Comparative assessment of the cytotoxicity of Nrf2-dependent signaling pathway modulators: the role of hormetic protective effect in Parkinson’s disease modeling in vitro

In the context of neurodegenerative diseases, one of the most pressing problems of modern medicine, neurohormesis – the mechanism by which the brain responds to low-intensity subtoxic stressors – deserves special attention. The aim of this study was to determine the concentration-dependent effects of inducers and inhibitors of the Keap1/Nrf2/ARE system on the proliferative activity of SH-SY5Y cells under conditions of a parkinsonism-like state induced by the neurotoxin MPP⁺. Material and methods. Human SH-SY5Y neuroblastoma cells were cultured according to standard procedures. For experiments, cells were seeded into 96-well culture plates at a density of 10 4 cells per well. After 24 h, inducers of the Keap1/Nrf2/ARE system (sulforaphane, original monophenols sodium 3-(3’- tert -butyl-4’-hydroxyphenyl)propyl thiosulfate (TS-13) and sodium 3-(3’- tert -butyl-4’-hydroxyphenyl)propyl selenosulfate (SeS-13)) or an inhibitor (brusatol) were added to the corresponding wells. To model the parkinsonism-like state, 24 h later serial dilutions of the neurotoxin MPP+ were added to the culture and incubated for 16 h. The effect of the compounds on proliferation was determined after 72 h using a resazurin assay. Results and discussion. The obtained results demonstrate the uniqueness of TS-13, which combines high neuroprotective activity in an in vitro model of Parkinson’s disease with an exceptional safety profile. The analogue of TS-13 in which the divalent sulfur atom in the para -propyl substituent is replaced by selenium (SeS-13) is somewhat more effective as a protective agent; however, its significantly higher intrinsic cytotoxicity limits its applicability. In contrast, sulforaphane, a classical Nrf2 activator, did not show a protective effect, which is likely due to the fact that its optimal protective concentration nearly coincides with the threshold of its own cytotoxicity, and in the experiment it acted at the edge of toxicity. Finally, the Nrf2 inhibitor brusatol, which enhances the degradation of this transcription factor, not only failed to protect the cells but, at higher concentrations, potentiated MPP⁺ toxicity. Taken together, these data indicate that the neuroprotective action of TS-13 and SeS-13 in the MPP⁺-induced toxicity model is mediated by activation of the Keap1/Nrf2/ARE system, and the dose-response curve exhibits a bell-shaped (hormetic) character.