Tetrodotoxin

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ImageFile=Tetrodotoxin-2D-skeletal.pngImageSize=
ImageFile2=Tetrodotoxin-3D-balls.pngIUPACName=Octahydro-12-(hydroxymethyl)-2-imino-
5,9:7,10a-dimethano-10aH-
[1,3] dioxocino [6,5-d] pyrimidine-4,7,10,11,12-pentol
OtherNames=anhydrotetrodotoxin 4-epitetrodotoxin, tetrodonic acid, TTX
Section1= Chembox Identifiers
CASNo=4368-28-9
PubChem=20382
SMILES=C( [C@@] 1( [C@@H] 2 [C@@H] 3 [C@H] (N=C(N [C@@]
34C( [C@@H] 1O [C@@] ( [C@H] 4O)(O2)O)O)N)O)O)O
Section2= Chembox Properties
Formula= C₁₁H₁₇N₃O₈
C =11 | H = 17| N =3 | O =8
MolarMass=319.268
Appearance=
Density=
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Section3= Chembox Hazards
MainHazards=
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Autoignition=

Tetrodotoxin (anhydrotetrodotoxin 4-epitetrodotoxin, tetrodonic acid, TTX) is a potent neurotoxin with no known antidote, which blocks action potentials in nerves by binding to the pores of the voltage-gated, fast sodium channels in nerve cell membranes.cite journal | author = Hwang DF, Noguchi T | title = Tetrodotoxin poisoning | journal = Adv. Food Nutr. Res | volume = 52 | issue = | pages = 141–236 | year = 2007 | pmid = 17425946 | doi = 10.1016/S1043-4526(06)52004-2 ] The binding site of this toxin is located at the pore opening of the voltage-gated Na⁺ channel. Its name derives from Tetraodontiformes, the name of the order that includes the pufferfish, porcupinefish, ocean sunfish or mola, and triggerfish, several species of which carry the toxin. Although tetrodotoxin was discovered in these fish and found in several other animals (e.g., Blue-ringed Octopus, Rough-skinned newt), it is actually the product of certain bacteria such as "Pseudoalteromonas tetraodonis", certain species of "Pseudomonas" and "Vibrio", as well as some others.

Its mechanism was discovered in the early 1960s by Toshio Narahashi working at Duke University.

Tetrodotoxin sources in nature

Tetrodotoxin has also been isolated from widely differing animal species, including western newts of the genus "Taricha" (where it was termed "tarichatoxin"), parrotfish, toads of the genus "Atelopus", several species of blue-ringed octopuses of the genus "Hapalochlaena" (where it was called "maculotoxin"), several starfish, an angelfish, a polyclad flatworm, several species of Chaetognatha (arrow worms), several nemerteans (ribbonworms) and several species of xanthid crabs. The toxin is variously used as a defensive biotoxin to ward off predation, or as both a defensive and predatory venom (the octopodes, chaetognaths and ribbonworms). Tarichatoxin and maculotoxin were shown to be identical to tetrodotoxin in 1964 and 1978, respectively. Recent evidence has shown the toxin to be produced by bacteria within blue-ringed octopuses.cite journal | author = Hwang DF, Arakawa O, Saito T, Noguchi T, Simidu U, Tsukamoto K, Shida Y, Hashimoto K | title = Tetrodotoxin-producing bacteria from the blue-ringed octopus Octopus maculosus | journal = Marine Biology | volume = 100 | issue = 3 | pages = 327–332 | year = 1989| doi = 10.1007/BF00391147 ] The most common source of bacteria associated with TTX production is "Vibrio" bacteria, with "Vibrio alginolyticus" being the most common species. Pufferfish, [Noguchi, T., Hwang, D. F., Arakawa, O., Sugita, H., Deguchi, Y., Shida, Y. & Hashimoto, K. 1987 Vibrio alginolyticus, a tetrodotoxin-producing bacterium, in the intestines of the fish Fugu vermicularis vermicularis. Marine Biology 94, 625-630] chaetognaths, [Thuesen, E. V. & Kogure, K. 1989 Bacterial production of tetrodotoxin in four species of Chaetognatha. Biological Bulletin 176, 191-194] and nemerteans [Carroll, S., McEvoy, E. G. & Gibson, R. 2003 The production of tetrodotoxin-like substances by nemertean worms in conjunction with bacteria. Journal of Experimental Marine Biology and Ecology 288, 51-63.] have been shown to contain "Vibrio alginolyticus" and TTX.

Biochemistry

Tetrodotoxin binds to what is known as "site 1" of the fast voltage-gated sodium channel. Site 1 is located at the extracellular pore opening of the ion channel. The binding of any molecules to this site will temporarily disable the function of the ion channel. Saxitoxin and several of the conotoxins also bind the same site.

The use of this toxin as a biochemical probe has elucidated two distinct types of voltage-gated sodium channels present in humans: the tetrodotoxin-sensitive voltage-gated sodium channel (TTX-s Na⁺ channel) and the tetrodotoxin-resistant voltage-gated sodium channel (TTX-r Na⁺ channel). Tetrodotoxin binds to TTX-s Na⁺ channels with a binding affinity of 5-15 nanomolar, while the TTX-r Na⁺ channels bind TTX with low micromolar affinity. Nerve cells containing TTX-r Na⁺ channels are located primarily in cardiac tissue, while nerve cells containing TTX-s Na⁺ channels dominate the rest of the body. The prevalence of TTX-s Na⁺ channels in the central nervous system makes tetrodotoxin a valuable agent for the silencing of neural activity within a cell culture.

Physiology

The toxin blocks the fast Na⁺ current in human myocytes (the contractile cells of the muscles), thereby inhibiting their contraction. By contrast, the sodium channels in pacemaker cells of the heart are of the slow variety, so action potentials in the cardiac nodes are not inhibited by the compound. The poisoned individual therefore dies not because the electrical activity of the heart is compromised, but because the muscles are effectively paralyzed.

Medical Uses

Blocking of fast Na⁺ channels has potential medical use in treating some cardiac arrhythmias. Tetrodotoxin has proved useful in the treatment of pain (originally used in Japan in the 1930s) from such diverse problems as terminal cancer,cite journal | author = Hagen NA, du Souich P, Lapointe B, Ong-Lam M, Dubuc B, Walde D, Love R, Ngoc AH; on behalf of the Canadian Tetrodotoxin Study Group | title = Tetrodotoxin for Moderate to Severe Cancer Pain: A Randomized, Double Blind, Parallel Design Multicenter Study | journal = J Pain Symptom Manage | volume = 35| issue = | pages = 420| year = 2008 | pmid = 18243639 | doi = 10.1016/j.jpainsymman.2007.05.011 ] migraines, and heroin withdrawal.

Total synthesis

Y. Kishi "et al." Nagoya University, Nagoya, Japan, (now at Harvard University) reported the first total synthesis of D,L-tetrodotoxin in 1972.cite journal | author = Kishi Y, Aratani M, Fukuyama T, Nakatsubo F, Goto T, Inoue S, Tanino H, Sugiura S, Kakoi H | title = Synthetic studies on tetrodotoxin and related compounds. 3. A stereospecific synthesis of an equivalent of acetylated tetrodamine | journal = J. Am. Chem. Soc | volume = 94 | issue = 26 | pages = 9217–9 | year = 1972 | month = December | pmid = 4642370 | doi = 10.1021/ja00781a038 | url = ] cite journal | author = Kishi Y, Fukuyama T, Aratani M, Nakatsubo F, Goto T, Inoue S, Tanino H, Sugiura S, Kakoi H | title = Synthetic studies on tetrodotoxin and related compounds. IV. Stereospecific total syntheses of DL-tetrodotoxin | journal = J. Am. Chem. Soc | volume = 94 | issue = 26 | pages = 9219–9221 | year = 1972 | pmid = 4642371 | doi = 10.1021/ja00781a039 ] M. Isobe "et al." at Nagoya University, Japancite journal | author = Ohyabu N, Nishikawa T, Isobe M | title = First Asymmetric Total Synthesis of Tetrodotoxin | journal = J. Am. Chem. Soc | volume = 125 | issue = 29 | pages = 8798–8805 | year = 2003 | pmid = 12862474 | doi = 10.1021/ja0342998 ] cite journal | author = Nishikawa T, Urabe D, Isobe M | title = An Efficient Total Synthesis of Optically Active Tetrodotoxin | journal = Angewandte Chemie International Edition | volume = 43 | issue = 36 | pages = 4782–4785 | year = 2004 | pmid = 15366086 | doi = 10.1002/anie.200460293 ] cite web | url = http://www.organic-chemistry.org/Highlights/2005/02May.shtm | title = Synthesis of (-)-Tetrodotoxin | author = Douglass Taber | authorlink = | coauthors = | date = 2005-05-02 | format = | work = Organic Chemistry Portal | publisher = organic-chemistry.org | pages = | language = | archiveurl = | archivedate = | quote = | accessdate = 2008-05-29] and J. Du Bois "et al." at Stanford University, USA, reported the asymmetric total synthesis of tetrodotoxin in 2003.cite journal | author = Hinman A, Du Bois J | title = A Stereoselective Synthesis of (-)-Tetrodotoxin | journal = J. Am. Chem. Soc | volume = 125 | issue = 38 | pages = 11510–11511| year = 2003 | pmid = 13129349 | doi = 10.1021/ja0368305 ] The two 2003 syntheses used very different strategies, with Isobe's route based on a Diels-Alder approach and Du Bois's work using C-H bond activation.

Tetrodotoxin poisoning

Fish poisoning by consumption of members of the order Tetraodontiformes is extremely serious. The skin and organs of the pufferfish can contain levels of tetrodotoxin sufficient to produce paralysis of the diaphragm and death due to respiratory failure.cite journal |author=Clark RF, Williams SR, Nordt SP, Manoguerra AS |title=A review of selected seafood poisonings |journal=Undersea Hyperb Med |volume=26 |issue=3 |pages=175–84 |year=1999 |pmid=10485519 |doi= |url=http://archive.rubicon-foundation.org/2314 |accessdate=2008-08-12] Toxicity varies between species and at different seasons and geographic localities, and the flesh of many pufferfish may not usually be dangerously toxic. It is not always entirely fatal, however; at near-lethal doses, it can leave a person in a state of near-death for several days, while the person continues to be conscious. It is for this reason that tetrodotoxin has been alleged to be an ingredient in Haitian voodooism and the closest actual manifestation to zombieism in the physical world, an idea that was popularized by Harvard-trained ethnobotanist Wade Davis in a 1983 paper, and in his 1985 book, "The Serpent and the Rainbow". However, this idea was dismissed by the scientific community in the 1980's, as the descriptions of voodoo zombies do not match the symptoms displayed by victims of tetrodotoxin poisoning, and the alleged incidents of zombies created in this manner could not be substantiated.Hines, Terence; "Zombies and Tetrodotoxin"; "Skeptical Inquirer"; May/June 2008; Volume 32, Issue 3; Pages 60-62.]

Toxicity

The Material Safety Data Sheet for tetrodotoxin lists the oral median lethal dose (LD₅₀) for mice as 334 μg per kg. [Material Safety Data Sheet Tetrodotoxin ACC# 01139 https://fscimage.fishersci.com/msds/01139.htm] Assuming that the lethal dose for humans is similar, 25 milligrams (0.000881 oz) of tetrodotoxin would be expected to kill a 75 kg (~165 lb.) person. The amount needed to reach a lethal dose by injection is much smaller, 8 μg per kg, [Material Safety Data Sheet Tetrodotoxin. Sigma-Aldrich Version 1.6 updated 10 March 2007. http://www.sigmaaldrich.com] or a little over one-half milligram (0.00001763698 oz) per person.

History

The first recorded cases of tetrodotoxin poisoning were from the logs of Captain James Cook from 7 September 1774. He recorded his crew eating some local tropic fish (pufferfish), then feeding the remains to the pigs kept on board. The crew experienced numbness and shortness of breath, while the pigs were all found dead the next morning. In hindsight, it is clear that the crew received a mild dose of tetrodotoxin, while the pigs ate the pufferfish body parts that contain most of the toxin, thus killing them.

The toxin was first isolated and named in 1909 by Japanese scientist Dr. Yoshizumi Tahara.

ymptoms and diagnosis

The diagnosis of pufferfish poisoning is based on the observed symptomology and recent dietary history.

Symptoms typically develop within 30 minutes of ingestion but may be delayed by up to four hours. Death has occurred within 17 minutes of ingestion. Paresthesias of the lips and tongue are followed by sialorrhea, sweating, headache, weakness, lethargy, ataxia, incoordination, tremor, paralysis, cyanosis, aphonia, dysphagia, seizures, dyspnea, bronchorrhea, bronchospasm, respiratory failure, coma, and hypotension. Gastroenteric symptoms are often severe and include nausea, vomiting, diarrhea,and abdominal pain. Cardiac arrhythmias may precede complete respiratory failure and cardiovascular collapse.

Treatment

Therapy is supportive and based on symptoms, with aggressive early airway management. If ingested, treatment can consist of emptying the stomach, feeding the victim activated charcoal to bind the toxin, and taking standard life-support measures to keep the victim alive until the effect of the poison has worn off. Alpha adrenergic agonists are recommended in addition to intravenous fluids to combat hypotension. Anticholinesterase agents have been used with mixed success. No antidote has been developed.

Course of tetrodotoxin poisoning and complications

The first symptom of intoxication is a slight numbness of the lips and tongue, appearing between 20 minutes to three hours after eating poisonous pufferfish. The next symptom is increasing paresthesia in the face and extremities, which may be followed by sensations of lightness or floating. Headache, epigastric pain, nausea, diarrhea, and/or vomiting may occur. Occasionally, some reeling or difficulty in walking may occur. The second stage of the intoxication is increasing paralysis. Many victims are unable to move; even sitting may be difficult. There is increasing respiratory distress. Speech is affected, and the victim usually exhibits dyspnea, cyanosis, and hypotension. Paralysis increases and convulsions, mental impairment, and cardiac arrhythmia may occur. The victim, although completely paralyzed, may be conscious and in some cases completely lucid until shortly before death. Death usually occurs within 4 to 6 hours, with a known range of about 20 minutes to 8 hours.

Geographic frequency of tetrodotoxin toxicity

Poisonings from tetrodotoxin have been almost exclusively associated with the consumption of pufferfish from waters of the Indo-Pacific ocean regions. Several reported cases of poisonings, including fatalities, involved pufferfish from the Atlantic Ocean, Gulf of Mexico, and Gulf of California. There have been no confirmed cases of tetrodotoxicity from the Atlantic pufferfish, "Sphoeroides maculatus". However, in three studies, extracts from fish of this species were highly toxic in mice. Several recent intoxications from these fishes in Florida were due to saxitoxin, which causes paralytic shellfish poisoning with very similar symptoms and signs. The trumpet shell Charonia sauliae has been implicated in food poisonings, and evidence suggests that it contains a tetrodotoxin derivative. There have been several reported poisonings from mislabelled pufferfish and at least one report of a fatal episode in Oregon when an individual swallowed a Rough-skinned Newt, "Taricha granulosa".

Relative frequency of tetrodotoxin ingestive poisonings

From 1974 through 1983 there were 646 reported cases of pufferfish poisoning in Japan, with 179 fatalities.Fact|date=April 2008 Statistics from the Tokyo Bureau of Social Welfare and Public Health indicate 20-44 incidents of fugu poisoning per year between 1996 and 2006 in the entire country, leading to 34-64 hospitalizations and 0-6 deaths per year, for an average fatality rate of 6.8%. [http://www.fukushihoken.metro.tokyo.jp/kenkou/anzen/anzen_info/shizendoku/hugu/ 危険がいっぱい ふぐの素人料理 東京都福祉保健局 ] ] Of the 23 incidents recorded within Tokyo between 1993 and 2006, only one took place in a restaurant, while the others all involved fishermen eating their catch.

Only a few cases have been reported in the United States, and outbreaks in countries outside the Indo-Pacific area are rare, except in Haiti, where tetrodotoxin is thought by some believers in voodoo mythology to play a key role in the creation of so-called zombie poisons.cite journal | author = Anderson WH | title = Tetrodotoxin and the zombi phenomenon | journal = Journal of Ethnopharmacology | volume = 23 | issue = 1 | pages = 121–6 | year = 1988 | pmid = 3419200 | doi = 10.1016/0378-8741(88)90122-5 ]

Target populations

Genetic background is not a factor in susceptibility to tetrodotoxin poisoning. This toxicosis may be avoided by not consuming animal species known to contain tetrodotoxin, principally pufferfish; other tetrodotoxic species are not usually consumed by humans. Poisoning from tetrodotoxin is of particular public health concern in Japan, where pufferfish, "fugu", is a traditional delicacy. It is prepared and sold in special restaurants where trained and licensed chefs carefully remove the viscera to reduce the danger of poisoning. There is potential for misidentification and mislabelling, particularly of prepared, frozen fish products.

Food analysis

The mouse bioassay developed for paralytic shellfish poisoning (PSP) can be used to monitor tetrodotoxin in pufferfish and is the current method of choice. An HPLC method with post-column reaction with alkali and fluorescence has been developed to determine tetrodotoxin and its associated toxins. The alkali degradation products can be confirmed as their trimethylsilyl derivatives by gas chromatography/mass spectrometry. These chromatographic methods have not yet been validated.

Regulation

In the USA, tetrodotoxin appears on the select agents list of the Department of Health and Human Services, [HHS and USDA Select Agents and Toxins 7 CFR Part 331, 9 CFR Part 121, and 42 CFR Part 73. http://www.cdc.gov/od/sap/docs/salist.pdf] and scientists must register with HHS in order to use tetrodotoxin in their research. However, investigators possessing less than 100 mg are exempt from regulation. [ Federal Register. Vol. 70, No. 52. Friday, March 18, 2005. http://www.cdc.gov/od/sap/42_cfr_73_final_rule.pdf]

ee also

* Conotoxin
* Neurotoxin
* Saxitoxin
* Tectin
* Clairvius Narcisse, a Haitian alleged to have been buried alive under the effect of the drug

References

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