Phenolic Bis-styrylbenzo[c]-1,2,5-thiadiazoles as Probes for Fluorescence Microscopy Mapping of Aβ Plaque Heterogeneity

Abstract

A fluorescent bis-styryl-benzothiadiazole (BTD) with carboxylic acid functional groups (X-34/Congo red analogue) showed lower binding affinity toward Aβ1-42 and Aβ1-40 fibrils than its neutral analogue. Hence, variable patterns of neutral OH-substituted bis-styryl-BTDs were generated. All bis-styryl-BTDs showed higher binding affinity to Aβ1-42 fibrils than to Aβ1-40 fibrils. The para-OH on the phenyl rings was beneficial for binding affinity while a meta-OH decreased the affinity. Differential staining of transgenic mouse Aβ amyloid plaque cores compared to peripheral coronas using neutral compared to anionic bis-styryl ligands indicate differential recognition of amyloid polymorphs. Hyperspectral imaging of transgenic mouse Aβ plaque stained with uncharged para-hydroxyl substituted bis-styryl-BTD implicated differences in binding site polarity of polymorphic amyloid plaque. Most properties of the corresponding bis-styryl-BTD were retained with a rigid alkyne linker rendering a probe insensitive to cis−trans isomerization. These new BTDbased ligands are promising probes for spectral imaging of different Aβ fibril polymorphs.

Insulin amyloid polymorphs: implications for iatrogenic cytotoxicity

“…14,15 It was also recently shown that several variants of uorescent phenolic styrylbenzo [c]-1,2,5-thiadiazoles, a new uorescent amyloid probe based on benzothiadiazole (BTD) stilbene, can be used for spectral imaging of different amyloid-b (Ab) bril deposits. 16 In this study, we demonstrated that the less toxic and exible insulin laments can be recognized with BTD21, 16 a BTD stilbene ligand. Based on pFTAA and BTD21 staining and hyperspectral microscopy of patient-derived tissue sections of iatrogenic localized insulin amyloidosis (i.e., insulin balls), we demonstrated that a variety of polymorphic amyloid aggregates, such as insulin brils and laments, 6,7 were co-localized in the tissue sections.…”

“…17 More recently, several variants of uorescent BTDs were developed for identifying amyloid polymorphs. 16 The BTD21 compound which lacks the carboxylate groups likely binds in a different binding pocket than Congo red on Ab brils in Alzheimer's disease mouse model brain. 16 Here, we rst examined the binding of pFTAA and BTD21 (chemical structures shown in Fig.…”

“…12 pFTAA and BTD21 were synthesized as described. 15,16 This study was approved by the Ethics Committee of Tokyo Medical University Ibaraki Medical Center. The ethics committee approval number is 10-40.…”

“…These conditions were optimized according to the previous reports. 12,13,16 Then, the sample solutions were centrifuged at 15 000 rpm for 30 min and the supernatant was removed. Aerwards, 5 mL of droplets were placed on the microscopy glass and covered with a cover glass.…”

Polymorphic protein aggregation in tauopathies

“…The styrylbenzothiadiazoles previously described and characterized were used to stain A plaques and neurofibrillary tangles or map heterogeneity in A plaques due to spectral shifts or preference towards coronas or core of the plaque [135,136]. Bi-thiophene-vinyl-benzothiazoles (bTVBTs) showed selective detection of tau pathology in brain sections from AD brains [137].…”