Histochemical and topo-optical investigations on tissue-isolated and in vitro amyloid fibrils
Thomas R Appel1, Susann Richter, Reinhold P Linke
1Leibniz Institute of Molecular Biotechnology, Jena, Germany.
Abstract:
An improved microscopic slide preparation for staining of tissue-isolated and in vitro amyloid fibrils is described in detail. Specimens were prepared by slow drying of an amyloid fibril suspension on aminoalkyl-silanised glass slides underneath a coverglass. The purpose of this method is to obtain microscopically visible fibers. Polarization microscopy was performed on unstained fibers in different embedding media, on fibers stained with Congo red, toluidine blue, 1,9-dimethylmethylene blue, anisotropic PAS reaction and Sudan black. Results were identical in 8 tissue-isolated amyloid fibril preparations. The refractive index of amyloid was about 1.5, as expected for protein fibrils. Congo red-stained fibrils showed yellow or blue-green polarization colors, while staining with toluidine blue or 1,9-dimethylmethylene blue induced green or orange polarization colors. The latter dyes stained the fibrils even in buffers with low pH or high ionic strength, pointing to strong acidic groups like sulphates in amyloid. The anisotropic PAS reaction for selective demonstration of periodate reactive carbohydrates in tissue-isolated amyloid fibrils was positive. Thus, linearly ordered acidic groups and carbohydrate residues could be detected for the first time in tissue-isolated amyloid fibrils using an improved technique for microscopic slide preparation on one side and topo-optical reactions on the other.
Insights
This study details an improved method for preparing and staining amyloid fibrils for microscopy. The technique enhances visualization of amyloid structures, revealing key chemical components like acidic groups and carbohydrates.
Area of Science:
- Biochemistry
- Microscopy
- Pathology
Background:
- Amyloid fibrils are protein aggregates implicated in various diseases.
- Accurate microscopic visualization is crucial for studying amyloid fibril structure and composition.
- Existing preparation methods can be suboptimal for detailed analysis.
Purpose of the Study:
- To develop an improved microscopic slide preparation technique for amyloid fibrils.
- To enhance the visibility and characterization of both tissue-isolated and in vitro amyloid fibrils.
- To identify specific chemical components within amyloid fibrils using advanced staining and microscopy.
Main Methods:
- Specimens prepared by slow drying of amyloid fibril suspension on aminoalkyl-silanised glass slides.
- Polarization microscopy employed on unstained and stained fibrils (Congo red, toluidine blue, 1,9-dimethylmethylene blue, PAS, Sudan black).
- Topo-optical reactions utilized to detect specific molecular arrangements.
Main Results:
- The improved method yielded microscopically visible amyloid fibers.
- Refractive index of amyloid was determined to be approximately 1.5.
- Specific polarization colors observed with different stains indicated the presence of ordered acidic groups (sulfates) and carbohydrates.
Conclusions:
- The developed technique effectively visualizes amyloid fibrils.
- Linearly ordered acidic groups and carbohydrate residues were detected in tissue-isolated amyloid fibrils for the first time.
- This method combines improved slide preparation with topo-optical reactions for detailed amyloid analysis.
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