Age-Dependent Change in the Levels of Aβ40 and Aβ42 in Cerebrospinal Fluid from Control Subjects, and a Decrease in the Ratio of Aβ42 to Aβ40 Level in Cerebrospinal Fluid from Alzheimer’s Disease Patients

Abstract
In order to address an age-dependent alteration in the concentration of β-amyloid polypeptides (Aβs) within the central nervous system and its probable predisposition to amyloidgenesis in Alzheimer’s disease (AD), we measured two species of soluble Aβs, Aβ40 and Aβ42, in cerebrospinal fluids (CSF) from randomly selected Japanese control subjects at various ages (n = 33) and then compared these data with those of probable Japanese AD patients (n = 23). CSF concentrations of Aβ40 and Aβ42 peptides were age-dependent (ANOVA, Bonferroni’s multiple comparison; p < 0.01 and p < 0.05, respectively) and were lower in the infant than in adults. From mid-20, the Aβ40 concentrations were decreasing while Aβ42 were rather stable. Aβs in CSF from AD patients (n = 23), whose ε4 allele frequency of the apolipoprotein E gene was higher than in controls (n = 83, p < 0.03), were not statistically different from those of age-matched controls (n = 13). A linear relationship was detected between the Aβ40 concentration and the Mini-Mental State Examination score (p < 0.05). The ratio of the Aβ42 to the Aβ40 level measured in the AD CSF samples was approximately 38% decreased compared to age-matched controls (p < 0.05). These data suggest that the physiological metabolism of soluble Aβs in the brain is regulated in an age-dependent manner, and that the ratio of Aβ42 to Aβ40 level in the CSF would be a useful marker for monitoring progression of AD.

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