Neuroprotective effects of disubstituted dithiolethione ACDT against manganese-induced toxicity in SH-SY5Y cells

Dithiolethiones are lipophilic, organosulfur compounds that activate the Nrf2 transcription factor causing an upregulation of various phase II antioxidant enzymes. A disubstituted dithiolethione 5-amino-3-thioxo-3H-(1,2) dithiole-4-carboxylic acid ethyl ester (ACDT) retains the functional pharmacophore while also containing modifiable functional groups. Neuroprotection against autoimmune encephalomyelitis in vivo and 6-hydroxy dopamine (a model for Parkinson's disease) in vitro have been previously reported with ACDT. Manganese (Mn) is a metal essential for metabolic processes at low concentrations. Overexposure and accumulation of Mn leads to a neurological condition called manganism which shares pathophysiological sequelae with parkinsonism. Here we hypothesized ACDT to be protective against manganese-induced cytotoxicity. SH-SY5Y human neuroblastoma cells exposed to 300 mu M MnCl2 displayed approximately 50% cell death, and a 24-h pretreatment with 75 mu M ACDT significantly reversed this cytotoxicity. ACDT pretreatment was also found to increase total GSH levels (2.18-fold) and the protein levels of NADPH:quinone oxidoreductase-1 (NQO1) enzyme (6.33-fold), indicating an overall increase in the cells' antioxidant defense stores. A corresponding 2.32-fold reduction in the level of Mn-induced reactive oxygen species was also observed in cells pretreated with ACDT. While no changes were observed in the protein levels of apoptotic markers Bax and Bcl-2, pretreatment with 75 mu M ACDT led to a 2.09-fold downregulation of ZIP14 import transporter, indicating a potential reduction in the cellular uptake of Mn as an additional neuroprotective mechanism. These effects did not extend to other transporters like the divalent metal transporter 1 (DMT1) or ferroportin. Collectively, ACDT showed substantial neuroprotection against Mn-induced cytotoxicity, opening a path for dithiolethiones as a potential novel therapeutic option against heavy metal neurotoxicity.