Reliable New Biomarkers of Mitochondrial Oxidative Stress and Neuroinflammation in Cerebrospinal Fluid and Plasma from Alzheimer’s Disease Patients: A Pilot Study

Mitochondrial oxidative stress and neuroinflammation are involved in the onset and progression of Alzheimer's disease (AD). Novel reliable, circulating biomarkers related to these processes were searched in cerebrospinal fluid (CSF) and plasma samples. Paired CSF and plasma samples from 20 subjective memory complaints (SMC) subjects, 20 mild cognitive impairment (MCI) due to AD subjects, and 20 Alzheimer's dementia (ADd) patients were analyzed. Protein amounts of manganese-containing superoxide dismutase 2 (SOD2), cell-free mitochondrial DNA (cf-mtDNA) level, DNase I, and matrix metalloproteinases 2 and 9 (MMP-2 and MMP-9) activities were determined. As for SOD2, an MCI male-specific significant increase in both biofluids and an ADd male-specific significant decrease in plasma were found. No significant differences were demonstrated in cf-mtDNA level. An ADd-specific significant increase in plasma DNase I and MMP-2 activities was found. A SMC female-specific significant higher value in CSF MMP-9 activity in comparison to male counterparts was demonstrated. The present results suggest a male patient-specific (MCI and ADd) regulation of SOD2 expression in plasma and support an ADd-specific increase in plasma DNase I and MMP-2 activities. Therefore, the potential of SOD2 amount, DNase I, and MMP-2 activities in plasma as new markers of ADd should be explored. The SMC female-specific high activity of MMP-9 might contribute to AD female-sex bias.