A Medical Use for Capsaicin

A few weeks ago, I wrote about a molecule called capsaicin, which is the ingredient that makes peppers spicy (‘Those red hot chili peppers”). Apparently, capsaicin is not only used in cooking – it also has medicinal value. Scientists are testing whether capsaicin can be used as a painkiller.

This may sound a bit odd. After all, capsaicin causes pain, doesn’t it? (Try pouring some tabasco sauce straight into your mouth and see how you feel.) It does, but here’s the catch. If you apply enough capsaicin to a nerve cell, it will stimulate so much pain that the nerve will become numb. And numb nerves can no longer signal pain. So a brief pain associated with the capsaicin treatment can result in a long time of no pain at all.

This idea is being used to treat long-term or throbbing pain, which is caused by a very specific set of nerve endings. Called C fibers, they are a type of sensory fiber associated with chronic pain and warmth. C fibers possess a protein that bridges the membrane of the nerve ending. This protein, called TRPV1, acts like a gate, which is usually closed. However, when capsaicin comes along, it binds TRPV1 and opens the gate. As a result, calcium ions flood the cell, and if there’s enough calcium ions, the nerve goes numb. A high enough dose of capsaicin can result in numbness that can last several weeks, in fact.

Capsaicin works only on the C fiber nerve endings, not those that work in other kinds of pain or for movement. That means that numbness associated with capsaicin treatment would only block this pain signal. It would not interfere with any other kind of nerve process. If you’ve ever had your mouth numbed by the dentist, you may be able to appreciate the distinction. When you are treated with Novocaine, all the nerves in your mouth go numb, including those for sensation and movement. That’s why you lose feeling across your entire mouth (and perhaps your tongue and nose). A capsaicin-based anesthesia would be much more selective in its ability to block pain. So a dental filling would not only be pain-free, you would also be free of that awkward drooling that results from an immobile mouth.

Doctors are using this treatment in patients undergoing extremely painful surgery. They treat the nerves exposed during the operation with an ultra-pure form of capsaicin - since the patients are anesthetized, it doesn’t hurt any more than the surgery does. However, once they recover from the anesthesia, doctors hope that their nerves will be numbed enough to allow for better, less painful recovery. And early indications suggest that it works as predicted. In small tests of those recovering from either open hernia repair or knee replacement, those who received the capsaicin treatment reported less pain than their untreated counterparts.

For an article discussing this work, you can check out:
http://www.baltimoresun.com/news/health/bal-te.peppers30oct30,0,1228065.story