I know what you’re probably thinking; snails have venom? This was exactly what I had thought when I came across a post on the popular social media website, Reddit. I was intrigued because I didn’t even know that snails have venoms and that they could even be used as painkillers. Turns out, the post wasn’t referring to the typical snails you find in a garden, but instead, the cone snails that are typically found in warm and tropical seas and oceans. Interested by the topic, I decided to investigate more on how exactly the snail venom can act as an analgesic, and its possible significance in the medical field.
Analgesics are commonly known as painkillers, and are divided into two types, mild and strong. Mild analgesics, such as aspirin and paracetamol, are used to treat the typical headaches, toothaches, or sore throats by, “preventing the stimulation of nerve endings at the site of pain and by inhibiting the release of prostaglandins, the chemical responsible for the widening of blood vessels near the site of the injury, from the site of injury to provide relief to inflammation, fever and pain” (Brown, Ford, 2008). For more severe pains, strong analgesics bind to opioid receptors in the brain to alter the perception of pain by blocking the transmission of pain signals between brain cells (Brown, Ford, 2008). Today, many cancer patients, diabetic patients, and other victims of chronic pain are treated with strong analgesics like morphine and heroine. The problem is that these opioids are highly addictive and repeated usage can lead to tolerance, which a reduced response to the drug. Scientists have discovered that the venom found in cone snails have analgesic properties that are 10000 times more powerful than morphine, and the best part about the venom is that it is not addictive. (National Geographic, n.d.) Since cone snail venom is clearly a better analgesic than opioids, I questioned why isn’t it replacing morphine and heroine as the common analgesics to treat victims with chronic pain?
Figure 1: Image of a Marble Cone Snail (National Geographic, (n.d.))
Although they are only about four to six inches long, these carnivorous mollusks they have venoms poisonous enough to kill 15 adult human beings (Compassionate Healthcare Network, 2004). To do this, the cone snails have teeth that are similar to hypodermic needles that inject venom into their preys. The venom instantly paralyzes the victims by interfering with the communications of the nervous systems. In a typical nervous system, the neurons transmit chemical signals to another neuron through ion channels. The chemical signals are repeatedly transmitted from neuron to neuron until it reaches a muscle cell and tells it to contract. The venom of cone snails contain hundreds of thousands of short polypeptide proteins that blocks specific ion channels to prevent neurons from transmitting chemical signals, inhibiting muscle movement, leading to paralysis (Chadwick, 2013)(Discovery News, 2013).
So how can something so deadly be beneficial to humans? For many years, scientists have studied several hundreds of the short polypeptide proteins, called conotoxins, before the isolating analgesic conotoxin agent and creating the synthetic version named Ziconotide, or often known by the name Prialt. Unlike other analgesics, Ziconotide inhibits pain in a different way. People feel pain because electrical signals are carried across a synapse from the pain fibers to the nerve cells in the spinal cord that signals the brain. In order for the electrical signals to cross the synapses, electrical signals has to be converted into a chemical signal with the help of calcium. Ziconotide blocks the calcium gateways in the nerve fibers so that the chemical signals cannot cross the synapse to reach the nerve cells in the spinal cord. As a result, the brain does not receive the signal and therefore, one does not perceive pain (Compassionate Healthcare Network, 2004).
Although Ziconotide is 10000 times more powerful than morphine and is non-addictive, it is not commonly use to treat patients with chronic pain. This is because like any other drug, Ziconotide comes with many side effects such as abnormal vision, amnesia, vertigo, anxiety and possibly more undiscovered side effects. Furthermore, ziconotide cannot be administered orally because the body will break down the swallowed ziconotide before it can reach the receptors they need to reach. Therefore, zinconotide is currently administered with a direct injection into the spinal cord, a costly and invasive method of drug delivery.
Figure 2: Structure of Ziconotide (ChemBlink, (n.d.))
The discovery of Ziconotide has many implications in the medical field. Firstly, future research can be synthesized or modified Ziconotide to withstand the digestive processes of the body so that zinconotide can be taken more conveniently and without economic strain. In fact, scientists have already engineered a circular shaped synthetic Ziconotide conotoxin that is more stable to be administered orally (Discovery News, 2013). Ziconotide that can be administered orally will be more accessible to patients with chronic pain that have developed tolerance to morphine and heroine and need stronger analgesics to suppress the pain. Secondly, the discovery of Ziconotide suggest a bigger picture that many medical issues that people face today could possibly be cured by something in nature. There are so many microorganisms, animals and plants on Earth that have not yet been discovered. Perhaps, the secret to the cures of cancer and other illnesses lie in the Amazon jungle or at the bottom of the Mirana Trench.
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