Assessment of Angiopep-2 targeting intracerebral α-synuclein aggregates in a PFF-induced rat model of Parkinson's disease based on 7T CEST-MRI.

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α-Synuclein has been demonstrated to deposit early in the brains of individuals with Parkinson's disease (PD). Detecting α-synuclein aggregates can enhance the accuracy of early PD diagnosis. In this study, we investigated the feasibility of the peptide probe Angiopep-2 (ANG) for targeting and visualizing α-synuclein deposits in a PFF-induced rat model of PD. ANG was selected based on its blood-brain barrier (BBB) penetrability mediated by low-density lipoprotein receptor-related protein-1 (LRP1) and its specific aromatic motifs that favor interaction with the hydrophobic grooves of α-synuclein aggregates. The affinity of ANG for α-synuclein was confirmed through molecular docking and fluorescence binding assays. Behavioral tests confirmed that PFF-injected rats exhibited motor deficits consistent with early-stage pathology. In vivo, the Chemical Exchange Saturation Transfer (CEST) ratio was significantly higher in PFF rats injected with ANG compared with Sham rats (15.3 ± 0.2 vs. 10.4 ± 0.2, p < 0.001), supporting its robustness for 7 T MRI-CEST imaging. Furthermore, in vivo 7 T MRI-CEST imaging showed strong spatial concordance with fluorescence staining and immunohistochemistry (R² = 0.967, p < 0.05). Crucially, ANG showed no signal retention in glioma or brain metastasis models despite their high vascular permeability and LRP1 expression, effectively ruling out the possibility that the signal in PFF rats is driven by non-specific leakage or the enhanced permeability and retention (EPR) effect. These findings demonstrate that ANG is a promising CEST contrast agent for visualizing α-synuclein deposits in the PFF-induced rat model, providing a potential foundation for translational imaging studies in PD.

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