Monoaminergic Disfunctions and Misfolded Proteins levels in the Alzheimer’s Disease Continuum

Abstract

AbstractBackgroundMonoaminergic systems are pharmacologically modulable and therefore both a target for symptomatic therapies and a window for the study of disease progression. Although these mechanisms are unclear. We explore the progression and the distribution of monoaminergic deficits in the Alzheimer’s Disease (AD) continuum, along with the accumulation of misfolded pathological proteins.MethodWe included 50 patients with Alzheimer’s Disease (AD) and 42 Healthy Controls (HC). We acquired brain [18F]FDG‐PET images as a marker of neurodegeneration and MMSE as a measure of global cognitive functioning. We performed voxel‐based analysis between AD vs. HC. Using JuSpace toolbox we explored the correlation between [18F]FDG‐PET images and PET maps of dopamine (DAT), serotonin (SERT), noradrenaline (NAT) and choline vesicular (VAChT) transporters cortical distribution. Moreover, we evaluated relative hypometabolism in the main cholinergic nucleus (Meynert nucleus). We divided in two groups the AD patients based on MMSE score (AD Dementia ‐ADD‐ <24; MCI ≥24), to explore the association between monoaminergic disfunction and pathological proteins burden, across the AD continuum.ResultSample characteristics are provided in Table 1. Results from voxel‐based analysis are shown in Figure 1. In the whole AD group, the distribution of relative cortical hypometabolism was associated with a significant reduction of VAChT availability (p = 0.018). This association remained significant when considering the ADD (p = 0.006), but not the MCI group. Figure 2.β‐amyloid42 levels and β‐amyloid42/40 ratio were inversely correlated with VAChT in the ADD group (p = 0.003; p = 0.038, respectively). No correlation was observed in the MCI group. Lastly, there was no correlation between Meynert nucleus relative hypometabolism and misfolded proteins levels in all groups.ConclusionIn the ADD phase we showed a significant damage in the cortical regions targeted by the cholinergic system. This result was not evident among the other systems studied, nor in the MCI phase. This provides an explanation of the reduction of the cholinesterase inhibitors efficiency in the dementia phase. Moreover, we showed that β‐amyloid accumulation was not associated with Meynert Nucleus degeneration, but that impacted on cholinergic function via damage accumulation in the cortical areas targeted by the cholinergic system.