Palytoxin
Encyclopedia
Palytoxin is a very dangerous toxin; it is considered to be one of the most toxic non-peptide substances known, second only to maitotoxin
in terms of toxicity in mice. Palytoxin is a natural compound that is produced by several marine species and can be found in many more species due to accumulation.
Palytoxin was originally isolated in 1971 in Hawaii
from the seaweed-like coral "Limu make o hana (Seaweed of Death from Hana)". Later, in 1982 its full chemical structure was published by Prof. Daisuke Uemura and co-workers at Nagoya University
. Professor Yoshito Kishi
's group at Harvard University
first synthesized palytoxin in 1994. This feat is still considered by some an accomplishment like the first ascent of Everest, others consider it foolish, in the spirit of the Charge of the Light Brigade
.
Palytoxin targets the sodium-potassium pump protein
by binding to the molecule in such a way that the molecule is locked in a position where it allows passive transport
of both the sodium
and potassium
ions, thereby destroying the ion gradient that is essential for most cells
.
Because palytoxin affects every cell in the body, the symptoms are very different for the different ways of exposure. The most common way of exposure in humans is oral. The onset of symptoms in a palytoxin poisoning is rapid, and death usually follows quickly.
The moss growing in the cursed tide pool became known as "limu-make-o-Hana" which literally means "seaweed of death from Hana." The Hawaiians believed that an ill curse came over them if they tried to collect the deadly seaweed.
Palytoxin is a huge molecule with chemical formula C129H223N3O54. To accomplish this, it was synthesized in eight separate parts and then joined together to form the entire molecule. First, palytoxin carboxylic acid was synthesized in 1989 by the group of Harvard professor Yushito Kishi, and in 1994 they succeeded in making palytoxin from this carboxylic acid. The accomplishment of this synthesis has been named "the Mount Everest of organic synthesis, the largest single molecule that anyone has ever even thought about making" by Crawford in 1989.
Palytoxin is the first toxic compound found to cause formation of a channel. Through this channel, which it forms within the sodium pump, monovalent positive ions such as sodium and potassium can diffuse freely thereby destroying the ion gradient of the cell. Once palytoxin is bound to the pump, it flips constantly between open and normal conformations. The open conformation is more likely (>90% probability). If palytoxin disscociates, the pump will return to closed conformation. In open conformation, millions of ions diffuse through the pump per second, whereas only about one hundred ions are transported through a normal functioning transporter.
Because the mechanism of action of palytoxin was so unlike any other, it was initially not widely accepted. This was primarily because it was not expected that a pump which provides active transport, could become an ion channel by binding of a compound such as palytoxin. Therefore, there were some alternative hypotheses, which were reviewed by Frelin and van Renterghem in 1995. The breakthrough research which is seen as proof for the sodium pump mechanism was performed in yeast cells. These cells do not have the sodium pump, and hence palytoxin does not affect them. But once they were given the DNA to encode for complete sheep Na+,K+-ATPase, they were killed by palytoxin.
Because toxin-producing organisms spread to temperate climates and palytoxin-contaminated shellfish were discovered in the Mediterranean Sea a study was done to better define the toxic effects of palytoxin after oral exposure in mice. Palytoxin was lethal from 600µg/kg doses. The number of deaths were dose-dependent and the LD50 calculated to be 767µg/kg. This is comparable to the LD50 of 510µg/kg referred by Munday (2008). The toxicity was not different if the mice had some food in their stomach. The oral toxicity is three times lower than the intraperitoneal toxicity. This is because palytoxin is a very big hydrophilic molecule and therefore the absorption is less efficient through the gastrointestinal tract than through the peritoneum.
Palytoxin is most toxic after intravenous injection. The LD50 in mice is 0.045µg/kg and in rats 0.089µg/kg. In other mammals (rabbits, dogs, monkeys and guinea pigs) the LD50 is ranged between 0.025 and 0.45µg/kg. They all died in several minutes to heart failure.
The lethal dose for mice by the intra-tracheal route is above 2µg/kg in 2 hours. Palytoxin is also very toxic after intramuscular or subcutaneous injection. No toxicity is found after intrarectal administration. Palytoxin is not lethal when topically applied to skin or eyes.
There are cases where humans died after consumption of palytoxin. In the Philippines people died after eating Demania reynaudii, a crab species. After eating the sardine species Herklotsichthys quadrimaculatus some people died in Madagascar. Near fatal cases took place in Hawaii and Japan.
In these cases people had eaten smoked fish and parrotfish respectively. There are also cases known that persons were poisoned by palytoxin through dermal absorption. Those people, in Germany and the USA , touched zoanthid corals in their aquariums at home. Another person was exposed to palytoxin via inhalation when he tried to kill a Palythoa in his aquarium with boiling water.
Combining all animal studies, the toxic dose for humans was estimated to be between 2.3 and 31.5µg palytoxin. An acute reference dose was suggested to be 64µg for a person with weight of 60 kg.
Clupeotoxism, poisoning after consuming clupeoid fish, is also suggested to be caused by palytoxin. Neurological and gastrointestinal disturbances are associated with clupeotoxism. The most common complication of palytoxin poisoning is rhabdomyolysis. This involves skeletal muscle breakdown and the leakage of intracellular contents into the blood plasma.
Other symptoms associated with palytoxin poisoning in humans are characterized by a bitter/metallic taste, abdominal cramps, nausea, vomiting, diarrhea, mild to acute lethargy, paresthesia, bradycardia, renal failure, impairment of sensation, muscle spasms, tremor myalgia, cyanosis, and respiratory distress. In the fatal cases of palytoxin poisoning, the poisoning mostly results in death due to myocardial injury.
Exposure to aerosols, as happened in Italy in 2005 and 2006 (see Incidents section), results mainly in respiratory illness. Other symptoms caused by these aerosols include fever associated with serious respiratory disturbs, such as bronchoconstriction, mild dyspnea, and wheezes, while conjunctivitis was observed in some cases. Palytoxin is also classified as a non-TPAtype tumor promoter.
and isosorbide dinitrate
, can be used as antidotes. The animal experiments only showed benefit if the antidotes were injected into the heart
immediately following exposure. Treatment in humans is symptomatic and supportive.
Maitotoxin
Maitotoxin is an extremely potent toxin produced by Gambierdiscus toxicus, a dinoflagellate species. Maitotoxin is so potent that it has been demonstrated that an intraperitoneal injection of 0.13 µg/kg was lethal in mice...
in terms of toxicity in mice. Palytoxin is a natural compound that is produced by several marine species and can be found in many more species due to accumulation.
Palytoxin was originally isolated in 1971 in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
from the seaweed-like coral "Limu make o hana (Seaweed of Death from Hana)". Later, in 1982 its full chemical structure was published by Prof. Daisuke Uemura and co-workers at Nagoya University
Nagoya University
Nagoya University is one of the most prestigious universities in Japan. It can be seen in the several rankings such as shown below.-General Rankings:...
. Professor Yoshito Kishi
Yoshito Kishi
Yoshito Kishi is the Morris Loeb Professor of Chemistry at Harvard University. He is known for his contributions to the sciences of organic synthesis and total synthesis....
's group at Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
first synthesized palytoxin in 1994. This feat is still considered by some an accomplishment like the first ascent of Everest, others consider it foolish, in the spirit of the Charge of the Light Brigade
Charge of the Light Brigade
The Charge of the Light Brigade was a charge of British cavalry led by Lord Cardigan against Russian forces during the Battle of Balaclava on 25 October 1854 in the Crimean War. The charge was the result of a miscommunication in such a way that the brigade attempted a much more difficult objective...
.
Palytoxin targets the sodium-potassium pump protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
by binding to the molecule in such a way that the molecule is locked in a position where it allows passive transport
Passive transport
Passive transport means moving biochemicals and other atomic or molecular substances across membranes. Unlike active transport, this process does not involve chemical energy, because, unlike in an active transport, the transport across membrane is always coupled with the growth of entropy of the...
of both the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
ions, thereby destroying the ion gradient that is essential for most cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
.
Because palytoxin affects every cell in the body, the symptoms are very different for the different ways of exposure. The most common way of exposure in humans is oral. The onset of symptoms in a palytoxin poisoning is rapid, and death usually follows quickly.
Legend
According to an ancient Hawaiian legend, (Malo 1951) on the island of Maui near the harbour of Hana there was a village of fishermen haunted by a curse. Upon their return from the sea one of the fishermen went missing. One day, enraged by another loss, the fishermen assaulted a hunchbacked hermit deemed culprit of the town's misery. While ripping of the cloak from the hermit the villagers were shocked because they uncovered rows of sharp and triangular teeth within huge jaws. A shark god had been caught. It was clear that the missing villagers had been eaten by the god on their journeys to the sea. The men mercilessly tore the shark god into pieces, burned him and threw the ashes into a tide pool near the harbour of Hana. Shortly after, a thick brown moss started to grow on the walls of the tide pool causing instant death to victims hit by spears smeared with the moss. Thus was the evil of the demon.The moss growing in the cursed tide pool became known as "limu-make-o-Hana" which literally means "seaweed of death from Hana." The Hawaiians believed that an ill curse came over them if they tried to collect the deadly seaweed.
Discovery
Palytoxin was first isolated in 1971, by Moore and Scheuer. It was then assessed that the limu-make-o-Hana was not a seaweed but an animal, a soft coral (Walsh and Bowers 1971). The molecule responsible for its high toxicity was named palytoxin.Synthesis
Because palytoxin is such a huge molecule, it took some time before the complete structure (including stereochemistry) was elucidated. In 1982, this problem was solved almost simultaneously by Moore and Hirata.Palytoxin is a huge molecule with chemical formula C129H223N3O54. To accomplish this, it was synthesized in eight separate parts and then joined together to form the entire molecule. First, palytoxin carboxylic acid was synthesized in 1989 by the group of Harvard professor Yushito Kishi, and in 1994 they succeeded in making palytoxin from this carboxylic acid. The accomplishment of this synthesis has been named "the Mount Everest of organic synthesis, the largest single molecule that anyone has ever even thought about making" by Crawford in 1989.
Incidents
A new type of palytoxin, ovatoxin-a, produced as a marine aerosol by the tropical microalga O. ovata caused hundreds of people in Genoa, Italy, to fall ill. In 2005 and 2006 enormous blooms of these algae occurred in the Mediterranean sea. All those affected needed medical attention. Symptoms were high fever, coughs and wheezes.Mechanism
The toxicity of palytoxin is due to its binding to Na+,K+-ATPase (sodium pump), where it interacts with the natural binding site of ouabain with very high affinity. Na+,K+-ATPase is a transmembranal protein, which is found on the surface of every vertebrate cell. Also, the sodium pump is necessary for viability of all cells, and this explains the fact that palytoxin affects all cells.Palytoxin is the first toxic compound found to cause formation of a channel. Through this channel, which it forms within the sodium pump, monovalent positive ions such as sodium and potassium can diffuse freely thereby destroying the ion gradient of the cell. Once palytoxin is bound to the pump, it flips constantly between open and normal conformations. The open conformation is more likely (>90% probability). If palytoxin disscociates, the pump will return to closed conformation. In open conformation, millions of ions diffuse through the pump per second, whereas only about one hundred ions are transported through a normal functioning transporter.
Because the mechanism of action of palytoxin was so unlike any other, it was initially not widely accepted. This was primarily because it was not expected that a pump which provides active transport, could become an ion channel by binding of a compound such as palytoxin. Therefore, there were some alternative hypotheses, which were reviewed by Frelin and van Renterghem in 1995. The breakthrough research which is seen as proof for the sodium pump mechanism was performed in yeast cells. These cells do not have the sodium pump, and hence palytoxin does not affect them. But once they were given the DNA to encode for complete sheep Na+,K+-ATPase, they were killed by palytoxin.
Toxicity
An early toxicological characterization classified palytoxin as "relatively non-toxic" after intragastric administration to rats. The lethal dose (LD50) was greater than 40µg/kg. The LD50 after parenteral administration was lower than 1µg/kg. However the doubtful purity of this study increased because of uncertainty concerning the toxicological data. In 1974, the structure of palytoxin was not completely elucidated and the molecular weight was a lot higher (3300 Da instead of 2681 Da). More recently a study discovered an LD50 of 510µg/kg after intragastric administration in mice, but histological or biochemical information was missing. (Rhodes and Munday, 2004) Furthermore palytoxin was not lethal to mice given an oral dose of 200µg/kg. It was also found that palytoxin is very toxic after intraperitoneal injection. The LD50 in mice was less than 1µg/kg.Because toxin-producing organisms spread to temperate climates and palytoxin-contaminated shellfish were discovered in the Mediterranean Sea a study was done to better define the toxic effects of palytoxin after oral exposure in mice. Palytoxin was lethal from 600µg/kg doses. The number of deaths were dose-dependent and the LD50 calculated to be 767µg/kg. This is comparable to the LD50 of 510µg/kg referred by Munday (2008). The toxicity was not different if the mice had some food in their stomach. The oral toxicity is three times lower than the intraperitoneal toxicity. This is because palytoxin is a very big hydrophilic molecule and therefore the absorption is less efficient through the gastrointestinal tract than through the peritoneum.
Palytoxin is most toxic after intravenous injection. The LD50 in mice is 0.045µg/kg and in rats 0.089µg/kg. In other mammals (rabbits, dogs, monkeys and guinea pigs) the LD50 is ranged between 0.025 and 0.45µg/kg. They all died in several minutes to heart failure.
The lethal dose for mice by the intra-tracheal route is above 2µg/kg in 2 hours. Palytoxin is also very toxic after intramuscular or subcutaneous injection. No toxicity is found after intrarectal administration. Palytoxin is not lethal when topically applied to skin or eyes.
There are cases where humans died after consumption of palytoxin. In the Philippines people died after eating Demania reynaudii, a crab species. After eating the sardine species Herklotsichthys quadrimaculatus some people died in Madagascar. Near fatal cases took place in Hawaii and Japan.
In these cases people had eaten smoked fish and parrotfish respectively. There are also cases known that persons were poisoned by palytoxin through dermal absorption. Those people, in Germany and the USA , touched zoanthid corals in their aquariums at home. Another person was exposed to palytoxin via inhalation when he tried to kill a Palythoa in his aquarium with boiling water.
Combining all animal studies, the toxic dose for humans was estimated to be between 2.3 and 31.5µg palytoxin. An acute reference dose was suggested to be 64µg for a person with weight of 60 kg.
| Exposure | LD50 in animals |
|---|---|
| Intravenous | Mice 0.054 μg/kg |
| Rats 0.089 μg/kg | |
| Intratracheal | Mice >2 μg/kg |
| Intraperitoneal | Mice <1 μg/kg |
| Oral | Mice 767 μg/kg |
Symptoms
Palytoxin could be related to ciguatera seafood poisoning and thus give rise to a number of symptoms related to this poisoning.Clupeotoxism, poisoning after consuming clupeoid fish, is also suggested to be caused by palytoxin. Neurological and gastrointestinal disturbances are associated with clupeotoxism. The most common complication of palytoxin poisoning is rhabdomyolysis. This involves skeletal muscle breakdown and the leakage of intracellular contents into the blood plasma.
Other symptoms associated with palytoxin poisoning in humans are characterized by a bitter/metallic taste, abdominal cramps, nausea, vomiting, diarrhea, mild to acute lethargy, paresthesia, bradycardia, renal failure, impairment of sensation, muscle spasms, tremor myalgia, cyanosis, and respiratory distress. In the fatal cases of palytoxin poisoning, the poisoning mostly results in death due to myocardial injury.
Exposure to aerosols, as happened in Italy in 2005 and 2006 (see Incidents section), results mainly in respiratory illness. Other symptoms caused by these aerosols include fever associated with serious respiratory disturbs, such as bronchoconstriction, mild dyspnea, and wheezes, while conjunctivitis was observed in some cases. Palytoxin is also classified as a non-TPAtype tumor promoter.
Treatment
Animal studies have shown that vasodilators, such as papaverinePapaverine
Papaverine is an opium alkaloid antispasmodic drug, used primarily in the treatment of visceral spasm, vasospasm , and occasionally in the treatment of erectile dysfunction...
and isosorbide dinitrate
Isosorbide dinitrate
Isosorbide dinitrate is a nitrate used pharmacologically as a vasodilator, e.g. in angina pectoris but also for anal fissure, a condition which is known to involve decreased blood supply leading to poor healing...
, can be used as antidotes. The animal experiments only showed benefit if the antidotes were injected into the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
immediately following exposure. Treatment in humans is symptomatic and supportive.