Exploratory Analysis of Cerebrospinal Fluid IL-6 and IL-17A Levels in Subcortical Small-Vessel Disease Compared to...

Background/Objectives: Low-grade inflammation in the form of microglial activation may be involved in neurodegenerative and vascular dementias. Subcortical small-vessel disease (SSVD) is the main form of vascular dementia, associated with brain barrier dysfunction and endothelial and monocyte activation. IL-6 and IL-17A are known proinflammatory cytokines that contribute to the disruption of blood-brain barrier integrity and microvascular dysfunction, features that are central to SSVD pathophysiological pathways. We herein compared cerebrospinal fluid (CSF) IL-6 and IL-17A concentrations in SSVD and AD patients as well as control subjects and examined the potential associations among IL-6 and IL-17A levels with cognitive and ΜRΙ changes. The albumin quotient (Qalb) was also calculated. Methods: CSF IL-6 and IL-17A (18 SSVD, 17 AD, and 12 healthy controls) were measured with solid-phase sandwich ELISAs, while albumin levels were measured by immunonephelometry. MMSE, FAB, and the CLOX tests were used for cognitive assessment and MRI was used for atrophy and white matter hyperintensities. Results: Significantly elevated CSF levels of Qalb and IL-6 were found in SSVD patients compared to both AD (p = 0.02) and controls (p = 0.002), respectively. Moreover, CSF IL-6 levels displayed a significant inverse correlation with CLOX2 scores (r = -0.641, p = 0.02), as well as a positive correlation with the total normalized CSF volume (r = 0.7, p = 0.01). CSF IL-17A levels were found to be reduced in SSVD patients, compared to controls and AD patients (p < 0.0001 and p = 0.002, respectively). The IL-6/IL-17A ratio with a cut-off value > 1.004 displayed a sensitivity of 83.33% (95%CI; 60.78% to 94.16%) and a specificity of 68.97% (95%CI; 50.77% to 82.72%) for the discrimination of SSVD from AD patients and controls. Conclusions: In the present pilot single-center study, we found increased CSF IL-6 and IL-6/IL-17A ratio levels in SSVD patients that correlated with reduced scores in the CLOX2 test and increased CSF volume. These preliminary findings deserve further evaluation in larger cohorts in order to elucidate their potential as surrogate biomarkers for the discrimination of SSVD from AD pathology.