Structural Features and Toxicity of α-Synuclein Oligomers Grown in the Presence of DOPAC

Olive oil tyrosols reduce α-synuclein aggregation in vitro and in vivo after ingestion in a Caenorhabditis elegans Parkinson's model

Parkinson's disease is the neurodegenerative motor disorder with the highest incidence worldwide. Among other factors, Parkinson's disease is caused by the accumulation of α-synuclein aggregates in a patient's brain. In this work, five molecules present in the diet are proposed as possible nutraceuticals to prevent and/or reduce the formation of α-synuclein oligomers that lead to Parkinson's disease. The olive oil polyphenols tyrosol, hydroxytyrosol (HT), hydroxytyrosol acetate (HTA) and dihydroxyphenyl acetic acid (DOPAC) besides vitamin C were tested using a cellular model of α-synuclein aggregation and a Caenorhabditis elegans Parkinson's disease animal model. Levodopa was included in the assays as the main drug prescribed to treat the disease as well as dopamine, its direct metabolite. HTA and DOPAC completely hindered α-synuclein aggregation in vitro, while dopamine reduced the aggregation by 28.7%. The Parallel Artificial Membrane Permeability Assay (PAMPA) showed that HTA had the highest permeability through brain lipids among the compounds tested. Furthermore, the C. elegans Parkinson's disease model made it possible to assess the chosen compounds in vivo. The more effective substances in vivo were DOPAC and HTA which reduced the αS aggregation inside the animals by 79.2% and 76.2%, respectively. Moreover, dopamine also reduced the aggregates by 67.4% in the in vivo experiment. Thus, the results reveal the potential of olive oil tyrosols as nutraceuticals against α-synuclein aggregation.

Catechol-induced covalent modifications modulate the aggregation tendency of α-synuclein: An in-solution and in-silico study

Parkinson's disease (PD) stands as a challenging neurodegenerative condition characterized by the emergence of Lewy Bodies (LBs), intracellular inclusions within dopaminergic neurons. These LBs harbor various proteins, prominently including α-Synuclein (Syn) aggregates, implicated in disease pathology. A promising avenue in PD treatment involves targeting Syn aggregation. Recent findings from our research have shown that 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylethanol (DOPET) possess the ability to impede the formation of Syn fibrils by disrupting the aggregation process. Notably, these compounds primarily engage in noncovalent interactions with the protein, leading to the formation of off-pathway oligomers that deter fibril growth. Through proteolysis studies and mass spectrometry (MS) analysis, we have identified potential covalent modifications of Syn in the presence of DOPAC, although the exact site remains elusive. Employing molecular dynamics simulations, we delved into how DOPAC-induced covalent alterations might affect the mechanism of Syn aggregation. Our findings indicate that the addition of a covalent adduct on certain residues enhances fibril flexibility without compromising its secondary structure stability. Furthermore, in the monomeric state, the modified residue fosters novel bonding interactions, thereby influencing long-range interactions between the N- and C-termini of the protein.

Disruption of Dopamine Homeostasis Associated with Alteration of Proteins in Synaptic Vesicles: A Putative Central Mechanism of Parkinson's Disease Pathogenesis

Vestigial dopaminergic cells in PD have selectivity for a sub-class of hypersensitive neurons with the nigrostriatal dopamine (DA) tract. DA is modulated in pre-synaptic nerve terminals to remain stable. To be specific, proteins at DA release sites that have a function of synthesizing and packing DA in cytoplasm, modulating release and reingestion, and changing excitability of neurons, display regional discrepancies that uncover relevancy of the observed sensitivity to neurodegenerative changes. Although the reasons of a majority of PD cases are still indistinct, heredity and environment are known to us to make significant influences. For decades, genetic analysis of PD patients with heredity in family have promoted our comprehension of pathogenesis to a great extent, which reveals correlative mechanisms including oxidative stress, abnormal protein homeostasis and mitochondrial dysfunction. In this review, we review the constitution of presynaptic vesicle related to DA homeostasis and describe the genetic and environmental evidence of presynaptic dysfunction that increase risky possibility of PD concerning intracellular vesicle transmission and their functional outcomes. We summarize alterations in synaptic vesicular proteins with great involvement in the reasons of some DA neurons highly vulnerable to neurodegenerative changes. We generalize different potential targets and therapeutic strategies for different pathogenic mechanisms, providing a reference for further studies of PD treatment in the future. But it remains to be further researched on this recently discovered and converging mechanism of vesicular dynamics and PD, which will provide a more profound comprehension and put up with new therapeutic tactics for PD patients.

Influence of Protonation on the Norepinephrine Inhibiting α-Synuclein 71-82 Oligomerization

The pathogenesis of Parkinson's disease (PD) is closely linked to the massive presence of Lewy vesicles and Lewy axons in the cytoplasm of neurons, mainly consisting of α-synuclein (αS). Norepinephrine (NE), whose secretion can be increased by exercise, has been demonstrated to prevent the fibrillation of αS and to break down the mature αS fibrils. In this work, we focus on the influence of protonation on the inhibitory ability of NE by using amyloid core fragment αS71-82 as a template. All-atom replica-exchange molecular dynamics simulations (accumulating to 33.6 μs) in explicit water were performed to explore the inhibitory effect of protonated and nonprotonated NE on αS oligomerization. Our results show that NE/NE+ can lead to a significant decrease in β-sheet content with increasing temperature, while isolated αS maintains relatively higher β-sheet conformations until 363 K, implying that both NE and NE+ can lower the critical temperature required for αS fibril decomposition. NE and NE+ also lead to the formation of less compact αS oligomers by preventing the backbone hydrogen bonds and the side-chain packing. The protonation would affect the binding affinity, interaction modes, and binding intensity of NE with αS. Interesting, NE and NE+ have a distinct binding free energy in the electrostatic and solvation terms, which mostly counter each other and produce a weak binding intensity with αS. Our work contributes to a better understanding of the inhibitory mechanism of NE and NE+ on αS oligomerization relevant to PD pathogenesis, which may provide clues for the design of antiamyloid medicine.

Protein Oligomerization

Protein self-association is a biologically remarkable event that involves and affects the structural and functional properties of proteins [...].

Dopamine-Induced Oligomers of α-Synuclein Inhibit Amyloid Fibril Growth and Show No Toxicity

Parkinson's disease is characterized by the selective death of dopaminergic neurons in the midbrain and accumulation of amyloid fibrils composed of α-synuclein (αSyn). Current treatment involves approaches that compensate the death of dopaminergic neurons by increasing the dopamine levels in remaining cells. However, dopamine can interact with αSyn and produce oligomeric species which were reported to be toxic in many models. We studied formation of dopamine-induced αSyn oligomers and their effect on the αSyn aggregation. Using the Thioflavin T kinetic assay, we have shown that small oligomers efficiently inhibit αSyn fibrillization by binding to fibril ends and blocking the elongation. Moreover, all the fractions of oligomer species proved to be nontoxic in the differentiated SH-SY5Y cell model and showed negligible neurotoxicity on isolated rat synaptosomes. The observed inhibition is an important insight in understanding of dopamine-enhancing therapy on Parkinson's disease progression and explains the absence of pathology enhancement.

A novel protective modality against rotenone-induced Parkinson's disease: A pre-clinical study with dulaglutide

Parkinson's disease (PD) drugs treat symptoms without inhibiting progression. In recent years, finding novel therapeutic medications that can halt disease progression has become crucial. Research on antidiabetic medicines is valuable in these investigations because of the parallels between the two disorders. Using Rotenone (ROT), a frequently used PD model, the possible neuroprotective benefits of Dulaglutide (DUL), an extended-acting glucagon-like peptide-1 agonist, were considered. Twenty-four rats were randomly assigned to 4 groups to complete this experiment (n = 6). 0.2 ml of the vehicle (1 ml of dimethyl sulfoxide (DMSO) diluted in sunflower oil) was administered to the standard control group subcutaneously with a 48-hour pause. The second group was administered ROT 2.5 mg/kg SC every 48 h for 20 days as a positive control group. The third and fourth groups were administered one dose of DUL each week (0.05 and 0.1 mg/kg SC, respectively) to their regimens. The mice received ROT (2.5 mg/kg SC) every 48 h for 20 days after receiving DUL for the initial dose (96 h later). The current study focused on the DUL's ability to preserve usual behavioral function, enhance antioxidant and anti-inflammatory pathways, inhibit alpha-synuclein (α-syn), and increase parkin levels. It is concluded that DUL acts as an antioxidant and an anti-inflammatory to protect against ROT-induced PD. However, more studies are required to support this finding.

A journey across dopamine Metabolism: A rotational study of DOPAC

DOPAC, a relevant scaffold in dopamine metabolism, was probed in the gas phase and interrogated by high-resolution rotational spectroscopy. Herein, three distinct conformers were isolated in a supersonic jet and identified for the first time through an examination of the trend of the rotational constants and the dipole moment selection rules. Additionally, we examined the plausible relaxation pathways of the low-energy conformers of DOPAC, which helped us to claim the indirect detection of two additional conformers, providing conclusive experimental evidence of the flexible nature of this biomolecule. The current investigation sheds some light on the differences between jet-cooled rotational experiments and matrix-isolation infrared spectroscopy.

Modulation of cytotoxic amyloid fibrillation and mitochondrial damage of α-synuclein by catechols mediated conformational changes

The interplay between α-synuclein (α-syn) and catechols plays a central role in Parkinson's disease. This may be related to the modulating effects of catechols on the various aspects of α-syn fibrillization. Some of these effects may be attributed to the membrane-binding properties of the protein. In this work, we compare the effect of some catechols, including dopamine, epinephrine, DOPAL, and levodopa in micromolar concentrations, on the in vitro cytotoxicity of α-syn fibrils on human neuroblastoma SH-SY5Y cells. The study was followed by comparing the interactions of resulting structures with rat brain mitochondria used as an in vitro biological model. The obtained results demonstrate that catechols-induced structures have lost their cytotoxicity mimicking apoptotic cell death mediated by α-syn aggregates in different proportions. Moreover, α-syn fibrils-induced mitochondrial dysfunction, evaluated by a range of biochemical assays, was modulated by catechols-modified α-syn oligomers in different manners, as levodopa and DOPAL demonstrated the maximal and minimal effects, respectively. The plausible mechanism causing the inhibition of α-syn cytotoxic fibrillization and mitochondrial dysfunction by catechols is discussed. Taken together, we propose that catechols can prevent the cytotoxic assembly of α-syn and its destructive effects on mitochondria at various stages, suggesting that decreased levels of catechols in dopaminergic neurons might accelerate the α-syn cytotoxicity and mitochondrial dysfunction implicating Parkinson's disease.

Anti-Aging and Neuroprotective Properties of Grifola frondosa and Hericium erinaceus Extracts

Nutrition has relevant consequences for human health and increasing pieces of evidence indicate that medicinal mushrooms have several beneficial effects. One of the main issues in Western countries is represented by the challenges of aging and age-related diseases, such as neurodegenerative disorders. Among these, Parkinson’s disease (PD) affects 10 million people worldwide and is associated with α-synuclein misfolding, also found in other pathologies collectively called synucleinopathies. Here, we show that aqueous extracts of two edible mushrooms, Grifola frondosa and Hericium erinaceus, represent a valuable source of β-glucans and exert anti-aging effects in yeast. Their beneficial effects are mediated through the inhibition of the Ras/PKA pathway, with increased expression of heat shock proteins, along with a consistent increase of both mean and maximal lifespans. These fungal extracts also reduce the toxicity of α-synuclein heterologously expressed in yeast cells, resulting in reduced ROS levels, lower α-synuclein membrane localization, and protein aggregation. The neuroprotective activity of G. frondosa extract was also confirmed in a PD model of Drosophila melanogaster. Taken together, our data suggest the use of G. frondosa and H. erinaceus as functional food to prevent aging and age-related disorders, further supporting the neuro-healthy properties of these medicinal mushroom extracts.

3,4-Dihydroxyphenylethanol and 3,4-dihydroxyphenylacetic acid affect the aggregation process of E46K variant of α-synuclein at different extent: Insights into the interplay between protein dynamics and catechol effect

Parkinson's disease (PD) is a chronic multifactorial disease, whose etiology is not completely understood. The amyloid aggregation of α-synuclein (Syn) is considered a major cause in the development of the disease. The presence of genetic mutations can boost the aggregation of the protein and the likelihood to develop PD. These mutations can lead to early onset (A30P, E46K, and A53T) or late-onset (H50Q) forms of PD. The disease is also linked to an increase in oxidative stress and altered levels of dopamine metabolites. The molecular interaction of these molecules with Syn has been previously studied, while their effect on the pathological mutant structure and function is not completely clarified. By using biochemical and biophysical approaches, here we have studied the interaction of the familial variant E46K with two dopamine-derived catechols, 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylethanol. We show that the presence of these catechols causes a decrease in the formation of amyloid fibrils in a dose-dependent manner. Native- and Hydrogen/deuterium exchange-mass spectrometry (HDX-MS) provide evidence that this effect is strongly conformation dependent. Indeed, these molecules interact differently with the interconverting conformers of Syn and its familial variant E46K in solution, selecting the most prone-to-aggregation one, confining it into an off-pathway oligomer. These findings suggest that catechols could be a molecular scaffold for the design of compounds potentially useful in the treatment of Parkinson's disease and related conditions.