2980The effect of monoclonal antibodies against PCSK9 on circulating CD34+ progenitor cells interactions with platelets in patients with familial hypercholesterolemia

Abstract

Abstract Introduction Platelets interact with circulating CD34+ progenitor cells inducing their differentiation into endothelial progenitor cells (EPCs) and further promoting EPC maturation into endothelial cells, an important step for endothelial regeneration and angiogenesis. PSCK9 is a serine protease that may not only play a crucial role in binding to the low density lipoprotein receptor (LDL-R) increasing its endosomal and lysosomal degradation thus inhibiting its recycling to the cell surface, leading to increasing LDL-cholesterol levels in plasma, but may also exhibit several, independent on LDL-R, activities on a plethora of cell types, including platelets. Purpose We investigated whether monoclonal antibodies (mabs) against PCSK9 could affect platelet interaction with CD34+ cells as well as their differentiation into EPCs, in patients with Familial Hypercholestorelemia (FH). Patients and methods Patients with FH (n=11, 8 men and 3 women, mean age 53±10 years) being under statin/ezetimibe therapy (40mg statin/ 10mg ezetimibe) participated in the study. Patients exhibited resisting high LDL-cholesterol levels, therefore following the existing guidelines, they received mab against PCSK9 (7 evolocumab, 140mg/ml and 4 alirocumab, 150mg/ml) every two weeks. Blood samples were drawn before and after 4 doses of the antibody i.e. after two months (Follow-up). In addition to the patients' serum lipid profile, the endothelial phenotype of CD34+ (membrane expression levels of KDR which is a receptor for VEGF and an endothelial phenotype marker) on CD34+ cells (CD34+-KDR+ cells) and the formation of platelet-CD34+ (CD61+-CD34+) and platelet-KDR+ (CD61+-KDR+) conjugates were also determined by flow cytometry on whole blood after dual labelling with anti-VEGFR-R2/KDR-PE, anti-CD61-PerCP and anti-CD34-FITC. The results were expressed as the %gated of CD34+-KDR+ cells, as well as CD61+-CD34+ and CD61+-KDR+ conjugates. Results The baseline LDL-cholesterol levels were significantly reduced from 172±43 mg/dl to 51±17 at follow-up, p=0.0001. Importantly, the formation of CD61+-CD34+ and CD61+-KDR+ conjugates were increased from baseline to follow-up (from 1.39±1.3 to 2.23±2.8, p=0.037) and (from 2.91±4.2 to 5.92±6.01, p=0.014), respectively. The membrane expression of KDR on CD34+ cells was also increased from 0.79±0.9 to 1.36±0.90, p=0.042, which reflects the increase in the CD34+ endothelial phenotype. Conclusion We show for the first time that the mabs against PCSK9, significantly increase the CD34+ endothelial phenotype in FH patients, which may at least partially attributed to the increase in the platelet interaction with CD34+ cells (platelet-CD34+ conjugates). The underlying mechanisms as well as the consequences of this effect at the clinical level for these patients are under investigation.