Oxyresveratrol reduces α-synuclein aggregation in a Caenorhabditis elegans model with a non-linear dose-response profile

Aggregation of α-synuclein is a central pathological feature of Parkinson’s disease and contributes to neuronal dysfunction and disease progression. Despite extensive research, effective modulators of this process remain limited. Natural polyphenols have been proposed as potential anti-aggregation agents, although their in vivo efficacy remains insufficiently characterised. Mulberry-derived metabolites represent a promising but underexplored source of bioactive compounds. We hypothesised that oxyresveratrol, a major mulberry-derived stilbene, modulates α-synuclein aggregation in vivo.

Mulberry (Morus alba) hairy roots were elicited with hydroxypropyl-β-cyclodextrin, and extracellular metabolites were extracted after 21 days using ethyl acetate. The extract composition was analysed by high-performance liquid chromatography (HPLC) to identify major constituents. Anti-aggregation activity was evaluated in the transgenic Caenorhabditis elegans strain NL5901 expressing human α-synuclein fused to GFP. Worms were exposed to elicited and non-elicited extracts, as well as to oxyresveratrol (0-100 µM). Aggregation was quantified on day 7 of adulthood by fluorescence microscopy as the integrated fluorescence density in ImageJ. Each condition included at least 40 animals, and two independent experiments were performed using different extract batches and separate worm generations, yielding consistent results across replicates. Data from independent experiments were pooled following consistency assessment. Data are presented as mean ± SEM. Statistical analysis was performed using one-way ANOVA followed by Tukey’s test or Kruskal-Wallis followed by Dunn’s test, as appropriate. Molecular docking simulations were conducted using the fibrillar α-synuclein structure (PDB 6CU7) to explore potential binding interactions.

Elicited extracts significantly reduced α-synuclein aggregation compared to non-elicited controls. At 10% extract concentration, aggregation decreased by 16.7% (p = 0.019), while a stronger reduction of 31.6% was observed at 50% concentration (p < 0.001), indicating concentration-dependent activity. High-performance liquid chromatography identified oxyresveratrol as one of the major components of the elicited extracts, supporting its selection for further evaluation. Oxyresveratrol significantly reduced aggregation in a concentration-dependent manner (Kruskal-Wallis H = 83.3, p < 0.001). Aggregation decreased from 100% in control conditions to 78% at 5 µM (p = 0.005), 63% at 25 µM, and reached maximal effects at 50-75 µM (54% and 53%, respectively; both p < 0.001 vs control). At 100 µM, the effect was attenuated (68%), indicating a non-linear dose-response profile. These effects were consistently observed across independent biological replicates, supporting the robustness of the observed response pattern. Docking analysis suggested preferential localisation of oxyresveratrol within the non-amyloid-β component region of α-synuclein, a highly hydrophobic domain which is critical for protein aggregation.

Oxyresveratrol reduces α-synuclein aggregation in vivo with maximal efficacy at intermediate concentrations, supporting a non-linear modulation of aggregation processes. The reproducibility across independent biological replicates strengthens the robustness of this effect. Predicted interactions within aggregation-prone regions of α-synuclein provide a plausible structural basis for the observed activity. These findings position oxyresveratrol as a biologically active modulator of α-synuclein aggregation and justify further mechanistic investigation in neurodegenerative models.

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