High-molecular-mass proteins in haemodialysis-associated amyloidosis

1. Protein constituents were determined in eight amyloid deposits from eight patients (five male and three female), 53 ± 4 years of age, treated by haemodialysis for 9-20 years using only cuprophane membranes and operated for carpal tunnel syndrome. 2. Soluble proteins were removed by solubilization in phosphate-buffered saline after osmotic lysis. The proteins of the insoluble fibrils were characterized by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and two-dimensional gel electrophoresis, and immunologically identified by Western blotting. 3. In addition to β2-microglobulin, α2-macroglobulin was identified in the fibrillar material. The presence of these two proteins in amyloid deposits was confirmed by immunofluorescent microscopic studies. 4. Our data confirm the presence of β2-microglobulin in haemodialysis-associated amyloidosis, and also suggest a possible role for α2-microglobulin: it may protect β2-microglobulin from proteolytic digestion, leading to its accumulation in intact form and to amyloid fibril formation.</jats:p

Haemodialysis-associated amyloidosis: <i>β</i>2-microglobulin alone or associated with globin chains?

1. The protein constituents of amyloid fibrils were characterized in amyloid deposits extracted from surgical material obtained from a 66-year-old patient undergoing maintenance haemodialysis and operated for a carpal tunnel syndrome. 2. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis disclosed the presence of bands at 12 and 14 kDa. Two-dimensional electrophoresis and Western blotting confirmed that the proteins were β2-microglobulin (β2M) and globin chains. 3. When the effluent of high-performance gel filtration chromatography corresponding to molecular masses of 10–15 kDa was subjected to Edman degradation, only one amino acid residue was found at each step. The 18 residues determined corresponded to the N-terminal sequence of β2M. 4. Although globin chains were clearly present in the amyloid material, they were not accessible for sequence determination. The identification of the other protein constituents present in the amyloid material, along with β2M, should provide a better understanding of haemodialysis-associated amyloidosis, the mechanisms of formation of which have not yet been completely determined.</jats:p