Cone Snail Venom - Medical Uses and Potential Benefits
Cone snails are ocean predators with beautifully patterned shells. The snails produce a potent venom to paralyze their prey. The venom contains a complex mixture of neurotoxins, chemicals that block the conduction of nerve impulses. Exciting research is showing that at least some of the neurotoxins have medical benefits for humans.
Scientists have found that certain chemicals in cone snail venom can act as pain relievers. Other chemicals in the venom are being used to help researchers learn about the functioning of the nervous system. These investigations may lead to the creation of new treatments for various diseases. Scientists suspect that venom chemicals may have even more benefits for us, including the prevention of epileptic seizures.
The Life of a Cone Snail
There are more than 600 different species of cone snails, all belonging to the phylum Mollusca and the genus Conus. Most inhabit the warm water of tropical reefs. The snails have roughly cone-shaped shells, which gives them their name.
Cone snails use their venom to catch small fish, mollusks and worms. Like other snails, cone snails move quite slowly. The exception to this rule is their equipment for catching prey, which moves impressively fast.
Cone snails have a tubular and extendable mouthpart called a proboscis. This contains a modified tooth that extends out of the proboscis and stabs the prey like a hypodermic needle. The tooth injects venom into the prey, immobilizing it. The tooth is withdrawn as the prey is swallowed whole by the proboscis. The tooth is barbed, which increases its effectiveness, and contains a hollow channel, which conducts venom from a poison sac at the base of the tooth.
Cone snails have an eye on the end of two eye stalks, but they detect their prey by means of their siphon. This is a large tube that draws in sea water. The snail absorbs oxygen from the water. It also detects the presence of dissolved chemicals in the water, including those released by the prey. Cone snails often hide in the sediments of the ocean bottom with just their siphon protruding.
A Deadly Snail
Cone Snail Venom
The smaller cone snails can give humans a painful sting but aren't dangerous. The bigger ones - which may be as long as nine inches - can be deadly for humans. They will attack to defend themselves as well as to catch their prey.
Cone snail venom contains a complex mixture of many different chemicals. There are thought to be at least fifty to a hundred biologically active compounds in a cone snail's venom. There may be as many as two hundred compounds in some venoms. The venom contains conotoxins, also known as conopeptides, which are short chains of amino acids that quickly stop nerve impulses from passing between nerve cells or from passing from nerve cells to muscles. These processes cause paralysis in the snail's prey.
Medical Uses of Cone Snail Venom
Research into the properties of cone snail venom is making some exciting discoveries. At least some conopeptides are able to relieve pain in humans, which they do very effectively. One conopeptide is already being used as an analgesic (pain reliever) and others are being tested in clinical trails. There may be many other uses for conopeptides in medicine.
Conopeptides are proving helpful in a non-medical context as well. Each conopeptide seems to work by a very specific mechanism in the nervous system. Researchers are learning more about how the nervous system works with the aid of conopeptides.
The venom of each species of cone snail contains its own unique mixture of chemicals, which increases the likelihood that some venom chemicals may be useful to humans.
Ziconotide for Pain Relief
After studying a conopeptide in the venom of a cone snail known as Conus magnus, researchers have made a synthetic version of the peptide. The artificial chemical, called ziconotide, has some very useful properties. It has been approved as a medication in the United States by the FDA (Food and Drug Administration) and is in current use as an analgesic.
Ziconotide is up to 1,000 times more effective than morphine at relieving pain and has the added advantage of not being addictive. In addition, it doesn't cause the development of tolerance in the patient. Tolerance is a state in which a medication that was once effective no longer works. Ziconotide is sold under the brand name of Prialt.
Ziconotide does have some drawbacks. It must be injected into the spinal canal (an intrathecal injection) in order to work. This is generally done continuously via an infusion pump. Serious side effects aren't common, but they do occur. One possible side effect is a severe mood change, including depression. Ziconotide is used after other analgesics have been tried and have failed to work. It is prescribed only for people who are suffering from intense and prolonged pain, such as the pain that may be experienced by people with certain types of cancer or for people experiencing neuropathic pain.
The Geography Cone Snail - Venom Functions and Uses
Other Potentially Helpful Chemicals in Cone Snail Venom
A New Analgesic
In 2013 the discovery of a new conopeptide with pain relieving properties was announced by Australian scientists. This chemical is said to be 100 times more effective than common analgesics and unlike Ziconotide can be taken by mouth. The researchers say that it isn't addictive. Once again, the scientists have designed a synthetic drug that resembles the natural one. At the moment the new analgesic is being tested on rats. The researchers are trying to get government approval and funding for clinical tests on humans.
A Possible Aid for Epilepsy
Conantokins are a family of conopeptides found in cone snail venom. The best known member of the family is conantokin-G from the geography (or geographic) cone snail. Conantokins are sometimes called "sleeper peptides" because when they are injected into the brain of young mice they trigger sleep. Researchers who are studying the peptides have discovered that they can also block seizures in mice. The peptides work by a mechanism that may be helpful for people with epilepsy. As is the case with other cone snail venoms, researchers have produced synthetic molecules based on the natural ones in order to improve the properties of the compounds for medical use.
A Weird Animal
The Red List
International Union for Conservation of Nature, or IUCN
Population Status of Cone Snails
Unfortunately, many cone snail populations are in trouble. Cone snails die due to coastal development, ocean pollution, destructive fishing methods and climate change. In addition, the snails are collected and killed for their beautiful shells, which are popular as decorations. Some shells are sold for thousands of dollars.
Researchers at the University of York in the UnIted Kingdom have just completed a population assessment for all of the 632 known cone snail species. The International Union for the Conservation of Nature (IUCN) assigns organisms to a "Red List" category according to their population status with respect to extinction. As a result of the cone snail survey, 67 species have been placed in the endangered, vulnerable or near threatened categories in the Red List.
It's sad when any species is threatened with extinction, but in this case the situation could hurt humans, too. What is especially worrying is that there are almost no conservation efforts for cone snails. The studies of the complex venoms of cone snails are slowly yielding wonderful possibilies for new medications. It would be very sad to lose the chance of improving treatment for pain and perhaps even discovering new treatments for diseases.
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