THURSDAY, Feb. 14 (HealthDay News) -- In news that might one day
help humans who struggle with type 1 diabetes every day, Spanish
researchers report that a single session of gene therapy injections
cured five beagle puppies who had the blood sugar disease.
Even four years later, the dogs showed no signs of diabetes.
"Our data represent the first demonstration of long-term correction of diabetes in a large animal model using gene transfer," the scientists wrote in the Feb. 7 online issue of Diabetes.
However, the dogs all had a chemically induced version of
diabetes that's meant to model human type 1 diabetes.
In humans, type 1 diabetes is an autoimmune disease, which means
the body's own immune system mistakenly attacks healthy cells as
though they were bacteria or viruses.
In the case of type 1 diabetes, the immune system destroys the
insulin-producing beta cells located in the pancreas. Insulin is a
hormone that's needed to transport glucose into the body's cells to
be used as fuel. Glucose is sugar that comes from the carbohydrates
you consume. Carbohydrates are nutrients found in a variety of
foods, including fruits, vegetables, breads and sweets.
Once the beta cells are destroyed, the body no longer makes
insulin (or makes very little of the hormone), and anyone with type
1 diabetes needs insulin injections or an insulin pump for the rest
of their lives.
However, insulin needs change constantly, depending on the type
and amount of food eaten and level of physical activity. Even
emotions can affect insulin levels. Too little insulin can cause
high blood sugar levels, while too much insulin can cause low blood
sugar levels. Neither condition is healthy and, if severe enough,
either can cause death.
In the current study, the researchers developed a gene therapy
that served two purposes: one was to sense the amount of glucose in
skeletal muscles and the other was to release insulin. This
research group had already tested this therapy in mice, where it
was found to be successful in controlling blood sugar levels.
To test the therapy, the researchers needed dogs with diabetes.
However, the types of diabetes that occur naturally in dogs aren't
the same as type 1 diabetes. So, the researchers induced diabetes
in a group of beagle puppies between 6 and 12 months old. The dogs
were then given daily insulin injections.
The gene therapy involved a single session of numerous
injections in the dog's rear legs. The needles used are like those
used in human cosmetic procedures.
The dogs quickly got better and maintained normal blood sugar
levels without insulin. The researchers continued to measure blood
sugar control and the animals' health for more than four years. The
dogs stayed healthy, and seem to have no long-term problems from
the gene therapy.
Lead researcher Fatima Bosch, director of the Center of Animal
Biotechnology and Gene Therapy at the Universitat Autonoma de
Barcelona in Spain, said the next step in their research is to test
the gene therapy on dogs with naturally occurring diabetes. The
dogs will also be pets, so their living conditions and glucose
levels will be varied, more closely mimicking what a person with
type 1 diabetes would encounter.
Dr. Camillo Ricordi, director of the Diabetes Research Institute
and the cell transplant center at the University of Miami, called
the new research "an important study, and a remarkable initial
finding. But, this is not a type 1 model of diabetes. This is a
model where you induce diabetes chemically and you may have
residual [beta] cell function."
Ricordi explained that because it's not naturally occurring type
1 diabetes, there's no worry of the immune system destroying the
insulin-releasing cells in the muscle. But, in a person with type 1
diabetes, the immune system could still attack and destroy these
Dr. Massimo Trucco, chief of the division of immunogenics at
Children's Hospital of Pittsburgh, said the issue of autoimmunity
is an important one. But, of greater concern to him is that while
this therapy worked in very controlled conditions -- the dogs'
diets and exercise sessions were controlled -- in real-life
conditions, this therapy might not work as well.
"Dogs get the food you want them to have. They probably spent most of their time in a cage. But, kids eat what they want and play when they want, meaning their [blood sugar level] varies dramatically. If you inject this therapy into the muscles, the muscle cells don't have the same apparatus to control the insulin levels that beta cells do. This would release insulin too well to give good control, and could cause [low blood sugar levels] when it does release," he said.
Trucco said he doesn't believe this therapy could translate to
"Human beings are not clones of dogs. Beta cells are more complicated than muscle cells. Muscles just can't secrete insulin quickly and efficiently like beta cells do," he said.
But, he added that this was a very well-done gene therapy study
that showed that the particular form of gene therapy used in this
research appears to be safe for long-term use.
Learn more about gene therapy from the
Human Genome Project.
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