Toxins are naturally occurring poisons made by living things. Lots of plants and animals produce toxins, which they use to deter predators and catch prey, says Helen Pilcher.
When we eat poisonous plants or get stung by venomous animals, the toxins they contain can make us very unwell, but there is a bright side to toxins too.
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Because they influence important biological processes, some toxins have medicinal value and are being turned into drugs. Meet some of the plants and animals that make them and find out about the terrifying toxins that are actually helping people.
Terrifying toxins that help
Pufferfish
Tetrodotoxin is a potent neurotoxin found in pufferfish, blue-ringed octopuses, rough-skinned newts and some other species. The toxin binds to nerve cells and stops them from working. In humans, this can lead to paralysis, and then death within 20 minutes to a few hours.
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Over 4,000 years ago, small doses of the toxin were used in Chinese medicine to “arrest convulsive diseases.” More recently, however, researchers have been studying its potential to help people quit heroin, and control pain in cancer.
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Clinical trials have hinted that tiny doses of the nerve-blocker can ease the pain both of cancer itself, and of the nerve pain that can be caused by chemotherapy. Now further trials are planned, and the US Food and Drug Administration (the body that oversees the safety of new drugs) has fast-tracked the development of a synthetic tetrodotoxin drug called Halneuron.
Deadly Nightshade
Atropa Belladonna, commonly known as deadly nightshade, is a herbaceous plant native to Europe and Western Asia. The foliage and berries contain toxic chemicals. If consumed, they can cause blurred vision, headaches, hallucinations, convulsions and sometimes even death.
Atropine is one of these toxic chemicals. It works blocking key receptors in the nervous system and relaxing smooth muscle. Small synthetic doses are widely used in medicine. Atropine eye drops are used by ophthalmologists to dilate pupils. Injectable atropine is used to treat certain types of nerve agent and pesticide poisonings, as well as some heart conditions. Atropine also stops the body from making certain secretions, so it is also used to decrease saliva production during surgery.
Mouldy hay
Around a hundred years ago, farmers in North America noticed that their cows were bleeding to death after eating mouldy hay. The hay was made from sweet clover, but when it went off, a non-toxic chemical produced by the plant was converted into a deadly one. Coumarin became dicoumarol, which interferes with blood’s clotting process, causing haemorrhaging and death.
This was bad news for the cows, but good news for modern medicine. Scientists made a synthetic version of dicoumarol which they called warfarin. Today, warfarin is a leading anticoagulant medicine, commonly used to prevent deep vein thrombosis and help protect people with certain heart conditions from stroke. In 2023, warfarin was the 116th most commonly prescribed medication in the United States, with more than 5 million prescriptions.
Fire ant
The venomous sting of the fire ant has been described as “sharp, sudden, mildly alarming. Like walking across a shag carpet and reaching for the light switch.” So, not deadly, but not pleasant either. Mild stings can cause redness, swelling and pustules, and anaphylaxis in those who are allergic.
Here, the chemical culprit is a molecule called solenopsin, which researchers suspect has anti-inflammatory, anti-microbial and anti-cancer properties. Synthetic versions of the molecule have shown promise as a topical treatment for skin conditions, such as psoriasis.
The same chemical also shows activity against a range of disease-causing organisms, including some bacteria. And solenopsin stymies the growth of blood vessels, raising hopes that it could curtail the growth of tumours, which depend on blood vessels for their nutrition.
Gila Monster
The Gila monster is a chunky, slow-moving lizard, native to the Southwestern United States and Mexico. It produces venom from glands in its lower jaws, which it releases through grooves in its teeth when it bites and chews its prey. The monster’s bite is rarely fatal to people, but it has been described by YouTuber Coyote Peterson as “like hot lava coursing through your veins.”
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More than a dozen peptides have been isolated from the reptile’s venom, including four toxins that cause bleeding of the internal organs and bulging of the eyes. One of the peptides, however, plays a role in the regulation of blood sugar.
In 2005, the US Food and Drug Administration approved the use of a drug based on this peptide, for the management of type 2 diabetes. The drug is called exenatide, and in clinical trials it has been shown to help people with the condition effectively regulate their blood sugar levels.
Pit viper
For many people, the mere sight of a venomous snake is enough to cause a temporary spike in blood pressure. It’s ironic then, that the venom of a Brazilian pit viper inspired the development of a medicine that actually lowers blood pressure.
In the late 1960s, scientists discovered that an ingredient in venom of the jararaca pit viper blocks the activity of an enzyme that helps to control blood pressure. Not long after, pharmacists developed a synthetic version of this ‘angiotensin-converting enzyme’ (ACE) inhibitor and called it captopril.
The drug makes blood vessels dilate, and in 1980, it was approved for the treatment of high blood pressure. It was the first ACE inhibitor to be made and spurred the development of subsequent similar drugs. Today, captopril is also used to treat other conditions, including heart attacks and kidney problems, and is currently being investigated as a potential anti-depressant.
Scorpions, honeybees, vipers
Lots of animal toxins have anti-cancer properties. Melittin, for example, is the main ingredient in honeybee venom. It’s what makes the sting so painful, but on the plus side, has been shown in tissue culture studies to make human cancer cells commit suicide. Yes, cell suicide is a thing.
Chlorotoxin comes from scorpion venom. In vitro studies show that when the drug binds to the surface of pancreatic cancer cells, it prevents them from proliferating and spreading.
Meanwhile, lebein is a protein that comes from the venom of the blunt-nosed viper. The drug blocks the activity of a molecule that usually encourages blood vessels to grow. Tumours rely on blood vessels to deliver the nutrients they need, so when this happens, it makes it harder for the tumour to grow.
All in all, there are a number of animal venom-derived molecules with promising anti-cancer activity, but further studies are needed to see if they are safe and effective in people.
Yew tree
Yew trees are evergreen conifers, with needle-like leaves and scaly, purple bark. Almost every part of the plant can be toxic, and whilst human fatalities are rare, people have died after eating it. The plant’s tissues contain a complex mix of chemicals called taxine alkaloids. These are toxic to the heart and can cause heart and respiratory failure.
However, the yew tree contains another molecule, called paclitaxel, which was discovered in its bark. Paclitaxel has anti-cancer properties. This was shown first in lab-grown cancer cells, then in animals, and later in people.
Today, paclitaxel is derived from the needles of the yew tree and used as a type of chemotherapy. The drug prevents cancer cells from dividing and so slows the growth of tumours. Now, paclitaxel is on the World Health Organization’s List of Essential Medicines, and is currently used to help treat ovarian, oesophageal, breast, cervical and other cancers.
Cone snail
Cone snails are stunning, visually and chemically. There are hundreds of species, all with brightly patterned conical shells. All of them are venomous, using a barb-like tooth and a venom gland to attack and paralyze their prey before engulfing it.
Conus magus, aka the magical cone, is found through the tropical and subtropical Indo-Pacific region, where it lives in shallow marine waters. Its sting can occasionally be fatal but often goes unnoticed because the venom contains natural painkillers. Researchers capitalised on this to develop a drug called ziconotide. The analgesic is ten times more powerful than morphine and because it not an opioid, its use doesn’t lead to tolerance or addiction. Approved by the US Food and Drug Administration in 2004, it is used to help treat severe chronic pain.
Sea anemone
Sea anemones are predatory marine animals which use their tentacles to catch prey. Unlike other animals which manufacture venom inside specialised glands, sea anemones produce venom in specialised cells found all over their body.
Sea anemone venom contains a complex mixture of chemicals. Some cause cells to physically break apart, whilst others, which degrade the membranes of brain and muscle cells, can lead to nerve damage and muscle inflammation.
Alongside these harmful substances, researchers have identified some molecules that are potentially helpful. One of them, extracted from the stinging cells of Caribbean sun anemone, blocks channels found in the membranes of certain immune cells.
This dampens the activity of the cells. Now a drug called dalazatide, that is based on the toxin, is being investigated as a potential treatment for autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis.
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