In vitro high affinity alpha-synuclein binding sites for the amyloid imaging agent PIB are not matched by binding to Lewy bodies in postmortem human brain.
Amyloid containing deposits are a defining neuropathological feature of a wide range of dementias and movement disorders. The positron emission tomography tracer PIB (Pittsburgh Compound-B, 2-[4'-(methylamino)phenyl]-6-hydroxybenzothiazole) was developed to target senile plaques, an amyloid containing pathological hallmark of Alzheimer's disease, formed from the amyloid-beta peptide. Despite the fact that PIB was developed from the pan-amyloid staining dye thioflavin T, no detailed characterisation of its interaction with other amyloid structures has been reported. In this study, we demonstrate the presence of a high affinity binding site (K(d) approximately 4 nM) for benzothiazole derivatives, including [3H]-PIB, on alpha-synuclein (AS) filaments generated in vitro, and further characterise this binding site through the use of radioligand displacement assays employing 4-N-methylamino-4'-hydroxystilbene (SB13) (K(i) = 87 nM) and 2-(1-{6-[(2-fluoroethyl(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP) (K(i) = 210 nM). Despite the presence of a high-affinity binding site on AS filaments, no discernible interaction of [3H]-PIB was detected with amygdala sections from Parkinson's disease cases containing frequent AS-immunoreactive Lewy bodies and related neurities. These findings suggest that the density and/or accessibility of AS binding sites in vivo are significantly less than those associated with amyloid-beta peptide lesions. Lewy bodies pathology is therefore unlikely to contribute significantly to the retention of PIB in positron emission tomography imaging studies.
Ye
Liang
L
GlaxoSmithKline, Clinical Science and Technology, Neurology DM, New Frontiers Science Park, Harlow, UK.
Velasco
Ana
A
Fraser
Graham
G
Beach
Thomas G
TG
Sue
Lucia
L
Osredkar
Tracy
T
Libri
Vincenzo
V
Spillantini
Maria Grazia
MG
Goedert
Michel
M
Lockhart
Andrew
A
D000682:Amyloid / Q000235:genetics / Q000378:metabolism*; D000814:Aniline Compounds / Q000378:metabolism*; D001665:Binding Sites / Q000502:physiology; D001921:Brain / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D016631:Lewy Bodies / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D013844:Thiazoles / Q000378:metabolism*; D051844:alpha-Synuclein / Q000235:genetics / Q000378:metabolism*
C475519:2-(4'-(methylamino)phenyl)-6-hydroxybenzothiazole; D000682:Amyloid; D000814:Aniline Compounds; D013844:Thiazoles; D051844:alpha-Synuclein