Rhinacanthin-C but Not -D Extracted from Rhinacanthus nasutus (L.) Kurz Offers Neuroprotection via ERK, CHOP, and LC3B Pathways

Abstract

Neurodegenerative diseases present an increasing problem as the world’s population ages; thus, the discovery of new drugs that prevent diseases such as Alzheimer’s, and Parkinson’s diseases are vital. In this study, Rhinacanthin-C and -D were isolated from Rhinacanthus nasustus, using ethyl acetate, followed by chromatography to isolate Rhinacanthin-C and -D. Both compounds were confirmed using NMR and ultra-performance-LCMS. Using glutamate toxicity in HT-22 cells, we measured cell viability and apoptosis, ROS build-up, and investigated signaling pathways. We show that Rhinacanthin-C and 2-hydroxy-1,4-naphthoquinone have neuroprotective effects against glutamate-induced apoptosis in HT-22 cells. Furthermore, we see that Rhinacanthin-C resulted in autophagy inhibition and increased ER stress. In contrast, low concentrations of Rhinacanthin-C and 2-hydroxy-1,4-naphthoquinone prevented ER stress and CHOP expression. All concentrations of Rhinacanthin-C prevented ROS production and ERK1/2 phosphorylation. We conclude that, while autophagy is present in HT-22 cells subjected to glutamate toxicity, its inhibition is not necessary for cryoprotection.

Neuroprotective Effects of Albizia lebbeck (L.) Benth. Leaf Extract against Glutamate-Induced Endoplasmic Reticulum Stress and Apoptosis in Human Microglial Cells

“…Interestingly, the pretreatment of cells with AHE protected against toxicity by reducing ERK phosphorylation (Figure 4A,B). Several studies demonstrated glutamate-induced toxicity through activation of ERK, which is associated with cell death in many neuronal death models, including microglial cells [37,41,57,58]. Furthermore, our investigation showed the inhibitory effect of AHE on glutamateinduced ER stress and apoptosis linked to cellular antioxidant enzymes defense in HMC3 cells.…”

“…The high concentration and accumulation of glutamate are involved in ER stress in the CNS, leading to apoptotic cell death. This event can stimulate the specific ER stress proteins, including the calcium ion-mediated calpain/caspase-12 pathway or the CHOP pathway [ 35 , 36 , 37 , 38 ]. To examine the effect of AHE on ER stress-induced apoptosis caused by glutamate, we evaluated protein expression of the markers of ER stress, including calpain1, cleaved caspase-12, and CHOP, using Western blot analysis.…”

“…Interestingly, the pretreatment of cells with AHE protected against toxicity by reducing ERK phosphorylation ( Figure 4 A,B). Several studies demonstrated glutamate-induced toxicity through activation of ERK, which is associated with cell death in many neuronal death models, including microglial cells [ 37 , 41 , 57 , 58 ].…”