[Diagnosis of neurodegenerative disease by mass spectrometry]

We analyzed wild-type and variant transthyretins (TTRs) by mass spectrometry and reported that all TTR preparations demonstrated free TTR, TTR conjugated with thiol compounds and several minor components. We previously described a component with a molecular mass 80 Da larger than free TTR, which was proven to be TTR conjugated with bisulfite. The amyloid fibril formation of purified TTR was monitored by the turbidity at 330 nm, and by a Congo red binding assay as a function of pH. The S-sulfonated TTR showed clear elevation of the turbidity and Congo red binding under acidic conditions. In contrast, TTR reduced by dithiothreitol, which was free of the S-sulfonated component, did not show evidence of amyloid fibril formation. We analyzed rabbit serum TTR obtained from a rabbit fed a diet containing sulfite and from a rabbit on a sulfite-free diet. Compared to that in the rabbit fed a sulfite-containing diet, sulfonated TTR was decreased on the 7th day of a sulfite-free diet. These results suggested that the S-sulfonated wild-type TTR is highly amyloidogenic, and that prolonged ingestion of antimicrobial and antioxidant agents containing sulfite/bisulfite, may cause senile systemic amyloidosis.