Abstract:In the past few years, the crucial role of different micro-RNAs (miRNAs) in the cardiovascular system has been widely recognized. Recently, it was discovered that extracellular miRNAs circulate in the bloodstream and that such circulating miRNAs are remarkably stable. This has raised the possibility that miRNAs may be probed in the circulation and can serve as novel diagnostic markers. Although the precise cellular release mechanisms of miRNAs remain largely unknown, the first studies revealed that these circulating miRNAs may be delivered to recipient cells, where they can regulate translation of target genes. In this review, we will discuss the nature of the stability of miRNAs that circulate in the bloodstream and discuss the available evidence regarding the possible function of these circulating miRNAs in distant cell-to-cell communication. Furthermore, we summarize and discuss the usefulness of circulating miRNAs as biomarkers for a wide range of cardiovascular diseases such as myocardial infarction, heart failure, atherosclerosis, hypertension, and type 2 diabetes mellitus. One of the major challenges in cardiovascular research is the identification of reliable biomarkers that can be measured routinely in easily accessible samples, such as plasma. Because of their stability in the circulation, miRNAs are currently being explored for their potential as biomarkers for cardiovascular disease. Thus far, distinctive patterns of circulating miRNAs have been found for myocardial infarction, 11 heart failure (HF), 12 atherosclerotic disease, 13 type 2 diabetes mellitus (DM), 14 and hypertension. 15 In the present review, we will discuss the available evidence of the cellular release mechanisms and the nature of the stability of miRNAs in the bloodstream (eg, microparticles, RNA-binding proteins, and HDL). Next, we will discuss the available evidence for a possible function of miRNAs in cell-to-cell communication. Finally, we will review the current knowledge about circulating miRNAs as putative biomarkers in cardiovascular disease. Cellular Release and Stability of Extracellular miRNAsAs early as 1972, it was reported that intact extracellular RNA could be detected in plasma despite the presence of ribonucleases that were expected to destroy any freely circulating RNA. 16 It has therefore been suggested that this extracellular RNA, including miRNAs, is somehow shielded to prevent its degradation. As discussed in the sections below, evidence is now accumulating that miRNAs are protected against degradation by being packaged in lipid vesicles or by being associated with protein or lipoprotein complexes (Figure). Plasma miRNAs in MicroparticlesEl-Hefnawy et al 17 were among the first to show that plasma RNA is protected from degradation by its inclusion in protein or lipid vesicles. Depending on their size and mode of release from cells, these particles are known as exosomes, microvesicles (MVs), or apoptotic bodies. 18 Exosomes are small vesicles (50 -100 nm) that originate from the endosome and are release...

Rationale: Aberrant expression profiles of circulating microRNAs (miRNAs) have been described in various diseases and provide high sensitivity and specificity. We explored circulating miRNAs as potential biomarkers in patients with heart failure (HF). Objective: The goal of this study was to determine whether miRNAs allow to distinguish clinical HF not only from healthy controls but also from non-HF forms of dyspnea. Methods and Results: A miRNA array was performed on plasma of 12 healthy controls and 12 HF patients. From this array, we selected 16 miRNAs for a second clinical study in 39 healthy controls and in 50 cases with reports of dyspnea, of whom 30 were diagnosed with HF and 20 were diagnosed with dyspnea attributable to non-HF-related causes. This revealed that miR423-5p was specifically enriched in blood of HF cases and receiver-operator-characteristics (ROC) curve analysis showed miR423-5p to be a diagnostic predictor of HF, with an area under the curve of 0.91 (P<0.001). Five other miRNAs were elevated in HF cases but also slightly increased in non-HF dyspnea cases. Conclusion: We identify 6 miRNAs that are elevated in patients with HF, among which miR423-5p is most strongly related to the clinical diagnosis of HF. Recent studies have unveiled powerful and unexpected roles for microRNAs (miRNAs) in cardiovascular diseases, including HF. There are estimated to be more than 1000 different miRNAs, many of which are expressed in a tissue and cell-specific manner. 3 It was discovered only recently that miRNAs are also abundantly present in blood, where they can be detected in plasma, platelets, and erythrocytes, as well as in nucleated blood cells. 4 Aberrant expression profiles of miRNAs have been identified in blood of subjects with sickle cell anemia, prostate cancer, lung cancer and myocardial injury. 4 -6 This led us to hypothesize that miRNA profiling can also be used for diagnostic approaches in HF.Here we explored whether circulating miRNAs can be used as biomarkers in patients with HF. We first performed miRNA arrays on RNA isolated from plasma and selected 16 miRNAs expressed differentially in HF patients. Next, we evaluated these miRNAs in a second group of patients, consisting of 50 cases with reports of dyspnea, of whom 30 were diagnosed with HF (HF cases) and 20 were diagnosed to have dyspnea attributable to non-HF causes (non-HF cases). One circulating miRNA in particular, miR423-5p, was able to distinguish HF cases from non-HF cases.In conclusion, we demonstrate a number of miRNAs as putative biomarkers for HF, in particular miR423-5p. MethodsHuman plasma samples were obtained with informed consent under a general waiver by the Academic Medical Center institutional review board for the proper secondary use of human material. For the dyspnea registry, plasma samples were obtained as part of a multicenter effort involving 3 centers in The Netherlands. Experiments described were performed on samples obtained at the Academic Medical Center. For a detailed description of the dyspnea registry,...