β₂-Microglobulin modified with advanced glycation end products is a major component of hemodialysis-associated amyloidosis

β₂-Microglobulin (β₂M) is a major constituent of amyloid fibrils in hemodialysis-associated amyloidosis, a complication of long-term hemodialysis patients. Amyloid fibril proteins were isolated from connective tissues forming carpal tunnels in hemodialysis patients with carpal tunnel syndrome. Two-dimensional polyacrylamide gel electrophoresis and Western blotting demonstrated that most of the β₂M forming amyloid fibrils exhibited a more acidic pI value than normal β₂M. This acidic β₂M was also found in a small fraction of β₂M in sera and urine from these patients, whereas heterogeneity was not observed in healthy individuals. We purified acidic and normal β₂M from the urine of long-term hemodialysis patients and compared their physicochemical and immunochemical properties. Acidic β₂M, but not normal β₂M, was brown in color and fluoresced, both of which are characteristics of advanced glycation end products (AGEs) of the Maillard reaction. Immunochemical studies showed that acidic β₂M reacted with anti-AGE antibody and also with an antibody against an Amadori product, an early product of the Maillard reaction, but normal β₂M did not react with either antibody. Incubating normal β₂M with glucose in vitro resulted in a shift to a more acidic pI, generation of fluorescence, and immunoreactivity to the anti-AGE antibody. The β₂M forming amyloid fibrils also reacted with anti-AGE antibody. These data provided evidence that AGE-modified β₂M is a dominant constituent of the amyloid deposits in hemodialysis-associated amyloidosis.