Intestinal Absorption of Trace Amounts of Aluminium in Rats Studied with 26Aluminium and Accelerator Mass Spectrometry

Abstract

1. Until recently studies of intestinal aluminium absorption used pharmacological amounts of stable 27Al. 2. To examine the intestinal absorption of trace amounts of different chemical compounds of aluminium, in the present study we have employed the long half-life isotope of aluminium, 26Al, and accelerator mass spectrometry. Trace amounts of 26Al (2.7-12.1 ng) as the hydroxide, citrate, citrate plus 1 mmol/kg sodium citrate, or maltolate respectively, were administered to four groups of rats (n = 9 per group) by gavage. Blood and urine samples were collected for 5 h and the 26Al content (as a percentage of the administered dose) determined by accelerator mass spectrometry. 3. The 5 h urinary 26Al excretion amounted to 0.1 +/- 0.02, 0.7 +/- 0.2, 5.1 +/- 1.5 and 0.1 +/- 0.1% of administered dose in the four groups respectively. There was a strong positive correlation between peak plasma 26Al (r = 0.98) and urinary 26Al excretion in individual animals (P < 0.001). 4. We conclude that the fractional intestinal absorption of trace oral doses of aluminium hydroxide is at least 0.1% (compared with the previous estimate of 0.01% using large 27Al oral loads). Absorption of aluminium citrate given alone is significantly greater (0.7%) and is further increased to 5% by the accompanying sodium citrate, consistent with an enhancing effect of added citrate upon mucosal aluminium permeability. Aluminium maltolate absorption approximates that of aluminium hydroxide (0.1%).

Effect of Long-Term Exposure to Aluminum on the Acetylcholinesterase Activity in the Central Nervous System and Erythrocytes

“…Some clinical reports demonstrated an increase in aluminum absorption during aging and certain pathologies, leading to aluminum accumulation in the body [32]. The relatively high fractional aluminum absorption observed when fasted animals were given aluminum by gavage with citrate reflects several factors [33]. This reflects the increased solubility of aluminum in a citrate solution, the enhancement of Al absorption by citrate, and the negative effect of other ions (iron and calcium) and organic factors (phytate) in diet and in the gut milieu of fed animals on aluminum bioavailability [34,35].…”

The influence of citrate, maltolate and fluoride on the gastrointestinal absorption of aluminum at a drinking water-relevant concentration: A 26Al and 14C study

“…Increasing the citrate to Al ratio would favor formation of a smaller 1:2 Al:citrate complex (Al(H À1 cta)(cta) 4À ), which might more easily diffuse through the paracellular pathway than the Al 3 (H À1 cta) 3 (OH) 4À trimer formed at lower citrate:Al ratios. The absorption of Al, when administered as the citrate (5 ng of 26 Al and 80 ng of 27 Al, 3.1 nmol total Al, pH 6.2, citrate dose not reported), was greater than when Al hydroxide was given (2.7 ng of 26 Al and 43.2 ng 27 Al, 1.7 nmol total Al, pH 7), 0.7% versus 0.1% [21]. When 1 mmol/kg sodium citrate was added to 12.1 ng of 26 Al as Al citrate at pH = 8.3 (Al:citrate 1:40,000), Al absorption increased to 5%.…”

“…The absorption of Al when administered as the maltolate approximated that of Al hydroxide ($0.1%) [21]. The Al was given as 5 ng 26 Al and 80 ng 27 Al, 3.1 nmol total Al, pH = 6, in 2 ml water (1.55 lm).…”

“…The only reported study that estimated oral Al bioavailability from Al maltolate found it to be $0.1% [21]. However the authors did not report the Al species, or Al:maltolate molar ratio under the conditions studied, preventing calculation of the Al species.…”

“…Oral Al bioavailability from drinking water was estimated in several studies in rats to be 0.05-0.36%, based on urinary Al output or Al in urine plus Al retained in bone, liver and brain [19][20][21]. Oral Al bioavailability was estimated to be 0.25-0.4% from a comparison of areas under the curve (AUC) of serum Al concentration versus time when Al was given po and iv [22].…”