4 Marine Toksin

 

Marine Natural Products

Metabolit sekunder dari biota laut TOKSIN LAUT

Pendahuluan ✔

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Toksin laut menarik perhatian akibat kasus-kasus keracunan yang terjadi dan pengaruhnya terhadap sosioekonomi. Beberapa hal yang menjadi titik perhatian utama meliputi: Penentuan/pengembangan metode deteksi, determinasi dan terapi. Pengetahuan atas mekanisme aksi di tingkat molekuler  Banyak toksin ditemukan perangkat yang berguna dalam menjelaskan fenomena biologis dan farmakologis (cth. Pengunaan tetrodotoksin untuk mempelajari kanal sodium, dan asam okadaik dalam mempelajari fosfatase protein Modifikasi kimia dari toksin yang diikuti dengan QSAR menyediakan target yang menarik bagi ahli kimia dan farmasi

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Marine toxins ●

Dalam pembahasan ini toksin laut dibedakan atas 5 kelompok:  – Penyebab keracunan kerang yang berakibat kelumpuhan  – Penyebab keracunan kerang yang meracuni syaraf   – Penyebab keracunan kerang yang berakibat diare  – Ciguatera (keracunan seafood)  – Penyebab keracunan lainnya

1. Paralytic shellfish poisoning (PSP) ●

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Keracunan akut yang sering letal akibat makan kerang dan kepiting Merupakan akibat dari fenomena RED TIDE : Pada saat yang tdk dapat diperkirakan terjadi ledakan populasi plankton-plankton merah (Gonyaulax (Gonyaulax tamarensis,, Pyrodinium bahamense, dll).Toksin yang tamarensis dihasilkan plankton tersebut (Saxitoxin (SXT) dan congenernya) menyebabkan kematian masal ikan. Kerang dan kepiting dapat bertahan tetapi menimbun racun di dalam tubuhnya dan selanjutnya menyebabkan keracunan pada manusia

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Saxitoksin

Deteksi PSP ●

Bioassay dengan mencit dan lalat  –

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Dipilih mencit BB 20 g di suntik ip dgn 1 ml larutan uji. Waktu kematian dicatat dan toksisitas ditentukan dalam mouse units (Mu) terhadap tabel standar dan dikoreksi dengan faktor fakt or yang diperoleh dari mencit kontrol yang disuntik dengan standar saxitoxin dihydrochloride dihydrochloride dan dinyatakan sebagai mikrogram equivalentt dari saxitoxin dihydrochloride. equivalen dihydrochloride. Satu Mu adalah jumlah racun yg dibutuhkan untuk membunuh satu mencit 20g dalam waktu 15'. Uji ini akurat ak urat tetapi akan menghadapi kesulitan untuk memperoleh keseragaman bobot hewan uji.

Uji ikatan dengan kanal sodium  –

 Aktivitas farmakologis SXT dikembangkan dikembangkan sbg teknik teknik deteksi. Racun berikatan dgn kanal sodium di membran sel syaraf, mencegah influx sodium dan depolarisasi sebagian dari membran. Uji ini cocok utk menentukan sifat farmakologis racun dan bukan untuk deteksi rutin.

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Deteksi PSP ●

Immunoassay  –

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Saxitoxin diikat oleh bovine serum albumin (BSA) dengan perlakuan formaldehyde dan antibodi yang dipreparasi dari antiserum kelinci. Uji ini kurang akurat tetapi cocok untuk digunakan sebagai field rapid test.

Uji kimiawi  –

Metode fluorometri terhadap saxitoksin dengan berdasar atas produk degradasinya akibat perlakukan dengan NaOHhidrogen peroksida. Metode ini sensitif tapi tdk bisa mendeteksi neosaxitoksin. Kelemahan lainnya adalah produk lain yang berfluoresensi akan mengganggu uji.

Kelompok racun PSP lainnya ●

Tetrodotoksin (TTX)  –

Merupakan racun laut yang paling dikenal karena sering menimbulkan keracunan makanan, keunikan struktur dan aktivitasnya.  – Mendapatkan namanya dari ikan buntal (pufferfish fam. tetraodontidae)  –  Aktivitas spesifik blocking kanal kanal sodium dari membran yang tereksitasi.

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Mekanisme aksi racun PSP ●

Tetrodotoxin and saxitoxin are the most widely studied marine toxins by physiologists and pharmacologists. In spite of their structural dissimilarities, both are known to inactivate the sodium channel in the skeletal muscles and nerve tissues of various animals. The effect of these toxins is specific as both selectively block the transient Na+ current without any effect on the steady state current by K+ ions. Owing to this specific action of these toxins, many investigators are using them as tools in the characterization of ion channels. These toxins have become an extremely useful and popular chemical tool for the study of neurophysiology and neuropharmacology. Tetrodotoxin binds to the entrance part of the Na+ channel and inhibits Na+ channel and Na+ influx, and generates an active potential, thus, causing the blockade of nerve of muscle function. Tetrodotoxin is commercially available and in carefully controlled doses is being used as muscle relaxant and pain killer in neurogenic

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2. Neurotoxic Shellfish Poisoning (NSP)

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The dinoflagellate Gymnodinium breve (Ptychodiscus brevis)) often forms blooms along the Florida coast and this brevis leads to mass mortality of fish. Large blooms of this organism (red tide) can kill hundreds of tons of fish a day. Sometimes the blooms cause human irritation in eyes and throat in the coastal areas, and the contamination of shellfish occasionally result in human intoxication. The symptoms of neurotoxic shellfish poisoning (NSP) are mild which generally subside within 36 hrs, and include tingling and numbness in the mouth and digits, ataxias, hot cold reversal of temperature sensation, myadriasis, reduced pulse rate, diarrhea and vomiting.126 NSP is not a lethal human intoxication.

Brevetoksin ●

Brevetoxin B is of particular interest not only because it is the most potent toxin of the family but also because it uniquely binds to sodium channels on excited membrane.

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Brevetoksin A & Hemibrevetoksin B ●

Hemibrevetoksin Hemibreveto ksin B

3. Ciguatera (Sea Food Poisoning) ●

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The term ciguatera is used to food poisoning caused by ingestion of toxic coral reef fish. fi sh. Ciguatera not only endangers endangers public health but also hampers local, fisheries f isheries in tropical and subtropical regions of the world. It is estimated that roughly 20,000 people suffer annually from such poisoning. Two groups of compounds implicated in the poisoning are ciguatoxin and maitotoxin. Both groups of toxins are produced by the epiphytic dinoflagellate Gambierdiscus Gambierdiscu s toxicus and transferred to herbivorous fish and subsequently subseque ntly to carnivores through the food f ood chain. Ciguatoxin is regarded as the principal toxin responsible for human illness. The clinical symptoms are diverse. Of tthese hese neurologic disturbances are prominent. The most characteristic symptoms of ciguatera are reversal of thermal sensation called “dry ice sensation”. Other symptoms are joint pain, miosis, erethism, cyanosis, and prostration. Gastrointestinal disorders are nausea, vomiting and diarrhea. Cardiovascular Cardiovascular disturbances are low blood pressure and bradycardia.

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Ciguatoksin The moray eel, which is placed near the top in the coral ecosystem was found to contain more polar (more oxygenated) congeners, whereas the dinoflagellate produces less polar ones. Ciguatoxin (70 (70)) itself, the more oxygenated member of this class of toxin was absent in the flagellates. f lagellates. These data suggested that less polar congeners produced by G. toxicus were probably the precursors of the more polar toxins found in fish. The latter appear to be formed by oxidative enzyme systems in the fish. Interestingly, toxicity of more oxygenated metabolite is often increased, as in the case with ciguatoxin which is 11 times more toxic than its plausible plausible precursor 

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Mode aksi dari Brevetoksin dan Ciguatoksin ●

Pharmacological studies on brevetoxins and ciguatoxins had revealed that the primary site of their action is voltage-sensitiv voltage-sensitive e sodium channel (VSSC). Brevetoxin-B activated VSSC in neuroblastoma cells in the presence of veratridine. The T he action was blocked by tetrodotoxin. A binding assay using a radioligand of brevetoxin, tritiated derivative of brevetoxin-B at 42-aldehyde 42-aldehyde indicated that both toxins shared the same binding site on the VSSC. Several studies have been carried out on ciguatoxin to understand its mode of pharmacological and toxicological action because its central role in human illness. Earlier it was thought that CTX is a inhibitor of choline esterase. However, subsequently it was revealed that CTX stimulated sodium ion influx into cells.

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Ciguatera lainnya ●

Maitotoksin  –

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Diverse actions of MTX have been reported. These are muscle contractions, stimulation of hormones/ neurotransmitter release, activation of phospholipase-C and A2 and activation of protein kinases some of which do not appear to be directly linked with simple elevation of intracellular Ca2+ concentration.

Palitoksin  –

 Action: Membrane Membrane depolariz depolarization, ation, Na+ or Ca2+ influx, stimulation of arachidonic arachidoni c acid release, stimulation of neurotransmitter release, inhibition of Na+/K+-ATPase, -ATPase, induction of contraction of smooth muscles and tumor-promoting, studies had been carried out on palytoxin,, while it is proposed that palytoxin (PTX) acts through palytoxin Na+/K+-ATPase, -ATPase, detailed mechanism of its action is still largely unknown.

4. Diarrheic Shellfish Poissoning ●

Diarrheic shellfish poisoning (DSP), a major public health problem even though it is not lethal. The toxic symptoms are abdominal cramps (1 hr elapse time), nausea progressing to diarrhea (2-7 hr), and a “raw”, “burning” feeling in the stomach. Diarrhea is noted in 92% of all cases, nausea in 80%, vomiting in 79%, abdominal pain in 53%, and chills in 10%. Diarrheic shellfish poisoning was first discovered in 1976 when a poisoning due to mussel occurred in North Eastern Japan, although no “red tide” t ide” was seen during the infestation period. The causative organisms of the illness have now been identified as several dinoflagellates in the genus Dinophysis Dinophysis.. Even at a low cell density (200 cells per liter) of dinoflagellates leads to toxification of shellfish. DSP is associated with eating bivalves such as mussels, scallops or clams which have accumulated dinoflagellate toxins. Lack of a proper method of detection of the toxins in the past made it difficult to diagnose the suspected gastroenteritis as the amount of toxin that can induce illness in man by oral intake is very small, equivalent to 32 g of dinophysistoxin-1 dinophysistoxin-1 (DTX-1). (DTX -1). Causative toxins that have been identified are okadaic acid and its analogs and

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Okadaic acid dan Denophysistoxin ●

Okadaic acid has been found to act act asand an inhibitor inhibi tor of the protein phosphatases. Numerous biochemical pharmacological studies have been carried out using as a probe. The biological activities of are now considered considered to be due to its in inhibitory hibitory action against protein phosphatases. Okadaic acid inhibited PP2A at the lowest concentration (Ki of 30 pm) PPI inhibited at the next lowest concentration, and PP2B at the highest concentration. Okadaic acid showed no effect on PP2C. Okadaic acid and DTX1 had been reported to be non-phorbol ester type cancer promoter.

Toksin DSP Lain ●

 – It was isolated as one of the diarrheic shellfish toxins toxins from the Pectenotoxin

digestive glands of the scallop, Patinopecten yessoensis found Northeastern Japan.

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Yessotoxin  –

Yessotoxin, a novel polyether toxin, had been isolated from scallops Patinopecten yessoensis implicated in diarrheic shellfish poisoning.

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5. Toksin-toksin lainnya ●

Screening microvariety algae for toxin production led tofrom the isolation ofof a wide of bioactive metabolites dinoflagellates. Some of these compounds were possibly implicated in poisonings.  –  Amphidinolid  –  Amphidinol  – Surugatoxin  – Macroalgaltoxin  – Peptida toksik

Amphidinolid ●

 Amphidinolid  – Three groups (suatu of macrolides makrolid) named amphidinolides had been isolated from the t he dinoflagellate  Amphidinium spp. symbiotic to flatworm  Amphiscolops breviviridis.

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Amphidinol ●

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It was isolated Amphidinium from culturedklebsii, cells (440 L) of the dinoflagellate Amphidinium dinoflagellate collected at Ishigaki island, Japan.  Amphidinol is exhibiting potent antifungal and hemolytic hemolytic activities.

Surugatoksin ●

In 1965, intoxication occurred due to ingestion of a carnivorous gastropod, Babylonia japonica. The patient complained of visual defects, including amblyopia, mydriasis, with thirst, numbness of lips, speech disorders, constipation and dysuria.

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Macroalgal toxin ●

 Although microalgae are frequently involved involved in various type of seafood poisoning, however, the involvement of macro algae in seafood poisoning is rare. Human intoxication due to ingestion of the red alga Polycaverosa tsudai (formerly Gracilaria edulis) occurred in Guam, Japan, in 1991. Thirteen people became ill, three of whom died. As the alga had been eaten widely with no previous record of potential risk, a toxic glycoside named polycavernoside-A isolated from the alg alga a has been as assumed sumed to be the causative agent of the t he poisoning.

Peptida toksik ●

The peptides from red, brown green and blue-green algae with toxic properties are known. From the brackish water Nodularia spumigena species, which caused problems in Baltic Sea S ea and New Zealand, cyclic pentapeptide, nodularin had been isolated. The peptide is closely related to microcystin, a potent hapatotoxin and protein phosphate 2 and 2A inhibitor isolated from the blue-green alga Microcystis aeruginosa.

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