By combining specific proteins found in rattlesnake blood, the researchers achieved unusually strong protection against venom from several dangerous snake species.

The study was led by Distinguished University Professor of BiologySean B. Carroll and published in the Proceedings of the National Academy of Sciences. The findings could help researchers develop more powerful antivenoms for deadly snakebites, which remain a major health threat in some regions of the world.

"This is one of those great stories when nature has already solved a problem we've been grappling with for decades," said Carroll, who also holds the Andrew and Mary Balo and Nicholas and Susan Simon Endowed Chair at UMD.

The Global Challenge of Snakebites

Snakebite is considered one of the world's most neglected tropical diseases. According to the World Health Organization, venomous snakes kill an estimated 80,000 to 140,000 people annually, while hundreds of thousands of survivors are left with permanent disabilities. Many of those affected live in rural areas where effective antivenom can be difficult to obtain.

Existing antivenoms save lives, but they also have major drawbacks. They are typically produced by exposing large animals to snake venom and then collecting the antibodies those animals generate. Manufacturing these treatments can be costly, their quality and effectiveness can vary, and they may not work equally well against the many different toxins found in venom from different snake species. They can also cause serious immune reactions.

Those limitations have pushed scientists to search for better options. In this case, the researchers turned to snakes themselves for clues.

"We've known from anecdotes for 100 years that vipers tend to be resistant to their own venom," Carroll said. "But for a long time, nobody knew what exactly was circulating in their blood that protected them."

A Natural Defense Hidden in Rattlesnake Blood

In 2022, Carroll's laboratory found part of the answer: a protein called FETUA-3. The researchers discovered that it could block the activity of many metalloproteinase toxins found in western diamondback rattlesnake venom. It could also bind to and inhibit toxins from the venoms of several other rattlesnake species.

"Here was evolution's way for snakes to protect themselves from accidental self-envenomation," he said, which prompted a follow-up question. "Why rely on horse antibodies when nature has packaged an effective antidote right there in the snake?"

For the new research, co-authors including Elda Sánchez, director of the National Natural Toxins Research Center at Texas A&M University-Kingsville, examined what each FETUA protein contributes to venom resistance.

The team found that individual proteins could counter certain effects of venom. One might reduce bleeding, for example, while another could interfere with enzyme activity. However, none of the FETUA proteins on its own was able to completely prevent death from a venomous bite.

Protein Combinations Dramatically Boost Protection

The results changed when researchers combined several FETUA proteins. These mixtures were far more effective at blocking the harmful effects of venom than the individual proteins alone.

Finding the best combinations is complicated because snake venom is extraordinarily complex. A single venom can contain around 100 toxin proteins belonging to multiple protein families, and venom composition differs from one snake species to another.

"The ingredients are there," Carroll said. "We just have to keep testing various mixtures."

In laboratory experiments, optimized combinations of the proteins were about 10 times more potent than the current sheep-derived rattlesnake antivenom. The mixtures completely neutralized the lethal effects of rattlesnake venom and also provided broad protection against venom from multiple viper species, including species separated by millions of years of evolution.

"The fact that parts of these inhibitors have been perfectly conserved over 50 million years of snake evolution tells you just how real a risk this is for these animals," Carroll said, noting that how snakes envenomate themselves, whether through mouth tissue during a bite, by eating envenomated prey, through cannibalism or all of the above, isn't well understood.

Toward a New Generation of Antivenoms

The present study concentrated on metalloproteinases, one important family of venom toxins. The researchers are now using the same general strategy to target other toxin families.

"We're getting remarkably close to having effective solutions for the three major toxin families in vipers," Carroll said. "What we've learned here, together with research we're doing now, gives us real confidence that nature-based recombinant [lab-produced] antivenoms are within reach."

Carroll expects that the first commercial applications of "nature's antivenom" could be in veterinary medicine, with treatments for human snakebites potentially following later.

He envisions future antivenoms that protect against a wider range of venoms while also being safer, less expensive and easier to manufacture on a large scale than many current treatments.

"We could make train cars-worth of this stuff and help solve a massive global health problem," Carroll said. "Many of our most important medicines have come from nature. I'm delighted that the components for a better-than-commercial antivenom were in these snakes all along."

Along with Carroll, the UMD co-authors included Department of Biology visiting faculty specialists Fiona Ukken and Yetunde Ayinuola.

The research was funded by the Howard Hughes Medical Institute and the Viper Resource Center (Grant #P40OD01960-22). This article does not necessarily reflect the views of these organizations.