An experimental gene therapy treatment for chronic pain enabled rats with this condition to go symptom-free for three months, a study released Monday said.

The rats were injected with a gene that tricks the body into releasing endorphins, a natural painkiller, in the nerve cells surrounding the spinal cord.

The treatment simulates the effect of painkilling drugs but is much narrower in scope, targeting nerve cells along the spinal cord, but not in the brain or in other parts of the central nervous system.

Researchers are hopeful that the therapy could potentially be used to treat people with severe or chronic pain sparing them some of the debilitating side effects of the opiod drugs currently on the market which act systemically, rather than locally.

"Chronic pain patients often do not experience satisfactory pain relief from available treatments due to poor efficacy or intolerable side effects like extreme sleepiness, mental clouding and hallucinations," said Andreas Beutler, an assistant professor of medicine, hematology and medical oncology at Mount Sinai School of Medicine in New York.

In some cases, "the side effects become dose limiting," Beutler said, noting that some patients opt for less pain relief in exchange for greater lucidity.

"Targeted gene therapy will likely avoid the unwanted side effects associated with opiod painkillers such as morphine."

For this experiment, the researchers packaged the prepro-b-endorphin gene in a disabled cold virus and injected it into the rats' spinal fluid by means of a lumbar puncture, or spinal tap.

The rats, which had an animal version of neuropathic pain, were symptom free for over three months.

The treatment is still in a preliminary testing phase, but if it's shown to be safe and effective in humans, it could ultimately help patients who cannot tolerate the side effects of the existing painkilling drugs, or who don't get sufficient relief from those drugs. Beutler said.

Patients with advanced cancer fall are among the potential beneficiaries, he said.

The paper appears in the Proceedings of the National Academy of Sciences.

CHICAGO, Jan 21, 2008 (AFP)


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