Australasian Science: Australia's authority on science since 1938

I ❤ Lizard Venom

Dr Bryan Fry with a desert spotted monitor.

Dr Bryan Fry with a desert spotted monitor.

By Stephen Luntz

Toxins found in lizard venom can reduce blood pressure, opening the possibility of developing them as drugs to treat heart disease.

If “snake oil salesmen” is a term used to describe people who make false claims, what should we make of those who advocate the health properties of lizard venom? While such medicines are a long way from being approved, it is possible that recently discovered lizard venoms could indeed one day be used to treat heart disease.

Five years ago a team led by Dr Bryan Fry of the University of Melbourne discovered that far more species of lizards produce venom than had previously been suspected (AS, Jan/Feb 2006, p.6). Now a study of anguimorph venom published in the Journal of Molecular and Cellular Proteomics has revealed its potential as a pharmaceutical.

Anguimorphs include monitor and legless lizards. Fry says anguimorphs were chosen because the clade is “over 130 million years old, with great variation in size and ecological niche occupied”. One of the most famous anguimorphs is the Komodo dragon, a monitor lizard that grows to 3 metres in length.

“We showed a great diversity of toxins in anguimorph venoms,” Fry says. “The drug design potential of these novel venoms is highlighted by the fact that three of these new toxins act to lower blood pressure.”

The original discovery that lizard venom is widespread led to the proposition that reptiles evolved venom only once rather than independently after snakes and lizards evolved along separate lineages, as had previously been suspected. Fry says that venom diversity arose despite this common origin because so much time has elapsed since it originally evolved, and because reptiles themselves have diversified so much over that period.

More than 20 species from around the world were investigated, although the majority were Australian. The scientific names of some of the lizard species offer insights into the attitudes of the scientists who named them, including Gerrhonotus infernalis and Heloderma horridum horridum.

Both similarities and differences with snake venom were revealed. The team believes that the common ancestors of snakes and lizards had venom glands on both the upper and lower jaw, but snakes ended up developing maxillary glands on the upper jaw while the anguimorphs went the opposite way. Both ended up losing the glands on the opposite jaw.

“The lizard venom delivery system is less sophisticated than the high pressure injection mechanism of the front-fanged advanced snakes, and the vast majority of the species pose trivial direct medical risks to humans,” Fry’s paper stated.

The lizards use the venom to capture prey by lowering their blood pressure, which Fry says “aids in immobilisation through unconsciousness or shock”. The lizards would surely not have encountered creatures as prone to high blood pressure as urbanised humans.

The research on lizards has not prevented Fry from obtaining an ARC Future Fellowship to continue his studies on venom in Antarctic octopus species (AS, November 2010, p.10).

Readers may be relieved to know that while alligator lizards are anguimorphs, these are something different and altogether less fearsome than alligators. Crocodiles and alligators are not venomous.