Circulating miRNA as fine regulators of the physiological responses to physical activity: Pre-analytical warnings for a novel class of biomarkers

MicroRNAs are endogenous non-coding RNAs that post-transcriptionally regulate gene expression by specifically binding the target mRNA and by consequently inducing its degradation. miRNAs can be released into the circulation where they remain stable and they can be measured. Their changes reflect individual biologic adaptation to exposures to specific environmental conditions. As such, measurement of circulating microRNAs represents an opportunity to evaluate biologic changes associated with interventions such as exercise and diet. Physical activity is, indeed, a very important modifying factor for circulating miRNAs. Toward their use in clinical settings several issues should be still solved. Their clinical application is hindered by the high heterogeneity of the analytical procedures used for their measurements. Furthermore, several pre-analytical concerns equally reduce the clinical applicability of miRNA. Pre-analytical phase in sports medicine is an important issue both because, often the conditions in which sampling are performed are peculiar (and not always canonical) and because some of the tested parameters, in the case of professional athletes, enters in routine anti-doping testing and, as such, they should be treated according to precise rules in order to avoid any false positive results. Aim of this review is to give an overview of the main available knowledges about the pre-analytical management of the sample for circulating miRNA evaluation along with the importance of miRNA as regulators of the response to physical activity and their possible future use in anti-doping settings.