Neuroprotective Effects of the Nutraceutical Dehydrozingerone and Its C2-Symmetric Dimer in a Drosophila Model of Parkinson's Disease

Abstract

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons responsible for unintended or uncontrollable movements. Mutations in the leucine-rich repeat kinase 2 locus contribute to genetic forms of PD. The fruit fly Drosophila melanogaster carrying this mutation (LRRK2-Dm) is an in vivo model of PD that develops motor impairment and stands for an eligible non-mammalian paradigm to test novel therapeutic approaches. Dehydrozingerone (DHZ) is a natural phenolic compound isolated from ginger and presents anti-inflammatory, antioxidant and neuroprotective properties, making it a potential therapeutic target for PD. We administered DHZ and its C₂-symmetric dimer (DHZ-DIM) at 0.5 and 1 mM for 14 and 21 days in the LRRK2-Dm, with the aim of assessing changes in rescuing motor behavior, brain dopaminergic neurons, mitochondria and synapses (T-bars). The shorter treatment with both molecules revealed efficacy at the higher dose, improving climbing behavior with a prevention of dopaminergic neuronal demise. After 21 days, a recovery of the motor disability, dopaminergic neuron loss, mitochondrial damage and T-bars failure was observed with the DHZ-DIM. Our data indicate that the DHZ-DIM exerts a more potent neuroprotective effect with respect to the monomer in LRRK2-Dm, prompting further investigation of these compounds in rodent models of PD.

Keywords: Drosophila melanogaster; LRRK2; Parkinson’s disease; dehydrozingerone; hydroxylated biphenyls; natural compounds; neuroprotection; nutraceutical compounds.

Figure 1

Chemical structures of (a) curcumin; (b) ferulic acid, vanillin and dehydrozingerone (DHZ).

Scheme 1

Synthesis of dehydrozingerone (DHZ) and its dimer (DHZ-DIM).

Figure 2

Effect of DHZ and DHZ-DIM at 0.5 mM and 1 mM on the climbing behavior parameters in both LRRK and w1118 WT flies and their respective control groups at 14 (a,b) and 21 days (c,d) of treatment. ^§ and **** p < 0.0001 vs. LRRK vehicle; ** p < 0.01 vs. LRRK vehicle.

Figure 3

Percentage of w1118 and LRRK individuals reaching the target within 10 s.

Figure 4

Life span. (a): reduced life span in LRRK compared to w1118 flies, both treated with vehicle; (b): survival rate observed in DHZ- and DHZ-DIM-treated LRRK flies at 1 mM compared to WT vehicle. Cumulative survival curve data are expressed as means ± SEM. *** p < 0.001 indicates significant difference between LRRK vehicle and WT vehicle. **** p < 0.0001 LRRK vehicle vs. LRRK treated with DHZ-DIM (Gehan–Breslow–Wilcoxon test).

Figure 5

Representative image stacks showing the entire brain ((a): 10× scale bar: 100 µm) and the dopaminergic brain neurons in all posterior clusters ((b): 63×, scale bar: 10 µm).

Figure 6

DHZ and DHZ-DIM prevent the loss of dopaminergic neurons. Both compounds at 1 mM significantly prevented the loss of dopaminergic neurons in all posterior clusters at 14 days of treatment, whereas at 21 days, a significant prevention of dopaminergic neuron loss was observed only with the DHZ-DIM treatment. * p < 0.05, ** p < 0.01, *** p < 0.001 and **** p < 0.0001 indicate significant differences between LRRK2 vehicle and LRRK2 treated with DHZ, DHZ-DIM or vehicle and treated WT groups. ^§ p < 0.0001 LRRK treated with DHZ-DIM vs. LRRK treated with DHZ.

Figure 7

Representative images of mitochondria (8000X) acquired from the protocerebrum of LRRK and w1118 flies treated with vehicle (a–d), LRRK treated with DHZ (b) and DHZ-DIM (c) for 21 days. Red arrows: mitochondria with swollen cristae; black arrows: mitochondria with normal cristae; white arrows: T-bars.

Figure 8

DHZ and DHZ-DIM effect on the number of total mitochondria, percentage of cristae and T-bars in the protocerebrum of LRRK after 21 days of treatment. * p < 0.05 and **** p < 0.0001 indicate significant differences between LRRK vehicle and LRRK treated with DHZ, DHZ-DIM or vehicle and treated WT groups. ^& p < 0.0001 LRRK treated with DHZ-DIM vs. LRRK treated with DHZ.