Relationship between cortisol, Interleukin-6 and homocysteine in Alzheimer's disease

Abstract

Objective: Alzheimer's disease (AD) is characterised by progressive cognitive decline due to neurodegeneration. Over activation of the hypothalamic-pituitary-adrenal axis, oxidative stress and inflammation potentially damage the neuronal system, affecting cognition.

Aim: This study aimed to assess the relationship between serum cortisol, Interleukin-6 (IL-6) and homocysteine (Hcy) levels in AD.

Methods: Case-Control observational study consisting of 71 patients with AD and 70 healthy controls above 60 years of age. Serum samples were analysed for cortisol, IL-6 and Hcy levels using chemiluminescence immunoassay (Immulite 1000) technique. Cognitive functions were measured using the Mini-Mental State Examination (MMSE) Score. AD subjects were categorised based on the modified Kuppuswamy socioeconomic status scale. Statistical evaluation was conducted using SPSS Statistics software. Group data were analysed using a two-tailed Student's t-test, analysis of variance (ANOVA), the Mann-Whitney U test and Pearson's correlation test.

Results: Serum cortisol, IL-6 and Hcy levels were significantly increased (p < 0.01) in AD (cortisol: 19.69 ± 8.96 ug/dl; IL-6: 10.27 ± 2.76 pg/ml; Hcy: 23.29 ± 3.81 μmol/l), as compared with the controls (cortisol: 13.37 ± 5.59 ug/dl; IL-6: 3.37 ± 0.79 pg/ml; Hcy: 8.25 ± 2.36 μmol/l). MMSE scores in AD were negatively correlated with cortisol, IL-6 and Hcy levels.

Conclusions: Serum cortisol, IL-6 and Hcy levels are independent biomarkers for AD progression. Hypercortisolaemia, hyperhomocysteinemia and inflammation play important roles in AD-related cognitive dysfunction and are interlinked.

Keywords: Alzheimer's disease; Interleukin-6; cortisol; homocysteine.

Figure 1.

Correlations between parameters in the AD group (a) MMSE score and cortisol, (b) MMSE score and IL-6 (c) MMSE and Hcy