Leukocyte lysosomal enzymes in Alzheimer's disease and Down's syndrome.

Previous studies suggested the possibility of accelerated lysosomal degradation of brain gangliosides in Alzheimer's disease (AD). As AD pathology affects both neural and nonneural tissues, the aim of this study was to determine possible changes of glycosphingolipid metabolism in available peripheral cells in AD and Down's syndrome (DS). The activities of several lysosomal enzymes involved in catabolism of gangliosides and sulfatides were measured in leukocytes from subjects with dementia of the Alzheimer type, DS, and age-matched controls, by fluorimetry and spectrophotometry using specific substrates. The results showed a statistically significant increase of beta-galactosidase activity in both dementia of the Alzheimer type and DS leukocytes when compared with age-matched controls (p <.01 and p <.05, respectively; Student's t test). Not significantly increased activities of beta-galactosidase, beta-hexosaminidase, beta-hexosaminidase A, and slightly decreased activity of arylsulfatase A were observed in control leukocytes with aging. Our results indicate that a metabolic dysfunction and the acceleration of at least some lysosomal catabolic pathways are present in AD and DS nonneural cells.