DAPI (4',6-diamidino-2-phenylindole) as a novel fluorochrome for amyloid staining that binds to β-pleated sheet

Area of Science:

• Biochemistry
• Molecular Biology
• Pathology

Background:

• Amyloidosis involves extracellular deposition of amyloid fibrils with a β-pleated sheet structure.
• Current diagnosis relies on Congo Red or Thioflavine T staining.
• 4',6-Diamidino-2-Phenylindole (DAPI), a nuclear fluorochrome, shows potential for amyloid staining, but its mechanism is unclear.

Purpose of the Study:

• To investigate the mechanism and specificity of DAPI staining for amyloid.
• To evaluate the utility of DAPI as an amyloid detection method.
• To compare DAPI staining with Thioflavine T based on stereochemical similarity.

Main Methods:

• Compared stereochemical similarity and staining properties of DAPI and Thioflavine T.
• Utilized formic acid-treated amyloid specimens to study structural changes affecting DAPI binding.
• Evaluated DAPI staining in four different types of amyloid specimens (AA, Aβ, AL, AIAPP).

Main Results:

• DAPI and Thioflavine T exhibited similar stereochemistry and staining behavior.
• Formic acid-treated amyloid, lacking the characteristic structure, was DAPI-negative, suggesting DAPI recognizes amyloid fibril conformation.
• DAPI demonstrated positive staining in AA, Aβ, AL, and AIAPP amyloid types.

Conclusions:

• DAPI staining recognizes the β-pleated sheet structure characteristic of amyloid fibrils.
• DAPI offers a simple and sensitive method for detecting amyloid deposition.
• DAPI's mechanism is linked to the conformational structure of amyloid fibrils.