Peripheral blood inflammatory markers in early Parkinson's disease

The aim of this study was to characterize peripheral inflammatory markers in patients with early Parkinson's disease (PD) and to explore whether these markers contribute to motor and non-motor symptoms. We collected serum from patients with early PD (n = 58) and from healthy control subjects (n = 20). The following inflammatory markers were measured: interleukin (IL)-1β, IL-2, IL-6, IL-10, tumor necrosis factor-α, and high-sensitivity C-reactive protein. The Movement Disorders Society Unified Parkinson's Disease Rating Scale part 3 and Hoehn and Yahr stage were used to assess motor symptoms, and the Non-motor Symptoms Scale, the Cross-Cultural Smell Identification Test, the Montreal Cognitive Assessment, and the Composite Autonomic Symptom Score 31 (COMPASS-31) were used to assess non-motor symptoms. The levels of IL-1β, IL-2, and IL-6 were higher in the PD group than in the control group. However, only IL-1β among those markers remained significant after Bonferroni correction (P = 0.024). In the PD group, the anti-inflammatory cytokine IL-10 levels correlated positively with the COMPASS-31 score (r = 0.277, P = 0.035), whereas no correlation was found between the other inflammatory marker levels and motor or non-motor symptoms. Among the domains of the COMPASS-31, the IL-10 levels correlated only with the gastrointestinal domain (r = 0.358, P = 0.006). Our results suggest increased peripheral inflammation in the early stage of PD, but the role of inflammation in motor and non-motor symptoms is unclear. Although we found a correlation between IL-10 levels and gastrointestinal symptoms, this finding may simply reflect a protective response against inflammatory processes associated with the disease.