Amino acid blood test illuminates abdominal aneurysms

2019 10 15 22 44 9097 Abdominal Aneurysm 400

The level of the amino acid desmosine in the blood is a good biomarker for potentially deadly abdominal aortic aneurysms and complements measurements of aneurysm size from imaging studies, U.K. researchers reported online October 9 in the Journal of the American Heart Association.

Abdominal aortic aneurysms are at risk of rupturing, which can be fatal. Desmosine has the potential to be a biomarker of rupture, as the amino acid is released into blood and urine through the breakdown of elastin in the aortic vessel wall.

Currently, risk is typically assessed by monitoring the diameter of the aneurysm. However, a high level of plasma desmosine (pDES) correlated with aneurysm diameter size and events in an analysis of data from two prospective studies: Magnetic Resonance Imaging for Abdominal Aortic Aneurysms to Predict Rupture or Surgery (MARS) and the United Kingdom Aneurysm Growth Study (UKAGS).

Desmosine added information beyond what was available from size, Dr. Anna Maria Choy, a senior clinical lecturer and honorary consultant cardiologist at the University of Dundee in Scotland, and colleagues reported in JAHA.

"Plasma desmosine may have potential as an additional marker for assessing the risk of rupture in patients with abdominal aortic aneurysms," they concluded.

Shadowy risk of rupture

Choy and colleagues noted that 1% to 2% of men have an abdominal aortic aneurysm by the time they reach the age of 65, and rupture is often fatal. If their aneurysm diameter is larger than 5.5 cm, patients may be monitored with surgical intervention, with good outcomes. But people with smaller aneurysms -- notably women -- are also at risk of aneurysm rupture, and there is a need for better risk management, the authors noted.

The study involved 507 patients, mostly older men, with abdominal aortic aneurysms and 162 control participants from MARS and UKAGS, both of which were observational studies. The researchers looked at what value desmosine added, on top of diameter size as measured with ultrasound.

"Although assessment of [abdominal aortic aneurysm] diameter using ultrasound does have limitations on intraobserver and interobserver variability, it is the main method used in clinical practice," they acknowledged.

Choy and colleagues wrote that there has been "intense interest" in whether biomarkers could be used to monitor size and predict rupture.

"Biomarkers, especially those related to pathophysiological processes of inflammation and aortic wall degradation, are attractive potential candidates," they wrote. "However, no biomarker has yet been shown to provide enough additional prognostic value to [abdominal aortic aneurysm] diameter to enter into routine clinical use."

Participants in MARS were drawn from Scottish centers; all individuals had an aneurysm diameter of at least 40 mm. UKAGS, which is still ongoing, is a study of patients in England and Wales with small aneurysms -- less than 55 mm in diameter.

For all patients studied, the mean plasma desmosine level was 0.46 ± 0.22 ng/mL. Desmosine was higher in those with aneurysms than in the controls, a statistically significant finding, and strongly correlated with aortic diameter, the researchers noted. Another significant finding was that high levels of desmosine were associated with twice the risk for abdominal aortic aneurysm events, after adjusting for aneurysm diameter.

Correlation with diameter and events was strongest for desmosine out of all blood biomarkers tested, including, for example, the inflammation marker interleukin-6 (IL-6). Desmosine offered improved risk stratification beyond what was possible with diameter alone, the authors concluded. Furthermore, they suggested 0.56 ng/mL as the threshold for predicting abdominal aortic aneurysm events.

An advantage of plasma desmosine is that it is not associated with lung dysfunction; rather, it is a more specific marker for vascular disease, according to the investigators.

"In our study, pDES was associated with aortic diameter independent of [chronic obstructive pulmonary disease] and smoking status," they wrote.

Choy and colleagues believe there could be a role for desmosine as a biomarker in patients with small aneurysms -- that is, with a diameter of 30 mm to 55 mm -- who are at some risk for rupture but not enough to call for surgical treatment.

The finding that plasma desmosine was associated with events independent of aortic diameter suggests it may be useful as an additional risk marker, "particularly given the improvements in net reclassification improvement and integrated discrimination improvement," the group wrote.

"The independent prognostic value of pDES suggests that it may be providing an additional pathophysiological insight beyond [abdominal aortic aneurysm] diameter," the researchers added.

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