Nourin-Dependent miR-137 and miR-106b: Novel Early Inflammatory Diagnostic Biomarkers for Unstable Angina Patients

Background: Currently, no blood biomarkers exist that can diagnose unstable angina (UA) patients. Nourin is an early inflammatory mediator rapidly released within 5 min by reversible ischemic myocardium, and if ischemia persists, it is also released by necrosis. Nourin is elevated in acute coronary syndrome (ACS) patients but not in symptomatic noncardiac and healthy subjects. Recently, circulating microRNAs (miRNAs) have been established as markers of disease, including cardiac injury and inflammation. Objectives: To profile and validate the potential diagnostic value of Nourin-dependent miR-137 (marker of cell damage) and miR-106b-5p (marker of inflammation) as early biomarkers in suspected UA patients and to investigate the association of their target and regulating genes. Methods: Using Nourin amino acid sequence, an integrated bioinformatics analysis was conducted. Analysis indicated that Nourin is a direct target for miR-137 and miR-106b-5p in myocardial ischemic injury. Two linked molecular networks of lncRNA/miRNAs/mRNAs were also retrieved, including CTB89H12.4/miR-137/FTHL-17 and CTB89H12.4/miR-106b-5p/ANAPC11. Gene expression profiling was assessed in serum samples collected at presentation to an emergency department (ED) from: (1) UA patients (n = 30) (confirmed by invasive coronary angiography with stenosis greater than 50% and troponin level below the clinical decision limit); (2) patients with acute ST elevation myocardial infarction (STEMI) (n = 16) (confirmed by persistent ST-segment changes and elevated troponin level); and (3) healthy subjects (n = 16). Results: Gene expression profiles showed that miR-137 and miR-106b-5p were significantly upregulated by 1382-fold and 192-fold in UA compared to healthy, and by 2.5-fold and 4.6-fold in STEMI compared to UA, respectively. Healthy subjects showed minimal expression profile. Receiver operator characteristics (ROC) analysis revealed that the two miRNAs were sensitive and specific biomarkers for assessment of UA and STEMI patients. Additionally, Spearman's correlation analysis revealed a significant association of miRNAs with the associated mRNA targets and the regulating lncRNA. Conclusions: Nourin-dependent gene expression of miR-137 and miR-106b-5p are novel blood-based biomarkers that can diagnose UA and STEMI patients at presentation and stratify severity of myocardial ischemia, with higher expression in STEMI compared to UA. Early diagnosis of suspected UA patients using the novel Nourin biomarkers is key for initiating guideline-based therapy that improves patients' health outcomes.