The high-fat “diet” that diabetic heart muscle consumes helps make cardiovascular disease the most common killer of diabetic patients, according to a School of Medicine study that appeared in the Feb. 7 issue of the Journal of the American College of Cardiology.
Sixty-five percent of people with diabetes die from heart attack or stroke. When the researchers investigated fuel consumption in heart muscle, they found that heart muscle of type 1 diabetic patients relies heavily on fat and very little on sugar for its energy needs.
In contrast, heart muscle in non-diabetics doesn’t have this strong preference for fat and can use either sugar (glucose) or fat for energy, depending on blood composition, hormone levels or how hard the heart is working.
“The diabetic heart’s overdependence on fat could partly explain why diabetic patients suffer more pronounced manifestations of coronary artery disease,” said senior author Robert J. Gropler, M.D., professor of radiology and of medicine in the School of Medicine, professor of biomedical engineering in the School of Engineering & Applied Science and director of the Cardiovascular Imaging Laboratory at the Mallinckrodt Institute of Radiology.
“The heart needs to use much more oxygen to metabolize fats than glucose, making the diabetic heart more sensitive to drops in oxygen levels that occur with coronary artery blockage.”
Compared to non-diabetics, diabetic patients often have larger infarctions and suffer more heart failure and sudden death when the heart experiences an ischemic, or low-oxygen, event.
In addition, when the diabetic heart burns fat, it accumulates reactive oxygen molecules that interfere with the fuel consumption mechanism and encourage the accumulation of fats in the muscle cells. This can lead to increased inflammation, cell death and heart dysfunction.
The diabetic heart’s reliance on fat molecules for energy was previously observed in experiments using diabetic animals. But this recent study is the first time researchers have confirmed that burning of fatty acids in the heart muscle is increased in humans with diabetes.
In the study, 11 healthy, non-diabetic people were compared with 11 otherwise healthy people with type 1 diabetes. The researchers found that the diabetic patients had much higher levels of fats in their blood and had an increased uptake of fatty acids into heart muscle cells.
The cells of diabetic hearts not only absorbed more fat, but they also burned a higher percentage of the fats they took in. As a result, diabetic heart muscle used about half as much glucose and four times more fat for energy than the hearts of non-diabetics.
The researchers are now studying heart muscle metabolism in type 2 diabetics. Patients in the study are divided into two groups; one receives standard therapies to normalize blood glucose levels, while the other receives additional therapies designed to decrease the amount of fat in the blood.
The study is still accruing patients; people who would like to participate can call 362-8608.
If the increased blood-fat levels are confirmed to be responsible for the dysfunctional metabolism of diabetic heart muscle, reducing fat levels may become an important way to decrease illness and death from cardiovascular disease in diabetics, according to the authors.
“We believe it’s not enough to control blood glucose in diabetes,” Gropler said. “You also have to target fat delivery to the heart. If you decrease the fat delivery through a combination of diet, exercise and drugs, you’ll improve the heart’s ability to use other energy sources, which will improve heart health.”