Influence of some dietary constituents on aluminum absorption and retention in rats

A geochemical perspective on the natural abundance of trace elements in beaver (Castor canadensis) from a rural region of southern Ontario, Canada

Chalcophile (Ag, Cd, Co, Cu, Mo, Ni, Pb, Se, Tl, Zn) and lithophile (Al, Ba, Ce, Cr, Cs, Fe, La, Li, Mn, Nd, Rb, Sr, V, Y) trace elements (TEs) were determined in kidney, liver and muscle of beaver (Castor canadensis) from a rural watershed in southern Ontario, Canada. To estimate the relative bioavailability of TEs in the landscape, they were also determined in the dissolved (<0.45 μm) fraction of water from the river where the animals were harvested. Concentration ratios (tissue/water) always showed the greatest enrichments for Cd (kidney, 1.1 × 10⁷; liver, 2.4 × 10⁶; muscle, 7.2 × 10⁵), most likely due to the metal binding properties of metallothioneins. Despite its potential toxicity, Tl also showed considerable enrichment: kidney, 4.2 × 10⁴; liver 1.2 × 10⁴; muscle 1.5 × 10⁴. Enrichments of Cs and Rb exceeded those of Tl in all three tissues, suggesting that the chemical similarity of their ionic species (Cs⁺, Rb⁺, Tl⁺) to K⁺ may be the key to their uptake. Lithophile elements of limited solubility in natural waters (Al, Ce, La, Nd) show moderate enrichments, despite the lack of physiological role. The smallest enrichments were found for Sr and Ba, the two TEs which are most abundant in the river. Of the TEs considered essential for animal nutrition, V was the least enriched in tissue relative to water (liver 19×, kidney, 33× and muscle 28×). Despite the lack of physiological function and absence of any known sources of contamination, Al, Ag, Cd, Ce, Cs, La, Pb, Rb, and Tl, are all enriched in beaver tissue, relative to water, by at least three orders of magnitude, due to natural processes. The widespread abundance of beaver in Canada combined with the growing need to manage their numbers in populated regions offer a unique opportunity for monitoring environmental quality in the riparian zone.

Is aluminum exposure a risk factor for neurological disorders?

Aluminum (Al) is widely found in the nature. Although the relation between Al and neurodegenerative diseases is still controversial, Al is related with many brain diseases including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Al exposure occurs mainly through environment, occupational, and dietary factors for humans. Al exposure with diet can be through foods, food additives, water, and contamination of Al equipment/utensils. The aim of this review is to summarize various hypotheses, which link Al and neurodegeneration, and to determine the roles of Al exposure through different sources including diet, environment, and occupation. Future studies should be done in vulnerable subgroups of population including children, patients receiving antacid or Al-containing pharmeteucials on a daily basis, patients with reduced renal function, and patients on parenteral nutrition regimens that are likely to be affected by possible adverse health effects of Al. In addition, gender, age, and Al interactions need to be determined. One of the most important challanges in future epidemiological studies is to determine which variables should be controlled. In addition, experimental studies should be more focused and translational. In this context, exposure dose, dose-response effects, and time lapse between exposures and cognitive assessments are very important.

Safety Assessment of Alumina and Aluminum Hydroxide as Used in Cosmetics

This is a safety assessment of alumina and aluminum hydroxide as used in cosmetics. Alumina functions as an abrasive, absorbent, anticaking agent, bulking agent, and opacifying agent. Aluminum hydroxide functions as a buffering agent, corrosion inhibitor, and pH adjuster. The Food and Drug Administration (FDA) evaluated the safe use of alumina in several medical devices and aluminum hydroxide in over-the-counter drugs, which included a review of human and animal safety data. The Cosmetic Ingredient Review (CIR) Expert Panel considered the FDA evaluations as part of the basis for determining the safety of these ingredients as used in cosmetics. Alumina used in cosmetics is essentially the same as that used in medical devices. This safety assessment does not include metallic or elemental aluminum as a cosmetic ingredient. The CIR Expert Panel concluded that alumina and aluminum hydroxide are safe in the present practices of use and concentration described in this safety assessment.

Bone Degeneration and Its Recovery in SMP30/GNL-Knockout Mice

Senescence marker protein-30 (SMP30) decreases androgen-independently with aging and is a lactone-hydrolyzing enzyme gluconolactonase (GNL) that is involved in vitamin C biosynthesis. In the present study, bone properties of SMP30/GNL knockout (KO) mice with deficiency in vitamin C synthesis were investigated to reveal the effects of SMP30/GNL and exogenous vitamin C supplementation on bone formation. Mineral content (BMC) and mineral density (BMD) of the mandible and femur of SMP30/GNL KO and wild-type mice at 2 and 3 months of age with or without vitamin C supplementation were measured by dual-energy X-ray absorptiometry. Body and bone weight of both age groups decreased and became significantly lower than those of wild-type mice. The bones of SMP30/GNL KO mice were rough and porous, with BMC and BMD significantly below wild-type. Oral supplementation with vitamin C eliminated differences in body weight, bone weight, BMC, and BMD between SMP30/GNL KO and wild-type mice at each age. These results indicate that bone degeneration in SMP30/GNL KO mice was caused by lack of vitamin C, and that this mouse strain is an appropriate model for bone metabolism in humans, which have no ability to synthesize vitamin C.

In vitro adsorption of aluminum by an edible biopolymer poly(γ-glutamic acid)

Accumulation of aluminum in human has been reported to be associated with dementia, Parkinson's disease, and Alzheimer's disease. The objectives of this study were to evaluate an edible biopolymer poly(γ-glutamic acid) (γ-PGA) for aluminum removal efficiency under in vitro conditions as affected by pH, contact time, aluminum concentration, temperature, ionic strength, and essential metals in both aqueous aluminum solution and simulated gastrointestinal fluid (GIF). A low aluminum adsorption occurred at pH 1.5-2.5, followed by a maximum adsorption at pH 3.0-4.0 and precipitating thereafter as aluminum hydroxide at pH > 4. Adsorption was extremely fast with 81-96% of total adsorption being attained within 1 min, reaching equilibrium in 5-10 min. Kinetic data at low (10 mg/L) and high (50 mg/L) concentrations were well described by pseudo-first-order and pseudo-second-order models, respectively. Equilibrium adsorption isotherms at different temperatures were precisely fitted by both Langmuir and Redlich-Peterson models with the maximum adsorption capacities at 25, 37, and 50 °C being 35.85, 38.68, and 44.23 mg/g, respectively. Thermodynamic calculations suggested endothermic and spontaneous nature of aluminum adsorption by γ-PGA with increased randomness at the solid/solution interface. Variation in ionic strengths did not alter the adsorption capacity, however, the incorporation of essential metals significantly reduced the aluminum adsorption by following the order copper > iron > zinc > calcium > potassium. Compared to aqueous solution, the aluminum adsorption from simulated GIF was high at all studied pH (1-4) with Langmuir monolayer adsorption capacity being 49.43 mg/g at 37 °C and pH 4. The outcome of this study suggests that γ-PGA could be used as a safe detoxifying agent for aluminum.

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+.

Chelating effect of novel pyrimidines in a model of aluminum intoxication

Long time ago aluminum (Al) was considered as a non-toxic element and its use had no restrictions. However, over the last two decades, scientific publications have indicated that Al is a toxic element. In line with this, aluminum accumulation in the organism is associated with a variety of human pathologies. Efficient therapeutics approach to treat Al intoxication are still not available, but there is a consensus that chelation therapy is the procedure to be used. However, the development of new chelating agents are highly desirable to improve the efficacy of the treatment of Al intoxication. The present study evaluates the chelating effect of two novel pyrimidines: 4-tricloromethyl-1-H-pyrimidin-2-one (THP) and (4-methyl-6-trifluoromethyl-6-pyrimidin-2-il)-hydrazine (MTPH) in a mice model of aluminum intoxication and compares their efficacy with those of desferrioxamine (DFO), a classical agent used for treat Al accumulation. The animals were exposed to aluminum by gavage (0.1 mmol aluminum/kg/day) 5 days/week for 4 weeks. At the end of this period, DFO was injected i.p. and the novel pyrimidines were given by gavage at 0.2 mmol/kg/day for five consecutive days. Aluminum concentration in tissues (brain, liver, kidney and blood) was determined by graphite furnace atomic absorption spectroscopy (GFAAS). The results showed that when administered by gavage, aluminum accumulated in the brain, kidney and liver of mice. MTPH was able to decrease aluminum levels in aluminum plus citrate animal groups, whereas THP was inefficient for this purpose. However, the novel pyrimidines used in this study were unable to surpass the aluminum chelating property of DFO. Thus, new studies must be performed utilizing other chelating agents which can decrease aluminum toxicity.

An open-label, crossover study of a new phosphate-binding agent in haemodialysis patients: ferric citrate

BACKGROUND

Hyperphosphataemia contributes to secondary hyperparathyroidism and renal osteodystrophy in patients with end-stage renal disease (ESRD). Calcium salts are widely employed to bind dietary phosphate (P) but they may promote positive net calcium balance and metastatic calcification. We recently reported that ferric compounds bind intestinal phosphate in studies of normal and azotemic rats.

METHODS

To extend this observation, we performed an open-label, random order, crossover comparison study of ferric citrate and calcium carbonate in haemodialysis patients from two teaching hospitals. The study sample consisted of 23 women and 22 men with an average age of 52.5 +/- 11.8 (SD) years and an average weight of 54.5 +/- 10.7 kg. All forms of iron therapy were discontinued. Two weeks before the study, patients were instructed to discontinue all P-binding agents. The patients were randomly assigned to receive either calcium carbonate (3 g/day) or ferric citrate (3 g/day) for 4 weeks followed by a 2 week washout period, and then crossed over to the other P-binding agent for 4 weeks.

RESULTS

From a baseline concentration of 5.6 +/- 1.5 mg/dl, the serum P increased during the washout period to 7.2 +/- 1.9 mg/dl prior to calcium carbonate treatment, and to 6.7 +/- 1.9 mg/dl prior to ferric citrate treatment. The serum P concentration fell significantly during treatment with both calcium carbonate (7.2 +/- 1.9 to 5.2 +/- 1.5 mg/dl, P<0.0001) and ferric citrate (6.7 +/- 1.9 to 5.7 +/- 1.6 mg/dl, P<0.0001). The results were not influenced by order of treatment. Under the conditions of the study protocol, ferric citrate was less effective than calcium carbonate at lowering the serum phosphate concentration. The serum Ca concentration increased during treatment with calcium carbonate but not ferric citrate. Ferric citrate treatment did not affect the serum concentration of aluminium. Ferric citrate treatment was associated with mild and generally tolerable gastrointestinal symptoms.

CONCLUSION

Ferric citrate shows promise as a means of lowering the serum phosphate concentration in haemodialysis patients. Further studies are needed to find the optimal dose.

Aluminum speciation studies in biological fluids. Part 7. A quantitative investigation of aluminum(III)-malate complex equilibria and their potential implications for aluminum metabolism and toxicity

As a nonessential element, aluminum may be toxic at both environmental and therapeutic levels, depending on ligand interactions. Dietary acids that normally occur in fruits and vegetables and commonly serve as taste enhancers are good ligands of the Al(3+) ion. Malic acid is one of these and also one of the most predominant in food and beverages. The present paper reports an examination of its potential influence on aluminum bioavailability through speciation calculations based on Al(III)-malate complex formation constants especially determined for physiological conditions. According to the results obtained, malate appears to be extremely effective in maintaining Al(OH)(3) soluble over the whole pH range of the small intestine under normal dietary conditions. In addition, two neutral Al(III)--malate complexes are formed whose percentages are maximum from very low malate levels. When aluminum is administered therapeutically as its trihydroxide, the amount of metal neutralized by malate peaks as its solubility pH range regresses to its original limits in the absence of malate. The enhancing effect of malate towards aluminum absorption is therefore virtually independent of the aluminum level in the gastrointestinal tract. The presence of phosphate in the gastrointestinal juice is expected to limit the potential influence of malate on aluminum absorption. Under normal dietary conditions, phosphate effectively reduces the fraction of aluminum neutralized by malate but without nullifying it. Aluminum phosphate is predicted to precipitate when aluminum levels are raised as with the administration of aluminum hydroxide, but a significant amount of neutral aluminum malate still remains in solution. Even therapeutic aluminum phosphate is not totally safe in the presence of malate, even at low malate concentrations. As plasma simulations predict that no compensatory effect in favor of aluminum excretion may be expected from malate, simultaneous ingestion of malic acid with any therapeutic aluminum salt should preferably be avoided.

Aluminum speciation studies in biological fluids. Part 6. Quantitative investigation of aluminum(III)-tartrate complex equilibria and their potential implications for aluminum metabolism and toxicity

Recent epidemiological studies have confirmed the existence of a correlation between aluminum level in low-silica drinking water and prevalence of Alzheimer's disease. Also, oral aluminum-based phosphate binders and antacids may induce acute aluminum toxicity. Whatever the source of the metal ingested, its bioavailability is a function of the chemical forms under which it occurs in the gastrointestinal tract, i.e. of the ligands with which the Al3+ ion may associate. Dietary acids in particular can favor the bioavailability of aluminum in different ways: by increasing its solubility, by complexing it into neutral species, and/or by acting indirectly on its absorption process. Among these, tartaric acid is commonly found in fruits and in industrial foods and drinks, and may therefore be ingested together with environmental or/and therapeutic aluminum. The present work examines its potential influence on aluminum bioavailability. Firstly, Al(III)-tartrate complex formation constants have been determined under physiological conditions (37 degrees C, 0.15 M NaCl). Then these constants have been used to simulate the influence of tartrate on aluminum speciation in different gastrointestinal situations in which phosphate was also taken into account. Under normal conditions of aluminum contamination, tartrate is expected to keep the metal soluble throughout the whole pH range of the small intestine, which is likely to enhance its bioavailability. Even at low concentrations, tartrate also gives rise to two neutral complexes that span over the 1.5-7.5 pH interval, a phenomenon that is aggravated by increased aluminum levels as may result from aluminum hydroxide therapy. The co-occurrence of dietary phosphate reduces the fraction of aluminum neutralized by tartrate under normal conditions, but this effect quickly decreases with increasing aluminum doses. Even the therapeutic use of aluminum phosphate is not expected to be totally safe in the presence of tartaric acid. As plasma simulations show that no aluminum mobilization can be expected from tartrate that could enhance aluminum excretion, avoiding ingestion of tartaric acid during any form of aluminum-based therapy appears advisable.

Evaluation of the protective activity of deferiprone, an aluminum chelator, on aluminum-induced developmental toxicity in mice

BACKGROUND

Since deferiprone can be an effective chelating agent for the treatment of aluminum (Al) overload, in the present study we investigated whether this chelator could protect against Al-induced maternal and developmental toxicity in mice.

METHODS

A single oral dose of Al nitrate nonahydrate (1,327 mg/kg) was given on gestation day 12, the most sensitive time for Al-induced maternal and developmental toxic effects in mice. At 2, 24, 48, and 72 hr thereafter, deferiprone was given by gavage at 0 and 24 mg/kg. Cesarean sections were performed on day 18 of gestation and fetuses were examined for malformations and variations.

RESULTS

Aluminum-induced maternal toxicity was evidenced by significant reductions in body weight gain, corrected body weight change, and food consumption. Developmental toxicity was evidenced by a significant decrease in fetal weight per litter and an increase in the total number of fetuses and litters showing bone retardation. No beneficial effects of deferiprone on these adverse effects could be observed. By contrast, a more pronounced decrease in maternal weight gain and corrected body weight change, as well as a higher number of litters with fetuses showing skeletal variations was noted in the group exposed to Al nitrate and treated with deferiprone at 24 mg/kg.

CONCLUSIONS

According to the current results, deferiprone would not be effective to prevent Al-induced maternal and embryo/fetal toxicity in mice.

Interaction of aluminum with exogenous and endogenous iron in the organism of rats

The aim of these experiments was to find changes in free erythrocyte protoporphyrins (FEP) and in the concentration of endogenous iron in the blood, erythrocytes, serum, liver, kidneys, and spleen of rats, as well as in the dynamics of aluminum concentrations in the serum of rats after oral application of aluminum chloride (AlCl(3)) separately or with ferrum chloride (FeCl(2)), depending on the time and doses administered. The experiments were carried out on female Wistar rats which received (p.o.) 100 mg Al/kg separately or with iron (4 mg Fe/kg) daily for 35 days. The effects of aluminum administration were noticed after the second week. The experiments demonstrated that the increase in the level of free erythrocyte protoporphyrins in the blood is the most sensitive indicator of exposure to AlCl(3). A decrease in iron concentration in erythrocytes, blood, and spleen was also noticed. The response and the sequence of the investigated effects were recorded according to aluminum and iron concentration in the serum. Joint administration of iron and aluminum decreases concentration of aluminum in serum and prevents changes in the investigated indicators in rats exposed to aluminum chloride.

Interference of aluminium on iron metabolism in erythroleukaemia K562 cells

It has been suggested that aluminium (Al) has a deleterious effect on erythropoiesis. However, there is still uncertainty as to its action mechanism. The present work was designed to determine how Al could affect the iron (Fe) metabolism in the human erythroleukaemia cell line K562. These cells, that express surface transferrin receptors (TfRs), were induced to erythroid differentiation by either haemin or hydroxyurea in 72 h cultures in media containing apotransferrin (apoTf). In the presence of aluminium citrate, the number of benzidine-positive cells decreased 18% when the cultures were induced by haemin, and 30% when hydroxyurea was the inducer. Cell viability was always unaffected. From competition assays, surface binding of 125I-Tf-Fe2 was found to be inversely related (p < 0.05) to Tf-Al2 concentration (from 2.5 to 10 nM). The dissociation constants (Kd) of the binding reaction between TfRs and the ligands Tf-Fe2 and Tf-Al2 were calculated. Kd values of the same order of magnitude demonstrated that TfR has a similar affinity for Tf-Fe2 (Kd = 1.75 x 10(-9) M) and Tf-Al2 (Kd = 1.37 x 10(-9) M). The number of surface TfRs, measured by kinetic 125I-Tf-Fe2 binding assays, was higher in induced cells cultured in the presence of Al. Nevertheless, in spite of the inhibition of cell haemoglobinization observed, 59Fe incorporation values were not different from those measured in control cultures for 72 h. As a consequence, it can be suggested that cellular Fe utilisation, and not Fe uptake, might be the main metabolic pathway impaired by Al.

Morphologic and functional alterations of erythroid cells induced by long-term ingestion of aluminium

Anaemia has been associated with aluminium (Al) accumulation in plasma and/or bone tissue in patients with chronic renal insufficiency. Nevertheless, in previous works, we have found shortened red-cell life span, increased osmotic resistance and inhibition of colony-forming units-erythroid (CFU-E) development in Al-overloaded rats with normal renal function. To elucidate further the action of Al on in vivo erythropoiesis, aluminium citrate was provided to Sprague Dawley rats (n = 18) in the drinking water for 8 months. Significant decreases in haematocrit (38.8 +/- 4.29 versus 43.1 +/- 3.58%, p < 0.05) and blood haemoglobin concentration (137 +/- 10.1 versus 148 +/- 8.5 g/l, p < 0.05), reticulocytosis (1.8/1.3-4.2 versus 1.2/0.4-3.7%, p < 0.05), and severe inhibition of CFU-E growth (670/120-950 versus 1530/810-2440 CFU-E/2 x 10(5) cells, p < 0.005) were found. Anysocytosis, poikilocytosis and schistocytosis were detected in peripheral blood stained films. Scanning electron microscopy revealed the presence of erythrocytes with abnormal shape, including crenated and target cells. Aluminium was localised specially inside the schistocytes by EDAX analysis. Decreased haptoglobin concentration (107/83-127 versus 139/89-169 mg/l, p < 0.05) supports the assumption of haemolytic nature of the anaemia. Rats were not iron depleted, as plasma iron concentration and total iron binding capacity were found in the range of control values, and sideroblasts and haemosiderin deposits were observed in bone marrow smears. Total 59Fe uptake and 59Fe incorporated to haem by the bone marrow cells were found decreased. In conclusion, the erythropoiesis impairment induced by Al may be a combined effect of direct action on circulating erythrocytes and interference with the cellular iron metabolism in erythroid progenitors.

Effects of aluminum sulphate and citric acid ingestion on lipid peroxidation and on activities of superoxide dismutase and catalase in cerebral hemisphere and liver of developing young chicks

Effect of oral administration of aluminum sulphate (200 and 400 mg/kg body wt/day) without or with citric acid (62 mg/kg body wt/day) to day-old White Leghorn male chicks (n = 5 per group) for 30 days was studied on the activities of superoxide dismutase (SOD) and catalase, and level of lipid peroxidation in cerebral hemisphere and liver. A 400 mg dose of Al in the presence of citric acid inhibited cytosolic total and CN -sensitive superoxide dismutase activities of the cerebral hemisphere in 7- and 30-day treated chicks, whereas in 15-day treated chicks the enzyme activities were decreased in response to both doses in the presence of citric acid. In case of liver, activities of these enzymes significantly decreased after 7, 15 and 30 days of treatment with 200 and 400 mg Al together with citric acid, whereas 400 mg Al alone inhibited the enzyme activities after 15 and 30 days of treatment. Cerebral catalase activity decreased in response to 400 mg Al when the chicks were also fed with citric acid for 7 and 30 days, but in 15-day treated chicks the enzyme activity was depleted following treatment with 200 and 400 mg Al combined with citric acid. 400 mg Al treatment for 7 days in combination with citric acid inhibited hepatic catalase activity and extension of the treatment period to 15 and 30 days also produced reduction in its activity even in response to the lower Al dose mixed with citric acid. CN -insensitive SOD activity of cerebral hemisphere and liver was unaffected by Al. Al also failed to induce lipid peroxidation in both the tissues throughout the course of exposure. Activities of SOD and catalase of cerebral hemisphere and liver of 30-day old chicks were observed to be inhibited by in vitro incubation with different concentrations of Al. Our in vivo study demonstrates that only CN -sensitive SOD is susceptible to Al. Further, responses of SOD and catalase to Al is tissue specific. The observed inhibition of antioxidant enzyme activities by Al is suggestive of a prooxidant state. Induction of such an oxidative condition of the tissues may be attributed to a direct effect of the metal on enzyme molecules or in their synthesis.

Oral aluminum administration to rats wih normal renal function. 1. Impairment of erythropoiesis

Aluminum (Al) toxicity has been mainly investigated in uremic patients although healthy subjects and patients without renal insufficiency are not exempt from its potential deleterious effects. This experimental study aims to elucidate the action of different doses of Al citrate on in vivo erythropoiesis and find out whether the metal exerts a local toxic effect upon the bone marrow late erythroid progenitor cells. The groups in the first experimental series were: C1 (n=5) controls and TAl-1 (n=5) rats receiving 1 micromol Al citrate/g body weight/day by gavage. Colony-forming units-erythroid (CFU-E) development was inhibited in the TAl-1 group, but the median osmotic fragility (MOF) and hematocrit (Ht) values were similar to those of the C1 group. The groups in the second series were C2 (n=5) controls and TAl-2 (n=5) rats receiving Al citrate in drinking water (100 mmol/l). The TAl-2 group showed decreased Ht, hemoglobin concentration, MOF and red blood-cell life-span values (P<0.05), and a marked inhibition of the CFU-E development (P<0.01). Serum and bone Al concentrations were increased in both Al-treated groups (P < 0.01). There was a dose-dependent increase in bone Al levels (P < 0.01) and a dose-dependent decrease of CFU-E development (P<0.05). The CFU-E development was inversely correlated with the bone Al content (r=-0.79; P<0.05). The results demonstrate that even very low doses of Al citrate impair erythropoiesis in vivo and higher doses exert a deleterious action on both CFU-E and mature erythrocytes. This might show a local effect of Al on CFU-E caused by the bone sensitivity to the metal accumulation.

Uptake of aluminum and gallium into tissues of the rat: influence of antibody against the transferrin receptor

Transport of aluminum and gallium from blood into rat tissues following continuous i.v. infusion of metals in different chemical forms has been investigated. Tissue uptake of aluminum and gallium was similar and highly dependent on the chemical species of the metals. Aluminum and gallium accumulated in liver and spleen when infused in the chloride form. Raised citrate markedly enhanced aluminum and gallium uptake into renal cortex and bone; in contrast with gallium-transferrin, citrate increased uptake of 67Ga into renal cortex and bone by 8- and 14-fold respectively. Uptake of 67Ga with citrate into renal cortex was around 3 times smaller than that of aluminum. The antitransferrin receptor antibody OX-26 enhanced 67Ga uptake from gallium citrate into all rat tissues. 67Ga from purified gallium-transferrin was also taken into all tissues in the presence of OX-26, the effect being greatest in renal cortex and bone. No influence of antibody on aluminum transport into rat tissues was, however, observed when aluminum was infused in the citrate form. Therefore, transport of aluminum and gallium into tissues is not similar under all conditions. Transport of each metal occurs into all tissues in the presence of antitransferrin receptor antibody. The potential for such transport is much greater in the case of gallium. Transport of aluminum and gallium citrate complexes appears important especially in the renal cortex and bone.

Gastrointestinal absorption of aluminium and citrate in man

Aluminium (Al) is an abundant terrestrial element, but toxic to tissues, including brain. The body is largely protected because systemic Al absorption is very low and in normal individuals almost all absorbed Al is excreted from the body. However gastrointestinal (Gl) absorption is enhanced by organic acids, including citrate. Aluminium and citrate Gl absorption was measured in three healthy males, aged 40-46. After overnight fast, subjects drank a 100 ml fruit drink containing 280 mg Al and 3.2 g citrate (104 and 167 mM, respectively). Al was measured in timed blood and urine samples by GFAAS and serum citrate by enzymatic assay. Blood Al peaked by an increase of 13 +/- 2.1 micrograms/l after 87 +/- 19 min then fell slowly over 24 h. Plasma citrate peaked after 32 min, returning to baseline by 90 min. Al was excreted at a constant rate for the first 24 h, 0.4% of the dose being excreted in urine by this time. It is unlikely that Al is absorbed as Al citrate because the blood citrate peak preceded the Al peak by 45-60 min.

Aluminum exposure and metabolism

Aluminum (Al) is a nonessential, toxic metal to which humans are frequently exposed. Oral exposure to aluminum occurs through ingestion of aluminum-containing pharmaceuticals and to a lesser extent foods and water. Parenteral exposure to aluminum can occur via contaminated total parenteral nutrition (TPN), intravenous (i.v.) solutions, or contaminated dialysates. Inhalation exposure may be important in some occupational settings. The gut is the most effective organ in preventing tissue aluminum accumulation after oral exposure. Typically gastrointestinal absorption of aluminum from diets is < 1%. Although the mechanisms of aluminum absorption have not been elucidated, both passive and active transcellular processes and paracellular transport are believed to occur. Aluminum and calcium may share some absorptive pathways. Aluminum absorption is also affected by the speciation of aluminum and a variety of other substances, including citrate, in the gut milieu. Not all absorbed or parenterally delivered aluminum is excreted in urine. Low glomerular filtration of aluminum reflects that most aluminum in plasma is nonfiltrable because of complexation to proteins, predominantly transferrin. The importance of biliary secretion of aluminum is debatable and the mechanism(s) is poorly understood and appears to be saturable by fairly low oral doses of aluminum.

Concentrations of some essential elements in the brain of aluminum-exposed rats in relation to the age of exposure

This study evaluated the influence of age on the aluminum (Al) interaction with calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) in the brain of rats. Since both Al and aging have been associated with neurobehavioral deficits in mammals, the brain was chosen to assess that influence. Male young (21 day), adult (8 months), and old (16 months) rats were given 0, 50, and 100 mg/kg per day of aluminum administered as aluminum nitrate in drinking water for 6.5 months. During that period, citric acid (0, 355 and 710 mg/kg per day) was also added to the drinking water. After 6.5 months of Al exposure, Al, Ca, Mg, Fe, Mn, Cu and Zn concentrations were determined in brain tissue as well as in a number of cerebral regions: cortex, hippocampus, striatum, cerebellum, thalamus, olfactory bulb, and rachidical bulb. While no significant age-related differences were found for Ca concentrations in the seven cerebral regions analyzed, most Mg, Fe, Mn and Zn levels were significantly higher in young than in adult and old rats. In turn, Al concentrations were mostly higher in the cerebral regions of young rats than in the same regions of adult and old rats. In contrast, Cu levels were lower in most brain regions of old animals than in those of young rats. According to the results of the present study, the age-related changes in brain Al, Ca, Mg, Fe, Mn, Cu and Zn concentrations induced by Al and aging would not suggest any influence on Al-induced neurobehavioral deficits.

Effect of small variations of aluminum intake on calcium metabolism in young rats

BACKGROUND

While in the adult Al intoxication requires high dosages, little is known on the threshold level of Al toxicity in the young.

METHODS

Weaning rats were fed for 90 days ore of four diets differing by their content in Ca (7.5 vs < 0.5 g/< g diet)(Ca+/-) and Al (10.6 vs 8.4 mg/kg)(Al+/-); Al supplementation was 30% above the standard level of diet. Ca and Al levels were measured in liver, bone (femur), and brain.

RESULTS

Ca- had a significant negative effect on growth which was further reduced by Al+; in Ca sufficient/Al+ animals, Al concentrations were significantly increased in bone and brain and tended to increase in liver; Ca decreases observed in these three organs were only significant in brain. Ca deficiency further enhanced the Al deposit in bone at both levels of Al intakes, and reduced Ca concentrations in these three organs in Al+ animals; in Ca-/Al- animals, the decrease in Ca displayed in the three tissues reached a significant level in brain.

CONCLUSIONS

This study suggests that in the growing subject the side effects of small variations of Al intake can be enhanced when they are combined with other mineral imbalances.

The effect of age on aluminum retention in rats

The present study was designed to assess potential changes in aluminum (Al) retention during advanced age. Young (21 day old), adult (8 months), and old (16 months) rats were exposed to 0, 50, and 100 mg Al/kg/day administered as aluminum nitrate in drinking water for a period of 6.5 months. Urinary Al levels were measured after 3 and 6.5 months of Al exposure. Organ weights and tissue Al concentrations were examined at 6.5 months of Al administration. Differences in the tissue accumulation of Al with age included higher liver, kidneys, spleen, bone and testes levels in old rats than in tissues of both young or adult animals. In contrast, brain concentrations were higher in young rats. Urinary Al levels of young, adult or old Al-exposed rats showed different trends at 6.5 months of Al exposure: compared with young values adult values declined, while those of old rats tended to increase further. The current results show that tissue Al retention patterns may be significantly altered depending on the age at Al exposure. This finding may be of concern for future investigations on the potential role of Al in certain neurological disorders.

Effects of aluminium on the mineral metabolism of rats in relation to age

The present study was conducted to assess in rats the effects of chronic aluminium (Al) exposure on calcium (Ca), magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn) and iron (Fe) accumulation and urinary excretion in relation to the age of the animals. Male young (21 day old), adult (8 months), and old (16 months) rats were orally exposed to 0, 50, or 100 mg Al/kg/day for a period of 6.5 months. Urinary levels of essential elements were determined after 3 and 6.5 months of exposure, whereas tissue Ca, Mg, Mn, Cu, Zn and Fe concentrations were examined after 6.5 months of Al administration. A number of age-related changes in tissue accumulation and urinary excretion of essential elements following chronic exposure to Al were found. Concentrations of essential elements in most tissues of young Al-exposed rats were generally lower than those of adult and old rats. The highest levels of essential elements were found in old animals. Liver, testes and spleen were the tissues that showed the most remarkable increases in relation to the levels found in those tissues of young rats. Adult rats showed a pattern comparable to that of old animals for mineral metabolism in brain, whereas in bone and testes the pattern of accumulation was closer to that of young rats. While the urinary levels of Ca were generally reduced in the Al-exposed groups, no Al-associated changes were noted for Mg, Mn, Cu and Zn. In turn, after 6.5 months of Al administration Fe excretion was increased in Al-treated adult and old rats. The results of this study suggest that early stages of life cycle should be of special concern for Al-induced changes in the metabolism of essential elements.

Effect of iron status on the intestinal absorption of aluminum: a reappraisal

Clinical and experimental studies have shown that serum aluminum (Al) is bound to transferrin and that cellular uptake of Al appears to be mediated by transferrin receptors. Based on these findings it is widely believed that intestinal Al absorption occurs via iron-specific, transferrin-dependent pathways and that iron (Fe) deficiency increases the intestinal absorption of Al. However, since no transferrin receptors are expressed on the absorptive surface of small intestinal epithelial cells this notion is doubtful. To further clarify the issue the present study investigated the effect of marked alterations of body Fe stores on the intestinal absorption of Al using three different rat models. (I) Serum Al concentrations and urinary excretion rates of Al were measured in iron-overloaded (Fe+) or iron-deficient (Fe-) rats with either normal (C) or impaired (5/6 nephrectomy) renal function (Nx) employing oral A1 loads in single dose studies. (II) Tissue A1 accumulation as well as serum and urine A1 were determined in respective experimental groups exposed to a prolonged (41 days) dietary Al load. (III) To assess the effect of Fe status on the intestinal absorption of Al directly at the organ level perfusions of in situ rat gut preparations were performed. In the single dose studies administration of Al resulted in similar urinary excretion rates of Al in intact kidney groups (C+Fe-, 229 +/- 85 nmol/5 days; C+Fe+, 240 +/- 59 nmol/5 days) despite marked differences in liver Fe (C+Fe-, 1.34 +/- 0.16 vs. C+Fe+, 55.69 +/- 13.20 mumol/g) and duodenal mucosal Fe (C+Fe-, 0.68 +/- 0.11 vs. C+Fe+, 3.17 +/- 0.82 mumol/g). In addition, mucosal Al concentration 24 hours after the load was not affected by the Fe status (C+Fe-, 37 +/- 16 nmol/g, C+Fe+, 56 +/- 19 nmol/g). Regardless of the Fe status post-load Al excretion was enhanced in Nx rats (Nx+Fe-, 533 +/- 234 nmol/five days, Nx+Fe+, 536 +/- 201 nmol/five days). Irrespective of Fe status a prolonged dietary Al load resulted in a similar increase in tissue Al concentration (nmol/g) in liver (baseline, 159 +/- 22; C+Fe-, 276 +/- 125; C+Fe+, 251 +/- 71; Nx+Fe-, 330 +/- 119; Nx+Fe+, 437 +/- 67) and in bone (baseline, 219 +/- 119; C+Fe-, 433 +/- 174, C+Fe+, 485 +/- 141; Nx+Fe-, 504 +/- 185; Nx+Fe+, 548 +/- 215). The increase in spleen Al was significantly larger in Fe-overloaded rats (baseline, 194 +/- 20; C+Fe+, 511 +/- 129 vs. C+Fe-, 308 +/- 62, P < 0.05; Nx+Fe+, 514 +/- 67 vs. Nx+Fe-, 389 +/- 119, P < 0.05). Brain Al tended to rise in Nx rats only (baseline, 96 +/- 33; Nx+Fe+, 174 +/- 100, Nx+Fe-, 156 +/- 78, P = NS). Analogous results were obtained in in situ intestinal perfusion studies: Fe deficiency and Fe overload both did not affect the time-dependent increase in serum Al in either systemic or portal vein blood. When paracellular intestinal permeability was assessed mannitol absorption was significantly higher in uremic animals as compared to controls. Pharmacological blockade (2 mM kinetin) of the paracellular permeability substantially reduced the time-dependent increase in serum Al in uremic rats but had little effect in control animals, suggesting that even the excess absorption of Al observed in uremia occurs via a paracellular rather than an iron-specific pathway. In conclusion, the findings of the present study provide several lines of evidence against the commonly accepted view that the intestinal absorption of Al occurs via iron-specific pathways. Most likely, this is related to the fact, that neither the absorption of Fe nor the absorption of Al are mediated via transferrin receptors. In addition, the enhanced intestinal absorption of Al observed in uremic rats does also not occur via iron-specific pathways, but seems to due to increased paracellular permeability of the intestine.

Age-related effects of aluminum ingestion on brain aluminum accumulation and behavior in rats

Both aluminum and aging have been associated with neurobehavioral changes in mammals. This study assessed in young (21 day old), adult (8 months), and old rats (16 months) the effects of prolonged aluminum ingestion on open-field activity and passive-avoidance conditioning. Aluminum was administered in drinking water as aluminum nitrate at doses of 0, 50, and 100 mg Al/kg/day over a 6.5 month period. There were no aluminum effects on the horizontal and vertical activity in an open-field, or in passive-avoidance learning in any group. On the other hand, measurement of aluminum concentrations in a number of brain regions indicated that the olfactory bulb and the rhachidical bulb were the regions with the highest aluminum levels, while the cortex and the thalamus were the cerebral regions showing the lowest aluminum content. For most brain regions analyzed the highest aluminum concentrations were found in young rats, which would indicate that early stages of the life cycle must be considered for enhanced brain aluminum accumulation.

Influence of organic acids on aluminium absorption and storage in rat tissues

Six groups of 16 rats each were fed a standard diet for 8 weeks. Aluminium (Al) complexed with organic anions (citrate, lactate, malate, or tartrate) was added to the diet of four of the groups and aluminium hydroxide to the diet of one group (control 'Al +'). Aluminium concentrations in the diets were 1500-2000 mg/kg. The sixth group (control 'Al -') served as control. Plasma, bone (femur), kidneys, cerebral cortex and cerebellum levels of aluminium were determined at 4 and 8 weeks. All the complexing agents increased tissue accumulations, compared with values in the two control groups, especially citrate in bone and kidneys and lactate in cerebral cortex. There were no significant differences (P < 0.05) in aluminium levels in the tissues considered between the 'Al +' and 'Al -' control groups. Our results show the ability of dietary organic acids to increase aluminium absorption and tissue accumulation and indicate that concurrent intake of aluminium and dietary organic acids is not appropriate.

Reproductive and developmental toxicity of aluminum: a review

It is well known that aluminum is a developmental toxicant when administered parenterally. However, until recently, there was little concern about embryo/fetal consequences of aluminum ingestion because bioavailability was considered low. The importance of the route of exposure and the chemical form of the aluminum compound on the developmental toxicity of this element are now well established. Although no evidence of maternal and embryo/fetal toxicity was observed when high doses of aluminum hydroxide were given orally to pregnant rats and mice during organogenesis, signs of maternal and developmental toxicity were found in mice when aluminum hydroxide was given concurrently with citric or lactic acids. On the other hand, studies in rabbits have shown that aluminum-induced behavioral toxicity is greater in adult and aged animals than in young adults. However, maternal dietary exposure to excess A1 during gestation and lactation which did not produce maternal toxicity would be capable of causing permanent neurobehavioral deficits in weanling mice and rats. Adverse effects of parenteral aluminum administration on the mouse male reproductive system have also been reported. The embryo/fetal toxicity of aluminum administration, the potential reproductive toxicology of aluminum exposure, and the neurodevelopmental effects of aluminum are here reviewed.

Metal-induced developmental toxicity in mammals: a review

It is well established that certain metals are toxic to embryonic and fetal tissues and can induce teratogenicity in mammals. The main objective of this paper has been to summarize the toxic effects that excesses of certain metals may cause on mammalian development. The reviewed elements have been divided into four groups: (a) metals of greatest toxicological significance (arsenic, cadmium, lead, mercury, and uranium) that are wide-spread in the human environment, (b) essential trace metals (chromium, cobalt, manganese, selenium, and zinc), (c) other metals with evident biological interest (nickel and vanadium), and (d) metals of pharmacological interest (aluminum, gallium, and lithium). A summary of the therapeutic use of chelating agents in the prevention of metal-induced developmental toxicity has also been included. meso-2,3-Dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane-1-sulfonate (DMPS) have been reported to be effective in alleviating arsenic- and mercury-induced teratogenesis, whereas sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) would protect against vanadium- and uranium-induced developmental toxicity.

Lack of maternal and developmental toxicity in mice given high doses of aluminium hydroxide and ascorbic acid during gestation

The present study was conducted to assess if the concurrent ingestion of high doses of aluminium hydroxide and ascorbic acid might result in maternal and developmental toxicity in mice. Three groups of pregnant Swiss mice were given by gavage daily doses of aluminium hydroxide (300 mg/kg), ascorbic acid (85 mg/kg), or aluminium hydroxide (300 mg/kg) concurrent with ascorbic acid 85 (mg/kg) on gestational days 6-15. A fourth group of animals received distilled water and served as control group. Dams were killed on gestation day 18 and foetuses were examined for external, internal, and skeletal abnormalities. The reproductive data did not show embryotoxic or foetotoxic effects in any group. No gross, internal, or skeletal malformations or variations related to the different treatments were found. There were no significant differences between control and treated groups on the aluminium levels in maternal liver and bone as well as in whole body foetuses, whereas aluminium concentrations were significantly higher in placenta and kidney of dams receiving aluminium hydroxide and aluminium hydroxide plus ascorbic acid than in those from the control group. Although in this study aluminium hydroxide was given at doses higher than those usually consumed by pregnant women, no signs of maternal or developmental toxicity were observed when the compound was given alone or concurrently with high doses of ascorbic acid.

Comparative aluminium mobilizing actions of several chelators in aluminium-loaded uraemic rats

The relative effectiveness of deferoxamine (DFO), 1,2-dimethyl-1,3-hydroxypyrid-4-one (L1), and citric and succinic acids in mobilizing and promoting excretion of aluminium (Al) were compared in female uraemic rats which had previously received aluminium nitrate nonahydrate i.p. in a daily dose of 45 mg kg-1 for 3 weeks (5 days/week). Chelators were administered s.c. at doses equal to one-eighth of their respective LD50 for five days. L1 was also given p.o. in doses of 200 mg kg-1 day-1. Total urines were collected 24 h after each chelator administration. Total urinary Al excreted over the 5-day period, expressed as mg kg-1, were: controls, 3.4; DFO-treated, 4.5 (P < 0.05); citric acid-treated, 3.7; and succinic acid-treated, 2.7. Although the daily amounts of Al excreted into urine by L1-treated rats were significantly higher (P < 0.001) than those of the controls, most animals died during the period of treatment. Measurements of Al in selected tissues 24 h after the last administration of each chelator revealed that none of the compounds significantly altered the Al concentration in bone, kidney, and brain, whereas only DFO and succinic acid significantly reduced the levels of Al in spleen. Moreover, L1 (given s.c. or p.o.) and citric acid treatment led to a significant reduction in the liver Al burden. These results indicate the need for further investigations to determine the toxicity and the therapeutical safety margins of L1.

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.

Is aluminium an etiologic contributor to alcoholic amnesia and dementia?

Neurotoxicity from excess brain exposure to aluminium (Al) is well-documented, from both clinical observations and animal experiments, to impair learning, memory and cognition. The etiology of the cognitive impairment in chronic abusers of ethanol--alcoholic amnesia or dementia--is not known, but it is likely to be multifactorial. We hypothesize that a slowly-progressive accumulation of Al in the brain, so as to reach functionally-toxic levels, may be one such factor. This could occur because of an increased permeability of intestinal mucosa to entry of Al, arising from sustained exposure of the gastrointestinal tract to alcoholic beverages, plus a trend for more frequent ingestion of antacids based on Al salts for treating gastritis or ulcers caused by such exposure. If this be true, use of Al-containing medications, as well as all avoidable exposures to Al, should be contra-indicated for chronic heavy drinkers.