Quantitative analysis of the therapeutic effect of magnolol on MPTP-induced mouse model of Parkinson's disease using in vivo18 F-9-fluoropropyl-(+)-dihydrotetrabenazine PET imaging

¹⁸F-9-Fluoropropyl-(+)-dihydrotetrabenazine [¹⁸ F-FP-(+)-DTBZ] positron emission tomography (PET) has been shown to detect dopaminergic neuron loss associated with Parkinson's disease (PD) in human and neurotoxin-induced animal models. A polyphenol compound, magnolol, was recently proposed as having a potentially restorative effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- or 6-hydroxydopamine-treated animal models. In this study,¹⁸ F-FP-(+)-DTBZ PET was used to determine the therapeutic efficacy of magnolol in an MPTP-PD mouse model that was prepared by giving an intraperitoneally (i.p.) daily dose of 25 mg/kg MPTP to male C57BL/6 mice for 5 consecutive days. Twentyminute static18 F-FP-(+)-DTBZ PET scans were performed before MPTP treatment and 5 days after the termination of MPTP treatment to set up the baseline control. Half of the MPTP-treated mice then received a daily dose of magnolol (10 mg/kg dissolved in corn oil, i.p.) for 6 days.¹⁸ F-FP-(+)-DTBZ PET imaging was performed the day after the final treatment. All¹⁸ F-FP-(+)-DTBZ PET images were analysed and the specific uptake ratio (SUr) was calculated. Ex vivo autoradiography (ARG) and corresponding immunohistochemistry (IHC) studies were conducted to confirm the distribution of dopaminergic terminals in the striatum. The striatal SUr ratios of¹⁸ F-FP-(+)-DTBZ PET images for the Sham, the MPTP, and the MPTP + Magnolol-treated groups were 1.25 ± 0.05, 0.75 ± 0.06, and 1.00 ± 0.11, respectively (n = 4 for each group). The ex vivo¹⁸ F-FP-(+)-DTBZ ARG and IHC results correlated favourably with the PET imaging results.¹⁸ F-FP-(+)-DTBZ PET imaging suggested that magnolol post-treatment may reverse the neuronal damage in the MPTP-lesioned PD mice. In vivo imaging of the striatal vesicular monoamine transporter type 2 (VMAT2) distribution using18 F-FP-(+)-DTBZ animal PET is a useful method to evaluate the efficacy of therapeutic drugs i.e., magnolol, for the management of PD.