Immunochemical characterization of amyloid in diagnostic biopsy tissues

Abstract

The heterogeneity of the amyloidoses requires the determination of the chemical type of amyloid protein deposited in tissues. in the present study of 15 diagnostic biopsy specimens classified as light chain amyloid, nonamyloid light chain disease, amyloid A and transthyretin amyloid by immunojluorescence microscopy, the residual frozen tissues were independently analyzed by immunochemical methods. The tissue deposits were extracted in aqueous 20% acetonitrile containing 0.1% trlfluoroacetic acid and the extracted material subjected to Western blotting. Similarly analyzed were 9 control amyloid negative and 6 amyloid positive tissues. From the previously characterized amyloid positive tissues, Western blotting of both isolated fibrils prepared by solubilization in distilled water and the material extracted in acetonitrile from the same specimens yielded identical low molecular weight proteins (>28kDa) immunoreactive with only one of the 4 antibodies tested, whereas the control amyloid negative tissue extracts, with one exception, contained only nonspecific large molecular weight proteins (>28kDa). Western blotting of the extracts from 13 of 15 residual frozen biopsy specimens revealed low molecular weight proteins, in each case immunoreactive with only one of the 4 antibodies tested that corresponded to the results obtained from the same specimen by immunofluorescence microscopy. These studies demostrate the effectiveness of the extraction method and its suitability for the characterization of microgram amounts of amyloid deposits in biopsy tissues. The correspondence between the results obtained by immunohistochemical and immunochemical analyses on the same specimens validates the reliability of the commercial antibodies to classifiy the chemical type of amyloid without the need of antibodies against the specific amyloid fibrils.