Increased Extracellular Nucleosome Levels and Microparticles in Atrial Fibrillation Patients Compared to the Age-Matched Normal Population

Introduction: Atrial fibrillation (AF) is currently the most common cardiac arrhythmia encountered in clinical practice and a major cause of morbidity and mortality among adults. It is estimated that atrial fibrillation affects approximately 2.7 million people in the United States. Extracellular plasma nucleosomes (PNs) are complexes of DNA and histones that are released during cell death. Histones have been shown to function as DAMPs when they are translocated from the nucleus to the extracellular space. It is hypothesized that these extracellular nucleosomes contribute to the observed hypercoagulable state and embolic complications in AF.

Methods: The concentration of PNs in 48 plasma samples of atrial fibrillation patients and 38 aged-matched controls were measured using the Cell Death Detection ELISA PLUS assay (Roche Diagnostics, Mannheim, Germany) and functional microparticle levels were measured using an annexin binding method (Hyphen Biomedical, Paris, France).

Results: When comparing the concentration of nucleosomes in plasma, the atrial fibrillation patients (306.1 ± 328.86 μg/mL) had much higher levels than the aged-matched controls (177.9 ± 146.7 μg/mL), (p = 0.0015). Functional microparticles were also markedly elevated in the AF patients (18.6 ± 4.1 nM) in comparison to the aged-matched controls (4.6 ± 3.1 nM), (p=0.001). A significant correlation was observed between the PN's and microparticles, (p < 0.05).

Conclusion: Both the microparticles and PNs were elevated in atrial fibrillation when compared to aged-matched controls, suggesting increased cell death resulting in the generation of these biomarkers. Extracellular nucleosomes function as DAMPs by binding to receptors and triggering the activation of multiple signal pathways which may contribute to the elevation of microparticles. Due to the involvement of inflammation and thrombosis in the pathology of atrial fibrillation, the simultaneously increased circulating nucleosome and microparticle levels in patients with AF implies their role in the pathogenesis of this syndrome.