Progressive endothelial coverage enhances hemocompatibility and prevents calcification in bioprosthetic valve tissue

Exploring the hemocompatibility of bioprosthetic heart valves (BHVs) has been challenging due to the scarcity of non-degenerated material. This study has two complementary objectives (1) To characterize the extent and temporal kinetics of endothelial coverage of BHVs implanted in humans; (2) To investigate, in a rat model, the impact of pericardial endothelialization on tissue calcification. We employed histology and electron microscopy to assess cellular organization in non-degenerated BHVs and conducted hemodynamic simulations to evaluate shear stress fields in the ejection valves area. Furthermore, we investigated the impact of pericardium endothelial coverage on calcification using endothelial colony-forming cells (ECFCs) cultured on bovine pericardium discs implanted in athymic nude rats for 18 days. Calcium content was quantified through acetylene flame atomic absorption spectrophotometry. We observed inflammatory cell infiltration within all explanted BHVs, as well as fibrin deposit on top of the leaflets. Endothelial coverage emerged in long-term implants (> 180 days) but remained incomplete in aortic valves, which could be linked to high shear stress levels in aortic position confirmed in hemodynamic simulations. Besides, the rat experiments revealed that the discs covered with fibrin + ECFCs were significantly less calcified than those covered with fibrin alone (respectively, median = 0.9 µg Ca/mg tissue; IQR: 0.7–1.1 vs median = 18.3 µg Ca/mg tissue; IQR: 9–34.9; p = 0.0003), and less extensively colonized by neutrophils. Human explanted BHVs showed intact leaflets with a fibrin layer and organized endothelial coverage, without detectable calcification over the short observation period. In rats, endothelialization was associated with significantly reduced pericardial calcification, suggesting a potential protective effect. However, the limited follow-up in humans precludes conclusions on a causal role of endothelial coverage in hemocompatibility or protection against calcification.