Gene therapy helps arthritis pain, damage in mice

WASHINGTON (Reuters) - A gene therapy treatment that helped make cells more sensitive to the body's own painkillers not only helped ease arthritis pain in mice but also reduced other symptoms, researchers said on Friday.

The researchers are now trying to get permission to try the treatment in people.

"This therapy can simply be injected anywhere in an injured joint, and the treatment will find the nerve endings," said Dr. Stephanos Kyrkanides of the University of Rochester Medical Center in New York, who led the study.

The researchers used a well-tested method of gene therapy, employing a virus called an adeno-associated virus to carry a new gene into the body. In this case, the new gene was one called the human mu-opioid receptor -- a kind of molecular doorway that the body's natural painkillers use to get into cells.

The more of them a cell has, the more sensitive it is to these painkilling chemicals.

The Kyrkanides team had mice genetically engineered to develop osteoarthritis in the same way that people do. They injected their gene-engineered virus into various joints.

"That strategy not only significantly reduced the pain behavior in the mice with arthritis, but it also helped to minimize the arthritis pathology itself," Kyrkanides said.

This suggests that the pain receptors play a role not only in the pain but also in the joint damage caused by arthritis, he said.

POTENTIAL FOR HUMAN THERAPY

Osteoarthritis affects close to 10 percent of men over the age of 60 and 18 percent of women over 60 worldwide, according to the World Health Organization. Aspirin and other analgesics can help, but they have often-deadly side effects.

Kyrkanides said he believes his gene therapy system would work in people, as all mammals have the same opiate receptor system.

"We used the actual human gene in our therapy," he said. "I am certain that if the human gene had a therapeutic effect in mice, it will certainly have it in humans as well."

Gene therapy has a mixed record. The idea is to replace faulty genes, or to amplify the effects of genes that people already have.

But many experiments have failed to show lasting effects in people.

In addition, one 18-year-old gene therapy volunteer was killed by an immune reaction to the virus that carried the gene, and two babies given gene therapy for a rare immune condition developed leukemia -- although they were successfully treated for the cancer.

Kyrkanides said his approach may be safer because the virus is injected into the joint rather than infused into an artery for delivery throughout the body.

"The great advantage of this is that it is confined to an encapsulated area of the body," he said. "It does not involve the whole body, thereby minimizing any general adverse effects of the gene therapy itself."