A Spider Bite That Soothes the Heart

Jan. 8, 2001 -- It's one of a handful of poisonous spiders that can really scare you to death. But researchers have now shown that an extract of the venom of the deadly tarantula spider can prevent the heart -- at least in rabbits -- from developing palpitations.


And scientists predict that the finding may mean that "atrial fibrillation," a potentially serious condition involving irregular, rapid heart beats, could be treated long before it begins to have damaging health effects. The common condition currently is treated with drugs that slow the heart rate, or with electrical shock to send an abnormally fast heartbeat back into a normal rhythm. But it remains a common cause of heart failure and stroke. Atrial fibrillation is often associated with stretching of the atrial, or upper chamber of the heart.


Reporting in this week's Nature, scientists looked at rabbits whose hearts had been provoked into atrial fibrillation and had been artificially stretched. They found that the abnormal heart rhythm could be suppressed when treated with the tarantula venom extract. What's causing the excitement is that as well as being highly effective, the extract, known as a peptide, does not appear to cause side effects in people with normal heart rhythms.


"The research shows that the peptide has no effect on a resting or unstretched heart, which means that side effects are, at least for the heart, probably not a serious problem," Frederick Sachs, PhD, professor of physiology and biophysics at State University of New York at Buffalo, tells WebMD. "We need to study the other organ systems in animals. But if, as we believe, side effects are minimal, we can readily make it into a useful drug."


"Atrial fibrillation is a common condition for which [available] treatments ... don't always work," Alison Shaw, cardiac nurse adviser at the British Heart Foundation, tells WebMD. "This new spider venom treatment is a novel approach that so far has only been performed on rabbit hearts. Widespread randomized trials on humans would be needed to evaluate its full potential."


The future of tarantula venom currently is the subject of negotiations with drug companies, according to Sachs, who carried out the research.


It's not the first time that a well-known poison has turned out to have therapeutic benefits.


"There's a well-known medical saying that poisons depend on the dose -- and it's certainly true that a chemical that kills at one dose may have extraordinary therapeutic benefits in smaller quantities," Vivienne Murray, MD, a clinical toxicologist at London's Guys Hospital, tells WebMD.


Botulinum, a deadly toxin developed for chemical warfare and responsible for the potentially fatal type of food poisoning known as botulism, currently is being tested as a treatment for cerebral palsy. Injecting a tiny amount into the leg muscles has enabled some children with the disorder to walk for the first time. The toxic chemical also is a safe and popular cosmetic therapy, used to smooth crow's feet and laughter lines.


Snake venom currently is being tested for treating a range of diseases including breast cancer and heart disease. Many existing anticancer drugs are extracted from toxic plants; for instance, Taxol -- used for breast and ovarian cancer treatment -- is made from the poisonous Yew tree. The notorious morning sickness drug thalidomide was sufficiently toxic to kill thousands of unborn babies and leave thousands more with serious deformities when it was widely prescribed in the 1950s, but is now being tested as a treatment for AIDS as well as skin and colorectal cancer.