Diagnostic potential of circulating cell-free microRNAs for community-acquired pneu-monia and pneumonia-related sepsis

Cell-free microRNAs (miRNAs) are transferred in disease state including inflammatory lung diseases and are often packed into extracellular vesicles (EVs). To assess their suitability as biomarkers for community-acquired pneumonia (CAP) and severe secondary complications such as sepsis, we studied patients with CAP (n=30), sepsis (n=65) and healthy volunteers (n=47) subdivided into a training (n=67) and a validation (n=75) cohort. After precipitating crude EVs from sera, associated small RNA was profiled by Next-Generation Sequencing (NGS) and evaluated in multivariate analyses. A subset of the thereby identified biomarker candidates was validated both technically and additionally by reverse transcription quantita-tive real-time PCR (RT-qPCR). Differential gene expression (DGE) analysis revealed 29 dif-ferentially expressed miRNAs in CAP patients when compared to volunteers, and 25 miRNAs in patients with CAP, compared to those with sepsis. Sparse-partial least discriminant analysis separated groups based on 12 miRNAs. Three miRNAs proved as a significant biomarker sig-nature. While expression levels of miR-1246 showed significant changes with an increase in overall disease severity from volunteers to CAP and to sepsis, miR-193a-5p and miR-542-3p differentiated patients with an infectious disease (CAP or sepsis) from volunteers. Cell-free miRNAs are potentially novel biomarkers for CAP and may help to identify patients at risk for progress to sepsis, facilitating early intervention and treatment.