Objective: Recent evidence suggests that insulin resistance may play an important role in the pathogenesis of Alzheimer's disease (AD). In this study, the probable role of insulin resistance in the pathogenesis of AD was investigated in patients with Type 2 Diabetes Mellitus (T2DM).

Methods: Serum amyloid beta (Aβ) (1-42), insulin like growth factor-1 (IGF-1), sirtuin1 (SIRT1) and leptin protein levels were measured in serum samples of control (n = 26), probable AD (n = 26), and probable AD+T2DM patients (n = 12) using ELISA method. Mini mental state examination (MMSE) was performed to the patient and control groups.

Result: Serum IGF-1 significantly increased in the probable AD+T2DM group as compared to the control and probable AD groups (p ˂ 0.05). The levels of serum leptin significantly decreased in the probable AD and AD+T2DM groups as compared to the control (p ˂ 0.05). There were no statistically significant differences in serum Aβ (1-42) and SIRT1 levels among groups (p > 0.05).

Conclusion: The significant decrease in serum leptin levels in AD patients may indicate that it may be a therapeutic marker in AD. The level of serum Aβ peptide and SIRT1 proteins can vary depending on the stage of the disease. Therefore, this study should be supported by more comprehensive studies in terms of the number of patients in advanced stage (Tab. 1, Fig. 4, Ref. 29).