Abstract
Many pufferfish of the family Tetraodontidae possess a potent neurotoxin, tetrodotoxin (TTX). In marine pufferfish species, toxicity is generally high in the liver and ovary, whereas in brackish water and freshwater species, toxicity is higher in the skin. In 1964, the toxin of the California newt was identified as TTX as well, and since then TTX has been detected in a variety of other organisms. TTX is produced primarily by marine bacteria, and pufferfish accumulate TTX via the food chain that begins with these bacteria. Consequently, pufferfish become non-toxic when they are fed TTX-free diets in an environment in which the invasion of TTX-bearing organisms is completely shut off. Although some researchers claim that the TTX of amphibians is endogenous, we believe that it also has an exogenous origin, i.e., from organisms consumed as food. TTX-bearing animals are equipped with a high tolerance to TTX, and thus retain or accumulate TTX possibly as a biologic defense substance. There have been many cases of human intoxication due to the ingestion of TTX-bearing pufferfish, mainly in Japan, China, and Taiwan, and several victims have died. Several cases of TTX intoxication due to the ingestion of small gastropods, including some lethal cases, were recently reported in China and Taiwan, revealing a serious public health issue.
Highlights
Pufferfish toxin is a potent neurotoxin of low molecular weight, which was first isolated in 1950 as a crystalline prism from toxic pufferfish by Yokoo [1]
Subsequent findings, such as the distribution of TTX among many other organisms [9], the TTX intoxication of the trumpet shell following the ingestion of toxic starfish [10], TTX production by marine bacteria [11], and the facts pufferfish become non-toxic when artificially reared with non-toxic diets [12,13,14] and that such non-toxic pufferfish become toxic when fed TTX-containing diets [15,16,17], have elucidated that the main mechanism of TTX accumulation in pufferfish is the food chain, consisting of several steps and starting with marine bacteria as a primary source of TTX
Marine pufferfish (Table 1) and flatworms [9,120] retain high toxicity in their eggs, and pufferfish and newts are equipped with TTX-secreting glands or cells in their skin [3840,121], suggesting that TTX is present as a defensive substance to protect their eggs or themselves from external enemies
Summary
Pufferfish toxin (tetrodotoxin, TTX) is a potent neurotoxin of low molecular weight, which was first isolated in 1950 as a crystalline prism from toxic pufferfish by Yokoo [1]. Many years ago when TTX was believed to be found exclusively in pufferfish, it was controversial whether TTX in the fish was endogenous (produced by the pufferfish itself) or exogenous (taken from the outside and accumulated) Subsequent findings, such as the distribution of TTX among many other organisms [9], the TTX intoxication of the trumpet shell following the ingestion of toxic starfish [10], TTX production by marine bacteria [11], and the facts pufferfish become non-toxic when artificially reared with non-toxic diets [12,13,14] and that such non-toxic pufferfish become toxic when fed TTX-containing diets [15,16,17], have elucidated that the main mechanism of TTX accumulation in pufferfish is the food chain, consisting of several steps and starting with marine bacteria as a primary source of TTX.
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