Physical activity and diurnal variation have no impact on plasma microRNA-140 expression levels in patients with knee osteoarthritis and healthy controls.

Objective: This study aimed to determine whether physical activity or diurnal variation influence circulating microRNA-140-3p (miR-140-3p) and miR-140-5p expression levels in patients with knee osteoarthritis (OA) compared to healthy controls. Method: Twenty-one patients with knee OA and ten healthy controls ran on a treadmill for 20 ​min and blood samples were taken prior to and after running. To assess diurnal variation, blood samples were drawn at six different times during a 24-h period. RNA was extracted from plasma and used for cDNA synthesis. Expression levels were assessed with real-time quantitative polymerase chain reaction and compared between patients and controls. Results: All participants had detectable expression levels of miR-140-3p and miR-140-5p. A paired analysis could not demonstrate statistically significant differences between the groups. Conclusions: Plasma miR-140-3p and miR-140-5p expression levels were found in all samples; however, the expression levels were not affected by physical activity and did not show diurnal variation. The observation of stable miR-140 expression supports its potential as a reliable biomarker for OA, providing a methodological foundation for future diagnostic and translational studies.