Rat brain endothelial cells are a target of manganese toxicity

Manganese (Mn) is an essential trace metal; however, exposure to high Mn levels can result in neurodegenerative changes resembling Parkinson's disease (PD). Information on Mn's effects on endothelial cells of the blood-brain barrier (BBB) is lacking. Accordingly, we tested the hypothesis that BBB endothelial cells are a primary target for Mn-induced neurotoxicity. The studies were conducted in an in vitro BBB model of immortalized rat brain endothelial (RBE4) cells. ROS production was determined by F₂-isoprostane (F₂-IsoPs) measurement. The relationship between Mn toxicity and redox status was investigated upon intracellular glutathione (GSH) depletion with diethylmaleate (DEM) or l-buthionine sulfoximine (BSO). Mn exposure (200 or 800 μM MnCl₂ or MnSO₄) for 4 or 24 h led to significant decrease in cell viability vs. controls. DEM or BSO pre-treatment led to further enhancement in cytotoxicity vs. exposure to Mn alone, with more pronounced cell death after 24-h DEM pre-treatment. F₂-IsoPs levels in cells exposed to MnCl₂ (200 or 800 μM) were significantly increased after 4 h and remained elevated 24 h after exposure compared with controls. Consistent with the effects on cell viability and F₂-IsoPs, treatment with MnCl₂ (200 or 800 μM) was also associated with a significant decrease in membrane potential. This effect was more pronounced in cells exposed to DEM plus MnCl₂ vs. cells exposed to Mn alone. We conclude that Mn induces direct injury to mitochondria in RBE4 cells. The ensuing impairment in energy metabolism and redox status may modify the restrictive properties of the BBB compromising its function.