How obesity may increase heart risk
Fat cells around coronary arteries may play a key role in heart disease, research suggests.
University of Iowa researchers found the cells release chemicals which can trigger inflammation.
Under certain circumstances, they might also stimulate potentially damaging growth of new blood vessels.
The findings may help explain why obesity increases heart disease risk.
The researchers suspected that the chemicals pumped out by the fat cells surrounding the coronary arteries might play a role in triggering heart disease by contributing to the deterioration of these vessels.
They isolated and cultured these cells, known as epicardial adipocytes, and compared them with cells taken from other fat tissue.
Tests showed that the epicardial adipocytes were prone to release greater amounts of potentially harmful, inflammation-producing cytokines in response to certain stimuli.
Unlike fat cells from other tissue, they also stimulated the cells lining the arteries to begin the process of forming new vessels.
And when oxygen was in short supply, this process was stepped up.
The fat tissue surrounding the coronary arteries gets its blood supply directly from the vessel.
The Iowa team believe their work suggests that when this blood supply is reduced, possibly by a blockage in the blood vessel, the fat cells respond by releasing cytokines, which trigger inflammation and make the problem worse.
At the same time, the fat cells may also trigger excessive formation of new blood vessels which could raise the risk of cardiovascular disease by raising the risk of fatty deposits hemorrhaging and causing a dangerous blockage.
Lead researcher Dr Lynn Stoll said: "The fat cells surrounding coronary arteries may ultimately prove to be an important link between obesity, type two diabetes, and coronary artery disease, all of which are increasing at epidemic rates.
Another new study indicates that older adults who carry their fat around the middle may be at risk of chronic heart failure, even in the absence of other serious health conditions.
Abdominal fat may contribute to heart failure in several ways, including through increased pressure within the abdominal cavity. Abdominal obesity may also lead to an enlargement of the heart's main pumping chamber, or to stiffness in the aorta, the major artery supplying blood to the rest of the body.
In contrast, the researchers found, body mass index (BMI), a measure of weight in relation to height, was not a good predictor of heart failure once waist circumference was taken into account.
Coupled with past studies, the researchers conclude, the findings suggest that excess fat -- particularly in the abdomen -- should be added to the list of risk factors for heart failure.