By Pat Anson, Editor

Researchers in Australia have isolated a toxin in the venom of a tarantula that shows promise as a pain reliever. The discovery could accelerate development of a new class of natural painkillers that are not addictive and more effective than opioids.

Thrixopelma pruriens, more commonly known as the Peruvian Green Velvet Tarantula, is native to South America.  The spider’s bite isn’t potent enough to kill humans, but researchers at the University of Queensland say its venom inhibits pain receptors.

"Our group is specifically interested in understanding the mode of action of this toxin to gain information that can guide us in the design and optimization of novel pain therapeutics," said Sónia Troeira Henriques, senior research officer at the University of Queensland's Institute for Molecular Bioscience.

The peptide toxin – known as ProTx-II – inhibits pain signals by binding to the membranes of nerve cells.

"Our results show that the cell membrane plays an important role in the ability of ProTx-II to inhibit the pain receptor. In particular, the neuronal cell membranes attract the peptide to the neurons, increase its concentration close to the pain receptors, and lock the peptide in the right orientation to maximize its interaction with the target," said Henriques.

Henriques and her colleagues were the first to discover the importance of membrane-binding properties of ProTx-II in inhibiting a human pain receptor known as Nav 1.7. Previous research has shown that people born without Nav 1.7 channels due to genetic mutation are indifferent to pain – so blocking those channels in people with normal pain pathways has the potential to “turn off” pain.

University of Queensland researchers have studied the venom of over 200 spider species and found that 40% of the venoms contain at least one compound that blocked Nav 1.7 channels. But they’ve only scratched the surface. There are over 45,000 species of spiders, many of which kill their prey with venom that contain hundreds - or even thousands - of protein molecules that block nerve activity.

Based on the group's findings, they're now designing new toxins with greater affinity for the cell membrane and fewer side effects.

"Our work creates an opportunity to explore the importance of the cell membrane in the activity of peptide toxins that target other voltage-gated ion channels involved in important disorders," said Henriques.

Researchers are also studying the potential of venom in cone snails for its potential for blocking pain signals in humans. German scientists at the Pharmaceutical Institute of the University of Bonn say one advantage of the peptides found in snail venom is that they decompose quickly and are unlikely to cause dependency.

A pharmaceutical drug derived from cone snail neurotoxins has already been developed and marketed under the brand name Prialt. The drug is injected in spinal cord fluid to treat severe pain caused by failed back surgery, injury, AIDS, and cancer.