Posted by: Andrew Haynes18 AUG 2014
In his book ‘A voyage towards the South Pole and around the world”, Captain James Cook recorded that in September 1774, while exploring islands in the South Pacific, he and two companions ate a little of a local fish that his clerk had bought from an islander.
“It was of a new species, something like a sun-fish, with a large long ugly head. Having no suspicion of its being of a poisonous nature, we ordered it to be dressed for supper; but, very luckily, the operation of drawing and describing took up so much time, that it was too late, so that only the liver and roe were dressed, of which the two Mr Forsters and myself did but taste.
“About three o’clock in the morning, we found ourselves seized with an extraordinary weakness and numbness all over our limbs. I had almost lost the sense of feeling; nor could I distinguish between light and heavy bodies, of such as I had strength to move; a quart-pot, full of water, and a feather, being the same in my hand. We each of us took an emetic, and after that a sweat, which gave us much relief. In the morning, one of the pigs, which had eaten the entrails, was found dead.
“When the natives came on board and saw the fish hanging up, they immediately gave us to understand it was not wholesome food, and expressed the utmost abhorrence of it; though no one was observed to do this when the fish was to be sold, or even after it was purchased.”
The fish that Cook’s cook had prepared for him was probably a toadfish (Lagocephalus sceleratus), a type of pufferfish, and Cook’s account is the earliest record of poisoning by tetrodotoxin.
Cook and his colleagues were lucky, since tetrodotoxin (TTX) is a highly potent neurotoxin that binds to the pores of sodium channel proteins in nerve cell membranes and shuts down electrical signalling. It is not affected by cooking, and in Japan dozens of people are poisoned every year by eating pufferfish (fugu) prepared by chefs who have not been trained to remove the poisonous parts.
We now know that tetrodotoxin can be found in many creatures other than the pufferfish, including other fish, cephalopods, starfish, xanthid crabs, flatworms, seaslugs and amphibians. These creatures use TTX as a defensive biotoxin to ward off predation and sometimes also as a predatory venom.
The fact that such a wide range of animals make use of TTX suggests that they acquire it rather than synthesise it, and it now seems that it is produced by some symbiotic bacteria, including species of Vibrio, Pseudomonas and Pseudoalteromonas.
The structure of TTX was elucidated in 1964, and since then researchers in Japan have developed methods of synthesising it and its analogues. It is now being investigated as a possible treatment for cancer-associated pain. Early clinical trials demonstrate significant pain relief in some patients.