Before refrigeration, many people from Russia and Finland used to follow an old practice of putting a frog into a bucket of milk in order to prevent the liquid from going sour. The unusual technique often worked, because frog skin is covered with a slimy mucus that can kill many different species of bacteria and viruses. (The milk preservation method is not something to try today, however, both for the sake of the frog and for the dairy consumer.)
Today, researchers announce that they have just discovered that a colorful tennis-ball sized frog from India produces a compound in its skin mucus that can neutralize numerous strains of H1 flu viruses, which are known to infect humans and other animals. As a result, the compound — a host defense peptide described in the journal Immunity — could lead to a future powerful influenza vaccine and/or drug treatment.
“In the past when you did drug discovery, you might have to investigate thousands or even millions of candidates to find one or two peptides that can neutralize viruses affecting humans,” senior author Joshy Jacob, an associate professor at Emory University’s Emory Vaccine Center, told Seeker. “In this case, we screened 32 peptides from the frog and had four hits. I was very surprised and was almost knocked off my chair!”
Out of the four frog peptides found to neutralize viruses that can infect humans, three proved to be toxic to our species. The scientists made this determination after exposing isolated human red blood cells in a dish to the compounds.
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The fourth appears to be safe for human use. Electron microscopy indicates that this defense peptide disrupts the integrity of the H1 flu virus while leaving overall cells intact. It achieves this feat by binding to the stalk of hemagglutinin, a less variable region of the flu virus that has been the focus of other research groups trying to develop a universal influenza vaccine.
The researchers named the flu-fighting peptide “urumin” after the urumi, which is a sword with a flexible blade that snaps and bends like a whip. The weapon comes from the same Indian province, Kerala, as the frog.
Jacob said that frogs are not somehow more antimicrobial than the rest of us. All animals, including humans, produce defense peptides to keep bacteria and viruses in check.
“It’s just that it is easier to collect the peptides from the mucus on frog skin,” he said, mentioning that giving the frogs very small electrical shocks or rubbing a powder on their skin can cause them to secrete their peptide-rich slime.