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| health > story page |         |
Novel approach to pain reduction could treat chronic painDecember 17, 1999
By Sarah Yang (WebMD) -- A new method of reducing pain may someday lead to promising chronic pain treatments for humans, scientists at the University of Minnesota have found. In the study, published in the journal Science, researchers used a newly derived compound to selectively kill off a group of spinal nerve cells in rats. Those that received an injection of the compound, named SP-SAP, exhibited significantly fewer signs of pain when exposed to common inflammatory irritants, compared to rats that were injected with saline. "I think this is absolutely fascinating research, and it's a potentially big breakthrough," said John D. Loeser, M.D., professor of neurological surgery and anesthesiology at the University of Washington, and former president of the International Association for the Study of Pain. "There's a huge, unmet need in the treatment of chronic pain. (This) research may turn out to be useful." The trick behind the compound's effectiveness seems to be in its ability to sneak into unsuspecting nerve cells in the spinal cord, said Patrick W. Mantyh, Ph.D., lead investigator of the study and professor of neuroscience at the University of Minnesota. These nerve cells stand as the midway point in the pain pathway, receiving signals from sensory cells located throughout the body and then directing the message to the brain. Researchers combined a natural toxin with substance P, a chemical messenger that signals pain in the body. The compound only affects nerve cells in the spinal cord with receptors for substance P, which enters the cells by acting like a key that unlocks the receptor. By attaching the toxin to substance P, researchers were able to trick the cell into letting the entire compound in. Once inside, the toxin effectively starved the cell to death, Mantyh said. Rats that had their nerves bound to mimic nerve damage in humans exhibited signs of pain reduction, even after 200 days, results showed. Even as the compound killed targeted nerve cells, it left neighboring nerve cells intact, an "attractive" feature of the approach, said Michael J. Kuhar, Ph.D., professor of neuropharmacology at Emory University. He said such an approach would enable the continued use of other painkillers such as morphine, if necessary, because morphine affects different nerve cells from the ones targeted in the study. People suffering from chronic pain now largely rely on non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen, or opiates, such as morphine. Both types of drugs, however, come with potential side effects. NSAIDS can cause stomach irritation, and morphine can lead to sedation or a depression of respiratory function. University of Washington's Loeser said that this new technique for attacking pain is unique in another way. "None (of the available medications) involves the concept of destroying any nerves, so they only work for as long as you take the medicine," he said. "The concept here is if you're knocking out nerve cells, it produces pain relief that can last forever." Although the studies look optimistic, Loeser did warn that the path leading from animal studies to drugs for humans is fraught with problems. While a rat's nervous system is remarkably similar to that of a human, particularly on the molecular level, "nobody really knows whether this stuff is safe and tolerated in normal human beings," he said. "We don't know whether the (toxin) will stay put or get out and go to other places." Mantyh said the next step will be to test the safety of the compound on larger animals. He also noted that the SP-SAP compound, when injected into the spine, remained localized, just like an epidural given to ease labor pains during childbirth. He said that if any of the compound were to escape into other parts of the body, it would be so diluted that it would have little effect. The impact of these findings is potentially huge. According to the American Chronic Pain Association, as many as one out of three Americans suffer from some form of chronic pain ranging from migraine headaches and arthritis to pain associated with diabetes and cancer. But until more studies are done to show the treatment's effectiveness in humans, Penny Cowan, founder of the association, cautioned chronic pain patients to be skeptical. "I'm cautious because people with pain are so gullible," she said. "There's so much hope and belief that pain can go away. At some point in time in our lives, that may be possible. The question is how do we get there."
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