Exploring the Structural Diversity in Inhibitors of α-Synuclein Amyloidogenic Folding, Aggregation, and Neurotoxicity

Abstract

Aggregation of α-Synuclein (αS) protein to amyloid fibrils is a neuropathological hallmark of Parkinson's disease (PD). Growing evidence suggests that extracellular αS aggregation plays a pivotal role in neurodegeneration found in PD in addition to the intracellular αS aggregates in Lewy bodies (LB). Here, we identified and compared a diverse set of molecules capable of mitigating protein aggregation and exogenous toxicity of αSA53T, a more aggregation-prone αS mutant found in familial PD. For the first time, we investigated the αS anti-amyloid activity of semi-synthetic flavonoid 2′, 3′, 4′ trihydroxyflavone or 2-D08, which was compared with natural flavones myricetin and transilitin, as well as such structurally diverse polyphenols as honokiol and punicalagin. Additionally, two novel synthetic compounds with a dibenzyl imidazolidine scaffold, Compound 1 and Compound 2, were also investigated as they exhibited favorable binding with αSA53T. All seven compounds inhibited αSA53T aggregation as demonstrated by Thioflavin T fluorescence assays, with modified fibril morphology observed by transmission electron microscopy. Ion mobility-mass spectrometry (IM-MS) was used to monitor the structural conversion of native αSA53T into amyloidogenic conformations and all seven compounds preserved the native unfolded conformations of αSA53T following 48 h incubation. The presence of each test compound in a 1:2 molar ratio was also shown to inhibit the neurotoxicity of preincubated αSA53T using phaeochromocytoma (PC12) cell viability assays. Among the seven tested compounds 2-D08, honokiol, and the synthetic Compound 2 demonstrated the highest inhibition of aggregation, coupled with neuroprotection from preincubated αSA53T in vitro. Molecular docking predicted that all compounds bound near the lysine-rich region of the N-terminus of αSA53T, where the flavonoids and honokiol predominantly interacted with Lys 23. Overall, these findings highlight that (i) restricted vicinal trihydroxylation in the flavone B-ring is more effective in stabilizing the native αS conformations, thus blocking amyloidogenic aggregation, than dihydroxylation aggregation in both A and B-ring, and (ii) honokiol, punicalagin, and the synthetic imidazolidine Compound 2 also inhibit αS amyloidogenic aggregation by stabilizing its native conformations. This diverse set of molecules acting on a singular pathological target with predicted binding to αSA53T in the folding-prone N-terminal region may contribute toward novel drug-design for PD.

Plant Extracts and Phytochemicals Targeting α-Synuclein Aggregation in Parkinson's Disease Models

“…Several biophysical and biochemical techniques used to assess the ability of phytochemicals and plant extracts in preventing α-syn oligomerization and fibrillation are represented in Table 6 . These experimental techniques include surface plasmon resonance imaging (SPRi), Thioflavin-T (ThT) fluorescence, transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), circular dichroism (CD) spectroscopy, fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and absorption spectroscopy of Congo red (CR) binding assay (Luk et al, 2007 ; Kostka et al, 2008 ; Celej et al, 2009 ; Yamaguchi et al, 2010 ; Giehm et al, 2011 ; da Silva et al, 2013 ; Aelvoet et al, 2014 ; Coelho-Cerqueira et al, 2014 ; Cheng et al, 2015 ; Fazili and Naeem, 2015 ; Takahashi et al, 2015 ; Pujols et al, 2017 ; Das et al, 2018 ). The biochemical and biophysical assays employed to measure the α-syn aggregation are efficient in providing a high-resolution structure of α-syn oligomers, but not free from the restrictions and misconceptions on their efficacy (Coelho-Cerqueira et al, 2014 ).…”

Metal Chelation Therapy and Parkinson’s Disease: A Critical Review on the Thermodynamics of Complex Formation between Relevant Metal Ions and Promising or Established Drugs

“…Imipramine [247] Isobavachalcone [248] Isochlorogenic acid [167] Isoquercetin (Isoquercitrin) [249] Kaempferol [128,160,193,194] Kaempferol, 3-O-a-l arabinofuranoside-7-O-a-l-rhamnopyranoside [214] KR33493 [250] Kukoamine [251] Lestaurtinib [164] Lipoic acid [252][253][254] Luteolin [128] LY354740 [115] M10 [24] M30 (VAR10303) [112,255] M99 [24] Macranthoin G [256] Magnesium lithospermate B [257] [160,193,194,267] [18F]MPPF [107] MSX-3 [268] Myricetin [128,269,270] Myricitrin [271] Naringenin [128,272] Naringin [117,273,274] Nicotinamide adenine dinucleotide phosphate (NADPH) [275,276] Nicotinamide mononucleotide [277] Nitecapone [278] Nordihydroguaiaretic [160,193,194] Oleuropein…”

The molecular chaperone β-casein prevents amorphous and fibrillar aggregation of α-lactalbumin by stabilisation of dynamic disorder

“…It is likely this structure does not expose enough hydrophobicity to self-assemble amorphously but, over time, associates in an ordered, fibrillar form. The phenomenon of intrinsically disordered proteins reorganising and gaining structure prior to fibril formation has been observed previously and may be a key step in the formation of amyloid fibrils [43,44]. The opposite occurs for DTT α-LA.…”