Abstract 15260: Higher Levels of Osteoblast-lineage Cells Are Associated With Cardiac Allograft Vasculopathy Progression

Abstract

Introduction: Cardiac allograft vasculopathy (CAV) is a major determinant of long term graft survival. Endothelial progenitor cells (EPC) expressing osteocalcin (OC) have been linked to atherosclerosis. However, little is known regarding bone-forming osteoblast-lineage (OL) cells, and their role in atherosclerosis and CAV. Methods: Heart transplant patients undergoing serial Intravascular Ultrasound (IVUS) and progenitor cell studies were included in the study. OL cells, defined as cells positive for alkaline phosphatase (AP) and OC, were counted using flow cytometry on the day of baseline IVUS. A follow up IVUS was done 3 years later. Gray-scale and virtual-histology IVUS were used to evaluate vessel size, plaque burden, and plaque composition (fibrous, fibrofatty, necrotic core, calcified). Patients were divided into two groups by the median change (Δ) in necrotic core volume and plaque volume over 3 years. Results: A total of 55 patients (mean age 52±15 years, 65% males) were included. At baseline, median time after transplant was 4.2 years. Average vessel area at baseline and three years were 15.8 ±4.6 and 15.3 ±5.4 mm2, respectively (p=0.32). However, 24/55 patients (44%) had positive remodeling. The number of OL cells was positively correlated with Δvessel (r=0.36, p=0.01) and Δlumen areas. (r=0.30, p=0.02). Patients with greater Δplaque volume and Δnecrotic core volume had higher OL cell levels compared to those with below medians (Δplaque volume: 95 [30,348] vs. 30 [10, 90] OL per 100,000 counts, p=0.01; Δnecrotic core volume: 95 [22.5, 320] vs. 30 [10, 90] OL per 100,000 counts, p=0.03) (Fig. 1A and 1B). Conclusions: The number of OL cells in heart transplant patients correlates with positive vascular remodeling, accompanied by increased lumen area over 3 months. Furthermore, patients with unstable plaque features had higher OL cells, suggesting a possible role in pathologic plaque progression.