Ameliorative effects of flavonoids and polyketides on the rotenone induced Drosophila model of Parkinson’s disease

Highlights

• Rotenone induced neurotoxicity in Drosophila melanogaster model of Parkinson’s disease.

• Plants derived flavonoids and polyketides reduced the oxidative stress in the brain.

• Flavonoids and polyketides rescued the locomotor behaviour deficit.

• Overall, studied compounds have high antioxidant potentials.

Abstract

Parkinson’s disease (PD) is a movement disorder associated with the progressive loss of dopaminergic neurons (DA). PD treatment remains unsatisfactory as the current synthetic drugs in clinical use relies on managing only motor symptoms. This study investigated antioxidant potentials of selected compounds namely, 5,6,7,4′-tetramethoxyflavone (1), 6-hydroxy-2,3,4,4′-tetramethoxychalcone (2), 6-methoxyhamiltone A (3), diosquinone (4) and toussantine D (5) against rotenone (6) induced PD in Drosophila melanogaster. Toxicity of these compounds was conducted by monitoring flies’ survival for seven days and determining the lethal concentrations (LC₅₀). Whereas compound 1 had LC₅₀ value of 91.3 μM within three days, compounds 2, 3, 4, and 5 had LC₅₀ values of 87.2, 58.0, 64.0 and > 1000 μM, respectively on the seventh day of the experiment. We exposed flies (1–4 days old) to 500 μM rotenone and co-treated with different doses of the test compounds in the diet for seven days at final concentrations of 11.0, 43.6 and 87.2 μM for compounds 2 and 3. The concentrations used for compound 4 were 8.0, 32.0 and 64.0 μM, while 250, 500 and 1000 μM were used for compound 5. Rotenone fed flies showed impaired climbing ability compared to control flies, the phenotype that was rescued by the treatment of tested phytochemicals. Rotenone toxicity also increased malondialdehyde levels assayed by lipid peroxidation in the brain tissues relative to control flies. This effect was reduced in flies exposed to rotenone and co-treated with the phytochemicals. Moreover, expression levels of mRNA of antioxidant enzymes; superoxide dismutase and catalase were elevated in flies exposed to rotenone and normalized in flies that were co-treated with tested compounds. Besides compound 1, this study provides overall evidence that the tested flavonoids and polyketides ameliorated the rotenone provoked neurotoxicity in D. melanogaster by battling the induced oxidative stress in brain cells including DA neurons and hence rescue the locomotor behaviour deficits.

Introduction

Parkinson’s disease (PD) is a movement disorder characterized by the progressive loss of dopaminergic (DA) neurons, presence of Lewy bodies in surviving neurons of the Substantia nigra and depletion of dopamine in striatum (Forno, 1996; Cuervo et al., 2010). PD is a complex disease, where both environmental factors and genetic liability contribute to its cause. While mechanisms involved in the pathogenesis of PD remain largely unknown, studies have shown the pivotal role of neuroinflammation and oxidative stress in the onset of PD (Gupta et al., 2008; Klingelhoefer and Reichmann, 2015). Likewise, ageing is also known to be a major risk factor of neurodegeneration in PD (Hindle, 2010).

Rotenone (6) is a naturally occurring pesticide derived from tropical plants such as Derris eliptica, Lonchocarpus and Tephrosia spp (Fabaceae) (Rattan, 2010). Due to its lipophilic property, it can cross the blood brain barrier and induces PD related symptoms in rodents and Drosophila melanogaster (Coulom and Birman, 2004; Testa et al., 2005; Stephano et al., 2018). Rotenone acts by inhibiting complex I of mitochondrial respiratory chain thereby enhancing the production of reactive oxygen species (ROS), depletion of ATP synthesis that brings oxidative stress and ultimately activate neuronal death pathways (Sherer et al., 2003; Heinz et al., 2017; Nagoshi, 2018a,b) Certainly, exposure to pesticides such as rotenone is associated with increased risk of PD (de Lau and Breteler, 2006; Tanner et al., 2011).

In two decades, D. melanogaster has been shown to be a resourceful model in the PD field. The fly has strong PD related phenotypes, including reduced locomotion, loss of DA neurons, protein aggregation, mitochondrial dysfunction and offensive behaviour of ROS (Feany and Bender, 2000; Whitworth, 2011; Nagoshi, 2018a,b). A recent study conducted in D. melanogaster model of PD gave insights on molecular pathways affected at the early phase of PD development (Stephano et al., 2018). Noticeably, D. melanogaster portrays strong homology of most genes allied with PD in human. Such genes among others comprise leucine-rich repeat kinase 2 (LRRK2), PTEN induced putative kinase 1 (PINK1), DJ-1 and Parkin (Xiong and Yu, 2018).

Since ageing and oxidative stress have been strongly associated with PD pathogenesis, the search for bioactive phytochemicals with the neuroprotective role and antioxidant properties is growing. The naturally occurring compounds are envisaged to provide better therapeutic actions than synthetic ones on several diseases and can also serve as food supplements to prevent diseases. Interestingly, D. melanogaster has recently been used as a potential model for identification of pharmacological properties of plants and plant-derived constituents against chemical-induced oxidative stress (Sudati et al., 2013; Panchal and Tiwari, 2017; Abolaji et al., 2018; Farombi et al., 2018). Natural products have shown promising results in clinical trials as neuroprotective agents targeting the treatment of neurodegenerative disorders (Seidl and Potashkin, 2011; de Andrade Teles et al., 2018).

In line with the current approach of searching for neuroprotective and antioxidant phytochemicals, the current study sought for the first time to investigate the roles of quinones from Diospyros kabuyeana (Moh'd, 2015), flavonoids from Erythrina schliebenii (Nyandoro et al., 2017) and N-cinnamoyltetraketide derivative from Toussantia orientalis (Samwel et al., 2011; Nyandoro et al., 2015) in the control of rotenone induced PD using D. melanogaster as an in vivo model. The selected compounds namely, 5,6,7,4′-tetramethoxyflavone (1), 6-hydroxy-2,3,4,4′-tetramethoxychalcone (2), 6-methoxyhamiltone A (3), diosquinone (4) and toussantine D (5) (Fig. 1) are known to possess antimicrobial, anticancer cells, antiviral or antioxidant properties (Samwel et al., 2011; Nyandoro et al., 2014; Moh'd, 2015; Nyandoro et al., 2015, 2017).