WASHINGTON (Reuters) - A new approach to anesthesia using the chemical that gives chili peppers their kick promises an improved way to treat pain in surgery, dentistry and childbirth, researchers said on Wednesday.
Current local anesthetics deaden all nerve cells and not just the pain-sensing ones, causing temporary paralysis and numbness. That’s why dental patients after a root canal, for example, may leave their dentist’s office drooling, with a numb mouth and some muscles temporarily paralyzed.
Now, researchers have found a way to target only the pain-sensing nerve cells while avoiding the neurons responsible for muscle movement or sensations such as touch.
They demonstrated the approach in rats and feel confident it will also work in people.
They gave the rats injections containing capsaicin, the active ingredient in hot peppers, and a derivative of the common local anesthetic lidocaine. Working in concert, these chemicals targeted pain-sensing neurons, stopping them from transmitting “ouch” signals to the brain.
The rats were placed on an uncomfortable heat source and had their paws pricked, but showed no signs of feeling pain and moved and behaved normally. The injections took effect within half an hour, and the pain relief lasted for several hours.
The first general anesthetic, ether, was introduced in 1846, revolutionizing surgery. But not much has changed conceptually in anesthesia in the past century or so.
Dr. Clifford Woolf of Massachusetts General Hospital, one of the researchers in the study published in the journal Nature, said the new approach could transform surgery as much as ether did in its day.
“I imagine it could expand to many operations,” Woolf said in a telephone interview.
HUMAN TESTS SOON
The researchers think this approach could be useful in dental procedures like tooth extractions, knee surgery and other joint operations, pain treatment for women during childbirth and potentially for chronic pain.
A similar approach, they added, could stop itchiness from eczema, poison ivy and other conditions.
“The pain sensing-neurons in rats and humans are close enough that the same strategy should work, in principle, in humans,” added Bruce Bean of Harvard Medical School, another of the researchers.
Woolf expressed optimism that the first tests on people could begin “in two or three years.”
The two chemicals in the injections take advantage of a unique characteristic of pain-sensing neurons to block their activity without blocking signals from other nerve cells.
Lidocaine interferes with electric currents in all nerve cells. But the lidocaine derivative used in this research, called QX-314, by itself is unable to enter cell membranes to block their electrical activity.
That’s where the hot chili chemical came into play.
Capsaicin is capable of opening pores found only on the cell membrane of pain-sensing nerve cells. With these pores opened by capsaicin, the QX-314 can then enter the cell membrane and selectively block the activity of the pain-sensing neurons while leaving alone other nerve cells.
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