N.C. – July 5, 2017 -- Researchers at Wake Forest Institute for
Regenerative Medicine have reached important milestones in their quest
to engineer replacement tissue in the lab to treat digestive system conditions
– from infants born with too-short bowels to adults with inflammatory bowel
disease, colon cancer, or fecal incontinence.
Reporting today in Stem
Cells Translational Medicine, the research team verified the effectiveness of lab-grown
anal sphincters to treat a large animal model for fecal incontinence, an
important step before advancing to studies in humans. And last month in Tissue
Engineering, the team reported success implanting human-engineered
intestines in rodents.
“Results from both projects
are promising and exciting,” said Khalil N. Bitar, Ph.D., AGAF, senior
researcher on the projects, and professor of regenerative medicine at the
institute. “Our goal is to use a patient’s own cells to engineer replacement
tissue in the lab for devastating conditions that affect the digestive system.”
Sphincter Project: The
lab-engineered sphincters are designed to treat passive incontinence, the involuntary discharge of stool due to a weakened ring-like muscle known as the internal anal sphincter.
The muscle can lose function due to age or can be damaged during child birth
and certain types of surgery, such as cancer.
Current options to repair
the internal anal sphincter include grafts of skeletal muscle, injectable
silicone material or implantation of mechanical devices, all of which have high
complication rates and limited success.
“The regenerative medicine
approach has a promising potential for people affected by passive fecal
incontinence,” said Bitar. “These patients face embarrassment, limited social
activities leading to depression and, because they are reluctant to report
their condition, they often suffer without help.”
Bitar’s team has been
working to engineer replacement sphincters for more than 10 years. In 2011, the
team was the first to report functional, lab-grown anal sphincters bioengineered
from human cells that were implanted in immune-suppressed rodents. The current
study involved 20 rabbits with fecal incontinence. Eight animals were treated
with sphincters engineered from their own muscle and nerve cells, eight animals
were not treated and four received a “sham” surgery.
The sphincters were
engineered using small biopsies from the animals’ sphincter and intestinal
tissue. From this tissue, smooth muscle and nerve cells were isolated and then
multiplied in the lab. In a ring-shaped mold, the two types of cells were
layered to build the sphincter. The entire process took about four to six
In the animals receiving the
sphincters, fecal continence was restored throughout a three month follow-up
period, compared to the other groups, which did not improve. Measurements of
sphincter pressure and tone showed that the sphincters were viable and
functional and maintained both the muscle and nerve components. Currently,
longer follow up of the implanted sphincters is close to completion with good
Intestine Project: The
intestine project is aimed at helping patients with intestinal failure, which
is when the small intestine malfunctions or is too short to digest food and
absorb nutrients essential to health. Patients must get nutrition through a
catheter or needle. The condition has a variety of causes. Infants can be born
with missing or dysfunctional small intestines. In adults, surgery to remove
sections of intestine due to cancer or other disease can result in a too-short
bowel. Intestinal transplant is an option, but donor tissue is in short supply
and the procedure has high mortality rates.
“A major challenge in
building replacement intestine tissue in the lab is that it is the combination
of smooth muscle and nerve cells in gut tissue that moves digested food
material through the gastrointestinal tract,” said Bitar.
Through much trial and
effort, his team has learned to use the two cell types to create “sheets” of muscle
pre-wired with nerves. The sheets are then wrapped around tubular molds made of
chitosan, a natural material derived from shrimp shells. The material is
already approved by the U.S. Food and Drug Administration for certain
In the current study, the
tubular structures were implanted in rats in two phases. In phase one, the
tubes were implanted in the omentum, which is fatty tissue in the lower abdomen,
for four weeks. Rich in oxygen, this tissue promoted the formation of blood
vessels to the tubes. During this phase, the muscle cells began releasing
materials that would eventually replace the scaffold as it degraded.
For phase two, the bioengineered
tubular intestines were connected to the animals’ intestines, similar to an
intestine transplant. During this six-week phase, the tubes developed a
cellular lining as the body’s epithelial cells migrated to the area. The rats gained
weight and studies showed that the replacement intestine was healthy in color
and contained digested food.
The researchers are excited
by the results and their next step is to test the structures in larger animals.
“Our results suggest that
engineered human intestine could provide a viable treatment to lengthen the gut
for patients with gastrointestinal disorders, or patients who lose parts of
their intestines due to cancer,” said Bitar.
Financial support for the
biosphincter project included the U.S. Armed Forces, the National Institutes of
Health under the Armed Forces Institute for Regenerative Medicine (W81XWH-13-2-0052)
and the National Institute of Diabetes and Digestive and Kidney Diseases (R01DK071614
and R42DK105593 to CELLF BIO LLC). Support for the intestine project came from
Wake Forest School of Medicine.
Co-researchers for the biosphincter
project were: co-lead authors Jaime L. Bohl, M.D., and Elie Zakhem, Ph.D., Wake
Forest Baptist. Researchers for the intestine project were: Elie Zakhem, Ph.D.,
lead author, Riccardo Tamburrini, M.D., Giuseppe Orlando, M.D., Ph.D., and Kenneth
Koch, M.D., Wake Forest Baptist.