News in Science

Centipede venom may fight chronic pain

Pain blocker The venom used by a centipede to paralyse prey contains a molecule that new research shows is more effective than morphine in blocking pain.

The finding in mice models could lead to the development of drugs for people with ongoing chronic pain, says co-author of the study Professor Glenn King, of the University of Queensland.

The current study targets human proteins known as voltage-gated sodium channels (Nav) that play a critical role in electrical signalling in neurons and other excitable cells.

King, a research fellow at the Institute for Molecular Bioscience, says humans have nine different Nav channels, with earlier studies showing the Nav1.7 channel plays a key role in pain transmission.

He says people with a mutation of this protein are unable to experience pain.

Previous research to target this channel has been hindered because of the impact of drug candidates on other Nav channels, which among other things play important roles in heart and muscle function.

"The difficulty is finding molecules that are selective for this one [Nav1.7] channel," he says.

In a study published this week in the Proceedings of the National Academy of Sciences, King and his Chinese colleagues show venom from the Chinese redheaded centipede (Scolopendra subspinipes mutilans) has 150 times selectivity for Nav1.7 over other Nav channels.

King says mice were injected with a peptide from the venom - Ssm6a - at a high dose and suffered no side effects with no impact on blood pressure or heart rate.

In thermal and acid-induced pain tests, the effect of the molecule "was similar to morphine", while in chemical-induced pain experiments it was more potent than morphine.

King says it is unlikely humans will develop a tolerance or addiction to drugs based on the venom molecule because unlike morphine it is not used to block receptors.

The work builds on an increasing body of research focusing on animal venoms for use in pain relief, but this is the first study to look at centipedes.

The current study focuses on a centipede that is farmed in China for consumption, but King and his colleagues believe the findings suggest centipede venom - which has been overlooked to date - may provide a source of lead molecules for drug development.

King agrees it is counterintuitive that a molecule used for predation could have therapeutic use.

However he says the key difference in ion channels between insects and humans makes this possible.

In contrast to humans, insects have only a single Nav channel, which is a common target of peptides in the venom of other arthropod predators such as scorpions and spiders.

"Centipedes worked out hundreds of millions of years ago the easiest way to catch prey was to paralyse them by blocking their Nav channel," King says.

"We're just lucky that of the nine Nav channels in humans, it hit the one we were after."

Recent US studies have shown the economic cost of chronic pain to be about $600 billion annually - more than the combined annual cost of cancer, heart disease and diabetes.

King says it is estimated at any one time about 20 per cent of the population on average is suffering from chronic pain, defined as pain that persists for three months or more.

He says the next step in their research is to trial the peptide using more sophisticated pain models that replicate pain associated with conditions such as rheumatoid arthritis and cancer.