Gene therapy may hold key to pain control
NEW YORK, May 06, 1999 (Reuters Health) -- 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 3 and 7 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.
SOURCE: Human Gene Therapy 1999;10:1251-1257.
Copyright © 1996, 1997, 1998, 1999 Reuters Ltd.
--
Judith Richards, London, Ontario, Canada
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