Various epidemiological studies have shown that type 2 diabetes and metabolic syndrome are highly correlated with Alzheimer's disease (AD). Here, we sought to assess the impact of metabolic syndrome characteristics on the progression of AD. Five-week-old male, spontaneously hypertensive (n = 32) and Wistar Kyoto (abbreviated WKY; n = 8) rats were divided into 5 groups (each n = 8): WKY, hypertension (HTN), streptozotocin-induced diabetes (STZ), high-fat diet (HFD), and STZ + high-fat diet-induced diabetes mellitus (DM). All animals were sacrificed and samples of the blood, liver, and brain were collected for further biological analysis. During the 15-week period of induction, the STZ and DM groups (animals injected with low-dose STZ) had significantly higher fasting glucose levels; the HFD group had elevated insulin levels, but normal blood glucose levels. The HFD and DM groups had hypercholesterolemia and higher hepatic levels of triglycerides and cholesterol. Additionally, correlations between HFD and elevated brain amyloid-beta 42 (Aβ-42), hyperglycemia and down-regulation of brain insulin receptor, and serum Aβ-42 and hepatic triglyceride concentrations (r2 = 0.41, p < 0.05) were observed. Serum C-reactive protein and malondialdehyde did not appear to have a significant influence on the association with biomarkers of AD. Thus, our study demonstrated that rats with characteristics of metabolic syndrome had a large number of biomarkers predicting AD; however, no relationship between traditional inflammatory and oxidative markers and AD was found. Further studies are necessary to prove that these findings in rats are relevant to AD processes in humans.
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