Effects of Methylmercury on Primary Brain Cells in Mono- and Co-culture

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Abstract
We report on the uptake of MeHg in astrocytes and neurons, as well as specific indicators of neurotoxicity. Cerebellar granule neurons and astrocytes separately and in co-culture were cultured in the presence of MeHg and changes in 3-[4, 5-dimethylthiazol-2-yl]-2, 5 diphenyltetrazolium bromide (MTT)-reduction, lactate dehydrogenase (LDH) leakage, and cellular content of glutathione and amino acids were used as indicators of MeHg toxicity. Mitochondria in cortical astrocytes were slightly more sensitive than those in cerebellar astrocytes to the toxic effects of MeHg; furthermore, cellular integrity was better preserved in cerebellar astrocytes. When neurons and astrocytes from cerebellum were incubated in separable co-cultures using inserts, the astrocytes showed cellular damage at lower exposure to MeHg while neurons showed less changes compared to respective cell types in mono-cultures. Mercury uptake studies at 25 μM MeHg (10% serum present) showed that for neurons in co-culture the uptake was 1/3 compared to mono-cultures. In contrast, for astrocytes in co-culture, uptake was increased by 75%. A MeHg concentration-dependent increase of glutamate content in mono-cultures was noted. When MeHg concentration was increased to 10, 25, or 50 μM, neurons in co-cultures decreased their glutamate content, whereas astrocytes showed an increase. Other amino acids, such as glutamine, serine, valine, isoleucine, taurine, and phenylalanine were unaffected by MeHg. Glutathione content showed MeHg concentration-dependent changes in astrocytes and was increased in neurons in co-culture incubated with 5 μM MeHg. In conclusion, astrocytes appear to increase neuronal resistance, indicating a possible protective role for astrocytes in MeHg neurotoxicity.