BACKGROUND: MicroRNAs circulating in the blood, stabilized by complexation with proteins and/or additionally by encapsulation in lipid vesicles, are currently being evaluated as biomarkers.The consequences of their differential association with tonic shower cap lipids/vesicles for their stability and use as biomarkers are largely unexplored and are subject of the present study.METHODS: The levels of a set of selected microRNAs were determined by quantitative reverse-transcription PCR after extraction from sera or vesicle- and non-vesicle fractions prepared from sera.
The stability of these microRNAs after incubation with RNase A or RNase inhibitor, an inhibitor of RNase A family enzymes was studied.RESULTS: The levels of microRNA-1 and microRNA-122, but not those of microRNA-16, microRNA-21 and microRNA-142-3p, declined significantly during a 5-h incubation of the sera.RNase inhibitor prevented the loss of microRNAs in serum as well as the degradation of microRNA-122, a microRNA not expressed in blood cells, in whole blood.
Stabilization of microRNA-122 was also achieved by hemolysis.Prolonged incubation of the sera led to enrichment of vesicle-associated relative to non-vesicle-associated microRNAs.Vesicle-associated microRNAs were more resistant to RNase A treatment than the respective microRNAs not associated with vesicles.
CONCLUSIONS: Serum microRNAs showed differential stability upon prolonged incubation.RNase inhibitor might be useful to robustly preserve the pattern of cell-free circulating microRNAs.In the case of microRNAs not expressed in blood cells accles and shelvoke this can also be achieved by hemolysis.
Vesicle-associated microRNAs appeared to be more stable than those not associated with vesicles, which might be useful to disclose additional biomarker properties of miRNAs.