Baicalein Inhibits Formation of α‐Synuclein Oligomers within Living Cells and Prevents Aβ Peptide Fibrillation and Oligomerisation

Abstract

Abnormal protein aggregation in the brain is linked to the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Recent studies revealed that the oligomeric form of aggregates is most likely the toxic species, and thus could be a good therapeutic target. To screen for potent inhibitors that can inhibit both oligomerisation and fibrillation of α-synuclein (α-syn), we systematically compared the antioligomeric and antifibrillar activities of eight compounds that were extracted from Chinese herbal medicines through three platforms that can monitor the formation of α-syn fibrils and oligomers in cell-free or cellular systems. Our results revealed that baicalein, a flavonoid extracted from the Chinese herbal medicine Scutellaria baicalensis Georgi ("huang qin" in Chinese), is a potent inhibitor of α-syn oligomerisation both in cell-free and cellular systems, and is also an effective inhibitor of α-syn fibrillation in cell-free systems. We further tested the protective effect of baicalein against α-syn-oligomer-induced toxicity in neuronal cells. Our data showed that baicalein inhibited the formation of α-syn oligomers in SH-SY5Y and Hela cells, and protected SH-SY5Y cells from α-syn-oligomer-induced toxicity. We also explored the effect of baicalein on amyloid-β peptide (Aβ) aggregation and toxicity. We found that baicalein can also inhibit Aβ fibrillation and oligomerisation, disaggregate pre-formed Aβ amyloid fibrils and prevent Aβ fibril-induced toxicity in PC12 cells. Our study indicates that baicalein is a good inhibitor of amyloid protein aggregation and toxicity. Given the role of these processes in neurodegenerative diseases such as AD and PD, our results suggest that baicalein has potential as a therapeutic agent for the treatment of these devastating disorders.

Isorhynchophylline, a natural alkaloid, promotes the degradation of alpha-synuclein in neuronal cells via inducing autophagy

“…Samples for native gels were lysed with detergent-free lysis buffer (50 mM Tris/HCl pH 7.4, 175 mM NaCl, 5 mM EDTA pH 8.0, 1 mM PMSF, 5 mg/ml aprotinin, 5 mg/ml leupeptin), and sheared five times through a 28-gauge needle followed by two times of sonication for 5 sec according to previously described protocol. 33 For denaturing, SDS-PAGE was performed using Tris-Glycine SDS running buffer and SDS sample buffer, and for native conditions, native-PAGE was run with detergent-free Tris-Glycine running buffer (BN2007, Invitrogen) and 4¾ native sample buffer (Invitrogen, BN2003) on a pre-casted native PAGE gel (Invitrogen, BN1002BOX). The proteins on the gels were then transferred to PVDF membrane (GE Healthcare, RPN303F) and processed for immunoblotting.…”

“…Second, we tested the effect of IsoRhy on a-syn oligomers clearance using a bimolecular fluorescence complementation (BiFC)-based cell model for visualizing a-syn oligomers. 32,33 IsoRhy promoted degradation of a-syn oligomers as illustrated by decreased fluorescence intensity ( Fig. 5H and I) and high molecular weight a-syn species (Fig.…”

Targeting α-Synuclein as a Parkinson’s Disease Therapeutic

“…Baicalein also shows modest anti-aggregation activity in a cell-based assay by reducing levels of toxic high molecular weight α-synuclein oligomers and protecting against oligomer-induced toxicity [264]. How might baicalein promote nontoxic oligomers in vitro but show no evidence for such an effect in a cell-based assay?…”

Targeting Assembly and Disassembly of Protein Aggregates

“…Baicalein disaggregates pre-formed a-synuclein fibrils by cleavage at internal sites, rather than by disassembly of terminal a-synuclein monomers [207]. Baicalein shows similar effects in SH-SY5Y and HeLa cells, alleviating either a-syn-or Ab-induced neurotoxicity [208]. Baicalein and other polyphenols prevent membrane permeabilization by a-syn-and Ab oligomers in cell-free liposome-based and mitochondrial membrane-based assays [209].…”