Ultrastructural localization of advanced glycation end products and beta 2-microglobulin in dialysis amyloidosis

Background: beta 2-microglobulin (beta 2m) is considered to be the amyloido genic precursor in dialysis-related amyloidosis (DRA, A beta 2M amyloidosis ), beta 2m modified with advanced glycation end products (AGE) may be an im portant factor in the pathogenesis of DRA. The presence of AGE in beta 2m-p ositive amyloid deposits and surrounding macrophages has been demonstrated by immunohistochemical techniques in light microscopy, Methods: In order to better define the localization of beta 2m and AGE in a myloid deposits and in cells, carpal tunnel connective tissues obtained fro m surgical specimens in six patients with DRA were studied by immunohistoch emistry and electron microscopy, using the avidine-biotine complex and immu nogold staining procedures, respectively. A polyclonal rabbit anti-human be ta 2m and two monoclonal mouse anti-AGE antibodies [AG-1 anti-imidazolone a nd AG-10 anti-N-epsilon-carboxymethyl-lysine] enabled us to label their res pective antigens at the optical and ultrastructural level, Results: with both techniques, extracellular amyloid deposits strongly reac ted with anti-beta 2m and anti-AGE antibodies, although the immunoreactivit y of beta 2m was more intense, Macrophage-like synovial cells (CD-68 positi ve) surrounding amyloid deposits were also immunoreactive for beta 2m and A GE, which were detected in lysosomes and in intracellular fibrillar materia l. Anti-AGE reactivity was also evident in collagenous structures in the ab sence of beta 2m or amyloid deposits, supporting the proposal that AGE modi fication of collagen might have pathogenic relevance in the development of DRA, Conclusions: The co-localization of AGE and beta 2m, both intra- and extra- cellularly, in amyloid fibrils was confirmed by immunoelectron microscopy; however, the positivity of collagen to anti-AGE antibodies and a different pattern of intracellular localization suggest that molecules other than bet a 2m may also be modified by AGE and may be involved in the pathogenesis of DRA.