Quantitative and Functional Evaluation of Endothelial Progenitor Cells in Patients with Cardiac Amyloidosis

Background: Endothelial microvascular dysfunction is a known mechanism of injury in cardiac amyloidosis (CA), but evidence regarding endothelial progenitor cells (EPCs) -levels and function- in patients with CA is lacking.

Methods: Study population included patients with light-chain or transthyretin (ATTR) CA. Patients with diagnosed heart failure and preserved ejection fraction (HFpEF) without monoclonal gammopathy and a 99mTc-DPD scan incompatible with TTR were used as controls. Blood circulating EPCs were assessed quantitatively by the expression of VEGFR-2⁽⁺⁾, CD34⁽⁺⁾ and CD133⁽⁺⁾ using flow cytometry, and functionally by the formation of colony forming units (CFUs). MTT assay was used to demonstrate cell viability. Tests were repeated 3 months following the initiation of targeted therapies (either Tafamidis or chemotherapy) in CA patients.

Results: Our preliminary cohort included 13 CA patients (median age 74 years, 62% ATTR CA). Patients with CA vs. patients with HFpEF (n=8) demonstrated lower expression of CD34⁽⁺⁾/VEGFR-2⁽⁺⁾ cells [0.51% (IQR 0.4, 0.7) vs. 1.03% (IQR 0.6, 1.4), P=0.043] and CD133⁽⁺⁾/VEGFR-2⁽⁺⁾ cells [0.35% (IQR 0.23, 0.52) to 1.07% (IQR 0.6, 1.5), P=0.003]. Functionally, no differences were noted between groups. Following the initiation of amyloid-targeted therapies in CA patients, we observed the up-regulation of CD34⁽⁺⁾/VEGFR-2⁽⁺⁾ cells [2.47% (IQR 2.1, 2.7), P<0.001] and CD133⁽⁺⁾/VEGFR-2⁽⁺⁾ cells [1.38% (IQR 1.1, 1.7), P=0.003]. Moreover, functionally, active EPCs were evident microscopically by their ability to form colonies (from 0.5 CFUs [IQR 0, 1.5) to 2 CFUs (IQR 1, 3.5), P=0.023]. EPCs’ viability was demonstrated by an MTT assay [0.12 (IQR 0.04, 0.12) to 0.24 (IQR 0.16, 0.3), p=0.014].

Conclusions: These preliminary results demonstrate reduced EPCs levels thus indicating significant microvascular impairment in CA vs. non-CA HFpEF patients . Amyloid-targeted therapies induce the activation of EPCs, thus possibly promoting endothelial regeneration. These findings may represent a novel mechanism of action of amyloid-targeted therapies