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

Aluminum and aluminum oxide nanomaterials uptake after oral exposure - a comparative study

The knowledge about a potential in vivo uptake and subsequent toxicological effects of aluminum (Al), especially in the nanoparticulate form, is still limited. This paper focuses on a three day oral gavage study with three different Al species in Sprague Dawley rats. The Al amount was investigated in major organs in order to determine the oral bioavailability and distribution. Al-containing nanoparticles (NMs composed of Al0 and aluminum oxide (Al2O3)) were administered at three different concentrations and soluble aluminum chloride (AlCl3·6H2O) was used as a reference control at one concentration. A microwave assisted acid digestion approach followed by inductively coupled plasma mass spectrometry (ICP-MS) analysis was developed to analyse the Al burden of individual organs. Special attention was paid on how the sample matrix affected the calibration procedure. After 3 days exposure, AlCl3·6H2O treated animals showed high Al levels in liver and intestine, while upon treatment with Al0 NMs significant amounts of Al were detected only in the latter. In contrast, following Al2O3 NMs treatment, Al was detected in all investigated organs with particular high concentrations in the spleen. A rapid absorption and systemic distribution of all three Al forms tested were found after 3-day oral exposure. The identified differences between Al0 and Al2O3 NMs point out that both, particle shape and surface composition could be key factors for Al biodistribution and accumulation.

Systematic review of potential health risks posed by pharmaceutical, occupational and consumer exposures to metallic and nanoscale aluminum, aluminum oxides, aluminum hydroxide and its soluble salts

Abstract Aluminum (Al) is a ubiquitous substance encountered both naturally (as the third most abundant element) and intentionally (used in water, foods, pharmaceuticals, and vaccines); it is also present in ambient and occupational airborne particulates. Existing data underscore the importance of Al physical and chemical forms in relation to its uptake, accumulation, and systemic bioavailability. The present review represents a systematic examination of the peer-reviewed literature on the adverse health effects of Al materials published since a previous critical evaluation compiled by Krewski et al. (2007) . Challenges encountered in carrying out the present review reflected the experimental use of different physical and chemical Al forms, different routes of administration, and different target organs in relation to the magnitude, frequency, and duration of exposure. Wide variations in diet can result in Al intakes that are often higher than the World Health Organization provisional tolerable weekly intake (PTWI), which is based on studies with Al citrate. Comparing daily dietary Al exposures on the basis of "total Al"assumes that gastrointestinal bioavailability for all dietary Al forms is equivalent to that for Al citrate, an approach that requires validation. Current occupational exposure limits (OELs) for identical Al substances vary as much as 15-fold. The toxicity of different Al forms depends in large measure on their physical behavior and relative solubility in water. The toxicity of soluble Al forms depends upon the delivered dose of Al(+3) to target tissues. Trivalent Al reacts with water to produce bidentate superoxide coordination spheres [Al(O2)(H2O4)(+2) and Al(H2O)6 (+3)] that after complexation with O2(•-), generate Al superoxides [Al(O2(•))](H2O5)](+2). Semireduced AlO2(•) radicals deplete mitochondrial Fe and promote generation of H2O2, O2 (•-) and OH(•). Thus, it is the Al(+3)-induced formation of oxygen radicals that accounts for the oxidative damage that leads to intrinsic apoptosis. In contrast, the toxicity of the insoluble Al oxides depends primarily on their behavior as particulates. Aluminum has been held responsible for human morbidity and mortality, but there is no consistent and convincing evidence to associate the Al found in food and drinking water at the doses and chemical forms presently consumed by people living in North America and Western Europe with increased risk for Alzheimer's disease (AD). Neither is there clear evidence to show use of Al-containing underarm antiperspirants or cosmetics increases the risk of AD or breast cancer. Metallic Al, its oxides, and common Al salts have not been shown to be either genotoxic or carcinogenic. Aluminum exposures during neonatal and pediatric parenteral nutrition (PN) can impair bone mineralization and delay neurological development. Adverse effects to vaccines with Al adjuvants have occurred; however, recent controlled trials found that the immunologic response to certain vaccines with Al adjuvants was no greater, and in some cases less than, that after identical vaccination without Al adjuvants. The scientific literature on the adverse health effects of Al is extensive. Health risk assessments for Al must take into account individual co-factors (e.g., age, renal function, diet, gastric pH). Conclusions from the current review point to the need for refinement of the PTWI, reduction of Al contamination in PN solutions, justification for routine addition of Al to vaccines, and harmonization of OELs for Al substances.

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.

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.

Entry, half-life, and desferrioxamine-accelerated clearance of brain aluminum after a single (26)Al exposure

The objectives of our study were to estimate the percentage of aluminum (Al) that enters the brain, the half-life of brain Al, and the ability of an Al chelator to reduce brain Al. Rats received an iv infusion of Al transferrin, the primary Al species in plasma, or Al citrate, the predominant small molecular weight Al species in plasma. The infusion contained approximately 0.2-0.3 nCi (0.4-0.6 nmol) (26)Al, enabling the study of Al distribution into and retention by the brain at physiological Al concentrations. Some Al transferrin-infused rats received ip injections of the Al chelator desferrioxamine (DFO), 0.15 mmol/kg, three times weekly. The others received saline injections. The rats were euthanized from 4 hr to 4 days (Al citrate) or 256 days (Al transferrin) later. Brain (26)Al was determined by accelerator mass spectrometry. Peak brain (26)Al concentration was approximately 0.005% of the (26)Al dose in each gram of brain, irrespective of Al species administered. In the absence of DFO treatments, brain (26)Al concentration decreased with a half-life of approximately 150 days. The brain Al half-life in the DFO-treated rats was approximately 55 days. The results show a small fraction of Al in blood enters the brain, where it persists for a long time. The ability of repeated DFO treatments to modestly accelerate the reduction of brain Al is consistent with the necessity of prolonged DFO therapy to significantly reduce Al-induced dialysis encephalopathy.

Oral aluminum administration to rats with normal renal function. 2. Body distribution

Aluminum (Al) has no known physiological function and is not considered an essential dietary compound. Nowadays, it is recognized as an element that can produce adverse effects on biological systems. The present study determined Al partitioning in the body compartments of rats that have been orally exposed for 15 weeks. Three experimental groups were studied: Controls (C, n=19), TAl-1 (n=10) rats receiving daily doses of Al citrate (1.0 micromol/g body weight) by gavage and TAl-2 (n=13), receiving Al citrate with the drinking water (100 mmol/ l). At the end of the experimental period, the Al contents of organs and sera were determined. Results are expressed as median and range values. Comparing the TAl-2 rats with the control ones, remarkable Al accumulation could be observed in serum (4.8/2.7-16.3 vs 0.4/0.2-1.2 micromol/l, P<0.001), bone (3.33/1.78-4.85 vs 1.00/0.48-1.59 micromol/ g, P<0.001), kidney (2.33/0.96-3.15 vs 0.52/0.22-2.07 micromol/g, P<0.001), spleen (2.22/0.70-4.19 vs 0.27/ 0.11 - 0.36 micromol/g, P< 0.001) and liver (0.60/0.42-0.91 vs 0.24/0.14-0.78 micromol/g, P<0.01) while brain Al content was not significantly increased. Aluminum levels were raised in the TAl-1 group only in serum (2.8/1.3 - 10.4 micromol/ g, P < 0.001), bone (1.85/1.00-3.41 micromol/g, P < 0.001) and kidney (1.74/0.96-2.07 micromol/g, P<0.01). Bone Al concentration increased in a dose-dependent manner (TAl-2 vs TAl-1, P<0.001). The results demonstrate different tissue Al accumulation in rats chronically exposed to Al citrate, irrespective of their intact renal function.

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.