A Thiol-Click-Based Dopaminequinone-Specific Fluorescent Probe for In Vivo Imaging in Parkinson's Disease Models

Parkinson's disease (PD) is closely associated with dopaminequinone (DAQ). However, DAQ's high reactivity, short half-life, and difficulty in in vivo detection have hindered direct observation of its spatiotemporal dynamics and pathological progression. In this study, a series of fluorescent probes were developed using dicyanoisophorone as the fluorescent parent molecule and 3-mercaptopropionic acid as the click group, while the electron density of the ester group was regulated by push-pull electron groups. In the presence of PBS buffer and Co2+, the probe responds specifically and rapidly to dopamine (DA), and among them, probe OCH3-HS could detect DAQ within 260 s. This mechanism relies on a click reaction between the quinone moiety of DAQ and the thiol group (-SH) of the probe, followed by an amine attack on the ester group, which ultimately releases the fluorophore, thereby enabling the in vivo monitoring of DAQ. Cell imaging results showed that during the 6-8 h incubation of cells with N-methyl-4-phenylpyridinium iodide (MPP+), DAQ levels increased significantly. The probe can cross the blood-brain barrier (BBB), and in vivo imaging of mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) showed that the brain fluorescence intensity increased by 2.8-fold, indicating a significant generation of DAQ. Behavioral analysis showed that DAQ accumulation was associated with motor deficits. The fluorescent probe developed in this study enables spatiotemporal dynamic monitoring of DAQ, providing a precise tool for the early diagnosis and intervention of PD, as well as a new strategy for the real-time monitoring of active intermediates in DA.