Scientists are investigating the possibility of using viruses to carry out pain-killing gene therapy in the spinal cord. So far the technique, which is the brain child of Andreas Beutler and his colleagues at Mount Sinai School of Medicine in New York, has only been tested on rats, but the results look promising.

Rattus norvegicus, the Brown Rat.The team have used an adeno-associated virus which has been genetically modified to replace the normal viral genetic material with a gene for one of the body's own natural pain-killing chemicals called beta-endorphin, which works in the same way as morphine.  Ten billion particles of the modified virus were injected by lumbar puncture into the spinal cords of each of a group of rats.  These animals had previously sustained nerve injuries that simulate the chronic pain experienced during certain human diseases.  At the same time a second group of animals were injected with a control virus containing a harmless marker gene instead of the beta-endorphin gene.  The animals were then followed up over three months to look for effects on their pain.  Initially nothing happened, but then after one month the animals that had been injected with the beta-endorphin containing virus began to show significant improvements in their pain, which continued until the end of the experiment two months later.  The control animals, on the other hand, remained unchanged.

The team think that their approach could make life much more comfortable for human patients experiencing severe pain, such as those with terminal cancers. This is because effective pain control is a delicate balancing act since doctors need to walk a tightrope between patient comfort and side effects.

"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," says Beutler. "But targeted gene therapy will likely avoid the unwanted side effects associated with opioid painkillers such as morphine."


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