Novel Mannitol-Based Small Molecules for Inhibiting Aggregation of α-Synuclein Amyloids in Parkinson's Disease

Abstract

The aggregation of the amyloidogenic protein α-synuclein (α-Syn) into toxic oligomers and mature fibrils is the major pathological hallmark of Parkinson's disease (PD). Small molecules that inhibit α-Syn aggregation thus may be useful therapeutics for PD. Mannitol and naphthoquinone-tryptophan (NQTrp) have been shown in the past to inhibit α-Syn aggregation by different mechanisms. Herein, we tested whether the conjugation of Mannitol and NQTrp may result in enhance efficacy toward α-Syn. The molecules were conjugated either by a click linker or via a PEG linker. The effect of the conjugate molecules on α-Syn aggregation in vitro was monitored using Thioflavin T fluorescence assay, circular dichroism, transmission electron microscopy, and Congo red birefringence assay. One of the conjugate molecules was found to be more effective than the two parent molecules and as effective as a mixture of the two. The conjugate molecules attenuated the disruptive effect of α-Syn on artificial membrane of Large Unilamellar Vesicles as monitored by dye leakage assay. The conjugates were found to be have low cytotoxicity and reduced toxicity of α-Syn toward SH-SY5Y neuroblastoma cells. These novel designed entities can be attractive scaffold for the development of therapeutic agents for PD.

Naphthoquinone Tryptophan Hybrids: A Promising Small Molecule Scaffold for Mitigating Aggregation of Amyloidogenic Proteins and Peptides

“…A fivefold molar excess of M3N inhibited ∼80% of α-Syn aggregation when compared with NQTrp (∼68%) and Mannitol (∼17%), or their mixture (∼73%) at the same molar ratio, indicating the synergistic effect achieved by their conjugation. This outcome was well corroborated by CD, TEM and Congo-red stained birefringence (Paul et al, 2019). Among these conjugates, M3N was found to be more effective possibly due to the longer linker between NQTrp and Mannitol.…”

Tryptophan-galactosylamine conjugates inhibit and disaggregate amyloid fibrils of Aβ42 and hIAPP peptides while reducing their toxicity

“…Tryptophan-coated gold and silver nanoparticles have been shown to inhibit both spontaneous and seed-induced aggregation of insulin 82 . Naphthoquinone-tryptophan hybrids displayed promising potential for mitigating the amyloidogenicity of several proteins and peptides 44,45,83 .…”

“…The conjugation of glycans to peptides increases the overall interaction surface of the hybrid molecules, therefore increasing solubility by expanding the number of possible interactions with the solvent 50 – 53 . Along the same rationale, aromatic molecules, which display high potential as anti-amyloidogenic agents, but are by themselves hydrophobic, were conjugated to mannitol and glucosamine 43 , 54 .…”

“…Combining the aromatic elements of amino acids and small molecules has also been attempted for amyloid inhibition. For example, a naphthoquinone-tryptophan hybrid was shown to be effective towards various amyloids (including Aβ42, IAPP, Tau, α-Syn) in vitro as well as in vivo [42][43][44][45][46] . However, a major limitation in the drugability of such molecules is their poor solubility in aqueous media [47][48][49] : Attaching a hydrophilic moiety for increasing solubility may enhance the overall therapeutic capacity of a drug 48 .…”

Antibiotic-induced microbiome depletion protects against MPTP-induced dopaminergic neurotoxicity in the brain

“…Interestingly, Clostridium sp. HGF2 plays an important role in the metabolism of mannitol [41], which could attenuate behavioral abnormalities and aggregations of α-synuclein in the rodent brain [42, 43]. Among the bacteria increased by MPTP, Bacteroides sp.…”