Inflammatory hypothesis as a link between Alzheimer's disease and diabetes mellitus.

Abstract

The aim of the present study was to evaluate whether there was an inflammation-mediated link between Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) status. An age-matched control group and patient groups designated as AD without treatment (AD); AD under cholinesterase inhibitors (AD-CEI); DM without treatment (DM); DM under oral antidiabetic agents (DM-OAD); AD under treatment, who had newly diagnosed DM (AD-CEI+DM); and DM under treatment, who had newly diagnosed probable AD (DM-OAD+AD) were studied. Serum inflammation status was evaluated by the determination of serum C-reactive protein (CRP), tumor necrosis factor-alpha, interleukin (IL)-1β and IL-6 levels. CRP levels were determined by an immunonephelometric method. The others were assayed by enzyme-linked immunosorbent assay methods. IL-1β levels were found to be significantly lower in the DM group than in the control group (P < 0.01). The AD group had significantly higher serum IL-1β levels than the DM group (P < 0.01). IL-6 levels were significantly higher in the AD and DM groups than in controls (P < 0.01 and P < 0.01). Serum tumor necrosis factor-alpha and CRP levels in the AD (P < 0.05 and P < 0.001, respectively) and DM groups (P < 0.05 and P < 0.001, respectively) were significantly higher when compared with the controls. The presence of AD or DM or therapies of the diseases did not significantly change in serum tumor necrosis factor-alpha levels. The AD-CEI + DM and DM-OAD+AD groups had significantly higher CRP levels than the AD-CEI group (P < 0.05) and DM-OAD groups (P < 0.001), respectively. Serum CRP levels showed a positive correlation with Mini-Mental State Examination scores (r = 0.339, P < 0.01). Our findings support the presence of a low-grade systemic inflammation link between AD and DM. Geriatr Gerontol Int 2016; 16: 1161-1166.