Abstract
Background:Various methodologies have been employed for the localization of amyloid plaques in numerous studies on Alzheimer’s disease. The majority of these stains are thought to label the plaques by virtue of their affinity for aggregated Aβ. However, plaques are known to contain numerous other components, including multivalent metals such as zinc.Objective:This investigates whether it is possible to localize the presence of zinc in parenchymal and vascular amyloid plaques in afflicted brains. To accomplish this, a novel fluorescent zinc chelator, HQ-O, was investigated to determine its mechanism of binding and to optimize a stain for the high contrast and resolution histological localization of amyloid plaques.Methods:A novel zinc chelator, HQ-O, was developed for localizing zinc within amyloid plaques. The histology involves incubating tissue sections in a dilute aqueous solution of HQ-O. Its compatibility with a variety of other fluorescent methodologies is described.Results:All amyloid plaques are stained in fine detail and appear bright green under blue light excitation. The staining of parenchymal plaques correlates closely with that seen following staining with antibodies to Aβ, however, the HQ-O sometimes also label additional globular structures within blood vessels. In situ mechanistic studies revealed that fluorescent plaque-like structures are only observed with HQ-O when synthetic Aβx-42 is aggregated in the presence of zinc.Conclusion:Zinc is intimately bound to all amyloid plaques, which was demonstrated by its histological localization using a novel fluorescent zinc chelator, HQ-O. Additionally, the tracer is also capable of labeling intravascular leucocytes due to their high zinc content.
Highlights
In 1906, Alois Alzheimer first described the presence of extracellular amyloid plaques and intracellular neurofibrillary tangles within the brains of patients with the neurodegenerative disease that bears his name
The staining of parenchymal plaques correlates closely with that seen following staining with antibodies to Aβ, the HQ-O sometimes label additional globular structures within blood vessels
Zinc is intimately bound to all amyloid plaques, which was demonstrated by its histological localization using a novel fluorescent zinc chelator, HQ-O
Summary
In 1906, Alois Alzheimer first described the presence of extracellular amyloid plaques and intracellular neurofibrillary tangles within the brains of patients with the neurodegenerative disease that bears his name. The first dye used as a fluorescent probe for amyloid plaques was Thioflavin S [2], which appears green under blue light excitation and is capable of staining intracellular Neurofibrillary Tangles (NFTs). Various methodologies have been employed for the localization of amyloid plaques in numerous studies on Alzheimer’s disease. The majority of these stains are thought to label the plaques by virtue of their affinity for aggregated Aβ.
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