Marine invertebrates specifically echinoderms have been the subject of researchers in recent times. Quite a few metabolites have been elucidated from echinoderms which have gained a demand in the in the fields of pharmacology and pharmaceutics. The sea star which belongs to the class Asteroidea and phylum Echinoderm produces unique natural products which show biological activities, and have gained demand for the therapy of fatal diseases in the fields of medicine. The major compounds isolated from marine sea stars include steroids, steroidal glycosides, anthraquinones, alkaloids, phospholipids and peptides. The aim of this review is to provide an upto-date analysis on the Bioactive compounds and the application of compounds isolated from diverse species of starfish illustrating Cytotoxic, Hemolytic, Antibacterial Antifungal, Antihelminthic, Antiparasitic, ltcthyotoxic and Antifouling activity.
Natural products obtained from marine sources have provided useful resource having medicinal values. When compared with the natural products obtained from terrestrial sources, marine origin also equally produces mammoth resources of novel compounds with possible pharmaceutical importance. These marine products from the marine invertebrates namely the echinoderms (sea stars) have been evolved over millions of years. The products specifically the secondary metabolites which are produced by them is an integral part of their survival tactic. The secondary metabolites are nothing but the chemical defenses produced by the marine sea star in order to protect them from the predators during attack. These chemical metabolites serve as a sole source of compounds having medicinal value for mankind.
Sea stars have gained their name principally due to their five arms which arises from the central disc resembling star; some of sea stars have more than five arms. Sea stars belong to the phylum Echinoderms and class Asteroidea. Though they are named as starfish they do not come under the category of vertebrates because they lack the spinal column for this reason they are classified under class invertebrates. Sea stars have a tough skin which acts as a solid shield over them giving them a protective covering. Sea stars are protected by a calcareous plate which serves as an external skeleton. These plates are connected by muscles and tissues to give flexibility. The locomotion of the sea stars is mainly through the tubular feet which is located at the ventral side of the body. They are otherwise called as water vascular system which functions with the hydraulic pressure and they are not only used for locomotion but also for respiration and feeding. The most remarkable uniqueness of star fish is their ability to regenerate their body namely the arms which has been damaged during their attack. The sea stars reproduce both sexually and asexually. Asexual reproduction is division of the whole body by the regeneration mechanism. The sexual reproduction is done by the male and female through the release of the egg and the sperm in the water which fuses and forms the adults.
Echinoderms represent an exceptional source of polar steroids of a immense structural diversity, showing a range of biological activities. The steroids are organic compounds which act as an integral part of the cell membrane. The steroidal components namely saponins, asterosaponins, and astropectenol are the major source of compounds abundantly found in sea stars [1-3]. A basic study of these facts reveals the search for "Drugs from the Sea" progresses at the rate of a 10 percent increase in new compounds per year . The isolation and characterization of bioactive compounds from the sea stars in the marine ecosystem is serving a good resource for the human population to fight against the deadly diseases like cancer.
Elucidation of novel compounds from far eastern sea star Leptasterias ochotensis illustrated cytotoxic activity towards cancer cell lines RPMI-7951 and T-47D . Steroidal compounds and asterosaponins were isolated from cold water star fish Ctenodiscus crispatus and starfish Culcita novaeguineae respectively showing cytotoxicity against human carcinoma cell lines HepG2 and U87MG ensuing the apoptosis of the cells hence playing a significant role in the anti tumor chemotherapy [2,3]. Steroidal compounds were elucidated from one another species of sea star Astropecten polyacanthus which showed cytotoxic activity against the Human cancer cell lines HL-60,PC-3 and SNU- C5 . The crude extracts of same species starfish Astropecten polyacanthus possessing inhibitory effects against the inflammatory components (TNF-α and IL-6) .
A polysaccharide compound extracted from the starfish Asterina pectinifera showed a chemo preventive activity against Human colon cancer (HT-29) and Human Breast cancer by initiating the enzymatic activity which plays a key task in the carcinogenesis inhibition [6,7]. Few new compounds of asterosaponins from the starfish Archaster typicus showed cytotoxic activity against human cervical cancer cell lines and mouse epidermal cell line . Glycolipids isolated from starfish Narcissia canariensis harvested from the coast of Africa showed cytotoxicity against various adherent human cancerous cell lines (multiple myeloma, colorectal adenocarcinoma and glioblastoma multiforme) . A comparative study was made with the crude Table 1: Natural products of Sea stars and its activity.extract from Acanthaster planci starfish with conventional medicine tamoxifen, a drug used against the human breast cancer the extract showed effective apoptotic activity than the drug tamoxifen in human breast cancer cell line .
Hemolytic activity was also studied from various star fish namely Ophiocoma erinaceus, Acanthaster planci (crown of thron), Protoreaster linckii (red knobbed), and Holothuria polii showed hemolysis when tested against human, chicken, goat and rabbit red blood cells hence having a naturally secondary metabolite possessing hemolytic properties [11-14].
Antimicrobial activity is a term coined as an agent that acts against the microbes either making them to be cidal or static against the microbes. The continued existence of the sea stars depends on capable antimicrobial mechanisms to safeguard themselves against microbial infections and fouling. The potent secondary metabolite produced by the sea star shows a rich source of activity against the microbes. The crude and fractioned ethanolic, nbutanol and methanolic extracts from sea star Luidia maculate, Stellaster equestris, Astropecten indicus, Protoreaster lincki, Pentaceraster regulus showed an effective antibacterial and antifungal activity against human pathogens namely Escherichia coli, Bacillus subtilus, Klebsiella sp, Shigella flexineri, Vibrio parahaemolyticus, Staphylococcus aureus, Salmonella paratyphi, and the fungal pathogens like Penicillium sp, Aspergillus sp and Trichophyton mentagropytes respectively[15-18] (Table 1).
The celomic cavity is the internal structure of star fish which contains celomic fluid holding the cells of immunity and the antimicrobial peptides. Antimicrobial peptides form the first line of defenses and hence termed as the host defense peptides. They come under the innate defense response in both unicellular and multi cellular organisms . They have a wide range of activity towards bacteria, fungi, viruses and parasites. Antimicrobial peptides (AMPs) are vital immune effect or molecules for invertebrates, including echinoderms, which lack a vertebrate-type adaptive immune system. The function of AMP binds to the bacterial surface and destructs the cell walls of the bacteria. Two peptides and four AMP compounds extracted from whole body and celomocyte extract of Asterias rubens showed antimicrobial activity. The peptides were identified as actin and filamin and these peptides are known for their antimicrobial properties [20,21]. New compounds namely sulfated steroidal compounds, crude compounds holding similar chemical properties of steroidal oligoglycosides and polyhydroxy steroids isolated from the whole body extract using various solvents and water as a solvent from star fishes namely Anasterias minuta, Asterias rubens, Asterina pectinifera and Dermasterias imbricate had shown antifungal activity against pathogenic fungi namely Cryptococus neoformans and other fungal pathogens and other fungal pathogens [22-24].
Generally outer surface of sea star are hard hence mostly they are free from fouling organisms like bacteria and algae studies were conducted in sea stars like and which has indicated that both the Physical and Chemical barriers stages a key role in keeping away the fouling organisms. The physical barriers present on the epidermal surface of the sea stars like thron, pedicellariae and paxillae acts as a mechanical hindrance for the fouling micro and macro organism from settling on the surfaces. The natural products secreted by the sea star also acts the chemical barrier the surface associated compounds like hexadeconoic acid, cholesterol and lathosterol showed antifouling activity .
Echinodermata is one of the most diverse phyla among the marine invertebrates, which include Sea stars, sea urchins, sea biscuits and sea cucumbers. The sea stars takes part in several biological role and hence proved itself as a future untapped source of bioactive molecules. Among them, the sea stars have variety of chemical constituents such as steroids, glycosides consisting of Asterosaponins, Steroids Cyclic glycosides, Steroid monoglycosides and di-glycosides, Saponins, Asterosaponins and Carotenoids. Hence sea stars poses a great efficacy of echinoderm-derived molecules for therapeutic relevance in selected fields of cancer research, in the control of bacterial intensification as substances with new antibiotic properties, restrain the fungal growth as an essence with new antifungal properties, and lastly in the circumstance of industrial applications such as antifouling agents.
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Guenther, Jana (2007) Natural antifouling defense of tropical sea stars. PhD thesis, James Cook University. Jana Gunther, Anthony D Wright, Karhryn Burns, Rocky de Nys. Chemical antifouling defences of Sea star: Effects of the natural products hexadeconic acid, cholesterol,lasthosterol and sitosterol. Marine ecology progress series 385: 137-149.