Assessment of exposure to parenteral and oral aluminum with and without citrate using a desferrioxamine test in rats

Mitonuclear incompatibility as a hidden driver behind the genome ancestry of African admixed cattle

Background

Africa is an important watershed in the genetic history of domestic cattle, as two lineages of modern cattle, Bos taurus and B. indicus, form distinct admixed cattle populations. Despite the predominant B. indicus nuclear ancestry of African admixed cattle, B. indicus mitochondria have not been found on the continent. This discrepancy between the mitochondrial and nuclear genomes has been previously hypothesized to be driven by male-biased introgression of Asian B. indicus into ancestral African B. taurus. Given that this hypothesis mandates extreme demographic assumptions relying on random genetic drift, we propose a novel hypothesis of selection induced by mitonuclear incompatibility and assess these hypotheses with regard to the current genomic status of African admixed cattle.

Results

By analyzing 494 mitochondrial and 235 nuclear genome sequences, we first confirmed the genotype discrepancy between mitochondrial and nuclear genome in African admixed cattle: the absence of B. indicus mitochondria and the predominant B. indicus autosomal ancestry. We applied approximate Bayesian computation (ABC) to assess the posterior probabilities of two selection hypotheses given this observation. The results of ABC indicated that the model assuming both male-biased B. indicus introgression and selection induced by mitonuclear incompatibility explains the current genomic discrepancy most accurately. Subsequently, we identified selection signatures at autosomal loci interacting with mitochondria that are responsible for integrity of the cellular respiration system. By contrast with B. indicus-enriched genome ancestry of African admixed cattle, local ancestries at these selection signatures were enriched with B. taurus alleles, concurring with the key expectation of selection induced by mitonuclear incompatibility.

Conclusions

Our findings support the current genome status of African admixed cattle as a potential outcome of male-biased B. indicus introgression, where mitonuclear incompatibility exerted selection pressure against B. indicus mitochondria. This study provides a novel perspective on African cattle demography and supports the role of mitonuclear incompatibility in the hybridization of mammalian species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01206-x.

Toxic element levels in ingredients and commercial pet foods

Nowadays, there is a growing concern about contamination of toxic metals (TM) in pet food due to the great potential for health risks of these elements. TM concentrations in commercial pet foods (n = 100) as well as in ingredients used in their composition (n = 100) were analyzed and compared to the Food and Drug Administration (FDA) maximum tolerable level (MTL), and the TM concentrations found in the different sources of carbohydrate, protein, and fat were compared. The TM concentrations were determined by inductively coupled plasma with optical emission spectrometry (ICP-OES). Concentrations above the MTL for aluminum, mercury, lead, uranium, and vanadium were observed in both dog and cat foods, and the percentage of dog foods that exceeded the MTL of these TM were: 31.9%; 100%; 80.55%; 95.83%; and 75%, respectively, and in cat foods: 10.71%; 100%; 32.14%; 85.71%; 28.57%, respectively. The MTL values of these TMs and the mean values in dog foods (mg/kg dry matter basis) (MTL [mean ± standard deviation]) were: aluminum: 200 (269.17 ± 393.74); mercury: 0.27 (2.51 ± 1.31); lead: 10 (12.55 ± 4.30); uranium: 10 (76.82 ± 28.09); vanadium: 1 (1.35 ± 0.69), while in cat foods were: aluminum: 200 (135.51 ± 143.95); mercury: 0.27 (3.47 ± 4.31); lead: 10 (9.13 ± 5.42); uranium: 10 (49.83 ± 29.18); vanadium: 1 (0.81 ± 0.77). Dry foods presented higher concentrations of most TM (P < 0.05) than wet foods (P < 0.05). Among the carbohydrate sources, there were the highest levels of all TM except cobalt, mercury, and nickel in wheat bran (P < 0.05), while among the protein sources, in general, animal by-products had higher TM concentrations than plant-based ingredients. Pork fat had higher concentrations of arsenic, mercury, and antimony than fish oil and poultry fat. It was concluded that the pet foods evaluated in this study presented high concentrations of the following TM: aluminum, mercury, lead, uranium, and vanadium.

Review: Vaccine Myth-Buster - Cleaning Up With Prejudices and Dangerous Misinformation

Although vaccines have already saved and will continue to save millions of lives, they are under attack. Vaccine safety is the main target of criticism. The rapid distribution of false information, or even conspiracy theories on the internet has tremendously favored vaccine hesitancy. The World Health Organization (WHO) named vaccine hesitancy one of the top ten threats to global health in 2019. Parents and patients have several concerns about vaccine safety, of which the ubiquitous anxieties include inactivating agents, adjuvants, preservatives, or new technologies such as genetic vaccines. In general, increasing doubts concerning side effects have been observed, which may lead to an increasing mistrust of scientific results and thus, the scientific method. Hence, this review targets five topics concerning vaccines and reviews current scientific publications in order to summarize the available information refuting conspiracy theories and myths about vaccination. The topics have been selected based on the author's personal perception of the most frequently occurring safety controversies: the inactivation agent formaldehyde, the adjuvant aluminum, the preservative mercury, the mistakenly-drawn correlation between vaccines and autism and genetic vaccines. The scientific literature shows that vaccine safety is constantly studied. Furthermore, the literature does not support the allegations that vaccines may cause a serious threat to general human life. The author suggests that more researchers explaining their research ideas, methods and results publicly could strengthen the general confidence in science. In general, vaccines present one of the safest and most cost-effective medications and none of the targeted topics raised serious health concerns.

Aluminum reproductive toxicity: a summary and interpretation of scientific reports

Publications addressing aluminum (Al)-induced reproductive toxicity were reviewed. Key details were compiled in summary tables. Approximate systemic Al exposure, a measure of bioavailability, was calculated for each exposure, based on the Al percentage in the dosed Al species, Al bioavailability, and absorption time course reports for the exposure route. This was limited to laboratory animal studies because no controlled-exposure human studies were found. Intended Al exposure was compared to unintended dietary Al exposure. The considerable and variable Al content of laboratory animal diets creates uncertainty about reproductive function in the absence of Al. Aluminum-induced reproductive toxicity in female mice and rats was evident after exposure to ≥25-fold the amount of Al consumed in the diet. Generally, the additional daily Al systemic exposure of studies that reported statistically significant results was greater than 100-fold above the typical human daily Al dietary consumption equivalent. Male reproductive endpoints were significantly affected after exposure to lower levels of Al than females. Increased Al intake increased fetus, placenta, and testes Al concentrations, to a greater extent in the placenta than fetus, and, in some cases, more in the testes than placenta. An adverse outcome pathway (AOP) was constructed for males based on the results of the reviewed studies. The proposed AOP includes oxidative stress as the molecular initiating event and increased malondialdehyde, DNA and spermatozoal damage, and decreased blood testosterone and sperm count as subsequent key events. Recommendations for the design of future studies of reproductive outcomes following exposure to Al are provided.

Mung bean (Phaseolus radiatus L.) polyphenol extract attenuates aluminum-induced cardiotoxicity through an ROS-triggered Ca2+/JNK/NF-κB signaling pathway in rats

Aluminum (Al) has been linked to the development of some cardiovascular diseases and mung bean is a functional food with the ability to detoxify. We aimed to evaluate the preventive effect and possible underlying mechanisms of the mung bean polyphenol extract (MPE) on Al-induced cardiotoxicity. Control, AlCl₃ (171.8 mg Al per kg body weight), MPE + AlCl₃ (Al-treatment plus 200 mg MPE per kg body weight), and a group of MPE per se were used. Al intake induced a significant increase of serum CK and LDH activity and the level of Na⁺, Ca²⁺, malondialdehyde and advanced oxidation protein products in the AlCl₃-treated rats' heart tissue. Administration of MPE significantly improved the integrity and normal ion levels of heart tissue, and attenuated oxidative damage and the accumulation of Al in Al-treated rats. MPE significantly inhibited Al-induced increase of myocardial p-JNK, cytoplasmic NF-κB, cytochrome C, and caspase-9 protein expressions. Therefore, these results showed that MPE has a cardiac protective effect against Al-induced biotoxicity through ROS-JNK and NF-κB-mediated caspase pathways. Furthermore, the stability constant for the vitexin-Al complex was analyzed (log K = log K₁ + log K₂ = 4.91 + 4.85 = 9.76). We found that MPE-mediated protection against Al-cardiotoxicity is connected both with MPE antioxidant and chelation properties.

Determination of Aluminum in Edible Jellyfish Using Chrome Azurol S with Spot Test on Filter Paper

Aluminum (Al) has been well known as an environmental factor that may affect several enzymes and other biomolecules related to Alzheimer's disease. The increasing use of Al in the preparation and storage of food currently represents the main form of Al exposure for the general public. The present study was aimed to develop a household procedure for the rapid test determination of Al in edible jellyfish. The method was developed based on the reaction of Chrome Azurol S with Al in acidic medium, forming a colored compound on the surface of filter paper. Experimental design methodologies were used to optimize the measurement conditions. The proposed method was applied successfully to the analysis of Al in edible jellyfish products in clinical laboratory and household settings.

Risk assessment of dietary exposure to aluminium in the Chinese population

In order to address the issue of excessive intake of aluminium (Al) from Al-containing food additives in the Chinese diet, this study conducted a dietary exposure assessment of Al in the general population based on the national surveillance data of Al content in foods and national food consumption data. It was found that the mean dietary exposure of the whole Chinese population to Al from Al-containing food additives was 1.795 mg kg^‒1 bw week^‒1, not exceeding the PTWI, while high dietary exposures (e.g., 97.5^th percentile) to Al were 7.660 and 2.103-2.903 mg kg^‒1 bw week^‒1 for children, respectively, both exceeding the PTWI. It was found that the dietary exposure to Al for 32.5% of the total Chinese population and 42.6% of children aged 4-6 years exceeded the PTWI. Wheat flour and wheat-based products are the main source of dietary A l exposure (85% of the total intake); and puffed foods are the major source of Al intake for children. These findings suggested that consumption of Al-containing food additives could be a health concern for consumers with high food consumption (97.5^th percentile) and children under the age of 14 years.

A study of the association between urinary aluminum concentration and pre-clinical findings among aluminum-handling and non-handling workers

BACKGROUND

Aluminum is considered to be a relatively safe metal for humans. However, there are some reports that aluminum can be toxic to humans and animals. In order to estimate the toxicity of aluminum with respect to humans, we measured the aluminum concentration in urine of aluminum-handling and non-handling workers and investigated the relationships between their urinary aluminum concentrations and pre-clinical findings.

METHODS

Twenty-three healthy aluminum-handling workers and 10 healthy non-aluminum-handling workers participated in this study. Their medical examinations, which were otherwise unremarkable, included the collection of urine and blood. Urinary aluminum levels were analyzed using ICP analysis. As pre-clinical tests, we measured KL-6, SP-D, TRCP-5b, IL-6, and IL-8 in blood and δ-ALA and β2-microglobulin in urine. These were considered to be lung, bone, kidney and inflammation markers. Moreover, we measured 8-OHdG in urine as an oxidative DNA damage marker.

RESULTS

The aluminum concentration in urine ranged from 6.9 to 55.1 μg/g cre (median: 20.1 μg/g cre) in the aluminum-handling workers and from 5.6 to 15.6 μg/g cre (median: 8.8 μg/g cre) in the non-aluminum-handling workers, with a significant difference between them. In the pre-clinical findings, there were no significant differences between these two groups except in the case of δ-ALA. However, there were no significant relationships between aluminum concentration and the pre-clinical findings, work years, age or 8-OHdG in the aluminum-handling workers.

CONCLUSIONS

While the excretion of aluminum in urine was elevated in aluminum-handling workers, our findings suggest that low-dose aluminum is not directly harmful to humans, at least when workers' urinary aluminum concentration is below 55 μg/g cre.

Effects of aluminum chloride on some trace elements and erythrocyte osmotic fragility in rats

Aluminum (Al) is a nonessential, toxic element to which humans are constantly exposed as a result of an increase in industrialization and improving technology practices. The aim of the study was to investigate the effects of different durations and doses of Al exposure on serum and tissue element levels and erythrocyte osmotic fragility in rats. A total of 40 male Wistar Albino rats were divided into five groups: control, group I (3 weeks, 8 mg/kg), group II (6 weeks, 8 mg/kg), group III (3 weeks, 16 mg/kg), and group IV (6 weeks, 16 mg/kg). Al chloride (AlCl3) was injected intraperitoneally (i.p.) five times a week. At the end of the experimental period, levels of Al, iron (Fe), copper (Cu), and zinc (Zn) in serum, liver, and kidney tissues were measured using inductively coupled plasma optical emission spectrometry. Osmotic fragility was determined using a spectrophotometer. The results of the experiment indicate that Al induced a statistically significant increase in Al and Fe concentrations in liver and serum as well as in Cu in the kidney. The Fe concentration in serum and kidney tissues was significantly lower in all the groups. As a result of our study, it may be concluded that tissue Al accumulation may lead to an increase in osmotic fragility of erythrocytes and abnormal trace element levels.

The Neuroprotective Effect of Picroside II from Hu-Huang-Lian against Oxidative Stress

Picroside II is an active constituent extracted from the traditional Chinese medicine (TCM) Hu-Huang-Lian. To evaluate the neuroprotective effect of picroside II, PC12 cells were treated with glutamate in vitro and male ICR mice were treated with AlCl 3in vivo. Pre-treatment of PC12 cells with picroside II could enhance the cell viability and decrease the level of intracellular reactive oxygen species (ROS) induced by glutamate. By DNA fragmentation and flow cytometry assay, picroside II (1.2 mg/ml) significantly prevented glutamate-induced cell apoptosis. In the animal study, amnesia was induced in mice by AlCl 3 (100 mg/kg/d, i.v.). Pricroside II, at the dose of 20 and 40 mg/kg/d (i.g.), markedly ameliorated AlCl 3-induced learning and memory dysfunctions and attenuated AlCl 3-induced histological changes. This was associated with the significant increased superoxide dismutase (SOD) activity in the brain of experimental mice. All these results indicated that picroside II possessed the therapeutic potential in protecting against neurological injuries damaged by oxidative stress.

Lethality, accumulation and toxicokinetics of aluminum in some tissues of male albino rats

In the present work, the lethality percentiles including median lethal doses (LD50), accumulation, distribution and toxicokinetics of aluminum in the liver, kidney, intestine, brain and serum of male albino rats, following a single oral administration were studied throughout 1, 3, 7, 14 and 28 days. The estimated LD50 at 24 h was 3.45 g Al/kg body weight (b.wt.). The utilized dose of Al was 1/50 LD50 (0.07 g Al/kg b.wt.). Aluminum residues, in Al-treated rats, were significantly decreased in response to the experimental periods and were negatively correlated with time. In addition, the hepatic, renal, intestinal, brain and serum Al contents were significantly higher than the corresponding controls at all experimental periods, except the brain that showed significant depletion when compared with its corresponding control after 28 days. Kinetically, the highest average of Al area under concentration − time curves (AUCtotal, μg/g day) and area under moment concentration − time curves (AUMCtotal, µg/g day2) recorded in the brain followed by kidney, serum, intestine and liver. The longest elimination half-life time ( t1/2, day) and the mean residence time (MRT, day) were recorded in the brain followed by the liver, kidney, serum and intestine. On the other hand, the slowest clearance rates (Cls, L/day) of Al, in order, were recorded in brain, kidney, serum, intestine and the liver. The elimination rate constant ( Lz, day−1) of Al from the brain was less than that in the intestine and serum was less than that in the liver and kidney. The computed maximum concentrations ( Cmax) of Al in the intestine > kidney > serum > brain > liver were recorded after 3, 3.8, 2.2, 5.4 and 3.8 days, respectively. The computed starting concentration ( C0, μg) of Al in serum was higher than its level in the intestine followed by the brain, kidney and liver.

Chelation of aluminum by combining deferasirox and deferiprone in rats

The hypothesis that two known chelators deferasirox and deferiprone (L1) might be more efficient as combined treatment than as single therapies in removing aluminum from the body was tested in a new acute rat model. Seven-week-old male Wistar rats received chelators: deferasirox (orally [p.o.]), L1 (p.o.) or deferasirox + L1 as 100 or 200 mg/kg dose half an hour after a single intraperitoneal administration of 6 mg Al/kg body weight in the form of chloride. Serum aluminum concentration, urinary aluminum and iron excretions were determined by graphite furnace atomic absorption spectrometry. Both chelators were effective only at the higher dose level. While deferasirox was more effective than L1 in enhancing urinary aluminum excretion, L1 was more effective than deferasirox in enhancing urinary iron excretion. In the combined treatment group, deferasirox did not increase the L1 effect on aluminum and L1 did not increase the effect of deferasirox on iron elimination. Our results support the usefulness of this animal model for preliminary in vivo testing of aluminum chelators. Urinary values were more useful due to the high variability of serum results.

Prophylactic and therapeutic effects of taurine against aluminum-induced acute hepatotoxicity in mice

Aluminum is a well known neurotoxin and a possible candidate of hepatotoxins to humans. Using natural antioxidants against metal-induced hepatotoxicity is a modern approach. In the present study, Aluminum (AlCl(3)) intoxication (a single injection of 25mg Al(3+)/kg, i.p.) for 24h in mice resulted in elevations in serum alanine aminotransferase activity and serum tumor necrosis factor and hepatic malondialdehyde levels. Aluminum reduced the activities of glutathione peroxidase, glutathione S-transferase, quinone oxidoreductase, and catalase in liver. In addition, Al caused hepatic hemorrhage, cellular degeneration as well as necrosis of hepatocytes. Ultrastructure examination showed swelling of mitochondria, derangement of rough endoplasmic reticulum cisternae and pleomorphic nuclei with abnormal chromatin distribution. Taurine, a sulfur-containing amino acid was administered to mice daily for 5 days before (at 100mg/kg, i.p.) or 2h after (a single dose of 1g/kg, i.p.) aluminum administration. Treating mice with taurine at either dosing regimens, pre- or post-aluminum administration alleviated aluminum oxidative damaging effects. The rate of recovery was better when taurine was administered prior to Al. Taurine had anaphylactic and therapeutic activity against hepatotoxicity induced by aluminum in mice.

Effects of aluminum on phosphate metabolism in rats: a possible interaction with vitamin D3 renal production

The effect of chronic aluminum (Al) administration on the phosphorous (Pi) metabolism of different target tissues was studied. Male Wistar rats received aluminum lactate for 3 months (5.75 mg/kg bodyweight of Al, i.p., three times per week). The animals were studied at the end of the 1st, 2nd and 3rd month of treatment. They were housed individually in metabolic cages for 4 days to study Pi and calcium (Ca) balance. Daily food and water intakes were recorded for all animals and urine and feces were collected for Pi and calcium assays. After 3 months the Pi intestinal absorption and the Pi deposition in bone were studied using 32Pi. Another group of rats was treated daily for 7 days with calcitriol (0.08 microg/kg body weight in sesame oil, i.p.) and the Pi balance was studied for the last 4 days. The results indicated that chronic administration of Al affected simultaneously the Pi and calcium balance, with a significant diminution of calcium and increased Pi accretion in bones, together with a diminution in the intestinal absorption of Pi. The treatment of the rats with calcitriol promoted a normalized Pi balance in Al treated rats. These findings suggest that Al could modify the Pi metabolism acting directly on intestine, kidney and bone, or indirectly through possible changes in the levels of vitamin D3.

Aluminum-induced oxidative stress in rat brain: response to combined administration of citric acid and HEDTA

Aluminum, a known neurotoxic substance, has been suggested as a contributing factor in the pathogenesis of Alzheimer's disease. Therapeutic efficacy of combined administration of citric acid (CA) and N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) was evaluated in decreasing blood and brain aluminum concentration and parameters indicative of hematological disorders and brain oxidative stress. Adult male wistar rats were exposed to drinking water containing 0.2% aluminum nitrate for 8 months and treated once daily for 5 consecutive days with CA (50 mg/kg, orally) or HEDTA (50 mg/kg, intraperitoneally) either individually or in combination. Aluminum exposure significantly inhibited blood delta-aminolevulinic acid dehydratase while increased zinc protoporphyrin confirming changed heme biosynthesis. Significant decrease in the level of glutathione S-transferase in various brain regions and an increase in whole brain thiobarbituric acid reactive substance, and oxidized glutathione (GSSG) levels were also observed. Glutathione peroxidase activity showed a significant increase in cerebellum of aluminum exposed rats. Most of the above parameters responded moderately to the individual treatment with CA and HEDTA, but significantly reduced blood and brain aluminum burden. However, more pronounced beneficial effects on some of the above described parameters were observed when CA and HEDTA were administered concomitantly. Blood and brain aluminum concentration however, showed no further decline on combined treatment over the individual effect with HEDTA or CA. We conclude that in order to achieve an optimum effect of chelation, combined administration of CA and HEDTA might be preferred. However, further work is needed before a final recommendation could be made.

The influence of complexing agents on the solubility and absorption of aluminium in rats exposed to aluminium in water

The influence of citrate (0-31 mM), fluoride (0 or 2.6 mM) and silicate (0 or 2.6 mM) on the absorption of Al (0-18 mM) was studied in rats. We tested the hypothesis that the solubility and absorption of Al increases in the gastrointestinal (GI) tract in the presence of the complexing agents. Male rats were exposed for 6 or 7 weeks to soluble Al in acidic drinking water (pH 2.5-3.0) with or without the complexing agents. At the end of exposure Al was fractionated in the stomach content, in order to study if the solubility of Al was changed after ingestion. Al absorption was estimated by Al analysis of the right femur bone. Speciation calculations indicated that citrate and fluoride caused formation of soluble Al-citrate (97%) and -fluoride (> 60%) complexes in the water. Silicate did not affect the theoretical speciation. In all cases, a large fraction of soluble Al became insoluble in the stomach after ingestion. The concentration of soluble Al increased only in the presence of citrate or a mixture of fluoride and silicate, but citrate was the only complexing agent that influenced the absorption of Al in the rat. This indicates that the form of Al may be changed in the GI tract when soluble drinking-water Al is ingested, and that the solubility of Al in drinking water and GI tract may not be good predictors of the bioavailability of Al even when chelating agents are present.

Safety evaluation of dietary aluminum

Aluminum is a nonessential metal to which humans are frequently exposed. Aluminum in the food supply comes from natural sources, water used in food preparation, food ingredients, and utensils used during food preparations. The amount of aluminum in the diet is small, compared with the amount of aluminum in antacids and some buffered analgesics. The healthy human body has effective barriers (skin, lungs, gastrointestinal tract) to reduce the systemic absorption of aluminum ingested from water, foods, drugs, and air. The small amount of aluminum (<1%) that is systemically absorbed is excreted principally in the urine and, to a lesser extent, in the feces. No reports of dietary aluminum toxicity to healthy individuals exist in the literature. Aluminum can be neurotoxic, when injected directly into the brains of animals and when accidentally introduced into human brains (by dialysis or shrapnel). A study from Canada reports cognitive and other neurological deficits among groups of workers occupationally exposed to dust containing high levels of aluminum. While the precise pathogenic role of aluminum in Alzheimer's disease (AD) remains to be defined, present data do not support a causative role for aluminum in AD. High intake of aluminum from antacid for gastrointestinal ailments has not been reported to cause any adverse effects and has not been correlated with neurotoxicity or AD. Foods and food ingredients are generally the major dietary sources of aluminum in the United States. Cooking in aluminum utensils often results in statistically significant, but relatively small, increases in aluminum content of food. Common aluminum-containing food ingredients are used mainly as preservatives, coloring agents, leavening agents, anticaking agents, etc. Safety evaluation and approval of these ingredients by the Food and Drug Administration indicate that these aluminum-containing compounds are safe for use in foods.

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.

Al and Si: their speciation, distribution, and toxicity

OBJECTIVES

In dialysis patients both aluminum (AI) and silicon (Si) may accumulate. Whereas the toxic effects of AI within this population are clearly established, little is known on the role of Si in the development/protection of particular dialysis-related diseases. A clear insight in the protein binding and speciation of trace elements is important to better understand the mechanisms underlying their toxicity/essentiality. Research in this field however is complex and often prone to analytical difficulties and inaccuracies.

DESIGN AND METHODS

In the first part of this review techniques used for speciation studies of AI and Si in biological fluids are discussed. Notwithstanding recent technical advances (a) extraneous metal contamination, (b) unrecognized aspecific binding of metals to proteins, and (c) unwanted interactions with separation equipment such as chromatography columns and ultrafiltration membranes remain important pitfalls and often lead to erroneous conclusions. The factors that determine the speciation of AI and Si and their ultimate tissue distribution and toxicity are dealt with in the second part. Here, experimental data obtained with various speciation techniques are linked to in vivo data on the tissue distribution, localization/toxicity of both elements.

CONCLUSIONS

A model in which the AI tissue distribution/toxicity is mediated by either its citrate or transferrin bound form is proposed.

Effect of the size of an oral dose of aluminium on the relative importance of biliary v. urinary aluminium excretion in conscious rats

We compared biliary and urinary aluminium (Al) excretion following ingestion of dietary or gavage dosing of low to moderate pharmacological doses of aluminium. Bile was collected from 26 conscious, male Sprague Dawley rats following administration of a single gavage dose of 0, 0.25, 0.5 or 1 mmol Al/kg body weight in 1 ml 16% citrate solution (equivalent to 0-650 mg Al to a 70-kg human). Urine was collected from 20 additional rats following similar dosing. Biliary Al secretion rates were highest in the first hour after dosing. Cumulatively, rats given 0.5 or 1 mmol Al/kg body weight excreted significantly more Al in bile than rats dosed with 0.25 mmol Al/kg body weight, which excreted more Al bile than control rats. Urinary Al excretion was many-fold higher than biliary Al excretion by rats dosed with Al but was less than biliary Al excretion by control rats exposed to dietary Al only. These results suggest that the liver was capable of secreting small amounts of absorbed dietary Al into bile but that the kidneys became the primary excretory organs for Al when the liver's secretory capacity was surpassed after ingestion of pharmacological doses of Al.

Kinetics of aluminum disposition after ingestion of low to moderate pharmacological doses of aluminum

We assessed the kinetics of aluminum uptake and elimination by tissues of Sprague Dawley rats following a single gavage dose of 0, 0.25, 0.5, or 1 mmol Al/kg body weight (b.w.) in 1 ml of 16% citrate (equivalent to 0-650 mg Al to a 70-kg human). Serum, liver, kidney, and tibia aluminum concentrations were measured 15, 30, 60, 120, 270, and 360 min after dosing. Serum aluminum concentrations were proportional to dose in rats dosed with 0.25 or 0.5 mmol Al/kg b.w. but were not proportional to dose for rats dosed with 1 mmol Al/kg b.w. Elimination half-lives of serum aluminum were similar for all treatments (102-119 min) which suggests that the non-linear aluminum kinetics in serum reflected a difference in absorption of the highest dose. Although fasted rats dosed with 0.25 or 1 mmol Al/kg b.w. with citrate absorbed aluminum with similar efficiency (4.2% of dose), the length of the absorptive period was prolonged in the rats given the highest does. Total absorbed aluminum mass in rats dosed with 0.25 and 0.5 mmol vs. 1 mmol Al/kg b.w. reached a plateau at 120 vs. 270 min after dosing, respectively. The kinetics of aluminum in liver, bone, and kidney were generally dose-independent. Elimination half-lives of liver aluminum were similar for all aluminum treatments (267-465 min); elimination half-lives could not be estimated in bone and kidney because of turnover exceeded the 6 h collection period.

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.

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.

Bile is an important route of elimination of ingested aluminum by conscious male Sprague-Dawley rats

We assessed the importance of bile as an excretory route for ingested aluminum (AI). Bile dusts in 30 male Sprague-Dawley rats were cannulated to allow both bile collection and reinfusion of bile acids. Five days after surgery, rats (average weight = 191 +/- 4 g) were given a single oral dose of aluminum (0, 0.2, 0.4, or 0.8 mmol) as aluminum lactate in 1 ml of 16% citrate by gavage. Bile was collected 1-7 h after dosing from unanesthetized rats. Biliary aluminum secretion was highest during the first hour of bile collection. All rats dosed with aluminum secreted significantly greater amounts of aluminum in bile than control rats. However, biliary aluminum secretion did not vary among animals given the different aluminum doses suggesting that biliary secretion of aluminum was saturated at these doses. Rats dosed with 0.8 mmol A1 retained significantly greater amounts of aluminum in soft tissues than those given 0.2 or 0.4 mmol A1. This result suggests that physiological were unable to prevent tissue aluminum accumulation in the rats given the highest dose.

Distribution of aluminum in different brain regions and body organs of rat

In the present study, an attempt has been made to investigate the distribution of aluminum in different regions of brain and body organs of male albino rats, following subacute and acute aluminum exposure. Aluminum was observed to accumulate in all regions of the brain with maximum accumulation in the hippocampus. Subcellular distribution of aluminum indicated that there was maximum localization in the nucleus followed by cytosolic, microsomal, and mitochondrial deposition. Elution profile of cytosolic proteins on G-75 Sephadex column revealed a substantial amount of aluminum bound to high-mol-wt protein fraction. Aluminum was also seen to compartmentalize in almost all the tissues of the body to varying extents, and the highest accumulation was in the spleen.

Tissue aluminium distribution in growing, mature and ageing rats: relationship to changes in gut, kidney and bone metabolism

The purpose of this study was to determine whether accumulation and turnover of aluminium differed among growing (2 month old), mature (8 month old) and ageing (19 month old) rats and assess whether these differences could be ascribed to physiological changes with age. One day after a large oral dose (0.8 mmol Al in 0.75 M citrate) growing rats had the highest concentrations of aluminium in tibias, whereas ageing rats had the highest concentrations of aluminium in kidneys. The half-life of aluminium in tibias (38 v. 58 v. 173 days in growing, mature and ageing rats, respectively) and kidneys (9 v. 12 v. 16 days) lengthened with age. According to stepwise multiple regression analysis, 73% variation in tibia aluminium concentrations was explained by final body weight of rats, length of time after dosing, tibia weights, haematocrits, urinary hydroxyproline excretion, ulna calcium concentrations, and urinary creatinine excretion but 57% variation in kidney aluminium concentrations was explained by length of time after dosing and feed intake. Although age, per se, was a significant predictor of spleen and liver aluminium concentrations, the measured changes in gut, kidney, bone and mineral metabolism were less predictive of aluminium concentrations in livers and spleens than in bone.

Comparison of tissue retention of aluminum and Ga-67: effects of iron status in rats

The purposes of this study were to separate the effect of iron status from the effect of acute iron intake on tissue retention of aluminum and Ga-67 and to evaluate Ga-67 as a marker for aluminum. Anemic and control rats were dosed by gavage with a citrate solution containing 20 microCi Ga-67 with no added aluminum and iron (Gavage Ga-67), with 0.8 mmol aluminum (Gavage Al), with 0.8 mmol iron (Gavage Fe), or with both 0.8 mmol aluminum and 0.8 mmol iron (Gavage Fe and Al). After 24 h, anemic rats in the Gavage Al treatment had lower concentrations of aluminum in their tibias, kidneys, and spleens than control rats in that treatment. In contrast, anemic rats dosed with only Ga-67 (Gavage Ga-67 treatment) had lower concentrations of Ga-67 in their tibias and kidneys, but greater concentrations of Ga-67 in their livers and spleens than control rats in that treatment. The single dose of iron had no effect on tissue aluminum concentrations but depressed tissue Ga-67 concentrations. All rats accumulated aluminum predominantly in bone and control rats accumulated Ga-67 predominantly in bone, but anemic rats accumulated Ga-67 predominantly in liver. A major limitation of Ga-67 as a marker for aluminum is its greater sensitivity than aluminum to iron intake and status.

Bioavailability of labile aluminium in acidic drinking water: a study in the rat

The bioavailability of labile Al (Allab; Al3+, and monomeric hydroxo and sulfato complexes) in drinking water was studied in the rat. The hypothesis was that Allab in drinking water is more available for absorption in the gastro-intestinal tract than Al complexed in the rat feed. Male Sprague-Dawley rats were exposed to 4 mg Al/litre in acidic drinking water (pH 4-5) and 5 mg Al/kg in the feed for 10 wk. The Al intake of these rats was about twice that in a control group of rats that received Al only in the feed. Both a theoretical speciation calculation and a speciation analysis of the water in a flow injection system showed that more than 98% of the Al in the water was present as Allab. However, intake of this water did not result in increased levels of Al in the bone, liver or brain tissue of the rats. Al speciation in a simulated rat stomach indicated that Allab in drinking water is rapidly complexed by feed constituents as the water enters the acidic milieu of the stomach, resulting in a very low concentration of Allab. The concentration of dissolved Al was also low in comparison to the added amount of labile Al. The possibility of complex formation between Allab and feed components in the gastro-intestinal tract should be taken into account in further studies of the bioavailability of drinking water Al in experimental animals and in humans.

Aluminum effects on blood chemistry and long bone development in the chick embryo

Body growth, blood chemistry, and long bone development of 10- to 16-day chick embryos (Gallus gallus) treated with aluminum (Al) citrate, sodium (Na) citrate, or sodium chloride (NaCl) were investigated. Two administration protocols were used. Acutely-treated embryos received 6.0 mumol Al citrate or Na citrate on day 8 of incubation. Chronically-treated embryos received a daily dose of 1.5 mumol Al citrate or Na citrate beginning on day 8 of incubation. For both protocols, Al citrate and Na citrate had no significant influence on viability or body weight. Al citrate-treated embryos had: (a) significantly shorter mean tibia lengths by day 16 of incubation, (b) a consistently lower ratio of tibia length: body weight on all days investigated, and (c) a persistent mid-diaphyseal malformation (angulation) of the femur and tibia. Spatially correlated with the malformation was a calcification defect detected by alizarin red S staining of intact tibias and the accumulation of aluminum as demonstrated by acid solochrome azurine staining of histological sections. Aluminum was localized at the mineralization front of the osteogenic collar surrounding the cartilage core of the tibia. Aluminum citrate or Na citrate had no significant effect on serum total calcium, inorganic phosphorus, total alkaline phosphatase activity, or creatinine, except for a transitory hypercalcemia (day 10) and phosphatemia (days 10 and 12) in Al citrate-treated embryos. The concomitant localization of Al and the early calcification defect in the region of tibial malformation implicate aluminum in the pathogenesis of the skeletal abnormality.

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.