Brain iron metabolism and its perturbation in neurological diseases

The Role of Glia in Wilson's Disease: Clinical, Neuroimaging, Neuropathological and Molecular Perspectives

Wilson's disease (WD) is inherited in an autosomal recessive manner and is caused by pathogenic variants of the ATP7B gene, which are responsible for impaired copper transport in the cell, inhibition of copper binding to apoceruloplasmin, and biliary excretion. This leads to the accumulation of copper in the tissues. Copper accumulation in the CNS leads to the neurological and psychiatric symptoms of WD. Abnormalities of copper metabolism in WD are associated with impaired iron metabolism. Both of these elements are redox active and may contribute to neuropathology. It has long been assumed that among parenchymal cells, astrocytes have the greatest impact on copper and iron homeostasis in the brain. Capillary endothelial cells are separated from the neuropil by astrocyte terminal legs, putting astrocytes in an ideal position to regulate the transport of iron and copper to other brain cells and protect them if metals breach the blood-brain barrier. Astrocytes are responsible for, among other things, maintaining extracellular ion homeostasis, modulating synaptic transmission and plasticity, obtaining metabolites, and protecting the brain against oxidative stress and toxins. However, excess copper and/or iron causes an increase in the number of astrocytes and their morphological changes observed in neuropathological studies, as well as a loss of the copper/iron storage function leading to macromolecule peroxidation and neuronal loss through apoptosis, autophagy, or cuproptosis/ferroptosis. The molecular mechanisms explaining the possible role of glia in copper- and iron-induced neurodegeneration in WD are largely understood from studies of neuropathology in Parkinson's disease and Alzheimer's disease. Understanding the mechanisms of glial involvement in neuroprotection/neurotoxicity is important for explaining the pathomechanisms of neuronal death in WD and, in the future, perhaps for developing more effective diagnostic/treatment methods.

Quercetin attenuates neurotoxicity induced by iron oxide nanoparticles

Iron oxide nanoparticles (IONPs) have been proposed as targeted carriers to deliver therapeutic molecules in the central nervous system (CNS). However, IONPs may damage neural tissue via free iron accumulation, protein aggregation, and oxidative stress. Neuroprotective effects of quercetin (QC) have been proven due to its antioxidant and anti-inflammatory properties. However, poor solubility and low bioavailability of QC have also led researchers to make various QC-involved nanoparticles to overcome these limitations. We wondered how high doses or prolonged treatment with quercetin conjugated superparamagnetic iron oxide nanoparticles (QCSPIONs) could improve cognitive dysfunction and promote neurogenesis without any toxicity. It can be explained that the QC inhibits protein aggregation and acts against iron overload via iron-chelating activity, iron homeostasis genes regulation, radical scavenging, and attenuation of Fenton/Haber-Weiss reaction. In this review, first, we present brain iron homeostasis, molecular mechanisms of iron overload that induced neurotoxicity, and the role of iron in dementia-associated diseases. Then by providing evidence of IONPs neurotoxicity, we discuss how QC neutralizes IONPs neurotoxicity, and finally, we make a brief comparison between QC and conventional iron chelators. In this review, we highlight that QC as supplementation and especially in conjugated form reduces iron oxide nanoparticles neurotoxicity in clinical application.

Tuning photoluminescence and surface properties of carbon nanodots for chemical sensing

Obtaining tunable photoluminescence (PL) with improved emission properties is crucial for successfully implementing fluorescent carbon nanodots (fCDs) in all practical applications such as multicolour imaging and multiplexed detection by a single excitation wavelength. In this study, we report a facile hydrothermal approach to adjust the PL peaks of fCDs from blue, green to orange by controlling the surface passivation reaction during the synthesis. This is achieved by tuning the passivating reagents in a step-by-step manner. The as-prepared fCDs with narrow size distribution show improved PL properties with different emission wavelengths. Detailed characterization of fCDs using elemental analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy suggested that the surface chemical composition results in this tunable PL emission. Surface passivation significantly alters the surface status, resulting in fCDs with either stronger surface oxidation or N element doping that ultimately determine their PL properties. Further experiments suggested that the as-prepared orange luminescent fCDs (O-fCDs) were sensitive and specific nanosensing platforms towards Fe(3+) determination in a complex biological environment, emphasizing their potential practical applications in clinical and biological fields.

Imbalance of iron influx and efflux causes brain iron accumulation over time in the healthy adult rat

A novel approach for studying brain iron homeostasis in animal models using stable isotope tracers.

Stable iron isotope tracing reveals significant brain iron uptake in adult rats

Iron deposits in the brain are a common hallmark of Alzheimer's disease and Parkinson's disease. This has spurred the hypothesis that iron may play a functional role in the pathogenesis of neurodegenerative disorders through free radical damage. Previous short-term studies using radiotracers suggested that brain iron uptake is small as compared to other tissues in adult rodents. This has led to the assumption that brain iron uptake must also be marginal in humans after brain development is complete. In this study we applied a novel approach to determine directly the fraction of iron that was transferred over time from diet to brain and other organs in adult rats. A known amount of a stable iron isotope ((57)Fe) was fed with drinking water to adult rats over 4 months. Uptake of the tracer iron and final iron content in tissues were assessed by Negative Thermal Ionization Mass Spectrometry (NTI-MS). We found that only a very small amount of dietary iron entered the brain (0.000537 ± 0.000076%). This amount, however, is considerable relative to the total brain iron content (9.19 ± 0.71%), which was lower but comparable to percentage uptake in other tissues. Whereas it remains unclear whether excessive dietary iron intake is a risk factor in neurodegenerative diseases or whether high systemic iron correlates with iron deposits in the brain, our study suggests that uptake of dietary iron is much higher than previously thought. This finding challenges current beliefs and points to a possible role of iron nutrition in the pathogenesis of neurodegenerative disorders.

Determination of iron(III) based on the fluorescence quenching of rhodamine B derivative

A new method for determination of iron(III) has been developed using a kind of rhodamine B derivative fluorescent probe, rhodamine amide (RHA), in acidic HAc-NaAc buffer solution. In this approach, the heavy atom effect of I₃(-) was applied to quench the fluorescence of RHA. When iron(III) and KI coexisted in HAc-NaAc buffer solution, iron(III) reacted with the excess KI to produce I₃(-) that quenched the fluorescence of RHA through the formation of a non-fluorescence compound. The results showed that the fluorescence intensity decrease of RHA presented a good linear relationship with the iron(III) concentrations in the range from 0.5 to 5.0 μmol L(-1) with the correlation coefficient of 0.9970, and the detection limit was 0.3 μmol L(-1) iron(III). The approach was applied to determination of iron(III) in water samples, and the recovery was found to be from 80.7% to 100. 8%.

Probing oxidative stress: Small molecule fluorescent sensors of metal ions, reactive oxygen species, and thiols

Oxidative stress is a common feature shared by many diseases, including neurodegenerative diseases. Factors that contribute to cellular oxidative stress include elevated levels of reactive oxygen species, diminished availability of detoxifying thiols, and the misregulation of metal ions (both redox-active iron and copper as well as non-redox active calcium and zinc). Deciphering how each of these components interacts to contribute to oxidative stress presents an interesting challenge. Fluorescent sensors can be powerful tools for detecting specific analytes within a complicated cellular environment. Reviewed here are several classes of small molecule fluorescent sensors designed to detect several molecular participants of oxidative stress. We focus our review on describing the design, function and application of probes to detect metal cations, reactive oxygen species, and intracellular thiol-containing compounds. In addition, we highlight the intricacies and complications that are often faced in sensor design and implementation.