Monomeric and dimeric β2-microglobulin may be extracted from amyloid deposits in vitro

Abstract

Background. There is a controversy as to whether β2-microglobulin (β2M amyloid deposits may be degraded resulting in regression and cure of amyloidosis. We have recently reported a long-term clinical study involving transplanted patients suggesting that there is no resorption of amyloid deposits in vivo, even after correction of the primary cause of amyloidosis. To progress in the study of the solubility of amyloid fibrils we performed an in vitro study with the intent to remove protein constituents from amyloid fibrils and amyloid deposits. Methods. Amyloid fibrils were prepurified from three amyloid deposits surgically obtained from carpal tunnel. They were incubated for 2 h with a phosphate-buffered saline (PBS) solution containing trypsin, collagenase, kallikrein, the three of them, or PBS alone. The experiments were repeated in the presence of the antiprotease α2 macroglobulin (α2M). Results. Several bands were observed when the supernatants were run through SDS-PAGE. Western blotting identified in these bands the presence of α2M, light chains of immunoglobulins and β2M in mono- and dimeric form. The same proteins were solubilized with PBS alone. Equivalent results were obtained with crude amyloid deposits; however, β2M presented almost exclusively in monomeric form. Conclusions. These results show that the protein constituents may be recovered from amyloid fibrils in vitro. They also show that even the more insoluble β2M dimers are resuspended by the action of PBS, with no need for proteases to cleave their attachement to the amyloid deposits.