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
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.
However, the dogs all had a chemically induced version of
diabetes that's meant to model human type 1 diabetes.
Diabetes in humans
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
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.
How the study was
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
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 new cells.
'Safe for long-term
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
"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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