Tetrodotoxin (TTX) is a quite powerful neurotoxin that blocks action potentials in nerves by binding to the voltage-gated, fast sodium channels in nerve cell membranes, essentially preventing any affected nerve cells from firing by blocking the channels used in the process. The binding site of this toxin is located at the pore opening of the voltage-gated Na+ channel. TTX is mostly associated with puffer fish , however several other unrelated organisms are also known to produce the toxins such as blue-ringed octopus, rough-skinned newt and certain bacteria, such as Pseudoalteromonas tetraodonis, and other certain species of Pseudomonas and Vibrio.
Although TTX- carriers are typically residents of warm waters , recent studies have noticed a migrations of these toxic species to Mediterranean Sea from the Red Sea directly attributed to warming of waters due to climate change. There have been several poisoning incidents in Egypt by the migrant elongated puffer (Lagocephalus sceleratus ) and also recently in Spain by marine snail Charonia lampa. This has prompted the investigation of the presence of TTX in several marine invertebrate species collected along the continental Portuguese coast.
They’ve collected 134 samples from 13 sites along the Portuguese coast. Collected samples mainly belonged to gastropods (Monodonta lineata, Monodonta turbinata, Gibbula umbilicalis, Gibbula magus, Littorina littorea, Littorina saxatilis, Nucella lapillus, Ocenebra erinacea, Calliostoma zizyphinum, Patella intermedia, Charonia lampas), bivalves (Mytilus galloprovincialis), sea-urchins (Paracentrotus lividus) and sea-stars (Marthasterias glacialis). Collcted samples were investigated for the presents of TTX and its analogues using UPLC-MS/MS (ultra-performance liquid chromatography–tandem mass spectrometry ) and LC-MS/MS (Liquid chromatography–mass spectrometry). Naturally TTX containg species such as L. sceleratus and C. lampa were used as standards in the analysis.
The results showed that out of these 134 species, two have shown to contain TTX or TTX equivalents. Two species of top shells : M. lineata and G. umbilicalis are well known to locals around the coasts. They are often harvested and consumed despite not being often found in markets. Therefore the exposure cannot be regulated or controlled . Although the amount of toxins found in those two snail were quite small, it still possess a high risk of poisoning through the bioaccumulation process.
This paper was quite interesting and showed how climate change can affect the distribution of poisonous species , moreover new vectors founds in a form of edible snails is quite alarming. There have now been many reports about migration of warm water species into the more temperate regions due to higher water temperature. Not only migration of exotic species is a problem caused by temperature rise but also altering of poison properties such accumulation, metabolism and detoxification kinetics in fish vectors. Higher temperature are also predicted to increase the occuurence of other fish poisoning such as the ciguatera fish poisoning. The numbers predicts the rise of 35–70 per thousand people in 1990 to 160–430 per thousand people in 2050 in Papua New Guinea. Moreover the temperature can also have an impact of TTX producing bacteria (such as V. alginolyticu) which were shown to grow much better and quicker in warmer temperatures. However more studies are still needed to exactly predict the impact of higher temperatures on poison kinetics.
The only drawback about this paper was its quite confusing layout , after the introduction they went straight to results and discussion with methods been placed at the end which I found confusing and quite odd, definitely makes a bit more difficult having to read back and forwards.However very interetsing and usufull study , especially in time of apparent climate change.
A review of Silva et al., (2012). New Gastropod Vectors and Tetrodotoxin Potential Expansion in Temperate Waters of the Atlantic Ocean . Mar. Drugs. 10: 712-726
2 comments:
Hi I was wondering if in the species that were found to contain TTX if any bacteria accociated with TTX production were found to be accosiated with them? This is because in Rachel's post she says that when Pufferfish are kept in isolated waters they produce no toxin but when exposed to normal water they are found to contain TTX and it is hypothesised that TTX is produced by some bacteria accociated with the pufferfish ?
Hi Katty
They haven’t investigated the origin of TTX in those species but they mention other studies that think that bacteria are responsible for producing it. Some other studies mentioned some species of Vibrio (such as the V. alginolyticus ) and Pseudoalteromonas tetraodonis produce it.
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