Kissing a frog might not get you the prince or princess of your dreams, but it will put you in close contact with frog slime — the mucus coating that keeps these amphibians’ skin moist and protected. But maybe a little frog slime, from the right species, isn’t such a bad thing: it could harbor antimicrobial powers.
Of course, the science doesn't say that frog-kissing is the recommended method. Instead a new study, published in the journal Immunity, suggests that the frog slime could contain a whole new class of antiviral drugs for researchers to explore, according to a press release from Emory University.
Specifically, the slime of a frog called Hydrophylax bahuvistara, found in the southern Indian province of Kerala, contains small molecules that can destroy strains of flu virus, reports George Dvorsky for Gizmodo. The compound isn't very stable in the human body, however, so scientists will need to figure out how to make a synthetic version that lasts longer.
The compound is a peptide, a small class of molecule that can regulate the chemical activity of other molecules. The researchers call it "urumin," after the urumi, a deadly, flexible, whip-like sword that originated in southern India.
To make the discovery, researchers first gave frogs a mild electrical shock to encourage extra slime production. Then they collected the slime and screened it for active compounds, coming up with 32 peptides. They chemically synthesized their own versions in the lab then tested those synthetic versions on strains of the human flu virus. The researchers found that four had some success at killing the virus, and only one of those four wasn't toxic to human cells. (So really, if it wasn't clear: Don't kiss frogs or toads.)
Under an electron microscope, which uses electrons instead of light waves to illuminate a sample, the scientists could see that urumin wraps around a protein that protrudes from the surface of some strains of flu virus. This particular protein, called hemagglutinin, helps the viruses bind to cells in the human respiratory tract.
"The virus needs this hemagglutinin to get inside our cells," says study co-author Joshy Jacob of Emory University in a press release. "What this peptide does is it binds to the hemagglutinin and destabilizes the virus. And then it kills the virus." (Hemagglutinin is the same part of the flu virus that future ‘universal’ flu vaccines could target.)
Tests in mice showed that urumin could protect the rodents from dozens of flu strains, but not all. The other strains have differences in their hemagglutinin that keep urumin from attaching. "It's very, very specific," Jacob tells Jacqueline Howard of CNN.
Frogs can't actually get the flu, so why do they make a compound that kills strains of the virus?
It's likely that urumin also kills other pathogens that could infect the frog. "Amphibians, especially certain groups of frogs, produce and store large amounts of antimicrobial peptides in specialized granular glands in the skin," Louise Rollins-Smith, an associate professor of pathology, microbiology, and immunology at Vanderbilt University School of Medicine, tells CNN. "When the skin is injured or the frog is alarmed, they release large amounts of the peptides to protect the skin."
It's possible that other potentially medicinal compounds are out there, just sitting on another frog's skin