Aluminum transfer as glutamate complex through blood-brain barrier. Possible implication in dialysis encephalopathy

The effects of glutamate and citrate on absorption and distribution of aluminum in rats

The objective of this study was to evaluate the effect of glutamate (Glu) and citrate (Cit) on the absorption and distribution of aluminum in rats. In the in vitro experiment, 18 adult male Sprague-Dawley rats (average weight of 250 ± 15 g) were randomly divided into three groups. The entire intestine was rapidly removed and cultured in prediction samples of 20 mmol AlCl(3), 20 mmol AlCl(3)+20 mmol Cit, and 20 mmol AlCl(3)+20 mmol Glu, respectively. Liquid in different intestines and the intestines were obtained for Al determination. In the in vivo chronic study, 24 adult male Sprague-Dawley rats (average weight of 127 ± 10 g) were divided into four groups fed with the following diets: no Al and Glu added (control), AlCl(3) (1.2 mmol), AlCl(3) (1.2 mmol) + Cit (1.2 mmol), and AlCl(3) (1.2 mmol) + Glu (1.2 mmol) daily for 50 days, respectively. After rat sacrifice, blood samples were obtained for biochemical analyses, and organ samples like the brain, kidney, liver, and bone were rapidly taken for Al determination. The results showed that the absorption rate of Al with the following order: duodenum > jejunum > ileum in the in vitro study and the administration of AlCl(3)+Cit or AlCl(3)+Glu resulted in significant increases in Al absorption in the three parts of the gut (duodenum, jejunum, and ileum) compared to the AlCl(3) alone group based on wet weight (P < 0.05). There were no differences between the AlCl(3)+Cit and AlCl(3)+Glu groups. In the in vivo chronic study, supplementing either AlCl(3) alone or AlCl(3)+Glu decreased food consumption significantly (P < 0.05) compared with the control group. Compared with the control group, animals fed with the AlCl(3) diet monitored for red blood cell, kidney, and liver showed a higher level (P < 0.05), but did not significantly increase Al retention in the brain and bone (P > 0.05); animals fed with AlCl(3)+Cit diets were monitored for higher Al retention in the brain, kidney, bone, and liver (P < 0.05), while animals fed with AlCl(3)+Glu diets were monitored for red blood cell, brain, and kidney (P < 0.05). Compared with the AlCl(3) group, simultaneous administration of AlCl(3) and Glu led to a significant increase in Al retention in red blood cell, brain, and kidney (P < 0.01) while AlCl(3) and Cit in the kidney and bone (P < 0.01). Simultaneous administration of AlCl(3) and Cit significantly increases plasma malondialdehyde level (P < 0.05); both simultaneous administration of AlCl(3) and Glu or AlCl(3) and Cit led to significant decreases in superoxide dismutase level in the plasma (P < 0.05), while AlCl3 alone did not. The results indicated that both Cit and Glu enhanced Al absorption in the intestine in vitro, and Glu increased Al deposition in red blood cell, brain, and kidney in vivo.

Combined effect of HEDTA and selenium against aluminum induced oxidative stress in rat brain

Aluminium (Al) is a potent neurotoxin and has together with other metals been suggested to be associated with Alzheimer's disease causality. The current study was carried out to investigate the potential role of N(2-hydroxyethyl) ethylenediamine triacetic acid (HEDTA) and Se in combination against Al induced toxicity. Animals were exposed to Al at a dose of 27 mg/kg/d i.p. for 60 days. HEDTA and Se were administered at a dose of 20mg/kg/d i.p. and 0.5mg/kg/d orally, respectively for 7 consecutive days. Induction of oxidative stress was recorded in the brain after Al exposure. Significant decrease was found in the levels of reduced glutathione activities of the enzymes glutathione reductase, glutathione peroxidase, catalase, superoxide dismutase, acetyl cholinesterase, and increased levels were observed in LPO and glutathione-S-transferase activity in brain and serum. These parameters responded positively to therapy with HEDTA, but more pronounced beneficial effects were observed when HEDTA was administered in combination with Se. The combination was effective in reducing the concentration of Al and level of DNA damage.

Aluminium speciation in biology

Before we can understand the role of Al3+ in living organisms we need to learn how it interacts with molecules found in biological systems. The only aluminium oxidation state in biology is 3+. In aqueous solutions there are only two main Al(III) species: the hexahydrate Al3+ at pH < 5.5 and the tetrahedral aluminate at pH > 6.2. In the blood plasma, citrate is the main small molecule carrier and transferrin the main protein carrier of Al3+. In fluids where the concentrations of these two ligands are low, nucleoside di- and triphosphates become Al3+ binders. Under these conditions Al3+ easily displaces Mg2+ from nucleotides. When all three classes of ligands are at low concentrations, catecholamines become likely Al3+ binders. Double-helical DNA binds Al3+ weakly and under no conditions should it compete with other ligands. Al(III) in the cell nucleus probably binds to nucleotides or phosphorylated proteins. Al3+ undergoes ligand exchange much more slowly than most metal ions: 10(5) times slower than Mg2+.

Accumulation of aluminum by primary cultured astrocytes from aluminum amino acid complex and its apoptotic effect

Aluminum salts or doses that are unlikely in the human system have been employed in toxicity studies and much attention had been focused on the secondary target (neurons) of its toxicity rather than the primary target (astroglia). In order to address these issues, we have investigated the uptake and apoptotic effects of aluminum amino acid complex on primary cultured astrocytes because these are fundamental in understanding the mechanism of aluminum neurotoxicity. Aluminum solubilized by various amino acids was differentially internalized by astrocytes (glycine>serine>>glutamine>>glutamate), but aluminum was not internalized from citrate complex following 24 h of exposure. Inhibition of glutamine synthetase, by methionine sulfoximine (MSO), enhanced the uptake of aluminum from various amino acid complexes within 8 h except from glutamine complex. Blockade of selective GLT-1 (EAAT2) and GlyT1, as well as nonspecific transporters, did not inhibit or had no effect on uptake of aluminum in complex with the corresponding amino acids. Ouabain also failed to inhibit uptake of aluminum complexed with glycine. Pulse exposure to aluminum glycinate in the absence or presence of MSO caused apoptosis in over 25% of primary cultured astrocytes, and apoptotic features such as chromatin condensation and fragmentation became evident as early as 3 days of culture in normal medium. Lower doses (as low as 0.0125 mM) also caused apoptosis. The present findings demonstrate that aluminum solubilized by amino acids, particularly glycine, could serve as better candidate for neurotoxicity studies. Citrate may be a chelator of aluminum rather than a candidate for its cellular uptake. Amino acid transporters may not participate in the uptake of aluminum solubilized by their substrates. Another pathway of aluminum internalization may be implicated in addition to passive diffusion but may not require energy in form of Na+/K+-ATPase. Impaired astrocyes' metabolism can aggravate their accumulation of aluminum and aluminum can compromise astrocytes via apoptosis. Thus, loss of astrocytic regulatory and supportive roles in the central nervous system (CNS) may be responsible for neurodegeneration observed in Alzheimer's disease.

Aluminum L-glutamate complex in rat brain cortex: in vivo prevention of aluminum deposit by magnesium D-aspartate

Our previous experiments in the rat showed that aluminum L-glutamate complex (Al L-Glu) crosses the blood-brain barrier and accumulates in selective brain areas and that Al salts may increase D-aspartic acid forms in living brain proteins, probably by inducing more thermodynamically stable structures than L isomers. As magnesium blocks NMDA receptors, D-aspartic acid was used in the present study in the form of magnesium salt to prevent the excitotoxicity of dicarboxylic amino acids. Effects on brain amino acids and Al cortex levels in mature rats were studied after chronic treatment with Al L-Glu or Na L-Glu alone or in association with magnesium D-aspartate (Mg D-Asp). Results demonstrate that treatment with Mg D-Asp induces a decrease in the Al concentration in brain cortex of Al L-Glu-treated rats. In aluminum-free treated controls, treatment with Mg D-Asp in association with Na L-Glu also induces a decrease in Al concentration in brain cortex. These data indicate that Mg D-Asp administration protects rat brain cortex from Al accumulation and suggest that this treatment may be useful in preventing brain Al intoxication.

Ultrastructural study of rat hippocampus after chronic administration of aluminum L-glutamate: an acceleration of the aging process

An ultrastructural study of rat hippocampus was performed on young (group 1) and old (group 4) rats receiving daily subcutaneous injections of aluminum L-glutamate and on old untreated rats (group 5). Young controls were treated with sodium L-glutamate (group 2) and physiological saline (group 3). Group 1 showed vacuolated astrocytes with numerous lipofuscin deposits, mitochondrial swelling, a thinning of the myelin sheath, and many multivesicular bodies invading the cytoplasm. Cellular structure did not appear to be affected in groups 2 and 3. Group 4 showed swollen mitochondria, a demyelination process in axonal regions, sizable perivascular oedema with vessel retraction and gliofilament bundles. In this group, lipofuscin deposits in astrocytes were associated with multivesicular bodies that thinned the myelin sheath to the breaking point; however, no excitotoxic glutamate-induced effects were observed. In group 5, extreme cytoplasmic vacuolation was observed, with massive mitochondrial swelling, considerable thinning of the myelin sheath (at times to the breaking point), sizable vacuolar degeneration and gliofilament bundles. These results indicate that ultrastructural alterations in the hippocampus, such as cell vacuolization, massive mitochondrial swelling and the demyelination process, occur with aging and independently of aluminum intoxication. Similar alterations were observed in aluminum L-glutamate-intoxicated young rats, but not in controls. These results are consistent with aluminum-induced acceleration of the aging process.

Altered dopamine turnover in murine hypothalamus after low-dose continuous oral administration of aluminum

Aluminum, a known neurotoxic substance, has been suggested as a possible contributing factor in the pathogenesis of Alzheimer's disease. Ground-water pollution by aluminum has been recently reported. In the current study groups of 5 male BALB/c mice were administered aluminum ammonium sulfate in drinking water ad libitum at 0, 5, 25, and 125 mg/L aluminum for 4 weeks. At the termination of aluminum exposure, their brains were removed and dissected into cerebrum, cerebellum, medulla oblongata, midbrain, corpus striatum, and hypothalamus. The concentration of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA), were determined in each brain area. DA, DOPAC, and HVA levels were lower in the hypothalamus of aluminum-treated mice, most notably in the low-dose group, as compared with control. No marked alterations in NE, 5-HT, and 5-HIAA levels were detected in any brain region. Changes in the concentration of DA and its metabolites measured in the hypothalamus suggest an inhibition of DA synthesis by aluminum.

Aluminum-induced degeneration of astrocytes occurs via apoptosis and results in neuronal death

The mechanisms by which aluminum interacts with the nervous system are only partly understood. In this study, we used cultured astrocytes and neurons to investigate the effects of long exposures to aluminum (1 mM). We found that aluminum accumulated both in neurons and astrocytes. After 8-12 days exposure, aluminum caused strong changes in the morphology of astrocytes including shrinkage of cell bodies and retraction of processes. Exposures over 15-18 days reduced astrocytes viability by 50%. Aluminum-induced degeneration of astrocytes involved the DNA fragmentation characteristic of apoptosis, and staining of aluminum-treated astrocytes with the DNA-binding fluorochrome Hoeschst 33258 revealed the typical apoptotic condensation and fragmentation of chromatin. Aluminum was also found to be neurotoxic, causing first (4-6 days) abnormal clustering and aggregation, and later (8-12 days) neuronal death. Interestingly, aluminum neurotoxicity occurred in neuroglial cultures containing approximately 10% astrocytes but not in near-pure neuronal cultures containing only 1% astrocytes. Staining of co-cultured cells with Hoeschst 33258 showed apoptotic condensation and fragmentation of chromatin in aluminum-treated astrocytes but not in co-cultured neurons. Our study demonstrates that aluminum can induce the apoptotic degeneration of astrocytes, and that this toxicity is critical in determining neuronal degeneration and death. Aluminum-mediated apoptosis of cultured astrocytes may be also a valuable model system to study the mechanisms underlying apoptosis in glial cells.

Chronic administration of aluminium L-glutamate in young mature rats: effects on iron levels and lipid peroxidation in selected brain areas

Clinical and experimental studies have demonstrated the neurotoxicity of aluminium (Al), notably as a result of lipid peroxidation in vitro. We previously showed that Al is able to cross the blood-brain barrier as an L-glutamate complex and be deposited in rat brain. The present work in young mature rats investigated the in vivo effects of chronic Al-L-glutamate treatment on Al and iron movement in plasma and selected brain regions. Brain lipid peroxidation was determined by evaluating the production of thiobarbituric acid reactive substances (TBARS) and analysing polyunsaturated fatty acids (PUFAs) such as C20:4n-6 and C22:6n-3. Our results indicate that iron concentration was decreased in plasma and that Al accumulated especially in striatum where iron levels were decreased and in the hippocampus where TBARS were increased without PUFA modifications. These data show that Al administered chronically as an L-glutamate complex is neurotoxic in vivo and thus provides a good model for studying Al toxic mechanisms.

Aluminum speciation studies in biological fluids. Part 4. A new investigation of aluminum-succinate complex formation under physiological conditions, and possible implications for aluminum metabolism and toxicity

Previous in vivo studies devoted to the capacity of succinate to influence aluminum metabolism have led to apparent contradictory results. Understanding the mechanisms that lie behind such discrepancies requires a knowledge of aluminum-succinate interactions at the molecular level. In the absence of possible direct analysis of the ultrafiltrable fraction of aluminum in vivo, computer simulations can help quantify the mobilizing power of succinate towards aluminum in the main biofluids. Based on this technique, a first attempt to elucidate the above issue was made using especially determined aluminum-succinate formation constants. However, further investigations have led to reconsider the stoichiometry of the aluminum-succinate complexes characterized on that occasion. The present work deals with these new investigations. The results obtained confirm the great complexity of the aluminum-succinate system. No less than seven species, among which five polynuclear complexes, have been characterized in two series of independent experiments. New simulations indicate that succinate is expected to facilitate aluminum gastrointestinal absorption to a greater extent than initially predicted when the metal is administered as its trihydroxide, especially at high concentrations of the metal. In contrast, succinate is not able to significantly increase aluminum absorption when ingested concomitantly with aluminum phosphate. It is also confirmed that succinate cannot influence the fate of aluminum in blood plasma, which supports the view that the protective effect of succinate against aluminum toxicity in mice is not due to aluminum complexation.

Absence of gastrointestinal absorption or urinary excretion of aluminium from an allantoinate complex contained in two antacid formulations in patients with normal renal function

We studied the plasma and urinary excretion levels of aluminum (Al) on day 0, 10 and 30 in 79 patients with gastrointestinal symptoms and normal renal function who were receiving a complex based on Al allantoinates [C4H5N4 O3 Al (OH)2] and [C4H5N4 O3 Cl Al2 (OH)4]. We evaluated the extent of Al absorption after repeated administration of this complex in two antacid formulations, Ulfon Lyoc in lyophilised tablet form (group 1; n = 40) and Ulfon suspension (group 2; n = 39). The total Al load for each antacid and patient was 512 mg daily for a total of 15360 mg during the 30-day treatment. No significant rise in plasma Al concentration was noted with either formulation between day 0 and 10, day 0 and 30 or day 10 and 30, nor was there any significant increase in urinary excretion levels. Al absorption was not increased and no toxic effects were noted, indicating that such formulations are suitable for long-term therapy in patients with gastrointestinal symptoms.

Modification of the blood-brain barrier through chronic intoxication by aluminum glutamate. Possible role in the etiology of Alzheimer's disease

The authors have used an experimental rat model of chronic aluminum (Al) intoxication to reproduce pathological signs analogous to those observed in humans for Alzheimer's disease or dialysis encephalopathy. Preliminary chronic intoxication was achieved during 5 wk by daily subcutaneous injection of a suspension of glutamate and Al prior to intravenous (i.v.) administration of sodium L-glutamate and Al chloride. A significant increase in Al content was observed in different areas of the brain, such as the hippocampus, the occipito-parietal cortex, the cerebellum, and the striatum. Moreover, half of the animals subcutaneously treated with Al glutamate had neurological disturbances, such as trembling, equilibrium difficulties, and convulsions leading to death about 1 h after i.v. administration. A significant increase in glutamic acid at the level of the occipito-parietal cortex was found in comparison with controls, which received only sodium L-glutamate or saline solution. These results show that the Al-L-glutamate complex may well induce a modification of the blood-brain barrier.

Aluminum chelation: chemistry, clinical, and experimental studies and the search for alternatives to desferrioxamine

This review focuses on aluminum (Al) chelation, its chemistry and biology. The toxicology and biology of Al in mammalian organisms are briefly reviewed to introduce the problems associated with excessive Al exposure and accumulation and the challenges facing an effective Al chelator. The basics of Al chelation chemistry are considered to help the reader understand the Al chelation chemical literature. The chemical properties of Al enable prediction of effective functional groups for Al chelation. A compilation of distribution coefficients between octanol and aqueous phases (Do/a) for chelators and their complexes with Al shows the effect of complexation on lipophilicity. A compilation of stability constants for Al.chelator complexes illustrates the role of oxygen in ligands that form stable complexes. The history of clinical Al chelation therapy is reviewed, with emphasis on desferrioxamine (DFO), which has been extensively used since 1980. The beneficial and adverse effects and limitations of DFO use in end-stage renal-diseased patients, in patients with neurodegenerative disorders, including Alzheimer's disease, and in animal models of Al intoxication are presented. The methods to evaluate potential Al chelators in vitro, in vivo, and using computer modeling are discussed. The Al chelation literature is reviewed by the chemical class of chelators, including fluoride, carboxylic acids, amino acids, catechols, polyamino carboxylic acids, phenyl carboxylic acids, the hydroxypyridinones, and hydroxamic acids.

Contribution of aluminum from packaging materials and cooking utensils to the daily aluminum intake

Migration of aluminum (Al) from packaging materials and cooking utensils into foods and beverages was determined at intervals during cooking or during storage by graphite furnace atomic absorption spectroscopy. High amounts of Al migrated into acidic products such as mashed tomatoes during normal processing in normal, non-coated Al pans. After 60 min cooking an Al content of 10-15 mg/kg was measured in tomato sauce. Surprisingly, the Al concentration was also increased up to 2.6 mg/L after boiling tap water for 15 min in Al pans. Storage of Coca-Cola in internally lacquered Al cans resulted in Al levels below 0.25 mg/L. In contrast, non-coated Al camping bottles containing lime blossom tea acidified with lemon juice released up to 7 mg Al/L within 5 days. The Al concentration in coffee was lower than that of the tap water used in its preparation, even if prepared in Al heaters. In Switzerland, where most pans nowadays are made of stainless steel or teflon-coated Al, the average contribution for the use of Al utensils to the daily Al intake of 2-5 mg from the diet is estimated to be less than 0.1 mg.

Hematological effects of aluminum on living organisms

1. Aluminum has been of great interest for many researchers over a number of years; its biochemical and physiological role is not yet fully clear. There are few papers describing the hematological consequences of its excess in living organisms and most of their data are cited in this paper. 2. Aluminum reduced the deformability of erythrocytes, and such cells are rather frequently retained in the reticuloendothelial system of the spleen and eliminated faster from the blood stream. 3. Aluminum produces peroxidative changes in the erythrocytes membrane, leading to hemolysis. Therefore, the depressed erythrocyte count in animals intoxicated with aluminum may be the consequence of both the hemolytic action of aluminum and the shortened time of survival of erythrocytes. 4. It was demonstrated that aluminum inhibits heme biosynthesis in vitro. This problem requires, however, further studies and observation. 5. Changes occurring under the influence of Al3+ on the leukocyte system of animals suggest the influence of this element on the resistance of the organism, but the mechanism of the action of Al3+ still requires elucidation. 6. Cell metabolism including blood cells may be affected by aluminum in many ways, the more so as the element may combine in vitro with amino acids, peptides, proteins, enzymes, substrates, cofactors, nucleotides and carbohydrates. Aluminum stimulates NADPH oxidation and takes part in the process of free radical formation.

The cellular toxicity of aluminium

Aluminium is a serious environmental toxicant and is inimical to biota. Omnipresent, it is linked with a number of disorders in man including Alzheimer's disease, Parkinson's dementia and osteomalacia. Evidence supporting aluminium as an aetiological agent in such disorders is not conclusive and suffers principally from a lack of consensus with respect to aluminium's toxic mode of action. Obligatory to the elucidation of toxic mechanisms is an understanding of the biological availability of aluminium. This describes the fate of and response to aluminium in any biological system and is thus an important influence of the toxicity of aluminium. A general theme in much aluminium toxicity is an accelerated cell death. Herein mechanisms are described to account for cell death from both acute and chronic aluminium challenges. Aluminium associations with both extracellular surfaces and intracellular ligands are implicated. The cellular response to aluminium is found to be biphasic having both stimulatory and inhibitory components. In either case the disruption of second messenger systems is observed and GTPase cycles are potential target sites. Specific ligands for aluminium at these sites are unknown though are likely to be proteins upon which oxygen-based functional groups are orientated to give exceptionally strong binding with the free aluminium ion.

Parenteral aluminum compounds produce a local toxic myopathy in rats: importance of the anion

Aluminum lactate, injected in rats, produced skeletal muscle necrosis of diaphragm and abdominal wall subjacent to peritoneal surfaces. Deeper muscle cells (distal from inoculum) were less severely affected. Ultrastructural studies of diaphragm revealed inoculum coating collagen fibrils, aggregating next to muscle basal lamina and localized within phagocytes. Aluminum lactate penetrated lymphatic vessels and caused reactive changes on the pleural as well as peritoneal surfaces of diaphragm. In contrast, injection of aluminum citrate did not produce myopathy. Also, mixtures of aluminum lactate with aluminum citrate, sodium citrate, or another chelating agent failed to produce myopathy. Therefore, the regional myopathy produced by the lactate salt provides a model for in vivo cytotoxicity of aluminum in which anionic binding is a critical determinant.

Oxidative damage in Alzheimer's dementia, and the potential etiopathogenic role of aluminosilicates, microglia and micronutrient interactions

While evidence implicating free radical oxidative processes in the etiopathogenesis of Alzheimer's dementia is accumulating, the specific cellular and biochemical mechanisms involved remain to be identified. The potential pathogenic role of microglial cells in neurodegenerative processes is indicated by the finding that purified murine microglial cells exposed in vitro to various model aluminosilicate particles stimulate the generation of tissue-injurious free radical reactive oxygen metabolites. Analogous inorganic aluminosilicate deposits have been reported to occur in the core of the characteristic senile plaques found in the brains of Alzheimer disease subjects. The possible modulation of free radical oxidative activity by antioxidant micronutrients and pharmacological agents, provides a rational basis for further preventative and therapeutic clinical investigations.

Mechanism of Alzheimer's disease: arguments for a neurotransmitter-aluminium complex implication

The authors are convinced that in Alzheimer's disease, as in Down's syndrome and Guam-Parkinson dementia, one may find an alteration in blood brain barrier transfer and a resultant imbalance in mineral metabolism. Metals, such as aluminium, which in vivo yield stable complexes with aspartic and glutamic acids act as previously been clearly shown with glutamic acid; they cross the blood brain barrier, and are deposited in the brain. The authors explain how amyloid protein or neurofibrillary tangles could well be produced by aluminium complex formation. Within the brain, in the form precisely of aluminium complex, L-glutamic acid is consequently unable to detoxify ammonia from neurons and to produce L-glutamin. Accumulation of ammonia is subsequently responsible for the neuronal death, affecting each and every neurotransmitter system.