Cerebrospinal fluid of patients with senile dementia of Alzheimer's type shows an increased inhibition of alpha-chymotrypsin.

The inhibition of alpha-chymotrypsin induced by cerebrospinal fluid from patients with senile dementia of Alzheimer's type, vascular dementia, and nondemented controls was investigated. We optimized the sensitivity of the assay so that the inhibition of alpha-chymotrypsin could be measured in all samples. The competitive inhibition was proportional to the amount of cerebrospinal fluid (CSF) added to the reaction mixture. After correction for protein concentration, the inhibition was higher with CSF from patients with senile dementia of Alzheimer's type than with those from patients with vascular dementia or controls. Inhibitory activity appeared to be specific for alpha-chymotrypsin because no inhibition for papain was found. Moreover, the depletion of alpha 1-antichymotrypsin from CSF by immunoadsorption revealed that this serpin was responsible for the disappearance of the inhibitory activity. Our findings suggested that the increased alpha-chymotrypsin inhibitory activity might represent an in vivo functional index of an abnormal protease metabolism in patients with Alzheimer's disease.