New Sensor Brings Fresh Hope to Diabetics

Rachel Stockton
“Diabetes kills one American every three minutes and is the seventh leading cause of death in the U.S. Life expectancy for people with diabetes has historically been shortened by an average of seven to 10 years, and the risk of death for people with diabetes is about double that of people of similar age without diabetes.” Juvenile Diabetes Research Foundation

In the United States, a new case of diabetes is diagnosed every 30 seconds; more than 1.6 million people are diagnosed each year. There is no cure.

There is bright news on the horizon; it is not a cure, but a device which can make monitoring and treatment of diabetes more accurate and reduce the long-term health problems associated with diabetes.

An implantable glucose sensor and wireless telemetry system that continuously monitors tissue glucose and transmits the information to an external receiver has been developed by Bioengineers at the University of California, San Diego and GlySens Incorporated.

In the July 28, 2010 issue of the journal Science Translational Medicine, the article titled “Function of an Implanted Tissue Glucose Sensor for More than 1 Year in Animals” describes the use of this glucose-sensing device as an implant in animals for over one year

At the conclusion of human clinical trials and Food and Drug Administration (FDA) approval, the device may be a welcome alternative for people with diabetes currently required to use finger sticks, and short-term needle-like glucose sensors that have to be replaced every three to seven days.

“The Science Translational Medicine paper shows our implanted sensors to be successful in animals. You can run the device for a year or more with it constantly working, and recording glucose quite satisfactorily. Now, we are focused on getting the human clinical trials going. We hope to begin the first human trial within in a few months,” said Gough, the lead bioengineering professor from the UC San Diego Jacobs School of Engineering. “If all goes well with the human clinical trials, we anticipate that in several years, this device could be purchased under prescription from a physician.”

Both Type 1 and Type 2 diabetics could benefit from using the long-term glucose sensor.

People with Type 1 diabetes do not make enough insulin of their own. The long-term glucose sensors could be used to adjust the insulin dose and timing of the injection, reducing the risk of taking too much insulin and becoming hypoglycemic, which can be immediately life threatening. Hypoglycemia occurs when there is too much insulin for the available glucose, or when insulin absorbs too rapidly causing dangerously low blood sugar.

Type 2 diabetics could use the long-term glucose sensors to help them adjust their diet and exercise schedule. Some Type 2 diabetics take insulin and share the same hypoglycemia risks as those with Type 1 diabetes.

Most often the method used to monitor levels of glucose in patients is “finger-sticking”, where the patient pricks his or her finger to get some blood to test in a portable reader usually 3-4 times per day. This practice reveals only a small window of glucose monitoring increasing the risk of dangerous ups and downs of glucose levels known as “glucose excursions”.

The highest risk for diabetics in developing long term health problems affecting the kidneys, eyes, heart, feet, brain, nerves and even death is due to increase incidence of “glucose excursions”.

“Four finger sticks per day to measure glucose levels is the current standard of care, but blood glucose can go on significant excursions between sticks,” said Gough. In contrast, the long-term implanted glucose monitor would provide continuous monitoring day and night. “We are moving toward something that will be automatic and quite unobtrusive. Others wouldn't even know if someone is using a glucose sensor. Our goal is to get people off the finger stick cycle,” said Gough.

During the animal trials, the glucose sensor implant developed by Gough and his team implanted under the skin in pigs is about 1.5 inches in diameter and about 5/8 inches thick. It continuously monitored tissue glucose and transmitted the glucose information to a data recorder the size of a cell phone.

A hurdle in the development of an effective glucose sensor that sits in tissue just below the surface of the skin, is prevent “tissue encapsulation” which causes unpredictable fluctuations in the readings.

Designing the sensor to remain insensitive to tissue encapsulation for over 500 days was, “the most important point of the paper”, said Gough. “That’s a big step from a scientific point of view, and it's due to the sensor's unique oxygen detection scheme.”

The device worked effectively, without being affected by the problem of tissue encapsulation, by taking in glucose and oxygen from surrounding tissue and using the enzyme glucose oxidase to catalyze a reaction where oxygen is consumed in proportion to the amount of glucose present. Any oxygen left over is measured and compared to the baseline oxygen recorded by a reference sensor, so the difference indicates how much glucose is present.

It is possible the data could be made useful in many ways, for example it could be sent to cell phones or displayed in other ways.

“There are parents with diabetic children who spend their nights worrying that their child in a nearby bedroom may go into nocturnal hypoglycemia,” said Gough, who explained that the glucose sensors could be used to send information to a phone that would alert parents if the child's glucose levels drop to a dangerous level during the night.

Today, there are approximately 800,000 people using external insulin pumps; they require a physician to program them since they are not connected to a glucose sensor directly. “You can manually adjust the pump schedule to some extent, but patients must keep rigid schedules to live with an insulin pump,” said Gough. Also, “With an insulin pump, there is always the concern that it will pump too much insulin, leading to dangerously low blood glucose levels. The sensor could serve as a safety mechanism against low blood glucose levels.”

The bioenineers'goal is to enable the pumps to automatically adjust the rate of insulin being administered based on glucose readings from the implanted sensors, i.e., to function like an artificial pancreatic beta cell.

“If insulin pumps were programmed based on near-real-time readings from implanted glucose sensors, the pumps would adjust insulin dosing based on what your glucose number is after a meal. You wouldn't have to be so rigorous about your schedule,” said Gough.

Major research efforts to use readings from glucose sensors to program insulin pumps are well underway. Researchers are primarily using needle-type glucose sensors, but these needle sensors could be replaced with the new implanted sensors if and when they are approved for human use.

The warning signs of Type 1 diabetes (also called juvenile diabetes or insulin-dependent diabetes), include:

** extreme thirst; frequent urination; drowsiness or lethargy; sugar in urine; sudden vision changes; increased appetite; sudden weightloss; fruity, sweet, or wine-like odor on breath; heavy, labored breathing; stupor; and unconsciousness.

Type 1 diabetes is generally diagnosed in children, teenagers, or young adults. Scientists do not yet know exactly what causes type 1 diabetes, but they believe that autoimmune, genetic, and environmental factors are involved.

The symptoms of Type 2 diabetes (adult-onset) include:
**increased thirst, frequent urination, increased hunger, weight loss, fatigue, blurred vision, slow healing sores, frequent infections, areas of darkened skin

Risk factors of Type 2 diabetes include:
**weight, inactivity, family history, age, prediabetes, gestational diabetes
, race

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