Amyloidosis

Abstract

The term amyloidosis refers to a family of heterogeneous diseases characterized by extracellular deposition of an abnormal protein-based material, called amyloid. Amyloidosis is caused by the production of misfolded insoluble proteins in increased amounts [1]. The proteins undergo partial proteolytic cleavage resulting in the formation of peptides, in an abnormal β-pleated sheet non-branching fibrillary conformation, which are resistant to further proteolysis and form linear, rigid, and 7.5–10 mm wide amyloid fibrils. Peptide P, apolipoprotein E, basement membrane components, as well as glycosaminoglycans, proteoglycans, and protease inhibitors are added to the fibrils, resulting to stabilization and deposition of amyloid [2] (Fig. 22.1). At least 30 different amyloidogenic proteins have been identified in humans, and they can be differentiated by mass spectroscopy after laser capture microdissection and genetic testing [3]. The physicochemical characteristics of amyloid will determine in which organs the amyloid will be deposited and therefore what lesions will occur. Although the amyloid composition changes according to the amyloidogenic protein, it has some common features: (i) It consists of protein fibrils, (ii) it is insoluble and resistant to proteolysis, and (iii) after Congo red staining, it gives an apple-green birefringence under cross-polarized light microscopy.