Enzyme eats scar tissue that blocks rat spine repair

CHICAGO (Reuters) - U.S. researchers have engineered an enzyme that can gobble up scar tissue formed after spinal cord injuries in rats, overcoming a key hurdle to getting injured nerves to reconnect and heal.

Spinal cord injuries trigger a cascade of events in the body that block the growth of nerve cells after a spinal cord injury.

"One of the major impediments has been this scar tissue that has formed," said Ravi Bellamkonda, a biomedical engineering professor at Georgia Institute of Technology Research and at Emory University, whose study appears in Tuesday's issue of the journal Proceedings of the National Academy of Sciences.

He said sugar proteins found near the scar tissue inhibit nerve fiber regeneration, and eliminating scar tissue is an essential step toward getting nerve fibers to grow back.

Other teams have shown that delivering an enzyme from bacteria that digests scar tissue may help.

"The problem has been this enzyme is really sensitive and degrades very fast," Bellamkonda said in a telephone interview.

He said the enzyme, chondroitinase ABC (chABC), is heat sensitive and must be repeatedly injected or infused into the body to work.

Bellamkonda's team found a way to overcome both of those issues. They mixed the enzyme with a sugar called trehalose that made it stable at internal body temperature.

And instead of injecting the enzyme into the spinal cord, they put it into tiny hollow straws just twice the length of a single cell. They inject these at the injury site in a special gel that keeps the straws in place.

Bellamkonda's team tested the system in rats and found the enzyme prevented scar tissue formation for up to six weeks.

"The goal is that at the time the surgeon is removing the offending (vertebrae) bone after the injury you would inject this gel to sit on top of the injury site and prevent whatever new scar is forming," he said.

Because the straw tubes are hollow, the team was also able to deliver growth factors to the injury site. Rats that got this treatment sprouted new axons or nerve fibers and regained some nerve function.

Although the chABC enzyme used by the team came from bacteria, Bellamkonda said Acorda Therapeutics is working on a human version.

Bellamkonda said many other approaches will be needed to repair spinal cord injuries in humans, including controlling inflammation, which can cause additional injury, stimulating nerve fiber growth and getting nerves to reconnect and communicate with the brain.

"It's a really daunting problem to solve," he said.

"The key is we've opened a little window at least to make it clinically viable system," he said.