Background: Cell-free DNA (cf-DNA) is known to be released from injured cells and act as a critical activator of inflammation and the immune system. Patients with COVID-19 could develop respiratory failure and therefore require oxygen therapy. In this study, we hypothesized that circulating cf-DNA level could reflect the severity of COVID-19.
Methods: Analyses of cf-DNA levels were performed on serum samples from 95 hospitalized-patients with confirmed COVID-19 at Showa University Hospital (Tokyo, Japan). Cf-DNA levels were assessed by measuring the copy number of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) using quantitative real-time PCR.
Results: Patients were grouped into Moderate, Severe, and Critical using the severity criteria by the National Institutes of Health in U.S.A. There was no significant difference on both cf-DNA levels between Moderate and Severe groups, and between Severe and Critical groups. Meanwhile, both of the levels were significantly higher in Critical group than Moderate group. Patients were also grouped by their respiratory treatment. Both cf-DNA levels significantly increased in patients with oxygen-supplementation and patients with intubation, compared to those with no oxygen supplementation and with non-intubation, respectively. There was negative association between oxygen saturation (SpO₂) and cf-nDNA levels, not cf-mtDNA.
Conclusion: These results suggest that serum cf-DNA could serve as a useful biomarker to help determining therapeutic management for respiratory failure in COVID-19.