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Some frogs have 10 times the amount of bitterness receptors as humans, a Northeastern researcher revealed. His findings could help humans understand and alter how humans detect allergens.
What if you could detect allergens even better, so that before you even put something in your mouth, you knew whether it was dangerous? And what if frogs could help you do it?
Those are the questions Jing-Ke Weng, a professor of chemistry, chemical biology and bioengineering at Northeastern University, tackled in a recent paper that sheds new light on frog biology –– and what it could mean for humans.
Weng and his team reveal that out of hundreds of animal species, amphibians, specifically frogs, have the highest number of bitter taste receptors, known as TAS2Rs. While humans have 25 TAS2Rs, mostly in the tongue but also in the gastrointestinal tract and even brain, a species like the wood frog has 248, nearly 10 times more, with some located in the liver and skin.
Weng says he hopes their findings –– attributed in part to an evolutionary adaptation –– could help scientists understand how humans detect similar signals, like allergens.
“It’s not only important for understanding how animals adapt to their chemical environment but also may have implications for understanding the chemical warning systems in humans,” Weng says. “We know that when you eat something extremely bitter, you want to either spit it out or poop it out if it’s in the intestine. We also want to understand whether that works hand in hand with the presence of certain toxic proteins to activate the immune system and whether this family of receptors may play a role in allergies.”
As a member of the Food Allergy Science Initiative, Weng was interested in understanding how animals, including humans, detect potentially dangerous signals from food. That goal led him and his team to bitterants, the molecules that work with allergen proteins to trigger warning signals in our bodies that are perceived by TAS2Rs.
“It’s not only important for understanding how animals adapt to their chemical environment but also may have implications for understanding the chemical warning systems in humans.”Jing-Ke Weng, a professor of chemistry, chemical biology and bioengineering at Northeastern University
“It’s not only important for understanding how animals adapt to their chemical environment but also may have implications for understanding the chemical warning systems in humans.”
Relatively little is known about the underlying mechanism and function of these receptors, even in the human body, Weng says. So, he and his team started working through a database of 680 species before finding a surprising evolutionary story: the amphibian family tree had an explosion in the number of bitter receptors.
The boneless fish that amphibians evolved from have one or even zero TAS2Rs, but in frogs that number ranges from 50 to almost 300. Weng attributes the remarkable increase to evolutionary adaptation.
Dolphins have zero bitter receptors because their diet is composed of entirely non-toxic fish. However, frogs feed on insects, which are involved in their own evolutionary “chemical arms race.” For animals that eat insects, that’s a problem.
“Insects are fast-evolving, so they just get more and more chemically protected so that they don’t get eaten by frogs or birds, and frogs have to catch up with this evolution and be able to develop more and more receptors so that they can tell these subtle chemical changes,” Weng says.
Weng and his team figured out that the TAS2Rs in a frog’s liver, for example, help detect certain toxins when they enter the body, triggering a process that metabolizes these potentially dangerous compounds.
In addition, some frogs, like poison dart frogs, have developed a way to make their own toxins as a natural defense mechanism. Detecting how much toxin has been produced would be invaluable information for a frog to have, which could also potentially explain why they have so many bitter receptors on their skin, Weng explains.
Similar to frogs, surprisingly little is known about the mechanisms that help humans detect potentially dangerous signals from their food. But the information Weng and his team have uncovered about frogs could help us understand, and even alter, these processes.
Weng is already exploring how TAS2Rs potentially play a role in perceiving antigens, molecules that tell our bodies whether something is dangerous or not to trigger immune responses.
“This will have broad implications in food allergies and even inflammation,” Weng says. “Sometimes inflammation is caused by an injury or autoimmune [issue]. Maybe some of the compounds that are present can serve as antigens that are perceived through TAS2Rs and amplify this immune response.”