Millions of Americans suffer from neuropathy, chronic pain caused by damaged nerves that is difficult to treat. But now a promising new therapy may provide relief, blocking the pain before it starts.
In animal studies, researchers at Boston Children’s Hospital and the Massachusetts Institute of Technology have developed a way to delay neuropathic pain by using tiny spheres filled with a powerful anesthetic.
Chronic neuropathic pain can be caused by shingles, nerve trauma, cancer, diabetes and other conditions. It arises when damaged nerves send unusual signals to the spinal cord and the brain. The constant signaling reprograms the central nervous system to react to any stimulus to the affected area, triggering unpleasant sensations that range from tingling and numbness to shooting, burning pain.
“Currently, neuropathic pain is treated with systemic medications, but there has been significant interest in using powerful local anesthetics to block aberrant nerve discharges from the site of injury to prevent the onset of neuropathic pain,” said Daniel Kohane, MD, PhD, of Boston Children’s Department of Anesthesia.
“Others have tried with varying degrees of success to do this in animal models using a variety of methods, but if applied clinically, those methods would require surgical intervention or could be toxic to tissues. We want to avoid both of those concerns.”
Researchers combined the powerful anesthetic saxitoxin with dexamethasone, a drug that prolongs saxitoxin’s effects. They then inserted the compound into liposomes – tiny lipid spheres smaller than a red blood cell – which were then injected into the damaged sciatic nerve tissue of animals.
Although a single injection only delayed the onset of neuropathic pain by about two days, three injections at the site of injury over the course of 12 days delayed the onset of pain by about a month. The injections also appeared to help prevent the reprogramming of the central nervous system by blocking pain signals.
The research team noted that astrocytes in the spine, which help maintain the pain signaling in neuropathic patients, showed no signs of pain-related activity for up to 60 days after the animals were treated.
“We’d like to develop a way to reversibly block nerve signaling for a month with a single injection without causing additional nerve damage,” Kohane said. “We’re trying to refine our methods so that we can get individual injections to last longer and figure out how to generalize the method to other models of neuropathic pain.”
“We also need to see whether it is safe to block nerve activity in this way for this long. We don’t want to inadvertently trade one problem for another. But we think that this approach could be fruitful for preventing and treating what is really a horrible condition.”
The results of the animal study were published online in the Proceedings of the National Academy of Sciences.