Telomere Length, Oxidative Stress Markers, and Related miRNAs in Non-Invasive Samples of Mild COVID-19 Cases

Oxidative stress and inflammation influence immune response and epigenetic mechanisms in infectious diseases. In mild COVID-19, host-encoded miRNA profiles remain underexplored, although they reveal mechanistic insights into disease pathogenesis. This study evaluated ageing and oxidative stress biomarkers (telomere length (TL), TBARS, 8-OHdG, and circulating related-miRNA expression) in 75 mild cases and 30 non-COVID-19 controls. TL correlated with age (R = -0.384, p = 0.005) and was shorter in cases compared to controls (rTL 1.46 ± 0.51 vs. 0.99 ± 0.37; p < 0.001), being similar between saliva and blood samples (p = 0.917). miR-138-5p was upregulated in COVID-19 cases (p = 0.026) and correlated with 8-OHdG (R = 0.403, p = 0.05), which was increased in cases (p = 0.040); miR-210-3p was downregulated in infected individuals (p = 0.008), while miR-182-5p expression correlated with TBARS (R = 0.582, p = 0.018). miR-34a-5p and miR155-5p expression was not altered in mild COVID-19. These findings suggest early systemic cellular damage in mild COVID-19 and highlight miR-138-5p and miR-182-5p as potential early biomarkers of oxidative stress.