Triprolidine Interferes with α-Synuclein Fibrillation and Remodels Aggregate Structure via Conformational Modulation

Parkinson's disease (PD) is characterized by the pathological aggregation of α-synuclein (α-syn) into β-sheet-rich fibrils, contributing to neuronal toxicity and oxidative stress. In this study, we investigated the inhibitory and disaggregating effects of Triprolidine (TC) on α-syn fibrillation through a combined experimental and computational approach. Biophysical assays, including ThT assay, DLS, and ANS assays, demonstrated that TC inhibits α-syn fibrillation in a concentration-dependent manner (IC50 ≈ 255 μM), disrupts preformed fibrils, and maintains the protein's native form. CD data further revealed that TC prevents the transition of α-syn to its toxic β-sheet-rich form and facilitates partial structural reversal during disaggregation. To elucidate the molecular mechanism of inhibition, we performed all-atom molecular dynamics (MD) simulations followed by Markov State Model (MSM) construction. The simulations revealed that TC binding remodels the conformational landscape of α-syn by stabilizing compact, disordered states and reducing the population of β-sheet-prone intermediates, particularly in the aggregation-prone NAC region. MSM analysis identified metastable states with diminished aggregation potential and reduced inter-residue contact probability, offering mechanistic insights into how TC interferes with early nucleation events. TC attenuates seeded fibrillation in a concentration-dependent manner too. Complementary cellular assays, including MTT and hemolytic assays, confirmed a significant reduction in α-syn-induced cytotoxicity upon TC treatment, with a decrease in ROS levels as confirmed by the DCFH-DA assay. Together, these findings demonstrate that TC modulates both the structural dynamics and functional toxicity of α-synuclein, and highlight its potential as a promising chemical modulator for further investigation in PD-related protein aggregation.