Flu virus, meet frog slime.
A component of mucus — yum — from the skin of South Indian frogs can destroy the H1 variety of influenza viruses, a new study found.
Defensive compounds in frogs' skins were already known to protect the amphibians against bacteria. But those same compounds can also neutralize dozens of flu strains, scientists in the U.S. and India found.
The early findings, published Tuesday in the journal Immunity, might make it possible to harness frog mucus for fighting flu viruses when vaccines aren't available, or when strains become resistant to existing drugs.
The flu-fighting compounds are called peptides, which are short chains of amino acids; those are the building blocks of proteins.
Scientists from Emory University in Atlanta and the Rajiv Gandhi Center for Biotechnology in India studied skin secretions from the Indian frog Hydrophylax bahuvistara. They collected these slimy samples by giving frogs mild electrical stimulations.
The Indian researchers had been isolating peptides from local frogs and screening them for potential bacteria-fighting benefits. But the Emory team wanted to see if the peptides could also take down human-infecting viruses.
U.S. researchers screened 32 frog defense peptides against a strain of influenza and found that four of the peptides had flu-fighting abilities.
"I was almost knocked off my chair," Joshy Jacobs, the study's senior author and an associate professor of microbiology and immunology at Emory, said of the discovery.
"In the beginning, I thought that when you do drug discovery, you have to go through thousands of drug candidates, even a million, before you get one or two hits. And here we did 32 peptides, and we had four hits," he said in a news release.
Image: SANIL GEORGE AND JESSICA SHARTOUNY
Jacobs and his colleagues identified one peptide that is particularly adept at fighting flu viruses. They named it "urumin," after an ancient whip-like sword from southern Indian, called "urumi."
In frogs, some bacteria-fighting peptides work by punching holes in cell membranes, which makes them toxic to the cells of mammals. While some of the Indian frogs' antiviral peptides also worked this way, urumin did not. Instead, that special peptide seemed to only disrupt the integrity of the flu virus, the scientists found when they looked through an electron microscope.
They saw that urumin bound itself to the stalk of hemagglutinin, which is found on the surface of influenza viruses. Because current flu-fighting drugs target other parts of the virus, this peptide may be particularly valuable in studying new vaccines, Jacobs said.
Scientists also tested the peptide in mice. When delivered into the rodents' noses, urumin protected unvaccinated mice against a lethal dose of some flu viruses.
Urumin specifically fought H1 strains of flu, which includes H1N1 (a.k.a swine flu) that swept North America in 2009.
The Emory team is now looking for other frog-derived peptides that could help fight mosquito-borne viruses like dengue and Zika.