A comparative study of gallic acid and its derivatives on the binding to Keap1 and their ability against 6-hydroxydopamine-induced cytotoxicity

This study compared gallic acid (GLA) and its derivatives, i.e. ginnalin A (GA), 1,2,3,4,6-penta-O-galloyl-β-D-glucose (PGG), and (-)-epigallocatechin-3-gallate (EGCG) on their ability against 6-hydroxydopamine (6-OHDA)-induced cytotoxicity. Their binding to the Kelch-like ECH-associated protein 1 (Keap1) Kelch domain was assessed using isothermal titration calorimetry (ITC) and molecular docking. Cellular assays, such as ROS quantification, In-Cell Western assay and quantitative real-time PCR (qRT-PCR) analysis, were performed using human neuroblastoma (SH-SY5Y) cells to investigate their involvement in the nuclear factor erythroid-2 related factor 2 (Nrf2)/Keap1 and the nuclear factor-κB (NF-κB) pathways. We found that these four natural products (NPs) can activate the Nrf2/Keap1 pathways with GLA exhibiting the highest and EGCG displaying the lowest activating capability. However, their inhibitory effects on the NF-κB pathway showed a different order of potencies, with EGCG exerting the least inhibitory effect. All these contribute to overall similar cell viability in counteracting 6-OHDA-induced cytotoxicity.