Small RNAs in Blood May Reveal Heart Injury

An increase in certain micro ribonucleic acids (RNAs) circulating in the blood are linked with injury to cardiac muscle and these molecules might provide the basis for a more sensitive diagnostic tool than those currently available.

These small RNA molecules are encoded in the genome, and they fine-tune the expression of genes in the cells that produce them, in addition they also become evident in the blood stream, outside the protective environment of the cell, but at extremely low levels.

Scientists at The Rockefeller University (New York, NY, USA) isolated RNA from left ventricular tissue samples from a total of 47 subjects: 21 patients with advanced heart failure (HF) due to dilated cardiomyopathy (DCM), 13 patients with advanced HF due to ischemic cardiomyopathy (ICM), 8 individuals without heart disease (NFs), and 5 fetuses (FETs). They compared their microRNA results with those of the protein cardiac troponin currently used to diagnose injury to heart muscle. This protein occurs within healthy heart muscle cells, but when injured, these cells leak cardiac troponin out into the blood stream, causing its levels to spike in circulation.

The RNA concentration and purity was determined by NanoDrop micro-volume UV- spectrophotometry (Thermo Scientific; Waltham, MA, USA) or using the fluorometric Molecular Probes Qubit RNA Assay (Life Technologies; Carlsbad, CA, USA). The RNA integrity of the tissue RNA samples was determined by a microchip based capillary electrophoresis (Agilent Bioanalyzer 2100; Santa Clara, CA, USA). Cardiac troponin I (cTnI) and B-type natriuretic peptide (BNP) were both measured by a chemiluminescent microparticle immunoassay performed for quantitative determination of BNP in plasma or cTnI in serum using the ARCHITECT iSystem (Abbott; Abbott Park, IL, USA).

The circulating small RNA profile was dominated by microRNAs, and fragments of transfer RNAs (tRNAs) and small cytoplasmic RNAs. Heart- and muscle-specific circulating miRNAs (myomirs) increased up to 140-fold in advanced HF, which coincided with a similar increase in cardiac troponin I (cTnI) protein, the established marker for heart injury. In stable HF, circulating miRNAs showed less than a five-fold difference compared with normal, and myomir and cTnI levels were only captured near the detection limit. These findings provide the underpinning for miRNA-based therapies and emphasize the usefulness of circulating miRNAs as biomarkers for heart injury, performing similar to established diagnostic protein biomarkers.

Thomas Tuschl, PhD, the lead author of the study said, “RNA sequencing can capture a wide spectrum of microRNAs and other potentially interesting RNA molecules from a tiny sample. This opens the possibility of finding many promising biomarkers like those we found from heart muscle, leading to a more universal test then the current monitoring of single proteins. Some technological barriers must still be overcome before tests based on RNA biomarkers like these can be brought into the clinic, but the potential is there for an entirely new type of clinically important diagnostic tool.” The study was published on July 29, 2014, in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

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