The stabilization of ferrous iron by a toxic beta-amyloid fragment and by an aluminum salt

Iron Overload in Brain: Transport Mismatches, Microbleeding Events, and How Nanochelating Therapies May Counteract Their Effects

Iron overload in many brain regions is a common feature of aging and most neurodegenerative diseases. In this review, the causes, mechanisms, mathematical models, and possible therapies are summarized. Indeed, physiological and pathological conditions can be investigated using compartmental models mimicking iron trafficking across the blood-brain barrier and the Cerebrospinal Fluid-Brain exchange membranes located in the choroid plexus. In silico models can investigate the alteration of iron homeostasis and simulate iron concentration in the brain environment, as well as the effects of intracerebral iron chelation, determining potential doses and timing to recover the physiological state. Novel formulations of non-toxic nanovectors with chelating capacity are already tested in organotypic brain models and could be available to move from in silico to in vivo experiments.

Evaluation of Environmental Contamination by Heavy Metals and Relationship with Cardiovascular Risk in a Population of Barcarena-PA

Heavy metals are widely used to sustain the living standards of the modern world. Due to their prevalence, the risk of human exposure is an increasing threat to public health as they can cause negative health effects, such as cardiovascular diseases (CVDs). In this study, the objective was to evaluate clinical-epidemiological and biochemical parameters in relation to the overall risk score (ERG) of developing CVDs in 112 individuals aged 30 to 74 years living in the city of Barcarena-PA. The results of heavy metal contamination and biochemical parameters were applied in the ERG calculation. A significance level of p < 0.05 was adopted in the statistical tests. The values were high for chromium (Cr) (45.8%) and aluminum (Al) (98.6%). As for the ERG for CVDs, they obtained low risk (42%), medium risk (40%), and high risk (18%). In individuals with high ERG, a significant association was detected with increasing age group, in individuals ≥ 60 years (p < 0.0001). The relationship between concomitant Al and Cr intoxication and increased ERG was also significant (p = 0.0016). The probability of high cardiovascular risk among individuals contaminated by Al + Cr is higher than that of individuals contaminated by Al alone (p = 0.0074). Such evidence indicates that continuous environmental monitoring in the municipality of Barcarena is of extreme importance, since the population is in a situation of vulnerability in relation to their health.

Iron Deposition in Brain: Does Aging Matter?

The alteration of iron homeostasis related to the aging process is responsible for increased iron levels, potentially leading to oxidative cellular damage. Iron is modulated in the Central Nervous System in a very sensitive manner and an abnormal accumulation of iron in the brain has been proposed as a biomarker of neurodegeneration. However, contrasting results have been presented regarding brain iron accumulation and the potential link with other factors during aging and neurodegeneration. Such uncertainties partly depend on the fact that different techniques can be used to estimate the distribution of iron in the brain, e.g., indirect (e.g., MRI) or direct (post-mortem estimation) approaches. Furthermore, recent evidence suggests that the propensity of brain cells to accumulate excessive iron as a function of aging largely depends on their anatomical location. This review aims to collect the available data on the association between iron concentration in the brain and aging, shedding light on potential mechanisms that may be helpful in the detection of physiological neurodegeneration processes and neurodegenerative diseases such as Alzheimer's disease.

Effects of Aluminium Contamination on the Nervous System of Freshwater Aquatic Vertebrates: A Review

Aluminium (Al) is the most common natural metallic element in the Earth’s crust. It is released into the environment through natural processes and human activities and accumulates in aquatic environments. This review compiles scientific data on the neurotoxicity of aluminium contamination on the nervous system of aquatic organisms. More precisely, it helps identify biomarkers of aluminium exposure for aquatic environment biomonitoring in freshwater aquatic vertebrates. Al is neurotoxic and accumulates in the nervous system of aquatic vertebrates, which is why it could be responsible for oxidative stress. In addition, it activates and inhibits antioxidant enzymes and leads to changes in acetylcholinesterase activity, neurotransmitter levels, and in the expression of several neural genes and nerve cell components. It also causes histological changes in nerve tissue, modifications of organism behaviour, and cognitive deficit. However, impacts of aluminium exposure on the early stages of aquatic vertebrate development are poorly described. Lastly, this review also poses the question of how accurate aquatic vertebrates (fishes and amphibians) could be used as model organisms to complement biological data relating to the developmental aspect. This “challenge” is very relevant since freshwater pollution with heavy metals has increased in the last few decades.

Dietary monosodium glutamate altered redox status and dopamine metabolism in lobster cockroach (Nauphoeta cinerea)

Monosodium Glutamate (MSG) is the most commonly utilized food additive in the world. However, data on possible biochemical reasons underlying the neurotoxic effects of dietary MSG is limited. Therefore, this study investigated the effects of dietary supplementation of MSG on redox status and neurochemical indices in lobster cockroach nymph. These were evaluated via assessment of enzymatic and nonenzymatic antioxidants, acetylcholinesterase and monoamine oxidase activities, and dopamine content in the cockroach nymph head homogenate. MSG supplemented diet caused dose-dependent significant (p < .05) reduction in % survival, thiol, GSH, dopamine contents, and GST activity, increased ROS, NO, Fe²⁺ , MDA contents, and MAO activity but no significant (p < .05) difference was obtained in GSH and TBARS contents, and AChE activity. Increased oxidative, cholinergic, and monoaminergic activities coupled with decreased dopamine level might be the plausible biochemical explanation for the neurotoxic effects observed during sub-chronic consumption of large amounts of MSG in diet. PRACTICAL APPLICATIONS: This study suggests that consumption of monosodium glutamate should be reduced to the barest minimum due to its capability to induce oxidative stress and nervous toxicological effects at high dosage.

Modulatory Effects of Ginkgo biloba Against Amyloid Aggregation Through Induction of Heat Shock Proteins in Aluminium Induced Neurotoxicity

Protein misfolding and aggregation of amyloid beta (Aβ) peptide, as well as formation of neurofibrillary tangles (NFTs) are the signature hallmarks of Alzheimer's disease (AD) pathology. To prevent this, molecular chaperones come into play as they facilitate the refolding of the misfolded proteins and cell protection under stress. Here, we have evaluated the possible effects of Ginkgo biloba (GBE) against aggregation of the Aβ through activation of heat shock proteins (HSPs) in the Aluminium (Al) induced AD based model. GBE (100 mg/kg body weight) was administered per oral to the female SD rats in conjunction with intraperitoneal (i.p.) injection of Al lactate (10 mg/kg body weight) for six weeks. Pretreated animals were administered GBE for additional two weeks prior to any exposure of Al. GBE administration resulted in decrease in Aβ aggregation, ubiquitin deposition, accompanying a significant decline in APP & Tau protein hyperphosphorylation which can be attributed to activation of Heat shock factor (HSF-1) and upregulation in the protein expression of HSPs. Histopathological investigation studies have also shown the decrease in aggregation of Aβ peptide by GBE administration. Additionally, the decrease in ROS levels and Aβ aggregation by GBE administration prohibited the decline in the neurotransmitter levels and monoamine oxidase levels in hippocampus and cortex. This further caused improvement in learning and memory of the animals. In conclusion, our results indicate that GBE prevents the symptoms of Al induced AD like pathophysiology by upregulating the HSPs levels and decreasing the aggregation load.

Causative Links between Protein Aggregation and Oxidative Stress: A Review

Compelling evidence supports a tight link between oxidative stress and protein aggregation processes, which are noticeably involved in the development of proteinopathies, such as Alzheimer’s disease, Parkinson’s disease, and prion disease. The literature is tremendously rich in studies that establish a functional link between both processes, revealing that oxidative stress can be either causative, or consecutive, to protein aggregation. Because oxidative stress monitoring is highly challenging and may often lead to artefactual results, cutting-edge technical tools have been developed recently in the redox field, improving the ability to measure oxidative perturbations in biological systems. This review aims at providing an update of the previously known functional links between oxidative stress and protein aggregation, thereby revisiting the long-established relationship between both processes.

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

Aluminum as a toxicant

Although aluminum is the most abundant metal in nature, it has no known biological function. However, it is known that there is a causal role for aluminum in dialysis encephalopathy, microcytic anemia, and osteomalacia. Aluminum has also been proposed to play a role in the pathogenesis of Alzheimer’s disease (AD) even though this issue is controversial. The exact mechanism of aluminum toxicity is not known but accumulating evidence suggests that the metal can potentiate oxidative and inflammatory events, eventually leading to tissue damage. This review encompasses the general toxicology of aluminum with emphasis on the potential mechanisms by which it may accelerate the progression of chronic age-related neurodegenerative disorders.

Hippocampal neuronal metal ion imbalance related oxidative stress in a rat model of chronic aluminum exposure and neuroprotection of meloxicam

Neurodegenerative diseases remain a significant unresolved societal burden afflicting millions of people worldwide. Neurons in the brain are highly sensitive to oxidative stress, which can be induced by metal toxicity. In this paper, a chronic aluminum overload-induced model of neurodegeneration was used to investigate whether metal ions (Al, Fe, Mn, Cu and Zn)-related oxidative stress was involved in neurodegenerative mechanism and to identify the protective action of meloxicam against rat hippocampal neuronal injury. The metal ion contents, activity of superoxide dismutase (SOD), and content of malondialdehyde (MDA) were detected. The results showed that the spatial learning and memory (SLM) function was significantly impaired in chronic aluminum overload rats. Considerable karyopycnosis was observed in hippocampal neurons. The SOD activity was weakened and the MDA content increased both significantly. In the hippocampus, Al, Fe, Mn, Cu, and Zn contents increased by 184.1%, 186.1%, 884.2%, 199.4% and 149.2%, respectively. Meloxicam administration (without Al) had no effect compared with the control group, while meloxicam treatment with aluminum exposure significantly protected rats from SLM function impairment, neuron death, lower SOD activity, higher MDA content and brain metal ion imbalance. Our findings suggest that the cerebral metal ion imbalance-related oxidative stress is involved in mechanism of cerebral injury and neurodegeneration induced by chronic Al overload in rats, and that meloxicam protects neurons by reducing metal ion imbalance-related oxidative stress.

Nanoparticles and colloids as contributing factors in neurodegenerative disease

This review explores the processes underlying the deleterious effects of the presence of insoluble or colloidal depositions within the central nervous system. These materials are chemically unreactive and can have a prolonged residence in the brain. They can be composed of mineral or proteinaceous materials of intrinsic or exogenous origin. Such nanoparticulates and colloids are associated with a range of slow-progressing neurodegenerative states. The potential common basis of toxicity of these materials is discussed. A shared feature of these disorders involves the appearance of deleterious inflammatory changes in the CNS. This may be due to extended and ineffective immune responses. Another aspect is the presence of excess levels of reactive oxygen species within the brain. In addition with their induction by inflammatory events, these may be further heightened by the presence of redox active transition metals to the large surface area afforded by nanoparticles and amphipathic micelles.

The neurotoxicity of environmental aluminum is still an issue

Evidence for the neurotoxicity of extended exposure to low levels of aluminum salts is described using an animal model treated with aluminum at low levels reflecting those found in some water supplies. Emphasis is given to the potential role of aluminum in acceleration and promotion of some indices characteristic of brain aging. These hallmarks include the appearance of excess levels of inflammation in specific brain areas. Aluminum salts can increase levels of glial activation, inflammatory cytokines and amyloid precursor protein within the brain. Both normal brain aging and to a greater extent, Alzheimer's disease are associated with elevated basal levels of markers for inflammation. These are not attributable to obvious exogenous stimuli and may reflect the lifespan history of the organism's immune responses. It is possible that aluminum salts can act as a subtle promoter of such apparently unprovoked responses.

The effect of aminoguanidine, an inducible nitric oxide synthase inhibitor, on AlCl3 toxicity in the rat hippocampus

The presented experiment was carried out to determine the effectiveness of the inducible nitric oxide synthase inhibitor - aminoguanidine in modulating the toxicity of aluminum chloride on the nitrite levels, malondialdehyde concentration, reduced glutathione content, as well as cytochrome c oxidase activity of Wistar rats. The animals were killed 3 h and 30 days after treatment and the hippocampus was removed. The biochemical results show that aluminum acts as a pro-oxidant, while aminoguanidine exerts an antioxidant action in aluminum chloride-treated animals. We have also applied immunohistochemical techniques to identify iNOS expression after the treatment. Our data suggest that aminoguanidine can be effective in the protection of toxicity induced by aluminum chloride.

Effects of L-NAME, a non-specific nitric oxide synthase inhibitor, on AlCl3-induced toxicity in the rat forebrain cortex

The present experiments were done to determine the effectiveness of a non-specific nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on oxidative stress parameters induced by aluminium chloride (AlCl₃) intrahippocampal injections in Wistar rats. Animals were sacrificed 3 h and 30 d after treatments, heads were immediately frozen in liquid nitrogen and forebrain cortices were removed. Crude mitochondrial fraction preparations of forebrain cortices were used for the biochemical analyses: nitrite levels, superoxide production, malondialdehyde concentrations, superoxide dismutase (SOD) activities and reduced glutathione contents. AlCl₃ injection resulted in increased nitrite concentrations, superoxide anion production, malondialdehyde concentrations and reduced glutathione contents in the forebrain cortex, suggesting that AlCl₃ exposure promoted oxidative stress in this brain structure. The biochemical changes observed in neuronal tissues showed that aluminium acted as a pro-oxidant. However, the non-specific nitric oxide synthase (NOS) inhibitor, L-NAME, exerted anti-oxidant actions in AlCl₃-treated animals. These results revealed that NO-mediated neurotoxicity due to intrahippocampal AlCl₃ injection spread temporally and spatially to the forebrain cortex, and suggested a potentially neuroprotective effect for L-NAME.

Effects of various nitric oxide synthase inhibitors on AlCl3-induced neuronal injury in rats

The present study was aimed at determining the effectiveness of nitric oxide synthase (NOS) inhibitors: N-nitro-L-arginine methyl ester, 7-nitroindazole and aminoguanidine in modulating the toxicity of AlCl3 on superoxide production and the malondialdehyde concentration of Wistar rats. The animals were sacrificed 10 min and 3 days after the treatment and the forebrain cortex was removed. The results show that AlCl3 exposure promotes oxidative stress in different neural areas. The biochemical changes observed in the neuronal tissues show that aluminum acts as pro-oxidant, while NOS inhibitors exert an anti-oxidant action in AlCl3-treated animals.

Interfacing capillary electrophoresis with inductively coupled plasma mass spectrometry for redox speciation of plutonium

A robust and efficient interface between a capillary electrophoresis (CE) and an ICP-MS for actinide speciation studies was developed. This interface was made of two stainless steel T-shape pieces connected to the ICP-MS through a PFA-50 nebulizer. Fast separations (typically in less that 15 min) were obtained. The performances of the technique in terms of chemical separations carried out by the capillary electrophoresis and in terms of detection limits were investigated. Concerning the detection limit of the CE-ICP-MS system for plutonium, it was determined as 5 × 10−10 mol L−1 or 9 × 10−18 mol under our injection conditions. The coupling enables to separate at least three (III, V and VI) of the four plutonium oxidation states which can exist in aqueous solutions and to monitor oxidation and reduction processes.

Further evidence of centrophenoxine mediated protection in aluminium exposed rats by biochemical and light microscopy analysis

The environmental agent aluminium has been intensively investigated in the initiation and progression of various neurological disorders and the role of oxidative stress in these disorders is a widely discussed phenomenon. In this light, the present study is focused on the role of aluminium in mediating oxidative stress, which may help in better understanding its role in neuronal degeneration. Further, we have exploited a known anti-aging drug centrophenoxine to explore its potential in the conditions of metal induced oxidative damage. Aluminium was administered orally at a dose level of 100 mg/kg b.wt./day for a period of 6 weeks followed by a post treatment of centrophenoxine at a dose level of 100 mg/kg b.wt./day for another 6 weeks. Following aluminium exposure, a significant increase in lipid peroxidation levels (estimated by MDA) were observed which was accompanied by a decrease in reduced glutathione content in both cerebrum and cerebellum of rat brain. Post treatment of centrophenoxine significantly reduced the lipid peroxidation levels and also increased the reduced glutathione content in both the regions. Histologically observed marked deteriorations in the organization of various cellular layers in both cerebrum and cerebellum were observed after aluminium administration. Centrophenoxine treated animals showed an appreciable improvement in the histoarchitecture of the cellular layers. Our results indicate that centrophenoxine has an antioxidant potential and should be examined further in aluminium toxic conditions.

Redox cycling of iron by Abeta42

The amyloid cascade hypothesis and oxidative damage have been inextricably linked in the neurodegeneration that is characteristic of Alzheimer's disease. We have investigated this link and sought to suggest a mechanism whereby the precipitation of Abeta42 might contribute to the redox cycling of iron and hence the generation of reactive oxygen species via Fenton-like chemistry. We have shown that the critical step in the auto-oxidation of Fe(II) under the near-physiological conditions of our study involved the generation of H2O2 via O2.- and that Abeta42 influenced Fenton chemistry through aggregation state-specific binding of both Fe(II) and Fe(III). The net result of these interactions was the delayed precipitation of kinetically redox-inactive Fe(OH)3(s) such that Fe(II)/Fe(III) were cycled in redox-active forms over a substantially longer time period than if peptide had been absent from preparations. The addition of physiologically significant concentrations of either Cu(II) or Zn(II) reduced the role played by Abeta42 in the Fe(II)/Fe(III) redox cycle whereas a pathophysiologically significant concentration of Al(III) potentiated the redox cycle in favour of Fe(II) whether or not Cu(II) or Zn(II) was additionally present. The results support the notion that oxidative damage in the immediate vicinity of, for example, senile plaques, may be the result of Fenton chemistry catalysed by the codeposition of Abeta42 with metals such as Fe(II)/Fe(III) and Al(III).

Decreased membrane fluidity and hyperpolarization in aluminum-treated PC-12 cells correlates with increased production of cellular oxidants

Effects of aluminum (Al) on membrane properties of excitable cells are not fully understood. Several reports have identified cellular membranes as sensitive targets for Al intoxication. In the present study, we tested the hypothesis that treatment with Al would alter membrane fluidity and potential and these changes would correlate with aberrant generation of cellular oxidants. The effects of in vitro Al exposure in resting rat pheochromocytoma (PC-12) cells, a model that exhibits neuron-like properties, were investigated. Treatment of PC-12 cells with Al (>0.01mM) resulted in a concentration-dependent decrease in membrane fluidity. Similar concentrations of Al increased the rate of extracellular acidification, measured by a cytosensor microphysiometer, indicating stimulation of proton extrusion from cells. This change in proton extrusion was accompanied by a rapid and concentration-dependent hyperpolarizion of the cell membrane as determined by decreased fluorescence of a potential-sensitive dye, bis-[1,3-dibutylbarbituric acid]trimethine oxonol [Dibac(4)(3)]. Al-induced perturbations of membrane properties correlated with an increased level of cellular oxidants, indicated by increasing dihydrorhodamine 123 oxidation. Results suggest that acute exposure to Al modifies membrane properties of neuron-like cells and therefore cellular membranes represent a plausible target for Al neurotoxicity. Alterations in membrane potential can have a dramatic impact on cellular communication especially in neurons and may be an important mechanism in Al neurotoxicity.

Accumulation of aluminum in ferritin isolated from rat brain

The neurotoxic effects of aluminum have been widely reported but the mechanism of action and detoxification is poorly understood. To investigate the toxic potential of aluminum, we found it necessary to detail the behavior of absorbed aluminum in brain. The aim of this study was to clarify the distribution of aluminum in the brain. Rats were exposed to aluminum lactate intraperitoneally for 7 weeks. Although no marked differences in aluminum content was observed in brain regions, aluminum was eluted by gel filtration chromatography of the ferritin fraction from aluminum-loaded brain extracts; 5.9% of the total brain aluminum was recovered in purified ferritin from aluminum-loaded rat brains. These results suggest that ferritin may function as an aluminum detoxicant in the cell.

Age-related myelin breakdown: a developmental model of cognitive decline and Alzheimer's disease

A hypothetical model of Alzheimer's disease (AD) as a uniquely human brain disorder rooted in its exceptional process of myelination is presented. Cortical regions with the most protracted development are most vulnerable to AD pathology, and this protracted development is driven by oligodendrocytes, which continue to differentiate into myelin producing cells late into the fifth decade of life. The unique metabolic demands of producing and maintaining their vast myelin sheaths and synthesizing the brain's cholesterol supply make oligodendrocytes especially susceptible to a variety of insults. Their vulnerability increases with increasing age at differentiation as later-differentiating cells myelinate increasing numbers of axonal segments. These vulnerable late-differentiating cells drive the protracted process of intracortical myelination and by increasing local cholesterol and iron levels, progressively increase the toxicity of the intracortical environment forming the basis for the age risk factor for AD. At older ages, the roughly bilaterally symmetrical continuum of oligodendrocyte vulnerability manifests as a progressive pattern of myelin breakdown that recapitulates the developmental process of myelination in reverse. The ensuing homeostatic responses to myelin breakdown further increase intracortical toxicity and results in the relentless progression and non-random anatomical distribution of AD lesions that eventually cause neuronal dysfunction and degeneration. This process causes a slowly progressive disruption of neural impulse transmission that degrades the temporal synchrony of widely distributed neural networks underlying normal brain function. The resulting network "disconnections" first impact functions that are most dependent on large-scale synchronization including higher cognitive functions and formation of new memories. Multiple genetic and environmental risk factors (e.g. amyloid beta-peptide and free radical toxicity, head trauma, anoxia, cholesterol levels, etc.) can contribute to the cognitive deficits observed in aging and AD through their impact on the life-long trajectory of myelin development and breakdown. This development-to-degeneration model is testable through imaging and post mortem methods and highlights the vital role of myelin in impulse transmission and synchronous brain function. The model offers a framework that explains the anatomical distribution and progressive course of AD pathology, some of the failures of promising therapeutic interventions, and suggests further testable hypotheses as well as novel approaches for intervention efforts.

The pro-oxidant activity of aluminum

Aluminum, a non-redox-active metal is, nevertheless, a pro-oxidant both in in vitro preparations and in vivo. It facilitates both superoxide- and iron-driven biological oxidation by mechanisms that remain to be resolved. More than 10 years ago Fridovich and colleagues suggested that the facilitation of superoxide-driven biological oxidation by aluminum was due to an interaction between the metal and the superoxide radical anion (Free Radic. Biol. Med. 13: 79-81; 1992). This thesis has been examined herein and it is concluded that much, if not all, of the pro-oxidant activity of aluminum might be explained by the formation of an aluminum superoxide semireduced radical ion.

Aluminum Facilitation of the Iron-Mediated Oxidation of DOPA to Melanin

Aluminum, a trivalent cation unable to undergo redox reactions, is shown to faciliate iron-initiated DOPA oxidation in the melanin pathway under acidic condition of pH 5.5, which is a favored medium for aluminum facilitation of iron-induced lipid peroxidation. In the process of oxidation of DOPA to melanin in the presence of the metal ions, Fe3+ and H2O2 oxidize DOPA to dopachrome (DC), then Al3+ catalyzes the conversion of DC to 5,6-dihydroxyindole (DHI) and finally Fe3+ oxidizes DHI to indole-5,6-quinone (IQ), which polymerizes immediately to melanochrome and melanin. The reactions involve the intermediate complexes of metal ions and DOPA or its derivative. The present results indicate that aluminum can enhance the oxidative stress on iron-mediated DOPA oxidation in melanin pathway under acidic condition through the cooperation of iron and aluminum ions.

Aluminum ions accelerated the oxidative stress of copper-mediated melanin formation

A comparison between the effects of aluminum and cupric ions on the dopachrome (DC) conversion and the cooperation effect of the both ions in the DOPA oxidation to melanin pathway has been studied by UV-Vis spectrophotometric method. Both aluminum and cupric ions catalyze the DC conversion reaction, which is an important step in the melanin synthesis pathway. However, cupric ions catalyze the conversion of DC to yield 5,6-dihydroxyindole-2-carboxylic acid (DHICA) but the product of DC conversion catalyzed by aluminum is 5,6-dihydroxyindole (DHI). DOPA oxidation catalyzed by aluminum and cupric ions is studied in the presence of hydrogen peroxide. The results from our experiments provide evidence that aluminum can markedly increase the oxidative stress of copper-mediated the melanin formation and influence the properties of the melanin by means of changing the ratio of DHICA/DHI in the acidic environment (pH 5.5).

Effect of aluminum (III) on the conversion of dopachrome in the melanin synthesis pathway

The effect of aluminum ions on the kinetics and mode of the conversion of dopachrome (DC) in acidic environment has been studied using UV-Vis spectrophotometric and cyclic voltammetric methods. The DC conversion step is an important reaction in melanogenesis. Aluminum ions catalyze greatly the decarboxylative transformation of DC to give 5,6-dihydroxyindole (DHI) rather than 5,6-dihydroxyindole-2-carboxylic acid (DHICA) at pH 5.5, which enhance the ratio of formation DHI/DHICA in melanin synthesis pathway. The kinetics of DC conversion catalyzed by aluminum ions is dependent on the concentration of DC and aluminum ions. These results provide evidence that aluminum ions could play a role in the synthesis of melanin pathway in acidic condition through catalyzing the DC decarboxylative transformation to yield DHI and influence the melanin structure and properties.

In vitro effects of ascorbate and Trolox on the biocompatibility of dental restorative materials

Previous in vitro studies on the cytotoxicity of eight dental restorative materials including composites, compomers, resin-modified glass ionomer cements and glass ionomer cements have demonstrated a depletion of intracellular glutathione in gingival fibroblasts incubated with eluates of these materials and a protective effect of N-acetylcysteine. In the present study, we investigate the effects of two other antioxidants: ascorbate and Trolox. It was found that Trolox reduced the cytotoxicity induced by resin-based biomaterial eluates. In contrast, ascorbate increased in a dose-dependent manner the toxic effect of all eluates except for Z100 MP and Tetric flow (composites). The effect of D-mannitol was studied for GC FUJI II and was found to neutralize the additional toxic effect of ascorbate. Ascorbate increased the depletion of intracellular glutathione of these dental material eluates (between 17% and 24%, depending on the material). Quantification of metal ions in the dental material eluates showed the presence of significant amounts of aluminum and iron in GC FUJI II > photac fil > GC FUJI II LC > F2000. The mechanism of this increased cytotoxicity could be explained by the Fenton reaction resulting from the pro-oxidant effect of ascorbate in the presence of iron (transition metal ions) and/or aluminum.

The role of iron and copper in the aetiology of neurodegenerative disorders: therapeutic implications

Abnormalities in the metabolism of the transition metals iron and copper have been demonstrated to play a crucial role in the pathogenesis of various neurodegenerative diseases. Metal homeostasis as it pertains to alterations in brain function in neurodegenerative diseases is reviewed in this article in depth. While there is documented evidence for alterations in the homeostasis, redox-activity and localisation of transition metals, it is also important to realise that alterations in specific copper- and iron-containing metalloenzymes appear to play a crucial role in the neurodegenerative process. These changes provide the opportunity to identify pathways where modification of the disease process can occur, potentially offering opportunities for clinical intervention. As understanding of disease aetiology evolves, so do the tools with which diseases are treated. In this article, we examine not only the possible mechanism of disease but also how pharmaceuticals may intervene, from direct and indirect antioxidant therapy to strategies involving gene therapy.

Iron overload, oxidative stress, and axonal dystrophy in brain disorders

Hallervorden-Spatz syndrome is an autosomal-recessive brain disorder with signs of extrapyramidal dysfunction and mental deterioration, which associate with iron accumulation in globus pallidus and substantia nigra pars reticulata. Studies of oxidant stress in parkinsonian animal models suggest a linkage of iron overload to axonal dystrophy. Redox cycling of iron complexes (i.e., ferrous citrate and hemoglobin) increases hydroxyl radicals, lipid peroxidation, axonal dystrophy, and necrotic or apoptotic cell death. An increase of oxidative stress in the basal ganglia because of redox cycling of iron complexes leads to dopamine overflow and psychomotor dysfunction. Iron overload-induced axonal dystrophy has been demonstrated consistently using in vitro and in vivo models with a prominent feature of lipid peroxidation. This iron-induced oxidative stress is often accentuated by ascorbate and oxidized glutathione, although it is suppressed by the following antioxidants: S-nitrosoglutathione or nitric oxide, MnSOD mimics, manganese, U-78517F, Trolox, and deferoxamine. Preconditioning induction of stress proteins (i.e., hemeoxygenase-1 and neuronal nitric oxide synthase) and hypothermia therapy suppress the generation of toxic reactive oxygen, lipid, and thiol species evoked by bioactive iron complexes in the brain. Finally, combined antioxidative therapeutics and gene induction procedures may prove to be useful for slowing progressive neurodegeneration caused by iron overload in the brain.

Lipid peroxidation and aluminium effects on the cholinergic system in nerve terminals

In the present study, we analyzed how aluminium and oxidative stress induced by ascorbate/Fe(2+) affect the mechanisms related with the cholinergic system in a crude synaptosomal fraction isolated from rat brain. [(3)H]Choline uptake, [(3)H]acetylcholine release, membrane potential and Na(+)/K(+)-ATPase activity were determined in the presence or in the absence of aluminium in control conditions and in the presence of ascorbate (0.8 mM)/Fe(2+) (2.5 micro M). The extent of lipid peroxidation was measured by quantifying thiobarbituric acid reactive substances (TBARS). Under oxidizing conditions aluminium increased the formation of TBARS by about 30%, but was without effect when the synaptosomal preparation was incubated in the absence of oxidants. Additionally, aluminium potentiated the inhibition of the high-affinity [(3)H]choline uptake observed following lipid peroxidation and had the same effect on the Na(+)/K(+)-ATPase activity. [(3)H]Acetylcholine release induced by 4-aminopyridine, and membrane potential were not significantly affected under oxidizing conditions, either in the absence or in the presence of aluminium. We can conclude that aluminium, by potentiating lipid peroxidation, affects the uptake of choline in nerve endings. This effect, occurring during brain oxidative injury, might contribute to the cholinergic dysfunction and neuronal cell degeneration known to occur in Alzheimer's disease.

Mechanisms by which metals promote events connected to neurodegenerative diseases

Although the exact causative phenomenon responsible for the onset and progression of neurodegenerative disorders is at present unresolved, there are some clues as to the mechanisms underlying these chronic diseases. This review addresses mechanisms by which endogenous or environmental factors, through interaction with redox active metals, may initiate a common cascade of events terminating in neurodegeneration.

Nanoscale biogenic iron oxides and neurodegenerative disease

One of the characteristics of many neurodegenerative diseases is the disruption of normal iron homeostasis in the brain. Recent experimental work indicates that nanoscale magnetic biominerals (primarily magnetite and maghemite) may be associated with senile plaques and tau filaments found in brain tissue affected by these diseases. These findings have important implications for our understanding of the role of iron in neurodegenerative disease as well as profound implications for their causes. In addition, the presence of biogenic magnetite in affected tissue should also provide improved mechanisms for early detection through the modification of MRI pulse sequences.

Configuration of thiols dictates their ability to promote iron-induced reactive oxygen species generation

Iron catalyzes the production of reactive oxygen species (ROS) through the Fenton reaction. The modification of this phenomenon in the presence of various thiol compounds that are nominally reducing agents has been studied. Using the synaptosomal/mitochondrial (P2) fraction of rat cerebral cortex as a biological source of reactive oxygen species (ROS) production, we studied the influence of four compounds, glutathione (GSH), cysteine, N-acetyl-cysteine (NAC), and homocysteine on iron-induced ROS production. None of the thiol compounds alone, at the concentrations used, affected the basal rate of ROS production in the P2 fraction. GSH, homocysteine and NAC did not alter Fe-induced ROS generation, while cysteine greatly potentiated ROS formation. Measurement of the rate of ROS production in the presence of varying concentrations of cysteine together with 20 microM ferrous iron revealed a dose-response relationship. The mechanism whereby free cysteine, but not the cysteine-containing peptide GSH, homocysteine or NAC with a blocked amino group, exacerbates the pro-oxidant properties of ferrous iron probably involves formation of a complex between iron, a sulfhydryl and a free carboxyl residue located at a critical distance from the -SH group. Cysteine-iron interactions may, in part, account for the excessive toxicity of free cysteine in contrast to GSH and NAC.

Ligand specific effects on aluminum incorporation and toxicity in neurons and astrocytes

Aluminum is present in many manufactured foods and medicines and is added to drinking water for purification purposes. It has been proposed that aluminum is a contributing factors to several neurodegenerative disorders such as Alzheimer's disease. However, this remains controversial primarily due to the unusual properties of aluminum and a lack of information on its cellular sites of action. To resolve some of these questions, we have examined aluminum uptake in both neuronal and astroglial cells as well as the role of metal speciation. The relative accumulation of four aluminum salts, aluminum maltolate, aluminum lactate, aluminum chloride and aluminum fluoride, was investigated and correlated with cell viability and intracellular distribution as determined by morin staining. Significant differences in aluminum incorporation and toxicity were observed in both neuronal and glia cells with the largest effects exhibited by the maltol species. This was accompanied by a nuclear accumulation in the neuronal cell line that was contrasted by the perinuclear, vesicular distribution in astrocytes that partially co-localized with cathepsin D, a lysosomal marker. These findings demonstrate differences in aluminum species and highlights the importance of these factors in modulating the toxic effect of aluminum.

Are hereditary hemochromatosis mutations involved in Alzheimer disease?

Mutations in the class I-like major histocompatibility complex gene called HFE are associated with hereditary hemochromatosis (HHC), a disorder of excessive iron uptake. We screened DNA samples from patients with familial Alzheimer disease (FAD) (n = 26), adults with Down syndrome (DS) (n = 50), and older (n = 41) and younger (n = 52) healthy normal individuals, for two HHC point mutations-C282Y and H63D. Because the apolipoprotein E (ApoE) E4 allele is a risk factor for AD and possibly also for dementia of the AD type in DS, DNA samples were also ApoE genotyped. Chi-squared analyses were interpreted at the 0.05 level of significance without Bonferroni corrections. In the pooled healthy normal individuals, C282Y was negatively associated with ApoE E4, an effect also apparent in individuals with DS but not with FAD. Relative to older normals, ApoE E4 was overrepresented in both males and females with FAD, consistent with ApoE E4 being a risk factor for AD; HFE mutations were overrepresented in males and underrepresented in females with FAD. Strong gender effects on the distribution of HFE mutations were apparent in comparisons among ApoE E4 negative individuals in the FAD and healthy normal groups (P < 0.002). Our findings are consistent with the proposition that among ApoE E4 negative individuals HFE mutations are predisposing to FAD in males but are somewhat protective in females. Further, ApoE E4 effects in our FAD group are strongest in females lacking HFE mutations. Relative to younger normals there was a tendency for ApoE E4 and H63D to be overrepresented in males and underrepresented in females with DS. The possibility that HFE mutations are important new genetic risk factors for AD should be pursued further.