Tissue turnover of aluminum and Ga-67: effect of iron status

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.

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.

Effect of long-term exposure to aluminum on the acetylcholinesterase activity in the central nervous system and erythrocytes

Aluminum (Al), a neurotoxic agent, has been associated with Alzheimer's disease (AD), which is characterized by cholinergic dysfunction in the central nervous system. In this study, we evaluated the effect of long-term exposure to aluminum on acetylcholinesterase (AChE) activity in the central nervous system in different brain regions, in synaptosomes of the cerebral cortex and in erythrocytes. The animals were loaded by gavage with AlCl(3) 50 mg/kg/day, 5 days per week, totalizing 60 administrations. Rats were divided into four groups: (1) control (C); (2) 50 mg/kg of citrate solution (Ci); (3) 50 mg/kg of Al plus citrate (Al + Ci), and (4) 50 mg/kg of Al (Al). AChE activity in striatum was increased by 15% for Ci, 19% for Al + Ci and 30% for Al, when compared to control (P < 0.05). The activity in hypothalamus increased 23% for Ci, 26% for Al + Ci and 28% for Al, when compared to control (P < 0.05). AChE activity in cerebellum, hippocampus and cerebral cortex was decreased by 11%, 23% and 21% respectively, for Al, when compared to the respective controls (P < 0.05). AChE activity in synaptosomes was increased by 14% for Al, when compared to control (P < 0.05). Erythrocyte AChE activity was increased by 17% for Al + Ci and 11% for Al, when compared to control (P < 0.05). These results indicate that Al affects at the same way AChE activity in the central nervous system and erythrocyte. AChE activity in erythrocytes may be considered a marker of easy access of the central cholinergic status.

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.

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.