Stability of circulating miRNA in saliva: The influence of sample associated pre-analytical variables

Background and aims: Increasing evidence supports the practicability of salivary cell-free (cf) miRNA as liquid biopsy markers in cancers. Its successful translation in the clinical setting requires reproducible approaches for saliva manipulation, in order to control for pre-analytical variables influencing miRNA stability. This study aims to define the optimal conditions to maintain the integrity of saliva during collection, transport and processing with respect to cf-miRNA quantification. Materials and methods: Saliva was collected from 20 healthy subjects and 8 oral cancer patients. Two sampling methods were tested and different storage temperatures and times were evaluated. Salivary expression level of target miRNAs was quantified by qPCR. Comparison between group mean values at specific conditions were performed using paired t-tests. Agreement between measurements was evaluated using a Bland-Altman plot. Results: Different collection methods revealed comparable levels of salivary miR-484 and miR-106b-5p in both subject cohorts. MiRNAs were stable for up to 48 h at 4 °C in saliva supernatant, showing significant alteration after 96 h. Mid-term storage of supernatant at -20 °C decreased miRNA stability significantly compared to standard -80 °C. Conclusions: Cf-miRNA in saliva were slightly altered by collection methods and storage conditions, both in healthy and in pathological contexts, and remained stable for a period of time compatible with main clinical routine needs.