apoptosis is a process of programmed cell death triggered by various extrinsic or intrinsic stimuli in unfavourable situations. The protein p53 and caspase-cascade signaling system are prime factors for promoting apoptosis . Caspases belong to the interleukin 1β converting enzyme family of proteases. The process of apoptosis has three stages, namely activation, execution and cell deletion. All these stages are interlinked by caspases . Tumour suppressor protein p53 triggers the apoptosis and induces cell growth arrest. The prevention of cancer is highly dependent on p53 for controlling the proliferation of cells with damaged DNA or with a potential for neoplastic transformation. Algae is a source of many phytochemicals which cause apoptosis.
The apoptosis is executed immunostimulation with two pathways, the NK cell and Fas receptor mediated pathways. The Fas receptor molecule plays an important role in the immune system, which allows the removal of auto-antibodies and the elimination of virally infected tumourigenic cells. Immune defence mechanisms do kill any abnormal cells including cancer. Polysaccharides are associated with biological activities of several microalgal species. Polysaccharide complexes from
2.4. Anti-viral/Anti- HIV activity
Acquired immunodeficiency syndrome AIDS is a disease caused by human immunodeficiency virus (HIV-1) . Marine algae derived SPs can inhibit replication of enveloped viruses such as herpes virus, togavirus, arenavirus, rhabdovirus, and orthopoxvirus families. These sulaphated polysaccharides have great potential for the development of novel anti-HIV therapeutics. Marine algae possess significant quantities of complex structural SPs that inhibit the HIV. The chemical structure, constituent sugars, stereochemistry, degree of sulfation, molecular weight and conformation are affected the antiviral activity of algal SPs .
SPs from red algae also exhibit significant HIV-1 inhibitory activity. Anti-HIV activity of
Carrageenan has been shown to demonstrate anti-HPV activity in vitro . Carrageenan inhibits HPV 3-fold higher in magnitude than heparin, a highly effective model for HPV. Carrageenan acts mainly by preventing the binding of HPV virions to cells and blocks HPV infection through a post attachment heparin sulfate-independent effect. This mechanism is consistent by the fact that carrageenan closely resembles heparin sulfate, which is recognized as HPV-cell attachment factor. Moreover, antigen-specific immune responses and antitumor effects of carrageenan were remarkable . Carrageenan are the promising candidates for production of new therapeutic agents for HPV by being a part of food additives. There are numerous advantages of carrageenan over other classes of antiviral agents, such as reasonably low production costs, novel modes of action, broad spectrum, low cytotoxicity and safety .
2.5. Anti-cardiovascular disease activity
Dyslipidemia is a main cardiovascular risk factor for coronary heart disease incidence and mortality. Lipid disorders can accelerate the atherosclerosis process and result could be chronic heart failure. Nutraceuticals are effectively able to reduce the atherosclerosis process and coronary heart disease progression. Carotenoids are produced by seaweeds, plants and microorganisms. These fat soluble are the fundamental component of Mediterranean foods, are well known to reduce the incidence and frequency of cardiovascular events, perhaps by means of their antioxidant action on free radicals or by anti-inflammatory action on lipoxygenase enzyme activity .
Cell membranes contain sterols as important structural components, and some of them are cardiac glycosides used therapeutically in the treatment of cardiac failure and atrial arrhythmias. The positive effect of eicosapentaenoic acid and docosa-hexaenoic acid on human health has been reported as far as cardiovascular system. Enrichment of foods with EPA/DHA show cardio protective effects. EPA and DHA may exert their cardio protective functions, namely influencing plasmatic triacylglycerol (TAG) and cholesterol levels, and modulation of the chronic inflammation in the vascular wall .
2.6. Anti-inflammatory activity
Inflammation underlies a mass of enormous malignancies such as asthma, myocardial ischemia, allergies, arthritis, atherosclerosis and cancer. Inflammation is a complex biological process and occurs in response to harmful stimuli such as presence of pathogens in vascular tissues or injury. Inflammation normally acts as a defense mechanism, and its deregulation is associated with a multitude of diseases. Chronic and acute inflammation is a physiological process mediated by the activation of immune cells such as mononuclear phagocytic cells and macrophages . The mechanism of inflammation is controlled by endogenous chemical mediators such as vasoactive amines, platelet activating factor, cytokines, bradykinin, fibrin, complement component, eicosanoids, nitric oxide and reactive oxygen species. These inflammatory mediators play a pivotal role in controlling various steps of inflammation. Marine algae produce a diverse array of secondary metabolites which play a pivotal role as inhibitors of inflammation .
Marine algae produce a combination of metabolites which are implicated in large number of diseases because of anti-inflammatory and antioxidant properties, with high commercial utilization. These compounds include fatty acids, marine terpenes, bioactive peptides, polysaccharides and their structures ranges from aliphatic molecules with a linear chain to complex polycyclic entities. Marine sulfated PS exhibit anti-coagulant, anti-inflammatory, anti-viral and anti-tumor activities and are important in pharmaceutical industries .
These algal compounds usually possess immune-modulatory activities which potentially instigate the immune system activities to alleviate undesirable responses such as inflammation. Sulfated polysaccharides may target numerous pathways in the immune and inflammatory systems. They can affect disease pathophysiology and outcome, including tumour development and septic shock. Fucoidan possess extensive of biological activities which include anti-inflammatory and anti-oxidative effects. Research revealed that the mechanism behind anti-inflammatory effect of fucoidan is due to its capability to interact with an adhesion molecule selectin on the seaweed cell membrane . Fucoidan show anti-oxidative effect by inhibiting the synthesis and release of reactive oxygen radicals as well as its clearance. Park et al.  studied the cellular and molecular mechanism underlying the anti-inflammatory properties of fucoidan.
According to research, ascophyllan is a discrete sulfated polysaccharide isolated from fucoidan with significant biological activity.
Algal polyphenols and phlorotannins have numerous biological properties besides their strong antioxidant properties. Phlorotannins are the main bioactive compounds found in marine algae. Yang
Alkaloids occur rarely in marine algae, alkaloids isolated from marine algae have been shown to possess anti-inflammatory properties . Algal fatty acids are either saturated or unsaturated with reported bioactivity. Commercially produced microalgal PUFAs are of particular interest because they lead the human body to more anti-inflammatory environment. Various benefits accrued from docosahexaenoic acid and palmitoleic acid are the reduction in the incidence of certain heart diseases and oleic acid retain antioxidant capacity .
Seaweeds are a valuable source of bioactive compounds and could be introduced for the preparation of novel functional ingredients in food and also a good approach for the treatment or prevention of chronic diseases. Recently, much att`ention has been paid by the consumers toward natural bioactive compounds as functional ingredients in foods, and hence, it can be suggested that, seaweeds are an alternative source for synthetic ingredients that can contribute to consumer’s well-being, by being a part of new functional foods and pharmaceuticals. Furthermore, the wide ranges of biological activities associated with marine algae-derived bioactive compounds have potential to expand its health beneficial value in food, and pharmaceutical industries.
Conflict of interest
Authors declare no potential conflict of interest.