By burning pain and hot food
Eating spicy foods and touching hot objects cause similar pain. Scientists have now identified a protein involved in both stimuli. They also succeeded in cloning the corresponding gene. After years of research, scientists have discovered and cloned the gene for a protein that, amazingly, causes the same searing pain felt when touching a stovetop or eating pepperoni. Their findings could lead to a new treatment for millions of people suffering from chronic headaches, back pain and arthritis.
"The protein we identified could be malfunctioning or failing and causing chronic pain," says David Julius of the University of California, San Francisco."With the gene for this protein, it is possible to develop new and more effective drugs to treat pain." For example, drugs that bind to the protein could block activation of sensory neurons, affecting pain perception, according to Julius and his colleagues.
Their results were published in Nature on October 23rd. "This is a very important and outstanding study," said Ronald Dubner, pain researcher at the University of Maryland. "This identifies a protein that not only responds to chemical stimuli, but also to heat strong enough to destroy tissue."
In particular, researchers have discovered that the active ingredient in pepperoni, capsaicin, binds to a specific receptor - a protein found on the surface of neurons. Capsaicin causes tingling and burning pain by directly irritating pain-sensitive nerve cells in the mouth and on the skin. Researchers believe that activation of the receptor triggers a cascade of biochemical events that lead to the sensation of pain. "Remarkably, we found that the same receptor that binds capsaicin on the surface of pain-sensing neurons also responds to intense heat," says Julius. "We think pepperoni are perceived as hot because capsaicin and heat stimulate the same sensory protein in neurons."
In the second part of the investigation, the researchers cloned the gene for the capsaicin receptor. Previous studies concluded that molecules targeting the capsaicin mechanism could be promising painkillers. However, testing these compounds was difficult because it required lengthy preparations to isolate pain-sensitive neurons from mice or rats. "Cloning the gene for the capsaicin receptor will enable us to produce large amounts of the protein in cells grown in petri dishes. This makes it easier to test the effectiveness of potential treatments,” says Julius.
The researchers also want to find out how capsaicin or heat activates the capsaicin receptor. "Biochemical studies will help pinpoint those areas of the receptor that are most important for signaling," says Julius. "This information will then be useful in the development of new drugs." In addition, the researchers are working on the question of whether capsaicin receptors pass on their signal within the nerve cell via other proteins.
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