Elevated plasma levels of miR-29a are associated with hemolysis in patients with hypertrophic cardiomyopathy.

Background: miR-29a is a small non-coding RNA that is known to repress collagen synthesis. Interestingly, elevated plasma miR-29a was reported to correlate with pronounced myocardial fibrosis in patients with hypertrophic cardiomyopathy. The objective of this study was to elucidate the origin of plasma miR-29a, and evaluate its significance as a biomarker.

Methods: miR-29a expression was evaluated in plasma (n=50) and myocardial samples (n=4) from patients with hypertrophic cardiomyopathy using RT-qPCR.

Results: Although miR-29a was highly expressed in the myocardium, miR-29a plasma levels did not show any correlation with serum troponin I levels (r=-0.12, p=0.43), and the heart does not release significant amounts of miR-29a into the circulation via exosome secretion. Conversely, miR-29a was present in red blood cells, and plasma levels correlated significantly with markers of hemolysis: lactic dehydrogenase (r=0.36, p=0.01) and the absorbance of oxyhemoglobin at 414nm (r=0.39, p=0.006). Furthermore, the association between serum haptoglobin and the maximal blood flow velocity in the left ventricle outflow tract (r=-0.42, p=0.008) indicated that intravascular hemolysis is a manifestation of the disease.

Conclusions: miR-29a is highly expressed in myocardial tissue from patients with hypertrophic cardiomyopathy. In contrast, plasma miR-29a is primarily of nonmyocardial origin and is correlated significantly with the extent of hemolysis observed in these patients.