Abstract :
[en] Background
Calcific aortic stenosis (CAS) is the most frequent valvular heart disease in industrialized
countries. CAS is characterized by progressive aortic valve remodelling and calcification,
which leads to valvular dysfunction and subsequent cardiac impairment. The extent of aortic
valve calcification accurately predicts AS severity and prognosis. A recent preclinical study
proposed a role for activated platelets in valvular calcification through transforming growth
factor-b (TGF-b) or autotaxin-lysophosphatidic acid (LPA). Platelet parameters may therefore
represent new circulating biomarkers of CAS progression and outcome.
Aim
To perform a longitudinal analysis of platelet markers in a new rabbit model of aorta and
aortic valve calcification and study their correlation with aortic valve calcium score in
patients with severe AS.
Methods
Twelve-week old male New Zealand White rabbits were fed for 16 weeks (W) with a palm
oil-enriched diet (5% palm oil) supplemented with vitamin D2 (25.000U/day/2.5kg) during
the first two weeks. Computed tomography (CT) was performed at baseline, W4, W8, W12
and W16 to analyze the appearance of macrocalcifications. Blood samples were collected at
the same time points to study the evolution of platelet count. ADP closure time (CT-ADP)
was measured in whole blood on a PFA-200. After 16 weeks, the heart and the aorta were
collected and fixed for histological analyses of tissue structure (hematoxylin-eosin staining)
and calcification (alizarin red staining). In parallel, platelet count, number of activated
platelets (CD62P+), CT-ADP, plasma levels of autotaxin, LPA and TGF-b, and CT aortic valve
calcium score (CT-AVC) were studied in 36 patients with severe AS undergoing transcatheter
aortic valve replacement implantation (TAVI).
Results
After 16 weeks, all rabbits fed with the palm-oil enriched diet exhibited massive aortic wall
calcification, characterized by the presence of large calcification nodules in the aortic media.
These aortic macrocalcifications were detectable in vivo by CT in 5 rabbits out of 6.
Calcification nodules were also detected in the aortic valve fibrosa of 2 rabbits out of 6 via
histological alizarin red staining of explanted hearts. Platelet count decreased as early as
after 8 weeks of diet (489 K/μl vs 373K/μl, P<0.05) and kept decreasing progressively along
with calcification development. No changes in CT-ADP values were observed over time. In AS
patients, as expected, CT-AVC correlated well with peak aortic jet velocity (r=0.49,
P=0.0054). Interestingly, CT-AVC was inversely correlated to platelet count (r=-0.52, P=0.0012) and to the number of circulating CD62P+ platelets (r=-0.45, P=0.0073). Although
CT-ADP values were above normal values for AS patients, CT-ADP did not correlate with CTAVC.
Finally, in agreement with a role for activated platelets as a major source of TGF-b,
levels of this cytokine showed good correlation with the number of CD62P+ platelets (r=0.46,
P=0.0053).
Conclusions
Platelet consumption is associated with aortic valve calcification both in our rabbit model
and in AS patients. These findings support a role for platelets in this process, possibly via
TGF-b. Hence, platelet count might help assessing AS severity and provide prognostic
information. This warrants further investigations.
