Determination of the detectable concentration of manganese used in neuronal MEMRI and its effect on cortical neurons in vitro

Abstract

Objective: Manganese (Mn2+)-enhanced magnetic resonance imaging (MEMRI) has received increasing attention because of its functional and anatomic value in brain studies. However, the contrast agent, Mn2+, will lead to neurotoxicity at high concentrations, which limits its use in biomedical research. This study was designed to determine whether Mn2+ can significantly enhance the signal intensity (SI) of primary cultured cortical neurons at non-toxic levels.Method: Neurons were incubated with different concentrations of Mn2+ (control and 0·01, 0·05, 0·10, and 0·20 mM), then a cellular MRI was performed in vitro and the intracellular Mn2+ concentrations were analyzed by ICP-MS. At the same time, the cell viability, LDH release assay, intracellular ROS level, and apoptosis were measured 24 h after treatment.Results: (1) After the neurons were treated with Mn2+ at a low concentration (0·01 mM), there was no impact on cell viability and cytotoxicity, and no significant signal was enhanced on MEMRI. (2) When the neurons were exposed to higher concentrations of Mn2+ (0·05, 0·1, and 0·2 mM), a significant increase in signal quality was achieved, but cell viability was significantly reduced and the intracellular ROS formation and percentage of TUNEL-positive cells were increased significantly.Conclusion: At Mn2+ concentrations > 0·05 mM, significant enhancement of MEMRI SI occurred, but with overt cytotoxicity.