Degradation of serum microRNAs during transient storage of serum samples at 4℃

Background Numerous studies demonstrate the potential of circulating microRNAs as non-invasive biomarkers for several diseases. Circulating microRNAs are much more stable than mRNAs and remain largely intact even after prolonged incubation at room temperature. However, recent reports show that microRNAs in serum or plasma samples have diverse stabilities. The aim of this pilot study is to evaluate the stabilities of miR-92a, miR-122 and miR-145 in serum during transient storage at 4℃ before freezing. Methods Serum samples were stored for 24 h at 4℃, and then RNA was extracted from whole serum or extracellular vesicles in serum. Total Exosome Isolation Reagent (from serum) was used for the fractionation of extracellular vesicles. Reverse transcription and real-time PCR of microRNAs were performed using the TaqMan MicroRNA Assays for miR-92a, miR-122 and miR-145. Results MiR-122 and miR-145 were degraded rapidly in serum; the concentrations dropped to 35.9% ( P < 0.001) and 29.3% ( P < 0.0001), respectively. These microRNAs in extracellular vesicles exhibited similar instability; the concentrations were 52.2% ( P < 0.05) and 56.5% ( P < 0.01), respectively. On the other hand, no significant degradation of miR-92a was observed (whole serum: P = 0.052, extracellular vesicles: P = 0.196). Conclusions MiR-122 and miR-145 in serum are extremely unstable and could be degraded during transient storage of serum at 4℃ prior to freezing.