Correlation between insulin-degrading enzyme versus total tau and selected cytokines in patients with Alzheimer´s disease compared to non-demented controls

It has been increasingly recognized that the pathological progress of Alzheimer´s disease (AD) is connected to metabolic function and inflammation. Insulin-degrading enzyme (IDE) is essential for glucose metabolism and the degradation of amyloid-β. We aimed to explore the associations between IDE, total tau, and cytokines levels in plasma from subjects with AD and non-demented controls. Plasma samples (18 patients diagnosed with AD and 6 non-demented controls) from the Netherlands Brain Bank were used to analyze IDE levels and total tau with an enzyme-linked immunosorbent assay. Cytokines were analyzed with Luminex custom plex assays for interleukin (IL)-6, IL-8, IL-10, and tumor necrosis factor-alpha (TNF-α). Results were analyzed using the Mann-Whitney U and Spearman´s rank correlation tests. Total tau in plasma was significantly increased in AD subjects compared to non-demented control subjects (p = 0.044). Total tau was positively correlated with IDE levels in plasma in all subjects (r = 0.494, p = 0.017). Significant correlations could be demonstrated between plasma levels of IDE and IL-6 (r = 0.546, p = 0.019), IL-8 (r = 0.664, p = 0.003), IL-10 (r = 0.833, p < 0.001), and TNF-α (r = 0.633, p = 0.005) in subjects with AD, but not in non-demented controls. Results from this study suggest that plasma IDE levels may be associated with inflammation and neurodegeneration and could potentially be a target for future diagnostic and treatment strategies.