Modification of beta(2)-microglobulin with D-glucose or 3-deoxyglucosone inhibits A beta 2M amyloid fibril extension in vitro

beta(2)-microglobulin (beta 2M) is a major constituent of amyloid fibrils ( fA beta 2M) deposited in patients with A beta 2M amyloidosis. Recently, adv anced glycation endproducts (AGE) of beta 2M and fA beta 2M have been sugge sted to play an important role in the pathogenesis of A beta 2M amyloidosis . We first characterized the states of AGE modification of fA beta 2M. West ern blot analysis with a monoclonal anti-AGE antibody showed that purified fA beta 2M was naturally modified with AGE. Immunohistochemical studies of amyloid-deposited tissue have revealed a patchy distribution of the AGE-mod ified area in the amyloid deposits. Then we modified beta 2-m either with D -glucose or with 3-deoxyglucosone (3-DG) and investigated the effect of the se modification on fA beta 2M extension in vitro, using the recently establ ished first order kinetic model of fA beta 2M extension in vitro. Western b lot analysis and enzyme linked immunosorbent assay with a monoclonal anti-A GE antibody showed that these sugar-modified beta 2M contained AGE. During the incubation of fA beta 2M with native beta 2-m at 37 degrees C, the fluo rescence of thioflavin T increased without a lag phase and proceeded to equ ilibrium. On the contrary, only a slight increase in fluorescence was obser ved during the incubation of fA beta 2M with sugar-modified beta 2M. Moreov er, sugar-modified beta 2M exhibited a dose-dependent inhibitory effect on the extension reaction of fA beta 2M with native beta 2M. These results may suggest that in some in vivo situations, the modification of beta 2-m with A GE could play an inhibitory role for the formation of fA beta 2M.