Neuroprotective Effects of Extracts from Tiger Milk Mushroom Lignosus rhinocerus Against Glutamate-Induced Toxicity in HT22 Hippocampal Neuronal Cells and Neurodegenerative Diseases in Caenorhabditis elegans

SIMPLE SUMMARY: Neurodegenerative diseases are recognized as one of the major public health issues in aging populations worldwide. High reactive oxygen species (ROS) cause oxidative stress, leading to cellular injury and neuronal cell death. While it has been used as traditional medicine, little is known about the neuroprotective effect of the Tiger Milk Mushroom Lignosus rhinocerus (LR). The aims of this study were to investigate the neuroprotective effect of three extracts of LR, including ethanol extract (LRE), cold water extract (LRC) and hot water extract (LRH), against glutamate-induced oxidative stress in mouse hippocampal (HT22) cells (in vitro model) as well as to determine their effect in Caenorhabditis elegans (in vivo model). We found that only LRE exhibited neuroprotective effects both in vitro (alleviation of glutamate-induced ROS in HT22 cells, resulting in increased cell survival) and in vivo (prevention of neurotoxicity in C. elegans). Therefore, active chemical constituents in LRE may serve as neuroprotectant candidates. Nevertheless, LRE extracts should be extensively studied for their neuroprotective activity in the future. ABSTRACT: Despite the Tiger Milk Mushroom Lignosus rhinocerus (LR) having been used as a traditional medicine, little is known about the neuroprotective effects of LR extracts. This study aims to investigate the neuroprotective effect of three extracts of LR against glutamate-induced oxidative stress in mouse hippocampal (HT22) cells as well as to determine their effect in Caenorhabditis elegans. In vitro, we assessed the toxicity of three LR extracts (ethanol extract (LRE), cold-water extract (LRC) and hot-water extract (LRH)) and their protective activity by MTT assay, Annexin V-FITC/propidium iodide staining, Mitochondrial Membrane Potential (MMP) and intracellular ROS accumulation. Furthermore, we determined the expression of antioxidant genes (catalase (CAT), superoxide dismutase (SOD1 and SOD2) and glutathione peroxidase (GPx)) by qRT-PCR. In vivo, we investigated the neuroprotective effect of LRE, not only against an Aβ-induced deficit in chemotaxis behavior (Alzheimer model) but also against PolyQ40 formation (model for Morbus Huntington) in transgenic C. elegans. Only LRE significantly reduced both apoptosis and intracellular ROS levels and significantly increased the expression of antioxidant genes after glutamate-induced oxidative stress in HT22 cells. In addition, LRE significantly improved the Chemotaxis Index (CI) in C. elegans and significantly decreased PolyQ40 aggregation. Altogether, the LRE exhibited neuroprotective properties both in vitro and in vivo.