Extracellular DNA and Deoxyribonuclease Activity as Potential Biomarkers of Inflammation in Multiple Sclerosis.

Neuroinflammation plays a critical role in the pathophysiology of multiple sclerosis (MS), involving complex interactions between reactive oxygen species (ROS), cytokines, chemokines, and immune cells. Among these, neutrophils contribute to sustained inflammation through degranulation, ROS production, and the release of neutrophil extracellular traps (NETs). Extracellular DNA (ecDNA), a key component of NETs, may act as an autoantigen, promoting chronic inflammation and tissue damage. Additionally, impaired NETs and ecDNA degradation by deoxyribonucleases (DNases) may contribute to persistence of inflammation. The aim of the present study was to determine the levels of ecDNA and DNase activity in both blood plasma and cerebrospinal fluid (CSF) in newly diagnosed, treatment-naïve adult patients with relapsing-remitting MS and whether it correlates with disease severity and inflammatory activity in MS. Fifty-one treatment-naïve relapsing-remitting MS patients without disease-modifying therapy and 16 healthy controls (HC) were included in our study. Blood and CSF samples were analyzed for ecDNA, mitochondrial DNA (mtDNA) levels, and DNase activity. Correlations with inflammatory cytokines, oxidative stress, MRI lesion burden, and the expanded disability status scale (EDSS) were analyzed. MS patients exhibited significantly elevated ecDNA levels and reduced DNase activity in blood plasma compared to HC. EcDNA levels positively correlated with inflammatory cytokines, oxidative stress, and disease severity (EDSS). Furthermore, ecDNA and mtDNA levels in CSF positively correlated with inflammatory gadolinium-enhancing MRI lesions. Interestingly, no DNase activity was detected in CSF in both MS patients and HC. Our findings demonstrate that MS patients exhibit significantly elevated ecDNA levels and reduced DNase activity in blood plasma, which correlate with inflammatory cytokines, oxidative stress, and disease severity (EDSS). Additionally, increased ecDNA and mtDNA levels in CSF are associated with higher inflammatory activity, as reflected by gadolinium-enhancing MRI lesions. Considering the pro-inflammatory nature of ecDNA in perpetuating sterile inflammation, these results suggest a potential role of circulating nucleic acids in MS pathogenesis. Furthermore, impaired DNase activity may contribute to the persistence of ecDNA, potentially sustaining pro-inflammatory state in MS. Nevertheless, it remains unclear whether elevated ecDNA actively contributes to neuroinflammation or simply reflects ongoing immune activation. Further research is needed to elucidate the mechanisms underlying ecDNA release and degradation and its implications in MS progression.