Circulating cell-free mitochondrial DNA as a candidate marker of hyperinflammation and immune activation in pre-adolescents, adolescents and young adults with COVID-19 and comorbidities

Abstract

Youth encompasses pre-adolescence (10-14 years), adolescence (15-17 years), and young adulthood (18-24 years). Adolescents in general, particularly those with comorbidities, appear more susceptible to severe COVID-19, a vulnerability also observed in newborns and young infants. The mechanisms underlying this increased risk remain unclear, highlighting the need for early disease biomarkers. Circulating cell-free mitochondrial DNA (ccf-mtDNA), a damage-associated molecular pattern (DAMP), has been linked to systemic inflammation and immune activation during viral infections. This study evaluated plasma ccf-mtDNA levels in pre-adolescents, adolescents, and young adults with and without COVID-19, all presenting respiratory symptoms and predominantly harboring comorbidities, some with coinfections by other respiratory viruses. In this prospective study of 88 participants aged 12-21 years, half tested positive and half negative for SARS-CoV-2 by Reverse-Transcribed Polymerase Chain Reaction (RT-PCR). Comorbidities were present in 75% of COVID-19-positive and 54.5% of COVID-19-negative participants. Coinfections were detected in 52.3% and 25% of tested participants, respectively. Plasma ccf-mtDNA was quantified by a quantitative Real Time PCR (qPCR) targeting the mitochondrial NADH dehydrogenase 2 (ND2) gene or MT-ND2. COVID-19-positive participants exhibited significantly higher ccf-mtDNA levels than both symptomatic COVID-19-negative individuals and healthy controls (p<0.001). Although median levels were numerically higher in severe/critical compared with mild/moderate cases (7,769 vs. 4,649 ccf-mtDNA/mL), the difference was not statistically significant, likely due to limited sample size. In conclusion, elevated ccf-mtDNA distinguishes young individuals with COVID-19 and comorbidities from non-COVID-19 symptomatic participants and healthy controls. Although not linked to disease severity in this preliminary study, ccf-mtDNA may serve as an early biomarker of SARS-CoV-2-induced hyperinflammation and immune activation, supporting further targeted clinical investigations.