Excitotoxic potential of exogenous ferritin and apoferritin: Changes in ambient level of glutamate and synaptic vesicle acidification in brain nerve terminals

Extracellular ferritin contributes to neuronal injury in an in vitro model of ischemic stroke

Previous clinical and experimental studies have shown that neurological decline and poor functional outcome after acute ischemic stroke in humans are associated with high ferritin levels in serum and cerebrospinal fluid (CSF) within 24 h of ischemic stroke onset. The aim of the present study was to find out if and how high extracellular ferritin concentrations can increase the excitotoxicity effect in a neuronal cortical culture model of stroke. Extracellular ferritin (100 ng/ml) significantly increased the excitotoxic effect caused by excessive exogenous glutamate (50 μM and 100 μM) by leading to an increase in lipid peroxidation, a reduction in mitochondrial membrane potential, and a decrease in neuron viability. Extracellular apoferritin (100 ng/ml), the iron-free form of the protein, does not increase the excitotoxicity of glutamate, which proves that iron was responsible for the neurotoxic effect of the exogenous ferritin. We present evidence that extracellular ferritin iron exacerbates the neurotoxic effect induced by glutamate excitotoxicity and that the effect of ferritin iron is dependent of glutamate excitotoxicity. Our results support the idea that body iron overload is involved in the severity of the brain damage caused by stroke and reveal the need to control systemic iron homeostasis.

In Situ Visualization of Ferritin Biomineralization via Graphene Liquid Cell-Transmission Electron Microscopy

Ferritin biomineralization is essential to regulate the toxic Fe²⁺ iron ions in the human body. Unravelling the mechanism of biomineralization in ferritin facilitates our understanding of the causes underlying many iron disorder-related diseases. Until now, no report of in situ visualization of ferritin biomineralization events at nanoscale exists due to the requirement for high-resolution imaging of nanometer-sized ferritin proteins in their hydrated states. Herein, for the first time, we show that the biomineralization processes within individual ferritin proteins can be visualized by means of graphene liquid cell-transmission electron microscopy (GLC-TEM). The increase in the ratio of Fe³⁺/Fe²⁺ ions over time monitored via electron energy loss spectroscopy (EELS) reveals the change in oxidation state of iron oxide phases with time. This study lays a foundation for future investigations on iron regulation mechanisms in healthy and dysfunctional ferritins.

The relationship between measurement of in vivo brain glutamate and markers of iron metabolism: A proton magnetic resonance spectroscopy study in healthy adults

Fundamental human studies which address associations between glutamate and iron metabolism are needed. Basic research reports associations between glutamate and iron metabolism. Human studies report sex differences in iron metabolism and glutamate concentrations, which suggest that these relationships may differ by sex. We hypothesised associations would be apparent between in vivo glutamate and peripheral markers of iron metabolism, and these associations would differ by sex. To test this, we recruited 40 healthy adults (20 men, 20 women) and measured (a) standard clinical biomarker concentrations for iron metabolism and (b) an in vivo proxy for glutamate concentration, glutamate with glutamine in relation to total creatine containing metabolites using proton magnetic resonance spectroscopy studies with a two-dimensional chemical shift imaging slice, with voxels located in bilateral dorsolateral prefrontal cortices, anterior cingulate cortices and frontal white matter. Only the female group reported significant associations between peripheral markers of iron metabolism and Glx:tCr concentration: (a) right dorsolateral prefrontal cortex Glx:tCr associated positively with serum transferrin (r = .60, p = .006) and negatively with transferrin saturation (r = -.62, p = .004) and (b) right frontal white matter Glx:tCr associated negatively with iron concentration (r = -.59, p = .008) and transferrin saturation (r = -.65, p = .002). Our results support associations between iron metabolism and our proxy for in vivo glutamate concentration (Glx:tCr). These associations were limited to women, suggesting a stronger regulatory control between iron and glutamate metabolism. These associations support additional fundamental research into the molecular mechanisms of this regulatory control.

Monitoring of the velocity of high-affinity glutamate uptake by isolated brain nerve terminals using amperometric glutamate biosensor

Glutamate is the major excitatory neurotransmitter in the central nervous system, which is involved in the main aspects of normal brain functioning. High-affinity Na(+)-dependent glutamate transporters is key proteins, which transport extracellular glutamate to the cytoplasm of nerve cells, thereby preventing continuous activation of glutamate receptors, and thus the development of neurotoxicity. Disturbance in glutamate uptake is involved in the pathogenesis of major neurological disorders. Amperometric biosensors are the most promising and successful among electrochemical biosensors. In this study, we developed (1) amperometric glutamate biosensor, (2) methodological approach for the analysis of glutamate uptake in liquid samples of isolated rat brain nerve terminals (synaptosomes). The basal level of glutamate, the initial velocity of glutamate uptake and time-dependent accumulation of glutamate by synaptosomes were determined using developed glutamate biosensor. Comparative analysis of the data with those obtained by radioactive analysis, spectrofluorimetry and ion exchange chromatography was performed. Therefore, the methodological approach for monitoring of the velocity of glutamate uptake, which takes into consideration the definite level of endogenous glutamate in nerve terminals, was developed using glutamate biosensor.