Background:
It is reported that patients with AS are characterised by endothelial dysfunction which is reversed after transcatheter aortic valve replacement (TAVR). To date, the impact of RBCs and the underlying mechanisms of endothelial dysfunction in AS are not well understood. Increased shear stress and turbulences are observed in AS and may influence RBC membrane integrity resulting in cell-free haemoglobin with impact on endothelial dysfunction. 

Hypothesis and aim:
We hypothesise that subhemolysis of red blood cells in AS leads to release of cell-free hemoglobin which acts as NO scavenger and may promote endothelial dysfunction in AS. We aimed to verify that RBCs from patients with AS promote endothelial dysfunction in bioassay. 

Methods:
To analyze the impact of red blood cells on endothelial dysfunction in AS, we used a bioassay approach with aortic rings from 12-week old male mice (C57BL/6J), which were coincubated as target organs with red blood cells from patients with aortic valve stenosis. Blood from the same patient is taken before and one to three days after transcatheter aortic valve replacement (TAVR). Endothelial function of aortic rings is assessed by standardised protocols. Age-matched patients with cardiovascular comorbidities without aortic valve stenosis were used as controls.

Results:
Co-incubation of aortic rings with RBCs from patients with aortic valve stenosis resulted in a significant impairment of endothelium-dependent relaxation compared with patients without aortic valve stenosis (Maximum relaxation patients with AS 57.16 +/- 11.42 % vs. maximum relaxation controls 76.97 +/- 7.742 %, p=0.0035, n=10 and n=6, respectively). Co-incubation of RBCs from the same patients one to three days after TAVR resulted in an improvement of endothelium-dependent relaxation by trend (Maximum relaxation before TAVR 57.16 +/- 11.42 % vs. maximum relaxation after TAVR 68.79 +/- 12.36 %, p=0.1100, n=10). 

Conclusion:
Impairment of endothelium-dependent relaxation in bioassay by RBCs from patients with aortic valve stenosis compared with patients without AS suggests that red blood cells from patients with AS cause altered nitric oxide bioavailability likely by release of cell-free hemoglobin. Improvement of endothelial function in bioassay is reversed after TAVR by tendency.