The Interaction Between Neuroinflammation and β-Amyloid in Cognitive Decline in Parkinson's Disease

Activated microglia have been reported to play an important role in Parkinson's disease (PD). A more rapid cognitive decline has been associated with deposits of β-amyloid. In this study, the aim was to evaluate the role of brain β-amyloid and its relationship with activated microglia in PD patients with normal and impaired cognition. We studied 17 PD patients with normal cognition (PDn), 12 PD patients with mild cognitive impairment (PD-MCI), and 12 healthy controls (HCs) with [¹¹C] Pittsburgh compound B (PIB) to assess the impact of β-amyloid deposition in the brain on microglial activation evaluated using the translocator protein 18-kDa (TSPO) radioligand [¹⁸F]-FEPPA. [¹¹C] PIB distribution volume ratio was measured in cortical and subcortical regions. [¹⁸F]-FEPPA total distribution volume values were compared for each brain region between groups to evaluate the effect of PIB positivity while adjusting for the TSPO rs6971 polymorphism. Factorial analysis of variance revealed a significant main effect of PIB positivity in the frontal lobe (F_{(1, 34)} = 7.1, p = 0.012). Besides the frontal (p = 0.006) and temporal lobe (p = 0.001), the striatum (p = 0.018), the precuneus (p = 0.019), and the dorsolateral prefrontal cortex (p = 0.010) showed significant group × PIB positivity interaction effects. In these regions, PD-MCIs had significantly higher FEPPA V_T if PIB-positive. Our results indicate an interaction between amyloid-β deposition and microglial activation in PD. Further investigations are necessary to evaluate if amyloid deposits cause neuroinflammation and further neurodegeneration or if increased microglia activation develops as a protective response.