Quantitative analysis of the therapeutic effect of magnolol on MPTP-induced mouse model of Parkinson's disease using in vivo 18F-9-fluoropropyl-(+)-dihydrotetrabenazine PET imaging

Abstract

18F-9-Fluoropropyl-(+)-dihydrotetrabenazine [18F-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, 18F-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. Twenty-minute static 18F-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. 18F-FP-(+)-DTBZ PET imaging was performed the day after the final treatment. All 18F-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 of 18F-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 vivo 18F-FP-(+)-DTBZ ARG and IHC results correlated favourably with the PET imaging results. 18F-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 using 18F-FP-(+)-DTBZ animal PET is a useful method to evaluate the efficacy of therapeutic drugs i.e., magnolol, for the management of PD.

Fig 1. Experimental paradigm of therapeutic effect of magnolol on MPTP-lesioned animals.

Fig 2. Coregistered ¹⁸F-FP-(+)-DTBZ PET and T2-weighted MRI representative images in coronal and axial views of C57BL/6 mouse brain.

(A) The Sham, (B) the MPTP, and (C) the MPTP + Magnolol groups. Images were acquired one day after the final magnolol treatment (day 17). CPu: caudate putamen; CB: cerebellum.

Fig 3. Ex vivo ARG of ¹⁸F-FP-(+)-DTBZ in C57BL/6 mouse brain.

ARG performed immediately after the third PET scan on day 17. (A) The Sham, (B) the MPTP, and (C) the MPTP + Magnolol mice. CPd: dorsal caudate putamen; CPv: ventral caudate putamen; SN: substantial nigra.

Fig 4. Quantitative analysis of the ex vivo ¹⁸F-FP-(+)-DTBZ ARG in the Sham, the MPTP, and the MPTP + Magnolol mice (n = 4 in each group).

*p < 0.05 vs. the Sham group; †p < 0.05 vs. the MPTP group.

Fig 5. Scatter plot and linear regression analysis between ex vivo ARG data and quantitative striatal ¹⁸F-FP-(+)-DTBZ SUr data obtained using PET imaging.

Fig 6. Immunohistochemical staining of anti-VMAT2 and anti-TH antibodies in striatal sections of the Sham, the MPTP, and the MPTP + Magnolol mice.

Bar = 400 μm.