There is no correlation between peripheral inflammation and cognitive status at diagnosis in Alzheimer's disease

Besides the neurofibrillary tangles and amyloid plaques, an inflammatory process is involved at central and peripheral levels in Alzheimer's disease (AD). We aimed to determine whether peripheral inflammatory parameter levels, in plasma and in peripheral blood mononuclear cells (PBMCs), could be correlated with the cognitive status at the time of AD diagnosis.

Patients were included at diagnosis with MMSE score between 16 and 25 and were naive of symptomatic treatment for AD. C-reactive protein >10 mg/L and any acute or chronic inflammation were considered as exclusion criteria. Cognitive assessment also included the ADAScog scale. Plasma interleukins (IL)-1β, IL-6, tumor necrosis factor (TNF)-α and the chemokine ligand 5 (CCL5) were measured using Luminex(®) X-MAP(®) technology. A subgroup of patients also underwent measures of these parameters in extracellular and intracellular compartments of PBMCs (ancillary study).

One hundred and nine patients were included; mean age 79.4 ± 6.8 years with 37 patients in the ancillary study. The mean values of IL-1β, TNF-α, IL-6 and CCL5 values were 1.49, 7.18, 3.09 and 69,615.81 pg/mL, respectively. No correlation between plasma cytokines or chemokine levels and cognitive scores was found. In PBMCs, the levels of cytokines were detectable but did not either show any correlation with cognitive scores.

Our data indicate that at diagnosis, peripheral levels of cytokines and CCL5 display low values without any correlation with the cognitive status. Further results of our study will show if these circulating markers are related to the progression of AD.