Serum insulin-like growth factor-I and amyloid beta protein in Alzheimer's disease: relationship with cognitive function.

AIMS: Previous studies have suggested that insulin-like growth factor-I (IGF-I) deficiency may lead to cognitive deficits in neurodegenerative diseases such as Alzheimer's disease. The present study aimed to investigate the possible relationship between cognitive function and concentration of IGF-I or amyloid beta protein (Aβ) in serum in Alzheimer's patients.

METHODS: A total of 81 Japanese patients were enrolled in this study. Concentrations of IGF-I, Aβ42, and Aβ40 in serum were measured. Two neuropsychological tests, Mini-Mental State Examination and Hasegawa's Dementia Scale-Revised (HDS-R), were also performed. Linear correlations among the age, serum IGF-I, serum Aβ42 or Aβ40, Aβ42/Aβ40 ratio, Mini-Mental State Examination or HDS-R total score, and the scores for six HDS-R subscales were analyzed by regression analysis.

RESULTS: IGF-I showed a significant negative correlation with age (β = -0.357, P = 0.002) and a positive correlation with Aβ42/Aβ40 ratio (β = 0.318, P = 0.007). Serum IGF-I and both the Mini-Mental State Examination and the HDS-R total score also correlated (β = 0.505, β = 0.524, P < 0.01). Among the HDS-R subscales, 'Recall' (ρ = 0.379, P < 0.01), 'Verbal fluency' (ρ = 0.360, P < 0.01), and 'Attention and calculation' (ρ = 0.389, P < 0.01) showed significant positive correlations with serum IGF-I.

CONCLUSION: The results, specifically that lower serum IGF-I was associated with cognitive impairment, suggest that metabolism of IGF-I may be involved in the pathogenesis of cognitive deficits in Alzheimer's disease.