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.
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