[acb-diabetics] experimental implanted fusion set...

[Patricia LaFrance-Wolf]

This article originally posted 20 April, 2010 and appeared in  

Issue 518

 

Experimental Artificial Pancreas Succeeds with Type 1 Diabetes Patients

 

In the first clinical trial of a system using two hormones, an artificial
pancreas delivered insulin and glucagon in a way that closely mimics the
body's

control of blood sugar and maintained near-normal levels of glucose in a
small group of Type 1 diabetes patients without them developing
hypoglycemia....

 

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Co-lead researcher Dr. Steven Russell, of the Massachusetts General Hospital
(MGH) Diabetes Center, Boston, told the press that, "This is the first study

to test an artificial pancreas using both insulin and glucagon in people
with Type 1 diabetes.... It showed that, by delivering both hormones in
response

to frequent blood sugar tests, it is possible to control blood sugar levels
without hypoglycemia, even after high-carbohydrate meals."

 

In the trial, Russell and the other co-lead investigator Dr. Edward Damiano,
an associate professor of Biomedical Engineering at Boston University, and

colleagues, tested a new type of artificial pancreas developed at Boston
University.

 

The new artificial pancreas system comprises a blood glucose monitor,
insulin pump technology and specialized software that controls the delivery
of insulin

and glucagon (a hormone that raises blood sugar levels).

 

In healthy people, blood sugar is controlled by a delicate balance between
two hormones: insulin, which encourages various parts of the body to take up

and use blood sugar, and glucagon, which raises blood sugar levels. Both
insulin and glucagon are produced in the pancreas: insulin by beta cells and
glucagon

by alpha cells. However, in people with Type 1 diabetes, their immune system
wipes out the beta cells, so they don't have enough insulin, resulting in

too much sugar in the blood.

 

To control their blood sugar level, Type 1 diabetes patients have insulin
treatment, which delays and can even prevent the long term effects of the
disease,

such as retinal damage, kidney failure and cardiovascular disease. 

 

Insulin treatment for Type 1 diabetes patients is further complicated by the
fact that although their glucagon-producing alpha cells are intact, they
don't

respond to low levels of blood sugar, so if they get too much insulin, they
are then at risk of developing a life-threatening drop in blood sugar, or
hypoglycemia.

 

Damiano commented that,"Large doses of glucagon are used as a rescue drug
for people with severely low blood sugar."

 

Because of this elevated risk of hypoglycemia, the researchers at Boston
University developed a new type of system that not only accounts for the
rate

of insulin absorption, but also includes glucagon. "Our system is designed
to counteract moderate drops in blood sugar with minute doses of glucagon
spread

out throughout the day, just as the body does in people without diabetes,"
explained Damiano.

 

The researchers tested their prototype system on diabetic pigs in 2007, as a
result of which they received Food and Drug Administration (FDA) approval

to test on humans. For the trial, Russell, Damiano and colleagues, recruited
11 adults with Type 1 diabetes. The trial was designed primarily to test the

software that controls the artificial pancreas. To get the most accurate
glucose readings they used a sensor placed directly into a vein instead of
taking

readings under the skin.

 

For 27 hours the system controlled the participants' glucose levels, during
which time they had three standardized, high-carbohydrate meals and slept at

the hospital overnight. For six participants the system kept their glucose
close to the target level, while five others had hypoglycemia that was
significant

enough that they had to drink a dose of orange juice to raise their glucose
level.

 

One of the results that surprised the researchers was the large differences
in insulin absorption rates among the patients, the fastest being four times

faster than the slowest, which was much slower than expected. They were able
to account for this by adjusting the system. 

 

The software controlling the system was initially designed to dispense
insulin at an expected absorption rate: this meant participants who absorbed
at

a slower rate got too much and developed hypoglycemia. When they tested
participants' response to a single insulin injection, the researchers
verified

that some had consistently slow and some had consistently faster insulin
absorption rates. They also observed that the rate of absorption varied a
lot

from experiment to experiment, even on an individual basis, to allow for
individually specific dosage calculations.

 

So, they adjusted the software and globally lowered insulin absorption rate
and repeated the experiments with the same participants.

 

The second time, none of the participants with slower absorption rates
became sufficiently hypoglycemic to need intervention, and blood sugar
levels were

only slightly higher among those who had the faster insulin absorption rate.
This showed, said the researchers, that the adjusted software parameters
worked

for all the participants, and may be adequate for all Type 1 diabetes
patients. They concluded that the elimination of hypoglycemic events in the
second

set of experiments in the same participants, confirmed that they were caused
by a mismatch between the parameter settings in the software and the
participants'

absorption rates.

 

They pointed out that all previously published studies of artificial
pancreas systems have reported hypoglycemic events, but this is the first
time that

one has confirmed and addressed their cause.

 

The researchers are now planning to follow up this study with another set of
experiments that will run for more than 48 hours, involving both adults and

children. This time they will use the revised settings and an FDA-approved
continuous glucose monitor. 

 

They also plan to compare this two-hormone system with one that only uses
insulin.

 

Russell said he imagined one day their system will be a wearable device,
incorporating a glucose sensor that fits under the skin and communicates
wirelessly

with a pump about the size of a cell phone. "The pump would administer
insulin and probably glucagon, and would contain a microchip that runs the
control

software," he added.

 

"It wouldn't be a cure, but it has the potential to be the ultimate
evolution of insulin therapy for Type 1 diabetes," said Damiano.

 

"A Bihormonal Closed-Loop Artificial Pancreas for Type 1 Diabetes." Firas H.
El-Khatib, Steven J. Russell, David M. Nathan, Robert G. Sutherlin, and
Edward

R. Damiano. Sci Transl Med, Vol. 2, Issue 27, p. 27ra27, published online 14
April 2010.

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