A specific nanobody prevents amyloidogenesis of D76N β 2 -microglobulin in vitro and modifies its tissue distribution in vivo.

Systemic amyloidosis is caused by misfolding and aggregation of globular proteins in vivo for which effective treatments are urgently needed. Inhibition of protein self-aggregation represents an attractive therapeutic strategy. Studies on the amyloidogenic variant of β ₂ -microglobulin, D76N, causing hereditary systemic amyloidosis, have become particularly relevant since fibrils are formed in vitro in physiologically relevant conditions. Here we compare the potency of two previously described inhibitors of wild type β ₂ -microglobulin fibrillogenesis, doxycycline and single domain antibodies (nanobodies). The β ₂ -microglobulin -binding nanobody, Nb24, more potently inhibits D76N β ₂ -microglobulin fibrillogenesis than doxycycline with complete abrogation of fibril formation. In β ₂ -microglobulin knock out mice, the D76N β ₂ -microglobulin/ Nb24 pre-formed complex, is cleared from the circulation at the same rate as the uncomplexed protein; however, the analysis of tissue distribution reveals that the interaction with the antibody reduces the concentration of the variant protein in the heart but does not modify the tissue distribution of wild type β ₂ -microglobulin. These findings strongly support the potential therapeutic use of this antibody in the treatment of systemic amyloidosis.