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Cone Snails (excerpt from Sustaining Life)

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Cone snails are a large group of predatory mollusks that live mostly in tropical coral reefs. Such reefs, which have been called the “rainforests of the seas” because they are home to vast biodiversity, are among the most endangered ecosystems on Earth, largely because of greenhouse gas emissions that ultimately warm the oceans (as ocean temperatures rise, corals loose their symbiotic algae and appear “bleached”, making them vulnerable to fatal infectious diseases), and that makes oceans more acidic (corals have calcium carbonate backbones that dissolve in acid). Scientists predict that coral reefs could be lost entirely by the end of this century, taking with them their resident organisms.

Cone snails defend themselves and paralyze their prey—worms, small fish, and other mollusks—by firing a poison-coated harpoon at them.

There are thought to be approximately 700 cone snail species, and as each species is believed to make as many as 200 distinct toxic compounds, there may be 140,000 different cone snail poisons in all. The toxins are small proteins called peptides, and they bind to receptors on the surface of cells, receptors common to all animal cells including our own, that govern how cells work, and in turn, how the organs these cells comprise function.

Because of the enormous number of cone snail peptides, and because they seem to target, with great potency and selectivity, almost every receptor we know about on our own cells, there has been great interest in these peptides as sources for new medicines.

Only 6 species and about 100 of the peptides have been studied in detail, and already several important new compounds have been found. One is a pain-killer called ziconotide (marketed as Prialt), an identical copy of a cone snail peptide. Opiates like morphine have been our most effective pain-killers, but they often don’t work well in cases of severe chronic pain, because patients develop tolerance to them. Tolerance is the state where one has to keep giving more medication to achieve the same effect. Ziconotide is 1000 times more potent than morphine, but it doesn’t cause addiction or tolerance. Its discovery may someday end the suffering of millions of people worldwide in severe chronic pain who cannot be treated by opiates.

Other cone snail peptides are in clinical trials for protecting nerve cells from dying when blood flow is reduced, such as during strokes or open-heart surgery, and for protecting heart cells during heart attacks. Some scientists believe that cone snails contain more leads to important medications for people than any other group of organisms in nature. 

Howard E. Stanton, MD

Howard Stanton, M.D., is a practicing internist at Brigham and Women’s Hospital in Boston.

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