Chlorogenic Acid: a Polyphenol from Coffee Rendered Neuroprotection Against Rotenone-Induced Parkinson's Disease by GLP-1 Secretion.

Parkinson's disease (PD) is a chronic motor disorder, characterized by progressive loss of dopaminergic neurons. Numerous studies suggest that glucagon-like peptide-1 (GLP-1) secretagogue has a neuroprotective role in PD models. The present study evaluated potential of coffee bioactive compounds in terms of their ability to bind GPR-40/43 and tested the neuroprotective effect of best candidate on rotenone-induced PD mice acting via GLP-1 release. In silico molecular docking followed by binding free energy calculation revealed that chlorogenic acid (CGA) has a strong binding affinity for GPR-40/43 in comparison to other bioactive polyphenols. Molecular dynamics simulation studies revealed stable nature of GPR40-CGA and GPR43-CGA interaction and also provided information about the amino acid residues involved in binding. Subsequently, in vitro studies demonstrated that CGA-induced secretion of GLP-1 via enhancing cAMP levels in GLUTag cells. Furthermore, in vivo experiments utilizing rotenone-induced mouse model of PD revealed a significant rise in plasma GLP-1 after CGA administration (50 mg/kg, orally for 13 weeks) with concomitant increase in colonic GPR-40 and GPR-43 mRNA expression. CGA treatment also prevented rotenone-induced motor and cognitive impairments and significantly restored the rotenone-induced oxidative stress. Meanwhile, western blot results confirmed that CGA treatment downregulated rotenone-induced phosphorylated alpha-synuclein levels by upregulating PI3K/AKT signaling and inactivating GSK-3β through the release of GLP-1. CGA treatment ameliorated rotenone-induced dopaminergic nerve degeneration and alpha-synuclein accumulation in substantia nigra and augmented mean density of dopaminergic nerve fibers in striatum. These findings demonstrated novel biological function of CGA as a GLP-1 secretagogue. An increase in endogenous GLP-1 may render neuroprotection against a rotenone mouse model of PD and has the potential to be used as a neuroprotective agent in management of PD.