Fugu toxin

Tetrodotoxin (TTX, tarichatoxin, spheroidin, fugu toxin, maculotoxin). 

Tetrodotoxin (TTX) is a toxin derived from bacteria which is concentrated in the gonads and liver of certain pufferfishes (fugu). Similar to saxitoxin, tetrodotoxin is a very potent blocker of most voltage-sensitive Na+ channels. 

The intraperitoneal LD50 values for fish, as for polkilotherms, are extremely low. This means that fish (with the exception perhaps of Fugu) are unable to tolerate even small amounts of the toxins in their bodies, and hence are unable to accumulate them. This important point will be discussed again below in connection with the effect of the toxins on the use of fish as food. 

Pufferfish. Toxic species are members of the order Tetrodontiformes (Plectognathi) and include the sharp-nosed puffers (Canthigaste-ridae). porcupine fish (Diodontidae) as well as the true puffers or fugu (Tetraodontidae). Many human fatalities continue to occur from eating these fish, including an occasional fatality in Florida (cf. 1.9 9 ). The toxin occurs principally in the ovaries9 liver and, in some species, the skin. 

Ovaries (100 g) of the pufferfish Fugu vermicularis porphgreus are extracted with 1% acetic acid in methanol. The extract is concentrated in vacuo and defatted by shaking with chloroform. The defatted extract is treated with activated charcoal. The toxin adsorbed is eluted with 1% acetic acid in 20% ethanol. The eluate is evaporated in vacuo to dryness. The residue is dissolved in a small a-mount of water and adjusted to pH 6 with 1 N NaOH. The toxic solution is applied to an Amberlite IRC-50 column (NH, 2.5 x 45 cm) and developed with 2 L of water, and then 1 L each of 1 and 10% acetic acid. The toxic fractions are freeze-dried, dissolved in 1 mL of water and analyzed by HPLC. 

Many fish species, over 700 species worldwide, are either directly toxic or upon ingestion are poisonous to humans. A classic example is the toxin produced by the puffer fishes (Sphaeroides spp.) called tetrodotoxin (TTX). Tetrodotoxin is concentrated in the gonads, liver, intestine, and skin, and poisonings occurs most frequently in Japan and other Asian countries where the flesh, considered a delicacy, is eaten as fugu. Death occurs within 5 to 30 minutes and the fatality rate is about 60%. TTX is an inhibitor of the voltage-sensitive Na channel (like saxitoxin) it may also be found in some salamanders and may be bacterial in origin. 

The poisonous properties of the puffer fish have been known for centuries, and were described as early as ad 220 in China. A Chinese treatise written in ad 600 by Chaun Yanfang (Studies on the Origin of Diseases) described the liver, ovaries, and roe as the most poisonous. Despite the risks, puffer fish is stiU eaten as a delicacy in Japan, where it is known as fugu. Fish that contain the toxin are also accidentally eaten sometimes. Consequently poisoning cases do occur. Between 1974 and 1983 there were 646 cases and 179 fatalities. It has been estimated that as many as 200 cases a year may occur, with a mortality rate of up to 50 per cent. A trained chef should know which parts of the fish to avoid. 

The puffer fish toxin. Captain Cook severely affected in 1774. The fish is prepared by trained cooks and eaten as fugu in Japan. Also found in ovaries and liver of related fish species and some cephalopods. Non-protein MW 319. Effects numbness and tingling of lips, vomiting, fall in BP, weakness, paralysis, respiratory failure, death. Lethal dose in mice 5 pg/kg among the most potent of toxins. Blocks sodium channels and prevents depolarization. Believed to be produced by bacteria in the fish. Looked at by Japan in WWII as a potential CW agent. 

Cases occur during all months of the year. It is not known whether the proportion of tetrodotoxic fish has increased. Simple incidence data would not necessarily answer this question since public health measures such as education and regulation of fugu chefs in Japan may effect incidence estimates regardless of changes in the proportion of animals containing toxin. In addition, it is possible that improved medical care has lowered the number of lethal cases. The retrospective analysis of 42 outbreaks of tetrodotoxin-associated paralytic snail poisoning in Asia found no temporal variation [140],... 

Endo, A., Khora, S.S., Murata, M., Naoki, H., and Yasumoto, T. 1988. Isolation of 11-norttetrodo-toxin-6R-ol and other tetrodotoxin derivatives from the puffer Fugu nipholes. Tetrahedron Lett. 29, 4127 128. 

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