Objective: In human abdominal aortic aneurysm, the accumulation of blood-derived cells and proteases within the mural thrombus plays a pivotal role in the evolution toward vessel wall rupture. We sought to identify peptides released from abdominal aortic aneurysm specimens, characterized by an intraluminal thrombus.
Methods and results: Intraluminal thrombus samples were analyzed by differential proteomics, using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. A 1309-Da peptide was detected in larger amounts in the newly formed luminal thrombus layer relative to older layers. It was identified as being LVVYPWTQRF (known as LVV-Hemorphin 7), a peptide generated from hemoglobin by cathepsin D. By immunohistochemical analysis, we showed that Hemorphin 7 (H7) colocalizes with cathepsin D and cathepsin G in the luminal layer of the intraluminal thrombus. In vitro, cathepsin G was able to generate H7 peptides at pH 7.4, whereas cathepsin D was only active in acidic conditions. Finally, H7 peptides were shown to be increased 3- to 4-fold in sera of abdominal aortic aneurysm patients relative to controls, and their levels were positively correlated with the volume of the thrombus.
Conclusions: Our results suggest that circulating H7 peptides may reflect proteolysis of hemoglobin in the aneurysmal intraluminal thrombus and may be used as a biological marker of pathological vascular remodeling.