3.52 p.m. ET (1952 GMT) May 7, 1999
NEW YORK - Researchers believe they may have discovered a better way to relieve chronic pain - by injecting pain-relieving genes directly into the tissue that surrounds the spinal cord.
Scientists from the National Institute of Dental and Craniofacial Research (NIDCR) and the University of Pennsylvania in Philadelphia report that animal tests show pain can be alleviated by injecting a gene that increases the production of beta-endorphins, a natural pain- reliever. Their report is published in the May issue of the journal Human Gene Therapy.
"We are totally pumped up that this approach is working in an animal model," Dr. Michael Iadarola, chief of NIDCR's Neuronal Gene Expression Unit said in a press statement. "The animal studies have shown us that genes are readily taken up by the connective tissue cells that surround the central nervous system. So, given the right gene, our approach has application to a broad range of conditions, from pain control to spinal cord injury and disorders like multiple sclerosis and Parkinson's disease."
There is much room for improvement in pain control. "In neuropathic
pain after nerve injury, pain is poorly controlled by currently
available methods," write the researchers. "In cancer pain, intravenous or oral morphine is only partially effective, and is accompanied by debilitating side effects. ..."
In their search for a new way to control pain, the research team used an adenovirus to deliver the beta-endorphin gene to the spinal cord of rats. Neither the brain nor the spinal cord was a hospitable environment for direct injection of virus, but the protective sheath of connective tissues that coats the spinal cord acted like a sponge and soaked up the virus.
At first this appeared to be an obstacle to controlling pain through gene therapy via the spinal cord, but then the investigators found that the spinal fluid was an "excellent medium to expose a wide swath of neurons to the therapeutic virus," said Iadarola.
Within 24 hours, the connective tissues began secreting beta-endorphin until beta-endorphin levels were 10 times greater than normal.
Tests of pain response in rats showed that the animals with increased levels of beta-endorphin had reduced pain.
The effects of beta-endorphin, however, were not permanent. Peak production occurred between three and seven days and was greatly reduced after 15 days. But researchers believe that improvements can result in a single injection that provides long-term gene expression, not only of beta-endorphin, but genes to treat a variety of spinal and brain disorders.