Selective Aggregation of Endogenous β‐Amyloid Peptide and Soluble Amyloid Precursor Protein in Cerebrospinal Fluid by Zinc

• Published in: Journal of neurochemistry 1997-09, Vol.69 (3), p.1204-1212
• Main Authors: Brown, Abraham M., Tummolo, Donna M., Rhodes, Kenneth J., Hofmann, John R., Jacobsen, J. Steven, Sonnenberg‐Reines, June
• Format: Article
• Language: English
• Subjects: Aggregation; Alzheimer's disease; Amyloid beta-Peptides - cerebrospinal fluid; Amyloid beta-Peptides - chemistry; Amyloid beta-Peptides - drug effects; Amyloid beta-Protein Precursor - cerebrospinal fluid; Amyloid beta-Protein Precursor - chemistry; Amyloid beta-Protein Precursor - drug effects; Amyloid deposit; Animals; Biological and medical sciences; Blotting, Western; Brain; Cerebrospinal fluid; Congo Red; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Dogs; Enzyme-Linked Immunosorbent Assay; Fluorescent Dyes; Humans; Medical sciences; Neurology; Thiazoles; Zinc; Zinc - pharmacology; β‐Amyloid peptide
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.1997.69031204.x

: Zinc added to buffered solutions of synthetic β‐amyloid peptide (Aβ) has been reported to induce accelerated formation of insoluble aggregates. This observation suggests that zinc may play a role in the formation of senile plaques, which contain Aβ, in Alzheimer's disease. To test this hypothesis under conditions more representative of the brain, we investigated the ability of zinc to induce aggregation of Aβ in freshly drawn canine CSF, which contains the same sequence as human Aβ. Aggregates were separated from CSF by ultracentrifugation before and after incubation with zinc and assayed by quantitative western blotting and ELISA. We found that zinc induced the rapid aggregation of endogenous Aβ in CSF, with an EC50 of 120–140 µM. The reaction was specific, because most (≥95%) CSF protein remained soluble under conditions where most Aβ was insoluble, as assayed by scanning densitometry of Coomassie‐stained gels. Staining of the precipitated material resulted in the visualization of punctate regions that were thioflavin positive or birefringent when stained with Congo red, suggesting the formation of amyloid‐related structures. These results suggest that zinc could play a role in amyloid deposition, because there is overlap between the regions of the brain where zinc concentrations are highest and regions with the highest amyloid content. It is surprising that zinc induced the aggregation of endogenous soluble APP at lower concentrations than required for Aβ (EC50 80 µM). The possibility that zinc‐induced aggregation of APP may precede the deposition of Aβ into plaques is discussed. Investigation of aggregation of Aβ in CSF will aid in assessing the biological relevance of other agents that have been reported to accelerate amyloid formation.