Peripheral inflammatory biomarkers and risk of Parkinson's disease.

Experimental and postmortem evidence indicates a role of neuroinflammation in the pathogenesis of Parkinson's disease. The authors prospectively examined whether plasma concentrations of inflammatory biomarkers assessed before Parkinson's disease diagnosis were predictive of future risk of the disease in a nested case-control study in the United States (1993-2002), including 84 incident cases and 165 matched controls. Blood was collected from patients on average 4.3 years before the diagnosis. After adjustment for potential confounders, higher level of interleukin-6 was associated with a greater risk of Parkinson's disease. Compared with the lowest quintile, the odds ratios were 1.5 for the second, 1.6 for the third, 2.7 for the fourth, and 3.4 for the fifth quintiles (p for trend = 0.03). In contrast, concentrations of other inflammatory biomarkers including C-reactive protein, fibrinogen, and tumor necrosis factor-alpha receptors were not related to the risk. These data suggest that men with high plasma concentrations of interleukin-6 have an increased risk of developing Parkinson's disease. However, this finding should be interpreted with caution because of the small sample size and the lack of associations with other biomarkers of inflammation.