Observations of amyloid breakdown by proteases over time using scanning acoustic microscopy

Abstract

Abstract Amyloid consists of insoluble beta-fibrillar proteins with stable structures. The gold standard Congo red staining method for histologically detecting amyloid yields unstable results. Scanning acoustic microscopy (SAM) detects the attenuation of sound (AOS) through sections. This study aimed to clarify whether AOS values reflected the amount of amyloid degradation in tissues. Formalin-fixed paraffin-embedded sections of various types of amyloidosis were digested with different endopeptidases. The sections were incubated at 37°C, and the AOS images obtained via SAM were observed over time. The corresponding Congo red-stained images were observed via light microscopy (LM). The amyloid and nonamyloid portions were examined over time to determine the changes in the AOS values. The AOS values were significantly reduced in most amyloid specimens after digestion. Background areas with high AOS masked the reduction in AOS in the amyloid areas. Most of the amyloid areas showed high AOS values before digestion and a significant decrease after digestion; these findings corresponded with the disappearance and waning of the Congo red staining in the LM images. The method used in this study may help determine the appropriate treatment method for removing amyloid deposits from tissues.