Neutrophils appear to play a key role in the inflammation associated with early-stage development of abdominal aortic aneurysms, according to an article in the July 12 issue of Circulation.

The two new papers show for the first time that neutrophils are important in the very early stages of aneurysm formation, when the aortic wall begins to weaken and bulge. The researchers think the cells may somehow act in combination with other known risk factors such as smoking, hypertension, and inherited genetic vulnerability.

The current work involved laboratory experiments on mice that had been treated to wipe out neutrophils temporarily and in rats that lacked the protein that allows neutrophils attach to tissue. The researchers exposed a small part of the rodent aortas to elastase, a chemical that breaks down vascular tissue, then studied what happened in the rodents that had altered neutrophil systems compared with rodents that were normal.

In both cases, said senior author Gilbert Upchurch, MD, the rodents that had low neutrophil levels or no neutrophil-attaching protein developed little or no sign of aneurysm. Meanwhile, the injury to the aortic wall prompted rapid formation of aneurysms in normal rodents - aneurysms that made the diameter of the blood vessel double or even quadruple.

In an accompanying editorial, Columbia University surgeon M. David Tilson, MD, noted that the studies bring research on abdominal aortic aneurysm formation and the role of the neutrophil to a new level and may lead to further discoveries that help sort out the puzzle of these aneurysms.

Abdominal aortic aneurysms are an under-appreciated and under-researched public health threat, said Upchurch, who operates on dozens of patients each year, including some whose aneurysms have already ruptured and who will die within minutes or hours if the bleeding isn’t stopped. The aneurysms can go undetected for years; experts sometimes refer to them as a “ticking time bomb” inside a patient's abdomen.

In fact, an estimated 10 percent of all men over the age of 70 years may have intact aortic aneurysms, which cause few symptoms except for occasional back pain or abdominal discomfort. If they are detected during this stage, for instance on a routine physical exam, X-Ray, MRI or CT scan, they can be repaired successfully 95 percent of the time.