Peripheral biomarkers of Parkinson's disease and its correlation with clinical symptoms: a case-control study.

Background: Inflammation significantly impacts Parkinson's disease (PD), yet the intricate relationship between inflammatory markers and PD remains elusive.

Objective: To identify the peripheral biomarkers of PD and its correlation with the motor and non-motor symptoms of PD.

Methods: 79 PD patients and 65 controls were included in this study. Clinical information and the serum levels of IL-8, IL-27, IL-33, β-NGF, AgRP, and TRAILR2 in the participants were collected. Appropriate scales were used to assess the symptoms of PD. For the factors with significant differences in the two groups, multivariable logistic regression was used to determine its relationship with PD. Moreover, spearman correlation was conducted to explore the correlation between the factors and PD related symptoms. The IL-27 level was compared between the cognitively healthy PD group and the mild cognitive impairment in PD (PD-MCI). The serum level of TRAILR2 was positively correlated with age and was not associated with other clinical characteristics related to PD.

Results: Compared to controls, the serum levels of IL-27(P = 0.013) were increased whereas the levels of TRAILR2(P = 0.008) were decreased in PD patients. IL-8, IL-33, β-NGF, and AgRP showed no significant differences between the two groups. After controlling for the other variables, IL-27 was considered as an independent risk factor for PD in the multivariable logistic regression model. The receiver operating characteristic (ROC) curve for diagnosing PD with IL-27 yielded an area under the curve (AUC) of 0.621. Additionally, IL-27 level in PD patients was positively correlated with age, the disease duration, LEDD and negatively correlated with the MoCA scores. However, no significant difference was found in IL-27 levels between cognitively healthy PD and PD-MCI groups.

Conclusion: Elevated serum IL-27 was a risk factor for PD and positively correlated with the cognitive decline in PD.