Comparison of Circulating MicroRNAs and Cardiac Troponin I Following Brief Ischemia‐Induced Myocardial Stunning

Abstract

ObjectiveOur laboratory has recently shown that a single episode of brief myocardial ischemia leading to reversible stunning is associated with a significant increase in serum cardiac troponin I (cTnI) in swine. The time‐course of cTnI elevation is delayed and reflects myocyte injury associated with apoptosis in the absence of pathological evidence of necrosis or infarction. In the present study, we compared this pattern of cTnI release to that of several circulating microRNAs (miRNAs) that have shown promise as novel biomarkers of myocardial ischemia to determine whether miRNAs are released into the circulation following brief ischemia‐induced stunning.MethodsClosed‐chest propofol‐anesthetized swine (n=8) were subjected to a 10‐minute occlusion of the distal left anterior descending coronary artery (LAD) to produce brief myocardial ischemia without infarction. Serial echocardiography was performed to evaluate left ventricular function before, during, and after ischemia. Circulating plasma concentrations of miR‐1, miR‐133a, miR‐133b, and miR‐499 were measured by quantitative RT‐PCR at baseline as well as 1‐hour and 24‐hours after reperfusion and compared to serum cTnI values detected by a porcine‐specific ELISA. PCR‐derived quantification cycle (Cq) values were normalized to a synthetic control (cel‐miR‐39) that was spiked‐in during RNA extraction and all data were expressed as a fold‐change vs. baseline.ResultsAnterior wall thickening became dyskinetic during LAD occlusion (61±2% to −6±2%, p<0.001) and remained depressed one‐hour after reperfusion (39±4%, p<0.01), indicative of myocardial stunning. An ~5‐fold increase in serum cTnI was observed 1‐hour after reperfusion (from 13±6 to 51±17 ng/L, p<0.05), followed by a marked, ~200‐fold elevation at 24‐hours (1021±574 ng/L, p<0.01 vs. baseline). Similarly, the circulating concentration of all four miRNAs tended to increase between 1‐hour and 24‐hours post‐reperfusion, although relative changes were variable (Figure). For example, miR‐1 was not significantly elevated 1‐hour after reperfusion but tended to be higher at 24‐hours, while miR‐133a and miR‐133b exhibited low, but significantly elevated concentrations at 1‐hour that rose to ~10‐fold higher levels at 24‐hours. The pattern of miR‐499 release was most similar to that of serum cTnI and was characterized by a 7‐fold elevation 1‐hour post‐reperfusion, followed by a large ~500‐fold increase 24‐hours later.ConclusionCirculating concentrations of several miRNAs are increased following a single episode of brief myocardial ischemia‐induced stunning in the absence of pathological necrosis or infarction. The relative magnitude of elevation varies among miRNAs, but the time‐course generally follows a pattern of delayed release that is comparable to that exhibited by cTnI. These results demonstrate that myocyte necrosis is not required for ischemia‐induced release of cardiac miRNAs, which may have implications for the use of circulating miRNAs as biomarkers for the clinical detection of myocardial infarction.Support or Funding InformationFunding Sources: The National Heart Lung and Blood Institute (HL‐055324, HL‐061610, and F32HL‐114335), the National Center for Advancing Translational Sciences (UL1TR001412), the Department of Veterans Affairs (1IO1BX002659) and the Albert and Elizabeth Rekate Fund in Cardiovascular Medicine.