Researchers have found evidence to explain why exercise is beneficial for heart function in type 2 diabetes in an animal study.
The research team, led by scientists at the Johns Hopkins University School of Medicine, found that greater amounts of fatty acids used by the heart during stressful conditions like exercise can counteract the detrimental effects of excess glucose and improve the diabetic heart's pumping ability in several ways.
The findings also shed light on the complex chain of events that lead to diabetic cardiomyopathy, a form of heart failure that is a life-threatening complication of type 2 diabetes.
The study was conducted in a mouse model of type 2 diabetes, and focused on the exchange of energy within heart muscle cells. The researchers looked at the impact of glucose and fatty acids, which are different types of "fuel" that provide energy to the cells-and how those affect heart muscle function.
"Our work offers a new view of the role of fatty acids in diabetic hearts under stress, and suggests potential new therapies to improve heart function," said Miguel Aon, Ph.D., assistant professor of medicine at the Johns Hopkins University School of Medicine and a senior author of the study article.
"It has been commonly assumed that fatty acids were detrimental to heart muscle function, but our study showed the opposite to be true in the diabetic heart," Aon stated.
In their experiments, the researchers "fed" the normal and diabetic hearts excess glucose and stimulated the hearts to beat faster by bathing them in a hormone-like substance, isoproterenol, which acts like the body's natural catecholamine, activated when a person is under stress or participating in high levels of physical activity.
While the normal hearts were able to handle the increased glucose load and pump normally, the diabetic hearts could not contract or relax enough to keep up with the load and pump normally.
Next, the scientists repeated the experiments by feeding twice the usual amount of fatty acids to the normal and the diabetic hearts.
"We found that the function of the normal heart did not change, but to our surprise, the diabetic hearts improved to the level of the normal hearts," explained Nazareno Paolocci, M.D., Ph.D., assistant professor of medicine at the Johns Hopkins University School of Medicine and co-author of the study.
According to Aon, fatty acids appear to improve the exchange of energy within cells and also help the heart to resist the negative effects of reactive oxygen species (ROS). These molecules have a positive role in signaling within cells, but too much ROS can cause oxidative stress, damaging or even killing cells.
The researchers found that the fatty acids also counteracted impairments in the function of diabetic hearts caused by too much glucose.
Aerobic exercise, such as brisk walking, jogging, biking and swimming, has long been known to modify the negative impact of diabetes on heart muscle.
Aerobic exercise breaks up stored fatty acids to provide more fuel to the heart, and this study demonstrates that additional fatty acids can be good for the diabetic heart when it needs to beat faster, Aon said.
"Now that we have shed light on why exercise can improve heart function in people with type 2 diabetes," said Aon, "the next step is figuring out how to harness that knowledge to prevent heart damage from diabetes, especially among those people who cannot bring their blood sugar levels under good control."