Terbutaline selectively reduces non-fibrillar α-synuclein aggregates and oxidative stress without affecting liquid-liquid phase separation or fibrillogenesis.

Aggregation of α-synuclein is intricately linked to Parkinson's disease (PD), progressing through liquid-liquid phase separation (LLPS) to toxic protofibrils and mature amyloid fibrils. Identifying compounds that selectively modulate toxic aggregation intermediates without interfering with normal cellular phase separation is a critical therapeutic goal. This study investigated the impact of terbutaline, a β2-adrenergic agonist, on the liquid-liquid phase separation, aggregation behaviour, cytotoxicity and oxidative stress induced by WT α-SYN and its variants. Terbutaline did not affect the size or physical properties of α-SYN condensates or alter fibril formation, as evidenced by unchanged Th T fluorescence and fluorescence polarization values. However, it significantly reduced the number of condensates and total aggregates, particularly amorphous moiety, in a concentration-dependent manner. This selective inhibition did not influence survival of SH-SY5Y cells but significantly reduced α-SYN-induced superoxide generation in rat RBCs-by up to 26% for WT and 53% for CT α-SYN aggregates. Distinct changes were observed in the oligomers formed by WT α-SYN and CT α-SYN. Direct interaction of terbutaline with both WT α-SYN and CT α-SYN was confirmed by isothermal titration calorimetry, with a stronger binding affinity observed for the CT α-SYN. Transmission electron microscopy showed discrete morphological changes in aggregate structure with terbutaline, supporting a shift away from toxic polymorphs. These findings highlight terbutaline's role as a potential modulator of early aggregation toxicity, warranting further exploration into structurally related compounds for therapeutic development in synucleinopathies.