Killer Snails and Novel Drug Breakthroughs

This are not your friendly fish tank-cleaning sails, harmlessly trailing their huge sucker mouth to wherever the next large algae deposit is; These are predatory, carnivorous sea snails. Yes, I said predatory. Venom that can paralyze, administered by a hypodermic-like radula tooth. They bury themselves under the surface, leaving exposed only a siphon, waiting for their next victim. The reason for why I am exposing you to yet another phobia you may ask? The venom of these snails is leading to new sources of medical importance, and demonstrate yet another reason why there is so much left in the world to be discovered.

One of the most notable characteristics about the cone snail is its beautifully colored shell. It varies in size yet typically maintain the classic geometric shape of a cone, theses shells have been used for ornamentation for thousands of years. Some of the larger species of cone snail can grow up to 23cm long. The brilliant colors and fascinating pattern of the shell are often hiding under a layer of periostracum, a yellow-brown transparent membrane that forms a line layer around the snail.

One of the most startling aspects of these snails is their carnivorous life style. They eat anything from small fish to worms, from mollusks even to other types of cone snails. When preparing to capture larger prey, the venom that is administered is potent enough to kill a human. The osphradium, a chemoreceptor organ that acts to enhance the sensory modality of the snail, alerts them to the presence of their soon-to-be dinner. Once the prey draws near…

WaaaBAM!

…a dart-like, barbed tooth jabs the prey, and neurotoxins are released from a poison gland through the needle-like modified tooth spear; the toxin paralyzes small fish instantly. The snail then retracts the radula, drawing the subdued prey into its mouth. If this isn’t alarming enough the snail, after consuming all edible parts, regurgitates spines, scales and any other waste as well as the now defunct harpoon. A second dart is always kept handy for the snail’s next meals and is stored in the radular sac.

The venom of cone snails contains hundreds of different compounds, and its exact composition varies widely from one species of cone snail to another. The various toxins in these venoms are called conotoxins. The toxins are composed of a number of peptides, each targeting a specific nerve channel or receptor. Some cone snail venoms also contain a pain-reducing toxin, which the snail uses to pacify the victim before immobilizing and then killing it.

There are over 600 different types of cone snails, which are dispersed across the warm tropical seas worldwide. Some have adapted to more temperate water, finding their way to the coasts of southern California. When one of these beautiful snails is seen, people often pick them up, therefore it is important to increase awareness among beach combers that the harpoons are sometime able to penetrate skin, even through gloves or wetsuits. According to Goldfrank’s Toxicologic Emergencies, only about 15 human deaths can be confidently attributed to cone snail envenomation. One of the fish-eating species, the geography cone, Conus geographus, is also known colloquially as the “cigarette snail,” a gallows humor exaggeration implying that, when stung by this creature, the victim will have only enough time to smoke a cigarette before dying.

For pharmacologists it is the speed in which the toxin acts, and its ability to target particular classes of receptors while excluding others that is of greatest interest. The goal of researchers studying cone snails is to isolate specific components of the toxin that quickly produce particular effects due to either receptor or channel regulation. The venom of some cone snails, such as the magician cone, shows much promise for providing a non-addictive pain reliever 1000 times as powerful as, and possibly a replacement for, morphine. Along with other potent pharmaceuticals produced from cone snails, the first painkiller derived from cone snail toxins, Ziconotide, was FDA approved in December 2004 under the name “Prialt” (hence the cute snail on it’s insignia). Other drugs are in clinical and preclinical trials, such as compounds of the toxin that may be prospective treatment for Alzheimer’s disease, Parkinson’s disease, and epilepsy.

So that next time you go to the beach, you not only have to look out for jellyfish, sharks, and stingrays (which we know are on a mission to spear helpless humans in the heart ), but now snails… basically never leave your lab.

Source of information for the article

https://en.wikipedia.org/wiki/Cone_snail

Image Sources

https://www.theguardian.com/science/2015/jan/19/venomous-sea-snail-insulin-prey-conus-geographus

https://nypost.com/2016/10/20/meet-the-adorable-little-snail-that-could-kill-you/

https://phys.org/news/2016-09-snails-speedy-insulin-bio-inspired-faster.html

https://phys.org/news/2017-10-cone-snail-deadly-venom-medicines.html