Aluminum potentiates glutamate-induced calcium accumulation and iron-induced oxygen free radical formation in primary neuronal cultures

Aspartame-induced cognitive dysfunction: Unveiling role of microglia-mediated neuroinflammation and molecular remediation

Aspartame, an artificial sweetener, is consumed by millions of people globally. There are multiple reports of aspartame and its metabolites affecting cognitive functions in animal models and humans, which include learning problems, headaches, seizures, migraines, irritable moods, anxiety, depression, and insomnia. These cognitive deficits and associated symptoms are partly attributed to dysregulated excitatory and inhibitory neurotransmitter balance due to aspartate released from aspartame, resulting in an excitotoxic effect in neurons, leading to neuronal damage. However, microglia, a central immunocompetent cell type in brain tissue and a significant player in inflammation can contribute to the impact. Microglia rapidly respond to changes in CNS homeostasis. Aspartame consumption might affect the microglia phenotype directly via methanol-induced toxic effects and indirectly via aspartic acid-mediated excitotoxicity, exacerbating symptoms of cognitive decline. Long-term oral consumption of aspartame thus might change microglia's phenotype from ramified to activated, resulting in chronic or sustained activation, releasing excess pro-inflammatory molecules. This pro-inflammatory surge might lead to the degeneration of healthy neurons and other glial cells, impairing cognition. This review will deliberate on possible links and research gaps that need to be explored concerning aspartame consumption, ecotoxicity and microglia-mediated inflammatory cognitive impairment. The study covers a comprehensive analysis of the impact of aspartame consumption on cognitive function, considering both direct and indirect effects, including the involvement of microglia-mediated neuroinflammation. We also propose a novel intervention strategy involving tryptophan supplementation to mitigate cognitive decline symptoms in individuals with prolonged aspartame consumption, providing a potential solution to address the adverse effects of aspartame on cognitive function.

Aging induced testicular damage: analyzing the ameliorative potential of Mucuna pruriens seed extract

Mucuna pruriens Linn. (M. pruriens), a leguminous plant, was used extensively in Ayurveda, to treat male-related infertility. Previous studies have demonstrated antioxidant, androgenic, aphrodisiac, and spermatogenic properties of M. pruriens seed extract. Surprisingly, the biological activities of M. pruriens on aging-induced pathological changes in the testis microenvironment have never been explored and the present study was focused on the testing therapeutic efficacy of M. pruriens on aged rat testis. Male Wistar albino rats were grouped as; adult (3 months), aged (24 months), aged + M. pruriens and adult + M. pruriens (N = 6/group). The extract was administrated at a dose of 200 mg/kg body weight (dosage determined in our previous study) daily by gavage for 60 days. The total and free testosterone, FSH and LH levels were considerably increased in aged + M. pruriens. The diameter & volume of the seminiferous tubules, the height & volume of the epithelium, and the number of Leydig cells number were significantly decreased in aged rat testis, concomitantly connective tissue proportion was increased compared to adult rats. The seminiferous epithelium indicates significant rejuvenation or restoration of spermatogenic cells in aged + M. pruriens rat testis. The highlighting observations in aged + M. pruriens was increased in the following parameters i.e., tubular diameter (25%), number of tubules (35%), epithelial height (25%) & volume (20%), and number of Leydig cells (35%) when compared to untreated aged rat testis. The TNFα, NF-κB, cytochrome c, Caspase-9, Caspase-3, Bcl-2, Bax, PARP iNOS, and inflammatory and apoptotic factors were downregulated in aged + M. pruriens. M. pruriens was able to restore spermatogenesis and enhance the activity of Sertoli cells and Leydig cells and improve the pituitary-gonadal axis in aged rat testis and observations indicate the therapeutic activity of M. pruriens in aged rat testis.

Synergistic oxidative impact of aluminum chloride and sodium fluoride exposure during early stages of brain development in the rat

Aluminum is widely used in industry and in cooking utensils, especially in countries with low economic and social standards. Fluoride is also used in industry, a major component of toothpaste and is added to the drinking water in many countries to fight teeth decay and cavities. Consequently, the coexistence of aluminum and fluoride is highly probable. Growing evidence indicates that environmental pollutants during the early stages of embryonic development may reprogram the offspring's brain capabilities to encounter oxidative stress during the rest of their postnatal life. This study investigated the impact of sodium fluoride (NaF, 0.15 g/L) and aluminum chloride (AlCl₃, 500 mg/L) added, individually or in combination, to the deionized drinking water starting from day 6 of gestation until just after weaning, or until the age of 70 days postnatal life. A significant decline was observed in tissue contents of vitamin C, reduced glutathione, GSH/GSSH ratio, and the total protein, as well as in the activities of Na⁺/K⁺-ATPase and superoxide dismutase (SOD) in almost all cases. On the contrary, lipid peroxidation and NO, as total nitrate, exhibited a significant increase in comparison with the corresponding control. Based on the present results, administration of Al and NaF, alone or in combination abated the quenching effects of the antioxidant system and induced oxidative stress in most brain regions under investigation. In conclusion, aluminum and fluoride are very noxious environmental pollutants that interfere with the proper functions of the brain neurons and their combination together aggravates their hazard.

Uptake and molecular impact of aluminum-containing nanomaterials on human intestinal caco-2 cells

Aluminum (Al) is one of the most common elements in the earth crust and increasingly used in food, consumer products and packaging. Its hazard potential for humans is still not completely understood. Besides the metallic form, Al also exists as mineral, including the insoluble oxide, and in soluble ionic forms. Representatives of these three species, namely a metallic and an oxidic species of Al-containing nanoparticles and soluble aluminum chloride, were applied to human intestinal cell lines as models for the intestinal barrier. We characterized physicochemical particle parameters, protein corona composition, ion release and cellular uptake. Different in vitro assays were performed to determine potential effects and molecular modes of action related to the individual chemical species. For a deeper insight into signaling processes, microarray transcriptome analyses followed by bioinformatic data analysis were employed. The particulate Al species showed different solubility in biological media. Metallic Al nanoparticles released more ions than Al₂O₃ nanoparticles, while AlCl₃ showed a mixture of dissolved and agglomerated particulate entities in biological media. The protein corona composition differed between both nanoparticle species. Cellular uptake, investigated in transwell experiments, occurred predominantly in particulate form, whereas ionic Al was not taken up by intestinal cell lines. Transcellular transport was not observed. None of the Al species showed cytotoxic effects up to 200 µg Al/mL. The transcriptome analysis indicated mainly effects on oxidative stress pathways, xenobiotic metabolism and metal homeostasis. We have shown for the first time that intestinal cellular uptake of Al occurs preferably in the particle form, while toxicological effects appear to be ion-related.

Protective effect of resveratrol against neuronal damage through oxidative stress in cerebral hemisphere of aluminum and fluoride treated rats

Aluminum has no defined biological function and it is potentially involved in the pathogenesis of neurodegenerative disorders. Furthermore, the presence of fluoride causes more aluminum to accumulate in the brain, resulting in increased neuronal damage. In recent years, resveratrol through its ameliorative effects was found to be a neuroprotectant. This study reports the protective effects of resveratrol on combined aluminum and fluoride induced neuronal damage through oxidative stress in rats. Protective effects of resveratrol (30 mg/kg b.w) on markers of oxidative stress were determined in rats exposed to aluminum chloride (100 mg/kg b.w) along with sodium fluoride (10 mg/kg b.w) for 8 weeks. The results showed a statistically significant (p<0.05) increase in lipid peroxidation (LPx) as well as a significant (p<0.05) decrease in superoxide dismutase and catalase activity. Enlarged cells, neurofibrillary tangles, and vacuolar spaces showing oxidative stress in the cerebral cortex were also observed in hematoxylin and eosin stained sections in aluminum and fluoride treated rats. Administration of resveratrol along with aluminum + fluoride showed significant reversal of oxidative stress and neuronal damage in rats. Thus resveratrol potentially acts as a neuroprotectant against aluminum chloride + sodium fluoride induced neuronal damage through its anti-oxidant efficacy.

A Pseudomonas strain isolated from date-palm rhizospheres improves root growth and promotes root formation in maize exposed to salt and aluminum stress

The aim of this study was to evaluate the effectiveness of Pseudomonas fluorescens 002 (P.f.002.), isolated from the rhizosphere of date palms from the Ghardaia region in the Algerian Sahara, to promote root growth of two varieties of maize under conditions of salt and aluminum stress. Primary roots of 5-day-old seedlings were inoculated with P.f.002., and seedlings were then grown under both control and stressed conditions. Primary, lateral, and seminal root lengths and numbers, as well as root dry mass, were evaluated. P.f.002 increased all parameters measured under both salt and aluminum stress. Hence, the use of P.f.002 may represent an important biotechnological approach to decrease the impact of salinity and acidity in crops.

Why industry propaganda and political interference cannot disguise the inevitable role played by human exposure to aluminum in neurodegenerative diseases, including Alzheimer's disease

In the aluminum age, it is clearly unpalatable for aluminum, the globe’s most successful metal, to be implicated in human disease. It is unpalatable because for approximately 100 years human beings have reaped the rewards of the most abundant metal of the Earth’s crust without seriously considering the potential consequences for human health. The aluminum industry is a pillar of the developed and developing world and irrespective of the tyranny of human exposure to aluminum it cannot be challenged without significant consequences for businesses, economies, and governments. However, no matter how deep the dependency or unthinkable the withdrawal, science continues to document, if not too slowly, a burgeoning body burden of aluminum in human beings. Herein, I will make the case that it is inevitable both today and in the future that an individual’s exposure to aluminum is impacting upon their health and is already contributing to, if not causing, chronic diseases such as Alzheimer’s disease. This is the logical, if uncomfortable, consequence of living in the aluminum age.

Metabolic reengineering invoked by microbial systems to decontaminate aluminum: implications for bioremediation technologies

As our reliance on aluminum (Al) increases, so too does its presence in the environment and living systems. Although generally recognized as safe, its interactions with most living systems have been nefarious. This review presents an overview of the noxious effects of Al and how a subset of microbes can rework their metabolic pathways in order to survive an Al-contaminated environment. For instance, in order to expulse the metal as an insoluble precipitate, Pseudomonas fluorescens shuttles metabolites toward the production of organic acids and lipids that play key roles in chelating, immobilizing and exuding Al. Further, the reconfiguration of metabolic modules enables the microorganism to combat the dearth of iron (Fe) and the excess of reactive oxygen species (ROS) promoted by Al toxicity. While in Rhizobium spp., exopolysaccharides have been invoked to sequester this metal, an ATPase is known to safeguard Anoxybacillus gonensis against the trivalent metal. Hydroxyl, carboxyl and phosphate moieties have also been exploited by microbes to trap Al. Hence, an understanding of the metabolic networks that are operative in microorganisms residing in polluted environments is critical in devising bioremediation technologies aimed at managing metal wastes. Metabolic engineering is essential in elaborating effective biotechnological processes to decontaminate metal-polluted surroundings.

Neuroprotective activity of Matricaria recutita against fluoride-induced stress in rats

CONTEXT

Oxidative stress plays a key role in pathophysiology of many neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and so on. Although Matricaria recutita L. (Asteraceae), German chamomile, is traditionally used for central nervous system (CNS)-related diseases, its antistress properties have received little attention.

OBJECTIVE

The present study evaluated the neuroprotective effect of German chamomile against aluminium fluoride (AlF₄⁻)-induced oxidative stress in rats.

MATERIALS AND METHODS

The Sprague-Dawley rats of either sex (200-250 g) were selected and grouped as: group I received normal saline; group II received AlF₄⁻ (negative control); groups III, IV, and V received 100, 200, and 300 mg/kg, orally, German chamomile methanol extract (GCME) along with AlF₄⁻; and group VI received quercetin (25 mg/kg, i.p.) + AlF₄⁻, respectively. After 10 days treatment with GCME, oxidative stress was induced by administering AlF₄⁻ through drinking water for 7 days. Then, the protective antioxidant enzyme levels were measured and the histopathological studies were carried out.

RESULTS

The GCME showed dose-dependent neuroprotective activity by significant decrease in lipid peroxidation (LPO) and increase in the superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and total thiol levels in extract-treated animals as compared with negative control group (P < 0.001). The histopathological studies also revealed the potent neuroprotective action of German chamomile against oxidative brain damage.

CONCLUSION

The present study for the first time shows potent neuroprotective activity of the methanol extract of German chamomile against AlF₄⁻-induced oxidative stress in rats.

Memory performance, brain excitatory amino acid and acetylcholinesterase activity of chronically aluminum exposed mice in response to soy isoflavones treatment

Memory performance, brain excitatory amino acid and acetylcholinesterase activity of chronically aluminum (Al) exposed mice in response to soy isoflavones (SI) treatment was investigated in the study. Forty eight mice were allotted randomly into a control group, an Al exposed group (100 mg/kg Al) and an Al exposed group treated with SI (100 mg/kg Al + 60 mg/kg SI) for 60 days. Chronic Al exposure significantly impaired long memory performance in mice as assessed using a passive avoidance task test (χ(2) analysis, p < 0.05). Interestingly, SI treatment markedly improved the memory performance score in the Al exposed mice. This improvement was associated with a total reversal of Al-induced increases in acetylcholinesterase activity in the cerebral cortex and hippocampus of mice. The Al exposure also led to significant decreases in brain levels of aspartic and glutamic acids, two excitatory amino acid neurotransmitters; whereas SI treatment partially reversed the decreased aspartic and glutamic acid contents in the hippocampus. The results suggest that SI can improve long memory performance in the Al exposed mice, possibly by modulating the metabolism of brain acetylcholine and amino acid neurotransmitters.

Pseudomonas fluorescens orchestrates a fine metabolic-balancing act to counter aluminium toxicity

Aluminium (Al), an environmental toxin, is known to disrupt cellular functions by perturbing iron (Fe) homeostasis. However, Fe is essential for such metabolic processes as the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, the two pivotal networks that mediate ATP production during aerobiosis. To counter the Fe conundrum induced by Al toxicity, Pseudomonas fluorescens utilizes isocitrate lyase and isocitrate dehydrogenase-NADP dependent to metabolize citrate when confronted with an ineffective aconitase provoked by Al stress. By invoking fumarase C, a hydratase devoid of Fe, this microbe is able to generate essential metabolites. To compensate for the severely diminished enzymes like Complex I, Complex II and Complex IV, the upregulation of a H(2)O-generating NADH oxidase enables the metabolism of citrate, the sole carbon source via a modified TCA cycle. The overexpression of succinyl-CoA synthetase affords an effective route to ATP production by substrate-level phosphorylation in the absence of O(2). This fine metabolic balance enables P. fluorescens to survive the dearth of bioavailable Fe triggered by an Al environment, a feature that may have potential applications in bioremediation technologies.

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.

Cellular and biochemical actions of melatonin which protect against free radicals: role in neurodegenerative disorders

Molecular oxygen is toxic for anaerobic organisms but it is also obvious that oxygen is poisonous to aerobic organisms as well, since oxygen plays an essential role for inducing molecular damage. Molecular oxygen is a triplet radical in its ground-stage (.O-O.) and has two unpaired electrons that can undergoes consecutive reductions of one electron and generates other more reactive forms of oxygen known as free radicals and reactive oxygen species. These reactants (including superoxide radicals, hydroxyl radicals) possess variable degrees of toxicity. Nitric oxide (NO*) contains one unpaired electron and is, therefore, a radical. NO* is generated in biological tissues by specific nitric oxide synthases and acts as an important biological signal. Excessive nitric oxide production, under pathological conditions, leads to detrimental effects of this molecule on tissues, which can be attributed to its diffusion-limited reaction with superoxide to form the powerful and toxic oxidant, peroxynitrite.Reactive oxygen and nitrogen species are molecular "renegades"; these highly unstable products tend to react rapidly with adjacent molecules, donating, abstracting, or even sharing their outer orbital electron(s). This reaction not only changes the target molecule, but often passes the unpaired electron along to the target, generating a second free radical, which can then go on to react with a new target amplifying their effects.This review describes the mechanisms of oxidative damage and its relationship with the most highly studied neurodegenerative diseases and the roles of melatonin as free radical scavenger and neurocytoskeletal protector.

Does neurotransmission impairment accompany aluminium neurotoxicity?

Neurobehavioral disorders, except their most overt form, tend to lie beyond the reach of clinicians. Presently, the use of molecular data in the decision-making processes is limited. However, as details of the mechanisms of neurotoxic action of aluminium become clearer, a more complete picture of possible molecular targets of aluminium can be anticipated, which promises better prediction of the neurotoxicological potential of aluminium exposure. In practical terms, a critical analysis of current data on the effects of aluminium on neurotransmission can be of great benefit due to the rapidly expanding knowledge of the neurotoxicological potential of aluminium. This review concludes that impairment of neurotransmission is a strong predictor of outcome in neurobehavioral disorders. Key questions and challenges for future research into aluminium neurotoxicity are also identified.

Reversal of an aluminium induced alteration in redox status in different regions of rat brain by administration of centrophenoxine

Aluminium is one of the most studied neurotoxin, and its effects on nervous system are both structural and functional, involving various regions of brain. Aluminium toxicity is known to have multiple mechanisms of action in the central nervous system. Affinity of aluminium for thiol substrates is considered a possible molecular mechanism involved in aluminium neurotoxicity. The reduced glutathione (GSH) is especially important for cellular defence against aluminium toxicity. This study pertains to the modulatory action of centrophenoxine on GSH status in aluminium exposed different brain regions of the female rats. Aluminium was administered orally at a dose of 40 mg/Kg x b x wt x /day for a period of eight weeks whereas, centrophenoxine was administered intraperitoneally at a dose of 100 mg/Kg x b x wt x /day for a period of six weeks. The study was carried out in different regions of brain namely cerebrum, cerebellum, medulla oblongata and hypothalamus. Animals exposed to aluminum, registered a significant decrease in the levels of reduced glutathione, and oxidized glutathione as well as in the activity of glutathione reductase in all the different regions studied when compared to normal control animals. Post-treatment with centrophenoxine, showed a significant improvement in the thiol levels in different regions. Centrophenoxine when administered alone also had a profound effect on the levels of reduced glutathione as well as on the activity of glutathione reductase. From the present results, it can be stated that centrophenoxine administration, as a thiol-antioxidant, arrests the aluminium induced cellular damage by improving the thiol status in brain regions.

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.

Dietary protein restriction causes modification in aluminum-induced alteration in glutamate and GABA system of rat brain

BACKGROUND

Alteration of glutamate and gamma-aminobutyrate system have been reported to be associated with neurodegenerative disorders and have been postulated to be involved in aluminum-induced neurotoxicity as well. Aluminum, an well known and commonly exposed neurotoxin, was found to alter glutamate and gamma-aminobutyrate levels as well as activities of associated enzymes with regional specificity. Protein malnutrition also reported to alter glutamate level and some of its metabolic enzymes. Thus the region-wise study of levels of brain glutamate and gamma-aminobutyrate system in protein adequacy and inadequacy may be worthwhile to understand the mechanism of aluminum-induced neurotoxicity.

RESULTS

Protein restriction does not have any significant impact on regional aluminum and gamma-aminobutyrate contents of rat brain. Significant interaction of dietary protein restriction and aluminum intoxication to alter regional brain glutamate level was observed in the tested brain regions except cerebellum. Alteration in glutamate alpha-decarboxylase and gamma-aminobutyrate transaminase activities were found to be significantly influenced by interaction of aluminum intoxication and dietary protein restriction in all the tested brain regions. In case of regional brain succinic semialdehyde content, this interaction was significant only in cerebrum and thalamic area.

CONCLUSION

The alterations of regional brain glutamate and gamma-aminobutyrate levels by aluminum are region specific as well as dependent on dietary protein intake. The impact of aluminum exposure on the metabolism of these amino acid neurotransmitters are also influenced by dietary protein level. Thus, modification of dietary protein level or manipulation of the brain amino acid homeostasis by any other means may be an useful tool to find out a path to restrict amino acid neurotransmitter alterations in aluminum-associated neurodisorders.

Effects of the new herbicide fentrazamide on the glucose utilization in neurons and erythrocytes in vitro

Treatment of rats with fentrazamide for 2 years at 3000 ppm (males) and 4000 ppm (females) led to an increased incidence and degree of axonal degeneration in sciatic nerve as well as to effects on red blood cells. The mechanism underlying these effects was investigated in vitro using various cell cultures (permanent rodent cell lines from the nervous system, liver, kidney, skeletal and heart muscle and fibroblasts, primary cortical neurons and erythrocytes from the rat). Added to cultured rat cortical neurons for 1 week, fentrazamide considerably decreased glucose consumption, ATP levels and mitochondrial membrane potential and lowered the GSH level, however, it had little impact on viability and neurofilaments and did not induce oxidative stress (ROS) over the first 2 h. After recovery for 1 week, in addition some destruction of neurofilaments had occurred probably secondary to the disturbance of energy production. These effects were prevented by pyruvate. Further studies indicated that fentrazamide primarily inhibited glucose utilization, most likely by interfering with glycolysis. Similar effects were found in erythrocytes treated with fentrazamide over a period of 7 days. Primarily, the glucose consumption was reduced after 1-day treatment, followed by a marked reduction of the energy supply at days 3 and 7. Comparable to the neurons, the GSH level was significantly reduced. A marked hemolysis of the red blood cells was then observed after prolonged treatment. The extensive energy demand and exclusive dependency on glucose utilization of neurons and erythrocytes may explain the specific vulnerability of motor neurons and erythrocytes. When comparing the concentrations necessary for inducing effects in vitro on neuronal cells and erythrocytes to the very low plasma concentrations of fentrazamide in treated rats it is suggested that only a small impact of fentrazamide on the energy status at high doses will occur in vivo. Therefore, aging of the rat as another factor compromising mitochondrial energy production in motor neurons must be considered as additional contribution for the induction of axonal degeneration. It is concluded that this effect of fentrazamide in rats poses no specific risk under the exposure conditions relevant to humans.

Hypoxia signaling to genes: significance in Alzheimer's disease

Aberrations in neural signaling, converging to and diverging from oxidative metabolism and blood supply, contribute to the initiation and maintenance of inflammatory responses, neuronal degeneration, and age-related cognitive decline in Alzheimer's disease (AD). Hypoxia/ischemia triggers phospholipase A2, leading to the accumulation of free arachidonic and docosahexaenoic acids (AA, DHA), as well as that of lysophospholipids. Some of these bioactive lipid messengers in turn give rise to several downstream lipid messengers, such as platelet-activating factor (PAF) and ecosanoids (prostaglandins and leukotrienes). Eicosanoid synthesis is highly regulated in hypoxia and in reperfusion subsequent to ischemia. As one of the consequences, mitochondrial function is disrupted and reactive oxygen species (ROS) both contribute to the expansion of cellular inflammatory responses and reduce the expression of genes required to maintain synaptic structure and function. On the other hand, pro-inflammatory genes are up-regulated. One of these, the inducible cyclooxygenase-2 (COX-2), along with oxygen-starved mitochondria, comprise the major sources of ROS in the brain during hypoxia, ischemia, and reperfusion. One outcome is a sustained metabolic stress that drives progressive dysfunction, apoptosis and/or necrosis, and brain cell death. How hypoxia modulates oxygen-sensitive gene expression is not well understood. Pro-inflammatory gene families that contribute to neurodegeneration are transiently activated in part by the heterodimeric oxygen-sensitive DNA-binding proteins nuclear factor for kappa B (NF-kappaB) and hypoxia-inducible factor-alpha (HIF-1alpha). Here the authors summarize current studies supporting the hypothesis that synaptically-derived lipid messengers play significant roles in ischemic stroke and that hypoxia is an important contributor to the onset and progression of AD neurodegeneration.

Chronic low-Ca/Mg high-Al diet induces neuronal loss

To evaluate the causative role of environmental aluminum (Al) in the development of neurodegeneration in Kiiamyotrophic lateral sclerosis (ALS), we examined how chronic exposure to a low-Ca/Mg and high-Al diet induced neuronal loss and tau-related neuronal degeneration in experimental animals. Optical microscopic examination showed tau-positive cells, atrophic neurons with darkly stained cytoplasms or swollen perikarya in the cerebrum, hippocampus and the brainstem of mice fed a low-Ca/Mg high-Al diet (Group 3). The neuronal loss was found in the frontal and parietal cortices of the mice and was not due to a classical apoptosis as detected by the terminal de ynucl otidyl transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) method. Neuronal degeneration and spheroid formation was also seen in the spinal cord of the Group 3 mice. The Morin fluorescence technique showed Al and Ca deposition in the cortical neurons and vessels in the basal ganglia of these mice. An electron microscopic examination showed intranuclear filamentous structures, intracytoplasmic vacuoles and/or darkly stained cytoplasm in the cortical neurons of Group 3 mice. These findings were seen in mice of the 11-month-experimental period and increased until the 25-month-experimental period. The present findings suggested that chronic exposure to a low-Ca/Mg high Al condition induced an accumulation of hyperphosphorylated tau in the cortical neurons, swelling of the neuronal cytoplasm and loss in the cerebrum and spinal cord of mice. Environmental factors such as a low-Ca/Mg high Al exposure might be one of the risk factors for the development of neuronal degeneration of ALS in the Kii Peninsula.

Oxidative stress in rat cortical neurons and astrocytes induced by paraquat in vitro

Oxidative stress has been discussed as crucial mechanism of neuronal cell death in the adult brain. However, it was not clear until now whether neurons are more sensitive to oxidative stress than the other cells in the brain, e.g. astrocytes. Therefore both cell types were exposed to oxidative stress provoked by the redox-cycling compound paraquat. Cortical neurons were found to be more sensitive towards paraquat toxicity than astrocytes as shown by MTT and Neutral Red assay, two different cytotoxicity assays. Mitochondrial functions were determined by the mitochondrial membrane potential and intracellular ATP concentrations. Again cortical neurons were more severely impaired (by paraquat than astrocytes). The production of reactive oxygen species after paraquat exposure was much higher in cortical neurons than in astrocytes and correlated with a higher depletion of GSH (intracellular glutathion). Lipid peroxidation could be shown in astrocytes via the breakdown product malondialdehyde (MDA) whereas in cortical neurons 4-hydroxynonenal (4-HNE) was detected as this endpoint. If and how oxidative stress influences the antioxidant defense was determined via changes in the expression of antioxidant enzymes. Paraquat exposure lead to a 2-3 fold increase of catalase, MnSOD and CuZnSOD mRNA expression in astrocytes. In contrast to astrocytes, in cortical neurons catalase and MnSOD mRNA levels were only marginally elevated above 1.5-fold by treatment with paraquat. Expression levels of glutathione peroxidase (GPx) mRNA were the only one that were not changed in both cell types after paraquat exposure. It is concluded that the more marked increase in expression levels of antioxidant enzymes may render astrocytes more resistant to oxidative stress than neuronal cells.

Aluminium increases xanthine oxidase activity and disturbs antioxidant status in the rat

The mechanisms responsible for the neurotoxic effects of Al remain poorly understood. In order to determine whether Al promotes oxidative stress in vivo, we measured the enzymatic activity of xanthine oxidase (XO), superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione-S-transferase (GST) and glutathione reductase (GR) in four groups of rats after eight days of intraperitoneal administration of variable concentrations of Al (0, 5, 10, and 15 mg/kg body weight, respectively). XO activity was measured in both plasma and liver samples, and the activities of the remaining enzymes were further determined in the brain and red blood cells (RBC). The most significant changes were observed in XO and GPX activities, that were enhanced and depressed, respectively. In both instances, the enzyme activities were correlated with Al concentrations, either positively (XO) or negatively (GPX). Enhancement of XO and inhibition of GPX activity may lead to the accumulation of intermediate toxic compounds such as hydrogen peroxide and hydroxyl radicals, since SOD activity is increased as well. The latter finding must be taken with some caution because previous studies have shown contradictory results in this field. Our data suggest that Al toxicity could be mediated by its action on both pro- and anti-oxidant enzymes. The biological significance of these findings remains to be established.

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.

Age-related changes in reactive oxygen species production in rat brain homogenates

The generation of reactive oxygen species (ROS) and resultant oxidative stress have been implicated in the mechanism of brain dysfunction due to age-related neurodegenerative diseases or exposure to environmental chemicals. We have investigated intrinsic age-related differences in the ability of the various brain regions to generate ROS in the absence and presence of Fe(2)+. ROS production in crude brain homogenates from adult rats was linear with respect to time and tissue concentration, and was stimulated to a greater extent by Fe(2)+ than was TBARS production. ROS production was then determined in homogenates from cerebral cortex, striatum, hippocampus, and cerebellum of 7-day-old, 14-day-old, 21-day-old, adult (3-6-month old), and aged (24-month-old) rats using the fluorescent probe 2',7'-dichlorodihydrofluorescin (DCFH). Basal levels of ROS production were similar in 7-, 14-, and 21-day olds, increased in adults, and highest in aged rats, and did not differ between brain regions. ROS production was stimulated by Fe(2)+ (0. 3-30 microM) in a concentration-dependent manner in all brain regions. However, the stimulation of ROS production by Fe(2)+ varied with age. ROS production was greater in 14- and 21-day-old rats compared with adult and aged animals. ROS production in 7-day-old rats was decreased at low Fe(2)+ concentrations and increased at high Fe(2)+ concentrations compared to adult and aged rats. These data show that brain homogenates from neonatal rats respond differently to Fe(2)+, and suggest that developing animals may be more sensitive to oxidative stress in the brain after exposure to toxicants. Published by Elsevier Science Inc.

Effect of dietary aluminum on tissue nonheme iron and ferritin levels in the chick

Aluminum toxicity is well documented but the mechanism of action is poorly understood. In renal failure patients with aluminum overload, disturbances in iron metabolism leading to anemia are apparent. Few animal models, however, have been used to study the effects of dietary aluminum on iron metabolism. The purpose of this study was to determine if dietary aluminum exposure alters tissue iron and ferritin concentrations in the chick, as has been found in cultured human cells exposed to aluminum. Groups of day-old chicks were fed purified diets containing one of two levels of iron (control or high iron), and one of three levels of aluminum chloride in a 2 x 3 factorial design. Diets were consumed ad libitum for 1 week, then pair-feeding was initiated for 2 more weeks. A seventh group consumed a low iron diet ad libitum for comparative purposes. After the 3-week feeding period, samples of kidney, liver, and intestinal mucosa were analyzed for nonheme iron and ferritin concentrations by a colorimetric assay and SDS-PAGE, respectively. Results showed that dietary aluminum intake reduced iron stores in liver and intestine, but had no effect on nonheme iron levels in the kidney. Ferritin levels were reduced by aluminum intake in all tissues studied. The decreases in tissue ferritin levels were proportionately more than the decreases in tissue nonheme iron levels. This resulted in increased nonheme iron to ferritin ratios that amounted to as much as 140 and 525% in kidney and intestine, respectively. These findings are consistent with the interpretation that, in the growing chick, dietary aluminum can inhibit iron absorption, disrupt the regulation of tissue ferritin levels by iron, and potentially alter the compartmentalization and protective sequestration of iron within cells.

A molecular mechanism of aluminium-induced Alzheimer's disease?

An abundance of research has continued to link aluminium (Al) with Alzheimer's disease (AD) (Strong et al., J. Toxicol. Environ. Health 48 (1996) 599; Savory et al., J. Toxicol. Environ. Health 48 (1996) 615). Animals loaded with Al develop both symptoms and brain lesions that are similar to those found in AD. However, these animal models of Al intoxication are not representative of human exposure to Al. They have not addressed the significance of a truly chronic exposure to Al. If Al is a cause of AD it is effective at the level of our everyday exposure to the metal and AD will be one possible outcome of the life-long presence of a low, though burgeoning, brain Al burden. Individual susceptibility to AD will be as much to do with differences in brain physiology as with changes in our everyday exposure to the metal. There will be a chemical response and indeed biochemical/physiological response in the brain to Al. The question is whether brain Al homeostasis could impact upon brain function. In reviewing the recent literature covering the neurotoxicity of Al and, in particular, of the known and probable mechanisms involved in brain Al homeostasis I have identified a mechanism through which a truly chronic exposure to Al would bring about subtle and persistent changes in neurotransmission which, in time, could instigate the cascade of events known collectively as AD. This mechanism involves the potentiation of the activities of neurotransmitters by the action of Al-ATP at adenosine 5'-triphosphate (ATP) receptors in the brain.

Aluminum but not iron treatment induces pro-oxidant events in the rat brain

In an attempt to delineate the capacity of aluminum (Al) to promote pro-oxidant events, several indices of oxidative stress have been determined in brains and livers of rats exposed to an Al salt, either alone or in combination with an iron (Fe) compound. Treatment with Al over a 3-wk period increased both cortical levels of glutathione (GSH) and the rates of generation of reactive oxygen species (ROS). Dosing with an Fe compound resulted in no parallel changes, and concurrent exposure to Fe together with Al prevented these elevations. Both Fe and Al dosing elevated glutamine synthetase activity in the cortex. Levels of creatine kinase, another enzyme susceptible to oxidative stress, were also elevated in cortices of Al-treated rats. These data are in contrast to the changes found in liver fractions where exposure to Fe greatly enhanced hepatic pro-oxidant events as judged by changes in all three of the test indices used. Concurrent treatment with Al did not potentiate the pro-oxidant effects of Fe in liver. Al treatment had very minor effects on hepatic parameters of oxidative events. The results suggest that the presence of Al may exert deleterious pro-oxidant changes within the brain, which may be related to induction of oxidant species. These changes are tissue-specific and appear to be independent of any promotion of pro-oxidant status induced by exogenous Fe.