Abstract
Neutrophil extracellular traps (NETs) have been implicated in the pathogenesis of abdominal aortic aneurysms (AAAs). This study has addressed the notion that NET components might serve as AAA biomarkers or novel targets of AAA therapy. Thus, parameters of neutrophil activation and NET formation were measured in plasma. Their diagnostic marker value was explored in 41 AAA patients and 38 healthy controls. The NET parameter citrullinated histone H3 (citH3) was then validated in 63 AAA patients and 63 controls matched for cardiovascular disease. The prognostic marker potential was investigated in 54 observation periods of AAA growth over 6 months. NETs were further assessed in conditioned medium and sections of aortic tissue. CitH3 was found to be increased in blood (median 362 vs 304 ng/mL, P = 0.004) and aortic tissue (50 vs 1.5 ng/mg, P < 0.001) of AAA patients compared to healthy controls and accumulated in the intraluminal thrombus (629 ng/mg). The diagnostic potential of citH3 ranged at 0.705 area under the ROC curve (AUROC) and was validated with the independent sample set. Furthermore, plasma citH3 predicted AAA growth over the next 6 months (AUROC: 0.707, P = 0.015) and dropped significantly after surgical aneurysm repair. In an angiotensin II - based mouse model of experimental AAA, an inhibitor of histone citrullination was applied to block NET formation and AAA progression. Of note, further growth of an established aneurysm was prevented in mice treated with the NET inhibitor (P = 0.040). In conclusion, histone citrullination represents a promising AAA biomarker and potential therapeutic target to control disease progression.
Highlights
Progressive dilatation of an abdominal aortic aneurysm (AAA) may lead to its rupture, which is associated with a death rate of around 80%.1 Whilst current evidence supports surgical repair of asymptomatic AAAs at a diameter of 5 to 5.5 cm, autopsy studies have shown that small AAAs may rupture.[2]
neutrophil extracellular traps (NETs) are known to play a role in the pathogenesis of AAA and the central NET component of histone citrullination is detectable in aneurysm tissue
We have recently reported that the frequency of activated neutrophils and neutrophil-derived myeloperoxidase (MPO) are significantly elevated in blood of AAA patients compared to healthy controls and have investigated the diagnostic and prognostic value of a score based on MPO and D-dimer plasma levels.[4]
Summary
Progressive dilatation of an abdominal aortic aneurysm (AAA) may lead to its rupture, which is associated with a death rate of around 80%.1 Whilst current evidence supports surgical repair of asymptomatic AAAs at a diameter of 5 to 5.5 cm, autopsy studies have shown that small AAAs may rupture.[2]. Besides the progressive weakening and widening of the vessel wall, development of an intraluminal thrombus (ILT) can further promote aneurysmal dilatation.[5] Among other leukocytes, neutrophils are recruited to the aortic wall as well as the ILT and substantially contribute to AAA development, since neutrophil-derived serine proteases, matrix metalloproteinases (MMPs) and reactive oxygen species induce matrix destruction and promote smooth muscle cell apoptosis.[6] We have recently reported that the frequency of activated neutrophils and neutrophil-derived myeloperoxidase (MPO) are significantly elevated in blood of AAA patients compared to healthy controls and have investigated the diagnostic and prognostic value of a score based on MPO and D-dimer plasma levels.[4] Of note, neutrophil depletion inhibits AAA formation in mice This effect is partly mediated by a decrease in MMP activity but additional neutrophil functions seem to be involved.[7]. Considering the current lack of conservative treatment options, this constitutes an attractive approach for AAA drug development with expectedly few side-effects
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