Plasma exosome hemoglobin released during surgery is associated with cardiac injury

Patients with valvular heart disease require cardiopulmonary bypass and cardiac arrest. Here researchers at the University of Alabama at Birmingham test the hypothesis that exosomal hemoglobin formed during cardiopulmonary bypass mediates acute cardiac injury in humans and in an animal model system.

Plasma exosomes were collected from arterial blood at baseline and 30 minutes after aortic cross clamp release in 20 patients with primary mitral regurgitation and 7 with aortic stenosis. These exosomes were injected into Sprague-Dawley rats and studied at multiple times up to 30 days. Tissue was examined by hematoxylin and eosin stain, immunohistochemistry, transmission electron microscopy, and brain natriuretic peptide.

Troponin I levels increased from 36 ± 88 ng/L to 3,622 ± 3,054 ng/L and correlated with exosome hemoglobin content (Spearman r = 0.7136, <0.0001, n=24). Injection of exosomes isolated 30 minutes after cross clamp release into Sprague-Dawley rats resulted in cardiomyocyte myofibrillar loss at 3 days. Transmission electron microscopy demonstrated accumulation of electron dense particles of ferritin within cardiomyocytes, in the interstitial space, and within exosomes. At 21 days after injection, there was myofibrillar and myosin breakdown, interstitial fibrosis, elevated brain natriuretic peptide, and LV diastolic dysfunction measured by Echocardiography/Doppler. Pericardial fluid exosomal hemoglobin content is 4-fold higher than simultaneous plasma exosome hemoglobin, suggesting a cardiac source of exosomal hemoglobin.

Red blood cell and cardiac-derived exosomal hemoglobin may be involved in myocardial injury during cardiopulmonary bypass in patients with valvular heart disease.