Accumulation of Non-Transferrin-Bound Iron by Neurons, Astrocytes, and Microglia

Abstract

Neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, and hemorrhagic stroke are associated with increased levels of non-transferrin-bound iron (NTBI) in the brain, which can promote Fenton chemistry. While all types of brain cells can take up NTBI, their efficiency of accumulation and capacity to withstand iron-mediated toxicity has not been directly compared. The present study assessed NTBI accumulation in cultures enriched in neurons, astrocytes, or microglia after exposure to ferric ammonium citrate (FAC). Microglia were found to be the most efficient in accumulating iron, followed by astrocytes, and then neurons. Exposure to 100μM FAC for 24h increased the specific iron content of cultured neurons, astrocytes, and microglial cells by 30-, 80-, and 100-fold, respectively. All cell types accumulated iron against the concentration gradient, resulting in intracellular iron concentrations that were several orders of magnitude higher than the extracellular iron concentrations. Accumulation of these large amounts of iron did not affect the viability of the cell cultures, indicating a high resistance to iron-mediated toxicity. These findings show that neurons, astrocytes and microglia cultured from neonatal mice all have the capacity to accumulate and safely store large quantities of iron, but that glial cells do this more efficiently than neurons. It is concluded that neurodegenerative conditions involving iron-mediated toxicity may be due to a failure of iron transport or storage mechanisms, rather than to the presence of high levels of NTBI.