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

Authors: Y. Zhang...X. Jiang Introduction: As with many new techniques, MeMRI presents a great opportunity for in vivo and in vitro studies on the plasticity of multiple tissue types, including neuronal. With a paramagnetic characteristic and the ability to act as a Calcium analong, manganese poses as a viable contrast agent for functional and anatomical MRI. As a trace mineral, manganese naturally acts at low concentrations as a co-factor for multiple enzymes in the body. However like most things, at high concentrations manganese is considered toxic. What this study did was examine the concentration of Mn2+ sufficient for a significant increase in signal intensity during an MRI, as well as determine the concentration of Mn2+ necessary to produce neurotoxic affects. Methods: -Cultured primary cortical neurons -Immunocytochemistry -MeMRI aquisition -Intracellular Mn2+ accumulation using mass spectrometry -Cell viability, cytotoxicity, intracellular ROS, and TUNEL assays Conclusion: Two important findings came from the following experiment. 1) Mn2+ intensity does not induce a significant signal intensity at a concentration less than .05mM MnCl2 and 2) Mn2+ exposure at concentrations greater than .05mM MnCl2 produce nuerotoxic effects such as decreased cellular viability as well as membrane integrity, intracellular ROS formation, and apoptosis. Based off of these two discoveries, it was determined that for in vitro neuronal MeMRI .05mM MnCl2 is the critical concentration that allows for a significant signal intensity and limited amounts of toxicity to the cells. As important as these results are, there has still been no concrete studies done examining neurotoxcity in vivo as a result of chronic manganese injections. This does however give the field a solid preliminary base to start with. ~JI