An international team of scientists from the United States and India has discovered that a component of the skin mucus secreted by a South Indian fungoid frog can destroy many strains of human influenza viruses and protect mice against influenza infection. The discovery is reported in the journal Immunity.
“Different frogs make different peptides, depending on where their habitat is,” said study senior author Dr. Joshy Jacob, an associate professor of microbiology and immunology at Emory Vaccine Center and the Department of Microbiology and Immunology at Emory University School of Medicine.
“You and I make host defense peptides ourselves. It’s a natural innate immune mediator that all living organisms maintain.”
“We just happened to find one that the frog makes that just happens to be effective against the H1 influenza type.”
The newly-identified antiviral peptide was found in skin secretions from the Wide-spread fungoid frog (Hydrophylax bahuvistara).
Dr. Jacob and his colleagues from Emory University and the Rajiv Gandhi Center for Biotechnology in Kerala, India, named this peptide ‘urumin,’ after the urumi, a sword with a flexible blade that snaps and bends like a whip, which comes from the same Indian province, Kerala, as the frog.
The scientists screened 32 frog defense peptides against an influenza strain and found that 4 of them had flu-busting abilities.
Unfortunately, when they exposed isolated human red blood cells to the flu-buster peptides, three out of the four proved toxic.
However, the fourth — urumin — seemed harmless to human cells but lethal to a wide range of influenza viruses.
The peptide was specific for H1 strains of flu, such as the 2009 pandemic strain H1N1/09, and was not effective against other current strains such as H3N2.
Delivered intranasally, urumin protected unvaccinated mice against a lethal dose of some flu viruses.
“We studied host defense peptides from the skin of the South Indian frog and demonstrated that one of these, which we named ‘urumin,’ is virucidal for H1 hemagglutinin-bearing human influenza A viruses,” the authors explained.
“This peptide specifically targeted the conserved stalk region of H1 hemagglutinin and was effective against drug-resistant H1 influenza viruses.”
Electron microscope images of the virus after exposure to urumin reveal a virus that has been completely dismantled.
“Peptides are short chains of amino acids, the building blocks of proteins. Some anti-bacterial peptides work by punching holes in cell membranes, and are thus toxic to mammalian cells, but urumin was not,” added Dr. Jacob, who is also a researcher at Yerkes National Primate Research Center.
“Instead, urumin appears to only disrupt the integrity of flu virus, as seen through electron microscopy.”
The researchers are still working out the details of the flu-destroying mechanism.
“Urumin is far from becoming an anti-flu drug, but this is the first evidence of its flu-killing ability,” they said.
David J. Holthausen et al. 2017. An Amphibian Host Defense Peptide is Virucidal for Human H1 Hemagglutinin-Bearing Influenza Viruses. Immunity 46 (4): 587-595; doi: 10.1016/j.immuni.2017.03.018