Diagnostic Potential of Extracellular MicroRNA in Respiratory Diseases

Lack of markers of subclinical disease state and clinical phenotype other than pulmonary function test has made the diagnosis and interventions of environmental respiratory diseases a major challenge. MicroRNAs (miRNAs), small non-coding single stranded RNAs, have emerged as potential disease-modifier in various environmental respiratory diseases. They can also be found in various body fluids and are remarkably stable. Because of their high stability, disease-specific expression, and the ease to detect and quantify them have raised the potential of miRNAs in body fluids to be useful clinical diagnostic biomarkers for lung disease phenotyping. In the present review, we provide a comprehensive overview of progress made in identifying miRNAs in various body fluids including blood, serum, plasma, bronchoalveolar lavage (BAL) fluid, and sputum as biomarkers for a wide range of human respiratory diseases such as acute lung injury/acute respiratory distress syndrome (ALI/ARDS), idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), and asthma. Finally, we discuss several challenges remain to be concerned and suggest few disease-specific and non-specific miRNAs to become part of future clinical practice.