NETosis is associated with the severity of aortic stenosis: Links with inflammation

An involvement of neutrophil extracellular traps (NETs) in the aortic stenosis (AS) pathogenesis is unknown.

We enrolled 50 patients, median age 66.5 years with isolated severe AS, after aortic valve replacement and 20 healthy sex/age-matched controls. Autopsy-derived aortic valves from 5 healthy donors served as controls. Valvular expression of citrullinated histone H3 (citH3), myeloperoxidase (MPO), and neutrophil elastase (NE) and macrophages (CD68) were evaluated by immunostaining. Plasma citH3 and interleukin 6 (IL-6) were also determined.

All stenotic and healthy valves expressed citH3 in the leaflets' endothelial and sub-endothelial layers at the aortic side. Amount of valvular citH3-positive cells was higher in AS patients compared with controls (53.5 [33-62]% vs. 5.7 [4.1-9.0]%, p < 0.0001) and correlated with aortic valve area (AVA; r = -0.69, p < 0.0001) and mean transvalvular gradient (r = 0.6, p < 0.0001). Double-staining revealed that in AS valves 27.2 ± 9.8% of cells were citH3/MPO- and 25.3 ± 8.9% citH3/NE-positive. Within stenotic valves, 6.4 ± 2.5% of cells showed citH3/CD68 double-positivity and were identified as macrophages. AS patients compared to controls had 83% higher plasma citH3 (p < 0.0001). In AS, plasma citH3 correlated with IL-6 (r = 0.39, p = 0.0054) levels and AVA (r = -0.45, p = 0.0009).

The presence of NETs in stenotic valves and association with AS severity suggest novel mechanisms involved in the disease progression.