Difficulty taking medication is a common problem, especially among children and the elderly, according to a recent study in the British Journal of Pharmacology. Pills can be hard to swallow while the alternative—liquid forms of the medications—often are extremely bitter.
Now, a group of scientists at the Monell Chemical Senses Center in Philadelphia have identified the first temporary, universal taste blocker that works in people.
“Remarkably, and unlike our experience with blockers of bitter taste receptors, the taste-nerve blocker we tested worked for every subject and every bitter compound we tested,” said first author Linda J. Flammer, PhD, Monell senior research associate and director of the Corporate Partners Program. “I have never seen this before.”
While masking bitterness by adding sugars, nonnutritive sweeteners, or other flavoring agents has been frequently used for liquid formulations to increase the acceptance of medications, it is only partially effective and has little effect when the bitterness is intense, the study noted.
As a result, efforts to block bitterness in foods and medicines have traditionally focused on finding blockers for bitter taste receptors on the tongue. Because different medications activate distinct sets of bitter taste receptors, targeting specific receptors might only suppress bitterness for certain, but not all, bitter-tasting compounds, however.
“There is a clear need to develop bitter blockers that are able to suppress the bitterness of many medications,” said coauthor Carol Christensen, PhD, Monell alumnus faculty member. “Although humans have 25 different bitter receptors, our ongoing research suggests only a handful of bitter receptors may be responsible for most of the bitterness of medicines.”
Sweet, bitter, and savory compounds stimulate taste cells in the mouth that express the TAS2R family of taste receptors; those, in turn, transmit signals to nerve fibers by releasing adenosine triphosphate (ATP)—the cell’s main source of energy. ATP activates a receptor called P2X2/P2X3 on the receiving nerve cells, which send information to the brain about the taste of foods and medications.
For this study, the researchers tested an inhibitor of P2X2/P2X3 receptors, AF-353, to block taste-nerve transmission and reduce the bitterness signal caused by medications and other taste compounds. Blockers of P2X2/P2X3 receptors have been tested in clinical trials to treat chronic cough but had a side effect of taste disturbance.
Rinsing the mouth with AF-353 significantly reduced the bitterness of two important medicines that treat common chronic diseases: Praziquantel for parasites and tenofovir alafenamide for hepatitis B and HIV, according to the report.
“AF-353 is the first universal bitter taste blocker that has been identified,” said Monell faculty member Peihua Jiang, PhD. “In addition to bitter taste, it also affects savory, salt, sweet, and sour tastes. However, AF-353 only blocks taste. Other oral sensations like the tingle from carbonation were not affected.”
The study also found that while AF-353 suppressed other taste qualities (i.e., salt, sweet, sour, and savory), it had no effects on other oral or nasal sensations (e.g, astringency and oral tingle).
“This is the first time a universal, reversible taste blocker in humans has been reported,” the authors concluded. “Topical application of P2X2/P2X3 inhibitor to suppress bitterness may improve medical compliance.”
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