Acetylcholinesterase and its association with heparan sulphate proteoglycans in cortical amyloid deposits of Alzheimer's disease.

Previous studies have used a sensitive histochemical technique to demonstrate acetylcholinesterase and butyrylcholinesterase within the pathological lesions of Alzheimer's disease. In this study, we used this technique to show that acetylcholinesterase localized in either frozen or fixed neocortical tissue sections is removed after treatment with various glycosaminoglycans, heparinases or proteases. Heparan sulphate, heparinase lyase type I and to a lesser degree, heparin and chondroitin sulphate were effective in solubilizing a large part of the cholinesterase activity. At physiological concentrations, the protease papain or trypsin readily removed activity but collagenase or pronase were relatively less effective. Peptide protease inhibitors and divalent metals did not exhibit any clear effect. The specificity of these observations was shown by inhibition of activity with various anticholinesterases including diisofluorophosphate. Our results suggest that acetylcholinesterase is anchored to and may be released from the heparan sulphate glycosaminoglycans shown to be contained in the lesions. We further suggest that the localization of cholinesterases is closely associated with the accumulation of the glycosaminoglycans in amyloid plaques and neurofibrillary tangles.

Transferrin receptors of rat and human brain and cerebral microvessels and their status in Alzheimer's disease.

We studied the regional distribution of specific [125I]transferrin binding to transferrin receptors in the brains and cerebral microvessels of humans and rats. We also assessed transferrin receptors in subjects with Alzheimer's disease. Human diferric [125I]transferrin bound to regional brain and cerebral microvessels with high affinity (dissociation constants of 1-10 nM), and the maximal binding densities ranged from 30 to 90 pmol/mg protein in the brain and were several-fold higher in cerebral microvessels. In Alzheimer's disease, transferrin receptor densities were significantly reduced in the hippocampus and the temporal and occipital cortex but were unchanged in the frontal and parietal cortex and the cerebellum. Although [125I]transferrin binding was higher in cerebral microvessels from subjects with Alzheimer's disease than in those of age-matched controls, this difference did not attain statistical significance. These results suggest that transferrin receptor density was decreased in some cortical areas including the hippocampus in Alzheimer's disease but relatively unchanged in cerebral microvessels.

Serum amyloid P immunoreactivity in hippocampal tangles, plaques and vessels: implications for leakage across the blood-brain barrier in Alzheimer's disease.

Serum amyloid P (SAP) has been shown to be consistently present in all types of amyloid deposits except cerebral lesions of neurofibrillary tangles and senile plaques. We used immunohistochemical methods to demonstrate SAP reactivity in both tangles and plaques, as well as vessels, in lightly fixed frozen tissue sections of hippocampus and parahippocampal gyrus from subjects with Alzheimer's disease (AD) and normal controls. As confirmed by thioflavin S staining, heavy deposition of immunoperoxidase reaction product was evident in Sommer's sector (CA1), the subiculum and entorhinal cortex with both the antisera to SAP used. Serial sections immunostained with antiserum to amyloid A or preimmune rabbit serum showed no evidence for staining in plaques or tangles. These observations provide evidence for extravasation of the protein across the blood-brain barrier (BBB) in disease although expression of it by cellular elements within or entering the brain through the BBB cannot be ruled out. Our results also implicate the use of lightly fixed tissue for localization of some antigens by immunohistochemistry in postmortem human brain.