α-
Synuclein (α-Syn) aggregation is a pathological feature of
synucleinopathies,
neurodegenerative disorders that include
Parkinson's disease (PD). We have tested whether N,N,N',N'-tetramethyl-10H-phenothiazine-3,7-diaminium bis(hydromethanesulfonate) (
leuco-methylthioninium bis(hydromethanesulfonate); LMTM), a tau aggregation inhibitor, affects α-Syn aggregation in vitro and in vivo. Both cellular and transgenic models in which the expression of full-length human α-Syn (h-α-Syn) fused with a
signal sequence peptide to promote α-Syn aggregation were used. Aggregated α-Syn was observed following differentiation of N1E-115
neuroblastoma cells transfected with h-α-Syn. The appearance of aggregated α-Syn was inhibited by LMTM, with an EC50 of 1.1 μM, with minimal effect on h-α-Syn
mRNA levels being observed. Two independent lines of mice (L58 and L62) transgenic for the same fusion
protein accumulated neuronal h-α-Syn that, with aging, developed into fibrillary inclusions characterized by both resistance to
proteinase K (PK)-cleavage and their ability to bind
thiazin red. There was a significant decrease in α-Syn-positive neurons in multiple brain regions following oral treatment of male and female mice with LMTM administered daily for 6 weeks at 5 and 15 mg MT/kg. The early aggregates of α-Syn and the late-stage fibrillar inclusions were both susceptible to inhibition by LMTM, a treatment that also resulted in the rescue of movement and anxiety-related traits in these mice. The results suggest that LMTM may provide a potential disease modification
therapy in PD and other
synucleinopathies through the inhibition of α-Syn aggregation.