Analysis of serum amyloid β₂ microglobulin from hemodialysis patients using liquid chromatography/mass spectrometry

Abstract

The protein responsible for dialysis-related amyloidosis (DRA) is irreversibly unfolded amyloid β₂ microglobulin (A-β₂M), but a partially unfolded conformer of β₂M (I-β₂M) has been detected during the amyloidization of native β₂M. In this study, we analyzed the serum I-β₂M of predialysis chronic kidney disease (CKD) patients, short-term hemodialysis patients, and long-term hemodialysis patients and tissue β₂M derived from amyloid tissue using liquid chromatography/mass spectrometry (LC/MS). Four ionized peaks at ＋7 to ＋10 were found in all samples. Since the ionized peak for native β₂M was located at＋7 and＋8, and that for A-β₂M was located at ＋9 and ＋10, we analyzed the ratio of (＋9 plus ＋10) to (＋7 plus ＋8) as the MS index (MS-I). The serum I-β₂M MS-I of the predialysis CKD patients, short-term hemodialysis patients, and long-term dialysis patients were 1.70±0.13, 1.90±0.13, and 1.79±0.25, respectively, and did not differ significantly among the 3 groups. On the other hand, the MS-I of the tissue β₂M derived from amyloid tissue were markedly higher (4.15 and 7.33). The main finding of this study; i.e., that A-β₂M, which causes the formation of amyloid, could not be detected in the sera of hemodialysis patients by LC/MS, was consistent with our hypothesis that some of the incompletely unfolded β₂M moves from the serum to the extravascular tissue, where it continues to unfold, and the accumulation of this substance leads to the onset of DRA.