In the first trial, the system kept blood-sugar levels normal for six of the subjects, but the other five experienced hypoglycemia that needed to be rescued by drinking fruit juice. The researchers found that these five patients took much longer than anticipated to absorb and clear the insulin they received. So they adjusted the parameters of the system to match a slower insulin absorption rate, and retested the same subjects. The system was then able to keep the blood-sugar levels of all participants under control, although levels were slightly higher in those who had absorbed insulin quickly in the first trial.
Bruce Buckingham, a pediatric endocrinologist at Stanford University who was not involved in the work, says that demonstrating that the system works even after subjects have eaten large meals is a key achievement. “Dealing with meals is the real obstacle” in developing any artificial pancreas, he says. A recent study from a group at Cambridge University, U.K., tested a similar system, but only overnight, when patients were not eating. Buckingham says that another challenge for the devices will be handling periods of exercise, which also causes blood sugar to fluctuate.
The team behind the new device is planning a further trial using an FDA-approved continuous glucose monitor and an automated system for delivering the two hormones. This trial will compare the dual-hormone system with an insulin-only one, and it will cover two days and include a period of exercise.
Aaron Kowalski, director of the Artificial Pancreas Project at the Juvenile Diabetes Research Foundation, which partially funded the study, says that the insulin-glucagon system represents the future of artificial-pancreas technologies. “Our ultimate goal is to try to come as close to a human physiology without diabetes as possible,” he says. But bringing such a system to market will be challenging. Kowalski says that there are no FDA-approved pumps that deliver two different substances, and glucagon is currently used only in emergencies when diabetic patients become dangerously hypoglycemic–it comes in the form of a powder that must be reconstituted.
In the more immediate term, Kowalski believes that insulin-only artificial-pancreas devices will become available much sooner. An insulin pump that can shut off automatically when blood sugar drops too low has already been approved in Europe. And the Artificial Pancreas Project is working with Animas Corporation, which makes glucose monitors, on a system that monitors blood sugar but only automatically delivers insulin when blood-sugar levels fall above or below a certain range. Kowalski believes that such a device, while not entirely automating the delivery of insulin, can offer diabetics crucial peace of mind.