University of Pittsburgh – January 22,
2020 -- University of Pittsburgh School of Medicine researchers have created a
biodegradable nerve guide -- a polymer tube -- filled with growth-promoting
protein that can regenerate long sections of damaged nerves, without the need
for transplanting stem cells or a donor nerve.
So far, the technology has been tested
in monkeys, and the results of those experiments appeared today in Science
Translational Medicine.
"We're the first to show a nerve
guide without any cells was able to bridge a large, 2-inch gap between the
nerve stump and its target muscle," said senior author Kacey Marra, Ph.D.,
professor of plastic surgery at Pitt and core faculty at the McGowan Institute
for Regenerative Medicine. "Our guide was comparable to, and in some ways
better than, a nerve graft."
Half of wounded American soldiers return
home with injuries to their arms and legs, which aren't well protected by body
armor, often resulting in damaged nerves and disability. Among civilians, car
crashes, machinery accidents, cancer treatment, diabetes and even birth trauma
can cause significant nerve damage, affecting more than 20 million Americans.
Peripheral nerves can regrow up to a
third of an inch on their own, but if the damaged section is longer than that,
the nerve can't find its target. Often, the disoriented nerve gets knotted into
a painful ball called a neuroma.
The most common treatment for longer
segments of nerve damage is to remove a skinny sensory nerve at the back of the
leg -- which causes numbness in the leg and other complications, but has the
least chance of being missed -- chop it into thirds, bundle the pieces together
and then sew them to the end of the damaged motor nerve, usually in the arm.
But only about 40 to 60% of the motor function typically returns.
"It's like you're replacing a piece
of linguini with a bundle of angel hair pasta," Marra said. "It just
doesn't work as well."
Marra's nerve guide returned about 80%
of fine motor control in the thumbs of four monkeys, each with a 2-inch nerve
gap in the forearm.
The guide is made of the same material
as dissolvable sutures and peppered with a growth-promoting protein -- the same
one delivered to the brain in a recent Parkinson's trial -- which releases
slowly over the course of months.
The experiment had two controls: an
empty polymer tube and a nerve graft. Since monkeys' legs are relatively short,
the usual clinical procedure of removing and dicing a leg nerve wouldn't work.
So, the scientists removed a 2-inch segment of nerve from the forearm, flipped
it around and sewed it into place, replacing linguini with linguini, and
setting a high bar for the nerve guide to match.
Functional recovery was just as good
with Marra's guide as it was with this best-case-scenario graft, and the guide
outperformed the graft when it came to restoring nerve conduction and
replenishing Schwann cells -- the insulating layer around nerves that boosts
electrical signals and supports regeneration. In both scenarios, it took a year
for the nerve to regrow. The empty guide performed significantly worse all
around.
With these promising results in monkeys,
Marra wants to bring her nerve guide to human patients. She's working with the
Food and Drug Administration (FDA) on a first-in-human clinical trial and
spinning out a startup company, AxoMax Technologies Inc.
"There are no hollow tubes on the
market that are approved by the FDA for nerve gaps greater than an inch. Once
you get past that, no off-the-shelf tube has been shown to work," Marra
said. "That's what's amazing here."
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