Nanoparticles to manage big problem: snakebites
An Epi-Pen to treat a snakebite?
It is a distant dream, but a Californian chemist and Costa Rican venom expert are reporting progress in a novel effort to make injectable nanoparticles that can neutralize snake venom and can be carried in backpacks.
In a recent study in PLOS Neglected Tropical Diseases, their particles protected mice against tissue damage from spitting-cobra venom without triggering allergic reactions.
In wealthy countries, snakes are an abiding threat to an unlucky few, among them hikers, ranch hands, soldiers, zookeepers and reptile collectors.
But in the tropics of Africa, Asia and Latin America, they are a major cause of death and disability in rural areas: More than 2 million people are bitten each year. About 100,000 of them die, and another 400,000 are left with serious disabilities, including amputations or nerve damage so extensive a leg or hand is permanently useless.
Antivenins have existed for decades, of course, but they are expensive, potentially dangerous and used only rarely in poor countries. The medicines contain antibodies harvested from the blood of sheep or horses that have been injected with diluted venom and allowed to recover.
The process is cumbersome, and the antibodies must be kept refrigerated. Few drug companies bother to make antivenins, so the prices are high.
Because they contain horse or sheep proteins, antivenins also can trigger life-threatening anaphylactic shock or hemorrhaging. They must be given intravenously in an emergency room, and many bite victims die before they can reach hospitals.
Moreover, antivenins are species-specific: A treatment for cobra bites, for example, will not help against rattlesnake or asp bites. Hospitals must keep many kinds of antivenins on hand, and victims must be able to produce or describe the snake that bit them.
“They have a lot of issues, but they’re the only show in town,” said Kenneth J. Shea, a chemist at the University of California, Irvine.
Shea’s lab is creating hydrogel nanoparticles coated with polymers — the building blocks of plastics — small enough to attach to proteins.
While screening them against common venoms, he isolated some nanoparticles that bind with and neutralize two poisons produced by snakes such as cobras, kraits, coral snakes, sea snakes and mambas.
A stopgap measure
José María Gutiérrez, a venom specialist at the University of Costa Rica, injected dozens of mice with the venom of the blacknecked spitting cobra. He found that Shea’s nanoparticles significantly reduced tissue damage in the mice. Importantly, the nanoparticles did not appear to interfere with normal proteins or to trigger dangerous allergic reactions.
It would not completely replace antivenins. But since the nanoparticles are relatively easy to make and need no refrigeration, they could be carried in the field and injected into the site of a bite, reducing tissue damage and stopping the poison from spreading. That would buy time to reach better treatment.
The path to regulatory acceptance might be a long one. Use of nanoparticles in medicine is relatively new, and for clinical trials involving snakebites, “there aren’t many volunteers,” Shea said.
Many incidents of snakebite occur when a person tries to catch, kill or interact with a venomous snake. Simply leaving the reptile alone is the surest way to avoid a potentially dangerous encounter.