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 study may explain why obesity increases heart disease risk

The findings, presented to the Experimental Biology 2006 conference in San Francisco, may help explain why obesity increases heart disease risk.

Fat cells - adipocytes - were once thought to do nothing other than simply store excess fat tissue.

However, they are now known to be highly active, releasing many chemicals that influence biological processes within the body.

Most large blood vessels in the body are enveloped in a layer of fat cells.

Vessel deterioration

The Iowa team 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 haemorrhaging and causing a dangerous blockage.

Regulation

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.

"A better understanding of how epicardial adipocytes sense and respond to inflammation and ischemia could lead to new, rationally designed therapies for heart disease."

Professor Jeremy Pearson, associate medical director of the British Heart Foundation, said: "This is an interesting piece of research.

"It has been recognised for several years that fat cells stored up around the body secrete hormones that affect blood vessel function, but this is the first time that researchers have paid careful attention to fat cells lying close to blood vessels in the heart.

"Dr Stoll's results strongly suggest that these cells may be important regulators of blood vessel growth and repair that have previously gone unrecognised.

"They should be investigated further in future to better understand their role in the development of coronary heart disease."

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