Exploring the Neuroprotective Role of GLP-1 Secretagogue in Rotenone Induced Mouse Model of Parkinson's Disease

Abstract

Background: Parkinson’s disease (PD) is the second most prevalent neurodegenerative disorder. People beyond the age 50 - 60 are affected by this age-related disorder. Progressive and considerable loss of dopaminergic (DA) neurons in substantia nigra pars compacta (SNpc) contributes primarily to initiation and advancement of PD pathology. Cinnamaldehyde, a natural occurring flavonoid, may increase the GLP1 release, acting on GLP1R. This may lead to GSK-3β inhibition and subsequently halt alpha-synuclein aggregation. Thus, it may hinder PD progression and render neuroprotective effect. Objectives: The present study was designed to investigate the neuroprotective action and mechanism of action of cinnamaldehyde against rotenone induced Parkinson’s disease in C57BL/6 mice. Methods: Docking studies targeted three proteins: Keap-1, PI3K, and GPR40, were carried out. Molecular docking utilizing Autodock Vina and Autodock Tools was performed, employing protein structures from the RCSB Protein Data Bank and drug molecules sourced from PubChem. Protein refinement and visualization were conducted using PyMol and BIOVIA Discovery Studio, with binding sites defined via Autogrid. Binding energies were determined with Autodock, and interactions were analyzed using BIOVIA Discovery Studio. To develop rotenone induced PD model, C57BL/6 mice were separated into four groups, with ten animals in each group. In the experimental setup, the Normal Control (NC) group received 0.5% carboxymethyl cellulose (CMC). The Rotenone (RT) group received Rotenone at 30 mg/kg orally (Disease group), while the Cinnamaldehyde (CN) at 50 mg/kg orally was administered to Treatment group for 28 days. In the CN against RT induced toxicity group, both Rotenone and Cinnamaldehyde were administered, with Rotenone at 30 mg/kg and Cinnamaldehyde at 50 mg/kg, respectively. The behavioral parameters were performed such as Y-maze, pole test, wire hang, and beam walk. These parameters were performed after every two weeks, taking the baseline behavioral studies. The study was carried out for 28 days with administration of Rotenone (30 mg/kg) as inducing agent in both disease group and treatment against disease group,with the parallel administration of cinnamaldehyde (50mg/kg) to treatment and treatment against disease group. At the end of the 4th week, the study animals were sacrificed and whole brain, hippocampus, striatum, cortex was collected. Oxidative stress marker parameters such as GSH and MDA were measured from tissue homogenate. Neuroprotective markers such as alpha-synuclein, PI3K, AKT, BDNF, GSK-3β, GLP1, NF-κB were analyzed from tissue homogenate using ELISA kits. Histopathological analysis such as H and E stain (hematoxylin and eosin staining) and Nissl stain were performed for neuronal shrinkage, inflamed cells, and loss of dopaminergic neurons. Results: Binding affinity of cinnamaldehyde was good with all the three targets (PI3K, Keap-1, and GPR40) in molecular docking studies. Motor coordination was assessed using beam walk and pole test. After 4 weeks of disease induction, it was found that there was a significant difference between control and rotenone treated groups in behavioral studies. This indicates the progression of the disease. Also, a significant data was observed between disease control group and combination group for Y maze (% alternation), pole test (time to descend) round beam walk (time taken to travel to home-cage) and wire-hang (latency to fall). Thus, restoration of behavioral deficits was observed. Upon analysis of molecular parameters, it was observed that cinnamaldehyde markedly increased the expression of PI3K/AKT, GSK-3β, and GLP-1, shedding light on the mechanism underlying the action. Neurotropic parameters like CREB, BDNF, Nrf-2 level was increased by CN treatment, whereas it downregulated alpha-synuclein. Also, in histopathological studies, it was observed that cinnamaldehyde was able to restore structural alterations caused due to rotenone exposure. Conclusion: Cinnamaldehyde demonstrated good binding affinity with all the three targets in in-silico studies. In in-vivo studies, cinnamaldehyde restored motor abnormalities, upregulated PI3K, AKT and BDNF levels. It also recued alpha-synuclein levels. Moreover, it restored neuronal density and integrity. Thus, our study demonstrated the neuroprotective actions of cinnamaldehyde.